An analysis of soil arsenic records of decision.

In 1986 the US EPA created the National Priority List (NPL) that now comprises in excess of 2,000 sites nationwide, with arsenic the second most common inorganic constituent. A survey of 69 Records of Decision (RODs) written between 1985 and 1998 for which arsenic was a major driver found that 84% of cleanup goals were risk-driven and 16% were background-driven, with a wide range of soil-arsenic cleanup standards for 10(-6) residential risk goals (2-305 mg/kg). In comparison, the range of background-based cleanup goals was much narrower (8-21 mg/kg). ROD soil arsenic concentrations exhibit no statistically significanttemporal trend, but on a geographic basis, EPA Regions 6, 8, 9, and 10 had some of the higher decisions. The risk assessment process is important in defining cleanup goals; however routine use of site-specific variables (i.e., bioavailability, realistic tenure in both residential and occupational settings, natural attenuation of arsenic in groundwater, etc.) is necessary to ensure an accurate assessment of potential site risks and to preclude over-remediation that may result from the use of default risk variables.