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SWMU B-11 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
SWMU B-11 was reportedly used as a solid waste disposal area during an unknown period of time for ammunition, scrap metal, and construction debris. An approximately 325-feet-long trench containing partially buried waste extends northwest to the southeast across the site. A geophysical survey conducted in 1995 revealed no EM anomalies; however, debris observed at the site includes concrete rubble, wooden posts, tires, asphalt, and metal debris. Soil boring logs report voids and lost circulation in three of the borings, indicating karst limestone conditions in the subsurface.
In February 2000, five soil borings were drilled at the site. Metals that were above the RRS1 limit included arsenic, barium, cadmium, chromium, and nickel. Arsenic, barium, cadmium, chromium and nickel were each detected above the RRS1 level only once, with the barium, nickel, and chromium detection occurring in the same sample. Zinc detections occurred in two samples, B11-SB01 and B11-SB03.
Methylene chloride, chloroform, and dichlorodifluoromethane were present in the subsurface at levels that exceeded RLs. Dichlorodifluoromethane was detected above the RRS1 level only once. Methylene chloride is a common laboratory contaminant, and chloroform was also detected in an associated blank sample.
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-11, along with an evaluation of whether each DQO has been attained, is provided in Appendix D. As described in Section 1, the main objectives of the SWMU B-11 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-11 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification reports are included in Appendix C. All data are considered usable for site characterization purposes. Although several results are flagged with a “J”, these results are considered usable because estimation of the quantitation does not significantly affect the sample results.
Waste including tires, asphalt, metal scrap, and concrete rubble has been disposed and partially buried at the site. This disposal area is apparently situated over karst voids, and the trench has not been graded or capped. Since the contents of this disposal area are not known and they are situated over a potential pathway for contamination of groundwater, it is recommended that the wastes be excavated and properly disposed of. Groundwater is being addressed as part of the groundwater investigation currently underway at CSSA. Since the results for the five borings sampled at SWMU B-11 indicate very low contaminant levels, only limited verification sampling for the chemicals detected (arsenic, barium, chromium, cadmium, nickel, and zinc) would be necessary to confirm that no contamination remains after excavation has been completed. Initial excavation is recommended at RW-B11-SB01, RW-B11-SB02, and RW-B11-SB03 in the former trench to a depth of four feet or until waste material is no longer encountered. An estimated 2,300 yd3 of soils and waste material will be generated in the initial excavation area. At that time, confirmation sampling for arsenic, barium, chromium, cadmium, nickel, and zinc should be conducted. If field investigation and excavation reveal additional waste material, the excavation area should be expanded and additional confirmation samples will be collected.