AETC Work Plan Addendum
Area of Concern 38

Soils: Krum Complex, and Trinity and Frio Soils.

Known: The site is approximately 35 acres in size and consists of open pasture area, south of SWMU B-8. It is located in the Inner Cantonment, southwest of Well 16.

Previous Investigations (Updated): Under Order 67, a geophysical survey was conducted in May 1995 at all "open" areas within a 2,000-foot radius of Well 16. One anomaly was found in this area (labeled South Pasture at the time) and is now included as AOC 38. A one and one-half inch diameter metal pipe was also discovered at the site during the geophysical survey field activities.

In June and July 1995, twenty-six soil gas survey samples were collected and analyzed for chlorinated and aromatic volatile organics from the northern portion of AOC 38. PCE (3.1 ug/L) and TCE (0.10 ug/L) were detected in this area.

In November 1995, an additional 94 soil gas survey samples were collected from the South Pasture Area which includes AOCs 38 and 62, and SWMU B-11. The rest of the survey area covered unvegetated areas between the northeastern portion of the H&I Area and Salado Creek (See Figure 9.1 of the Technical Memorandum on Soil Gas Surveys, June 1996). This survey was a southern extension to the original June/July 1995 survey. However, only a total of 18 additional points were added to the AOC 38 area during this effort. Again, PCE (2.6 ug/L) and TCE (0.21 ug/L) were detected at AOC 38. The combination of both these surveys indicated PCE concentrations above 0.10 ug/L over most of AOC 38. Three areas with PCE concentrations above 1.0 ug/L were also noted within AOC 38. Two other areas above 1.0 ug/L were delineated southeast of AOC 38. Isopleth mapping of PCE concentrations indicate potential northeast trending linear features along which elevated levels are concentrated.

Data Needs: Analytical data (VOCs – TCE, PCE, and DCE) for surface soils.

Rationale for Analytical Program: Based on the site’s vicinity to well 16 and previous investigations at the site, chemicals of potential concern include VOCs (TCE, PCE, and DCE). Metals, explosives, and SVOCs are not included due to the results of the geophysical surveys completed in the area.

Closure Activities: The following activities constitute an initial investigation of the area of concern 38. This work will be completed as part of the requirements under the RCRA 3008(h) Order under AETC delivery order 5068.

1. Collect 60 surface grab samples to a maximum depth of 2 feet to characterize surface soils surrounding the area. The surface samples will be collected in a grid-like fashion, and will biased toward the soil gas survey points with the highest PCE readings. Figure AOC38-1 depicts the proposed locations for the surface samples. This work is being performed in conjunction with sampling efforts at AOCs 36, 39, and 40. Each sample will be analyzed for VOCs (TCE, PCE, and DCE). QA/QC samples will be collected as described in Section 2.4 of the FSP.

2. Handle IDW as specified in the FSP.

3. If the results of the above work indicate that the site can be closed under RRS1 without any further investigation and/or remediation, a technical/closure report will be prepared and submitted in accordance with TNRCC closure requirements. If the site does not meet RRS1 requirements, a technical report describing the results of the investigation and recommended additional investigation and/or remediation will be prepared.