[RFI Report]

SWMU Demo Dud Area (DD) Area RCRA Facility Investigation Report

Section 3 - Conclusions and Recommendations

3.1 - Conclusions

Records regarding past historic use of this site are not available, but investigation results indicate that this area was used for disposal of metal scrap and UXO. UXO removal activities were performed in May 1997 by UXO specialists. The UXO removal actions resulted in the removal of 240 UXO items and approximately 10,040 pounds of metal scrap, and the stockpiling of 278 cubic yards of sifted soil.

Soil borings drilled at the site in March 2000 showed some slight exceedances above RRS1 criteria in subsurface soil/rock samples. The only analytes detected above RRS1 criteria in subsurface samples were methylene chloride, which was also detected in the laboratory blank, and cadmium. The cadmium exceedance was detected in a sample collected at the interface of soil and Glen Rose Limestone. The concentration of cadmium detected there (0.20 mg/kg) is consistent with soil sample concentrations. It is possible that this Glen Rose sample contained some soils, which would result in a higher cadmium concentration. No other samples collected at the site showed cadmium levels above CSSA background levels. Based on soil boring results, contamination has apparently not migrated from the trench.

However, soil samples collected around the trench and samples of sifted soil showed above background levels of several analytes, including copper, lead, mercury, zinc, toluene, and SVOCs, in surface soils at the site. Additional efforts are required by the Consent Order to address the sifted soils generated during the UXO activities, and a soil pile disposition assessment is currently underway. Based on the surface soil and sifted soil sample results, COPCs include copper, lead, mercury, zinc, toluene, and SVOCs.

3.2 - Evaluation of Data Quality Objectives Attainment

Overall data quality objectives (DQOs) for the investigations at CSSA are provided in Volume 1-1, RFI Addendum (Section 11 of the Work Plan Overview). A detailed list of DQOs for the DD Area, 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 DD Area 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 DD Area investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification report is included in Appendix E. Several samples were flagged with an "M" due to matrix interference. All data are considered useable for site characterization purposes. All "M" flagged data is considered usable per the AFCEE QAPP.

Review of the inorganic sample results indicates the matrix interference in these samples is significant. After verifying all compliant laboratory control data, and the spiking solutions, it was determined that the matrix effect was due to the occurrence of high-level concentrations of metals in some samples. However, the level of bias toward accuracy of results cannot be mathematically determined.

Review of the organic sample results also indicates that the matrix interference is significant. Two months of laboratory control charts were checked and it appeared that the percent recoveries were compliant, however, they were on the low end of the acceptable control limits.

Excavation and soil sifting activities completed at the site have removed all identified buried wastes at the DD Area. Several of the 3008(h) RFI requirements, such as determination of vertical extent of contamination, have not yet been met. The 3008(h) IM requirements are currently underway.

3.3 - Recommendations

Contaminated soil stockpiled at SWMU DD is being addressed as part of a Soil Pile Disposition Assessment. The purpose of this assessment is to test remediation options for this and similarly contaminated soils stockpiled at SWMUs B-8, B-20, B-24, and B-28. It is recommended that the remediation option identified during this assessment also be utilized on contaminated surface soils still in place at SWMU DD.

Prior to initiating this remediation, additional surface soil samples should be collected at this site to identify the extent of contamination. This surface soil sampling should focus on the former trench where COCs were identified close to the closure criteria and soil stockpile/areas around them where soils would erode. Based on results of the RFI surface soil sampling and the IM stockpile soil sampling, additional surface soil samples should be analyzed for copper and zinc (SW-6010B), lead (SW-7421), mercury (SW-7471A), VOCs (SW-8260B), and SVOCs (SW-8270C). It is recommended that arsenic, barium, cadmium, chromium, nickel, and explosives be deleted from the COPCs list for SWMU DD since they were not detected above background levels.