Strategies for Complying With Limits for Toxic Metals in NPDES Permits, 1994 Environmental Conference Proceedings

Gerald L. Bills, Dr. James Albrecht

The US. Environmental Protection Agency has established national ambient water quality criteria for several metals to protect freshwater and saltwater organisms from acute and chronic toxicity. As a result many wastewater dischargers are being issued metals limits for their discharge. The proposed limits can be difficult if not impossible to routinely meet. Several strategies can be used to determine if there is a need for a metal limit to protect water quality.

Metal limits, although proposed for a permit, may not be needed if accurate sampling and analytical techniques are used to determine effluent and/or background concentrations.

The national ambient criteria for metals are very conservative and can be based on very few data points. The national ambient criterion metals should be thought of as default, worst case criteria. The US EPA has published several procedures to develop site specific criteria. These procedures include a recalculation procedure, indicator species procedure and a resident species procedure.

Each of these strategies should be examined and evaluated before accepting a metal limit.