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L NOW <br /> Mr. Ron Rowe <br /> Page 4 <br /> concentrations of TPHg, BTEX, MTBE, or oxygenate additives, except for minor xylenes at 24 <br /> feet bgs. Consequently, no apparent residual hydrocarbons are present in soil beneath the <br /> former UST. Additionally, the concentration of lead detected in soil is a background or <br /> naturally occurring level. <br /> Since petroleum hydrocarbons were not detected in soil samples collected beneath the western <br /> end of the UST in 1992 or from borings SBI. through SB3, it does not appear that soil <br /> surrounding the former UST has been impacted by petroleum hydrocarbons. <br /> As recommended by Mr. Ron Rowe, in the event contamination was evident soil samples <br /> collected at the depths of record high and low groundwater were to be analyzed for oxygenates. <br /> Based on San Joaquin County Groundwater Reports, the depth to the record high groundwater <br /> beneath the site was expected to be approximately 25 feet bgs while the depth to record low <br /> groundwater was estimated to be 50 feet bgs. Current depth to water was estimated to be <br /> approximately 35 feet bgs. However, groundwater was encountered at less than 20 feet bgs in <br /> all site borings. As a result, collecting discrete soil samples in saturated soil deeper than 10 feet <br /> below groundwater was not possible due to soil sloughing back into the boring. Due to lack of <br /> field evidence of contamination other than an FID reading of 1 ppm in sample SBI-24', this <br /> sample was selected for oxygenate analysis. No oxygenates were detected. <br /> Groundwater samples collected from borings SB1 through SB3 did not contain detectable <br /> hydrocarbons and oxygenates were not detected in the sample from SBI. The groundwater <br /> sample collected from SBI, located east of the former UST, was analyzed for oxygenates <br /> because the San Joaquin County Groundwater Reports indicated that the groundwater flow <br /> direction beneath the site was toward the east. Consequently, groundwater beneath the site does <br /> not appear to have been impacted by petroleum hydrocarbons. <br /> Recommendations <br /> Based on the results of this investigation, no residual hydrocarbons or oxygenate additives are <br /> present in soil or groundwater. Ground Zero recommends case closure. <br /> wbmisubsurf.ro <br />