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SWMU B-11 is located on the bank of the Salado Creek (Figure B11-2) and encompasses an area of approximately 0.92 acres. SWMU B-11 was reportedly used as a solid waste disposal area for an unknown period of time. The terrain at the site is very rough, due to erosion and trenching activities. Ammunition boxes, arms packing crates, and construction debris were found at SWMU B-11 during the initial field survey in 1993. Other types of waste visible at the western end of the site include cedar stumps, concrete rubble, wooden posts, tires, asphalt, and metal debris. Some of this debris is partially buried. No UXO has been observed at the site.
A partially-filled trench trending northwest-southeast is present immediately south of the creek bank. The trench, which is estimated to be 15 ft deep and 325 ft long, widens from 25 ft wide on the southeastern end to 100 ft wide on the northwestern end. A small soil mound is present west of the trench. Presumably, the soil mound is related to trenching activities.
Geophysical Survey
An EM geophysical survey was performed at SWMU B-11 in April 1995 to investigate the presence of subsurface metallic anomalies potentially related to past waste management activities. Two anomalies were identified, but they were both caused by the fenceline to the south of the site.
Soil Gas Survey
In July 1995, soil gas surveys were performed in the South Pasture at CSSA. Only one soil gas point was sampled within SWMU B-11. This soil gas survey point had a PCE concentration of 0.28 µg/L. Due to the very low concentrations detected in soil gas, the proximity of the groundwater PCE plume associated with SWMUs B-3 and O-1, and the lack of PCE detections in soil borings at the site, this low PCE concentration detected in soil gas at SWMU B-11 is presumed to be associated with groundwater contamination in the vicinity of Well CS-MW16. No other VOCs were detected in this sample.
Soil Borings
Five soil borings were drilled and sampled in February 2000 to investigate potential COCs in areas within the trench at SWMU B-11. A surface soil and two subsurface bedrock samples were collected from each boring and analyzed for VOCs, SVOCs, metals, and explosives. The borings indicated subsurface voids consistent with karst topography.
Of the surface soil samples, zinc and cadmium were detected above RRS1 closure standards for soils at SB01 and SB02, respectively. Bedrock samples retained from B11‑SB01 (19.5 to 20 ft bgs) contained arsenic, while B11-SB03 (4.5 to 5 ft bgs) contained barium, chromium, nickel, and zinc, all in excess of RRS1 closure standards.
Three VOCs were detected above RRS1 levels in the environmental samples: chloroform (3 samples), dichlorodifluoromethane (B11-SB01, 9.5 to 10 ft bgs only), and methylene chloride (14 out of 16 samples). However, as discussed in the SWMU B-11 RCRA Facility Investigation Report, the presence of these COCs is excluded from closure considerations due to the limited detections and/or their presence in associated blank samples. Methylene chloride is typically present in sampling equipment and was detected in low concentrations in the associated equipment blank, as was chloroform. The one detection of dichlorodifluoromethane was at a concentration of only 0.0106 mg/kg. Dichlorodifluoromethane, or Freon, is not known to have been disposed at any CSSA sites. Although associated blank samples did not contain dichlorodifluoromethane, its presence in only one sample from SWMU B-11 at such a low concentration could be related to the air-conditioning system at the laboratory.
Waste including tires, asphalt, metal scrap, and concrete rubble need to be excavated from the trench and removed from CSSA for off-post disposal to pursue RRS1 closure with respect to the soil unit at SWMU B-11. 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. It will include, at a minimum, the area around B11-SB01, B11‑SB02, and B11-SB03, and all waste in the trench.
An estimated 2,300 CY of soils and waste material will be generated in the excavation area. At that time, confirmation samples will be collected from the excavation area and analyzed for arsenic (SW-7060A), cadmium (SW-7131A), barium, chromium, nickel, and zinc (SW-6010B). Samples will be collected at a frequency of one per 100 linear ft of sidewall, with a minimum of one per sidewall. 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). If field investigation and excavation reveal additional waste material, the excavation area will be expanded and additional confirmation samples will be collected. After all excavation activities are complete, the entire site will be regraded to allow proper drainage.
After sample analysis confirms that all waste and waste residue have been removed from the site, the excavated areas will be backfilled with clean fill material, and the site will be re-graded and seeded.
1. Amend CSSA’s Waste Profile using B-11 RFI data. RFI data indicates that the waste at this site meets nonhazardous Class 2 criteria.
2. Excavate waste and waste residue in disposal trench. If practical, separate metal debris for recycling. It is estimated that 2,300 CY of contaminated soil and waste will be removed from the site. Dispose of any soils exceeding CSSA background criteria at Covel Gardens Landfill under waste profile CG-25591 C-2.
3. Excavate soils exceeding background criteria at B11-SB01, B11-SB02, and B11-SB03.
4. Collect samples of the trench/excavation sidewalls and bottom. Samples will be analyzed for arsenic, barium, cadmium, chromium, nickel, and zinc; these parameters exceeded RRS1 criteria in the soil samples collected in the trench area in 2000.
5. Continue excavation until RRS1 soil criteria or competent bedrock, whichever comes first, is reached.
6. Re-grade the site with clean fill and reseed.
7. Validate data and prepare Closure Report for SWMU B-11.