On November 15, 2013, the Environmental Protection Agency (EPA) issued a highly anticipated decision on Kentucky's proposed revisions to its water quality standard for selenium.  Specifically, EPA approved Kentucky's novel fish tissue-based chronic criterion but disapproved its revised acute criterion. This revision process has been closely watched by industry groups, environmental organizations, and several other states that are expected to follow Kentucky's lead and propose similar revisions to their selenium standards.

Selenium is a naturally occurring element that is released through a variety of activities, including agriculture, coal-fired power generation, and coal mining. High levels of selenium have been linked to adverse effects on aquatic species. Water quality criteria play an important role in implementing water permitting requirements and other programs under the Clean Water Act. States establish their own water quality criteria, but the EPA must approve any revisions before they take effect in the state.

Most significantly, EPA approved Kentucky's cutting-edge proposed criterion for chronic (long-term) effects of selenium. The new standard is expressed in terms of an allowable concentration of selenium in the tissue of fish, instead of the traditional limit on the concentration of selenium in the water. The new chronic selenium criterion will be implemented through a two-step process:  exceeding a concentration of 5 µg/L in the water will trigger a requirement to test selenium levels in fish tissue to compare against the 8.6 µg/g tissue standard. 

Kentucky's previous water quality criteria for selenium were based on recommended limits set by EPA, which have been widely criticized, and have not been updated in over a decade. EPA agreed that Kentucky's proposed revision to the chronic criterion reflects the latest scientific research into the long-term effects of selenium, and is protective of aquatic species. The former water concentration-based chronic criterion of 5 µg/L proved particularly difficult to meet for large-scale coal mining operations, leading to a flood of lawsuits by environmental groups.  The acute, or short-term, selenium criterion will remain at 20 µg/L after EPA disapproved Kentucky's revision to that value.

The proposed changes to Kentucky's selenium water quality standard were strongly supported by the mining industry, as well as representatives from the manufacturing and construction industries. Several environmental groups opposed the changes, and may seek to challenge EPA's approval in court. Now that EPA has weighed in on Kentucky's proposed standards, other Appalachian states like Ohio, Virginia, and West Virginia are expected to propose similar revisions to their states' selenium standards