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ABSTRACT: Stratigraphy Sedimentology and Trichloroethylene in Groundwater at the Lawrence Livermore National Laboratory Site 300 General Services Area, Southeast of Livermore, California

Michael Wade, S. Vonder Haar, W. McIlvride, R. Ferry, L. Glick, A. Lamarre, N. Crow, D. Carpenter, M. Taffet

Hydrogeology of a 500-ft-thick section of the late Miocene Neroly Formation and overlying alluvial/terrace deposits is under investigation in the General Services Area (GSA) at the Lawrence Livermore National Laboratory Site 300, located 15 mi southeast of Livermore, California. Analysis of groundwater from 45 monitor wells in the area identified trichloroethylene (TCE) in the shallow groundwater at concentrations of up to 380 µg/L. Groundwater from deeper water-supply wells do not have TCE. Concern about possible vertical migration has prompted an

evaluation of the degree to which stratigraphy and sedimentology influence groundwater movement.

The Neroly Formation is composed of poorly consolidated, blue-weathering volcaniclastic, andesitic sandstones and siltstones, interbedded claystones and conglomerates. The depositional environment appears to be estuarine or wave-active embayment. Some sandstones contain angular grains of plagioclase (<An32), quartz, mafics, and unweathered sedimentary clasts suggesting rapid movement from their source area, historically considered to be the Sierra Nevada 90 mi to the east.

Beds of the Neroly Formation in the eastern GSA dip from 14 to 21° southwest. In the western GSA, bedding dips about 18° south. The Neroly Formation includes an upper water-bearing sandstone unit about 50 ft thick, and a lower section 450 ft thick that contains multiple water-bearing sandstone beds that range from 10 to 100 ft in thickness. These sandstone beds extend to the surface, and in places intersect the base of the overlying alluvial deposits that contain the shallow aquifer.

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