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REMEDIATION CONFIRMATION SAMPLING RESULTS <br /> AND CLOSURE RECOMMENDATION REPORT <br /> (March 1994 Revision) <br /> 909 West Hammer Lane 5[oddon Caldoma <br /> • <br /> I The November 1993 excavation removed the majority of soil containing residual <br /> petroleum hydrocarbons The exception was soil from 26 to 31 feet in confirmation boring <br /> SB-9, which contained TPH as gasoline concentrations ranging from 180 to 240 ppm <br /> Because of equipment limitations, this soil could not be removed However, Aegis <br /> estimated a maximum of 8 6 pounds (or less than 1 5 gallons) of residual TPH remains <br /> in the soil Benzene, the most mobile and potentially hazardous gasoline constituent, was <br /> not detected in any of the recent soil boring and excavation samples <br /> Since June 1991, groundwater analytical results have not indicated the presence of <br /> petroleum hydrocarbons in any of the monitoring wells During this time, the groundwater <br /> elevation has fluctuated from approximately 39 to 45 feet, corresponding to depths <br /> ranging from approximately 54 to 61 feet below grade The groundwater elevation has <br /> been within this zone since 1988 The vertical fluctuation of the groundwater does not <br /> appear to have had an impact on groundwater quality No TPH-G was present in soil <br /> samples collected every five feet from 36 feet below grade to groundwater at 57 feet <br /> below grade The soil boring results indicate at least a 15-foot thick interval (41 to 56 feet <br /> below grade) of mostly silty soil containing nondetectable TPH-G and less than 0 04 ppm <br /> BTEX concentrations exists immediately above the water table <br /> Also, the proximity of clean confirmation soil borings indicates limited lateral extent of <br /> petroleum-impacted soil <br /> Based on the above observations, Aegis believes the remaining petroleum hydrocarbons <br /> present in the vadose zone are immobile and localized, and do not present a threat to the <br /> relatively deep groundwater Therefore, Aegis recommends this site for certified closure <br /> by San Joaquin County and the California Regional Water Quality Board, Central Valley <br /> Region <br /> I <br /> 93-OOSC QMR 9 <br />