Unsaturated-Zone Air Flow at Picatinny Arsenal, New Jersey: Implications for Natural Remediation of the Trichloroethylene-Contaminated Aquifer

By James A. Smith, Whitney Katchmark, Jee-Won Choi, and Fred D. Tillman, Jr.

ABSTRACT

The purpose of this study is to determine if natural atmospheric pressure variations contribute to unsaturated-zone air flow and the intrinsic remediation of trichloroethylene (TCE) in shallow ground water and the unsaturated zone at Picatinny Arsenal, New Jersey. Air pressure, temperature, and moisture content were measured as functions of depth and time at a location approximately above the center of the TCE ground-water plume during dry periods in August and October, 1996. Significant air-pressure gradients between the subsurface and the atmosphere were observed, but air pressures at depths between 0.5 to 1.7 m showed little variation at any given sampling time. Soil moisture content was relatively constant in time, with the highest moisture contents observed for the top 15-cm of soil. Attempts to simulate subsurface air pressures in response to changing atmospheric pressures were largely unsuccessful, even when two distinct subsurface air-permeability zones were used. Based on these results, the following conclusions were made: i) air flow is occurring in the unsaturated zone; ii) unsaturated zone air flow likely influences the transport of TCE vapors; iii) unsaturated-zone air flow cannot solely be explained by one-dimensional (vertical) air flow driven by atmospheric-pressure variations.