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SWMU B-30 RCRA Facility Investigation Report
Section 3 - Conclusions and Recommendations
SWMU B-30 is a former quarry area that has been used for disposal of miscellaneous construction debris. A visual reconnaissance field survey revealed scrap concrete, roofing shingles, and construction debris. An EM geophysical survey of the site identified a subsurface anomalous area that may be related to past waste management activities. Boring RW-B30-SB01 was installed as close as possible to the anomaly and no non-native materials were observed throughout the advancement of the boring where bedrock was encountered at a depth of 5 feet bgs. Four surface and six subsurface soil samples were collected at the site from areas that would likely contribute to soil contamination (e.g. construction debris, geophysical anomalies, and concrete slabs).
Methylene chloride was identified at a concentration of 0.0072 mg/kg within sample RW-B30-SB03 (2.5-3.0 ft). The low reported concentration of this compound, the knowledge that methylene chloride is a common lab contaminant, and the fact that the exceedances are limited to a single sample forms the basis of our conclusion that methylene chloride does not pose a concern at SWMU B-30. Furthermore, methylene chloride is not a contaminant of concern at SWMU B-30.
It may be argued that the bis(2-ethylhexyl)phthalate found in five of the subsurface soil/rock samples may be eliminated from closure considerations as a COC as phthalate concentrations, especially when detected alone, are typically related to field sampling equipment. Phthalates are related to plasticizers associated with rubber gloves used by field personnel during sampling. When a soil or rock sample is collected, the sample is handled using a trowel and gloves. The sample typically must be pushed into the glass jar, and as such there is significant contact between the gloves and the sample. Since bis(2-ethylhexyl)phthalate is a common contaminant specifically associated with gloves, and it was also detected in low quantities (0.0045 mg/L) in the equipment blank, it may be argued that the bis(2-ethylhexyl)phthalate detected in soil/rock samples at SWMU B-30 is associated with the use of gloves, and is not present as an environmental COC. Bis(2-ethylhexyl)phthalate is not a transformation product of any COC at the site and there is no historical evidence to support the association of bis(2-ethylhexyl)phthalate with SWMU B-30.
Finally, the barium, cadmium, copper, nickel, lead, and zinc concentrations in SWMU B-30 samples are not significantly above their respective CSSA background concentrations, and these metals were each only detected above background in only one sample. Barium and cadmium were only detected above the laboratory RLs in one sample, RW-B30-SB01 (12.5-13.0). Barium was reported at 11.1 mg/kg, which is only 1.1 mg/kg above the background level of 10.0 mg/kg. The cadmium concentration in this sample was 0.13 mg/kg, only 0.03 mg/kg above the background level of 0.1 mg/kg. The background levels for these metals in the overlying soils are 186 mg/kg for barium and 3.00 mg/kg for cadmium. Nickel was reported at a concentration of 7.9 mg/kg in sample number RW-B30-SB03 (2.5 ft bgs). This value is only 1.1 mg/kg higher than the RRS1 standard of 6.8 mg/kg for Glen Rose Limestone but significantly lower than the calculated background level for the overlying soil which is 35.5 mg/kg. In surface soil at RW-B30-SS03, copper, lead, and zinc slightly exceeded background.
Although these concentrations for some metals constituents exceed RRS1 criteria, the values do not exceed the TRRP Tier 1 applicable soil PCLs when compared to the most stringent and/or most applicable PCLs for areas less than 0.5 acres in size, whether it is the TotSoilComb PCL or GWSoilIng PCL.
3.2 - Evaluation of Data Quality Objectives Attainment
Overall 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-30, 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-30 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-30 investigation were reviewed to confirm conformance with the AFCEE QAPP; the data verification reports are included in Appendix D. All data are considered useable for site characterization purposes, except for chloromethane data for six of the SWMU B-30 samples.. However, chloromethane is not considered a contaminant of concern for this site. Although several results are flagged with an “M,” these results are considered useable because the matrix interference is minimal and doesn’t significantly affect the sample results. Despite non-compliance of the percent difference for the continuing calibration, all of the initial calibration, second source verification and internal standard criteria were within quality control limits, as described in the data verification reports (Appendix D).
Because construction debris is present on the ground surface, the site does not meet the TNRCC RRS1 or TRRP requirement for removal of all waste. Furthermore, the geophysical survey identified an anomaly potentially associated with subsurface waste. Because of the possibility that buried waste exists at the site, requirements of the consent order such as determination of vertical extent of contamination have also not been met.
Construction debris at the site must be removed to pursue closure under RRS1 or TRRP Tier 1. In addition, the geophysical anomaly should be excavated. Based on the combined size of geophysical anomalies A and B and an assumed potential waste depth of 10 feet, approximately 2,300 cubic yards of material could require removal and disposal. Waste should be characterized for disposal, verification samples should be collected, and any excavated areas should be brought up to grade with clean fill. The number of verification samples necessary will depend on the size of the excavation and the initial success in excavating all waste and waste residue; however, the total number of samples is not anticipated to exceed 25. Due to the lack of analytical data for the area within anomaly B, it is recommended that future samples be analyzed for the complete list of potential COCs: VOCs (SW-8260B); SVOCs (SW-8270C); arsenic (SW-7060A); barium, chromium, copper, nickel, and zinc (SW-6010B); cadmium (SW-7131A); lead (SW-7421); and mercury (SW-7471A). Results of verification sampling should be compared to both RRS1 and TRRP Tier 1 standards to determine the best closure option for SWMU B-30.