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Final AOC 65 Interim Removal Action Report
Section 2 - Investigation Activities
2.1 - Characterization Sampling
Soil samples were collected via a split-spoon sampler from 13 soil borings advanced west and south of Building 90 in April 2002 to delineate the extent of contaminated material outside of Building 90 that required excavation. The soil profile descriptions from these borings as provided in the field notes are presented in Appendix A. Composite soil samples were also collected from drummed soil generated during installation of site soil borings to profile the boring-generated waste for disposal. Twelve soil borings were drilled inside Building 90 for installing the subslab ventilation system. Collection of soil samples from these borings was planned to characterize contaminant levels beneath Building 90. However, samples were not collected from these borings, due to compaction of the material and because high heat generated by the auguring method would likely volatilize any residual VOCs. The 13 soil borings that were advanced by hollow-stem auger in April 2002 in areas west of Building 90 focused on the drainage ditch near the drainpipe outfall. One additional boring (CS-SB24) was advanced to the south of Building 90. The exterior boring locations, shown in Figure 2-1, were chosen to provide information regarding the volume of contaminated soils to be excavated. All soil borings outside of Building 90 were advanced until refusal was encountered, which was three feet or less for every boring. One soil sample was collected from each of the borings and analyzed for VOCs. Sample methodology and quality control procedures are described in the AOC-65 Treatability Study Sampling and Analysis Plan (SAP) Addendum. Analyticalresults from the soil borings were used to further define the limits of the planned excavation. Characterization soil samples taken from borings west and south of building 90 were analyzed for VOCs using Environmental Protection Agency (EPA) method SW8260B. The VOC analytical detections for the characterization soil borings advanced in April 2002 as part of the IRA are summarized in Table 2-1, Table 2-2, and Table 2-3 present comprehensive analytical results for all investigations conducted at AOC-65 for comparison purposes. Figure 2-2, Figure 2-3, Figure 2-4, and Figure 2-5 shows comprehensive sample locations for all investigations conducted at AOC-65 and presents analytical results for PCE, TCE, polychlorinated byphenyls (PCBs), and metals, respectively. Complete analytical results for all investigations conducted at AOC-65 and a sample chain of custody form are provided in Appendix B. PCE was detected in four characterization samples collected during the April 2002 sampling event. TCE was detected in three samples. The compound cis-1,2-dichloroethene (cis-1,2-DCE) was detected in two samples. Trans-1,2-dichloroethene (trans-1,2-DCE) was detected in one sample. The compound p-Isopropyltoluene was detected in one sample. The compound sec- was detected in one sample. The sample CS-SB18 (5-6�) had detectable concentrations of TCE,cis-1,2-DCE, trans-1,2-DCE, p-isopropyltoluene, and sec-butylbenzene. The concentrations of these compounds were, respectively, 12 micrograms per kilogram (�g/kg), 2.7�g/kg, 2.3�g/kg, 0.92 �g/kg, and 1.3 �g/kg. The sample CS-SB17 (12-13�) had a PCE concentration of 105 �g/kg. The sample CS-SB17 (6-8�) had PCE concentration of 122 �g/kg, a TCE concentration of 10.8 �g/kg, and cis-1,2-DCE concentration of 1.2�g/kg. The sample CS-SB16 (6-8�) had a PCE concentration of 14.1 �g/kg, and a TCE concentration of 10.5 �g/kg. The sample CS-SB15 (6-8�) had a PCE concentration of 0.93 �g/kg. All other samples were below detection limits for these compounds. Characterization subsurface soil samples taken from borings west of building 90 were also analyzed for PCBs using EPA method SW8081A/8082. The PCB analytical results are summarized in Table 2-1. All of these analytes were below detection limits except for 1254 in one sample. Sample CS-SB20 had an Arochlor 1254 concentration of 0.275 milligrams per kilogram (mg/kg).
The PCB levels are significantly below the Toxic Substance Control Act (TSCA) regulated concentrations of greater than 50 mg/kg, but it is important to note that PCBs were also identified in a sample collected from a ditch (AOC65-SB03) during a previous investigation, while CS-SB20 was sampled from soil underlying the asphalt pavement. These two detections suggest that PCBs need to be retained as contaminants of concern (COCs) for the portion of AOC-65 represented by the completed excavation.
Six ambient air samples were collected inside Building 90. Three of these samples were collected prior to commencing drilling activities inside the building and the other three samples were collected after drilling operations were completed. The samples were analyzed for PCE and TCE only.
One of the pre-drilling ambient air samples had nondetections for both analytes, while the other two pre-drilling samples had low PCE concentrations of 0.0152 milligram (mg) and 0.0126 mg. One of the post-drilling ambient air samples also had nondetections for PCE and TCE. A PCE concentration of 0.013 mg and a TCE concentration of 0.0168 mg were found in one of the post-drilling samples. The other post-drilling sample contained a low PCE concentration of 0.104 mg. The results of the ambient air sampling inside Building 90 indicate that low concentrations of PCE and TCE vapors are present. The analytical results for the ambient air samples are provided in Appendix B. Investigation-derived waste, mostly soil cuttings from drilling activities inside Building 90 and the shallow borings outside Building 90, were containerized in 18 drums. All analytes were below detection limits for the drill-cuttings drum samples. The analytes included toxicity characteristic leachate procedure (TCLP) metals (SW1311/6020), TCLP mercury (SW1311/7470A), and VOCs (SW8260B). These drums were added to excavated material generated during the IRA for off-post transport and disposal.
The soil borings in areas outside Building 90 were plugged to land surface with a cement and bentonite mix. Completion of borings completed in the asphalt parking lot west of Building 90 included a two-inch thick layer of asphalt patch at the surface.