[Home]
Final Solid Waste Management Unit B-4 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
SWMU B-4 was reportedly used as a solid waste disposal area during an unknown period of time to burn classified documents, miscellaneous trash, and ordnance-related materiel. Three long, linear, anomalous areas oriented in the north-south direction were identified on the SWMU B-4 EM contour maps in 1995. The anomalies possessed large deviations from background values in the EM readings. Three separate trenches can be inferred from a GPR profile acquired at the site and these are probably the result of ground disturbance related to past waste disposal activities. Soil gas samples collected at the site detected a maximum PCE concentration of 3.8 mg/L.
Barium, cadmium, chromium, mercury, copper, nickel, and zinc concentrations exceeded applicable RRS1 comparison at SWMU B-4. Of these metals, only barium, mercury, and nickel concentrations exceeded the Texas-specific median background concentrations. There is no median background level for cadmium.
Three target VOC compounds were detected above RRS1 (RL) levels in the subsurface soil samples; toluene, methylene chloride, and dichlorodifluoromethane. Toluene was detected above the RL (0.005 mg/kg) in three samples. The highest detected toluene concentration of 0.0103 was found in sample B4-SB09 (0-0.5 ft). Methylene chloride concentrations exceeded the RL in three samples; however, each of these detections were B flagged indicating the analyte was found in an associated QA/QC blank sample. The methylene chloride concentration in the associated blank samples may indicate contamination of the normal samples at the laboratory during handling and analysis. The RL for dichlorodifluoromethane of 0.005 mg/kg was exceeded twice. Dichlorodifluoromethane is also named Freon, which is not known to have been disposed at CSSA.
The SVOC bis(2-ethylhexyl)phthalate was detected above the RL (0.7 mg/kg) in four samples. Those samples were B4-SB09 (14.5-15 ft) FD, B4-SB11 (5-5.5 ft), B4-SB11 (9.5-10 ft), and B4-SB11 (15-15.5 ft) and the concentrations were 4.7 mg/kg, 14.0 mg/kg, 6.9 mg/kg, and 2.2 mg/kg, respectively. This was the only detection of an SVOC in the environmental samples submitted for analysis. The detections of bis(2-ethylhexyl)phthalate may be due to the samples being contaminated by the gloves that were worn by the samplers or may have been introduced in the laboratory. For health and safety reasons, the use of gloves when field sampling was necessary. Use of trowels was not practical due to the difficulty in breaking up rock samples to fit into sampling jars. Alternatively, bis(2-ethylhexyl)phthalate is a common laboratory contaminant and may have been introduced during analysis.
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-4, 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-4 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-4 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification reports are included in Appendix C. The majority of the data are considered useable for site characterization purposes. Twelve SVOCs in the duplicate sample collected at B4-SB16 (0-0.5 ft bgs) have been rejected due to poor surrogate recovery. However, these analytes were not detected in the original sample collected at this location, and the 12 analytes are not contaminants of concern. In addition, mercury results at B4-SB14 (4.5-5 ft, 8-10 ft, and 8-10 ft FD) and B4-SB13 (14.5-15 ft) were rejected, and arsenic results at B4-SB11 (15-15.5 ft) and B4-SB08 (10-10.5 ft) were rejected. However, since such a small number of samples were rejected and since these analytes did not exceed background in the majority of the site samples, these rejections do not compromise the site characterization.
Because there is known to be buried waste at the site, it does not meet the TNRCC 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.
Analytical results for the numerous soil boring samples collected at the site show only limited contamination at levels above RRS1 criteria. However, there is known to be buried waste at the site, and the nature of the waste is not fully known.
Closure of SWMU B-4 under RRS1 would require excavation and proper disposal of the waste. Because of the possibility of UXO within the trenches, the excavation should be overseen by a UXO specialist. Analytical results indicate that significant over-excavation of the trenches to remove waste residue would not be necessary. The location of boring B4-SB16 should also be excavated to a depth of one foot and a confirmation sample for cadmium and mercury should be collected. Prior to backfilling the trench areas with clean fill, confirmation samples should be collected from the trench bottoms and walls to verify that waste residue has been removed. Due to concentrations of barium, cadmium, chromium, mercury, copper, nickel and zinc reported at levels above RRS1 criteria, these metals should be analyzed during confirmation sampling.