ENV-95-173 RESPONDING TO WATER QUALITY CRITERIA-BASED LIMITS IN YOUR NPDES PERMIT

Description:

The federal Clean Water Act requires industrial plants to obtain National Pollutant Discharge Elimination System (NPDES) permits for discharging wastewater. These permits specify numerical limits on the mass or concentration of contaminants. Historically, as permits are renewed, these limits are made more restrictive. Permit limits can be “technology-based;” i.e., established on the basis of removal technology capability. For the petroleum refming industry and each other industrial category, the U.S. Environmental Protection Agency (U.S. EPA) determines the concentrations or mass of contaminants expected from a facility employing “best available technology economically achievable,” or BAT. U.S. EPA publishes these values as effluent guidelines for use by local permitting authorities. Permit limits can also be “water quality-based;” i.e., derived from receiving water quality criteria. Local regulatory agencies are charged with maintaining or improving water quality, with a goal of meeting national water quality standards. If a water body is determined to be out of compliance with these standards due to discharge from point sources, and BAT is fully implemented, then the permit limits for these point sources must be reduced. Water quality-based permit limits are used when technology-based limits are not sufficiently protective.