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AOC 39 RFI/Closure Report
Section 2 - Field Investigation
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 two geophysical anomalies were identified. Additional investigation included the 1995 soil gas survey. In accordance with the AETC Work Plan Addendum for AOC 39 (Volume 1-3, AOC 39), additional surface soil samples were recommended based on AOC 39’s proximity to well CS-16 and the detections of VOCs, specifically TCE and PCE reported in the 1995 soil gas surveys (Technical Memorandum on Soil Gas Surveys).
The scope of the current investigation included sampling and analysis of surface soil at five locations within AOC 39. The purpose of the surface soil sampling was to determine if soil gas results reflect soil contamination levels, or if site concentrations meet TNRCC requirements for RRS1 closure.
In accordance with the approved work plan, an additional geophysical survey was not performed in association with the current investigation conducted for AOC 39. 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 39. Results of the 1995 soil gas survey are summarized in Section 1.3.
Six surface soil samples (AOC39-SS01 through AOC39-SS05 and one field duplicate) were collected 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. Each sample was collected from a ½ foot interval within the top two feet of soil, adjacent to grid points from the soil gas survey with reported concentrations of the applicable COCs (Figures AOC39-4 and AOC 39-5). The sampling depths were chosen to be within the depth interval in which soil gases may have been found. 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 (1-meter accuracy) 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 39 are Krum Complex, Trinity and Frio and Brackett-Tarrant association soils. Generally, the soils in the topmost foot of the soil profile at AOC 39 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 39.
In accordance with the approved work plan, groundwater was not investigated in association with the current investigation conducted for AOC 39.
As described in Section 1.3.1, two geophysical anomalies, labeled “A” and “B” in Figure AOC39-4, were identified during the 1995 survey. The locations of these anomalies were later found to correspond with locations of abandoned livestock wells CS-B and CS-C.
As described in Section 1.3.2, low levels of PCE were detected in six of eight soil gas samples collected at the site. The maximum concentration detected was 0.18 m/L PCE at location 45,5.
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. Analytical results for surface samples are presented in Appendix A. The detected constituents are summarized in Table AOC39-1, with the RRS1 standards applicable to the data.
In accordance with the approved work plan, additional subsurface soil samples were not collected in association with the current investigation conducted for AOC 39.
In accordance with the approved work plan, groundwater samples were not collected in association with the current investigation conducted for AOC 39.