Open System Ex-situ Mineralization

This Protocol provides the requirements and procedures for the calculation of net carbon dioxide equivalent (CO₂e) removal through ex-situ mineralization of alkaline materials within an open system via Enhanced Air Capture (EAC). Within this Protocol, EAC refers to the accelerated absorption of CO₂ from the atmosphere into an alkaline feedstock through an applicable removal strategy.

Open-system ex-situ mineralization (OSEM) via EAC, often referred to as surficial mineralization, is a subset of carbon mineralization CDR pathways. Projects that utilize natural rocks/minerals (e.g., silicate rocks) and industrial alkaline materials (e.g., mine tailings, steel slag, cement kiln dust, red mud, and fly ash) for long-term capture and storage of atmospheric CO₂ via open-system ex-situ mineralization may use this Protocol as a framework for Crediting under the Isometric Standard. Within this Protocol, materials used for OSEM via EAC are referred to as feedstock.

Carbon mineralization, also known as mineral carbonation, is a natural process in which metal cations (such as Ca²⁺, Fe²⁺/Fe³⁺ and Mg²⁺), liberated from minerals via dissolution or surface-ion exchange, react with CO₂ to form carbonate minerals. Carbon mineralization pathways are often divided into ex-situ processes, involving mineralization of a feedstock removed from its source location or formation, and in-situ processes, involving transport and injection of CO₂ and other carbon sources into existing rock formations. Ex-situ mineralization may take place in closed systems, such as an engineered reactor (see CO₂ Storage via Ex-Situ Mineralization in Closed Engineered Systems Module), or in open systems, such as a tailings storage facility (TSF) (as described in this Protocol).

In open systems, carbon mineralization takes place in a non-enclosed environment, where the exchange of gasses, liquids and solids materials with the surrounding environment may occur. In open systems, natural interactions with the surrounding environment, such as diffusion of atmospheric CO₂ into the system, can promote conditions conducive to carbonation. These conditions are typical in surface and near-surface environments, where suitable feedstocks containing minerals such as olivine, serpentine, or basaltic rocks are exposed to the atmosphere allowing for ongoing CO₂ uptake and carbonate formation. This passive influence from the surrounding environment contrasts with ex-situ mineralization that occurs in a closed, engineered system, where carbonation processes take place in a controlled environment, such as a reactor or contained facility.

This Protocol is applicable to ex-situ mineralization Projects operating in open system settings for the purpose of carbon removal via EAC. Specific applicability conditions can be found in Section 6 of this Protocol. This Protocol outlines requirements for direct measurements, monitoring and modeling of carbon removals. Requirements related to characterization of both feedstock and produced carbonated materials are outlined within Isometric’s Rock and Mineral Feedstock Characterization Module 1.0. Mineralization processes that are coupled with Direct Air Capture (DAC) are not applicable under this Protocol, Project Proponents that utilize DAC should refer to Isometrics DAC Protocol 1.1.

Project Proponents are required to meet the requirements outlined within this Protocol, as well as relevant Isometric Modules. Figure 1 displays the storage, feedstock characterization and Greenhouse Gas (GHG) Statement Modules that are linked to requirements throughout this Protocol.

Figure 1 Storage, feedstock characterization and Greenhouse Gas Statement (GHG) Modules linked to the OSEM Protocol

In addition to Carbon Dioxide Removal (CDR), Projects utilizing this Protocol and accompanying Modules may generate co-benefits, including but not be limited to:

• A potential reduction in waste volumes where extractive waste is removed from a designated waste facility at a mining, or other industrial, operation for use in CDR activities.
• Increased commodity recovery from extractive wastes that would otherwise pose a risk to the environment.
• A reduction in the potential for the onset of Acid Mine Drainage (AMD) (also referred to as acid rock drainage), and/or metalliferous drainage. In locations where alkaline minerals are prevalent, they can neutralize the acidity typically associated with sulfidic minerals, effectively mitigating the risk of AMD.
• An increased social license to operate (SLO) for mining operators - CDR activities utilizing industrial alkaline by-products and/or mining wastes, may reduce the overall environmental harm associated with the storage of these materials, while also reducing the long-term costs related to management and maintenance of storage facilities.

Note: The impact of CDR activities on a project operation, and its target feedstock, must be assessed on a project-by-project basis. It is acknowledged that under certain circumstanced CDR activities may mobilise or destabilise material that was previously immobile and stable. It is the responsibility of the Project Proponent to assess the potential environmental and social impacts of CDR activities prior to Project Commencement.

This Protocol utilizes and is intended to be compliant with the following standards and Protocols:

• Isometric Standard v1.5.0
• ISO, EN, 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

This Protocol is developed to adhere to the requirements of ISO 14064-2: 2019 -- Greenhouse Gas -- 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 weathering and mineralization processes required to account for of net CO₂e removals.
• Consistent system boundaries and calculations are utilized to quantify net CO₂e removal for open system ex-situ mineralization 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.

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

Additional standards, methodologies, and Protocols that were reviewed, referenced, or for which attempts to align with or leverage in the development of this Protocol include:

• Criteria for High-Quality Carbon Dioxide Removal, Carbon Direct, Microsoft, 2023
• Global Acid Rock Drainage Guide (Guard Guide), The International Network for Acid Prevention (INAP), 2009

This Protocol was developed based on the current state of the art and publicly available science regarding Open System Ex-Situ Mineralization (OSEM). As OSEM is a novel CDR approach, with limited published literature specifically related to Monitoring, Reporting and Verification (MRV) development, this Protocol incorporates requirements that may be more stringent than existing relevant regulations or other Protocols related to mineralization for CDR.

Future versions of this Protocol may be altered, particularly regarding requirements for demonstrating durability of stored carbon produced via OSEM, as the stability of CO₂ captured via dissolution, and subsequent mineralization, of suitable feedstocks becomes well demonstrated and documented; reversal risks are proven to be limited; and the overall body of knowledge and data regarding all processes, from feedstock supply to permanent storage, is significantly increased.

Additionality requirements are outlined in Section 2.5.3 of the Isometric Standard. Additionality determinations should be reviewed and completed every 2 years, at a minimum, or whenever Project operating conditions change significantly, such as in the following circumstances:

• Changes to Regulatory requirements or other legal obligations for Project implementation or implementation of new requirements including the introduction of new mandates, are enforced.
• Project financials indicate carbon finance is no longer required, potentially due to, for example:
  • Increased fees related to payments made to the Project Proponent for utilization of waste feedstocks, or a reduction in fees relating to payments paid by the Project Proponent for utilization of waste feedstocks
  • Sale of co-products that make the business viable without carbon finance
  • Reduced rates for capital access

Any review and change in the determination of additionality will not affect the availability of carbon finance or carbon Credits for the current or past Crediting periods. However, if the review indicates the Project has become non-additional, the Project will be ineligible for future Credits.

This Protocol applies to Projects or processes which:

• Use alkaline feedstocks to mineralize CO₂ as carbonate minerals in open system settings.
• Use either feedstock pretreatment or physical manipulation to facilitate mineralization.
• Demonstrate that net CO₂ removal occurs in excess of baseline mineralization rates.

This Protocol applies to Projects and associated operations that meet all of the following conditions:

• The Project provides a net-negative CO₂ impact, as calculated in the Projects GHG statement.
• The Project is considered additional, in accordance with the requirements of Section 9.4.
• The Project provides long duration CO₂ storage (> 1,000 years) in accordance with the requirements of the Carbonated Materials Storage and Monitoring Module and the Isometric Standard.

Applicable removal mechanisms include:

• Indirect carbonation - occurs in a two-step or multi-step process involving the extraction of reactive components, such as Mg²⁺ and Ca²⁺, from the host minerals. Following extraction, these components react with CO₂ dissolved in porewater, facilitating carbonation through aqueous-solid interactions rather than gas-solid reactions.

Applicable storage mechanisms include:

• Solid phase storage (i.e., mineral storage) - CO₂ removal and storage occurs through mineralization reactions that result in the formation of carbonate minerals. This storage mechanism constitutes a stable carbon reservoir on geological timescales (>1,000 years). This storage mechanism is eligible for Crediting under this Protocol following the monitoring requirements outlined within the Carbonated Material Storage and Monitoring Module and Section 12 of this Protocol.
• Aqueous phase storage (i.e., aqueous storage) - CO₂ removal and storage in aqueous forms such as dissolved bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions, creating dissolved inorganic carbon (DIC) in an alkaline solution. This occurs as CO₂ interacts with water and alkaline minerals that release metal cations, which further stabilize these ions. In stable environments like deep groundwater or oceans, DIC acts as durable CO₂ storage (> 1000 years), remaining in non-gaseous, dissolved forms, resistant to re-release. Studies on ocean and deep saline aquifers as natural CO₂ reservoirs and analogs include refs ^{1 2}. Refer to Section 12 for monitoring requirements regarding this storage mechanism.

Applicable Project Facilities include:

• Operational facilities that are used to store suitable alkaline material feedstocks produced as a by-product/waste in extractive or production-based industries.
• Operational alkaline Tailings Storage Facilities (TSF) containing tailings that are stored under partial saturation.
• Closed alkaline TSF containing tailings that are stored under partial saturation.
• Areas where industrial alkaline waste, such as construction debris, cement dust, and other carbon-reactive materials, are disposed of, such as landfills or other waste disposal areas.

The following feedstocks are considered applicable for use in Crediting Projects under this Protocol:

• Natural minerals and rocks, such as igneous and metamorphic rocks that are rich in alkaline earth metals. This may include:
  • Mafic and ultramafic rocks, such as basalt³ and peridotite⁴
  • Mg- and Ca-rich minerals such as wollastonite^{5 6}, olivine ^{7 8 9 10} , brucite¹¹, hydrotalcite¹² and serpentine group minerals ^{13 14 15}
  • Aluminosilicates such as plagioclase [Ca-endmember anorthite; CaAl₂Si₂O₈] ^{16 17}
  • Natural volcanic glasses ^{16 18}
• Industrial by-products & wastes, including:
  • Mine tailings ^{19 20}
  • Iron and steelmaking slag ^{21 22}
  • Red mud ²³
  • Cement kiln dust, waste cement and demolition waste ^{24 25}
  • Waste ash and combustion products ^{26 27}
  • Alkaline paper mill and acetylene production waste ²⁸
  • Waste brines ²⁹

The above list is not exhaustive. Applicability criteria will be assessed on a Project-by-Project basis. Where a Project does not meet the applicability conditions outlined in this section, the Project Proponent may consult with Isometric to determine potential allowances or adjustments.

It is noted that the applicability of a feedstock, Project location and condition is dependent on the Project Proponent demonstrating compliance with the requirements outlined in the Isometric Standard, Rock and Mineral Feedstock Characterization Module 1.0, and Carbonated Materials Storage and Monitoring Module.

Under this Protocol, the following Project conditions locations are not considered applicable for Crediting:

• Operational or closed alkaline TSF that contain tailings that are stored under fully saturated or flooded conditions.
• New extractive waste storage facilities or operations within which production has increased due to the financial incentivization related to CDR Crediting or carbon financing.
• New or existing extractive waste storage facilities that contain materials/proposed feedstocks have been designated as Potentially Acid Forming (PAF) under regulatory frameworks at the Project location.
• New or existing extractive or production process waste storage facilities within which CDR processes have been implemented to meet regulatory requirements.
• Projects that are unable to demonstrate detailed baseline conditions may include Projects within which mineralization of a feedstock may occur, irrespective of the implemented removal mechanism.

Note: Facilities containing extractive waste materials designated as PAF under regulatory frameworks may be considered for Crediting under this Protocol, where a Project Proponent can demonstrate there is not an enhanced risk of acid mine (or metaliferous) drainage (AMD) as a result of Project activities. The applicability of such instances will be considered on a Project-by-Project basis by Isometric.

Further information on applicability criteria is provided in Section 7.

Carbon mineralization reactions can be classified as either direct carbonation or indirect carbonation. Direct mineral carbonation occurs when mineral dissolution and carbonate precipitation occurs in a single step. Indirect carbon mineralization involves multiple steps where metal cation extraction and carbonate precipitation occurs in separate steps. Direct and indirect carbonation can be carried out as either a gas-solid process or as an aqueous process. Sections 7.1.1 and 7.1.2 of this Protocol explain and summarize both reaction mechanisms. Under this Protocol, only Projects that utilize Indirect carbonation as a removal mechanism are applicable for Crediting.

Direct carbonation occurs in a single step during which carbonate minerals are formed by interacting with CO₂. Various reactions, depending on the feedstock, are possible.

Equations 1, 2 and 3 outline direct carbonation of serpentine, forsterite and brucite as examples for direct gas-solid carbonation:

$Mg_3Si_2O_5(OH)_4(s) + 3CO_2(g) \leftrightarrow 3MgCO_3(s) + 2SiO_2(s) +2H_2O(l)$

(Equation 1)

$Mg_2SiO_4(s) + 2CO_2(g) \leftrightarrow 2MgCO_3(s) + SiO_2(s)$

(Equation 2)

$Mg(OH)_2(s) + CO_2(g) \leftrightarrow MgCO_3 + H_2O(l)$

(Equation 3)

Direct gas-solid mineral carbonation reactions can occur in either dry or humid conditions. In dry conditions, high temperatures facilitate reactions ³⁰. In humid conditions, water-assisted reactions ^{31 31}. Gas-solid carbonation reactions generally require high pressure, elevated temperatures, and steam for effective reaction rates ³². Under milder conditions, at lower temperatures and pressures, gas-solid carbonation has less effective reaction kinetics ³³.

Direct aqueous carbonation involves the reaction of CO₂ and water directly with solids. Aqueous reaction mechanisms occur when CO₂ dissolved in water reacts with a mineral surface, resulting in carbonate precipitation. It is noted that silicate dissolution rates increase as pH decreases, whereas carbonate minerals are stable in alkaline conditions. To optimize carbonate precipitation without hindering silicate dissolution, as the applicable pH range is narrow, a careful balance between pH levels must be achieved.

Direct carbonation is not applicable under this Protocol as it requires precise control of reaction conditions such as temperature, pressure, and pH, which are challenging to maintain in open-system settings. In contrast, a closed, engineered system can effectively manage these conditions, making them better suited for direct carbonation processes that demand controlled environment to achieve optimal reaction rates and mineral stability.

Indirect carbonation is a multi-step process involving the dissolution of CO₂ in water thereby forming carbonic acid (H₂CO₃). Carbonic acid reacts with rocks and minerals, releasing metal cations (e.g., Ca²⁺, Mg²⁺, Fe²⁺/³⁺) into aqueous solutions. Concurrently, the buffering of H⁺ ions by the process of mineral dissolution enhances the transformation of dissolved atmospheric CO₂ into bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions. These ions then react with the available metal cations, resulting in the formation of solid carbonate minerals.

Indirect gas-solid reaction is distinguished from direct carbonation by the additional step of cation extraction from the feedstock. This is followed by reacting the leached cations with CO₂ to produce the desired carbonates. Indirect carbonation in an aqueous environment typically involves three key steps to complete the process:

1. Dissolution and hydration of CO₂ in aqueous solution (Equations 4, 5 and 6)
2. Liberation of divalent metal cations from host minerals (Equations 7)
3. Precipitation of a metal-bearing carbonate minerals and silica (Equation 8, 9, 10)

First, the dissolution of CO₂ in water follows the following reaction mechanism:

$CO_2(g) + H_2O(l) \leftrightarrow H_2CO_3(aq)$

(Equation 4)

Dissolution of CO₂ in water forming carbonic acid (H₂CO₃)

$H_2CO_3(aq) \leftrightarrow H^{+}(aq) +HCO_3^{-}(aq)$

(Equation 5)

The dissociation of carbonic acid into protons (H⁺) and bicarbonate (HCO₃^-)

$HCO_3^{-}(aq)\leftrightarrow H^{+}(aq) + CO_3^{2-}(aq)$

(Equation 6)

The further dissociation of bicarbonate into protons ($H^{+}$) and carbonate ions ($CO_3^{2-}$)

Second, the liberation of divalent metals from host minerals, take forsterite dissolution as an example:

$Mg_2SiO_4(s) + 4H^{+}(aq) \leftrightarrow 2Mg^{2+}(aq) + SiO_2(aq) + 2H_2O(l)$

(Equation 7)

Finally, carbonation and precipitation of metal-bearing bicarbonate, carbonates and silica, the following reactions assume formation of Mg²⁺-bearing carbonates:

$Mg^{2+}(aq) +2HCO_3^{-}(aq) \leftrightarrow Mg(HCO_3)_2(aq) \leftrightarrow Mg(HCO_3)_2(s)$

(Equation 8)

$Mg^{2+}(aq) + CO_3^{2-}(aq) \leftrightarrow MgCO)3(s)$

(Equation 9)

$H_4SiO_4(aq)\leftrightarrow SiO_2(s) + 2H_2O(l)$

(Equation 10)

Another illustrative example of indirect mineral carbonation is acid extraction. Acid extraction is an effective method for extracting divalent metals from unreactive silicate minerals. Acid extraction may use a range of acids including HCl, H₂SO₄ and HNO₃. An example mechanism for acid extraction involving serpentine, a magnesium bearing silicate, and hydrochloric acid is shown in Equations 11-13^{33 34}:

$Mg_3Si_2O_5(OH)_4(s) + 6HCl(l) + H_2O(l)\leftrightarrow 3MgCl_2\cdot6H_2O(aq) + SiO_2(aq)$

(Equation 11)

$MgCl_2(aq_\cdot6H_2O(aq)\leftrightarrow MgCl(OH)(aq) + HCl(aq) + 5H_2O(l)$

(Equation 12)

$2MgCl(OH)(aq) \leftrightarrow Mg(OH)_2(s) + MgCl_2(aq)$

(Equation 13)

Alternative methods of indirect carbonation include molten salt extraction and sodium hydroxide extraction as well as pH swing processes ^{33 34}.

Removal strategies are processes which lead to CDR in excess of baseline scenarios where no removal strategies have been implemented at the Project site, over the Reporting Period (RP). Requirements related to calculation of Project baselines can be found in Section 10.3.

Under this Protocol the following removal strategies are eligible for Crediting:

• Feedstock Pretreatment
• Physical Manipulation

Sections 7.2.1 and 7.2.2 of this Protocol outline and summarize the types of pre-treatment and physical manipulation methods that are applicable under this Protocol. Where Projects utilize a mixture of feedstock pretreatment and physical manipulation, the Project Proponent must refer to Section 7.2.3.

Project Proponents may opt to pre-treat suitable feedstock materials to enhance their reactivity. Chemical, thermal and mechanical pre-treatment methods are applicable under this Protocol. Table 1 summarizes proposed pre-treatment techniques that can accelerate ex-situ carbon mineralization of alkaline feedstocks, such as mine tailings or fly ash. The pretreatment methods outlined in Table 1 are not exhaustive. Alternative pretreatment methods may be allowable in consultation with Isometric.

Project Proponents are required to clearly outline pretreatment methodologies within the Project Design Documnet (PDD) upon submission to Isometric and the Project Validation and Verification Body (VVB). This description must include:

• Rationale for pre-treatment
• Standard Operating Procedure (SOP) or methodology used
• Physical and chemical characteristics of feedstock prior to and following pre-treatment, including, but not limited to:
  • Particle Size Distribution (PSD)
  • Surface area
  • Total Inorganic Carbon (TIC)

Further details related to characterization requirements of project feedstocks and sampled solids can be found in the Rock and Mineral Feedstock Characterization Module 1.0 and Section 12.5.3 of this Protocol.

Table 1. Examples of applicable feedstock pretreatment removal strategies.

Project Proponents may choose to undertake physical manipulation of suitable feedstock to:

1. Increase reactive surface area
2. Enhance rate and efficiency of CO₂ uptake and diffusion
3. Reduce surface passivation
4. Optimize gas solid contact

Table 2 summarizes physical manipulation removal strategies applicable under this Protocol. Alternative physical manipulation methods may be allowable in consultation with Isometric.

Project Proponents are required to clearly outline physical manipulation methodologies within the PDD upon submission to Isometric and the Project VVB.

Table 2. Examples of applicable physical feedstock manipulation removal strategies

Project Proponents may combine pretreatment and physical manipulation methods. Projects that utilize a combination of these removal strategies are required to identify all methods utilized to Credit under this Protocol within the Project PDD.

Projects are eligible for Crediting under this Protocol if there is sufficient evidence to demonstrate that the mechanisms and strategies utilized to achieve removals, qualify as an open-system engineered process as described in Section 1 of this Protocol.

The Project must consider environmental and social impacts at all Project locations, including at the mining or quarrying operation that produced Project feedstocks, during feedstock transportation (if applicable), and at the deployment/treatment areas. Appropriate measures must be implemented to identify and eliminate potential risks to terrestrial and aquatic ecosystems and biodiversity. Where risks cannot be eliminated, the Project Proponent is required to identify measures to monitor ecosystem health and mitigate adverse effects through a Project-specific mitigation plan, outlined the the PDD submitted to the Project VVB. Mitigation plans are required to be carried out by subject matter experts, in consultation with Isometric.

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 safeguards, in accordance with Section 3.7 of the Isometric Standard, is a condition for all Crediting Projects.

Project Proponents must comply with all national and local laws, regulations and policies, and receive permits from the relevant authorities, where applicable. Project Proponents must document, within the PDD, activities conducted under the Project that necessitate environmental permits. Where relevant, Projects must comply with international conventions and standards governing human rights and uses of the environment, when conducted within or foreseeably impacting party jurisdictions.

Ongoing environmental assessments must be completed in accordance with the Isometric Standard to identify potential risks, followed by the development of tailored mitigation plans by subject matter experts where necessary. Project Proponents must first strive to avoid negative environmental impacts. To account for potential cases where adverse environmental impacts are unavoidable, the Project Proponent must develop mitigation plans to minimize and remediate adverse effects, while preventing future negative impacts. For example, this could include measures such as pollution control technologies. Effective implementation of these measures must also be accompanied by a robust monitoring plan to ensure efficacy. Project Proponents must demonstrate active stakeholder engagement throughout this process, in accordance with Section 3.5 of the Isometric Standard. All mitigation strategies must align with local and international environmental laws and contribute to sustainable Project outcomes.

The weathering and subsequent mineralization of rock or mineral feedstock may be associated with the release of trace metals, such as nickel (Ni) and chromium (Cr), which may pose a risk to the surrounding environment. To prevent or mitigate such risks, the Project Proponent must take the following measures:

• Comprehensive feedstock analysis must be conducted in accordance with Isometric's Rock and Mineral Feedstock Characterization Module 1.0. Project Proponents should select rock or mineral feedstocks that minimize the risk of soil and groundwater contamination.
• A robust monitoring system must be established to regularly check for potentially harmful metals in surface and groundwater. This will likely involve periodic sampling and analyses alongside field monitoring for removals. The concentration of metals in soil and water must not exceed the limits established by the local authority where the Project is located. In the absence of local regulations, the Project Proponent must adhere to standards set by the European Union (EU), the World Health Organization (WHO) or the United States Environmental Protection Agency (US EPA). Justification behind the regulatory body selection must be provided in the PDD.
• If pre-existing heavy metal concentrations exceed applicable regulatory limits or guidance (as identified in the baseline scenario), the Project may still be considered for Crediting against this Protocol. Projects utilizing extractive feedstocks (such as mining wastes) must demonstrate that the Project activities do not enhance the release of heavy metals outside of the designated Project boundaries, see Section 8.5 of this Protocol.

Where a Project utilizes extractive wastes as a removal feedstock, on an active or closed mining operation, the Project Proponent is responsible for ensuring all Project activities comply with local and regional regulations. Project Proponents are required to identify how the implementation of the Project may impact mine permitting, operation, and closure, specifically where the implementation of a Project may impact waste production volumes, waste management and the mine operators net emissions.

Where a Project is undertaken within a mining or quarrying location, the Project Proponent must monitor surface and groundwater sources within and immediately outside the Project boundary for negative environmental impacts, including but not limited to: acidic and/or metalliferous drainage into the wider environment.

Where a Project is undertaken within an active mining operation, the Project Proponent is required to engage with the operator and Engineer of Record (where appropriate), to ensure compliance with relevant environmental permitting and regulations. A Project Proponent should engage with the Engineer of Record prior to undertaking CDR activities to assess the potential impacts and suitability of undertaking CDR activities at the project location.

Under this Protocol it is permissible for a Project Proponent to submit data generated by a partner operator, where a Project is undertaken within an active extractive operation or quarry. Such data may be used for both environmental monitoring, site characterization and carbon removal quantification, as long as the data is judged as suitable for such purposes by Isometric and the project VVB. Refer to Section 12 for specific monitoring requirements.

Project Proponents are required to provide documentation that demonstrates the VVB entrusted with validating removals are able to visit the Project site to undertake inspections at agreed intervals, at a minimum of every 2 years. Where access is limited due to safety concerns of the active mine operator, the Project Proponent is required to consult with Isometric to resolve validation issues. Such resolutions may include engaging the Project’s or operation’s Engineer of Record, where applicable, or a qualified third-party, to undertake measurements required by the VVB.

Projects that store carbon as a carbonated material must meet the storage and long-term monitoring requirements outlined in Section 4.1.2.1 of the Carbonated Material Storage and Monitoring Module. Adherence to the requirements and safeguards outlined in this module must be clearly described in the PDD upon submission to Isometric and the VVB. Appendices 2 and 3 outline the key requirements of the Carbonated Material Storage and Monitoring Module.

The Project must consider other environmental and social impacts, and the Project Proponent must provide evidence that the Project will not cause net environmental or social harm. The Project Proponent must comply with the full requirements for the evaluation of environmental and social safeguards in accordance with the Isometric Standard, as well as any local and national permitting/regulation.

Considering all aspects of the Project from feedstock production and utilization through deposition and storage, the Project Proponent must:

• Document activities conducted under the Project which may require it to obtain permits under the relevant governmental body or regulator.
• Document activities that would require the Project Proponent to obtain any drilling permits, access agreements, or any encroachment permits under local or national guidelines.
• Provide a listing of all permits or construction approvals received or applied for related to the Project and their status under any local or national programs.
• Provide documentation of safety programs and compliance, especially as related to the production and handling of extractive waste products.

In addition to the previously listed requirements, Project Proponents are required to submit the following information in the PDD related to potential Project impacts:

• Provide information on the potential impact of the Project on biodiversity.
• Document the potential for deforestation or loss of arable land.
• Address any potential impacts of feedstock utilization on food security (where applicable).

It is the responsibility of the Project Proponent to ensure that all permitting and regulatory requirements have been fulfilled and adhered to over the duration of the Crediting period and post closure.

Projects are required to ensure social safeguarding through compliance with Section 3.7.2 of the Isometric Standard. This includes, where applicable, the undertaking of a social impact assessment (or social risk assessment). Such assessments should consider specific risks related to human health and wellbeing associated with planned or ongoing Project activities. Assessments should be included in the PDD, upon submission to the Isometric and the Project VVB, prior to Crediting.

In accordance with Section 3.5 Isometric Standard, Project Proponents must demonstrate active stakeholder engagement through a Stakeholder Input Process 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 project location and provide invaluable insights and recommendations on the potential risks, necessary safeguards and specific monitoring needs. 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.

Project Proponents must include in a plan for information sharing, emergency response and conditions for stopping or pausing a deployment within the PDD. Adaptive management plans should meet/fulfill the requirements outlined in Sections 8.4 and 8.5. Plans for pausing or stopping a deployment must be in place in instances where there is a risk of:

• Regulatory non-compliance,such as:
  • Danger to ecosystem health detected (such as by the local community or a government agency) or
  • Pollutants/metals of concern exceeding thresholds outlined in the PDD
• Compromised health and/or safety of workers and/or local stakeholders

Where a Project Proponent does not pause removal/ deployment activities in such instances, in line with the respective Project adaptive management plan, this may result in the pausing of Credit issuance by Isometric.

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.

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

• Detailed feedstock characterization (refer to the Rock and Mineral Feedstock Module).
• Detailed Project boundary descriptions, which will include spatial designations of control areas within the project site. These descriptions will be required to include clear demonstration of a storage location for Projects within which carbonated materials are stored (refer to the Carbonated Materials Storage and Monitoring Module).
• Description of measurement methods for all required analyses, cross-referenced with relevant standards where applicable.
• Description of any geochemical models used to quantify processes relevant to the calculation of CO₂ removal that are not directly measurable.
• A comprehensive sampling plan with demonstrated statistical significance.
• A clear outline of compliance with mining/quarrying specific permitting and regulation requirements (where applicable).

Projects must be validated and Project GHG Statement (net CO₂e removal) verified by an independent third party consistent with the requirements described in this Protocol as well as in Section 4 of the Isometric Standard.

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

• Validate that feedstock adheres to the requirements listed in the Rock and Mineral Feedstock Characterization Module 1.0.
• Verify that the quantification approach and monitoring plan adheres to requirements that are outlined within this Protocol.
• Verify that the Environmental & Social Safeguards requirements that will be outlined in this Protocol and the Isometric Standard are met.
• Verify that the Project is compliant with all requirements outlined in the Isometric Standard, OSEM Protocol and any relevant Isometric Modules used as part of the Project Crediting framework.

Within this Protocol, Materiality refers to an acceptable difference between reported removals/emissions and what an auditor determines is the actual removal/emissions.

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

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

• Control issues that erode the verifier's confidence in the reported data.
• Poorly managed documented information.
• Difficulty in locating requested information.
• Noncompliance with regulations indirectly related to GHG emissions, removals or storage.

Project validation and verification must incorporate site visits to Project facilities, including control, baseline and deployment locations, in accordance with the requirements of ISO 14064-3, 6.1.4.2. This is to include, at a minimum, site visits during validation and initial verification to the Project site(s). Validators should, whenever possible, observe Project operation to ensure full documentation of process inputs and outputs through visual observation. A site visit must occur at least once during each Project validation. Additional site visits may be required if there are substantial changes to field operations over the course of a Project's validation period, or if deemed necessary by Isometric or the VVB.

The Project Proponent is required to ensure that the VVB has access to the site for all required site visits. Where an OSEM Project is undertaken on an operational or closed mining/quarrying site, it is the responsibility of the Project Proponent to ensure that access will be made available when required.

Verifiers and validators must comply with the requirements defined in Section 4 of the Isometric Standard. In addition, teams must maintain and demonstrate expertise associated with the specific technologies of interest, including feedstock and soil (where applicable) sampling, analysis and data processing.

CDR via mineralization is often a result of a multi-step process, including for example, mining/quarrying, transporting and deposition of waste/by product feedstocks. As a result, multiple entities may be involved in the process of removals, such as instances where a CDR technology supplier is working directly with a mining operator.

When there are multiple parties involved in the removal process, and to avoid double counting of CO₂e removals, a single Project Proponent must be specified contractually as the sole owner of the Credits at the point of issuance. Contracts must comply with all requirements defined in Section 3.1 of the Isometric Standard.

Where Project Proponents have pre-existing contractual agreements (that have been agreed prior to engagement with Isometric), to undertake Credit splitting, the involved parties are required to engage with Isometric and the VVB to ensure double counting has not occurred. Such Crediting situations will be handled on a Project-by-Project basis. Credits issued by Isometric will only be issued to a single Project Proponent for a designated Crediting Project location over a Reporting Period (RP).

The Project Proponent shall be able to demonstrate additionality through compliance with Section 2.5.3 of the Isometric Standard. The baseline scenarios and counterfactual utilized to assess additionality must be Project-specific and comply with Section 10.3 of this Protocol. In instances where reviews or changes to additionality are undertaken or required, refer to Section 5 of this Protocol.

The uncertainty in the overall estimate of the net CO₂e removal as a result of the Project must be accounted for. The total net CO₂e removed for a specific Reporting Period, RP, (CO₂e_{Removal, RP}), must be conservatively determined in accordance with the requirements outlined in Section 2.5.7 of the Isometric Standard.

Projects must report a list of all input variables used in the net CO₂e removal calculation and their uncertainties, including:

• Required measurements (see Section 12).
• Data used to model and estimate aqueous losses outside the Project site boundaries.
• Emission factors utilized, as published in public and other databases used.
• Values of measured parameters from process instrumentation, such as truck weights from weigh scales, electricity usage from utility power meters and other similar equipment.
• Laboratory analyses, including analysis of rock or mineral feedstocks.

More detailed uncertainty information should be provided if available, as outlined in Section 2.5.7 of the Isometric Standard.

In addition, a sensitivity analysis that demonstrates the impact of each input parameter's uncertainty on the overall net CO₂e removal uncertainty must be provided. Details of the sensitivity analysis method must be provided so that the results can be re-created. Input variables may be omitted, but should be listed, if they contribute to a < 1% change in the net CO₂e removal.

In accordance with the Isometric Standard, all evidence and data related to the underlying quantification of CO₂e removal and environmental and social safeguards monitoring will be available to the public through Isometric's platform. This includes:

• Project Design Document
• Greenhouse Gas Statement
• Measurements taken and supporting documentation, such as calibration certificates
• Emission factors used
• Scientific literature used
• Proof of approval for necessary permits

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. This may include:

• Emissions factors from licensed databases
• Intellectual Property (IP) related to the a Project Proponents process
• GHG data that does not contribute towards Project emission calculations

However, all other numerical data produced or used as part of the quantification of net CO₂e removal will be made publicly available.

Within this Section, the key requirements related to system boundaries, GHG accounting and quantification of removals are outlined.

Project Proponents are required to define the temporal and geographic Project boundary. The Project boundary must include all activities associated with Crediting, including areas where removal mechanisms/processes occur, removed carbon storage locations and potential reversal/loss pathways.

Where a Project activity takes place on a mining or quarry operation, a Project Proponent is required to identify the Project boundary within the existing operation. This will require detailed documentation nof Project baseline scenarios, specifically within the designated Project boundary. Projects will be required to identify control sites/locations within the Project boundary that will serve to validate baseline measurements over the course of the Crediting period. Section 12.4 of this Protocol outlines the requirements for designating a Project control plot.

Project Proponents are required to submit a detailed physical Project boundary description as part of the submitted PDD to the VVB prior to Crediting. This submission should include clear definitions of the Project site, inclusive of storage areas and potential reversal/loss pathways.

As outlined in Section 10.1, Projects are required to provide detailed descriptions of Project boundaries for all Crediting activities. Project boundaries delineate the scope of the Project, specifying which activities, sources, and emissions are included and excluded from the accounting and Crediting framework. The system boundary for GHG accounting sets out the GHG sources, sinks, and reservoirs (SSRs) associated with the Project boundary and to be considered in the GHG statement. A cradle-to-grave GHG statement must be prepared encompassing the GHG emissions relating to the activities outlined within the system boundary. Emissions for processes within the system boundary must include all GHG SSRs from the construction and manufacturing of any Project-specific physical site and associated equipments; closure and disposal of each site and associated equipments; and operation of each process (including feedstock production, transport, pre-treatment and sampling for MRV) to include embodied emissions of consumables in the process. Any emissions from process or sub-processes changes that would not have taken place without the CDR Project, such as subsequent transportation and refining, must be fully considered in the system boundary. Paired with exclusion of waste input emissions when the criteria are met, this allows for accurate consideration of additional, incremental emissions induced by the CDR process. The system boundary must include all SSRs controlled by and related to the Project, including but not limited to the SSRs in Table 3. If any GHG SSRs within Table 3 are deemed not appropriate to include in the system boundary, they may be excluded provided that robust justification and appropriate evidence is provided. Information related to defining a Project Reporting Period can be found in Sections 10.1 and 10.4.1 of this Protocol.

Table 3. Systems boundary and scope of activities to be included for open system ex-situ mineralization Projects

The Project Proponent must consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s (EPA) 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 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.

All GHGs must be quantified and converted to CO₂e in the GHG statement using the 100-yr 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).

Miscellaneous GHG emissions are those that cannot be categorized by the GHG SSRs categories provided in Table 3. 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 SSRs categories identified as miscellaneous emissions.

Emissions associated with a Project's impact on activities that fall outside of the system boundary of a Project must also be considered.

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

OSEM may have additional impacts on GHG emissions beyond the scope of this Protocol. For example, there may be the potential for reduced GHG emissions relating to carbonate dissolution in the presence of AMD, in an instance where OSEM processes delay/restrict the onset of sulfide oxidation within waste facilities. These potential secondary climate effects are uncertain at this time and are not covered by this Protocol version.

Emissions associated with activities that occurred and will continue to occur without the Project may be excluded from the system boundary. For example:

1. Existing electricity consumption of a mining or quarrying operations.
2. Emissions from the use of pre-existing shared transportation infrastructure, such as roads, railways, or conveyor systems if there is no additional transportation infrastructure use associated with the Project.
3. Emissions from the shared use of equipment and integrated processing facilities. However, any additional activities beyond normal operations under a baseline scenario must be accounted for.
4. Feedstock transport: When feedstocks are used at their intended end-of-life location, such as being deployed at an existing tailings storage facility (TSF), transportation emissions can be excluded, as the material remains within its designated final use site.

Embodied emissions associated with system inputs considered to be waste products can be excluded from the accounting of the GHG Statement system boundary provided the appropriate criteria are met.

For waste energy inputs, for example the use of waste heat, refer to the Energy Use Accounting Module 1.2.

For all other waste inputs, the following eligibility criteria (EC) shall be considered. If EC1, in Table 4, is satisfied, embodied emissions associated with the waste product input can be excluded from the system boundary. Market leakage emissions associated with waste inputs may also be excluded from the system boundary, as compliance with EC1 would result in no change to the waste producer behavior (i.e. no market leakage) and indicates there are no alternative users of the waste product (i.e. no replacement emissions).

If EC1 is not satisfied, but both EC2 and EC3 in Table 4 are satisfied, embodied emissions associated with the waste product input can be excluded 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 (i.e. no market leakage) and there are no alternative use cases for the waste product (i.e. no replacement emissions).

Table 4. Waste input emissions exclusion criteria, EC1, EC2 and EC3

OSEM processes may be part of a wider mining, quarrying or industrial operation, which may result in the production of co-products such as metal commodities. In this Protocol co-products are defined as products that have a significant market value and are planned for as part of production. By-products are materials of value that are produced incidentally or as a residual of the production process and are not considered here.

To allocate Project emissions associated with CDR and co-product(s), the Project Proponent may use one or a combination of, where relevant, the following co-product allocation procedures outlined below.

Procedure 1: Allocate all emissions to CDR

Projects may opt to allocate all Project emissions to CDR. The co-product(s) must still comply with all relevant emission accounting regulations and requirements, which may mean emissions are double counted. Removals must not be double counted.

Note: This is the most conservative approach to take.

Procedure 2: Divide the process into sub-processes

Where possible, the process may be divided into sub-processes. For example it may be possible to isolate processes relating to processing of the co-product, or the OSEM process may be a retrofit/part of an existing process.

Eligibility criteria, evidence requirements and GHG system boundary considerations are set out in Table 5. One of EC4 or EC5 must be satisfied in order to divide the process into sub-processes.

Table 5. Procedure 2 Eligibility Criteria, EC4 and EC5

Procedure 3: Substituting emissions

Project Proponents may substitute the co-product emissions with emissions for an equivalent product and subtract these from total Project GHG emissions. When undertaking this approach the full facility GHG emissions must be included within the system boundary before substitution takes place. In practice, the co-product emissions are substituted with emissions for an equivalent product and subtracted from total Project GHG emissions.

The calculation approach to be followed is set out below:

1. Report the quantity and type for all marketed co-products produced within the Project system boundary.

2. Identify the use of the co-product and the appropriate alternative product (the “substitute product”) considering the product qualities and specific use case.

3. Determine the emissions intensity associated with the substitute product, in line with the following requirements:

   • Where multiple similar substitute products with variable emissions intensities are available, the most conservative substitute product must be selected. This is the substitute product with the lowest emissions intensity.
   • If the use of the product is electricity generation which is supplied to the grid, then the emissions intensity associated with the substitute product will be the average grid intensity of the region for the most recent year.
   • The emissions intensity associated with the substitute product must be conservative, from a Reputable Source and approved by Isometric ahead of verification.
   • Where the product will be subject to policy or regulatory requirements, for example in relation to tax Credits or to satisfy specific marketing claims, the most conservative threshold for emissions intensity shall be selected.

4. The quantity of merchantable co-products sold should be multiplied by the approved substitute product emissions intensity factor to determine the total substituted emissions.

5. The total substituted emissions should be subtracted from $CO₂e_{Emissions}$ (see Section 10.5). Both the gross Project emissions, and the adjusted Project emissions post-substitution must be documented.

In order to ensure that the substitution method yields a conservative result, the following safeguards are in place:

• Only one co-product may be used for substitution. This should be the primary co-product, meaning the co-product which results in the highest revenue stream and is not CDR.
• Only substitution factors approved by Isometric may be used. Isometric approved substitution factors will include factors used in government regulation, provided such factors are conservative.
• The outcome of step 4 must not result in higher emissions than the gross Project emissions.

Procedure 4: Carbon mass balance if the co-product leads to Crediting

Physical allocation based on carbon mass balance shall be used in instances where the co-product leads to Crediting for CDR with Isometric. This is so that emissions are distributed according to the CO₂ balance output of the system. The requirement for Crediting to be with an Isometric Project ensures that co-product allocation can be traced and verified appropriately and according to the same set of allocation and emissions accounting requirements. The co-product allocation between CDR products can be made after process subdivision and substitution has taken place.

Baselines are required to be quantified in line with Section 2.5.2 of the Isometric Standard. The baseline scenario for OSEM Projects assumes no activities associated with the Project have taken place, and assumes that business-as-usual industrial practices occur. A Project Proponent is required to quantify counterfactual carbon removals from the atmosphere that would have been durably stored (>1,000 years) as a result of natural/passive weathering under baseline conditions. Measurements and modeling used to quantify a Project's counterfactual under baseline conditions should be carried out in line with Section 12 of this Protocol.

As the rate of carbon mineralization process occurs is variable and can be affected by climate, seasonal change, weather systems and infrastructure design, a Project-specific baseline (counterfactual) must be established. In addition, baseline measurements should be carried out both prior to Project implementation and throughout the Project duration. Baseline monitoring should be carried out on a designated control plot, within the Project deployment area. Counterfactual measurements should take place over the same Reporting Period as the Crediting measurements, at the same temporal and spatial frequency and density, refer to Section 12.4.

A Project's counterfactual under baseline conditions is required to calculate CO₂e net removal over a Reporting Period (RP), in line with the guidance outlined in Section 10.5 of this Protocol. Project Proponents are required to clearly define baseline scenarios and counterfactual quantification within the PDD upon submission to Isometric and the Project VVB.

This Section outlines the required quantification framework for calculating net CDR removal from a Project. This Section also outlines how Project Proponents must designate a Reporting Period (RP) and quantify emissions within outlined CDR calculations.

OSEM typically involves the utilization of processed materials as a substrate for CO₂ removal and storage. This process begins with the sourcing of raw materials, which may require transportation, processing (e.g., grinding) and activation before they are suitable for mineralization. A combination of chemical and physical measurements are then used to quantify the total CO₂ removals over a period of time.

The $RP$ for OSEM represents an interval of time over which CO₂ removals are quantified and reported for verification. Monitoring of CO₂ removals must include a combination of discrete sampling (e.g., TSF sampling) and/or continuous monitoring techniques. The formulas used to calculate net $CO_2e_{Removals}$ within this Protocol account for all greenhouse gas (GHG) emissions associated with Project activities, as well as CO₂ removals that occur as a direct result of Project intervention over the $RP$. Net carbon removals must be calculated based on monitoring of a Project’s deployment area (Section 12) and counterfactual deductions based on baseline scenario measurements over the $RP$.

Note: In most cases, this $RP$ will be an interval of time bounded by sampling events. Project Proponents are required to clearly define sampling intervals and RPs for Crediting Projects within the PDD. Data submitted for a defined RP must clearly outline the GHG emissions accounted for in that period, as well as counterfactual measurements taken from the defined Project control plot, (Section 12.4.1.3).

GHG emissions calculations must encompass all emissions related to or allocated to the Project activities during the $RP$. This may include:

• Any emissions linked with the initial setup of the Project, such as preprocessing of the materials allocated to the RP;
• Emissions occurring within the RP itself from, for example, land use change emissions and operational Project emissions;
• Anticipated emissions expected after the RP but attributed to it; such as land use change that leads to increased CO₂ release over time. In this way, emissions beyond RP will still be accounted for;
• Leakage emissions that happen outside of the Project boundary due to induced market shifts associated with the RP;

The guidelines for assigning emissions to Reporting Periods are detailed in Section 10.2.

$CO_2e_{Removed, RP}$ from OSEM Projects within individual Reporting Periods (RP) can be calculated as follows. A Project's $CO_2e_{Removed, RP}$ is quantified by calculating the gross quantity of CO₂ removed in the Project scenario, subtracting the loss portion and accounting for the total GHG emissions associated with the Project in a predefined Reporting Period. The final $CO_2e_{Removed, RP}$ Quantification must be conservatively determined and supported with solid evidence (e.g., data and geochemical models), giving high confidence that, at a minimum, the reported amount of CO₂e was removed. Equation 14 outlines the basic framework for quantification of net Project removals over a set Reporting Period ($CO_2e_{Removed, RP}$).

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

(Equation 14)

Where:

• $CO_2e_{Removed, RP}$ is the total quantity of net CO₂e removal for the Reporting Period, RP, in tonnes of CO₂e
• $CO_2e_{Stored, RP}$ is the total quantity of CO₂ removed from the atmosphere based on quantification measurements for the RP, in tonnes of CO₂e
• $CO_2e_{Counterfactual, RP}$ is the total counterfactual CO₂ removed from the atmosphere and stored as inorganic carbon in the soil or aqueous form for the RP, in tonnes of CO₂e
• $CO_2e_{Emissions, RP}$ is the total GHG emissions for the RP, in tonnes of $CO_2e$

Note: Reversals occur after Credits have been issued so are not included in this equation. See Section 12.2 and Section 5 of the Isometric Standard for further information.

$CO_2e_{Stored, RP}$ is calculated as:

$CO_2e_{Stored, RP} = CO_2e_{Drawdown, RP} - CO_2e_{Losses, RP}$

(Equation 15)

Where:

• $CO_2e_{Drawdown, RP}$ is the amount of CO₂ removed from the atmosphere as a result of OSEM processes. The value for this parameter may come from direct measurements of the mineralized material and process water in the vicinity of mineralization, or through gas phase measurements (provided that the mineralization setting is reasonably isolated from other significant sources or sinks of CO₂ such as biological respiration and photosynthesis).
• $CO_2e_{Losses, RP}$ is representative of the inorganic carbon lost due to (bio)geochemical processes for the Reporting Period, RP, as well as downstream riverine and marine, in tonnes CO₂e. This term will primarily pertain to Projects seeking Credits for carbon stored as dissolved inorganic carbon (DIC) that may leave the Project site, and may include processes such as non-carbonic acid neutralization and losses due to carbonate system re-equilibration in rivers or oceans.

Project Proponents have two options for quantification and validation of OSEM removals:

Quantification Option 1 - Quantification with solid- and aqueous-phase geochemical measurements and local validation by gas-flux measurements

Quantification Option 2 - Quantification with gas-flux measurements and local validation by solid- and aqueous-phase geochemical measurements

Project Proponents should consider aspects such as signal-to-noise ratios, inherent heterogeneity of feedstock and other relevant Project site environmental factors when choosing their primary quantification medium. These quantification and validation options are addressed in detail in the sections that follow.

Equation 16 outlines the calculation of $CO_2e_{Stored, RP}$ for Projects that quantify removals using Quantification Option 1:

$CO_2e_{Stored, RP} = CO_2e_{Mineral, RP} + CO_2e_{Aqueous, RP} - CO_2e_{RiverineLoss, RP} - CO_2e_{MarineLoss, RP} - CO_2e_{Misc, RP}$

(Equation 16)

Where:

• $CO_2e_{Mineral, RP}$ is the total quantity of CO₂ stored via mineral storage during a Reporting Period, in tonnes of CO₂e;
• $CO_2e_{Aqueous, RP}$ is the total quantity of CO₂ stored via aqueous phase storage during a Reporting Period, in tonnes of CO₂e. This term implicitly includes any non-carbonic acid neutralization that may occur in the Project site.
• $CO_2e_{RiverineLoss, RP}$ is the total amount of $CO_2e_{Aqueous, RP}$ that is expected to be released back to the atmosphere due to outgassing in river systems, in tonnes of CO₂e;
• $CO_2e_{MarineLoss, RP}$ is the total amount of $CO_2e_{Aqueous, RP}$ that is expected to be released back to the atmosphere due to outgassing in the ocean, in tonnes of CO₂e;
• $CO_2e_{Misc, RP}$ is the total amount of $CO_2e_{Aqueous, RP}$ that is expected to be released back to the atmosphere not in the categories above, such as through dissolution of carbonates by interaction with acidic fluids, in tonnes of CO₂e.

The Project Proponent is eligible to Credit for CO₂ removal when $CO_2e_{Stored, RP}$ can be fully accounted for by CO₂ storage in both the mineral and aqueous phases. Project Proponents must follow the monitoring, measurement and modeling approaches outlined in Section 12 of this Protocol.

Additionally, it is noted that a Project Proponent must consider relative uncertainty around reporting aqueous storage over a Reporting Period. To claim aqueous removals, a Project Proponent is required to consider downstream losses (see Section 12.5.2).

Below is a brief overview of how each term in Equation 16 is determined, with more details provided in Section 10.5.2 to Section 10.5.7.

$CO_2e_{Mineral, RP}$ represents the amount of CO₂e that is stored in the mineral phase over the course of the Reporting Period. This term must be determined through direct measurement of representative samples that are collected from the Project site. Guidance for representative sampling can be found in Section 4 of the Rock and Mineral Feedstock Characterization Module 1.0. Analytical methods that quantify carbon content, carbonate mineral type and abundance are acceptable for determining $CO_2e_{Mineral, RP}$(see Section 12.5 for details) .

$CO_2e_{Mineral, RP} = CO_2e_{Mineral, t=1} - CO_2e_{Mineral, t=0}$

(Equation 17)

Where:

• $CO_2e_{Mineral, t}$ the amount of CO₂ stored as carbonate minerals at time point t, in tonnes. $CO_2e_{Mineral, RP}$ will be determined from the difference in carbonate content from the beginning to the end of a Reporting Period.

$CO_2e_{Aqueous, RP}$ is the amount of CO₂e that is stored in the aqueous phase (as dissolved inorganic carbon) over the course of the Reporting Period. This includes all aqueous phase alkalinity that will be exported from the Project site to groundwater, rivers and ultimately the ocean. $CO_2e_{Aqueous, RP}$ may be determined by characterization of representative samples of porewater, ground water or process water within and beneath the region in which active mineralization is occurring. Characterization of representative aqueous phase samples will include either direct measurement of multiple carbonate system variables or direct measurements of cation and anion abundances (see Section 12.5). Since this term considers either the dissolved inorganic carbon present or the cation and anion abundance in fluids, this term implicitly considers the impact of non-carbonic acid neutralization on the net removal.

$CO_2e_{RiverineLoss, RP}$ includes all future losses that will occur in river systems downstream of in-field activities. In most cases, this will be a modeled result. Models used to estimate riverine losses must use historic river geochemical data to estimate relevant parameters. This may include publicly available datasets or scientific publications. The source of such data must be reported. Models must include explicit consideration of:

• Formation of new carbonate minerals outside of $CO_2e_{Mineral, RP}$
• Outgassing of CO₂ due to re-equilibration of DIC system

$CO_2e_{MarineLoss, RP}$ includes all future losses that will occur after the alkalinity is exported to the ocean. This must include explicit consideration of:

• Formation of new carbonate minerals outside of $CO_2e_{Mineral, RP}$
• Outgassing of CO₂ due to re-equilibration of DIC system $CO_2e_{Misc, RP}$ includes any Project specific considerations that may impact the net amount of carbon stored as a result of Project activities. This may include processes whose effects on carbon removal occur during or after the Project activities such as secondary mineral precipitation other than carbonate or leaching of alkaline components leading to downstream carbonation.

Equation 18 outlines the calculation of $CO_2e_{Stored, RP}$ for Projects that quantify removals using Quantification Option 2:

$CO_2e_{Stored, RP} = CO_2e_{GasFlux, RP} - CO_2e_{RiverineLoss, RP} - CO_2e_{MarineLoss, RP} - CO_2e_{Misc, RP}$

(Equation 18)

Where:

• $CO_2e_{Gas flux, RP}$ is the total quantity of CO₂ stored as determined by gas flux measurements over the course of the Reporting Period, in tonnes of CO₂e. In this instance, gas flux will represent the net flux of CO₂ into the mineralized feedstock, and will likely integrate storage in solid and aqueous phases, and may include applicable local loss terms, such as non-carbonic acid neutralization.
• $CO_2e_{RiverineLoss, RP}$ is the total amount of $CO_2e_{Aqueous, RP}$ that is expected to be released back to the atmosphere due to outgassing in river systems, in tonnes of CO₂e;
• $CO_2e_{MarineLoss, RP}$ s the total amount of $CO_2e_{Aqueous, RP}$ that is expected to be released back to the atmosphere due to outgassing in the ocean, in tonnes of CO₂e;
• $CO_2e_{Misc, RP}$ is the total amount of $CO_2e_{Aqueous, RP}$ that is expected to be released back to the atmosphere not accounted for in the parameters previously described, in tonnes of CO₂e.

Below is a brief overview of how each term in Equation 18 is determined:

$CO_2e_{Gas flux, RP}$ represents the net flux of CO₂ between the atmosphere and a feedstock that is undergoing mineralization. This will include direct measurement through eddy-covariance measurements and gas flux chambers. The Project Proponent must demonstrate that the gas flux measurements are not subject to appreciable influence from other biogeochemical reactions that produce and consume CO₂, such as photosynthesis and respiration. This can be done through a combination of approaches, including direct measurement of organic carbon in, underneath and in the vicinity of mineralization, demonstrating that the area is free of photosynthetic organisms, and inclusion of a control area into the net removal calculation (described in Section 12.5.1). Project Proponents must employ measurement approaches, as detailed in Section 12.4, to ensure that CO₂ capture is attributable to geochemical and mineralogical storage processes.

The suitability of $CO_2e_{Stored, RP}$ based on gas flux measurements will be evaluated on a Project-by-Project basis, taking into account the Project’s design, configuration, measurement equipment, and monitoring and verification plans to confirm that CO₂ removal metrics reflect actual drawdown exclusive of biological artifacts.

Gas flux measurements demonstrate that CO₂ has infiltrated the system, but do not distinguish between storage in the liquid and solid phases. Thus, when gas flux measurements are utilized for the quantification of carbon removals, the Project Proponent must constrain the fraction of mineralized carbon that may leave the Project site in the aqueous phase and apply downstream losses accordingly. The loss of CO₂ from the aqueous phase to the atmosphere can occur through re-equilibration of the carbonic acid system through pH change, water evaporation, mineral precipitation, and temperature change. Project Proponents are required to provide an estimated water budget and flow path to the final storage reservoir for CO₂ stored in the aqueous phase. This may be demonstrated through hydrogeologic mapping, implementation of physical barriers that impede infiltration or direct measurements of porewater or groundwater to constrain the local water budget. Downstream losses that cannot be directly measured must be estimated through geochemical models, as described in (refer to Section 12.7). Aqueous phase losses are required to be reported as $CO_2e_{RiverineLoss, RP}$ , $CO_2e_{MarineLoss, RP}$ and $CO_2e_{Misc, RP}$, see Section 12.5.2 of this Protocol.

$CO_2e_{Counterfactual, RP}$ is defined as the amount of CO₂ that would have been stored in the aqueous or solid phase as a result of passive weathering of the feedstock used, without Project intervention, across a Reporting Period. This Protocol requires the utilization of a control plot for explicit determination of counterfactual (baseline) carbon removal (see Section 12.4.1). A Project Proponent must collect the same suite of measurements, with the same temporal and spatial density, for quantifying removals in the control plot to directly measure counterfactual baseline. The control plot serves as the baseline for quantifying removals

If the Project is associated with an active mining operation, the Project Proponent may base Project activities and calculations on the mine’s tailings deposition timelines over the life of mine (LOM), so long as relevant monitoring and verification planning documentation is included in the PDD. Alternatively, where documentation demonstrates that waste piles of the feedstock are only exposed to the environment for a limited duration, the counterfactual determination can be confined to that period.

In some instances, counterfactual mineralization may not be readily observable using a control plot. For example, if a Project utilizes mine tailings that are located in an environment that is inaccessible, and they tailings are relocated as part of a Project activity, a control plot would not capture an appropriate mineralization baseline. In such instances, a Project Proponent may address estimating a counterfactual mineralization baseline through a combination of direct measurement and geochemical modeling.

Geochemical models must be justified by empirical data from sampling of the feedstock; guidelines for sampling procedures that adequately capture feedstock heterogeneity are described in the Rock and Mineral Feedstock Characterization Module 1.0. Models must take into account:

• Feedstock mineralogy (direct measurement)
• Feedstock chemistry, including major and trace elements (direct measurement)
• Feedstock surface area (direct measurement)
• Baseline mineral carbon content of the feedstock pile (direct measurement)
• CDR potential of the feedstock in the top meter (100cm) of the feedstock (calculated from direct measurements), where possible
• Environmental conditions of the source site (direct measurement or publicly available data), including:
  • Temperature
  • Hydrogeology condition (water level, discharge rate, infiltration rate) (direct measurement)
  • Precipitation
  • Rainwater pH
  • Groundwater pH
  • Carbonate saturation
  • Porosity & Permeability (direct measurement or calculated from direct measurement)
  • Water saturation (direct measurement or calculated from direct measurement)
  • Any applicable microbial influences

The measurements or geochemical models used to quantify counterfactuals must be reported within the PDD upon submission to Isometric and the Project VVB.

$CO_2e_{Emission, RP}$ is the total quantity of GHG emitted associated with a Reporting Period. The term should be the sum of each activity's emissions. Equation 19 outlines how $CO_2e_{Emission, RP}$ is calculated within this Protocol:

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

(Equation 19)

Where:

• $CO_2e_{Emissions, RP}$ is the total GHG emissions for a Reporting Period, RP, in tonnes of CO₂e
• $CO_2e_{Establishment, RP}$ is the total GHG emissions associated with Project establishment for a RP, in tonnes of CO₂e
• $CO_2e_{Operations, RP}$ is the total GHG emissions associated with operational processes for a RP, in tonnes of CO₂e
• $CO_2e_{End-of-Life, RP}$ is the total GHG emissions that occur after the RP and are allocated to the RP, in tonnes of CO₂e
• $CO_2e_{Leakage, RP}$ is the total 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

Note: $CO_2e_{Baseline\ Emitted, RP}$ = 0 where there are no process emissions from the mine that occur in both the baseline and the Project scenario, and therefore are not included in this emissions term.

The following Sections set out specific quantification requirements for each variable. It is anticipated that most emissions associated with Ex-situ mineralization Projects will occur during the calculation of $CO_2e_{Establishment, RP}$ and $CO_2e_{Operations, RP}$..

GHG emissions associated with $CO_2e_{Establishment, RP}$ should include all historic emissions incurred as a result of Project establishment, including but not limited to the SSRs set out in Table 3.

Project establishment emissions occur from the point of Project inception through to after the operational event has taken place. GHG emissions associated with Project establishment may be allocated in one of the following ways, with the allocation method selected and justified by the Project Proponent in the PDD:

• As a one time deduction to the first Reporting Period(s)
• Allocated over the anticipated Project lifetime as annual emissions
• Allocated per output of product (i.e., per ton CO₂ removed)

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

Allocation of $CO_2e_{Establishment, RP}$ emissions to removals must be reviewed at each Crediting Period renewal and any necessary adjustments made. If the Project Proponent is not able to comply with the allocation schedule described in the PDD (e.g., due to changes in delivered volume or anticipated Project lifetime), the Project Proponent should notify Isometric as early as possible in order to adjust the allocation schedule for future removals. If that is not possible, the Reversal process will be triggered in accordance with the Isometric Standard, to account for any remaining emissions.

Embodied emissions associated with equipment that is built for CDR purposes but used across multiple CDR Projects owned by the Project Proponent may be shared proportionally across Projects. For example this may be based on total equipment capacity and Projected throughput of all combined Projects. Projections and actual equipment use must be reviewed at each Crediting Period for each Project and adjustments must be made where required. In cases where the Project Proponent ceases operations for all Projects with an outstanding emissions debt, the emissions must be taken out of the buffer pools proportionally for all Projects that used the equipment.

GHG emissions associated with $CO_2e_{Operation, RP}$ should include all emissions associated with operational activities including but not limited to the SSRs set out in Table 3.

$CO_2e_{Operation, RP}$ emissions occur over the Reporting Period for the deployment being credited and are applicable to the current deployment only. $CO_2e_{Operation, RP}$ 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 Reporting Period, but are directly or indirectly related to the Reporting Period and Project activities. For example, this could include ongoing sampling activities for MRV for the specific deployment (directly related) if applicable, or end-of-life emissions for Project facilities (indirectly related to all deployments).

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

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

Given the uncertain nature of $CO_2e_{End-of-Life, RP}$ emissions, assumptions must be revisited at each Crediting Period and any necessary adjustments made. Furthermore, if there are unexpected $CO_2e_{End-of-Life, RP}$ 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.

$CO_2e_{Leakage, RP}$ 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. This includes emissions associated with activity-shifting, market leakage and ecological leakage. It is the Project Proponent's responsibility to identify potential sources of leakage emissions.

$CO_2e_{Leakage, RP}$ 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.

This Section of the Protocol outlines requirements for open systems ex-situ mineralization emissions accounting relating to energy use, transportation, and embodied emissions associated with a CDR Project.

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

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

• Electricity consumption for equipment for drying rock or mineral feedstock after milling

Examples of fuel consumption may include, but are not limited to:

• Handling equipment, such as fork trucks or loaders
• Fuel consumption of machinery for spreading, material manipulation, tilling, and sampling

The Energy Use Accounting Module 1.2 provides guidance on how energy-related emissions must be calculated in a CDR Project so that they can be subtracted in the net $CO_2e_{Removed}$ calculation. It sets out the calculation approach to be followed for intensive facilities and non-intensive facilities and acceptable emissions factors.

This Section sets out specific requirements relating to quantification of emissions related to transportation.

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

• Transportation of feedstock to the Project location (where applicable)
• Transportation of rock from quarry to crushing site
• Transportation and shipping related to collecting samples for environmental monitoring

The Transportation Emissions Accounting Module 1.0 provides guidance on how transportation-related emissions must be calculated in a CDR Project so that they can be subtracted in the net $CO_2e_{Removed}$ calculation. It sets out the calculation approach to be followed and acceptable emissions factors.

This Section sets out specific requirements relating to quantification of embodied emissions as part of the GHG Statement. Embodied emissions are those related to the life cycle impact of infrastructure, equipment and consumables.

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

• Rock or mineral feedstock and associated production, processing, treatment and transportation equipment
• Sampling equipment and consumable materials such as augers and storage containers
• Raw materials and equipment used in the fabrication, assembly and construction of machinery utilized for spreading, tilling, churning, feedstock manipulation and sampling

The Embodied Emissions Accounting Module 1.0 sets out the calculation approach to be followed including allocation of embodied emissions, life cycle stages to be considered, data sources and emission factors.

This Protocol requires feedstock characterization and reporting in accordance with Isometric's Rock and Mineral Feedstock Characterization Module 1.0.

Table 6 outlines the main measurement/characterization requirements for rock and mineral materials under this Protocol.

Table 6. Feedstock Characterization Requirements and Recommendations

If a Project utilizes techniques outside the scope of the Rock and Mineral Feedstock Characterization Module when characterizing feedstock, a Project Proponent should consult with Isometric to determine the suitability of the suggested methodology/technique. Where an alternative characterization technique has been utilized by a Project Proponent, the full methodology/standard operating procedure (SOP) must be outlined in the PDD upon submission to the VVB, prior to Crediting.

This Section outlines the monitoring, measurement and modeling requirements for Projects seeking Credits under this Protocol.

Monitoring refers to the ongoing systematic observation and tracking of processes, conditions and parameters over time. It involves both the repeated measurement of certain variables and the assessment of trends or changes in those variables to ensure that processes are operating as expected. Effective monitoring also addresses potential reversal risks by identifying early warning signs of deviations from desired outcomes, enabling corrective actions to prevent backsliding and ensure long-term stability.

Measurement refers to the process of quantifying specific parameters or variables using tools, instruments or methodologies. In the context of an OSEM Project, measurement involves determining the exact values of certain indicators, such as: $CO_2e_{Counterfactual, RP}$, $CO_2e_{Stored, RP}$, $CO_2e_{Drawdown, RP}$, and $CO_2e_{Losses, RP}$.

Monitoring and measurement requirements for the storage of stable carbonate minerals can be found in the Isometric Carbonated Materials Storage and Monitoring Module. Where a Project process deviates from the requirements of this storage Module, or other requirements outlined in the following Sections of this Protocol, a Project Proponent is required to engage with Isometric, prior to Crediting, to assess the suitability of proposed methods.

The durability of removed carbon refers to the length of time that CO₂ is sequestered in stable forms, preventing its re-release into the Earth’s atmosphere. In the context of OSEM, CO₂ is stored in two primary forms: alkalinity/dissolved inorganic carbon (DIC) in the aqueous phase and solid carbonates in the mineral phase. The long-term stability of these reservoirs is critical to the Project's overall success in achieving durable carbon removal.

Under applicable removal strategies a significant portion of the sequestered CO₂ is stored as solid carbonates (e.g., calcite, magnesite) in the mineral phase. Once dissolved inorganic carbon reacts with cations, like calcium (Ca²⁺) and magnesium (Mg²⁺), released through the weathering of alkaline feedstocks, it forms stable carbonate minerals. These carbonates are chemically stable over geological timescales, with durability in excess of 1,000 years when isolated from acid and in undersaturated conditions.

Dissolved alkalinity charge-balances bicarbonate (HCO₃⁻) and carbonate (CO₃^2-) ions, allowing CO₂ to be stored in the aqueous phase. This aqueous storage, particularly when it reaches stable environments like deep groundwater or ocean systems, can sequester carbon over long timescales (1,000+ years). Dissolved inorganic carbon (DIC) stored in the ocean or other stable reservoirs can be credited under this Protocol ^{62 63 51} .

The Project Proponent is required to demonstrate the durability of removed carbon and account for any reversals within the Project lifetime through the implementation of an ongoing storage monitoring plan. This monitoring plan must encompass the Project's operational phase, closure and post closure. Monitoring plans implemented by the Project Proponent must be clearly outlined within the PDD upon submission to Isometric and the Project VVB. Specific requirements related to the long-term monitoring of carbonated materials and aqueous CO₂ storage can be found in Section 4.2 of the Carbonated Materials Storage and Monitoring Module and Section 12.5.2 of this Protocol.

Based on present scientific understanding, OSEM Projects are categorized as having a “Very Low Risk Level of Reversal” according to the Isometric StandardRisk Assessment Questionnaire. While the risk is currently considered minimal, a conservative 2% buffer pool of Credits will be set aside, allowing for any future reassessment of reversal risks as new scientific research emerges. This buffer ensures that even if future data identifies unforeseen risks, the overall integrity of the carbon removal Credits is maintained.

The reversal risk of OSEM using mine tailings as a feedstock may also arise when secondary mining activities (such as re-mining) disturb previously stabilized carbonates, potentially re-releasing CO₂ into the atmosphere. This risk is heightened in sulfide bearing tailings, where oxidation can lead to acid formation that dissolves carbonates, refer to Section 6 for feedstock applicability conditions. Additionally, some feedstocks may pose a risk of reversal from reprocessing, whereby future economic conditions or technological advancements make reprocessing of mineralized feedstock viable. Project Proponents must work in consultation with Isometric to identify such Project specific risks. Project specific risks may elevate the Project to “Low Risk Level of Reversal,” with a corresponding buffer pool of 5%.

Any reversals that do occur will be accounted for and addressed through mechanisms outlined in Section 5.6 of the Isometric Standard. This includes ongoing monitoring and reassessment of the stability of stored carbon, ensuring that any reversals are properly managed and that carbon removal remains verifiable over the long term. Project Proponents are required to undertake storage reversal monitoring in line with Section 4.1.2 of the Carbonated Materials Storage and Monitoring Module.

Site characterization is required to demonstrate the suitability of the deployment/storage location for durable storage of carbonated materials; characterization must include an assessment of the local and regional hydrogeology, as well as potential leakage pathways. Storage site characterization is required to be carried out in line with Section 2 of the Carbonated Materials Storage and Monitoring Module.

Note: Where a Project takes place within an existing industrial operation, such as a mine site, a Project Proponent may submit pre-existing data related to site characterization. The suitability of pre-existing characterization data will be considered on a Project by Project basis, by Isometric, prior to Crediting.

This section outlines the possible quantification and monitoring approaches that Project Proponents can undertake when Crediting under this Protocol. Several of the monitoring requirements described below include measurements that will be used in the quantification of CO₂ stored, captured and determination of removals (see Section 10.5 of this Protocol).

A Project is an area or group of areas that are to be managed together for the purposes of deployments and Crediting. A single Project Proponent may choose to have multiple Projects deployments, each with an individual PDD, or group operations under a single Project. All deployments and sampling events across a Project must follow a similar schedule, as defined in the PDD.

When designing a Project’s measurement and monitoring plan a Project Proponent has the choice between two frameworks under this Protocol: the 2-plot and the 3-plot approach. These approach frameworks are described in the following Sections and summarized in Table 7. Figure 2 shows a schematic of indicative 2 and 3 plot approaches that may be employed under this Protocol.

Table 7. Summary of Project Area

Figure 2 Schematic of in-field monitoring approaches, illustrating the relative size of the control, treatment, and deployment plots in the 3- and 2-plot approaches.

The 2-plot approach for quantifying CO₂ removals via OSEM calls for the designation of the Project site into one of two categories:

• Control Plot - An area utilized to assess the Project counterfactual, demonstrating representative passive CO₂ removal under baseline conditions
• Treatment Plot - An area encompassing CO₂ removal activities undertaken by the Project Proponent, which will be used to quantify creditable removals resulting from Project activities

The 3-plot approach allows for collection of high-resolution data from OSEM Projects on a smaller scale, while enabling lower-resolution monitoring across the remainder of the Project site. In this setup, the Project site is divided into three distinct sections: control, treatment, and deployment areas, defined as follows:

• Control: An area utilized to assess the Project counterfactual, demonstrating representative passive CO₂ removal under baseline conditions.
• Treatment: A densely monitored area where CO₂ removal from the application of mineral feedstock is measured in detail, providing high-resolution data on carbon mineralization performance.
• Deployment: A less densely monitored area where CO₂ removal from mineral feedstock application is tracked at a broader scale.

Unless specified otherwise, data collected in each of these areas will be used to quantify CO₂ removal specifically within that area (e.g., samples from the deployment area are used to quantify removals in that area). In some cases, data from the treatment area may be extrapolated to the deployment area to quantify metrics that may not be quantifiable at the scale of the deployment area, for example solid and aqueous samples for Projects where Quantification Option 2 has been employed.

The purpose of the control plot(s) is to quantify the baseline carbon removal or emissions that would occur naturally in the absence of Project intervention. The control plot area must represent at least 2.5% of the total project area. The control plot should remain untreated over the Project Reporting Period, reflecting baseline conditions without any additional interventions by the Project Proponent.

The treatment plot encompasses the Project site where rock or mineral feedstock is treated for the purpose of carbon removal. Typically, this plot covers 97.5% (2-plot) or 2.5% (3-plot) of the defined Project site and is monitored according to the Project’s monitoring and sampling plans. The treatment plot encompasses the Project site on which rock or mineral feedstock is applied or treated for the purpose of carbon removal. The treatment area will be subject to monitoring as prescribed by the Project monitoring and sampling plans.

The deployment area encompasses the remaining Project site not included within the control or treatment plots and typically represents 95% of the total Project site.

The Project Proponent must designate one or more control plot areas that are representative of the Project’s treatment plot/deployment area. Project Proponent should assess the representativeness of control plots when designating areas within the Project deployment. Such assessments should consider aspects including, but not limited to, climatic conditions (such as temperature, annual precipitation rate, precipitation pH), storage conditions (such as porewater pH), hydrology, lithology and the chemical properties of alkaline feedstocks (e.g., mineral type and abundance and particle size) within the Project site. Hydrological assessments are especially important for plots located on a TSF, as aqueous transport paths and exported fluids need to be assessed for accurate quantification of potential losses/reversals.

All data used to determine the representativeness of control, treatment and deployment (in 3-plot models) plots must be documented in the PDD. Where public or partner data is unavailable, a detailed characterization of the alkaline feedstocks (e.g., mineral surveys) must be performed, following the requirements in the Rock and Mineral Feedstock Characterization Module 1.0. Control plots should represent both the central tendencies and variance of relevant continuous variables .

Clear boundaries of all plots, including GPS coordinates and deployment maps, must be provided in the PDD. The use of buffer zones at plot boundaries is required to avoid cross-contamination between treatment and control plots. Where buffer zones are not able to be implemented, Project Proponents should engage with Isometric and provide clear justification to the omission of buffer zones within the PDD.

The control plot must be maintained under business-as-usual operational practices, and should be utilized to measure and monitor counterfactual baseline weathering rates over the Project Reporting Period (RP). Table 7 outlines minimal area designations required for Projects utilizing 2- or 3-plot models under this Protocol.

Under this Protocol’s Crediting frameworks, a combination of solid, aqueous and gaseous phase measurements are required to demonstrate durable carbon removals via OSEM, (see Section 10.4). Sampling plans should be designed to accurately assess net CO₂ removal, efficiency of removal activities, leakage/reversals and environmental safeguarding.

Sampling depth for solid and aqueous sampling within a Project site must be stated and justified in the PDD. The justification should include evidence that the depth range captures the relevant geochemical processes.

The following sampling details must be reported and justified in the PDD:

• Sampling Frequency and Timing
• Sampling Locations
• Sample Types and Properties
• Sample Size and Volume
• Analytical Techniques (including minimum detection limits)
• Data Quality and Control

The number of samples needed should be designated on a Project by Project basis, depending on the size of the Project site and heterogeneity of the utilized alkaline feedstock.

For aqueous samples, such as pore water, groundwater, surface water and leachate, which are used to quantify CO₂ removals and undertake environmental monitoring, Project Proponents must include and document measurements in line with the requirements outlined in Section 12.5 (refer to Table 8).

Sampling techniques, designs, methodologies and equipment must be documented in the PDD, and any changes to sampling procedures must be approved by Isometric.

This Section provides guidance on determining the number of control and treatment samples needed to demonstrate statistical significance under this Protocol.

The sampling density utilized to quantify carbon removal and environmental monitoring must be determined based on the variability observed during the feedstock characterization. In areas with low variability, the number of sampling points may be reduced while still ensuring that the data remains statistically representative. However, in zones exhibiting high measurement variability, the number of sampling locations must be increased proportionally to accurately capture spatial differences in feedstock composition. The total number of sampling points should be sufficient to cover the entire Project site. In some instances, repositioning sampling equipment during the monitoring period is allowed to achieve broader spatial coverage, ensuring that measurements reflect the full scope of the carbon removal processes across the treatment and control plots.

Equation 20 provides an estimate of the minimum number of samples needed to achieve statistical significance, assuming normally distributed data:

$N \geq \frac{2\sigma^2Z\sigma^2}{S_{min}^2}$

(Equation 20)

Where:

• N is the number of samples needed for statistical significance
• σ is the standard deviation of parameters been measured, such as base cation concentration (or other geochemical signal of mineralization) over an area of interest
• $Z_\alpha$ is the the Z-score associated with the significant level of interest (1.96 for two-tailed, 1.645 for one-tailed)
• $Smin$ the minimal detectable changes which the project aims to statistically validate. This could be changes in baseline cation concentration or other geochemical signals of mineralization from the beginning to the end of the Reporting Period. This value helps determine the sensitivity of the study — the smaller the value of $Smin$, the larger the sample size required to statistically detect such a change.

With a rearrangement of the formula based on the mean of the quantifying measurement, the Project Proponent can derive the minimum number of samples needed to achieve statistical significance. It is recommended that the Project Proponent uses a conservative estimate for S_min when using this equation to determine the number of samples needed for statistical significance.

This Section outlines the key measurements that will be required by a Project Proponent to demonstrate removals, emissions and quantify potential reversals. Project Proponents have two options for quantification and validation of OSEM removals (as outlined in Section 10.5.1.1):

Quantification Option 1 - Quantification with solid- and aqueous-phase geochemical measurements and local validation by gas-flux measurements

Quantification Option 2 - Quantification with gas-flux measurements and local validation by solid- and aqueous-phase geochemical measurements.

Local validation checks need only be collected in the control and 2.5% of the Project site (or the treatment plot in the 3-plot approach).

Under this Protocol, the following measurement types are required for removal quantification and validation:

• Gaseous Phase Measurements: Measurement of gas flux and composition can be used to quantify $CO_2e_{Stored, RP}$. Direct quantification of the gas phase represents the gross CO₂e stored, without adjustments for any losses from the removal process; these losses should be accounted for during monitoring and verification to ensure accurate net storage values.
• Solution/Aqueous Measurements: Characterization of aqueous phases is required to quantify and calculate parameters such as $CO_2e_{Stored, RP}$ and $CO_2e_{Counterfactual, RP}$, especially when gas-phase measurement is the primary method for quantification. This characterization is also essential when aqueous and solid phases are the primary storage mechanisms for $CO_2e_{Stored, RP}$. Additionally, these measurements are required to account for any CO₂e losses and gains within the aqueous phase.
• Physical/Solid phase Measurements: Characterization of solid phases are required to quantify and calculate parameters such as $CO_2e_{Counterfactual, RP}$ and $CO_2e_{Stored, RP}$ in mineral phase, especially when gas-phase measurement is the primary method for quantification. This characterization is also essential when aqueous and mineral phases are the primary storage mechanisms of $CO_2e_{Stored, RP}$.

Table 8 summarizes the required and recommended measurements for quantification and validation. Solid phase measurement techniques should follow the guidance outlined within Isometric Rock and Mineral Feedstock characterization. The measurement requirements and recommendations outlined in Table 8 should be applied to control, treatment and deployment plots (where applicable) by the Project Proponent.

Where a Project Proponent deviates from the required measurement techniques, or has developed a novel technique or procedure that satisfies the purpose of a required measurement, a Project may still be considered for Crediting under this Protocol. In such an instance, the Project Proponent is required to submit the alternative method to Isometric for assessment and approval, prior to Credit issuance or removal validation within a Reporting Period (RP). Where alternative measurements have been used by a Project Proponent, the methodology and rationale for use must be outlined clearly in the PDD upon submission to Isometric and the Project VVB.

Table 8. Measurement requirement and recommendation summary

Note: Where a parameter is required or recommended for a specific Quantification Option this has been outlined in bold text within this table.

Where applicable, analytical methods must be cross-referenced with an appropriate standard (e.g., ISO, EN, BSI, ASTM, EPA) or standard operating procedure (SOP). Where a Project utilizes a non-standardized methodology or SOP for the determination of a listed parameter, the Project Proponent is required to outline the relevant method within the PDD submitted to the Validation and Verification Bodies (VVB).

Where a Project Proponent utilizes gas phase measurements for quantification or validation of net Project removals, a comprehensive monitoring plan is required. Removals may be quantified via quantification option 2 (or verified in quantification option 1, see Section 12.5) via CO₂ flux measurements collected using eddy-covariance and dynamic-closed chambers.

Where a Project Proponent utilizes solid and aqueous phase measurements to quantify net removals, Project Proponents must use gas phase monitoring to validate removals (Quantification Option 1). Project Proponents are not required to quantify gas composition, pressure and temperature, although these measurements are recommended for all Projects.

If the Project location facility (e.g., alkaline waste facility or TSF) does not have a liner (such as a geo-membrane) the Project Proponent is required to measure gas compositions and undertake a biological assessment of the underlying material to determine the potential influence on gas flux measurements. This should be carried out within the control and deployment plots to account for variations across the Project site.

Gas phase measurements are required to be carried out at day and night, in order to account for diurnal cycles, for both quantification option 1 and 2.

Gas phase measurement plans should be clearly outlined in the PDD. The installation methodologies, device types and sampling frequency must be outlined in the PDD. Project Proponents should ensure that the same device types and procedures are used for the RP to maintain consistency in data collection. Any changes in device type or sampling methods must be approved by Isometric.

Projects must directly measure porewater as part of a comprehensive monitoring plan. Porewater must be sampled at a frequency that is appropriate considering the local hydrology, precipitation, and temporal evolution of dissolved ions. The water sampling plan must be described and justified in the PDD. The sampling plan should additionally consider events that significantly impact moisture content, such as heavy rainfall and extreme weather events; this will be determined on a Project- and event-specific basis. All fluid sampling devices (porewater, groundwater, and process water) must be installed and maintained consistently throughout the Project. The installation methodology, device types and sampling frequency must be outlined in the PDD. Project Proponents should ensure that the same device types and procedures are used for the Project duration to maintain consistency in data collection. Any variations in device type or sampling methods must be approved by Isometric.

In some instances, it may be appropriate to implement groundwater or mine process water monitoring as part of a comprehensive monitoring plan for either removal quantification or estimation of downstream losses. In such instances, the Project Proponent must describe the monitoring plan in the PDD, including frequency, specific analyses, and how these measurements will be used as part of carbon accounting.

Project Proponents utilizing aqueous measurements must complete a full suite of fluid characterization measurements. A comprehensive monitoring plan of aqueous phase samples must be designed in line with Section 12.4, Table 8 and Appendix 3, to ensure accurate tracking of CO₂e stored, alkalinity flux and potential environmental impacts (See Section 8).

Analytical Methods and Standards

All water samples should be analyzed using standardized methods suitable for high-accuracy environmental monitoring. Common techniques include:

• Cation and anion analysis - Ion Chromatography (IC), ICP-MS and/or ICP-MS
• Measurement of at least two carbonate system parameters

Carbonic acid system measurements may include carbonate alkalinity titration to the CO₂ equivalence point, pH, DIC and/or pCO₂, followed by calculating the concentration of bicarbonate using the 2-for-6 method. Calibration and maintenance records for all instruments must be kept up-to-date and made available for audit, ensuring data accuracy and consistency over the Project’s lifetime.

Aqueous phase CO₂ storage must also consider the potential for downstream reversal, including outgassing associated with carbonate system re-equilibration in streams, rivers, or the ocean. Project Proponents must identify potential flow paths for aqueous phases and the final storage reservoir, whether that is located at the Project site or eventually transported to the ocean. A reversal risk monitoring plan must include an assessment of flow paths within and outside the defined Project boundaries for a deployment.

Geochemical modeling of aqueous phase storage and interactions with the wider environment may be used to quantify downstream losses associated with carbonate system equilibration. It is recommended that such models consider:

• pH of the reservoir and the alkaline fluid
• Carbonate saturation state
• Discharge & recharge rate
• Groundwater flow rate
• Hydraulic conductivity & gradient

Further guidance on utilizing models to quantify downstream aqueous losses can be found in Section 12.7 of this Protocol.

CO₂ stored in aqueous phase represents a stable and durable mechanism for CO₂ removal, as dissolved bicarbonate and carbonate ions can persist over long periods, especially in deep groundwater or marine systems with long alkalinity residence times. However, CO₂ degassing may occur during the downstream transport of captured CO₂ to the ocean, resulting in reversal/leakage of stored carbon. This may occur through the following processes when exported alkalinity is transported out of the Project site:

• Re-equilibration and outgassing in groundwater and/or river networks
• Calcium or Magnesium carbonate precipitation in groundwater and/or river networks

Leakage as a result of re-equilibration of the carbonic acid system occurs following the CO₂ dissolution in aqueous solution reactions listed in Equations 4-6 in Section 7.1.2.

Speciation of dissolved inorganic carbon (DIC) is pH-dependent, and mixing of two fluid parcels can result in outgassing from re-equilibration of these dissolved species.

Ca²⁺, Mg²⁺ and/or Fe²⁺ carbonate forms through the reaction shown in Equation 21:

$M^{2+}(aq) + 2HCO_3^{-}(aq)\rightarrow MCO_3(s) + H_2O(l) +CO_2(g)$