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Evaluation of Background Metals Concentrations in Soils and Bedrock at CSSA
This section presents the results of the laboratory analyses and the statistical calculations. Possible future uses of the calculated background values are also described.
Analytical results for background Glen Rose Formation limestone samples are presented in Table 3.1. Background limestone samples were collected from ten borings drilled in 1994 during the F-14 investigation (ES, 1994a) and ten borings drilled in 1999 as part of the background investigation. All 20 lab samples were used in the statistical evaluations, except for the lead and nickel evaluations. As shown in Table 3.1, concentrations of lead and nickel detected in 1999 were significantly lower than the concentrations detected in 1994. Although the data packages for each data set were carefully reviewed and no problems were identified with the analysis, QA/QC of the recent samples is presumed to be superior to that of the 1994 samples. Therefore, the ten higher 1994 lead and nickel results have been omitted from the statistical evaluation, leaving a sample size of ten for these two metals.
Analytical results for background soil samples are presented in Table 3.2. As described in Section 2, samples SS1 through SS10 were collected during the F-14 investigation (ES, 1994a), and samples SS11 through SS35 (all metals except copper, nickel, and zinc) were collected during the B-20 investigation (Parsons ES, 1995). The remaining samples were collected as part of this investigation.
The concentrations in Tables 3.1 and 3.2 were used for the statistical calculations presented in Appendices A and B. Calculated background concentrations are summarized in Table 3.3. Sample locations are presented on Figure 2.1. The values in Table 3.3 represent background metals concentrations in the Glen Rose Formation limestone and soils at the entire CSSA facility.
The concentrations listed in Table 3.3, or PQLs, whichever are higher, will be used as comparison criteria for closure of CSSA SWMUs under RRS1. CSSA will pursue closure of SWMUs at the facility under RRS1 wherever it is technically and economically feasible. CSSA intends to use this report as a reference document for these future closures, as well as other appropriate environmental activities at the facility.
In addition to the metals analyses, one sample of each soil type was analyzed to determine pH. These results are listed in Table 3.4 and the data package for the pH analysis is included in Appendix E.