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Technical Memorandum on Surface Geophysical Surveys, Well 16 Source Characterization
Section 4 - SWMU B-3
4.1 - Site History and Description
SWMU B-3 is located in the inner cantonment southeast of Well 16. This site was a landfill area primarily used for garbage disposal and burning. The landfill was covered in 1990-1991. Miscellaneous debris was found on the ground (plastic, burned wood, fuel filter, metal bands, etc.) during the field investigation. The site is characterized by north-south oriented dirt roads, a short, steep downhill slope to the west, a gradual uphill slope to the east, limestone outcrop and fragments to the east and southeast, and a small depression or "crater" in the north-central area (Figure 4.1). Also present are aboveground steel pipes on the northern perimeter of the site which are believed to continue underground towards Well 16 to the northwest. Minor amounts of surface metal are present at isolated locations near the "crater" and at the southwest corner of the site. The perimeter of the site is bounded by trees and other vegetation.
4.2 - Geophysical Survey Results
Figure 4.2 and Figure 4.3 depict contour maps of apparent ground conductivity and in-phase EM data, respectively, for the east-west EM transects at SWMU B-3. EM readings were collected every 2 feet along east-west transects separated by 25 feet. Two anomalous areas were observed at B-3, both oriented in the north-south direction. The areas are especially evident on the in-phase data, where values ranged from -8 to 34 parts per thousand (ppt). There was miscellaneous debris (plastic, metal) located on the ground surface on the western edge of the site. The wide range and distribution of readings on the in-phase EM data at B-3 infers that there are two disturbed areas potentially containing an abundance of buried metal. Evidence on the ground surface indicates that various types and amounts of trash is buried as well as the metal.
Both the GSSI SIR-3 and Pulse EKKO IV GPR surveys were conducted at B-3. The GSSI SIR-3 GPR survey was conducted in the east-west orientation at 50-foot intervals. Results from this survey were generally inconclusive. No clear evidence of ground disturbance could be identified from the SIR-3 data. This is attributed to clay soils present at the surface. A total of four Pulse EKKO IV GPR transects were conducted at B-3, two across each of the anomalies identified during the EM survey. One transect revealed the presence of deeper and broken reflectors in the same area corresponding to the EM anomaly (Figure 4.4). The reflectors may also outline the base of the trench in this area which might be about 10 to 12 feet deep. The location of this Pulse EKKO GPR transect is shown on Figure 4.1.
Two large linear anomalous areas were detected at SWMU B-3 during the EM survey, listed as A and B on Figure 4.5. Anomaly C is associated with an aboveground metal pipe. From historical records and conversations with former CSSA employees, anomalies A and B apparently correspond to trenches containing buried waste material. Pulse EKKO GPR results confirmed that there are areas of ground disturbance which correspond to the anomalies detected during the EM survey at B-3.