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Carbonated Material Storage and Monitoring
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This Module (Independent components of Isometric Certified Protocols which are transferable between and applicable to different Protocols.) details 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.) and monitoring requirements for carbonated mineral 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”.) 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 in the built environment, as engineering fill or as an agricultural amendment. In open systems, feedstocks (Raw material which is used for CO₂ Removal or GHG Reduction.) 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 (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.) (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 by strong acids (e.g. H2SO4, HNO3, etc) 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. These risks will likely be greater if storage occurs within mining operations, and very low within most other environments. Note that, where carbonic acid is the acidity source, dissolution of carbonate minerals will lead to storage of CO2 as dissolved bicarbonate (HCO3-).
Section 2 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 defined temporal and geographical boundary of a Project.). The storage site shall be monitored in accordance with any relevant regulatory authority permit.
The monitoring approach developed and implemented by the Project Proponent (The organization that develops and/or has overall legal ownership or control of a Removal or Reduction Project.) shall address, via the permitting process and permit compliance, or by additional efforts and documentation:
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:
It is recommended, based on site specific factors, that site characterization also includes:
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) 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 (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.), 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 (Standard physical constants as well as standard values set forth by bodies such as the National Institute of Standards and Technology (NIST) or others.) (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:
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 the atmosphere as well as groundwater, and surface water and(particularly thein atmosphereareas 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.
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 permitrequired permits. Monitoring plans should be updated every five years, unless the regulatory body that issues the permit requires this to be updated more oftenfrequent updates, 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 withinof 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.
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 not lead to reversal 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 X4.1.2.1.
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:
It is recommended that monitoring also includes:
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:
It is recommended that monitoring also includes:
Projects operating in low reversal risk environments outside of mining facilities may justify omission of the following monitoring requirements:
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 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:
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 (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 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:
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.
As above, the requirements for long-term monitoring are given for high-risk environments (e.g. mining sites) and low-risk environments.
For closed systems, long-term monitoring therefore must include:
Long term monitoring of closed systems may also include:
For open systems long-term monitoring must include:
Long term monitoring of open systems may also include:
TheProjects operating in low reversal risk environments outside of mining facilities may justify omission of the following monitoring requirements:
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.
For all Projects, 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:
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.
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.
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.
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 (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.
| 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 | Direct/Literature | |||
| Geotechnical analysis of underlying strata | Geophysical measurements | Ensure sufficient strength | Recommended | Once (Pre-crediting) | Direct/Literature |
| Topographic survey | Storage site depth | Determine storage capacity | Recommended | Once (Pre-crediting) followed by every 5 years or prior ro 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) followed by every 5 years or prior ro a new crediting period (whichever is shorter) | Direct |
| pH | Required | Direct | |||
| Alkalinity of DIC | Required | Direct | |||
| Organic ligands | Recommended for sites located on mines | Direct | |||
| Groundwater flowpath | Recommended | Direct/modeled/ | |||
| Recharge dynamics | Recommended | Direct/modeled/ | |||
| Water table depth, including seasonal variation | Required | Direct/ | |||
| Climatic considerations | Average precipitation amount | Determine likelihood of reversal from surface water interactions | Required | Once (Pre-crediting) followed by every 5 years or prior ro a new crediting period (whichever is shorter) | Direct/ |
| Average precipitation chemical composition | Required | Direct/ | |||
| Average surface temperature | Climatic monitoring | Recommended | Direct/ | ||
| Monthly temperature fluctuation | Recommended | Direct/ | |||
| Surface water properties | Surface water flowpaths | Determine likelihood of reversal from surface water interactions | Recommended | Once (Pre-crediting) followed by every 5 years or prior ro a new crediting period (whichever is shorter) | Direct/ |
| System | Parameter | Purpose | Required or Reccomended? | Monitoring Phase | Frequency | Evidence | Data Sharing Post Crediting (Public vs Private) |
|---|---|---|---|---|---|---|---|
| Closed and open systems | 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 proejct basis based on risk | Direct | Public | |
| Depth to fluid | Characterization of fluids present at storage site | Required | Operation & Post-closure | Defined on a project by proejct basis based on risk | Direct | Private | |
| pH | Required | Direct | Public | ||||
| Alkalinity or DIC | Required | Direct | Public | ||||
| Electrical conductivity | Required | Direct | Private | ||||
| Carbonate saturation | Required | Direct | Public | ||||
| Non-carbonate mineral saturation | Recommended | Direct | Private | ||||
| Organic species/ligands | Recommended for sites located on mines | Direct | Private | ||||
| Heavy metal concentration | Required | 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; dailt if taken from | Direct/ | Private | |
| Humidity | |||||||
| Seismic monitoring | Geologic monitoring | Required | Operation & Post Closure | Continuous | Direct/ | Private | |
| Passive carbonation | Determination of changes in carbon content | Required | Operation | Yearly direct measurements & continuous modeling | Modeled with yearly direct | Public | |
| Open system only | Groundwater composition down flowpath | 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 | Recommended | Post-closure | |||||
| Water Table Depth | Determine likelihood of reversal from groundwater interactions | Required | Operation & Post Closure | Monthly during operation then at a decreasing frequency post closure | Direct | Private | |
| Groundwater Flowpath | Determine likelihood of reversal from groundwater interactions | Recommended | Post Closure | Every 5 years | Modeled and/or | 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 | |
| Surface CO2 flux | Reversal identification and quantification | Required | Operation & Post-closure | Defined on a project by proejct basis based on risk | Direct | Public |
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. ↩