- 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 less than $100 per ton without new technical breakthroughs. - Frontier has facilitated offtake agreements for river de-acidification carbon removal through CarbonRun's use of established river liming methods. - The initiative starts with deployments in Nova Scotia, Canada, marking the first carbon removal offtake via river liming. - River liming involves adding crushed limestone to acidified rivers to mitigate the effects of acid rain. - The practice of river liming has seen success in treating acid rain problems in Scandinavia but is in decline due to increased costs. - CarbonRun found that limestone addition enhances rivers' natural ability to capture atmospheric CO₂, converting it into bicarbonate for long-term storage in oceans. - The Frontier offtake targets pollution and climate change-affected rivers, offering carbon removal alongside ecosystem restoration benefits like salmon and shellfish population recovery. - Expanding river liming could potentially scale up carbon removal efforts significantly. - Stripe is providing an additional $1 million R&D grant to investigate river liming's effectiveness in neutral pH rivers. - CarbonRun aims to achieve a credible trajectory for costs under $100 per ton due to the widespread availability and low cost of limestone. - Lime-dosing technology is simple and can be automated, limiting operational costs. - CO₂ removal measurement is facilitated by direct chemical analysis of river water both above and below treatment points. - River liming is a well-established conservation practice that restores river ecosystems and has improved salmon populations historically. - CarbonRun's team possesses unique expertise in both river liming for carbon removal and river ecology, particularly salmon rehabilitation. - The company’s community engagement is effective, involving local and Indigenous groups in project decision-making processes. - River liming as a carbon removal strategy has been underexplored and underfunded, with this initial agreement set to enhance data collection and understanding of limestone deployment in rivers. - Frontier has facilitated purchases from various organizations, including Stripe, Alphabet, and other founding members. - Nan Ransohoff from Frontier highlights river liming as a cost-effective, measurable, and scalable solution deserving of more attention and funding. - Luke Connell from CarbonRun emphasizes the importance of this offtake for researching river liming’s capabilities across different river types for future large-scale carbon removal.

Frontier buyers sign world’s first river liming carbon removal deal with CarbonRun

September 23, 2024

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.

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."