Wastewater Alkalinity Enhancement

1.0 Introduction

This Protocol (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.) provides the requirements and procedures for the calculation of net carbon dioxide equivalent (CO₂e) removal (The term used to represent the CO₂ taken out of the atmosphere as a result of a CDR process.) 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 (​​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.) 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 (A facility that receives and treats municipal and/or industrial wastewater.) (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 processes^1,2. 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 frameworks^4, 5, thus the removal of this biogenic CO₂ through WAE qualifies as carbon dioxide removal (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.) (CDR), rather than emissions avoidance.

In Wastewater Alkalinity Enhancement, rock or mineral feedstock (Raw material which is used for CO₂ Removal or GHG Reduction.) 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 (The amount of dissolved oxygen consumed by microorganisms while breaking down organic matter in water over a specific time period.) (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 (A type of biological wastewater treatment process that uses microorganisms to break down organic waste.) (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 (An activity or process or group of activities or processes that alter the condition of a Baseline and leads to Removals or Reductions.) 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 ISO (A worldwide federation (NGO) of national standards bodies from more than 160 countries, one from each member country.)14064-2: 2019 -- Greenhouse Gases -- Part 2: Specification with guidance at the project level for quantification, monitoring, and reporting of greenhouse gas emission reductions (Lowering future GHG releases from a specific entity.) 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 (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.)
• 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 (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).) and validation (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).) 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 (A collection of Removal or Reduction processes that have mechanisms in common.) 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 (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.) 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 v1.2.
• [R-C7DT-0, Projects must submit proof of an official partnership with the partner wastewater treatment facility. Evidence can include an MoU, written consent, or agreements with relevant parties.]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.[/R-C7DT-0]

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 (Operations and processes that would have occurred in the absence of project activities.) (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.

• [G-A54P-0, Projects must demonstrate that the partner WWTPs discharge into the ocean or to waterways that flow directly to the ocean.]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. [/G-A54P-0]
• [G-XT0B-0, Projects must describe the type of biological treatment used in the partner WWTP.]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.[/G-XT0B-0]
• [G-HEW0-0, Projects must describe how alkalinity is added to the biological treatment portion of the facility.]Alkalinity addition occurs in the biological treatment portion of the facility. [/G-HEW0-0]
• [G-53QN-0, Projects must evidence that they operate as retrofits to pre-existing WWTPs.]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.[/G-53QN-0]

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

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 the Validation and Verification Requirements Section 4 of the Isometric Standard.

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

1. Validate that the feedstock adheres to the requirements listed in the Rock and Mineral Feedstock Characterization Module v1.2.
2. Verify that the quantification approach adheres to requirements of Section 8, including demonstration of required records.
3. Verify that the Environmental & Social Safeguards outlined in Section 6 are met.
4. Verify that the Project is compliant with requirements outlined in the Isometric Standard.

5.2.1 Verification Materiality

The threshold for Materiality (An acceptable difference between reported Removals/emissions or Reductions/emissions and what an auditor determines is the actual Removal/emissions or Reduction/emissions.), considering the totality of all omissions, errors and mis-statements, is 5%, in accordance with the Materiality Threshold Section 4.3 of the Isometric Standard.

Verifiers should also verify the documentation of uncertainty (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.) of the GHG statement as required by the Uncertainty 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 the Validation and Verification Requirements 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 the Validation and Verification Requirements 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 (Improperly allocating the same Removal or Reduction from a Project Proponent more than once to multiple Buyers.) 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 the Ownership Section 3.1 of the Isometric Standard.

5.4 Additionality

The Project Proponent must be able to demonstrate additionality through compliance with the Additionality Section 2.5.3 of the Isometric Standard. The counterfactual (An assessment of what would have happened in the absence of a particular intervention – i.e., assuming the Baseline scenario.) scenarios and baselines (A set of data describing pre-intervention or control conditions to be used as a reference scenario for comparison.) 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 (Resources provided to projects that are generating, or are expected to generate, greenhouse gas (GHG) Emission Reductions or Removals.) 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 (The period of time over which a Project Design Document is valid, and over which Removals or Reductions may be Verified, resulting in Issued Credits.), 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 (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.) determined, and projects must conduct an uncertainty analysis for the net CO₂e removal calculation in compliance with requirements outlined in the Uncertainty 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 the Uncertainty Section 2.5.7 of the Isometric Standard.

In addition, a sensitivity analysis (An analysis of how much different components in a Model contribute to the overall Uncertainty.) 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 (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.) specifications and output
• Emission factors used
• Scientific literature used

The Project Proponent can request certain information to be restricted (only available to authorized Buyers (An entity that purchases Removals or Reductions, often with the purpose of Retiring Credits to make a Removal or Reduction claim.), the Registry (A database that holds information on Verified Removals and Reductions based on Protocols. Registries Issue Credits, and track their ownership and Retirement.) 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:

• [G-CDEZ-0, Projects must identify the jurisdictional authorities of the receiving water bodies of the project site.]Project Proponents must identify the jurisdictional authorities of the receiving water bodies of the project site, and as outlined in Section 4 (Applicability). [/G-CDEZ-0]
• [R-KH54-0, Projects must describe how they will ensure compliance with existing WWTP permits.]Projects must operate within the existing permits, or an approved modified permit, of a wastewater treatment plant. [/R-KH54-0]
• 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 the Environmental and Social Impacts 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 the Environmental Impacts 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:

• [G-W6QP-0, Risk assessment must consider potential risks associated with 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.[/G-W6QP-0]

Co-products and waste:

• [G-3GF0-0, Risk assessment must consider potential risks associated with co-products and waste.]Generation of waste products or additional waste must be accompanied by a plan which ensures safe handling, containment and disposal.[/G-3GF0-0]

Pollution prevention:

• [G-Q5AN-0, Risk assessment must consider potential risks associated with pollution and water quality changes.]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. [/G-Q5AN-0]
• [G-YF1Z-0, Risk assessment must consider potential risk of the WWTP not being able to meet its discharge permit requirements.]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.[/G-YF1Z-0]

6.3.2 Social Safeguards

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

6.4 Stakeholder Engagement

Per the Stakeholder Input Process 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

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 (The increase in GHG emissions outside the geographic or temporal boundary of a project that results from that project's activities.) 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 (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).) (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.

GHG emissions and removals associated with The Project may be direct emissions from a process, or indirect emissions from combustion of fuels, electricity generation, or other sources. Emissions must include all GHG SSRs within the system boundary, from the construction or manufacturing of each physical site and associated equipment, closure and disposal of each site and associated equipment, and operation of each process, including embodied emissions of equipment and consumables used in the project. The Project Proponent is responsible for identifying all sources of emissions directly or indirectly related to project activities.

Any emissions from sub-processes or process changes that would not have taken place without the CDR Project must be fully considered in the system boundary. Any activity that ultimately leads to the issuance of Credits should be included in the system boundary.

The system boundary must include all relevant GHG SSRs controlled and related to The Project, including but not limited to the SSRs set out in Table 1. If any GHG SSRs within Table 1 are deemed not appropriate to include in the system boundary, they may be excluded provided that robust justification and appropriate evidence is provided in the PDD.

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.

[Image: Figure 1 System Boundaries]

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

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 (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.) 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 aThe projectProject's impact on activities that fall outside of the system boundary of aThe projectProject must also be considered. This is covered under Leakage in Section 8.45.4.

7.2.1

In System Boundary Considerations

Ancillary Activities

Ancillary activities, such as supplementary research and development activities and corporate administrative activities, that are associatedline 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 EnergyGHG Accounting Module v1.21, the Project 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 (N20) and fluorinated gasses such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3). For otherCO2 waste inputsstored, theonly following criteriaCO2 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 boundaryincluded as compliance with EC1 would result in no change to the waste producer behavior (no market leakage) and indicates there are no alternative userspart of the waste product (no replacement emissions).

  Table 2quantification. WasteFor 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 andall other monitoringactivities equipmentall 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,GHGs must be considered. withinFor example, the systemrelease boundary.of IncrementalCO2, increasesCH4, and N2O is expected during diesel consumption;

• Quantify emissions in activitytonnes fromCO₂ BAU,equivalent such(t asCO₂e) incrementalusing additionalthe energy100-year requirements,Global mustWarming bePotential accounted(GWP) for inthe GHG of interest, based on the systemmost boundaryrecent volume of the IPCC Assessment Report (currently the Sixth Assessment Report); and
• Consider evidencedmateriality of SSRs in full.

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

7.32 Baseline

8.0 Quantification of CO₂e Removal

8.1 Calculation Approach and Reporting Period

The Reporting Period, RP, for WAE projects represents an interval of time over which removals are calculated and reported for verification. The equations used to calculate net CO₂e removals will pertain to all GHG emissions and CO₂ removals occurring over a Reporting Period.

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 (See Section 8.5.1) (b) any emissions that occur within the Reporting Period (See Section 8.5.2), (c) any anticipated emissions that would occur after the Reporting Period that have been allocated to the Reporting Period (See Section 8.5.3) and (d) leakage emissions that occur outside of the system boundary that are associated with the Reporting Period (See Section 8.5.4).

Total net CO2e removal is calculated for each Reporting Period, and is written hereafter as [math: CO_2e_{Removal,\ RP}]. The final net CO₂e removal quantification must be conservatively determined, giving high confidence that at a minimum, the estimated amount of CO₂e was removed.

In line with the Isometric Standard, this Protocol requires that Removal Credits are issued ex-post. Credits may be issued once CO₂ has been durably stored in the identified storage reservoir.

8.2 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_{Removal,\ RP} = CO_2e_{Stored,\ RP} - CO_2e_{Counterfactual,\ RP} - 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.

8.23 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_{3 (s)} + CO_{2 (aq)} + 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 8.23.3 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.

8.23.1 Calculation of Average Feedstock Dissolution Rate and P

[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:

• [R-EFR3-0, Projects must describe the quantification approach for Option 1 (solid phase) and specify if this will be used as the primary quantification method.]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.[/R-EFR3-0]
• [R-24KR-0, Projects must describe the quantification approach for Option 2 (aqueous phase) and specify if this will be used as the primary quantification method.]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.[/R-24KR-0]

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.

8.23.1.1 Option 1: Quantification in the Solid Phase

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

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

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

• [G-ENS8-0, The measurements and method(s) used for calculating each term in the mass balance equation, including references to peer reviewed publications and/or standard methodologies must be provided.]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. [/G-ENS8-0]
• 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}}]

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

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

[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})]]

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

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

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

8.23.2 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.

8.23.2.1 Confirmation of Steady State Operations

8.23.2.2 Mass Balance Calculations

8.23.2.2.1 Sorption

Several studies have documented the sorption of metals and organic compounds to waste activated sludge ^10,11,12,13. 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.

8.23.2.2.2 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.

8.23.2.3 Upper Limit of Biogenic CO₂ Outgassing

In the absence of WAE project activities, wastewater treatment plants have direct CO₂  emissions from evasion of biogenic CO₂^1413,1514. 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.

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).

8.23.3 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.

8.23.3.1 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

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 body¹⁷¹⁶. 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 ^{17,18, 19, 20, 21, 22}. Furthermore, precipitation dynamics occur on a timescale between minutes to hours^1817, 2019, which suggests that dilution could be an effective risk mitigation strategy²³²².

Quantification

Natural Alkalinity Flux Reduction

Concept

Increased alkalinity in wastewater effluent can potentially reduce the natural alkalinity flux from marine or river sediments²⁴²³. 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

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 state^{24,25,26,27, 28}. Alkaline feedstock dissolution may release trace metals which has the potential to fertilize blooms of calcifiers²⁸²⁷.

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 ocean^2928,3029. However, the Black Sea, a naturally elevated alkaline environment, harbors extensive blooms of the coccolithophores ^3130,3231, a major group of calcifying plankton. This is thought to be due to the favorable carbonate chemistry promoted by the elevated alkalinity regime²⁸²⁷.

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 ^32,33,34,35. 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 ³⁶³⁵. Coastal areas with significant benthic calcification of CaCO₃ sediments may be especially susceptible to this feedback.

Quantification

8.23.3.2 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.

8.23.3.2.1 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 Ca^{2+}] and [math: \alpha CO_3^{2-}] in Equation 25 are the measured solution activities of those ions
• [math: \alpha_{sat} Ca^{2+}] and [math: \alpha_{sat} CO_3^{2-}] in Equation 26 are the ion activities at saturation. Note that Equation 26 is defined at saturation, where the solution is in equilibrium with the solid phase.

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 ³⁹³⁸.

8.23.3.2.2 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 circulation^39,40,41,42. 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 precipitation⁴³⁴².

Quantification

1. Using the Renforth and Henderson (2017)⁴⁴⁴³ uptake efficiency equation
2. Using a 3D Earth Systems Model or ocean physical-biogeochemical model to explicitly simulate ocean circulation and air-sea CO₂ fluxes⁴²⁴¹
3. 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 is⁴⁴⁴³:

[math: \eta_{RH} = \frac{\Delta C_T}{\Delta A_T} = (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_{RH}] is the Renforth and Henderson uptake efficiency of CO₂ upon mixing with ocean waters, in mol C/mol alkalinity;
• [math: \Delta C_T] is the change in Total DIC in the ocean as a result of WAE, in mol C;
• [math: \Delta A_T] is the change in Total Alkalinity in the ocean as a result of WAE, in mol alkalinity;
• [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 calculate the Renforth and Henderson uptake efficiency with Equation 27.

[math: \eta_{RH}] is in units of mol C/mol alkalinity and must be converted to a dimensionless retention factor [math: \eta_i], representing the fraction of CO₂ retained upon discharge to the ocean.

If a noncarbonate feedstock is used, then [math: \eta_{RH}] is converted by assuming that 1 mole CO₂ is removed per mole alkalinity generated. However if a carbonate feedstock is used, then dissolution of the feedstock itself contributes to an increase in ocean DIC, and 1 mole of CO₂ is removed per 2 moles alkalinity generated. Project Proponents should use the following equation--derived from Equation 6 in Bach (2024)²⁴²³--to determine the fraction of CO₂ retained upon ocean discharge:

[math: \eta_i = f(2 \eta_{RH} - 1) + (1-f)\eta_{RH} ]

Equation 28

Where:

• [math: \eta_{RH}] is defined in Equation 27, in units of mol C/mol alkalinity
• [math: f] is the fraction of alkalinity from carbonate feedstock sources, between 0 and 1.

If 0% carboante feedstocks are used, then [math: f=0] and Equation 28 simplifes to [math: \eta_i = \eta_{RH}]. If 100% carbonate feedstocks are used, then [math: f = 1] and Equation 28 becomes [math: \eta_i = 2 \eta_{RH} - 1]. As stated in Section 8.23, if a feedstock of mixed mineralogy is used, Project Proponents must make conservative assumptions in quantifying CDR and determining [math: f]. For example, if a feedstock contains MgO and MgCO₃, [math: f] represents the fraction of alkalinity from MgCO₃ dissolution. Project Proponent may choose to allocate all carbon removal to the mineral phase with lowest conversion potential and take [math: f=1]. Alternatively, 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. In this scenario, if 50% of the total feedstock dissolved, then [math: f=0.2] since 20% of the total dissolved weathering products is attributed to MgCO₃. All assumptions and calculations must be documented in the PDD.

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 projects⁴²⁴¹. 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.

8.23.4 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.

8.34 Calculation of CO₂eCounterfactualeCounterfactual, 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 8.45.

See Appendix 3 for further explainationexplanation on this approach.

[Image: **Figure 4** Counterfactual]

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

8.45 Calculation of CO₂eEmissionseEmissions, 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_{Emissions,\ RP} = CO_2e_{Establishment,\ RP} + CO_2e_{Operations,\ RP} + CO_2e_{End-of-Life,\ RP} + CO_2e_{Leakage,\ RP}]

Equation 29

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 8.45.1.
• [math: CO_2e_{Operations,\ RP}] represents the total GHG emissions associated with operational processes for a Reporting Period, in tonnes of CO₂e, see Section 8.45.2.
• [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 8.45.3.
• [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 8.45.4.

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.

8.45.1 Calculation of CO₂eEstablishmenteEstablishment, 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 untilto the firstmoment 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 frombefore the first removal
• allocated toactivity removalstakes asplace. annualGHG emissions associated with project establishment may be amortized over the anticipated project lifetime
• allocated, or per output of product. (i.e.,Requirements perfor tonamortization CO₂are removed)outlined basedin on++Section estimated total production over project lifetime

The anticipated lifetime7 of the ProjectGHG shouldAccounting beModule based on reasonable justification and should be included in the Project Design Document (PDD) to be assessed as part of project validationv1.1++.

8.45.2 Calculation of CO₂eOperationeOperation, 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.

8.45.3 Calculation of CO₂e EndeEnd-of-Life, RP

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

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 quantifiedestimated asupfront part of that Reporting Period. GHG emissions associated with activities that are indirectly related to all deployments may beand allocated in the same waysway as set out infor calculation of [math: CO_2e_{Establishment,\ RP}].

Given the uncertain nature of [math: CO_2e_{End-of-Life,\ RP}] emissions, assumptions must be revisited at each CreditingReporting 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.

8.45.4 Calculation of CO₂e LeakageeLeakage, 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.

[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.

8.45.5 Emissions Accounting Requirements

GHG emissions accounting must be undertaken in alignment with the GHG Accounting Module v1.1, which ensures a consistently rigorous standard in how GHG emissions are quantified and reported between different CDR Projects and approaches. This includes:

• Requirements for data quality, including a detailed data quality hierarchy for activity data and emission factors;
• Consideration of materiality in emissions accounting;
• Emissions amortization requirements;
• Co-product allocation requirements.
• By-product accounting relating to inputs to the process that are by-products; and
• Waste input accounting relating to inputs to the process that are wastes,.

The Energy Use Accounting

This sectionModule v1.3 provides requirements on how energy-related emissions must be calculated for The Project so that they can be subtracted in the net CO₂e removal calculation. It sets out specificthe requirementscalculation relatingapproach to quantificationbe offollowed energyfor useintensive asfacilities partand ofnon-intensive thefacilities GHGand assessmentacceptable emission factors.

Energy Emissionsemissions associatedare withthose energyrelated usage result from the consumption ofto electricity or fuel.

Examples of electricity usage. They may include, but are not limited to:

• Electricity theusage in operation of process equipment, (i.e.,such as pumps, mixers, blowers, flow control, measurement instruments).
• Fuel consumption for handling equipment, such as fork trucks or loaders.

The Energy UseGHG Accounting Module v1.21 provides requirements on how energy-relatedtransportation and embodied emissions must be calculated infor aThe CDR projectProject so that they can be subtracted in the net CO₂e removal calculation.

Embodied Itemissions setsare outthose related to the calculationlife 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 consequentialcycle 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.

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 productsequipment and equipment as part of a Reporting Period’s activitiesconsumables. ExamplesThey 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.

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 manufacturetransportation of equipment and materials used in a process.

Examples of project-specific materialsproducts and equipment. thatThey must be considered as part of the embodied emission calculationmay 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.

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 (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.) and reversal risks of this storage reservoir are discussed in the Ocean DIC Storage Module.

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

9.2 Buffer PoolsPool

As outlined in the Reversals and Buffer Pools Section 2.5.9 of the Isometric Standard, the Buffer Pool (A common and recognized insurance mechanism among Registries allowing Credits to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.) is a mechanism used to insure against Reversal risks that may be observable and attributable to a particular project through monitoring.

BasedIn onWastewater presentAlkalinity understandingEnhancement, reversalscarbon inis thestored globalas oceandissolved Dissolvedinorganic Inorganic Carboncarbon (DIC) reservoir will not be directly observable with measurements and attributable to a particular project. Reversals of DIC in the ocean, a vast and well-mixed reservoir where storage durability is aexpected system-wide storage uncertainty that shouldto be addressedbetween through10,000 furtherand scientific100,000 researchyears. Projects applicable toAs this Protocolconstitutes arean generallyopen categorizedsystem aswith havingno adirectly Veryobservable Low Risk Level of Reversal according toreversals, the Isometric Standard Riskclassifies AssessmentProjects Questionnaire.operating Riskunder this Protocol as “No observable risk” for the purposes of reversal information is given in Appendix 4:the Risk of Reversal Questionnaireassessment, withand furthersuch informationProjects providedare withinnot the relevant storage module storage module.

For more details on Reversals, referrequired to Sectionscomplete 2.5.9a and 5.6Risk of theReversal Isometric Standardquestionnaire.

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:

• [R-G79X-0, Projects 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. ]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. [/R-G79X-0]
• [R-3W5J-0, Projects 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.]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.[/R-3W5J-0]
• [R-QH17-0, Projects 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 have sufficient plans for restoring water quality conditions prior to discharge in the event that negative environmental impacts result from project activities.[/R-QH17-0]
• Project Proponents must chacterize rocks and minerals utilized as feedstock following Isometric’s Rock and Mineral Feedstock Characterization Module v1.2.
• [R-B5WW-0, Projects must provide information on how dosing rate is calculated, including any partner data that was used in those calculations.]Project Proponents must provide information on how dosing rate is calculated, including any partner data that was used in those calculations[/R-B5WW-0]
• [R-YTRH-0, Projects must provide the information on the WWTP business as usual operations.]Project Proponents must provide the following information on the WWTP during business as usual operation:  [/R-YTRH-0]
  • [G-W0G1-0, Projects must provide information on the WWTP's business as usual energy usage.]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. [/G-W0G1-0]
  • [G-FNBP-0, Projects must provide information on the WWTP's business as usual solids and/or WAS generation and fate of the solids/WAS.]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.[/G-FNBP-0]
  • [G-3A7B-0, Projects must provide information on the WWTP's business as usual retention and settling times of solids and/or WAS within the WWTP.]Retention and settling times of solids and/or WAS within the WWTP.[/G-3A7B-0]
• Project[R-JFM6-0, PropnentsProjects must designate the control volume boundaries for the project, including the control volume in L.]Project Proponents must designate the control volume boundaries for the project, including the control volume in L.[/R-JFM6-0]

11.0 Monitoring

11.1 Monitoring Locations

1. 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.
2. Feedstock dosing ([math: B]): Measurements of alkaline feedstock dosing into the control volume.
3. Effluent ([math: C]): The effluent stream exiting the control volume.
4. 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).
5. 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.
6. 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]

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

11.2.1 Influent, A

11.2.2 Feedstock Dosing, B

11.2.3 Effluent, C

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 8.23.3.1 for losses upon mixing with receiving waters.

11.2.4 Waste Activated Sludge, D

11.2.5 Within the Control Volume, E

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.

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 high⁴⁸⁴⁶. 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

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

Two types of thresholds are used:

1. Safety thresholds are imposed on the effluent characteristics and controlled prior to discharge.
2. 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.

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 or Reductions may be Verified, resulting in Issued Credits.

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 or Reductions, often with the purpose of Retiring Credits to make a Removal or Reduction claim.

A database that holds information on Verified Removals and Reductions based on Protocols. Registries Issue Credits, 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 Credit 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 Credits to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.

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.

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 ⁴⁵⁴⁴. 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 ⁴⁹⁴⁷. Metadata should be complete according to the NOAA ocean acidification metadata template ⁵⁰⁴⁸.

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 geologists⁵¹⁴⁹. 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 point⁵²⁵⁰. 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 0.1⁵³⁵¹. 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 used⁵⁴⁵². 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 ⁵⁵⁵³. 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) ⁵⁶⁵⁴.

Recommended analytical methods for bottle samples include:

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

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)⁵⁷⁵⁵.

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 ⁵⁸⁵⁶.

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 (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.).

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 Procedure⁵⁹⁵⁷ and USGS Procedure for Dye Tracer Measurements⁶⁰⁵⁸ 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, 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:

1. A WWTP does no prior pH amendment

2. 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

Projects applicable to this Protocol are generally categorized as having No Observable Risk of Reversal according to the Isometric Standard Risk Assessment Questionnaire. This results in a 0% buffer pool for Projects using this Protocol and Storage Module. However, if a Project identifies project-specific factors which impact the Risk of Reversal, they are required to complete the Risk of Reversal Questionnaire below.

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:

Note the Risk Score at any step cannot be negative.

Risk Score Categories:

• 0: Very Low Risk Level (21% 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