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COLLINS, SUE S., Sandia National Laboratories/New Mexico, MICHAEL F. SKELLY, Roy F. Weston, Inc., and JOHN P. McCORD, Duke Engineering Services, Inc.

ABSTRACT: Investigation of Volatile Organic Compound Contamination in a Shallow Groundwater System Beneath Sandia National Laboratories, New Mexico

The Sandia North Groundwater Investigation is currently studying the occurrence of trichloroethene in groundwater at concentrations above regulatory limits of 5 parts per billion. Groundwater occurs in both the regional aquifer and in a localized shallow groundwater system. The regional aquifer is Albuquerque's drinking water source and is 500 to 600 ft deep in unconsolidated sediments of the upper unit of the Tertiary Santa Fe Group. Flow direction in the study area is north-northwest toward municipal well fields.

The shallow system consists of multiple, perched saturated intervals 175 to 275 ft above the regional aquifer. This system has only been identified in the north-central portion of Sandia and flows southeast. This system does not appear to be hydraulically connected to the regional aquifer.

Trichloroethene has been detected in 5 of 12 shallow-system monitoring wells; concentrations exceed regulatory limits at 3 of the 5 locations. Other chlorinated compounds have been detected in some of the 12 wells at concentrations below their respective allowable levels. This low-level contamination is laterally widespread yet discontinuous. To date, investigations of surface releases to identify potential groundwater contaminant sources in the study area are inconclusive, but extensive underground waste-water utilities may have produced a diffuse source.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico