Use Of Marine-Seismic Profiling To Study Ground-Water Contamination At Aberdeen Proving Ground, Maryland

Continuous high-frequency marine-seismic profiling was used to define the extent of geologic units offshore<br>of J-Field, Aberdeen Proving Ground, Maryland, during March and April of 1988. J-Field was used by the U.S. Army<br>for disposal of chemical warfare agents, munitions, and organic solvents from the early 1920’s through the 1970’s. A<br>major concern at this site has been the discharge of contaminated ground water into offshore areas and eventually into<br>the Chesapeake Bay. A 150-foot-deep paleochannel containing Pleistocene fluvial and estuarine sediments was<br>identified from onshore geologic borings. The paleochannel sediments consist of three geologic units: a basal unit of<br>gravel and sand, a middle unit of silty clay, and an overlying unit of interbedded clay and sand. The seismic profiles<br>identified the extent of these units and were used to map them in offshore areas. An accurate knowledge of the<br>distribution of the geologic units in onshore and offshore areas is important to the investigation because the coarsegrained<br>paleochannel sediments could provide a preferential flow path for hazardous wastes and the fine-grained<br>sediments could impede their movement. The seismic data were also used in a ground-water-flow model of the study<br>area to define the boundary conditions and to aid in the design of the finite-difference grid.