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Technical Memorandum on Surface Geophysical Surveys, Well 16 Source Characterization
Section 3 - SWMU B-2
3.1 - Site History and Description
SWMU B-2 is located in the north pasture north of Well 16. Two trenches were observed at this site on aerial photographs and confirmed during this field investigation. Soil mounds are present on the ends of the two trenches (Figure 3.1). These trenches were apparently used for burning small arms ammunition in 1954. Munition canister lids (57mm guns), an unidentified munition, and bricks were also observed. The site is relatively flat and unobstructed except for an occasional small tree or brush and dense overgrowth in the two trenches which was cleared prior to this investigation. In addition, isolated surface metal was removed from this site and placed outside the area of investigation to reduce interference during the survey. SWMU B-2 is bounded by a dirt road to the north and trees to the east, south and west, as well as the fenceline between B-1 and B-2.
3.2 - Geophysical Survey Results
Figure 3.2 and Figure 3.3 depict contour maps of apparent ground conductivity and in-phase EM data, respectively, for the north-south EM transects at SWMU B-2. EM readings were taken every 2 feet along transects separated by 25 feet. A total of five anomalies were detected during the EM survey at B-2, listed as A, B, C, D, and E on Figure 3.4. EM anomalies A and B correspond to the two linear depressions shown on Figure 3.1. EM anomaly C corresponds to the small mound in the north-central part of the site also shown on Figure 3.1. EM anomalies D and E (Figure 3.4) are isolated and do not correspond to any surface features. GPR profiles of anomalies A and B reinforced EM results and indicate that these are areas of ground disturbance. Ground disturbance is also indicated at EM anomalies C, D, and E.
GPR surveys were conducted at B-2 using the GSSI SIR-3 system and the Pulse EKKO IV system. The GSSI SIR-3 data were collected along north-south transects separated by 50 feet. This GPR method provided mixed results. Figure 3.5 depicts the GPR data collected over the northern linear depression shown on Figure 3.1 from coordinates K,65 to K,75. This response provides a vague indication of ground disturbance. However, clear indications of those disturbed areas, or anomalies, identified during the EM survey were generally not detected by the GSSI SIR-3 GPR method.
Four transects varying from 50 to 150 feet in length were collected by using the Pulse EKKO IV system. These transects were performed in order to substantiate the location of disturbed areas and to evaluate the ability of this system to detect these disturbed areas. The Pulse EKKO IV data generally provided better resolution of the anomalies identified during the EM survey. The Pulse EKKO reflectors appear to be broken up (e.g., not laterally continuous) in the anomalous areas mentioned above. Figure 3.6 illustrates a comparison of profiles from the EM and GPR (GSSI SIR-3 and Pulse EKKO IV) methods. The location of this comparison profile at B-2 is shown on Figure 3.1.