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AOC 36 RFI/Closure Report

Section 3 - Conclusions and Recommendations

3.1 - Conclusions

According to CSSA records, AOC 36 was used for disposal of 155mm mustard gas shells in 1942. The Army Chemical Corps Technical Escort Unit decontaminated the shells in 1958 and certified the site as cleared. Additional efforts were undertaken in 1997 to confirm the removal of the mustard gas shells. In February 1997, a magnetometer sweep was completed of the area to detect buried mustard gas canisters or other UXO material. Subsequently, AOC 36 was closed by TNRCC in July 1999 with regard to mustard gas contamination. 

Based on the 1995 soil gas survey results additional soil samples were collected in January 2000. These samples were collected to evaluate the occurrence of chlorinated hydrocarbons in a soil gas plume in the vicinity of Well CS-16. No VOCs were detected in the ten surface soil samples collected at the site, indicating that the source of the soil gas plume in the vicinity of Well CS-16 originates from another waste management unit other than AOC 36. Although the soil sampling effort did not include carbon tetrachloride analysis, this analyte was found in only one soil gas sample collected at the site, and the concentration was only 0.2 mg/L. PCE was also detected in soil gas at this location, but PCE was not detected in any of the surface soil samples.

Table AOC36-1 indicates that no VOCs were detected in any sample and all concentrations reported were less than the RLs. Therefore, AOC 36 should be considered clean and closure should be granted.

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 AOC 36, 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 AOC 36 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 AOC 36 investigation were reviewed to confirm conformance with the AFCEE QAPP. The data verification report is included in Appendix B. All data are considered useable for site characterization and closure purposes, as described in Appendix C.

3.3 - Recommendations

Closure under RRS1 is recommended for AOC 36. Although low levels of chlorinated hydrocarbons were detected in soil gas samples collected at the site in 1995, surface soil samples show that these analytes are not detectable in surface soil. Furthermore, former removal of mustard gas canisters has been confirmed and approved by TNRCC and no geophysical anomalies related to past waste disposal activities were identified at the site. 

For the reasons aforementioned, it is respectfully requested that AOC 36 be granted closure by the TNRCC in accordance with RRS1.

3.4 - Certification

Partial Facility Closure Certification

Area of Concern 36

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.