Pennsylvania Water Science Center



Fractured Rock Hydrology Research

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Dan Goode
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In cooperation with the Strategic Environmental Research and Development Program

Changes in distribution of trichloroethene and other contaminants in fractures and the rock matrix during bioaugmentation at the former Naval Air Warfare Center, West Trenton, N.J. (Goode & others, 2011)

by Daniel J Goode, Thomas E Imbrigiotta, Pierre J Lacombe, Claire R Tiedeman, Steven Walker, and Matthew A Miller

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 underway at the former Naval Air Warfare Center, West Trenton, NJ, where trichloroethene (TCE) migrated from land surface into underlying fractured mudstones of the Newark Basin, and where hydraulic containment by pumping has been ongoing for 16 years. Concentrations in 297 rock core samples collected from five coreholes (ranging in depth from 2.7 to 52 m) are used to delineate the mass distribution of TCE and other contaminants and to evaluate the effect of bioaugmentation on these contaminants in the rock matrix.

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 were detected in all core samples collected in the contaminated area from the shallow weathered zone and the underlying shallow, 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. Concentrations were below detection limits in many core samples of unfractured massive mudstone more than 15 meters below land surface.

Representative aqueous-phase concentrations of TCE are identified for water in fractures, using water-quality samples collected during coring and by pumping from nearby multi-level monitoring wells. These aqueous-phase concentrations and concentrations in methanol extractions from rock core are correlated with a detailed lithostratigraphic model. The mass distribution is calculated for a volume of aquifer associated with a bioaugmentation experiment area where hydraulic and tracer tests have been conducted. Using average rock bulk density and assumed porosities for permeable fractures, it is estimated that more than 99 percent of the TCE mass in the bioaugmentation experiment area in unweathered bedrock was contained in or adsorbed to the rock matrix. In this area, about half of the total TCE mass was in the weathered zone, above the competent-rock fracture flow zone affected by bioaugmentation amendments. The effect of bioaugmentation amendments on TCE in the rock matrix is evaluated by comparison of rock cores sampled before inoculation to recently-analyzed rock core collected almost two years after inoculation.

Citation: Goode, D.J., Imbrigiotta, T.E., Lacombe, P.J., Tiedeman, C.R., Walker, Steven, and Miller, M.A., 2011, Changes in distribution of trichloroethene and other contaminants in fractures and the rock matrix during bioaugmentation 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 29 - December 1, 2011, Washington, DC. (/projects/frhr/goode2011.php)

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