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r;. <br /> 6•. <br /> encountered at any of the wells. ;The ground water sampling and analytical results to date do <br /> not indicate the presence of free or separate-phase product in the soil or ground water. <br /> Concentrations of diesel, gasoline, and benzene seen in soil samples from below the ground <br /> water do not indicate the presence of separate-phase hydrocarbons or free product. In addition, <br /> during the excavation activities, !where ground water stood in the open excavation, no free <br /> product was observed. <br /> Fourth Bullet Item <br /> r <br /> Alton Geoscience does not agree that liquid-phase or "separate-phase" hydrocarbons are present <br /> beneath the site. The 1991 ground water data from Boring B-7 contained gasoline and diesel <br /> concentrations of 110,000 and 60,000 micrograms per liter (ppb), respectively. However, this <br /> ground water sample was obtained as a "grab" sample from the drill auger and is not (1) <br /> representative of chemical concentrations within the ground water formation, (2) from an <br /> installed, developed, and purged ground water monitoring well, or (3) consistent with historical <br /> ground water concentrations. In'addition, Monitoring Well AW-9 was`installed within 5 feet <br /> of boring B-7. Quarterly groundwater sampling of AW-9 has been conducted since April 1992. <br /> The highest concentration of TPH=D detected in AW-9 was 130 ppb (4124192)and neither liquid- <br /> phase hydrocarbons nor detectable concentrations of petroleum hydrocarbons have been observed <br /> since that time. <br /> Furthermore, Alton Geoscience does not agree that the hydrocarbon concentrations exceed the <br /> respective solubility limits for gasoline and diesel. For example, Lyman',et al. (1992) state that <br /> the solubility of additive-free gasoline ranges between 130,000 and 250,000 ppb, and with <br /> additives, the total concentration:'may be higher. Alton Geoscience does 'not agree with the <br /> Geomatrix statement that concentrations of gasoline and diesel in soil, (590 and 3,700 milligrams <br /> per kilogram (ppm), respectively) indicates that separate-phase hydrocarbons remain in soil <br /> beneath the site. <br /> Fifth Bullet Item <br /> On March 16, 1990, Alton Geoscience transmitted a copy of the "Proposed Scope of Work for <br /> Subsurface Investigation and Soil Remediation" to Dr., Jogi Khanna at the San Joaquin County <br /> Department of Public Health Services, Environmental Health Division (SJC PHS/OM), in <br /> addition, copies went to Mr. Tom Peltier at the Regional Water Quality Control Board, and Mr. <br /> George Turner at the City of Tracy, Department of Public Works. Soil sampling protocol was <br /> succinctly stated within this document. Agency approval on the document was given on March <br /> 30, 1990, without amendments. <br /> Offsite soil analytical data (north of the site) indicates that no detectable concentrations of TPH- <br /> G, TPH-D, or BTEX were present in the samples, except in Soil .-Boring B-2 (AW-6). <br /> However, total petroleum hydrocarbons quantified as diesel (TPH-D) concentrations detected in <br /> AW-6 decreased with depth from 180 ppm at 6 feet below grade (fbg) to 5.4 ppm at 11 fbg. <br /> The reported occurrence in AW-6 appears unrelated to any unidentified petroleum releases at <br /> 2 <br />