Description of Field Site

The field site for the air pressure studies was Picatinny Arsenal in Morris County, New Jersey, a U.S. Geological Survey Toxic Substances Hydrology Program National Research Site. The site is located in a glaciated valley on top of 50-65 m of stratified and unstratified drift, which overlies a weathered bedrock surface. The unconsolidated sediments form three major hydrogeologic units: a 15-21-m thick unconfined sand-and-gravel aquifer, an 8-21-m thick confining layer composed of fine sand, silt, and clay, and an 8-35-m thick confined sand-and-gravel aquifer (Smith et al. 1992). From 1960 to 1981, wastewater from metal-plating and degreasing operations was discharged into two unlined wastewater lagoons and an unlined overflow dry well adjacent to building 24 (Figure 9). As a result, several chlorinated organic compounds, including trichloroethene (TCE), have contaminated the unconfined sand and gravel aquifer that underlies the site. The unsaturated zone is 2-4 m thick over most of the study area (Smith et al. 1992) and TCE has been detected in the vadose-zone water and soil gas at the site (Smith et al. 1990)). This site was chosen for study because of extensive previous characterization of the unsaturated zone (Smith et al. 1990; Smith et al. 1996) and the presence of primarily a single organic contaminant. A location above the TCE-contaminated ground-water plume at Picatinny Arsenal was chosen (Figure 9) with an unsaturated zone composed of medium-to-course sand with low organic-carbon content ranging from 0.08% (Choi 1999) to 1.02% (Sahoo and Smith 1997) and a thickness of 2.2-2.3m.

EXPLANATION ^

TCE ground-water concentrations greater than IQug/L H Pump-ancf-treat remedial fori well

1 Field Instrumentation site o , , FEET

0 100 METERS

Green Pgrrd Bmnk

EXPLANATION ^

TCE ground-water concentrations greater than IQug/L H Pump-ancf-treat remedial fori well

1 Field Instrumentation site o , , FEET

0 100 METERS

Figure 9. Map of field site at Picatinny Arsenal, NJ showing the location of 10 jjg'L trichloroethene (TCE) plume boundary, subsurface air pressure and moisture content sampling site, and withdrawal wells for the pump-and-treat remediation system.

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