TEN-YEAR DEMONSTRATION OF ALTERNATE CONCENTRATION LIMITS FOR GROUNDWATER

A risk-based corrective action (RBCA) approach was utilized to determine whether human health and the environment could be adequately protected by employing alternate concentration limits (ACLs) for groundwater downgradient from two waste management units. The ACL demonstration was prepared in 1987 for a southeastern manufacturing facility which maintains two previously closed RCRA-regulated hazardous waste units: a stabilized, encapsulated closure cell; and a wastewater surface impoundment. Twenty-three Appendix IX hazardous constituents were detected in groundwater, including metals, pesticides, and solvents. The site is located adjacent to a major, flow-regulated river. The uppermost aquifer flow discharges to the river.This paper summarizes the approach used in preparing an ACL demonstration and demonstrating compliance for a large chemical manufacturing facility in the southeast. The most recent federal and state guidance documents available at that time were used in preparing the ACL demonstration. The ACLs were subsequently approved by U.S. EPA and the state regulatory agency. This RBCA approach precluded the need for potential long-term groundwater corrective action, with savings in excess of 1 million. Groundwater and surface water monitoring programs on a quarterly frequency over ten years have demonstrated compliance with the ACLs at the point of compliance (POC), as well as the absence of statistically significant impacts at the point of exposure (POE) in the river.