-RESPONDENTS IN THIS MATTER HAV OWNED OR OPERATED, AN ELECTROPLATING OPERATION IN RAPID CITY, S.D. RESPONDENTS DISHCHRGED OVERFLOW FROM ITS FINAL RINSE TANK ON-SITE FROM THE TIME IT BEGAN OPERATIONS UNTIL SOMETIME BETWEEN JULY 17 AND SEPTEMBER 30, 1985. THE OVERFLOW WAS INITIALLY DISCHARGED INTO A DRAIN FIELD AT THE FACILITY. AFTER MAY 1985, THE OVERFLOW WAS DISCHARGED TO AN ABANDONED WILL LOCATED NE THE FACILITY BUILDING. SOMETIME BETWEEN JULY 17, 1985 AND SEPTMEBER 30, 1985, RESPONDENT STOPPED DISCHARGING THE RINSE TANK INTO THE ABANDONED WILL AND THE AGANDONED WELL WAS BACKFILLED WITH ON-SITE MATERIAL.