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Daniel J Goode
Thomas E Imbrigiotta
Pierre J Lacombe
Allen M Shapiro
Claire R Tiedeman
U.S. Geological Survey

Abstract

Pump-and-treat remediation, a widely used and often effective approach in porous formations, has been applied to fractured-rock aquifers with limited success. Contaminants can remain at high concentrations after years of pumping. The distribution of contaminants, whether in open fractures, or in the rock matrix, or sorbed onto aquifer media, is a critical factor in the effectiveness of pump-and-treat remediation. While significant resources have been focused on measuring dissolved concentrations in water pumped from high-permeability fractures, new approaches are needed to quantify contaminant mass in lower-permeability, or diffusion-controlled, parts of fractured-rock formations.

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 aqueous-phase chlorinated solvents by pumping, monitored natural attenuation, and bioaugmentation in fractured-rock aquifers. The investigation is being conducted at the former Naval Air Warfare Center (NAWC), West Trenton, NJ, where trichloroethene (TCE), used for heat exchange, migrated from land surface into underlying fractured mudstones of the Newark Basin. Dissolved TCE has been observed at depths down to 60 meters below land surface. A pump-and-treat system has operated since the mid-1990s; however, TCE concentrations in many bedrock boreholes have remained relatively constant; highest current concentrations are about 106,000 micrograms per liter.

Research progress is reported on screening methods for detection of pure phase TCE (a dense, non-aqueous-phase liquid, or DNAPL), bulk rock core measurements of TCE and related compounds, and in situ measurement of diffusion from the rock matrix into boreholes. Vapor monitoring of rock cuttings, oil shake tests, and cloth impregnated with hydrophobic dye were used to positively identify DNAPL presence during drilling. Bulk rock core measurements quantify the contaminant mass that has diffused into, or sorbed onto, the rock matrix. Assuming all TCE mass is dissolved in the pore water, concentrations range from below detection to saturation, and concentrations change significantly with small changes in depth. Diffusion rates are measured in situ in wells or isolated intervals having low permeability by removing contaminants from the water column in the borehole and measuring the transient concentration response. Determination of bulk diffusion rates in the field allows realistic assessment of contaminant removal rates and prediction of clean-up times for pump-and-treat remediation. Diffusion rates may also be important for assessing the effectiveness of other remediation approaches that require transport of contaminants or amendments at fractured-rock sites.

Citation: Goode, D.J., Imbrigiotta, T.E., Lacombe, P.J., Shapiro, A.M., and Tiedeman, C.R., 2008, Distribution of trichloroethene in a fractured-rock aquifer: Detection of pure phase, core measurements, diffusion into boreholes, and implications for pump-and-treat remediation (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), December 2-4, 2008, Washington, DC. (http://pa.water.usgs.gov/projects/frhr/goode08.html)

Keywords: Lockatong Formation, Stockton Formation, sedimentary fractured rock, VOC solvent contamination, Ewing NJ, Mercer County NJ

To USGS Pennsylvania Fractured Rock Hydrology Research page.

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URL: http://pa.water.usgs.gov/projects/frhr/goode08.html
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To find out more about research on fractured rock hydrology in Pennsylvania, contact Daniel J Goode
|| E-mail: djgoode@usgs.gov || Phone: (610) 321-2434 x203 || Fax: (610) 321-2509 ||
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