PHOENIX OWNS AND OPERATES THE PHOENIX 23RD AVENUE WASTEWATER TREATMENT PLANT AND THE PHOENIX 91ST AVENUE WASTEWATER TREATMENT PLANT. EACH PLANT TREATS INDUSTRIAL AND DOMESTIC SEWAGE FROM SOURCES IN PHOENIX. THE 91ST AVENUE PLANT ALSO TREATS INDUSTRIAL AND DOMESTIC SOURCES FROM SEVERAL NEARBY MUNICIPALITIES. IN 1984, EPA REVISED THE NPDES PERMITS APPLICABLE TO EACH PLANT IN ORDER TO REQUIRE THE CITY TO IMPLEMENT A PROGRAM GOVERNING THE PRETREATMENT OF INDUSTRIAL WASTES DISCHARGED INTO THE RESPECTIVE PLANT'S COLLECTION SYSTEM. PHOENIX HAS FAILED TO IMPLEMENT ITS PRETREATMENT PROGRAM, AND HAS VIOLATED EFFLUENT LIMITS RELATED TO COPPER, CADMIUM AND TOXICITY.