Should Category 5 include an impaired water if the specific pollutant causing the impairment has not been identified?
States are required to identify the pollutant causing the impairment or threat for each water/pollutant combination in Category 5 (40 CFR 130.7(d)). States should include impaired and threatened waters in Category 5 when a water is shown to be impaired or threatened in relation to biological assessments used to evaluate aquatic life uses or narrative or numeric criteria adopted to protect those uses even if the specific pollutant is not known. These waters should be listed unless the State can demonstrate that non-pollutant stressors cause the impairment, or that no pollutant(s) causes or contribute to the impairment. Prior to establishing a TMDL for such waters, the pollutant causing the impairment would need to be identified. EPA has developed guidance to assist States in identifying the causes of a biological impairment. This document, “Stressor Identification Guidance,” was released in December 2000 (EPA 822-B-00-025). This document is also available on the Internet at: http://www.
