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SWMU B-31 RCRA Facility Investigation/Closure Report

Section 3 - Conclusions and Recommendations

3.1 - Conclusions

SWMU B-31 is a site where contaminated sand was suspected to have been used as backfill around a PVC sanitary sewer pipe. A geophysical investigation in 1996 revealed three subsurface geophysical anomalies, none of which were related to waste or closure considerations. In 1996, three surface samples were collected and three soil borings were advanced to determine the extent of contamination. In 1997, test pits were dug at the site with the intent of identifying the extent of waste material, excavating it, and disposing of the waste material. However, no evidence of waste material could be found. All analytical data from 1996 and 1997 associated with the surface, subsurface and test pit samples were rejected by the EPA in 1999.

In March of 2000, surface and subsurface samples were collected in support of site closure and the analytical results indicated that RRS1 was met for explosives and VOCs. However, zinc concentrations for samples from a depth of 9.5 feet bgs slightly exceeded CSSA background levels in the central (RW-B31-SB02) and north-central (RW-B31-SB01) portions of the site. The zinc concentrations were 21.2 mg/kg and 14.2 mg/kg for SB01 and SB02, respectively and the background value is 11.3 mg/kg (as reported in the TNRCC-approved Second Revision to the Background Metals Concentrations in Soils and Rock at CSSA). These concentrations do not exceed the Texas-specific median concentration for zinc background is 30 mg/kg (30 TAC 350.51 [m]).

3.2 - Evaluation of Data Quality Objectives Attainment

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-31, along with an evaluation of whether each DQO has been attained, is provided in Appendix C. As described in Section 1, the main objectives of the SWMU B-31 investigation are to determine if the site meets TNRCC requirements for RRS1 closure and to meet requirements of the 3008(h) Administrative Consent Order.

All data generated during the SWMU B-31 investigation were reviewed to confirm conformance with the AFCEE QAPP. The data verification report is included in Appendix D. All data are considered usable for site characterization and closure 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. Results for one analyte, cadmium, were flagged with “R”. However, the data are still considered usable, as described in Appendix D.

Since no evidence of waste material was found, all requirements have been met for TNRCC RRS1 closure and the consent order.

3.3 - Recommendations

The work plan indicates that, if subsurface sampling reveals constituent concentrations greater than the concentrations required for RRS1 closure, the site may not be closed under RRS1, and further actions are required for RRS1 site closure. However, it is suggested that SWMU B-31 may be closed under RRS1, despite slightly exceeding background values for zinc in samples collected at 9.5 ft bgs.

The site was suspected of having lead-shot-contaminated sand surrounding a pipe. This sand was thought to have extended to a depth of three feet. However, no shot or any other sign of contamination was visually observed in any fieldwork, including the excavation of seven test pits with dimensions of six feet square by five feet deep. 

Lead, copper and zinc were detected in the shallow surface samples from SWMU B-31 at concentrations below RRS1. These metals are typically associated with lead shot contamination. Concentrations of the three metals are also less than background values for samples collected at depths from five to seven feet bgs. These depths are intermediate between the suspected contaminated sand and the detected zinc samples at 9.5 feet bgs. This suggests that the samples with elevated levels of zinc from a depth of 9.5 feet bgs, are not related to suspected lead shot contaminated sand near the surface.

Finally, the zinc concentrations of these samples, 14.2 and 21.2 mg/kg, are not significantly above the background concentration of 11.3 mg/kg. The Texas-specific median background concentration (30 TAC §350.51(m)), which replaces the background number for metals in the event that background numbers have not been determined, is 30 mg/kg for zinc. The concentrations that exceed CSSA background are 14.2 and 21.2 mg/kg, which are significantly less than the Texas-specific median background concentration.

Several conclusions can be drawn from the zinc concentrations at SWMU B-31. First, the zinc concentrations that exceed RRS1 are less than the Texas-specific median background concentration. Second, the concentrations are not significantly greater than background and appear to be unrelated to potential surface contamination. Third, no other COCs were detected above RRS1 closure concentrations. For these reasons, it is suggested that the elevated zinc concentrations should not be an issue relative to the closure of SWMU B-31 under RRS1.

For the reasons aforementioned, it is respectfully requested that SWMU B-31 be granted closure by the TNRCC in accordance with RRS1.

3.4 - Certification

PARTIAL FACILITY CLOSURE CERTIFICATION
SOLID WASTE MANAGEMENT UNIT B-31

Department of the Army
Camp Stanley Storage Activity
Boerne, Texas

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.