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SWMU B-20 Investigation Report Addendum
Section 5 - Closure Options and Recommendations
This section presents recommendations for additional work at the B-20 site to prepare it for future closure under RRS1 or RRS2. Possible remedial alternatives for the site are also briefly summarized.
Closure under RRS1 provides a permanent remedy with a great degree of risk reduction. RRS1 requires that all waste, waste residues, leachate, and contaminated media be removed to background levels unaffected by waste management activities. The facility must submit a report to the TNRCC documenting compliance with the requirements of RRS1. This report must include descriptions of procedures and conclusions of the investigation to characterize the nature and extent of contamination, descriptions of removal actions performed, and summaries of sampling methodology and analytical results which demonstrate that contaminants have been removed or decontaminated to applicable levels. There are no requirements for post-closure care or deed recordation at sites closed under RRS1.
Due to chemical contamination of surface soil in areas of the site and the possibility of UXO still remaining at the surface in the area to the north of the site, the site does not meet RRS1 requirements. The following actions are recommended for surface soil:
A controlled burn should be conducted at the site to destroy the very low levels of TNT detected in very small areas of surface soil. Following the burn, surface soil samples should be collected in areas where raw explosives were found to determine if the compounds were destroyed.
Contaminants in surface soils covering approximately 10 acres exceed background metals concentrations. Remedial alternatives listed in Table 5.1, including soil washing, electrokinetics, phytoremediaion, and offiste disposal, should be evaluated. A treatability study of the recommended remedial alternatives may be practical due to the large volume of contaminated soils. A preliminary evaluation of remedial alternatives is included in Appendix G.
Three small ammunition disposal areas and associated metals-contaminated soil must be removed or remediated to meet RRS1 requirements. It is estimated that approximately 200 cubic yards of soil and small ammunition need to be removed and/or remediated.
Each of the three recommendations made in the RI report for subsurface soils at the B-20 site were acted on in the second phase of the RI. Anomalies in the craters were investigated and removed, the northern portion of the site was investigated for subsurface UXO, and samples from three borings were analyzed by the SPLP for metals. Based on that work, the following recommendations remain:
Subsurface investigation work in two grids (A2 and A3) of the northern 6-acre area should be completed. A large number of UXO items were found in the other grids, and it is likely that the remaining grids also contain UXO.
Subsurface investigations in the north 6-acre area indicate that the area was used for some solid waste landfill activities. If the solid waste is left in place in this area, it cannot be closued under RRS1. Remedial alternatives, including the risk-based (RRS2) no action alternative, should be evaluated for this area.
Leachate analytical results for the shallow soil boring sample collected near two small ammunition disposal areas indicated an elevated lead level. When the disposal areas are removed and/or remediated, samples should be collected to confirm that all contaminated material has been removed. The elevated lead level in the leachate sample suggests that soluble lead may be migrating from the disposal areas.
5.1.2.3 Surface Water and Sediment
The second phase of the RI did not addres surface water or sediment contamination. Therefore, the recommendation made in the RI report are still relevant. The following actions are recommended:
Sediments within crater 8 did not meet RRS1 cleanup criteria. Remedial alternatives for the sediment should be evaluated. This crater is located within the area described in Section 5.1.2.1 where metals concentrations in surface soil exceed background.
During the phase I RI, surface water analytical results for three craters exceeded freshwater criteria. The RI report recommended collecting sediment samples for leachate analysis to determine if the sediments are leaching the metals. If they are, the affected areas should be included in the evaluation of remedial alternatives.
Closure under risk reduction standard 2 provides a permanent remedy with a high degree of risk reduction. RRS2 requires that all waste, waste residues, leachate, and contaminated media be removed to risk-based levels specified at 335.556 through 335.559. The facility must submit a report to the TNRCC documenting compliance with the requirements of RRS2. This report must include descriptions of procedures and conclusions of the investigation to characterize the nature and extent of contamination, descriptions of removal actions performed, and summaries of sampling methodology and analytical results which demonstrate that contaminants have been removed or decontaminated to applicable levels. A requirement for post-closure care is possible under RRS2. Deed recordation is required.
Due to chemical contamination of surface soil in areas of the site and the possibility of UXO still remaining at the surface in the area to the north of the site, the site does not meet RRS2 requirements. The following actions are recommended for surface soil:
A controlled burn should be conducted at the site to destroy the very low levels of TNT detected in very small areas of surface soil.
Three small ammunition disposal areas and associated metals-contaminated soil must be removed or remediated to meet RRS2 requirements.
Each of the three recommendations made in the RI report for subsurface soils at the B-20 site were acted on in the second phase RI. Anomalies in the craters were investigated and removed, the northern portion of the site was investigated for subsurface UXO , and samples from three borings were analyzed by the SPLP for metals. Based on that work, the following recommendations remain:
Subsurface investigation work in two grids (A2 and A3) of the northern 6-acre area should be completed.
When the small ammunition disposal areas are removed and/or remediated, samples should be collected to confirm that all contaminated material has been removed. The elevated lead level in a 2.0 to 4.0-feet deep leachate sample suggests that soluble lead may be migrating from the disposal areas.
The second phase of the RI did not address surface water contamination exceeding RRS2. Therefore, the recommendation made in the RI report are still relevant. The following action is recommended:
The RI report recommended collecting sediment samples for leachate analysis to determine if the sediments are leaching the metals. If they are, the affected areas should be included in the evaluation of remedial alternatives.