Studies of Contaminant Diffusion in an Aquitard and Groundwater Remediation by Reactive Metals at Dover Air Force Base, Delaware

Abstract : This project focused on analysis of in-situ concentrations of chlorinated hydrocarbons in an aquitard underlying the site of a prior field-scale investigation of pump-and-treat remediation in sheet-pile "test cells" at Dover AFB, DE. Another aspect was the conduct of exploratory long-term column investigations of zero-valent metal barrier technologies, as applied to contaminated groundwater taken from the aquifer surrounding the cells. During the post-pumping period, unique conditions of zero flow were maintained within the sheet-pile enclosures. Extensive soil coring was conducted at times corresponding to roughly seven and sixteen months after the termination of the prior project. New modeling approaches were developed both to: (1) apply concentration profile information toward more accurate estimation of plume history (inverse modeling for forensic interpretation); and (2) obtain predictions of the post-pumping contaminant movement (multi-layer diffusion modeling). Results were used to: (1) test the assumption that diffusion alone affected contaminant fate, and (2) conduct additional forensic interpretations and field-scale simulations. The column investigations provided long-term verification of halogenated alkene removal under essentially in situ groundwater conditions, including continuous removal of cis-1,2-dichloroethene. Results also confirmed that dichloromethane is not removed and showed apparent breakthrough of two other chemicals, tentatively identified as dichloroethanes.