Abstract: Hydrostratigraphic Analysis - Ground Water Cleanup at Lawrence Livermore National Laboratory

BLAKE, RICHARD G., Lawrence Livermore National Laboratory,P.O. Box 808, L-530 Livermore, CA 94550

Cost-effective ground water cleanup requires a thorough understanding of the hydrogeologic factors that control subsurface flow and transport of contaminants. At Lawrence Livermore National Laboratory (LLNL), a methodology termed hydrostratigraphic analysis is employed to divide the complex alluvial sediments beneath LLNL into hydrostratigraphic units (HSUs). HSUs are defined as sedimentary sequences whose permeable layers show evidence of hydraulic communication and interconnection. In contrast, hydraulic communication between HSUs is restricted across HSU boundaries. HSUs are based on a comprehensive analysis and integration of chemical, hydrogeological, geological, geophysical, and aquifer test data. At LLNL, eight HSUs have been identified in the underlying 300 foot thick sequence of unconsolidated sediments. The HSU approach is used to optimize the location of wells associated with the monitoring, hydraulic containment, and systematic cleanup of ground water contaminant plumes and their source areas. Borehole and well locations are based on detailed mapping of higher-permeability sediment distribution, ground water gradients, and contaminant distributions in soil and ground water in each HSU. Understanding the subsurface features that control contaminant flow and transport has enabled LLNL to effectively implement remediation plans, decrease cleanup times, and reduce overall project costs. The significant progress made towards hydraulically controlling and cleaning up the contaminant plumes over the last eight years is clearly evidenced by isoconcentration time series maps, hydraulic capture maps, and mass removal rate plots for each HSU. Hydrostratigraphic analysis is a key tool for demonstrating cost-effective ground water cleanup to DOE, the regulators, and the community.

Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under ContractW-7405-Eng-48.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California