Agricultural company Archer-Daniels-Midland (ADM) has halted its injection of carbon dioxide (CO2) at its ethanol plant in Decatur, Illinois, after the discovery of a potential underground leak, Reuters reported Wednesday.

ADM’s CO2 storage project has received $281 million in taxpayer dollars via Department of Energy grants, with department officials touting it as “the largest demonstration of its kind in the U.S.” U.S. Environmental Protection Agency records show that as of April it had stored nearly 4 million metric tons of CO2 since 2011.

However, on Sept. 24, ADM detected the movement of brine among different geologic formations deep underground, indicating a potential leak, Reuters reported. An ADM spokesperson told the news agency that the company is pausing CO2 injections to conduct additional tests.

Last month, the U.S. Environmental Protection Agency found that ADM had violated federal safe drinking water rules meant to protect groundwater after a leak from one of the facility’s monitoring wells, according to Reuters.

A previous Oil & Gas Watch News review of EPA data found that the ADM facility is only capturing and storing 10-12 percent of facility-wide emissions, raising questions about whether industrial-scale carbon capture technology can be a meaningful solution to climate change.