Biomass burial

This is a Carbon Storage Module and covers biomass burial. This module is part of the Rainbow BiCRS methodology, which allows Project Developers to choose the relevant modules for their project, and shall be used with the necessary accompanying modules.

See more details on how modules are organized in the BiCRS home page.

How to use this module

BiCRS Methodology

Eligibility and scope

Eligible technologies

All projects certified under this module shall cause additional carbon removals by storing eligible biomass for at least 100 years in eligible subsurface storage sites. Reversal risks and baseline removals are assessed according to this duration.

The Project Developer and entity eligible for receiving carbon finance is a natural or legal person, or public entity, that operates or controls the carbon removal project, or holds decisive economic power over the technical functioning of the project.

Eligible biomass

Project Developers shall demonstrate that biomass:

• could not have been used as valuable material products (e.g. wood for construction),

• was not grown for the purpose of CDR or bioenergy production, and

• falls into one of the categories listed below.

Separate Environmental and social safeguards and Leakage requirements apply for each biomass type.

Table 1 Eligible biomass types for the purpose of biomass burial.

To ensure resistance against degradation, biomass shall also comply with the requirements set out in Risk mitigation: Use of recalcitrant biomass.

Eligible storage site

Eligible storage sites shall be subsurface (i.e. below the ground) and maintain conditions that inhibit the decomposition of biomass, naturally or by engineered design. This includes all of the following:

• oxygen isolation (anoxic environment)

• water isolation

• physical stability

Project Developers shall submit a Site characterization report upon validation to demonstrate suitability of the storage site. Eligible storage sites can be classified as either of the following types:

Table 2 Eligible types of storage sites.

Eligible conversion technologies

Unless biomass is naturally resistant to microbial degradation due to a high lignin content and a high carbon to nitrogen ratio, thermochemical conversion of the biomass is necessary to enhance stability and resistance.

Eligible technologies to convert feedstock listed in the Biomass feedstock module are outlined in the table below.

Table 3 Eligible conversion technologies for biomass feedstock.

Certification requirements

Certification requirements for this module are defined in the BiCRS methodology. These cover crediting period duration, monitoring period duration, site audits, and versioning and project compliance. This module sets out an additional certification requirement:

Post-closure monitoring period. This is the period after storage site closure during which the site is monitored for integrity and reversals. It extends for 100 years after site closure. Project Developers shall submit a Storage site monitoring Plan at validation, outlining the post-closure monitoring procedures.

Project scope

One project is defined as:

• the operation of one or more storage sites, complying with the rules in Eligible storage site

• located within a single country

• operated at sites that are under the oversight or data access of a single Project Developer, regardless of whether the developer directly owns or manages each site.

The project scope is cradle-to-grave and includes all processes that result from biomass burial. This includes but is not limited to the following:

• all removals from biomass burial

• all project emissions from the biomass burial activity, including any operational and embodied emissions from project establishment, storage site operations, and storage site closure.

Any processes that would have occurred regardless of the biomass burial activities may be excluded from the project scope.

Baseline scope

The baseline shall include any permanent carbon storage from biomass burial that would have occurred in the absence of the project.

• It is assumed that no biomass burial activity would have occurred under the business-as-usual conditions.

• Permanent carbon storage from the alternate fate of the biomass used by the project shall be evaluated following the rules set out in the Baseline scenario of the Biomass feedstock module and applied as biomass leakage emissions in Eq. 11.

The baseline scenario structure remains valid for the entire crediting period but may be significantly revised earlier if:

• The Project Developer notifies Rainbow of a substantial change in project operations or baseline conditions, and/or

• The methodology is revised, affecting the baseline scenario.

The specific values within the baseline scenario will be updated during each crediting period, using project data to accurately reflect the equivalent of the project’s operations.

Production batches

A production batch definition depends on the type of biomass used by the project:

Table 4 Definition of production batch for different biomass types.

It is assumed that biomass from the same production batch has similar characteristics (i.e. carbon content, moisture content, $C_{\text{org}}/N$, lignin content or $H/C_{\text{org}}$, $O/C_{\text{org}}$). Measurement and reporting of these characteristics is done at the production batch level.

A production batch has a maximum validity of 365 days, after which the biomass shall be considered part of a different production batch even if conditions are unchanged. In other words, the production batch ID number resets and a new production batch is created, and new monitoring requirements applied, after 365 days, regardless of if other production batch properties change or not.

Storage batches

A storage batch is defined as a biomass burial activity where one or several production batches are buried at an eligible storage site or in a storage unit and the the site or unit are permanently closed.

Project emissions and net carbon removals are quantified at the storage batch level.

The relationship between production batch, storage batch, storage unit and storage site is illustrated in Figure 1.

Point of credit issuance

Removal credits are issued for a given storage batch or batches once the Project Developer demonstrates stable storage conditions at the respective storage site or storage unit.

Stability is demonstrated when, for at least 4 weeks after closure of the storage site or storage unit, the parameters set out in the Storage site monitoring plan show no unexpected changes. Expected changes, such as seasonal fluctuations in temperature and humidity, or emissions consistent with anticipated biomass degradation, shall be reported by the Project Developers together with a justification for why they are expected, and do not constitute a failure of stability.

When the storage site consists of several storage units, stability shall be demonstrated for each unit. Credits for the carbon stored in a given unit shall be issued once stability has been demonstrated for that unit.

Principles & requirements

The principles and requirements specific to this module are detailed in the sections below. Other principles and requirements shall be taken from the accompanying modules and methodologies:

BiCRS methodology

• Additionality

• No double counting

• Environmental and social safeguards

Other modules

• Co-benefits

• No double counting

• Environmental and social safeguards

• Leakage

Durability

Durability threshold

All projects certified under this methodology shall prove durable carbon removals for at least 100 years.

Reversal risk assessment

Biomass burial stores biogenic carbon by burying biomass under conditions that prevent it from decaying. The durability of the carbon depends on two things working together: the properties of the biomass that is buried, and the design of the storage site.

Certain types of biomass resist microbial decomposition naturally. For woody biomass, the main indicators are a high lignin content and a high ratio of organic carbon to nitrogen. Lignin is difficult for microbes to break down, and shields the more easily degraded cellulose and hemicellulose from microbial attack. A high carbon to nitrogen ratio means there is little nitrogen available to feed decomposers. Less stable biomass can be made more resistant through thermochemical conversion, which rearranges the biomass into condensed aromatic structures that microbes cannot easily access. The molar ratio of hydrogen to organic carbon is used as a proxy for how aromatic, and therefore how recalcitrant, the converted material is.

The storage site is designed to inhibit decomposition by limiting oxygen and water, which microbes both need in order to be active. In practice this means burying the biomass below the biologically active soil layer and enclosing it in low-permeability barriers. Additionally, any potential risk of natural disturbances that could breach the storage containment has to be assessed when choosing a suitable storage site. Areas exposed to flooding, erosion, landslides, subsidence and seismic activity shall be avoided and the local hydrology (surface- and groundwater) taken into account. Site selection shall equally assess risks of anthropogenic disturbance, including excavation or changes in land use or ownership, after the project has ended.

Even without oxygen and water ingress, as prevented by the storage site design, decomposition of the biomass does not stop entirely. Biomass usually contains enough water at the point of burial to start microbial decomposition. Upon depletion of oxygen, anaerobic degradation prevails, generating CO₂ and CH₄. The fraction of carbon decomposed under anaerobic conditions is called degradable organic carbon that decomposes, or $DOC_f$. Recalcitrant biomass is more resistant to decay and consequently has a lower $DOC_f$ value.

The major carbon reversal risks from biomass burial are:

• Insufficient biomass recalcitrance, where the buried biomass is too easily degraded by microbes,

• anaerobic degradation of the buried biomass, where microbial activity continues in the absence of oxygen, resulting in emissions of CO₂ and CH₄ from the storage site.

• loss of storage site integrity, where oxygen or water enter the storage site (e.g. through a failed barrier, flooding, erosion or subsidence), resulting in renewed aerobic or anaerobic decomposition.

• disturbance of the storage site, where the buried biomass is exposed or destroyed by natural or anthropogenic events (e.g. excavation, land use change, fire, or loss of control over the site), resulting in re-emission of the stored carbon.

This module establishes the following mandatory project design requirements to mitigate these risks, detailed in the following sections:

• Use of recalcitrant biomass

• Anaerobic biomass degradation

• Site characterization report

• Monitoring of storage site

• Site closure plan

Upon meeting these requirements for each verification and credit issuance, projects significantly mitigate and reduce the risk of reversal for biomass burial. However, biomass burial is a comparably novel carbon storage pathway and the risk of reversal cannot be considered negligible. Projects shall therefore conduct post-closure monitoring for reversals for the entire post-closure monitoring period.

All projects certified under this methodology shall contribute the default minimum 2% of their verified removal RCCs to the Rainbow Buffer Pool, as defined in the Rainbow Standard Rules.

Risk mitigation: Use of recalcitrant biomass

Woody biomass

The resistance to biological decay, also called recalcitrance, of woody biomass is influenced by the carbon-to-nitrogen ratio and the abundance and composition of the components of the plant cell wall (i.e lignin, cellulose and hemicellulose). A higher $C_{\text{org}}/N$ ratio as well as a high relative abundance of lignin in the biomass reduce the decomposition rate and microbial accessibility, increasing the recalcitrance.

Project Developers using woody biomass (i.e. forest waste and necessary tree removal) shall demonstrate that the biomass used has

• a carbon-to-nitrogen ratio of $C_{\text{org}}/N$≥ 100,

• a sufficiently high lignin content of ≥ 25%, by determining the amount and type of lignin, cellulose and hemicellulose in the biomass.

Thermochemically converted biomass

The recalcitrance of thermochemically converted biomass is dependent on both the processing conditions (temperature, heating rate, reactor design) and the type of biomass input. A metric to assess durability is the $H/C_{\text{org}}$ ratio, where a low value corresponds to a high degree of aromaticity conferring chemical recalcitrance. Similarly, a low $O/C_{\text{org}}$ ratio corresponds to fewer oxygenated hydrocarbons capable of decomposing.

Project Developers using thermochemically converted biomass shall demonstrate that biomass converted to

• biochar has a molar $H/C_{\text{org}}$ below 0.7 and molar $O/C_{\text{org}}$ below 0.2.

• hydrochar has a molar $H/C_{\text{org}}$ below 1.2 and molar $O/C_{\text{org}}$ below 0.6.

Analysis of the biomass shall be conducted for each production batch, according to the requirements set out in the Sampling and measurements section.

Risk mitigation: Anaerobic biomass degradation

Biomass stored under anoxic conditions is still subject to anaerobic decomposition. The fraction of the biomass carbon that decomposes under anoxic conditions is called degradable organic carbon that decomposes, or $DOC_f$. In the quantification of the project removals, the $DOC_f$ of the biomass carbon is assumed to be re-emitted as CO₂ and CH₄, and therefore deducted from the gross removals (see Project removals in the GHG Quantification section).

The value for $DOC_f$ is highly dependent on the biomass type. Project Developers shall use the default $DOC_f$ values listed in Table 5, or use a project-specific value, subject to the requirements below.

Table 5 Default $DOC_f$ values for different biomass types.

Project Developers shall provide scientific evidence from one of the following approaches in order to apply a project-specific value for $DOC_f$. Any proposed value is subject to review and approval by Rainbow, and, where deemed necessary, by an independent technical expert, prior to its use in the project's GHG quantification.

Biochemical methane potential testing

• Project Developers shall conduct a standardized biochemical methane potential (BMP) test on biomass that has been processed and converted in the same way as the project's biomass, following a recognized protocol (e.g. EN ISO 20675, ISO 11734).

• The test shall be performed by laboratories with at least one quality assurance accreditation. Wherever practicable, the test shall include a microbial inoculum representative of the storage site.

Ex-situ testing

• Project Developers shall conduct a time-series measurement of GHG evolution, or a time-series measurement of carbon loss, from biomass that has been processed and converted in the same way as the project's biomass and incubated under laboratory conditions analogous to the intended storage environment. This includes, but is not limited to packing strategy, engineered barriers used, and wherever practicable, a microbial inoculum representative of the storage site. Laboratory incubations may use an elevated temperature relative to the storage site in order to accelerate degradation within a practical measurement window. The measurement shall be benchmarked against a control sample, and its duration shall be mutually agreed upon by the Project Developer and Rainbow.

• Project Developers shall fit the observed cumulative GHG or carbon-loss data to an appropriate decay model and use this model to project cumulative carbon loss over the durability period. Project Developers shall derive the project-specific $DOC_f$ value as the ratio of this projected cumulative carbon loss to the total degradable organic carbon content (= total organic carbon content) of the initial biomass.

In-situ testing

• Project Developers shall conduct a time-series measurement of GHG evolution from biomass buried in a closed storage unit or site, with data collected inside the storage unit or site. The observation period shall cover a minimum of twelve months.

• Project Developers shall fit the observed cumulative GHG or carbon-loss data to an appropriate decay model and use this model to project cumulative carbon loss over the durability period. Project Developers shall derive the project-specific $DOC_f$ value as the ratio of this projected cumulative carbon loss to the total degradable organic carbon content (= total organic carbon content) of the initial biomass.

Project Developers may switch from a default to a project-specific value at each verification. Reverting from a project-specific value to a default vault is not permitted. Retrospective application of a project-specific value to a completed verification is not possible. In other words, no additional credits will be issued for a storage batch that has already been buried and verified.

Risk mitigation: Site characterization report

Storage sites shall be designed to prevent biomass degradation through suitable geochemical and geological conditions, as well as the avoidance of natural and anthropogenic disturbances. Where the natural properties of the storage site are insufficient, Project Developers shall rely on engineered barriers to achieve the required level of containment. Storage sites may consist of several storage units. Storage units shall be uniquely identified and characterized, including stored volume, location, and technical drawings of each unit.

Project Developers shall produce a Site Characterization Report demonstrating how the storage site, or combination of storage site and unit, mitigates each of the reversal risks listed below in Table 6.

Table 6 Reversal risks that Project Developers shall address in the Site characterization report.

Risk mitigation: Monitoring of storage site

Storage site monitoring plan

Monitoring of the storage site is required to

• demonstrate stability of storage conditions for credit issuance (see Point of credit issuance),

• ensure the storage site integrity,

• detect and quantify potential reversal events.

The storage site shall be monitored during ongoing operations (i.e. if multiple storage units are filled at a single storage site over a given period of time before full closure of the storage site) and after closure of the storage site for the duration of the post-closure monitoring period.

At validation, Project Developers shall prepare a storage site monitoring plan, including but not limited to

• a systematic approach to monitoring

  • greenhouse gases CH₄ and CO₂ outside the storage site. For void-type storage sites, outside means outside of the seal closing the entry/exit of the void.

  • greenhouse gases CH₄ and CO₂ inside the storage site. If the storage site consists of several storage units, Project Developers shall monitor each unit.

    • Where ongoing monitoring of each individual unit is not feasible due to engineering or access restrictions beyond the control of the Project Developer, alternative monitoring approaches may be considered on a case-by-case basis.

  • temperature, humidity and oxygen inside the storage site or unit.

  • the physical conditions of the site (e.g. engineered barrier integrity, leachate management, groundwater monitoring).

• the methods and equipment used, including calibration procedures and detection limits

  • equipment shall be adjusted for the relevant measurement conditions (i.e. atmospheric temperature and pressure in the subsurface, or above ground)

  • equipment shall be calibrated according to the manufacturer's specification, either by the manufacturer or by a certified service prior to entering service and recalibrated periodically.

• a description of how access for maintenance, replacement and repair of the monitoring equipment is ensured.

• a description of how a site-specific baseline is established for each monitored parameter, including:

  • the timing of baseline measurements relative to construction and/or filling of the storage site (i.e. before any material is introduced),

  • the minimum duration and frequency of baseline data collection needed to characterize natural variability (e.g. seasonal fluctuations).

• a protocol outlining actions taken if a reversal event is detected (i.e. timeline for response steps, corrective measures, documentation of any reversal events). This protocol shall be in accordance with the Rainbow Cancelation Procedure and its Cancelation Notice.

Monitoring shall be conducted continuously or discretely, with a recommended minimum frequency of once per week for the first three years after site closure. If storage conditions are proven to be stable after three years, the Project Developers may reduce the monitoring frequency until the end of the post-closure monitoring period.

Monitoring records shall be made available to Rainbow and the VVB upon request throughout the entire post-closure monitoring period.

Ensuring long-term monitoring

At validation, Project Developers shall justify that they have sufficient resources to guarantee the following throughout the entire post-closure monitoring period:

• monitoring of the storage site,

• maintenance, repair and replacement of monitoring equipment,

• repair of compromised storage units,

• meeting the Buffer pool replacement requirements for avoidable reversals.

This shall be demonstrated by establishing a binding contractual framework, for example a trust or endowment fund or an equivalent instrument under the laws of the country the project is located in.

The contractual framework shall further be formulated in such a way that the requirements above can be fulfilled even where:

• the Project Developer ceases to exist as a legal entity,

• the ownership of the storage site is transferred to a third party.

Risk mitigation: Site closure plan

At validation, Project Developers shall submit a site closure plan, including at least:

• a description of the final configuration of the storage site upon closure,

• the methods and procedures to be applied to achieve closure, and

• a schedule of closure activities, including timelines for individual storage unit and/or the overall site.

The closure plan shall be formulated in accordance with any applicable local regulation or standard. If the storage site is a mine (void-type), Project Developers shall ensure that the closure plan is compliant with or integrated in the mine closure and remediation plan.

No double counting

See the BiCRS methodology No double counting section for general requirements on this topic.

Co-benefits

Projects should support at least two quantifiable and verifiable environmental or social co-benefits, aligned with the UN Sustainable Development Goals (SDGs) framework. Any co-benefits claimed by the Project Developer shall be quantified, monitored, and audited for each verification and credit issuance.

Common co-benefits under this methodology are detailed in the table below. Project Developers may suggest and prove other co-benefits not mentioned here.

SDG 13 on Climate Action by default is not considered a co-benefit here, since it is implicitly accounted for in the issuance of carbon credits. If the project delivers climate benefits that are not accounted for in the GHG reduction quantifications, then they may be considered as co-benefits.

Table 7 Common co-benefits that projects under this methodology may provide are detailed, including types of proof that can be used to justify each co-benefit.

Environmental and social safeguards

Project Developers shall prove that the project does not contribute to substantial environmental and social harms.

Projects shall follow all national, local, and European (if located in Europe) environmental regulations, including but not limited to those related to waste feedstock management, biomass conversion (if applicable) and underground storage of biomass.

Project Developers shall transparently report the mass, type and source of all biomass used, and shall demonstrate that the biomass complies with the requirements set out for the relevant biomass type in the Biomass Feedstock module. For thermochemically converted biomass, the sustainability criteria apply to the feedstock prior to conversion.

Additionally, Project Developers shall demonstrate that the biomass is not classified as hazardous waste under the applicable regional or national regulation. For thermochemically converted biomass, this applies to the converted biomass, i.e. to the hydrochar and biochar.

Environmental and social risk assessment

Project Developers shall fill in the Rainbow Biomass burial risk assessment, to evaluate the identified environmental and social risks of projects. The identified risks include:

• Release of methane due to compromised storage conditions

• Disruption of local hydrology or groundwater tables from storage site excavation

• Soil disturbance, compaction and erosion from storage site excavation

• Loss of habitat or biodiversity at storage site

• Contamination of soil and groundwater from leaching of pollutants or heavy metals from biomass

• Contamination of soil and groundwater from degradation of synthetic engineered barriers

The risk assessment also contains the identified risks from the Biomass feedstock module and the risks from the Processing and energy use module relevant for this carbon storage module.

Project Developers shall assign a likelihood and severity score of each risk, and provide an explanation of their choices. The VVB and Rainbow’s Certification team shall evaluate the assessment and may recommend changes to the assigned scores.

Any identified material risk (defined as issues with a risk score of moderate or higher) shall be subject to a Risk Mitigation Plan, which outlines how Project Developers will mitigate, monitor, report, and if necessary, compensate for any environmental and/or social harms.

Additional proof may be required for certain high risk environmental and social problems.

The Project Developer, the Rainbow Certification Team, or the VVB may suggest additional risks to be considered for a specific project.

Leakage

According to the Rainbow Standard Rules, carbon removal projects shall minimize leakage, where carbon-emitting activities are displaced or shifted outside of the project boundary. Leakage from the alternative use of the biomass is addressed in the Biomass feedstock module.

Monitoring

Monitoring Plans for this module shall include, but are not limited to, tracking of the following information for each Production Batch:

Monitoring Plans for this module shall include, but are not limited to, tracking of the following information for each Storage Batch:

• Number of production batches in storage batch

• ID of each production batch in storage batch

• Amount of biomass in each production batch contained in the storage batch, where a single production batch may be going into a single storage batch or split across multiple storage batches

• Total amount of biomass in each storage batch

• Demonstration of stable storage conditions, see Point of credit issuance

Monitoring Plans for this module shall include, but are not limited to, tracking of the following information for each Monitoring Period:

• Number of storage batches buried in monitoring period

• Co-benefits

Monitoring Plans shall include the following information for each monitored parameter:

• monitoring frequency

• emission sources and sinks

• data source

• measurement methods/procedures, and their accuracy and calibration

• quality assessment or quality control procedures

• responsible party for collecting and archiving data

GHG quantification

The GHG quantification instructions from all other BiCRS modules used by the project shall be used in conjunction with this module to obtain full life-cycle GHG quantifications.

The system boundary of this quantification starts at the project establishment and ends at the site closure.

Quantification shall be done at a minimum for each storage batch. Several quantifications can be credited in a monitoring period.

Data sources

The required primary data for GHG calculations from projects are presented in Table 8. These data shall be provided for each storage batch and made publicly available.

Table 8 Summary of primary data needed from projects and their source. All primary data sources listed here are required to be monitored and updated during verification (see Monitoring section).

Assumptions

• All biomass from the same production batch has the same properties (carbon content, moisture content, $O/C_{\text{org}}$ , $H/C_{\text{org}}$, lignin content, $C_{\text{org}}/N$)

• The default value for the fraction of degradable organic carbon that decomposes, $DOC_f$, is 8.8% for woody biomass, 12% for hydrochar and $(1-F_{perm, 100}) \times 100$ for biochar.

• The default value for the methane oxidation factor is 0%, i.e. the percentage of methane that is oxidized when passing the soil above the storage site.

• Emissions from post-closure monitoring are assumed to be negligible and excluded from the GHG quantification.

Baseline scenario

It is assumed that no carbon removal from biomass burial would have occurred in the absence of the project. Permanent carbon storage from the alternate fate of the biomass is quantified according to the Biomass feedstock module and accounted for in the calculation of the project emissions (as Biomass leakage in Eq. 11).

Project scenario

The project scenario is broken down into four main life-cycle stages, also illustrated in Figure 3 below:

• CO₂ removal from stored biomass

• Project establishment

• Storage operations

• Site closure

Project removals

Project gross removals are calculated as the removals from the carbon stored in the biomass minus the amount of carbon re-emitted during storage under anoxic storage conditions.

The carbon re-emitted during storage is released as a mix of CO₂ and CH₄. Chemically, under anaerobic conditions the fraction of degradable organic carbon that decomposes, $DOC_f$, is converted in equal parts to CO₂ and CH₄ (50% as CO₂, 50% as CH₄). However, as the CH₄ migrates through the overlying soil layer, a fraction may get oxidized to CO₂ before reaching the atmosphere. This oxidation is accounted for in the calculations via an oxidation factor, determined according to the rules set out below.

Methane oxidation factor

The degree of methane oxidation is highly site specific and depends on a multitude of factors including methane flux, soil composition and microbiota, temperature, moisture and pH.

The default value for the methane oxidation factor is set to 0%, meaning that no methane is oxidized when passing the soil above the storage site. Project Developers can choose to either

• use a methane oxidation factor from Table 9 below, provided they prove that the storage site meets the corresponding requirements, or

• use a project-specific value for the methane oxidation factor, following the requirements set out below.

Table 9 Methane flux rate and cover conditions for storage sites and the corresponding methane oxidation factor. The table is a conservative simplification of the US EPAs rules on determination of the landfill methane oxidation factor. *Methane flux rate is the mass flow rate of methane per unit area at the bottom of the surface soil prior to any oxidation.

Project Developers may propose a project-specific value for the methane oxidation factor by providing scientific evidence from one of the following two approaches. Any proposed value is subject to review and approval by Rainbow, and, where deemed necessary, by an independent technical expert, prior to its use in the project's GHG quantification.

In-situ testing

• Project Developers shall conduct measurements at a closed storage site or unit, provided the unit is covered with the final configuration of the cover/ cap (if applicable). Measurements of the methane oxidation rate of the soil cover shall be taken over a 6-month period beginning once the storage site or unit has reached anoxic conditions (oxygen levels below 5%).

Representative testing

• Project Developers shall conduct measurements at a representative sample plot located in the vicinity of the storage site, constructed with the same packing strategy as the storage unit (i.e. no biomass, identical natural barriers and cap/ cover system). Measurements of the methane oxidation rate of the soil cover shall be taken over a 6-month period representative of the seasonal conditions. Testing can be carried out before storage site establishment, allowing a project-specific value to be obtained as early as possible.

Project Developers shall use technologies that can directly quantify the percentage of methane oxidized in the soil. This includes, for example stable isotope method, gas push-pull tests or gas concentration/ mass balance measurements.

Project Developers may switch from a default to a project-specific value at each verification. Reverting from a project-specific value to a default vault is not permitted. Retrospective application of a project-specific value to a completed verification is not possible. In other words, no additional credits will be issued for a storage batch that has already been buried and verified.

Emissions from project establishment

This life-cycle stage includes all operational and embodied emissions from the establishment of the project. This includes emissions from:

• storage site establishment

  • energy and material used for storage site construction (e.g. fuel combustion from excavators, waste management of excavated material),

  • energy and material used for storage site preparation (e.g. lining, installation of monitoring equipment, installation of drainage system),

  • energy and material used for storage site characterization (e.g. surveys, studies, soil measurements).

  • infrastructure and machinery built at storage site,

  • direct land use change at the storage site location, assessed relative to the historical state of the land, i.e. its condition prior to use by the project. It shall account for any loss of above-ground and below-ground biogenic carbon stocks relative to that historical state.

• other project infrastructure. This shall include, but is not limited to

  • any equipment used for biomass processing (e.g feedstock shredder or dryer, hydrothermal conversion or pyrolysis unit).

Storage site establishment emissions

Emissions from storage site establishment are front-loaded, they occur before the first storage activity takes place. As such, they are treated as embodied emissions from project infrastructure: rather than being accounted entirely upfront, they shall be distributed proportionally ("amortized") across the monitoring periods of the project.

The amortization shall ensure that all storage site establishment emissions are fully accounted for within the first 50% of the total biomass the project plans to bury. In other words, by the point at which 50% of the biomass intended for burial at the storage site has been buried, all establishment emissions shall have been allocated to the monitoring periods up to that point. Note that this allocation is only relevant where a storage site comprises multiple storage units that are filled over time. Where a storage site consists of a single unit filled in a single burial event, all establishment emissions are accounted for in the first, and only, monitoring period.

At validation, Project Developers shall provide an estimate of the total amount of biomass planned to be buried at the storage site, to be used as the basis for this amortization calculation.

Project Developers may choose how to distribute the emissions across monitoring periods:

• Proportionally: deducting establishment emissions in each monitoring period in proportion to the biomass buried in that period, relative to the first 50% of total biomass planned to be buried; or

• Front-loaded: deducting a greater share in early monitoring periods, including full deduction in the first monitoring period.

Emissions from other project infrastructure

Embodied emissions from project infrastructure not related to the storage site establishment (i.e. equipment used for biomass processing and conversion) shall be quantified using the Infrastructure and machinery module. These emissions are amortized not in relation to the amount of biomass stored, but in relation to the lifetime of the item (e.g. pyrolysis unit, feedstock shredder).

Emissions from storage operations

This life-cycle stage includes all emissions from the operations of the storage site. This shall include the following steps:

• biomass supply, calculated according to Eq. 10.

  • biomass cultivation: The only biomass types allowed are classified as waste and are assigned no environmental impacts from their cultivation stage,

  • biomass transport to processing facility,

  • biomass processing prior to storage, if any

  • biomass conversion prior to storage, if any. This shall include any potential methane emissions (see Eligible conversion technologies)

  • leakage from baseline carbon storage and diversion of biomass.

• biomass transport, calculated using the Transportation module.

  • biomass transport to storage site (directly from harvesting location if no intermediate processing/conversion step exists, or from processing location).

• biomass storage, calculated using the Processing and energy use module.

  • energy and materials used to store biomass in closed unit (e.g placement of biomass in storage unit, material used as engineered barrier, sealing of unit),

  • energy and materials used to install additional monitoring equipment.

Emissions from site closure

This life-cycle stage includes all emissions associated with the final closing of the storage site. It shall be calculated using the Processing and energy use module and includes:

• energy and materials used to permanently close the storage site with a cap/ cover/ seal system,

• energy and materials used to install additional monitoring system.

Uncertainty assessment

An uncertainty assessment is presented below for all aspects of GHG quantification set at the methodology level. The findings from this assessment are then applied at the project level, where project-specific GHG quantification also undergoes an uncertainty assessment.

The overall project GHG quantification uncertainty is determined by qualitatively combining both the methodology-level and project-specific uncertainties for each identified source of uncertainty.

• The assumption that all biomass from the same production batch has the same properties has low uncertainty, as the definition of a production batch is narrow and representative sampling requirements account for any source of major variability.

• The $DOC_f$ of 8.8% for woody biomass is taken directly from the IPCC Guidelines for National Greenhouse Gas Inventories. This value carries medium uncertainty, since it was derived for solid waste disposal sites rather than anoxic underground storage and does not differentiate between wood species. However, applying this value here is conservative since storage conditions in this module are designed to reduce biomass degradation. The assumption carries low uncertainty.

• Evidence on hydrochar burial is scarce and not representative of storage conditions (existing data covers aerobic soil application or use as an additive in anaerobic digesters, not anaerobic burial). This gives high underlying uncertainty. To compensate, the value was set conservatively: starting from IPCC's more conservative default for less degradable biomass (10%) and adding 2 percentage points as a safety margin, yielding 12%. The assumption carries medium uncertainty.

• Assuming that the non-permanent fraction of biochar, as calculated using the Woolf model, corresponds to the $DOC_f$ carries high uncertainty, as the Woolf model was developed for biochar degradation in soil, and is not representative for anoxic underground storage conditions. Using this value is conservative, hence the uncertainty for the GHG quantification is low.

• Methane oxidation during passage through soil is highly site- and season-specific, and the oxidation rate carries high uncertainty. However, assuming zero oxidation is the most conservative possible choice, and the uncertainty of this parameter is low.

• Emissions from post-closure monitoring are expected to be minor, consisting mainly of electricity use. The majority of monitoring-related emissions occur earlier, during equipment installation and are accounted for in the GHG quantification. The assumption carries low uncertainty.

The uncertainty at the methodology level is estimated to be low. This translates to an expected discount factor of at least 3% for projects under this module.

Sampling and measurements

The following indicators shall be measured from a representative sample of each production batch:

• organic carbon content

• moisture content

• for woody biomass (forest waste and necessary tree removal)

  • amount of lignin, cellulose and hemicellulose

  • $C_{\text{org}}/N$

• for thermochemically converted biomass

  • $H/C_{\text{org}}$

  • $O/C_{\text{org}}$

Measurements shall be performed by laboratories with at least one quality assurance accreditation, such as:

• ISO/IEC 17025

• CEN/TS 17225-1

• ISO 10694

Representative sampling

Woody biomass

For projects using woody biomass (i.e. forest waste and necessary tree removal), a minimum of three samples shall be taken for each production batch and measured individually. The sample shall be representative of the biomass or biomass mix used, as follows:

• If the batch consists of a single wood species, each sample shall be drawn from material representative of that batch (e.g. across different loads, positions, or sizes within the batch).

• If the batch consists of a mix of species and the mix ratio (by mass) is known, it shall be documented, and either

  • each sample shall be composited to reflect that ratio, or

  • samples shall be drawn separately per species and results weighted according to the mass ratio of each species in the batch.

• If the batch consists of a mix of species and the mix ratio is not known, a representative portion of the batch shall be physically homogenized (e.g. mixed, chipped, or shredded together) prior to sampling, so that each sample drawn reflects the actual species composition of the batch.

Thermochemically converted biomass

The sampling procedure detailed in sections below and summarized in Figure 4 is the recommended approach for representative sampling on thermochemically converted biomass (i.e. biochar and hydrochar). However, Project Developers may implement their own approach if it is detailed in the PDD and in Sampling Records; ensures one representative sample per production batch; addresses samples and composite samples amount and frequency; and ensures homogenization. The VVB and the Rainbow Certification team shall validate the rigor and representativeness of the proposed sampling approach.

The recommended approach sampling requirements are based on the following sources:

• EU Fertilising Products Regulation (EU) 2019/1009

• European Biochar Certificate Guidelines Annex 4 Representative Sampling

One representative sample per production batch shall be created and sent for laboratory testing. This sample ensures that any within-batch variability is captured in the measurements.

Table 10 details the number of composite samples that shall be taken per production batch to obtain one representative sample, based on the EU Fertilising Products Regulation (EU) 2019/1009.

The representative sample size should be 24 liters * the n number of composite samples per production batch detailed in Table 10.

Table 10 Recommendations for the number of composite samples of biochar or hydrochar to take, based on the site's annual biochar or hydrochar production output.

The European Biochar Certificate Guidelines Annex 4 Representative Sampling should be followed for taking composite samples. Those requirements are summarized below.

Homogenization

The representative sample shall be homogenized by the Project Developer or by the laboratory that performs testing. The biochar or hydrochar shall be ground to a size of <3 mm.

The ground sample is mixed by shoveling the pile three times from one pile to another.

A sub-sample of 1.5 liters shall be taken from 15 spots in the mixed pile.

The 15 sub-samples are re-combined, and then mixed by shoveling the pile three times from one pile to another.

From the mixed pile of the combined sub-samples, 15 subsamples of 150 ml each should be taken at 15 different spots in the pile and combined. This combined homogenized representative cross sample is used for laboratory testing.

Retention samples

A one-liter retention sample shall be collected each day that biochar or hydrochar is produced. These samples should be combined for storage over the calendar month. Retention samples shall be stored for a minimum of two years.

Sampling records

For each production batch, Project Developers shall submit a Sampling Record for verification to prove their adherence to the requirements above. Sampling Records shall include the following information for each sample taken:

• Date of sampling

• Amount of biomass samples (i.e. woody biomass or thermochemically converted biomass) sampled

• Description of representative sampling process (for thermochemically converted biomass: either followed the recommended approach, or describe the individual approach)

• Sample ID

• Visual description and observation of biomass

• Description of any potential anomalies

• Only for thermochemically converted biomass: Proof of retention sampling

• Photos showing the date, sample ID, and amount of biomass that is included in the present Sampling Record

Risk assessment template

This module uses the risk assessment template version 1.0.

👉 Download the template here.

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