Results of 2001 Groundwater Sampling in Support of Conditional No Longer Contained-In Determination for the Snake River Plain Aquifer in the Vicinity of the Idaho Nuclear Technology and Engineering Center

Abstract

Based on the results of the October sampling of the five indicator wells, the cumulative cancer risk associated with organic constituents is below the 1E-05 cumulative risk required by the DEQ for the NLCI determination.For metal constituents, cumulative risk is determined solely from arsenic, since arsenic is the only metal with the PRG based on a cancer risk. During the October sampling, arsenic was detected in two of the indicator wells (i.e., USGS-038 and USGS-047) at concentrations in excess of those associated with a 1E-05 risk. Arsenic was not detected in any of the five indicator wells during the April 2001 sampling. While the concentrations of arsenic detected in the two indicator wells exceeded the concentrations associated with a 1E-05 risk, the concentrations are within levels historically detected in the Snake River Plain Aquifer (SRPA) and do not necessarily indicate an impact from INTEC operations. In addition, the concentrations of arsenic detected in USGS-038 and iv USGS-047 in October 2001 were both below the recently adopted drinking water standard of 10 µg/L.