Rock and Mineral Feedstock Characterization

This Module provides the requirements and recommendations for the characterization of solid rock and mineral feedstocks that may be used in carbon dioxide removal (CDR) projects by Project Proponents. This Module is intended for use in conjunction with other Isometric Protocols and Modules. This Module applies where physical and geochemical characterization of rock or mineral feedstocks is required for use in a Crediting Project.

The characterization requirements and recommendations outlined within this Module are based on best known scientific practices at the time of writing. Requirements may be updated in future versions of this Module in line with changes in scientific consensus. This Module outlines methodologies that may be employed to characterize feedstocks to the best of the Project Proponent’s ability, considering scientific rigor, method employment economics, best practice and feasibility. Specific analytical method standard details are outlined in Appendix 1.

Within this Module framework, the key physical and geochemical characteristics of rock feedstocks required for CDR pathways are outlined. Requirements that are specific to different feedstock types, such as commercially produced feedstocks and waste products, are clearly differentiated in distinct sections of this Module. Project Proponents must characterize all feedstocks prior to application in a Crediting Project to ensure safety, suitability, and compliance with this Module and applicable Protocols. Where a specific Protocol outlines requirements that deviate from or supersede the requirements in this Module, those Protocol requirements take precedence. In all other instances where a Protocol does not specify requirements for a particular characterization element, the requirements outlined in this Module apply in full.

The characterization requirements and recommendations outlined in this Module are applied with consideration of feedstock type. Three primary feedstock categories are addressed: (1) commercially produced feedstocks obtained from established suppliers; (2) feedstocks sourced from extractive industries (mining, quarrying) or designated as waste products under national law; and (3) general characterization applicable to all feedstock types regardless of origin. Table 2 (presented in Section 3) provides a summary of which characterization elements are required, recommended, or conditionally applicable to each feedstock category. Project Proponents should consult this table alongside the detailed requirements in Sections 3.1 through 3.5 to determine the full scope of characterization required for their specific feedstock type and origin.

Project Proponents must submit documentation to the Project's Validation & Verification Body (VVB) that outlines the origin and nature of the feedstock used. This documentation must address all of the following information:

• A general description of the feedstock.
• Origin location - Project Proponents must identify the location from which the feedstock was recovered or collected, including:
  • The name of the recovery location (such as the mine, quarry, or waste facility name)
  • Precise geographic coordinates
  • Classification of recovery source (virgin mineral extraction, mining/quarrying operation, waste facility, or other)
  • Geological maps and deposit descriptions
• Recovery and transport process - Project Proponents must document the methods used to recover or collect the feedstock from its source location and transport it to the Project location, including:
  • Detailed description of sampling and recovery processes employed at the feedstock source location
  • Chain of custody documentation from the feedstock source location to the Project location (see Section 5.3 for Chain of Custody guidelines)
• Pre-processing activities - Project Proponents must document all pre-processing undertaken on the feedstock after collection from its source location and prior to geochemical or physical characterization. Pre-processing activities may include:
  • Crushing or milling operations
  • Drying procedures
  • Creation of representative composite samples
  • Any other mechanical, thermal, or physical treatment applied to the feedstock

Where feedstocks are obtained from a commercial feedstock producer, Project Proponents may submit a summary of pre-processing and production procedures in lieu of detailed documentation of each process step. Any such summary must be signed off by the commercial feedstock producer for accuracy and completeness.

Project Proponents may submit prior geochemical or physical characterization carried out by the organization that produced or sourced the feedstock. Prior characterization may be submitted in the following instances:

• Feedstocks recovered from a waste facility (such as a tailings storage facility) where characterization was conducted by the source organization
• Feedstocks procured from a commercial feedstock producer where such producers have conducted their own characterization program

Isometric and the Project VVB will assess the suitability of all submitted prior characterization data on a case-by-case basis, evaluating whether the methodologies, standards, and quality assurance procedures meet the requirements outlined in Section 3 and Appendix 1. If prior characterization is deemed not suitable for submission, Project Proponents are required to carry out supplementary or complete characterization of feedstocks. See Section 5.2 for guidance on third-party characterization submissions.

Project Proponents must provide adequate supporting documentation to explain any information listed above that is not available at the time of PDD submission. Such circumstances may occur when mining waste materials or proprietary commercial feedstocks are used, and some information is classified as confidential by the source organization. Where confidentiality applies, Project Proponents must:

• Clearly identify which information elements are withheld and state the reason (e.g., commercial confidentiality, proprietary operations)
• Provide alternative evidence of feedstock origin, such as supply contracts, source certification, or third-party attestation
• Consult with the VVB in advance of PDD submissions to agree on acceptable alternatives to unavailable documentation

Where feedstocks have been recovered as a by-product of an extractive process (mining, quarrying, or similar operations), Project Proponents must report on the legal classification and status of the source material prior to use in a Crediting Project.

Specifically, Project Proponents must:

• Determine whether the feedstock has been classified, designated, or defined as a waste product under applicable national regulations and laws
• Document the legal framework applicable to the feedstock in its source country (including relevant waste, mining, or environmental legislation)
• Provide evidence that the feedstock’s use as a CDR feedstock complies with all applicable local and national laws and regulations
• Describe how the feedstock has been handled, stored, and repurposed from its original extractive context to its use in the CDR project

Legal frameworks applicable to extractive waste include, but are not limited to, the Extractive Waste Directive 2006/21/EC in the European Union. Project Proponents operating in other jurisdictions must consult applicable national waste and extractive industry regulations.

There are a wide range of characteristics that can influence a feedstock’s weathering or dissolution rate for CO₂ removal. These include both physical properties (e.g., particle size distribution, permeability, density, etc.) and geochemical properties (e.g., mineralogy and elemental composition). Understanding how these characteristics interact with environmental variables to determine weathering and dissolution rates is an active area of scientific investigation, and characterization methodologies continue to evolve with advances in analytical technology and field understanding.

This Module’s core feedstock characterization requirements and recommendations are summarized in Table 1. The characterization parameters outlined here apply to all pathway-level Protocols that utilize this Module, except where those Protocols specify alternative or additional requirements (as described in the Introduction Section). Table 2 identifies which of the Table 1 parameters are required, recommended, or conditionally required based on feedstock type and origin. The detailed methodologies and applicability conditions for each characterization parameter are outlined in Sections 3.1 through 3.5 below.

Table 1: Feedstock Characterization Requirements and Recommendations

Table 2: Feedstock-Type Applicability

The characterization requirements outlined in Table 1 provide a summary of core parameters applicable to feedstock characterization across all feedstock types. Table 2 identifies which Table 1 parameters are mandatory, recommended, or conditionally applicable to different feedstock categories (commercial, extractive/waste). Project Proponents must use both tables in conjunction with the detailed requirements in Sections 3.1–3.5 to establish the complete characterization scope for their specific feedstock.

Where feedstocks are sourced from extractive processes (mining, quarrying, or similar operations) or have been designated as waste products under national law, additional characterization requirements may apply based on relevant regulatory frameworks. See Section 3.5.5 for characterization methods specific to feedstocks recovered from extractive (e.g., mining) and other industrial processes (e.g., steel production) and Section 2 for legal status reporting requirements.

Analytical standards and methodologies form the foundation of reliable feedstock characterization. Adherence to established standards (whether national, international, or manufacturer-defined) ensures that characterization results are reproducible, defensible, and comparable across projects. This section outlines the standard-hierarchy approach required for all feedstock characterization and addresses situations where standards may not fully cover the analysis being undertaken.

Project Proponents must characterize feedstocks in accordance with the following standards hierarchy, applied in order of priority:

1. National standards: Where the Project is located, Project Proponents must first apply relevant national standards for feedstock characterization, testing, and analysis of solid materials used in CDR applications.
2. International standards: Where national standards do not exist or do not adequately address the characterization requirements of this Module, Project Proponents must apply appropriate International Organization for Standardization (ISO) standards.
3. Manufacturer standards: Where specific standards do not exist for analytical techniques (e.g., X-ray diffraction-based mineralogy), Project Proponents must follow the Standard Operating Procedures (SOPs) defined by the analytical instrument manufacturer.
4. In-house methodology with approval: Where analytical facilities do not conform to ISO or national standards and instead utilize their own methodologies, Project Proponents may use in-house methods only with explicit prior approval from Isometric and the Project VVB.

For each analytical method, Project Proponents must clearly identify and document in the PDD submission:

• All standards applied (national, ISO, manufacturer, or in-house)
• Any amendments or deviations from standard protocols
• The rationale for any deviations
• Quality assurance procedures employed to verify compliance

(See Appendix 1 for detailed standards and measurement guidance.)

For analytical techniques where no applicable national or ISO standard exists, Project Proponents must provide detailed documentation of the analytical method employed. This must include:

• The instrument manufacturer's Standard Operating Procedure (SOP) if a commercial instrument is used (e.g., X-ray diffraction (XRD) for mineralogy)
• Specific reference to manufacturer documentation
• Any modifications or adaptations made to the manufacturer's SOP, with scientific justification
• Quality control procedures to ensure consistency and accuracy

Where analytical facilities utilize in-house methodologies that do not conform to established standards, Project Proponents must obtain written approval from Isometric and the VVB prior to employing such methodologies. Such approval should be sought during early Project planning (before sample analysis begins) to avoid delays. The Project Proponent must provide:

• Detailed description of the in-house methodology
• Validation or verification data demonstrating the reliability of the method
• Quality assurance records from prior applications of the method
• Documentation of why an established standard is not suitable for the Project's characterization needs

Where analysis is carried out by a third party (such as a commercial feedstock producer, external laboratory, or specialist analytical facility), the Project Proponent remains responsible for ensuring that all standards, methods, and SOPs requirements outlined above are met. Specifically, Project Proponents must:

• Obtain complete documentation of standards and methods employed by the third party
• Confirm that any deviations from established standards are documented and justified
• Retain all third-party documentation (including quality assurance records) for submission to the VVB

See Section 5.2 for detailed guidance on submitting third-party characterization data.

In some instances, analytical or characterization methods other than those listed as required in this Module may be scientifically justified or more appropriate for the specific feedstock and Project context. Advances in analytical technology, constraints imposed by feedstock availability or budget, or site-specific conditions may necessitate the use of alternative methods. This section describes when and how alternatives may be employed.

Project Proponents may propose and employ characterization methods other than those specified as required in Table 1 and Sections 3.1–3.5, provided that:

1. Scientific justification: The alternative method must be scientifically sound, defensible, and capable of providing equivalent or superior information compared to the standard method.
2. Prior approval: Project Proponents must obtain written approval from Isometric and the Project VVB for any alternative method prior to conducting the analysis.
3. Documentation: The alternative method must be fully documented in the PDD submission, including the scientific rationale, method protocol, quality assurance procedures, and validation data.
4. Comparability: Where possible, the alternative method should produce results comparable to (or compatible with interpretation of results from) the standard method, to facilitate cross-project consistency.

Approval Process

Project Proponents should consult with Isometric and the Project VVB during early Project development to discuss alternative methods. Approval is typically granted as part of the PDD submission review, but early consultation can identify potential issues and improve approval likelihood. Requests for alternative method approval should include:

• Detailed description of the proposed method
• Published scientific literature supporting the method's reliability and relevance
• Comparison to the standard method (advantages, disadvantages, data compatibility)
• Instrument specifications and quality control protocols
• Training and competency evidence for the personnel conducting the analysis
• Cost and timeline justification (if relevant to the decision)

Reliable characterization results depend critically on proper sample handling from collection through storage and analysis. Representative sampling, careful preparation, and secure identification and storage ensure that analytical results truly reflect the feedstock being characterized and can be reproduced if needed. This section establishes requirements and recommendations for all aspects of sample management throughout the characterization program.

• Project Proponents must conduct all sample preparation, identification, sub-sampling, and storage in accordance with applicable International or national standards. Project Proponents must document in PDD submissions:
  • All standards, methods, and SOPs employed in sample preparation and handling
  • Any deviations or amendments to standard procedures, with scientific justification
  • Quality assurance measures used to verify compliance with standards

Project Proponents should undertake sample preparation for geochemical analysis in accordance with one of, or a combination of, the following standards:

• ISO 23909:2008 — Soil quality: Preparation of laboratory samples from large samples
• BS EN 14899:2005 — Characterization of waste: Sampling framework and sampling plan application
• CEN/TR 16365:2012 — Characterization of waste: Sampling from extractive industries
• EN 15002:2015 — Characterization of waste: Preparation of test portions from laboratory sample

Note: The applicability of the standards listed above for a specific feedstock type should be assessed and implemented on a Project by Project basis.

• Where extractive ‘waste’ materials (such as mine tailings, mine waste rock, or quarry residue) are utilized as the Project feedstock, Project Proponents must follow industry-specific standards and SOPs, such as those outlined in CEN/TR 16365:2012.
  • Any deviations from the specified standard must be clearly documented and justified in the PDD submission.

• Sample preparation and pre-processing procedures must be designed to ensure that feedstock samples submitted for characterization are representative of the feedstock material that will actually be used in the Crediting Project.
• Project Proponents must consider how sample preparation techniques may alter feedstock characteristics and must choose preparation methods accordingly. For example:
  • Samples for mineralogical analysis via X-ray diffraction (XRD) or Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX) should not be sonicated or washed during sample preparation, as these techniques may selectively remove clay mineral phases and produce unrepresentative results.
  • Samples for elemental composition analysis should be prepared to reflect the weathering state (if any) of the feedstock as it will be deployed in the Project.
  • Compositing procedures must ensure that sub-samples are proportionally representative of the parent feedstock lot.

• Project Proponents must assign each sample and sub-sample a unique identifier (ID number or code) that enables tracking throughout the entire characterization program. This sample ID must be:
  • Consistently documented across all analysis types (mineralogy, geochemistry, geotechnical tests, etc.)
  • Maintained during sample storage and retrieval
  • Linked to the collection location, date, and handling history in a centralized sample register or database

• Project Proponents must document all procedures and conditions used for sample handling and storage, both before and after the characterization program. The methods employed for storage must not alter the feedstock's chemical composition, mineralogy, or geotechnical properties.
• At a minimum, the following storage and handling conditions must be documented and controlled:
  • Storage environment: The storage environment must be controlled to prevent degradation, oxidation, carbonation, or other chemical weathering of the feedstock samples. Variable storage conditions that may affect feedstock composition include temperature, humidity, light exposure, and atmospheric composition.
  • Sample container materials: Sample containers must be composed of materials that do not chemically interact with or absorb components from the feedstock. Suitable materials include high-density polyethylene (HDPE) or glass. Materials that may absorb moisture or react with mineral phases (such as certain plastics or paper-based containers) must not be used.
  • Headspace management: Sample container headspace must be minimized to prevent oxidation, carbonation, or volatile loss from the samples. Containers must be sealed appropriately, with consideration of any gases that may be generated (e.g., from sulfide oxidation). In some cases, inert atmosphere storage or purging may be necessary.
  • Long-term storage: Where samples will be stored for extended periods (more than 30 days) prior to complete characterization, storage conditions must be explicitly designed to minimize continued weathering of feedstocks. Cold storage, inert atmosphere, or other specialized preservation techniques may be required depending on the feedstock mineralogy.

• Project Proponents must maintain all available sample duplicates or retained splits in secure storage for a minimum of 12 months following Project Validation. These retained samples serve as verification standards should questions arise about the characterization results or analytical methods.
  • Samples must be stored under the same controlled conditions outlined above (temperature, humidity, container integrity) and must remain accessible to Isometric and the VVB for quality assurance or verification purposes upon request.

Within this Module, a batch is defined as unit of feedstock that is expected to be compositionally homogeneous, derived from a consistent feedstock source, production process and/or storage location. A batch may represent a discrete stockpile, or defined volume of material aggregated over time, provided homogeneity can be demonstrated by a Project Proponent.

Project Proponents must determine the specific number of samples or replicates that need to be collected for any one batch of feedstock, conduct characterization of every batch, and justify the sampling procedure and number of analyses based on project-specific considerations. Project Proponents must ensure that data is spatially representative of the entire project area and that sampling captures both horizontal and vertical variability within the feedstock used in a Crediting Project. Projects must demonstrate the degree of homogeneity within a single feedstock batch and report this to Isometric.

Project Proponents must:

• Determine and outline the number of composite samples and replicates collected per batch
• Conduct characterization of every batch
• Justify sampling and sub-sampling procedures
• Demonstrate and report the degree of homogeneity within each batch to Isometric

Projects that utilize a commercially available feedstock are not required to implement a specific sampling plan if the characterization data provided by the feedstock producer demonstrates consistent homogeneity and satisfies all other requirements of this Module.

Where data and information provided by commercial feedstock producers does not meet all requirements of this Module, the Project Proponent must carry out additional analysis and outline a sampling plan for additional characterization analysis within the PDD submission.

The Project Proponent must consider a broad range of feedstock characteristics and relevant context that may influence rock homogeneity when determining a sampling plan. These considerations include, but are not limited to, grain size distribution, particle sorting that may occur during processing and transport, the amount of feedstock being spread and the geological/geochemical setting from which the feedstock was extracted.

Note: All relevant details of the sampling plan, number of analyses, and adequate justification for these choices must be included in the PDD submission.

Recommended methods for assessing feedstock homogeneity include compositional variance analysis, such as ANOVA (Analysis of Variance) (see ISO 33405:2024), performed on major element or mineralogical characterization data; field screening techniques using handheld XRF or near-infrared spectroscopy; and approaches such as the ITRC Incremental Sampling Methodology¹, which suggests collecting a large number of small increments — typically 30–100 — systematically and randomly distributed throughout the bulk feedstock pile. It is acknowledged that rock feedstocks are likely to vary in composition as an extractive material, depending on the source location.

Project Proponents must include in the PDD submission a detailed description of how the chosen sampling plan addresses any heterogeneity that might be present within the batch. This may include sampling across horizontal and vertical dimensions of a feedstock batch as a consideration of particle sorting that may happen during processing.

Where feedstocks are delivered to a Project site that is geographically separate from the source location, Project Proponents must undertake the following to ensure homogeneity across deliveries:

• Project Proponents must establish a characterization approach that demonstrates that feedstock properties are consistent within and across deliveries derived from the same source/ stockpile.
• This may include:
  • Initial representative characterization of the feedstock source/stockpile
  • Ongoing sub-sampling of deliveries at a frequency justified by demonstrated batch homogeneity
• All feedstock deliveries must be documented and tracked in line with the Chain of Custody (CoC) requirements outlined in Section 5.2.

Note: The sampling frequency of ongoing deliveries must be assessed on a Project by Project basis, informed by the demonstrated homogeneity of the source feedstock batch. Delivery characterisation approaches should be agreed in consultation with Isometric and the Project VVB.

To determine the variability of a feedstock material, is it recommended that Project Proponents use relevant ISO standards, such as those outlined in Table 3 below.

For example, Annex 2 of ISO 3082:2017 outlines a variability experiment using duplicate sampling, where

• High Variability (Heterogeneous): More increments are required (e.g., n 50+ for a 1,000-tonne material mass)
• Low Variability (Homogeneous): Fewer increments are required (e.g., n 10–20)

The variability of feedstock materials, and subsequent sampling increments (n), must be demonstrated and justified within the PDD submission. A Project Proponent must outline the specific method used to assess variability, such as compositional variance analysis (such as ANOVA).

Table 3: Example ISO standards that may be utilized when designing a sampling plan

In line with ISO 3082:2017 sampling increments, composite sampling and aliquots are defined as follows:

• Increments: These are the individual sample masses taken across a feedstock stockpile (e.g., 50 individual bulk samples)
• Composite Sample: All collected increments are combined and mixed thoroughly. This "averages out" the variability of the rock, creating a ‘representative’ composite
• Laboratory Sample: The composite is representatively split down to about 1–2 kg sub-samples to send to a laboratory facility for characterization
• Aliquots: The laboratory may reduce sample sizes (e.g., 0.5g) to utilize in individual analysis methods.
• Replicates: 2 or 3 aliquots (Replicates) are typically tested to demonstrate the laboratories analysis accuracy

Project Proponents are required to collect a minimum of 40 representative sample increments from their feedstock source in order to create a composite sample mass for characterization. The sampling plan employed to collect sample increments must be described in detail within the PDD submission.

All Information related to the creation of composite samples, laboratory samples and aliquots for the purpose of feedstock characterization must be outlined within the PDD submission. Information must include utilized material characterization, preparation and sampling standards, methods and SOPs (where applicable).

While Project Proponents are required to collect a minimum of 40 representative sample increments from their feedstock source (e.g. stockpile or TSF), it is highly recommended that Project Proponents follow the methods and guidances outlined in relevant ISO standards.

For example, where a specific standard deviation is not known for a feedstock yet, ISO 3082:2017 (Annex 2 recommends default sample increment numbers based on the mass of the feedstock source / stockpile and the variability of the feedstock (high or low). Table 4 outlines recommended sampling increments, in line with ISO 3082:2017 (Annex 2).

Table 4: Recommended Sample Increments for high and low variability feedstocks

Alternative sampling increment plans may be acceptable where Project Proponents can demonstrate statistical representativeness or have followed a specific ISO standard for sampling and sample preparation. For guidance on alternative methods and approval processes, see Section 3.1 (Consolidated Alternative Methods).

The physical properties of rock and mineral feedstocks are required to be characterized before use in a Crediting Project. Physical characteristics are required to be assessed in line with the methods and standards outlined within this Module. Within this Module, physical characterization covers a material's geotechnical and physical characteristics.

Geotechnical properties are key to understanding the physical nature of rock feedstocks at the time of analysis. Key parameters include water content, specific gravity, particle density, bulk density and permeability. Geotechnical investigation and testing follow the ISO 17892 standards group, adapted to feedstock-specific contexts.

Project Proponents must undertake geotechnical investigation and testing aligned with ISO 17892 standards or equivalent national standards and report results within the PDD submission.

Required tests for all pathways:

• Determination of water content — e.g., ISO 17892-1:2014
• Determination of particle size distribution — e.g., ISO 17892-4:2016

Recommended tests for all pathways:

• Determination of bulk density — e.g., ISO 17892-2:2014
• Determination of particle density — e.g., ISO 17892-3:2015
• Incremental loading oedometer test — e.g., ISO 17892-5:2017
• Fall cone test — e.g., ISO 17892-6:2017
• Unconfined compression test — e.g., ISO 17892-7:2017
• Unconsolidated undrained triaxial test — e.g., ISO 17892-8:2018
• Consolidated triaxial compression tests on water-saturated soils — e.g., ISO 17892-9:2018
• Direct shear tests — e.g., ISO 17892-10:2018
• Permeability tests — e.g., ISO 17892-11:2019

Project Proponents must ensure that all geotechnical laboratory testing meets standards in accordance with national regulations in the project's location. Where national alternatives to ISO 17892 standards are used, this must be reported within the PDD submission.

Commercially produced carbonate feedstocks are exempt from geotechnical and radioactivity measurement requirements.

Particle size distribution (PSD) and specific surface area analysis quantify the physical characteristics of feedstock materials. PSD characterizes the range of particle sizes present, while surface area analysis determines the reactive surface available for chemical weathering. Within this Module, gravimetric sieving and BET analysis are the required methods for these parameters.

Project Proponents must carry out PSD and specific surface area analysis for all rock and mineral feedstocks used within Crediting Projects.

Gravimetric Sieving

Gravimetric sieving determines particle size distribution by mechanically separating particles into defined size fractions.

Project Proponents must:

• Analyze all proposed rock and mineral feedstock materials for particle size distribution through gravimetric sieving
• Conduct this analysis in line with ISO 11277:2020 or ISO 17892-4:2016 standardized procedures, or an equivalent national or regional standard
• Clearly report any variations from the ISO procedures if using a specific national variation (e.g., BS ISO 11277:2020)

BET Analysis

BET (Brunauer-Emmett-Teller) analysis quantifies specific surface area by measuring the extent of gas adsorption on the feedstock surface. This quantifies the potential reactive surface area of rock feedstock and aids in estimating the relative reaction kinetics for CDR applications.

Project Proponents must:

• Undertake BET analysis for all rock and mineral feedstocks
• Conduct the BET method in line with ISO 9277:2022

Other PSD and Surface Area Techniques

Alternative techniques may be used to measure or validate a rock feedstock's PSD or relative surface area, subject to approval.

Project Proponents may perform alternate techniques such as small angle X-ray scattering (SAXS) to estimate mean particle sizes between 1 nm and 100 nm. Where such techniques are utilized, the procedures must be clearly and adequately reported with reference to SOPs or standards, such as ISO 17867:2020. For approval processes and guidance on alternative methods, see Section 3.1 (Consolidated Alternative Methods).

Geochemical characterization is required for all proposed rock and mineral feedstock materials. Project Proponents are required to determine the abundance of major and minor elements within a feedstock, the mineralogy of the feedstock, the total elemental carbon and sulfur and feedstock radioactivity using the methods described in the following section.

Elemental characterization establishes the baseline metal cation and anion contents of a rock feedstock material. Elemental composition is determined using methods selected based on the specific composition and characteristics of the feedstock rock, including ED-XRF, WD-XRF, or fusion/acid digestion coupled with ICP-MS or ICP-OES.

Project Proponents must:

• Undertake elemental characterization on all utilized rock feedstocks using ED-XRF, WD-XRF, or fusion/acid digestion coupled with ICP-MS or ICP-OES
• Initially characterize rock feedstocks for a minimum of the following elements: Na, Mg, Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Cd, Ba, W, Hg, Tl, Pb and Zr
• Include any elements, isotopes, and/or isotope ratios not listed above that will be used to quantify weathering rates in the field
• Following initial assessment, refine elemental analysis to reduce the total number of elements measured only where it can be demonstrated that eliminated target elements do not represent a measurable portion of the assessed feedstock material
• Quantify non-measurable elements through elemental mass balance calculations

ED-XRF

ED-XRF (Energy Dispersive X-ray Fluorescence) determines major and minor elemental composition, allowing identification of key elements such as Mg and Ca (typically reported as oxides MgO and CaO) and assessment of potentially environmentally harmful elements within the feedstock.

Project Proponents are recommended to analyze major and minor elemental compositions via ED-XRF to assess both the suitability of the material for CDR projects and the concentrations of potentially harmful elements.

Data collected by portable XRF is not eligible for elemental characterization within this Module. Portable XRF data may be used to demonstrate homogeneity when creating a sampling plan (see Section 3.3.2), but must not be used as a primary elemental characterization analysis method.

Acid Digestion and/or Fusion Coupled with ICP-MS/OES

Acid digestion and fusion methods coupled with ICP-MS or ICP-OES provide detailed elemental analysis with higher analytical resolution than fluorescence-based methods alone. While digestion, fusion, and fluorescence-based methods are not directly comparable, the additional level of analysis reduces analytical uncertainties in rock feedstock characterization and is particularly important for trace element determination.

Project Proponents must undertake detailed elemental analysis of rock feedstocks. At least one of the following analyses must be performed:

• Fusion or Two-Acid Digest / Aqua Regia Digest (with ICP-OES/MS)
• Fusion or Multi-Acid (4-Acid) Digest (with ICP-OES/MS)
• Fusion or Nitric Acid Digest (with ICP-OES/MS)

Other Elemental Measurement Techniques

Additional elemental measurement techniques such as Atomic Absorption Spectroscopy (AAS) or WD-XRF may be used as supplementary methods.

Project Proponents should consider the analytical uncertainty associated with various measurement techniques when developing an analytical framework for feedstock characterization. For example, XRF techniques may have sufficient precision for major elemental composition, but higher analytical resolution may be required for full characterization of trace elements.

Project Proponents must:

• Provide justification for their chosen analytical methods in the PDD submission
• Include evidence that there is sufficient analytical resolution to determine the concentrations of trace elements relevant to calculation of weathering rates and environmental safeguards
• Outline details of any additional elemental measurement techniques within the PDD submission

To assess the theoretical maximum carbon removal potential of an alkaline rock or mineral feedstock, Project Proponents must use an adjusted version of the Steinour equation, see Equation 1². The equation uses bulk elemental oxide composition to estimate the maximum CO₂ removal potential of a feedstock material:

$${E_{pot}} = 
(\frac{1000}{100}) \times (\frac{CaO}{M_{W, CaO}} + \frac{MgO}{M_{W, MgO}} + \frac{Na_2O}{M_{W, Na_2O}} + \frac{K_2O}{M_{W, K_2O}} - \frac{SO_4}{M_{W, SO_4}} - \frac{P_2O_5}{M_{W, P_2O_5}}) \times M_{W, CO_2} \times \eta  - C_{feedstock}$$

(Equation 1)

Where:

• $Epot$ is the CO₂ capture potential of an alkaline rock and mineral feedstock used in enhanced weathering, in kg of
  CO₂ per ton of feedstock
• The factor $(\frac{1000}{100})$ is a unit conversion that adjusts oxide weight percentages to kilograms per ton of feedstock
• $Mw$ is the molecular mass of the specific oxide
• All oxides are in the unit of weight percent of the bulk feedstock (i.e., 5 wt% is input as 5
• $η$ is the molar ratio of CO₂ storage potential to divalent alkalinity released from feedstock. This term has a maximum value of 2
• $C_{feedstock}$ is the carbon content (organic and inorganic) of the feedstock

The adjusted equation utilizes elemental composition to identify maximum CO₂ capture potential of an enhanced mineralization project (Epot) based solely on bulk elemental analysis. The calculation output is in the form of kg of CO₂ per tonne of feedstock and represents the quantitative hypothetical potential of the material to capture CO₂ as bicarbonate or carbonate. It must be noted that this equation does not take into consideration variables that effect carbonation and carbonation rates such as temperature, known reaction rates, pressure, moisture content and PSD. The equation considers the presence of elemental sulfur and phosphorus as having a reducing effect on overall theoretical potential. This is due to two distinct rationales: (1) their dissolution has no implicit reaction with CO₂ directly and (2) they may become acid compounds, producing acidity which has implications on the carbonate system as CO₂ may be produced³.

Elemental abundance data should be produced according to methods prescribed in this Module. The CDR potential calculated in Equation 1 represents the upper limit of Creditable removals for a single batch of feedstock as defined in Section 3.3.1. Project Proponents are required to report the CDR potential of each batch of feedstock used pursuant to project activities in the PDD submission.

Project Proponents may use an alternative version of the Steinour equation when calculating the theoretical maximum carbon removal potential of a feedstock. For approval of alternative calculation approaches or methods, see Section 3.1 (Consolidated Alternative Methods).

It is recommended that the Project Proponent determines the impact of previous chemical alteration and weathering on rock and mineral feedstocks as part of a suitability assessment prior to application. One tool that may be used for aluminosilicate rocks and minerals that are not Mg²⁺ or Fe³⁺ rich, such as plagioclase and other feldspars, is the chemical index of alteration ($CIA$)⁴. This geochemical tool was introduced by Nesbitt and Young (1982) and is commonly used in sedimentary geology, geochemistry, and paleoclimatology to infer the intensity of weathering processes and climatic conditions. The $CIA$ is calculated from the molar proportions of major oxides in a sample, focusing on the loss of mobile cations (like Ca²⁺, Na⁺, and K⁺) relative to immobile aluminum. The $CIA$ has been historically used in the weathering literature^4,5,67,8,9 including mafic terrains, and provides the most straightforward interpretation of incipient alteration. The maximum CDR potential of the feedstock will be inherently limited by the initial degree of alteration. Additionally, the $CIA$ value can be used in concert with the mineralogical assessment of the feedstock to evaluate the input of clay minerals from weathered feedstock and/or a source of contamination to the feedstock (e.g., atmospheric dust). The equations uses molar proportions of elements as follows:

$$CIA= \frac{Al_2O_3}{Al_2O_3 + CaO^*+ Na_2O + K_2O} \times 100$$

(Equation 2)

Where $CaO^*$ is traditionally the amount of CaO incorporated into only the silicate fraction, i.e., a correction for any calcium in carbonate or apatite in the feedstock. Pairing the $CIA$ calculation with the mineralogy of the feedstock, this $CaO^*$ correction can be ignored if these phases are absent. Lower values (less than 50 tend to indicate very limited weathering and high CDR potential. Values approaching 100 indicate significant weathering and very low CDR potential. Project Proponents may also consider applying alternative weathering indices that are more appropriate for a given feedstock chemistry (e.g., Mafic Index of Alteration and/or Weathering Intensity Scale).

Total carbon and sulfur analysis determines the quantity of carbon (measured as total carbon, inorganic carbon, and/or organic carbon) and sulfur within feedstock materials. These parameters are essential for calculating CO₂ removal potential and assessing environmental risks such as acid generation from sulfide oxidation.

Project Proponents must:

• Undertake analysis to determine total carbon and sulfur contents within all rock and mineral feedstock materials used in Crediting Projects
• Utilize standardized analytical techniques such as ISO 14855-1:2021, ISO 6235:2021, or equivalent national standards
• Document the analytical method and results in the PDD submission

Feedstock radiation levels must be assessed prior to feedstock utilization to ensure compliance with all applicable local, national and international regulations and to protect human health and environmental quality. Assessment may involve direct measurement of radioactivity or evaluation of pre-existing data demonstrating negligible radioactivity.

Project Proponents must ensure adherence to all applicable local, national and international laws regarding acceptable levels of radiation within the context of the Project.

For feedstocks from extractive or mining sources, the Project Proponent must either:

• Determine gross alpha and beta activities using ISO 18589:2019 (Measurement of radioactivity in the environment — Soil) or equivalent standard, or
• Provide adequate, geologically and geographically specific justification demonstrating low radiation levels

Where an alternative standard to ISO 18589:2019 is used, documentation of such standard must be provided to the VVB.

In some cases, sufficient pre-existing data may demonstrate that radioactivity of a feedstock—such as commercially available feedstock products—is negligible. Project Proponents may submit pre-existing data with sufficient justification in the PDD submission, demonstrating that measurement is not necessary. For guidance on submitting alternative evidence, see Section 3.1 (Consolidated Alternative Methods).

Mineralogical characterization determines the mineral types and relative abundances within rock feedstock materials, essential for assessing CO₂ removal potential, reaction kinetics, and environmental and health risks. Characterization typically combines X-ray diffraction (XRD), light microscopy, and/or scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) to provide qualitative and quantitative mineral data.

Project Proponents must undertake mineralogical characterization for all rock feedstock materials used within Crediting Projects.

Mineralogical Analytical Methods

Mineralogical characterization combines XRD, light microscopy, and/or SEM-EDS mineral mapping to determine mineral type and abundance. Quantitative XRD (qXRD) is used to measure the relative abundances of mineral phases (in contrast to qualitative XRD, which only identifies mineral phases present).

Project Proponents must:

• Use a combination of XRD, light microscopy and/or SEM-EDS mineral mapping to determine rock feedstock mineral type and abundance
• Employ quantitative XRD (qXRD) when examining mineral type and abundance in feedstock materials
• Report bulk mineral abundances for all rock and mineral feedstocks
• Outline the specific methodology used, with reference to source laboratory SOPs or equipment manufacturer methodologies
• When utilizing light microscopy, send rock samples to an accredited external laboratory for analysis and cross-check results with qXRD, SEM-EDS and/or geologic information
• Include in submitted methodology: sample preparation, coating types, instrument calibration and certified reference materials (CRM) used (where relevant for SEM-EDX/EDS)

Risk Assessment: Target Mineral Groups

Rock feedstocks may contain mineral groups that pose project risks related to human health, environmental quality, or CO₂ removal efficiency. Key target mineral groups that warrant assessment include carbonates, sulfides, and asbestos group minerals. The specific risks depend on the application, feedstock source, and project context.

Project Proponents must:

• Identify and assess key target mineral groups that may pose a project risk, including but not limited to human/health risk, environmental risk, and CO₂ removal inefficiency
• Provide detailed quantitative and qualitative descriptions of the feedstock with direct reference to target mineral groups
• For feedstocks containing sulfide minerals, assess the potential for reversals—such as acid generation from sulfide oxidation—and report findings in the PDD submission
• For feedstocks containing asbestos group minerals, assess the potential for environmental harm (e.g., release of fibrous asbestos particles) and report findings in the PDD submission
• Conduct risk assessments on a project-by-project basis in consultation with the Project registry, VVB and relevant regulatory bodies

Feedstocks sourced from mining operations or extractive industries require documented evidence of origin and detailed characterization to ensure traceability, quality, and environmental compliance. Clear sourcing documentation supports chain-of-custody (CoC) and feedstock homogeneity claims.

Where a rock feedstock has been sourced from a mining operation or extractive industry, the Project Proponent is required to provide documented evidence that the material has been characterized following all requirements outlined in this Module. The Project Proponent must provide the following information:

1. Sourcing and Location:

• Mine/quarry location (latitude/longitude) and associated geological setting
• Specific geological unit or ore body from which feedstock was extracted

2. Extraction Method:

• Exploitation method (e.g., open pit, underground, alluvial)

3. Processing:

• Processing and beneficiation steps undertaken prior to feedstock use

4. Quality Assurance:

• Quality assurance/quality control (QA/QC) procedures undertaken to ensure material homogeneity and traceability
• Clear demonstration of characterization procedures and quality assurance information related to sourcing and preparation

This information must be verified by Project VVB.

Where specific regulatory guidance on the characterization of mining wastes and by-products does not exist within the locality of a Crediting Project, Project Proponents are recommended to revert to the mandated characterization standards outlined by the European Commission. These standards provide a detailed baseline for the characterization of rock feedstocks sourced from mining operations. The following standards are recommended:

• EN 15875:2011 Characterization of waste Static test for determination of acid potential and neutralization potential of sulfidic waste
• CEN/TR 16363:2012 Characterization of waste Kinetic testing for assessing acid generation potential of sulfidic waste from extractive industries
• CEN/TR 16376:2012 Characterization of waste Overall guidance document for characterization of waste from extractive industries
• CEN/TS 16229:2011 Characterization of waste Sampling and analysis of weak acid dissociable cyanide discharged into tailings ponds
• CEN/TR 16365:2012 Characterization of waste Sampling of waste from extractive industries

Where a mining operation's waste characterization program follows specific guidance based on best practices, rather than ISO or CEN standards, the Project Proponent is required to outline the specific methods and procedures that have been utilized to characterize the mining waste materials. Such alternative guides or handbooks may include the following:

• The predictive manual for drainage chemistry from sulfidic geological materials (MEND Report 1.20.1)
• The Global Acid Rock Drainage Guide (GARD Guide)
• EPA 530-R-94-036 (Technical Document Acid Mine Drainage Prediction)

Project Proponents must carry out the following additional analyses when feedstocks recovered from a mining operation or other extractive industry are applied to agricultural land:

1. Elemental Deportment Analysis (EDA): EDA determines how elements are distributed among mineral phases within a feedstock, identifying the mineral hosts of elements of concern and whether they are structurally bound (low mobility) or present in more labile, potentially leachable phases (higher risk). This enables project proponents to either demonstrate a low likelihood of release or design systems to mitigate the mobilization of harmful elements. There is not a single methodology or standard for EDA, as it is achieved through a combination of elemental and mineralogical analysis. The following combination of methods are recommended to undertake EDA:

• Bulk elemental composition (e.g., XRF, ICP-OES/MS):
  • Quantifies total concentrations of major and trace elements
  • Provides the mass balance basis required to allocate elements to mineral phases
• Quantitative mineralogy (e.g., XRD, Rietveld refinement):
  • Identifies and quantifies mineral phases present in the feedstock
  • Enables linkage between bulk chemistry and mineral hosts
• Automated mineralogy (e.g., MLA, QEMSCAN):
  • Maps mineral phases and associated elemental distributions at the particle scale
  • Directly quantifies element deportment and mineral associations
  • Provides information on grain size, liberation, and mineral accessibility
• Micro-scale chemical analysis (e.g., SEM-EDS, EPMA):
  • Confirms element hosting within specific mineral phases
  • Provides higher-resolution or more precise compositional data for key phases

While the methods listed above are recommended for EDA, Project Proponents may undertake alternative analysis. Where alternative analysis or method types are utilised to assess elemental deportment, Project Proponents must provide full justifications.

2. Leaching Tests: Leaching tests are standardized laboratory procedures that are used to quantify how and under what conditions elements are released from a feedstock into solution. Project Proponents must undertake leaching tests that rigorously assess the leaching potential of potential environmentally harmful elements (such as Cr, Ni and Hg) under varied pH conditions. The following leaching tests types and standards are recommended:

• Toxicity Characteristic Leaching Procedures (TCLP) - TCLP is a worst-case scenario acidic leaching test, designed to assess landfill disposal risk.
  • EPA SW-846 Test Method 1311: Toxicity Characteristic Leaching Procedure (TCLP)
• Synthetic Precipitation Leaching Procedure (SPLP) - SPLP is an environmental exposure test designed to assess leaching under simulated precipitation (acid rain) conditions.
  • EPA SW-846 Test Method 1312: Synthetic Precipitation Leaching Procedure (SPLP)
• pH-dependent Leach Tests - pH-dependent leach tests are mechanistic leaching methods that quantify contaminant release as a function of pH, enabling evaluation of geochemical controls on elemental solubility.
  • EPA SW-846 Test Method 1313: Liquid-Solid Partitioning as a Function of Extract pH Using a Parallel Batch Extraction Procedure
  • ISO 21268-4:2019: Soil quality — Leaching procedures for subsequent chemical and ecotoxicological testing of soil and soil-like material

pH-dependent tests are particularly relevant to Enhanced Weathering Projects, where field pH conditions vary significantly by project design, soil type, and over the reporting period as feedstocks weather.

Project Proponents must justify the type of leach tests employed when characterising a feedstock. Where leaching tests are required as part of permit approval or regulatory compliance, additional testing is not required. Pre-existing results should be submitted directly in PDD.

Note: Project Proponents may propose alternative tests to demonstrate safety, at the discretion of approval from Isometric and the VVB.

Analytical laboratories conducting feedstock characterization must maintain rigorous quality standards to ensure data reliability and reproducibility. Reputable laboratories implement systematic quality assurance procedures and maintain recognized accreditation for their specific test methods.

Project Proponents must ensure that all analytical work is completed by laboratories accredited to ISO 17025 or equivalent standards for laboratory quality management, specific to the test method employed (e.g., ASTM D5291).

Sub-requirements:

• Project Proponents must report all analytical laboratories utilized for feedstock characterization within the PDD submission
• Project Proponents must ensure that chosen analytical facilities conduct characterization techniques to the standards indicated in this Module and Appendix 1
• Laboratories must complete standard quality assurance procedures in accordance with their quality management plans and accreditation requirements, including:
  • Analysis of blanks
  • Analysis of duplicates
  • Instrumentation calibrations and analysis of calibration standards
• Project Proponents should utilize UKAS, MCERTS, DWTS and ISO accredited analytical services whenever feasible

This section applies if the Project Proponent's analysis is performed at a non-accredited academic facility, non-accredited commercial laboratory, or internally owned/operated laboratory.

When feedstock characterization is performed outside of ISO 17025-accredited facilities, external validation by an accredited laboratory provides independent verification of analytical results. This validation ensures data reliability and identifies potential systematic errors or methodological discrepancies.

Project Proponents must undertake periodic external validation of all results that directly influence Crediting volumes, at a minimum during the Project's first verification and annually thereafter.

Sub-requirements:

• External validation must be carried out by an ISO 17025-accredited facility on a minimum of 3 samples, which are either representative or duplicates of samples analysed during the Project feedstock characterization program
• Project Proponents must report the frequency of external validation checks within their PDD submission prior to use of feedstock in a CDR Project
• The following analysis types must be validated by an external, accredited laboratory annually (at a minimum):
  • Elemental Composition: ED-XRF, WD-XRF or fusion / acid digestion coupled with ICP-MS or ICP-OES
  • Total Carbon and Sulfur: Dry Combustion
• The following analysis types should be validated by an external, accredited laboratory annually:
  • Mineralogical characterization: XRD, SEM-EDX
• Results validated by an external, accredited laboratory should be consistent with non-accredited results, taking into account method precision and sample heterogeneity. A discrepancy of less than 5% (calculated as percent error between the mean of replicate measurements and the external laboratory result) represents a target level of agreement under well controlled conditions. Discrepancies in the range of 5 - 15% may be acceptable and do not necessarily indicate an issue with data quality.
• Where discrepancies exceed 15%, Project Proponents must undertake further investigation to identify the source of discrepancy. This may include additional analysis, review of sample preparation and analytical methods, or assessment of sample heterogeneity. Where discrepancies remain unresolved, the selection of results for Crediting must be justified and agreed with Isometric prior to submission, with conservative approaches applied where appropriate.

Quality assurance and quality control (QA/QC) procedures are fundamental to ensuring that characterization data are accurate, reproducible, and suitable for crediting calculations. Systematic documentation of calibration, analytical checks, and certified reference materials (CRM) provides evidence of data reliability.

Project Proponents must report comprehensive QA/QC processes within the PDD submission and provide supporting documentation to the relevant VVB when submitting feedstock characterization data.

Sub-requirements:

• Project Proponents must report calibration records (where available) from analytical facilities to the relevant VVB
• Project Proponents must outline specific analytical checks carried out to maintain data quality, with specific reference to the certified reference materials (CRM) used by the laboratory facility
• Project Proponents must clearly describe all analytical checks as part of QA/QC procedures, including:
  • Duplicate analyses
  • Blank analyses
  • Analytical standards checks
• Project Proponents must describe calibration procedures employed by the laboratory
• Characterization data should be validated through set quality assurance and quality control criteria established in accordance with the requirements of this Module

Comprehensive reporting of feedstock characterization data enables independent verification of results and reproducibility of analytical methods. Complete data documentation, including raw measurements, standards data, and metadata, supports the transparency and credibility required for crediting determinations.

Project Proponents must provide all feedstock characterization data within the PDD submission and maintain records in a form that enables external verification and replication of analytical methods.

Sub-requirements:

• Project Proponents must ensure that the data submitted is accurate and externally verifiable, even where characterization and analysis are conducted at an external facility
• Project Proponents must include results of all utilized standards within submitted data reports to verify data quality
• Project Proponents must report data such that the data analysis methods used are easily identified, verified and replicated
• Project Proponents must include raw data from which any data analysis or reduction was performed, including standards and replicate measurements
• Project Proponents must include a summary containing the following metadata:
  • Number of samples run
  • Analytical uncertainty
  • Standards used
  • Number of standards run
  • Standard deviation
  • Percentage error on standards
• Project Proponents should structure data reporting in a format that clearly separates raw data, reduced/summarized data, and data reduction calculations (where applicable). This may take the form of a multi-sheet spreadsheet containing:
  • Summary sheet detailing metadata
  • Reduced data sheet (data summary)
  • Data reduction sheet (if applicable; e.g. processing of ICP-MS data)
  • Raw data

Data Record Retention Requirement: Project Proponents must maintain all feedstock characterization data records for a minimum of 5 years following the date of data collection.

When characterization data is generated by third parties, such as commercial feedstock producers, mining operators, or contract laboratories, clear submission protocols ensure data quality, intellectual property protection, and efficient verification. Different submission pathways apply depending on the data source and whether third parties submit information directly or through the Project Proponent.

The following table outlines which submission pathway applies based on who performed the characterization:

Results and data submissions by third parties must meet all requirements outlined in this Module, unless explicitly stated otherwise in Section 5.1.2 or by Isometric approval.

Sub-requirements:

• Results and data produced by third parties may be submitted by the Project Proponent within the PDD submission
• Where the third party is unable or unwilling to provide results or characterization information (such as utilized methods or internal SOPs) to the Project Proponent, the third party may submit this information directly to Isometric and the Project VVB. In such cases, the Project Proponent must still be informed of the scope and nature of the information being submitted, even where the detailed content is shared directly.
• In instances where information will be submitted directly by the third party to Isometric and the VVB, Project Proponents must consider the following:
  • Project Proponents are responsible for identifying whether Isometric must engage with a third party to receive required results or characterization information to fulfill the requirements of this Module. Introductions to third parties should occur as early as possible to reduce potential delays in validation and verification
  • Project Proponents remain responsible for ensuring that the scope of third-party analysis is sufficient to meet**** the requirements of this Module,and for confirming that the third party has been engaged to provide the necessary characterization information 
  • Where Isometric or the VVB identifies that results or characterization information submitted by the third party does not  meet the requirements of this Module, Isometric will notify the Project Proponent of the nature of the deficiency. The Project Proponent is then responsible for coordinating with the third party to resolve the issue, or for undertaking this analysis independently

When third parties submit characterization methods and results directly to Isometric and the VVB, the following provisions apply:

Sub-requirements:

• Information provided by third parties will be assessed by Isometric and the VVB for compliance with this Module
• Where agreed with the third party, Isometric and the VVB will not share proprietary or sensitive information with the Project Proponent
• Proprietary or sensitive information provided by the third party may be redacted within the public PDD on the Isometric Registry. Any redactions must be pre-agreed in consultation with the VVB prior to completion of Validation and Verification.
• Characterization methods must be outlined in all submissions. Where an internal SOP is utilized, a general summary of the methods and related standards will be accepted upon review by Isometric and the Project VVB
• Characterization methods and data submission information must include (at a minimum):
  • The analysis type (e.g., ICP-OES or ED-XRF)
  • Standard, method or SOP followed
  • Sample preparation method (fusion, aqua regia, multi-acid digestion, etc.)
  • QA/QC data and information

Definition: Commercial feedstocks are feedstocks that are commercially available for purchase by a Project Proponent and have not been mined or quarried specifically for the Project. An example of this would include Calcium Carbonate that is purposely quarried and produced for commercial sale, which is not a waste or by-product of other extractive activities (such as the mining of rare earth elements).

Feedstocks procured from commercial producers may have been subject to rigorous quality control by the producer. In such cases, certain characterization data generated by the producer under ISO-compliant quality management systems may be accepted without the full external validation requirements that apply to academic or non-accredited laboratories.

Project Proponents procuring feedstock from commercial feedstock producers must provide producer information to Isometric and the VVB within the PDD submission and may submit commercial characterization data to fulfill the requirements of this Module.

Sub-requirements:

• Submitted information on commercial feedstocks must contain all required analyses outlined in previous sections of this Module, unless specified otherwise below
• Commercial information and characterization data related to the procured feedstock product may be submitted by the Project Proponent or the commercial producer
• Collection and production information may be summarized for commercial feedstocks where the information is not easily available to the Project Proponent
• If the commercial feedstock producer can demonstrate adherence with ISO standards for its own internal characterization:
  • External validation is not required
  • Submissions must include a bulleted list of all relevant standards and/or SOPs used in the generation of data submitted within the PDD
  • Analytical and calibration data does not need to be submitted in full detail
• If raw data is not available for commercial feedstocks: Summarized data for characterization requirements will be considered on a Project-by-Project basis in consultation with Isometric and the VVB
• If the feedstock producer can demonstrate negligible radioactivity levels: Distinct radiation analysis is not required for commercially available feedstocks. Negligible radioactivity may be evidenced by elemental analysis or geological assessments of the host deposit
• Sampling plans do not need to be submitted for data generated by a commercial feedstock producer
• If information or results provided by the commercial feedstock producer does not meet the requirements of this Module: The Project Proponent must undertake supplementary analysis. In such instances, all characterization, sampling, and QA/QC requirements of Section 4 and 5.1 will apply. Isometric reserves the right to request full characterization of commercial feedstocks where information provided by the feedstock producer is not suitable to satisfy the requirements of this Module.

Chain of custody documentation provides a complete audit trail of feedstock handling, from production through characterization analysis. This documentation demonstrates proper sample integrity, prevents contamination, and ensures that analytical results are traceable to specific feedstock batches, deliveries and individual samples. Depending on the feedstock type and characterization pathway, different CoC formats and standards apply.

Project Proponents must submit chains of custody (CoC) that cover feedstock production, transportation, and characterization programs in accordance with recognized standards.

When non-commercial feedstocks are used, the Project Proponent must provide either a single chain CoC or separate feedstock production and characterization CoCs.

• A single chain CoC covers production, storage, transport, and characterization of the feedstock.
• A feedstock Production/Collection CoC covers sourcing of the feedstock by the feedstock producer through delivery to the Project Proponent
• A feedstock Characterization CoC covers handling of feedstocks from the supplier or producer to the characterization location/laboratory

Chains of custody must be created, implemented, and documented in accordance with recognized standards to ensure consistency and credibility.

Sub-requirements:

• Chains of Custodies must be created, implemented, and utilized in line with either of the following standards:
  • ISO 22095:2020 Chain of custody — General terminology and models
  • ASTM D4840-99 Standard Guide for Sampling Chain-of-Custody Procedures
• Project Proponents may follow other CoC standards or internal SOPs, as long as they meet the requirements outlined in this Module section. Where an alternative CoC system or SOP has been implemented, the Project Proponent must describe this system within the PDD submission
• CoCs must be submitted in either table format or directly within the PDD
• All CoCs must include the following (at a minimum):
  • Document Serial Number
  • Project Name
  • Project Proponent Name
  • Primary Contact
  • Batch ID / Number
  • Sample IDs
  • Sample Description
  • Described actions (transport, storage, etc.)
  • Analysis Requested (for single chain or feedstock characterization CoCs)
  • Locations
  • Dates
  • Custody Log including information such as:
    • Relinquished By: Signature, Date, and Time
    • Received By: Signature, Date, and Time
    • Transport Method: Courier name and tracking codes (where applicable)
• Appendix 2 contains an example single chain CoC that is recommended for all Projects. The CoC template within Appendix 2 has been designed to be compliant with ISO 22095:2020

Sub-requirements:

• Where sampling and characterization programs are carried out by the Project Proponent, a detailed Feedstock Characterization CoC must be maintained from the point of sample collection through analysis completion
• All CoC documents must clearly identify the sample(s) to which they apply and track handling through all stages

This subsection applies if the Project Proponent is using commercially available feedstocks or where the feedstock producer has already carried out characterization.

For commercial feedstocks, simplified documentation is acceptable where sampling and analysis have already been completed by the commercial producer prior to delivery to the Project Proponent.

Sub-requirements:

• Where commercial feedstocks have been provided directly by the feedstock producer, a Bill of Lading (BOL) is acceptable in place of a Feedstock Production/Collection CoC
• For all subsequent sampling and analysis carried out by external third-party laboratories (including accredited and academic institutions), a Single Chain or Feedstock Characterization CoC must still be submitted
• For commercial feedstock CoCs, the following information must be documented (in place of full transport and storage details for the producer):
  • Information on the feedstock producer (Name)
  • The BOL number
  • The date the feedstock was shipped
  • Who received and signed for the materials (Physical or digital signature)
  • How the material was stored by the supplier upon being received
• In instances where sampling and characterization programs are carried out entirely by a commercial feedstock producer prior to direct delivery to the Project Proponent, a BOL may be accepted in place of a full CoC. In such situations, a simplified CoC may be required where samples are stored by the Project Proponent prior to use in Crediting Projects

This section applies only if the feedstock constitutes a waste product that was not mined or quarried specifically for the Project. This section does not apply to feedstocks that are primary materials or commercially produced materials created specifically for sale.

When waste feedstocks are used for mineral carbonation, the counterfactual fate of the feedstock (the baseline scenario in the absence of the Project) may include naturally occurring weathering or exposure to environmental conditions. Quantifying this counterfactual weathering is necessary to avoid crediting carbon removal that would have occurred regardless of Project implementation. Counterfactual weathering scenarios vary depending on the intended disposal or use of the waste product.

For waste feedstocks, Project Proponents must quantify the counterfactual fate and the carbon removal that would occur through counterfactual feedstock weathering in the absence of the Project.

• Project Proponents must describe the counterfactual fate for the feedstock (the baseline scenario)
• Project Proponents must quantify the counterfactual feedstock weathering that would occur in the absence of the Project
• If counterfactual weathering modes other than surficial weathering or ocean alkalinity enhancement (OAE) are relevant to the Project, Project Proponents must describe a quantification strategy in the PDD submission and obtain Isometric approval prior to implementation

The following sections describe two dominant modes of counterfactual feedstock weathering. Project Proponents must apply the applicable section(s) to their Project scenario.

Conditional applicability: This subsection applies if the counterfactual fate of the feedstock is storage in open-air conditions, which would result in natural weathering of the feedstock surface when exposed to atmosphere and precipitation.

Geochemical modeling provides the scientific foundation for quantifying weathering rates under baseline storage conditions. Accurate modeling requires detailed characterization of feedstock properties, site conditions, and environmental parameters.

If the feedstock would have counterfactual surficial weathering under open-air storage, Project Proponents must calculate surficial weathering using geochemical modeling of feedstock weathering under storage conditions relevant to the source site.

• Project Proponents must provide a written description of the baseline storage site
• The model must accurately reflect the feedstock mineralogy, surface area, and CDR potential, based on the data reported for feedstock characterization
• The model must accurately reflect the baseline carbonation, permeability, and water saturation of the feedstock pile based on direct measurements of the feedstock pile over the course of a Crediting Project. Inclusion of microbial activity in the feedstock pile is recommended
• The model must accurately reflect the environmental conditions of the source site, including:
  • Temperature
  • Average annual precipitation
  • Rainwater pH and carbonate saturation
  • Groundwater pH and carbonate saturation
  • All parameters may be based on direct measurement or publicly available data
• The modeled domain must be justified. Studies have shown that the vast majority of weathering in tailings piles occurs in the surface layer exposed to the atmosphere (provided there is no mechanical overturn). By default, Project Proponents must model the top meter of the feedstock pile
• Project Proponents must provide the model, input data, and output data used to calculate surficial feedstock weathering
• All assumptions and criteria for evaluating uncertainties in utilized models must be described. Assumptions about storage conditions and potential reversal risks must be justified or substantiated with operational data. Where relevant, assumptions must be conservative

Conditional applicability: This subsection applies if the counterfactual fate of the feedstock is discharge into surface waters (ocean or coastal systems), which would result in feedstock dissolution and alkalinity enhancement of the water column.

Geochemical modeling of feedstock dissolution and air-sea gas exchange quantifies the carbon removal from counterfactual OAE. Accurate modeling requires characterization of feedstock reactivity, dissolution environments, and ocean chemistry at the discharge site.

If the feedstock would have counterfactual weathering via ocean alkalinity enhancement (OAE), Project Proponents must calculate weathering using geochemical modeling of feedstock dissolution and subsequent air-sea gas exchange relevant to the receiving ocean waters.

• Project Proponents must provide a written description of the discharge process, discharge site, and receiving ocean waters
• By default, it is assumed that all feedstock discharged into the ocean fully dissolves and remains in contact with the surface ocean, unless otherwise justified by the Project Proponent
• Models used to determine the proportion of feedstock dissolution must accurately reflect the feedstock mineralogy, surface area, and CDR potential, based on the data reported for feedstock characterization
• Models used to determine the proportion of feedstock dissolution must accurately reflect all locations where feedstock dissolution may occur, including:
  • Pre-processing of discharge
  • During discharge
  • During plume transport and dispersion
  • Upon settling
  • This may include interactions with other compounds, bulk freshwater, bulk seawater, or micro-environments enhancing dissolution (e.g., metabolic carbonate dissolution in submarine tailings piles)
• Models used to determine the proportion of feedstock dissolution must accurately reflect the environmental conditions where dissolution may occur, including:
  • Temperature
  • Salinity
  • pH
  • Carbonate saturation
  • Organic matter deposition and remineralization
  • Sedimentation
  • Parameters may be directly measured or estimated conservatively
• The resulting atmospheric carbon removal from dissolved feedstock must follow the quantification approach outlined in Section 4.2.1.1 of the River and Ocean Losses Module
• Project Proponents must provide the model, input data, and output data used to calculate OAE weathering
• All assumptions must be described. Assumptions about discharge conditions and potential dissolution pathways must be justified or substantiated with operational data. Where relevant, assumptions must be conservative

The timescale used for modeling counterfactual feedstock weathering must be justified and internally consistent with the Credit durability requirement of 1,000+ years. Different Project scenarios may support different modeling timescales based on documented site conditions and closure plans.

Project Proponents must establish and justify the timescale used for calculating counterfactual feedstock weathering.

• The default timescale for modeling counterfactual feedstock weathering is 1,000 years, aligned with the Module's definition of durability for Credits

• Project Proponents may justify an alternative timescale if additional information on the conditions and duration of feedstock storage at the feedstock supplier are available and documented. The alternative timescale must be relevant to the specific mine, quarry, or feedstock source and must be clearly described in the PDD submission

• Examples of justifiable alternative timescales include:

  • For projects operating in conjunction with active mines: the documented time of mine closure, with details of the closure plan provided in the PDD submission
  • Where sufficient documentation demonstrates that piles of waste materials will not be exposed to ambient environmental conditions for a defined period: the counterfactual may be calculated across that time span

Isometric would like to thank following external reviewers of this Module:

• Michael T. Thorpe (University of Maryland and NASA Goddard Space Flight Center). Michael T. Thorpe's contribution to this Module was not part of his University of Maryland or NASA GSFC duties or responsibilities.
• Julianne DeAngelo (CREW Carbon)
• Will Savage (MEM Consultants)
• Jack Tucker (CarbonRun)
• Jonah Bernstein-Schalet (Mati Carbon)
• Amanda Stubbs (University of Glasgow)
• James Campbell, Ph.D. (Heriot-Watt University)
• Alison Marklein, Ph.D. (Terradot)
• Christina Larkin, Ph.D. (InPlanet)

Isometric would like to thank the following external contributors to this protocol/module:

• Rhys Savage, Ph.D.

This appendix outlines the various analytical techniques and measurements that may be used to satisfy the requirements and recommendations of this Module. The tables below summarize the analytical methods, the parameters they provide, their purpose in calculation of CO₂ removal and material characterization, and examples of acceptable standards. Required analyses will be pathway and project-specific, and Project Proponents must refer to specific Isometric Protocols for any additional pathway-specific requirements. This appendix is intended to provide a comprehensive, but not exhaustive, overview of analytical methods relevant to carbon dioxide removal calculations and feedstock characterization. All analytical methods used must be submitted for feedstock validation and, where applicable, cross-referenced with an appropriate standard (e.g. ISO, EN, BSI, ASTM and EPA) or standardized operating procedure. Where a project utilizes a non-standardized methodology or SOP for the determination of a listed parameter, the Project Proponent is required to outline the relevant method within the PDD submission to the VVB.

Carbonate feedstocks

Please note that commercially produced carbonate feedstocks are exempt from having to comply with geotechnical and radioactivity measurements.

Note: The CoC template provided within this Appendix has been provided as an example for Project Proponents to build off. Rows should be expanded and added as required.

It is the responsibility of the Project Proponent to ensure all information is correct and compliant with any relevant national or international standards.

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2. Gunning PJ, Hills CD, Carey PJ. (2010). Accelerated carbonation treatment of industrial wastes. Waste Management, (6):1081-90. https://doi.org/10.1016/j.wasman.2010.01.005 ↩

3. Renforth, P. (2019) The negative emission potential of alkaline materials. Nature Communications 10, 1401 https://doi.org/10.1038/s41467-019-09475-5 ↩

4. Nesbitt, HW, and Young, GM. (1982). Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature, 299(5885), 715-717. DOI: https://doi.org/10.1038/299715a0 ↩ ↩²

5. McLennan, SM, Hemming, S, McDaniel, DK, Hanson, GN. (1993). Geochemical approaches to sedimentation, provenance, and tectonics. DOI: https://doi.org/10.1130/SPE284-p21 ↩

6. Babechuk, MG, Widdowson, M, Kamber, BS. (2014). Quantifying chemical weathering intensity and trace element release from two contrasting basalt profiles, Deccan Traps, India. Chemical Geology, 363, 56-75. DOI: https://doi.org/10.1016/j.chemgeo.2013.10.027 ↩

7. Babechuk, MG, and Fedo, CM. (2023). Analysis of chemical weathering trends across three compositional dimensions: applications to modern and ancient mafic-rock weathering profiles. Canadian Journal of Earth Sciences, 60(7), 839-864. DOI: https://doi.org/10.1139/cjes-2022-0053 ↩

8. Fedo, CM, and Babechuk, MG (2023). Petrogenesis of siliciclastic sediments and sedimentary rocks explored in three-dimensional Al2O3–CaO+ Na2O–K2O–FeO+ MgO (A–CN–K–FM) compositional space. Canadian Journal of Earth Sciences, 60(7), 818-838. DOI: https://doi.org/10.1139/cjes-2022-0051 ↩

9. Thorpe, MT, Hurowitz, JA, Dehouck, E.(2019). Sediment geochemistry and mineralogy from a glacial terrain river system in southwest Iceland, Geochim. Cosmochim. Ac., 263, 140–166,DOI: https://doi.org/10.1016/j.gca.2019.08.003. ↩