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:.a`i. k i!y.sa: -_. � .L- 't= -. .' .'Ky5 . •.• .f ` -YVk-Y.- �' <br /> Y <br /> US <br /> f <br /> Chevron/S. E1 Dorado <br /> August 1990 4 <br /> HYDROGEOLOGY <br /> The site is situated in the Central Valley Physiographic <br /> Povince near the margin of the lowlands of the Sacramento pelta. <br /> Sediments underlying the site consist of fine sandy silts and <br /> clays deposited in an interfingering alluvial and estuarine or <br /> lacustrine environment. These sediments are of considerable <br /> thicj„ness (measured in thousands of feet) . Groundwater was <br /> w, encountered during drilling at approximately 47-Feet below grade. <br /> Subsequent monitoring data showed that groundwater levels had <br /> risen to 40-feet below grade. This suggests that the water- <br /> bearing zone is under semi-confined conditions. <br /> ;.off <br /> PREVIOUS WORK PERFORMED <br /> On September 1, 1989, Siebold Construction Company was <br /> subcontracted by Entrit, Inc. to remove three 10,000-gallon <br /> kx� <br /> underground fuel-storage tanks, one 1,000-gallon waste-oil tank, <br /> and associated piping from the site. Six soil samples were <br /> collected from within the fuel-storage tank excavation, two from <br /> r within the waste-oil tank excavation, and four soil samples were <br /> taken from points along the product-line trenches. Analytical <br /> r <br /> results for the soil samples collected from the fuel-tank <br /> excavation (Entrix 1989) , indicated that concentrations of total <br /> petroleum hydrocarbons (TPH)-as-gasoline were as high as 890 <br /> . i , parts per million (ppm) {sample no. S-8) . Analytical results Of a <br /> soil sample collected from the waste-oil tank excavation (S-2) <br /> indicated a concentratic:l of total oil-and-grease of 1,80o ppm. <br /> " Analytical results of a sample collected from the tank-pit <br /> excavation-near- the--northern <br /> the--northern- um --- - — --- <br /> ---- - - p p-island;S-9,-showed-a--- <br /> ,. <br /> concentration of 60 ppm TPH-as-gasoline. <br /> GROI-NDWATER <br /> J ITONMAKA'.INC. <br />