DURING THE OPERATION OF THE ANACONDA SMELTER HILL COMPLEX AND ASSOCIATED PROPERTIES, LARGE QUANTITIES OF ORE BENEFICIATION AND PROCESSING WASTES, INCLUDING TAILINGS, SLAG, AND FLUE DUST OF VARIOUS COMPOSITIONS, WERE STORED OR DISPOSED OF, AND ARE STILL LOCATED ON AND AROUND THE SITE. ON 09/28/88, ARCO AND EPA ENTERED INTO AN ADMINISTRATIVE ORDER ON CONSENT TO CONDUCT AN ENVIRONMENTAL ENGINEERING/ COST ANALYSIS STUDY AND INVESTIGATION FOR THE OLD WORKS AND COMMUNITY SOILS OPERABLE UNITS OF THE ANACONDA SMELTER SUPERFUND SITE. THIS RESULTED IN THE INVESTIGATION OF FLOODPLAIN WASTES, SURFACE WATER, GROUNDWATER, WASTES PILES IN THE OLD WORKS AREA IN 1988 THROUGH 1991. IN DECEMBER 1990, ARCO AND EPA ENTERED INTO AN AMENDMENT TO THE ADMINISTRATIVE ORDER ON CONSENT TO CONDUCT SEPARATE OLD WORKS AND COMMUNITY SOILS INVESTIGATIONS, AND TO CONDUCT ADDITIONAL SAMPLING AND TOXICITY CHARACTERISTIC ANALYSIS ON SELECTED WASTE PILES AT THE OLD WORKS. IN DECEMBER 1990, ARCO AND EPA ENTERED INTO AN AMENDMENT TO THE OLD WORKS EE/CA CONSENT ORDER TO CONDUCT SEPARATE OLD WORKS AND COMMUNITY SOILS INVESTIGATIONS. IN JUNE 1991, EPA AND ARCO AGREED TO AMEND THE OLD WORKS EE/CA CONSENT ORDER TO LIMIT THE SCOPE OF THE OLD WORKS EE/CA AND TO CONDUCT ADDITIONAL SAMPLING AND TOXICITY CHARACTERISTIC ANALYSIS ON SELECTED WASTE PILES AT THE OLD WORKS. DATA RESULTS FROM THE SAMPLING EVENTS CONFIRMED THE PRESEN