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AOC 36 RFI/Closure 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 no geophysical anomalies related to past waste disposal activities were identified. Additional investigation included the 1995 soil gas survey and the 1997 mustard gas investigation described in Section 1.3. In accordance with the AETC Work Plan Addendum for AOC 36 (Volume 1-3, AOC 36), additional surface soil samples were recommended based on AOC 36’s proximity to Well CS-16 and the detections of VOCs, specifically TCE and PCE, reported in the 1995 soil gas survey (Technical Memorandum on Soil Gas Surveys).

The scope of the current investigation included sampling and analysis of surface soil at ten locations within AOC 36. 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 36. Results of the 1995 geophysical survey are summarized in Section 1.3.

2.1.2   Soil Gas Survey Samples

In accordance with the approved work plan, a soil gas survey was not performed in association with the current investigation conducted for AOC 36. Results of the 1995 soil gas surveys are summarized in Section 1.3.

2.1.3   Surface Soil Samples

Ten surface soil samples (AOC36-SS01 through AOC36-SS10) were collected on January 12, 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 AOC36-5). 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 (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 36 are Krum Complex soils and Tarrant association (gently undulating) soils. Generally, the soils in the topmost foot of the soil profile at AOC 36 were observed to be stiff, dry, calcareous clays with a measurable gravelly component (less than 25 percent). 

2.1.4   Subsurface Soil Samples

In accordance with the approved work plan, subsurface soil sampling was not performed in association with the current investigation conducted for AOC 36.

2.1.5   Groundwater Samples

In accordance with the approved work plan, groundwater was not investigated in association with the current investigation conducted for AOC 36.

2.2 - Results and Comparisons

2.2.1   Geophysical Survey

As described in Section 1.3.1, no geophysical anomalies potentially associated with waste management activities were identified during the 1995 geophysical survey at the site.

2.2.2   Soil Gas Survey Samples

As described in Section 1.3.2, PCE was detected in every soil gas sample collected at the site, at concentrations ranging from 0.02 mg/L to 28 mg/L.

2.2.3   Surface Soil Samples

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 AOC36-1, with the RRS1 standards applicable to the data. 

2.2.4   Subsurface Soil Samples

In accordance with the approved work plan, additional subsurface soil samples were not collected in association with the current investigation conducted for AOC 36.

2.2.5   Groundwater Samples

In accordance with the approved work plan, groundwater samples were not collected in association with the current investigation conducted for AOC 36.

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