ABSTRACT: Computer-Aided Analysis of a Superfund Site

Bern J. Qualheim

The groundwater investigation at the Lawrence Livermore National Laboratory was initiated in 1983 after perchloroethylene (PCE) and trichloroethylene (TCE) were detected in the groundwater. Since that time, more than 300 monitor wells have been completed, logged, sampled, and hydraulically tested. In 1987, the Livermore site was placed on the Environmental Protection Agency's National Priority List (Superfund).

The Livermore valley is relatively flat, underlain by a complex alluvial sedimentary basin drained by two intermittent streams. The subsurface consists of unconsolidated sand, gravel, silt, and clay with multiple water-bearing zones of relatively high permeability. The hydrogeologic system is characterized as leaky, with horizontal hydraulic communication of up to 800 ft and vertical communication between aquifers of up to 50 ft.

Computer-based analysis of the site stratigraphy was used to analyze and characterize the subsurface. We used a computer-aided design and drafting (CADD) system to create two-dimensional slices of the subsurface. The slice program takes a subsurface slice at any specified depositional gradient and at any slice thickness. A slice displays the lithology type, unit thickness, depth of slice, and chemical analyses for volatile organic compounds (VOCs).

The lateral continuity of subsurface channels was mapped for each depth slice. By stacking these maps, we interpreted a pseudo-three-dimensional representation of probably pathways for VOC movement in

the subsurface. An enhanced computer graphics system was also used to map the movement of VOCs in the subsurface.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990