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KLEINFELDER o Regional Water Quality Control Board files o Department of Health Services, TSCP files o Commercial aerial photograph files o San Joaquin County aerial photograph files o California Integrated Waste Management Board files o Department of Fish And Game files o Department of Water Resources files 5.2 VADOSE ZONE ASSESSMENT The presence of contaminants of concern (see Section 3.2) and certain properties in the vadose zone near MW-5A will be assessed by drilling and sampling three of the four slant borings under WMU B, the old solar evaporation pond area, and South Littlejohns Creek. These three slant borings will be drilled at the locations shown on Plate 5-1. Soil samples will be collected at 10-foot intervals or in each significant lithology, from the depth of the bottom of the WMUs to ground water, and will be submitted to the analytical laboratory for the constituents listed in Table 5-1. Six of the samples collected wil be analyzed for the parameters in Table 5-1. Additionally, one vertical soil boring (BKG-1) will be drilled and sampled at a location unlikely to be affected by waste (Plate 5-1). BKG-1 will be sampled at 7-foot intervals, starting at the depth of the bottom of WMU B and ending at ground water. Four samples will be collected at each sampling depth to generate a statistically significant population. Soil samples from this boring will be submitted to the analytical laboratory for the analyses listed on Table 5-1, except for volatile organics. The background soil samples will not be analyzed for aromatic or halogenated organic compounds, based on the assumption that these organic compounds do not occur naturally in soil. The sampling plan is summarized on Table 5-3. The soil sampling protocol is described in Appendix B. The analytical protocol is described in Appendix C. Profiles of contaminant concentration versus vertical depth will be developed for the slant borings near MW-5A and for the background boring, based on the analytical results for the submitted samples. Background soil concentrations of the metals of concern will be subtracted from the concentrations observed at similar depths/lithologies near MW-5A to assess if, and how much of, the contaminants of concern are present in the vadose zone. C7-90-99 10