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Technical Memorandum on Surface Geophysical Surveys, Well 16 Source Characterization
Section 5 - SWMU B-4
5.1 - Site History and Description
SWMU B-4 is located just south of SWMU B-4 in the inner cantonment. B-4 was apparently used to burn classified documents and trash. B-4 is similar in nature to B-3 in the respect that it contains a north-south oriented dirt road, limestone outcrop to the south and northwest, isolated surface metal, and trees which surround the site (Figure 5.1). B-4 also contains drainage channels which trend east to west in the west-central portion of the site. Exposed in the drainage channels are pieces of plywood. The topography of the site slopes from north to south. The southwest quadrant of B-4 was extended to cover an open area with a drainage channel. This additional area (B-4A) is depicted west of B-4 and shows the locations of surrounding trees and continuation of the small drainage channel at B-4.
5.2 - Geophysical Survey Results
Figure 5.2 and Figure 5.3 depict contour maps of apparent ground conductivity and in-phase EM data, respectively, for the east-west EM transects at SWMU B-4. EM readings were taken every 2 feet along east-west transects separated by 25 feet. Three anomalous areas, A, B, and C, were identified on the B-4 EM contour maps (Figure 5.4). Anomalies A and B are long, linear features oriented in the north-south direction. The large variation in the EM values infers ground disturbance related to past waste disposal activities. Anomaly C exhibits some variability in the EM values from which minor amounts of ground disturbance in this area can be inferred. There was no evidence in the field or on aerial photographs of trenches being present in this area. However, conversations with former CSSA employees indicated that trenches containing buried waste material are present at B-4, and their locations correspond to the anomalies identified during the EM survey.
An additional open area was surveyed southwest of B-4. The site was named B-4A and its location is shown on Figure 5.1. Figure 5.2 and Figure 5.3 depict contour maps of apparent ground conductivity and in-phase EM data, respectively, for the east-west EM transects at B-4A. The results show anomalies at B-4A which indicate the potential presence of additional trenches in the area (Figure 5.4). The anomalies D and E are linear features oriented north-south. Anomaly F is an isolated conductivity anomaly. Values of apparent conductivity at B-4A ranged from -40 to 120 mS/m, and in-phase data ranged from -30 to 45 ppt. There is no surface expression of buried trenches at B-4A, just a small drainage channel and miscellaneous wood fragments in the area.
GPR surveys were performed at B-4 using the GSSI SIR-3 system and the Pulse EKKO IV system. The GSSI SIR-3 data was collected along east-west transects separated by 50 feet. No indications of buried trenches were evident during this survey. Surface or near-surface metal at B-4 resulted in isolated "echo" type responses on the GPR profiles. A strong GPR response was observed where limestone bedrock cropped out to the east of line 8 (Figure 5.5). the location of line 8 is shown on Figure 5.1. A total of four Pulse EKKO transects were conducted at the site. The locations were chosen based on the results from the EM survey. One of the Pulse EKKO transects resulted in a clear image of anomalies A and B identified during the EM survey at B-4 (Figure 5.6). The location of this GPR transect is shown on Figure 5.1. The GPR profile infers the location of three separate trenches with the outlines of the trench bases clearly identified. These inferred trenches correspond to anomalies A and B detected from the EM data (Figure 5.4). Using an assumed material velocity of 0.328 feet per nanosecond according to the GPR results, the base of the trenches are estimated to be 10 to 12 feet below ground surface. The width of the trenches are approximately 20 feet each.
In summary, a total of six anomalies were identified at SWMUs B-4 and B-4A from the EM data, listed as A, B, C, D, E, and F on Figure 5.4. Anomalies A, B, and C at B-4 are long, linear features oriented north-south. Anomalies D and E and B-4A are also north-south linear features. These EM anomalies infer areas of ground disturbance. According to former CSSA employees, trenches containing buried waste material are present at B-4 and B-4A and their locations and orientations correspond to the EM survey results. The Pulse EKKO GPR profile shown on Figure 5.6 infers the outline of the three trenches at B-4. They are approximately 10 to 12 feet deep and 20 feet wide. The locations of the three trenches illustrated on Figure 5.6 correspond to the locations of disturbed areas at B-4 identified as anomalies A and B from the EM data (Figure 5.4). Two trenches were identified at anomaly A, and one trench was identified at anomaly B on the Pulse EKKO GPR profile.