Biochar Storage in Low Oxygen Burial Environments

This Module details the durability, reversal risks and requirements for storage of carbon as biochar in buried, low oxygen conditions. This Module is intended for use in conjunction with other Isometric Protocols and Modules, and assumes the following:

• The full quantification of the net tonnes of CO₂e removal for Crediting occurs following the Isometric Biochar Production and Storage Protocol
• All environmental and social safeguards have been followed according to Section 5 in the Biochar Production and Storage Protocol

This Module was developed based on the current state of the art and publicly available science regarding biochar storage under low oxygen conditions. Biochar storage in low oxygen environments is a novel CDR approach, so this Module incorporates requirements that may be more stringent than some current relevant regulations or other protocols related to biochar for CDR. This Module will be reviewed when there is an update to scientific published literature which would affect net CO₂e removal quantification, durability claims or the monitoring guidelines outlined in this Module. Future versions of this Module may be altered, particularly regarding requirements for demonstrating durability of biochar, as the stability of CO₂ captured by biochar is better demonstrated and documented; quantification of biochar degradation is further improved and refined; and the overall body of knowledge and data regarding all processes, from feedstock supply to conversion and to permanent storage, is significantly increased.

This Module applies to Projects that meet all of the following criteria.

1. The Project must bury biochar in waste management lined landfill sites under a local authority jurisdiction, where a permit has been issued by the local authority to allow such activity to take place. This permit must:
   • be for solid waste disposal (i.e. residential and commercial waste, industrial waste, and/or construction and demolition debris)
   • incorporate findings of an environmental impact statement (EIS) or equivalent, if required by the local jurisdiction (which would also be consistent with Section 3.7 of the Isometric Standard)
   • require a post-closure care plan to be in place for at least 20 years after the date of site closure, with an adaptive management approach to respond to gas, leachate or ground and surface water monitoring results required under the permit during the post-closure period that may indicate risk to the environment
   • have safeguards in place to prevent disturbance after closure of the site (defined in Section 11), such as ensuring the integrity of final covers, liners, or any other components of any containment system, or the function of the facility's monitoring system
2. If the biochar is applied to the landfill site as part of Daily Cover (DC):
   • The DC must not be removed from the landfill site once it has been applied. Daily scraping practices are permitted as long as the daily cover does not leave the active waste disposal area and is re-applied for burial
   • The DC must be permanently buried within 1 week of application to ensure functional low oxygen conditions are achieved for storage of biochar (see Section 1.2)
3. The Project must result in biochar being stored in a low oxygen environment such that biochar degradation pathways are limited in scope (defined as functionally anoxic, see Section 1.2)
4. The Project must be located in areas governed by the US, Canada, United Kingdom and European Union. 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

Future versions of this Module may expand applicability to include more categories of eligible project sites, such as specifically designed burial storage pits.

Biochar is a carbon rich material with a significant fraction of the carbon being stable and durable over a time horizon of 200 years and beyond (see Isometric Biochar Production and Storage Protocol). Differences in production processes and feedstocks directly impact biochar quality and stability as they may result in variations in the labile (carbon that decomposes at rapid turnover times) and recalcitrant (stable carbon) fractions within the biochar.

The labile fraction of biochar is subject to degradation over a longer period of time due to different degradation pathways that are applicable to the physical storage location. These pathways can include:

1. Physical (dust loss, particle size reduction due to plowing or tillage)
2. Abiotic degradation - Chemical reactions related to environmental factors including but not limited to: natural mineralization, photodegradation, leaching due to water flows or freeze - thaw cycles¹
3. Microbial degradation can be either aerobic (presence of mycelial and fungal microbes)² or anaerobic (e.g., methanogenic microorganisms and consortia) ^3,1

Figure 1 Degradation pathways for biochar. Once low oxygen conditions are achieved in biochar burial storage sites the applicable pathway is highlighted in green. Pathways in grey can have minor short term effects and reverse impacts are not accounted for under this Module.

Each of these pathways is directly influenced by the storage environment, with the relevant site characteristics influencing which degradation pathways may be most prevalent in that storage environment. The durability of biochar is dependent not only on the storage site conditions but on biochar physical and chemical properties (see Section 3 for more information). Several storage options are available for biochar removal, including burial of biochar in low oxygen environments. In the case of burial storage where low oxygen conditions are achieved and maintained with engineered controls and specific site characteristics, abiotic degradation will become negligible allowing only biotic degradation to take place³.

"Low oxygen" as used in this Module is defined as functional anoxia, where there is a functional absence of oxygen in soil, which occurs when the supply of oxygen is slower than the demand and oxic respiration and other oxygen-consuming biological reactions are severely limited⁴. The requirements of this Module are written to ensure that landfill conditions facilitate a sufficiently rapid transition to functional anoxia such that oxic degradation is negligible. The supply of oxygen below-surface soils and burial environments can be influenced by water content/flow and soil characteristics. To ensure water ingression is not an issue, the requirements outlined in the Section 6 (Site Characterization) of this Module must be met. In a waste management landfill for solid waste, each day, biochar can be mixed with the Daily Cover (DC), where DC is applied on top of the daily deposited waste to ensure that waste is undisturbed and mitigate odour and dust control issues in the landfill. New fresh waste cover is introduced to the site each day, and within 1 week, as per the Applicability conditions outlined in Section 1.1, the buried biochar as part of daily cover (DC) will be permanently buried. Once the DC can be judged to be buried at a sufficient depth to ensure a functionally anoxic environment, anaerobic decomposition pathways present the primary biochar degradation pathway under low oxygen storage conditions, as outlined in Section 4.2. Most soils, mud and lower permeability saturated soil environments become functionally anoxic at depths of 10s of cm ^5,6. Additionally, landfill environments contain significant labile organic carbon that will lead to rapid oxygen drawdown⁷.

Quantification of the durability of biochar according to the current best available science must focus on the use of rigorous characterization of the biochar to calculate the fraction of biochar that is stable beyond the desired crediting time horizon. This should be coupled with conservative treatment of the uncertainty associated with that calculation (see Section 6.5 of the Biochar Production and Storage Protocol).

This Module sets requirements on the storage of biochar buried in permitted waste management sites (see Section 1.1, Applicability) for the purpose of carbon dioxide removal and describes how characterization of biochar should be used to quantify the number of Credits that are issued for a Project storing biochar in those sites. It also includes details of the environmental conditions that must be met and documented in the Project Design Document (PDD) to ensure that biochar-C is stably sequestered in these burial conditions for at least 1,000 years. This Module addresses storage site conditions and quantification of CO₂e_stored for biochar burial for storage in waste management sites. For more information on biomass feedstock eligibility and accounting and pyrolysis conditions please refer to the Biomass Feedstock Accounting Module which must be followed as outlined in the Biochar Production and Storage Protocol and Section 9.0 of the Biochar Production and Storage Protocol.

The Project Proponent must document in the Project Design Document (PDD) how the Project will monitor contaminant levels that may impact soil quality and the surrounding environment, contaminants to be monitored and the frequency of testing. If soil quality or groundwater are demonstrated or anticipated to be adversely affected as a result of runoff from the DC, the Project Proponent must complete the following:

• The Project Proponent must collaborate with land managers or owners to implement site storage management practices that maintain or enhance soil and groundwater quality. Examples of such practices at a landfill may include base liner construction, landfil gas management, odor contorol, leachate management systems, site closure and storwater management (See Section 11) in the landfill or appropriate storage and burial containment layers in the landfill (See Section 6)
• The Project Proponent must provide technical support, training and resources to help relevant stakeholders adapt to any changes in soil conditions due to the CDR project. This support could include optimizing biochar properties to facilitate remediation

Guidelines on appropriate site closure, leachate management, use of liners and covers, and odor control are provided in Section 9, Section 10 and Section 11 to minimize adverse impacts on soil, air, water and human health.

In addition, landfill sites must have a landfill gas and methane emissions monitoring and management system in place. The monitoring management system must be described in the PDD. The management system must have appropriate emissions control to minimize methane emissions such as an installed flare system.

As outlined in the Biochar Production and Storage Protocol, there are some potential risks to environmental and human health associated with biochar composition, for example:

• Heavy metals, potassium and phosphorus that may impact soil health and soil amendment properties (reduced fertilizer needs)
• Soil contamination by heavy metals or Persistent Organic Pollutants

Project Proponents should outline in the PDD what legal and regulatory requirements their Project adheres to in terms of environmental risks. In the absence of regulation, Projects should adhere to safe limits associated with the upper bounds set for the following by the World Biochar Certificate (WBC)⁸ for storage of biochar in agricultural soils:

1. Heavy metals; including Pb, Cd, Cu, Ni, Hg, Zn, Cr, As, Sb, Co, V
2. Organic contaminants; including PAHs, Benzo(a)pyrene, PCBs, PCDD/F⁹

Methods of measurement for these parameters should be outlined in full in the PDD and must adhere to the sampling guidance and monitoring frequency requirements set out in this Storage Module. Heavy metals, PBCs and PCDD/F measurements should adhere to the same sampling guidance and monitoring frequency included in Table 2 for PAHs ¹⁰.

Certain characteristics of biochar have demonstrated a potential positive impact on soil remediation and contaminant removal particularly in soils that are heavily impacted by elevated contaminant levels^11,12. There is evidence that biochar applied to locations with high concentrations of contaminants/hazards¹³ to human health could potentially lead to a decrease in the bioavailability of these contaminants^14,15by means of adsorption, therefore serving as a land remediation medium ^16,17,18.

Potential co-benefits of biochar burial in waste management landfill sites with elevated contaminant levels may include:

• Remediation of environmental pollutants ^19,10
• Decreased bioavailability of heavy metals ²⁰
• Reduced soil acidity ²¹
• Potential reduction of Persistent Organic Pollutants, including, but not limited to, PAHs, PCBs, Dioxins and Furans ^17,22
• Gas pollutant adsorption ²³

Section 3 outlines key parameters that influence biochar contaminant remediation potential, including properties that impact sorption capacity²⁴. Project Proponents may choose to report in the PDD any specific wider co-benefits related to remediation.

The analyses described in this section include measurements of physical properties that can influence a biochar's durability and capacity to absorb contaminants (PAHs, heavy metals) and landfill gas.

Table 1. Requirements for physical characterization of biochar

The following chemical analyses will be used to assess the reactivity and durability of biochar-C in different storage environments. Some of these measurements will be used in the quantification of CO₂e_stored, as outlined in Quantification of biochar durability Section 4.1 . The required and recommended measurements listed below investigate multiple mechanisms of reactivity (or prevention of), including aromaticity and aromatic condensation, functional groups, and volatility.

Specific analysis, including Heavy metals and PAHs are related to the impact the biochar can have as a soil remediating agent and are included to monitor long- term effect on heavy metal retention or PAHs impact.

Table 2. Requirements for physical characterization of biochar

There are multiple methods³¹ available to estimate biochar stability over long timeframes. These methods include: 1) upfront biochar characterization² and estimating the long term durability of the stable fractions and 2) using incubation studies and field³⁶ trials. Field trials and incubation studies are able to more accurately measure carbon and its impacts, capturing the unique interaction between biochar, soil and the surrounding environment³⁷. However, incubation studies or field trials are time consuming and location specific, making this option difficult for wide adoption³⁸.

Incubation experiments and field trials examining the durability of biochar application to soil have shown that a significant volume of the labile carbon (up to 50%)² can be lost within the first year under aerobic conditions. These reported carbon loss values span from 2.2% after two years of controlled incubation tests³⁸ to >27% after two years of field experiments ^1,37 and have been conducted to study degradation of biochar under aerobic conditions. The wide range in reported carbon loss can be attributed not only to variations in labile carbon and biochar quality but also to site conditions and whether the tests or trials were conducted in a controlled or open field experiments. In open field aerobic experiments other factors such as abiotic degradation will also take place.

Incubation tests conducted in a representative inoculum environment^39,40can simulate site storage conditions, and are therefore a valuable approach to quantifying carbon loss in biochar^41,42,43. Maintaining controlled storage conditions under an anaerobic environment significantly lowers abiotic degradation (which can be greater than 10% of the total carbon ³), making microbial degradation the primary factor in carbon loss (which accounts for 5% - 10% of the total carbon loss). At present there is insuffient data for anaerobic degradation of biochar in field trials or smaller scale incubation studies.

This Module presents two quantification frameworks for calculating the fraction of biochar ($F_{durable}$) that is stable for 1,000+ years.

Both quantification frameworks calculate the carbon stored, or $CO_2e_{stored}$, as follows:

$$CO_2e_{stored} = C_{biochar} \times m_{biochar} \times F_{durable} \times \frac{44}{12}$$

Equation 1

Where

• $C_{biochar}$ is the carbon content of the biochar (empirical), expressed as a fraction
• $m_{biochar}$ is the dry mass of biochar applied, in tonnes
• $F_{durable}$ is the fraction of durable biochar that remains in the soil for the full duration of the crediting timeline (1,000 years), and can be credited under this Module
• $\frac{44}{12}$ is the mass fraction of carbon dioxide and elemental carbon

Measurement of Carbon Content

See Section 8.3.1 of the Biochar Production and Storage Protocol for full guidelines on measurement of biochar carbon content, $C_{biochar}$.

Measurement of Mass of biochar buried

See Section 8.3.1.1 of the Biochar Production and Storage Protocol for full guidelines on measurement of mass of biochar buried, $m_{biochar}$.

Calculation of $F_{durable}$

Calculation of $F_{durable}$ is carried out differently in Option 1 (incubation testing combined with Random Reflectance, R₀) and Option 2 (Random Reflectance, R₀). Project Proponents must designate which quantification framework, Option 1 or Option 2 (outlined in full below), they will use for Crediting their Project in the PDD. Option 1 and Option 2 cannot be used in conjunction with one another. The quantification framework and corresponding durability associated must be clearly outlined in the PDD.

Option 1 is a two step approach for the quantification of carbon stored:

Step 1: Project Proponents must report a set of at least 500 measurements of R₀, calculated at the maceral-level, for quantifying the amount of carbon stored durably in the biochar which is buried in the low oxygen environment. Project Proponents are credited for the fraction of biochar which passes the 2% R₀ benchmark, outlined in Sanei et al. (2024). The histogram of the R₀ values should be submitted at the point of project verification for this crediting option. Biochar passing the benchmark of R₀ = 2% is considered durable for 1,000 years³¹, and is defined as $F_{inertinite}$ in Equation 2 below. The remaining non-durable fractions are eligible for additional crediting as outlined in step 2.

Step 2: Some of the non-durable (or labile) fraction of biochar stored in low oxygen conditions ($F_{labile}$) may be eligible for crediting. This must be done by quantifying the labile carbon that will persist after accelerated aging/degradation incubation tests optimized to represent biotic and abiotic storage conditions and including a conservative safety factor to account for potential future degradation (described below). The Project Proponent must report the results from direct, time-series observation of GHG evolution from representative biochar samples that have been incubated in a context analogous to the storage conditions. Time-series evidence of biochar stability must be included in the PDD with a minimum of six months of observation demonstrating biochar stability compared to control observations (longer observation windows are recommended). A description of the experimental conditions, positive and negative controls, and minimum detection limit (including how the minimum detection limit is determined) must be included in the PDD. Given the often unpredictable nature of biological replicates, more than one incubation study is required to characterize the mean and variance of biochar degradation. Individual degradation incubation studies will be considered valid for a period of six months; additional incubations must be conducted and submitted for the first verification after this six month period. Incubation results will be considered on a cumulative basis, meaning re-emissions estimates will be conservatively estimated from all previous biological replicates. The Project Proponent may seek approval from Isometric to discontinue incubations once there is sufficient data to characterize re-emission uncertainty (typically more than 30 biological replicates). Suitable tests could include standard ASTM tests for aging of polymers in landfill conditions in both anaerobic and aerobic conditions (ASTM D5526-18: accelerated anaerobic degradation in landfills; and ASTM D7475-20: accelerated aerobic degradation in landfills) or equivalent anaerobic incubation test (Biochemical Methane Potential: BMP test). This must include microbial inoculum representative of the storage site.

At this early stage in understanding of degradation of biochar under functionally anoxic conditions, the true degradation risk over a Project's durability horizon has some uncertainty and reversals via GHG emissions cannot be directly observed given that they are co-mingled with organic waste baseline GHG emissions. The presence of alternative electron acceptors (e.g., nitrates, oxides) or site conditions not included in incubations studies may present some risk of microbial degradation. While there is a reasonable likelihood that accelerated degradation experiments will capture a significant fraction of biochar degradation in functional anoxia, this Module requires that the fraction of biochar degradation observed be multiplied by a safety factor of 3 for the purpose of crediting. As such, the deduction associated with the degradation of the labile fraction is meant to be conservative based on available data from incubation, giving a high confidence in the credited outcome.

If the corresponding deduction is greater than the non-inertinite fraction, the Project Proponent must use option 2 instead.

This approach, and the safety factor used, will be reassessed and revised as new evidence from scientific research and commercial deployment are surfaced.

$$F_{durable}= F_{inertinite} + F_{labile}$$

Equation 2

Where

• $F_{durable}$ is the fraction of durable biochar that remains in the soil for the full duration of the crediting timeline (1,000 years), and can be credited under this Module
• $F_{inertinite}$ is the fraction of biochar carbon that is stable for the durability period as determined by random reflectance
• $F_{labile}$ is fraction of biochar carbon that is not inertinite but determined to be observationally stable from incubation studies

It may be the case that no GHG evolution is observed over the period of time-series analysis beyond the detection limit. Even when no detectable GHG production is measured, the Project Proponent, in consultation with Isometric, must produce a conservative estimate of the GHG production that may occur. This is because small, undetectable GHG production rates can yield significant reversals over longer periods of time. Given that empirical studies of biochar degradation in low-oxygen and functionally low oxygen environment are limited, analogous studies of oxic degradation are suitable for conservative estimation (this is because the rate and extent of oxic degradation is expected to be greater due to higher thermodynamic driving force). Project Proponents may choose one of the following options to determine a conservative discount factor:

A. Minimum detection limit of the incubation tests conducted, multiplied by a conservative factor of 3 to account for any GHG release that may occur over the Project duration.

B. Maximum carbon loss amount derived from literature studies of analogous (low-oxygen) or less-favorable (oxic) conditions.

C. Minimum value of a suitable decay rate extrapolated to a justified end-point. This rate may be derived from the minimum detection limit from incubation studies described above or literature values of analogous (low-oxygen) or less-favorable (oxic) conditions.

In any case, the evidence used to support a durability claim and conservative reversal estimate must be specific to a feedstock and processing method. All evidence supporting implementations of B and C above must be reviewed and approved by Isometric and provided in the PDD. Evidence of durability and conservative reversal estimates using option A must be conducted as described above. Indicative reference values for the calculation of a conservative discount factor (reported as maximum reported carbon loss or a suitable decay rate) are included in Appendix 1 (data used are based on aerobic degradation which is considerably higher than anaerobic) for guidance. Project Proponents can refer to reference values or choose an appropriate alternative, which must be pre-approved by Isometric prior to verification, provided sufficient justification is provided in the PDD. Alternative approaches to conservatively estimating long-term biochar degradation must be approved by the Isometric science team.

Option 2 allows Project Proponents to use Random Reflectance to estimate durability. Random reflectance is an indicator of aromaticity, aromatic ring unit size and condensation. A R₀ value greater than 2% has been proposed as a benchmark for quantifying the permanent pool of carbon in a biochar. Project Proponents using this option must report a set of at least 500 measurements of R₀, calculated at the maceral-level. Batches that adopt this measurement approach can be credited for the fraction of biochar which passes the 2% R₀ benchmark outlined in Sanei et al. (2024). The histogram of the R₀ values should be submitted at the point of project verification for this crediting option. Biochar passing the benchmark of R₀ = 2% is considered durable for 1,000 years³¹. Project Proponents using Option 2 for calculating the durable fraction should complete analysis of R₀ measurements as set out in Section 4.1.1. Option 2 will inherently deduct the remaining carbon stored in the biochar from the removal quantification.

Additional evidence and data, supporting the durability of the stored carbon can be submitted from Project Proponents for review. Type of additional data can include experimental site data or biochar sampling post application in the storage site and can be used to review the durability calculations for both Option 1 and Option 2.

In the 1,000 year durability timeline, evidence indicates that biotic degradation (fungi and anaerobic methanogenic bacteria) ⁴⁴ of complex organics under low oxygen conditions is exceedingly slow. However, some studies have shown degradation of very small fractions of the fused aromatic hydrocarbons in coal and potentially in biochar^45,46.

Data from previous studies were mainly reported on coal and hydrocarbons and involved some form of pre-treatment to increase the biodegradability of the hydrocarbons and are therefore not representative of the storage environments described in this Module. In addition, all relevant studies were conducted on coals and hydrocarbons and reported decreasing anaerobic degradation efficiency with decreasing number of hydrolytic bonds⁴⁷. Certain bacterial strains have been shown to be able to degrade low grade coals especially, those with higher H/C and O/C ratios⁴⁸. The impact and applicability on biochar samples is expected to be limited^44,49.

Certain physical and chemical characteristics of biochar, such as the active surface area, functional groups and cation exchange capacity have been shown to have a positive impact on soil remediation and contaminant removal. This impact is significant especially in cases with existing issues of soil contamination which affects 33% of global soils ^11,12.

Recent research has explored the potential of biochar for additional CO₂ capture by selective adsorption in gas streams ^24,50, which has the potential to serve as an additional carbon dioxide removal pathway. Some research^51,52,23 indicates that biochar (dependent on biochar properties), may be an effective sorbent of some greenhouse gasses including methane and carbon dioxide ⁵¹. Biochar sorption capacity can potentially have a significant impact in storage locations where large volumes of gasses are emitted (landfill sites) as it could result in selectively absorbing gasses. When the latter is combined with an effective site closure and appropriately maintained storage conditions, carbon may be absorbed by biochar and stored durably. If the additional absorbed carbon was biogenic in origin, then this could be classified as additional CO₂ removal. If the additional carbon absorbed was fossil fuel in origin, then this would represent an emissions reduction.

At the time of writing, there is not sufficient evidence to include this in the quantification framework for net CDR achieved by biochar storage in low oxygen environments. This will be revisited in future editions of the Module as new evidence is published and/or presented to Isometric by Project Proponents as proof of quantification.

As outlined in Background (Section 1.2), "low oxygen" storage conditions can be reasonably assumed in landfills in a matter of days after Daily Cover (DC) has been applied. This is because the depth of burial and high rate of organic matter degradation in landfills is sufficient to ensure functional anoxia (see Section 1.2). The thickness of Daily Cover (DC) applied to landfills should be at an average depth of 15 cm, so that biochar applied as DC reaches depths of meters within a few weeks depending on the landfill size and operations ⁷. Daily cover material can include materials such as foundry sand, recycling fluff, soil, quarry minerals, green waste, compost based materials, bottom ash or synthetic materials like foam, so long that the materials comply with the site's permit requirements ⁵³. Additional landfill practices including compaction of the waste and daily cover once applied ensure that relatively consistent density of the waste mass is achieved which can help avoid differential settlement, slope stability issues and oxygen intrusion. The Project Proponent should clearly outline in the PDD the daily cover practices that apply to the Project boundary.

To confirm that low oxygen conditions are maintained, oxygen monitoring must be carried out at the waste management site for the duration of the Project until site closure has been undertaken (see Section 11). A constant vacuum will be maintained in landfill sites to draw the methane to the flare system (as outlined in Section 2.1). Project Proponents must submit a detailed oxygen monitoring plan in the PDD. The average O₂ sensor reading within landfills should not typically be above 0-2% O₂ ⁵⁴. For example, the EPA dictates a regulated limit of 5% to ensure that waste management sites do not present an explosion risk ^55,56. Safe oxygen limits for operation will be determined by the permit issued to the Project Proponent. If readings from the oxygen sensor exceed safety limits set by the permit, this should be reported immediately to (i) the VVB undertaking verification of the Project and (ii) Isometric for assessment of Project risk and risk of reversal. Follow-on actions may include cessation of credit issuance until oxygen readings are returned to expected levels at the waste management site. In the absence of a safe oxygen limit being set for operation by the permit, the limit must be 5%.

For biochar burial storage site selection, several site attributes need to be assessed for their suitability as a storage site according to the criteria listed below, prior to project initiation. These categories include surface water, groundwater, geology and soil, and regional seismicity. Project Proponents must provide detailed information on the following site characteristics and demonstrate that they pose limited risk to the Project.

Storage sites must be located outside of the flood plain of all major waterways and arterial streams based on the governmental flood maps with longest available time duration. Where natural permeability of soils is impacted by the development of landfill sites, adequate drainage must be installed to transfer all precipitation and meltwater away from the site. No pooling of water is permitted within the waste limits of the disposal facility in areas where biochar has been deposited, with the exception of leachate transmission along the base liner and/or sump areas. If any sedentary water is found in areas where biochar has been deposited after 48 hours following a precipitation event during the course of regular inspection, it must be immediately reported to Isometric and addressed with a permanent solution within 90 days. Where floodplain maps are drawn for 1,000-year storms based on historical considerations and multi-decadal records, or where future climate change is likely to considerably affect the distribution of suitable locations, modeling or additional conservative buffer zones must be applied. For all sites located near existing water bodies, such as oceans, ponds, or lakes, modeling must confirm that the proposed site will not be impacted over a 1,000-year period by changes in sea level or shifting precipitation patterns. It is recommended that Project Proponents consult a professional hydrogeologist who is certified in the jurisdiction containing the Project as part of assessing a Project's 1,000 year risk from surface water. For landfill sites, this information may already be available from the landfill site operator and in the site permit application.

Project sites must be located outside of the zone of influence of local groundwater and aquifers, both laterally and vertically. The evaluation of suitability for project sites, as well as 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.

The requisite number of groundwater sampling location sites, spacing, and depth is determined on a site-specific basis, based upon applicable regulations and in accordance with the site permit, which may depend on aquifer thickness, groundwater flow rate and direction, and the other geologic and hydro-geologic characteristics of the site. The Project Proponent must also assess the general direction and magnitude of groundwater level change that may result from climate change. It is recommended that Project Proponents consult a professional hydrogeologist who is certified in the jurisdiction containing the Project as part of assessing a Project's 1,000 year risk from groundwater.

To ensure that containment can be guaranteed as per Section 11, Site Closure, lithology must be considered by Project Proponents to prove there is a low risk of migration of stored biochar from the intended storage site. For such Projects, the Project Proponent must describe the following site properties, including how each property will be evaluated and addressed to ensure permanence of the stored biomass. Often the site permit can be relied on to meet these requirements.

• Permeability - soil composition and texture and bedrock composition and texture
• Soil properties - Including pH and clay content
• Hydraulic conductivity - hydraulic conductivity values for all materials
• Plasticity - liquid limit and plasticity index values for all materials
• Sorption capacity - mineral composition, especially abundance of expandable phyllosilicates

The Project Proponent must characterize any material seismic risk in the vicinity of the storage site. This must include the following:

• Peak Ground Acceleration (PGA) - PGA from shock waves, modeled for 50-year or longer timescale and wave-amplification potential implied by local lithology
• Peak Ground Displacement (PGD) - mechanical response model for site materials and geologic evidence for absence of land surface disturbance by earthquake activity

The table below contains target values against which a potential biochar storage site should be assessed and compared. Any deviations from the ranges specified here must be justified in the PDD. Deviation from the below specified values is generally permissible when specified by local regulations and/or permitting requirements.

Table 3. Target values for site characterization

There is no single credible mechanism that can ensure, without uncertainty, that biochar buried in waste management sites 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.

Project Proponents must incorporate land-use restrictions to ensure a high likelihood that stored biochar remains undisturbed. Project Proponents are required to 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. The Project Proponent must demonstrate that the restrictive agreement provides legal protection against biochar 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 or interference with the storage facility for the entirety of the Project lifetime, at a minimum. All of the following eligibility criteria must be met for a Project to be considered sufficiently legally protected for the purposes of carbon Credit generation:

Table 4. Land durability requirements

When developing on sites suitable for low oxygen burial (see Section 1.1, Applicability, for guidelines on applicable location categories), Project Proponents must account for the land use impacts by calculating Replacement Emissions for the quantity of CO₂ removal that would counterfactually have been conducted on the site used. The Project Proponent must consider counterfactual CO₂ sequestration associated with vegetation at the Project site(s) that was present before the site was cleared for the Project purposes. This must include all project sites that were cleared as a result of the CDR project including sites for project facilities and storage sites. The quantification of CO₂e Counterfactual must consider counterfactual CO₂ sequestration using annual CO₂ sequestration rates and consider sequestration over a period of 15 years.

The storage of biochar must be permanently contained at the storage site. The PDD must include a detailed description of the liner system, leak detection, leachate collection, leachate removal, and how the facility will prevent run-on and run-off.

The base liner system provides a barrier between the waste and the underlying ground and prevents water that has percolated through the waste (i.e. leachate) from reaching groundwater. The components and geometric design of the base liner system must be modeled using local climate data to demonstrate compliance with the jurisdictional regulations on the portion of precipitation that falls within the waste limits that is captured and removed by the liner and leachate collection system, and/or the maximum average leachate head allowed on the liner. One such model available through the Unites States Environmental Protection Agency (U.S. EPA) is the Hydrologic Evaluation of Landfill Performance (HELP) Model. In the absence of regulations on leachate collection as a fraction of total precipitation over the waste limit, a maximum of 30 cm of leachate head shall be allowed to accumulate on the base liner (not including sumps or leachate collection trenches).

The PDD must include a description of how the facility will monitor, collect and treat landfill gas. A plan must be prepared to address and manage odors and complaints from nearby properties. Landfill gas collection and treatment shall comply with the jurisdictional regulations, or the facility’s air permit on the destruction of methane and/or other parameters included in the permit.

Direct monitoring of stored biochar will be difficult due to:

1. the challenges in exhuming stored solid wastes from landfill sites, and
2. the impossibility of attributing landfill gas emissions to biochar degradation, rather than from baseline waste degradation at the waste management site.

Proper site closure and post-closure care is central to the maintenance of low oxygen conditions for storage of buried biochar, due to the above challenges with direct monitoring. Project Proponents utilizing this storage Module must provide a closure plan that describes the details of how the site will be closed and maintained after biochar burial activities have concluded. The site closure must be carried out according to the permit requirements, and include:

• A description of how final closure of the facility will be achieved
• An estimate of the maximum amount of possible hazardous additives (if used) kept on site during the facility's operating life, with a description of each hazardous additive (if applicable) and management to be performed
• A detailed description of closure methods
• A description of any other required steps, such as groundwater monitoring and leachate management that will continue post-closure
• A schedule of closure activities, including closure dates for each unit and the entire facility
• A description of procedures, structures and equipment to prevent surface water run - on and control run - off
• As outlined in Section 2.1, landfill sites should have a landfill gas and methane emissions monitoring and management system in place with appropriate emissions control to minimize methane emissions such as an installed flare system

Permits issued for undertaking carbon removal activities, dependent on the issuing body, may not describe a process or criteria for allowing landfills to exit post-closure care and move into the less stringent phase of landfill maintenance. In these cases, the Project Proponent must provide a post-closure care plan that includes:

• At least 20 years of post-closure care after the date of closure
• A monitoring plan (described below)
• A description of planned maintenance activities for carbon storage (e.g., liners, final covers, leachate management systems)
• Contact information during the required post-closure care period

In addition, the Project Proponent must provide any supplementary information which is required of the Project by the permit issued by the local permitting and regulatory authorities in the PDD.

The closure standards for municipal solid waste facilities in the United States (MSWLFs)⁵⁷ require owner/operators to install a final cover system to minimize infiltration of liquids, limit soil erosion and prevent adverse environmental impacts (e.g., odors, release of leachate, emissions of methane). Project Proponents must formalize closure plans in accordance with local regulations.

Projects should not, for any reason, encourage or incentivize the creation or expansion of industrial wastelands due to Project activities. The reclamation of Project sites and their surroundings, while potentially required by the legal mechanism for land preservation (e.g. conservation easement), will be supportive of positive stewardship of lands and demonstrating respect for local stakeholders.

As outlined in Section 2.5.9 of the Isometric Standard, the Buffer Pool is a mechanism used to insure against Reversal risks that may be observable and attributable to a particular project through monitoring. Based on present understanding, reversals in Biochar storage in low oxygen burial environments will not be directly observable with measurements and attributable to a particular project. Projects Crediting against this Module are credited conservatively to account for degradation of labile pools of biochar within the relevant crediting time horizon. Projects that meet the applicability criteria of this Module are categorized as having a Very Low Risk Level of Reversal according to the Isometric Standard Risk Assessment Questionnaire. The Buffer Pool corresponding to this lowest risk score is 2% and is intended as an additional precaution against unknowns.

Following Section 2.5.9 of the Isometric Standard, storage uncertainty for open systems is primarily accounted for within the removal quantification framework. For more details on Reversals, refer to Section 2.5.9 and Section 5.6 of the Isometric Standard.

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.

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

Isometric would like to thank following contributors to this Module:

• Konstantina Stamouli, Ph.D.
• Sophie Gill, Ph.D.
• Kevin Sutherland, Ph. D.

Isometric would like to thank following reviewers of this Module:

• Christian Wurzer, Ph.D. (UK Biochar Research Centre)
• Anne Ware, Ph.D. (National Renewable Energy Laboratory)
• Isaac Fuhr (Carlson McCain)
• Nick Bonow (Carlson McCain)

This appendix contains indicative reference values for the selection of a discount factor as according to the quantification framework set out in Section 4.1.1. Please see Section 4.1.1 for full details on how these values will be pre-approved prior to verification by Isometric.

Data on the table were extracted from different sources and studies and only the upper values of reported carbon loss have been included for the longest reported experiment duration⁵⁸. Selection of a value should be based on feedstock and if available on process conditions for the longest duration included.

Table A1. Cumulative Carbon Loss reference values. All material types are biochar.

Table A2. Residual Decay Rates reference values. All material types are biochar.

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