Abstract: Relative Contributions of Plume Migration, Source Impact, and Radioactive Decay in the Attenuation of Two Tritium Ground Water Plumes at Lawrence Livermore National Laboratory Site 300

WOODWARD, R., V. MADRID, and L. GREEN-HORNER, Weiss Associates, Emeryville, CA;M. TAFFET, Lawrence Livermore National Laboratory, Livermore CA; andJ. OBERDORFER, San Jose State University, San Jose, CA

We are studying spatial and temporal variations in two tritium ground water plumes in the complex hydrogeologic setting of Lawrence Livermore National Laboratory Site 300. Site 300 is an 11-square mile Department of Energy explosives test facility and Superfund site located in the semi-arid, rugged terrain of the California Coast Ranges near Tracy, California.

The sources for one plume are two unlined landfills containing tritium-bearing debris. Local changes in ground water levels have caused releases of tritium from the landfills to the vadose zone and ground water. The source for the second plume is an explosives testing platform, where tritium has accumulated in the shallow subsurface. Rainfall percolating through the platform carries tritium downward to ground water.

Semi-annual tritium activity contour maps and saturated thickness maps from 1985 to 1997 (approximately one tritium halflife) were developed to determine changes in plume locations and total tritium activity. We find that despite releases of tritium to ground water, 1) the locations of the lower tritium-activity contours do not change substantially with time, and 2) the dominant plume attenuation mechanism appears to be radioactive decay.

Work performed under the auspices of the U.S. Dpertament of Energy by Lawrence Livermore National Laboartory under contract W-7405-Eng-48.

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