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F 1 LEVI N E•FRICKE i? I; 9.0 SOIL AND GROUND-WATER INVESTIGATION II3 Levine•Fricke performed a field sample caIllection program at the Site on and b Sitw E et een January 23 and 27, 1989 to assess the f possible presence of suspected chemicals1,asso,ciated with the . potential sources identified during the background review in soil and/or ground water at the Site. AdditioInal 'shallow soil samples were collected in the vicinity of the Quonset, hut on February 16, I1 1989 to further assess the lateral extent- of DDT and related compounds found in shallow soils as a result of the initial I` sampling and analysis. The specific methods used for sample collection are described in Appendix D. a , 9.1 Field Area j Soil samples were collected in the cultivated area (field area) of the Site to enable assessment of the possible presence of elevated concentrations of pesticides associated with past Site 'l usage. For the field area sampling program, the Site was divided into six sections (Figure 3) . These section divisions are based on the current irrigation and drainage layoutfof the cultivated portion of the Site. Soil samples were collected at approx- imately 1- and 3--foot depths below groundisurface from a total of 21 sampling points (see Figure 3 for field area sampling locations) . , �. � Sail samples collected at the 1-fact depth interval from sampling locations within each of the six sections� of the field area of the Site were composited at the laboratory into one sample for each section; the six resulting composited samples were submitted for chemical analysis. A portion of each of the 21 discrete samples from the 1-foot depth interval and the discrete samples from the 3-foot depth samples were held by the laboratory for possible future analysis, depending on the results from the composited samples. 3i I{ Field area soil samples were tested for the presence of methane gas using a portable Organic Vapor Analyzer (OVA) with a wheat- stone bridge detector. An earlier geotechnical investigation conducted by J.H. Kleinfelder and Associates, ' June 16, 1987, and entitled "Report, Geotechnical lnvestigation`' Proposed Brookside Development, Stockton, California, " reported that high organic content soils were encountered at shallow1 (1 to 3 foot) depths in the northeast portion of the Site. Methane gas sampling was therefore conducted in the field area to 'investigate the possi- bility that methane gas is present in shallow) soils in areas where high organic content soils were previously encountered. -12-