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620 N. SAN JUAN- 2 ­29 JUNE 1995 <br />SAN JOAQUIN COUNTY <br />-The monitoring wells, approximately 21, 45 and 75 feet away from the excavation, are too distant <br />to describe a possible ground water problem in the tank excavation area. However; mathematical <br />modeling conducted by Resna suggests that the residual contaminants under the building do not <br />pose a significant threat to ground water beneath the site. Using a highly conservative approach, <br />the benzene plume would take over 130 years to move 4 feet. Also, the relatively low effective <br />porosity (high specific retention) of the silt and clay soils impedes the movement of dissolved <br />hydrocarbons. Furthermore, because the property is in a highly industrialized area near. the port of <br />Stockton,'Resna believes the amount of remediation performed to date is sufficient. k <br />WEG <br />•Ground water samples from -the monitoring wells showed ND-levels-for.six. consecutive-quarters <br />with the ground water level rising approximately three feet during that time. Based on the results <br />of the.ground water samples, and Resna's fate and transport calculations, I agree that the , , <br />concentrations remaining in place beneath the building do not pose a significant threat to ground <br />water quality. <br />SDJ <br />441 JJ }} <br />r <br />i <br />. J <br />