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Groundwater Investigation and Associated Source
Characterization Appendix F - Technical Memorandum on Soil Gas Surveys
Section 6 - SWMU B-28
SWMU B-28 is located approximately 100 feet west of B-19 and 1,500 feet south of well 16. Molten metal, small arms ammunition, and metal ammunition parts were disposed of at B-28. This was verified during the field investigation when two shallow trenches were encountered with fragments of molten metal exposed at the surface. Metal debris was also found scattered throughout the site. both trenches trend northwest-southeast and are approximately 5 feet wide at the surface. The northern trench is a linear feature approximately 300 feet in length that intersects a drainage ditch to the northwest. The southern trench is slightly curved and extends approximately 100 feet. The topography of the site is flat and is located in an open, grassy area with an occasional isolated tree (Figure 6.1).
Only PCE was detected in soil gas samples from SWMU B-28. The soil gas survey data are presented in Table 6.1. A depth profile was attempted at location 100,300, but a 3-foot sample could not be obtained because of a clay layer present from bedrock to the surface. Results from this location indicated that the probe needed to be driven to the bedrock-soil interface to collect a representative soil gas sample. Samples were only collected at this site during the reconnaissance survey.
The highest concentration of PCE detected was 0.70 ug/L at location 50,50, near the center portion of the southern trench. Detections of PCE in excess of 0.10 ug/L tended to occur in the immediate vicinity of teh trenches. The relatively low levels of PCE detected suggests that the site does not have a source of PCE that could cause groundwater contamination. The occurrence of PCE at this site could be related to migration from the oxidation pond which is located on a hill above and east of B-28.