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SWMU B-23A TO0019 Work Plan Addendum
December 2003
Site Description and History
SWMU B-23A is an area where an in-filled trench was observed in a 1966 aerial photograph. The dates of usage are unknown. The site covers approximately 0.3 acres in the north pasture (Figure B23A-2).
Several small (1/2-inch length, 1/4-inch diameter) ampoules are present on the surface of the in-filled trench, which were determined to be time-delay fuses for M34 Delay Firing Devices. The ampoules contained liquids of various colors, which correspond to different delay periods.
Summary of Previous Investigation Results
Geophysical Surveys
A geophysical survey was conducted at SWMU B-23A in 1995. No geophysical anomalies were found within the site.
Soil Gas Surveys
In 1996, a soil gas survey was performed at the site. The samples were analyzed for benzene, toluene, ethylbenzene, total xylenes, DCE, TCE, and PCE. Toluene was detected in one of the soil gas samples collected at the site. No other VOCs were detected in the samples.
Surface and Ampoule Samples
In January 2003, three surface samples were collected within the trench area at SWMU B-23A and analyzed for metals, VOCs, and SVOCs. Seven ampoules have also been collected from the site for analysis. Five of these were collected in 2001 and two more were collected in 2003.
VOCs and SVOCs were not detected above RRS1 closure standards in surface soils; however, copper slightly exceeded RRS1 standards in one soil sample, CS-B23A-1. The ampoule samples did not contain any COCs above RRS1 concentrations; however, they did contain a number of tentatively-identified compounds at elevated concentrations including n-butyl acetate, dimethyl phthalate, ethyl ester, and butyl or isobutyl ester.
Closure Plan and Sampling Recommendations
Closure of SWMU B-23A under RRS1 requires removal of waste visible on the ground surface at the site (ampoules) and removal of contaminated soil at the site. Geophysical survey results indicate that there is no buried metal within the trench. However, test pits will be excavated within the trench area to confirm that no other waste has been disposed of in the trench. The ampoules and any other waste encountered must be removed from CSSA for off-post disposal to pursue RRS1 closure with respect to the soil unit at SWMU B-23A. 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 should be characterized with TPH and TCLP metals (Texas Eleven) analyses prior to disposal. The estimated volume of waste material and waste residue present at SWMU B-23A could be up to 2,420 CY, if the trench does contain waste. This estimate is based on an assumed trench depth of 5 ft. Based on waste at most other SWMUs at CSSA, it is likely that this waste is non-hazardous. Confirmation samples should be collected following removal/remediation to verify that no contamination remains. Analysis should include copper (SW-6010B) and SVOCs (SW-8270C). 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 samples per excavation area. If the bottom of the excavation is soil, bottom samples will be collected at a frequency of one per 100 square ft.
Following excavation of waste and waste residue, any resulting trenches should be backfilled with clean fill and the site restored.
Summary of Planned Work
Excavate waste and waste residue on the ground surface and within the trench. If practical, separate metal debris for recycling.
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 SWMU B-23A waste. It is estimated that approximately 2,420 CY of waste and contaminated soil will require disposal.
Collect samples of the excavation sidewalls and bottom. Samples will be analyzed for copper and SVOCs; copper exceeded RRS1 criteria in the samples collected at the site in January 2003, and SVOCs (tentatively-identified compounds) were detected in the ampoules.
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-23A.