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Groundwater Investigation and Associated Source
Characterization Appendix F - Technical Memorandum on Soil Gas Surveys
Section 4 - SWMU B-4
SWMU B-4 is located just south of SWMU B-3 in the inner cantonment. B-4 was apparently used to burn classified documents and trash. B-4 is similar in nature to B-3 in the respect that it contains a north-south oriented dirt road, limestone outcrop to the south and northwest, isolated surface metal, and trees which surround the site (Figure 4.1). B-4 also contains drainage channels which trend east to west in the west-central portion of the site. Exposed in the drainage channels are pieces of plywood. The topography of the site slopes from north to south. The southwest quadrant of B-4 was extended to cover an open area with a drainage channel. This additional area (B-4A) is depicted west of B-4 and shows the locations of surrounding trees and continuation of the small drainage channel initiated at B-4.
PCE was detected in soil gas samples from SWMU B-4. The highest concentration detected was 10 ug/L and was detected at location A,0.5 located along the edge of the grid that borders the oxidation pond. A complete listing of the soil gas survey data from the site reconnaissance survey is given in Table 4.1. Soil gas sampling locations are shown on Figure 4.1. All but five soil gas samples were collected from this site during the initial phase of the soil gas survey. The additional samples were collected from the southeast corner of the landfill to define the limits of the PCE contamination in that area; the results are in Table 4.2.
The results of soil gas surveys indicated that the distribution of PCE shows a trend of decreasing concentrations away from the oxidation pond located at the northwest corner of the site (Figure 4.1). Based on this distribution, the oxidation pond is probably the source of the PCE detected at SWMU B-4.