Pennsylvania Water Science Center



Fractured Rock Hydrology Research

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Dan Goode
(djgoode@usgs.gov)

 

In cooperation with the Strategic Environmental Research and Development Program

Mass of trichloroethene and other contaminants in the rock matrix and estimates of diffusion coefficients and rates at the former Naval Air Warfare Center, West Trenton, N.J. (Goode & others, 2010)

by Daniel J. Goode, Thomas E. Imbrigiotta, Pierre J. Lacombe, Allen M. Shapiro, and Claire R. Tiedeman

Abstract

The U.S. Geological Survey, with the support of SERDP (ER-1555) and the U.S. Navy, is developing field techniques and interpretive methods to evaluate mass removal of chlorinated-solvent contaminants by pumping, monitored natural attenuation, and bioaugmentation in fractured-rock aquifers. A field investigation is being conducted at the former Naval Air Warfare Center, West Trenton, NJ, where trichloroethene (TCE), used for heat exchange, migrated from land surface into underlying fractured mudstones of the Newark Basin, and where hydraulic containment by pumping has been ongoing for 15 years. Remediation technologies that rely on removal of mass in the dissolved phase, or delivery of amendments via flow in fractures, may have limited effectiveness at sites with large mass in the rock matrix, and with low bulk diffusion rates. Research progress is reported on bulk rock core measurements of TCE and related compounds, and in situ measurement of diffusion from the rock matrix into boreholes.

Measured concentrations of TCE and other contaminants in rock core suggest that highly fractured and weathered bedrock near the land surface has undergone extensive contact with pure-phase TCE and high aqueous-phase concentrations. TCE and its degradation daughter products are detected in all samples from the shallow weathered zone and the underlying highly fractured bedrock. In deeper strata, fractures are less frequent and the high contaminant concentrations in the rock matrix are associated with relatively high-transmissivity fractures. Contaminants are below detection in many samples of unfractured massive mudstone more than 15 meters below land surface. Using a detailed lithostratigraphic model, it is estimated that more than 90 percent of the contaminant mass in a bioaugmentation experiment area is contained in or adsorbed to the rock matrix.

Borehole diffusion tests in two low-yield monitoring wells provide data on diffusion rates and coefficients. At the beginning of each test, all water in each borehole was replaced with water having different specific conductivity (SC). SC was monitored continuously, and TCE sampled periodically, as constituents diffused into and out of the borehole. After four months, the recovery of SC to pre-test levels was about 80 percent complete. Field-scale effective bulk diffusion coefficients are estimated using a borehole diffusion model that assumes negligible advection, and accounts for sorption. Determination of diffusion rates in the field allows realistic assessment of contaminant delivery to fractures and prediction of clean-up times for pump-and-treat and other remediation technologies in fractured-rock aquifers.

Citation: Goode, D.J., Imbrigiotta, T.E., Lacombe, P.J., Shapiro, A.M., and Tiedeman, C.R., 2010, Mass of trichloroethene and other contaminants in the rock matrix and estimates of diffusion coefficients and rates at the former Naval Air Warfare Center, West Trenton, N.J. (abstract): SERDP/ESTCP Partners in Environmental Technology Technical Symposium and Workshop, Strategic Environmental Research and Development Program (SERDP) and Environmental Security Technology Certification Program (ESTCP), November 30 -- December 2, 2010, Washington, DC. (/projects/frhr/goode10.php)

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