Eligible technologies

Project type

In addition to the general Rainbow requirements outlined in the Rainbow Standard Rules, eligible projects must:

• Spread eligible feedstock rocks on eligible sites to generate alkalinity and drive net carbon removals.

• Demonstrate capability to perform MRV as agreed upon in the validated project documentation (PDD and Monitoring Plan).

• Demonstrate a net-negative project carbon footprint based on initial LCA estimates of induced emissions and initial modeled CDR estimates.

Project scope

One project shall be defined as any spreading activities within eligible sites within the project lifetime (i.e. the crediting period), and all removal that occurs as a result of that spreading over the project lifetime, plus the upstream/downstream activities associated with that spreading (e.g. GHG emissions from rock souring, transport...).

Projects certified under this methodology shall have a maximum crediting period duration of 10 years, which can be renewed for a total of 20 years. See the Crediting Period Renewal section of the Procedures Manual for procedural details.

Eligible sites

Rocks shall be spread on soils already affected by human activity, including but not limited to agricultural fields, forests, prairies, golf courses, and parks. There is no predefined maximum area of a project: spreading sites must be within the same administrative, jurisdictional and geographic area.

See the Site characterization section for measurement requirements.

Eligible feedstock

Eligible types of feedstock are silicate rocks that also contain alkaline materials. This includes minerals such as olivine, pyroxene, and plagioclase feldspar, and rocks such as basalt, dunite and peridotite. Removals from carbonate feedstocks are currently excluded, but may be added in future revisions of the present methodology.

The quantity of feedstock applied must comply with jurisdictional regulations on nutrient and metal additions to soils (e.g., national fertilizer guidelines). The frequency of application is determined by the Project Developer but is restricted to the extent that a robust sampling and MRV plan can effectively distinguish overlapping weathering signals from successive spreading events.

See the Feedstock characterization section for measurement requirements.

Retroactive project eligibility

Projects that spread feedstock before or shortly after the publication of this methodology may deviate from its requirements but remain eligible for Rainbow certification. Eligibility is determined on a case-by-case basis, with such projects labeled "Retroactively approved" on the registry. The aim is to be inclusive in a field with rapidly evolving scientific knowledge and best-practices, and to support Project Developers in upgrading their deployment setup and/or MRV approach.

The following minimum requirements must still be met:

• Demonstrate a statistically significant weathering signal between treatment and representative control plots.

• Estimate and deduct far-field zone (FFZ) carbon loss.

• Estimate and deduct project-induced emissions.

• Demonstrate a net-negative project carbon footprint based on initial LCA estimates of induced emissions and modeled CDR estimates.

• Provide sufficient documentation of past activities (e.g., feedstock sourcing and spreading, sampling protocols, locations).

Project Developers must:

• Identify which requirements they currently meet, which they will meet in the future, and which are impossible to meet due to project timing (e.g., pre-spreading measurements).

• Outline their timeline and approach for future compliance.

• Detail the implications of non-compliance on quantification uncertainty, environmental and social risks, and any remediation or conservative measures taken.

Any new spreading events or site expansions in subsequent years of the crediting period must fully comply with this methodology.