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AOC-56 is located in the southeast portion of the inner cantonment at the intersection of Bernard Road and East Outer Road, approximately 100 ft east of the outer cantonment boundary. Bernard Road marks the north boundary of AOC-56 and East Outer Road marks the boundary on the east side. The site is oblong in shape and covers approximately 0.5 acres. The site length is approximately 400 ft and oriented northwest-southeast, while the site width is approximately 150 ft and oriented northeast-southwest. A site location map is shown in Figure AOC56-2. Except for cattle grazing, no other activities are currently practiced at AOC-56. There is no development upon AOC-56 except for overhead utilities and roadside drainage control.
Information obtained concerning AOC-56 indicates that the site was used as a construction debris landfill. Visual observation of the site indicates an area of excavation on the western side of the site. Although the site was generally known as being used to dispose of metal debris and construction materials, it is possible that solvents or fuels, which were commonly used at CSSA, may also have been discarded in the area.
Geophysical Survey
EM and GPR geophysical surveys were conducted at AOC-56 in August 1999. Prior to collecting EM or GPR data, a grid system was established at the site encompassing the areas of suspected ground disturbance. This grid consisted of staked locations separated by intervals ranging from 20 to 50 ft, depending on the size of the area and the amount of obstructions, if any. Figure AOC56-2 illustrates the layout of the geophysical survey grid located at AOC-56 as well as the GPR survey profile locations.
During the geophysical survey of AOC-56, it was determined that there were several areas that indicated EM anomalies. Both in-phase and quadrature data from the EM survey indicated several large anomalies. The GPR surveys were used to check the anomalous areas from the EM survey. The surveys showed evidence that bedrock may have been excavated for a disposal trench and multiple reflections indicated possible debris. Some of the anomalies were attributed to road construction activities and a previously removed rail line. The survey data suggest one area is possibly indicative of past waste management activities.
Surface Soil Samples
In January 2000, three surface soil samples were collected as part of the AOC-56 site investigation and analyzed for VOCs, SVOCs, and metals (barium, chromium, copper, nickel, zinc, arsenic, cadmium, lead, and mercury). Sample locations were biased towards any anomalies discovered in the geophysical surveys. AOC56-SS01 was collected in the northwest portion of the AOC. AOC56-SS02 was collected approximately 140 ft southeast of AOC56-SS01. AOC56-SS03 was collected just west of East Outer Road in the southeastern portion of the site (Figure AOC56-2).
Analytical data from the surface soil samples indicated slight RRS1 exceedances of lead and zinc at AOC56-SS01. Lead was detected at a concentration of 88.32 milligrams pre kilogram (mg/kg) and zinc at 97.75 mg/kg. Background levels for lead and zinc are 84.5 mg/kg and 73.2 mg/kg, respectively. All samples reported VOC and SVOC concentrations below RLs, therefore RRS1 criteria for VOCs and SVOCs have been met.
Based on surface soil sampling results, the possibility of subsurface waste and/or contamination has not been confirmed or denied. The geophysical anomalies discovered during the RFI need to be excavated to determine if waste is present in the subsurface. The anomaly suspected of being associated with past waste management activities may be a burial trench and should be excavated. The anomaly measures approximately 200 ft by 100 ft. Assuming a potential waste depth of 10 ft, the volume of material in the suspected trench is approximately 7,400 CY. Groundwater and competent bedrock will be addressed as part of the groundwater operable unit. The soil excavation will extend to the depth that waste or waste residue is encountered or to bedrock, whichever comes first.
Excavated material will be characterized with TPH and TCLP metals (Texas Eleven) analyses prior to disposal. The estimated volume of waste material and waste residue present at AOC-56 is approximately 7,400 CY. Based on waste at most other SWMUs at CSSA, it is likely that this waste is non-hazardous.
Confirmation samples will be collected following removal/remediation to verify that no contamination remains. Analysis will include barium, chromium, copper, nickel, and zinc (SW-6010B), arsenic (SW-7060), cadmium (SW-7131A), lead (SW-7421), mercury (SW-7471A), VOCs (SW-8260B), SVOCs (SW-8270C), and explosives (SW-8330). Samples will be collected at a frequency of one per 100 linear ft of sidewall, with a minimum of one sample per wall. If the bottom of the excavation is bedrock, bottom samples will be collected at a frequency of one per 20,000 ft2 of bottom surface area, with a minimum of two per excavation area. If the bottom of the excavation is soil, bottom samples will be collected at a frequency of one per 100 ft (100-ft grids).
1. Excavate waste and waste residue in trench. If practical, separate metal debris for recycling.
2. Collect samples of excavated soils for waste characterization purposes. One composite sample consisting of five aliquots will be collected per 1,000 CY of soil. Analyze samples for TPH and TCLP antimony, arsenic, barium, beryllium, cadmium, chromium, lead, mercury, nickel, selenium, and silver. Dispose of any soils exceeding CSSA background criteria at Covel Gardens Landfill under waste profile CG-25591. The profile will be amended to include AOC-56 waste. It is estimated that approximately 7,400 CY of waste and contaminated soil will require disposal.
3. Collect samples of the excavation sidewalls and bottom. Samples will be analyzed for arsenic, barium, cadmium, chromium, copper, lead, mercury, nickel, zinc, VOCs, SVOCs, and explosives.
4. Continue excavation until RRS1 soil criteria or competent bedrock, whichever comes first, is reached.
5. Re-grade the site with clean fill and reseed.
6. Validate data and prepare Closure Report for AOC-56.