SWMU B-10 RFI Closure Report Section 3 - Conclusions and Recommendations

SWMU B-10 is a site used for disposal of metal scrap waste in the past, during an unknown time period. The site is located in the inner cantonment and has an area of approximately 3,700 ft². The vicinity of B-10 was included in soil gas surveys performed in July and December 1995 to investigate possible sources of groundwater contamination reported in Well CS-16. In March 1996 a geophysical survey was conducted in an adjacent area just south of SWMU B-10, and another soil gas survey was conducted in August 1996. The soil gas survey identified a detection of PCE in soil gas. The reported PCE concentration is part of a larger soil gas plume present in the vicinity of Well CS-16. In August 1997, UXO identification efforts at SWMU B-10 did not detect any UXO.

In August 2000, excavation to remove the buried metal scrap waste was conducted. Fourteen roll-off boxes of metal banding material (118.7 tons) were recycled off-post at Newell Salvage. Over 3,600 cubic yards of soil excavated from SWMU B-10 were disposed off-post at Covel Gardens Landfill and clean fill material was placed in the excavated areas at SWMU B-10. The majority of the waste material consisted of metal banding material. Other waste encountered during excavation included mufflers, brake pads, oil filters, miscellaneous five-gallon containers, empty 55-gallon drums, miscellaneous machine gun parts, and an engine block.

Confirmation soil samples collected from the base and sidewalls of the trenches following excavation, did not indicate any further contamination present at SWMU B-10, except for zinc and lead at various sample locations. Following the restoration of SWMU B-10 with clean fill to surface grade, the site was used temporarily as a depository for soils which were part of treatability studies being conducted for CSSA. Additional information concerning the PIMS treatability studies is located in Volume 4, Treatment Technologies, behind the Stabilization and Offsite Disposal tab.

Overall data quality objectives (DQOs) for the investigations at CSSA are provided in Volume 1-1 behind the RFI Addendum tab (Section 11 of the Work Plan Overview). A detailed list of DQOs for SWMU B-10, along with an evaluation of whether each DQO has been attained, is provided in Appendix B. As described in Section 1, the main objectives of the SWMU B-10 investigation are to determine if the site meets TCEQ requirements for RRS1 closure and to meet requirements of the 3008(h) Administrative Consent Order.

All data generated during the SWMU B-10 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification report is included in Appendix C. All data are considered useable for site characterization purposes. Although several results are flagged with an “M,” these results are considered usable because the matrix interference is minimal and does not significantly affect the sample results. Some results are flagged with a “J,” these results are considered usable because the estimation of quantitation does not significantly affect the sample results. Some results are flagged with an “R,” and this data is not considered usable, specifically two analytes, naphthalene and 1,2,4-trimethylbenzene, from sample B10-DE1. Results from six samples were flagged with a “B” for one analyte, methylene chloride, which was detected in the blanks associated with the samples on two different sampling dates, January 13, 2000 and August 22, 2000. All of the initial calibration, second source verification and internal standard criteria were within quality control limits, as described in the data verification report (Appendix C).

Soils that were treated as part of the PIMS remediation study at SWMU B-10 have been removed from the site. The location of the former study area at SWMU B-10 is shown in Figure B10-10.

Confirmation samples were collected in the fall of 2000 after all waste had been removed from SWMU B-10. An elemental lead concentration of 2343 mg/kg was reported for a confirmation sample collected from the base of the trench (#16). Confirmation samples collected from the bottom of the trench or the side wall were reported with elevated zinc concentrations of 226 mg/kg (#8), 131 mg/kg (#13), 89 mg/kg (#15), 1100 mg/kg (#17), and 148 mg/kg (#18). Background levels for lead and zinc are 85 mg/kg and 73 mg/kg, respectively. Because all waste material and soil were removed to the bedrock contact, the elevated concentrations at two locations were considered suspect. Therefore, a second sampling event was conducted on April 8, 2003, to resample the two locations with the highest concentrations, #16 and #17. The results were 1.27 mg/kg lead at #16 and 0.63 mg/kg zinc at #17. It should be noted that the licensed engineer certifying this report supervised the collection of the second set of samples to make sure native soils were sampled and not backfilled soils.

Because the waste has been removed and all remaining metals levels for soil samples (with the exception of the four samples with slightly elevated zinc levels well within one order of magnitude of the zinc background value) collected from the site are below the background concentrations for CSSA soils, closure under RRS1 is recommended.

I certify that the above-described closure was performed under my direction, in accordance with the work plan and 30 TAC §335 Subpart S, and as described in this report, and that, to the best of my knowledge and belief, said closure has been successfully accomplished.

Jason D. Shirley		May 29, 2003
Jason D. Shirley Installation Manager Camp Stanley Storage Activity		Date
Kirk W. Lawson		May 22, 2003
Kirk W. Lawson, P.E. State of Texas #79204 Parsons		Date

The Data Verification Report for SWMU B-10 analytical data also contains verification information for analytical data from other SWMU sites at CSSA.