Wastewater Alkalinity Enhancement v1.0

1.0 Introduction

This Protocol provides the requirements and procedures for the calculation of net carbon dioxide equivalent (CO₂e) removal from the atmosphere via Wastewater Alkalinity Enhancement (WAE). This Protocol is developed for application in Wastewater Alkalinity Enhancement processes in which a cradle-to-grave Greenhouse Gas (GHG) Statement can be accurately applied and in which the carbon dioxide (CO₂) captured is durably stored for over 1,000 years.

Conventional wastewater treatment plants (WWTP) use a combination of physical, chemical and biological processes to remove soluble and insoluble contaminants prior to effluent discharge, which is essential to safeguard both human and environmental health. Commonly, WWTPs consist of preliminary and primary treatment, in which large particles are removed via screens and gravity settling, and secondary treatment, in which pollutants and unreacted biomass (sludge) are removed and effluent is clarified and disinfected for discharge. Finally, some WWTPs with more stringent discharge limits (e.g. those that discharge into recreational or drinking water bodies) receive a tertiary treatment, which may consist of targeted approaches for treating specific constituents before discharge.

Secondary treatment is typically a large source of biogenic CO₂ emissions in WWTPs as that is the step where a majority of solid and dissolved organic carbon in the wastewater is transformed into CO₂ through biological processes¹^,². The secondary treatment process also leads to emissions of both methane (CH₄) and nitrous oxide (N₂O)², which are 29.8 and 273 times more potent GHGs, respectively, than CO₂ on 100-year timescales³. This Protocol focuses on the removal of biogenic CO₂ emissions and not other GHGs. It is important to note that biogenic CO₂ emissions from wastewater treatment are not typically counted in standard GHG accounting frameworks⁴^,⁵, thus the removal of this biogenic CO₂ through WAE qualifies as carbon dioxide removal (CDR), rather than emissions avoidance.

In Wastewater Alkalinity Enhancement, rock or mineral feedstock is added into the secondary treatment process. This feedstock reacts with carbonic acid generated through the degradation of organic matter to produce stable bicarbonate (HCO₃^-) ions, analogous to natural rock weathering processes that regulate atmospheric CO₂ concentrations on geologic timescales⁶. When the effluent is discharged into the ocean or into a river that drains into the ocean, the constituent bicarbonate is stably stored on millennial timescales. Because Wastewater Alkalinity Enhancement leverages existing wastewater infrastructure and permits, it has high potential for scaling.

This Protocol specifically applies to municipal and industrial WWTPs that reduce biochemical oxygen demand (BOD) using biological treatment. In contrast, chemical treatment for wastewater treatment from industrial processes such as mining or oil and gas extraction is ineligible under this Protocol. The goals of biological treatment are to a) convert solid and dissolved organic matter into biomass (sludge) and CO₂; b) remove excess nutrients, such as phosphorus and nitrogen, from the wastewater stream; and c) clarify effluent prior to disinfection and discharge. Several methods for biological treatment exist in practice, but the most common example is the activated sludge process, in which a bacterial biomass suspension (or activated sludge) is used for pollutant removal⁷. Depending on WWTP design and specific requirements for treatment, activated sludge can remove nitrogen and phosphorus in addition to organic materials. In the activated sludge process, the sludge is settled in clarifier tanks prior to disinfection. A portion of this sludge is recycled through the system and a portion, termed waste activated sludge (WAS) is removed. WAS is referenced throughout this Protocol with respect to solid-phase sampling (see Section 11.4).

For the purposes of this Protocol, a Wastewater Alkalinity Enhancement process must be retrofitted into existing WWTP operations. A retrofit is defined as the introduction of new materials, products or technologies to an existing process or facility. See Section 4 for more details on eligible projects. A Project refers to the system boundaries of the retrofitted process, as described in Section 7.3.

This Protocol is developed to adhere to the requirements of ISO14064-2: 2019 -- Greenhouse Gases -- Part 2: Specification with guidance at the project level for quantification, monitoring, and reporting of greenhouse gas emission reductions or removal enhancements. The Protocol ensures:

consistent, accurate procedures are used to measure and monitor all aspects of the WAE process required to enable accurate accounting of net CO₂e removals
consistent system boundaries and calculations are utilized to quantify net CO₂e removal for WAE projects
requirements are met to ensure the CO₂e removals are additional
evidence is provided and verified by independent third parties to support all net CO₂e removal claims

Note that throughout this Protocol, use of the word "must" indicates a requirement, whereas "should" indicates a recommendation.

2.0 Sources and Reference Standards and Methodologies

Specific standards and protocols which are utilized as the foundation of this Protocol and for which this Protocol is intended to be fully compliant with are the following:

Isometric Standard
ISO (International Organization for Standardization) 14064-2: 2019 – Greenhouse Gases – Part 2: Specification with guidance at the project level for quantification, monitoring and reporting of greenhouse gas emission reductions or removal enhancements

Additional reference standards that inform the requirements and overall practices incorporated in this Protocol include:

ISO 14064-3: 2019 - Greenhouse Gases - Part 3: Specification with Guidance for the verification and validation of greenhouse gas statements
ISO 14040: 2006 - Environmental Management - Lifecycle Assessment - Principles & Framework
ISO 14044: 2006 - Environmental Management - Lifecycle Assessment - Requirements & Guidelines

3.0 Future Versions

This Protocol was developed based on the current state of the art and publicly available science regarding Wastewater Alkalinity Enhancement. As Wastewater Alkalinity Enhancement is a novel CDR approach, with limited published literature, this Protocol incorporates requirements that may be highly stringent to minimize risk and for the purposes of environmental and social safeguarding.

This Protocol will be altered in future versions as the science underlying this pathway evolves, and the overall body of knowledge and data across all processes is increased, for example regarding feedstock supply, conversion, ecosystem impacts and durable storage. Future updates will also increase the scope of eligible projects for this Protocol, see Appendix 2 for planned areas of improvement for future versions.

This Protocol will be reviewed at a minimum every 2 years and/or when there is an update to scientific published literature which would affect net CO₂e removal quantification or the monitoring and modeling guidelines outlined in this Protocol.

4.0 Applicability

The aim of this Protocol is to ensure that projects seeking carbon removal Credits for Wastewater Alkalinity Enhancement are safe and have a demonstrable net-negative climate impact. The scope of this Protocol may be expanded in future versions to allow for more discharge locations and provide additional guidance for different types of wastewater treatment facilities. To be eligible for crediting under this Protocol, projects and associated operations must meet all of the following conditions.

To ensure human and environmental health, eligible projects must:

Operate within the existing permits, or an approved modified permit, of a wastewater treatment plant.
Characterize feedstock prior to usage according to the Rock and Mineral Feedstock Characterization Module.
Submit proof of an official partnership with partner facilities to ensure that the Project is consensual and that the WWTP will continue to provide access to the Project Proponent for any continual monitoring required for the WAE project. This can be evidenced by documents such as a Memorandum of Understanding (MoU), written consent, or other agreement with involved parties, such as the WWTP, wastewater utility, contracted operators, or contracted feedstock supplier.

To ensure additional net-negative climate impacts, eligible projects must:

Do one of the following:
- Add alkaline feedstock to a wastewater treatment plant (WWTP) that would not otherwise add an alkalinity-enhancing feedstock, such as lime, as evidenced from historical records of plant operations.
- In a WWTP that does currently add alkalinity (e.g. in the form of CaCO₃, NaOH, MgOH₂, etc.) for process control, the following scenarios are eligible. See Section 7.3 for more information on the baselines for these different scenarios.
  - Using the same feedstock and increasing the dosage above business as usual (BAU) operations.
  - Switching the feedstock such that the carbon removal potential is above that of BAU operations, adjusting the dosage if necessary.
Be considered additional, in accordance with the requirements of Section 5.4.
Provide a net-negative CO₂e impact (net CO₂e removal) as calculated in compliance with Section 8, on a cradle to grave GHG assessment basis.
Provide long duration storage (>1,000 yr estimated) of CO₂ as dissolved inorganic carbon (DIC) in seawater.

The following applicability requirements are to limit the scope of eligible projects that the present version of this Protocol is developed for. However, these may be expanded in future versions.

This Protocol currently includes storage of removed CO₂ as dissolved inorganic carbon in the ocean. Thus, eligible Projects must operate in WWTPs that discharge directly into the ocean from coastal outfalls, or to rivers and estuaries where the discharge will be transported to the ocean. Most rivers will reach their basin outlet within one to two months⁸. Long term storage in inland waters (e.g. lakes) is being explored for future iterations.
The quantification framework in this Protocol is developed for WWTPs treating biogenic waste with activated sludge reactors and variations on activated sludge processes, which is the most common form of biological treatment. Alternative types of biological treatment require modifications to this Protocol, particularly Section 8 and Section 11, and they may be allowed on a case-by-case basis in consultation with Isometric. More guidelines for other types of WWTPs, such as membrane bioreactors, will be explored for future versions of this Protocol.
Alkalinity addition occurs in the biological treatment portion of the facility.
Projects must operate as retrofits to existing WWTP facilities. A retrofit is defined as the introduction of new materials, products or technologies to an existing process or facility. This can include adding alkalinity dosing to WWTPs that did not previously add alkalinity, increasing dosing in plants that already add alkalinity, adding additional monitoring to the WWTP to quantify CDR, etc.

This Protocol only quantifies CDR within the project facility (i.e. within a closed system). Additional uptake of CO₂ that occurs in the open ocean after discharge is not eligible for crediting under this Protocol, but may be eligible for further crediting under the Ocean Alkalinity Enhancement from Coastal Outfalls Protocol.

5.0 Relation to the Isometric Standard

The following topics are covered briefly in this Protocol due to their inclusion in the Isometric Standard, which governs all Isometric Protocols. See in-text references to the Isometric Standard for further guidance.

5.1 Project Design Document

For each specific project to be evaluated under this Protocol, Project Proponents must document project characteristics in a Project Design Document (PDD) as outlined in Section 3.2 of the Isometric Standard. The PDD will form the basis for project verification and evaluation in accordance with this Protocol, and must include consideration of processes unique to Wastewater Alkalinity Enhancement projects, such as:

detailed feedstock characterization following the Rock and Mineral Feedstock Characterization Module
description of discharge site and WWTP business as usual operations, following Section 10
description of the mitigation plan according to the environmental and social risk assessment in adherence with Appendix 1, including a robust monitoring plan to ensure efficacy
description of the quantification strategy for net CO₂e removal following Section 8
description of all measurement and methods used to quantify processes relevant to the calculation of net CO₂e removal, cross-referenced with relevant standards where applicable
documentation of official permitting and proof of partnership, such as a Memorandum of Understanding, with partner WWTP

5.2 Verification and Validation

Projects must be validated and net CO₂e removals verified by an independent third party, consistent with the requirements described in this Protocol as well as in Section 4 of the Isometric Standard.

The Validation and Verification Body (VVB) must consider the following requisite components:

Validate that the feedstock adheres to the requirements listed in the Rock and Mineral Feedstock Characterization Module.
Verify that the quantification approach adheres to requirements of Section 8, including demonstration of required records.
Verify that the Environmental & Social Safeguards outlined in Section 6 are met.
Verify that the Project is compliant with requirements outlined in the Isometric Standard.

5.2.1 Verification Materiality

The threshold for Materiality, considering the totality of all omissions, errors and mis-statements, is 5%, in accordance with Section 4.3 of the Isometric Standard.

Verifiers should also verify the documentation of uncertainty of the GHG statement as required by Section 2.5.7 of the Isometric Standard. Qualitative Materiality issues may also be identified and documented, such as:

control issues that erode the verifier’s confidence in the reported data
poorly managed documented information
difficulty in locating requested information
noncompliance with regulations indirectly related to GHG emissions, removals or storage

5.2.2 Site Visits

Project validation and verification must incorporate site visits to project facilities in accordance with the requirements of ISO 14064-3, 6.1.4.2, including, at a minimum, site visits during validation and initial verification. Validators should, whenever possible, observe project operations to ensure full documentation of process inputs and outputs through visual observation (see Section 4 of the Isometric Standard).

A site visit must occur at least once per project validation at each location.

5.2.3 Verifier Qualifications & Requirements

Verifiers and validators must comply with the requirements defined in Section 4 of the Isometric Standard. In addition, VVB teams shall maintain and demonstrate expertise associated with the specific technologies of interest.

All VVBs are approved by Isometric independently and impartially based on alignment with Conflict of Interest policies, rotation of VVB policies, oversight on quality and the following requirements:

VVBs must be able to demonstrate accreditation from:
- an International Accreditation Forum member against ISO 14065: 2020 or other relevant ISO standard, including but not limited to ISO 14034:2016, ISO/IEC 17020:2012, ISO/IEC 17029:2019; or
- a relevant governmental or intergovernmental regulatory body.
Alternatively, on a case-by-case basis, if VVBs are able to demonstrate to Isometric that they satisfy all required Verification needs and competencies required for the relevant Protocol and follow the guidelines of ISO 19011:2018 or other relevant standards, they may be approved.

5.3 Ownership

CDR via Wastewater Alkalinity Enhancement can often be a result of a multi-step process (such as quarrying, alkaline feedstock processing, transportation, on-site operations and monitoring), with activities in each step managed and operated by a different operator, company or owner. When there are multiple parties involved in the process, and to avoid double counting of net CO₂e removal, a single Project Proponent must be specified contractually as the sole owner of Credits. Contracts must comply with all requirements defined in Section 3.1 of the Isometric Standard.

5.4 Additionality

The Project Proponent must be able to demonstrate additionality through compliance with Section 2.5.3 of the Isometric Standard. The counterfactual scenarios and baselines utilized to assess additionality must be project-specific, and are described in Section 8 of this Protocol.

Additionality determinations must be reviewed and completed every two years, at a minimum, or whenever project operating conditions change significantly, such as the following:

regulatory requirements or other legal obligations for project implementation change or new requirements are implemented
project financials indicate Carbon Finance is no longer required, potentially due to, for example:
- increased tipping fees for waste feedstocks
- sale of co-products that make the business viable without Carbon Finance
- reduced rates for capital access
- subsidies for WWTP emissions reduction

Any review and change in the determination of additionality will not affect the availability of Carbon Finance and Credits for the current or past Crediting Periods, but, if the review indicates the Project has become non-additional, this shall make the Project ineligible for future Credits.

5.5 Uncertainty

The uncertainty in the overall estimate of net CO₂e removal as a result of the Project must be accounted for. The total net CO₂e removal for a specific Reporting Period must be conservatively determined, and projects must conduct an uncertainty analysis for the net CO₂e removal calculation in compliance with requirements outlined in Section 2.5.7 of the Isometric Standard.

5.5.1 Reporting of Uncertainty

Projects must report a list of all key variables used in the net CO₂e removal calculation and their uncertainties, as well as a description of the uncertainty analysis approach, including:

required measurements used for net CO₂e removal calculation
emission factors utilized, as published in public and other databases
values of measured parameters from process instrumentation, such as electricity usage from utility power meters
laboratory analyses, including analysis of seawater chemistry and alkaline feedstocks

The uncertainty information should at least include the minimum and maximum values of each variable that goes into the net CO₂e removal calculation (see Section 8 for more details). More detailed uncertainty information should be provided if available, as outlined in Section 2.5.7 of the Isometric Standard.

In addition, a sensitivity analysis that demonstrates the impact of each input parameter’s uncertainty on the final CO₂e removal uncertainty must be provided. Details of the sensitivity analysis method must be provided such that a third party can reproduce the results. Input variables may be omitted from an uncertainty analysis if they contribute to a < 1% change in the net CO₂e removal. For all other parameters, information about uncertainty must be specified.

5.6 Data Reporting and Availability

In accordance with the Isometric Standard, all evidence and data related to the underlying quantification of net CO₂e removal and environmental monitoring will be available to the public through Isometric’s Science Platform. That includes:

Project Design Document
GHG Statement
Measurements taken
Model specifications and output
Emission factors used
Scientific literature used

The Project Proponent can request certain information to be restricted (only available to authorized Buyers, the Registry and VVB) where it is subject to confidentiality. However, that does not apply to any numerical data produced or used as part of the quantification of net CO₂e removal, or to any monitoring data that is required for regulatory compliance.

6.0 Environmental and Social Safeguarding

6.1 Overarching Principles

Following the Isometric Standard, Credits issued under this Protocol are contingent on the implementation, transparent reporting, and independent verification of comprehensive safeguards. These safeguards encompass a wide range of considerations, including environmental protection, social equity, community engagement and respect for cultural values. The process mandates that safeguard plans be incorporated into all major project phases, with detailed reports made accessible to stakeholders. Adherence to and verification of environmental and social economic safeguards is a condition for all Crediting Projects.

Since Projects under this Protocol are retrofitted into existing WWTP operations, the scope of environmental and social safeguarding is applicable for the additional impacts relative to BAU.

6.2 Governance and Legal Framework

Projects must adhere to the following governance and legal requirements:

Official permitting:

Project Proponents must identify the jurisdictional authorities of the receiving water bodies of the project site, and as outlined in Section 4 (Applicability).
Projects must operate within the existing permits, or an approved modified permit, of a wastewater treatment plant.
Project Proponents must hold an official partnership, such as through an MoU, with the wastewater facility the Project intends to integrate with.

Compliance:

Project Proponents must comply with all national and local laws, regulations and policies.
Where relevant, Projects must comply with international conventions and standards governing human rights and uses of the environment, when conducted within or where it is foreseeable for it to impact Party jurisdictions.

6.3 Risk Mitigation Strategies

An environmental and social risk assessment in adherence with Section 3.7 of the Isometric Standard must be completed by a subject matter expert to identify potential risks, followed by the development of tailored mitigation plans. These plans must encompass specific actions to avoid, minimize or rectify identified impacts. Effective implementation of these measures must also be accompanied by a robust monitoring plan to detect negative impacts and stop projects when necessary (see Section 11). Since Wastewater Alkalinity Enhancement is integrated with existing wastewater treatment plants, in many cases, the existing monitoring requirements for BAU wastewater treatment operations may be sufficient.

Environmental and social risk identification, assessment, avoidance and mitigation planning will be unique to each Project’s technological, environmental and social contexts. The severity of these risks vary based on site specifics and the wastewater effluent characteristics.

6.3.1 Environmental Safeguards

The Project Proponent must conduct an environmental risk assessment which adheres to Section 3.7.1 of the Isometric Standard.

When assessing aquatic environmental risks, it is important to holistically consider the risk compared to the baseline scenario of business as usual wastewater treatment. For context, existing pollutant and nutrient loads from wastewater discharge have a documented impact of leading to acidification, hypoxia, and toxic algae blooms. Alkalinity enhancement has previously been demonstrated as an intervention to mitigate these environmental impacts. Generally, it is expected that Wastewater Alkalinity Enhancement will reduce the risks already contained within business as usual wastewater discharge.

Particular environmental risks associated with Wastewater Alkalinity Enhancement which must be assessed, avoided and/or mitigated are:

Feedstock sourcing:

Potential risks associated with feedstocks include land use impacts from sourcing, production, preparation, storage and distribution, such as land degradation, land occupation, dust pollution, deforestation and localized watershed contamination.

Co-products and waste:

Generation of waste products or additional waste must be accompanied by a plan which ensures safe handling, containment and disposal.

Pollution prevention:

Additional pollutants, such as nutrients or toxic elements, from dissolution of feedstock(s), which may result in bioaccumulation in biota or water quality impacts for downstream water users. Rock and Mineral Feedstock Characterization is mandatory as a first line of defense for safeguarding against the release of harmful pollutants.
The risk of the WWTP not being able to meet its discharge permit requirements must be assessed and there should be a plan in place for mitigating this.

Ecological impacts:

Shock to the ecosystem due to rapid or sudden changes in carbonate system parameters.
Changes in carbonate chemistry, such as pH, could directly help or harm aquatic life depending on the magnitude and direction of the pH shift. For example, a risk of elevated pH in the wastewater effluent is an increase in the free ammonia fraction, which is toxic to aquatic life particularly if there is insufficient dilution upon discharge.
Cascading impacts of altered carbonate chemistry, nutrient fields, or particle deposition on biodiversity and ecosystem functions at and downstream of the receiving water body.

6.3.2 Social Safeguards

The Project Proponent must conduct a social risk assessment which adheres to Section 3.7.2 of the Isometric Standard on Social Impacts.

In particular, Wastewater Alkalinity Enhancement projects must:

have a plan for safeguarding working conditions, especially for safe handling and sampling of wastewater, activated sludge and fine particulate feedstocks
adhere to all health and safety standards set by the partner facility
consider the risks to water justice for users of the receiving water body and downstream water bodies
consider the risks to environmental justice due to historical inequities in siting of wastewater treatment facilities

6.4 Stakeholder Engagement

Per Section 3.5 of the Isometric Standard, Project Proponents must demonstrate active stakeholder engagement throughout project planning and operation, ensuring that all risk mitigation strategies contribute to sustainable project outcomes. Local stakeholders situated in the vicinity of the project site may contribute an in-depth understanding of the local system and provide invaluable insights and recommendations on the potential risks, necessary safeguards and specific monitoring needs. Relevant local stakeholders may include municipal utilities operators, local members of academia, Indigenous groups, environmental groups, and citizen associations. The Stakeholder Input Process must adhere to requirements outlined in Section 3.5 of the Isometric Standard, and evidence of these meetings must be submitted in the PDD.

6.5 Adaptive Management

Project Proponents must include in the PDD a plan for information sharing, emergency response and conditions for stopping or pausing alkaline feedstock dosing. Plans for pausing or stopping dosing must be in place in instances where:

instrument malfunctions lead to data-gaps in required monitoring
effluent exceeds thresholds outlined in the PDD
regulatory non-compliance, e.g. danger to ecosystem health detected (such as by the local community or government agency)
compromised health and/or safety of workers and/or local stakeholders

7.0 System Boundary and Baseline

7.1 Reporting Period

The Reporting Period represents an interval of time over which removals are calculated and reported for verification. The total net CO₂e removal is calculated using a series of measurements for a specified Reporting Period, and is written hereafter as [math: CO_2e_{Removal,RP}]. See Section 8.1 for details on how [math: CO_2e_{Removal,RP}] is calculated. Only CO₂ is included for the quantification of gross removal, while all GHG emissions are included when calculating the net removal (see Section 7.2 and Table 1).

GHG emission calculations must include all emissions related to the project activities that occur within the Reporting Period. This includes: a) any emissions associated with project establishment allocated to the Reporting Period, b) any emissions that occur within the Reporting Period, c) any anticipated emissions that would occur after the Reporting Period that have been allocated to the Reporting Period and d) leakage emissions that occur outside of the system boundary as a result of induced market changes that are associated with the Reporting Period.

7.2 System Boundary & GHG Emissions Scope

The scope of this Protocol includes GHG sources, sinks and reservoirs (SSRs) associated with a Wastewater Alkalinity Enhancement (WAE) Project. A cradle-to-grave GHG Statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary. The system boundary must include all SSRs controlled by and related to the Project, including but not limited to the SSRs in Figure 1 and Table 1.

The system boundary must include all GHG SSRs from activities related to the Credits delivered within the Reporting Period that are associated with the establishment of the Project, operations and end-of-life activities that occur after the Reporting Period.

As noted in Section 7.3, the baseline scenario assumes that the activities associated with the WAE component of the wider WWTP facility do not take place and no additional infrastructure associated with the WAE project is built. Therefore, some elements of the process included within the system boundary will only apply to the additional emissions attributed to activities that are above business as usual (BAU) emissions for the WWTP. Any emissions from sub-processes or process changes that would not have taken place without the involvement of the CDR process must be fully considered in the system boundary. This allows for accurate consideration of additional, incremental emissions induced by the CDR process. For example, if a WWTP was using NaOH as a pH amendment as part of their BAU operations, and a WAE project replaces NaOH with a lower emission feedstock, then this constitutes a process change and the resulting new feedstock manufacturing and transport emissions must be fully accounted for in the system boundary. If a WWTP is using the same feedstock as the BAU scenario and increasing dosing, then only the feedstock emissions associated with the increased feedstock need to be accounted for.

If any GHG SSRs within Table 1 are deemed not appropriate to include in the system boundary, they may be excluded if robust justification and appropriate evidence is provided. Exclusions that are based on no activity above BAU WWTP activities must be evidenced.

[Image: **Figure 1** System Boundaries]

Figure 1 System boundaries for a Wastewater Alkalinity Enhancement (WAE) project integrated into an existing Wastewater Treatment Plant (WWTP). Any components in color with a dotted boundary are those where emissions are associated with WAE activities that are shared with BAU WWTP activities. Only activities above BAU are accounted for within the system boundary. The accounting of feedstock manufacturing and transport emissions depend on the specific WWTP BAU operations, see Table 1 for more details. Components in grayscale with a dotted boundary are those where activities are unlikely to be accounted for within the system boundary but which are an integral part of the process, and so are included for completeness.

Table 1. Scope of activities and GHG SSRs to be included by the removal project

Activity	GHG source, sink or reservoir	GHG	Scope	Timescale
Project Establishment	Initial surveys and feasibility studies	All GHGs	Any embodied, energy and transport emissions associated with surveys or feasibility studies required for establishment of the project site for WAE CDR activities.	Before dosing starts - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 8.4.1).
Equipment & materials manufacture	All GHGs	Embodied emissions associated with equipment and materials manufacture for project establishment (lifecycle Modules A1-3⁹). To include product manufacture emissions for equipment, buildings, infrastructure, and temporary structures associated with WAE CDR processes. Must include any additional material or infrastructure requirements at the WWTP as a result of WAE, for example any additional load bearing structures.
Equipment & materials transport to site	All GHGs	Transport emissions associated with transporting equipment and materials associated with WAE CDR processes to the project site(s) (lifecycle Module A4⁹). Must include any additional material or infrastructure requirements at the WWTP as a result of WAE, for example any additional load bearing structures.
Construction and installation	All GHGs	Emissions associated with construction and installation of the project site(s) (lifecycle Module A5⁹) for WAE CDR activities and any additional infrastructure requirements to WWTP as a result of WAE activities. To include energy use for construction, installation and groundworks, as well as waste processing activities and emissions associated with land use change.
Misc.	All GHGs	Any SSRs not captured by categories above. Any SSRs not captured by categories above. Only those that occur over the level of BAU WWTP activities should be accounted for.
Operations	Energy use	All GHGs	Electricity and fuel consumption associated operational processes, including marginal pumping, pre-treatment, waste-water treatment, solids separation and disposal, and discharge of treated to the environment. Only those that occur over the level of BAU WWTP activities should be accounted for.	Over each Reporting Period - must be accounted for in the relevant Reporting Period (See Section 8.4.2)
Feedstock manufacturing and transport	All GHGs	Feedstock raw material extraction and manufacturing including rock quarrying, crushing, grinding and drying. Feedstock transport from source manufacturer to project site. Only those that occur over the level of business as usual WWTP activities should be accounted for, which is applicable if the same feedstock as BAU is used for the WAE project. Switching to a new feedstock constitutes a deviation from BAU activities, and all feedstock manufacturing and transport emissions must be accounted for in that case.
Consumables (other than feedstock)	All GHGs	Embodied emissions associated with consumables required for operation of the project site (excluding feedstock). Only those that occur over the level of BAU WWTP activities should be accounted for. This could include consumables for treatment of waters, cleaning or coagulants within the WWTP above BAU.
Waste Activated Sludge (WAS) transport	All GHGs	Transport of waste activated sludge (WAS) to disposal locations. Only activities that occur over the level of BAU WWTP activities should be accounted for.
Incineration of Waste Activated Sludge (WAS)	CO₂	CO₂ released from the incineration of waste activated sludge (WAS), if applicable. Only those that occur over the level of BAU WWTP activities should be accounted for.
Landfill disposal of Waste Activated Sludge (WAS)	All GHGs	Emissions associated with the landfilling of waste activated sludge (WAS), if applicable. Only those that occur over the level of BAU WWTP activities should be accounted for.
Sampling required for MRV	All GHGs	Monitoring, including consumables used for measurement and transportation or shipping of samples for laboratory analysis and sample processing for MRV.
Staff travel	All GHGs	Flight, car, train or other travel required for the project operations, including contractors and suppliers required on site. Only those that occur over the level of BAU WWTP activities should be accounted for.
Surveys	All GHGs	Embodied, energy and transport emissions associated with undertaking required surveys e.g. environmental impact surveys. Only those that occur over the level of BAU WWTP activities should be accounted for.
CO₂ Stored	CO₂	The gross amount of CO₂ removed and durably stored from the Wastewater Alkalinity Enhancement process as ocean dissolved inorganic carbon (DIC). This must include ocean losses and broader impacts on CDR described in Section 8.2.3 and Section 8.2.4 respectively.
Maintenance of project site	All GHGs	To include maintenance (lifecycle Modules B2⁹), repair (B3), replacement (B4) and refurbishment (B5) activities associated with equipment, buildings and infrastructure. Only those that occur over the level of BAU WWTP activities should be accounted for. For example, if there is increased fouling of membranes or wear on pipes and pumps that lead to more frequent replacement, then the emissions related to replacing those parts must be accounted for.
Misc.	All GHGs	Any SSRs not captured by categories above. For example, accidental or unintended release of treated waters may result in secondary precipitation and ocean outgassing, or unneutralized streams may result in ocean outgassing. If these events occur, their impacts must be quantified. Only those that occur over the level of business as usual WWTP activities should be accounted for.
End-of-Life	End-of-life of emissions	All GHGs	To include anticipated end-of-life emissions (lifecycle Modules C1-4⁹). Only those that occur over the level of BAU WWTP activities should be accounted for.	After Reporting Period - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 8.4.1)
Ongoing sampling and monitoring required for MRV	All GHGs	Embodied, energy and transport emissions related to ongoing monitoring of carbonate mineral storage site, measurement equipment, and energy use associated with monitoring equipment, sampling systems, laboratory analysis, operation and management of monitoring facility buildings and handling equipment. This could include ongoing environmental monitoring of discharge to marine environments. Only those that occur over the level of BAU WWTP activities should be accounted for.
Ongoing surveys	All GHGs	Embodied, energy and transport emissions associated with undertaking long-term required surveys e.g. ecological surveys. Only those that occur over the level of BAU WWTP activities should be accounted for.
Misc.	All GHGs	Any emissions source, sink or reservoir not captured by categories above. Only those that occur over the level of BAU WWTP activities should be accounted for.

The Project Proponent must consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s definition of GHGs, which includes: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and fluorinated gasses such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆) and nitrogen trifluoride (NF₃). For CO₂ capture and CO₂ leakage, only CO₂ is expected to be included as part of the quantification. For all other activities, all GHGs must be considered. For example, CO₂, CH₄ and N₂O are all associated with diesel consumption.

All GHGs must be quantified and converted to CO₂e. GHGs must be converted to CO₂e in the GHG Statement using the 100-yr GWP for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report)¹⁰.

Miscellaneous GHG emissions are those that cannot be categorized by the GHG SSR categories provided in Table 1. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities and must report any outside of the SSR categories identified as miscellaneous emissions.

Emissions associated with a project's impact on activities that fall outside of the system boundary of a project must also be considered. This is covered under Leakage in Section 8.4.4.

7.2.1 System Boundary Considerations

Ancillary Activities

Ancillary activities, such as supplementary research and development activities and corporate administrative activities, that are associated with a project but are not directly or indirectly related to the issuance of Credits can be excluded from the system boundary.

Secondary Impacts on GHG Emissions

Wastewater Alkalinity Enhancement has additional impacts on GHG emissions beyond the scope of this Protocol, for example by reducing CH₄ and N₂O emissions, or by increasing energy efficiency at WWTPs. Crediting the avoidance of emissions is beyond the scope of this Protocol, and thus is not considered.

Considerations for Waste Input Emissions

Embodied emissions associated with system inputs considered as waste products can be excluded from the system boundary provided the appropriate criteria are met. For energy inputs, for example the use of waste heat, refer to the Energy Accounting Module. For other waste inputs, the following criteria shall be considered.

If EC1 in Table 2 is satisfied then this is sufficient to exclude embodied emissions from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary as compliance with EC1 would result in no change to the waste producer behavior (no market leakage) and indicates there are no alternative users of the waste product (no replacement emissions).

Table 2. Waste input emissions exclusion criteria, EC1

Criteria	Description	Documentation required
EC1	No payment was made for the material, or only a “tipping fee” is paid.	Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, a signed affidavit from the Project Proponent stating that no in-kind compensation was made to the feedstock supplier must be provided.

If EC2 and EC3 in Table 3 are both satisfied then this is sufficient to exclude embodied emissions from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary as compliance with EC2 and EC3 would result in no significant change to the waste producer behavior (no market leakage) and there are no alternative use cases for the waste product (no replacement emissions).

Table 3. Waste input emissions exclusion criteria, EC2 and EC3

Criteria	Description	Documentation required
EC2	The amount of the waste product used by the CDR project was not already being utilized as a valuable product by another party for non-CDR uses. Therefore, the producer of the waste product has no alternative use case for the waste product.	Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, an affidavit from the waste supplier identifying that there are no alternative use cases for the waste product.
EC3	Payments for the waste product do not constitute a significant share of upstream operations revenue for the waste producer.	Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, an affidavit from the waste supplier that documents that payments from the Project do not constitute a significant share of upstream operations revenue.

Considerations for Project Activities Integrated into Separate Practices

WAE projects eligible under this Protocol are integrated into existing WWTP (see Section 4), and thus will be reliant on processes occurring separately from the CDR activity. This may include operations of bioreactors, existing flowmeters and other monitoring equipment and making use of discharge outfalls. Activities that were already occurring and would continue to occur without the WAE project may be omitted from the system boundary, provided that evidence that the activity was already occurring and would have continued to occur in the absence of the WAE project can be provided. These principles are reflected in Table 1 and Figure 1.

Any impacts on the WWTP as a result of WAE that would require changes to the existing separate facility, such as additional infrastructure requirements associated with heavier loads for incorporating WAE processes, shall be considered within the system boundary. Incremental increases in activity from BAU, such as incremental additional energy requirements, must be accounted for in the system boundary and evidenced in full.

The separate facility must not include any CO₂ removals associated with the WAE CDR activity in their company GHG accounting to avoid double counting of removals.

7.3 Baseline

Under this Protocol, a Project must be a retrofit to an existing WWTP facility (see Section 4). The baseline scenario for a WAE project assumes the WAE activities associated with CDR do not take place and the WWTP operates in a BAU manner.

The counterfactual removal scenario for each Project will depend on if the BAU operations of the WWTP include some level of alkalinity addition or not. If the BAU operations use a high carbon intensity feedstock (e.g. NaOH) such that the feedstock manufacturing emissions exceed the potential CO₂ drawdown in the WWTP, then the carbon removal potential of the BAU operation may be considered 0 as it is a net-emitting process. Projects operating under this scenario must be cleared ahead of time in consultation with Isometric. See Section 8.3 for details on calculating the counterfactual, [math: CO_2e _{Counterfactual,\ RP}], for different scenarios.

In some instances, it may be necessary to consider weathering of alkaline feedstock that would have occurred without the Wastewater Alkalinity Enhancement project. For example, if the feedstock used is a waste product that was not mined or quarried specifically for project activities and was stored in open-air conditions, some degree of surficial weathering may be expected over timescales relevant to a project lifetime. Project Proponents using these feedstocks must account for the counterfactual weathering of the feedstock.

8.0 Quantification of CO₂e Removal

8.1 Net CDR Calculation

Net CO₂e removal from Wastewater Alkalinity Enhancement for each Reporting Period, RP, must be calculated conservatively so as to give high confidence that, at minimum, the estimated net CO₂e was removed.

The net CO₂e removal equation is:

[math: ~~CO_2e_~~CO*2e*{Removal,\ RP} = ~~CO_2e_~~CO*2e*{Stored,\ RP} - ~~CO_2e_~~CO*2e*{Counterfactual,\ RP} - ~~CO_2e_~~CO*2e*{Emissions,\ RP}]

Equation 1

Where

[math: CO_2e_{Removal,\ RP}] represents the total net CO₂e removal for Reporting Period, RP, in tonnes of CO₂e;
[math: CO_2e_{Stored,\ RP}] represents the total CO₂ removed from the conversion of biogenic CO₂ in wastewater to stable dissolved inorganic carbon due to the Project activity for Reporting Period, RP, in tonnes CO₂e;
[math: CO_2e_{Counterfactual,\ RP}] represents the total counterfactual CO₂ removed from the atmosphere for the Reporting Period, RP, in tonnes of CO₂e. This term is calculated using BAU operations. See Section 8.3 for more details on how to calculate this term for different scenarios;
[math: CO_2e_{Emissions,\ RP}] represents the total GHG emissions associated with the Project including leakage, over a Reporting Period, RP, in tonnes of CO₂e.

8.2 Calculation of CO₂eStored, RP

During biological treatment, organic carbon is oxidized to form CO₂, which may then be released to the atmosphere. Outgassing of CO₂ largely occurs during secondary treatment, where mixing, aeration, carbonic acid generation and contact with the atmosphere are enhanced.

Alkalinity addition, such as through addition of carbonates or hydroxides, convert CO₂ to carbonate and bicarbonate ions, and prevent the release of CO₂ to the atmosphere. As a reminder, Wastewater Alkalinity Enhancement projects prevent the release of biogenic CO₂ to the atmosphere, which is not counted in standard GHG accounting frameworks⁵. Thus, Wastewater Alkalinity Enhancement qualifies as carbon dioxide removal, rather than emissions avoidance.

For example, the dissolution of calcium carbonate (CaCO₃) as an alkaline feedstock follows the chemical reaction:

[math: ~~CaCO_~~CaCO*{3 (s)} + ~~CO_~~CO*{2 (aq)} + ~~H_2O_~~H*2O*{(l)} \rightarrow Ca^{2+}_{(aq)} + 2HCO_{3 (aq)}^{-}]

Equation 2

In this example, CO₂ conversion has a 1:1 molar ratio to CaCO₃ consumption and CO₂ consumption. Thus, CO₂ conversion to bicarbonate (HCO₃^-) can be measured by direct measurement of solid feedstock, (ie. CaCO_3(s)), or dissolved weathering products (ie. Ca²⁺_(aq)).

The total CO₂ that is converted to bicarbonate ions in the wastewater stream is determined using direct measurements within the WWTP and subtracting any potential losses upon effluent discharge.

The total amount of carbon stored can be determined as follows:

[math: CO_2e_{Stored,\ RP} = m_{Dissolved,\ RP} *\frac{M_{CO_2}}{M_{FS}}* ((1-P)*X_{carbonic}* \eta_{Losses,\ RP} - P*X_{non-carbonic})]

Equation 3

Where

[math: m_{Dissolved,\ RP}] is the total mass of feedstock dissolved within a Reporting Period, RP, in tonnes;
[math: M_{CO_2}] is the molar mass of CO₂ in tonnes/mol;
[math: M_{FS}] is the molar mass of the chosen feedstock in tonnes/mol;
[math: P] is the fraction of feedstock dissolved by non-carbonic acid. [math: P] is a dimensionless value between 0 and 1;
[math: X_{carbonic}] is the molar ratio of CO₂ consumption and feedstock consumption from carbonic acid weathering, in mol CO₂/mol feedstock;
[math: X_{non-carbonic}] is the molar ratio of CO₂ release and feedstock consumption from non-carbonic acid weathering, in mol CO₂/mol feedstock. This term is 0 for non-carbonate feedstocks which do not release CO₂ upon contact with a non-carbonic acid;
[math: \eta_{Losses,\ RP}] are losses of CO₂ due to riverine and oceanic processes. [math: \eta_{Losses,\ RP}] is a dimensionless term. See Section 8.2.3 for calculation of this term.

The mass of feedstock dissolved within a Reporting Period, [math: m_{Dissolved,\ RP}], can be determined by:

[math: m_{Dissolved,\ RP} = \sum_{i}^{T} ( \dot m_{Dissolved,\ i} * \Delta t_i) ]

Equation 4

Where

[math: m_{Dissolved,\ RP}] is the total mass of feedstock dissolved within a Reporting Period, RP, in tonnes;
[math: \dot m_{Dissolved,\ i}] is the average feedstock dissolution rate over time interval, [math: i], in tonnes/day;
[math: \Delta t_i] is the duration of time, [math: i], over which measurements are averaged, in days;
[math: T] is the total number of time intervals in the Reporting Period, RP, to be summed over.

Note that this quantification approach assumes the use of a pure mineral feedstock. In cases where a feedstock of mixed mineralogy is used, Project Proponents must make conservative assumptions in quantifying CDR. For example, a Project Proponent may choose to allocate all carbon removal to the mineral phase with lowest conversion potential (e.g., if a feedstock contains MgO and MgCO₃, these phases store 2 and 1 moles of CO₂ per mole of feedstock, respectively), or a Project Proponent may choose to assume that the phase with the lowest conversion potential dissolves first (e.g., if a feedstock is 90% MgO and 10% MgCO₃ by mass, the first 10% of dissolved weathering products by mass are assumed to come from MgCO₃). All assumptions and calculations must be documented in the PDD.

8.2.1 Calculation of Average Feedstock Dissolution Rate and P

[math: \dot m_{Dissolved}] is determined using a mass balance on a control volume (see Figure 2 for an example). Project Proponents must define the boundaries of their control volume in the PDD. For example, for an activated sludge system, the control volume should encompass the total volume of the secondary treatment process, including the bioreactor and secondary clarifier (Figure 2). All inputs and outputs of the control volume must be clearly defined and identified in the PDD. Modifications to mass balance equations may be required based on the control volume boundaries, and must be described in the PDD. All calculations must be submitted for verification.

[Image: **Figure 2** Control Volume]

Figure 2: Example process diagram, control volume and monitoring locations for Wastewater Alkalinity Enhancement. The control volume, [math: V], shown in pink, may encompass any volume inclusive of the biological treatment and solids separation. The control volume and exact input and output locations may differ depending on the WWTP.

[math: \dot m_{Dissolved}] can be calculated based on the following options:

Option 1: Mass balance on solid feedstock, where the difference between solid feedstock into and out of the control volume is assumed to be the result of feedstock dissolution.
Option 2: Mass balance on conservative dissolved weathering products, such as Ca²⁺ or Mg²⁺, where the difference in weathering product concentration between the influent and effluent is assumed to the result of feedstock dissolution.

The choice of these metrics used for quantification will depend on site-specific WWTP design. The equations used for both options are detailed below. Project Proponents must specify which measurement phase will be used for primary quantification in the PDD.

Note that Figure 2 represents one possible WWTP configuration, and as such the equations given below represent the minimum terms that must be considered for quantification. Additional considerations may be required based on WWTP design. All site-specific considerations must be documented in the PDD. Examples of site-specific variations include (but are not limited to):

Recycle streams produced within the plant that constitute a significant alkalinity source or sink;
Chemical addition that constitutes a significant alkalinity source or sink;
Trickling filter/solid contact (TF/SC) treatment and similar hybrid processes;
WWTPs using high purity oxygen (HPO) for the aeration process.

8.2.1.1 Option 1: Quantification in the Solid Phase

The mass flow rate of solid feedstock is defined as:

[math: \dot m_{FS} = Q * FS * 10^{-9}]

Equation 5

Where

[math: \dot m_{FS}] is mass flow rate of feedstock in tonnes/day;
[math: Q] is flow rate in L/day;
[math: FS] is mass concentration of feedstock in mg/L;
A factor of 10^-9 is used to convert units from mg to tonnes.

Alternative formulations of flow rate can be used where applicable, this must be described in the PDD.

The mass balance of the solid feedstock within the control volume, [math: V], (Figure 2) can be defined as:

[math: \frac{dFS}{dt} = \dot m_m*{FS,\ Dosing} - \dot m_m*{FS,\ Effluent} - \dot m_m*{FS,\ WAS} - \dot m_m*{Dissolved}]

Equation 6

Where:

[math: \frac{dFS}{dt}] is the change in feedstock mass in the control volume over time t;
[math: \dot m_{FS,\ Dosing}] is the mass flow rate of feedstock added in tonnes/day;
[math: \dot m_{FS,\ Effluent}] is the mass flow rate of feedstock in the effluent stream in tonnes/day;
[math: \dot m_{FS,\ WAS}] is the mass flow rate of feedstock in the waste activated sludge (WAS) stream in tonnes/day;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day.

By assuming steady state, [math: \frac{dFS}{dt} = 0], no feedstock present in the influent, and the control volume shown in Figure 2, [math: \dot m_{Dissolved}] can be calculated as:

[math: \dot m_{Dissolved} = \dot m_{FS,\ Dosing} - \dot m_{FS,\ Effluent} - \dot m_{FS,\ WAS}]

Equation 7

Where:

[math: \dot m_{FS, Dosing}] is the mass flow rate of feedstock from dosing in tonnes/day;
[math: \dot m_{FS, Effluent}] is the mass flow rate of the feedstock in the effluent stream in tonnes/day:
- [math: \dot m_{FS, Effluent} = Q_{Effluent} * FS_{Effluent} * 10^{-9}] (Equation 8)
  - [math: Q_{Effluent}] is the flow rate of plant effluent in L/day;
  - [math: FS_{Effluent}] is the concentration of feedstock suspended in plant effluent in mg/L;
  - A factor of 10^-9 is used to convert units from mg to tonnes
[math: \dot m_{FS,\ WAS}] is the mass flow rate of feedstock in the waste activated sludge (WAS) stream in tonnes/day:
- [math: \dot m_{FS,\ WAS} = Q_{WAS} * FS_{WAS} * 10^{-9}] (Equation 9)
  - [math: Q_{WAS}] is the flow rate of waste activated sludge in L/day;
  - [math: FS_{WAS}] is the concentration of feedstock settled in waste activated sludge in mg/L;
  - A factor of 10^-9 is used to convert units from mg to tonnes.

Requirements for measurements of concentration of the feedstock in effluent and waste activated sludge will vary depending on the feedstock used:

When carbonate feedstocks, such as calcite (CaCO₃) are used, [math: FS_{Effluent}] and [math: FS_{WAS}] can be assumed to be equivalent to the total inorganic carbon (TIC) in samples taken from these streams. This approach assumes that any inorganic carbon present in plant effluent and waste activated sludge comes from dosing of carbonate feedstocks, which is a conservative assumption. Methods for TIC analysis must be described in detail in the PDD and must include any standards or SOPs used. Acceptable analyses may include, but are not limited to, use of a TIC analyzer.
Where non-carbonate feedstocks are used, [math: FS_{Effluent}] and [math: FS_{WAS}] must be determined from direct measurements of cations relevant to the chosen feedstock (e.g. Ca²⁺, Mg²⁺) in each stream, relative to the influent stream. Acceptable methods include, but are not limited to, sample digestion and/or or analysis on ICP-MS or ICP-OES. Sample digestion is required for [math: FS_{WAS}]. Note that for [math: FS_{Effluent}], samples must be acidified prior to filtration. Methods used for cation analysis must be described in detail in the PDD and must include any standards or SOPs used.

A portion of the feedstock may be dissolved by non-carbonic acids, in which case there is no conversion of CO₂ to stable bicarbonate within the WWTP and CDR cannot be credited for any non-carbonic acid weathering that occurs. Furthermore, for carbonate feedstocks, dissolution by non-carbonic acids leads to emission of CO₂. The proportion of feedstock dissolved by non-carbonic acid, [math: P], must be determined:

[math: P = \frac{\dot m_{NCA}}{\dot m_{Dissolved}}]

Equation 10

Where

[math: \dot m_{NCA}] is mass flow rate of feedstock dissolved by non-carbonic acid, in tonnes/day;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day.

The recommended approach to determine [math: \dot m_{NCA}] is measuring anion concentrations in the aqueous phase:

[math: \dot m_{NCA} = \frac{\sum_{i} (Q_i*[A^x]_i)}{1 * 10^6}]

Equation 11

Where:

[math: Q_i] is the flow rate of stream [math: i], in L/day;
[math: [A^x]_i = \sum_{y} (a_y * n_y * M_y)] (Equation 12), where:
- [math: a_y] is the concentration of anion [math: y], in mol/L;
- [math: n_y] is the charge of anion [math: y];
- [math: M_y] is the molar mass of anion [math: y], in g/mol;
[math: 1 * 10^6] is a conversion factor for g to tonnes.

Note that, where anion concentrations are not available, alternative estimations of [math: \dot m_{NCA}] or [math: P] may be used. All data sources and calculations must be provided in the PDD and approved by Isometric.

8.2.1.2 Option 2: Quantification in the Aqueous Phase Using Conservative Dissolved Weathering Products

The molar flow rate of a dissolved weathering product, [math: C^x], is defined as:

[math: n_{C^x}= Q * [C^x]]

Equation 13

Where

[math: n_{C^x}] is the molar flow rate of dissolved weathering product [math: C^x], in mol/day;
[math: Q] is flow rate in L/day;
[math: [C^x]] is the molar concentration of dissolved weathering product [math: C^x], in mol/L.

The mass balance of the dissolved weathering product, [math: C^x], within the control volume V (Figure 2) can be defined as:

[math: \frac{d[C^x]}{dt} = (1/V)* [(n_{C^x,\ Influent} - n_{C^x,\ WAS} -n_{C^x,\ Effluent}) + (\dot m_{Dissolved}/M_{FS})]]

Equation 14

Where:

[math: \frac{d[C^x]}{dt}] is the change in molar concentration of dissolved weathering product, [math: C^x], in the control volume over time, in mol/(L day);
[math: V] is the volume of the control volume, in L;
[math: n_{C^x,\ Influent}] is the molar flow rate of dissolved weathering product [math: C^x] in the influent stream in mol/day;
[math: n_{C^x,\ WAS}] is the molar flow rate of dissolved weathering product [math: C^x] in the WAS stream in mol/day;
[math: n_{C^x,\ Effluent}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day;
[math: M_{FS}] is the molar mass of the feedstock, in tonnes/mol.

Assuming steady state, [math: \frac{d[C^x]}{dt} = 0], the rate of feedstock dissolved can be calculated in the aqueous phase using the following equation:

[math: \dot m_{Dissolved} = ( M_{FS})*(n_{C^x,\ Effluent} + n_{C^x,\ WAS} -n_{C^x,\ Influent})]

Equation 15

Where

[math: n_{C^x,\ Effluent}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day:
- [math: n_{C^x,\ Effluent}= Q_{Effluent} * [C^x]_{Effluent}] (Equation 16)
  - [math: Q_{Effluent}] is the flow rate of plant effluent in L/day;
  - [math: [C^x]_{Effluent}] is the molar concentration of dissolved weathering product [math: C^x] in the effluent stream mol/L.
[math: n_{C^x,\ WAS}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day:
- [math: n_{C^x,\ WAS}= Q_{WAS} * [C^x]_{WAS}] (Equation 17)
  - [math: Q_{WAS}] is the flow rate of plant effluent in L/day;
  - [math: [C^x]_{WAS}] is the molar concentration of dissolved weathering product [math: C^x] in the effluent stream mol/L.
[math: n_{C^x,\ Influent}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day:
- [math: n_{C^x,\ Influent}= Q_{Influent} * [C^x]_{Influent}] (Equation 18)
  - [math: Q_{Influent}] is the flow rate of plant effluent in L/day;
  - [math: [C^x]_{Influent}] is the molar concentration of dissolved weathering product [math: C^x] in the influent stream mol/L.
[math: M_{FS}] is the molar mass of the feedstock, in tonnes/mol.

The proportion of feedstock dissolved by non-carbonic acid, [math: P], must be determined.

[math: P = \frac{n_{C^x,\ NCA}*M_{FS}}{\dot m_{Dissolved}}]

Equation 19

Where

[math: n_{C^x,\ NCA}] is the molar flow rate of dissolved weathering product [math: C^x] resulting from non-carbonic acid dissolution of feedstock within the control volume, in mol/day;
[math: M_{FS}] is the molar mass of the feedstock, in tonnes/mol;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day.

The recommended approach to determined [math: n_{C^x,\ NCA}] is measuring anion concentrations in the aqueous phase.

[math: n_{C^x,\ NCA} = \sum_{i} ( Q_i*[C^x]_i)]Equation 20

Where:

[math: Q_i] is the flow rate of stream [math: i];
[math: [C^x]_i = \sum_{y} (a_y*n_y]) (Equation 21)
- [math: a_y] is the concentration of anion y;
- [math: n_y] is the charge of anion y.

Note that, where anion concentrations are not available, alternative estimations of [math: n_{C^x,\ NCA}] or [math: P] may be used. All data sources and calculations must be provided in the PDD and approved by Isometric.

8.2.2 Validation and Reconciliation Calculations

Project Proponents must conduct the following validation checks each Reporting Period. Discrepancies beyond the analytical precision of the methods used must be reported to the VVB and Isometric, and addressed with a system audit.

8.2.2.1 Confirmation of Steady State Operations

This framework assumes that [math: \frac{dFS}{dt} = 0], meaning that no feedstock accumulates in the control volume; this is the functional definition of steady state for the purpose of this Protocol. Verifying this assumption is important for determining [math: CO_2e_{Stored}], as accumulated feedstock is not accounted for in Equation 7 and may thus lead to overcrediting. Project Proponents are required to confirm this assumption through measurements of any feedstock accumulation in the system, either through sludge sampling devices or during routine cleaning and maintenance of the bioreactors. The frequency of these measurements will depend on site-specific operations and must be justified in the PDD. In instances where feedstock is accumulating, the amount of accumulated feedstock must be conservatively estimated and appropriately deducted from [math: CO_2e_{Stored}].

8.2.2.2 Mass Balance Calculations

There are two options available for quantifying [math: m_{Dissolved}] which are described in Section 8.2.1. Both Option 1 (solid phase measurements) and Option 2 (aqueous phase measurements) are expected to result in the same estimate for [math: m_{Dissolved}]. Project Proponents must check that the results of both options for calculating [math: m_{Dissolved}] agree within propagated error of the relevant measurements once per Reporting Period. If this is not the case, an audit must be performed to determine the cause of the discrepancy.

8.2.2.2.1 Sorption

Several studies have documented the sorption of metals and organic compounds to waste activated sludge ¹¹^,¹²^,¹³. This may be a possible cause of a discrepancy in mass balance calculations. If mass balance calculations cannot be resolved, Project Proponents should investigate sorption onto WAS by extracting sorbed weathering products from dried solid samples that have been washed with deionized water to remove any non-sorbed weathering products. Project Proponents are required to detail the extraction procedure in the PDD.

8.2.2.2.2 Future Updates to Quantification and Validation Approaches

It is anticipated that new technologies and methods for quantifying and validating wastewater alkalinity enhancement will emerge in the coming years. These new technologies will be regularly assessed by the Isometric science team for inclusion in this Protocol. New technologies and methods that have some demonstrated efficacy when compared to conventional solid-phase and aqueous-phase mass balance approaches may be used as a validation approach. New technologies and methods that have demonstrated efficacy and have gathered wider scientific consensus may be used for either quantification or validation.

8.2.2.3 Upper Limit of Biogenic CO₂ Outgassing

In the absence of WAE project activities, wastewater treatment plants have direct CO₂ emissions from evasion of biogenic CO₂¹⁴^,¹⁵. Secondary biological treatment contributes the majority of direct CO₂ emissions of wastewater treatment due to the generation of carbonic acid and the aeration process enhancing equilibration with the atmosphere.

Wastewater Alkalinity Enhancement reduces or eliminates direct outgassing of biogenic CO₂ emissions from the secondary treatment process. This Protocol only credits the avoided biogenic CO₂ emissions that occur within the confines of the WWTP, and not any reduced outgassing that might occur upon discharge into receiving waters. As a validation check, Project Proponents are required to calculate the amount of biogenic CO₂ outgassing within the residence time of the control volume, summed across the full timescale of the Reporting Period. This sets an the upper limit for [math: CO_2e_{Stored}].

There are several methods that can be used to provide an estimate of total biogenic CO₂ emissions:

Calculation based on WWTP data of chemical oxygen demand (COD) removed and a relevant emission factor. For example, a default emission factor of 560g CO₂/kg COD removed during treatment can be used¹⁵.
Measurement of dissolved CO₂ concentrations prior to aeration and in the outflow from secondary treatment. The difference in these values can be taken as the CO₂ loss during the treatment process. This method requires extensive baselining of CO₂ concentrations across the full range of typical environmental conditions that may impact the efficiency of microbial communities within the secondary treatment process. At a minimum, Project Proponents must measure baseline CO₂ concentrations in the relevant streams during standard operational conditions 3 times per quarter for 1 year prior to the onset of Project activities, due to the dependence of CO₂ solubility and microbial activity on temperature. Where available, data from partner facilities may be substituted for direct measurements. Where direct measurements are required, Project Proponents must describe the methods used for measurement of CO₂ concentrations. This Protocol recommends the equilibration method, in which a volume of fluid is equilibrated with the headspace of a vessel (typically a syringe) and the headspace gas is collected and injected into a vacuum-sealed vial (Vacutainer) for analysis on a gas chromatograph. Care should be taken to ensure that gas samples are properly stored. Other methods may be suitable and must be described in the PDD. Due to the high pCO₂ of wastewater with a high organic load, it is not recommended to measure the dissolved inorganic carbon (DIC) of the fluid, as outgassing is likely to occur during sample collection.
Modeling of outgassing in secondary treatment based on known fluid parameters. Model construction will be dependent on the project site and should follow best practices for the relevant treatment system ¹⁶. At a minimum, models should consider the following parameters within the biological treatment tanks:
- Concentration of CO₂
- pH
- Flow rate of the fluid
- Flow rate of the gas
- Temperature
- Gas pressure within the system
- Gas transfer velocity of the aeration tanks
Alternatively, an upper limit may be established from the total biogenic CO₂ production, which may be calculated from measurements of biological oxygen demand (BOD) in the influent stream. This provides a more crude estimate as it assumes that all of the biogenic CO₂ produced is outgassed within the WWTP.

There may be some instances where addition of alkalinity may result in increased efficiency of organic matter degradation within the control volume. This would increase the CO₂ available to react with feedstock relative to baseline conditions. This may increase the upper limit of [math: CO_2e _{Stored}], if sufficient evidence is provided (e.g. through modeling changes in the biological treatment process from feedstock dosing, based on expected dissolution rates and system conditions).

8.2.3 Calculation of Loss Discount

The effluent exiting the WWTP is enriched in TA and DIC compared to the receiving waters. After discharge into the receiving waters, losses may reduce the efficiency of CO₂ stored as a result of Wastewater Alkalinity Enhancement.

Processes that can lead to losses include:

Re-equilibration of the DIC system
Carbonate precipitation
Reduction in natural alkalinity fluxes
Changes in biotic calcification (for ocean discharge only)

Losses may occur in a number of locations, depending on the Project. In general, losses must be considered in the near field of the discharge site, as that is where the risk of losses are highest. For river discharges, losses may also occur along the transport pathway from the effluent discharge to the final storage reservoir, the ocean. As such, losses along river transport and upon entering the ocean must also be considered. Any losses that cannot be justified as negligible must be quantified and deducted from gross carbon removal.

[Image: **Figure 3** Losses]

Figure 3. Example schematic of where downstream losses may occur, and the spatial zones which must be considered for coastal and river discharges.

The overall loss discount for a Wastewater Alkalinity Enhancement project is the product of the loss factors associated with each loss process:

[math: \eta_{Losses,\ RP} = \prod_{i=1}^{N} \eta_i]

Equation 22

Where:

[math: \eta_{Losses,\ RP}] is the overall loss discount for Reporting Period;
[math: \eta_i] is the fraction of CO₂ that is retained after a given loss, [math: i];
[math: N] is the total number of loss processes.

The loss processes which must be considered for ocean and river discharge are indicated in Table 4.

Table 4. Losses and their corresponding spatial zones. All losses in column 1 "Mixing zone of discharge site" are to be considered for both coastal and riverine discharge, unless otherwise indicated. Transport losses in columns 2 and 3 apply only to riverine discharge. The risk of these losses must be described in the PDD, and justified if they are negligible or need to be quantified.

Loss process	1) Mixing zone of discharge site	Transport (riverine discharge only)
2) Along river to estuary	3) At ocean
Re-equilibration of DIC	x	x	x
Carbonate precipitation	x	x
Natural alkalinity reduction	x
Biotic calcification	x (coastal discharge only)

In the PDD, Project Proponents must describe the risk of these losses, as well as either (1) a justification of why the losses are negligible or (2) a strategy for quantifying a corresponding loss factor. Due to the difficulty and uncertainty in quantifying the impact of these processes at this time, acceptable treatment of losses in this Protocol include:

avoiding the likelihood of these losses by identifying avoidance strategies around conditions which lead to non-negligible loss terms, with corresponding monitoring to demonstrate adherence to those guardrails
estimating a conservative upper limit of loss based on scientific literature, first principles calculations, and/or experimentation
process-based modeling studies
direct measurements
alternative approaches that are sufficiently justified

Data, measurements and evidence used in the quantification of loss factors must be publicly disclosed. Example recommendations for each loss process are discussed below. Much of the existing research in these losses have been motivated by research in Enhanced Weathering, River Liming, and Ocean Alkalinity Enhancement, which may not exactly simulate the carbonate chemistry state of the effluent from the Wastewater Alkalinity Enhancement process described in this Protocol. Project Proponents are recommended to conduct research on these potential losses in the relevant carbonate chemistry parameter space for their specific process.

8.2.3.1 Near-Field Losses

The near-field zone comprises the spatial extent of initial mixing upon discharge, sometimes known as the mixing zone. Generally, the risk of losses are modulated by saturation states and environmental conditions including TSS. Since the effluent is controlled and solids are separated within the treatment plant, the influence of high effluent saturation states and TSS is expected to be limited. Additionally, existing thresholds for wastewater treatment plant permits provide an additional guardrail against these potential downstream losses. The risk of these losses declines further from the discharge site, since the perturbation from the wastewater effluent will become increasingly dilute.

Re-equilibration of DIC

Concept

Equilibrium speciation of DIC is primarily dependent on pH, and to a lesser extent temperature, salinity and pressure:

[math: CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow H^+ + HCO_3^- \leftrightarrow 2H^+ + CO_3^{2-} ]

Equation 23

The release of CO₂ due to re-equilibration of DIC may occur due to mixing of fluids. This may occur upon initial mixing of effluent with the receiving water body, or at river confluences and when rivers discharge to the ocean.

Quantification

The recommended quantification approach for outgassing upon initial mixing is to use a two endmember mixing model to predict the DIC and TA of the mixture of effluent and receiving waters. The difference between the observed DIC and predicted DIC of the mixture can be used to estimate the loss by CO₂ outgassing. This can be done using CO2SYS or PHREEQC. Alternate approaches, such as using a physical-biogeochemical model for the discharge site, can also be used.

Carbonate Precipitation

Concept

Secondary precipitation of calcium carbonate could cause CO₂ outgassing by the following reaction:

[math: Ca^{2+} + 2HCO_3^{-} \rightarrow CaCO_3 + CO_2 + H_2O]

Equation 24

Calcium carbonate precipitation may result in a reduction in carbon loss by 50% for non-carbonate feedstocks or 100% for carbonate feedstocks.

Discussion

In rivers and coastal areas, higher suspended particulates may increase nucleation. Early research suggests there is a relationship between increased alkalinity loss with higher TSS in the receiving water body¹⁷. Thus, the risk of secondary precipitation is most pronounced in the mixing zone of the outfall, where the carbonate chemistry and TSS perturbation are largest.

Limiting pH and the saturation state has been shown to be effective at avoiding this result, and laboratory research to characterize the critical thresholds that trigger precipitation under close-to-natural conditions are ongoing ¹⁸^,¹⁹^,²⁰^,²¹^,²². Furthermore, precipitation dynamics occur on a timescale between minutes to hours¹⁸^,²⁰, which suggests that dilution could be an effective risk mitigation strategy²³.

Quantification

An example avoidance strategy is setting a threshold on TA and saturation state, with consideration of environmental conditions including carbonate chemistry variables, TSS and dilution at the site²². Continuous monitoring of carbonate chemistry variables and TSS is recommended to ensure that conditions for secondary precipitation are avoided. In some cases, secondary precipitation can be identified by an observed increase in turbidity. Monitoring of turbidity is recommended, however it may be difficult to isolate a signal from secondary precipitation over natural fluctuations.

Natural Alkalinity Flux Reduction

Concept

Increased alkalinity in wastewater effluent can potentially reduce the natural alkalinity flux from marine or river sediments²⁴. This risk may be exacerbated by projects with settling particles that result in local alkalinity enrichment in marine or river sediments, and the potential impacts on the net removal calculation is uncertain at this time. More research in this area is needed and the Protocol will be updated with future advancements.

Quantification

A recommended avoidance strategy for Wastewater Alkalinity Enhancement projects is to limit accumulation of alkalinity on the sea bed through careful design of discharge rates, TSS thresholds, and solids separation prior to discharge, which will likely already be done as part of the WWTP. If this risk cannot be avoided, then additional monitoring or modeling is needed to assess the likely impact. Potential approaches may include numerical modeling of particle transport in receiving waters, sediment sampling, measuring benthic alkalinity fluxes.

Changes in Biotic Calcification

Concept

For coastal discharges, increases in marine biotic calcification can cause CO₂ outgassing. The carbonate chemistry conditions promoted by coastal discharge of alkalinity-enhanced wastewater could promote calcification due to the lowered H⁺ or elevated saturation state²⁵^,²⁶^,²⁷^,²⁸. Alkaline feedstock dissolution may release trace metals which has the potential to fertilize blooms of calcifiers²⁸.

Discussion

Early stage research manipulating Total Alkalinity with the aim of simulating OAE has found no significant increase in biologically produced calcium carbonate at elevated alkalinity in the ocean²⁹^,³⁰. However, the Black Sea, a naturally elevated alkaline environment, harbors extensive blooms of the coccolithophores ³¹^,³², a major group of calcifying plankton. This is thought to be due to the favorable carbonate chemistry promoted by the elevated alkalinity regime²⁸.

This is still an area where more research is needed, particularly through mesocosm and field trials, albeit there is a rich body of literature on lab and mesocosm scale species-specific responses to changing seawater carbonate chemistry ³³. The risk of outgassing due to biotic calcification may be project and location specific. Recently published meta-analyses synthesizing data from ocean acidification studies for OAE supports this claim that species and functional group specificity is likely ³⁴. Coastal areas with significant benthic calcification of CaCO₃ sediments may be especially susceptible to this feedback.

Quantification

A recommended avoidance strategy is setting thresholds on pH and TA based on what has been shown in previous studies to have no significant increase in biologically produced CaCO₃³⁵, or as determined for the specific deployment site), and monitoring for changes in ocean biota.

8.2.3.2 Transport Losses

For riverine discharge, the WWTP effluent generated alkalinity is transported through rivers and eventually, to the oceans. The transport of carbonate and bicarbonate ions along the river may result in carbon losses through the re-equilibration of DIC or calcium carbonate precipitation. Risks of these losses are more pronounced at major confluences along the river network. Project Proponents must quantify a loss discount for both re-equilibration and precipitation along rivers and upon entering the ocean.

8.2.3.2.1 Outgassing During River Transport

Quantification

To account for potential losses along river transport, Project Proponents must estimate potential losses along the river network through measurement or models. Recent publications have outlined modeling approaches that combine baseline river geochemical data, equilibrium modeling of water chemistry and scenarios of terrestrially exported DIC, which may serve as useful references ³⁶^,³⁷.

The minimum requirements for river transport loss models are:

Domain:
- Full river network through which bicarbonate and carbonate ions will be transported
Inputs:
- River characteristics:
  - Baseline calcite saturation index (SI_c)
  - pH
  - pCO₂
  - Alkalinity
- Effluent characteristics:
  - Discharge rate
  - Alkalinity fluxes
  - Cation fluxes
Outputs:
- SI_c along river*
- pH along river
- Efficiency or discount factor on river transport loss for re-equilibration of DIC
- Efficiency or discount factor on river transport loss for carbonate precipitation

Project Proponents are required to submit a detailed description of their modeling approach, including the model used, the river/watershed data used in model construction and the source of that data. Alternate approaches may be considered on a case by case basis.

*Note on calcite saturation index in rivers

Calcite saturation index (SI_C) is a useful parameter to determine the likelihood of carbonate precipitation. Calcite saturation index (SI_C) is calculated as:

[math: SI_c = \log_{10} \frac{\alpha Ca^{2+} * \alpha CO_3^{2-}}{K_{sp(calcite)}}]

Equation 25

With

[math: K_{sp(calcite)} = \alpha_{sat} Ca^{2+} * \alpha_{sat} CO_3^{2-}]

Equation 26

Where:

[math: \alpha] is the measured solution activities of those ions
[math: \alpha_{sat}] is the ion activity at saturation

When SI_C > 0, a river is considered supersaturated. Although supersaturation with respect to calcium carbonate does not necessarily result in calcium carbonate precipitation, typically, calcium carbonate precipitation is predicted at a SI_C > 1 ³⁷.

8.2.3.2.2 Outgassing Upon Entering Ocean

Discussion

Once alkalinity reaches the ocean, changes in pH, temperature or salinity can shift the carbonate system and result in a re-equilibration of DIC. Estimates from peer-reviewed studies suggest that marine losses of terrestrially exported DIC could amount to 10-30% loss of carbon, depending on temperature, salinity, pCO₂, ocean circulation³⁸^,³⁹^,⁴⁰. Typically, the ocean has a higher pH than rivers which shifts the carbonate equilibrium towards a higher proportion of CO₃^2- in oceans. As a result, the amount of DIC stored per unit of alkalinity decreases between inland waters and the ocean. In addition, changes in salinity and saturation state upon reaching the ocean can lead to calcium carbonate precipitation⁴¹.

Quantification

Outgassing upon entering the ocean must be quantified using regional data specific to the area where the river reaches the ocean. This loss can be estimated with one of the following approaches:

Using the Renforth and Henderson (2017) uptake efficiency equation
Using a 3D Earth Systems Model or ocean physical-biogeochemical model to explicitly simulate ocean circulation and air-sea CO₂ fluxes⁴⁰
Alternate approaches may be considered on a case by case basis, provided it is sufficiently described and justified in the PDD.

Option 1 assumes thermodynamic equilibrium with the atmosphere and provides an upper limit on the expected ocean losses. Option 2 considers the 3D ocean circulation and does not assume equilibrium with the atmosphere, which may lead to fewer losses in certain regions if the exported DIC is subducted out of atmospheric contact for long periods of time.

Option 1

The Renforth and Henderson (2017) uptake efficiency equation is:

[math: \frac{\Delta C_T}{\Delta A_T} = \eta = (S \cdot 10^{-3.009} + 10^{-1.519}) \text{ln}(pCO_2)-(S \cdot 10^{-2.100}) - \\ (T \cdot pCO_2)(S \cdot 10^{-7.501} - 10^{-5.598}) - (T \cdot 10^{-2.337}) + 10^{-0.102}]

Equation 27

Where

[math: \eta] is the uptake efficiency of CO₂ upon mixing with ocean waters, dimensionless;
[math: \Delta C_T] is the change in Total DIC in the ocean as a result of WAE, in mol;
[math: \Delta A_T] is the change in Total Alkalinity in the ocean as a result of WAE, in mol;
[math: pCO_2] is the local ocean partial pressure of CO₂ at the discharge site, in μatm;
[math: T] is the local surface ocean temperature, in °C;
[math: S] is the local ocean salinity, in %.

Project Proponents should use the oceanographic conditions from publicly available, locationally-specific time-series data, such as the NOAA climate indices list, OceanSODA-ETHZ, or equivalent, to the uptake efficiency (Equation 28). The efficiency can be used in Equation 23 to determine the size of the loss term. Equilibrium conditions can be assumed.

Option 2

An alternative approach to quantifying ocean losses is to use a 3D Earth Systems Model or ocean physical-biogeochemical model to explicitly simulate ocean transport and air-sea CO₂ fluxes. For example, Kanzaki et al., 2023 used an Earth system model to estimate the ocean leakage of CO₂ from terrestrial enhanced weathering projects⁴⁰. Similar model-based approaches may be used, however the calculation of ocean losses must be regionally specific to the project-site. A globally averaged loss factor may not be used at this time since it may not be conservative, given the large variability that exists in different regions of the ocean.

Projects Proponents must submit a detailed description of their modeling approach in the PDD, including the following:

the model used and domain
inputs and forcing data, including atmospheric forcing and initial conditions
carbonate system representation and parameterization of air-sea CO₂ fluxes
representation of WAE project, e.g. as represented through an additional flux of DIC and alkalinity into the ocean at a particular river mouth
baseline simulations

Furthermore, the model must be well-validated and skillful for the purpose that it is used for. Proof of model validation can be achieved through either:

A track record of use in science, industry, or government applications, which is demonstrated through multiple peer-reviewed papers, or proof of usage in a number of previous applications.
Newly developed models without a track record of usage must be validated against reputable data sources, which include quality-controlled in situ measurements and public datasets adhering to FAIR (Findable, Accessible, Interoperable and Reusable) principles⁴². Sufficient model validation data must be provided with the PDD.

8.2.4 Broader Impacts on CDR

Discharge of Undissolved Alkalinity

Any undissolved feedstock which is released in the effluent as TSS may dissolve in the open environment depending on local saturation states and enhance alkalinity in the receiving water body. This will result in increased pH, total alkalinity (TA), and potentially facilitate additional carbon uptake via air-sea gas exchange if the alkaline-enriched waters remain in contact in the atmosphere.

Additional solids separation prior to discharge may be required to prevent release of undissolved feedstock to the open environment. Projects which aim to discharge undissolved feedstock into the ocean and quantify open ocean CDR must refer to the Ocean Alkalinity Enhancement from Coastal Outfalls Protocol. Projects that wish to seek Credits under both the WAE and OAE Protocols must consult with Isometric ahead of time to establish clear boundaries between the Projects and ensure no potential double-counting.

Biological Fertilization

The release of elements (such as iron, silica, nitrogen and phosphorus) and DIC-enriched waters could lead to increases in primary production or changes in phytoplankton community structure, which may have a broader impact on biological carbon export.

There is significant nutrient export from wastewater treatment plants under BAU operations, and the additional fertilization from alkaline feedstocks are relatively small in comparison to the existing nutrient export from WWTPs. Furthermore, it is challenging to attribute additional primary production above the baseline scenario to the CDR intervention. For these reasons, the potential impacts of increased primary production on carbon removal are not accounted for in this Protocol. Project Proponents must select alkaline feedstocks which minimize the risk of fertilization and ensure effluent concentrations of key nutrients are not increased beyond the standard range for the wastewater treatment plant.

8.3 Calculation of CO₂e_{Counterfactual, RP}

Type: Counterfactual

[math: CO_2e_{Counterfactual,\ RP}] represents the amount of CO₂ removed from the conversion of biogenic CO₂ in wastewater to bicarbonate in the absence of the WAE project, under the WWTP's BAU operations. This term represents the counterfactual scenario of the [math: CO_2e_{Stored,\ RP}] term, and does not include GHG emissions in the counterfactual scenario. The quantification of GHG emissions relative to BAU operations is described in Section 8.4.

The calculation of [math: CO_2e_{Counterfactual,\ RP}] depends on the BAU scenario for the WWTP (Figure 4).

For projects operating in WWTPs that do not add any alkalinity for their process control, the counterfactual in [math: CO_2e_{Counterfactual,\ RP}] is considered to be 0, since [math: CO_2e_{Stored,\ RP}] is calculated relative to a BAU where no alkaline feedstock is added to the WWTP to react with the biogenic CO₂ generated during wastewater treatment. This assumes there is no limestone or feedstock present in the WWTP after primary treatment.

For projects in which the partner WWTP does add alkalinity, [math: CO_2e_{Counterfactual,\ RP}] is calculated as follows:

If the feedstock emissions of the prior pH amendment is less than or close to equal to its carbon removal potential upon dissolution in wastewater, then [math: CO_2e_{Counterfactual,\ RP}] must be estimated based on the BAU dosing rate. This may be determined based on: historical dosing records from the WWTP, using a nitrogen balance to calculate the amount of alkalinity needed for the nitrification process (e.g. 7.14g of alkalinity as CaCO₃ is needed for 1g of NH₄⁺ nitrified⁴³), or an alternative approach which must be justified and evidenced in the PDD.
If the feedstock emissions of the prior pH amendment is significantly greater than its carbon removal potential upon dissolution in wastewater, then the BAU operation is emitting more CO₂ than is being removed through feedstock dissolution. Since this is a net-emitting scenario, this is not considered CDR by definition and [math: CO_2e_{Counterfactual,\ RP}] may be set to 0 on a case by case basis for each project in consultation with Isometric.

See Appendix 3 for further explaination on this approach.

[Image: **Figure 4** Counterfactual]

Figure 4 Decision tree for determining CO₂e_{Counterfactual, RP} for a WAE project.

8.4 Calculation of CO₂e_{Emissions, RP}

Type: Emissions

[math: CO_2e_{Emissions,\ RP}] is the total GHG emissions associated with a Reporting Period, [math: {RP}]. This can be calculated as:

[math: ~~CO_2e_~~CO*2e*{Emissions,\ RP} = ~~CO_2e_~~CO*2e*{Establishment,\ RP} + ~~CO_2e_~~CO*2e*{Operations,\ RP} + ~~CO_2e_~~CO*2e*{End-of-Life,\ RP} + ~~CO_2e_~~CO*2e*{Leakage,\ RP}]

Equation 28

Where

[math: CO_2e_{Emissions,\ RP}] represents the total GHG emissions for a Reporting Period, in tonnes of CO₂e.
[math: CO_2e_{Establishment,\ RP}] represents the GHG emissions associated with project establishment, represented for the Reporting Period, in tonnes of CO₂e, see Section 8.4.1.
[math: CO_2e_{Operations,\ RP}] represents the total GHG emissions associated with operational processes for a Reporting Period, in tonnes of CO₂e, see Section 8.4.2.
[math: CO_2e_{End-of-Life,\ RP}] represents GHG emissions that occur after the Reporting Period and are allocated to a Reporting Period, in tonnes of CO₂e, see Section 8.4.3.
[math: CO_2e_{Leakage,\ RP}] represents GHG emissions associated with the Project’s impact on activities that fall outside of the system boundary of a project, over a given Reporting Period, in tonnes of CO₂e, see Section 8.4.4.

The following sections set out specific quantification requirements for each variable. Projects applicable under this Protocol are integrated with existing WWTP, so only the additional activities beyond the WWTP BAU operations are included in the calculation of [math: CO_2e_{Emissions,\ RP}]. This is set out in Table 1 and Figure 1. Emissions relative to BAU must be positive, i.e. avoided emissions relative to BAU are not eligible for crediting.

8.4.1 Calculation of CO₂e_{Establishment, RP}

GHG emissions associated with project establishment should include all historic emissions incurred as a result of project establishment, including but not limited to the SSRs set out in Table 1.

Project establishment emissions occur from the point of project inception up until the first Reporting Period. Establishment emissions may be accounted for in the following ways, with the allocation method selected and justified by the Project Proponent:

as a one time deduction from the first removal
allocated to removals as annual emissions over the anticipated project lifetime
allocated per output of product (i.e., per ton CO₂ removed) based on estimated total production over project lifetime

The anticipated lifetime of the Project should be based on reasonable justification and should be included in the Project Design Document (PDD) to be assessed as part of project validation.

Allocation of project establishment emissions to removals must be reviewed at each Crediting Period renewal and any adjustments made. If the Project Proponent is not able to comply with the allocation schedule described in the PDD, e.g. due to changes in delivered volume or anticipated project lifetime, the Project Proponent should notify Isometric as early as possible in order to adjust the allocation schedule for future removals. If that is not possible, the Reversal process will be triggered in accordance with the Isometric Standard, to account for any remaining emissions.

8.4.2 Calculation of CO₂e_{Operation, RP}

GHG emissions associated with [math: CO_2e_{Operations,\ RP}] should include all emissions associated with operational activities, including but not limited to the SSRs set out in Table 1. In particular for WAE projects, the state of Waste activated sludge must be described in the PDD. If the WAS is incinerated, the CO₂ emissions from incineration must be included in the calculation of [math: CO_2e_{Operations,\ RP}].

[math: CO_2e_{Operations,\ RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis in agreement with Isometric.

8.4.3 Calculation of CO₂e End-of-Life, RP

[math: CO_2e_{End-of-Life,\ RP}] includes all emissions associated with activities that are anticipated to occur after the Reporting Period, but are directly or indirectly related to the Reporting Period. For example, this could include ongoing sampling activities for MRV for the specific deployment (directly related), or end-of-life emissions for the project facility (indirectly related to all deployments).

GHG emissions associated with [math: CO_2e_{End-of-Life,\ RP}] may occur from the end of the Reporting Period onwards, and typically through to completion of project site deconstruction and any other end-of-life activities.

GHG emissions associated with activities that are directly related to each deployment must be quantified as part of that Reporting Period. GHG emissions associated with activities that are indirectly related to all deployments may be allocated in the same ways as set out in [math: CO_2e_{Establishment,\ RP}].

Given the uncertain nature of [math: CO_2e_{End-of-Life,\ RP}] emissions, assumptions must be revisited at each Crediting Period and any necessary adjustments made. Furthermore, if there are unexpected [math: CO_2e_{End-of-Life,\ RP}] emissions associated with a Reporting Period, or the Project as a whole, that occur after the Project has ended, then the Reversal process will be triggered to compensate for any emissions not accounted for.

8.4.4 Calculation of CO₂e Leakage, RP

[math: CO_2e_{Leakage,\ RP}] includes emissions associated with a project's impact on activities that fall outside of the system boundary of a project. It includes increases in GHG emissions as a result of the Project displacing emissions or causing a knock on effect that increases emissions elsewhere. As an example, creating a market for feedstocks may generate new revenue in the source sector that alters producer behavior in ways that result in additional GHG emissions.

It is the Project Proponent's responsibility to identify potential sources of leakage emissions, however, for an Wastewater Alkalinity Enhancement project the following must be considered as a minimum:

Feedstock replacement
Consumables replacement

[math: CO_2e_{Leakage,\ RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis in agreement with Isometric.

8.4.5 Energy Use Accounting

This section sets out specific requirements relating to quantification of energy use as part of the GHG assessment. Emissions associated with energy usage result from the consumption of electricity or fuel.

Examples of electricity usage may include, but are not limited to the operation of process equipment (i.e., pumps, mixers, blowers, flow control, measurement instruments). WAE may increase or decrease energy consumption for secondary treatment. For example, reduced oxygen transfer efficiency requiring increased blower energy or increased mixing energy required to keep feedstock in suspension. If this is the case for a WWTP under this Protocol, a means to monitor energy consumption before/after implementation should be outlined in the PDD. In cases where it is not possible to measure this directly, energy could be estimated based on rotating equipment duty points (e.g.; flow, pressure) and a pump curve.⁴⁴

Examples of fuel consumption may include, but are not limited to handling equipment, such as fork trucks or loaders.

The Energy Use Accounting Module v1.2 provides requirements on how energy-related emissions must be calculated in a CDR project so that they can be subtracted in the net CO₂e removal calculation. It sets out the calculation approach to be followed for intensive facilities and non-intensive facilities and acceptable emissions factors.

In alignment with the Energy Use Accounting Module v1.2, the consequential impact of electricity usage on the system it is procured from must be included in calculations for intensive projects, as determined in the Energy Use Accounting Module v1.2.

[Module: energy-use-accounting v1.2]

Refer to Energy Use Accounting Module for the calculation requirements.

8.4.6 Transportation Emissions Accounting

This section sets out specific requirements relating to quantification of transportation emissions as part of the GHG Statement.

Emissions associated with transportation include transportation of products and equipment as part of a Reporting Period’s activities. Examples may include, but are not limited to:

transportation of equipment, feedstock and consumables to the facility
transportation of sludge to storage site
transportation and shipping related to collection and analysis of samples

The Transportation Emissions Accounting Module v1.1 provides requirements on how transportation-related emissions must be calculated in a CDR project so that they can be subtracted in the net CO₂e removal calculation. It sets out the calculation approach to be followed and acceptable emissions factors.

[Module: transportation v1.1]

Refer to Transportation Emissions Accounting Module for the calculation requirements.

8.4.7 Embodied Emissions Accounting

This section sets out specific requirements relating to quantification of embodied emissions as part of the GHG Statement. Embodied emissions are those related to energy use or other emissions during the manufacture of equipment and materials used in a process.

Examples of project-specific materials and equipment that must be considered as part of the embodied emission calculation include but are not limited to:

feedstock, consumables and associated equipment produced, constructed and utilized explicitly for the CDR project
process equipment (i.e., pumps, mixers, blowers, flow control, measurement instruments)
equipment related to waste handling and disposal

The Embodied Emissions Accounting Module v1.0 sets out the calculation approach to be followed including allocation of embodied emissions, life cycle stages to be considered, data sources and emission factors.

[Module: embodied-emissions v1.0]

Refer to Embodied Emissions Accounting Module for the calculation guidelines.

9.0 Storage

9.1 Marine Dissolved Inorganic Carbon (DIC) Storage

The primary storage reservoir of the CO₂ removed through Wastewater Alkalinity Enhancement is Dissolved Inorganic Carbon (DIC) in the ocean. The durability and reversal risks of this storage reservoir are discussed in the Ocean DIC Storage Module.

[Module: dic-storage-in-oceans v1.0]

Ocean DIC Storage Module

Future versions of this Protocol will include expanded storage options, such as storage of DIC in lakes.

9.2 Buffer Pools

As outlined in Section 2.5.9 of the Isometric Standard, the Buffer Pool is a mechanism used to insure against Reversal risks that may be observable and attributable to a particular project through monitoring.

Based on present understanding, reversals in the global ocean Dissolved Inorganic Carbon (DIC) reservoir will not be directly observable with measurements and attributable to a particular project. Reversals of DIC in the ocean is a system-wide storage uncertainty that should be addressed through further scientific research. Projects applicable to this Protocol are generally categorized as having a Very Low Risk Level of Reversal according to the Isometric Standard Risk Assessment Questionnaire. ~~The~~Risk ~~Buffer~~of ~~Pool~~reversal ~~corresponding to this lowest risk score~~information is 2%given ~~and~~in isAppendix ~~intended~~4: asRisk anof ~~additional~~Reversal ~~precaution~~Questionnaire, ~~against~~with ~~unknowns~~further information provided within the relevant storage module storage module.

For more details on Reversals, refer to Sections 2.5.9 and 5.6 of the Isometric Standard.

10.0 Pre-Deployment Requirements

All pre-deployment requirements must be described in the PDD, as outlined in Section 5.1. The requirements are as follows:

Project Proponents must provide a site description of the discharge location, including the dominant circulation and modes of variability, as well as the frequency of various environmental conditions. This must include, at minimum, information on seasonal patterns, predominant currents, periods of maximum stratification and periods when receiving water quality conditions may be more critical.
Project Proponents must develop a conceptual model of dispersion of discharge, and produce a mixing zone model, which will likely already be a part of the existing WWTP discharge permit. The mixing zone model will estimate initial dispersal of the discharge, and will dictate the recommended reach of the monitoring efforts. Sensitivity analysis is required to demonstrate adherence to water quality limits at the boundary of the mixing zone under varying environmental conditions.
Project Proponents must have sufficient plans for restoring water quality conditions prior to discharge in the event that negative environmental impacts result from project activities.
Project Proponents must chacterize rocks and minerals utilized as feedstock following Isometric’s Rock and Mineral Feedstock Characterization Module.
Project Proponents must provide information on how dosing rate is calculated, including any partner data that was used in those calculations
Project Proponents must provide the following information on the WWTP during business as usual operation:
- Energy usage (e.g. from pumping, aeration, mixing, maintenance and/or cleaning). It is recommended to have at least 1 year of monthly energy data, normalized by the flow rate. If direct energy usage data is unavailable, estimates based on proxies (such as flow rate and BOD) are allowable. Alternatively, Project Proponents may provide a justification of why their WAE project will not increase WWTP operating energy usage above BAU, this should be based on data, literature, or other reasoning.
- Range of solids and/or WAS generation and the fate of the solids and/or WAS (e.g. incineration, anaerobic digestion, aerobic digestion). It is recommended to report at least 1 year of monthly data, normalized by the flow rate. This will be used to assess trends of solids and/or WAS generation over a Reporting Period that exceed the normal variation.
- Retention and settling times of solids and/or WAS within the WWTP.
Project Propnents must designate the control volume boundaries for the project, including the control volume in L.

11.0 Monitoring

11.1 Monitoring Locations

This Protocol requires and recommends monitoring to occur at the following locations, which are illustrated in Figure 5. The monitoring locations are defined relative to a control volume, which in most cases encompasses the secondary treatment portion of the WWTP and includes the bioreactor and settling tank (see Section 8.2.1 for more details).

Influent ([math: A]): The influent stream of wastewater entering the control volume. Typically for control volumes that encompass the secondary treatment step, the influent stream measurements will be taken after primary treatment and before entering secondary treatment.
Feedstock dosing ([math: B]): Measurements of alkaline feedstock dosing into the control volume.
Effluent ([math: C]): The effluent stream exiting the control volume.
Waste activated sludge ([math: D]): Measurements of the waste activated sludge that is settled out of the water at the end of the secondary treatment step, and prior to transport and disposal of the WAS (e.g. incineration or landfill) or onsite solids treatment (e.g. anaerobic or aerobic digestion).
Within the Control Volume ([math: E]): This refers to measurements taken from within control volume, such as from the bioreactor. In contrast, the previous measurement locations [math: A], [math: B], [math: C] and [math: D] are referring to streams entering or exiting the control volume.
Edge of mixing zone ([math: F]): This refers to measurements made in the receiving waters, in the vicinity of the WWTP discharge. The region near the discharge may be referred to as a mixing zone, or mixing length, and is where signals of the WWTP discharge will be highest before being diluted farther away from the discharge location.

Note that exact monitoring locations may differ for various WWTPs depending on plant-specific processes. For example, plants that do Garrett wasting (i.e. remove WAS from the aeration tank) may have a separate WAS stream to monitor. Plant-specific monitoring locations and a description of the control volume must be included in the monitoring plan submitted in the PDD.

[Image: **Figure 5** Monitoring locations]

Figure 5 Monitoring locations relative to a control volume representing the secondary treatment step in a WWTP. Monitoring locations referred to throughout this Protocol are shown in green. Note that the control volume provided is an example, and the exact control volume may be drawn differently for other WWTPs. Exact locations of inputs and outflows from the control volume may look different for projects.

11.2 Control Volume Measurements

The following sections summarize the measurements that must be reported in each of the monitoring locations. The purpose of monitoring is for quantification of the net CDR. Some of these measurements may already be collected as part of the WWTP BAU operations, and some may be collected by the Project Proponent. The breakdown of data collection between the Project Proponent and partner WWTP should be specified in the PDD.

11.2.1 Influent, A

Required measurements in the influent stream entering the control volume include: the flow rate ([math: Q_{Influent}], L/day) and the concentration of the dissolved weathering product ([math: [C^x]_{Influent}]; mol/L), both of which are used for the aqueous phase mass balance for quantifying the amount of feedstock dissolved in Equation 15. This is either used as the primary approach for quantifying [math: \dot m_{Dissolved}], or must be used as a validation check (see Section 8.2). In addition, measurements of anions are recommended for determining the amount of non-carbonic acid weathering (see Section 8.2.1.2, Equations 10-12 and/or 19-21). If anion measurements are not available, an alternative approach for determining non-carbonic acid weathering is required.

11.2.2 Feedstock Dosing, B

The addition of feedstock into the control volume must be quantified in terms of the feedstock mass flow rate ([math: \dot m_{FS,\ Dosing}]; tonnes/day) for the solid phase mass balance (See Equation 7). This is used either as the primary approach for quantifying [math: \dot m_{Dissolved}], or is required as a validation check (see Section 8.2). For projects where slurry dosing is used, the flow rate [math: Q_{dosing}] (L/day) must also be reported here.

11.2.3 Effluent, C

Measurements of the flow rate ([math: Q_{Effluent}]; L/day), dissolved weathering product concentration ( [math: [C^x]_{Effluent}] ; mol/L), and concentration of suspended feedstock ([math: FS_{Effluent}]; tonnes/day) are required in the effluent stream. Depending on the type of feedstock (e.g. carbonate vs non-carbonates), different approaches are used for determining the feedstock concentration in the effluent, such as TIC for carbonate feedstocks (see Section 8.2 for more details). These measurements are used in both the aqueous and solid phase mass balance calculations (see Equations 7 and 15). In addition, measurements of anions are recommended for determining the amount of non-carbonic acid weathering (see Section 8.2.1.2, Equations 10-12 and/or 19-21). If anion measurements are not available, an alternative approach for determining non-carbonic acid weathering is required.

Depending on how the Control Volume is drawn, the effluent may refer to the wastewater stream exiting the secondary treatment and entering tertiary treatment, or it may refer to the final effluent exiting the WWTP into receiving waters. Additional measurements at the final effluent are needed for monitoring of environmental impacts and the calculation of losses upon mixing with receiving waters. These include measurements of at least two carbonate system parameters (pH, DIC, TA, pCO₂) and TSS. See Section 11.3.2 for environmental monitoring, and Section 8.2.3.1 for losses upon mixing with receiving waters.

11.2.4 Waste Activated Sludge, D

Measurements of the waste activated sludge are used in both the aqueous and solid phase mass balances (see Section 8.2). Required measurements of the WAS include the dissolved weathering product concentration ([math: [C^x]_{WAS}]; mol/L), flow rate ([math: Q_{WAS}]; L/day), and concentration of feedstock settled in the WAS ([math: FS_{WAS}]; mg/L). Depending on the type of feedstock (e.g. carbonate vs non-carbonates), different approaches are used for determining the feedstock concentration in the WAS, such as TIC for carbonate feedstocks (see Section 8.2 for more details). Measurements of anions are recommended for determining the amount of non-carbonic acid weathering (see Section 8.2.1.2, Equations 10-12 and 19-21). If anion measurements are not available, an alternative approach for determining non-carbonic acid weathering is required.

11.2.5 Within the Control Volume, E

Monitoring for feedstock accumulation in the control volume is required to confirm the steady state assumption that no feedstock accumulates in the control volume. See Section 8.2.2.1 for more details.

Confirmation of steady state operations may be demonstrated with sludge sampling devices in the WAS removal, WAS recycling streams and effluent streams or periodically during routine cleaning and maintenance of bioreactors.

11.3 Receiving Waters

The aims of monitoring in receiving waters are to demonstrate permit compliance, monitor environmental conditions, conduct ongoing monitoring for quantification of downstream losses, and establish processes for adaptive management to ensure that Project activities are stopped if negative impacts are identified.

All measurements in receiving waters are recommended. It may be the case that no additional measurements beyond the WWTP BAU are needed if it can be demonstrated that the WAE project either (1) does not change effluent characteristics compared to BAU, or (2) effluent changes are improved or reduce environmental risks compared to BAU. For example, if BOD in the final effluent is decreased as a result of the WAE project compared to the BAU of the WWTP, then it may not be necessary to do additional monitoring of dissolved oxygen in receiving waters as an indicator of ecosystem health.

The receiving waters monitoring plan should span the general locations listed below. This Protocol does not prescribe exact monitoring locations, as this will be site specific. Project Proponents are responsible for determining appropriate monitoring locations. It is recommended that Project Proponents use models to plan and optimize sampling design. A diagram of the monitoring locations, including the location in the water column, must be included in the monitoring plan submitted in the PDD.

11.3.1 Mixing Zone

The area where initial dilution takes place is often called the mixing zone (or "a reasonable mixing zone" or "zone of initial dilution"), typically on the scale of ~100m, depending on the scale of discharge. A mixing zone is a regulatory concept, which describes a spatial area surrounding the discharge infrastructure where water quality criteria can be exceeded. Permits which allow for a mixing zone require water quality criteria to be met at the edge of a mixing zone. A mixing zone is a simplified representation of initial mixing of discharge with receiving waters, the true spatial extent of this mixing changes dynamically with environmental conditions.

Detection of a measurable signal may be difficult beyond the mixing zone, especially for small-scale deployments. Beyond the mixing zone, receiving waters are expected to be well-mixed, which can provide more representative measurements of the impact of the discharge. Thus, environmental monitoring should be focused on the edge of the mixing zone.

It is recommended that Project Proponents monitor temperature, salinity, at least two carbonate chemistry parameters (pH, TA, DIC, pCO₂), dissolved oxygen (DO), turbidity and total suspended solids (TSS) at the edge of the mixing zone. Temperature and salinity are necessary for determining physical conditions, and should be co-located with other measured quantities. Two carbonate chemistry parameters (pH, TA, DIC, pCO₂) can be used to characterize the carbonate system. It is a known limitation of using pH and pCO₂ measurements to constrain the full carbonate system that uncertainty can be high⁴⁵. It is therefore recommended a third carbonate system measurement is collected and measured to constrain the full carbonate system (including the state of carbonate disequilibrium) and recalibrate autonomous sensors. DO, turbidity and TSS are water quality indicators. Action thresholds are placed on pH, TSS and DO (see Section 11.3.3). Monitoring Chl-a and dissolved inorganic nutrients are also recommended.

11.3.2 Biological and Ecological Monitoring in Deployment Area

Tailored biological and ecological monitoring for specific projects and sites must be determined by conducting an environmental risk assessment and mitigation strategy (see Section 6).

Project Proponents are recommended to conduct periodic ecological surveys to monitor phytoplankton community abundance and composition, benthic community abundance and diversity and presence and potential interactions with species of special concern (IUCN listed, commercially exploited or keystone species). Functional diversity should be considered in addition to taxonomic diversity. Survey sites should include the immediate vicinity of the discharge pipe and specific benthic habitats within the affected area of the project activities to be identified and determined on a site-by-site basis.

Action thresholds are not imposed on ecological indicators due to the difficulty of establishing ecological baselines and attributing ecological changes, particularly compared to BAU operations of WWTP. Data collection remains imperative for establishing a foundation for future analysis and enabling the assessment of cumulative impacts of Wastewater Alkalinity Enhancement, including assessing co-benefits and restoration impacts. Ecological data must be made publicly available, and the location of where data is stored publicly must be included in the PDD.

11.3.3 Monitoring for Ecosystem Safety

Project Proponents must conduct an environmental risk assessment and develop a mitigation strategy (see Section 6.3). Thresholds on environmental monitoring parameters are used to determine safe limits for discharge, mitigate environmental risks and identify negative environmental impact.

Two types of thresholds are used:

Safety thresholds are imposed on the effluent characteristics and controlled prior to discharge.
Action thresholds are measured at the edge of the mixing zone. Parameters measured are indicators of water quality and/or unintended environmental changes. Action thresholds can be absolute or relative, and can be determined by regulatory limits, relative to natural variability based on historical data or relative to a control site. For example, the action threshold on pH could be 6.5 < pH < 9 or ±0.2 relative to natural variability, whichever is more conservative. Action thresholds may vary seasonally, and should be consistent with monitoring requirements under official permitting.

Effective implementation of these measures must also be accompanied by a robust monitoring plan to detect negative impacts and stop projects when necessary.

11.3.3.1 Threshold Violations

Violations are determined based on the threshold type, and specifics of the site, permit and intended activities. For example, exceedance of safety thresholds may be determined by daily mean or max values and exceedance of action thresholds in the mixing zone may be determined by weekly and/or monthly mean or max values. All violations need to be reported, and gaps in ocean monitoring data must be justified.

11.3.3.2 Enforcement Actions

Credits cannot be issued for time periods without sufficient measurements to demonstrate compliance with action and safety thresholds. The handling of data gaps must be reported in the PDD. Removal activity from discharges that occur during time periods of safety threshold violations will not be eligible for crediting. Action threshold violations must trigger adaptive management plans. Failure to adequately address environmental risks or remediate any harm will lead to a project being subject to Credit cessation.

11.4 Summary of Monitored Parameters

Table 5 below summarizes the required and recommended monitoring parameters. Required measurements indicate the minimum common set of measurements needed for all projects under this Protocol. Additional required measurements may be necessary based on specifics of the Project, site and environmental risk mitigation plan.

Table 5. Summary of required and recommended measurements for monitoring. Required measurements indicate the minimum common set of measurements needed for all projects under this Protocol. Additional required measurements for ocean monitoring may be necessary based on specifics of the Project, site, and environmental risk mitigation plan. The exact monitoring plan must be described in the PDD.

Location	Parameter	Requirement Scope	Reason for Measurement	Methods	Frequency
Influent (A)	Q, Flow rate (L/day)	Required for all projects	Required for determining volume of water processed, used in carbon removal calculation	Flow meter	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment.
[C^x], Concentration of dissolved weathering products (mol/L)	Required for Option 2	Required for quantifying amount of carbon removed	Discrete bottle samples (e.g., ICP-MS, ICP-OES) or using an ion-selective electrode).
Anions	Recommended for all projects.	Recommended to determine non-carbonic acid weathering. If anion measurements are not available, an alternative approach for determining non-carbonic acid weather is required (see Section 8.2.1.1 and 8.2.1.2)	Ion chromatography; measured ions must include, at a minimum, Cl^-, NO₃^-, PO₄^3- and SO₄^2-
Feedstock dosing (B)	Q, flow rate (L/day)	Required for all projects where slurry dosing is used	Required for determining volume of water processed, used in carbon removal calculation	Flow meter	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment.
m_{FS, Dosing}, mass flow rate of feedstock dosing (tonnes/day)	Required for all projects	Required for determining the amount of carbon removed.	Weigh scales of alkaline feedstock, or calculated from mass concentration of feedstock and dosing flow rate
Effluent (C)	Q_Effluent, Flow rate (L/day)	Required for all projects	Required for determining volume of water processed, used in carbon removal calculation	Flow meter; where not directly measured, Project Proponents may assume flow rate is constant throughout the system	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment.
FS_Effluent, concentration of suspended feedstock in effluent (mg/L)	Required for Option 1	Required to determine total amount of undissolved feedstock in effluent	May be derived from TSS and analytical measurement (e.g., TIC) of feedstock relative to other solid materials present.
[C^x], concentration of dissolved weathering products (e.g. Ca²⁺, Mg²⁺) (mol/L)	Required for Option 2	Required for quantifying amount of carbon removed	Discrete bottle samples (e.g., ICP-MS, ICP-OES) or using an ion-selective electrode).
Anions	Recommended for all projects	Recommended to determine non-carbonic acid weathering. If anion measurements are not available, an alternative approach for determining non-carbonic acid weather is required (see Section 8.2.1.1 and 8.2.1.2)	Ion chromatography; measured ions must include, at a minimum, Cl^-, NO₃^-, PO₄^3- and SO₄^2-
Total Suspended Solids (TSS)	Required for all projects at final effluent prior to discharge	Required for monitoring water quality, assessing and mitigating risk of downstream losses, and may be used for determination of FS_Effluent.	Discrete bottle samples and filtering directly onto pre-weighed filter and subsequent measurement of mass change through drying (for example, in an oven), or TSS analyzers from existing WWTP infrastructure.
At least two carbonate system parameters: pH, DIC, TA, pCO₂	Required for all projects at final effluent prior to discharge	Required for constraining carbonate system and determining outgassing upon mixing with receiving waters	Sensor (for pH or pCO₂) or discrete bottle samples
Waste Activated Sludge (WAS) (D)	Q_WAS, Flow rate (L/day)	Required for all projects	Required for determining volume of water processed, used in carbon removal calculation	Flow meter	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment
FS_WAS, concentration of settled feedstock in WAS (mg/L)	Required for Option 1	Required for quantification of carbon removed	Methods may vary based on feedstock
[C^x], concentration of dissolved weathering products, e.g. Ca²⁺, Mg²⁺ (mol/L)	Required for Option 2	Required for quantifying amount of carbon removed	Discrete bottle samples (e.g., ICP-MS, ICP-OES) or using an ion-selective electrode). Samples must be acidified prior to preparation for measurement.
Total Inorganic Carbon (TIC)	May be used to determine FS_WAS for projects utilizing carbonate feedstocks	Where carbon feedstocks are used, FS_effluent and FS_WAS can be assumed to be equivalent to TIC in samples taken from these streams	Discrete bottle samples taken from streams. Acceptable analyses include TIC analyzer or LOI analyses.
Anions	Recommended for all projects	Recommended to determine non-carbonic acid weathering. If anion measurements are not available, an alternative approach for determining non-carbonic acid weather is required (see Section 8.2.1.1 and 8.2.1.2)	Ion chromatography; measured ions must include, at a minimum, Cl^-, NO₃^-, PO₄^3- and SO₄^2-
Within the control volume, i.e. biological treatment tanks	Feedstock accumulation	Required for all projects	Required for assessing steady state assumption of no feedstock accumulation in control volume	Sludge sampling devices, or during routine cleaning and maintenance of bioreactors	Dependent on site-specific operations and must be justified.
Receiving waters, i.e. edge of mixing zone	Temperature	Recommended for all projects	Recommended for determining physical conditions and making calculations to fully constrain the seawater carbonate system	Sensor	(a) at high frequency when ramp-up is occurring and shortly after any dosing rate changes are made, (b) with low frequency when the dosing rate is occurring at a steady state (defined as dFS/dt=0 or d[C^x]/dt=0)
Salinity	Recommended for all projects	Recommended for determining physical conditions and making calculations to fully constrain the seawater carbonate system	Sensor
Any two carbonate system paramters: pH, DIC, TA, pCO₂	Recommended for all projects	Recommended to constrain the seawater carbonate system, monitor water quality and local carbonate saturation state	Sensor (for pH or pCO₂) or discrete bottle samples
Third carbonate system parameter	Recommended for all projects	Recommended to assess the local state of carbonate disequilibrium	Sensor (for pH or pCO₂) or discrete bottle samples
Dissolved Oxygen (DO)	Recommended for all projects	Recommended as indicator of general ecosystem health	Sensor
Total Suspended Solids (TSS)	Recommended for all projects	Recommended for monitoring water quality and for mitigation of losses	Discrete bottle samples and filtering directly onto pre-weighed filter and subsequent measurement of mass change through drying (for example, in an oven) or derived from turbidity measurements with routine validation from bottle samples
Turbidity	Recommended for all projects	Recommended as part of ecosystem monitoring because elevated turbidity can impact photosynthesis and benthic ecosystem health	Sensor or discrete water sample
Chlorophyll-a	Recommended for all projects	Recommended as an indicator of general ecosystem health (phytoplankton primary productivity)	Sensor or discrete water sample
Dissolved inorganic nutrients	Recommended for all projects	Recommended as an indicator of general ecosystem health (available nutrients for primary productivity) and nutrient limitation impacts from secondary precipitation.	In situ sensor or discrete water sample via mooring or routine boat sampling
Deployment area	Plankton community	Recommended for all projects, may be required as part of project-specific environmental risk mitigation strategy	Recommended periodically for monitoring of ecosystem health, documentation of shifting baseline ecology and contributions to primary research	Plankton tow or other methods	At agreed upon intervals, before, during and after deployment
Benthic community	Recommended for all projects, may be required as part of project-specific environmental risk mitigation strategy	Recommended periodically for monitoring of ecosystem health, documentation of shifting baseline ecology and contributions to primary research Recommended for water and tissue samples in keystone biological species to track potential trace and heavy metal accumulation	Benthic survey or other methods

12.0 Acknowledgments

The following authors from Isometric contributed to writing this Protocol:

Jing He, Ph.D.
Ella Holme, Ph.D.
Jennifer Yin, Ph.D.
Sophie Gill, Ph.D.
Emma Marsland

Isometric would like to thank the following reviewers of this Protocol:

Jeff Peeters
Wei-Jun Cai, Ph.D.
Kevin Sutherland, Ph.D.
Adam Ward, Ph.D.
Marya Matlin-Wainer

13.0 Definitions and Acronyms

: A document that describes how to quantitatively assess the net amount of CO₂ removed by a process. To Isometric, a Protocol is specific to a Project Proponent's process and comprised of Modules representing the Carbon Fluxes involved in the CDR process. A Protocol measures the full carbon impact of a process against the Baseline of it not occurring.
: The term used to represent the CO₂ taken out of the atmosphere as a result of a CDR process.
: Considering impacts at each stage of a product's life cycle, from the time natural resources are extracted from the ground and processed through each subsequent stage of manufacturing, transportation, product use, and ultimately, disposal.
: A facility that receives and treats municipal and/or industrial wastewater.
: Activities that remove carbon dioxide (CO₂) from the atmosphere and store it in products or geological, terrestrial, and oceanic Reservoirs. CDR includes the enhancement of biological or geochemical sinks and direct air capture (DAC) and storage, but excludes natural CO₂ uptake not directly caused by human intervention.
: Raw material which is used for CO₂ Removal or GHG Reduction.
: The amount of dissolved oxygen consumed by microorganisms while breaking down organic matter in water over a specific time period.
: A type of biological wastewater treatment process that uses microorganisms to break down organic waste.
: An activity or process or group of activities or processes that alter the condition of a Baseline and leads to Removals or Reductions.
: A worldwide federation (NGO) of national standards bodies from more than 160 countries, one from each member country.
: Lowering future GHG releases from a specific entity.
: An evaluation of the likelihood that an intervention—for example, a CDR Project—causes a climate benefit above and beyond what would have happened in a no-intervention Baseline scenario.
: A process for evaluating and confirming the net Removals and Reductions for a Project, using data and information collected from the Project and assessing conformity with the criteria set forth in the Isometric Standard and the Protocol by which it is governed. Verification must be completed by an Isometric approved third-party (VVB).
: A systematic and independent process for evaluating the reasonableness of the assumptions, limitations and methods that support a Project and assessing whether the Project conforms to the criteria set forth in the Isometric Standard and the Protocol by which the Project is governed. Validation must be completed by an Isometric approved third-party (VVB).
: A collection of Removal or Reduction processes that have mechanisms in common.
: A publicly visible uniquely identifiable Credit Certificate Issued by a Registry that gives the owner of the Credit the right to account for one net metric tonne of Verified CO₂e Removal or Reduction. In the case of this Standard, the net tonne of CO₂e Removal or Reduction comes from a Project Validated against a Certified Protocol.
: Operations and processes that would have occurred in the absence of project activities.
: The organization that develops and/or has overall legal ownership or control of a Removal or Reduction Project.
: The document that clearly outlines how a Project will generate rigorously quantifiable Additional high-quality Removals or Reductions.
: Third-party auditing organizations that are experts in their sector and used to determine if a project conforms to the rules, regulations, and standards set out by a governing body. A VVB must be approved by Isometric prior to conducting validation and verification.
: An acceptable difference between reported Removals/emissions or Reductions/emissions and what an auditor determines is the actual Removal/emissions or Reduction/emissions.
: A lack of knowledge of the exact amount of CO₂ removed by a particular process, Uncertainty may be quantified using probability distributions, confidence intervals, or variance estimates.
: Improperly allocating the same Removal or Reduction from a Project Proponent more than once to multiple Buyers.
: An assessment of what would have happened in the absence of a particular intervention – i.e., assuming the Baseline scenario.
: A set of data describing pre-intervention or control conditions to be used as a reference scenario for comparison.
: Resources provided to projects that are generating, or are expected to generate, greenhouse gas (GHG) Emission Reductions or Removals.
: The period of time over which a Project Design Document is valid, and over which Removals, Reductions or Environmental Attributes may be Verified, resulting in Issued Certificates.
: Purposefully erring on the side of caution under conditions of Uncertainty by choosing input parameter values that will result in a lower net CO₂ Removal or GHG Reduction than if using the median input values. This is done to increase the likelihood that a given Removal or Reduction calculation is an underestimation rather than an overestimation.
: An analysis of how much different components in a Model contribute to the overall Uncertainty.
: A calculation, series of calculations or simulations that use input variables in order to generate values for variables of interest that are not directly measured.
: An entity that purchases Removals, Reductions, or Environmental Attributes, often with the purpose of Retiring Certificates to make a Removal, Reduction, or Environmental Attribute claim.
: A database that holds information on Verified Removals and Reductions, and reviewed EACs, based on Protocols. Registries Issue Certificates, and track their ownership and Retirement.
: The increase in GHG emissions outside the geographic or temporal boundary of a project that results from that project's activities.
: A location where carbon is stored. This can be via physical barriers (such as geological formations) or through partitioning based on chemical or biological processes (such as mineralization or photosynthesis).
: Life cycle GHG emissions associated with production of materials, transportation, and construction or other processes for goods or buildings.
: A measure of how much energy the emissions of 1 tonne of a GHG will absorb over a given period of time, relative to the emissions of 1 ton of CO₂.
: The amount of dissolved oxygen required to chemically oxidize organic and inorganic compounds in water.
: An estimate of the emissions intensity per unit of an activity.
: The escape of CO₂ to the atmosphere after it has been stored, and after a Certificate has been Issued. A Reversal is classified as avoidable if a Project Proponent has influence or control over it and it likely could have been averted through application of reasonable risk mitigation measures. Any other Reversals will be classified as unavoidable.
: The amount of time carbon removed from the atmosphere by an intervention – for example, a CDR project – is expected to reside in a given Reservoir, taking into account both physical risks and socioeconomic constructs (such as contracts) to protect the Reservoir in question.
: A common and recognized insurance mechanism among Registries allowing Certificates to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.

Deployment area

The area over which ecological and biological indicators should be monitored for changes due to chronic exposure to modified carbonate chemistry, determined on a project-specific basis in the PDD. This is likely to be larger than the mixing zone.

DIC

Dissolved inorganic carbon

EPA

Environmental Protection Agency

GHG

Greenhouse gas

Mixing Zone

A regulatory concept describing the spatial area surrounding the discharge infrastructure where water quality criteria can be exceeded.

MRV

Monitoring, Reporting and Verification

PDD

Project design document

Reporting Period

The Reporting Period (RP) represents an interval of time over which removals are calculated and reported for verification. See Section 7.1 for full details.

SOP

Standard Operating Procedure

14.0 Appendix 1 : Guidance for High Quality Marine Data Collection

This Appendix is general for marine CDR approaches: Ocean Alkalinity Enhancement (OAE), Direct Ocean Capture (DOC), Wastewater Alkalinity Enhancement

14.1 Introduction

Field measurements play an important role in:

ensuring sufficient and up to date baseline marine data
providing data for calibration and validation of ocean models
monitoring environmental health during and after project activity

Broadly, field measurements may include moored in-situ sensors, ship-based or autonomous transecting and profiling, discrete bottle sampling, field surveys, aerial imaging and remote sensing. There is significant variability in the specific instruments and field methods that may be used to conduct collect data.

Project Proponents must provide thorough documentation on planned and completed field campaigns, including details on the campaign design (spatial and temporal coverage, sampling density, data collection techniques, instrument resolution), metadata, data processing, analytical and statistical techniques, instrument calibration and data quality control. In the sections that follow, we highlight some recommended references and best practices to ensure high quality data generation from field measurements.

Collecting discrete bottle samples alongside continuous autonomous sensor measurements is recommended. Both measurement types offer advantages, for example autonomous sensors can offer wider temporal coverage, while bottle samples are crucial for ground truthing absolute values. Additionally, bottle samples can be used to calibrate drift of long term autonomous sensor deployments.

To facilitate accessibility, transparency and interoperability of research relevant data, data collected from field campaigns must adhere to FAIR data principles ⁴². Project Proponents should follow the data standards and controlled vocabularies described in Guide to Best Practices in Ocean Alkalinity Research: Chapter 13–Data reporting and sharing for ocean alkalinity enhancement research ⁴⁶. Metadata should be complete according to the NOAA ocean acidification metadata template ⁴⁷.

14.2 Alkalinity and pH Measurements

Alkalinity is used in multiple fields that may have different terminology and definitions. For example, total or titration alkalinity is widely used in oceanography, whereas charge balance alkalinity is commonly used in freshwater systems and by geologists⁴⁸. This Protocol uses the oceanographic community terminology when referring to measurements taken in the ocean, where total alkalinity (TA) for seawater is defined following Dickson 1981 based on acid titration to the CO₂ equivalence point⁴⁹. However, alternative definitions of alkalinity that may be more appropriate for specific projects (e.g. for non-seawater systems, such as effluent from a wastewater stream) should be specified in the PDD.

There are also different scales used for pH measurements which may differ by over 0.1⁵⁰. For example, the National Bureau of Standards (NBS) scale is suitable for freshwater systems and waters with low ionic strength, while for seawater, the total hydrogen ion scale is more commonly used⁵¹. This Protocol recommends the total hydrogen ion scale for seawater pH measurements, following the SOPs below in the Guide to Best Practices for Ocean CO₂ Measurements. Care should be taken to account for differences in pH scales, such as when comparing pH measurements against regulatory thresholds.

14.3 Specific Guidance for Bottle Samples

For discrete bottle samples, we refer Project Proponents to the Best Practice Data Standards for Discrete Chemical Oceanographic Observations ⁵². Additional considerations for discrete bottle sampling of carbonate chemistry are discussed in Guide to Best Practices in Ocean Alkalinity Research: Chapter 2 (Seawater carbonate chemistry considerations for ocean alkalinity enhancement research: theory, measurements and calculations) ⁵³.

Recommended analytical methods for bottle samples include:

Parameter	Recommended Method
Carbonate Chemistry parameters (pH, DIC, TA)	Guide to Best Practices for Ocean CO₂ Measurements
Nutrients	Methods of Seawater Analysis
Salinity	TEOS-10
Dissolved Oxygen	Methods of Seawater Analysis
Chl-a	Welschmeyer 1994
TSS	Methods of Seawater Analysis
Trace metals	GEOTRACES cookbook

The following methods are approved by the Clean Water Act, EPA:

Parameter	Approved Method
pH	150.2: pH, Continuous Monitoring (Electrometric) by pH Meter (pdf)
Turbidity	180.1: Determination of Turbidity by Nephelometry (pdf)
Alkalinity	310.2: Alkalinity (Colorimetric, Automated, Methyl Orange) by Autoanalyzer (pdf)
Trace Metals	200.7: Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry; Rev. 4.4 200.8: Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma – Mass Spectrometry; Rev. 5.4 (pdf) 200.9: Determination of Trace Elements by Stabilized Temperature Graphic Furnace Atomic Absorption; Rev. 2.2 (pdf)

14.4 Specific Guidance for Autonomous Ocean Instruments

For autonomous instruments, Project Proponents are recommended to follow manufacturer provided user manuals for instrument preparation, maintenance, calibration and quality control. Environmental and deployment factors which may affect the quality and interpretation of data, (e.g. instrument orientation, interference, presence of bubbles, sediment, and biology) must be described.

Adoption of innovative sensor technologies is encouraged. For novel sensors, additional information that would typically be available from a manufacturer would also have to be provided. These include detection range, resolution, accuracy, performance under different environmental conditions (i.e., temperature ranges) and response time. The expected measurement conditions must be within the sensor’s range.

14.4.1 Pre-deployment

Project Proponents must perform instrument calibration before deployment, and recalibrate instruments at an interval recommended by the manufacturer. Calibration curves or equations for the instrument or sensor must be documented. Post-deployment calibration is recommended to account for instrument drift over the deployment duration.

14.4.2 Maintenance During Deployment

Project Proponents must develop a maintenance plan for moored instruments deployed longer than 30 days. This should include plans to clean or replace sensors that may be impacted by biofoul, such as optical sensors, conductivity cells or flow through sensors.

14.4.3 Data Post-processing

Data processing techniques must be documented, including quality control, filtering, despiking and statistical analysis. The recommended quality control process differs between instruments. Data should be reported using quality control flags consistent with International Oceanographic Data and Information Exchange (IODE)⁵⁴.

The quality control manuals for autonomous instruments prepared by the Integrated Ocean Observing System are a recommended resource.

Quality control checks could include:

completeness of observations
ordering of data
check against physically valid limits
check data obeys physical laws
checking statistical tests
checking regularities of space and time variations

Data Analysis Methods for Physical Oceanography is a recommended resource for statistical analysis methods ⁵⁵.

14.5 Specific Guidance for Tracer Studies

Tracer studies track effluent using a tracer that is either naturally present or added. They can be useful for mCDR projects to:

characterize DIC-deficient or alkalinity-enhanced plume transport
validate physical transport in the ocean model via tracking plume movement
validate alkalinity uptake via dual tracer regression for OAE projects (Project Proponents are not expected to perform dual tracer regression)

Ideal tracers are not harmful to the environment, have near zero background concentration, are conservative or decay very slowly in relation to the duration of field work, mix freely and can be measured in the field at low concentrations. As such, examples of tracers that may be used in DOC are fluorescent dyes (i.e. rhodamine dye) and gas tracers (SF6, CH3, SF5, 3He).

Fluorescent dye tracers, such as rhodamine dye, are preferable because they can be detected from aerial imaging or high frequency in situ sensors. Rhodamine dye degrades in days to weeks, and can be helpful for characterizing near-field mixing. Gas tracers have a lifespan on the order of years, and can be useful for large scale experiments, however, they have high Global Warming Potential.

Tracers can be injected into the effluent to increase the trackability of the effluent. Alternatively, the tracer dye can be released directly into the water column as a slug release, to help constrain localized dispersion characteristics for coastal models.

If a tracer study is conducted to characterize pCO₂-plume transport, the sampling plan must include vertical profiling along transects. A sufficient number of studies are required to produce a sensitivity analysis. Sampling plan, data analysis and interpretation will be evaluated on a case by case basis.

The US EPA Operating Procedure⁵⁶ and USGS Procedure for Dye Tracer Measurements⁵⁷ are recommended resources.

The following checklist can be referenced for tracer release studies using rhodamine dye to validate an ocean model or characterize plume transport.

Study planning:

duration of release should give sufficient time for the field team to complete sampling (this will be site specific)
required tracer quantity should be based on sensor detection limit, effluent flow rate, duration of test and site specific dilution capacity

Materials preparation:

prepare dye mixture, ensuring the correct units of dye concentration are used
dye injection pump should be calibrated in lab to confirm desired volumetric dosage rate
include release rate at different battery levels and temperature
prepare instrument and site specific calibration curve between dye concentration and effluent concentration

Release:

if released with effluent, released at a rate proportional to effluent release rate
if released with effluent, tracer must be added at an adequate mixing length before final discharge
if released with effluent, sample from an access valve to measure concentration prior to final discharge
density and velocity matching for effluent or slug release are considered
no additions after the injection point

Sampling (ship-based or underway system):

prior to release, conduct spatial salinity and temperature profiling.
for ship based sampling, sensor should be placed off the bow, firmly braced and clear of bow waves to minimize disturbance due to wake of the vessel.
positioning via GPS or triangulation should be +/- 2.5m to ensure sampling station. positions and boat tracks are accurate
for all measurements, record metadata including sample location, time, depth, sensor probe and other visual observations.
note areas of high concentrations beyond the mixing zone, as this can signal accumulation or recirculation, which cause the effluent to resurface elsewhere.

Data quality and interpretation:

consider accuracy of positioning data, variation in discharge flow rate, variability in environmental conditions, calibration curve and measurement method in the interpretation of results.

14.6 Ocean Monitoring Examples

Below are some hypothetical examples that are for illustrative purposes only, to demonstrate some of the site and project considerations when determining the appropriate monitoring duration and frequency for a particular parameter and use case.

Example 1

An OAE project is monitoring for changes in ocean pH near the discharge site to make sure the change in pH does not exceed a threshold of +/-0.2 of the natural variability of pH. The dosing period is 1 week, and the residence time of the region where pH sensors are deployed is 1 day. At this site, it is known from previous studies and published literature that the dominant temporal modes of variability for pH are diurnal and seasonal, due to biological activity. Monitoring duration: Because the activity and dosing period are much shorter than the seasonal variability in this case, it is not necessary for the baseline characterization to span a full year to resolve the seasonal cycle. Instead, the baseline monitoring for a few days before deployment is sufficient. There is ongoing monitoring during the 7 day dosing period, and the post-dosing monitoring for pH should additionally span at least the residence time. To be conservative and to collect additional safety data though, the Project decides to extend post-dosing monitoring for 1 week. Monitoring frequency: To resolve the diurnal cycle variability, sampling should be conducted at a higher frequency than daily, e.g. sampling at minimum every 6 hours would result in at least 4 measurements per day and would be sufficient here. Luckily, the Project uses continuous pH sensors, which allows them to sample much more frequently to fully resolve the diurnal cycle.

Example 2

An environmental risk of a mineral OAE project that the local community is concerned about is bioaccumulation of metals in a nearby oyster farm. To address this, the Project is monitoring the concentration of trace metals in oyster tissues before and after the project activity. The Project is dosing feedstock particles into the ocean for 1 week, but some of the feedstock will accumulate on the seafloor and it can take up to 3 months for the particles to fully dissolve. The farm grows oysters in the ocean for 1 year before harvesting. Monitoring frequency: The accumulation of any metals in oysters will take some time, especially because it will take a few months after project dosing completes for the feedstock particles to dissolve. Thus it was decided to sample the oysters once a month for the first 3 months following the Project since that is the period during which particle dissolution is expected to occur, and then once a season after that. Monitoring duration: In this case, the community would like to know the impacts on the oysters that are being harvested for food. So the post-deployment monitoring lasts for 1 year post-dosing (taking seasonal samples) to span the oysters growth cycle and to ensure that metal concentrations do not exceed the local food safety regulatory limits. A control sample was collected from a number of oysters pre-deployment.

15.0 Appendix 2: Future Improvements

This Protocol only quantifies the carbon removal within-the-fence of the wastewater treatment plant. The release of CO₂ from carbonic acid in the wastewater stream is assumed to be imminent and avoided through the addition of alkalinity. CO₂-reactive alkalinity that is released in the effluent may facilitate carbon uptake in the open environment, which must be quantified through the River Alkalinity Enhancement Protocol or Ocean Alkalinity Enhancement from Coastal Outfalls Protocol.

In future versions of this Protocol, we plan to explore the following additional applicability criteria:

Expanding eligible discharge locations to inland waters, e.g. lakes
Expanding to include more variety of WWTP, e.g. membrane bioreactors

Future versions of this Protocol will also include:

Guidance for projects who wish to credit under this Protocol in addition to the OAE Protocol

16.0 Appendix 3: Companion Document for Wastewater Alkalinity Enhancement Protocol

16.1 Introduction

This document is a companion to the Isometric Wastewater Alkalinity Enhancement Protocol V1.0, providing supporting information regarding the rationale and factors considered when determining the requirements of the Protocol, specifically relating to the treatment of CDR vs emissions avoidance in WWTPs. This document should be read in conjunction with the Protocol and is provided as guidance. Should there be any discrepancy or inconsistency between this companion document and the Protocol itself, the requirements of the Protocol will prevail.

16.2 Defining carbon dioxide removal and emissions reductions for Wastewater Alkalinity Enhancement projects

Many CDR projects are more emissions intensive than their counterfactual scenarios because they involve building new facilities (e.g. Direct Air Capture, Electrolytic Seawater Mineralization, projects involving pyrolysis). However, some CDR activities are integrated into existing practices and infrastructure, such as Enhanced Weathering or Wastewater Alkalinity Enhancement. In these instances, the counterfactual business-as-usual (BAU) of existing practices might be more emissions intensive than the CDR project. For example, a WWTP may use NaOH, a carbon intensive pH amendment, in their normal operations. A WAE project operating in that plant would have to switch the NaOH out for a lower carbon intensity feedstock in order to do CDR. This scenario raises the question of how to ensure we are only crediting for CDR and not emissions reductions. The Isometric Standard dictates that credits should only be issued for carbon removal, not emissions avoidance or reductions, and it is very important to clearly distinguish between the two.

The net CDR that is eligible for crediting is given by:

net CDR = drawdown - counterfactual BAU drawdown - project emissions

The purpose of the counterfactual BAU term is to solely account for any CDR that would have happened in the absence of the project activity. This avoids crediting emissions reductions because the counterfactual emissions are excluded from the equation.

It is important to define what project activities are considered CDR vs. emissions reductions. The difference is that in a net-zero world, CDR activities are those that can remove residual emissions and lead to net negative emissions, whereas emissions reduction activities will never get us below net-zero.

For WAE, we have the following possible BAU scenarios:

A WWTP does no prior pH amendment
A WWTP does use a prior pH amendment
a. pH amendment emissions - pH amendment drawdown potential > 0
b. pH amendment emissions - pH amendment drawdown potential < 0

In Scenario 1, there is no CDR occurring, so counterfactual BAU drawdown = 0.

In Scenario 2a, the WWTP is using a pH amendment whose production emissions exceed its drawdown potential when dissolved in wastewater. This activity will never be net-negative no matter the dosing amounts. In this case, the “drawdown” from the pH amendment dissolving in wastewater is doing the job of emissions reductions instead of CDR, as it is compensating for the emissions of producing the pH amendment. There is no CDR occurring, so counterfactual BAU drawdown = 0.

In Scenario 2b, the WWTP is using a low carbon intensity pH amendment such that this activity is net-negative and can be defined as CDR, as opposed to emissions reductions. In this case, the full drawdown from the pH amendment dissolving in wastewater does need to be included in the counterfactual BAU drawdown term.

17.0 Appendix 4: Risk of Reversal Questionnaire

This risk assessment identifies the pathway specific risk factors relevant to a carbon removal project. The relevant risk factors identified as part of a risk assessment are included in the monitoring plan requirements for the project, with details included in the Project Design Document. Project specific risk factors inform the required duration of monitoring along with the monitoring requirements set out in the Protocol and the requirements set out in the Monitoring Section of the Isometric Standard.

The risk score, as determined by the Risk of Reversal Questionnaire, will determine a project’s buffer pool contribution. Projects must re-assess their reversal risk at the renewal of each crediting period, or if monitoring identifies a reversal-related risk, or if an actual reversal event takes place. In any event, projects should reassess their reversal risk at a minimum every 5 years.

The Risk of Reversal Questionnaire questions that pertain to this protocol, drawn from the programme-level Risk of Reversal Questionnaire defined in Appendix B: Risk Reversal Questionnaire of the Isometric Standard, include the following:

# in Isometric Standard Questionnaire	Question	If answered “Yes”	If answered “No”
1	Is a reversal directly observable with a physical or chemical measurement as opposed to a modeled result?	Proceed to questions 2-9	Proceed to questions 8-9
5	Does this approach have a material risk of reversal due to natural disasters including, but not limited to, floods, storms, earthquakes, fires, etc.?	Add 1 to Risk Score
6	Does this approach have a material risk of reversal due to human-induced events from outside actors, such as change in farming practices, change in ownership and management of project sites, or similar?	Add up to 2 to Risk Score
8	Is there 10+ years of monitoring and/or lab data demonstrating low project risk?	Minus up to 2 to Risk Score
9	Does this pathway have a documented history of reversals?	Add 2 to Risk Score
10	Is there one or more project-specific factors that merit a high risk level?	Add up to 2 to Risk Score

Risk Score Categories

0: Very Low Risk Level (2% buffer)
1-2: Low Risk Level (5% buffer)
3-4: Medium Risk Level (7% buffer)
5+: High Risk Level (10-20% buffer)

Project specific risk factors will depend on the form of carbon being stored (i.e., organic vs. inorganic), the method of storage (e.g., mineralization, encapsulation), the location of carbon storage (e.g., subsurface, ocean), and the proximity of that carbon to potential agents of reversal.

For projects with carbon storage as inorganic carbon, the presence of the following risk factors must be reflected in the risk score corresponding to question 10:

Acidic fluid
Alkaline fluid (if stored as dissolved inorganic carbon)
Temperatures in excess of 800 degrees celsius

18.0 Relevant Works

Footnotes

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IPCC AR6 Global Warming Potential Values. 2024. https://ghgprotocol.org/sites/default/files/2024-08/Global-Warming-Potential-Values%20%28August%202024%29.pdf. ↩
Mo, Weiwei, and Qiong Zhang. "Can municipal wastewater treatment systems be carbon neutral?." Journal of environmental management 112 (2012): 360-367. ↩
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Cheng, M., Patterson, J., and Minear, R. (1975). Heavy Metals Uptake by Activated Sludge, Water Pollution Control Federation, Vol. 47, No. 2 https://www.jstor.org/stable/25038635?seq=1 ↩
Al-Qodah, Z. (2006). Biosorption of Heavy Metal Ions From Aqueous Solutions by Activated Sludge. Desalination. 196. 164-176. 10.1016/j.desal.2005.12.012. ↩
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Wurgaft, E., Wang, Z. A., Churchill, J. H., Dellapenna, T., Song, S., Du, J., et al. (2021). Particle triggered reactions as an important mechanism of alkalinity and inorganic carbon removal in river plumes. Geophysical Research Letters, 48, e2021GL093178. https://doi.org/10.1029/2021GL093178 ↩
Ringham, M. C., Hirtle, N., Shaw, C., Lu, X., Herndon, J., Carter, B. R., and Eisaman, M. D. (2024). An assessment of ocean alkalinity enhancement using aqueous hydroxides: kinetics, efficiency, and precipitation thresholds, Biogeosciences, 21, 3551–3570, https://doi.org/10.5194/bg-21-3551-2024. ↩↩²
Schulz, K. G., Bach, L. T., and Dickson, A. G. (2023). Seawater carbonate chemistry considerations for ocean alkalinity enhancement research: theory, measurements, and calculations. State of the Planet, 2-oae2023, 2, https://doi.org/10.5194/sp-2-oae2023-2-2023. ↩
Moras, C. A., Bach, L. T., Cyronak, T., Joannes-Boyau, R., and Schulz, K. G. (2022) Ocean alkalinity enhancement – avoiding runaway CaCO3 precipitation during quick and hydrated lime dissolution, Biogeosciences, 19, 3537–3557, https://doi.org/10.5194/bg-19-3537-2022 ↩↩²
Iglesias-Rodríguez, M. D., Rickaby, R. E. M., Singh, A., and Gately, J. A. (2023). Laboratory experiments in ocean alkalinity enhancement research, in: Guide to Best Practices in Ocean Alkalinity Enhancement Research, Copernicus Publications, State Planet, 2-oae2023, 5, https://doi.org/10.5194/sp-2-oae2023-5-2023 ↩
Suitner, N., Faucher, G., Lim, C., Schneider, J., Moras, C. A., Riebesell, U., and Hartmann, J. (2024). Ocean alkalinity enhancement approaches and the predictability of runaway precipitation processes: results of an experimental study to determine critical alkalinity ranges for safe and sustainable application scenarios, Biogeosciences, 21, 4587–4604, https://doi.org/10.5194/bg-21-4587-2024 ↩↩²
He and Tyka (2023) Limits and CO2 equilibration of near-coast alkalinity enhancement. Biogeosciences, 20, 27–43. https://doi.org/10.5194/bg-20-27-2023 ↩
Bach, L. T. (2023) The additionality problem of Ocean Alkalinity Enhancement. Biogeosciences 21, 261–277. https://bg.copernicus.org/articles/21/261/2024/↩
Jokiel, P. L. (2011). The reef coral two compartment proton flux model: A new approach relating tissue-level physiological processes to gross corallum morphology. Journal of Experimental Marine Biology and Ecology, 409(1–2), 1–12. https://doi.org/10.1016/j.jembe.2011.10.008 ↩
Bach, L. T. (2015). Reconsidering the role of carbonate ion concentration in calcification by marine organisms. Biogeosciences, 12(16), 4939-4951. ↩
Monteiro, F. M., Bach, L. T., Brownlee, C., Bown, P., Rickaby, R. E. M., Poulton, A. J., et al. (2016). Why marine phytoplankton calcify (supplement). Sci. Adv. 2:e1501822. doi: 10.1126/sciadv.1501822 ↩
Bach, L.T., Gill, S.J., Rickaby R.E.M., et. al. (2019) CO₂ Removal With Enhanced Weathering and Ocean Alkalinity Enhancement: Potential Risks and Co-benefits for Marine Pelagic Ecosystems. Frontiers in Climate. 1:7. doi: 10.3389/fclim.2019.00007 ↩↩² ↩³
Langer, G., M. Geisen, K.-H. Baumann, J., et. al. (2006). Species-specific responses of calcifying algae to changing seawater carbonate chemistry. Geochemistry, Geophysics, Geosystems, 7, Q09006, doi:10.1029/2005GC001227 ↩
Renforth, P. (2019) The negative emission potential of alkaline materials. Nature Communications 10, 1401. https://doi.org/10.1038/s41467-019-09475-5 ↩
Hay, B. J. (1988). Sediment accumulation in the central western part of the Black Sea over the last 5100 years. Paleoocenography 3, 491–508. doi:10.1029/PA003i004p00491 ↩
Kopelevich, O., Burenkov, V., Sheberstov, S., Vazyulya, S., Kravchishina, M., Pautova, L., et al. (2014). Satellite monitoring of coccolithophore blooms in the Black Sea from ocean color data. Remote Sens. Environ. 146, 113–123. doi: 10.1016/j.rse.2013.09.009 ↩
For example, see Bach et al. (2013) New Phytologist, Bach et al. (2015) Progress in Oceanography, Gafar et al.(2018) Frontiers in Marine Science and others. ↩
Bednaršek, N., Pelletier, G., van de Mortel, H., García-Reyes, M., Feely, R., and Dickson, A.: Unifying framework for assessing sensitivity for marine calcifiers to ocean alkalinity enhancement identifies winners, losers and biological thresholds – importance of caution with precautionary principle, EGUsphere [preprint] doi.org/10.5194/egusphere-2024-947 ↩
Gately, J..A., Kim, S.M., Jin, B., et al. (2023). Coccolithophores and diatoms resilient to ocean alkalinity enhancement: A glimpse of hope?. Science Advances 9, eadg6066. doi:10.1126/sciadv.adg6066 ↩
Zhang, S., Planavsky, N. J., Katchinoff, J., Raymond, P. A., Kanzaki, Y., Reershemius, T., & Reinhard, C. T. (2022). River chemistry constraints on the carbon capture potential of surficial enhanced rock weathering. Limnology and Oceanography, 67(S2), S148–S157. https://doi.org/10.1002/lno.12244 ↩
Harrington, K. J., Hilton, R. G., & Henderson, G. M. (2023). Implications of the Riverine Response to Enhanced Weathering for CO2 removal in the UK. Applied Geochemistry, 152, 105643. https://doi.org/10.1016/j.apgeochem.2023.105643 ↩↩²
Kantzas, E.P., Val Martin, M., Lomas, M.R. et al. (2022). Substantial carbon drawdown potential from enhanced rock weathering in the United Kingdom. Nat. Geosci. 15, 382–389. https://doi.org/10.1038/s41561-022-00925-2 ↩
Beerling, D.J., Kantzas, E.P., Lomas, M.R. et al. (2020). Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature 583, 242–248. https://doi.org/10.1038/s41586-020-2448-9 ↩
Kanzaki, Y., Planavsky, N.J., Reinhard, C.T. (2023). New estimates of the storage permanence and ocean co-benefits of enhanced rock weathering, PNAS Nexus, Volume 2, Issue 4, pgad059. https://doi.org/10.1093/pnasnexus/pgad059 ↩↩² ↩³
Mu, L., Palter, J. B., and Wang, H. (2023). Considerations for hypothetical carbon dioxide removal via alkalinity addition in the Amazon River watershed, Biogeosciences, 20, 1963–1977. https://doi.org/10.5194/bg-20-1963-2023. ↩
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Jiang, L.-Q., Subhas, A. V., Basso, D., Fennel, K., and Gattuso, J.-P. (2023) Data reporting and sharing for ocean alkalinity enhancement research. State of the Planet 2-oae2023, 13, https://doi.org/10.5194/sp-2-oae2023-13-2023 ↩
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1.0 Introduction

consistent, accurate procedures are used to measure and monitor all aspects of the WAE process required to enable accurate accounting of net CO₂e removals
consistent system boundaries and calculations are utilized to quantify net CO₂e removal for WAE projects
requirements are met to ensure the CO₂e removals are additional
evidence is provided and verified by independent third parties to support all net CO₂e removal claims

Note that throughout this Protocol, use of the word "must" indicates a requirement, whereas "should" indicates a recommendation.

2.0 Sources and Reference Standards and Methodologies

Specific standards and protocols which are utilized as the foundation of this Protocol and for which this Protocol is intended to be fully compliant with are the following:

Isometric Standard
ISO (International Organization for Standardization) 14064-2: 2019 – Greenhouse Gases – Part 2: Specification with guidance at the project level for quantification, monitoring and reporting of greenhouse gas emission reductions or removal enhancements

Additional reference standards that inform the requirements and overall practices incorporated in this Protocol include:

ISO 14064-3: 2019 - Greenhouse Gases - Part 3: Specification with Guidance for the verification and validation of greenhouse gas statements
ISO 14040: 2006 - Environmental Management - Lifecycle Assessment - Principles & Framework
ISO 14044: 2006 - Environmental Management - Lifecycle Assessment - Requirements & Guidelines

3.0 Future Versions

4.0 Applicability

To ensure human and environmental health, eligible projects must:

Operate within the existing permits, or an approved modified permit, of a wastewater treatment plant.
Characterize feedstock prior to usage according to the Rock and Mineral Feedstock Characterization Module.
Submit proof of an official partnership with partner facilities to ensure that the Project is consensual and that the WWTP will continue to provide access to the Project Proponent for any continual monitoring required for the WAE project. This can be evidenced by documents such as a Memorandum of Understanding (MoU), written consent, or other agreement with involved parties, such as the WWTP, wastewater utility, contracted operators, or contracted feedstock supplier.

To ensure additional net-negative climate impacts, eligible projects must:

Do one of the following:
- Add alkaline feedstock to a wastewater treatment plant (WWTP) that would not otherwise add an alkalinity-enhancing feedstock, such as lime, as evidenced from historical records of plant operations.
- In a WWTP that does currently add alkalinity (e.g. in the form of CaCO₃, NaOH, MgOH₂, etc.) for process control, the following scenarios are eligible. See Section 7.3 for more information on the baselines for these different scenarios.
  - Using the same feedstock and increasing the dosage above business as usual (BAU) operations.
  - Switching the feedstock such that the carbon removal potential is above that of BAU operations, adjusting the dosage if necessary.
Be considered additional, in accordance with the requirements of Section 5.4.
Provide a net-negative CO₂e impact (net CO₂e removal) as calculated in compliance with Section 8, on a cradle to grave GHG assessment basis.
Provide long duration storage (>1,000 yr estimated) of CO₂ as dissolved inorganic carbon (DIC) in seawater.

The following applicability requirements are to limit the scope of eligible projects that the present version of this Protocol is developed for. However, these may be expanded in future versions.

This Protocol currently includes storage of removed CO₂ as dissolved inorganic carbon in the ocean. Thus, eligible Projects must operate in WWTPs that discharge directly into the ocean from coastal outfalls, or to rivers and estuaries where the discharge will be transported to the ocean. Most rivers will reach their basin outlet within one to two months⁸. Long term storage in inland waters (e.g. lakes) is being explored for future iterations.
The quantification framework in this Protocol is developed for WWTPs treating biogenic waste with activated sludge reactors and variations on activated sludge processes, which is the most common form of biological treatment. Alternative types of biological treatment require modifications to this Protocol, particularly Section 8 and Section 11, and they may be allowed on a case-by-case basis in consultation with Isometric. More guidelines for other types of WWTPs, such as membrane bioreactors, will be explored for future versions of this Protocol.
Alkalinity addition occurs in the biological treatment portion of the facility.
Projects must operate as retrofits to existing WWTP facilities. A retrofit is defined as the introduction of new materials, products or technologies to an existing process or facility. This can include adding alkalinity dosing to WWTPs that did not previously add alkalinity, increasing dosing in plants that already add alkalinity, adding additional monitoring to the WWTP to quantify CDR, etc.

5.0 Relation to the Isometric Standard

5.1 Project Design Document

detailed feedstock characterization following the Rock and Mineral Feedstock Characterization Module
description of discharge site and WWTP business as usual operations, following Section 10
description of the mitigation plan according to the environmental and social risk assessment in adherence with Appendix 1, including a robust monitoring plan to ensure efficacy
description of the quantification strategy for net CO₂e removal following Section 8
description of all measurement and methods used to quantify processes relevant to the calculation of net CO₂e removal, cross-referenced with relevant standards where applicable
documentation of official permitting and proof of partnership, such as a Memorandum of Understanding, with partner WWTP

5.2 Verification and Validation

The Validation and Verification Body (VVB) must consider the following requisite components:

Validate that the feedstock adheres to the requirements listed in the Rock and Mineral Feedstock Characterization Module.
Verify that the quantification approach adheres to requirements of Section 8, including demonstration of required records.
Verify that the Environmental & Social Safeguards outlined in Section 6 are met.
Verify that the Project is compliant with requirements outlined in the Isometric Standard.

5.2.1 Verification Materiality

The threshold for Materiality, considering the totality of all omissions, errors and mis-statements, is 5%, in accordance with Section 4.3 of the Isometric Standard.

control issues that erode the verifier’s confidence in the reported data
poorly managed documented information
difficulty in locating requested information
noncompliance with regulations indirectly related to GHG emissions, removals or storage

5.2.2 Site Visits

A site visit must occur at least once per project validation at each location.

5.2.3 Verifier Qualifications & Requirements

All VVBs are approved by Isometric independently and impartially based on alignment with Conflict of Interest policies, rotation of VVB policies, oversight on quality and the following requirements:

VVBs must be able to demonstrate accreditation from:
- an International Accreditation Forum member against ISO 14065: 2020 or other relevant ISO standard, including but not limited to ISO 14034:2016, ISO/IEC 17020:2012, ISO/IEC 17029:2019; or
- a relevant governmental or intergovernmental regulatory body.
Alternatively, on a case-by-case basis, if VVBs are able to demonstrate to Isometric that they satisfy all required Verification needs and competencies required for the relevant Protocol and follow the guidelines of ISO 19011:2018 or other relevant standards, they may be approved.

5.3 Ownership

5.4 Additionality

Additionality determinations must be reviewed and completed every two years, at a minimum, or whenever project operating conditions change significantly, such as the following:

regulatory requirements or other legal obligations for project implementation change or new requirements are implemented
project financials indicate Carbon Finance is no longer required, potentially due to, for example:
- increased tipping fees for waste feedstocks
- sale of co-products that make the business viable without Carbon Finance
- reduced rates for capital access
- subsidies for WWTP emissions reduction

5.5 Uncertainty

5.5.1 Reporting of Uncertainty

Projects must report a list of all key variables used in the net CO₂e removal calculation and their uncertainties, as well as a description of the uncertainty analysis approach, including:

required measurements used for net CO₂e removal calculation
emission factors utilized, as published in public and other databases
values of measured parameters from process instrumentation, such as electricity usage from utility power meters
laboratory analyses, including analysis of seawater chemistry and alkaline feedstocks

5.6 Data Reporting and Availability

Project Design Document
GHG Statement
Measurements taken
Model specifications and output
Emission factors used
Scientific literature used

6.0 Environmental and Social Safeguarding

6.1 Overarching Principles

Since Projects under this Protocol are retrofitted into existing WWTP operations, the scope of environmental and social safeguarding is applicable for the additional impacts relative to BAU.

6.2 Governance and Legal Framework

Projects must adhere to the following governance and legal requirements:

Official permitting:

Project Proponents must identify the jurisdictional authorities of the receiving water bodies of the project site, and as outlined in Section 4 (Applicability).
Projects must operate within the existing permits, or an approved modified permit, of a wastewater treatment plant.
Project Proponents must hold an official partnership, such as through an MoU, with the wastewater facility the Project intends to integrate with.

Compliance:

Project Proponents must comply with all national and local laws, regulations and policies.
Where relevant, Projects must comply with international conventions and standards governing human rights and uses of the environment, when conducted within or where it is foreseeable for it to impact Party jurisdictions.

6.3 Risk Mitigation Strategies

6.3.1 Environmental Safeguards

The Project Proponent must conduct an environmental risk assessment which adheres to Section 3.7.1 of the Isometric Standard.

Particular environmental risks associated with Wastewater Alkalinity Enhancement which must be assessed, avoided and/or mitigated are:

Feedstock sourcing:

Potential risks associated with feedstocks include land use impacts from sourcing, production, preparation, storage and distribution, such as land degradation, land occupation, dust pollution, deforestation and localized watershed contamination.

Co-products and waste:

Generation of waste products or additional waste must be accompanied by a plan which ensures safe handling, containment and disposal.

Pollution prevention:

Additional pollutants, such as nutrients or toxic elements, from dissolution of feedstock(s), which may result in bioaccumulation in biota or water quality impacts for downstream water users. Rock and Mineral Feedstock Characterization is mandatory as a first line of defense for safeguarding against the release of harmful pollutants.
The risk of the WWTP not being able to meet its discharge permit requirements must be assessed and there should be a plan in place for mitigating this.

Ecological impacts:

Shock to the ecosystem due to rapid or sudden changes in carbonate system parameters.
Changes in carbonate chemistry, such as pH, could directly help or harm aquatic life depending on the magnitude and direction of the pH shift. For example, a risk of elevated pH in the wastewater effluent is an increase in the free ammonia fraction, which is toxic to aquatic life particularly if there is insufficient dilution upon discharge.
Cascading impacts of altered carbonate chemistry, nutrient fields, or particle deposition on biodiversity and ecosystem functions at and downstream of the receiving water body.

6.3.2 Social Safeguards

The Project Proponent must conduct a social risk assessment which adheres to Section 3.7.2 of the Isometric Standard on Social Impacts.

In particular, Wastewater Alkalinity Enhancement projects must:

have a plan for safeguarding working conditions, especially for safe handling and sampling of wastewater, activated sludge and fine particulate feedstocks
adhere to all health and safety standards set by the partner facility
consider the risks to water justice for users of the receiving water body and downstream water bodies
consider the risks to environmental justice due to historical inequities in siting of wastewater treatment facilities

6.4 Stakeholder Engagement

6.5 Adaptive Management

instrument malfunctions lead to data-gaps in required monitoring
effluent exceeds thresholds outlined in the PDD
regulatory non-compliance, e.g. danger to ecosystem health detected (such as by the local community or government agency)
compromised health and/or safety of workers and/or local stakeholders

7.0 System Boundary and Baseline

7.1 Reporting Period

7.2 System Boundary & GHG Emissions Scope

[Image: **Figure 1** System Boundaries]

Table 1. Scope of activities and GHG SSRs to be included by the removal project

Activity	GHG source, sink or reservoir	GHG	Scope	Timescale
Project Establishment	Initial surveys and feasibility studies	All GHGs	Any embodied, energy and transport emissions associated with surveys or feasibility studies required for establishment of the project site for WAE CDR activities.	Before dosing starts - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 8.4.1).
Equipment & materials manufacture	All GHGs	Embodied emissions associated with equipment and materials manufacture for project establishment (lifecycle Modules A1-3⁹). To include product manufacture emissions for equipment, buildings, infrastructure, and temporary structures associated with WAE CDR processes. Must include any additional material or infrastructure requirements at the WWTP as a result of WAE, for example any additional load bearing structures.
Equipment & materials transport to site	All GHGs	Transport emissions associated with transporting equipment and materials associated with WAE CDR processes to the project site(s) (lifecycle Module A4⁹). Must include any additional material or infrastructure requirements at the WWTP as a result of WAE, for example any additional load bearing structures.
Construction and installation	All GHGs	Emissions associated with construction and installation of the project site(s) (lifecycle Module A5⁹) for WAE CDR activities and any additional infrastructure requirements to WWTP as a result of WAE activities. To include energy use for construction, installation and groundworks, as well as waste processing activities and emissions associated with land use change.
Misc.	All GHGs	Any SSRs not captured by categories above. Any SSRs not captured by categories above. Only those that occur over the level of BAU WWTP activities should be accounted for.
Operations	Energy use	All GHGs	Electricity and fuel consumption associated operational processes, including marginal pumping, pre-treatment, waste-water treatment, solids separation and disposal, and discharge of treated to the environment. Only those that occur over the level of BAU WWTP activities should be accounted for.	Over each Reporting Period - must be accounted for in the relevant Reporting Period (See Section 8.4.2)
Feedstock manufacturing and transport	All GHGs	Feedstock raw material extraction and manufacturing including rock quarrying, crushing, grinding and drying. Feedstock transport from source manufacturer to project site. Only those that occur over the level of business as usual WWTP activities should be accounted for, which is applicable if the same feedstock as BAU is used for the WAE project. Switching to a new feedstock constitutes a deviation from BAU activities, and all feedstock manufacturing and transport emissions must be accounted for in that case.
Consumables (other than feedstock)	All GHGs	Embodied emissions associated with consumables required for operation of the project site (excluding feedstock). Only those that occur over the level of BAU WWTP activities should be accounted for. This could include consumables for treatment of waters, cleaning or coagulants within the WWTP above BAU.
Waste Activated Sludge (WAS) transport	All GHGs	Transport of waste activated sludge (WAS) to disposal locations. Only activities that occur over the level of BAU WWTP activities should be accounted for.
Incineration of Waste Activated Sludge (WAS)	CO₂	CO₂ released from the incineration of waste activated sludge (WAS), if applicable. Only those that occur over the level of BAU WWTP activities should be accounted for.
Landfill disposal of Waste Activated Sludge (WAS)	All GHGs	Emissions associated with the landfilling of waste activated sludge (WAS), if applicable. Only those that occur over the level of BAU WWTP activities should be accounted for.
Sampling required for MRV	All GHGs	Monitoring, including consumables used for measurement and transportation or shipping of samples for laboratory analysis and sample processing for MRV.
Staff travel	All GHGs	Flight, car, train or other travel required for the project operations, including contractors and suppliers required on site. Only those that occur over the level of BAU WWTP activities should be accounted for.
Surveys	All GHGs	Embodied, energy and transport emissions associated with undertaking required surveys e.g. environmental impact surveys. Only those that occur over the level of BAU WWTP activities should be accounted for.
CO₂ Stored	CO₂	The gross amount of CO₂ removed and durably stored from the Wastewater Alkalinity Enhancement process as ocean dissolved inorganic carbon (DIC). This must include ocean losses and broader impacts on CDR described in Section 8.2.3 and Section 8.2.4 respectively.
Maintenance of project site	All GHGs	To include maintenance (lifecycle Modules B2⁹), repair (B3), replacement (B4) and refurbishment (B5) activities associated with equipment, buildings and infrastructure. Only those that occur over the level of BAU WWTP activities should be accounted for. For example, if there is increased fouling of membranes or wear on pipes and pumps that lead to more frequent replacement, then the emissions related to replacing those parts must be accounted for.
Misc.	All GHGs	Any SSRs not captured by categories above. For example, accidental or unintended release of treated waters may result in secondary precipitation and ocean outgassing, or unneutralized streams may result in ocean outgassing. If these events occur, their impacts must be quantified. Only those that occur over the level of business as usual WWTP activities should be accounted for.
End-of-Life	End-of-life of emissions	All GHGs	To include anticipated end-of-life emissions (lifecycle Modules C1-4⁹). Only those that occur over the level of BAU WWTP activities should be accounted for.	After Reporting Period - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 8.4.1)
Ongoing sampling and monitoring required for MRV	All GHGs	Embodied, energy and transport emissions related to ongoing monitoring of carbonate mineral storage site, measurement equipment, and energy use associated with monitoring equipment, sampling systems, laboratory analysis, operation and management of monitoring facility buildings and handling equipment. This could include ongoing environmental monitoring of discharge to marine environments. Only those that occur over the level of BAU WWTP activities should be accounted for.
Ongoing surveys	All GHGs	Embodied, energy and transport emissions associated with undertaking long-term required surveys e.g. ecological surveys. Only those that occur over the level of BAU WWTP activities should be accounted for.
Misc.	All GHGs	Any emissions source, sink or reservoir not captured by categories above. Only those that occur over the level of BAU WWTP activities should be accounted for.

Emissions associated with a project's impact on activities that fall outside of the system boundary of a project must also be considered. This is covered under Leakage in Section 8.4.4.

7.2.1 System Boundary Considerations

Ancillary Activities

Secondary Impacts on GHG Emissions

Considerations for Waste Input Emissions

Table 2. Waste input emissions exclusion criteria, EC1

Criteria	Description	Documentation required
EC1	No payment was made for the material, or only a “tipping fee” is paid.	Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, a signed affidavit from the Project Proponent stating that no in-kind compensation was made to the feedstock supplier must be provided.

Table 3. Waste input emissions exclusion criteria, EC2 and EC3

Criteria	Description	Documentation required
EC2	The amount of the waste product used by the CDR project was not already being utilized as a valuable product by another party for non-CDR uses. Therefore, the producer of the waste product has no alternative use case for the waste product.	Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, an affidavit from the waste supplier identifying that there are no alternative use cases for the waste product.
EC3	Payments for the waste product do not constitute a significant share of upstream operations revenue for the waste producer.	Feedstock purchase or removal records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, an affidavit from the waste supplier that documents that payments from the Project do not constitute a significant share of upstream operations revenue.

Considerations for Project Activities Integrated into Separate Practices

The separate facility must not include any CO₂ removals associated with the WAE CDR activity in their company GHG accounting to avoid double counting of removals.

7.3 Baseline

8.0 Quantification of CO₂e Removal

8.1 Net CDR Calculation

The net CO₂e removal equation is:

[math: ~~CO_2e_~~CO*2e*{Removal,\ RP} = ~~CO_2e_~~CO*2e*{Stored,\ RP} - ~~CO_2e_~~CO*2e*{Counterfactual,\ RP} - ~~CO_2e_~~CO*2e*{Emissions,\ RP}]

Equation 1

Where

[math: CO_2e_{Removal,\ RP}] represents the total net CO₂e removal for Reporting Period, RP, in tonnes of CO₂e;
[math: CO_2e_{Stored,\ RP}] represents the total CO₂ removed from the conversion of biogenic CO₂ in wastewater to stable dissolved inorganic carbon due to the Project activity for Reporting Period, RP, in tonnes CO₂e;
[math: CO_2e_{Counterfactual,\ RP}] represents the total counterfactual CO₂ removed from the atmosphere for the Reporting Period, RP, in tonnes of CO₂e. This term is calculated using BAU operations. See Section 8.3 for more details on how to calculate this term for different scenarios;
[math: CO_2e_{Emissions,\ RP}] represents the total GHG emissions associated with the Project including leakage, over a Reporting Period, RP, in tonnes of CO₂e.

8.2 Calculation of CO₂eStored, RP

For example, the dissolution of calcium carbonate (CaCO₃) as an alkaline feedstock follows the chemical reaction:

[math: ~~CaCO_~~CaCO*{3 (s)} + ~~CO_~~CO*{2 (aq)} + ~~H_2O_~~H*2O*{(l)} \rightarrow Ca^{2+}_{(aq)} + 2HCO_{3 (aq)}^{-}]

Equation 2

The total CO₂ that is converted to bicarbonate ions in the wastewater stream is determined using direct measurements within the WWTP and subtracting any potential losses upon effluent discharge.

The total amount of carbon stored can be determined as follows:

[math: CO_2e_{Stored,\ RP} = m_{Dissolved,\ RP} *\frac{M_{CO_2}}{M_{FS}}* ((1-P)*X_{carbonic}* \eta_{Losses,\ RP} - P*X_{non-carbonic})]

Equation 3

Where

[math: m_{Dissolved,\ RP}] is the total mass of feedstock dissolved within a Reporting Period, RP, in tonnes;
[math: M_{CO_2}] is the molar mass of CO₂ in tonnes/mol;
[math: M_{FS}] is the molar mass of the chosen feedstock in tonnes/mol;
[math: P] is the fraction of feedstock dissolved by non-carbonic acid. [math: P] is a dimensionless value between 0 and 1;
[math: X_{carbonic}] is the molar ratio of CO₂ consumption and feedstock consumption from carbonic acid weathering, in mol CO₂/mol feedstock;
[math: X_{non-carbonic}] is the molar ratio of CO₂ release and feedstock consumption from non-carbonic acid weathering, in mol CO₂/mol feedstock. This term is 0 for non-carbonate feedstocks which do not release CO₂ upon contact with a non-carbonic acid;
[math: \eta_{Losses,\ RP}] are losses of CO₂ due to riverine and oceanic processes. [math: \eta_{Losses,\ RP}] is a dimensionless term. See Section 8.2.3 for calculation of this term.

The mass of feedstock dissolved within a Reporting Period, [math: m_{Dissolved,\ RP}], can be determined by:

[math: m_{Dissolved,\ RP} = \sum_{i}^{T} ( \dot m_{Dissolved,\ i} * \Delta t_i) ]

Equation 4

Where

[math: m_{Dissolved,\ RP}] is the total mass of feedstock dissolved within a Reporting Period, RP, in tonnes;
[math: \dot m_{Dissolved,\ i}] is the average feedstock dissolution rate over time interval, [math: i], in tonnes/day;
[math: \Delta t_i] is the duration of time, [math: i], over which measurements are averaged, in days;
[math: T] is the total number of time intervals in the Reporting Period, RP, to be summed over.

8.2.1 Calculation of Average Feedstock Dissolution Rate and P

[Image: **Figure 2** Control Volume]

[math: \dot m_{Dissolved}] can be calculated based on the following options:

Option 1: Mass balance on solid feedstock, where the difference between solid feedstock into and out of the control volume is assumed to be the result of feedstock dissolution.
Option 2: Mass balance on conservative dissolved weathering products, such as Ca²⁺ or Mg²⁺, where the difference in weathering product concentration between the influent and effluent is assumed to the result of feedstock dissolution.

Recycle streams produced within the plant that constitute a significant alkalinity source or sink;
Chemical addition that constitutes a significant alkalinity source or sink;
Trickling filter/solid contact (TF/SC) treatment and similar hybrid processes;
WWTPs using high purity oxygen (HPO) for the aeration process.

8.2.1.1 Option 1: Quantification in the Solid Phase

The mass flow rate of solid feedstock is defined as:

[math: \dot m_{FS} = Q * FS * 10^{-9}]

Equation 5

Where

[math: \dot m_{FS}] is mass flow rate of feedstock in tonnes/day;
[math: Q] is flow rate in L/day;
[math: FS] is mass concentration of feedstock in mg/L;
A factor of 10^-9 is used to convert units from mg to tonnes.

Alternative formulations of flow rate can be used where applicable, this must be described in the PDD.

The mass balance of the solid feedstock within the control volume, [math: V], (Figure 2) can be defined as:

[math: \frac{dFS}{dt} = \dot m_m*{FS,\ Dosing} - \dot m_m*{FS,\ Effluent} - \dot m_m*{FS,\ WAS} - \dot m_m*{Dissolved}]

Equation 6

Where:

[math: \frac{dFS}{dt}] is the change in feedstock mass in the control volume over time t;
[math: \dot m_{FS,\ Dosing}] is the mass flow rate of feedstock added in tonnes/day;
[math: \dot m_{FS,\ Effluent}] is the mass flow rate of feedstock in the effluent stream in tonnes/day;
[math: \dot m_{FS,\ WAS}] is the mass flow rate of feedstock in the waste activated sludge (WAS) stream in tonnes/day;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day.

By assuming steady state, [math: \frac{dFS}{dt} = 0], no feedstock present in the influent, and the control volume shown in Figure 2, [math: \dot m_{Dissolved}] can be calculated as:

[math: \dot m_{Dissolved} = \dot m_{FS,\ Dosing} - \dot m_{FS,\ Effluent} - \dot m_{FS,\ WAS}]

Equation 7

Where:

[math: \dot m_{FS, Dosing}] is the mass flow rate of feedstock from dosing in tonnes/day;
[math: \dot m_{FS, Effluent}] is the mass flow rate of the feedstock in the effluent stream in tonnes/day:
- [math: \dot m_{FS, Effluent} = Q_{Effluent} * FS_{Effluent} * 10^{-9}] (Equation 8)
  - [math: Q_{Effluent}] is the flow rate of plant effluent in L/day;
  - [math: FS_{Effluent}] is the concentration of feedstock suspended in plant effluent in mg/L;
  - A factor of 10^-9 is used to convert units from mg to tonnes
[math: \dot m_{FS,\ WAS}] is the mass flow rate of feedstock in the waste activated sludge (WAS) stream in tonnes/day:
- [math: \dot m_{FS,\ WAS} = Q_{WAS} * FS_{WAS} * 10^{-9}] (Equation 9)
  - [math: Q_{WAS}] is the flow rate of waste activated sludge in L/day;
  - [math: FS_{WAS}] is the concentration of feedstock settled in waste activated sludge in mg/L;
  - A factor of 10^-9 is used to convert units from mg to tonnes.

Requirements for measurements of concentration of the feedstock in effluent and waste activated sludge will vary depending on the feedstock used:

When carbonate feedstocks, such as calcite (CaCO₃) are used, [math: FS_{Effluent}] and [math: FS_{WAS}] can be assumed to be equivalent to the total inorganic carbon (TIC) in samples taken from these streams. This approach assumes that any inorganic carbon present in plant effluent and waste activated sludge comes from dosing of carbonate feedstocks, which is a conservative assumption. Methods for TIC analysis must be described in detail in the PDD and must include any standards or SOPs used. Acceptable analyses may include, but are not limited to, use of a TIC analyzer.
Where non-carbonate feedstocks are used, [math: FS_{Effluent}] and [math: FS_{WAS}] must be determined from direct measurements of cations relevant to the chosen feedstock (e.g. Ca²⁺, Mg²⁺) in each stream, relative to the influent stream. Acceptable methods include, but are not limited to, sample digestion and/or or analysis on ICP-MS or ICP-OES. Sample digestion is required for [math: FS_{WAS}]. Note that for [math: FS_{Effluent}], samples must be acidified prior to filtration. Methods used for cation analysis must be described in detail in the PDD and must include any standards or SOPs used.

[math: P = \frac{\dot m_{NCA}}{\dot m_{Dissolved}}]

Equation 10

Where

[math: \dot m_{NCA}] is mass flow rate of feedstock dissolved by non-carbonic acid, in tonnes/day;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day.

The recommended approach to determine [math: \dot m_{NCA}] is measuring anion concentrations in the aqueous phase:

[math: \dot m_{NCA} = \frac{\sum_{i} (Q_i*[A^x]_i)}{1 * 10^6}]

Equation 11

Where:

[math: Q_i] is the flow rate of stream [math: i], in L/day;
[math: [A^x]_i = \sum_{y} (a_y * n_y * M_y)] (Equation 12), where:
- [math: a_y] is the concentration of anion [math: y], in mol/L;
- [math: n_y] is the charge of anion [math: y];
- [math: M_y] is the molar mass of anion [math: y], in g/mol;
[math: 1 * 10^6] is a conversion factor for g to tonnes.

8.2.1.2 Option 2: Quantification in the Aqueous Phase Using Conservative Dissolved Weathering Products

The molar flow rate of a dissolved weathering product, [math: C^x], is defined as:

[math: n_{C^x}= Q * [C^x]]

Equation 13

Where

[math: n_{C^x}] is the molar flow rate of dissolved weathering product [math: C^x], in mol/day;
[math: Q] is flow rate in L/day;
[math: [C^x]] is the molar concentration of dissolved weathering product [math: C^x], in mol/L.

The mass balance of the dissolved weathering product, [math: C^x], within the control volume V (Figure 2) can be defined as:

[math: \frac{d[C^x]}{dt} = (1/V)* [(n_{C^x,\ Influent} - n_{C^x,\ WAS} -n_{C^x,\ Effluent}) + (\dot m_{Dissolved}/M_{FS})]]

Equation 14

Where:

[math: \frac{d[C^x]}{dt}] is the change in molar concentration of dissolved weathering product, [math: C^x], in the control volume over time, in mol/(L day);
[math: V] is the volume of the control volume, in L;
[math: n_{C^x,\ Influent}] is the molar flow rate of dissolved weathering product [math: C^x] in the influent stream in mol/day;
[math: n_{C^x,\ WAS}] is the molar flow rate of dissolved weathering product [math: C^x] in the WAS stream in mol/day;
[math: n_{C^x,\ Effluent}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day;
[math: M_{FS}] is the molar mass of the feedstock, in tonnes/mol.

Assuming steady state, [math: \frac{d[C^x]}{dt} = 0], the rate of feedstock dissolved can be calculated in the aqueous phase using the following equation:

[math: \dot m_{Dissolved} = ( M_{FS})*(n_{C^x,\ Effluent} + n_{C^x,\ WAS} -n_{C^x,\ Influent})]

Equation 15

Where

[math: n_{C^x,\ Effluent}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day:
- [math: n_{C^x,\ Effluent}= Q_{Effluent} * [C^x]_{Effluent}] (Equation 16)
  - [math: Q_{Effluent}] is the flow rate of plant effluent in L/day;
  - [math: [C^x]_{Effluent}] is the molar concentration of dissolved weathering product [math: C^x] in the effluent stream mol/L.
[math: n_{C^x,\ WAS}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day:
- [math: n_{C^x,\ WAS}= Q_{WAS} * [C^x]_{WAS}] (Equation 17)
  - [math: Q_{WAS}] is the flow rate of plant effluent in L/day;
  - [math: [C^x]_{WAS}] is the molar concentration of dissolved weathering product [math: C^x] in the effluent stream mol/L.
[math: n_{C^x,\ Influent}] is the molar flow rate of dissolved weathering product [math: C^x] in the effluent stream in mol/day:
- [math: n_{C^x,\ Influent}= Q_{Influent} * [C^x]_{Influent}] (Equation 18)
  - [math: Q_{Influent}] is the flow rate of plant effluent in L/day;
  - [math: [C^x]_{Influent}] is the molar concentration of dissolved weathering product [math: C^x] in the influent stream mol/L.
[math: M_{FS}] is the molar mass of the feedstock, in tonnes/mol.

The proportion of feedstock dissolved by non-carbonic acid, [math: P], must be determined.

[math: P = \frac{n_{C^x,\ NCA}*M_{FS}}{\dot m_{Dissolved}}]

Equation 19

Where

[math: n_{C^x,\ NCA}] is the molar flow rate of dissolved weathering product [math: C^x] resulting from non-carbonic acid dissolution of feedstock within the control volume, in mol/day;
[math: M_{FS}] is the molar mass of the feedstock, in tonnes/mol;
[math: \dot m_{Dissolved}] is the mass of feedstock dissolved in tonnes/day.

The recommended approach to determined [math: n_{C^x,\ NCA}] is measuring anion concentrations in the aqueous phase.

[math: n_{C^x,\ NCA} = \sum_{i} ( Q_i*[C^x]_i)]Equation 20

Where:

[math: Q_i] is the flow rate of stream [math: i];
[math: [C^x]_i = \sum_{y} (a_y*n_y]) (Equation 21)
- [math: a_y] is the concentration of anion y;
- [math: n_y] is the charge of anion y.

8.2.2 Validation and Reconciliation Calculations

8.2.2.1 Confirmation of Steady State Operations

8.2.2.2 Mass Balance Calculations

8.2.2.2.1 Sorption

8.2.2.2.2 Future Updates to Quantification and Validation Approaches

8.2.2.3 Upper Limit of Biogenic CO₂ Outgassing

There are several methods that can be used to provide an estimate of total biogenic CO₂ emissions:

Calculation based on WWTP data of chemical oxygen demand (COD) removed and a relevant emission factor. For example, a default emission factor of 560g CO₂/kg COD removed during treatment can be used¹⁵.
Measurement of dissolved CO₂ concentrations prior to aeration and in the outflow from secondary treatment. The difference in these values can be taken as the CO₂ loss during the treatment process. This method requires extensive baselining of CO₂ concentrations across the full range of typical environmental conditions that may impact the efficiency of microbial communities within the secondary treatment process. At a minimum, Project Proponents must measure baseline CO₂ concentrations in the relevant streams during standard operational conditions 3 times per quarter for 1 year prior to the onset of Project activities, due to the dependence of CO₂ solubility and microbial activity on temperature. Where available, data from partner facilities may be substituted for direct measurements. Where direct measurements are required, Project Proponents must describe the methods used for measurement of CO₂ concentrations. This Protocol recommends the equilibration method, in which a volume of fluid is equilibrated with the headspace of a vessel (typically a syringe) and the headspace gas is collected and injected into a vacuum-sealed vial (Vacutainer) for analysis on a gas chromatograph. Care should be taken to ensure that gas samples are properly stored. Other methods may be suitable and must be described in the PDD. Due to the high pCO₂ of wastewater with a high organic load, it is not recommended to measure the dissolved inorganic carbon (DIC) of the fluid, as outgassing is likely to occur during sample collection.
Modeling of outgassing in secondary treatment based on known fluid parameters. Model construction will be dependent on the project site and should follow best practices for the relevant treatment system ¹⁶. At a minimum, models should consider the following parameters within the biological treatment tanks:
- Concentration of CO₂
- pH
- Flow rate of the fluid
- Flow rate of the gas
- Temperature
- Gas pressure within the system
- Gas transfer velocity of the aeration tanks
Alternatively, an upper limit may be established from the total biogenic CO₂ production, which may be calculated from measurements of biological oxygen demand (BOD) in the influent stream. This provides a more crude estimate as it assumes that all of the biogenic CO₂ produced is outgassed within the WWTP.

8.2.3 Calculation of Loss Discount

Processes that can lead to losses include:

Re-equilibration of the DIC system
Carbonate precipitation
Reduction in natural alkalinity fluxes
Changes in biotic calcification (for ocean discharge only)

[Image: **Figure 3** Losses]

Figure 3. Example schematic of where downstream losses may occur, and the spatial zones which must be considered for coastal and river discharges.

The overall loss discount for a Wastewater Alkalinity Enhancement project is the product of the loss factors associated with each loss process:

[math: \eta_{Losses,\ RP} = \prod_{i=1}^{N} \eta_i]

Equation 22

Where:

[math: \eta_{Losses,\ RP}] is the overall loss discount for Reporting Period;
[math: \eta_i] is the fraction of CO₂ that is retained after a given loss, [math: i];
[math: N] is the total number of loss processes.

The loss processes which must be considered for ocean and river discharge are indicated in Table 4.

Loss process	1) Mixing zone of discharge site	Transport (riverine discharge only)
2) Along river to estuary	3) At ocean
Re-equilibration of DIC	x	x	x
Carbonate precipitation	x	x
Natural alkalinity reduction	x
Biotic calcification	x (coastal discharge only)

avoiding the likelihood of these losses by identifying avoidance strategies around conditions which lead to non-negligible loss terms, with corresponding monitoring to demonstrate adherence to those guardrails
estimating a conservative upper limit of loss based on scientific literature, first principles calculations, and/or experimentation
process-based modeling studies
direct measurements
alternative approaches that are sufficiently justified

8.2.3.1 Near-Field Losses

Re-equilibration of DIC

Concept

Equilibrium speciation of DIC is primarily dependent on pH, and to a lesser extent temperature, salinity and pressure:

[math: CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow H^+ + HCO_3^- \leftrightarrow 2H^+ + CO_3^{2-} ]

Equation 23

Quantification

Carbonate Precipitation

Concept

Secondary precipitation of calcium carbonate could cause CO₂ outgassing by the following reaction:

[math: Ca^{2+} + 2HCO_3^{-} \rightarrow CaCO_3 + CO_2 + H_2O]

Equation 24

Calcium carbonate precipitation may result in a reduction in carbon loss by 50% for non-carbonate feedstocks or 100% for carbonate feedstocks.

Discussion

Quantification

Natural Alkalinity Flux Reduction

Concept

Quantification

Changes in Biotic Calcification

Concept

Discussion

Quantification

8.2.3.2 Transport Losses

8.2.3.2.1 Outgassing During River Transport

Quantification

The minimum requirements for river transport loss models are:

Domain:
- Full river network through which bicarbonate and carbonate ions will be transported
Inputs:
- River characteristics:
  - Baseline calcite saturation index (SI_c)
  - pH
  - pCO₂
  - Alkalinity
- Effluent characteristics:
  - Discharge rate
  - Alkalinity fluxes
  - Cation fluxes
Outputs:
- SI_c along river*
- pH along river
- Efficiency or discount factor on river transport loss for re-equilibration of DIC
- Efficiency or discount factor on river transport loss for carbonate precipitation

*Note on calcite saturation index in rivers

Calcite saturation index (SI_C) is a useful parameter to determine the likelihood of carbonate precipitation. Calcite saturation index (SI_C) is calculated as:

[math: SI_c = \log_{10} \frac{\alpha Ca^{2+} * \alpha CO_3^{2-}}{K_{sp(calcite)}}]

Equation 25

With

[math: K_{sp(calcite)} = \alpha_{sat} Ca^{2+} * \alpha_{sat} CO_3^{2-}]

Equation 26

Where:

[math: \alpha] is the measured solution activities of those ions
[math: \alpha_{sat}] is the ion activity at saturation

8.2.3.2.2 Outgassing Upon Entering Ocean

Discussion

Quantification

Outgassing upon entering the ocean must be quantified using regional data specific to the area where the river reaches the ocean. This loss can be estimated with one of the following approaches:

Using the Renforth and Henderson (2017) uptake efficiency equation
Using a 3D Earth Systems Model or ocean physical-biogeochemical model to explicitly simulate ocean circulation and air-sea CO₂ fluxes⁴⁰
Alternate approaches may be considered on a case by case basis, provided it is sufficiently described and justified in the PDD.

Option 1

The Renforth and Henderson (2017) uptake efficiency equation is:

[math: \frac{\Delta C_T}{\Delta A_T} = \eta = (S \cdot 10^{-3.009} + 10^{-1.519}) \text{ln}(pCO_2)-(S \cdot 10^{-2.100}) - \\ (T \cdot pCO_2)(S \cdot 10^{-7.501} - 10^{-5.598}) - (T \cdot 10^{-2.337}) + 10^{-0.102}]

Equation 27

Where

[math: \eta] is the uptake efficiency of CO₂ upon mixing with ocean waters, dimensionless;
[math: \Delta C_T] is the change in Total DIC in the ocean as a result of WAE, in mol;
[math: \Delta A_T] is the change in Total Alkalinity in the ocean as a result of WAE, in mol;
[math: pCO_2] is the local ocean partial pressure of CO₂ at the discharge site, in μatm;
[math: T] is the local surface ocean temperature, in °C;
[math: S] is the local ocean salinity, in %.

Option 2

Projects Proponents must submit a detailed description of their modeling approach in the PDD, including the following:

the model used and domain
inputs and forcing data, including atmospheric forcing and initial conditions
carbonate system representation and parameterization of air-sea CO₂ fluxes
representation of WAE project, e.g. as represented through an additional flux of DIC and alkalinity into the ocean at a particular river mouth
baseline simulations

Furthermore, the model must be well-validated and skillful for the purpose that it is used for. Proof of model validation can be achieved through either:

A track record of use in science, industry, or government applications, which is demonstrated through multiple peer-reviewed papers, or proof of usage in a number of previous applications.
Newly developed models without a track record of usage must be validated against reputable data sources, which include quality-controlled in situ measurements and public datasets adhering to FAIR (Findable, Accessible, Interoperable and Reusable) principles⁴². Sufficient model validation data must be provided with the PDD.

8.2.4 Broader Impacts on CDR

Discharge of Undissolved Alkalinity

Biological Fertilization

8.3 Calculation of CO₂e_{Counterfactual, RP}

Type: Counterfactual

The calculation of [math: CO_2e_{Counterfactual,\ RP}] depends on the BAU scenario for the WWTP (Figure 4).

For projects in which the partner WWTP does add alkalinity, [math: CO_2e_{Counterfactual,\ RP}] is calculated as follows:

If the feedstock emissions of the prior pH amendment is less than or close to equal to its carbon removal potential upon dissolution in wastewater, then [math: CO_2e_{Counterfactual,\ RP}] must be estimated based on the BAU dosing rate. This may be determined based on: historical dosing records from the WWTP, using a nitrogen balance to calculate the amount of alkalinity needed for the nitrification process (e.g. 7.14g of alkalinity as CaCO₃ is needed for 1g of NH₄⁺ nitrified⁴³), or an alternative approach which must be justified and evidenced in the PDD.
If the feedstock emissions of the prior pH amendment is significantly greater than its carbon removal potential upon dissolution in wastewater, then the BAU operation is emitting more CO₂ than is being removed through feedstock dissolution. Since this is a net-emitting scenario, this is not considered CDR by definition and [math: CO_2e_{Counterfactual,\ RP}] may be set to 0 on a case by case basis for each project in consultation with Isometric.

See Appendix 3 for further explaination on this approach.

[Image: **Figure 4** Counterfactual]

Figure 4 Decision tree for determining CO₂e_{Counterfactual, RP} for a WAE project.

8.4 Calculation of CO₂e_{Emissions, RP}

Type: Emissions

[math: CO_2e_{Emissions,\ RP}] is the total GHG emissions associated with a Reporting Period, [math: {RP}]. This can be calculated as:

[math: ~~CO_2e_~~CO*2e*{Emissions,\ RP} = ~~CO_2e_~~CO*2e*{Establishment,\ RP} + ~~CO_2e_~~CO*2e*{Operations,\ RP} + ~~CO_2e_~~CO*2e*{End-of-Life,\ RP} + ~~CO_2e_~~CO*2e*{Leakage,\ RP}]

Equation 28

Where

[math: CO_2e_{Emissions,\ RP}] represents the total GHG emissions for a Reporting Period, in tonnes of CO₂e.
[math: CO_2e_{Establishment,\ RP}] represents the GHG emissions associated with project establishment, represented for the Reporting Period, in tonnes of CO₂e, see Section 8.4.1.
[math: CO_2e_{Operations,\ RP}] represents the total GHG emissions associated with operational processes for a Reporting Period, in tonnes of CO₂e, see Section 8.4.2.
[math: CO_2e_{End-of-Life,\ RP}] represents GHG emissions that occur after the Reporting Period and are allocated to a Reporting Period, in tonnes of CO₂e, see Section 8.4.3.
[math: CO_2e_{Leakage,\ RP}] represents GHG emissions associated with the Project’s impact on activities that fall outside of the system boundary of a project, over a given Reporting Period, in tonnes of CO₂e, see Section 8.4.4.

8.4.1 Calculation of CO₂e_{Establishment, RP}

GHG emissions associated with project establishment should include all historic emissions incurred as a result of project establishment, including but not limited to the SSRs set out in Table 1.

as a one time deduction from the first removal
allocated to removals as annual emissions over the anticipated project lifetime
allocated per output of product (i.e., per ton CO₂ removed) based on estimated total production over project lifetime

The anticipated lifetime of the Project should be based on reasonable justification and should be included in the Project Design Document (PDD) to be assessed as part of project validation.

8.4.2 Calculation of CO₂e_{Operation, RP}

8.4.3 Calculation of CO₂e End-of-Life, RP

8.4.4 Calculation of CO₂e Leakage, RP

Feedstock replacement
Consumables replacement

8.4.5 Energy Use Accounting

Examples of fuel consumption may include, but are not limited to handling equipment, such as fork trucks or loaders.

[Module: energy-use-accounting v1.2]

Refer to Energy Use Accounting Module for the calculation requirements.

8.4.6 Transportation Emissions Accounting

This section sets out specific requirements relating to quantification of transportation emissions as part of the GHG Statement.

Emissions associated with transportation include transportation of products and equipment as part of a Reporting Period’s activities. Examples may include, but are not limited to:

transportation of equipment, feedstock and consumables to the facility
transportation of sludge to storage site
transportation and shipping related to collection and analysis of samples

[Module: transportation v1.1]

Refer to Transportation Emissions Accounting Module for the calculation requirements.

8.4.7 Embodied Emissions Accounting

Examples of project-specific materials and equipment that must be considered as part of the embodied emission calculation include but are not limited to:

feedstock, consumables and associated equipment produced, constructed and utilized explicitly for the CDR project
process equipment (i.e., pumps, mixers, blowers, flow control, measurement instruments)
equipment related to waste handling and disposal

[Module: embodied-emissions v1.0]

Refer to Embodied Emissions Accounting Module for the calculation guidelines.

9.0 Storage

9.1 Marine Dissolved Inorganic Carbon (DIC) Storage

[Module: dic-storage-in-oceans v1.0]

Ocean DIC Storage Module

Future versions of this Protocol will include expanded storage options, such as storage of DIC in lakes.

9.2 Buffer Pools

For more details on Reversals, refer to Sections 2.5.9 and 5.6 of the Isometric Standard.

10.0 Pre-Deployment Requirements

All pre-deployment requirements must be described in the PDD, as outlined in Section 5.1. The requirements are as follows:

Project Proponents must provide a site description of the discharge location, including the dominant circulation and modes of variability, as well as the frequency of various environmental conditions. This must include, at minimum, information on seasonal patterns, predominant currents, periods of maximum stratification and periods when receiving water quality conditions may be more critical.
Project Proponents must develop a conceptual model of dispersion of discharge, and produce a mixing zone model, which will likely already be a part of the existing WWTP discharge permit. The mixing zone model will estimate initial dispersal of the discharge, and will dictate the recommended reach of the monitoring efforts. Sensitivity analysis is required to demonstrate adherence to water quality limits at the boundary of the mixing zone under varying environmental conditions.
Project Proponents must have sufficient plans for restoring water quality conditions prior to discharge in the event that negative environmental impacts result from project activities.
Project Proponents must chacterize rocks and minerals utilized as feedstock following Isometric’s Rock and Mineral Feedstock Characterization Module.
Project Proponents must provide information on how dosing rate is calculated, including any partner data that was used in those calculations
Project Proponents must provide the following information on the WWTP during business as usual operation:
- Energy usage (e.g. from pumping, aeration, mixing, maintenance and/or cleaning). It is recommended to have at least 1 year of monthly energy data, normalized by the flow rate. If direct energy usage data is unavailable, estimates based on proxies (such as flow rate and BOD) are allowable. Alternatively, Project Proponents may provide a justification of why their WAE project will not increase WWTP operating energy usage above BAU, this should be based on data, literature, or other reasoning.
- Range of solids and/or WAS generation and the fate of the solids and/or WAS (e.g. incineration, anaerobic digestion, aerobic digestion). It is recommended to report at least 1 year of monthly data, normalized by the flow rate. This will be used to assess trends of solids and/or WAS generation over a Reporting Period that exceed the normal variation.
- Retention and settling times of solids and/or WAS within the WWTP.
Project Propnents must designate the control volume boundaries for the project, including the control volume in L.

11.0 Monitoring

11.1 Monitoring Locations

Influent ([math: A]): The influent stream of wastewater entering the control volume. Typically for control volumes that encompass the secondary treatment step, the influent stream measurements will be taken after primary treatment and before entering secondary treatment.
Feedstock dosing ([math: B]): Measurements of alkaline feedstock dosing into the control volume.
Effluent ([math: C]): The effluent stream exiting the control volume.
Waste activated sludge ([math: D]): Measurements of the waste activated sludge that is settled out of the water at the end of the secondary treatment step, and prior to transport and disposal of the WAS (e.g. incineration or landfill) or onsite solids treatment (e.g. anaerobic or aerobic digestion).
Within the Control Volume ([math: E]): This refers to measurements taken from within control volume, such as from the bioreactor. In contrast, the previous measurement locations [math: A], [math: B], [math: C] and [math: D] are referring to streams entering or exiting the control volume.
Edge of mixing zone ([math: F]): This refers to measurements made in the receiving waters, in the vicinity of the WWTP discharge. The region near the discharge may be referred to as a mixing zone, or mixing length, and is where signals of the WWTP discharge will be highest before being diluted farther away from the discharge location.

[Image: **Figure 5** Monitoring locations]

11.2 Control Volume Measurements

11.2.1 Influent, A

11.2.2 Feedstock Dosing, B

11.2.3 Effluent, C

11.2.4 Waste Activated Sludge, D

11.2.5 Within the Control Volume, E

11.3 Receiving Waters

11.3.1 Mixing Zone

11.3.2 Biological and Ecological Monitoring in Deployment Area

Tailored biological and ecological monitoring for specific projects and sites must be determined by conducting an environmental risk assessment and mitigation strategy (see Section 6).

11.3.3 Monitoring for Ecosystem Safety

Two types of thresholds are used:

Safety thresholds are imposed on the effluent characteristics and controlled prior to discharge.
Action thresholds are measured at the edge of the mixing zone. Parameters measured are indicators of water quality and/or unintended environmental changes. Action thresholds can be absolute or relative, and can be determined by regulatory limits, relative to natural variability based on historical data or relative to a control site. For example, the action threshold on pH could be 6.5 < pH < 9 or ±0.2 relative to natural variability, whichever is more conservative. Action thresholds may vary seasonally, and should be consistent with monitoring requirements under official permitting.

Effective implementation of these measures must also be accompanied by a robust monitoring plan to detect negative impacts and stop projects when necessary.

11.3.3.1 Threshold Violations

11.3.3.2 Enforcement Actions

11.4 Summary of Monitored Parameters

Location	Parameter	Requirement Scope	Reason for Measurement	Methods	Frequency
Influent (A)	Q, Flow rate (L/day)	Required for all projects	Required for determining volume of water processed, used in carbon removal calculation	Flow meter	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment.
[C^x], Concentration of dissolved weathering products (mol/L)	Required for Option 2	Required for quantifying amount of carbon removed	Discrete bottle samples (e.g., ICP-MS, ICP-OES) or using an ion-selective electrode).
Anions	Recommended for all projects.	Recommended to determine non-carbonic acid weathering. If anion measurements are not available, an alternative approach for determining non-carbonic acid weather is required (see Section 8.2.1.1 and 8.2.1.2)	Ion chromatography; measured ions must include, at a minimum, Cl^-, NO₃^-, PO₄^3- and SO₄^2-
Feedstock dosing (B)	Q, flow rate (L/day)	Required for all projects where slurry dosing is used	Required for determining volume of water processed, used in carbon removal calculation	Flow meter	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment.
m_{FS, Dosing}, mass flow rate of feedstock dosing (tonnes/day)	Required for all projects	Required for determining the amount of carbon removed.	Weigh scales of alkaline feedstock, or calculated from mass concentration of feedstock and dosing flow rate
Effluent (C)	Q_Effluent, Flow rate (L/day)	Required for all projects	Required for determining volume of water processed, used in carbon removal calculation	Flow meter; where not directly measured, Project Proponents may assume flow rate is constant throughout the system	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment.
FS_Effluent, concentration of suspended feedstock in effluent (mg/L)	Required for Option 1	Required to determine total amount of undissolved feedstock in effluent	May be derived from TSS and analytical measurement (e.g., TIC) of feedstock relative to other solid materials present.
[C^x], concentration of dissolved weathering products (e.g. Ca²⁺, Mg²⁺) (mol/L)	Required for Option 2	Required for quantifying amount of carbon removed	Discrete bottle samples (e.g., ICP-MS, ICP-OES) or using an ion-selective electrode).
Anions	Recommended for all projects	Recommended to determine non-carbonic acid weathering. If anion measurements are not available, an alternative approach for determining non-carbonic acid weather is required (see Section 8.2.1.1 and 8.2.1.2)	Ion chromatography; measured ions must include, at a minimum, Cl^-, NO₃^-, PO₄^3- and SO₄^2-
Total Suspended Solids (TSS)	Required for all projects at final effluent prior to discharge	Required for monitoring water quality, assessing and mitigating risk of downstream losses, and may be used for determination of FS_Effluent.	Discrete bottle samples and filtering directly onto pre-weighed filter and subsequent measurement of mass change through drying (for example, in an oven), or TSS analyzers from existing WWTP infrastructure.
At least two carbonate system parameters: pH, DIC, TA, pCO₂	Required for all projects at final effluent prior to discharge	Required for constraining carbonate system and determining outgassing upon mixing with receiving waters	Sensor (for pH or pCO₂) or discrete bottle samples
Waste Activated Sludge (WAS) (D)	Q_WAS, Flow rate (L/day)	Required for all projects	Required for determining volume of water processed, used in carbon removal calculation	Flow meter	At least once per residence time at the onset of project activities until steady state (defined as dFS/dt=0 or d[C^x]/dt=0) is reached. Ongoing throughout deployment
FS_WAS, concentration of settled feedstock in WAS (mg/L)	Required for Option 1	Required for quantification of carbon removed	Methods may vary based on feedstock
[C^x], concentration of dissolved weathering products, e.g. Ca²⁺, Mg²⁺ (mol/L)	Required for Option 2	Required for quantifying amount of carbon removed	Discrete bottle samples (e.g., ICP-MS, ICP-OES) or using an ion-selective electrode). Samples must be acidified prior to preparation for measurement.
Total Inorganic Carbon (TIC)	May be used to determine FS_WAS for projects utilizing carbonate feedstocks	Where carbon feedstocks are used, FS_effluent and FS_WAS can be assumed to be equivalent to TIC in samples taken from these streams	Discrete bottle samples taken from streams. Acceptable analyses include TIC analyzer or LOI analyses.
Anions	Recommended for all projects	Recommended to determine non-carbonic acid weathering. If anion measurements are not available, an alternative approach for determining non-carbonic acid weather is required (see Section 8.2.1.1 and 8.2.1.2)	Ion chromatography; measured ions must include, at a minimum, Cl^-, NO₃^-, PO₄^3- and SO₄^2-
Within the control volume, i.e. biological treatment tanks	Feedstock accumulation	Required for all projects	Required for assessing steady state assumption of no feedstock accumulation in control volume	Sludge sampling devices, or during routine cleaning and maintenance of bioreactors	Dependent on site-specific operations and must be justified.
Receiving waters, i.e. edge of mixing zone	Temperature	Recommended for all projects	Recommended for determining physical conditions and making calculations to fully constrain the seawater carbonate system	Sensor	(a) at high frequency when ramp-up is occurring and shortly after any dosing rate changes are made, (b) with low frequency when the dosing rate is occurring at a steady state (defined as dFS/dt=0 or d[C^x]/dt=0)
Salinity	Recommended for all projects	Recommended for determining physical conditions and making calculations to fully constrain the seawater carbonate system	Sensor
Any two carbonate system paramters: pH, DIC, TA, pCO₂	Recommended for all projects	Recommended to constrain the seawater carbonate system, monitor water quality and local carbonate saturation state	Sensor (for pH or pCO₂) or discrete bottle samples
Third carbonate system parameter	Recommended for all projects	Recommended to assess the local state of carbonate disequilibrium	Sensor (for pH or pCO₂) or discrete bottle samples
Dissolved Oxygen (DO)	Recommended for all projects	Recommended as indicator of general ecosystem health	Sensor
Total Suspended Solids (TSS)	Recommended for all projects	Recommended for monitoring water quality and for mitigation of losses	Discrete bottle samples and filtering directly onto pre-weighed filter and subsequent measurement of mass change through drying (for example, in an oven) or derived from turbidity measurements with routine validation from bottle samples
Turbidity	Recommended for all projects	Recommended as part of ecosystem monitoring because elevated turbidity can impact photosynthesis and benthic ecosystem health	Sensor or discrete water sample
Chlorophyll-a	Recommended for all projects	Recommended as an indicator of general ecosystem health (phytoplankton primary productivity)	Sensor or discrete water sample
Dissolved inorganic nutrients	Recommended for all projects	Recommended as an indicator of general ecosystem health (available nutrients for primary productivity) and nutrient limitation impacts from secondary precipitation.	In situ sensor or discrete water sample via mooring or routine boat sampling
Deployment area	Plankton community	Recommended for all projects, may be required as part of project-specific environmental risk mitigation strategy	Recommended periodically for monitoring of ecosystem health, documentation of shifting baseline ecology and contributions to primary research	Plankton tow or other methods	At agreed upon intervals, before, during and after deployment
Benthic community	Recommended for all projects, may be required as part of project-specific environmental risk mitigation strategy	Recommended periodically for monitoring of ecosystem health, documentation of shifting baseline ecology and contributions to primary research Recommended for water and tissue samples in keystone biological species to track potential trace and heavy metal accumulation	Benthic survey or other methods

12.0 Acknowledgments

The following authors from Isometric contributed to writing this Protocol:

Jing He, Ph.D.
Ella Holme, Ph.D.
Jennifer Yin, Ph.D.
Sophie Gill, Ph.D.
Emma Marsland

Isometric would like to thank the following reviewers of this Protocol:

Jeff Peeters
Wei-Jun Cai, Ph.D.
Kevin Sutherland, Ph.D.
Adam Ward, Ph.D.
Marya Matlin-Wainer

13.0 Definitions and Acronyms

: A document that describes how to quantitatively assess the net amount of CO₂ removed by a process. To Isometric, a Protocol is specific to a Project Proponent's process and comprised of Modules representing the Carbon Fluxes involved in the CDR process. A Protocol measures the full carbon impact of a process against the Baseline of it not occurring.
: The term used to represent the CO₂ taken out of the atmosphere as a result of a CDR process.
: Considering impacts at each stage of a product's life cycle, from the time natural resources are extracted from the ground and processed through each subsequent stage of manufacturing, transportation, product use, and ultimately, disposal.
: A facility that receives and treats municipal and/or industrial wastewater.
: Activities that remove carbon dioxide (CO₂) from the atmosphere and store it in products or geological, terrestrial, and oceanic Reservoirs. CDR includes the enhancement of biological or geochemical sinks and direct air capture (DAC) and storage, but excludes natural CO₂ uptake not directly caused by human intervention.
: Raw material which is used for CO₂ Removal or GHG Reduction.
: The amount of dissolved oxygen consumed by microorganisms while breaking down organic matter in water over a specific time period.
: A type of biological wastewater treatment process that uses microorganisms to break down organic waste.
: An activity or process or group of activities or processes that alter the condition of a Baseline and leads to Removals or Reductions.
: A worldwide federation (NGO) of national standards bodies from more than 160 countries, one from each member country.
: Lowering future GHG releases from a specific entity.
: An evaluation of the likelihood that an intervention—for example, a CDR Project—causes a climate benefit above and beyond what would have happened in a no-intervention Baseline scenario.
: A process for evaluating and confirming the net Removals and Reductions for a Project, using data and information collected from the Project and assessing conformity with the criteria set forth in the Isometric Standard and the Protocol by which it is governed. Verification must be completed by an Isometric approved third-party (VVB).
: A systematic and independent process for evaluating the reasonableness of the assumptions, limitations and methods that support a Project and assessing whether the Project conforms to the criteria set forth in the Isometric Standard and the Protocol by which the Project is governed. Validation must be completed by an Isometric approved third-party (VVB).
: A collection of Removal or Reduction processes that have mechanisms in common.
: A publicly visible uniquely identifiable Credit Certificate Issued by a Registry that gives the owner of the Credit the right to account for one net metric tonne of Verified CO₂e Removal or Reduction. In the case of this Standard, the net tonne of CO₂e Removal or Reduction comes from a Project Validated against a Certified Protocol.
: Operations and processes that would have occurred in the absence of project activities.
: The organization that develops and/or has overall legal ownership or control of a Removal or Reduction Project.
: The document that clearly outlines how a Project will generate rigorously quantifiable Additional high-quality Removals or Reductions.
: Third-party auditing organizations that are experts in their sector and used to determine if a project conforms to the rules, regulations, and standards set out by a governing body. A VVB must be approved by Isometric prior to conducting validation and verification.
: An acceptable difference between reported Removals/emissions or Reductions/emissions and what an auditor determines is the actual Removal/emissions or Reduction/emissions.
: A lack of knowledge of the exact amount of CO₂ removed by a particular process, Uncertainty may be quantified using probability distributions, confidence intervals, or variance estimates.
: Improperly allocating the same Removal or Reduction from a Project Proponent more than once to multiple Buyers.
: An assessment of what would have happened in the absence of a particular intervention – i.e., assuming the Baseline scenario.
: A set of data describing pre-intervention or control conditions to be used as a reference scenario for comparison.
: Resources provided to projects that are generating, or are expected to generate, greenhouse gas (GHG) Emission Reductions or Removals.
: The period of time over which a Project Design Document is valid, and over which Removals, Reductions or Environmental Attributes may be Verified, resulting in Issued Certificates.
: Purposefully erring on the side of caution under conditions of Uncertainty by choosing input parameter values that will result in a lower net CO₂ Removal or GHG Reduction than if using the median input values. This is done to increase the likelihood that a given Removal or Reduction calculation is an underestimation rather than an overestimation.
: An analysis of how much different components in a Model contribute to the overall Uncertainty.
: A calculation, series of calculations or simulations that use input variables in order to generate values for variables of interest that are not directly measured.
: An entity that purchases Removals, Reductions, or Environmental Attributes, often with the purpose of Retiring Certificates to make a Removal, Reduction, or Environmental Attribute claim.
: A database that holds information on Verified Removals and Reductions, and reviewed EACs, based on Protocols. Registries Issue Certificates, and track their ownership and Retirement.
: The increase in GHG emissions outside the geographic or temporal boundary of a project that results from that project's activities.
: A location where carbon is stored. This can be via physical barriers (such as geological formations) or through partitioning based on chemical or biological processes (such as mineralization or photosynthesis).
: Life cycle GHG emissions associated with production of materials, transportation, and construction or other processes for goods or buildings.
: A measure of how much energy the emissions of 1 tonne of a GHG will absorb over a given period of time, relative to the emissions of 1 ton of CO₂.
: The amount of dissolved oxygen required to chemically oxidize organic and inorganic compounds in water.
: An estimate of the emissions intensity per unit of an activity.
: The escape of CO₂ to the atmosphere after it has been stored, and after a Certificate has been Issued. A Reversal is classified as avoidable if a Project Proponent has influence or control over it and it likely could have been averted through application of reasonable risk mitigation measures. Any other Reversals will be classified as unavoidable.
: The amount of time carbon removed from the atmosphere by an intervention – for example, a CDR project – is expected to reside in a given Reservoir, taking into account both physical risks and socioeconomic constructs (such as contracts) to protect the Reservoir in question.
: A common and recognized insurance mechanism among Registries allowing Certificates to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.

Deployment area

DIC

Dissolved inorganic carbon

EPA

Environmental Protection Agency

GHG

Greenhouse gas

Mixing Zone

A regulatory concept describing the spatial area surrounding the discharge infrastructure where water quality criteria can be exceeded.

MRV

Monitoring, Reporting and Verification

PDD

Project design document

Reporting Period

The Reporting Period (RP) represents an interval of time over which removals are calculated and reported for verification. See Section 7.1 for full details.

SOP

Standard Operating Procedure

14.0 Appendix 1 : Guidance for High Quality Marine Data Collection

This Appendix is general for marine CDR approaches: Ocean Alkalinity Enhancement (OAE), Direct Ocean Capture (DOC), Wastewater Alkalinity Enhancement

14.1 Introduction

Field measurements play an important role in:

ensuring sufficient and up to date baseline marine data
providing data for calibration and validation of ocean models
monitoring environmental health during and after project activity

14.2 Alkalinity and pH Measurements

14.3 Specific Guidance for Bottle Samples

Recommended analytical methods for bottle samples include:

Parameter	Recommended Method
Carbonate Chemistry parameters (pH, DIC, TA)	Guide to Best Practices for Ocean CO₂ Measurements
Nutrients	Methods of Seawater Analysis
Salinity	TEOS-10
Dissolved Oxygen	Methods of Seawater Analysis
Chl-a	Welschmeyer 1994
TSS	Methods of Seawater Analysis
Trace metals	GEOTRACES cookbook

The following methods are approved by the Clean Water Act, EPA:

Parameter	Approved Method
pH	150.2: pH, Continuous Monitoring (Electrometric) by pH Meter (pdf)
Turbidity	180.1: Determination of Turbidity by Nephelometry (pdf)
Alkalinity	310.2: Alkalinity (Colorimetric, Automated, Methyl Orange) by Autoanalyzer (pdf)
Trace Metals	200.7: Determination of Metals and Trace Elements in Water and Wastes by Inductively Coupled Plasma-Atomic Emission Spectrometry; Rev. 4.4 200.8: Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma – Mass Spectrometry; Rev. 5.4 (pdf) 200.9: Determination of Trace Elements by Stabilized Temperature Graphic Furnace Atomic Absorption; Rev. 2.2 (pdf)

14.4 Specific Guidance for Autonomous Ocean Instruments

14.4.1 Pre-deployment

14.4.2 Maintenance During Deployment

14.4.3 Data Post-processing

The quality control manuals for autonomous instruments prepared by the Integrated Ocean Observing System are a recommended resource.

Quality control checks could include:

completeness of observations
ordering of data
check against physically valid limits
check data obeys physical laws
checking statistical tests
checking regularities of space and time variations

Data Analysis Methods for Physical Oceanography is a recommended resource for statistical analysis methods ⁵⁵.

14.5 Specific Guidance for Tracer Studies

Tracer studies track effluent using a tracer that is either naturally present or added. They can be useful for mCDR projects to:

characterize DIC-deficient or alkalinity-enhanced plume transport
validate physical transport in the ocean model via tracking plume movement
validate alkalinity uptake via dual tracer regression for OAE projects (Project Proponents are not expected to perform dual tracer regression)

The US EPA Operating Procedure⁵⁶ and USGS Procedure for Dye Tracer Measurements⁵⁷ are recommended resources.

The following checklist can be referenced for tracer release studies using rhodamine dye to validate an ocean model or characterize plume transport.

Study planning:

duration of release should give sufficient time for the field team to complete sampling (this will be site specific)
required tracer quantity should be based on sensor detection limit, effluent flow rate, duration of test and site specific dilution capacity

Materials preparation:

prepare dye mixture, ensuring the correct units of dye concentration are used
dye injection pump should be calibrated in lab to confirm desired volumetric dosage rate
include release rate at different battery levels and temperature
prepare instrument and site specific calibration curve between dye concentration and effluent concentration

Release:

if released with effluent, released at a rate proportional to effluent release rate
if released with effluent, tracer must be added at an adequate mixing length before final discharge
if released with effluent, sample from an access valve to measure concentration prior to final discharge
density and velocity matching for effluent or slug release are considered
no additions after the injection point

Sampling (ship-based or underway system):

prior to release, conduct spatial salinity and temperature profiling.
for ship based sampling, sensor should be placed off the bow, firmly braced and clear of bow waves to minimize disturbance due to wake of the vessel.
positioning via GPS or triangulation should be +/- 2.5m to ensure sampling station. positions and boat tracks are accurate
for all measurements, record metadata including sample location, time, depth, sensor probe and other visual observations.
note areas of high concentrations beyond the mixing zone, as this can signal accumulation or recirculation, which cause the effluent to resurface elsewhere.

Data quality and interpretation:

consider accuracy of positioning data, variation in discharge flow rate, variability in environmental conditions, calibration curve and measurement method in the interpretation of results.

14.6 Ocean Monitoring Examples

Example 1

Example 2

15.0 Appendix 2: Future Improvements

In future versions of this Protocol, we plan to explore the following additional applicability criteria:

Expanding eligible discharge locations to inland waters, e.g. lakes
Expanding to include more variety of WWTP, e.g. membrane bioreactors

Future versions of this Protocol will also include:

Guidance for projects who wish to credit under this Protocol in addition to the OAE Protocol

16.0 Appendix 3: Companion Document for Wastewater Alkalinity Enhancement Protocol

16.1 Introduction

16.2 Defining carbon dioxide removal and emissions reductions for Wastewater Alkalinity Enhancement projects

The net CDR that is eligible for crediting is given by:

net CDR = drawdown - counterfactual BAU drawdown - project emissions

For WAE, we have the following possible BAU scenarios:

A WWTP does no prior pH amendment
A WWTP does use a prior pH amendment
a. pH amendment emissions - pH amendment drawdown potential > 0
b. pH amendment emissions - pH amendment drawdown potential < 0

In Scenario 1, there is no CDR occurring, so counterfactual BAU drawdown = 0.

17.0 Appendix 4: Risk of Reversal Questionnaire

# in Isometric Standard Questionnaire	Question	If answered “Yes”	If answered “No”
1	Is a reversal directly observable with a physical or chemical measurement as opposed to a modeled result?	Proceed to questions 2-9	Proceed to questions 8-9
5	Does this approach have a material risk of reversal due to natural disasters including, but not limited to, floods, storms, earthquakes, fires, etc.?	Add 1 to Risk Score
6	Does this approach have a material risk of reversal due to human-induced events from outside actors, such as change in farming practices, change in ownership and management of project sites, or similar?	Add up to 2 to Risk Score
8	Is there 10+ years of monitoring and/or lab data demonstrating low project risk?	Minus up to 2 to Risk Score
9	Does this pathway have a documented history of reversals?	Add 2 to Risk Score
10	Is there one or more project-specific factors that merit a high risk level?	Add up to 2 to Risk Score

Risk Score Categories

0: Very Low Risk Level (2% buffer)
1-2: Low Risk Level (5% buffer)
3-4: Medium Risk Level (7% buffer)
5+: High Risk Level (10-20% buffer)

For projects with carbon storage as inorganic carbon, the presence of the following risk factors must be reflected in the risk score corresponding to question 10:

Acidic fluid
Alkaline fluid (if stored as dissolved inorganic carbon)
Temperatures in excess of 800 degrees celsius

18.0 Relevant Works

Footnotes

Rittman, B. E., and P. L. McCarty. "Environmental biotechnology: principles & applications. USA: McGrawHill." (2001). ↩
Rodriguez-Garcia, G., A. Hospido, D. M. Bagley, M. T. Moreira, and G. Feijoo. "A methodology to estimate greenhouse gases emissions in life cycle inventories of wastewater treatment plants." Environmental Impact Assessment Review 37 (2012): 37-46. ↩↩²
IPCC AR6 Global Warming Potential Values. 2024. https://ghgprotocol.org/sites/default/files/2024-08/Global-Warming-Potential-Values%20%28August%202024%29.pdf. ↩
Mo, Weiwei, and Qiong Zhang. "Can municipal wastewater treatment systems be carbon neutral?." Journal of environmental management 112 (2012): 360-367. ↩
2006 IPCC Guidelines for National Greenhouse Gas Inventories. Volume 5: Waste. https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/5_Volume5/V5_6_Ch6_Wastewater.pdf ↩↩²
Gaillardet, J., Dupré, B., Louvat, P. et al. (1999). Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers. Chemical Geology 159, 3-30. https://doi.org/10.1016/S0009-2541(99)00031-5. ↩
Gernaey, Krist V., Mark CM Van Loosdrecht, Mogens Henze, Morten Lind, and Sten B. Jørgensen. "Activated sludge wastewater treatment plant modelling and simulation: state of the art." Environmental modelling & software 19, no. 9 (2004): 763-783. https://doi.org/10.1016/j.envsoft.2003.03.005 ↩
Allen, G. H., David, C. H., Andreadis, K. M., Hossain, F., & Famiglietti, J. S. (2018). Global estimates of river flow wave travel times and implications for low-latency satellite data. Geophysical Research Letters, 45, 7551–7560. https://doi.org/10.1029/2018GL077914 ↩
BS EN 15978:2011 Sustainability of construction works - Assessment of environmental performance of buildings - Calculation method ↩↩² ↩³ ↩⁴ ↩⁵
IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC. https://doi.org/10.59327/IPCC/AR6-9789291691647 ↩
Cheng, M., Patterson, J., and Minear, R. (1975). Heavy Metals Uptake by Activated Sludge, Water Pollution Control Federation, Vol. 47, No. 2 https://www.jstor.org/stable/25038635?seq=1 ↩
Al-Qodah, Z. (2006). Biosorption of Heavy Metal Ions From Aqueous Solutions by Activated Sludge. Desalination. 196. 164-176. 10.1016/j.desal.2005.12.012. ↩
Hammaini, A., González, F., Ballester, A., Blázquez, M.L., and Muñoz, J.A. (2007) Biosorption of heavy metals by activated sludge and their desorption characteristics. Journal of Environmental Management, Volume 84, Issue 4. https://doi.org/10.1016/j.jenvman.2006.06.015. ↩
Bao, Z., Sun, S., & Sun, D. (2015). Characteristics of direct CO2 emissions in four full-scale wastewater treatment plants. Desalination and Water Treatment, 54(4-5), 1070-1079. https://doi.org/10.1080/19443994.2014.940389 ↩
Wang, D., Ye, W., Wu, G. et al. (2022). Greenhouse gas emissions from municipal wastewater treatment facilities in China from 2006 to 2019. Sci Data 9, 317. https://doi.org/10.1038/s41597-022-01439-7 ↩↩²
Nemcik, J., Krupa, F., Ozana, S., Slanina, Z. (2022) Wastewater Treatment Modeling Methods Review, Volume 55, Issue 4. https://doi.org/10.1016/j.ifacol.2022.06.032. ↩
Wurgaft, E., Wang, Z. A., Churchill, J. H., Dellapenna, T., Song, S., Du, J., et al. (2021). Particle triggered reactions as an important mechanism of alkalinity and inorganic carbon removal in river plumes. Geophysical Research Letters, 48, e2021GL093178. https://doi.org/10.1029/2021GL093178 ↩
Ringham, M. C., Hirtle, N., Shaw, C., Lu, X., Herndon, J., Carter, B. R., and Eisaman, M. D. (2024). An assessment of ocean alkalinity enhancement using aqueous hydroxides: kinetics, efficiency, and precipitation thresholds, Biogeosciences, 21, 3551–3570, https://doi.org/10.5194/bg-21-3551-2024. ↩↩²
Schulz, K. G., Bach, L. T., and Dickson, A. G. (2023). Seawater carbonate chemistry considerations for ocean alkalinity enhancement research: theory, measurements, and calculations. State of the Planet, 2-oae2023, 2, https://doi.org/10.5194/sp-2-oae2023-2-2023. ↩
Moras, C. A., Bach, L. T., Cyronak, T., Joannes-Boyau, R., and Schulz, K. G. (2022) Ocean alkalinity enhancement – avoiding runaway CaCO3 precipitation during quick and hydrated lime dissolution, Biogeosciences, 19, 3537–3557, https://doi.org/10.5194/bg-19-3537-2022 ↩↩²
Iglesias-Rodríguez, M. D., Rickaby, R. E. M., Singh, A., and Gately, J. A. (2023). Laboratory experiments in ocean alkalinity enhancement research, in: Guide to Best Practices in Ocean Alkalinity Enhancement Research, Copernicus Publications, State Planet, 2-oae2023, 5, https://doi.org/10.5194/sp-2-oae2023-5-2023 ↩
Suitner, N., Faucher, G., Lim, C., Schneider, J., Moras, C. A., Riebesell, U., and Hartmann, J. (2024). Ocean alkalinity enhancement approaches and the predictability of runaway precipitation processes: results of an experimental study to determine critical alkalinity ranges for safe and sustainable application scenarios, Biogeosciences, 21, 4587–4604, https://doi.org/10.5194/bg-21-4587-2024 ↩↩²
He and Tyka (2023) Limits and CO2 equilibration of near-coast alkalinity enhancement. Biogeosciences, 20, 27–43. https://doi.org/10.5194/bg-20-27-2023 ↩
Bach, L. T. (2023) The additionality problem of Ocean Alkalinity Enhancement. Biogeosciences 21, 261–277. https://bg.copernicus.org/articles/21/261/2024/↩
Jokiel, P. L. (2011). The reef coral two compartment proton flux model: A new approach relating tissue-level physiological processes to gross corallum morphology. Journal of Experimental Marine Biology and Ecology, 409(1–2), 1–12. https://doi.org/10.1016/j.jembe.2011.10.008 ↩
Bach, L. T. (2015). Reconsidering the role of carbonate ion concentration in calcification by marine organisms. Biogeosciences, 12(16), 4939-4951. ↩
Monteiro, F. M., Bach, L. T., Brownlee, C., Bown, P., Rickaby, R. E. M., Poulton, A. J., et al. (2016). Why marine phytoplankton calcify (supplement). Sci. Adv. 2:e1501822. doi: 10.1126/sciadv.1501822 ↩
Bach, L.T., Gill, S.J., Rickaby R.E.M., et. al. (2019) CO₂ Removal With Enhanced Weathering and Ocean Alkalinity Enhancement: Potential Risks and Co-benefits for Marine Pelagic Ecosystems. Frontiers in Climate. 1:7. doi: 10.3389/fclim.2019.00007 ↩↩² ↩³
Langer, G., M. Geisen, K.-H. Baumann, J., et. al. (2006). Species-specific responses of calcifying algae to changing seawater carbonate chemistry. Geochemistry, Geophysics, Geosystems, 7, Q09006, doi:10.1029/2005GC001227 ↩
Renforth, P. (2019) The negative emission potential of alkaline materials. Nature Communications 10, 1401. https://doi.org/10.1038/s41467-019-09475-5 ↩
Hay, B. J. (1988). Sediment accumulation in the central western part of the Black Sea over the last 5100 years. Paleoocenography 3, 491–508. doi:10.1029/PA003i004p00491 ↩
Kopelevich, O., Burenkov, V., Sheberstov, S., Vazyulya, S., Kravchishina, M., Pautova, L., et al. (2014). Satellite monitoring of coccolithophore blooms in the Black Sea from ocean color data. Remote Sens. Environ. 146, 113–123. doi: 10.1016/j.rse.2013.09.009 ↩
For example, see Bach et al. (2013) New Phytologist, Bach et al. (2015) Progress in Oceanography, Gafar et al.(2018) Frontiers in Marine Science and others. ↩
Bednaršek, N., Pelletier, G., van de Mortel, H., García-Reyes, M., Feely, R., and Dickson, A.: Unifying framework for assessing sensitivity for marine calcifiers to ocean alkalinity enhancement identifies winners, losers and biological thresholds – importance of caution with precautionary principle, EGUsphere [preprint] doi.org/10.5194/egusphere-2024-947 ↩
Gately, J..A., Kim, S.M., Jin, B., et al. (2023). Coccolithophores and diatoms resilient to ocean alkalinity enhancement: A glimpse of hope?. Science Advances 9, eadg6066. doi:10.1126/sciadv.adg6066 ↩
Zhang, S., Planavsky, N. J., Katchinoff, J., Raymond, P. A., Kanzaki, Y., Reershemius, T., & Reinhard, C. T. (2022). River chemistry constraints on the carbon capture potential of surficial enhanced rock weathering. Limnology and Oceanography, 67(S2), S148–S157. https://doi.org/10.1002/lno.12244 ↩
Harrington, K. J., Hilton, R. G., & Henderson, G. M. (2023). Implications of the Riverine Response to Enhanced Weathering for CO2 removal in the UK. Applied Geochemistry, 152, 105643. https://doi.org/10.1016/j.apgeochem.2023.105643 ↩↩²
Kantzas, E.P., Val Martin, M., Lomas, M.R. et al. (2022). Substantial carbon drawdown potential from enhanced rock weathering in the United Kingdom. Nat. Geosci. 15, 382–389. https://doi.org/10.1038/s41561-022-00925-2 ↩
Beerling, D.J., Kantzas, E.P., Lomas, M.R. et al. (2020). Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature 583, 242–248. https://doi.org/10.1038/s41586-020-2448-9 ↩
Kanzaki, Y., Planavsky, N.J., Reinhard, C.T. (2023). New estimates of the storage permanence and ocean co-benefits of enhanced rock weathering, PNAS Nexus, Volume 2, Issue 4, pgad059. https://doi.org/10.1093/pnasnexus/pgad059 ↩↩² ↩³
Mu, L., Palter, J. B., and Wang, H. (2023). Considerations for hypothetical carbon dioxide removal via alkalinity addition in the Amazon River watershed, Biogeosciences, 20, 1963–1977. https://doi.org/10.5194/bg-20-1963-2023. ↩
Wilkinson, M., Dumontier, M., Aalbersberg, I. et al. (2016). The FAIR Guiding Principles for scientific data management and stewardship. Scientific Data 3, 160018. https://doi.org/10.1038/sdata.2016.18 ↩↩²
Metcalf & Eddy, Inc. (2003) Wastewater Engineering: Treatment and Reuse (Fourth Edition). McGraw-Hill. ↩
https://www.mclanahan.com/blog/how-to-read-a-pump-curve-chart ↩
Dickson, A.G. Sabine, C.L. and Christian, J.R. (2007) Guide to best practices for ocean CO2 measurement. North Pacific Marine Science Organization, 191pp. (PICES Special Publication 3; IOCCP Report 8). DOI: https://doi.org/10.25607/OBP-1342 ↩
Jiang, L.-Q., Subhas, A. V., Basso, D., Fennel, K., and Gattuso, J.-P. (2023) Data reporting and sharing for ocean alkalinity enhancement research. State of the Planet 2-oae2023, 13, https://doi.org/10.5194/sp-2-oae2023-13-2023 ↩
National Oceanic and Atmospheric Administration , (2023). OA Metadata Template (Version 2.0). National Centers for Environmental Information. https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/oa-metadata-template/↩
Middelburg, J. J., Soetaert, K., and Hagens, M. (2020) Ocean Alkalinity, Buffering and Biogeochemical Processes. Reviews of Geophysics, 58, https://doi.org/10.1029/2019RG000681 ↩
Dickson, A. G., An exact definition of total alkalinity and a procedure for the estimation of alkalinity and total inorganic carbon from titration data. Deep Sea Research Part A. Oceanographic Research Papers, 28 (6), 609-623. https://doi.org/10.1016/0198-0149(81)90121-7 ↩
Mario, G. M., Millero, F. J., Camões, M.F., Spitzer, P., Feistel, R., and Chen, C.-T.A. (2011) pH of seawater. Marine Chemistry, 126(1-4), 89-96. https://doi.org/10.1016/j.marchem.2011.04.002 ↩
Pimenta, A. R., and Grear, J. S. (2018). Guidelines for Measuring Changes in Seawater pH and Associated Carbonate Chemistry in Coastal Environments of the Eastern United States. United States Environmental Protection Agency. Retrieved July 1, 2024, from https://www.goa-on.org/documents/resources/east-us-measuring_seawater_ph_changes-guide.pdf ↩
Jiang, L., Pierrot, D., Wanninkhof, R. et al. (2023). Best Practice Data Standards for Discrete Chemical Oceanographic Observations. Frontiers in Marine Science. https://www.frontiersin.org/articles/10.3389/fmars.2021.705638/full ↩
Schulz, K. G., Bach, L. T., and Dickson, A. G.: Seawater carbonate chemistry considerations for ocean alkalinity enhancement research: theory, measurements, and calculations. State of the Planet, 2-oae2023, 2, https://doi.org/10.5194/sp-2-oae2023-2-2023. ↩
Bushnell M, Waldmann C, Seitz S, et al. (2019). Quality Assurance of Oceanographic Observations: Standards and Guidance Adopted by an International Partnership. Frontiers in Marine Science, 6:706 https://www.frontiersin.org/articles/10.3389/fmars.2019.00706/full ↩
Thomson, R. and Emery, W. (2014) Data Analysis Methods in Physical Oceanography. https://www.sciencedirect.com/book/9780123877826/data-analysis-methods-in-physical-oceanography#book-description ↩
Science and Ecosystem Support Divison (2017). Dye Tracer Measurements Operating Procedure. U.S. Environmental Protection Agency. https://www.epa.gov/sites/default/files/2017-07/documents/dye_tracer_measurements514_af.r2.pdf ↩
Wilson, J. F., Cobb, E. D., & Kilpatrick, F. A. (1986). Fluorometric procedures for dye tracing. In Techniques of Water-Resources Investigations (03-A12). Dept. of the Interior, U.S. Geological Survey; For sale by the Books and Open-File Reports Section, U.S. Geological Survey,. https://doi.org/10.3133/twri03A12 ↩

1.0 Introduction

2.0 Sources and Reference Standards and Methodologies

3.0 Future Versions

4.0 Applicability

5.0 Relation to the Isometric Standard

5.1 Project Design Document

5.2 Verification and Validation

5.2.1 Verification Materiality

5.2.2 Site Visits

5.2.3 Verifier Qualifications & Requirements

5.3 Ownership

5.4 Additionality

5.5 Uncertainty

5.5.1 Reporting of Uncertainty

5.6 Data Reporting and Availability

6.0 Environmental and Social Safeguarding

6.1 Overarching Principles

6.2 Governance and Legal Framework

6.3 Risk Mitigation Strategies

6.3.1 Environmental Safeguards

6.3.2 Social Safeguards

6.4 Stakeholder Engagement

6.5 Adaptive Management

7.0 System Boundary and Baseline

7.1 Reporting Period

7.2 System Boundary & GHG Emissions Scope

7.2.1 System Boundary Considerations

7.3 Baseline

8.0 Quantification of CO₂e Removal

8.1 Net CDR Calculation

8.2 Calculation of CO₂eStored, RP

8.2.1 Calculation of Average Feedstock Dissolution Rate and P

8.2.1.1 Option 1: Quantification in the Solid Phase

8.2.1.2 Option 2: Quantification in the Aqueous Phase Using Conservative Dissolved Weathering Products

8.2.2 Validation and Reconciliation Calculations

8.2.2.1 Confirmation of Steady State Operations

8.2.2.2 Mass Balance Calculations

8.2.2.2.1 Sorption

8.2.2.2.2 Future Updates to Quantification and Validation Approaches

8.2.2.3 Upper Limit of Biogenic CO₂ Outgassing

8.2.3 Calculation of Loss Discount

8.2.3.1 Near-Field Losses

8.2.3.2 Transport Losses

8.2.3.2.1 Outgassing During River Transport

8.2.3.2.2 Outgassing Upon Entering Ocean

8.2.4 Broader Impacts on CDR

8.3 Calculation of CO₂eCounterfactual, RP

8.4 Calculation of CO₂eEmissions, RP

8.4.1 Calculation of CO₂eEstablishment, RP

8.4.2 Calculation of CO₂eOperation, RP

8.4.3 Calculation of CO₂e End-of-Life, RP

8.4.4 Calculation of CO₂e Leakage, RP

8.4.5 Energy Use Accounting

8.4.6 Transportation Emissions Accounting

8.4.7 Embodied Emissions Accounting

9.0 Storage

9.1 Marine Dissolved Inorganic Carbon (DIC) Storage

9.2 Buffer Pools

10.0 Pre-Deployment Requirements

11.0 Monitoring

11.1 Monitoring Locations

11.2 Control Volume Measurements

11.2.1 Influent, A

11.2.2 Feedstock Dosing, B

11.2.3 Effluent, C

11.2.4 Waste Activated Sludge, D

11.2.5 Within the Control Volume, E

11.3 Receiving Waters

11.3.1 Mixing Zone

11.3.2 Biological and Ecological Monitoring in Deployment Area

11.3.3 Monitoring for Ecosystem Safety

11.3.3.1 Threshold Violations

11.3.3.2 Enforcement Actions

11.4 Summary of Monitored Parameters

12.0 Acknowledgments

13.0 Definitions and Acronyms

14.0 Appendix 1 : Guidance for High Quality Marine Data Collection

14.1 Introduction

14.2 Alkalinity and pH Measurements

14.3 Specific Guidance for Bottle Samples

8.3 Calculation of CO₂e_{Counterfactual, RP}

8.4 Calculation of CO₂e_{Emissions, RP}

8.4.1 Calculation of CO₂e_{Establishment, RP}

8.4.2 Calculation of CO₂e_{Operation, RP}

8.3 Calculation of CO₂e_{Counterfactual, RP}

8.4 Calculation of CO₂e_{Emissions, RP}

8.4.1 Calculation of CO₂e_{Establishment, RP}

8.4.2 Calculation of CO₂e_{Operation, RP}