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Final AOC-38 Closure Report
Section 2 - Closure Field Activities
Previous investigations suggested the presence of a suspected geophysical anomaly (Anomaly A) in the northeastern portion of AOC‑38 (Figure AOC38‑8). The area of the suspected anomaly was located using a geographic positioning system (GPS) and excavated to bedrock in November 2003. No waste material was found and the soil was replaced in the trenched area. Because the prior investigations did not detect any analytes above the background levels, no further excavation was required at AOC‑38. In addition, because no further excavation was required, no confirmation sampling was conducted.
In addition to Anomaly A, three areas within the southern and central portions of AOC‑38 caused unexplained geophysical data fluctuations/aberrations during the geophysical survey (Figure 11.10 of the Technical Memorandum on Surface Geophysical Surveys, Well 16 Source Characterization, Parsons, 1995). During May 2004, these areas were investigated using a Magna Trak® ferrous metal detector tool. Several pieces of shallow metal debris (horse shoes, wire, fencing debris) were found at each of the locations. Subsequently, a backhoe was mobilized to the site to excavate the areas and check for additional debris. Eight holes were excavated to bedrock, but no additional metal debris was revealed. The soil horizons at each location appeared undisturbed.
The AOC‑38 area lies within the floodplain of Salado Creek tributaries. During precipitation events, various debris gets washed down into the site area. This debris includes barb wire, wood, and other miscellaneous items. Barb wire and concrete material were removed from the surface of the site during the closure activities. In addition to Anomaly A and the geophysical aberrations produced during the geophysical survey, a small (10-foot diameter) burn area, metal fencing, and metal piping, were discovered at the site. The fencing and piping have been removed from the site and disposed.
The burn area present at AOC‑38 was described as a bermed burn pit in previous reports, which is not correct. The burn area appears to represent the location of some barb wire and vegetation debris that washed into the site during a flood event. To eliminate the debris pile, it was burned in place. The burn area does not contain signs of an established burn pit where burn activities were regularly conducted. The barb wire material has been removed from the burn area and disposed. Some charcoaled remains of the burned vegetation remain at the burn area. Since the burn area is not associated with waste management, sampling was not necessary.
All of the metal debris discovered at the site during closure activities was removed from the site and excavated soils were replaced. A final field walkover was conducted to verify that no additional waste items remained at the site.