ASARCO, INC., OWNS AND OPERATES A COPPER MINE AND PROCESSING PLANT IN PINAL COUNTY, NEAR THE TOWN OF KELVIN IN THE STATE OF ARIZONA. IN THE PAST FOUR YEARS, ASARCO HAS HAD SIXTEEN DISCHARGES OF POLLUTANTS FROM THE RAY MINE FACILITY TO THE GILA RIVER AND ITS TRIBUTARIES. TWELVE OF THE SIXTEEN DISCHARGES ARE NOT AUTHORIZED BY THE FACILITY'S NPDES PERMIT, WHICH PROHIBITS THE DISCHARGE OF PROCESS WASTEWATER POLLUTANTS FROM THE MINE PLANT'S WASTE CONTROL FACILITIES TO WATERS OF THE UNITED STATES. THE ONLY EXCEPTION TO THIS NO-DISCHARGE PROHIBITION IS WHEN THERE IS AN OVERFLOW FROM THESE FACILITIES RESULTING FROM OVER 3.05 INCHES OF RAIN DURING 24 HOURS. THE OTHER FOUR DISCHARGES, WHILE ARGUABLY NOT SUBJECT TO THE NO-DISCHARGE LIMITATION OF THE PERMIT, VIOLATED EFFLUENT LIMITATIONS AND RECEIVING WATER QUALITY STANDARDS CONTAINED IN THE PERMIT. ASARCO ALSO VIOLATED MONITORING AND REPORTING REQUIREMENTS LISTED IN THE PERMIT.