THE NORTHWESTERN STATES PORTLAND CEMENT COMPANY (NWSPCC) SITE IS LOCATED ADJACENT TO UNITED STATES HIGHWAY 65 IN THE NORTHERN SECTION OF MASON CITY, IOWA. IT IS LOCATED JUST ACROSS THE ROAD FROM LEHIGH PORTLAND CEMENT COMPANY, WHICH IS ALSO A SUPERFUND SITE. CALMUS CREEK FLOWS BETWEEN THE TWO CEMENT PLANTS AND THEN INTO THE WINNEBAGO RIVER EAST OF THE TWO FACILITIES. IN 1950, NWSPCC CEASED LIMESTONE MINING OPERATIONS AT THE QUARRY WEST OF THE PLANT. THE WEST QUARRY HAD REACHED A DEPTH OF APPROXIMATELY 40 FEET AND COVERED ABOUT 150 ACRES. IN 1969, NWSPCC BEGAN USING THE WEST QUARRY FOR THE DISPOSAL OF WASTE KILN DUST. IN 1979 TWO SEEPS EMERGED INTO CALMUS CREEK FROM THE NORTHEASTERN PORTION OF THE PARTIALLY FILLED WEST QUARRY. WHEN DISPOSAL ACTIVITIES CEASED IN 1985, APPROXIMATELY TWO MILLION TONS OF KILN DUST HAD BEEN PLACED IN THE QUARRY AND THE QUARRY'S UNFILLED AREA HAD BEEN REDUCED TO APPROXIMATELY 40 ACRES. WASTE KILN DUST IS EXTREMELY CAUSTIC AND CONTAINS POTASSIUM OXIDE, CHROMUIM, IRON AND SULFATE. DURING THE PERIOD THE WEST QUARRY WAS USED FOR DISPOSAL OF WASTE KILN DUST, IT FILLED WITH APPROXIMATELY 420 MILLION GALLONS OF WATER. THE SITE SCORED A 58.15 ON EPA'S HAZARDOUS RANKING SYSTEM (A SCORE OF 28.5 IS SUFFICIENT TO PLACE A SITE ON THE NATIONAL PRIORITY LIST ?NPL?). IT WAS PROPOSED TO BE ADDED TO THE NPL IN THE FEDERAL REGISTER ON JUN