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y Lobserved in the core sample collected from 4 to b feet bgs in boring B5-5, and moderate to strong petroleum product odor was detected in the headspace of boring B5-5 at this depth (Appendix A). Soil discoloration was absent in the subsequent core sample collected from 9 L to I I feet bgs in boring B5-5, and no volatile organics were detected using the PID in this core sample. The PID readings within the headspace of boring B5-5 diminished to non-detect with continued drilling to the total depth (Appendix A). No soil discoloration or petroleum product L odors were detected in the core samples collected from boring B5-4 (Appendix A). Based on these field observations, Carol Oz requested that soil samples be submitted for laboratory Lanalysis of PHCs at 5, 10, 15, and 20 feet bgs in boring B5-5, and at 10 and 15 feet bgs in boring B5-4. Groundwater samples were collected at 21 feet bgs in both borings using the method described above. A replicate groundwater sample was collected from boring B5-4. L Soil and groundwater samples from the five borings were placed in an ice-cooled chest and Lsubmitted under chain-of-custody procedures to BSK Analytical Laboratories (BSK), a California DHS-certified laboratory for PHC analyses. Samples were analyzed for BTEX, TPHg, and MTBE using EPA Methods 801518020. The groundwater samples collected from Lw boring B5-1 (W-003), and boring B5-5 (W-006) were also analyzed for oxygenates using EPA Method 8260. The Work Plan stated that EPA Method,200.8 would be used for analysis of L lead in soil and water samples. .This method uses inductively coupled plasma and mass spectrometry (ICP/MS) as the analytical technique and is typically used on low turbidity drinking water samples. However;=due to the high turbidity in water samples collected during Lthis investigation, BSK performed lead analyses for water samples using EPA Method 200.7. Soil samples were analyzed using,EPA Method 6010. Both these methods use ICP as the analytical technique. According to BSK, these ICP methods provide the same detection limits Las the ICP/MS method while offering the advantage of being able to accommodate analysis of turbid water samples. 9 4.0 INVESTIGATION FINDINGS L Findings of the investigation, including geologic and hydrologic characteristics, and analytical Lresults of the soil and groundwater samples, are discussed in the following sections. L4.1 GEOLOGIC AND HYDROLOGIC CHARACTERISTICS The site is located on the delta of the San Joaquin River, approximately 2--miles east of the Lconfluence of the San Joaquin and Calaveras Rivers. The subsurface geology consists of a thick sequence of alluvial deposits of late Tertiary to Holocene Age, overlying sedimentary Lrocks of Cretaceous to Tertiary age, which in turn overlie crystalline basement rocks (Bartow 5 "117U rvurraWusrMV.xrr L BOYAJIAN & ROSS, INC. Environmental Scientists & Engineers