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In summary, significant levels of diesel residues and low levels of aromatic <br /> volatile compounds were found under the former tank site. The extent of soil <br /> contamination is leas than to feet laterally from the edge of the tank site. It <br /> appears that contaminants have moved vertically. <br /> Based on the results of the soli Investigation, it Is proposed to installi a <br /> boring to the water table. A groundwater elevation map for the Spring of 1986 <br /> prepared by San Joaauln County Flood Control District (attachment #2) shows that <br /> the regional groundwater gradients in the area are generally northeasterly. <br /> Therefore, 1t is recommended that the boring to the water table be located 10 <br /> Feet northeast of the tank excavation. This would be in the downgrad€ent <br /> direction and yet close enough to the tank site to allow the observation of any <br /> diesel products floating on the water table surface. From the results of the <br /> ,,oil investigation of 3/30/87. it is known that soils 10 ft. from the excavation <br /> are not contaminated and that drilling through such soils with a hollow stem <br /> auger wouid not introduce contaminants to the groundwater. The boring will be <br /> completed as a well with sufficient screen length to allow the observation of <br /> any formation of a separate phase. The proposed location of the boring will not <br /> Impede any remedial action that may be selected for the contaminated soil under <br /> the tank site. <br /> it is our intent to proceed with the boring to the water table as soon as <br /> scheduling permits. if you have any comments, please call me at 415/231-1242 <br /> or Frank Yoneshige at 209/466-9580. <br /> Sincerely, <br /> Larry E.' all <br /> Senior Hydrogeologist <br /> LEH:lb <br /> Attachments <br /> cc: Rex Defenbaugh <br /> Frank Yoneshige <br />