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AOC-38 RCRA Facility Investigation Report
Section 2 - Field Investigation
2.1 - Field Actions
In an effort to identify potential sources for contamination at Well CS-16, a geophysical survey was conducted at the site in 1995, during which one geophysical anomaly was identified. Additional investigation included the 1995 soil gas survey described in Section 1.3. In accordance with the AETC Work Plan Addendum for AOC 38 (Volume 1-3, AOC 38), additional surface soil samples were recommended based on AOC 38’s proximity to well CS-16 and the detections of VOCs, specifically TCE and PCE reported in the 1995 soil gas surveys (Section 9 of Technical Memorandum on Soil Gas Surveys).
The scope of the current investigation included sampling and analysis of surface soil collected at 60 locations within AOC 38. The purpose of the surface soil sampling was to determine if soil gas results reflect soil contamination levels, if site concentrations meet TNRCC requirements for RRSI closure.
In accordance with the approved work plan, an additional geophysical survey was not performed in association with the current investigation conducted for AOC 38. Results of the 1995 geophysical survey are summarized in Section 1.3.
In accordance with the approved work plan, a soil gas survey was not performed in association with the current investigation conducted for AOC 38. Results of the 1995 soil gas survey are summarized in Section 1.3.
Sixty surface soil samples (AOC38-SS01 through AOC38-SS60) were collected on from January 11, 2000 through January 13, 2000, and analyzed for selected VOCs (method SW-8260B) by O’Brien & Gere Laboratory in Syracuse, New York. Analytes included 1,1-DCE, cis-1,2-DCE, trans-1,2-DCE, PCE, and TCE only. The samples were collected from the top two feet of soil adjacent to grid points from the soil gas survey with concentrations of the applicable COCs (Figure AOC38-5). Equipment decontamination procedures, as well as sample collection, preparation, handling, and shipping, are described in the Field Sampling and Analysis Plan (Volume 1-5, Field Sampling Plan, Quality Assurance Project Plan). QA and QC samples were collected as described in the AFCEE QAPP (Volume 1-4, Quality Assurance Project Plan). Sampling locations were recorded with a Trimble Asset-grade GPS by Parsons ES. Surveying methodology is described in the Amendment to the Field Sampling Plan (Parsons ES, 2001b). All sample locations and analytical data will be incorporated into the CSSA GIS after approval from AFCEE and CSSA.
The soils at AOC 38 are Krum Complex, Trinity and Frio, and Crawford and Bexar soils. Generally, the soils in the topmost foot of the soil profile at AOC 38 were observed to be stiff, dry, calcareous clays.
In accordance with the approved work plan, subsurface soil sampling was not performed in association with the current investigation conducted for AOC 38.
In accordance with the approved work plan, groundwater was not investigated in association with the current investigation conducted for AOC 38.
2.2 - Results and Comparisons
As described in Section 1.3.1, one geophysical anomaly potentially associated with past waste management activities (labeled as “A” in Figure AOC38-4) was identified during the 1995 geophysical survey.
As described in Section 1.3.2, PCE was detected in soil gas samples collected in July 1995 at concentrations ranging from 0.02 µg/L to 3.1 µg/L and in soil gas samples collected in November 1995, at concentrations ranging from 0.01 μg/L to 2.6 μg/L.
None of the analytes were detected above their respective RLs. As described in Section 4.1.5 of the Risk Assessment Technical Approach Document, AFCEE RLs are equivalent to PQLs; therefore, the site meets RRS1 criteria for VOCs. Very low levels of PCE were detected in three samples, SS36, SS39, and SS58. As shown in Figure AOC38-5, both of these samples were collected in the southeast corner of the site.
Analytical results for surface samples are presented in Appendix A. The detected constituents are summarized in Table AOC38-1, with the RRS1 standards applicable to the data.
In accordance with the approved work plan, subsurface soil samples were not collected in association with the current investigation conducted for AOC 38.
In accordance with the approved work plan, groundwater samples were not collected in association with the investigation conducted for AOC 38.