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AOC 55 RCRA Facility Investigation Report

Section 3 - Conclusions and Recommendations

3.1 - Conclusions

The material encountered in the test trenches included ash that appeared to have been generated from an incinerator operation in the AOC 55 area. The landfill also contained bottles that appeared to be waste from the on base cafeteria. These bottles included numerous ketchup bottles, Worcestershire sauce bottles, discarded coke bottles and other types of bottles that were unidentifiable. Also found were several metal water pitchers and broken China plates. One of the broken China plates found was dated 1915. The time of the landfill operation is unknown, but is thought to be between 1920 till 1950 based on aerial photos and on dates found on bottles and plates from the disposal area.

In October 2002, excavation to remove the buried waste was conducted. One thousand eight hundred and ninety 20‑cubic yard end-dump trucks were used to transport the waste/contaminated media from CSSA’s AOC 55. An estimated 34,020 cubic yards of soil excavated from AOC 55 were disposed off-post at Covel Gardens Landfill and clean fill material was placed in the excavated areas at AOC 55. The excavation and removal of waste and affected soils at AOC 55 was completed November 2003.

Confirmation/Closure soil samples were collected from the base and linear extent of the landfill following excavation and removal of visibly affected soil media. Results of analyses indicated additional removal actions were necessary and completed near Tenberg Drive. Additional confirmation/closure samples were taken to verify completeness of the removal actions. Results indicate that all affected soil media and waste were effectively removed. Samples AOC55-CL03 and AOC55-CL14 contained zinc and lead concentrations, respectively, which slightly exceeded CSSA soil background values.

The following UCL calculations are based on the revised data, that is, the data collected as part of the initial sampling effort at AOC55, plus the two new data points that were collected after the fill pile was removed. The fill pile removal eliminated sampling site AOC 55 CL01, and that data point was removed from the data set. In addition, after the removal of the fill pile, two additional samples were collected, now named AOC 55 CL13 and AOC 55 CL14. These two additional samples have been added to the data set.

For determining appropriateness for site closure of AOC 55 with the slight exceedences of concentrations of zinc and lead, the 95 percent upper confidence level (95% UCL) were calculated. To calculate 95% UCL, use of the Shapiro-Wilks test of normality in the ProUCL software (EPA 2003), the W=0.744 (W_{critical, 0.05, 12} = 0.866) was determined. Because the test statistic W is less than the critical value, the data were determined to be non-normally distributed.

If the data are log-transformed and a Shapiro-Wilks test is applied, W = 0.896 (W_{critical, 0.05, 13} = 0.866). The data are log-normally distributed. Therefore, the calculated 95% UCL for lead is shown in Table 3.1

Table 3.1 - 95% UCL for Lead

The MVU estimate of the mean for lead (values are log-normally distributed) is 27.73 mg/kg, with a standard deviation of 19.74 mg/kg. The 95% H-UCL value for lead is 48.19 mg/kg.

Using the Shapiro-Wilks test of normality in the ProUCL software (EPA 2003) for zinc, the W=0.867 (W_{critical, 0.05, 13} = 0.866) therefore, the data were determined to be normally distributed. Table 3.2 shows the estimated the 95% UCL for Zinc.

Table 3.2 - 95% UCL for Zinc

The estimated mean of the zinc data is 43.57 mg/kg, with a standard deviation of 23.29 mg/kg. The Student’s t - 95% UCL is 56.07 mg/kg.

3.2 - Evaluation of Data Quality Objectives Attainment

Overall data quality objectives (DQO) 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 AOC-55, along with an evaluation of whether each DQO has been attained, is provided in Appendix B. As described in Section 1, the main objectives of the AOC-55 removal actions are to obtain closure under TCEQ requirements for RRS1 closure and to meet requirements of the 3008(h) Administrative Consent Order.

All closure data generated during the AOC 55 removal actions 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 closure purposes. Although several results are flagged with an “M,” these results are considered usable because the matrix interference is minimal and does not significantly affect the sample results. Some results are flagged with a “J,” these results are considered usable because the estimation of quantitation does not significantly affect the sample results. All the initial calibration, second source verification, and internal standard criteria were within quality control limits, as described in the data verification report (Appendix C).

3.3 - Recommendations

Confirmation samples were collected in the fall of 2003 after all waste had been removed from AOC 55. An elemental lead concentration of 545 mg/kg was reported for a confirmation sample collected from the fill material located near Tenberg Drive (AOC 55‑CL01). Additional soil removal was completed with two additional samples collected along the northern extent of AOC 55.

Because the waste has been removed and all remaining metals levels for soil samples (with the exception of the one sample with slightly elevated zinc level well within one order of magnitude of the zinc background value) collected from the site are below the background concentrations for CSSA soils, closure under RRS1 is recommended.