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Final AOC 56 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
As described in Section 1, AOC-56 is an area suspected to have been used as a construction debris landfill. To investigate this possible waste management unit a geophysical survey was conducted and three surface soil samples were collected.
During the geophysical survey of AOC-56, it was determined that there were several areas that indicated EM anomalies. One of these areas suggested past waste management activities. Evidence that bedrock was removed was observed during the geophysical survey and multiple reflections indicating possible debris was also noted in both the EM and GPR surveys.
Surface soil samples were obtained to verify the presence or absence of VOCs, SVOCs, and metals. Analytical data gathered from the surface soil samples indicate slight RRS1 exceedances at SOC56-SS01 for the metals lead and zinc. Furthermore, the possibility of subsurface waste and/or contamination has not been confirmed or denied.
The anomaly suspected of being associated with past waste management activities measures approximately 200 feet by 100 feet. Assuming a potential waste depth of 10 feet, the volume of material in the suspected trench could be approximately 7,400 yd3.
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-56, 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-56 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 AOC-56 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification reports are included in Appendix B. All data are considered useable for site characterization purposes. Although several results are flagged with an “M”, these results are considered useable because the matrix interference is minimal and does not significantly affect the sample results. Results for one analyte, 3,3’-dichlorobenzidine, were flagged with “R”. This compound is not a constituent of concern at the site. Despite non-compliance of the percent difference for the continuing calibration, 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 B).
Because geophysical anomalies possibly indicative of buried waste have been identified, the site will not meet the TCEQ RRS1 requirement for removal of all waste. Several of the 3008(h) RFI requirements, such as identification of waste characteristics and determination of vertical extent of contamination, have also not yet been met.
Data evaluation regarding the geophysical survey performed at AOC-56 indicates probable locations of buried trash. Anomalies in the northwest portion of the area indicate landfill type anomalies that include multiple reflections. Additional actions are recommended to address the geophysical anomalies that give evidence to buried debris.
To identify the nature of the anomalies (grid points 50,50 to 50,100 (Figure AOC56-10) and 17,60 to 42,60 (Figure AOC56-7), it is recommended that the excavation of this anomaly be completed. It is estimated that approximately 7,400 yd3 could require excavation and disposal.
If buried waste is encountered, environmental sampling of the excavation is recommended to determine if contamination of the subsurface soil is significant and/or to verify that all waste residue has been removed. Samples should be collected from the sidewalls and the bottom of the excavation and analyzed for VOCs (SW-8260B), SVOCs (SW-8270C), barium, chromium, copper, nickel, and zinc (SW-6010B); arsenic (SW-7060A); cadmium (SW-7131A); lead (SW-7421A); and mercury (SW-7471A). If concentrations of excavation bottom and sidewalls exceed RRS1 levels, additional excavation would be necessary.