PNNL

Abstract

This paper presents a refinement and expansion of our previously described efforts to estimate contaminant plume history from observed contaminant concentration within a low-permeability aquitard at the site of a field-scale groundwater remediation experiment at Dover Air Force Base. At this site, a two-layer aquitard has been contaminated with tetrachloroethene and trichloroethene through diffusive mass transfer from an overlying contaminated aquifer. Measurements of contaminant concentration in sorption and diffusion properties of the aquitard medium, to estimate the timewise variation of the boundary concentration at the interface between the aquitard and aquifer, thus providing evidence related to the overlying plume history. In our refined analysis, we assume the contaminant source history to be function of time with unknown form, and we supplement our interpretations with a second coring result at a different location. The results demonstrate how "forensic" interpretation of this kind can provide useful and important information regarding the contaminant release history at sites of groundwater contamination and cleanup; however, the results also show that the forensic problem is a highly nonunique problem associated with potentially large uncertaninty. Interpretation of the estimated results therefore requires careful consideration in the context of other available information.