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TO0019 Work Plan Addendum, SWMU B-23
December 2003
Site Description and History
SWMU B-23 contains a trench identified from a 1966 aerial photograph. During a field survey in September 1993, a northeast-southwest trending trench was identified. The trench is approximately 150 ft long and 30 ft wide. The trench has partially filled in with locally eroded sediments and is covered in native grass. Several unidentified, half-buried, green canisters and a large soil mound were located towards the southern-most end of the trench. Metal banding was also littered across the surface of the trench area. UXO specialists from UXB International visually surveyed the site in 1997 and suggested that the unidentified canisters were likely Jet-Assisted Take-Off (JATO) canisters. The exact dates of usage for the trench are unknown. The boundary for SWMU B-23 is shown in Figure B23-2.
Summary of Previous Investigation Results
Geophysical Survey
In March 1995, an EM survey was conducted at SWMU B-23. Two anomalies were revealed by the survey. Both of these anomalies correspond to known metallic surface items (JATO canisters and metal banding).
Soil Gas Survey
In August 1996, a soil gas survey was performed at SWMU B-23. Seven soil gas points were sampled along the length of the trench area for benzene, toluene, ethylbenzene, and xylenes (BTEX) compounds, cis-1,2-dichloroethene (DCE), 1,1,1-trichloroethane (TCA), trichloroethene (TCE), and PCE. Samples were collected at depths ranging from 3 to 5 ft bgs. None of the seven soil gas samples reported detectable concentrations.
Soil Borings
In March 2000, three soil borings were advanced to characterize the subsurface in and around the trench. B23-SB01, B23-SB02, and B23-SB03 were drilled to depths of 9.5 ft bgs, 10.5 ft bgs, and 10 ft bgs, respectively. The soil borings were located in the most probable areas of contamination. One of the soil borings (B23-SB03) was advanced near the middle of the trench, where metal banding was present. The other borings, B23-SB01 and B23-SB02, were advanced in the southernmost end of the trench, near the green canisters and the soil mound identified during the field survey effort. Four surface soil samples and six subsurface bedrock samples were collected and analyzed for VOCs, SVOCs, metals, and explosives.
Borings SB01 and SB02 were advanced were advanced in the area of the JATO canisters and the soil mound. The soil samples for boring SB01 contained copper in excess of RRS1 closure standards and the subsurface samples for SB02 contained barium and zinc at 5.5 to 6 ft bgs and 10 to 10.5 ft bgs, respectively. Both soil samples also contained VOCs, as did the bedrock samples from SB02. VOCs detected at concentrations greater than the reporting limit included benzene, ethylbenzene, toluene, and xylenes.
Boring SB03 was advanced near the middle of the trench, near the metal banding. Barium, lead, nickel, and zinc were found in concentrations above RRS1 closure standards in the deepest bedrock sample (9.5 to 10 ft bgs). All the SB03 samples contained dichlorodifluoromethane (Freon). Dichlorodifluoromethane is not known to have been disposed of at CSSA, and its presence in the B-23 samples is suspected of being associated with the laboratory analysis.
No other COCs were detected in the samples retained from these borings.
Closure Plan and Sampling Recommendations
Closure of SWMU B-23 under RRS1 requires removal of waste visible on the ground surface at the site and delineation and subsequent remediation or removal of contaminated soil at the site. The trench may potentially contain buried metallic waste, so test pits will be excavated to determine of further excavation is necessary, after the surficial metallic waste is removed from the site. Soil in the vicinity of SB01 must also be excavated and disposed of due to above-background copper concentrations at that location. The waste must be removed from CSSA for off-post disposal to pursue RRS1 closure with respect to the soil unit at SWMU B-23. 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.
The estimated volume of waste material and waste residue present at SWMU B-23 is approximately 1,700 CY. This estimate is based on an assumed trench depth of 10 ft. Waste characterization will be accomplished with existing RFI analytical data. Confirmation samples should be collected following removal/remediation to verify that no contamination remains. Analysis should include barium, copper, nickel, and zinc (SW-6010B), lead (SW-7421), benzene, toluene, ethylbenzene, xylenes, and dichlorodifluoromethane (SW-8260B), based on RFI soil boring results. Samples should also be analyzed for perchlorates (EPA 314.0 modified for soil), which has not been analyzed at this site in the past. Samples will be collected at a frequency of one per 100 linear ft of sidewall, with a minimum of per 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 samples 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).
Following excavation of waste and waste residue, any resulting trenches should be backfilled with clean fill and the site restored. If no buried waste is encountered, three surface soil samples should be collected in the area in which the JATO tanks were found. These samples should be analyzed for perchlorates only.
Summary Of Planned Work
Amend CSSA’s Waste Profile using B-23 RFI data. RFI data indicates that the waste at this site meets nonhazardous Class 2 criteria.
Collect three soil samples in the area in which the JATO tanks were found on the ground surface.
Excavate waste and waste residue on the ground surface and within the trench. Excavate soil in the vicinity of SB01, where the JATO canisters were located and surface soil contained above-background concentrations of copper. If practical, separate metal debris for recycling. It is estimated that 1,700 CY of soil and waste material will be excavated and disposed of from this site. Dispose of any soils exceeding CSSA background criteria at Covel Gardens Landfill under waste profile CG-25591 C-3.
Collect samples of the excavation sidewalls and bottom. Samples will be analyzed for benzene, ethylbenzene, toluene, xylenes, dichlorodifluoromethane, barium, copper, lead, nickel, and zinc; these parameters exceeded RRS1 criteria in samples collected at the site in 2000.
Continue excavation until RRS1 soil criteria or competent bedrock, whichever comes first, is reached.
Re-grade the site with clean fill and reseed.
Validate data and prepare Closure Report for SWMU B-23.