DEVELOPMENT AND COMPARISON OF FINITE-ELEMENT AND FINITE DIFFERENCE MODELS AT AN ELECTRO OSMOSIS REMEDIATION TEST SITE

Lawrence Livermore National Laboratory (LLNL) is located near the southeast end of the Livermore Valley. The LLNL site is underlain by the Livermore Fm. comprised of an upper and lower member. The upper member is characterized by gravel, sand, silt, and clay, and is host to the underlying contaminant plumes. In 1982, volatile organic compounds (VOCs) were discovered in the ground water and a thorough investigation began of the subsurface hydrology, geology, and chemistry. In 1987, LLNL was placed on the Superfund National Priority List. The East Traffic Circle Area is of interest because it was an unpaved parking apron between the runways of the Naval Air Station prior to 1951. These aprons were used to clean and repair airplanes. In 1984, the same area revealed landfill debris containing materials such as metal shavings, capacitors (containing PCBs), broken bottles, drums (containing chemical wastes), plating tank contents, and sandblasting sand. Pump-and-treat remedial procedures have been implemented to remove contamination from the coarse subsurface sediments, but the problem of recalcitrant contaminants remains to be solved for the less permeable zones. An experimental method of contaminant removal, Electro Osmosis (EO), has begun in the finer grained sediments and my goal is to evaluate the performance of this innovative remedial procedure. A simple flow model was constructed using the finite-element program, FlexPDE, to help understand the hydraulic communication that occurs between wells in the test site under pumping conditions. This poster describes the hydraulic test information used in the study and compares the results from the finite-element model to those obtained from a finite-difference model created in MODFLOW. The next step is to create a coupled model that includes transport of the contaminant through low-permeable units. These estimations will then be compared to EO predictive analyses and used to evaluate future EO remediation design and operation.