In cooperation with the Strategic Environmental Research and Development Program
Field-scale borehole diffusion experiments at the former Naval Air Warfare Center, West Trenton, New Jersey
by Daniel J Goode,
Thomas E Imbrigiotta, and Allen M Shapiro
The U.S. Geological Survey, in cooperation with the U.S. Navy and the Strategic Environmental Research and Development Program, is conducting multidisciplinary investigations of the distribution and fate of chlorinated volatile organic compounds (CVOCs) in gently-dipping fractured mudstones that underlie the former Naval Air Warfare Center (NAWC), West Trenton, N.J. The site is underlain primarily by mudstones of the Triassic Lockatong Formation of the Newark Basin, in which bedding-plane fractures and thin fissile or laminated strata are transport paths. High concentrations of CVOCs in rock core show that most contaminant mass lies in less-permeable fractured rock and in the primary porosity of unfractured rock. Diffusion characteristics in low-permeability areas limit the effectiveness of pump-and-treat and enhanced bioremediation. Field diffusion experiments in two low-yield boreholes at NAWC were conducted by replacing borehole fluid with tap water. CVOC concentrations were measured in pumped samples and downhole fluid specific conductance was continuously recorded. Increasing conductance for about 4 months was well-matched by an analytical solution of radial diffusion. The model fit for both boreholes yielded an effective field-scale bulk diffusion coefficient of about 10-4 m2/day, on the order of the free-water diffusion coefficient. This result is inconsistent with the typical reduction by an order of magnitude or more in effective diffusion coefficient caused by the formation tortuosity. The fitted porosity at one borehole, 5 percent, was consistent with direct measurements of rock core porosity, but the 35 percent porosity at the other borehole was substantially higher than those results. Further analysis of these experimental data will include effects of sorption and other processes that may be important for diffusion and remediation of CVOCs at the NAWC site, and other sites underlain by low-permeability sedimentary formations.
Citation: Goode, D.J., Imbrigiotta, T.E., and Shapiro, A.M., 2011, Field-scale borehole diffusion experiments at the former Naval Air Warfare Center, West Trenton, New Jersey (abstract): National Ground Water Association Focus Conference on Fractured Rock and Eastern Groundwater Regional Issues, September 26-27, 2011, Burlington, Vermont. (/projects/frhr/goode2011b.php)