Kingston Ash Release

Fish and Aquatic Life Water Quality Criteria

EPA and TDEC have established general water quality criteria for protection of fish and aquatic life in waters of the United States and Tennessee. Two criteria have been set; one for short-term exposure and another for long-term exposure.  The allowable limits for exposure to a substance in the short-term are referred to as acute exposure limits.  Long-term allowable exposure limits are called chronic exposure limits.

Acute exposure is the one-hour average concentration of a substance in the receiving water, measured at the point of discharge or outfall.  Chronic exposure is a four-day average concentration that is measured at the edge of a discharge area where initial dilution takes place, which is also known as the mixing zone.  The different exposure limits reflect the fact that fish and aquatic life can tolerate higher concentrations over a brief period of exposure than over a long, continuous period of exposure.

Visit the EPA and TDEC websites to learn more about acute and chronic exposure limits.

EPA & TDEC General Water Quality Criteria

Substance	Acute Exposure Limits (Parts per billion)	Chronic Exposure Limits (Parts per billion)
Arsenic	340	150
Cadmium*	2	.25
Copper*	13	9
Lead*	65	2.5
Mercury	1.4	.77
Selenium	20	5
Zinc*	120	120

*Acute and Chronic toxicity limits for water with 100 parts per million of hardness