During the 1970s, water pollution regulations focused primarily on controlling conventional pollutants – oxygen-demanding materials, heat, and suspended solids. These pollutants had caused severe degradation of rivers, lakes, and streams. In response to these regulations, industries and municipalities spent billions of dollars constructing facilities to control the discharge of these pollutants. By the mid-1980s, regulators considered conventional pollution problems to be largely under control. Their focus shifted to the control of toxic chemicals and toxicity in general. The case study described here is an example of how one petroleum refinery is dealing with the need industrial waste managers are facing today – controlling toxicity in wastewater treatment plant effluent. The state regulatory agency ordered a major West Coast petroleum refinery to upgrade its wastewater treatment plant (WWTP) to meet new toxicity-based discharge requirements. The refinery’s existing WWTP has the capacity to treat 2,500 gallons per minute (gpm) of combined process and rain water flows. The new order required the refinery to treat all process water and rain water flows and to upgrade the treatment process to meet newly adopted effluent toxicity requirements.