[Home]
SWMU B-26 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
SWMU B-26 was identified to contain a trenched area with a series of low soil piles paralleling the trench and circular soil piles at both ends. The dates of its usage are unknown, and it is presently not used. However, it is suspected of being a previous waste disposal site. Investigations revealed only one subsurface geophysical anomaly potentially related to waste management activities. The analyses of surface and subsurface samples collected in 1996 were rejected in 1999 by the EPA.
Surface and subsurface soil samples were collected at five locations as part of the resampling event conducted in March 2000. None of the surface soil samples contained contaminants of concern at concentrations above RRS1 criteria.
Within the Upper Glen Rose Limestone, zinc and chromium were the only metals for which the sample analytical results were greater than the calculated background level. The chromium concentration of 9.7 mg/kg, reported for one subsurface sample, only slightly exceeds the background concentration of 8.1 mg/kg. The total chromium Texas-specific median background concentration (30 TAC §350.51(m)), which replaces the background number for metals in the event that background numbers have not been determined, is 30 mg/kg. Further, there is no known historical usage of chromium (VI) at CSSA. Therefore, any chromium present is the soils is likely to be trivalent chromium, which is very insoluble and therefore immobile. This significantly reduces the concern for chromium at SWMU B-26 and suggests the chromium does not require additional work at SWMU B-26.
Reported zinc concentrations of 11.9 mg/kg, 13.9 mg/kg, 14.8 mg/kg, and 17.5 mg/kg in the subsurface at SWMU B-26 do not greatly exceed background (11.3 mg/kg). The reported concentrations are less than the Texas-specific median background concentration (30 mg/kg).
Bis(2-ethylhexyl)phthalate was detected in samples collected from the Upper Glen Rose Limestone in RW-B26-SB01 and RW-B26-SB03. Since bis(2-ethylhexyl)phthalate is a common field and lab contaminant, and it is the only SVOC present in the samples, it may be argued that the bis(2-ethylhexyl)phthalate detected in rock samples at SWMU B‑26 is related to field/lab bias, and is not present at SWMU B-26.
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-26, 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-26 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-26 investigation were
reviewed to confirm conformance with the
AFCEE
QAPP; the data verification report is included in
Appendix C.
All data are
considered useable for site characterization purposes.
Because a geophysical anomaly possibly indicative of buried waste has been identified, the site may 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.
Although chromium and zinc concentrations slightly exceed background in several subsurface samples, the concentrations were below the Texas-specific median background concentrations. Therefore, further work to address these metals levels is not recommended. In addition, further work to address the detections of the common laboratory contaminant, bis(2-ethylhexyl)phthalate, is not recommended.
However, because the source of the anomaly in the northwest corner of SWMU B‑26 has not been identified, excavation of a test pit in the area of this anomaly is recommended. A hand-held magnetometer can be used to reacquire the anomaly. If no waste is encountered, closure of the site under RRS1 is recommended. If waste is encountered, it should be characterized and disposed of. After all waste and waste residue has been removed and verification sampling results confirm cleanup is complete, the site should be re-graded with the available stockpiled soil.