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y 30 May 1996 <br /> AGE-NC Project No. 96-0224 <br /> Page 2 of 5 <br /> samples collected near the gasoline and heating oil USTs at concentrations of 32,000 ppm (TPH-g) <br /> and 17,000 ppm(TPH-d), respectively. A copy of the laboratory report is included in Appendix A. <br /> Based upon the preliminary soil samples, notification of the PHS-EHD and additional investigation <br /> to determine the lateral and vertical extent of hydrocarbon-impacted soil was recommended. <br /> w. <br /> 2.3. GROUND WATER DEPTH AND GRADIENT <br /> Based on information from the map entitled Lines of Equal Depth of Water Wells, Fall 1956, <br /> published by the San Joaquin County Flood Control District and Water Conservation District, the <br /> estimated depth to ground water at site is approximately 70 feet below surface grade. The prevailing <br /> ground water flow in north San Joaquin County is generally westward, but ground water flow may <br /> vary locally and seasonally. <br /> V <br /> 3.0. SITE ASSESSMENT <br /> 3.1. SOIL PROBING AND SAMPLING <br /> Four soil probe borings were advanced at the site on 20 May 1996. Figure 2 depicts the locations of <br /> the probe borings. The probe borings were advanced using AGE's van-mounted Geoprobe 5400 soil <br /> probing machine equipped with a 1.125-inch diameter soil sampler on the leading end of the probe <br /> twe rods. <br /> Probe borings P I and P3 were advanced vertically to depths of 25 below surface grade (bsg) in the <br /> vicinity of the gasoline UST. Probe boring P2 was advanced at an angle of 20° from vertical to a <br /> linear depth of approximately 15 feet near the gasoline UST. <br /> Probe boring P4 was advanced near the heating oil UST at an angle of 20° from vertical to a linear <br /> depth of 30 feet. Vertical access to soil beneath the former heating oil UST location could not be <br /> �. obtained due to a deck and awning structure. <br /> Discrete soil samples were collected in each probe boring using a 1.375-inch diameter, two-foot long, <br /> �. piston type sampler loaded with four precleaned 6-inch brass sleeves. Soil samples were collected <br /> from vertical probings at 5-foot intervals; samples collected from the angle probings were collected <br /> every five linear feet. <br /> Sampling equipment was washed in an Aiconox solution and rinsed with water prior to each sampling <br /> run to prevent cross-contamination. <br /> Upon sample retrieval,both ends of the second brass sleeve were covered with Teflon sheets, capped <br />