[Home]
SWMU B-8 RCRA Facility Investigation Report Addendum
Section 3 - Conclusions and Recommendations
SWMU B-8 was initially identified during the 1993 Environmental Assessment when debris was visually observed on the ground surface. The location of this material corresponded to the location in a 1966 aerial photograph which showed ground disturbance. Based on the presence of fire bricks and ammunition on the ground surface, it was presumed that the area was used to burn ammunition and related waste.
A potential for buried waste, possibly including UXO, was also identified based on results of the 1995 geophysical survey, which identified a magnetic anomaly in the presumed former burn area. Therefore, in 1997, UXO specialists excavated the anomaly with the intention of removing any UXO. However, only a shallow concrete platform was found. This platform was removed and disposed, and approximately 250 cubic yards of excavated soil were stockpiled on site for future disposition. No other evidence of subsurface waste or disturbance was identified.
Soil borings drilled at the site in 2000 were located around the former location of the concrete platform. Concentrations of metals in surface soil greatly exceed RRS1 criteria, and also exceed Tier 1 criteria. Concentrations in the underlying limestone also exceed RRS1 criteria; however, the exceedances are very slight and may be representative of background. Furthermore, only one sample (SB02, 7 to 7.5 feet bgs) exceeded Texas-specific median background concentrations (for copper and zinc).
Based on the elevated contaminant concentrations in surface soil and the presence of the concrete platform, it is concluded that the site was most likely used only as a burn area, and that the burns may have taken place on top of the concrete platform. Surface soil contamination is similar to that found in the stockpiled soil.
3.2 - Evaluation of Data Quality Objectives Attainment
Overall DQOs for the investigations at CSSA are provided in Section 11 of the Work Plan overview (Volume 1-1, RFI Addendum). A detailed list of DQOs for SWMU B-8, 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 SWMU B-8 investigation are to determine if the site meets TNRCC requirements for RRS1 closure and to meet requirements of the consent order.
All data generated during the SWMU B-8 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification reports are included in Appendix D. All data are considered usable for site characterization purposes. Although several results are flagged “M,” these results are considered usable because the matrix interference is minimal and does not significantly affect results. Two cadmium results flagged “R” are also considered usable. These results were flagged with R” due to non-compliance of the relative percent difference of the field duplicate. Since the field duplicate typically assesses the precision of the field sampling methods for detected values and the affected samples showed no detectable concentrations of cadmium.
Because metals in surface soil samples exceed background levels, TNRCC requirements for RRS1 closure have not been met. Furthermore, the consent order requirement to identify the horizontal extent of contamination has not been met.
Contaminated soil stockpiled at SWMU B-8 is being addressed as part of a Soil Pile Disposition Assessment currently underway. The purpose of this assessment is to test remediation options for this and similarly contaminated soils stockpiled at SWMUs B-20, B-24, B-28, and DD. It is recommended that the remediation option identified during this assessment also be utilized on contaminated surface soils which are currently still in place at SWMU B-8.
Prior to initiating this remediation, additional surface soil samples should be collected at this site to identify the extent of contamination. Based on results of the RFI surface soil sampling and the IM stockpile soil sampling, additional surface soil samples should be analyzed for barium, chromium, copper, and zinc (SW-6010B); lead (SW-7421). Arsenic, cadmium, mercury, VOCs, and explosives can be deleted from the COPCs list for SWMU B-8 since they were not detected above background or RRS1 levels. Nickel should also be deleted since it was detected in only one duplicate sample above the background level, but was detected well below background in the parent sample.
Due to above-background concentrations of metals in the underlying limestone, either closure under TRRP Tier 1 or re-evaluation of Glen Rose background concentrations should be considered.