> For the complete documentation index, see [llms.txt](https://docs.rainbowstandard.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rainbowstandard.io/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-storage/biomass-burial.md).

# Biomass burial

| **Module name**      | Biomass burial                             |
| -------------------- | ------------------------------------------ |
| **Module category**  | Carbon storage                             |
| **Methodology name** | Biomass carbon removal and storage (BiCRS) |
| **Version**          | 1.0                                        |
| **Methodology ID**   | RBW-BICRS-CS-BMB-V1                        |
| **Release date**     | October 9, 2026                            |
| **Status**           | In use                                     |

{% content-ref url="/pages/D1bECpowUAiJorSGzbQY" %}
[Glossary](/glossary.md)
{% endcontent-ref %}

<details>

<summary>Acknowledgements <span data-gb-custom-inline data-tag="emoji" data-code="1f91d">🤝</span></summary>

*This module was developed by Rainbow with valuable input and support from the Rainbow Biomass burial Working Group members and other expert contributors.*

*We would like to thank Timothy Baars (Recoal), Tiffani Manteuffel-Ross, Geoff de Ruiter and Maria Huyer (Mast Reforestation) and Sinéad Crotty (Carbon Containment Lab) for their insights and contributions throughout the development process.*

</details>

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](/methodologies/biomass-carbon-removal-and-storage-bicrs.md#efpqng3v3ute).

<table data-view="cards" data-full-width="false"><thead><tr><th></th><th></th><th></th><th data-hidden data-card-target data-type="content-ref"></th><th data-hidden data-card-cover data-type="files"></th></tr></thead><tbody><tr><td><strong>How to use this module</strong></td><td></td><td></td><td><a href="/methodologies/biomass-carbon-removal-and-storage-bicrs.md#efpqng3v3ute">Biomass carbon removal and storage (BiCRS)</a></td><td><a href="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FWRAnXQMFNSn97t9GOrFx%2Fpexels-eberhardgross-1612461.jpg?alt=media&amp;token=2c97e54f-1b97-4eb7-aead-e423aea08c21">pexels-eberhardgross-1612461.jpg</a></td></tr><tr><td><strong>BiCRS Methodology</strong></td><td></td><td></td><td><a href="/methodologies/biomass-carbon-removal-and-storage-bicrs.md">Biomass carbon removal and storage (BiCRS)</a></td><td><a href="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FR0TN0FvXWcrjcVsSjXI1%2Fbiochar.png?alt=media&amp;token=53fc0925-3647-46c4-9485-01a72039cebe">BiCRS methodology.png</a></td></tr></tbody></table>

## Eligibility and scope <a href="#uikucys7r1rk" id="uikucys7r1rk"></a>

### Eligible technologies

All projects certified under this module shall cause additional[^1] carbon removals by storing eligible biomass for at least **200 years** in eligible subsurface storage sites.

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), and
* falls into one of the categories listed below.

Separate [Environmental and social safeguards](#id-82n4j72vjt9v) and [Leakage](#leakage) requirements apply for each biomass type. To ensure resistance against degradation, biomass shall also comply with the requirements in [Risk mitigation: Biomass stability](#kmzukpswu89).

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

<table><thead><tr><th width="173">Biomass type</th><th>Description</th></tr></thead><tbody><tr><td>Forest waste from secondary forest</td><td>Natural but not primary old-growth forest, may still be managed for timber.</td></tr><tr><td>Forest waste from managed forest</td><td>Managed mixed-use forests that may include agroforestry, plantations or rotational logging.</td></tr><tr><td>Necessary tree removal from any forest</td><td>Damaged trees, or trees removed for planned forest management such as preventing disease spread or fires.</td></tr><tr><td>Agricultural residues with value</td><td>Residues left on soil or reapplied to soils for nutrient recycling (e.g., mulching, composting, spreading fast-decaying cellulose-based residues)</td></tr><tr><td>Agricultural residues with no value</td><td>Plowed into soil, burnt in the field, with no substantial return of nutrients to soil</td></tr><tr><td>Thermochemically converted biomass</td><td>Obtained through thermochemical conversion of eligible feedstock listed in the <a href="/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md">Biomass feedstock module</a> using an <a data-mention href="#eligible-conversion-technologies">#eligible-conversion-technologies</a></td></tr><tr><td>Purpose-grown algae</td><td>Algae grown in dedicated tanks on land for the purpose of carbon sequestration</td></tr></tbody></table>

#### Eligible storage site

Eligible storage sites shall be **subsurface** (i.e., below the ground) and **maintain conditions that prevent the decomposition of biomass**, naturally or by engineered design. Project Developers shall submit a [Site characterization report](#id-5a8ye61po9ri) upon validation to demonstrate suitability of the storage site.

***

Eligible storage sites shall follow the classification and eligibility requirements outlined below, referred to hereafter as **storage site types**:

*Table 2 Eligible types of storage sites.*

<table><thead><tr><th width="83.09375">Type</th><th width="208.94140625">Definition</th><th>Requirements</th></tr></thead><tbody><tr><td>Void</td><td>An existing underground opening with an <a data-footnote-ref href="#user-content-fn-2">overburden</a> that is naturally formed or excavated (e.g., natural caverns, mines and tunnels).</td><td><ul><li>the void was not created or extended for biomass storage purposes,</li><li>there are no active excavation operations or planned future disturbances (i.e., no operational mines),</li><li><p>where the storage site is a closed mine or a mine in the closing process, demonstrate that</p><ul><li>the mine is not fully remediated, and</li><li>the infrastructure of the mine is functional and accessible.</li></ul></li><li>a permanent seal is installed at the exit/entry point of the void at site closure.</li></ul></td></tr><tr><td>Pit</td><td>An existing land depression (e.g., quarries, gravel pit), or a depression excavated for the purpose of biomass storage.</td><td><ul><li>storage sites shall not be located on land classified as <a data-footnote-ref href="#user-content-fn-3">highly biodiverse</a> land, or <a data-footnote-ref href="#user-content-fn-4">high carbon stock</a> land in the five years before the project's starting date. Land use maps, land register extracts or other official documentation shall be provided as evidence,</li><li>a permanent cover system is installed at site closure, and</li><li>a natural restoration plan of the closed storage site is developed.</li></ul></td></tr></tbody></table>

***

Storage sites are categorized by the following environmental conditions they establish and maintain, referred to hereafter as **storage site conditions**:

<table data-card-size="large" data-view="cards"><thead><tr><th></th></tr></thead><tbody><tr><td><p><strong>Humidity</strong></p><ul><li><strong>Dry conditions</strong>: an environment in which the biomass is maintained at a <a data-footnote-ref href="#user-content-fn-5">water activity</a> <span class="math">a_w</span> below 0.6, the threshold below which fungal and bacterial growth cannot be sustained and biological decomposition effectively ceases, regardless of ambient temperature or nutrient availability.</li><li><strong>Wet conditions</strong>: biomass maintained at a water activity of <span class="math">a_w</span> > 0.6.</li></ul></td></tr><tr><td><p><strong>Presence of oxygen</strong></p><ul><li><strong>Anoxic conditions</strong>: an environment with negligible oxygen concentration, such that aerobic microbial decomposition cannot occur.</li><li><strong>Oxic conditions</strong>: an environment with oxygen present at a concentration sufficient to sustain aerobic microbial activity.</li></ul></td></tr></tbody></table>

***

Storage sites shall further be categorized by its internal structure. The possible structures are detailed below, and referred to hereafter as **storage site structures:**

* a single, undivided volume, that is filled and closed, called **single-unit storage**
* divided into discrete units, each filled and closed sequentially before the overall site is closed, called **multiple-units storage**

***

The three main storage site characteristics are summarized as:

<table data-view="cards"><thead><tr><th></th><th></th></tr></thead><tbody><tr><td><strong>Storage site type:</strong> the general land area where biomass is buried</td><td><ul><li>Void</li><li>Pit</li></ul></td></tr><tr><td><strong>Conditions at storage site</strong>: environmental conditions most relevant for biomass decay</td><td><ul><li>Wet and anoxic</li><li>Dry and anoxic</li><li>Dry and oxic</li></ul></td></tr><tr><td><strong>Storage site structure</strong>: the specific layout of biomass burial within a storage site</td><td><ul><li>single unit</li><li>multiple units</li></ul></td></tr></tbody></table>

#### Eligible conversion technologies

Biomass may be buried without undergoing any processing or conversion steps, or may be thermochemically converted. Project Developers burying **thermochemically converted biomass** shall use one of the technologies outlined below to convert feedstock listed in the [Biomass feedstock module](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md).

*Table 3 Eligible conversion technologies for biomass feedstock.*

<table><thead><tr><th width="132.328125">Technology</th><th width="107.078125">Minimum temperature</th><th width="112.55859375">Product</th><th width="371.19921875">Syngas treatment</th></tr></thead><tbody><tr><td>Hydrothermal conversion</td><td>180°C</td><td>Hydrochar</td><td><ul><li><p>Measure the quantity and composition of syngas, either continuously or via batch measurement during a representative run. If using batch measurement,</p><ul><li>demonstrate that processing conditions are stable enough for the results to apply to future runs,</li><li>repeat batch measurement at least annually.</li></ul></li><li>Report methane emissions from conversion, using the <a href="/modules/processing-and-energy-use.md">Processing and Energy Use</a> module, and include them in the GHG quantification.</li></ul></td></tr><tr><td>Pyrolysis</td><td>350°C</td><td>Biochar</td><td><ul><li>Capture or cleanly burn syngas, as outlined in the <a href="/modules/processing-and-energy-use.md">Processing and Energy Use</a> module</li><li>Report methane emissions from pyrolysis, using the <a href="/modules/processing-and-energy-use.md">Processing and Energy Use</a> module, and include them in the GHG quantification.</li><li>Follow any other requirements outlined in the <a href="/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-storage/biochar-application-to-soils.md">Biochar application to soils</a> module related to methane treatment.</li></ul></td></tr></tbody></table>

### Certification requirements

Certification requirements for this module are defined in the [BiCRS methodology](/methodologies/biomass-carbon-removal-and-storage-bicrs.md#certification-requirements). 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 **200 years** after site closure, applying a tiered approach, as outlined in [#id-8f3i2uvmiuhl](#id-8f3i2uvmiuhl "mention").

### Project scope

One project is defined as:

* the operation of one or more storage sites, complying with the rules in [#eligible-storage-site](#eligible-storage-site "mention")
  * storing biomass in the same storage type (pit or void)
  * storing biomass under the same conditions (wet or dry, oxic or anoxic)
* 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](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md#id-4l7lx2ihb6hj-2) module and applied as biomass leakage emissions in [Eq. 11](#calculation-project-emissions).

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 href="#id-2xck12gc2auz" id="id-2xck12gc2auz"></a>

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 $$H/C\_{\text{org}}$$, $$O/C\_{\text{org}}$$). Sampling, measurement and reporting of these characteristics is done **at the production batch level**.

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

*Table 4 Definition of production batch for different biomass types.*

<table><thead><tr><th width="205.14453125">Type of biomass</th><th>Production batch properties</th><th>New batch triggered if</th></tr></thead><tbody><tr><td>Forest waste, necessary tree removal</td><td><ul><li>same species of biomass or mix of biomass species</li></ul></td><td><ul><li>biomass species changes</li><li>mix of biomass species changes by more than ±20%</li></ul></td></tr><tr><td>Agricultural residues</td><td><ul><li>same species of biomass or mix of biomass species</li></ul></td><td><ul><li>biomass species changes</li><li>mix of biomass species changes by more than ±20%</li></ul></td></tr><tr><td>Thermochemically converted biomass</td><td><ul><li>same biomass feedstock or feedstock mix going into conversion</li><li>same conversion temperature</li></ul></td><td><ul><li>biomass feedstock type changes</li><li>feedstock mix changes by more than ±20%</li><li>conversion temperature changes by more than ±20%</li></ul></td></tr><tr><td>Purpose-grown algae</td><td><ul><li>same source of growth medium (i.e., wastewater)</li><li>same algae species or species mix</li></ul></td><td><ul><li>source of growth medium changes</li><li>algae species changes</li><li>mix of algae species changes by more than ±20%</li></ul></td></tr></tbody></table>

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 batch

A storage batch is defined as a **biomass burial event** where one or several production batches are buried at an [eligible storage site](#eligible-storage-site).

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.

<figure><img src="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FaRalgeWnMIn8Rw9Yt1DM%2FScience%20team%20diagrams-17.jpg?alt=media&amp;token=de075f38-ed75-4d3c-8613-f885153ea8cb" alt=""><figcaption><p>Figure 1: Illustration of the relation between production batch (PB), storage batch, storage unit and storage site. (a) and (b) are examples of a <strong>single-unit</strong> storage site, while (c) - (e) represent a <strong>multiple-units</strong> storage site. (a) A single production batch is buried as one storage batch at a storage site. (b) multiple production batches are buried together as a single storage batch at a storage site. (c) multiple production batches are buried together as a single storage batch in a storage unit at the storage site. (d) a single production batch is split across two burial events (i.e., two storage batches that are buried in individual units at the storage site). (e) a single storage batch cannot be stored in two storage units, because a storage batch is by definition a single burial event.</p></figcaption></figure>

### Point of credit issuance

Removal credits are issued for a given storage batch after completing all of the following steps:

* burial
* closure of the site or unit
* measured and proven stable storage conditions at the closed storage site for at least a 4-week period. Further details are in [#id-8f3i2uvmiuhl](#id-8f3i2uvmiuhl "mention").

For multiple-units[^6] storage sites, stability shall be demonstrated for each closed storage unit. Project Developers may decide to issue credits on an ongoing basis for each batch stored in a closed unit, or at final storage site closure for all batches stored.

## 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:

<table data-view="cards"><thead><tr><th></th><th></th><th></th><th data-hidden data-card-target data-type="content-ref"></th><th data-hidden data-card-cover data-type="files"></th></tr></thead><tbody><tr><td><strong>BiCRS methodology</strong></td><td><ul><li>Additionality</li><li>No double counting</li><li>Environmental and social safeguards</li></ul></td><td></td><td><a href="/methodologies/biomass-carbon-removal-and-storage-bicrs.md">Biomass carbon removal and storage (BiCRS)</a></td><td><a href="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FR0TN0FvXWcrjcVsSjXI1%2Fbiochar.png?alt=media&amp;token=53fc0925-3647-46c4-9485-01a72039cebe">BiCRS methodology.png</a></td></tr><tr><td><strong>Other modules</strong></td><td><ul><li>Co-benefits</li><li>No double counting</li><li>Environmental and social safeguards</li><li>Leakage</li></ul></td><td></td><td><a href="/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-storage.md">Carbon storage modules</a></td><td><a href="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FF1IanyzrKsw31BYTsPoH%2Ffre-sonneveld-q6n8nIrDQHE-unsplash.jpg?alt=media&amp;token=208fac4c-8056-41fd-b7c3-1bb14c9e20a2">energy co products module.jpg</a></td></tr></tbody></table>

### Durability <a href="#lc9eewbyvlyk" id="lc9eewbyvlyk"></a>

#### Durability threshold

All projects certified under this methodology shall prove **durable carbon removals for at least 200 years**.

#### Reversal risk assessment

Biomass burial projects store biogenic carbon by burying biomass under conditions that prevent it from decaying. The durability of the carbon depends on two project design components working together: the properties of the biomass that is buried, and the design of the storage site. Failure of either of these components increases the likelihood of a reversal event.

The major specific carbon reversal risks from biomass burial are:

* insufficient stability of biomass against degradation
* loss of storage site integrity, where biomass is exposed to conditions promoting degradation (i.e., ingress of water or oxygen) through
  * failure of barriers
  * natural disturbance (e.g., flood, fire, seismicity)
  * anthropogenic disturbance (e.g., excavation)

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

* Biomass stability
* Storage site suitability

Upon meeting these requirements, projects significantly mitigate the risk of reversal for biomass burial. However it cannot be considered **negligible.** Project Developers shall therefore conduct operational and post-closure monitoring for reversals, following the requirements set out in [Storage site monitoring](#id-8f3i2uvmiuhl).

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: Biomass stability <a href="#kmzukpswu89" id="kmzukpswu89"></a>

The resistance of biomass to biological decay is governed by its stability and the conditions under which it is stored. Storage of biomass that is **not inherently stable heavily depends on site conditions to prevent decomposition**. Eligible sites for this type of biomass are therefore restricted to dry storage. Biomass that is more stable (e.g., woody biomass or thermochemically converted biomass) may be stored under a wider range of storage site conditions.

Each eligible combination of biomass type and storage condition is subject to its own requirements. Table 5 lists these combinations and their corresponding requirements.

*Table 5 Requirements for different biomass types under the storage conditions.*

<table><thead><tr><th width="176.33984375" valign="top">Type of biomass</th><th valign="top">Wet, anoxic pit-type storage</th><th valign="top">Wet, anoxic void-type storage</th><th valign="top">Dry, oxic or anoxic pit- or void-type storage</th></tr></thead><tbody><tr><td valign="top"><a data-footnote-ref href="#user-content-fn-7">Woody biomass</a></td><td valign="top"><p>Eligible if the following is demonstrated for the biomass:</p><ul><li>a carbon-to-nitrogen ratio of <span class="math">C_{\text{org}}/N</span>≥ 100, and</li><li>a lignin content of ≥ 21%</li></ul></td><td valign="top"><p>Eligible if either of the following is demonstrated:</p><ul><li>biomass is enclosed in a sealed engineered barrier (natural or synthetic)</li></ul><p>or</p><ul><li>biomass has a carbon-to-nitrogen ratio of <span class="math">C_{\text{org}}/N</span>≥ 100, and</li><li>a lignin content of ≥ 21%</li></ul></td><td rowspan="3" valign="top"><p>Eligible if the following is demonstrated:</p><ul><li>biomass is dried to a water activity <span class="math">a_w</span> &#x3C; 0.6 (see Dry storage: water activity below), and</li><li>biomass is enclosed in a sealed engineered barrier (natural or synthetic) to maintain dry conditions</li></ul></td></tr><tr><td valign="top">Thermochemically converted biomass</td><td valign="top"><p>Eligible if the following is demonstrated for the biomass:</p><ul><li><span class="math">H/C_{\text{org}}</span> &#x3C; 0.4, and</li><li><span class="math">O/C_{\text{org}}</span> &#x3C; 0.2</li></ul></td><td valign="top"><p>Eligible if either of the following is demonstrated for the biomass:</p><ul><li><span class="math">H/C_{\text{org}}</span> &#x3C; 1.2, and</li><li><span class="math">O/C_{\text{org}}</span> &#x3C; 0.6, and</li><li>biomass is enclosed in a sealed engineered barrier (natural or synthetic),</li></ul><p>or biomass has</p><ul><li><span class="math">H/C_{\text{org}}</span> &#x3C; 0.4, and</li><li><span class="math">O/C_{\text{org}}</span> &#x3C; 0.2</li></ul></td></tr><tr><td valign="top">Agricultural residues, purpose-grown algae</td><td valign="top">Not eligible</td><td valign="top">Not eligible</td></tr></tbody></table>

**Dry storage: Water activity**

Biomass water activity ($$a\_w$$) measurements are required for projects using dry storage sites. Water activity is the ratio of the vapor pressure of water in the biomass to the vapor pressure of pure water at the same temperature, and reflects the **fraction of water available to support microbial and enzymatic activity**. It is specific to the biomass type, since porosity and composition both affect how tightly water is bound within the material. At equilibrium, water activity can be approximated by dividing the relative humidity of the surrounding air (in %) by 100.

For **dry storage conditions**, Project Developers shall dry the biomass to or below a moisture content corresponding to a water activity of $$a\_w$$ < 0.6 at [room temperature](#user-content-fn-8)[^8]. This is evidenced by moisture content measurements for each production batch, as outlined in the [#monitoring](#monitoring "mention") section.

* For woody biomass, this corresponds to [10% moisture content](#user-content-fn-9)[^9].
* For any other type of biomass, Project Developers shall determine the moisture content corresponding to a water activity of $$a\_w$$ < 0.6, either through direct measurements of a [**moisture sorption isotherm**](#user-content-fn-10)[^10] or using peer-reviewed literature values representative of the biomass type used. The moisture content at $$a\_w$$ < 0.6 shall be derived from the **adsorption branch** of the isotherm.
* At validation, Project Developers shall submit the moisture sorption isotherm (or, where literature values are used, the full reference with the relevant data) for each biomass type, the experimental method applied, and the resulting moisture content threshold.

#### Risk mitigation: Storage site suitability <a href="#id-5a8ye61po9ri" id="id-5a8ye61po9ri"></a>

Storage site design shall prevent conditions that promote degradation, primarily **water and oxygen ingress**. This shall be achieved through suitable geochemical and geological site conditions, an engineered storage design, and long-term land-use restrictions.

Project Developers shall demonstrate that the storage site meets these general principles by addressing all of the requirements below in a **Storage site characterization report**, provided for each storage site used by the project.

*Table 6 Sections of the Storage site characterization report and respective requirements.*

<table data-header-hidden data-search="false"><thead><tr><th width="160.7578125"></th><th></th></tr></thead><tbody><tr><td>Site description</td><td><p>Project Developers shall provide a description of the storage site, including:</p><ul><li><p>the typology of the storage site, according to <a data-mention href="#eligible-storage-site">#eligible-storage-site</a>, including</p><ul><li>storage type (void or pit)</li><li>storage conditions (wet or dry, anoxic or oxic)</li><li>storage layout (<a data-footnote-ref href="#user-content-fn-11">single-unit</a> or <a data-footnote-ref href="#user-content-fn-6">multiple-units</a>)</li></ul></li><li>GPS location, dimensions of storage area and available storage volume</li><li>Storage site design, including technical drawings and descriptions of any barriers (natural or synthetic)</li><li><p>For <a data-footnote-ref href="#user-content-fn-6">multiple-units</a> storage sites:</p><ul><li>Identification and characterization of each storage unit (stored volume, location, technical drawings)</li><li>a schedule of storage operations, including a timeline of when individual storage units are filled and closed</li></ul></li><li>Detailed description of how storage site design and biomass properties mitigate risk of biomass degradation</li></ul></td></tr><tr><td>Site closure</td><td><p>Project Developers shall provide:</p><ul><li>a description of the final configuration of the storage site upon closure, including the contained units, the cover system or seal, with technical details</li><li>the methods and procedures to be applied to achieve closure, and</li><li>a schedule of closure activities</li></ul><p>The closure plan shall comply with any applicable local regulation or standard. If the storage site is a mine (<em>void-type</em>), Project Developers shall ensure that the closure plan is compliant with or integrated in the mine closure and remediation plan.</p></td></tr><tr><td>Prevention against anthropogenic disturbance</td><td><p>Project Developers shall</p><ul><li>hold ownership of land or be authorized to use land. Evidence includes property title or proof of land ownership, or land-use authorization</li><li><p>guarantee restriction of land-use for the entire durability period (200 years) and guard against risk of potential new owner not maintaining storage conditions. This is demonstrated by both of the following:</p><ul><li>a legally binding restriction that runs with the land and survives a change in owner (i.e., Project Developer ceases to exist). Evidence includes, but is not limited to, conservation easement, covenant, servitude, long-term stewardship agreement with a land trust or governmental entity, or equivalent legal mechanism recognized in the jurisdiction</li><li>record of the restriction in the relevant public registry, cadastre, or database (e.g., land registry, geological survey, mining cadastre) to ensure enforceability against future landowners</li></ul></li></ul></td></tr><tr><td>Prevention against natural disturbance</td><td><p>Project Developers shall</p><ul><li><p>demonstrate that the storage site is not located in a zone with seismic activity, by assessing the Peak Ground Acceleration (PGA) over a minimum return period of 476 years</p><ul><li>PGA &#x3C; 9% (or 0.09g), automatically eligible</li><li>9% ≤ PGA ≤ 18%: site-specific seismic assessment demonstrating storage system withstands expected seismic loading without compromising integrity</li><li>PGA > 18%, site not eligible</li></ul></li><li><p>demonstrate the following</p><ul><li><strong>for pit-type storage:</strong> the cover system and surrounding land surface resist erosion under expected precipitation and runoff conditions throughout the durability period</li><li><p><strong>for void-type storage:</strong></p><ul><li>the overburden is sufficiently deep to remain intact under erosion</li><li>geomechanical stability of site is guaranteed (e.g., presence of faults, fractures, discontinuities). Evidence includes, but is not limited to inspection records, operational history, available site information, or other relevant documents demonstrating the absence of instability risk</li></ul></li></ul></li></ul></td></tr><tr><td>Limiting water ingress</td><td><p><strong>Groundwater</strong></p><p>Project Developers shall assess the flow direction, depth, and seasonal fluctuation of water table and demonstrate that the site</p><ul><li>is outside the zone of influence of local groundwater/aquifers, vertically and laterally</li><li>is not impacted by groundwater infiltration (void-type storage only)</li></ul><p>The assessment shall at least extend to the depth required by applicable regional or national regulations. Where the water table is not reached, Project Developers shall demonstrate, using existing hydrogeological information (e.g., regional hydrogeological maps, nearby wells, historical monitoring records), that groundwater lies below the investigated depth and that the criteria above are met.</p><p><strong>Surface water</strong></p><p>Project Developers shall demonstrate the following</p><ul><li>the site is outside a flood risk zone</li><li>natural or engineered drainage systems are in place to prevent water pooling inside the storage site</li><li>If near a body of water (river, lake, sea), the risk of lateral channel migration, avulsion, or rising water levels reaching the storage site over the durability period is negligible</li></ul><p><strong>Containment system</strong></p><p>Project Developers shall demonstrate that the containment system limits groundwater and surface water ingress to the storage site. This is evidenced by showing that the material(s) separating the biomass from the groundwater and surface water (e.g., cap system, engineered barrier, containing soil or rock) have a low hydraulic conductivity.</p><ul><li>Target value: ≤ 1×10<sup>-10</sup> m/s</li><li>Project Developers shall justify any deviation from the target value up to a value of 1×10<sup>-8</sup> m/s (e.g., through percolation modeling across the containment system, demonstrating a water flux no greater than that of a system with a hydraulic conductivity of ≤ 1×10<sup>-10</sup> m/s)</li><li>containment systems with values above 1×10<sup>-8</sup> m/s are not eligible</li></ul><p>Where no synthetic barrier is in place, Project Developers shall further assess the water-limiting properties (i.e., the lithology) of the containment system. This includes, but is not limited to</p><ul><li>soil or rock composition</li><li>permeability</li><li>plasticity (liquid limit and plasticity index)</li><li>sorption capacity</li></ul></td></tr><tr><td>Limiting oxygen ingress</td><td><p>Project Developers shall describe how and when <strong>anoxic conditions</strong> are established at the storage site, and demonstrate oxygen diffusion resistance of the containment system. This is informed by</p><ul><li>the oxygen transmission rate of a synthetic barrier, taken from the manufacturer's specifications, or where no such barrier is in place,</li><li><p>the lithology of the containment system. This includes, but is not limited to</p><ul><li>hydraulic conductivity</li><li>soil or rock composition</li><li>permeability</li><li>plasticity (liquid limit and plasticity index)</li><li>sorption capacity</li></ul></li></ul><p>Where biomass is stored under <strong>dry, oxic conditions</strong>, Project Developers shall demonstrate that the self-heating risk of biomass is mitigated throughout the durability period.</p></td></tr><tr><td>Barrier integrity</td><td><p>Project Developers shall assess the performance of all barriers including any natural or synthetic liners, as well as the cover system (pit-type storage) and the seal (void-type storage). This includes</p><ul><li><p>Assessment of barrier performance under storage conditions, including, but not limited to</p><ul><li>bearing capacity,</li><li>gas pressure resistance (for synthetic barriers, this includes seal integrity)</li><li>biodegradability</li></ul></li><li>Description of how access for inspection, maintenance, replacement or repair is guaranteed</li><li>Modeling of expected barrier performance (water ingress, oxygen ingress, mechanical/structural integrity) over the full claimed durability period under a worst-case scenario, demonstrating that confining function is maintained throughout and risk of biomass degradation is negligible or measures are in place to mitigate risk.</li></ul></td></tr><tr><td>Gas diffusion modeling (for void-type storage only)</td><td><p>Project Developers shall demonstrate that gases produced by biomass degradation do not migrate beyond the storage site within the durability period of 200 years.</p><p>This assessment shall include:</p><ul><li><p>Evaluation of gas diffusion through the barriers, host rock and seal, by using Fick's law to calculate</p><ul><li><p>the diffusion time (in years) required for gas (CO<sub>2</sub> and CH<sub>4</sub>) to migrate through the confining layer to the atmosphere,</p><ul><li>using diffusion coefficients that are measured, taken from literature, or obtained from manufacturer specifications (for barriers and/or seal),</li></ul></li><li>the diffusive flux out of the storage site, reported either as a maximum flux or as a time-dependent flux.</li></ul></li><li>The presence of any preferential diffusion pathways, such as tunnel connections, faults, fractures, or shafts. Where such pathways are identified, mitigation measures shall be proposed.</li></ul></td></tr></tbody></table>

### Storage site monitoring <a href="#id-8f3i2uvmiuhl" id="id-8f3i2uvmiuhl"></a>

Degradation of carbon and emission of GHGs are expected even under stable storage conditions. These GHG emissions are modeled upfront, and deducted from the project's gross removals as a loss (see [#carbon-loss-measurements](#carbon-loss-measurements "mention")). Any GHG emissions that surpass these expected and deducted GHGs are treated as reversals. Storage site monitoring enables the timely detection of reversals and confirms the stability of the storage conditions over time.

Three types of storage site monitoring are required at different stages of the project lifetime. They are described below and illustrated in Figure 2:

* **Batch stability monitoring**: demonstrates stable storage conditions for a given storage batch at a closed site (single-unit[^11] storage) or a closed unit (multiple-units[^6] storage), over a 4-week period, as a condition for credit issuance, see [#point-of-credit-issuance](#point-of-credit-issuance "mention").
* **Operational monitoring**: monitors for stability and reversal during ongoing operations. This type of monitoring applies only for multiple-units[^6] storage sites. Operational monitoring starts when the first batch's stability monitoring period ends, and ends when the storage site is permanently closed.
* **Post-closure monitoring**: monitors for stability and reversal after final closure of the storage site and credit issuance. This type of monitoring is required for the full 200-year durability period, divided into three distinct periods, with monitoring intensity matched to how reversal risk evolves over the storage site's lifetime:
  * Year 0-3: Reversal risk is highest because the site is still settling and seals are under real long-term load for the first time. Monitoring is most intensive here to catch emerging problems early.
  * Year 4-30: Biomass degradation, if any, is expected to occur during the first decades after storage site closure. Monitoring continues at a reduced but meaningful level to confirm stability of conditions.
  * Year 31-200: The site is presumed to have reached a steady state. Monitoring is reduced to frequencies that allow for detection of irregularities.

At validation Project Developers shall prepare a **Storage site monitoring plan**. That includes all of the following:

* a description of the procedure to monitor the parameters described in [#storage-site-monitoring-parameters](#storage-site-monitoring-parameters "mention") according to the requirements in [#storage-site-monitoring-duration-and-frequency](#storage-site-monitoring-duration-and-frequency "mention") for each type of storage site monitoring (i.e., batch stability, operational and post-closure monitoring)
* a description of how long-term storage site monitoring is guaranteed (see [#ensuring-long-term-storage-site-monitoring](#ensuring-long-term-storage-site-monitoring "mention"))
* the methods and equipment used, including calibration procedures and detection limits, demonstrating compliance with the following:
  * 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 before entering service and recalibrated periodically according to the manufacturer's specification and procedures, either by the manufacturer, a certified service or the Project Developer.
* a description of how access for maintenance, replacement and repair of the monitoring equipment is ensured
* 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](/rainbow-standard-documents/procedures-manual/rainbow-carbon-credits.md#cancelation) and its [Cancelation Notice](#user-content-fn-12)[^12].

<figure><img src="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FQppS3u6b9ckK4lrngmCW%2FScience%20team%20diagrams-18.jpg?alt=media&amp;token=10475cf2-e7b6-489e-90ca-e4b2747e35be" alt="" width="563"><figcaption><p>Figure 2: Illustrative examples of storage site monitoring for (a) a single-unit storage site and (b) a multiple-unit storage site. (a) A storage batch is buried and the storage site is closed. The site is then monitored for batch stability for four weeks. If stability is demonstrated, credits are issued for the storage batch. The 200-year post-closure monitoring period starts after issuance. (b) Three storage batches are buried in separate storage units in a single storage site over time. Each batch is monitored for stability for four weeks before its credits can be issued. Operational monitoring starts when the first batch's stability monitoring period ends. It continues until the storage site is closed and credits are issued for the last buried batch. The 200-year post-closure monitoring period then begins.</p></figcaption></figure>

#### **Storage site monitoring: Parameters**

Project Developers shall monitor the following parameters at the indicated locations at the storage site.

*Table 7 Storage site monitoring parameters and locations.*

<table><thead><tr><th width="137.80078125">Monitored parameter</th><th valign="top">Batch stability monitoring</th><th valign="top">Operational monitoring (multiple-units sites only)</th><th valign="top">Post-closure monitoring</th></tr></thead><tbody><tr><td><strong>CH</strong><sub><strong>4</strong></sub><strong> and CO</strong><sub><strong>2</strong></sub></td><td valign="top"><ul><li><a data-footnote-ref href="#user-content-fn-11">Single-unit</a> storage: inside the storage site*</li><li><a data-footnote-ref href="#user-content-fn-6">Multiple-units</a> storage: inside the storage unit</li></ul></td><td valign="top"><p>Inside each storage unit</p><ul><li>Where ongoing monitoring of each individual unit is not feasible due to engineering or access restrictions beyond the Project Developer's control, alternative monitoring approaches may be considered on a case-by-case basis.</li></ul></td><td valign="top"><ul><li>Single-unit storage site: Inside the storage site*</li><li>Multiple-units storage site: inside the storage site*, monitoring inside each unit is recommended</li></ul></td></tr><tr><td><strong>Temperature and humidity</strong></td><td valign="top"><ul><li>Single-unit storage: inside the storage site</li><li>Multiple-units storage: inside the storage unit or site</li></ul></td><td valign="top">Inside the storage unit or site</td><td valign="top"><ul><li>Single-unit storage: inside the storage site</li><li>Multiple-units storage: inside the storage unit or site</li></ul></td></tr><tr><td><strong>Physical integrity</strong></td><td valign="top"><ul><li>Single-unit storage: at the storage site</li><li>Multiple-units storage: at the storage unit and site</li></ul></td><td valign="top">At the storage unit and site</td><td valign="top">At the storage site</td></tr></tbody></table>

\*If monitoring of CH<sub>4</sub> and CO<sub>2</sub> inside the storage site is not feasible (e.g., no headspace), measurement may be taken outside the storage site, with justification provided by the Project Developer. Outside the storage site means at the seal for void-type storage sites and above-ground for pit-type storage site&#x73;*.*

Upon validation, Rainbow, the Validation and Verification Body (VVB, the auditor) or the Project Developer may require additional parameters to be monitored on a case-by-case basis, depending on the project design. Where monitoring of additional parameters is required, monitoring location, monitoring frequency, and the stability criteria for any additional parameter shall be defined.

#### Storage site monitoring: Duration and frequency

Project Developers shall measure the storage site monitoring parameters defined in [#storage-site-monitoring-parameters](#storage-site-monitoring-parameters "mention") at the frequencies described below for the different storage site monitoring types:

*Table 8 Duration and frequency of storage site monitoring.*

<table><thead><tr><th>Storage site monitoring</th><th>Duration</th><th valign="top">Monitoring frequency for CO2, CH4, temperature and humidity</th><th valign="top">Monitoring frequency for physical integrity (i.e., site visits)</th></tr></thead><tbody><tr><td><strong>Batch stability monitoring</strong></td><td>Four weeks (consecutive or a representative cumulative 4-week period)</td><td valign="top">At least twice a week</td><td valign="top">At least twice, at the start and end of the stability monitoring period</td></tr><tr><td><strong>Operational monitoring (</strong><a data-footnote-ref href="#user-content-fn-13"><strong>multiple-units</strong></a> <strong>sites only)</strong></td><td>During <a data-footnote-ref href="#user-content-fn-14">ongoing operations</a></td><td valign="top">At least monthly</td><td valign="top">At least every six months</td></tr><tr><td><strong>Post-closure monitoring</strong></td><td>200 years after site's permanent closure</td><td valign="top"><ul><li>Year 0-3: at least monthly</li><li>Year 4-30: at least every six months</li><li>Year 31-200: reduced to frequency that allows for detection of leakages or significant irregularities</li></ul></td><td valign="top"><ul><li>Year 0-3: at least every six months</li><li>Year 4-30: at least every five years</li><li><p>Year 31-200: event-triggered (i.e., in response to detected irregularities, or natural or anthropogenic disturbances).</p><p>Remote sensing, including satellite imagery, can be used to detect such events.</p></li></ul></td></tr></tbody></table>

For years 31-200 of the post-closure monitoring period, Project Developers shall suggest a reduced monitoring frequency of all parameters (i.e., CO<sub>2</sub>, CH<sub>4</sub>, temperature, humidity, physical integrity). This can include cessation of measurements of one or several parameters, however at least one shall be measured. Justification of which parameter(s) are most relevant for the project shall be provided, as well as normal, alert and threshold values for monitored parameters and procedures implemented in case the alert or threshold values are reached.

Where physical access to the storage site is prevented by circumstances beyond the Project Developer's control (e.g., severe weather, snow cover, or physical barriers) and measurements cannot be conducted at the required frequency, the Project Developer may postpone monitoring until access is re-established and shall resume monitoring as soon as possible thereafter. The Project Developer shall document and justify each interruption, including its cause, duration, and the date monitoring is resumed.

If access is prevented in the **post-closure monitoring phase** for a duration that causes the Project Developer to **miss four consecutive** monitoring events, the carbon is assumed to have been reversed, and the [Cancelation procedure](/rainbow-standard-documents/procedures-manual/rainbow-carbon-credits.md#canceling-removal-credits-due-to-reversals) for unavoidable reversals is triggered.

In the case of batch stability monitoring, only full weeks of monitoring with at least two measurements for each CO<sub>2</sub>, CH<sub>4</sub>, temperature and humidity shall count towards the cumulative total of four weeks of monitoring.

{% hint style="info" %}
For example, a Project Developer buries biomass in a pit and monitors the storage site's stability for credit issuance for three weeks, in accordance with the requirements in [#storage-site-monitoring-parameters](#storage-site-monitoring-parameters "mention") and [#storage-site-monitoring-duration-and-frequency](#storage-site-monitoring-duration-and-frequency "mention"). At the beginning of the fourth week, heavy snowfall prevents the Project Developer from accessing the storage site for an entire month. Once the site is accessible again, the Project Developer continues monitoring for another full week, reaching a cumulative total of four weeks of measurements. Provided the monitored parameters comply with the stability criteria (see [#storage-site-monitoring-storage-stability-criteria](#storage-site-monitoring-storage-stability-criteria "mention")), credits are then issued for the buried biomass.
{% endhint %}

#### Storage site monitoring: Storage stability criteria

Project Developers shall demonstrate that the measured storage site monitoring parameters defined in [#storage-site-monitoring-parameters](#storage-site-monitoring-parameters "mention") and measured at frequencies defined in [#storage-site-monitoring-duration-and-frequency](#storage-site-monitoring-duration-and-frequency "mention") meet the stability criteria defined below.

*Table 9 Storage stability criteria for each monitored parameter in storage site monitoring*.

<table><thead><tr><th width="143.75390625">Parameter</th><th>Storage stability criteria</th></tr></thead><tbody><tr><td><strong>CH</strong><sub><strong>4</strong></sub><strong> and CO</strong><sub><strong>2</strong></sub></td><td><p><strong>Batch stability monitoring</strong></p><p>For batch stability monitoring, a trend line shall be fitted to the emission time series of CO<sub>2</sub> and CH<sub>4</sub>, each, collected during the 4 weeks of monitoring. Conditions are considered stable where no significant increase in GHG concentration is detected, assessed on the 95% confidence level.</p><p>If an increase in concentration is detected, Project Developers shall report and quantify the GHG emissions, which shall be counted towards the <strong>cumulative detected emissions</strong>. Project Developers shall then address the increase as follows:</p><ul><li><strong>Expected increase:</strong> Even under stable conditions, an increase in gas concentration may be expected (e.g., under wet, anoxic storage conditions). Project Developers shall justify the expected increase using biomass decay dynamics, either measured through <a data-mention href="#carbon-loss-measurements">#carbon-loss-measurements</a> or modeled using peer-reviewed literature representative of the biomass type and storage conditions.</li><li><strong>Unexpected or higher-than-expected increase:</strong> Project Developers shall identify the cause of the increase and implement corrective measures at the storage site. Stability monitoring shall continue until stability is demonstrated. Crediting shall be withheld until the stability criteria are met.</li></ul><p><strong>Operational and post-closure monitoring</strong></p><p>During operational and post-closure monitoring, any increase in GHG emission shall be recorded and quantified.</p><p>If the cumulative detected emissions surpass the expected <a data-footnote-ref href="#user-content-fn-15">carbon loss fraction</a>, a reversal event is triggered and Project Developers shall follow the <a href="https://docs.rainbowstandard.io/rainbow-standard-documents/procedures-manual/rainbow-carbon-credits#canceling-removal-credits-due-to-reversals">Cancelation</a> procedure outlined in the Rainbow Procedures Manual.</p></td></tr><tr><td><strong>Temperature and humidity</strong></td><td>Project Developers shall report the measured values for each parameter and demonstrate that they remain stable over time within the storage site or storage unit, accounting for any expected seasonal variability. Unexpected changes may indicate exposure of the biomass or a failure of storage integrity.</td></tr><tr><td><strong>Physical</strong> <strong>integrity</strong></td><td><p>Stability is demonstrated if the storage unit or site shows no visible evidence of:</p><ul><li>cracking or fracturing of the seal, cover, or containment structure,</li><li>subsidence or settlement beyond design tolerances,</li><li>erosion affecting the integrity of the storage structure,</li><li>water ingress or ponding at the seal or storage boundary,</li><li>unauthorized excavation, disturbance, or access,</li><li>(where applicable) vegetation or root intrusion compromising the seal or cover.</li></ul><p>Inspections shall be documented with dated photographic evidence.</p></td></tr></tbody></table>

#### **Storage-site monitoring: Reports**

Project Developers shall report storage site monitoring data and demonstrate compliance with the criteria in [#storage-site-monitoring-storage-stability-criteria](#storage-site-monitoring-storage-stability-criteria "mention") in the form of **storage site monitoring reports** for

* **batch stability** for a given storage batch, as a condition for credit issuance (see [#monitoring](#monitoring "mention")),
* **operational monitoring** at final site closure (only for multiple-units[^6] storage sites),
* **post-closure monitoring** at the frequency of monitoring for physical integrity (i.e., site visits), as defined in [#storage-site-monitoring-duration-and-frequency](#storage-site-monitoring-duration-and-frequency "mention"), or at least every ten years, even if there is no reversal event, to confirm that the carbon remains stored.
  * If a reversal has occurred during the post-closure monitoring period, Project Developers shall follow the [Cancelation](https://docs.rainbowstandard.io/rainbow-standard-documents/procedures-manual/rainbow-carbon-credits#canceling-removal-credits-due-to-reversals) procedure outlined in the Rainbow Procedures Manual.

The reports shall include the most recent calibration records of the monitoring equipment.

#### **Ensuring long-term storage site monitoring**

The Project Developer is responsible for conducting post-closure monitoring, and shall commit to following the procedures outlined herein upon project validation.

The Project Developer shall remain liable for the post-closure monitoring unless liability is formally transferred and accepted by a new party. Upon transfer of liability, the new party shall be registered under the Rainbow certification scheme and assume the role of Project Developer and all associated responsibilities, including the submission of future post-closure monitoring reports. The Project Developer shall inform Rainbow of any transfer of liability, provide proof of the agreement, and provide the name and contact information of the new Project Developer.

Additionally, 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 and report responsibilities
* maintenance, repair and replacement of monitoring equipment
* repair of compromised storage units
* compliance with the [Buffer pool replacement requirements](/rainbow-standard-documents/procedures-manual/rainbow-carbon-credits.md#canceling-removal-credits-due-to-reversals) 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

### No double counting <a href="#id-8f3i2uvmiuhl" id="id-8f3i2uvmiuhl"></a>

See the [BiCRS methodology No double counting](/methodologies/biomass-carbon-removal-and-storage-bicrs.md#n1iy4xaxuthk) section for general requirements on this topic.

### Co-benefits <a href="#id-8f3i2uvmiuhl" id="id-8f3i2uvmiuhl"></a>

Projects should support at least two **quantifiable and verifiable** environmental or social co-benefits, aligned with the [UN Sustainable Development Goals](https://unstats.un.org/sdgs/indicators/Global-Indicator-Framework-after-2024-refinement-English.pdf) (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 10 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.*

<table><thead><tr><th width="200">UN SDG</th><th width="345">Example</th><th>Proof</th></tr></thead><tbody><tr><td><strong>SDG 11.6:</strong> Reduce adverse environmental impact of waste</td><td>Diverting waste biomass from open dumps or unmanaged disposal sites into engineered burial reduces uncontrolled waste accumulation.</td><td>Type of biomass used, records proving alternative fate of biomass</td></tr><tr><td><strong>SDG 12.2:</strong> Achieve sustainable management and efficient use of natural resources.</td><td>Sustainable reuse of biomass, avoiding open field burning of biomass or landfilling.</td><td>Type of biomass used, records proving alternative fate of biomass</td></tr><tr><td><strong>SDG 15.3:</strong> Combat land degradation</td><td>If storage sites are on marginal/degraded land, buried biomass can improve soil organic matter and structure over time, aiding land restoration.</td><td>Soil sampling pre/post burial at storage site, land classification records</td></tr></tbody></table>

### Environmental and social safeguards <a href="#id-82n4j72vjt9v" id="id-82n4j72vjt9v"></a>

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

<details>

<summary>Forest waste and necessary tree removal</summary>

The sustainability criteria in the [Biomass Feedstock module](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md#id-82n4j72vjt9v) apply.

Project Developers shall demonstrate that the biomass is not classified as hazardous waste under the applicable regional or national regulation.

</details>

<details>

<summary>Agricultural residues</summary>

The sustainability criteria in the [Biomass Feedstock module](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md#id-82n4j72vjt9v) apply.

Project Developers shall demonstrate that the biomass is not classified as hazardous waste under the applicable regional or national regulation.

</details>

<details>

<summary>Thermochemically converted biomass</summary>

The sustainability criteria in the [Biomass Feedstock module](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md#id-82n4j72vjt9v) apply to the biomass feedstock before conversion.

For each production batch, Project Developers shall demonstrate that thermochemically converted biomass is below the pollutant concentration thresholds outlined in Table 11, defined by the [World Biochar Certificate (WBC) Guidelines](#user-content-fn-16)[^16] (for WBC-Agro).

*Table 11 The thresholds for pollutant concentrations allowed in thermochemically converted biomass, as detailed in the* [*World Biochar Certificate Guidelines*](#user-content-fn-16)[^16]*.*

<table><thead><tr><th width="353.44439697265625">Substance</th><th>Limit amount (g/tonne dry matter)</th></tr></thead><tbody><tr><td>Pb</td><td>300</td></tr><tr><td>Cd</td><td>5</td></tr><tr><td>Cu</td><td>200</td></tr><tr><td>Ni</td><td>100</td></tr><tr><td>Hg</td><td>2</td></tr><tr><td>Zn</td><td>1000</td></tr><tr><td>Cr</td><td>200</td></tr><tr><td>As</td><td>20</td></tr><tr><td><a data-footnote-ref href="#user-content-fn-17">8 EFSA PAH</a></td><td>1</td></tr></tbody></table>

Where biomass exceeds these thresholds, Project Developers shall report the concentrations of the pollutants listed in the table above, and shall demonstrate all of the following:

* the thermochemically converted biomass is below the pollutant concentration threshold for the 8 [EFSA PAHs](#user-content-fn-17)[^17] of 4 gram per tonne of dry matter (as taken from WBC[^16]-Material)
* the biomass is not in direct contact with the surrounding soil (e.g., through isolation with a barrier)
* the risk of pollutant leaching from biomass through water intrusion is negligible

Rainbow reserves the right to refuse a project on a case-by-case basis even where the requirements above are met.

{% hint style="info" %}
*Disclaimer: The European Biochar Certificate (EBC) and the World Biochar Certificate are independent certification programs designed to ensure the quality of biochar products. These certifications are administered and trademarked by Carbon Standards International (CSI) and are distinct from the Rainbow certification and the issuance of carbon credits.*

*The threshold values provided here are based on the voluntary guidelines of the World Biochar Certificate (WBC), reproduced with permission. While these values have been adopted by the Rainbow standard as pollutant thresholds, they are only indicative. Meeting these thresholds for Rainbow certification does not imply eligibility for or any association with the EBC or WBC programs. Project Developers certified under the Rainbow standard shall not make claims or use any trademarked materials from CSI, unless explicitly allowed by CSI.*

*Voluntary certification under the WBC and EBC schemes is overseen by CSI and includes additional requirements beyond pollutant thresholds.*
{% endhint %}

</details>

<details>

<summary>Purpose-grown algae</summary>

Project Developers shall demonstrate all of the following:

* Algae are cultivated on land in dedicated infrastructure (e.g., open raceway ponds) and not in open water (i.e., sea or natural ponds).
* A residual stream is used as cultivation medium and nutrient source (e.g., municipal wastewater). No synthetic nutrient sources are added.
* The water released after algae cultivation complies with applicable regulations on water quality.
* Where cultivation takes place at existing wastewater treatment plants,
  * the algae cultivation causes no adverse interference with business-as-usual wastewater treatment, and
  * any hazardous waste at the plant is managed sustainably, following the applicable regulation.
* The algae are not classified as hazardous waste under the applicable regional or national regulation. Where the biomass exceeds the applicable thresholds, Project Developers shall provide a justification and demonstrate that both of the following conditions are met. Rainbow reserves the right to refuse a project on a case-by-case basis even where these are demonstrated:
  * the biomass is not in direct contact with the surrounding soil (e.g., through isolation with a barrier), and
  * the risk of pollutant leaching through water intrusion is negligible.

</details>

#### 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](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md) module and the risks from the [Processing and energy use](/modules/processing-and-energy-use.md) 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](/rainbow-standard-documents/rainbow-standard-rules/principles-and-requirements.md#environmental-and-social-risk-assessment), 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.

{% hint style="info" %}
Note that the **life-cycle GHG reduction calculations account for the climate change impacts of most environmental risks**. Nonetheless, Project Developers shall transparently describe any substantial and sensitive GHG emission risks in the risk evaluation template.
{% endhint %}

{% hint style="info" %}
All risk assessments shall also address the [Minimum environmental and social risks ](/rainbow-standard-documents/rainbow-standard-rules/principles-and-requirements.md#environmental-and-social-risk-assessment)defined in the Rainbow Standard Rules.
{% endhint %}

### Leakage

According to the [Rainbow Standard Rules](/rainbow-standard-documents/rainbow-standard-rules/principles-and-requirements.md#leakage), 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](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md#lc9eewbyvlyk).

### Monitoring

Monitoring plans for this module shall include, but are not limited to, tracking of the following information.

{% tabs %}
{% tab title="Production Batch" %}
The following shall be tracked for each [production batch](#id-2xck12gc2auz):

* Type of biomass or biomass mix (this includes different species of a single biomass type)
* Amount of biomass input (i.e., biomass going into processing or conversion step)
* Amount of biomass produced (i.e., biomass coming out of processing or conversion step)
* Organic carbon content
* Moisture content
* Compliance with [#id-82n4j72vjt9v](#id-82n4j72vjt9v "mention")
* [#sampling-records](#sampling-records "mention")
* for woody biomass only:
  * $$C\_{\text{org}}/N$$
  * Lignin, cellulose and hemicellulose content
* for thermochemically converted biomass only:
  * $$H/C\_{\text{org}}$$
  * $$O/C\_{\text{org}}$$
    {% endtab %}

{% tab title="Storage Batch" %}
The following shall be tracked for each [storage batch](#storage-batches):

* 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
* Storage batch ID
* Storage batch location (i.e., identification of storage site or storage unit)
* Date of storage
* Demonstration of stable storage conditions, see [#point-of-credit-issuance](#point-of-credit-issuance "mention")
* Carbon loss fraction applied, see [#carbon-loss-measurements](#carbon-loss-measurements "mention")
* Methane oxidation factor (if relevant) applied, see [#methane-oxidation-factor-measurements](#methane-oxidation-factor-measurements "mention")
  {% endtab %}

{% tab title="Monitoring Period" %}
The following shall be tracked in each monitoring period:

* Number of storage batches buried in monitoring period
* Co-benefits
  {% endtab %}
  {% endtabs %}

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

* a description of the parameter to be monitored
* monitoring frequency
* emission sources and sinks
* data storage and management plan, including the format, location and duration of data keeping records
* Primary data
  * description of measurement methods/procedures, and their level of accuracy and calibration procedures
  * quality assessment or quality control procedures
  * laboratory name and relevant accreditations for any measurement conducted by external laboratories
  * responsible party for collecting and archiving data, including how they are assigned/selected, and how their competence to monitor the parameter is assessed
  * plan in case of unexpected interruption or errors in monitoring, ensuring conservative treatment of data and an appropriate deduction of emission reductions
* Secondary data
  * data source and, where applicable, value and frequency of update

## 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 for each **storage batch.** Several quantifications may be credited in a monitoring period.

<details>

<summary><strong>Calculation:</strong> Net removals</summary>

$$\textbf{(Eq.1)}\ Net\ Removal = R\_{baseline}-R\_{project}-E\_{project}$$

where:

* $$Net\ Removal$$ represents the project's net removals from one storage batch, in tCO$$\_2$$eq. Its sign is positive.
* $$R\_{baseline}$$ represents baseline GHG removals from one storage batch, in tCO<sub>2</sub>eq. Its sign is negative. It is set to zero.
* $$R\_{project}$$ represents the project's gross GHG removals from one storage batch, in tCO$$\_2$$eq. Its sign is negative. It is calculated according to Eq. 2 for pit-type storage sites and according to Eq. 6 for void-type storage sites.
* $$E\_{project}$$ represents the project's total induced GHG emissions from one storage batch, in tCO<sub>2</sub>eq. Its sign is positive. It is calculated according to Eq. 7.

</details>

### Data sources <a href="#kpxsamb8logm" id="kpxsamb8logm"></a>

The required **primary data** for GHG calculations from projects are presented in Table 12. These data shall be provided **for each storage batch** and made publicly available.

*Table 12 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*](#monitoring) *section).*

<table><thead><tr><th width="249">Parameter</th><th>Unit</th><th>Source</th></tr></thead><tbody><tr><td>Number of production batches going into storage batch</td><td>Number</td><td>Internal tracking documents, invoices, contracts</td></tr><tr><td>Total amount of biomass in storage batch</td><td>Tonnes of fresh matter</td><td>Internal tracking documents, invoices, contracts</td></tr><tr><td><p><strong>For each production batch going into the storage batch:</strong></p><p>amount of biomass input (i.e., biomass used to generate production batch), <span class="math">A_{biomass\ input, i}</span></p></td><td>Tonnes of fresh matter</td><td>Internal tracking documents, invoices, contracts</td></tr><tr><td><p><strong>For each production batch going into the storage batch:</strong></p><p><br>amount of biomass produced (i.e., total amount of biomass in the production batch), <span class="math">A_{biomass\ produced, i}</span></p></td><td>Tonnes of fresh matter</td><td>Internal tracking documents, invoices, contracts</td></tr><tr><td><strong>For each production batch going into the storage batch:</strong><br><br>organic carbon content of the biomass produced, <span class="math">C_{org}</span></td><td>Fraction</td><td>Laboratory measurements</td></tr><tr><td><strong>For each production batch going into the storage batch:</strong><br><br>moisture content of the biomass produced, <span class="math">\%M</span></td><td>Fraction</td><td>On-site or laboratory measurements</td></tr><tr><td><strong>For each production batch going into the storage batch:</strong><br><br>amount of biomass produced going into storage batch (i.e., share of total biomass in the production batch that is stored ), <span class="math">A_{biomass\ stored, i}</span></td><td>Tonnes of fresh matter</td><td>Internal tracking documents</td></tr><tr><td>Carbon loss fraction</td><td>Fraction</td><td><ul><li>secondary data, see Table 13, or</li><li>measured data, see <a data-mention href="#carbon-loss-measurements">#carbon-loss-measurements</a></li></ul></td></tr><tr><td>Methane oxidation factor (for pit-type storage only)</td><td>Fraction</td><td><ul><li>secondary data, see Table 14, or</li><li>measured data, see <a data-mention href="#methane-oxidation-factor-measurements">#methane-oxidation-factor-measurements</a></li></ul></td></tr></tbody></table>

{% hint style="info" %}

* Biomass input, $$A\_{biomass\ input, i}$$ is the quantity of biomass processed or converted to generate a given production batch *i*.
* Biomass produced, $$A\_{biomass \ produced, i}$$, is the quantity of biomass generated through processing and conversion of $$A\_{biomass\ input, i}$$. It is the total amount of biomass in a production batch *i*.
  * Projects using woody biomass often do not process or convert their biomass feedstock before burying it. In this case, since no processing or conversion step is involved, the total amount of biomass in a production batch $$A\_{biomass \ produced, i}$$ corresponds to $$A\_{biomass\ input, i}$$.
* Biomass stored, $${A}\_{biomass\ stored, i}$$ is the quantity of biomass from a given production batch *i*\
  that ends up in a storage batch.

For example

* a project collects 1000 t of forest waste from necessary tree removal, $$A\_{biomass\ input, i}$$. The biomass is transported directly to an eligible storage site, without any prior processing or conversion step, hence $$A\_{biomass \ produced, i}=A\_{biomass\ input, i}$$. At the storage site, the 1000 t of woody biomass are buried in a single burial event (i.e., a single storage batch), and $$A\_{biomass\ stored, i} = A\_{biomass \ produced, i}$$.
* a project uses 120 t of agricultural residues, $$A\_{biomass\ input, i}$$, and thermochemically converts it to 100 t of hydrochar, corresponding to $$A\_{biomass \ produced, i}$$. If 50 t of the produced hydrochar in this production batch, $$A\_{biomass \ produced, i}$$, is subsequently placed into a storage batch and buried, that 50 t is $${A}\_{biomass\ stored, i}$$.
* a project harvests 120 t of purpose-grown algae, $$A\_{biomass\ input, i}$$. After drying and shredding of the biomass, 100 t of algae remain, $$A\_{biomass \ produced, i}$$. These 100 t of algae are subsequently placed into a storage batch and buried, hence $$A\_{biomass\ stored, i} = A\_{biomass \ produced, i}$$.
  {% endhint %}

### 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, $$C\_{\text{org}}/N$$).
* For biomass storage under wet, anoxic conditions in a pit
  * The default value for the carbon loss fraction is 0.088 for woody biomass and $$(1-F\_{perm, 100})$$ 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. All methane is assumed to be emitted to the atmosphere as methane, and none is oxidized to CO<sub>2</sub>.)
* Carbon loss is re-emitted in equal parts as CO<sub>2</sub> and CH<sub>4</sub>. This also applies to biomass stored under dry conditions, regardless of whether it is under anoxic or oxic conditions.

### Baseline scenario <a href="#ly65klblzpa9" id="ly65klblzpa9"></a>

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](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md) and accounted for in the calculation of the project emissions (as *Biomass leakage* in Eq. 12 of [Calculation: Project emissions](#calculation-project-emissions)).

### Project scenario

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

* CO<sub>2</sub> removal from stored biomass
* Project establishment
* Storage operations
* Site closure

<div align="center"><figure><img src="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2FyufmmEdDstuQPh266z0W%2FScience%20team%20diagrams-21.jpg?alt=media&amp;token=c8dc85b6-3fd5-4214-8bed-33c66f14b86b" alt="" width="563"><figcaption><p>Figure 3: System diagram of a biomass burial project, indicating emission sources, process stages, carbon removal and losses in each of the four main life cycle stages.</p></figcaption></figure></div>

### Project removals

Project gross removals are calculated differently for the different storage types and conditions. They are calculated as the carbon stored in the biomass minus the expected amount of carbon loss over 200 years. The expected amount of carbon loss over 200 years is obtained according to Table 13.

*Table 13 Determination of carbon loss fraction under different storage conditions.*

<table><thead><tr><th width="244.375">Storage conditions</th><th>Determination of carbon loss fraction</th></tr></thead><tbody><tr><td>Wet, anoxic in a pit</td><td><p><a data-footnote-ref href="#user-content-fn-18">Eligible</a> woody biomass:</p><ul><li>default value of 0.088 taken from the <a data-footnote-ref href="#user-content-fn-19">IPCC</a>, or</li><li>site-specific value using <a data-mention href="#carbon-loss-measurements">#carbon-loss-measurements</a></li></ul><p><a data-footnote-ref href="#user-content-fn-20">Eligible</a> thermochemically converted biomass</p><ul><li><span class="math">(1-F_{perm, 100}) </span>, with <span class="math">F_{perm, 100}</span> calculated according to Eq. 1 in the <a href="/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-storage/biochar-application-to-soils.md">Biochar application to soil</a> module, or</li><li>site-specific value using <a data-mention href="#carbon-loss-measurements">#carbon-loss-measurements</a></li></ul></td></tr><tr><td>Wet, anoxic in a void</td><td>No default value allowed. At validation, <a data-mention href="#carbon-loss-measurements">#carbon-loss-measurements</a> are required, using the ex-situ testing approach.</td></tr><tr><td>Dry, anoxic or oxic in a pit or a void</td><td>No default value allowed. At validation, <a data-mention href="#carbon-loss-measurements">#carbon-loss-measurements</a> are required, using the ex-situ testing approach.</td></tr></tbody></table>

The carbon loss is assumed to be re-emitted as CO<sub>2</sub> and CH<sub>4</sub> in equal parts. The re-emission of greenhouse gases from the storage site is treated differently for different storage types:

* **In a pit**, the generated gases will migrate through the overlying soil layer and eventually reach the atmosphere. Before reaching the atmosphere, a fraction of the CH<sub>4</sub> may get oxidized to CO<sub>2</sub> in the soil layer. This oxidation is accounted for in the calculations via a **methane oxidation factor**. This oxidation factor is determined according to the section [#methane-oxidation-factor-measurements](#methane-oxidation-factor-measurements "mention"). The share of the carbon loss fraction emitted as CO<sub>2</sub> and the share emitted as CH<sub>4</sub> are deducted from the biomass carbon.
* **In a void**, the generated gases will not migrate beyond the storage site and reach the atmosphere within the durability period of 200 years, as demonstrated in [#id-5a8ye61po9ri](#id-5a8ye61po9ri "mention"). Out of an abundance of caution, the carbon loss fraction is not credited and deducted from the biomass carbon.

<details>

<summary><strong>Calculation:</strong> Gross removals from biomass stored in a pit</summary>

Gross removals from biomass stored in a pit under all storage conditions (i.e., wet and anoxic, dry and anoxic, dry and oxic) are calculated using the following equations.

$$\textbf{(Eq.2)}\ R\_{project} = ({R}*{biomass} - ({E}*{loss,\ CO\_2}+ {E}\_{loss,\ CH\_4}))\times -1$$

* $$R\_{project}$$ is defined in Eq. 1.
* $$R\_{biomass}$$ represents the theoretical amount of CO<sub>2</sub> stored in the biomass in a given storage batch, in tCO<sub>2</sub>eq. It is calculated according to Eq. 3.
* $${E}\_{loss,\ CO\_2}$$ represents the amount of CO<sub>2</sub> re-emitted from the stored biomass, in tCO<sub>2</sub>eq. It is calculated according to Eq. 4.
* $${E}\_{loss,\ CH\_4}$$ represents the amount of CH<sub>4</sub> re-emitted from the stored biomass, converted into CO<sub>2</sub> equivalents using the 100-year global warming potential of CH<sub>4</sub>, in tCO<sub>2</sub>eq. It is calculated according to Eq. 5.
* It is multiplied by -1 to obtain a negative sign. Removals are reported as a negative value.

$$\textbf{(Eq.3)}\ {R}*{biomass} = \sum\_i A*{biomass \ stored, i} \times (1-%M\_i) \times C\_{org,i} \times C\_{to}CO\_2$$

* $$R\_{biomass}$$ is defined in Eq. 2.
* $${A}\_{biomass\ stored, i}$$ represents the amount of biomass from [production batch](#id-2xck12gc2auz) $$i$$ contained in the [storage batch](#storage-batches) and buried at the storage site, in tonnes.
* $$%M\_i$$ represents the moisture content of the biomass in the production batch $$i$$, as a mass fraction.
* $$C\_{org,i}$$ represents the organic carbon content of the biomass in production batch $$i$$, as a mass fraction.
* $$C\_{to}CO\_2 = \frac {44}{12}=3.67$$, and represents the molar masses of CO<sub>2</sub> and C respectively, and is used to convert tonnes C to tonnes of CO<sub>2</sub>eq

$$\textbf{(Eq.4)}\ {E}*{loss,\ CO\_2} = (\ \sum\_i A*{biomass \ stored, i} \times (1-%M\_i) \times C\_{org,i} \times C\_{to}CO\_2) \times (F\_{CO\_2} \times C\_{loss} + F\_{CH\_4}\times C\_{loss}\times F\_{oxi})$$

* $${E}\_{loss,\ CO\_2}$$ is defined in Eq. 2.
* $${A}*{biomass\ stored, i}$$, $$%M\_i$$, $$C*{org,i}$$, $$C\_{to}CO\_2$$ are defined in Eq. 3.
* $$C\_{loss}$$ represents the fraction of biomass carbon that is lost under storage conditions, the carbon loss fraction. It is determined according to the rules set out in Table 13.
* $${F}*{CO\_2}$$ represents the fraction of $$C*{loss}$$ emitted as CO<sub>2</sub>. It is set to $$0.5$$.
* $${F}*{CH\_4}$$ represents the fraction of $$C*{loss}$$ emitted as CH<sub>4</sub>. It is set to $$0.5$$.
* $${F}\_{oxi}$$ represents the methane oxidation factor. It represents the fraction of methane emitted that will be oxidized to CO<sub>2</sub> as it passes through the soil layer. It is determined according to the [#methane-oxidation-factor-measurements](#methane-oxidation-factor-measurements "mention") section.

$$\textbf{(Eq.5)}\ {E}*{loss,\ CH\_4} = (\ \sum\_i A*{biomass \ stored, i} \times (1-%M\_i) \times C\_{org,i} \times C\_{to}CH\_4) \times F\_{CH\_4}\times C\_{loss}\times (1-F\_{oxi})\times GWP\_{100, CH\_4}$$

* $${E}\_{loss,\ CH\_4}$$ is defined in Eq. 2.
* $${A}*{biomass\ stored, i}$$, $$%M\_i$$ and $$C*{org,i}$$ are defined in Eq. 3.
* $$C\_{to}CH\_4 = \frac {16}{12}=1.33$$ and represents the molar masses of CH<sub>4</sub> and C respectively, and is used to convert tonnes C to tonnes of CH<sub>4</sub>.
* $$C\_{loss}$$, $${F}*{CH\_4}$$ and $${F}*{oxi}$$ are defined in Eq. 4.
* $$GWP\_{100,CH\_4}$$ represents the [100-year global warming potential](#user-content-fn-21)[^21] of biogenic methane. It is used to convert tCH<sub>4</sub> into tCO<sub>2</sub>eq.

</details>

<details>

<summary><strong>Calculation:</strong> Gross removals from biomass stored in a void</summary>

Gross removals from biomass stored in a void are calculated according to the following equation

$$\textbf{(Eq.6)}\ R\_{project} = {R}*{biomass}\times (1 - {C}*{loss})\times -1$$

* $$R\_{project}$$ is defined in Eq. 1.
* $$R\_{biomass}$$ is defined in Eq. 2.
* $$C\_{loss}$$ is defined in Eq. 4.
* It is multiplied by -1 to obtain a negative sign. Removals are reported as a negative value.

</details>

#### Carbon loss measurements

Project Developers **may conduct carbon loss measurements** for eligible biomass stored under wet, anoxic conditions in a pit, using one of the three approaches described below. This is to obtain a site-specific value and avoid using a conservative default value.

Project Developers **shall conduct carbon loss measurements at validation** for eligible biomass stored in a void (any conditions[^22]) or under dry conditions (any [storage type](#user-content-fn-23)[^23]), using the ex-situ approach only. This is to provide evidence of the durability of the biomass under storage conditions.

In order to use a site-specific value, Project Developers shall provide scientific evidence from the relevant approach described below. Any proposed value is subject to review and approval by Rainbow, and, where deemed necessary, by an independent technical expert, before its use in the project's GHG quantification.

For biomass storage under wet, anoxic conditions in a pit, Project Developers may switch from a default to a site-specific value at each verification. Retrospective application of a site-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.

The experimentally determined **carbon loss** fraction is valid for any following verification at the same storage site, provided it is representative of the biomass used. This includes but is not limited to biomass species or mix of species, and the biomass processing or conversion process (see [#id-2xck12gc2auz](#id-2xck12gc2auz "mention")).

{% tabs %}
{% tab title="Ex-situ testing" %}
{% hint style="info" %}
This approach shall be used for biomass stored in a void (any conditions[^22]) or under dry conditions (any [storage type](#user-content-fn-23)[^23]). No other approach is eligible.\
This approach may be used for biomass stored under wet, anoxic conditions in a pit.
{% endhint %}

Project Developers shall conduct a **time-series measurement of GHG evolution, or of carbon loss** from biomass that has been processed[^24] and converted[^25] in the same way as the project's biomass, and incubated under **laboratory conditions analogous to the intended storage environment**. The experimental setup shall be representative of the project's packing strategy, and engineered barriers used, and shall include, wherever practicable, a microbial inoculum representative of the storage site. Laboratory incubations may use an elevated temperature relative to the storage site to accelerate degradation within a practical measurement window. The measurement shall be benchmarked against a control sample.

The experimental setup may be either in a laboratory under controlled conditions simulating the project setup, or directly in the field on a sample of test storage sites.

Project Developers shall justify an incubation duration that is appropriate for the biomass and storage conditions. The justification shall demonstrate at least all of the following:

* the duration is adjusted to the decay behavior of the biomass
* the duration is long enough to capture any lag phase or delayed onset of decay under the intended storage conditions
* the duration is long enough to support a statistically robust fit of the decay model described below

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 200-year durability period as a fraction of the total organic carbon content. This fraction **shall be treated as carbon loss and deducted from the removals calculation**

Project Developers shall report the modeled decay curve, called the **biomass decay profile,** alongside the carbon loss fraction.

If no GHG evolution or carbon loss is observed during the time-series measurements, the Project Developer shall provide the minimum detection limit of the measurement system used, expressed as a fraction of the total organic carbon content of the incubated sample. This limit shall be treated as carbon loss and applied as a **one-time deduction** from the removals calculation.
{% endtab %}

{% tab title="In-situ testing" %}
{% hint style="info" %}
This approach is only eligible for biomass stored under wet, anoxic conditions in a pit.
{% endhint %}

When choosing this approach, Project Developers bury a storage batch and close the storage site or unit. Rather than issuing credits immediately after burial (provided stability is demonstrated in accordance with [#id-8f3i2uvmiuhl](#id-8f3i2uvmiuhl "mention")) using the default value in Table 13, Project Developers measure the site-specific carbon loss fraction over a 12-month period and apply this site-specific value for credit issuance of the storage batch. As a result, a minimum of 12 months passes between burial and issuance.

* 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 **site-specific carbon loss** value as the ratio of this projected cumulative carbon loss to total organic carbon content of the biomass, and report the modeled decay curve, the **biomass decay profile.**
  {% endtab %}

{% tab title="Biochemical methane potential testing" %}
{% hint style="info" %}
This approach is only eligible for biomass stored under wet, anoxic conditions in a pit.
{% endhint %}

Project Developers shall conduct a standardized biochemical methane potential (BMP) test on biomass that has been processed and converted[^26] 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](#user-content-fn-27)[^27]. Wherever practicable, the test shall include a microbial inoculum representative of the storage site.
{% endtab %}
{% endtabs %}

#### Methane oxidation factor measurements

Oxidation of methane in the soil cover above the storage site is only relevant for pit-type storage sites. 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 shall choose either of the following:

* use the default value of 0%
* use a methane oxidation factor from Table 14 below, provided they prove that the storage site meets the corresponding requirements
* use a project-specific value for the methane oxidation factor, following the requirements set out below

*Table 14 Methane flux rate and cover conditions for storage sites and the corresponding methane oxidation factor. The table is a conservative simplification of the* [*US EPA's rules on determination of the landfill methane oxidation factor*](#user-content-fn-28)[^28]*. \*Methane flux rate is the mass flow rate of methane per unit area at the bottom of the surface soil before any oxidation.*

<table><thead><tr><th>Methane flux rate*</th><th width="205.17578125">Cover conditions</th><th>Methane oxidation</th></tr></thead><tbody><tr><td>Not measured or > 70 g/m<sup>2</sup>/d</td><td>Soil cover of ≥ 30 cm</td><td>10%</td></tr><tr><td>10 ≤ <em>x</em> ≤ 70 g/m<sup>2</sup>/d</td><td>Soil cover of ≥ 30 cm</td><td>25%</td></tr><tr><td>&#x3C; 10 g/m<sup>2</sup>/d</td><td>Soil cover of ≥ 30 cm</td><td>35%</td></tr></tbody></table>

If Project Developers choose to determine a site-specific value for the methane oxidation factor, they shall provide scientific evidence from one of the suggested approaches below. Any proposed value is subject to review and approval by Rainbow, and, where deemed necessary, by an independent technical expert, before its use in the project's GHG quantification.

Project Developers may switch from a default to a site-specific value at each verification. Retrospective application of a site-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.

The experimentally determined methane oxidation factor is valid for any following verification at the same storage site, provided the cover system of the pit does not change.

{% tabs %}
{% tab title="In-situ testing" %}
When choosing this approach, Project Developers bury a storage batch and close the storage site with the final configuration of the cover system. Rather than issuing credits immediately after burial (provided stability is demonstrated in accordance with [#id-8f3i2uvmiuhl](#id-8f3i2uvmiuhl "mention")) using a 0% oxidation factor or a value from Table 14, Project Developers measure the methane oxidation factor of the soil cover over a 6-month period and apply this site-specific value for credit issuance of the storage batch. As a result, a minimum of 6 months passes between burial and issuance.

* Project Developers shall conduct measurements at a **closed storage site**, provided the unit is covered with the final configuration of the cover system. 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 constant [oxygen levels below 5%](#user-content-fn-29)[^29] for at least two weeks.
* Project Developers shall justify a sampling frequency that is appropriate for the site and cover system. The justification shall demonstrate, at a minimum, that the sampling frequency:
  * is sufficient to capture the seasonal and temporal variability of the methane oxidation rate driven by changing environmental conditions
  * yields enough measurements to support a statistically robust estimate of the mean oxidation rate and its uncertainty
* Additionally, Project Developers shall justify the number and placement of sampling locations, demonstrating that they capture the spatial variability of the methane oxidation rate across the cover.
* Project Developers shall use technologies that can directly quantify the percentage of methane oxidized in the soil. This includes, for example [stable isotope method](#user-content-fn-30)[^30], or gas concentration/mass balance measurements.
  {% endtab %}

{% tab title="Representative testing" %}
Project Developers may carry out this approach before the first burial event takes place, allowing to obtain a site-specific value as early as possible and apply it in the quantification for the first storage batch buried.

* Project Developers shall conduct measurements at a **representative sample plot** located in the vicinity[^31] of the storage site, constructed with the same packing strategy as the storage unit (i.e., identical barriers and cover system), but with no biomass buried in the site, using instead a controlled source as the methane source. Project Developers shall use isotopically labeled methane or methane that is isotopically characterized (i.e., of known isotopic composition).
* Measurements of the methane oxidation rate of the soil cover shall be taken over a **6-month period representative of the seasonal conditions**.
* Project Developers shall use technologies that can directly quantify the percentage of methane oxidized in the soil. This includes, for example [stable isotope method](#user-content-fn-30)[^30], [gas push-pull tests](#user-content-fn-32)[^32] or gas concentration/mass balance measurements.
* Project Developers shall justify a sampling frequency that is appropriate for the site and cover system. The justification shall demonstrate, at a minimum, that the sampling frequency:
  * is sufficient to capture the seasonal and temporal variability of the methane oxidation rate driven by changing environmental conditions
  * yields enough measurements to support a statistically robust estimate of the mean oxidation rate and its uncertainty
* Additionally, Project Developers shall justify the number and placement of sampling locations, demonstrating that they capture the spatial variability of the methane oxidation rate across the cover.
  {% endtab %}
  {% endtabs %}

### Project emissions

Project induced emissions are broken down into three life cycle stages, detailed in the following sections:

* Project establishment
* Storage operations
* Site closure

{% hint style="info" %}
To avoid disincentivizing monitoring and storage site characterization, the following emission sources are excluded from the project boundary:

* energy and material used for storage site characterization (e.g., surveys, studies, soil measurements)
* energy and material used for monitoring of the storage site
* emissions from manufacturing and installation of monitoring and characterization equipment
  {% endhint %}

#### 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)
  * emissions from infrastructure and machinery built at storage site or built elsewhere and used at the storage site
  * direct land use change at the storage site location (only relevant for pit-type storage sites)
    * as per requirements for pit-type storage sites in [#eligible-storage-site](#eligible-storage-site "mention"), Project Developers shall prepare a nature restoration plan for the land used by the project at the storage site. Any direct land use change not addressed in this plan shall be quantified and included in the emissions calculation.
* 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**

All 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.

For [**single-unit**](#user-content-fn-11)[^11] storage sites, credits are issued for the stored biomass in a single monitoring period, after closure of the storage site. Hence, all storage site establishment emissions shall be accounted for in that monitoring period.

For [**multiple-units**](#user-content-fn-6)[^6] storage sites, storage site establishment emissions shall be fully amortized by the time 50% of the total biomass planned for burial at the site has been buried, or three years after the project start date, whichever comes first. 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.

{% hint style="info" %}
For example, Project A plans to store 5000t of biomass over the course of 10 months, with burial of a new storage batch every 2 months and credit issuance after each burial (i.e., one storage batch per monitoring period, length of monitoring period = 2 months). The total storage site establishment emissions amount to 150 tCO<sub>2</sub>eq. According to the module's requirement, the storage site establishment emissions shall be amortized over the first 2500 t of biomass stored.

The biomass burial events are as follows:

* storage batch (SB) 1 , after month 2: 100 t biomass buried in SB1, 100 t in total
* SB2, after month 4: 400 t biomass buried in SB2, 500 t in total
* SB3, after month 6: 2000 t biomass buried in SB3, 2500 t in total
* SB4, after month 8: 2000 t biomass buried in SB4, 4500 t in total
* SB5, after month 10: 500 t biomass buried in SB5, 5000 t in total

The storage site establishment emissions are amortized proportionally over the storage batches. For SB1, this means $$E\_{site\ establishment,\ SB1}= 150 \ tCO\_2eq \ \times \frac{100 \ t }{2500\ t} = 6 \ tCO\_2eq$$. In SB2 and SB3, site establishment emissions correspond to 24 tCO<sub>2</sub>eq, and 120 tCO<sub>2</sub>eq, respectively.

With the amount of biomass stored in SB3, the cumulative amount of biomass stored in SB1 to SB3 corresponds to 2500 t, and all storage site establishment emissions are amortized.
{% endhint %}

**Emissions from other project infrastructure**

Embodied emissions from project infrastructure not related to the storage site establishment (i.e., equipment used for biomass cultivation, processing and conversion) shall be quantified using the [Infrastructure and machinery](/modules/infrastructure-and-machinery.md) 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, dryer, open raceway pond).

#### 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**
  * biomass cultivation:
    * Biomass types classified as waste are assigned no environmental impacts from their cultivation stage
    * For purpose-grown algae: emissions from material and energy used for algae cultivation (e.g., mixing and pumping of the growth medium)
  * biomass transport to processing facility
  * biomass processing before storage (i.e., drying, shredding), if any
  * biomass conversion before storage, if any. This shall include any potential methane emissions from thermochemical conversion (see [#eligible-conversion-technologies](#eligible-conversion-technologies "mention"))
  * leakage from baseline carbon storage and diversion of biomass
* **biomass transport**, calculated using the [Transportation](/modules/transportation.md) 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](/modules/processing-and-energy-use.md) module
  * energy used to store biomass in closed unit
  * material and transport emissions of the biomass containment system (i.e., barriers, liners)

#### Emissions from site closure <a href="#dk35zb8m2b1p" id="dk35zb8m2b1p"></a>

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](/modules/processing-and-energy-use.md) module and includes:

* energy and materials used to permanently close the storage site with a cover or seal.

<details>

<summary><strong>Calculation:</strong> Project emissions</summary>

Project emissions are calculated as the sum of emissions from project establishment, storage operations and site closure.

$$\textbf{(Eq.7)}\ E\_{project} = {E}*{project\ establishment} +{E}*{storage \ operations}+ {E}\_{site\ closure}$$

* $${E}\_{project}$$ is defined in Eq. 1.
* $${E}\_{project\ establishment}$$ represents the emissions from the establishment of the project, in tCO<sub>2</sub>eq. It is calculated according to Eq. 8.
* $${E}\_{storage\ operations}$$ represents the emissions from the operations of the storage site, in tCO<sub>2</sub>eq. It is calculated according to Eq. 10.
* $${E}\_{site\ closure}$$ represents the emissions from closure of the storage site, in tCO<sub>2</sub>eq. It is calculated using the [Processing and energy use](/modules/processing-and-energy-use.md) module.

***

**Project establishment**

$$\textbf{(Eq.8)}\ E\_{project\ establishment} = {E}*{site\ establishment} + E*{other\ infrastructure}$$

* $${E}\_{project\ establishment}$$ is defined in Eq. 7.
* $${E}\_{site\ establishment}$$ represents the emissions from establishment of the storage site, in tCO<sub>2</sub>eq.
  * for [**single-unit**](#user-content-fn-11)[^11] storage sites, it corresponds to $${E}\_{site\ establishment, total}$$, the total storage site establishment emissions, in tCO<sub>2</sub>eq. It is calculated according to Eq. 1 in the [Infrastructure and machinery](/modules/infrastructure-and-machinery.md) module, subject to the following:
    * the *item* in Eq. 1 is *storage site establishment*
    * all emission sources listed under storage site establishment in [Emissions from project establishment](#emissions-from-project-establishment) shall be included in the calculation (i.e., material, energy and fuel consumption, direct land use change).
  * for [**multiple-units**](#user-content-fn-6)[^6] storage sites, it is calculated according to Eq. 9.
* $${E}\_{other\ infrastructure}$$ represents the embodied emissions from other project infrastructure, in tCO<sub>2</sub>eq. It is calculated according to the [Infrastructure and machinery](/modules/infrastructure-and-machinery.md) module.

For [**multiple-units**](#user-content-fn-6)[^6] storage sites, storage site establishment emissions are calculated by multiplying the total storage site establishment emissions with the amount of biomass stored in a given storage batch (calculated as the sum of biomass from all [production batches](#id-2xck12gc2auz) $$i$$ contained in the [storage batch](#storage-batches)) divided by the amount corresponding to 50% of the project's total planned biomass storage.

$$\textbf{(Eq.9)}\ E\_{site\ establishment} = {E}*{site\ establishment, total} \times \frac {\sum\_i A*{biomass\ stored, i}}{A\_{50%\ total \ biomass \ planned}}$$

* $${E}\_{site\ establishment}$$ represents the emissions from establishment of the storage site, in tCO<sub>2</sub>eq.
* $${E}\_{site\ establishment, total}$$ is defined in Eq. 8.
* $$A\_{biomass \ stored, \ i}$$ is defined in Eq. 3.
* $$A\_{50% \ total \ biomass \ planned }$$ represents 50% of the total planned biomass storage at the storage site, in tonnes.

All storage site establishment emissions are amortized the moment the cumulative biomass stored at a single site reaches the amount corresponding to 50% of the project's total planned biomass storage.

***

**Storage operations**

The emissions from storage operations are calculated as the sum of biomass supply, transport and storage emissions.

$$\textbf{(Eq.10)}\ E\_{storage \ operations} = {E}*{biomass\ supply} +{E}*{biomass \ transport}+ {E}\_{biomass\ storage}$$

* $${E}\_{storage\ operations}$$ is defined in Eq. 7.
* $${E}\_{biomass\ supply}$$ represents the emissions from biomass supply, in tCO<sub>2</sub>eq, calculated according to Eq. 11.
* $${E}\_{biomass\ transport}$$ represents the emissions from biomass transport to the storage site, in tCO<sub>2</sub>eq. This may be from the sourcing location directly to the storage site, if no intermediate processing or conversion step is involved, or from the processing facility to the storage site. It is calculated using the [Transportation](/modules/transportation.md) module.
* $${E}\_{biomass\ storage}$$ represents the emissions from biomass storage, in tCO<sub>2</sub>eq. It is calculated using the [Processing and energy use](/modules/processing-and-energy-use.md) module.

Emissions from **biomass supply** are calculated by multiplying the amount of biomass stored from a given production batch (i.e., buried as part of a storage batch) with an emission factor for the production of that production batch. The emission factor, expressed in tCO<sub>2</sub>eq per tonne of biomass produced, is calculated by dividing the sum of emissions from biomass transport to the processing facility, biomass processing and conversion emissions and leakage emissions by the total amount of biomass produced in that production batch.

$$\textbf{(Eq.11)}\ E\_{biomass \ supply} = \sum\_i {EF}\_{production\ batch,i} \times A \_{biomass \ stored, i}$$

* $${E}\_{biomass\ supply}$$ is defined in Eq. 10.
* $${EF}\_{production\ batch, i}$$ represents the emission factor for the production of one tonne of biomass in the production batch $$i$$. It is calculated according to Eq. 12.
* $${A}\_{biomass\ stored, i}$$ is defined in Eq. 3.

$$\textbf{(Eq.12)}\ EF\_{production\ batch, i} = ({E}*{input\ cultivation,i}+{E}*{input\ transport,i} + {E}*{input\ processing,i}+ {E}*{input\ conversion,i} + {E}*{input\ leakage, i})\div A*{biomass \ produced, i}$$

* $$EF\_{production\ batch, i}$$ represents the emission factor for all operational processes related to the production of a production batch $$i$$, in tCO<sub>2</sub>eq per tonne of biomass produced.
* $${E}*{input\ cultivation,i}$$ represents the emissions from cultivation of the biomass input (i.e., the amount of biomass going into the production batch $$i$$), $$A*{biomass\ input, i}$$, in tCO<sub>2</sub>eq. This term is only relevant for projects using purpose-grown algae. It is calculated using the [Processing and energy use](/modules/processing-and-energy-use.md) module.
* $${E}*{input\ transport,i}$$ represents the emissions from the transport of the biomass input (i.e., the amount of biomass going into the production batch $$i$$), $$A*{biomass\ input, i}$$, to the processing facility, in tCO<sub>2</sub>eq. It is calculated using the [Transportation](/modules/transportation.md) module.
* $${E}*{input\ processing,i}$$ represents the emissions from processing (i.e., drying, shredding, grinding) of the biomass input, $$A*{biomass\ input, i}$$, in tCO<sub>2</sub>eq. It is calculated using the [Processing and energy use](/modules/processing-and-energy-use.md) module.
* $${E}*{input\ conversion,i}$$ represents the emissions from thermochemical conversion (i.e., using hydrothermal conversion or pyrolysis) of the biomass input (i.e., the amount of biomass going into the production batch $$i$$), $$A*{biomass\ input, i}$$, in tCO<sub>2</sub>eq. It is calculated using the [Processing and energy use](/modules/processing-and-energy-use.md) module.
* $${E}*{input\ leakage,i}$$ represents the leakage emissions from the biomass input (i.e., the amount of biomass going into the production batch $$i$$), $$A*{biomass\ input, i}$$, in tCO<sub>2</sub>eq. This includes baseline carbon storage and emissions from the diversion of the biomass from its alternative use. It is determined according to the Baseline scenario of the [Biomass feedstock](/methodologies/biomass-carbon-removal-and-storage-bicrs/carbon-capture/biomass-feedstock.md#id-4l7lx2ihb6hj-2) module.
* $$A\_{biomass \ produced, i}$$ represents the amount of biomass produced in production batch $$i$$, in tonnes.

{% hint style="info" %}

* Biomass input, $$A\_{biomass\ input, i}$$ is the quantity of biomass processed or converted to generate a given production batch *i*.
* Biomass produced, $$A\_{biomass \ produced, i}$$, is the quantity of biomass generated through processing and conversion of $$A\_{biomass\ input, i}$$. It is the total amount of biomass in a production batch *i*.
  * Projects using woody biomass often do not process or convert their biomass feedstock before burying it. In this case, since no processing or conversion step is involved, the total amount of biomass in a production batch $$A\_{biomass \ produced, i}$$ corresponds to $$A\_{biomass\ input, i}$$.
* Biomass stored, $${A}\_{biomass\ stored, i}$$ is the quantity of biomass from a given production batch *i*\
  that ends up in a storage batch.

For example, producing 100 t of hydrochar via hydrothermal conversion requires 120 t of feedstock input. The 120 t of feedstock is $$A\_{biomass\ input, i}$$ and the 100 t of hydrochar produced is $$A\_{biomass \ produced, i}$$. Emissions from transporting and converting the full 120 t of feedstock, along with any associated leakage emissions, feed into the biomass supply emission factor calculation. If 50 t of the $$A\_{biomass \ produced, i}$$ is subsequently placed into a storage batch and buried, that 50 t is $${A}\_{biomass\ stored, i}$$.
{% endhint %}

</details>

### Uncertainty assessment <a href="#dk35zb8m2b1p" id="dk35zb8m2b1p"></a>

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.&#x20;

* 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.
* For wet, anoxic storage in a pit
  * The default carbon loss fraction of 0.088 for woody biomass is taken directly from the [IPCC Guidelines for National Greenhouse Gas Inventories](#user-content-fn-33)[^33] (therein referred to as $$DOC\_f$$). This value carries moderate 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**.
  * Assuming that the non-permanent fraction of biochar, as calculated using the Woolf model, corresponds to the carbon loss fraction carries high uncertainty, as the [Woolf model](#user-content-fn-34)[^34] was developed for biochar degradation in soil, and is not representative for anoxic underground storage conditions. Using this value is conservative, therefore 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**.
* Under anoxic conditions, degraded biomass carbon is assumed to be released as CO<sub>2</sub> and CH<sub>4</sub> in a 50:50 ratio, as defined by the stoichiometric mass balance of anaerobic degradation. This carries low uncertainty. The same ratio is applied to dry storage conditions, oxic or anoxic, where degradation releases mainly CO<sub>2</sub>. Assuming a 50% CH<sub>4</sub> share there is conservative, so the **uncertainty is low**.

The uncertainty at the methodology level is estimated to be low. According to the [Rainbow Standard Rules](https://docs.rainbowstandard.io/rainbow-standard-documents/rainbow-standard-rules/ghg-quantification#discount-factor), 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 **for each production batch**:

*Table 15 Indicators measured for each production batch, which biomass they apply to, and how and where they are measured.*

<table data-search="false"><thead><tr><th width="148.86328125">Indicator</th><th width="157.44921875">Biomass type</th><th>Measurement</th></tr></thead><tbody><tr><td>Organic carbon content</td><td>All</td><td><p>Measured on a <a href="#representative-sampling">representative sample</a> of the production batch by laboratories with at least one quality assurance accreditation, such as:</p><ul><li>ISO/IEC 17025</li><li>CEN/TS 17225-1</li><li>ISO 10694</li></ul></td></tr><tr><td>Moisture content</td><td>All</td><td><p>Measured on a <a href="#representative-sampling">representative sample</a> of the production batch. Where a production batch is split across two or more storage batches, moisture content shall be measured separately on a representative sample of each portion of the production batch allocated to a different storage batch.</p><p>Moisture content shall be measured</p><ul><li>using calibrated moisture measurement equipment (e.g., a handheld moisture sensor)</li><li><p>right before placement</p><ul><li>in storage site or unit, or</li><li>in a sealed barrier</li></ul></li></ul><p>Calibration records shall be made available upon request by Rainbow or the VVB.</p></td></tr><tr><td>Weight</td><td>All</td><td><p>Measured on the entire production batch. Where a production batch is split across two or more storage batches, the weight shall be measured separately for each portion of the production batch allocated to a different storage batch.</p><p>Weight shall be measured</p><ul><li>using a calibrated scale</li><li><p>right before placement</p><ul><li>in storage site or unit, or</li><li>in wrapped and sealed barrier</li></ul></li></ul><p>Calibration records shall be made available upon request by Rainbow or the VVB.</p></td></tr><tr><td><span class="math">C_{\text{org}}/N</span></td><td>Woody biomass</td><td><ul><li>Measured on a <a href="#representative-sampling">representative sample</a> of the production batch by laboratories with at least one <a data-footnote-ref href="#user-content-fn-35">quality assurance accreditation</a>, or</li><li>literature value. Sources may include peer-reviewed literature, institutional databases or governmental reports.</li></ul></td></tr><tr><td>Lignin, cellulose and hemicellulose content</td><td>Woody biomass</td><td><ul><li>Measured on a <a href="#representative-sampling">representative sample</a> of the production batch by laboratories with at least one <a data-footnote-ref href="#user-content-fn-35">quality assurance accreditation</a>, or</li><li>literature value. Sources may include peer-reviewed literature, institutional databases or governmental reports.</li></ul></td></tr><tr><td><span class="math">H/C_{\text{org}}</span></td><td>Thermochemically converted biomass</td><td>Measured on a <a href="#representative-sampling">representative sample</a> of the production batch by laboratories with at least one <a data-footnote-ref href="#user-content-fn-35">quality assurance accreditation</a></td></tr><tr><td><span class="math">O/C_{\text{org}}</span></td><td>Thermochemically converted biomass</td><td>Measured on a <a href="#representative-sampling">representative sample</a> of the production batch by laboratories with at least one <a data-footnote-ref href="#user-content-fn-35">quality assurance accreditation</a></td></tr></tbody></table>

### Representative sampling

#### Woody biomass and agricultural residues

Samples shall be taken from **biomass that is representative of the actual composition of the batch**. To account for variability within a single batch, the following sampling procedures apply:

* **moisture content measurements:**
  * Moisture content shall be measured right before placement of the production batch in the storage site, unit, or in a sealed barrier in **at least twenty** different locations in the production batch. The mean average of the measurement results shall be used.
  * Project Developers shall justify how sampling is representative for any heterogeneity in the moisture content of the production batch. This may include mixing piles, taking samples outside and within pile, accounting for variability in temperature and relative humidity.
* **organic carbon content measurements:**
  * At least three samples shall be taken for each production batch and homogenized. The measurement shall be done in replicates of three, and the mean average of the measurement results shall be used.

#### Thermochemically converted biomass

**Moisture content measurements**

At least three samples shall be taken from each production batch right before placement of the production batch in the storage site, unit, or a sealed barrier. Samples shall be kept separate from each other and not mixed. The moisture content of each sample shall be determined, using either a calibrated moisture analyzer on site or in an [accredited laboratory](#user-content-fn-36)[^36], provided that the samples are prepared and transported in a way that preserves their moisture content.

**Organic carbon content,** $$H/C\_{\text{org}}$$**,** $$O/C\_{\text{org}}$$ **, and** [**pollutants**](#user-content-fn-37)[^37] **measurements**

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 Project Design Document (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](#user-content-fn-38)[^38]
* [European Biochar Certificate Guidelines Annex 4 Representative Sampling](#user-content-fn-39)[^39]

<div align="center"><figure><img src="https://1461901304-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FE1FUJsBoIj20nqp3CtMf%2Fuploads%2Fjyf0hsV2tHKsu26bddrZ%2FClimate%20team%20-%20Schemes%20-%20BiCRS%20sampling%20protocol.jpg?alt=media&amp;token=46684224-8e2f-4981-a8b1-e8f59f96aeae" alt=""><figcaption><p>Figure 4: The Rainbow recommended sampling approach for thermochemically converted biomass (i.e., biochar and hydrochar) is summarized here, and detailed in the text in following sections.</p></figcaption></figure></div>

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 16 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](#user-content-fn-38)[^38].

The representative sample size shall be 24 liters multiplied by the *n* number of composite samples per production batch detailed in Table 16.

*Table 16 Recommendations for the number of composite samples to take, based on the site's annual biochar or hydrochar production output.*

<table data-search="false"><thead><tr><th>Annual output (tonnes)</th><th>Composite samples per production batch (n)</th></tr></thead><tbody><tr><td>≤ 3000</td><td>4</td></tr><tr><td>3001-10,000</td><td>8</td></tr><tr><td>10,001-20,000</td><td>12</td></tr><tr><td>20,001-40,000</td><td>16</td></tr><tr><td>40,001-60,000</td><td>20</td></tr><tr><td>60,001-80,000</td><td>24</td></tr><tr><td>80,001-100,000</td><td>28</td></tr></tbody></table>

The [European Biochar Certificate Guidelines Annex 4 Representative Sampling](#user-content-fn-39)[^39] shall be followed for **taking composite samples**. Those requirements are summarized below.

{% tabs %}
{% tab title="Continuous production" %}

* The first sample shall be taken within 7 days of the start of the production batch.
* To prepare **one sample**, 8 sub-samples of 3 liters each are taken at intervals of at least one hour directly at the discharge of the freshly produced material. This shall be repeated for three consecutive days.
* The 24 samples are combined to form one composite sample.
  {% endtab %}

{% tab title="Non-continuous production" %}

* The first sample shall be taken within 7 days of the start of the production batch.
* Samples may be taken from a well-mixed pile of biochar produced within the last 7 days.
* The amount of biochar used for one sample shall be equivalent to at least one day's production.
* 24 sub-samples of 3 liters each shall be taken from different spots in the pile.
* The 24 subsamples are combined to form one composite sample.
  {% endtab %}
  {% endtabs %}

The representative sample shall be **homogenized** by the Project Developer or by the laboratory that performs testing, following the procedure outlined below:

* 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 shall be taken at 15 different spots in the pile and combined. This combined homogenized representative cross sample is used for laboratory testing.

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

#### Purpose-grown algae

Project Developers shall suggest an approach for representative sampling of purpose-grown algae, accounting for any within-batch heterogeneity. The approach shall include but is not limited to the following:

* sources of heterogeneity
* [sampling strategy](#user-content-fn-40)[^40]
* sampling amount and frequency
* homogenization

The VVB and the Rainbow Certification team shall validate the rigor and representativeness of the proposed sampling approach.

### 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 sampled
* Description of representative sampling process
* 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.

:point\_right: Download the template [here](https://docs.google.com/spreadsheets/d/1l1NmXw1YVLZkr1_C-cNdA-3AECkXZbWXFrvJR7VSmqo/edit?usp=sharing).

{% embed url="<https://docs.google.com/spreadsheets/d/1l1NmXw1YVLZkr1_C-cNdA-3AECkXZbWXFrvJR7VSmqo/edit?usp=sharing>" %}

## Version history

| Description of the change | Justification | Date            | Version changed |
| ------------------------- | ------------- | --------------- | --------------- |
| Publication of module     | --            | October 9, 2026 | V1.0            |

[^1]: beyond what would have happened in the business-as-usual, baseline scenario

[^2]: The layer of rock and soil that lies above and covers an underground opening.

[^3]: * Primary/old-growth forests
    * Species-rich forests identified as highly biodiverse
    * Legally protected nature areas or areas protecting endangered species
    * Natural or species-rich highly biodiverse grassland
    * Heathland

    as identified by the relevant competent authority

[^4]: wetlands, peatlands and forests

[^5]: Ratio of vapor pressure of water in the biomass to vapor pressure of pure water at the same temperature. Reflects the fraction of water available to support microbial and enzymatic activity.

[^6]: A storage site that is divided into discrete units, each filled and closed sequentially before the overall site is closed.

[^7]: This includes the biomass types:

    * forest waste from secondary forests
    * forest waste from managed forest
    * necessary tree removal

[^8]: Moisture content at room temperature is a conservative choice. Since the moisture content at a given water activity is generally higher at lower temperatures, and real storage conditions are typically cooler, using room temperature yields a stricter (lower) target moisture content.

[^9]: Value taken from Ross, R. J., USDA Forest Service, Forest Products Laboratory. (2010). *Wood handbook: Wood as an engineering material* (General Technical Report FPL-GTR-190). U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, [URL](https://doi.org/10.2737/FPL-GTR-190).

[^10]: The relationship between water activity and the equilibrium moisture content of a material at a given temperature is provided by a moisture sorption isotherm.

[^11]: single, undivided volume, that is filled and closed

[^12]: The Project Developer must submit a **Cancelation Notice** to notify Rainbow within **30 calendar days** of becoming aware of the reversal event.

[^13]: **A storage site that is divided into discrete units, each filled and closed sequentially before the overall site is closed.**

[^14]: Operational monitoring starts when the first batch's stability monitoring period ends, and ends when the storage site is permanently closed.

[^15]: Fraction of biomass carbon that is expected to degrade under stable storage conditions, and deducted from the project's gross removals as a loss. See Table 13 and [#carbon-loss-measurements](#carbon-loss-measurements "mention") in the [#project-removals](#project-removals "mention") section.

[^16]: WBC (2023): World Biochar Certificate – Guidelines for a Sustainable Production of Biochar and its Certification.' Carbon Standards International, Frick, Switzerland, (<http://www.european-biochar.org>), version 1.1 from 20th December 2024. [URL](https://www.carbon-standards.com/en/standards/service-514~production-of-biochar.html).

[^17]: The European Food Safety Authority's (EFSA) list of eight carcinogenic polycyclic aromatic hydrocarbons (PAH), namely Benzo\[*a*]pyrene,

    Benzo\[*a*]anthracene, Chrysene, Benzo\[*b*]fluoranthene, Benzo\[*k*]fluoranthene, Dibenzo\[*a,h*]anthracene,

    Indeno\[1,2,3-*cd*]pyrene, Benzo\[*ghi*]perylene

[^18]: * $$C\_{\text{org}}/N$$≥ 100
    * lignin content ≥ 21%

[^19]: Volume 5 of the 2019 Refinement of the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, [Chapter 3](https://www.ipcc-nggip.iges.or.jp/public/2019rf/pdf/5_Volume5/19R_V5_3_Ch03_SWDS.pdf), Table 3.

[^20]: * $$H/C\_{\text{org}}$$ < 0.4
    * $$O/C\_{\text{org}}$$ < 0.2

[^21]: See Global Warming Potentials in the GHG Quantification section of the Rainbow Standard Rules, [URL](https://docs.rainbowstandard.io/rainbow-standard-documents/rainbow-standard-rules/ghg-quantification#global-warming-potentials).

[^22]: * wet and anoxic
    * dry and anoxic
    * dry and oxic

[^23]: pit- or void-type storage

[^24]: i.e. drying, shredding

[^25]: i.e. thermochemical conversion to hydrochar or biochar

[^26]: i.e. Hydrothermal conversion or pyrolysis of biomass. Only applicable for projects using the biomass type *thermochemically converted biomass*.

[^27]: one of the following:

    * ISO/IEC 17025
    * CEN/TS 17225-1
    * ISO 10694

[^28]: The requirements are taken from the United States Code of Federal Regulations, Title 40, Chapter I, Subchapter C, Part 98 (Mandatory GHG Reporting), Subpart HH, Table HH-4, conditions C5-C7, [URL](https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-98/subpart-HH/appendix-Table%20HH-4%20to%20Subpart%20HH%20of%20Part%2098).

[^29]: This oxygen level is chosen as a proxy for anoxic conditions. Below 5% oxygen content, methane production is expected to start.

[^30]: as described by e.g.

    * Sparrow et al., DOI: [10.1016/j.wasman.2019.07.032](https://doi.org/10.1016/j.wasman.2019.07.032)
    * Abedini et al., DOI: [10.2174/2212717803666160905114423](http://dx.doi.org/10.2174/2212717803666160905114423)

[^31]: i.e. next to the storage site or its intended location, ensuring the representative sample plot is within the same type of soil as the storage site.

[^32]: As described by e.g.

    * Melaouhia et al., DOI:[10.1061/9780784480144.018](https://doi.org/10.1061/9780784480144.018)
    * Streese-Kleeber et al., DOI: [10.1016/j.wasman.2010.08.026](https://doi.org/10.1016/j.wasman.2010.08.026)
    * Gonzales-Gil et al., DOI: [10.1016/j.ics.2006.01.030](https://doi.org/10.1016/j.ics.2006.01.030)

[^33]: As taken from Volume 5 of the 2019 Refinement of the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Chapter 3, Table 3, [URL](https://www.ipcc-nggip.iges.or.jp/public/2019rf/pdf/5_Volume5/19R_V5_3_Ch03_SWDS.pdf).

[^34]: Woolf, D., Lehmann, J., Ogle, S., Kishimoto-Mo, A.W., McConkey, B., Baldock, J., 2021. Greenhouse Gas Inventory Model for Biochar Additions to Soil. Environmental Science & Technology 55, 14795–14805.<https://doi.org/10.1021/acs.est.1c02425>

[^35]: * ISO/IEC 17025
    * CEN/TS 17225-1
    * ISO 10694

[^36]: with at least one of the following quality assurance accreditations:

    * ISO/IEC 17025
    * CEN/TS 17225-1
    * ISO 10694

[^37]: see [#id-82n4j72vjt9v](#id-82n4j72vjt9v "mention")

[^38]: Regulation (EU) 2019/1009 of the European Parliament and of the Council of 5 June 2019 laying down rules on the making available on the market of EU fertilising products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 and repealing Regulation (EC) No 2003/2003 (Text with EEA relevance), 2024. [URL](https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:02019R1009-20240703)

[^39]: EBC (2012-2025) ‘European Biochar Certificate – Guidelines for a Sustainable Production of Biochar.’ Carbon Standards International (CSI), Frick, Switzerland.\
    Version 10.5E from 14th August 2025 [URL](https://www.carbon-standards.com/en/standards/service-492~production-of-biochar.html).

[^40]: E.g. composite, random, stratified, or systematic sampling.


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