Detailed Characterization of a Technical Impracticability Zone Using Drive Point Profiling

A team of geologists and engineers conducted an investigation in a dense, non-aqueous phase liquid contaminant (DNAPL) source area at Pease Air Force Base (AFB) Installation Restoration Program Site 32. The investigation was designed to (1) demonstrate that vertical drive point profiling using techniques and equipment developed by the Waterloo Centre for Groundwater Research would work at this hydrogeologically complex site and (2) locate solute concentrations indicative of DNAPL. The original contaminant source at Site 32 was a 1,200-gallon (≅ 4500 L) underground storage tank with an overflow discharge pipe. The tank held waste solvents from aircraft maintenance in Building 113 at the former Pease AFB. The tank was removed in 1988. The overflow discharge pipe and contaminated soil under and along the pipe were removed in 1990. The results of the Site 32 Source Area Remedial Investigation/Feasibility Study indicate that solvent-related contaminants are present in soil and overburden and in bedrock groundwater and that there is a residual DNAPL source resulting in dissolved-phase groundwater contamination. Efforts to locate DNAPL using monitor wells have been unsuccessful. A limited action remedial alternative based on technical impracticability is proposed for this site. A drive point profiler was used to obtain 40 discrete interval groundwater samples from a total of five locations in nine days of field work. The drive point profiler enabled sampling of fine-grained, low permeability units in which monitor wells would not usually be installed. Samples were analyzed in a mobile laboratory for volatile organic compounds: trichloroethene, 1,2-dichloroethene, and vinyl chloride. The investigation produced useful information about the highly variable distribution of these compounds in the overburden units.