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GEa MA-r R I x <br /> BTEX or TPHd. Soil samples from boring SB-2 contained TPHd at concentrations ranging <br /> from 11,800 to 17,200 milligrams per kilogram {mg/kg} and TRPH at a concentration of 17.600 <br /> mg/kg. <br /> Boring SB-2 contained separate-phase petroleum coincident with the water table <br /> (approximately 33 feet bgs). A wipe sample of this material was collected and analyzed for <br /> BTEX and TPH. No benzene or ethylbenzene was detected; and concentrations of toluene and <br /> xylenes were 37 and 42 micrograms per kilogram (µg/kg), respectively. Concentrations of <br /> 167,000 mg/kg for TPHd,kerosene, dielectric and motor oil and of 44,000 mg/kg of TRPH <br /> were reported.' Historical data are summarized in Table 1. <br /> 3.0 CURRENT SITE INVESTIGATION <br /> Investigative activities described herein were conducted in two phases, the first by Radian and <br /> the second by Geomatrix. Radiant sampled soil and installed and monitored groundwater wells <br /> at the site in July 1998. Site investigation activities conducted by Radian included: <br /> ■ drilling and sampling six soil borings (SB-3 through SB-8) to delineate the lateral <br /> extent of petroleum hydrocarbon-impacted soil; and <br /> ■ installing, developing, and sampling four groundwater monitoring wells (MW-1, <br /> MW-2,MW-3, and MW-4)to estimate the hydraulic gradient and assess <br /> groundwater quality. <br /> Soil boring and monitoring well locations are shown on Figure 3. A soil boring/well <br /> installation permit was obtained by Radian from the San Joaquin County Environmental Health <br /> Division(SJC-EHD)prior to the start of field activities; a copy is included in Appendix A. <br /> Prior to drilling,utility clearance was conducted by Precision Locating, Inc., of Brentwood, <br /> California. In addition, Underground Services Alert was notified one week prior to the <br /> subsurface exploration. Field operations reportedly were supervised by a field engineer who <br /> was overseen by a Radian registered geologist. <br /> Between October and November 1998, Geomatrix sampled all four monitoring wells and <br /> collected a sample of separate-phase petroleum for a chemical "fingerprint"evaluation. <br /> l The sample of separate-phase petroleum reportedly was Iiquid,yet the laboratory reported concentration values <br /> as units of mass per mass, and no density calculations were provided in the laboratory report. <br /> I�sf3ldeptdatalDoc_Safc\50DOs15011NSI HRA Rpt.dm 3 <br />