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Technical Memorandum on Surface Geophysical Surveys, High Priority SWMUs
Section 6 - SWMU B-15/16
6.1 - Site History and Description
SWMU B-15/16 (previously identified as B-15 and B-16) is located in the east pasture near the firing range (Figure 1.1). The site is densely vegetated with no indication of subsurface disturbance. Immediately south of the surveyed area lies a "covered" trench and corresponding soil mounds (Figure 6.1). This "covered" trench is long and narrow, and contains buried metal debris partially exposed in certain areas. B-15/16 was apparently used as a landfill for target vehicles and weapon mounts. This was verified in the field upon examination of the exposed metal debris mentioned above.
6.2 - Geophysical Survey Results
An EM survey was performed at B-15/16 along north-south transects spaced at 25-foot intervals. The transects were expanded south of the gridded area to incorporate portions of the covered trench discussed above. The EM conductivity and in-phase contour maps are shown on Figure 6.2 and Figure 6.3. The results show that three anomalies were detected at B-15/16, identified as A, B, and C on Figure 6.4. Anomaly A is associated with the covered trench containing partially exposed metal debris south of the gridded area. The other two intersecting anomalies (B and C) are located within the gridded area and at approximate right angles to each other. Anomaly B trends northeast-southwest and intersects the covered trench to the south. This anomaly was observed on both the conductivity and in-phase contour maps. Anomaly C trends northeast-southwest and intersects Anomaly B at an approximate right angle. This anomaly was observed only on the conductivity contour map (Figure 6.2). Anomalies B and C are associated with areas of ground disturbance assumed to be buried trenches containing unknown waste material. The absence of anomaly C on the in-phase contour map suggests a lack of buried metal debris in this potential waste disposal area. There is no surface expression of anomalies B and C and the area is densely vegetated with trees and brush.
A GPR survey was conducted at B-15/16 across Anomaly A. The location of the transect is shown on Figure 6.4. Anomaly A was chosen due to the lack of vegetation in the area which facilitated the transect. The GPR profile reveals an image of a trench approximately 25 feet wide and 11 feet deep (Figure 6.5). This trench corresponds to the known "covered" trench containing partially exposed metal debris (Figure 6.4). Furthermore, this GPR anomaly corresponds with the EM conductivity and in-phase anomalies shown on Figure 6.2 and Figure 6.3.
In summary, there were three anomalies (A, B, and C) detected at SWMU B-15/16 by EM and GPR methods. One anomaly (A) is associated with a known (covered) trench containing partially exposed metal debris. The other two anomalies (B and C) were discovered north of the covered trench in an area of dense vegetation. Anomalies B and C are associated with areas of subsurface disturbance assumed to be long, narrow trenches containing buried waste material. The anomalies (i.e., trenches) form an intersecting pattern at this site (Figure 6.4).