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Groundwater Investigation and Associated Source
Characterization Appendix F - Technical Memorandum on Soil Gas Surveys
Section 8 - Southeast Well 16
Southeast Well 16 is located southeast of well 16 on the south side of North Outer Road. Former CSSA employees indicated that mustard gas canisters might be buried here. However, there was no visible surface evidence of such burial. Approximately half of the site is covered with dense vegetation. The site is bounded to the north and west by paved roads and B-3 lies to the southeast. These is a small drainage ditch oriented north-south along which exposed metal piping was observed. This underground piping trends northwest-southeast and originate at the B-3 site where it is above ground. Also present at Southeast Well 16 is a small fiberglass box, a telephone pole, and an area of reinforced concrete rubble (Figure 8.1).
During the initial phase of the soil gas survey, the compounds PCE, TCE, and cis-1,2-DCE were detected in soil gas samples from the Southeast Well 16 area. Additional samples were collected in the second phase of the soil gas survey to better define the extent of contamination. The additional samples were taken at 100-foot spacings from the base of the Southeast Well 16 grid south to B-28 and by extending the M row to the west. In the second phase of the soil gas survey, carbon tetrachloride was also detected. The soil gas survey data for the reconnaissance survey are presented in Table 8.1 and for the follow-up in Table 8.2.
A depth profile was done at location O,25 and the results indicated that a clay layer was present from the surface to near bedrock soil interface. The best sampling depth was determined to be the bedrock-soil interface.
PCE was the dominant compound detected in the Southeast Well 16 area with the highest concentration, 33 ug/L, occurring at location M,40 (Figure 8.1). The highest concentrations occurred along the boundary with SWMU B-3 and the distribution of PCE in this area appears to be an extension of the PCE contamination detected immediately adjacent to the area at SWMU B-3 (Section 3). Consequently, the occurrence of PCE at Southeast Well 16 is probably due to migration of this compound into the area from SWMU B-3.
The occurrence of PCE and DCE at Southeast Well 16 is probably due to migration from SWMU B-3. The highest concentration of TCE detected was 0.98 ug/L and occurred at location AA,5 while the highest concentration of DCE was 8.2 ug/L at location AA,10. Locations AA,5 and AA,10 are located to the west of TCE and DCE anomalies at SWMU B-3.
Carbon tetrachloride was detected at location AA,200 located between Southeast Well 16 and SWMU B-28. This occurrence could be the result of migration from a source located between B-3 and the oxidation pond. The occurrence of carbon tetrachloride in the are between B-3 and the oxidation pond is discussed below in the section on open area.