CONSOL Energy has signed on to a legal settlement that marks the first time a coal company has agreed to clean up conductivity pollution associated with a valley fill.

An environmental group lawyer said that under the deal, CONSOL could eventually be forced to install an expensive treatment system to clean up water quality violations in Boardtree Branch related to the subsidiary Fola Coal's Surface Mine No 3 in Clay and Nicholas counties.

The settlement, which requires approval from US District Judge John T Copenhaver, resolves a lawsuit filed by the Sierra Club and the West Virginia Highlands Conservancy in October 2010.

Lawyers for the groups alleged that the mine was discharging pollutants that cause acute and chronic toxicity and biological impairment to the aquatic life in Boardtree Branch. The suit cited the state's narrative water quality standard, meant to protect aquatic life, and increased electrical conductivity related to the mine's pollution.

Scientists use electrical conductivity as a key indicator of stream health and the presence of other important pollutants such as chlorides, sulfides and dissolved solids. Recent research has found increased conductivity downstream from mining operations in Appalachia and scientists have linked impaired aquatic life to those increased conductivity levels.

Both the US Environmental Protection Agency and the state Environmental Quality Board have cited conductivity increases downstream from mining operations as a key problem the state Department of Environmental Protection isn't doing enough about.

Under the settlement, CONSOL will first be able to try its own version of a stream restoration project, involving creation of a floodplain and sulfate-reducing wetlands, to clean up about 3,000 feet of Boardtree Branch. Biological samples will be taken after the project and an independent biologist will decide if aquatic life has improved.

The settlement said that if the CONSOL project doesn't work, the company will be on the hook to build a more expensive treatment system at the site.

Mr Joe Lovett of Appalachian Mountain Advocates a lawyer for citizen groups that filed the case said that "It's significant because for the first time a coal operator has agreed to comply with the narrative water quality standard related to a valley fill. It's scientifically indisputable that valley fills cause high conductivity and impair life in streams. This coal company has agreed to remedy that."