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Biomass Storage in Subsurface Mines
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This Module outlines the requirements for the storage of biomass in subsurface mining operations for the purpose of carbon dioxide removal (CDR). A net decrease in atmospheric CO2 will occur when biomass is processed and stored in a way to substantially slow or arrest microbial degradation and prevent decay products migrating to the atmosphere. When these carbon cycle interventions are combined with engineered controls and favorable site characteristics to limit disturbance, this stored carbon may persist for long periods of time.
While this Module provides specific requirements on how biomass can be stored to significantly delay the degradation of biomass and contain decay products, it is noted that adherence to the storage provisions outlined in this Module does not guarantee durability of carbon storage. Given the significant diversity in the chemical characteristics of biomass, biomass processing prior to storage, storage environments, and other site-specific considerations, the durability claims associated with removals utilizing this Module must be evidenced with direct, time-series evidence and a detailed, quantitative description of how those storage conditions will be maintained throughout the Project lifetime. Additionally, this Module describes the requirements of monitoring and reporting of fugitive gasses. Any biomass processing and carbon quantification must be conducted in accordance with other Isometric Protocols and Modules.
Biomass is inherently labile with respect to degradation by fungi, microorganisms and other biogeochemical redox reactions. While there are many biomass processing technologies (e.g., desiccation, biochar, bio-oil) and storage options (e.g., burial, injection, sinking) present in the market today, scientific literature has not yet reached consensus on the carbon storage durability of different processing and storage techniques.
Given this current state of understanding of subsurface biomass burial for CDR, Isometric takes a restrictive approach to Project eligibility. Specifically, Isometric will assess the current state of scientific understanding and consensus on subsurface biomass burial technologies on an individual Project basis. Once such technologies have demonstrably met a reasonable burden of scientific evidence, they will be added to the Eligible Biomass Processing and Storage Options listed below as the Module is updated. Isometric will update this list as frequently as necessary, guided by scientific research and market learnings.
All Projects must have biomass feedstocks that meet all the applicable eligibility requirements outlined in the Isometric Biomass Feedstock Accounting Module including sustainability, market leakage, and counterfactual storage criteria and quantification.
The eligibility of subsurface mining operations for subsurface biomass storage will be assessed by Isometric on a Project by Project basis.
Eligibility requirements for all mine types:
The following mining operation types may be considered as applicable biomass storage Project locations under this Module:
Operational Subsurface Mines
Closed or Closing Subsurface Mines
The following mining operation types will not be considered as applicable biomass storage Project locations under this Module:
Mining Operations Developed for Carbon Storage
Mining Operations with Life-of-Mine Extensions
Note: Where a mining operator has extended the LOM for reasons not related to carbon removal activities, a signed affidavit may be provided by the operator as evidence.
Fully Closed and Remediated Mines
Surface Mining Operations
The permanence of CO2 storage through biomass burial in subsurface mines depends on preventing or minimizing potential leaks out of the storage area which could lead to stored CO2 could be re-emitted to the atmosphere or mobilized to other subsurface environments. Within this Module ‘storage area’ is defined as the chamber or sealed area within which biomass is placed for the purpose of permanent burial, as well as the surrounding area of expected diffusion. In this context, leaks refers to any release of GHGs that originate from the stored biomass, including CO2 and methane generated by anaerobic decomposition of that biomass after burial and storage.
This section details the potential risks and leak pathways in subsurface biomass storage Projects. Leak pathways represent routes through which CO2 stored in biomass could be lost from storage reservoirs, through gaseous emissions (e.g., CO2, CH4), aqueous transport (dissolved organic/inorganic carbon (DOC/DIC) or particulate organic carbon (POC) and/or physical displacement (subsidence, seismic activities) 1.
Projects must conduct a site-specific assessment of all potential pathways for leaks when characterizing the storage environment and design appropriate engineering controls and MRV systems for the monitoring of stored biomass (see Section 7).
[/R-EDJS-0]Potential risks to expected durability are site specific, but may include:
Risk A: Gas phase formation and migration out of the storage area
Subsurface environments host diverse microbial communities capable of degrading organic matter under both aerobic and anaerobic conditions. If residual oxygen is present within the storage chamber at the time of closure, aerobic heterotrophic microorganisms will oxidize organic carbon to CO2, consuming oxygen until anoxic conditions are established. Once oxygen is depleted, anaerobic metabolic pathways become dominant, including fermentation, sulfate reduction, iron reduction, and methanogenesis. Even under anoxic conditions designed to minimize decomposition, some fraction of stored biomass may undergo anaerobic degradation, producing GHGs 2. The gas phase formed by biomass degradation may leak from the storage area and provide the most direct pathway for GHGs release to the atmosphere. This is especially important for coal bearing mines that have natural sources of CH4 emissions. Such GHGs migration occurring via:
Risk B: Injected biomass interacts with fluids, rock, and minerals within and surrounding the storage area, especially dissolution/migration with an aqueous phase
CO2 storage through biomass burial in subsurface mines can be mobilized through aqueous pathways in the form of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), or particulate organic carbon (POC) and dissolved gases (CH4), this can then migrate out of the storage area. Water may intrude into the storage chamber as a result of:
To avoid monitoring of risk associated with aqueous phase, the Project Proponent must demonstrate that no water will infiltrate the storage area. This demonstration must be supported by site-specific hydrogeological evidences confirming the absence of groundwater flow and surface water infiltration pathways at the operating depth of the Project. This evidence must be provided in the Project Design Document (PDD) and must include, at minimum:
Note: Where applicable, the Project Proponent must also demonstrate that the storage depth is sufficient to preclude surface water ingress under extreme precipitation or flood scenarios.
Risk C: Physical disturbance, such as structural failures and ground movement caused by seismic activity within the storage area, could result in leaks and the release of stored carbon
Note: Requirements that align with the specific risk categories (Risk Categories A, B and C) outlined within this Section can be identified within squared brackets throughout this Module.
Projects utilizing subsurface biomass burial have diverse characteristics, using a range of feedstocks, processing technologies, and storage solutions. Additionally, the environmental context will differ from operation to operation. Given this diversity in Project level characteristics and the potential diversity in true durability of the associated removal, suppliers utilizing this Module must provide evidence of their durability claims with the following requirements. These requirements are in place to assess durability of biomass, as well as microbial degradation potential [A].
[/R-A6VG-0]Project Proponents must outline the process by which biomass will be placed and stored in subsurface mine chambers. Such outlines must include the following information:
[/R-EB9G-0]Project Proponents must provide detailed documentation of all engineered barrier systems.
[/R-7F1Z-0]Documentation must address risks and potential pathways for leaks [A,C].
[/G-2MN7-0]Documentation must include the following:
Project Proponents must submit the required evidence of biomass durability to the Isometric and the VVB for review and approval prior to crediting.
The Project must have an active permit that was issued by the responsible authority for the location of the storage site.
[/R-WZZX-0]The permit must identify biomass as acceptable for storage at the site.
[/G-RJVQ-0]Projects must adhere to regulations regarding the responsible operation of mines, including mines which are operational, closed or undergoing remediation.
[/G-9DA5-0]In addition, The Project must comply with all applicable local environmental, ecological and social requirements as well as those set out in the relevant Protocol and Sectionthe 3.7relevant section of the Isometric standardStandard.
At present, Projects in locations governed by the US, Canada, United Kingdom and European Union are eligible under this Protocol. Projects in other locations may be eligible for crediting if the Project Proponent can demonstrate adherence to an equally rigorous set of requirements for permitting and environmental protection as would be required for a similar Project in one of the above jurisdictions. Such exceptions must be approved by Isometric.
[/G-31FX-0]When Project Proponents select a mining operation for the purpose of subsurface biomass storage, several operational attributes must be assessed to confirm suitability as a storage site.
[/R-BV27-0]Site characterization must encompass evaluation of mine storage conditions and, where required, surrounding site conditions, to ensure that biomass will be stored safely and durably.
[/G-8CFH-0]At a minimum, site characterization must include the following evaluation:
To be considered for crediting under this Module, biomass must be stored at a minimum depth of 150m below the ground surface at the Project storage location.
[/G-X98K-0]The rationale for this requirement is based on considering the zone of active surface weathering and soil formation (approximately <10m) 6,7, seasonal temperature and moisture fluctuations (approximately <50m)8,9, reducing the risks to durability of stored carbon [A,B,C]. Below this 150m there is also minimal risk of impact from potential surface disturbances and land use activities [C]. The minimum depth requirement is established to ensure:
Note: Isometric may accept Projects with a minimum depth of <150m, where a Project Proponent provides justification for a reduction in minimum depth. Reductions in minimum depth requirements will be assessed on a case by case basis by Isometric, in consultation with The Project VVB.
Project Proponents are required to provide accurate depth measurements for all storage locations, this must include the depth measured as true vertical depth from ground surface to the shallowest point of the biomass storage area, survey measurements from mine establishment may be used. Depth verification documentations must also be available upon request.
[/G-TT5B-0]Evidence required to demonstrate the storage area depth must include at least one of the following: mine survey plans, 3D modelling (e.g., leapfrog modelling) showing storage location, cross-sections showing depth profile from surface to storage areas, topographic maps showing surface elevation.
[/G-8KHW-0]In addition, Project Proponents must also account for any variation in storage area depth, monitoring must distinguish between different depth zones if any variability is identified.
[/G-YHCX-0]Characterization of the storage area must provide sufficient evidence that the selected mine can accommodate biomass at the volumes and conditions required for safe, durable storage.
[/G-VNQK-0]This includes an assessment of the physical, geological, hydrological, geomicrobiological, thermal, and atmospheric conditions within the mine, as well as gas transport dynamics that may affect the integrity of stored biomass and the surrounding environment.
[/G-C1HT-0]Mine Geometry
Project Proponents must conduct comprehensive characterization of the mine through 2D mapping of all storage areas, entries, and infrastructure, including calculations of available void space suitable for biomass storage based on environmental criteria such as stability and accessibility.
[/G-HYFB-0]Void space calculations must account for biomass packing efficiency, anticipated settling and compaction over time, and the presence of any existing infrastructure within chambers (e.g., rails, supports, or equipment) that may reduce usable storage volume. 3D mapping of the Project mine is recommended for all Projects.
[/G-BDPR-0]Where a partner operator has existing 2D or 3D mapping models of the mine, Project Proponents may submit these within the PDD, in lieu of, or as well as, characterization mapping carried out by the Project Proponent. Mapping of the Project mining location must include, at a minimum, the storage chambers that will be utilized for Biomass emplacement and storage (See Section 5.1).
[/G-N34A-0]Mine Geological Configuration
The geological evaluation must characterize the host rock lithology, stratigraphy, structural features (e.g., faults, folds and fractures), and overburden depth, while employing recognized rock mass classification systems (e.g., RMR, Q-system) to assess rock quality through strength testing and discontinuity analysis.
[/G-4AJ5-0]For room-and-pillar configurations, pillar stability analysis is critical, requiring width-to-height ratio calculations, stress assessments, and safety factors, along with evaluation of pillar performance history 11.
[/G-8C9F-0]Additionally, roof and floor stability must be assessed through span analysis, competency evaluation, ground support requirements, and documentation of any fall or heave history to ensure the mine's structural integrity for safe, phased biomass storage operations [A].
[/G-NQJP-0]Project Proponents must provide geological survey and structural mapping documents demonstrating the presence or absence of faults, fracture zones and other vertical discontinuities or geological features within the area of the storage site and a buffer zone of approximately 50m radius [A,C].
[/G-GB3Q-0]If active faults, defined by the USGS Earthquake Hazards Program as faults that have moved one or more times in the last 10,000 years, are identified, the Project Proponents must ensure the chambers and sealing barriers are designed to withstand seismic loads. If any fault (active or inactive) is found to intersect with the storage chambers, the Project Proponent must:
Mine Ventilation Configuration
In addition, Project Proponents must ensure mine ventilation conditions enable the effective monitoring of atmospheric mine conditions, as specified in the monitoring plan (fugitive gases, oxygen etc.) over the full Crediting Period.
[/G-VDV9-0]Where natural ventilation is insufficient, engineered control systems must be implemented to ensure monitoring is representative and any compromised storage is identified [A].
[/G-1V8W-0]Project Proponents must submit all characterization information within the PDD. Such evidence must demonstrate compliance with all local and national regulations applicable to the Project operation, including those governing mine structural safety, subsurface operations, occupational health and atmospheric monitoring, and environmental protection.
[/G-CX7D-0]Mine Infrastructure
Project Proponents must conduct infrastructure assessment evaluating the condition and stability of all access routes including portals, adits, and shafts to ensure the capability for biomass transportation to storage locations and sustained monitoring access throughout the period of biomass emplacement and subsequent project Reporting Period.
[/G-B719-0]Existing infrastructure must be inventoried for condition and utility, including availability of power for monitoring systems, communication systems for remote monitoring capabilities, and storage facilities for equipment and materials necessary to support long-term biomass storage operations [A].
[/G-J90W-0]Mine History
Documentation and reviews of the mining history for the site must be submitted, with records of the type of operations, materials extracted, timelines of mining and closure activities, any hazardous materials used or stored, and post-closure uses of mine workings. Such information will be used to assess the suitability of the chosen mine operation for storage of biomass.
[/G-ZVY4-0]The mine's current regulatory closure status must be documented, including existing closure plans and integration strategies for biomass storage with closure requirements, and the identification of responsible parties for long-term mine stewardship to ensure regulatory compliance and environmental protection throughout the storage duration [A,B,C].
[/G-TN5W-0]Hydrological Characterization
Storage chambers must not be subject to groundwater infiltration [B]. The Project Proponent must demonstrate this as part of site characterization.
[/R-9ZJ6-0]Storage chambers must be shown to not be impacted by groundwater, and no groundwater infiltration must occur. Evidence must confirm that storage chambers are not impacted by groundwater, and must include visual inspection of mine walls and surrounding tunnels showing no signs of leaks, supported by at least two of the following methods:
The biomass–geologic material mix must also exhibit low permeability, which should be demonstrated through permeability testing prior to biomass emplacement.
[/G-HKM6-0]In addition, a comprehensive groundwater evaluation must be undertaken to identify nearby aquifers, determine groundwater flow directions and hydraulic gradients, measure hydraulic conductivity of host rock and overburden, assess surface water infiltration potential, and define the zone of influence of mine workings on local and regional groundwater systems 12,13.
[/G-PXKR-0]Project sites must be located outside of the zone of influence of local groundwater and aquifers, both laterally and vertically.
[/G-YTES-0]The evaluation of suitability for Project site, additionally all groundwater monitoring systems must be certified by a qualified groundwater scientist (e.g., certified hydrogeologist or similar in the jurisdiction of the Project) and must comply with the sampling and analytical procedures outlined in the site permit or by applicable regulations [B].
[/G-MDJY-0]The design of groundwater monitoring plan (e.g., sampling location sites, spacing, depth etc.) must be determined on a site-specific basis by the Project Proponent and must be included in the PDD. The plan should be designed based on applicable regional, local regulations, aquifer thickness, depth, groundwater flow rate, direction and other relevant geological and hydrogeological characteristics of the site.
[/G-6NMS-0]While surface water intrusion through mine infrastructure, as a result of flood events, are unlikely, Project Proponents must undertake a site characterization assessment to identify the likelihood of flood events.
[/G-RPTB-0]Such assessments should include:
Additional environmental baseline assessment must be conducted include air and water quality measurements, identification of any contamination from previous mining activities, and an evaluation of any materials incompatible with biomass storage.
[/G-VQ7X-0]The following are recommended for all Projects when undertaking site characterization studies:
Geomicrobiological Characterization
Project Proponents should undertake baseline geomicrobiological characterization of the storage environment to assess the potential for microbially-mediated decomposition of stored biomass 14. This should include enumeration and characterization of indigenous microbial communities present within the mine, with particular attention to functional guilds relevant to organic matter degradation, including aerobic heterotrophs, fermenters, sulfate-reducing bacteria, iron-reducing bacteria, and methanogenic archaea 15. Geomicrobiological characterization should be conducted prior to biomass emplacement to establish a pre-injection baseline against which post-emplacement microbial changes can be assessed [A,B].
[/G-11D1-0]Thermal Environment Characterization
Project Proponents should document the thermal regime of the storage environment, including in-situ temperature profiles at the proposed storage depth. Temperature exerts a primary control on microbial metabolic rates and the kinetics of geochemical reactions relevant to carbon stability 4, elevated temperatures accelerate both aerobic and anaerobic decomposition processes and increase rates of mineral dissolution and organic compound leaching 16,17. Thermal characterization should include measurement of the ambient geothermal gradient at the site and assessment of any localized heat sources (e.g., exothermic oxidation reactions, residual mining equipment) that could elevate temperatures within storage chambers. This information should be submitted in the PDD and used to inform predictions of long-term biomass stability [A,B].
[/G-BZTM-0]Project Proponents must characterize the potential for gases produced by biomass degradation, including CO2, CH4, and other volatile compounds to migrate beyond the intended storage boundary.
[/R-TRNM-0]As the storage area will likely not be completely sealed from the surrounding strata, the Project Proponents must assess gas transport both through the biomass matrix and into the surrounding geological environment [A].
[/G-5C8E-0]Storage area (chamber) must be selected such that the surrounding strata exhibit sufficiently low permeability and porosity to minimize diffusion of any generated gases beyond the storage zone.
[/G-PHPH-0]Characterization for gas transport must address the permeability and diffusivity of the host rock and any engineered barriers, the connectivity of the mine workings to surface or adjacent subsurface environments, and the presence of preferential migration pathways such as fracture networks, legacy boreholes, or improperly sealed shafts.
[/G-QAC2-0]To limit gas transport out of the biomass, biomass must be mixed with mud, clay, or other geological media within the storage chambers to ensure sufficiently low diffusivity.
[/G-4R8Q-0]Diffusivity biomass and expected migration distances must be calculated in line with Section 6.2.2.3.1 and used to define the Project storage area boundary.
Where available, baseline gas concentrations and flux rates within the mine must be reported to enable detection of any anomalous emissions attributable to stored biomass.
[/G-Q15D-0]For Projects relying on minimal diffusive transport to ensure permanence, leak assessments must include robust diffusion modelling that estimates the migration rate and distance of GHGs under varying site-specific conditions 18.
[/G-F7PP-0]These models must be fully documented and included within the PDD upon submission to Isometric and the Project VVB. The selection and applicability of specific gas diffusion models will be assessed on a case-by-case basis.
[/G-C3P8-0]Where material migration risks are identified, a mitigation plan must accompany the gas migration assessment.
[/G-SR7Z-0]Diffusion within geological media follows Fick’s laws of diffusion, proceeding at a rate determined by the material's effective diffusion coefficient (Deff).
[/R-7M9A-0]To allow such quantification, Project Proponents must:
If appropriate, include biogeochemical consumption/mineralization terms that may further limit migration. The relationship between time and distance in a diffusive system is described by the characteristic diffusion timescale:
[math: t = \frac{L^2}{D_{\mathrm{eff}}}]
(Equation 1)
Where:
To determine the potential migration distance of gas over a specific Project lifespan, this formula can be rearranged to solve for the length of the diffusion path (i.e., confining layer thickness) (L):
[math: L = \sqrt{t \cdot D_{\mathrm{eff}}}]
(Equation 2)
Using the relationship in Equation 2, the time (t) can be set to 1000 years (converted to seconds), and [math: {D_{\mathrm{eff}}}] varies based on the grain size and material properties. This allows the calculation of the distance GHGs produced from biomass will diffuse during the lifespan of The Project, and determine whether GHGs are expected to reach the surface 19.
To calculate amount of instantaneous diffusive flux, Fick’s laws of diffusion can be used:
[math: J = -D_{\mathrm{eff}} \cdot \frac{dC}{dx}]
(Equation 3)
Where:
This allows the estimation of diffusive flux out of the storage area per unit area, either as a conservative maximum (Jmax) or as a time dependent flux J(t). By further multiplying this value with the disposal footprint area A (i.e., vertical area of the containment layer) (m2), the calculation allows the estimation of the mass transfer rate (mol s-1) across the containment layer. As part of the modelling exercise, the transient diffusion should be modeled with appropriate boundary conditions and reporting time dependent flux J(t), including the peak flux Jmax reporting and cumulative mass transferred over the assessment period 20.
Geotechnical Characterization
Project Proponents must conduct geotechnical hazard evaluation including a comprehensive subsidence assessment incorporating historical monitoring data, predictive modeling, analysis of surface effects from past or potential future subsidence, and a risk assessment of subsidence impacts on storage containment integrity [C].
[/R-PS26-0]Project Proponents must conduct and provide a geotechnical evaluation of long-term mine stability, including:
Where Project Proponents can provide evidence from a partnered mining operator that satisfies the above requirements, the Project Proponent will not be required to undertake additional geotechnical evaluations. In such instances, the Project Proponent shall provide evidence and documentation that the mining activities and storage chambers are in compliance and certified by the relevant engineering methodologies and regulations.
For mines with historical subsidence or marginally stable conditions, enhanced safeguards must be outlined in the PDD, which must at minimum include:
Seismic Hazards Assessment
Seismic hazard characterization must be undertaken, encompassing regional assessments of both natural and induced seismicity [C]. The modeling must cover 1,000-year durability, incorporating data from historical seismicity records within the mining district, evaluation of mine-induced seismicity potential from past or ongoing operations, and an analysis of mine working structural response to seismic loading to ensure long-term stability and safety of biomass storage areas under potential geotechnical hazard scenarios 21.
[/R-AFGW-0]The peak acceleration for the storage area must be calculated and reported. Base peak acceleration should be less than 0.1 g with >10% probability of exceedance within 250 years. However, if sequestration is determined to be subject to >0.1 g base acceleration then all systems must be designed to withstand maximum horizontal acceleration and prevent permanent deformation of the sequestered materials.
Project Proponents are required to describe and provide evidence to demonstrate how biomass will be stored within subsurface systems at the Project mining operation.
[/R-3J6E-0]Descriptions must outline how geological permanence and any leaks will be assessed and monitored and how implemented storage strategies will ensure durability of stored carbon. These must be detailed within the PDD.
[/G-17NC-0]Note: Requirements that align with the specific risk categories (Risk Categories A, B and C) outlined within Section 4 can be identified within squared brackets.
Subsurface biomass burial is a nascent storage technology for carbon dioxide removal, therefore addressing potential risks to durability is important for ensuring robust quantification and monitoring of CO2 removals.
Monitoring frequency must be defined based on monitoring phases, monitoring frequency must be the highest during the post-closure phase where chambers are sealed and anoxic environments are established.
The Project Proponent must describe all the methods, equipment, detection limits and any applicable standards that will be used for monitoring.
[/R-WQ8X-0]The Project Proponent must provide a theoretical or empirical justification demonstrating that the monitoring system can detect CO2 reversals, as well as CH4 and N2O emissions (if relevant), equivalent to the decay of 1% of the total stored biomass mass over a 20-year period.
[/R-X7P7-0]All equipment used for sampling must be properly adjusted for atmospheric temperature and pressure and calibrated per manufacturer requirements, with documentation available upon request. All meters must be calibrated by the manufacturer or a certified third-party calibration service as per the manufacturer’s guidance. Calibration certificates must be maintained in accordance with Section 13.
[/G-F3QN-0]Direct monitoring of stored biomass is a core component of ensuring durability. Prior to emplacement of biomass into target mine chambers, Project Proponents must periodically sample the biomass and slurry mixture in line with the requirements outlined in the relevant Protocol. In addition the following parameters must be characterized:
[/R-59FW-0]Projects must monitor gas concentrations and airflow outside mine chambers utilised for storage of biomass [A].
[/R-JWM4-0]Gas concentrations within the storage chambers must be monitored, until such a point that the storage chambers have been filled.
[/R-5X21-0]Project Proponents must, at a minimum, undertake ongoing monitoring of CO2, CH4 and airflow, over the Project's monitoring period. It is recommended that Project Proponents measure temperature and relative humidity (RH) outside of the filled storage chamber over the Project Reporting Period.
[/G-B63H-0]Baseline measurements must be collected prior to the injection and storage of biomass within mine chambers.
[/R-7F86-0]If gas is detected, Projects may utilize tracing techniques (e.g., isotope tracers) in order to quantify how much of the gas sampled is the result of biomass decomposition or mining activities. If no such methods are used, all increases in greenhouse gas will be considered reversals. Detection of reversals must be immediately reported to Isometric and will be handled according to Isometric’s reversal policy (See the Isometric Standard for more details).
[/G-DGKE-0]Where Projects employ sealing barriers between differing mine chambers, Project Proponents must undertake ongoing monitoring within every individual chamber utilized for biomass storage.
[/R-F0GC-0]In situations where ongoing monitoring within every individual chamber is not feasible, due to engineering or access restrictions that are out of the control of the Project Proponent, alternative monitoring approaches may be considered. In such instances the Project Proponent should engage with Isometric to assess the suitability of alternative approaches, which will be determined on a Project by Project basis.
[/G-Y5G7-0]Gas monitoring outside chamber seals is required to detect potential gas breakthroughs. This should include:
[/G-DDV4-0]Where chambers, and sealing barriers, are no longer accessible for monitoring, due to the progression or closure of the mining operation, the Project Proponent must report this to Isometric. Such situations will be assessed on a case by case basis in consultation with the Project Proponent and the Project VVB.
[/G-CVS0-0]Where a Project Proponent utilizes an engineered backfill material for the purpose of storage and sealing [A]. A full description of the backfill composition must be provided within the PDD upon submission to Isometric and the Project VVB. Projects may utilize a backfill material that is composed of Biomass and geological materials (such as mud or slurry).
[/R-TC7H-0]Where biomass is mixed into the Project backfill material, Project Proponents are required to demonstrate the composition and geotechnical efficiency of the backfill compared to materials that would have been utilized in the absence of the Project, the baseline scenario.
[/R-M0S7-0]Engineered barriers must be regularly inspected for its physcial condition and signs of degradation.
[/G-K5C0-0]If the Project requires additional excavation of land, in excess of excavation that would have occurred in absence of the Project activities, the baseline carbon stocks must be established and monitored after disturbance, with reductions in stocks accounted for as foregone counterfactual storage. Such excavations may be for the purpose of providing additional geological material, such as mud, as a binder/ slurry feedstock that is mixed with biomass prior to emplacement and storage.
[/R-TPVT-0]Where the project activities necessitate excavations that would not have occurred in the counterfactual scenario, Project Proponents must account for any reductions in soil organic carbon due to these excavations. This must be accounted for by measuring the drop in concentration of soil organic carbon compared with a representative control site. Increases in soil organic carbon are not considered creditable removals under this Module.
As specified in the Section 6.2, for Projects that take place within active seismic zones, Project Proponents must perform a site-specific study of regional seismicity to establish a baseline of seismic hazards [C] 22.
A seismic monitoring program may be required at the discretion of the relevant regulatory authority (e.g., UIC Director or equivalent) in areas of increased seismic risk, or where it is demonstrated that seismicity may impact the durability of the carbon storage 23. The monitoring program should adhere to the following specifications:
[/R-HHFT-0]If groundwater infiltration into the storage chambers does occur, the Project Proponents must [B]:
Note: Where groundwater infiltration does occur the Project Proponent is required to consult with Isometric on potential remediation steps. The suitability of remediation steps to restrict groundwater infiltration will be assessed on a Project by Project basis.
[/G-E88P-0]Geological and/or structural seals are required between each storage chamber and remaining mine infrastructure [A,B,C].
[/R-ZF6B-0]This may include:
These barriers must ensure there are no leaks through the barriers over relevant timescales (1,000+ years) under site representative conditions and characteristics (e.g., expected pressure gradients, hydrostatic head, geochemical exposure, and mechanical stress).
The Project Proponent must provide a detailed plan for seal integrity testing of sealing barriers between storage chambers, in conditions representative of the storage site.
[/R-GJS0-0]The plan must specify the test methods and inspection approach appropriate to the identified transport pathways, the acceptance criteria, the minimum testing frequency, and the procedures for addressing non conformities. Any seal that does not meet acceptance criteria must be remediated and retested prior to commencing storage operations in the relevant chamber, and material deviations and corrective actions must be documented in the PDD.
[/G-VRQ8-0]Project Proponents are required to conduct monitoring at the storage site for a minimum of 20 years after site closure. A post-closure monitoring plan must be included in the PDD and must include the following monitoring at the wall of the last accessible storage chamber:
[/G-95FK-0]Incremental changes of CO2, CH4, and/or pressure may indicate that there is a decay of feedstock within the storage site. Monitoring of gasses, pressure and other parameters as applicable, may be conducted through continuous or discrete sampling. If discrete sampling is used, weekly measurements are required over a three-year period to confirm functional stability, with ongoing monitoring for reversals required for 20 years. Where the Project Proponent conducts discrete sampling, sampling must be conducted weekly until conditions at the site are shown to be stable and less frequent monitoring is warranted in consultation with Isometric and the VVB.
[/G-HD31-0]Project Proponents utilizing this storage Module must provide a closure plan that describes the details of how the site/facility will be closed and storage chambers maintained after biomass burial activities have concluded. The site closure must include:
[/R-JTZX-0]The Project Proponent must provide a post-closure care plan that includes:
In addition, the Project Proponent must provide any supplementary information which is required of the Project by the local permitting and regulatory authorities.
[/G-Z82G-0]To limit long term environmental impacts from storage facilities, Project partner operators (where relevant) must formalize closure plans in accordance with local regulations and standards.
Project closure plans must be integrated with the mine operators' existing, or updated, mine closure and remediation plans. This requirement is relevant for Projects utilizing naturally derived materials for feedstock processing and containment in subsurface mine storage chambers.
[/G-RQZX-0]Project Proponents must provide the Project closure plan, as well as the mining operations closure plan within the PDD, upon submission to Isometric and The Project VVB.
[/G-JC2S-0]Note: Where the mining operator's mine closure plan cannot be provided, due to confidentiality or access issues, the Project Proponent must provide a signed affidavit from the mining operator outlining the impact of the Crediting Project on the existing mine closure plans, as well as any changes to plans as a result of the Project activities.
[/G-RXR3-0]Project Proponents must assess potential leaks that may be a result of intentional or inadvertent human disturbance of storage sites.
[/R-DVR5-0]Such potential scenarios may include, but not be limited to:
Where Project Proponents can provide a signed affidavit from a partner operator that demonstrates safeguards against potential leaks that may be a result of intentional or inadvertent human disturbance of storage sites, additional assessment may not be required.
[/G-Q2F9-0]Note: The suitability of an operator affidavit in lieu of a distinct assessment will be assessed on a Project by Project basis by Isometric and the Project VVB.
Project Proponents must assess the potential for reversals, as a result of human activities, both during the Project crediting period and post closure. Mitigation plans, or actions, must be outlined within the PDD upon submission to Isometric and the VVB.
[/R-4Y7H-0]Mitigating future human activity risks may require legal and institutional measures rather than purely technical controls, such measures may include:
Projects utilizing this storage Module must assess the Risk of Reversal according to the Isometric Standard Risk Assessment Questionnaire in consultation with Isometric. The Risk of Reversal may vary due to Project specific considerations. The Risk of Reversal will be reassessed every 5 years, aligning with the Crediting Period, or when new scientific research and knowledge are produced that highlights significant risks to the durability of the stored carbon.
When quantifying reversals, the Project Proponent must use a 100-year time horizon when selecting GWP. For this Module, GWP100 values provided in the IPCC 6th Assessment Report 24 (for CH4, N2O, and other relevant non-CO2 gasses must be used, or most recent updates. For methane, biogenic and non-biogenic GWP differentiation can be applied, where appropriate.
[math: CO_{2}e_{Storage}] represents the amount of CO2 (stored as organic carbon, C) that is buried and stored in the mine. This is the gross amount stored for each batch burial and does not account for reversals of storage from the storage formation.
Equations and storage calculation requirements for [math: CO_{2}e_{Storage}], including considerations for monitoring activities, are set out in Section 7.3.3 of the Subsurface Biomass Carbon Removal and Storage Protocol and are not repeated in this Module.
Project Proponents are required to identify how the implementation of the Project may impact mine permitting, operation, and closure, specifically where the implementation of a Project may impact waste production volumes, waste management and the mine operators net emissions.
[/R-F5ZT-0]Where a Project is undertaken within an active mining operation, the Project Proponent must engage with the operator and Engineer of Record (where appropriate), to ensure compliance with relevant environmental permitting and regulations.
[/G-JTBE-0]A Project Proponent must engage with the Engineer of Record prior to undertaking CDR activities to assess the potential impacts and suitability of undertaking CDR activities at the Project location.
[/G-QAMW-0]The Project Proponent is responsible for collecting and submitting Project data, including data generated by a partner operator, where a Project is undertaken within an active extractive operation or quarry. Such data may be used for both environmental monitoring, site characterization and carbon removal quantification, as long as the data is judged as suitable for such purposes by Isometric and the Project VVB. Where data submitted has been generated, or collected, by a partner operator, the Project Proponent must submit information related to uncertainty analysis, as well as any standard operating procedures (SOP) used by the partner operator.
Project Proponents must provide documentation that demonstrates the VVB entrusted with validating removals are able to visit the project site to undertake inspections at agreed intervals, at a minimum of every 2 years. Where access is limited due to safety concerns of the active mine operator, the Project Proponent must consult with Isometric to resolve validation issues. Such resolutions may include engaging the Project’s or operation’s Engineer of Record, where applicable, or a qualified third-party, to undertake measurements required by the VVB.
[/G-3RGD-0]Note: It is the sole responsibility of the Project Proponent to retrieve, manage and submit all data and information required to meet the requirements of this Module and relevant Protocols, even in instances where data has been generated by a partner operator.
Project Proponents must incorporate land-use restrictions to ensure that stored biomass remains undisturbed.
[/R-H505-0]Project Proponents must incorporate a legally binding mechanism on the storage site, such as a conservation easement, covenant, or other similarly restrictive agreement relevant to the jurisdiction which transfers between land owners.
[/G-AGSQ-0]The Project Proponent must demonstrate that the restrictive agreement provides legal protection against biomass disturbance for either 1,000 years or a restriction that is enforceable in perpetuity. The purpose of such a legal mechanism is to prevent excavation of and/or the interference with the storage facility for the entirety of the Project lifetime, at a minimum.
All of the eligibility criteria outlined in Table 1 must be met for a Project to be considered sufficiently legally protected for the purposes of carbon Credit generation:
[/G-WGEY-0]Table 1 Land Durability Requirements
ID |
| Documentation |
|---|---|---|
EC1 | Project Proponents must either own the storage site for the duration of the Project, or have a legally binding agreement with the mining operator that covers the duration of the Project. | Deed or other proof of ownership. |
EC2 | Project Proponents shall obtain and place a restrictive covenant or conservation easement on the land that prohibits all activities that may disturb stored carbon. These activities include, but are not limited to: the construction of residential or commercial buildings, the construction of wells or pipelines, digging or excavating, etc. | Full documentation of the restrictive covenant or conservation easement. |
EC3 | Project Proponents must identify a corporate, non-profit, or governmental stakeholder who will hold the legal right to enforce the covenant or easement in the event that the Project Proponent is not capable of pursuing enforcement of the covenant or easement. In the event where land ownership moves from the Project Proponent to a third party, this stakeholder shall be contractually entitled to receive a stake of property equal to 12% of the value of the land holdings operated by the Project. The purpose of this entitlement is to ensure that there exists an entity with both the incentive and resources to pursue legal enforcement should such action be necessary. | The Project Proponent must provide all of the following: Signed contracts outlining the relationship between the Project Proponent and the Stakeholder. Sufficient evidence and documentation to demonstrate that the criteria has been met. Evidence that the third-party verifier has assessed whether the Project Proponent has sufficiently developed a plan that is likely to ensure that there exists an entity with both the incentive and resources to pursue legal enforcement should such action be necessary. |
All records associated with the characterization, design, construction, burial operations, monitoring, site closure, and site maintenance must be developed and submitted to proper authorities as required by any applicable permitting authority.
Records Projectsof laboratory analyses and relevant permit limitations to demonstrate compliance must maintainbe maintained in accordance with the permit and available for review at any point during the Crediting Period or post closure. Where not required by the permit, records of all recordsanalyses and injections must be maintained by the storage facility or Project Proponent and provided for verification purposes for a minimum of 10five years after the end of the monitoring period.]
All recordsclosure must be maintained for a minimum of 10 years. Alland post-closure monitoring records must be maintained by the Project Proponent for a minimum of 10 years after collectionclosure. These records must be available to be consulted by interested parties for future clarifications if needed.
There is no single credible mechanism that can ensure, without uncertainty, that biomass buried in the subsurface will remain undisturbed in perpetuity given the relative nascency of such legal mechanisms relative to the time horizons required in the Isometric Standard. Land durability claims are subject to social and political factors and are thus different in nature from claims regarding physical or geologic durability. Isometric has developed a set of land security eligibility criteria that align with current best practices for legal strategies to restrict future uses of land. ThisThe Protocol and this Module also considers the risk associated with land ownership as a risk factor in determining the Risk of Reversal and corresponding buffer pool.
Where the Project Proponent has partnered with a mining operator, for the purpose of biomass storage, evidence is required to demonstrate intended land use following Project cessation and subsequent mine closure. Such evidence may take the form of the operations closure plan or any relevant permitting documents. Where closure plans and remediation schemes have been updated, or amended, to take into consideration the storage of biomass within the mines subsurface, such documents must be submitted to Isometric and the Project VVB for review.
Isometric would like to thank following contributors to this Module:
Isometric would like to thank the following reviewers of this Module:
Zhang, Y., Wang, S., & Li, X. (2023). Diffusion of gases through low-permeability barriers: Implications for geological CO2 storage. Applied Geochemistry, 152, 105641 ↩
Whiticar, M. J. (1999). Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane. Chemical Geology, 161(1–3), 291–314. ↩
Martin Landrø, Daniel Wehner, Noralf Vedvik, Philip Ringrose, Nora Løw Løhre, Karl Berteussen, Gas flow through shallow sediments—A case study using passive and active seismic field data, International Journal of Greenhouse Gas Control, Volume 87, 2019,Pages 121-133, ISSN 1750-5836,https://doi.org/10.1016/j.ijggc.2019.05.001. ↩
Appelo, C.A.J. & Postma, D. (2005) Geochemistry, Groundwater and Pollution, 2nd ed., Balkema ↩↩2
Pettersen, R. C. (1984). The chemical composition of wood. In R. M. Rowell (Ed.), The chemistry of solid wood (pp. 57–126). American Chemical Society. ↩
Brantley, S. L., Goldhaber, M. B., & Ragnarsdottir, K. V. (2007). Crossing the disciplinary divides: an introduction. In Kinetics of water-rock interaction (pp. 1-18). ↩
Blume, HP., Beyer, L., Kalk, E., Kuhn, D. (2002). Weathering and Soil Formation. In: Beyer, L., Bölter, M. (eds) Geoecology of Antarctic Ice-Free Coastal Landscapes. Ecological Studies, vol 154 Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56318-88↩
Freeze, R. A., & Cherry, J. A. (1979). Groundwater. Prentice-Hall. https://fc79.gw-project.org/english/↩
Yining Wang, Jiefeng Wu, Jian-yun Zhang, Tiesheng Guan, Guoqing Wang, Junliang Jin, Zhenlong Wang,Depth distributions of soil temperature: Seasonal sensitivity and simulation across dryness/wetness conditions,Agricultural Water Management,Volume 316,2025,109571,ISSN 0378-3774,https://doi.org/10.1016/j.agwat.2025.109571. ↩
Pedro J L C, Julio T C, Francisco J G Á, Manuel J H O. Influence of Moisture, Temperature and Microbial Activity in Biomass Sustainable Storage. Special Focus on Olive Biomasses. Int J Environ Sci Nat Res. 2020; 25(3): 556165. DOI : 10.19080/IJESNR.2020.25.556165 ↩
Guy Reed, Kent Mctyer, Russell Frith,An assessment of coal pillar system stability criteria based on a mechanistic evaluation of the interaction between coal pillars and the overburden, International Journal of Mining Science and Technology, Volume 27, Issue 1,2017,Pages 9-15,ISSN 2095-2686,https://doi.org/10.1016/j.ijmst.2016.09.031. ↩
Manning, A. H. , Ball, L. B. , Wanty, R. B. , & Williams, K. H. (2020). Direct observation of the depth of active groundwater circulation in an alpine watershed. Water Resources Research, 56, e2020WR028548. https://doi.org/10.1029/2020WR028548↩
O'Connor, M. T., Cardenas, M. B., Neilson, B. T., Nicholaides, K. D., & Kling, G. W. (2019). Active layer groundwater flow: The interrelated effects of stratigraphy, thaw, and topography. Water Resources Research, 55, 6555–6576. https://doi.org/10.1029/2018WR024636↩
Chapelle, F.H. (2000) Ground-Water Microbiology and Geochemistry, 2nd ed., John Wiley & Sons, New York. ISBN: 978-0-471-34852-8. ↩
Lovley, D.R. & Chapelle, F.H. (1995) "Deep subsurface microbial processes," Reviews of Geophysics, 33(3), 365–381. https://doi.org/10.1029/95RG01305↩
Conrad, R. (2023). Complexity of temperature dependence in methanogenic microbial environments. Frontiers in Microbiology, 14, Article 1232946. https://doi.org/10.3389/fmicb.2023.1232946↩
Wu, H., et al. (2021). Limitations of the Q10 coefficient for quantifying temperature sensitivity of anaerobic organic matter decomposition: A modelling-based assessment. Journal of Geophysical Research: Biogeosciences, 126. https://doi.org/10.1029/2021JG006264↩
Felice, M., de Sieyes, N., Peng, J., Schmidt, R., Buelow, M., Jourabchi, P., Scow, K. and Mackay, D. (2018), Methane Transport during a Controlled Release in the Vadose Zone. Vadose Zone Journal, 17: 1-11 180028 https://doi.org/10.2136/vzj2018.02.0028↩
Iversen, N., & Joergensen, B. B. (1993). Diffusion coefficients of sulfate and methane in marine sediments: Influence of porosity. Geochimica Et Cosmochimica Acta, 57(3), p. 571–578. ↩
Boudreau, B. P. (1997). Diagenetic Models and Their Implementation: Modelling Transport and Reactions in Aquatic Sediments. Springer. ↩
Khalid, F., Razbin, M. Modeling peak ground acceleration for earthquake hazard safety evaluation. Sci Rep 14, 31032 (2024). https://doi.org/10.1038/s41598-024-82171-7↩
Mendoza, R. B., Hobbs, T. E., & Bostock, M. G. (2025). Exploring Seismic Hazard Scenarios of Potentially Active Faults in the Southern Coast Mountains of British Columbia, Canada. Bulletin of the Seismological Society of America, 115(5), 2002–2020. https://doi.org/10.1785/0120250089↩
Giardini, D., Grünthal, G., Shedlock, K.M., & Zhang, P. (1999). The GSHAP Global Seismic Hazard Map. Annali di Geofisica, 42(6), 1225-1228. ↩
Intergovernmental Panel on Climate Change (IPCC). (2023). Climate Change 2022 – Impacts, Adaptation and Vulnerability: Working Group II Contribution to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press; Cambridge Core. https://doi.org/10.1017/9781009325844↩