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a s <br /> i <br /> O Na detectable concentrations of total petroleum <br /> hydrocarbons as gasoline (TPH-G) were detected .in <br /> soil samples collected from any of the soil borings. <br /> one soil sample had low concentrations of BTEX <br /> constit;lents. <br /> a Monitoring Well MW-3 remains the only well at the <br /> site with free-floating product, which was measured <br /> at approximately 0.01 foot on .July 7, 1990. <br /> Monitoring Well MW-5, which is only 8 feet east of <br /> nW-3, has no free product, and the water level was <br /> 0,07 foot higher than MW-3. Because of slow recharge <br /> in MW-3 compared to MW-2 and MW-5, and the difference <br /> in water level and hydrocarbon concentrations, data <br /> from MW-3 was not considered in the development of <br /> the ground water elevation and isoconcentration maps. <br /> o A water sample from the offsite well, MW-6, which is <br /> adjacent to an Exxon service station and cross- <br /> gradient of the former Mobil site, had the highest <br /> concentrations of TPH-G and benzene at 14,000 parts <br /> per billion (ppb) and 590 ppb, respectively. <br /> o A water sample from MW-8, located offsite and <br /> adjacent to the Chevron service station, and directly <br /> downgradient of MW-6, had the next highest <br /> concentrations of TPH-G and benzene, detected at <br /> 11,000 ppb and 27 ppb, respectively. <br /> o No dissolved-phase TPH-G or BTEX constituents were <br /> detected in a sample from MW-7, which is downgradient <br /> of the former Mobil site. A contour map of benzene <br /> r concentrations in the ground water is shown in <br /> Figure 4, while TPH-G concentrations are shown in <br /> Figure 5. <br /> o A total of four additional ground water monitoring <br /> wells were constructed, AMW-1 through AMW-4. Water <br /> samples collected from these wells had no detectable <br /> to low concentrations of TPH-G and BTEX constituents, <br /> as presented in Table 1. <br /> o The dissolved-phase hydrocarbon constituents detected <br /> in the ground water onsite appear to be limited to <br /> the northeast corner of the property extending <br /> towards Tracy Boulevard and Grant Line Road. <br /> o Based on the results of the field activities and <br /> laboratory analysis, there are potentially three <br /> hydrocarbon contaminant plumes in the vicinity of the <br /> site that have commingled: one onsite on the <br /> - ..._ _._._.... ert one <br /> __...... northeast-corner -of ..the._.former..f�iobil.prog. .... y.► ..... <br /> 4 <br />