Biochar Storage in Low Oxygen Burial Environments v1.0

1.0

Introduction

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.

1.1

Applicability

Projects must meet all of the following criteria to be eligible under this module

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 the relevant Standard section)
- 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

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)

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)
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.

1.2

Background

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:

Physical (dust loss, particle size reduction due to plowing or tillage)
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
Microbial degradation can be either aerobic (presence of mycelial and fungal microbes)² or anaerobic (e.g., methanogenic microorganisms and consortia) ³^,¹

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.

2.0

Environmental and Social Safeguards

2.1

Safeguarding of low oxygen burial storage sites

The Project 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, landfill gas management, odor control, leachate management systems, site closure and water 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.

2.2

Required measurements

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:

Heavy metals; including Pb, Cd, Cu, Ni, Hg, Zn, Cr, As, Sb, Co, V
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.

2.3

Co-benefits and soil remediation

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 levels¹¹^,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 contaminants¹⁴^,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.

3.0

Biochar Characterization

Projects must use the following analyses of the physical and chemical composition of biochar to assess the reactivity potential of biochar-associated carbon in low-oxygen burial environments. Additionally, certain measurements are not mandatory; however, Projects are strongly encouraged to measure and report them to support scientific progress.

3.1

Physical Characteristics

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

Property	Analytical Method	Description	Monitoring Frequency	Recommended or required?
Specific surface area	BET ISO 9277:2022	Surface area of applied material may influence a number of biochar stability and soil health characteristics, including: SOC stocks, adsorption rates, water retention and porosity²⁵^,²⁶. Given the relative high porosity of biochar, specific surface area as opposed to external surface area may also indicate how the biochar will evolve as it ages in soil. The specific surface area will change overtime in soil ²⁷^,²⁸, but there is no minimum or maximum surface area to prevent the acceleration of biochar degradation. Higher specific surface area is likely to accelerate degradation, especially in the case of large particles(where most area is internal)¹.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Required
Porosity	Mercury porosimetry and gas adsorption ISO 15901-2:2022	Porosity is an indicator of water adsorption potential²⁹^,³⁰. Increased water sorption is associated with the acceleration of physical weathering of the biochar material, thus affecting biochar stability. Biochar porosity will not be constant over time, but there is no minimum or maximum porosity to prevent the acceleration of biochar degradation.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Required
Specific external surface area	Sieving ISO 17892-4:2016	Specific external surface area can be estimated from the particle size distribution, which is the parameter measured by sieving. Generally, larger biochar particles will degrade slower.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Required

3.2

Chemical Characteristics

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

Property	Threshold	Analytical Method	Description	Monitoring Frequency	Recommended or required?
$C_{biochar}$		Standard Test Methods for Determination of Carbon, Hydrogen and Nitrogen in Analysis Samples of Coal and Carbon in Analysis Samples of Coal and Coke ASTM D5373 or Standard Test Method for Determination of Carbon, Hydrogen and Nitrogen in Analysis of Solid Biofuels EN ISO 16948:2015	The carbon content of applied biochar is necessary for the quantification of CO₂e_stored, in accordance with Section 8.0 of the Biochar Production and Storage Protocol.	Measure every production/storage batch as per method A or B applicable. Minimum number of 3 samples per storage batch	Required
$m_{biochar}$		Direct mass measurement with calibrated weigh scales	The mass of applied biochar is necessary for the quantification of CO₂e_stored, in accordance with Section 8.0 of the Biochar Production and Storage Protocol.	Measure every storage batch	Required
Moisture Content		Standard Test Methods for Determination of Moisture Content in Analysis Samples of Wood Charcoal ASTM D1762-84 or Standard Test Method for Determination of Moisture Content in Analysis of Solid Biofuels ISO 18134-1:2022	The moisture content of applied biochar is necessary for the quantification of CO₂e_stored, in accordance with Section 8.0 of the Biochar Production and Storage Protocol. Carbon content can be reported on a dry basis to account for differences in total biochar mass.	Measure every production/storage batch as per method A or B applicable. Minimum number of 3 samples per storage batch	Required
Random Reflectance (R₀)	2% ³¹	White-light microscopy, eg ISO 7404-5:2009	Random reflectance is an indicator of aromaticity, aromatic ring unit size and condensation ³². A R₀ value greater than 2% has been proposed as a benchmark for quantifying the permanent pool of carbon in a biochar. The R₀ frequency distribution histogram can be used to decide what fraction of biochar above this benchmark can be classified as chemically inert.	Measure every production/storage batch as per method A or B applicable. Minimum number of 3 samples per storage batch	Required
H/C_organic	< 0.5 ³³	C_org is calculated by subtracting the inorganic carbon from the total carbon content. H/C_organic is calculated by dividing H content by C_org. C_org and H content may be calculated with ASTM D5373 or ISO 16948 and reported on dry basis. Inorganic carbon may be measured after biochar is ashed at 550 ⁰C with direct measurement of the inorganic carbon content in the ash content with ISO 16948:2015	Low H/C_organic ratios indicate the presence of significant amounts of aromatic compounds within the biochar. Aromatic compounds are highly stable, which is conducive to long-term stability of sequestered biochar in soil.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Recommended
Cation Exchange Capacity (CEC)		CEC is measured by cation extraction and subsequent measurement using ICP-MS (ISO 17294-1:2004) /OES (ISO 11885:2007) or AAS (standard). Appropriate extraction methods include ISO 11260:2018, ISO 23470:2018, or the Chapman method.	High CEC values are correlated with the presence of oxygen containing functional groups³⁴. An increase in oxygen containing functional groups may increase the reactivity of the biochar. CEC is also an indicator of biochar's ability to retain and exchange nutrients³⁵.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Required
Ash Content		Standard Test Method for the Determination of Ash Content in Solid Biofuels ISO 18122:2022	Ash is the inorganic portion of biochar that will not volatilize even if combusted	Measure every production/storage batch as per method A or B applicable. Minimum number of 3 samples per storage batch	Required
Polycyclic Aromatic Hydrocarbons PAHs, sum of USEPA 16		Gas Chromatography coupled with Mass Spectrometry (GC-MS)and/or High Performance Liquid Chromatography analysis eg ISO 13859:2014 or BS EN 17503:2022	Polycyclic aromatic hydrocarbons are organic molecules with fused aromatic rings that can be formed during the pyrolysis process and retained in the biochar. They are chemically stable with a high sorption capacity, known carcinogens and are persistent pollutants that can travel in the environment chain.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Required
Heavy metals including As, Cr, Cd, Co, Cu, Hg, Ni, Pb, Sb, Zn, V		Elements As, Cd, Cr, Cu, Ni, Pb, Zn refer to EN ISO 17294-2 ICP MS standard test method for determination of selected elements Element Hg refer to ISO 16772:2004 standard test method for the determination of Mercury using cold vapor atomic absorption spectrometry Elements Sb, Co, V refer to EN 15411:2011 standard test method for the determination of trace elements	Concentration of heavy metals in biochar is dependent on the feedstock and the process used¹¹. Specific heavy metals have adverse effects and are selected for monitoring²⁰. High concentrations of heavy metals may result in bioaccumulation in biotic systems and increase toxicity in soils and the environment ¹².	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Required
pH		Slurry pH probe. Refer to ISO 10390:2021	Biochar pH indicates how biochar may influence soil health and quality, and thereby microbial activity. In this way, pH may have a secondary impact on biochar durability. There is no eligibility threshold associated with biochar pH.	Measure at project validation unless feedstock, reactor or process parameters change Minimum number of 1 sample	Recommended

4.0

Quantification of biochar durability in low oxygen environments

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 environment³⁹^,⁴⁰can simulate site storage conditions, and are therefore a valuable approach to quantifying carbon loss in biochar⁴¹^,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.

4.1

Quantification of CO₂eStored

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.

4.1.1

Option 1: Random Reflectance to quantify the stable or inertinite fraction plus Incubation Experiments to quantify the likelihood of degradation of the labile biochar fraction

If choosing option 1, project must follow the 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 A (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.

4.1.2

Option 2: Use of Random Reflectance to quantify stable fraction of biochar

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.

4.2

Long-term carbon degradation under low oxygen conditions

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 biochar⁴⁵^,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 limited⁴⁴^,⁴⁹.

4.3

Emissions reductions or removal potential

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 research⁵¹^,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.

5.0

Maintenance of low oxygen conditions

5.1

Landfill site best practice guidelines

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.

5.2

Oxygen monitoring

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%.

6.0

Site Characterization

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.

6.1

Hydrology Surface water

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.

6.2

Hydrology groundwater

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.

6.3

Local Geology and Soil Properties

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

6.4

Seismicity

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

6.5

Target values

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

Parameter	Target value
Groundwater hydraulic conductivity (Kgw)	≤ 1x10^-10 meter per second
Confining layer thickness (LC)	10 30 meters
Surface hydraulic conductivity (KSI)	≤ 5 10^-10 meters per second
Cap thickness (LCI)	3.5 5 meters
Peak ground acceleration (PGA)	9% (0.88) percent of g (meters per second squared)
Peak ground displacement (PGD)	0.012 meters

7.0

Legal Framework to Ensure Permanence

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

	Condition	Documentation required
EC1	Project Proponent must own the storage site for the duration of the Project. (Note: Exceptions will be considered for leasing of land, or agreement for operation within land owned by a waste management operator, provided that documentation is provided to demonstrate leasing or formal agreement for use of the land for the duration of the Project)	Deed or other proof of ownership.
EC2	Project Proponent or its contracted partners must obtain and place a restrictive covenant or conservation easement on the land included within the Project's boundaries (landfill cells where biochar is stored) that prohibits activities that may disturb stored carbon. Activities in adjacent cell and in the remaining landfill area are excluded from this criteria. 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. It is noted that routine closure activities (e.g. installation of wells) or post-closure activities and care or maintenance of existing infrastructure as required by permits or applicable regulations are generally permissible under this Module.	Full documentation of the restrictive covenant or conservation easement.
EC3	Project Proponent 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. If the Stakeholder is a government or regulatory body, the Project Proponent must provide evidence that the Stakeholder will fulfill all permitted and regulatory requirements pertaining to site closure, care and maintenance. If the Stakeholder is a non-government entity the Stakeholder shall be entitled to receive a stake of property equal to at least 10% of the value of the land holdings operated by the Project in the event where land ownership moved from the Project Proponent to a third party. 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.	Signed contracts outlining the relationship between the Project Proponent and the Stakeholder or proof of applicable regulations (for regulatory or governmental Stakeholders). The VVB must determine 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.

8.0

Counterfactual Land Use

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.

9.0

Base Liner Construction and Leachate Management

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).

10.0

Landfill Gas Management and Odor Control

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.

11.0

Site Closure

Direct monitoring of stored biochar will be difficult due to:

the challenges in exhuming stored solid wastes from landfill sites, and
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.

12.0

Risk of Reversal and Buffer Pool

As outlined in the relevant section 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 the relevant section 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 the relevant sections of the Isometric Standard.

13.0

Record Keeping

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 for a minimum of 10 years after collection.

14.0

Acknowledgements

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)

15.0

Definitions and Acronyms

BaselineA set of data describing pre-intervention or control conditions to be used as a reference scenario for comparison.
Buffer PoolA common and recognized insurance mechanism among Registries allowing Credits to be set aside (in this case by Isometric) to compensate for Reversals which may occur in the future.
Carbon Dioxide Equivalent Emissions (CO₂e)The amount of CO₂ emissions that would cause the same integrated radiative forcing or temperature change, over a given time horizon, as an emitted amount of GHG or a mixture of GHGs. One common metric of CO₂e is the 100-year Global Warming Potential.
ConservativePurposefully erring on the side of caution under conditions of Uncertainty by choosing input parameter values that will result in a lower net CO₂ Removal or GHG Reduction than if using the median input values. This is done to increase the likelihood that a given Removal or Reduction calculation is an underestimation rather than an overestimation.
CounterfactualAn assessment of what would have happened in the absence of a particular intervention – i.e., assuming the Baseline scenario.
CreditA publicly visible uniquely identifiable Credit Certificate Issued by a Registry that gives the owner of the Credit the right to account for one net metric tonne of Verified CO₂e Removal or Reduction. In the case of this Standard, the net tonne of CO₂e Removal or Reduction comes from a Project Validated against a Certified Protocol.
DurabilityThe amount of time carbon removed from the atmosphere by an intervention – for example, a CDR project – is expected to reside in a given Reservoir, taking into account both physical risks and socioeconomic constructs (such as contracts) to protect the Reservoir in question.
FeedstockRaw material which is used for CO₂ Removal or GHG Reduction.
Greenhouse Gas (GHG)Those gaseous constituents of the atmosphere, both natural and anthropogenic (human-caused), that absorb and emit radiation at specific wavelengths within the spectrum of terrestrial radiation emitted by the Earth’s surface, by the atmosphere itself, and by clouds. This property causes the greenhouse effect, whereby heat is trapped in Earth’s atmosphere (CDR Primer, 2022).
Issuance (of a Credit)Credits are issued to the Credit Account of a Project Proponent with whom Isometric has a Validated Protocol after an Order for Verification and Credit Issuance services from a Buyer and once a Verified Removal or Reduction has taken place.
ModelA calculation, series of calculations or simulations that use input variables in order to generate values for variables of interest that are not directly measured.
ModuleIndependent components of Isometric Certified Protocols which are transferable between and applicable to different Protocols.
ProjectAn activity or process or group of activities or processes that alter the condition of a Baseline and leads to Removals or Reductions.
Project Design Document (PDD)The document that clearly outlines how a Project will generate rigorously quantifiable Additional high-quality Removals or Reductions.
Project ProponentThe organization that develops and/or has overall legal ownership or control of a Removal or Reduction Project.
ProtocolA document that describes how to quantitatively assess the net amount of CO₂ removed by a process. To Isometric, a Protocol is specific to a Project Proponent's process and comprised of Modules representing the Carbon Fluxes involved in the CDR process. A Protocol measures the full carbon impact of a process against the Baseline of it not occurring.
RemovalThe term used to represent the CO₂ taken out of the atmosphere as a result of a CDR process.
Replacement EmissionsAny emissions that occur to compensate for biomass that was previously serving another purpose and is now being used for carbon removal or GHG reduction. For example, if agricultural waste was previously left on a field to decompose - fertilizer production to replace those nutrients need to be accounted for.
ReversalThe escape of CO₂ to the atmosphere after it has been stored, and after a Credit has been Issued. A Reversal is classified as avoidable if a Project Proponent has influence or control over it and it likely could have been averted through application of reasonable risk mitigation measures. Any other Reversals will be classified as unavoidable.
StakeholderAny person or entity who can potentially affect or be affected by Isometric or an individual Project activity.
Standards (scientific)Standard physical constants as well as standard values set forth by bodies such as the National Institute of Standards and Technology (NIST) or others.
StorageDescribes the addition of carbon dioxide removed from the atmosphere to a reservoir, which serves as its ultimate destination. This is also referred to as “sequestration”.
UncertaintyA lack of knowledge of the exact amount of CO₂ removed by a particular process, Uncertainty may be quantified using probability distributions, confidence intervals, or variance estimates.
ValidationA systematic and independent process for evaluating the reasonableness of the assumptions, limitations and methods that support a Project and assessing whether the Project conforms to the criteria set forth in the Isometric Standard and the Protocol by which the Project is governed. Validation must be completed by an Isometric approved third-party (VVB).
VerificationA process for evaluating and confirming the net Removals and Reductions for a Project, using data and information collected from the Project and assessing conformity with the criteria set forth in the Isometric Standard and the Protocol by which it is governed. Verification must be completed by an Isometric approved third-party (VVB).

16.0

Appendix A

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.

Material type	Feedstock	Decay experiment	Reported carbon loss	Study Duration	Experiment conditions	Reference
Biochar	Oak wood (600^oC)	Incubation studies	8.9%	1 year		Zimmerman et al.³⁹
	Oak wood (650^oC)	Incubation studies	1.1%	3.2 years		Zimmerman et al.³⁹
Biochar	Mango prunings (400 600^oC)	Field studies with stable isotope measurement method	3.3%	2 years	Aerobic conditions	Major et al. ³⁸
Biochar	Eucalyptus (450^oC)	Field studies	7.0%	1 year	Aerobic field conditions	Singh et al. ⁵⁹
Biochar	Straw and corn cob	Incubation study	0.6%	1 year	Aerobic conditions	Budai et al. ⁶⁰
Biochar	Eucalyptus (550^oC)	Incubation study	1.0%	2 years	Aerobic conditions	Fang et al. ⁴⁰
Biochar	Orchard prunings ( 500^oC)	Field trial	7%	15 years	Aerobic field study	Chiaramonti et al. ⁴¹
Biochar	Wood	Incubation studies and field trials	10.9%	2 years	Aerobic lab. incubation studies	Azzi et al. ⁴²
	Agricultural Residues	Incubation studies and field trials	22.6%	2 years	Incubation studies	Azzi et al. ⁴²
	Manure	Incubation studies and field trials	7.3%	2 years	Incubation studies	Azzi et al. ⁴²
	Biosolids	Incubation studies and field trials	8.9%	2 years	Incubation studies	Azzi et al. ⁴²
	Grass	Incubation studies and field trials	5.8%	2 years	Incubation studies	Azzi et al. ⁴²

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

Material type	Feedstock	Decay experiment	Decay rate	Study Duration	Experiment conditions	Reference
Biochar	Mean value for different feedstocks	¹³C & ¹⁴C measurements	0.013 %.day^-1 - 0.005 %.day^-1	Data from 24 studies Duration range 6 months 8 years 1 year	Field aerobic conditions	Wang et al. ⁴³
Biochar	Wood	¹³C & ¹⁴C measurements	0.004 %.day^-1	Range 6 months 5 years		Wang et al. ⁴³
Biochar	Agricultural residues	¹³C & ¹⁴C measurements	0.025 %.day^-1	Range 6 months 2 years		Wang et al. ⁴³
Biochar	Grass	¹³C & ¹⁴C measurements	0.007 %.day^-1	Range 6 months 8 yr		Wang et al. ⁴³
Biochar	N/A		0.0093%.day^-1	Max 10 years	Aerobic laboratory and field studies	Chiaramonti et al.⁴¹
Biochar	Wood	Incubation studies and field trials	0.001 gC gC₀^-1 yr^-1	5 years	Aerobic laboratory and field studies	Azzi et al. ⁴²
Biochar	Manure	Incubation studies and field trials	0.01 gC gC₀^-1 yr^-1	5 years	Aerobic laboratory and field studies	Azzi et al. ⁴²
Biochar	Biosolids	Incubation studies and field trials	0.01 gC gC₀^-1 yr^-1	5 years	Aerobic laboratory and field studies	Azzi et al. ⁴²
Biochar	Grass	Incubation studies and field trials	0.05gC gC₀^-1 yr^-1	8.5 years	Aerobic laboratory and field studies	Azzi et al. ⁴²

17.0

Relevant Works

Biochar Storage in Low Oxygen Burial Environments

Contents

Introduction

Applicability

Background

Safeguarding of low oxygen burial storage sites

Required measurements

Co-benefits and soil remediation

Biochar Characterization

Physical Characteristics

Chemical Characteristics

Quantification of biochar durability in low oxygen environments

Quantification of CO₂eStored

Option 1: Random Reflectance to quantify the stable or inertinite fraction plus Incubation Experiments to quantify the likelihood of degradation of the labile biochar fraction

Option 2: Use of Random Reflectance to quantify stable fraction of biochar

Long-term carbon degradation under low oxygen conditions

Emissions reductions or removal potential

Maintenance of low oxygen conditions

Landfill site best practice guidelines

Oxygen monitoring

Site Characterization

Hydrology Surface water

Hydrology groundwater

Local Geology and Soil Properties

Seismicity

Target values

Legal Framework to Ensure Permanence

Counterfactual Land Use

Base Liner Construction and Leachate Management

Landfill Gas Management and Odor Control

Site Closure

Risk of Reversal and Buffer Pool

Record Keeping

Acknowledgements

Definitions and Acronyms

Appendix A

Relevant Works

Contributors

Contents

Introduction

Applicability

Background

Environmental and Social Safeguards

Safeguarding of low oxygen burial storage sites

Required measurements

Co-benefits and soil remediation

Biochar Characterization

Physical Characteristics

Chemical Characteristics

Quantification of biochar durability in low oxygen environments

Quantification of CO₂eStored

Option 1: Random Reflectance to quantify the stable or inertinite fraction plus Incubation Experiments to quantify the likelihood of degradation of the labile biochar fraction

Option 2: Use of Random Reflectance to quantify stable fraction of biochar

Long-term carbon degradation under low oxygen conditions

Emissions reductions or removal potential

Maintenance of low oxygen conditions

Landfill site best practice guidelines

Oxygen monitoring

Site Characterization

Hydrology Surface water

Hydrology groundwater

Local Geology and Soil Properties

Seismicity

Target values

Legal Framework to Ensure Permanence

Counterfactual Land Use

Base Liner Construction and Leachate Management

Landfill Gas Management and Odor Control

Site Closure

Risk of Reversal and Buffer Pool

Record Keeping

Acknowledgements

Definitions and Acronyms

Appendix A

Relevant Works

Footnotes

Contributors