The approach
River liming is a longstanding practice of adding crushed up limestone to acidified rivers in order to raise pH. It successfully treated the acid rain problem in Scandinavia and is still commonly used to this day. In rivers acidified by pollution, this practice can generate ecosystem benefits like salmon and shellfish population restoration.
CarbonRun discovered that adding limestone to rivers also causes the drawdown of carbon dioxide from the atmosphere, constituting a new carbon removal pathway called “river alkalinity enhancement”. The limestone combines with carbon dioxide to produce bicarbonate, a stable form of carbon that then makes its way to the open ocean for permanent storage.
The case for CarbonRun
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.
Pricing and delivery
Frontier buyers’ total offtake is $25.4M to deliver 55,442 tons between 2025 and 2029. The price accounts for both the removal itself as well as measuring, reporting and verifying (MRV) that each ton is safely and permanently stored. Deliveries for this offtake will come from rivers acidified by pollution and climate change, where river liming has both carbon removal and ecosystem benefits such as salmon and shellfish population restoration.
CarbonRun scientists collecting data and samples.