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Hydrogeologic Report for Evaluation of Groundwater Contamination

Section 2 - Project Background

Facility Description and History

CSSA is located approximately 19 miles northwest of downtown San Antonio in the northern part of Bexar County, Texas (Figure 2.1). The CSSA facility is a subinstallation of the U.S. Red River Army Depot (RRAD) located in Texarkana, Texas. CSSA lies on approximately 4,000 acres adjacent to the western boundary of the U.S. Department of the Army Camp Bullis post.

The CSSA area was a segment of the original Leon Springs Military Reservation and was transferred to the jurisdiction of the Chief of Ordnance as an ammunition depot for the San Antonio Arsenal in 1933. In June 1949, CSSA was transferred to the jurisdiction of the RRAD. Historically, the mission of CSSA was training, evolving to ordnance storage, maintenance, and testing.

There are nineteen wells known to exist on CSSA (Figure 2.2). CSSA identification numbers for the wells are alphabetic or numeric designations. Five wells are in the north pastures (wells E, F, G, H, and I); eight wells are located along the northern boundary of the inner CSSA cantonment lands (wells A, B, C, D, 2, 3, 4, and 16); three wells are in the CSSA housing area (wells 9, 10, and 11); two wells are found in the southern area of CSSA (wells 5 and 6); and well 1 is located southeast of CSSA on Camp Bullis property. These wells have produced water for drinking, livestock, and agriculture. The majority of the wells are now inactive. During the 1980s, drinking water was taken from wells 1, 9, 10, 11, and 16.

Summary of Previous Investigations

During a routine pesticide screening site visit on August 9, 1991, TDH sampled the active water supply wells to analyze for pesticides and volatile organic compounds (VOCs). Analytical results revealed the sample from CSSA well 16 contained 127 micrograms per liter (ug/L) cis- and trans-1,2-dichloroethylene (DCE), 151 ug/L trichloroethylene (TCE), and 137 ug/L tetrachloroethylene (PCE). These concentrations are above the drinking water standard of 5 ug/L that applies to TCE and PCE, individually, and the DCE standard of 70 ug/L. Subsequent sampling on August 23, 1991, confirmed the earlier results. CSSA took the well out of service and notified previous well users on a quarterly basis of the analytical testing and results.

The TWC collected samples on December 4, 1991, from well 16 and from two inactive wells (wells D and 4). Well 16 continued to show concentrations of TCE and PCE above drinking water standards. Inactive well D also contained a DCE concentration of 43 ug/L, which was below the DCE drinking water standard. Well 4 did not contain concentrations of halogenated compounds above drinking water standards.

Project Goals and Overview of Hydrogeologic Assessment

ES performed a preliminary evaluation of pertinent records, groundwater and well information, and chemical analyses concerning groundwater contamination at CSSA. The goal of this evaluation was to review the site background, analyze available data, and determine current groundwater conditions for design of a comprehensive and cost-effective SI work plan.

As part of the evaluation, ES assessed the general hydrogeology of the region and the CSSA site. The tasks of this hydrogeologic assessment were to research records and data for an understanding of site background, previous investigations, and potential sources of the groundwater contamination and to assess the site hydrogeology by examining current well conditions, comparing previous groundwater chemical data with current concentrations, surveying geologic surface conditions, and inspecting actual borehole conditions.

To accomplish these tasks, the following work actions were specified in the project scope of work:

Results from the research and field actions of the preliminary evaluation are discussed in this hydrogeologic report, and recommendations are presented for development of a work plan for the next phase of investigation. The regional and site hydrogeology discussion in this report will serve to guide selection of optimum location for soil borings and groundwater monitoring wells, depths of well completion, and sampling efforts.

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