Methods for Determining Compliance with Groundwater Quality Regulations at Waste Disposal Facilities

1.0 Overview: The groundwater resources in the State of Wisconsin are protected by the Wisconsin Department of Natural Resources (DNR). Groundwater quality standards are established under Chapter NR 140 of the Wisconsin Administrative Code (Wisconsin DNR, 1988). Also addressed in NR 140 are statistical methods for 1) evaluating background (clean) water quality and 2) determining exceedance of a water quality standard or finding an environmentally significant change in water quality. In this paper we address the complex issue of how to “defensibly” establish background water quality at waste disposal facilities, and subsequently how to “defensibly” discern standard exceedances and/or significant water quality changes. “Defensibly” is meant to imply that the technical approach should be acceptable to concerned parties and, if necessary, in a court of law. In the regulatory context, the intent of this study is to evaluate alternative analytic methods to meet the objectives of NR 140. Analytic techniques are also evaluated with respect to existing and proposed federal regulations for hazardous waste facilities and for municipal solid waste landfills. While the focus of this paper is on solid waste disposal facilities, the techniques are also applicable to most types of hazardous waste sites, land disposal systems and storage facilities.