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Final AOC 65 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
Previous
work
AOC-65 consists of Building 90 and potential source areas located in and adjacent to Building 90. Potential VOC source areas included a sub-slab, concrete-lined former solvent vault where a metal vat used for processing of ordinance with chlorinated cleaning solvents was located, building drain lines, and the rain gutter drain line outfall. Use of chlorinated solvents ceased in 1995 the vat was removed, and the vault was covered for installation of a citrus-based cleaning machine.
Investigations at the site began in 2000, when soil samples were collected underneath the former solvent vault area that housed the metal vat in Building 90, and a soil boring was advanced 15 feet down gradient of the building drain line terminus extending from Building 90. A soil gas survey, performed in January and February 2001, revealed a PCE plume in the soils beneath and to the south and west of Building 90. The highest PCE concentrations were recorded in the vicinity of the former metal vault. A smaller TCE plume near the same area in Building 90 was also defined. In 2001, 14 borings were advanced in and around Building 90. Four of those borings were completed as five monitoring wells. Groundwater samples were collected from borings and monitoring wells, as available.
The
Drainage Outfall
Soils in the area where the drainage line from Building 90 meets the drainage ditch and where borings SB-3 and SB-1 were advanced contain the highest soil COC concentrations from the samples collected in this field effort. PCE (124.434 mg/kg) TCE, TPH-DRO, TPH-GRO, Arochlor, and several metals (chromium, copper, zinc, lead, and cadmium) in the soils of SB-3 all significantly exceeded soil background/RL concentrations. However, in the SB-3 bedrock sample (21.0 to 21.5 feet), lead, barium, chromium, and nickel only slightly exceeded background, suggesting that the COCs are limited to the soils.
The borings nearest SB-3 contain considerably lower concentrations of the COCs than those encountered in the SB-3 soil sample. Bedrock PCE does not exceed the RL for nearby SB-1, and exceeds the RL by a less than a factor of 10 for nearby SB-11. Therefore, the lateral extent of PCE and the other COCs may be limited to the portion of the drain line represented by sample SB-3, and the vertical extent appears to be limited to the near surface.
However, TPH-DRO and TPH-GRO concentrations were 1,500 and 500 mg/kg, respectively, for both SB-1 (0.75 to 1.25 feet) and SB-3 (1.5 to 2.0 feet). These concentrations exceed RLs (50 mg/kg) for both samples, suggesting that the vertical extent of contamination in the area extends to SB-1.
Under
Building 90
3.2 - Evaluation of Data Quality Objectives Attainment
Overall 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-65, along with an evaluation of whether each DQO was attained, is provided in Appendix G. As described in Section 1, the main objectives of the AOC-65 investigation are to determine if the site meets TNRCC requirements for RRS1 closure and requirements of the 3008(h) Administrative Consent Order.
All data generated during the AOC-65 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification report is included in Appendix F. All data are considered usable 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.
Because contamination has been identified, the site will not meet the TNRCC RRS1 requirement for removal of all waste. Several of the 3008(h) RFI requirements, such as determination of lateral and vertical extent of contamination, have also not yet been met. Because the possibility that remedial activities need to be considered, analytical results were not compared to TRRP standards.
At this time, closure under RRS1 is not attainable and will likely not be possible, given the nature of the contamination, the accessibility to the source area, and the complexity of the subsurface soils and fractured bedrock. Further work should be done at and around AOC-65 to define the extent and treatability of the PCE plume and to delineate the extent of contamination around the drainage lines.
Specifically, the area where the drainage line from Building 90 meets the drainage ditch, where borings SB-3 and SB-1 were advanced, should be characterized for the extent of contamination via soil sampling. Removal actions of the surface soils along the drain line, associated ditch, and the former vault area in Building 90 should be undertaken.
Treatability studies should be undertaken at Building 90 as an interim removal action to evaluate SVE or other potential treatment technologies. The extent of the PCE plume should be determined on the west and south sides of Building 90 by sampling the soil borings to be drilled for installation of a treatability test system.
Continued monitoring of groundwater samples and remediation of the soils where the highest concentrations of PCE occur will contribute to determining and reducing the mobility of PCE under and around Building 90.