Carbonated Material Storage and Monitoring

This Module details durability and monitoring requirements for carbonated mineral storage in closed or open systems. Within this Module, durability refers to the length of time for which carbon is removed from the Earth’s atmosphere and cannot contribute to further climate change.

This Module is applicable to the surface storage of carbonated materials made via open- or closed-system mineralization reactions. Storage can take place in either closed (lined and capped landfills) or open (e.g. open pits within mines) systems. This does not include storage as engineering fill or agricultural amendment. In open systems, feedstocks are exposed to atmospheric or hydrospheric conditions, leading to potential changes over time in temperature, pressure and chemical composition. Such variations can influence the stability of stored carbonate minerals. In comparison, closed systems are isolated from external environmental changes, potentially offering a more controlled and secure environment for the long-term storage of mineralized carbon. Closed systems may constitute one large system that is capped when full or take the form of a system of cells that are individually isolated from the atmosphere and external conditions after a certain amount is stored, further reducing the risk of reversal (similar to landfill filling system).

The stability of carbon within the carbonated materials, and thus its durability, depends on their interactions with the surrounding environment. Potential risks to the expected durability of carbonate minerals include dissolution or other reactions with surrounding fluids, erosion as a result of changes in pressure and temperature, the presence of water and changes in geochemical and environmental parameters. Section 2.0 outlines requirements for evaluating carbonated mineral storage, with a focus on site characterization. The monitoring plan detailed in Section 4 acts to address and mitigate these potential remaining risks to durability. Section 6 addresses accounting for any emissions associated with these risks. Monitoring of operations and the project site shall be completed to ensure that CO₂ remains mineralised and stable and within the storage site or project boundary. The storage site shall be monitored in accordance with any relevant regulatory authority permit.

The monitoring approach developed and implemented by the Project Proponent shall address, via the permitting process and permit compliance, or by additional efforts and documentation:

• Storage site characterization: The storage site must be properly characterized and evaluated and the local and regional hydrogeology and leakage pathways must be identified. Measurements prior to storage may act as background or baseline measurements for models or for comparison with future measurements.
• Monitoring of materials and storage: the Project Proponent must specify operating conditions and monitoring systems and approaches such as gas detection, groundwater quality and pH to ensure that the carbonated minerals remain stable. Monitoring and reporting of operations must be in accordance with this protocol and any relevant regulatory body. Any non-compliance must be reported to the VVB and Isometric and addressed with corrective actions.
• Closure and Post-Closure Requirements: These include requirements for proper closure of the storage facility, as well as post closure requirements and monitoring to ensure the carbon remains sequestered durably as stable carbonate minerals at the site, and the site is properly monitored and closed when the regulatory authority determines conditions have been met to demonstrate containment. A Project Proponent is responsible for the long term durability of stored carbon within the utilized storage facility, as such we recommend that project assesses the long term risk of reversal, based on planned or potential land uses post crediting.

Specifically, the following requirements must be met to ensure durable storage of ex-situ carbonated materials.

The site for the proposed storage complex must be properly characterized to demonstrate site suitability for storage of the carbonated materials including the local and regional hydrogeology and leakage pathways. This characterization should also include the following conditions to act as baseline measurements against which to compare future monitoring and help with modeling.

Site characterizations must include evaluation of physical and chemical conditions to ensure compatibility of the storage of carbonated minerals. The site characterization must include:

• Geological maps to define surrounding lithology including the strength, porosity and permeability and hydraulic properties (including hydraulic conductivity) of these lithologies (for example using boreholes/logs) to ensure sufficient strength and determine site connectivity
• Groundwater quality and composition including carbon saturation, pH and alkalinity or dissolved inorganic carbon (DIC)
• Water table depth and seasonal variations
• Average precipitation amounts and chemical composition (e.g., pH)
• Likelihood and magnitude of seismic activity

It is recommended, based on site specific factors, that site characterization also includes:

• Geotechnical properties of the underlying strata to ensure sufficient strength.
• Topographic survey to determine the size and depth of the intended storage site and thus capacity to store the carbonated minerals.
• Groundwater flowpaths and recharge dynamics
• Surface water flow paths
• Average surface temperature and monthly climate fluctuations
• Organic ligands/microbial communities present (in mining sites)

Expected changes through time as a result of climate change must also be considered. These site characterisation parameters must be input in conceptual site models which specifically look at groundwater and surface water flow, background conditions, the environmental impact of the site and engineering design. Site characterisation parameters should also be used as comparisons for future measurements e.g., in identifying changes in groundwater composition/quality.

The Project Proponent must demonstrate and justify that there is limited degradation of the carbonated materials and result in long term stability of carbon within the minerals at the site, with no migration out of the site. Justification must include modeling of the site which considers site and mineral characteristics.

Site characterizations and analytical modeling shall be reviewed every five years or at the request of the permitting authority, or when monitoring and operational conditions warrant, as indicated by a significant change in site conditions or mineral characteristics, based on monitoring data. The review shall include a comparison of pre-storage project assumptions to actual measured conditions including but not limited to the amount of carbonated materials stored, pH and predicted changes in groundwater and surface water flow paths. Revised models should demonstrate that the carbonated materials will remain stable for at least 1000 years.

Potential leakage pathways must be evaluated through a combination of site characterization (Section 2.0) and empirically validated models that predict the long term stability of the carbonated minerals . This includes ensuring that all permitting requirements (Section 3.1) are met.

The Project Proponent must demonstrate that all relevant permitting requirements are met. The permit must specifically include the storage location as well as identify the feedstocks being stored. This permit must be shared with the VVB and Isometric prior to project crediting.

The Project Proponent must ensure that the storage site is designed and constructed based on the conceptual site model and in compliance with the relevant regulatory authority's permit or equivalent and documentation and records of well construction are maintained and available for review for the duration of the crediting period, as well as 10 years post closure.

If any type of pit is being used for storage, geotechnical assessments must take place to ensure slope stability. If a mound is being created, the maximum gradient of slope must also be determined. These assessments should be made following the relevant national or international standards (such as Sections 3.4.3 and 3.4.4 of ISO 20305:2020).

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.

Open systems storage will result in a connection and exchange 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 sites must be designed to minimize interactions with groundwater, surface water and the atmosphere. 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.

All projects are required to undergo detailed site characterization prior to storage of carbonated materials. For projects operating outside of mining facilities, direct monitoring requirements may be considerably reduced 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. 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, direct monitoring of stored carbonates is required. Further detail is given in Section 4.1.2.2.1.

Monitoring of carbonated minerals and the storage site is required in order to identify potential leakage pathways, measure leakage and/or validate models as appropriate.

The Project Proponent will ensure that the storage site complies with any permit. Monitoring plans should be updated every five years, unless the regulatory body that issues the permit requires this to be updated more often, to take account of changes to the assessed risk of leakage, changes to the assessed risks to the environment and human health, new scientific knowledge, and improvements in best available technology. At a minimum, the Project Proponent shall consider the following:

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 favored mineralogy within the carbonated minerals will impact its stability in the environment, and thus guide 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.

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 to the VVB and Isometric.

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 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.
• 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.
• 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.

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 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.
• 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.
• 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)

Projects operating 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 not come into contact with fluids below a pH of 5.5 at the storage site or downstream watershed. Groundwater surveys must be conducted every five years, at a minimum.

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 out 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 lost must also be quantified and subtracted from CO₂e_Stored.

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.

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 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.

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 is defined as monitoring between 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 within the storage site. It is recommended that, for long-term monitoring, a similar strategy as implemented during operation is used (with the exception of operation specific parameters; for example, the composition of new carbonated minerals added), with a focus on methods tailored 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.

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 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 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 - as described in Section 4.1.2.4.

Long term monitoring of closed systems may also include:

• Temperature within the site
• Partial pressure of CO₂ within the storage site

For open systems long-term monitoring must include:

• 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. 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 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).

Long term monitoring of open systems may also include:

• Organic species/ligands & microbial communities present within mining facilities. The presence of organic species and microbes can influence the carbonation reaction's efficiency, rate and stability.
• Groundwater flowpaths
• Groundwater composition up the flowpath from the storage 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)

The frequency of long-term monitoring may be reduced, determined by specific, risk-based, quantitative criteria and may be detailed as part of the regulating permit. Such criteria could include the isolation of the site from groundwater surface water and the atmosphere or favorable trends in observed geochemical monitoring results over a predefined period, and agreement with model predictions. The timeframe for long-term monitoring should be aligned with regulatory guidance and based on site specific operation and monitoring data, for example whether durability can be demonstrated. If the regulating authority does not have guidance on the minimum timeframe, this is set at a minimum of 50 years. The length of ongoing monitoring will be subject to 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 in 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.

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.

CO₂e_emissions is the total greenhouse gas emissions associated with a given Reporting Period, RP.

Equations and emissions calculation requirements for CO₂e_emissions, including considerations for monitoring activities, are set out in the relevant Protocol and are not repeated in this Module.

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). 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.

When a reversal is detected and quantified, there 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 ceased.

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. 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 of submitted data prior to crediting.

1. A geomembrane is very low permeability synthetic barrier used with any geotechnical engineering to control fluid migration in a human-made project, structure, or system. ↩