Wastewater Alkalinity Enhancement

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

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

Secondary treatment is typically a large source of biogenic CO₂ emissions in WWTPs as that is the step where a majority of solid and dissolved organic carbon in the wastewater is transformed into CO₂ through biological 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 (CDR), rather than emissions avoidance.

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

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

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

This Protocol is developed to adhere to the requirements of ISO 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. The Protocol ensures:

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

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

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

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

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

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

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

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

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

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

To ensure human and environmental health, eligible projects must:

• Operate within the existing permits, or an approved modified permit, of a wastewater treatment plant.
• Characterize feedstock prior to usage according to the Rock and Mineral Feedstock Characterization Module v1.2.
• R-C7DT-0Submit proof of an official partnership with partner facilities to ensure that the Project is consensual and that the WWTP will continue to provide access to the Project Proponent for any continual monitoring required for the WAE project. This can be evidenced by documents such as a Memorandum of Understanding (MoU), written consent, or other agreement with involved parties, such as the WWTP, wastewater utility, contracted operators, or contracted feedstock supplier.

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

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

• G-A54P-0This 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-XT0B-0The 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-HEW0-0Alkalinity addition occurs in the biological treatment portion of the facility.
• G-53QN-0Projects must operate as retrofits to existing WWTP facilities. A retrofit is defined as the introduction of new materials, products or technologies to an existing process or facility. This can include adding alkalinity dosing to WWTPs that did not previously add alkalinity, increasing dosing in plants that already add alkalinity, adding additional monitoring to the WWTP to quantify CDR, etc.

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

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.

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 of the Isometric Standard.

The Validation and Verification Body (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.

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

Verifiers should also verify the documentation of uncertainty of the GHG statement as required by the Uncertainty Section 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

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 of the Isometric Standard).

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

Verifiers and validators must comply with the requirements defined in the Validation and Verification Requirements Section 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.

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

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

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

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

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

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

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 of the Isometric Standard.

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

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

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

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

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.

Projects must adhere to the following governance and legal requirements:

Official permitting:

• G-CDEZ-0Project Proponents must identify the jurisdictional authorities of the receiving water bodies of the project site, and as outlined in Section 4 (Applicability).
• R-KH54-0Projects must operate within the existing permits, or an approved modified permit, of a wastewater treatment plant.
• Project Proponents must hold an official partnership, such as through an MoU, with the wastewater facility the Project intends to integrate with.

Compliance:

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

An environmental and social risk assessment in adherence with the Environmental and Social Impacts Section 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.

The Project Proponent must conduct an environmental risk assessment which adheres to the Environmental Impacts Section 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-0Potential risks associated with feedstocks include land use impacts from sourcing, production, preparation, storage and distribution, such as land degradation, land occupation, dust pollution, deforestation and localized watershed contamination.

Co-products and waste:

• G-3GF0-0Generation of waste products or additional waste must be accompanied by a plan which ensures safe handling, containment and disposal.

Pollution prevention:

• G-Q5AN-0Additional 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-YF1Z-0The 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.

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

Per the Stakeholder Input Process Section 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 the Isometric Standard, and evidence of these meetings must be submitted in the PDD.

The scope of this Protocol includes GHG sources, sinks and reservoirs (SSRs) associated with a Wastewater Alkalinity Enhancement (WAE) Project.

A cradle-to-grave GHG Statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary.

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.

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

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

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 The Project's impact on activities that fall outside of the system boundary of The Project must also be considered. This is covered under Leakage in Section 8.5.4.

In line with the GHG Accounting Module v1.1, 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 CO2 stored, only CO2 shall be included as part of the quantification. For all other activities all GHGs must be considered. For example, the release of CO2, CH4, and N2O is expected during diesel consumption;
• Quantify emissions in tonnes CO₂ equivalent (t CO₂e) using the 100-year Global Warming Potential (GWP) for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report); and
• Consider materiality of SSRs in line with Isometric requirements.

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 $CO_2e_{Removal,\ RP}$. 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.

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:

$$CO_2e_{Removal,\ RP} = CO_2e_{Stored,\ RP} - CO_2e_{Counterfactual,\ RP} - CO_2e_{Emissions,\ RP}$$

Equation 1

Where

• $CO_2e_{Removal,\ RP}$ represents the total net CO₂e removal for Reporting Period, RP, in tonnes of CO₂e;
• $CO_2e_{Stored,\ RP}$ 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;
• $CO_2e_{Counterfactual,\ RP}$ 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;
• $CO_2e_{Emissions,\ RP}$ represents the total GHG emissions associated with the Project including leakage, over a Reporting Period, RP, in tonnes of CO₂e.

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:

$$CaCO_{3 (s)} + CO_{2 (aq)} + H_2O_{(l)} \rightarrow Ca^{2+}_{(aq)} + 2HCO_{3 (aq)}^{-}$$

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:

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

Equation 3

Where

• $m_{Dissolved,\ RP}$ is the total mass of feedstock dissolved within a Reporting Period, RP, in tonnes;
• $M_{CO_2}$ is the molar mass of CO₂ in tonnes/mol;
• $M_{FS}$ is the molar mass of the chosen feedstock in tonnes/mol;
• $P$ is the fraction of feedstock dissolved by non-carbonic acid. $P$ is a dimensionless value between 0 and 1;
• $X_{carbonic}$ is the molar ratio of CO₂ consumption and feedstock consumption from carbonic acid weathering, in mol CO₂/mol feedstock;
• $X_{non-carbonic}$ 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;
• $\eta_{Losses,\ RP}$ are losses of CO₂ due to riverine and oceanic processes. $\eta_{Losses,\ RP}$ is a dimensionless term. See Section 8.3.3 for calculation of this term.

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

$$m_{Dissolved,\ RP} = \sum_{i}^{T} ( \dot m_{Dissolved,\ i} * \Delta t_i)$$

Equation 4

Where

• $m_{Dissolved,\ RP}$ is the total mass of feedstock dissolved within a Reporting Period, RP, in tonnes;
• $\dot m_{Dissolved,\ i}$ is the average feedstock dissolution rate over time interval, $i$, in tonnes/day;
• $\Delta t_i$ is the duration of time, $i$, over which measurements are averaged, in days;
• $T$ 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.

Figure 2: Example process diagram, control volume and monitoring locations for Wastewater Alkalinity Enhancement. The control volume, $V$, 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.

$\dot m_{Dissolved}$ can be calculated based on the following options:

• R-EFR3-0Option 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-24KR-0Option 2: Mass balance on conservative dissolved weathering products, such as Ca²⁺ or Mg²⁺, where the difference in weathering product concentration between the influent and effluent is assumed to the result of feedstock dissolution.

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

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

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

$$\dot m_{FS} = Q * FS * 10^{-9}$$

$$\frac{dFS}{dt} = \dot m_{FS,\ Dosing} - \dot m_{FS,\ Effluent} - \dot m_{FS,\ WAS} - \dot m_{Dissolved}$$

$$\dot m_{Dissolved} = \dot m_{FS,\ Dosing} - \dot m_{FS,\ Effluent} - \dot m_{FS,\ WAS}$$

• G-ENS8-0When carbonate feedstocks, such as calcite (CaCO₃) are used, $FS_{Effluent}$ and $FS_{WAS}$ can be assumed to be equivalent to the total inorganic carbon (TIC) in samples taken from these streams. This approach assumes that any inorganic carbon present in plant effluent and waste activated sludge comes from dosing of carbonate feedstocks, which is a conservative assumption. Methods for TIC analysis must be described in detail in the PDD and must include any standards or SOPs used. Acceptable analyses may include, but are not limited to, use of a TIC analyzer.
• Where non-carbonate feedstocks are used, $FS_{Effluent}$ and $FS_{WAS}$ 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 $FS_{WAS}$. Note that for $FS_{Effluent}$, 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.

$$P = \frac{\dot m_{NCA}}{\dot m_{Dissolved}}$$

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.

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

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.

In the absence of WAE project activities, wastewater treatment plants have direct CO₂ emissions from evasion of biogenic CO₂^13,14. 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 $CO_2e _{Stored}$, 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).

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.

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:

$$\eta_{Losses,\ RP} =  \prod_{i=1}^{N} \eta_i$$

Equation 22

Where:

• $\eta_{Losses,\ RP}$ is the overall loss discount for Reporting Period;
• $\eta_i$ is the fraction of CO₂ that is retained after a given loss, $i$;
• $N$ 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.

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:

$$CO_2 + H_2O \leftrightarrow H_2CO_3 \leftrightarrow H^+ + HCO_3^- \leftrightarrow 2H^+ + CO_3^{2-}$$

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:

$$Ca^{2+} + 2HCO_3^{-} \rightarrow CaCO_3 + CO_2 + H_2O$$

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 body¹⁶. 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}. Furthermore, precipitation dynamics occur on a timescale between minutes to hours^17,19, which suggests that dilution could be an effective risk mitigation strategy²².

Quantification

Natural Alkalinity Flux Reduction

Concept

Increased alkalinity in wastewater effluent can potentially reduce the natural alkalinity flux from marine or river sediments²³. 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}. Alkaline feedstock dissolution may release trace metals which has the potential to fertilize blooms of calcifiers²⁷.

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^{28, 29}. However, the Black Sea, a naturally elevated alkaline environment, harbors extensive blooms of the coccolithophores ^{30, 31}, a major group of calcifying plankton. This is thought to be due to the favorable carbonate chemistry promoted by the elevated alkalinity regime²⁷.

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. 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 ³⁵. Coastal areas with significant benthic calcification of CaCO₃ sediments may be especially susceptible to this feedback.

Quantification

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.

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:

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

Equation 25

With

$$K_{sp(calcite)} = \alpha_{sat} Ca^{2+} * \alpha_{sat} CO_3^{2-}$$

Equation 26

Where:

• $\alpha Ca^{2+}$ and $\alpha CO_3^{2-}$ in Equation 25 are the measured solution activities of those ions
• $\alpha_{sat} Ca^{2+}$ and $\alpha_{sat} CO_3^{2-}$ 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 ³⁸.

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. 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 precipitation⁴².

Quantification

1. Using the Renforth and Henderson (2017)⁴³ uptake efficiency equation
2. Using a 3D Earth Systems Model or ocean physical-biogeochemical model to explicitly simulate ocean circulation and air-sea CO₂ fluxes⁴¹
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 is⁴³:

$$\eta_{RH} = \frac{\Delta C_T}{\Delta A_T} = (S \cdot 10^{-3.009} + 10^{-1.519}) \text{ln}(pCO_2)-(S \cdot 10^{-2.100}) - \\ (T \cdot pCO_2)(S \cdot 10^{-7.501} - 10^{-5.598}) - (T \cdot 10^{-2.337}) + 10^{-0.102}$$

Equation 27

Where

• $\eta_{RH}$ is the Renforth and Henderson uptake efficiency of CO₂ upon mixing with ocean waters, in mol C/mol alkalinity;
• $\Delta C_T$ is the change in Total DIC in the ocean as a result of WAE, in mol C;
• $\Delta A_T$ is the change in Total Alkalinity in the ocean as a result of WAE, in mol alkalinity;
• $pCO_2$ is the local ocean partial pressure of CO₂ at the discharge site, in μatm;
• $T$ is the local surface ocean temperature, in °C;
• $S$ 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.

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

If a noncarbonate feedstock is used, then $\eta_{RH}$ 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)²³--to determine the fraction of CO₂ retained upon ocean discharge:

$$\eta_i = f(2 \eta_{RH} - 1) + (1-f)\eta_{RH}$$

Equation 28

Where:

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

If 0% carboante feedstocks are used, then $f=0$ and Equation 28 simplifes to $\eta_i = \eta_{RH}$. If 100% carbonate feedstocks are used, then $f = 1$ and Equation 28 becomes $\eta_i = 2 \eta_{RH} - 1$. As stated in Section 8.3, if a feedstock of mixed mineralogy is used, Project Proponents must make conservative assumptions in quantifying CDR and determining $f$. For example, if a feedstock contains MgO and MgCO₃, $f$ 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 $f=1$. 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 $f=0.2$ 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 projects⁴¹. 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.

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.

$CO_2e_{Counterfactual,\ RP}$ 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 $CO_2e_{Stored,\ RP}$ term, and does not include GHG emissions in the counterfactual scenario. The quantification of GHG emissions relative to BAU operations is described in Section 8.5.

See Appendix 3 for further explanation on this approach.

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

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

$$CO_2e_{Emissions,\ RP} = CO_2e_{Establishment,\ RP} + CO_2e_{Operations,\ RP} + CO_2e_{End-of-Life,\ RP} + CO_2e_{Leakage,\ RP}$$

Equation 29

Where

• $CO_2e_{Emissions,\ RP}$ represents the total GHG emissions for a Reporting Period, in tonnes of CO₂e.
• $CO_2e_{Establishment,\ RP}$ represents the GHG emissions associated with project establishment, represented for the Reporting Period, in tonnes of CO₂e, see Section 8.5.1.
• $CO_2e_{Operations,\ RP}$ represents the total GHG emissions associated with operational processes for a Reporting Period, in tonnes of CO₂e, see Section 8.5.2.
• $CO_2e_{End-of-Life,\ RP}$ represents GHG emissions that occur after the Reporting Period and are allocated to a Reporting Period, in tonnes of CO₂e, see Section 8.5.3.
• $CO_2e_{Leakage,\ RP}$ 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 8.5.4.

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 $CO_2e_{Emissions,\ RP}$. 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.

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 to the moment before the first removal activity takes place. GHG emissions associated with project establishment may be amortized over the anticipated project lifetime, or per output of product. Requirements for amortization are outlined in ++Section 7 of the GHG Accounting Module v1.1++.

GHG emissions associated with $CO_2e_{Operations,\ RP}$ 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 $CO_2e_{Operations,\ RP}$.

$CO_2e_{Operations,\ RP}$ 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.

$CO_2e_{End-of-Life,\ RP}$ includes all emissions associated with activities that are anticipated to occur after the Crediting Period until the end of the Project Commitment Period. This includes activities related to ongoing monitoring for Reversals.

$CO_2e_{End-of-Life,\ RP}$ must be estimated upfront and allocated in the same way as set out for calculation of $CO_2e_{Establishment,\ RP}$.

Given the uncertain nature of $CO_2e_{End-of-Life,\ RP}$ emissions, assumptions must be revisited at each Reporting Period and any necessary adjustments made.