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Groundwater Investigation and Associated Source
Characterization Appendix F - Technical Memorandum on Soil Gas Surveys
Section 1 - Introduction
In August 1991, chlorinated hydrocarbons were found in the groundwater at well 16 at concentrations above the drinking water limit. Camp Stanley Storage Activity (CSSA) requested that Parsons Engineering Science (Parsons ES) investigate the groundwater contamination, a project which began in September 1992 and is continuing to date. As the source of groundwater contamination was not known, investigations were initiated to characterize potential source sites. geophysical surveys were performed prior to drilling and subsurface sampling to locate areas potentially related to past waste disposal activities. After the geophysical surveys, a soil gas investigation was conducted to investigate the geophysical anomalies.
Soil gas surveys were performed at seven Solid Waste Management Units (SWMUs) and six open areas near well 16 on CSSA. Soil gas samples were collected from the following sites: B-2, B-3, B-4, B-28, Gate 6, Salado Creek, Oxidation Pond, Well 16, Well 16 East, Well 16 West, South Pasture, Southeast Well 16, and the area between SWMUs B-3 and B-4.
The soil gas surveys were performed in two phases. Initially, a reconnaissance soil gas survey was conducted from June through July 1996, at seven potential source sites to determine the source of contaminants present in groundwater at well 16 and other CSSA monitoring wells. In November and December 1995, a detailed survey was performed to define the extent of contamination and provide more in-depth information on the source area.
The purpose of this technical memorandum is to provide site-specific soil gas data, figures, and results. A summary of the soil gas survey, and methodologies and procedures used, are described in the groundwater investigation and source characterization report, to which this technical memorandum is appended.