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Open System Ex-situ Mineralization
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This Protocol (A document that describes how to quantitatively assess the net amount of CO₂ removed by a process. To Isometric, a Protocol is specific to a Project Proponent's process and comprised of Modules representing the Carbon Fluxes involved in the CDR process. A Protocol measures the full carbon impact of a process against the Baseline of it not occurring.) provides the requirements and procedures for the calculation of carbon dioxide equivalent (CO2e) (The amount of CO₂ emissions that would cause the same integrated radiative forcing or temperature change, over a given time horizon, as an emitted amount of GHG or a mixture of GHGs. One common metric of CO₂e is the 100-year Global Warming Potential.)removals (The term used to represent the CO₂ taken out of the atmosphere as a result of a CDR process.) 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 (Raw material which is used for CO₂ Removal or GHG Reduction.) 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 (Activities that remove carbon dioxide (CO₂) from the atmosphere and store it in products or geological, terrestrial, and oceanic Reservoirs. CDR includes the enhancement of biological or geochemical sinks and direct air capture (DAC) and storage, but excludes natural CO₂ uptake not directly caused by human intervention.)pathways (A collection of Removal or Reduction processes that have mechanisms in common.). Projects (An activity or process or group of activities or processes that alter the condition of a Baseline and leads to Removals or Reductions.) 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 (Describes the addition of carbon dioxide removed from the atmosphere to a reservoir, which serves as its ultimate destination. This is also referred to as “sequestration”.) 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 (Any process or activity that releases a greenhouse gas, an aerosol, or a precursor of a greenhouse gas into the atmosphere.) 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 modelling (A calculation, series of calculations or simulations that use input variables in order to generate values for variables of interest that are not directly measured.) 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 (The organization that develops and/or has overall legal ownership or control of a Removal or Reduction Project.) 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 (Independent components of Isometric Certified Protocols which are transferable between and applicable to different Protocols.). Figure 1 displays the storage, feedstock characterization and Greenhouse Gas (GHG) Statement (A document submitted alongside Claimed Removals and/or Reductions that details the calculations associated with a Removal or Reduction, including the Project's emissions, Removals, Reductions and Leakages, presented together in net metric tonnes of CO₂e per Removal or Reduction.) Modules that are linked to requirements throughout this Protocol.
[Image: **Figure 1**]
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:
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:
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:
Additional reference standards that inform the requirements and overall practices incorporated in this Protocol will include:
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:
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) (The multi-step process to monitor the Removals or Reductions and impacts of a Project, report the findings to an accredited third party, and have this third party Verify the report so that the results can be Certified.) 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 (The amount of time carbon removed from the atmosphere by an intervention – for example, a CDR project – is expected to reside in a given Reservoir, taking into account both physical risks and socioeconomic constructs (such as contracts) to protect the Reservoir in question.) 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 (The escape of CO₂ to the atmosphere after it has been stored, and after a Credit has been Issued. A Reversal is classified as avoidable if a Project Proponent has influence or control over it and it likely could have been averted through application of reasonable risk mitigation measures. Any other Reversals will be classified as unavoidable.) 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 (An evaluation of the likelihood that an intervention—for example, a CDR Project—causes a climate benefit above and beyond what would have happened in a no-intervention Baseline scenario.) 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:
Any review and change in the determination of additionality will not affect the availability of Carbon Finance or carbon Credits (A publicly visible uniquely identifiable Credit Certificate Issued by a Registry that gives the owner of the Credit the right to account for one net metric tonne of Verified CO₂e Removal or Reduction. In the case of this Standard, the net tonne of CO₂e Removal or Reduction comes from a Project Validated against a Certified Protocol.) for the current or past Crediting periods (The period of time over which a Project Design Document is valid, and over which Removals or Reductions may be Verified, resulting in Issued Credits.). 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:
This Protocol applies to Projects and associated operations that meet all of the following conditions:
Applicable removal mechanisms include:
Applicable storage mechanisms include:
Applicable Project Facilities include:
The following feedstocks are considered applicable for use in Crediting Projects under this Protocol:
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 v1.1.
Under this Protocol, the following Project conditions locations are not considered applicable for Crediting:
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:
[math: Mg_3Si_2O_5(OH)_4(s) + 3CO_2(g) \leftrightarrow 3MgCO_3(s) + 2SiO_2(s) +2H_2O(l)]
(Equation 1)
[math: Mg_2SiO_4(s) + 2CO_2(g) \leftrightarrow 2MgCO_3(s) + SiO_2(s)]
(Equation 2)
[math: 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 3131. 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 (CO32-) 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:
First, the dissolution of CO2 in water follows the following reaction mechanism:
[math: CO_2(g) + H_2O(l) \leftrightarrow H_2CO_3(aq)]
(Equation 4)
Dissolution of CO2 in water forming carbonic acid (H2CO3)
[math: H_2CO_3(aq) \leftrightarrow H^{+}(aq) +HCO_3^{-}(aq)]
(Equation 5)
The dissociation of carbonic acid into protons (H+) and bicarbonate (HCO3-)
[math: HCO_3^{-}(aq)\leftrightarrow H^{+}(aq) + CO_3^{2-}(aq)]
(Equation 6)
The further dissociation of bicarbonate into protons ([math: H^{+}]) and carbonate ions ([math: CO_3^{2-}])
Second, the liberation of divalent metals from host minerals, take forsterite dissolution as an example:
[math: 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:
[math: Mg^{2+}(aq) +2HCO_3^{-}(aq) \leftrightarrow Mg(HCO_3)_2(aq) \leftrightarrow Mg(HCO_3)_2(s)]
(Equation 8)
[math: Mg^{2+}(aq) + CO_3^{2-}(aq) \leftrightarrow MgCO)3(s)]
(Equation 9)
[math: 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 11-133334:
[math: Mg_3Si_2O_5(OH)_4(s) + 6HCl(l) + H_2O(l)\leftrightarrow 3MgCl_2\cdot6H_2O(aq) + SiO_2(aq)]
(Equation 11)
[math: MgCl_2(aq_\cdot6H_2O(aq)\leftrightarrow MgCl(OH)(aq) + HCl(aq) + 5H_2O(l)]
(Equation 12)
[math: 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 3334.
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) (Reporting Period). 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:
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 Document (PDD) (The document that clearly outlines how a Project will generate rigorously quantifiable Additional high-quality Removals or Reductions.) upon submission to Isometric and The Project Validation and Verification Body (VVB) (Third-party auditing organizations that are experts in their sector and used to determine if a project conforms to the rules, regulations, and standards set out by a governing body. A VVB must be approved by Isometric prior to conducting validation and verification.). This description must include:
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.
| Treatment Type | Treatment Method | Explanation of Treatment Method | Examples | References |
|---|---|---|---|---|
| Thermal | Thermal activation, heating | Feedstock is heated to accelerate reaction kinetics, undergo dehydroxylation, breakdown crystal structure etc. This method is particularly applicable to serpentine minerals. | Thermally treated serpentine remove hydroxyl group, resulting in chemical transformation that improves the reactivity and CO2 storage capacity of a feedstock. Pre-treatment of feedstock using high intensity electromagnetic radiation (e.g., microwave, x-rays, lasers). For example,when serpentine minerals are exposed to microwave radiation, the high-intensity energy is converted to heat that disrupts the crystal structure and transforms the mineral into an amorphous phase. The process makes Mg2+ more accessible for mineralization. | |
| Chemical | Chemical Reagent addition, acid leaching, increase CO2 concentration | The addition of chemical reagents, strong acids, and an increase in CO2 concentration from ambient levels to flue gas or pure CO2 can improve carbon mineralization kinetics and enhance the conversion rate of aqueous CO2 to bicarbonate, thereby increasing overall reactivity. | Example reagents include:
| |
| Mechanical/Physical | Mineral Activation | Physical and mechanical treatment of feedstock to enhance reactivity. | Grinding feedstock to prevent surface passivation and increase reactive surface areas. The addition of abrasive particles or grinding media to optimize in-situ grinding systems, eliminate the formation of passivated layers, refresh mineral surface, enhance reactive surface area, enhance the reaction rate. |
Project Proponents may choose to undertake physical manipulation of suitable feedstock to:
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
| Treatment Type | Summary/Example of Treatment Method | References |
|---|---|---|
| Surface Manipulation | Surface churning: physical churning and manipulating of a feedstock in order to increase reactive surface area, disperse particles and increase the rate of CO2 uptake and diffusion. Example: Smart churning using an autonomous amphibious rover. | 6061 |
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 (The diversity of life across taxonomic and spatial scales. Biodiversity can be measured within species (i.e. genetic diversity and variations in allele frequencies across populations), between species (i.e. the total number and abundance of species within and across defined regions), within ecosystems (i.e. the variation in functional diversity, such as guilds, life-history traits, and food-webs), and between ecosystems (variation in the services of abiotic and biotic communities across large, landscape-level scales) that support ecoregions and biomes.). 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 (Any person or entity who can potentially affect or be affected by Isometric or an individual Project activity.). 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:
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 (The defined temporal and geographical boundary of a Project.) 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 must 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. Where data submitted has been generated, or collected, by a partner operator, the Project Proponent is still required to submit information related to uncertainty (A lack of knowledge of the exact amount of CO₂ removed by a particular process, Uncertainty may be quantified using probability distributions, confidence intervals, or variance estimates.) analysis, as well as any standard operating procedures (SOP) used by the partner operator. 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 (A systematic and independent process for evaluating the reasonableness of the assumptions, limitations and methods that support a Project and assessing whether the Project conforms to the criteria set forth in the Isometric Standard and the Protocol by which the Project is governed. Validation must be completed by an Isometric approved third-party (VVB).) 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 CO2 as carbonated material must identify their storage type and determine the project-specific reversal risk, as outlined in Sections 4.2 and 4.3 of the Carbonated Materials Storage and Monitoring Module v1.1. Adherence to the requirements and safeguards outlined in this Module must be clearly described in the PDD upon submission to Isometric and the VVB.
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:
In addition to the previously listed requirements, Project Proponents are required to submit the following information in the PDD related to potential Project impacts:
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 must 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 engage with local and regional stakeholders that the project may impact, as defined by a Social Impact Assessment (SIA) where applicable. Where a Project takes place on a mining operation it is recommended that the Project Proponent engage with any relevant worker unions. If a Project Proponent has partnered with a mining operator, stakeholder engagement may be undertaken by the partnered project operator, this may include engagement with local communities and indigenous groups.
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 must 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:
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 (Credits are issued to the Credit Account of a Project Proponent with whom Isometric has a Validated Protocol after an Order for Verification and Credit Issuance services from a Buyer and once a Verified Removal or Reduction has taken place.) 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 (A process for evaluating and confirming the net Removals and Reductions for a Project, using data and information collected from the Project and assessing conformity with the criteria set forth in the Isometric Standard and the Protocol by which it is governed. Verification must be completed by an Isometric approved third-party (VVB).) and evaluation in accordance with this Protocol, and must include consideration of processes unique to OSEM Projects such as:
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:
Within this Protocol, Materiality (An acceptable difference between reported Removals/emissions or Reductions/emissions and what an auditor determines is the actual Removal/emissions or Reduction/emissions.) 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 must 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:
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 must, 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 (Improperly allocating the same Removal or Reduction from a Project Proponent more than once to multiple Buyers.) 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, (CO2eRemoval, 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:
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 (An analysis of how much different components in a Model contribute to the overall Uncertainty.) that demonstrates the impact of each input parameter's uncertainty on the 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:
The Project Proponent can request certain information to be restricted (only available to authorized Buyers (An entity that purchases Removals or Reductions, often with the purpose of Retiring Credits to make a Removal or Reduction claim.), the Registry and VVB) where it is subject to confidentiality. This may include:
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 (The steps of a Project Proponent’s Removal or Reduction process that result in carbon fluxes. The carbon flux associated with an activity is a component of the Project Proponent’s Protocol.) takes place on a mining or quarry operation, the Project Proponent is required to identify The Project boundary within the existing operation. This will require detailed documentation of 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 must 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 (GHG sources, sinks and reservoirs (SSRs) associated with the project boundary and included in the GHG Statement.) 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 (Considering impacts at each stage of a product's life cycle, from the time natural resources are extracted from the ground and processed through each subsequent stage of manufacturing, transportation, product use, and ultimately, disposal.) 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 (Life cycle GHG emissions associated with production of materials, transportation, and construction or other processes for goods or buildings.) 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 (outlined in Section 10.2.1.4) 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
| Activity | GHG sources, sinks and reservoirs | GHG | Scope | Timescale |
|---|---|---|---|---|
| Establishment of Project | Equipment and materials manufacture | All GHGs | Embodied emissions associated with equipment and materials manufactured for Project establishment (lifecycle Modules A1-3). To include product manufacture emissions for equipment, buildings, infrastructure and temporary structures. | Before Project operations start - must be accounted for in the first Reporting Period or amortized in line with allocation rules |
| Equipment and materials transport to site | All GHGs | Transport emissions associated with transporting materials and equipment to The Project site(s) (lifecycle Module A4). | ||
| Construction and installation | All GHGs | Emissions related to construction and installation of The Project site(s) (lifecycle Module A5). To include energy use for construction, installation and groundworks, as well as waste processing activities and emissions associated with land use change. | ||
| Initial surveys and feasibility studies | All GHGs | Any embodied energy and transport emissions associated with surveys or feasibility studies required for establishment of The Project site. | ||
| Misc. | All GHGs | Any SSRs not captured by categories above, for example staff transport. | ||
| Operation | Feedstock sourcing | All GHGs | Quarrying, crushing and grinding (including additional processing steps such as drying) activities including the following emissions sources:
| Over each Reporting Period - must be accounted for in the relevant Reporting Period (See Section 10.4.1) |
| Feedstock characterization | All GHGs | Embodied, energy use and transport emissions associated with sampling the feedstock for physical and geochemical characterization | ||
| Feedstock Pre-Treatment | All GHGs | Embodied, energy use and transport emissions associated with the pre-treatment of feedstocks. This must include:
| ||
| Feedstock transport to the application site | All GHGs | Transporting the feedstock material from the operational facilities or quarrying site to the deployment area - this only applies if the feedstock is transported away from its intended end of life location for the purpose of CDR | ||
| Physical manipulation of feedstock | All GHGs | Embodied, energy use and transport emissions associated with the physical manipulation of feedstocks. This must include:
| ||
| Sampling and analysis | CO2 | Sampling and analysis activities, including:
| ||
| Land use change | CO2 | Additional land use change as a result of Project expansion (not in the industrial footprint). | ||
CO2 stored | CO2 | The gross amount of CO2 removed and durably stored via ex-situ mineralization over a Reporting Period | ||
| Misc. | All GHGs | Any GHG SSRs not captured by categories above, for example: field surveys. | ||
| End of Life | End-of-life of Project facilities | All GHGs | To include anticipated end-of-life emissions (lifecycle Modules C1-4) associated with deconstruction and demolition, transport, waste processing and disposal of any equipment, buildings or infrastructure. | After Reporting Period - must be accounted for in the first Reporting Period or amortized in line with allocation rules (See Section 10.4.1) |
| Closure of storage site | All GHGs | Closure of storage site, including embodied emissions associated with equipment and materials manufacture, transport of equipment and materials to site and emissions associated with energy use and consumables use for closure operations including installation and groundworks, as well as waste processing activities and emissions associated with land use change. | ||
| Misc. | All GHGs | Any emissions source, sink or reservoir not captured by categories above. |
The Project Proponent must consider all GHGs associated with SSRs, in alignment with the United States Environmental Protection Agency’s (EPA) (A United States Government agency that protects human health and the environment.) 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) (A measure of how much energy the emissions of 1 tonne of a GHG will absorb over a given period of time, relative to the emissions of 1 ton of CO₂.) for the GHG of interest, based on the most recent volume of the IPCC Assessment Report (currently the Sixth Assessment Report).
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:
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 (Any emissions that occur to compensate for biomass that was previously serving another purpose and is now being used for carbon removal or GHG reduction. For example, if agricultural waste was previously left on a field to decompose - fertilizer production to replace those nutrients need to be accounted for.)).
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
| Eligibility Criteria | Description | Documentation required |
|---|---|---|
| EC1 | No payment was made for the material or access, or only a “tipping fee” is paid. | Feedstock purchase, removal, or access agreement records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, a signed affidavit from the feedstock supplier stating that no in-kind compensation was made to the feedstock supplier must be provided.
|
| EC2 | The amount of the waste product used by the CDR Project was not already being utilized as a valuable product by another party for non-CDR uses. Therefore, the producer of the waste product has no alternative use case for the waste product. | Feedstock purchase, removal, or access agreement records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, an affidavit from the waste supplier identifying that there are no alternative use cases for the waste product. |
| EC3 | Payments for the waste product do not constitute a significant share of upstream operations revenue for the waste producer. | Feedstock purchase, removal, or access agreement records between Project Proponent and feedstock supplier demonstrating price paid, amount, Buyer, seller and date. Additionally, a purchase agreement of waste material that documents that payments from The Project do not constitute a large share of upstream operations revenue must be provided. |
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
| Eligibility Criteria | Description | Documentation required |
|---|---|---|
| EC4 | Ex-situ mineralization processes is a retrofit to an existing facility that was operable prior to the introduction of the CDR process. The purpose of the existing facility must not have been CDR prior to retrofit. | Records of existing facility activities dating back 3 years must be provided for major infrastructure Projects where a planning application was required. For all other Projects, records of the existing facility activities dating back 6 months is required. The distinction between major infrastructure Projects and other Projects is to ensure that the ex-situ mineralization process is a retrofit, as major infrastructure Project construction may be staged over many years. The GHG system boundary in this case is limited to materials and processes necessary for the retrofit and processes that directly contribute to ex-situ mineralization, including existing processes at the facility that are operated at increased capacity and additional load bearing structures. Evidence of fractional differences in inputs, for example the step-change in energy requirements for the addition of an Ex-Situ Mineralization process as a retrofit to an existing facility, must be evidenced in full. Within this Protocol a 'Major Infrastructure Project' refers to a large-scale construction or developtment project that requires permitting, and may result in significant economic, envrionmental and/or social impacts. The definition of such a Project may differ by Project location and applicable regulations. Within the U.S. a Project defined as a Major Infrastructure Project is likely subject to a NEPA Review. |
| EC5 | The process has components and operations that are physically separate from one another. | Evidence of separation, for example engineering diagrams showing separate equipment or electricity metering systems for separate components of the process. Sub-processes that can be isolated from the CDR process and do not contribute to CDR may be excluded from the system boundary. |
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:
Determine the emissions intensity associated with the substitute product, in line with the following requirements:
The quantity of merchantable co-products sold should be multiplied by the approved substitute product emissions intensity factor to determine the total substituted emissions.
In order to ensure that the substitution method yields a conservative result, the following safeguards are in place:
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 modelling used to quantify a Project's counterfactual under baseline conditions must 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 must be carried out both prior to Project implementation and throughout The Project duration. Baseline monitoring may include a designated control plot and/or feedstock characterization, direct measurment of total inorganic carbon content and/or a project-specific geochemical model. 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 [math: 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 continuous monitoring techniques. The formulas used to calculate net [math: 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 [math: 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 [math: RP].
Note: In most cases, this [math: 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 [math: RP]. This may include:
The guidelines for assigning emissions to Reporting Periods are detailed in Section 10.2.
[math: CO_2e_{Removed, RP}] from OSEM Projects within individual Reporting Periods (RP) can be calculated as follows. A Project's [math: 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 [math: 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 ([math: CO_2e_{Removed, RP}]).
[math: CO_2e_{Removed,\ RP} = CO_2e_{Stored,\ RP} - CO_2e_{Counterfactual, RP} - CO_2e_{Emissions, RP}]
(Equation 14)
Where:
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.
[math: CO_2e_{Stored, RP}] is calculated as:
[math: CO_2e_{Stored, RP} = CO_2e_{Drawdown, RP} - CO_2e_{Losses, RP}]
(Equation 15)
Where:
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 [math: CO_2e_{Stored, RP}] for Projects that quantify removals using Quantification Option 1:
[math: 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:
The Project Proponent is eligible to Credit for CO2 removal when [math: 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 modelling 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.
[math: 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 [math: CO_2e_{Mineral, RP}](see Section 12.5 for details) .
[math: CO_2e_{Mineral, RP} = CO_2e_{Mineral, t=1} - CO_2e_{Mineral, t=0}]
(Equation 17)
Where:
[math: 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. [math: 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.
[math: 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:
[math: 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:
Equation 18 outlines the calculation of [math: CO_2e_{Stored, RP}] for Projects that quantify removals using Quantification Option 2:
[math: CO_2e_{Stored, RP} = CO_2e_{GasFlux, RP} - CO_2e_{RiverineLoss, RP} - CO_2e_{MarineLoss, RP} - CO_2e_{Misc, RP}]
(Equation 18)
Where:
Below is a brief overview of how each term in Equation 18 is determined:
[math: 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 [math: CO_2e_{Stored, RP}] based on gas flux measurements will be evaluated on a Project-by-Project basis, in consultation with Isometric and the Project VVB, 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 of this Protocol and Section 4.3.1 of the Carbonated Material Storage Module v1.1). Aqueous phase losses are required to be reported as [math: CO_2e_{RiverineLoss, RP}] , [math: CO_2e_{MarineLoss, RP}] and [math: CO_2e_{Misc, RP}], see Section 12.5.2 of this Protocol.
[math: 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 that Project Proponents estimate the cumulative counterfactual (baseline) carbon removal. This must include, at a minimum, an estimate of the carbon removal rate over time, and a conservative estimate of the time horizon over which counterfactual carbon removal would have occurred in the absence of the removal activities. A default time horizon of 100 years should be used for estimating counterfactual weathering unless site specific factors indicate a clear and substantial deviation from this time horizon. Any deviation from a 100-year time horizon should be described and justified in the PDD.
Project Proponents must use one or more of the following options to estimate cumulative counterfactual carbon uptake rates over a project Reporting Period:
Table 6 outlines the options for quantifying [math: CO_2e_{Counterfactual, RP}] under this Protocol, with specific reference to required Project documentation and recommended Project use cases. Where possible, it is strongly recommended to use at least two of the options given in this table.
For feedstocks that have not been exposed to surface environmental conditions prior to project commencement, it is recommended that Project Proponents determine counterfactual carbon removal using a control plot and a geochemical model, in line with either a 2-plot or 3-plot model as outlined in Section 12.4.1. For feedstocks that have been exposed to surface environmental conditions, it is recommended that Project Proponents determine counterfactual carbon removal using pre-existing inorganic carbon content and a geochemical model. Where a Project Proponent utilises a control plot, for the explicit determination of counterfactual (baseline) carbon removal, the same suite of measurements, with the same temporal and spatial density, must be employed as the deployment and treatments areas, see Section 12.4.
If the Project is associated with an active mining operation, the Project Proponent may base Project activities and counterfactual calculations on the mine’s tailings, or waste rock, deposition timelines over the life of mine (LOM), so long as all monitoring and verification planning documentation is included in the PDD, upon submission to the Project VVB. Alternatively, where a Project Proponent is able to provide documentation that demonstrates that waste piles of the Project 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 the 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 geochemical characterization, modeling and in field measurements.
In all instances where geochemical models are used, they 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:
The measurements or geochemical models used to quantify counterfactuals must be reported within the PDD upon submission to Isometric and the Project VVB.
Table 6. Options for quantifying [math: CO_2e_{Counterfactual, RP}].
| Quantification Method | Description | Documentation Required | Recommended Project Use |
|---|---|---|---|
| Control plot | Counterfactual carbonation is quantified using samples collected from a subset of the project area. | Sampling plan, including discussion of how feedstock heterogeneity is addressed Measurement technique(s), including SOPs for sample preparation and analysis Metadata for all analyses (see Section 5.1 of the Rock and Mineral Feedstock Characterization Module) Description of how control areas were designated, including data used to determine control area boundaries | Recommended for Projects using feedstock that has not been directly exposed to surface environmental conditions prior to commencement of project activities |
| Direct measurement of exposed feedstock | Quantification of feedstock TIC after a known period of surface exposure allows for the estimation of ambient carbonation rates. These rates can inform counterfactual scenarios over the relevant time horizon. The duration of this exposure period will be determined on a project-specific basis, depending on the project scenario, site conditions, and monitoring approach. | Sampling plan, including discussion of how feedstock heterogeneity is addressed Measurement technique, including SOPs for sample preparation and analysis TIC values Metadata (see Section 5.1 of the Rock and Mineral Feedstock Characterization Module) Calculations for extrapolation Justification for chosen time horizon | Recommended for Projects using feedstock that has been directly exposed to surface environmental conditions prior to commencement of project activities |
| Project-specific geochemical model | Geochemical models validated with empirical measurements of feedstock samples can be used for counterfactual quantification, taking into account the parameters listed in this table. | Sampling plan, including discussion of how feedstock heterogeneity is addressed Measurement technique(s), including SOPs for sample preparation and analysis Metadata for all analyses, including null or missing results (see Section 5.1 of the Rock and Mineral Feedstock Characterization Module) Justification for chosen time horizon Model description and justification for chosen model Model script Results of any sensitivity tests conducted Model output, including error propagation Literature data and external references Version control: Models and scripts must be version-controlled to track updates and maintain transparency Calibration and validation: If models are calibrated using field or lab data, calibration procedures and validation results must be disclosed | Recommended for all Projects |
Note:within this table, the recommendations refer to recommended project use cases; quantification of [math: CO_2e_{Counterfactual, RP}], is a requirement for all Projects.
[math: 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 [math: CO_2e_{Emission, RP}] is calculated within this Protocol:
[math: 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:
Note:[math: 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 [math: CO_2e_{Establishment, RP}] and [math: CO_2e_{Operations, RP}]..
GHG emissions associated with [math: CO_2e_{Establishment, RP}] must 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:
The anticipated lifetime of The Project must be based on reasonable justification and must be included in the Project Design Document (PDD) to be assessed as part of Project validation.
Allocation of [math: 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 must 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 (A common and recognized insurance mechanism among Registries allowing Credits to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.) proportionally for all Projects that used the equipment.
GHG emissions associated with [math: CO_2e_{Operation, RP}] must include all emissions associated with operational activities including but not limited to the SSRs set out in Table 3.
[math: CO_2e_{Operation, RP}] emissions occur over the Reporting Period for the deployment being credited and are applicable to the current deployment only. [math: 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.
[math: CO_2e_{End-of-Life, RP}]includes all emissions associated with activities that are anticipated to occur after the Reporting Period, but are directly or indirectly related to the Reporting Period 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 [math: CO_2e_{End-of-Life, RP}] may occur from the end of the Reporting Period onwards, and typically through to completion of Project site deconstruction and any other end-of-life activities.
GHG emissions associated with activities that are directly related to each deployment must be quantified as part of that Reporting Period. GHG emissions associated with activities that are indirectly related to all deployments may be allocated in the same ways as set out in [math: CO_2e_{Establishment, RP}].
Given the uncertain nature of [math: CO_2e_{End-of-Life, RP}] emissions, assumptions must be revisited at each Crediting Period and any necessary adjustments made. Furthermore, if there are unexpected [math: CO_2e_{End-of-Life, RP}] emissions associated with a Reporting Period, or The Project as a whole, that occur after The Project has ended, then the Reversal process will be triggered to compensate for any emissions not accounted for.
[math: CO_2e_{Leakage, RP}] includes emissions associated with a Project's impact on activities that fall outside of the system boundary of a Project.
It includes increases in GHG emissions as a result of The Project displacing emissions or causing a knock on effect that increases emissions elsewhere. 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.
[math: CO_2e_{Leakage, RP}] emissions must be attributed to the Reporting Period in which they occur. Allocation may be permitted in certain instances, on a case by case basis in agreement with Isometric.
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:
Examples of fuel consumption may include, but are not limited to:
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 [math: CO_2e_{Removed}] calculation. It sets out the calculation approach to be followed for intensive facilities and non-intensive facilities and acceptable emissions factors.
Refer to Energy Use Accounting Module for the calculation guidelines.
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:
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 [math: CO_2e_{Removed}] calculation. It sets out the calculation approach to be followed and acceptable emissions factors.
Refer to Transportation Emissions Accounting Module for the calculation guidelines.
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:
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.
Refer to Embodied Emissions Accounting Module for the calculation guidelines.
This Protocol requires feedstock characterization and reporting in accordance with Isometric's Rock and Mineral Feedstock Characterization Module 1.0.
Refer to Rock and Mineral Feedstock Characterization Module for the calculation guidelines.
Table 7 summarises the main measurement/characterization requirements for rock and mineral materials under this Protocol. Detailed requirments are outlined within Isometric's Rock and Mineral Feedstock Characterization Module 1.0.
Table 7. Feedstock Characterization Requirements and Recommendations
| Parameter | Purpose of measurement | How should this be determined? |
|---|---|---|
| Mineralogy | Assessment of weathering potential Assessment of safety (e.g., presence of asbestiform minerals) | Required: XRD Mineral mapping with SEM-EDS/EDX (e.g., QEMSCAN) Geological maps and information on rock source location Recommended: Light-microscopy Raman spectroscopy Wavelength-dispersive XRF |
| Particle Size Distribution (PSD) | Assessment of weathering potential Assessment of safety | Required: Gravimetric Sieving Recommended: Particle size analyzer (e.g., laser granulometry) |
| Trace and major elemental composition | Assessment of weathering potential Assessment of safety, mineral dissolution and precipitation | Required: ED-XRF WD-XRF Total digestion of rock (e.g., fusion or multi-acid (HF+HNO3+HCl) digestion) coupled with ICP-MS/OES |
| Total Carbon and Sulfur | Assessment of baseline inorganic and organic carbon content Assessment of acidity production potential | Required: Dry Combustion (Elemental Analysis) – for Total Carbon (TC) and Total Sulfur (TS) Recommended: Acidification and CO2 Measurement – for Inorganic Carbon (IC) Calcimeter Analysis – for Inorganic Carbon (IC) Loss-on-Ignition (LOI) – for Organic Matter Estimation Thermogravimetric Analysis (TGA) – to separate Organic and Inorganic Carbon by heating stages Carbon-13 Nuclear Magnetic Resonance (NMR) – for detailed organic carbon analysis Fourier Transform Infrared Spectroscopy (FTIR) – for analyzing carbon bonding and organic carbon types |
| Surface area | Assessment of weathering potential | Required: Brunauer-Emmett-Teller (BET) surface area (determine the specific surface area of solid materials based on gas adsorption measurements) Recommended: Geometric surface area (calculated from particle size) |
If a Project utilizes techniques outside the scope of the Rock and Mineral Feedstock Characterization 1.0 Module when characterizing feedstock, a Project Proponent must 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 modelling 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: [math: CO_2e_{Counterfactual, RP}], [math: CO_2e_{Stored, RP}], [math: CO_2e_{Drawdown, RP}], and [math: 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 v1.1. 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, heat and stored in undersaturated conditions.
Dissolved alkalinity charge-balances bicarbonate (HCO3-) and carbonate (CO32-) 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 626351 .
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 pathways for CO2 loss from carbonated materials, along with definitions of storage types (open vs. closed systems) and the methodology for assessing reversal risk, are detailed in Section 4 of the Carbonated Materials Storage and Monitoring Module v1.1 and Section 12.5.2 of this Protocol.
Based on present scientific understanding, OSEM Projects are generally categorized as having a “Very Low Risk Level of Reversal” according to the Isometric Standard Risk 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. ProjectMore Proponentsrisk mustof workreversal information is given in consultationAppendix with Isometric to identify such Project specific risks. Project specific risks may elevate The Project to “Low4: Risk Level of Reversal Questionnaire,” with afurther correspondinginformation bufferprovided poolwithin ofthe 5%relevant storage module.
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 the Carbonated Materials Storage and Monitoring Module v1.1, which details specific pathways for CO2 loss from carbonated materials, definitions of storage types (open vs closed vs high-risk systems), and the methodology for assessing reversal risk.
Site characterization is required to demonstrate the suitability of the deployment location for durable storage of carbonated materials. This must include classification of the storage system as either “open” or “closed” or "high-risk" based on its exposure to environmental conditions, an assessment of local and regional climate and environmental conditions, and identification of potential CO2 loss pathways from the carbonated materials. Storage site characterization is required to be carried out in line with Section 4.2 and should follow the requirements listed in Appendix 1 of the Carbonated Materials Storage and Monitoring Module v1.1.
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 and the Project VVB, 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).
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 8. Figure 2 shows a schematic of indicative 2 and 3 plot approaches that may be employed under this Protocol.
Table 8. Summary of Project Area
| Area Designation | 2-plot Project Recommended Area | 3-plot Project Recommended Area |
|---|---|---|
| Control Plot | 2.5% Project site | 2.5% of Project site |
| Treatment Plot (Credited deployment area) | 97.5% of Project site | 2.5% of Project site |
| Deployment | Not applicable | 95% of Project site |
[Image: **Figure 2**]
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.
Where Projects take place on an active tailings storage facility (TSF), Project Proponents are required to assess the frequency of new tailings deposition within control and treatment/deployment areas. The area chosen for control plots must be representative of the deployment and treatment areas. Where tailings deposition rates are variable between the control and treatment/deployment areas, the Project Proponent is required to report deposition rates and the potential implications of variable deposition on net CDR calculations and the project counterfactual calculations.
The 2-plot approach for quantifying CO2 removals via OSEM calls for the designation of The Project site into one of two categories:
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:
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. In instances where a Project Proponent plans to extrapolate data collected from the treatment area to the deployment area, the Project Proponent is required to consult with Isometric and the Project VVB, to ensure the suitability of the extrapolation, data accuracy and transparency.
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. It is recommended that the control plot area represent at least 2.5% of the total project area. The control plot must remain untreated over the Project Reporting Period, reflecting baseline conditions without any additional interventions by the Project Proponent. Alternatives to maintaining a control plot for quantifying counterfactual carbon update are described in Section 10.5.2.
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.
Project's utilizing a control plot to quantify counterfactual carbon uptake must designate one or more control plot areas that are representative of the Project’s treatment plot/deployment area. Project Proponent must assess the representativeness of control plots when designating areas within The Project deployment. Such assessments must 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 must 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 must engage with Isometric and provide clear justification to the omission of buffer zones within the PDD.
Control plots, when used, must be maintained under business-as-usual operational practices, and must be utilized to measure and monitor counterfactual baseline weathering rates over the Project Reporting Period (RP). Table 8 outlines the recommended 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 must 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 must include evidence that the depth range captures the relevant geochemical processes.
The following sampling details must be reported and justified in the PDD:
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 9).
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 must 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:
[math: N \geq \frac{2\sigma^2Z\sigma^2}{S_{min}^2}]
(Equation 20)
Where:
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 Smin 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:
Table 9 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 1.0. The measurement requirements and recommendations outlined in Table 9 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 9. Measurement requirement and recommendation summary
| Phase | Measurements | Required or Recommended | Reason for measurements |
|---|---|---|---|
| Gaseous Phase Measurements | CO2 fluxes via e.g., eddy-covariance and dynamic-closed chamber | Quantification Option 1 - Required Quantification Option 2 - Required | Validation and quantification of CO2 fluxes which encompass both flow rate and amount of CO2 in a given volume of air or gas mixture allows:
|
| Non-CO2 Gas composition | Quantification Option 1 - Recommended Quantification Option 2 - Recommended | Analyze overall composition of gas stream (e.g., presence of other gasses like oxygen or nitrogen) as well as measuring trace gasses. | |
| Gas pressure and temperature | Quantification Option 1 - Recommended Quantification Option 2 - Recommended | Temperature affects the solubility of CO2 in solution; Partial pressure of gas influences reaction kinetics; both must be measured, both temporally and spatially for Project related activities. | |
| Solution/Aqueous Measurements | Mineral saturation | Required | Composition of any fluids (leachate/groundwater) within the storage sites. This should be collected via a monitoring well or “leachate collection pipeline” within The Project site. Solution/aqueous measurements provide insight into the interactions between CO₂, minerals and the aqueous solution, allowing:
|
| Depth to fluid | Required | ||
| Temperature | Recommended | ||
| pH | Required | ||
| Alkalinity | Required | ||
| Electrical conductivity | Recommended | ||
| Dissolved Inorganic Carbon (DIC) | Required | ||
| pCO2 | Recommended | ||
Major cations (e.g., Mg2+, Ca2+, Na+, K+, Fe2+/Fe3+, Mn2+) | Required | ||
Major anions (e.g., HCO3-, Cl-, SO42-, NO3-) | Required | ||
| Total dissolved solids | Recommended | ||
| OPR (Oxidation-Reduction Potential) | Recommended | ||
| Solid Phase Measurements | Mass of feedstock | Required | Solid measurements can be used to quantify mineralized CO2 . Solid phase measurements also allows:
|
| Total inorganic carbon (TIC) | Required | ||
| Mineral composition | Required | ||
| Major and trace elements | Required | ||
| Particle size distribution | Quantification Option 1 - Required Quantification Option 2 - Recommended | ||
| Surface area | Quantification Option 1 - Required Quantification Option 2 - Recommended | ||
| Porosity | Quantification Option 1 - Required Quantification Option 2 - Recommended | ||
| Morphology and microstructure | Recommended | ||
| Temperature & pressure | Recommended |
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).
Deviations from the analytical requirements listed above will be considered by Isometric science team on a case by case basis. Approved deviations must be described in the PDD.
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 must 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.
In instances where Project Proponents quantify and validate CO2 removals with aqueous-phase measurements — for example, by including porewater CO2 storage as part of their carbon removal quantification — direct measurement of porewater must be incorporated into the comprehensive monitoring plan. In such cases, porewater must be sampled at a frequency appropriate to local hydrology, precipitation, and the temporal evolution of dissolved ions. The water sampling plan must be described and justified in the PDD, upon submission to the project VVB. 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.
Projects that do not include CO2 storage in porewater or downstream waters as part of their carbon accounting are recommended to collect direct measurement of porewater as part of a comprehensive monitoring plan. Monitoring of downstream losses through groundwater or process water measurements may be appropriate, depending on the project design and storage location. Where such monitoring is implemented, the Project Proponent must describe the plan in the PDD, including sampling frequency, specific analyses types, and an outline of how these measurements will be incorporated into the carbon accounting framework under this Protocol.
All aqueous sampling devices, used for 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 9 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 must be analyzed using standardized methods suitable for high-accuracy environmental monitoring. Common techniques include:
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.
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 modelling 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:
Further guidance on using models to quantify downstream aqueous losses and assess reversal risk from interactions between carbonated materials and aqueous can be found in Section 12.7 of this Protocol and Section 4.3.1 of the Carboanted Material Storage and Monitoring modeule v1.1.
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:
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:
[math: M^{2+}(aq) + 2HCO_3^{-}(aq)\rightarrow MCO_3(s) + H_2O(l) +CO_2(g)]
(Equation 21)
Where:
Carbonate formation in river systems must be quantified separately from carbonate formation in feedstocks as rivers represent an open system where dissolved CO2 may degas across the water surface. Any carbonate formation will result in a loss of 50% of the corresponding exported alkalinity.
The fate of exported alkalinity during river transport remains poorly constrained. To account for potential downstream losses, Project Proponents seeking Credits for aqueous phases alkalinity are required to model expected losses based on expected feedstock dissolution rate, watershed chemistry and river basin chemistry. These models should be based on publicly available historic watershed and river network data. Several recent publications have discussed modelling approaches that combine baseline river geochemical data, equilibrium modelling of water chemistry and scenarios of OSEM in ultramafic tailings 6465. For example, to characterize Mg-carbonate precipitation, 66 demonstrated that carbonate saturation state (SIm) may be calculated as follows for magnesite:
[math: SI_m = log_{10}\left(\frac{\alpha_{Mg^{2+}}\times\alpha_{CO_3^{2-}}}{K_{sp,m}}\right)]
(Equation 22)
With:
[math: K_{sp, m} = \alpha_{sat, Mg^{2+}} \times \alpha_{sat, CO_3^{2-}}]
Where:
When [math: SI_m] > 0, a river is considered supersaturated
Geochemical models of riverine losses must include the following parameters in both the full river network through which dissolved weathering products will be transported and the groundwater that drains from the deployment field to the river network:
Project Proponents are required to submit a detailed description of their modelling approach, including the model used, the river/watershed data, measurements used in model construction and the source of that data, in the PDD.
For OSEM Projects, such as those using ultramafic mine tailings, the ultimate storage reservoir for CO2 sequestered as alkalinity may include bicarbonate (HCO3-) and carbonate (CO32-) ions in the ocean. However, when the generated alkalinity reaches marine environments, similar processes to those observed in river systems can lead to reductions in the overall amount of CO2 effectively removed. These reduction mechanisms are important to consider for accurate quantification of net carbon removal:
Carbonate Precipitation
Once alkalinity enters the ocean, carbonate precipitation can occur, reducing the amount of DIC stored in bicarbonate form. This precipitation process can happen either abiotically or through biological mediation, particularly in surface waters where specific biogeochemical conditions support calcifying organisms. Calcium and magnesium carbonate precipitation reduces the storage efficiency of CO2, as the bicarbonate reservoir becomes partly converted into solid mineral phases that do not persist as dissolved forms of carbon. Because of the small volumes of export anticipated from OSEM Projects, it is unlikely that exported alkalinity will significantly impact the carbonate saturation of the ocean basin; thus, carbonate precipitation is not considered further here.
Re-Equilibration of Dissolved Inorganic Carbon (DIC)
Upon entering the ocean, the newly introduced alkalinity may undergo re-equilibration due to changes in pH, temperature, and salinity, which impact the balance of bicarbonate, carbonate, and dissolved CO2 species. Typically, ocean waters have a higher pH than inland waterways, resulting in a shift toward greater concentrations of carbonate ions (CO32-) within the DIC pool. This shift in speciation slightly reduces the CO2 removal efficiency as it increases the proportion of carbonate ions relative to bicarbonate ions, leading to a reduction in the total CO2 stored in the ocean as a result of the mineralization process.
While these processes introduce a level of reduction in total CO2 storage, it is necessary to account for these factors upfront, given that the timescales and spatial scales over which CO2 reaches the ocean are too extensive for direct monitoring over a Reporting Period. Depending on The Project location and the hydrological system, the time it may take for removed CO2 to reach marine systems could span decades, with marine dilution further dispersing the generated alkalinity.
Quantifying Carbon Losses
Projects with removals that include exported DIC must consider losses that result from re-equilibration upon entering the ocean. A Project Proponent can account for these potential losses using either applicable scientific literature or thermodynamic modelling of the carbonate system. The equation for uptake efficiency developed by Renforth and Henderson (2017)67 quantifies the change in total DIC as a function of the change in total alkalinity (Defined as an excess of proton acceptors over proton donors, which functionally describes the ability of a solution to neutralize acids to the CO₂ equivalence point.) upon reaching the ocean, providing a tool for estimating these impacts. In such instances a Project Proponent would be required to identify which ocean basin their deployment site drains into, based on river catchment flows. Oceanographic conditions identified from publicly available locationally-specific time-series data, such as the NOAA climate indices list, OceanSODA-ETHZ, or equivalent. This data should be used to quantify uptake efficiency and to determine the appropriate deduction for marine loss. These variables may also be calculated using softwares such as CO2SYS or PyCO2SYS. The Project Proponent must include a detailed description of how oceanic losses are determined in the PDD.
Project Proponents are required to undertake solid phase measurements as part of a comprehensive monitoring plan. Solid phase measurements must be used to quantify or validate net Project removals, especially when gas phase measurements are the core measurements used to quantify removal (Quantification Option 2). A detailed monitoring plan is required for solid phase sampling within control, treatment and deployment (3-plot approach) plots within a Project site . Solid phase measurements may be conducted through periodic sampling and analysis of the solid matrix to evaluate inorganic carbon content increase, mineralogical transformations, and other relevant indicators of net carbon removal. Project Proponents must specify the sampling strategy, including frequency, depth, and location, in accordance with the characteristics of The Project site and targeted solid materials.
The sampling plan must be clearly outlined in the Project Design Document (PDD) and justified based on the project’s geological and mineralogical context. Sampling should account for any events that could influence the solid phase, such as mining operations, waste deposition activities, or environmental events that might impact carbon removal rates. Sample preparation and analysis methods must also be undertaken in line with Isometric’s Rock and Mineral Feedstock Characterization Module 1.0. Project Proponents are required to clearly document the type of analyses (e.g., mineral carbonation assessment, carbon content determination) and laboratory techniques utilized for all solid phase measurements.
Where the presence of other media (such as soil and peats) may impact carbon storage estimates, Project Proponents are required to include a biological and chemical assessment of these materials, both in the control and deployment plots. Measurement and monitoring plans are required to be designed to account for heterogeneity in solid-phase measurements across The Project site. Specific guidance for monitoring mine Tailings are outlined in Section 12.6.3 of this Protocol.
All solid sampling devices and Protocols must be consistent throughout The Project to ensure reliable data collection. Any modifications to device types or analytical procedures must be approved by Isometric.
Project Proponents are recommended to measure non-carbonate mineral formation during OSEM processes. Secondary minerals that may form as a result of the reaction between CO2, water and the alkaline materials include clays and hydroxides, such as Layered Double Hydroxide (LDH) group minerals which could enhance the reactivity of the system and promote further CO2 uptake. Secondary hydroxides and clays should be investigated through mineral identification and quantification analysis such as X-ray diffraction (XRD), short-wave infrared technologies (SWIR), hyperspectral imaging (HSI) that are adopted commonly in industries such as mining exploration. Further mineralogical and chemical analysis, such as scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), are recommended for additional quantification. Secondary clay formations are difficult to quantify using widely accessible techniques at this time, and will not be counted towards CDR quantification.
While these mineral formation dynamics are central to developing a mechanistic understanding of OSEM, explicit quantification of these mineral phases is not required. Any reversals that result from secondary mineral phase formation within The Project site during Project activities will otherwise be accounted for in the quantification measurements outlined in this Protocol.
Theoretical maximum removal potential of a feedstock material, based on an adjusted version of the Steinour Equation (see Section 3.4.1.1 of the Isometric Rock and Mineral Feedstock Characterization Module 1.0) is required for all Projects.
Elemental abundance data should be produced according to methods prescribed in the Rock and Mineral Feedstock Characterization Module 1.0. The calculated CDR potential represents the upper limit of creditable removals for a single batch of feedstock as defined in the Rock and Mineral Feedstock Characterization Module 1.0. Project Proponents are required to report the CDR potential of each batch of feedstock used pursuant to Project activities in the PDD.
The use of an alternative calculation of a feedstock's maximum removal potential may be utilized by a Project Proponent. The suitability of alternative methods will be assessed on a Project by Project basis. Project Proponents must engage with Isometric to determine the suitability of alternative quantification methods.
Storage monitoring should focus on ensuring the long-term stability and integrity of the stored carbon within The Project deployment/storage location. Effective storage monitoring involves a combination of geochemical, geophysical, and environmental techniques to track the stability of the sequestered carbon, detection of potential leakage, and monitoring of environmental impacts, directly or indirectly related to The Project activity. Section 4 of the Carbonated Materials Storage and Monitoring Module v1.1 outlines requirements for classifying storage systems, assessing reversal risks, conducting site characterization, and implementing appropriate monitoring approaches that Project Proponents must follow for Crediting Projects.
Project Proponents are required to implement measures, from Project conception, to prevent reversals and leakage. If any reversal or leakage, as highlighted in Section 12.2, is detected from the storage site, or there is greater than 5% deviations from utilized models, the Project Proponent must undertake corrective measures as set out in The Project monitoring plan. Where reversals are confirmed through direct measurements or ongoing monitoring, a Project Proponent may be required to complete additional monitoring or measurements to fully quantify reversals . Changes to monitoring plans due to the identification of Project reversals will be assessed and approved by Isometric on a Project by Project basis. Where leakage is potentially identified, a Project Proponent is required to notify Isometric within 30 days.
For OSEM Projects where interactions with the surrounding environment are more dynamic and less contained than closed system processes, a comprehensive reversal risk assessment must be conducted. When developing a reversal risk monitoring plan, Project Proponents are required to follow the criteria outlined in Section 4 of the Carbonated Materials Storage and Monitoring Module v1.1.
Refer to Carbonated Materials Storage and Monitoring Module for details.
The following is an overview of reversal risk storage monitoring under this Protocol:
Note: Project Proponents are recommended to reference the IUCN red list, or other reputable endangered species list to monitor changes in biodiversity in their project region as potential indicators for environmental monitoring
This Section outlines specific monitoring criteria required when Projects are undertaken using mine tailings within a mining operations tailings storage facility (TSF).
Sampling of utilized mine tailings is essential for monitoring OSEM Project activities and within the tailings storage facility (TSF). The physical and chemical characteristics of tailings evolve over time, influenced by factors such as addition of new tailings, weathering, particle size distribution (PSD), mineral type and abundance and exposure to environmental conditions. As such, regular sampling to account for heterogeneity in tailings is required to monitor CO2 removal and storage progress throughout The Project.
Key considerations for sampling tailings:
The Project must undertake sampling at time intervals and density that capture the progression of carbon mineralization and heterogeneity within the TSF. Initial baseline sampling must be taken at the start of The Project, followed by repeated sampling campaigns at regular time intervals (e.g., every 6 to 12 months) to track mineralization depth and the degree of carbonation.
Details on the coring frequency, depth, location and equipment must be included in the PDD upon submission to Isometric and The Project VVB.
Where Projects are undertaken on an active TSF and newly generated tailings are added to the TSF over the course of The Project, freshly deposited layers must also be accounted for in the monitoring and verification of carbon removal and emissions estimations. New tailings may have different physical and chemical properties, which can influence their reactivity and capacity for CO2 removal.
Key requirements for managing and monitoring new tailings include:
There may be instances throughout a Project where models are appropriate for both quantification and reversal monitoring that cannot be readily observed. Additionally, geochemical models are useful tools for estimating the carbon removal baseline and Project scenarios during a Reporting Period. At this early stage of carbon removals, geochemical models are not sufficient for Crediting and should only be used as a guide for Project activities. It is anticipated that the role of geochemical models in quantification of carbon removal projects will evolve in the coming years, and future updates in this Protocol will reflect this evolving consensus.
We recommend that any models used or developed alongside Project activities meet the following criteria:
For models used to simulate geochemical reactions, the following are essential components and considerations to include in developed models:
For models to simulate reversal risk, the following are recommended components and considerations to include in developed models:
In some cases, extreme, localized heterogeneity may result in measurements or data that are missing, incomplete or out of line with expectations given The Project design or previous measurements. Similarly, disruptions to The Project site and ongoing monitoring (e.g., extreme weather events or equipment failure) may result in missing data, outliers or unexplained results. For the purposes of this Protocol, outliers are defined as data that are more than three standard deviations from the mean (or equivalent percentiles for non-normal distributions). In such instances, the Project Proponent may seek clarification on how the data should be handled. When such instances occur, the details must be remedied and reported to the VVB and Isometric as quickly as possible after identification. In such situations, and on a case-by-case basis, Isometric will work to remedy the situation in consultation with the Project Proponent and VVB.
All records associated with the characterization, design, deployment and monitoring must be kept for a minimum of 10 years after cessation of removal activities and closure of the storage location. All documentation should be submitted to relevant authorities, such as environmental regulatory bodies, as required by local permitting regulations. In instances where project ownership changes ,during or post removal activities, the Project Proponent should contact Isometric to assess the potential implication of ownership change on Removal durability and reversal risk.
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.
Where site and feedstock characterization may have been carried out as part of permitting, or for other regulatory and compliance purposes, a Project Proponent may submit such results to meet the requirements of this Protocol. The use of such data for Crediting purposes must be approved by The Project VVB and Isometric prior to the issuance of removal Credits. If a Project Proponent intends to use pre-existing data sets in accordance with this Protocol, the data source, methodologies and data collection must be clearly outlined within the PDD to allow validation of submitted data prior to Crediting.
The use of existing data sets is contingent upon the approval of the relevant organization, or individuals, that are responsible for that data set, in instances where the data was not collected by the Project Proponent directly. It is the responsibility of the Project Proponent to ensure submitted data has been adequately checked for accuracy and that relevant permissions have been sought, and subsequently approved, prior to submission to Isometric and The Project VVB.
Projects that were started prior to the publication of this Protocol may be eligible for Crediting under this Protocol on a case-by-case basis. Project Proponents seeking Credits for pre-existing deployments must justify the approach taken in these Projects in the PDD, with special attention paid to:
Projects started prior to the publication of this Protocol are subject to the same statistical significance requirements referred to in Section 12.4.3.1
Isometric would like to thank following contributors to this Protocol and relevant Modules:
Isometric would like to thank following reviewers of this Protocol and relevant Modules:
Acid Mine Drainage (AMD)
Acid mine drainage (AMD), often referred to as acid rock drainage (ARD), if a term used to describe acidic ,and often metalliferous, drainage produced through the weathering of mining wastes, such as waste rock and tailings materials.
Activity
The steps of a Project Proponent’s Removal process that result in carbon fluxes. The carbon flux associated with an activity is a component of the Project Proponent’s Protocol.
Additionality
An evaluation of the likelihood that an intervention—for example, a CDR Project—causes a climate benefit above and beyond what would have happened in a no-intervention Baseline scenario.
Baseline
A set of data describing pre-intervention or control conditions to be used as a reference scenario for comparison.
Buffer Pool
A common and recognized insurance mechanism among Registries allowing Credits to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.
Buyer
An entity that purchases Removals, often with the purpose of Retiring Credits to make a Removal claim.
CEC
Cation Exchange Capacity
Carbon Dioxide Equivalent Emissions (CO2e)
The amount of CO2 emissions that would cause the same integrated radiative forcing or temperature change, over a given time horizon, as an emitted amount of GHG or a mixture of GHGs. One common metric of CO₂e is the 100-year Global Warming Potential.
Carbon Dioxide Removal (CDR)
Activities that remove carbon dioxide (CO2) from the atmosphere and store it in products or geological, terrestrial, and oceanic Reservoirs. CDR includes the enhancement of biological or geochemical sinks and direct air capture (DAC) and storage, but excludes natural CO2 uptake not directly caused by human intervention.
Carbon Finance
Resources provided to Projects that are generating, or are expected to generate, greenhouse gas (GHG) Emission Reductions or Removals.
Carbon Flux
The amount of carbon exchanged between two or more Reservoirs over a period of time.
Conservative
Purposefully erring on the side of caution under conditions of Uncertainty by choosing input parameter values that will result in a lower net CO2 Removal than if using the median input values. This is done to increase the likelihood that a given Removal calculation is an underestimation rather than an overestimation.
Counterfactual
A quantification of what would have happened in the absence of a particular intervention – i.e., assuming the Baseline scenario.
Cradle-to-Grave
Considering impacts at each stage of a product's life cycle, from the time natural resources are extracted from the ground and processed through each subsequent stage of manufacturing, transportation, product use, and ultimately, disposal.
Credit
A publicly visible uniquely identifiable Credit Certificate Issued by a Registry that gives the owner of the Credit the right to account for one net metric tonne of Verified CO₂e Removal. In the case of this Standard, the net tonne of CO2e Removal comes from a Project Validated against a Certified Protocol.
Crediting Period
The period of time over which a Project Design Document is valid, and over which Removals may be Verified, resulting in Issued Credits.
DIC
Dissolved Inorganic Carbon.
Double Counting
Improperly allocating the same Removal from a Project Proponent more than once to multiple Buyers.
Durability
The amount of time carbon removed from the atmosphere by an intervention – for example, a CDR Project – is expected to reside in a given Reservoir, taking into account both physical risks and socioeconomic constructs (such as contracts) to protect the Reservoir in question.
EW
Enhanced Weathering
Embodied Emissions
Life cycle GHG emissions associated with production of materials, transportation, and construction or other processes for goods or buildings.
Emission Reductions
Lowering future GHG releases from a specific entity.
Feedstock
Raw material which is used for CO2 Removal.
GHG Statement
A document submitted alongside Claimed Removals (A Removal which has been submitted by a Project Proponent, but which has not yet been Verified.), where The Project's emissions, Removals and Leakages are presented in net metric tonnes of CO₂e.
Global Warming Potential
A measure of how much energy the emissions of 1 tonne of a GHG will absorb over a given period of time, relative to the emissions of 1 ton of CO2.
Greenhouse Gas (GHG)
Those gaseous constituents of the atmosphere, both natural and anthropogenic (human-caused), that absorb and emit radiation at specific wavelengths within the spectrum of terrestrial radiation emitted by the Earth’s surface, by the atmosphere itself, and by clouds. This property causes the greenhouse effect, whereby heat is trapped in Earth’s atmosphere (CDR Primer, 2022).
GtC
Gigatonnes of carbon
ICP-MS
Inductively coupled plasma mass spectrometry.
ICP-OES
Inductively Coupled Plasma Optical Emission spectroscopy.
International Standards Organization (ISO)
A worldwide federation (NGO) of national standards bodies from more than 160 countries, one from each member country.
Issuance (of a Credit)
Credits are issued to the Credit Account of a Project Proponent with whom Isometric has a Validated Protocol after an Order for Verification and Credit Issuance services from a Buyer and once a Verified Removal has taken place.
Leakage
The increase in GHG emissions outside the geographic or temporal boundary of a Project that results from that Project's activities.
Life Cycle Analysis (LCA)
An analysis of the balance of positive and negative emissions associated with a certain process, which includes all of the flows of CO2 and other GHGs, along with other environmental or social impacts of concern.
Materiality
An acceptable difference between reported Removals/emissions and what an auditor determines is the actual Removal/emissions.
Model
A calculation, series of calculations or simulations that use input variables in order to generate values for variables of interest that are not directly measured.
Monitoring, Reporting, and Verification (MRV)
The multi-step process to monitor the Removals and impacts of a Project, report the findings to an accredited third party, and have this third party Verify the report so that the results can be Certified.
Pathway
A collection of Removal processes that have mechanisms in common.
Project
An activity or process or group of activities or processes that alter the condition of a Baseline and leads to Removals.
Project Design Document (PDD)
The document that clearly outlines how a Project will generate rigorously quantifiable Additional, Durable, and high-quality Removals.
Project Proponent
The organization that develops and/or has overall legal ownership or control of a Removal Project.
Protocol
A document that describes how to quantitatively assess the net amount of CO2 removed by a process. To Isometric, a Protocol is specific to a Project Proponent's process and comprised of Modules representing the Carbon Fluxes involved in the CDR process. A Protocol measures the full carbon impact of a process against the Baseline of it not occurring.
Proxy
A measurement which correlates with but is not a direct measurement of the variable of interest.
RP
Reporting Period
RTM
Reactive Transport Model
Registry
A database that holds information on Verified Removals based on Protocols. Registries Issue Credits, and track their ownership and Retirement.
Removal
The term used to represent the CO2 taken out of the atmosphere as a result of a CDR process.
Reversal
The escape of CO2 to the atmosphere after it has been stored, and after a Credit has been Issued. A Reversal is classified as avoidable if a Project Proponent has influence or control over it and it likely could have been averted through application of reasonable risk mitigation measures. Any other Reversals will be classified as unavoidable.
SEM-EDS
Scanning Electron Microscopy with Energy Dispersive Spectroscopy.
Sensitivity Analysis
An analysis of how much different components in a Model contribute to the overall Uncertainty.
Stakeholder
Any person or entity who can potentially affect or be affected by Isometric or an individual Project activity.
Standards (scientific)
Standard physical constants as well as standard values set forth by bodies such as the National Institute of Standards and Technology (NIST) or others.
Storage
Describes the addition of carbon dioxide removed from the atmosphere to a reservoir, which serves as its ultimate destination. This is also referred to as “sequestration”.
Tailings Storage Facility (TSF)
Tailings storage facility (TSF) refers to a storage facility within which fine mining wastes (Tailings), that are produced as a by-product following the processing of mined ore, are stored.
Uncertainty
A lack of knowledge of the exact amount of CO2 removed by a particular process, Uncertainty may be quantified using probability distributions, confidence intervals, or variance estimates.
Validation
A systematic and independent process for evaluating the reasonableness of the assumptions, limitations and methods that support a Project and assessing whether The Project conforms to the criteria set forth in the Isometric Standard and the Protocol by which The Project is governed. Validation must be completed by an Isometric approved third-party (VVB).
Validation and Verification Bodies (VVBs)
Third-party auditing organizations that are experts in their sector and used to determine if a Project conforms to the rules, regulations, and standards set out by a governing body. A VVB must be approved by Isometric prior to conducting validation and verification.
Verification
A process for evaluating and confirming the net Removals for a Project, using data and information collected from the Project and assessing conformity with the criteria set forth in the Isometric Standard and the Protocol by which it is governed. Verification must be completed by an Isometric approved third-party (VVB).
Refer to the Rock and Mineral Feedstock Characterization Module v1.0.
This appendix has been adapted from Appendix 1 of the Isometric Carbonated Material Storage and Monitoring module. This Appendix should be utilized in line with Section 2 of the aforementioned module.
| Method | Parameter | Purpose | Required or Recommended | Frequency | Evidence |
|---|---|---|---|---|---|
| Geological mapping | Lithologic strength | Define surrounding lithology | Required | Once (pre crediting) | Direct/Literature |
| Porosity | Required | Direct/Literature | |||
| Permeability | Required | Direct/Literature | |||
| Hydraulic properties | Required | Direct/Literature | |||
| Likelihood and magnitude of seismic activity | Required | Literature | |||
| Geotechnical analysis of underlying strata | Geophysical measurements | Ensure sufficient strength | Recommended | Once (pre crediting) | Direct |
| Topographic survey | Storage site depth | Determine storage capacity | Recommended | Pre crediting, followed by every 5 years or prior to a new crediting period (whichever is shorter) | Direct |
| Storage site size | Recommended | Direct | |||
| Groundwater properties | Carbonate saturation | Determine likelihood of reversal from groundwater interactions | Required | Once (pre crediting) and if not actively monitored every 5 years or prior to a new crediting period (whichever is shorter) | Direct |
| Ionic concentration | Required | Once (pre crediting) and if not actively monitored every 5 years or prior to a new crediting period(whichever is shorter) | Direct | ||
| pH | Required | Once (pre crediting) and if not actively monitored every 5 years or prior to a new crediting period(whichever is shorter) | Direct | ||
| Alkalinity or DIC | Required | Defined on a Project by Project basis | Direct | ||
| Organic ligands/microbial communities | Recommended for sites located on mines Required for projects where gas-flux measurements are the main quantification measurement | Once (pre crediting) and if not actively monitored every 5 years or prior to a new crediting period (whichever is shorter) | Direct | ||
| Groundwater flowpath | Recommended | Pre crediting, followed by every 5 years or prior to a new crediting period (whichever is shorter) | Model/publicly available data? | ||
| Recharge dynamics | Recommended | Pre crediting, followed by every 5 years or prior to a new crediting period (whichever is shorter) | Model/publicly available data | ||
| Water table depth, including seasonal variation | Required | Once (pre crediting) and if not actively monitored every 5 years or prior to a new crediting period (whichever is shorter) | Direct | ||
| Climatic considerations | Average precipitation amount | Determine likelihood of reversal from surface water interactions | Required | Pre crediting, followed by every 5 years or prior to a new crediting period (Whichever is shorter) | Direct or publicly available data |
| Average precipitation chemical composition | Required | Pre crediting, followed by every 5 years or prior to a new crediting period (Whichever is shorter) | Direct or publicly available data | ||
| Average surface temperature | Climatic monitoring | Recommended | Pre crediting, followed by every 5 years or prior to a new crediting period (Whichever is shorter) | Direct or publicly available data | |
| Monthly temperature fluctuation | Recommended | Pre crediting, followed by every 5 years or prior to a new crediting period (Whichever is shorter) | Direct or publicly available data | ||
| Surface water properties | Surface water flow paths | Determine likelihood of reversal from surface water interactions | Recommended | Pre crediting, followed by every 5 years or prior to a new crediting period (Whichever is shorter) | Direct or publicly available data |
This appendix has been adapted from Appendix 1 of the Isometric Carbonated Material Storage and Monitoring module v1.1.
| Parameter | Purpose | Required by Protocol? | Monitoring phase | Frequency | Evidence | Data sharing post crediting (Public/ Private) |
|---|---|---|---|---|---|---|
CO2 and O2 influx | Storage site gas phase monitoring | Required | Operation | Continuous | Direct | Public |
Partial pressure of CO2 within the storage site | Determine carbonate stability | Required | Operation & Post-closure | Defined on a Project by Project basis based on risk. | Modeled or direct | Public |
| Depth to fluid | Characterization of fluids present at storage site | Required | Operation and Post-closure | Defined on a Project by Project basis based on risk. | Direct | Private |
| pH | Required | Defined on a Project by Project basis based on risk. | Direct | Public | ||
| Alkalinity or Dissolved Inorganic Carbon (DIC) | Required | Defined on a Project by Project basis based on risk. | Direct | Public | ||
| Electrical conductivity | Required | Defined on a Project by Project basis based on risk. | Direct | Private | ||
| Carbonate saturation | Required | Defined on a Project by Project basis based on risk. | Direct | Public | ||
| Non-carbonate mineral saturation | Recommended | Defined on a Project by Project basis based on risk. | Direct | Private | ||
| Organic species/ligands | Recommended in mine sites | Defined on a Project by Project basis based on risk. | Direct | Private | ||
| Heavy metal concentration | Required | Defined on a Project by Project basis based on risk. | Direct | Private | ||
| Topographic survey | Storage site characterization | Required for cellular systems and piles otherwise recommended | Operation | Yearly or when a cell is completed for cellular systems. | Direct | Private |
| Air temperature | Climatic monitoring | Recommended | Operation & Post-closure | Continuous if monitored directly; daily if taken from publicly available data | Publically available data or direct | Private |
| Humidity | Recommended | Operation & Post-closure | Continuous if monitored directly; daily if taken from publicly available data | Publically available data or direct | Private | |
| Seismic monitoring | Geologic monitoring | Required | Operation & Post-closure | Continuous | Publically available data or direct | Private |
Surface CO2 flux | Reversal identification and quantification | Required | Operation & Post-closure | Defined on a Project by Project basis based on risk. | Public | |
| Passive carbonation | Determination of changes in carbon content | Required | Operation | Yearly direct measurements Continuous modeling | Modeled with yearly direct measurements | Public |
| Groundwater down flow path composition | Characterization of fluid at storage site (see specific monitoring requirements above under “characterization of fluids”) | Required | Operation & Post-closure | see specific monitoring requirements above under “characterization of fluids” | See specific monitoring requirements above under “characterization of fluids” | See specific monitoring requirements above under “characterization of fluids” |
| Surface water composition, including precipitation volume and pH | Characterization of fluid at storage site (see specific monitoring requirements above under “characterization of fluids”) | Recommended | Post-closure | See specific monitoring requirements above under “characterization of fluids” | See specific monitoring requirements above under “characterization of fluids” | See specific monitoring requirements above under “characterization of fluids” |
| Water table depth | Determine likelihood of reversal from groundwater interactions | Required | Operation and Post Closure | Monthly during operation then decreasing frequency post closure | Direct | Private |
| Groundwater flow paths | Determine likelihood of reversal from groundwater interactions | Recommended | Post Closure | Every 5 years | Modeled and/or publically available data | Private |
| Groundwater composition up flowpath | Characterization of fluid at storage site (see specific monitoring requirements above under “characterization of fluids”) | Recommended | Post Closure | See specific monitoring requirements above under “characterization of fluids” | See specific monitoring requirements above under “characterization of fluids” | See specific monitoring requirements above under “characterization of fluids” |
This risk assessment identifies the pathway specific risk factors relevant to a carbon removal project. The relevant risk factors identified as part of a risk assessment are included in the monitoring plan requirements for the project, with details included in the Project Design Document. Project specific risk factors inform the required duration of monitoring along with the monitoring requirements set out in the Protocol and the requirements set out in the Monitoring Section of the Isometric Standard.
The risk score, as determined by the Risk of Reversal Questionnaire, will determine a project’s buffer pool contribution. Projects must re-assess their reversal risk at the renewal of each crediting period, or if monitoring identifies a reversal-related risk, or if an actual reversal event takes place. In any event, projects should reassess their reversal risk at a minimum every 5 years.
The Risk of Reversal Questionnaire questions that pertain to this protocol, drawn from the programme-level Risk of Reversal Questionnaire defined in Appendix B: Risk Reversal Questionnaire of the Isometric Standard, include the following:
| # in Isometric Standard Questionnaire | Question | If answered “Yes” | If answered “No” |
|---|---|---|---|
| 1 | Is a reversal directly observable with a physical or chemical measurement as opposed to a modeled result? | Proceed to questions 2-9 | Proceed to questions 8-9 |
| 2 | Is the carbon being stored in an impermeable geologic system? (e.g., salt cavern) | Proceed to questions 8-9 | Add 1 to Risk Score and proceed to questions 3-9 |
| 5 | Does this approach have a material risk of reversal due to natural disasters including, but not limited to, floods, storms, earthquakes, fires, etc.? | Add 1 to Risk Score | |
| 6 | Does this approach have a material risk of reversal due to human-induced events from outside actors, such as change in farming practices, change in ownership and management of project sites, or similar? | Add up to 2 to Risk Score | |
| 8 | Is there 10+ years of monitoring and/or lab data demonstrating low project risk? | Minus up to 2 to Risk Score | |
| 9 | Does this pathway have a documented history of reversals? | Add 2 to Risk Score | |
| 10 | Is there one or more project-specific factors that merit a high risk level? | Add up to 2 to Risk Score |
Risk Score Categories
Project specific risk factors will depend on the form of carbon being stored (i.e., organic vs. inorganic), the method of storage (e.g., mineralization, encapsulation), the location of carbon storage (e.g., subsurface, ocean), and the proximity of that carbon to potential agents of reversal.
For projects with carbon storage as inorganic carbon, the presence of the following risk factors must be reflected in the risk score corresponding to question 10:
For projects with any form of subsurface carbon storage, the presence of the following risk factors must be reflected in the risk score corresponding to question 10:
Keleman, P.B., Benson, S.M., Pilorge, H., Psarras, P., Willcox, J., 2019. An overview of the status and challenges of CO2 storage in minerals and geological formations. Sec. Carbon Dioxide Removal. https://doi.org/10.3389/fclim.2019.00009↩
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