Carbonated Material Storage and Monitoring

3.0 Carbonated Materials Characterization

4.0 Reversal Risk Approach

4.1 Reversal Risks for Carbonated Materials

The two primary pathways by which CO₂ can be lost from carbonated materials are exposure to high temperatures (e.g., >300 °C)¹ and contact with low pH fluids. These conditions, though not necessarily common globally, can occur in some instances; for example, mine tailing are sometimes heated to high temperatures during reprocessing,² and the pH of groundwater that is impacted by industrial pollution (e.g. acid mine drainage, AMD) can be below 3.³

Carbon loss resulting from high temperatures is referred to as calcination and occurs by the reaction:

[math: CaCO_3(s) \to CaO(s) + CO_2(g)]

Equation 1

The kinetics of this reaction are strongly dependent on both temperature and crystal structure.⁴ Multiple polymorphs of CaCO₃ exist in nature, the most common of which is calcite. Studies have shown that, depending on the reaction conditions, calcination of calcite can occur between 680–900°C.⁵ Other possible CaCO₃ polymorphs include aragonite and vaterite, both of which decompose at lower temperatures than calcite (450–725°C).⁴ Depending on the feedstock mineralogy, magnesium carbonates may also be present, which can decompose at temperatures as low as 300 °C.¹ Thus, conservative estimates of carbon loss due to calcination require either detailed carbonate mineralogy data or the assumption that at least some of the CaCO₃ present is in non-calcite carbonate phases.

Carbon loss resulting from contact with low pH fluids is dependent on a) pH, b) the acid source, c) ambient temperature, d) the material's initial composition and porosity, and e) length of exposure. In particular, interaction of carbonate minerals with strong acids, such as sulfuric, nitric or phosphoric acid, lead to release of CO₂ following the reactions:

[math: CaCO_3 (s) + H_2SO_4(aq) \to CaSO_4 + CO_2 (g) + H_2O(l)]

Equation 2

[math: CaCO_3 (s) + 2HNO_3 (aq) \to Ca(NO_3)_2 + CO_2 (g) + H_2O(l)]

Equation 3

[math: CaCO_3 (s) + H_3PO_4 (aq) \to CaHPO_4 + CO_2 (g) + H_2O(l)]

Equation 4

Conversely, where the acid source is carbonic acid, interaction with calcium carbonates can result in either carbon loss or carbon storage depending on the pH of the solution. Dissolution of CaCO₃ by carbonic acid (here represented as CO₂ + H₂O) occurs following the reaction:

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

Equation 5

In this reaction, dissolution of 1 mole of CaCO₃ results in the capture of 1 mole of CO₂ as bicarbonate (HCO₃^-). Bicarbonate is part of the carbonic acid system, the speciation of which is highly pH-dependent ⁶. As pH decreases, the relative concentration of dissolved CO₂ increases. This dissolved CO₂ can exchange with the atmosphere, resulting in a release of CO₂.

4.2 SiteStorage construction requirementsTypes

This Module considers three broad categories of storage environment: open system, closed system and high-risk. The reversal risk for carbonated materials is determined separately for each type of storage according to the likelihood of exposure to conditions resulting in CO₂ loss from carbonate minerals.

4.2.1 Closed System Storage

3.2.1 Closed system

Closed systems must be isolated from the surrounding lithologies to ensure there is no active connection and exchange of fluids within the system. Conceptual site models must be used to assess the required engineering and site design.

Ideally, closed systems will have a geological barrier that extends along the base and sides of the storage site, consisting of very low permeability rocks in order to prevent groundwater infiltration and soil and groundwater pollution. An artificially enhanced geological barrier of at least 500mm thick may be used if required. Conceptual site models may show that the geological barriers add little value to the site. If this is the case it must be agreed in the permit that none will exist and reported in the PDD. Regardless of whether there is a geological barrier, the site must be lined with the geomembrane1 with an expected lifespan (50% degradation) of >400 years. The Project Proponent must report the following information about the geomembrane in the PDD:

• The tensile strength of the chosen geomembrane
• Justification of how the proposed material will withstand the physical, biological and chemical stresses it will be subjected to
• Detail of how the Project Proponent will secure the geosynthetic material both during construction and for the full design life of your site
• Results of site-specific shear strength testing for each soil to geosynthetic and geosynthetic to geosynthetic interface
• For each roll of material used you must include the manufacturer’s quality control certificates, summary of the manufacturer’s quality control procedures, the procedure for sampling and testing the geosynthetic material that is to be used and the corresponding results. Laboratory testing must be completed to the latest appropriate standards - for example, British Standards, ASTM standards and the standards and guidance provided by the Geosynthetic Research Institute.

Closed system storage may occur in a single large system, where material is continuously added to the site until capping and closure, or as multiple cells within the site which are isolated from each other and the atmosphere, once a set amount is stored, with geomembranes. Geomembranes between cells must be assessed and reported as above.

Any monitoring infrastructure (for example fluid collection pipes or groundwater monitoring wells) must be designed to be compatible with the expected fluids with which the materials may be expected to come into contact and must meet or exceed standards developed for such materials by API, ASTM International, or comparable standards. Any wells and pipelines must be designed to prevent the movement of fluids. Standards used by projects must be clearly outlined within the project's PDD. Wells and pipelines must also permit the use of appropriate testing devices and workover tools.

34.2.2 Open systemSystem Storage

OpenCarbonated materials stored in open systems storageare willexposed resultto inambient aenvironmental connectionconditions, including precipitation, temperature fluctuations and exchangewind. Examples of fluids within the system. This means that it is much harder to control the environment (when compared to closed systems) and there are increased environmental reversal risks. Conceptual site models must be used to assess the site and engineering design. In addition, open system storage sitesinclude mustopen bepit designedstorage, to minimize interactions with the atmosphere as well as groundwater and surface water (particularlystorage in areas that are impacted by strong acids present in soil or acid rain). In storage facilities where stored carbonates materials may interact with surrounding strata, potential leakage pathways must be identified, quantified and minimized. This information should be reported within the PDD and assessed on a project by project basis in consultation with the project’s engineer of record and Isometric. Open system storage facilities are required to have clearly identified project boundaries, within which monitoring infrastructure is operated and maintained

Any monitoring infrastructure (for example fluid collection pipes or groundwater monitoring wells) must be designed to be compatible with the expected fluids with which the materials may be expected to come into contact and must meet or exceed standards developed for such materials by API, ASTM International, or comparable standards. Any wells and pipelines must be designed to prevent the movement of fluids. Standards used by projects must be clearly outlined within the project's PDD. Wells and pipelines must also permit the use of appropriate testing devices and workover tools.

4.0 Monitoring

Monitoring of carbonated minerals and the storage site is required in order to identify potential leakage pathways, measure leakageunlined and/or validateuncapped modelslandfills and storage in non-dedicated use facilities, such as appropriate.

The Project Proponent will ensure that the storage site complies with any required permits. Monitoring plans should be updated every five years, unless the regulatory body that issues the permit requires more frequent updates, to take account of changes to the assessed risk of leakage, changes to the assessed risks to the environmentconstruction and humandemolition health,waste new scientific knowledge, and improvements in best available technologylandfills. AtDepending a minimum, the Project Proponent shall consider the following:

4.1 Operational Monitoring

4.1.1 Carbonate Mineral Composition Monitoring

The mineralogy of the carbonated minerals and their particle size will determine their reactivity and thus impact their durability. For example, a smaller particle size results in an increased mineral surface area and exposure time and increased risk of dissolution and reversals. In addition, the mineralogy of the carbonated minerals will impact its stability in the environment, and thus guideon the environmental conditions for storage and durability models as well as help identify leakage pathways. The potential of leaching for heavy metals and other hazardous components should also be assessed. The mineralogy of the carbonated minerals should be defined as per the requirements of the Isometric Rock and Mineral Feedstock Characterization Module.

4.1.2 Storage Reversal Monitoring

Monitoring is required to ensure that potential reversals are measured and quantified. Changes versus baseline conditions and/or modeled behavior/predictions may indicate reversals. These measurements should be used to assess whether any corrective measures should be taken and used to make an updated assessment of the durability of the storage site both in the short and long term. In a situation where reversals are measured or suspected via monitoring or modeling, Project Proponents are required to report this toexposure the VVB and Isometric.

This Module distinguishes between projects operating in high reversal risk environments (e.g. mining facilities impacted by acid mine drainage or other industrial pollution) and projects operating in low reversal risk environments. On Earth's surface, the vast majority of environments will notmay lead to reversalloss of CO₂ stored in carbonate minerals.

All projects are required to undergo detailed site characterization prior to storage of carbonated materials. If site hydrogeologic characterization indicates carbonate minerals are stable or will not encounter aqueous geochemical conditions that decrease the carbonate storage capacity below that of pre-existing carbonate minerals and the site is outside of a mining facilities, direct monitoring requirements may be considerably reduced. Further detail is given in Section 4.1.2.2.1. If hydrogeologic properties (e.g., carbonate saturation state, groundwater pH) indicate a likelihood that carbonate minerals will dissolve and encounter aqueous geochemical conditions that decrease the carbonate storage capacity below that of the pre-existing carbonate minerals or is within a mining facility, direct monitoring of stored carbonates is required and the requirements for operation within mine sites or high reversal risk environments must be followed Section 4.1.2.1.

4.1.2.1 Requirements for operation within mine sites or high reversal risk environments

4.1.2.1.1 Closed system storage

Monitoring of closed systems must focus on the distribution of carbon within the system and the combination of environmental and geochemical conditions within the storage site that could lead to a reversal. The risk of reversal is further reduced if a cellular system is used. These monitored parameters should be added to models of the site (see Section 4.1.2.4) to understand durability. Monitoring must include:

• Influx of CO2 and O2 to the storage site. For example, using a continuous gas monitoring system (such as infrared sensors).
• Partial pressure of CO2 within the storage site to determine carbonate stability. This may be done via pH measurement in solution or employing pressure transducers and gas composition analyzers.
• Composition of any fluids within the storage sites (these should be collected via “leachate collection pipes” from within the site). This must include measurements of:
  • Depth to fluid
  • pH
  • Alkalinity or DIC - to help determine the capacity of an aqueous solution to neutralize acids and thus influence the overall chemical reactions involved in forming stable carbonate minerals.
  • Electrical conductivity (EC)- EC can be a good indicator for monitoring the reaction progress, pH and other parameters of solution chemistry.
  • Carbonate mineral saturation
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
• A seismic monitoring program of the site. This must be monitored for magnitude 2.7 or greater seismic events to determine the presence or absence of any induced micro-seismic activity associated with storage or any seismic activity.
• Passive carbonation. This should be done via modeling that is grounded by yearly direct sampling for stored materials and analysis of carbon content to determine any changes. Measurements should be completed following the guidance in the Rock and Mineral Feedstock Characterization Module.
• Topographic surveys are required if a cellular system or pile is being used. For cellular systems, a topographic survey must be taken once each cell has been completed.

It is recommended that monitoring also includes:

• Yearly topographic surveys until the site is closed.
• Climatic conditions within the storage site including temperature and humidity. These could be measurements taken on site or from local weather stations and climate models. Extreme weather events such as extreme temperature or pressure should be recorded.

4.1.2.1.2 Open system storage

Monitoring of open systems must focus on the distribution of carbon within the system, groundwater migration and quality and the combination of environment and geochemical conditions within the storage site that could lead to a reversal. These monitored parameters should be added to models of the site (see Section 4.1.2.4) to understand durability. Monitoring is required to include:

• Influx of CO2 and O2 to the storage site. For example, using a continuous gas monitoring system (such as infrared sensors).
• Partial pressure of CO2 within the storage site to determine carbonate stability. This may be done via pH measurement in solution or employing pressure transducers and gas composition analyzers.
• Water table depth
• Composition of any fluids (leachate/groundwater) within the storage sites. This should be collected via a monitoring well or “leachate collection pipeline” within the site. This must include measurements of:
  • pH
  • Alkalinity or DIC- to help determine the capacity of an aqueous solution to neutralize acids and thus influence the overall chemical reactions involved in forming stable carbonate minerals.
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
  • Electrical conductivity (EC)- EC can be a good indicator for monitoring the reaction progress, pH, and other parameters of solution chemistry.
  • Carbonate mineral saturation
• A seismic monitoring program of the site. This must be monitored for magnitude 2.7 or greater seismic events to determine the presence or absence of any induced micro-seismic activity associated with storage or any seismic activity.
• Passive carbonation. This should be done via modeling that is grounded by yearly direct sampling for stored materials and analysis of carbon content to determine any changes. Measurements should be completed following the guidance in the Rock and Mineral Feedstock Characterization Module.
• Groundwater composition up and down the flowpath from the storage site. This must include measurements of:
  • pH
  • Alkalinity or dissolved inorganic carbon (DIC)
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
  • Electrical conductivity (EC)
• Topographic surveys are required if a cellular system or pile is being used. For cellular systems, a topographic survey must be taken once each cell has been completed.

It is recommended that monitoring also includes:

• Yearly topographic surveys until the site is closed.
• Climatic conditions including temperature, humidity and precipitation. These could be measurements taken on site or from local weather stations and climate models. The average pH of precipitation should also be measured. Extreme weather events such as extreme temperature or pressure should be recorded.
• Surface water composition at the site including:
  • pH
  • Alkalinity or DIC
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
  • Electrical conductivity (EC)
• Surface CO2 flux measurements to identify and quantify reversals. Monitoring frequency and spatial distribution shall be determined using baseline data. Monitoring can be completed using one or more of the following methods:
  • Optical CO2 sensors, such as airborne Infrared spectroscopy, non-dispersive infrared spectroscopy, cavity ring-down spectroscopy or LIDAR (light detection and ranging)
  • Eddy covariance (EC) flux measurement at a specified height above the ground surface
  • Portable or stationary carbon dioxide detectors
  • Tracer testing using inherent tracers such as CH4, radon, noble gasses, and isotopes of CO2 or introduced tracers, such as δ13C of CO2/CH4, provide a unique fingerprint for the CO2 that can be identified in above ground emissions.

4.1.2.2 Requirements for projects operating in low risk environments

Projects operating in low reversal risk environments outside of mining facilities may justify omission of the following monitoring requirements:

• Influx of CO2 and O2 to the storage site
• Partial pressure of CO2 within the storage site
• Composition of any fluids (leachate/groundwater) within the storage sites
• Climatic conditions including temperature, humidity and precipitation
• Surface CO2 flux measurements
• Groundwater composition up and down the flowpath from the storage site
• Surface water composition at the site

To justify reducing the monitoring requirements, the Project Proponent must demonstrate through a detailed groundwater and geologic survey that the carbonated materials will(Section not4.1) comeor intoadditional contactcarbon withremoval, fluidssuch belowas aby pHadditional mineralization or dissolution of carbonate minerals by carbonic acid (Equation 5.5 at the storage site or downstream watershed). GroundwaterThis surveysleads mustto be conducted every five years, at a minimum.

4.1.2.3 Leakage

If any leakage is detected from the storage site or there are significant irregularities from the used model(s), the Project Proponent/operators must undertake corrective measures as set outuncertainty in their monitoring plan submitted and approved by the competent authority. For a loss of conformance with models/expected behaviors, the Project Proponent must halt further storage at the site while they identify the cause of this loss, and then revise the monitoring plan to account for this change. If there is a leakage, the Project Proponent must halt further storage while they conduct an assessment to determine if the loss of containment can be repaired prior to further storage beginning again. The amount of CO₂ lostthat mustremains alsostored be quantified and subtracted from CO2eStored.

Re-evaluations of the reversal potential must also be implemented when warranted based on observational or quantitative changes of the monitoring parameters of the storage site, including but not limited to:

• observed reversals
• new site characterization data which changes the model inputs.

Further information on the risk and attribution of reversals Section 6.0 and Section 6.1.

4.1.2.4 Modeling

Modeling must be used to ensure no reversals will occur under the storage conditions and thus determine its long term durability. This must include geochemical reaction models accounting for the equilibrium chemistry of aqueous solutions interacting with minerals, gas, and solid solutions and reactive transport models. This should be compared to data directly collected from the storage site (e.g., pH, temperature) and any other nearby relevant subsurface data (i.e., porosity and permeability of the storage site, groundwater flow, etc) to ensure model validity and confirm the stability of the carbonated minerals. Uncertainty (A lack of knowledge of the exact amount of CO₂ removed byover a particular process, Uncertainty may be quantified using probability distributions, confidence intervals, or variance estimates.) analysis is required around key variables in the simulation to evaluate durability across a variety of scenarios within the realistic range of values. All parameters used within the models, their values and accuracy must be reported and submitted to Isometric and the VVB, where they will be validated by an appropriately qualified independent expert.

Geochemical reactions models should be conducted in PHREEQC and forecast into the future. These models should be run with the Carbfix PHREEQC mineral dissolution kinetics database. This should include investigating:

• Speciation (to examine saturation state of carbonate minerals). PHREEQC speciation program can calculate saturation indices specific conductance of a solution with given parameters of pH, temperature, ions concentration, etc and vice versa
• Batch-reaction calculations (modeling of coupled dissolution + precipitation process). PHREEQC is oriented towards system equilibrium for reaction and can be set to examine open vs closed systems. Non-equilibrium reactions can be modeled with user-specified kinetically controlled reactions and related parameters. With this function, a sensitivity test could be performed. The temperature effect can be modeled with reaction enthalpy, and the pressure effect can be simulated by entering molar volumes. In the case of CO2, it could be entered as a gas phase or aqueous species. Equilibrium dissolution/precipitation of minerals like chrysotile, brucite, dolomite, magnesite, calcite, hydrotalcite, hydromagnesite, olivine(forsterite) could also be modeled using this function.
• Sorption, desorption, ion exchange. Surface complexation reactions, the activity of exchange sites, and species can be modeled for situations where surface-driven dissolution/precipitation of carbonates occurs. For example, for serpentine, the leaching of Mg initially happens on the mineral surface and surface passivation could occur by carbonate minerals precipitating on the mineral surface, prohibiting continuous dissolution. In this case, ion exchange could be used to model the activity of the exchange site and the chemical conditions where carbonate precipitated on the serpentine surface dissolves.
• Kinetically controlled reaction. Rate expression can be included in the input file during modeling with PHREEQC. Multiple rates can be integrated simultaneously with proper formulations of the components. Examples of how to write rate formulations can be found in the PHREEQC user manual. This allows for the freedom of self-defining rates observed in the field, enabling more accurate modeling of the dissolution/precipitation reactions.
• Transport Modelling. 1D flow path reactive transport modeling is achievable in PHREEQC. The initial compositions of the aqueous, gas, and solid phases can be specified. The changes due to advection, dispersion and (or) diffusion can be modeled. This modeling can be advantageous when monitoring reversible and irreversible chemical reactions. A simple advective-transport simulation would be a good option when modeling for example, CDR via injection or surface reaction with ultramafic tailings. Mineral dissolution from acidity of CO2 dissolution and carbonate precipitation are reversible reactions. Thus, reversal risk from reverse reaction can be modeled.

Within open systems, reactive transport models should also be used to predict the distribution and timing of the chemical reactions that occur along a flowpath within the site. This must include forward monitoring for durability calculations.

4.2 Site Closure and Long-Term Monitoring

The aim of these closure and long-term monitoring requirements is to put in place monitoring practices that prove that CO2 will be durable within the minerals on 1,000 year timescales. Addressing potential risks to durability (Section 1.0) is important for ensuring robust and diligent carbon dioxide removals. The Project Proponent must follow any long-term monitoring and site decommissioning requirements of the permit for the specified project. The long-term monitoring period isunless definedadditional asmeasurements monitoringare betweenperformed site closure and the confirmation of durable storage.

The Project Proponent must adhere to all permitting requirements during site closure. This must include a report of the total amount of carbonated waste stored and a final topographic survey. A Site Closure Plan shall be prepared in accordance with the relevant regulatory authority permit requirements. As part of closure, the Project Proponent should evaluate appropriately whether the site must be capped to minimize infiltration of precipitation and reduce leakage pathways. Cap specifications should be evaluated on a project and site specific basis with justification for capping or non capping agreed with the engineer of record and Isometric prior to crediting.

In projects where capping is required, the cap shall include a sealing layer (such as HDPE or impermeable mineral), surface water drainage system (above the sealing layer) and cover soils to protect the sealing layer and drainage system. The thicknesses and design shall be based on durability modeling data and site specific data.

Monitoring should continue after closure to ensure the stability of the minerals withinat the storage site. It isAs recommended thatsuch, forProjects long-term monitoring, a similar strategy as implemented during operation is used (with the exception of operation specific parameters; for example, the composition of newstoring carbonated mineralsmaterials added),in withopen asystems focusare on methods tailoredsubject to address the anticipated system changes and risks that may occur. Any loss of carbonate mineral stability and reversal prior to closure of the site should be sampled and measured for carbon content and accounted for as outlined in Section 6.0.

As above, the requirements for long-term monitoring are given for high-risk environments (e.g. mining sites) and low-risk environments.

4.2.1 Requirements for operation within mine sites or high reversal risk environments

For closed systems, long-term monitoring therefore must include:

• Composition of any fluids within the storage sites (these should be collected via “leachate collection pipes” from within the site). This must include measurements of:
  • Depth to fluid
  • pH
  • Either Alkalinity or DIC - to help determine the capacity of an aqueousuncertainty solution to neutralize acids and thus influence the overall chemical reactions involved in forming stable carbonate minerals.
  • Electrical conductivity (EC)- EC can be a good indicator for monitoring the reaction progress, pH and other parameters of solution chemistry.
  • Carbonate mineral saturation
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
• A seismic monitoring program of the site. This must be monitored for magnitude 2.7 or greater seismic events to determine the presence or absence of any induced micro-seismic activity associated with storage or any seismic activity.
• Changes in CO2 gas concentrations within the site to identify and quantify reversals. Monitoring frequency and spatial distribution shall be determined using baseline data on a project by project basis, based on risk. It is recommended CO2 concentrations are monitored via a monitoring well.
• Modeling -discount as described in Section 4.3.1.

4.2.3 Storage in High-Risk Environments

Within this Module, a high-risk environment is defined as a storage location where there is significant risk that carbonated materials may be exposed to either high temperatures or acidic solutions (see Section 4.1).

Long termThis includes storage at mine sites, where there may be contamination by acid mine drainage (AMD) or where carbonated tailings may be reprocessed in the future. Projects storing carbonated materials in high-risk environments are required to conduct additional site characterization and ongoing monitoring in accordance with Appendix A. In addition to required measurements, Projects storing carbonated materials in mining environments may be subject to an additional uncertainty discount associated with high-temperature reprocessing of carbonated tailings (Section 4.3.2).

4.3 Determination of Reversal Risk

Within this Module, reversal risk is determined based on the storage type. As stated in Section 4.2.1, Projects storing carbonated materials in closed systems maywith alsono include:

• Temperatureadditional withinrisk thefactors site
• Partialare pressurenot ofrequired CO2to withinassume thean storageuncertainty site

Fordiscount, openbut systemsare long-termrequired monitoringto must include:

• Water table depth
• Composition of any fluids (leachate/groundwater) within the storage sites. This should be collected viamaintain a monitoringbuffer wellpool or “leachate collection pipeline” within the site. This must include measurements of:
  • pH
  • Alkalinity or DIC - to help determine the capacity of an aqueous solution to neutralize acids and thus influence the overall chemical reactions involved in forming stable carbonate minerals. Combined with pH this can also be used to determine if there is any gas formation
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
  • Electrical conductivity (EC)- EC can be a good indicator for monitoring the reaction progress, pH and other parameters of solution chemistry.
  • Carbonate mineral saturation
• A seismic monitoring program of the site. This must be monitored for magnitude 2.7 or greater seismic events to determine the presence or absence of any induced micro-seismic activity associated with storage or any seismic activity.
• Changes in CO2 gas concentrations within the site to identify and quantify reversals. Monitoring frequency and spatial distribution shall be determined using baseline data on a project by project basis based on risk. It is recommended CO2 concentrations are monitored via a monitoring well.
• Groundwater composition down the flowpath from the storage site (If minerals are stored below the water table). This must include measurements of:
  • pH
  • Alkalinity or DIC
  • Heavy metal concentrations including lead, copper and arsenic. Specific monitoring requirements will vary on a site-to-site basis and the monitoring plan must be justified based on local lithology and feedstock mineralogy.
  • Electrical conductivity (EC)
• Modeling (as described in Section 4.1.2.4).

LongTo termensure monitoringthat ofuncertainty discounts are conservative, the reversal risk approach described here assumes the worst-case scenario for environmental conditions if no additional information can be provided. For example, the reversal risk for Projects operating in open systems outside of high-risk areas will be determined based on the lowest groundwater pH within the operational region. Project Proponents can provide additional information for model inputs that may alsoresult in a lower uncertainty discount. This may include (but is not limited to):

• OrganicAverage species/ligandspH &of microbialgroundwater communitiesat presentthe withinstorage location
• Average pH of precipitation at the storage location
• Average annual temperature at the storage location
• Where applicable, description of any tailings reprocessing procedures (or lack thereof), signed by the mining facilitiesoperator

4. The3.1 presenceDetermination of organicReversal speciesRisk Through Aqueous Interactions

As described in Section 4.1, interaction with surrounding fluids is the most direct reversal risk for carbonated materials stored in open systems or high-risk environments. This can be determined using geochemical models, such as PHREEQC or Geochemist's Workbench. Geochemical modeling must consider the following inputs:

• Mineralogy of the materials stored through direct measurement, including:
  • Carbonate content and microbes can influence the carbonation reaction's efficiency, rate and stability.mineralogy
  • GroundwaterAny flowpathsother minerals present
• GroundwaterClimatic compositionconditions up the flowpath fromof the storage site, determined by direct measurement or weather station data, including:
  • Average annual precipitation volume
  • Average precipitation pH
  • Average annual temperature
• Groundwater chemistry, determined by direct measurement or open source data, including:
  • pH
  • Alkalinity or DIC
  • HeavyCarbonate metalsaturation

Of concentrationsthese including leadparameters, coppermineralogy and arsenic. Specific monitoring requirements will vary on a site-to-site basis andof the monitoringstored planmaterials must be justifieddirectly measured. It is recommended to directly measure climatic conditions and groundwater chemistry where possible, but where direct measurement is not possible and open source data is unavailable, conservative assumptions must be applied as described above. Project Proponents may run their own models based on localthe lithologyparameters given above and feedstockmust mineralogy.

4.2.2 Requirements for projects operating in low risk environments

Projects operating in low reversal risk environments outside of mining facilities may justify omissiondetails of the followingmodel, monitoringincluding requirements:the software used, input parameters and any additional code to Isometric. Project Proponents may also request that Isometric runs a PHREEQC model, and in this case must provide data on all required parameters to Isometric.

• Influx

4.3.2 Determination of CO2Reversal andRisk O2from Exposure to theHigh storageTemperatures

4.4 Buffer Pools

Based on present levels of scientific knowledge, Projects applicable to this Module are categorized as having a Very Low Risk Level of Reversal according to the Isometric Standard Risk Assessment Questionnaire. This storage pathway does not have guidancea ondocumented thehistory minimumof timeframereversals; however, thiscertain isenvironmental setconditions at(described above in Section 4.1) can lead to reversal. As a minimumresult, ofa 502% years.buffer The length of ongoing monitoringpool will be subjectset toaside change given subsequent reanalyses.

The Project Proponent will actively explore emerging technologies for measuring stabilization. The stabilization assessment shall be conducted in one of the following ways:

• Utilize predictive modeling based on monitoring data collected during post-closure monitoring to demonstrate the stability of carbonated minerals and no release into the atmosphere.
  • Modeling must be validated by comparison to historical monitoring data
  • Models must utilize site specific geochemical and hydrological characteristics & conditions from analyses required in Sections 4.1.2 and 4.2 of this Module.
  • Models must assess the potential reversal extent over 1,000 years and demonstrate that the carbonate minerals are stable and will not result inas a reversal nor cause other environmental harms.
• New methods as outlined in subsequent protocol versions and as measurement and monitoring technologies advance.

If the carbonated minerals can be demonstrated as stable over 1,000 years, and is independently reviewed and certified by a registered Professional Geologist (i.e. Chartered Geologist or equivalent), the project will be considered durable.

A site report (providing information on the operation, monitoring & modeling and closure procedures) should be created by the Project Proponent and submitted to regulatory bodies and make future land owners aware. The Project Proponent must notify other stakeholders, such as nearby drinking water utilities and agencies with primacy for drinking water regulations. A copy of the site decommissioning plan should also be retained by the Project Proponent for a minimum of 10 years (or longer if required by the regulator) following site decommissioning.

4.2.1 Recordkeeping

All records associated with the characterization, design, construction, storage, monitoring, and site closure must be developed, reported in the project design document, to the VVB's and to proper authorities as required by the relevant regulatory authority permit.

All records must be maintained for a minimum of 10 years after site closure. All closure and post-closure monitoring records must be maintained by the Project Proponent for a minimum of 10 years after closure.

5.0 Calculation of CO2e emissions

CO2eemissions is the total greenhouse gas emissions associated with a given Reporting Period, RP.

Equations and emissions calculation requirements for CO2eemissions, including considerations for monitoring activities, are set out in the relevant 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.) and are not repeated in this Module.

6.0 Risk of Reversals

There should be no reversals unless the geochemical conditions result in the instability of carbonated minerals such as through interaction with an acidic fluid or weathering. The reversal risk shall be determined on a project by project basis (see Isometric standard risk of reversal questionnaire)precaution. This reversal risk will be reassessed when new scientific research and understanding arises.

Reversals will be accounted for by projects and the Isometric Registry as detailed in Section 5.6 of the Isometric Standard.

6.1 Attribution of reversals

When a reversal is detected and quantified, thereknowledge are multiple considerations that will be taken into account to attribute the reversal to whatever has been stored at the storage site.

1. If the Project Proponent was the only entity storing at given storage site, the Project Proponent will take on 100% of the reversal.
2. If the Project Proponent was one of multiple entities storing at that storage site, the Project Proponent will be allocated a percentage of the reversed CO2 proportional to the mass of material stored. For example:
   • A storage site has a total of 200t of material stored at the time when the reversal is detected (this information should be provided by the Operator).
   • The Project Proponent has stored 50t of material at that storage site.
   • The amount of reversed CO2 has been quantified to be 10t.
   • The Project Proponent must compensate for 25% (50/200) of 10t CO2 = 2.5t of CO2.

In instances where leakage or reversals are determined to be a result of negligence by the Operator or Project Proponent, project crediting may be ceasedproduced.

7.0 Use of existing data sets

Where site 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 Module. The use of such data for crediting purposes must be approved by the project VVB and Isometric prior to the issuance of removal credits (A publicly visible uniquely identifiable Credit Certificate Issued by a Registry that gives the owner of the Credit the right to account for one net metric tonne of Verified CO₂e Removal or Reduction. In the case of this Standard, the net tonne of CO₂e Removal or Reduction comes from a Project Validated against a Certified Protocol.). If a Project Proponent intends to use pre-existing data sets in accordance with this Module, the data source, methodologies and data collection must be clearly outlined within the PDD to allow validation (A systematic and independent process for evaluating the reasonableness of the assumptions, limitations and methods that support a Project and assessing whether the Project conforms to the criteria set forth in the Isometric Standard and the Protocol by which the Project is governed. Validation must be completed by an Isometric approved third-party (VVB).) of submitted data prior to crediting.

85.0 Definitions and Acronyms

Independent components of Isometric Certified Protocols which are transferable between and applicable to different Protocols.

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.

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”.

RawA materialcalculation, whichseries isof usedcalculations or simulations that use input variables in order to generate values for variables of interest that are not directly measured.

Purposefully erring on the side of caution under conditions of Uncertainty by choosing input parameter values that will result in a lower net CO₂ Removal or GHG Reduction than if using the median input values. This is done to increase the likelihood that a given Removal or Reduction calculation is an underestimation rather than an overestimation.

TheA escapelack of knowledge of the exact amount of CO₂ toremoved the atmosphere after it has been stored, and afterby a Creditparticular hasprocess, beenUncertainty Issued.may Abe Reversalquantified isusing classifiedprobability asdistributions, avoidableconfidence if a Project Proponent has influenceintervals, or controlvariance over it and it likely could have been averted through application of reasonable risk mitigation measures. Any other Reversals will be classified as unavoidableestimates.

TheAn definedactivity temporalor andprocess geographicalor boundarygroup of activities or processes that alter the condition of a ProjectBaseline and leads to Removals or Reductions.

The organization that develops and/or has overall legal ownership or control of a Removal or Reduction Project.

TheRaw increasematerial inwhich is used for CO₂ Removal or GHG emissions outside the geographic or temporal boundary of a project that results from that project's activitiesReduction.

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.

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.

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.

Standard physical constants as well as standard values set forth by bodies such as the National Institute of Standards and Technology (NIST) or others.

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.

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.

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.

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).

96.0 Appendix 1A: Site Characterization Requirementsand Monitoring

107.0 AppendixRelevant 2: Storage Monitoring RequirementsWorks