EPA BELIEVES THAT THE HEAVY METALS CONTENT OF TAILINGS AND SLUDGES FOUND AT THE SITE, SPECIFICALLY LEAD AND ARSENIC, MAY BE RELATED TO GROUND WATER CONTAMINATION IN THE AREA. THE RESERVOIR WAS CONSTRUCTED IN 1965 TO SERVE AS A SURGE BASIN FOR EXCESS LEACH WATERS AND TO COLLECT AND STORE STORMWATER RUNOFF FROM AREAS IN BINGHAM CANYON. THE SEDIMENTS ACCUMULATED IN THE RESERVOIR ARE COMPOSED OF SLUDGE FROM LEACH WATER AND PREEXISTING TAILINGS. THE SLUDGE AND TAILINGS CONTAIN HEAVY METALS.