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' Brldgestone/Firestone, Inc. 400 N. El Dorado, Stockton, California February 2, 1994 Site Assessment Report—PIM 207201 Page 5 of 12 The subsurface soil horizon at this site generally consisted of approximately 15- feet of medium-dense silt with varying amounts of clay and fine sand Beneath the silt is a 5-foot layer of clean, fine to medium grained, medium dense sand, followed ' by approximately 15-feet of sandy to clayey silt Complete soil profile information may be reviewed in the soil boring logs in Appendix 8 4 ' 3.5 Field Screening — Observations PID readings were used at the site to evaluate soil samples on 5-foot intervals for the presence of volatile hydrocarbon compounds Ambient temperature headspace (ATH) procedures were utilized by isolating and sealing representative portions of ' soil in heavy-gauge sealable plastic bags and allowing the soil to approach an ambient temperature of approximately 68-degrees Fahrenheit Semi-quantitative measurements were made by puncturing the sealed bags with the PID probe and analyzing headspace gas concentrations Field instruments were calibrated b ated according to procedures, calibration gases, and frequencies designated by the manufacturer ' ATH field-screeningresults is indicated varying amounts of VOC concentrations in the headspace of the soil samples collected from SB-1, SB-2, and SB-3 The following range of values were observed within the associated soil depth 0- to 10-feet < 10-ppm ' 13- to 25-feet 2- to 858-ppm 30- to 35-feet 6-ppm to 21-ppm ' ATH field-screening results for soil samples collected from SB-4 and S13-5 were all less than 10-ppm for the entire soil profile screened ' These PID results parallel field observations made during the drilling operation In soil borings SB-1, SB-2, and SB-3, hydrocarbon odors were not evident in any of the soil samples collected at 5-feet and 10-feet below the surface. Hydrocarbon ' odors were strong in soil samples collected from 15- and 20-feet below the surface Odors were less noticeable in samples collected at 25-feet in two of the three soil borings Samples collected at 30- and 35-feet had no noticeable ' hydrocarbon odor Information collected from this assessment and the tank removal indicated that evidence of contamination (PID results, odor) decreased as distance from the former tank pit increased. None of the soil samples collected from SB-4 or SB-5 exhibited hydrocarbon odors Specific PID readings are included on the soil boring logs in Appendix 8 4 ' RYAN-MURPgy, INCORPORATED Deaver Fav&omnnental Coasibvetion Management Los Angelis