- Frontier buyers will pay CarbonRun $25.4 million to remove 55,442 tons of CO₂ between 2025 and 2029.
- River liming brings significant co-benefits and can reach <$100/ton without new technical breakthroughs.
Frontier has facilitated offtake agreements with CarbonRun, a Canadian company using a well-established method of river de-acidification called river liming for carbon removal. Frontier buyers will pay $25.4 million to permanently remove 55,442 tons of CO₂ between 2025 and 2029 at multiple sites, starting with deployments in Nova Scotia, Canada. This is the first carbon removal offtake via river liming.
River liming adds crushed up limestone (alkalinity) to acidified rivers to repair the damage caused by acid rain. It was successful in treating the acid rain problem in Scandinavia. Due to increased costs, the practice is in a state of decline, with many applicable regions having to cease or reduce river liming activities. CarbonRun discovered that adding limestone also boosts rivers’ natural ability to extract CO₂ from the air. The atmospheric and land-based carbon found in rivers combines with the limestone to produce bicarbonate. Bicarbonate in the river water makes its way to the open ocean for permanent storage.
The Frontier offtake focuses on rivers acidified by pollution and climate change, where river liming has both carbon removal and ecosystem benefits such as salmon and shellfish population restoration. Expanding river liming to pH-neutral rivers would give this approach the potential to reach gigaton scale. To that end, Stripe is making an additional $1M R&D grant for CarbonRun to better understand the potential of river liming to remove carbon and benefit ecosystems in neutral pH rivers.
CarbonRun’s method of removing CO₂ via river liming
The case for CarbonRun
CarbonRun’s approach is compelling for a number of reasons:
CarbonRun has a credible, near-term trajectory to less than $100/ton: Limestone is widely available and cheap. Limestone dosers are a simple, inexpensive and proven technology which makes R&D costs minimal. They’re easy to operate and can largely be automated, limiting labor costs.
Measurement is relatively straightforward: Rivers allow for direct measurement of the water's chemistry to be taken both upstream and downstream of a treatment point. This allows for relatively accurate measurement of CO₂ removal without having to rely on nascent scientific models.
River liming is a well understood practice: River and lake liming practices were originally developed as a conservation practice and successful in remediating the effects of acid rain. Liming programs helped restore river health and in many cases improved salmon stock in previously impacted rivers, but only operate at small scale now. Importantly this means the technological roadmap for scaling this approach does not require new engineering.
The team brings a unique blend of expertise: They are the only team in the world that has combined expertise in river liming for carbon removal and for river ecology, especially salmon rehabilitation.
The community engagement approach is best-in-class, which facilitates fast scaling: CarbonRun has a chorus of support from local governments, First Nations groups, and environmental organizations. Their community benefits plan (that we’re making publicly available) involves local communities and First Nations communities in the site selection process, project design and the sharing of project data.
River liming is a new carbon removal pathway that has received little attention or financial support to date. This offtake will enable the data collection necessary to understand how quickly limestone dissolves and how much can be safely added to different types of rivers. This approach is part of a broader pathway for carbon removal through ocean deacidification. To help buyers responsibly evaluate these approaches, we’ve put together a marine carbon removal buyer’s guide.
Frontier has facilitated purchases on behalf of Frontier founding members Stripe, Alphabet, Shopify, and McKinsey Sustainability as well as Autodesk, H&M Group, JPMorganChase, Workday and Salesforce. Also, Aledade, Canva, Match Group, Samsara, SKIMS, Skyscanner, Wise, and Zendesk have purchased via Watershed's partnership with Frontier.
Nan Ransohoff, Head of Frontier: “River liming for carbon removal is cheap, scalable, and measurable. And yet it’s underexplored and underfunded relative to its potential. Moreover, CarbonRun’s work will help establish the foundation for more rigorous evaluation and measurement of aquatic approaches to carbon removal more broadly.”
Luke Connell, Cofounder and CEO, CarbonRun: “Beyond removing tons of CO₂, this offtake will enable us to do the research on river liming’s potential in different kinds of rivers. Those findings will make the difference between a pathway that is promising into one we can potentially deploy safely and at scale, putting it on the map as a serious contender for gigaton-scale carbon removal."