The Environmental Protection Agency on April 1 issued guidance that for the first time provides a numeric benchmark to measure the level of salt in water affected by mountaintop mining in Appalachia. Currently, states use “narrative” standards, which do not include numeric benchmarks. The guidance, a blow to the mining industry, identifies a range of conductivity of 300-500 microSiemens per centimeter in streams affected by mining runoff.

The guidance took effect immediately but may be modified after a public comment period, EPA says. Ed Hopkins, the Sierra Club’s director of environmental programs, says the new policy will make it easier for regulators to determine safe conductivity levels in water and to deny permits when necessary.