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�� ,/ � g ffi 1 in the immediate vicinity of the site. DEPTH 70 DATER TAS -r= According to maps published by the San Joaquin County Flood Control and Water Conservation District, (Plate V,) depth to ground water in this area is about 53', with the regional gradient to the south. However, as noted above, the first occurence Cf sufficient volumes of water for domestic or irrigation uses is below 150 feet. BRIEF HISTORY ❑F SITE PFir❑F: TO THIS - The property has been used for a concrete batch plant for many years. Records are not . available can when the UST's were installed, but it was sometime prior to 1975. On December 18, 1989, two (2) 1,000 gallon underground fuel tanks were removed by Jim Thorpe Oil, Xnc. One tank was used for gasoline, (leaded first, unleaded last;) the other had contained diesel fuel. A pump island for dispensing fuel was located to the south of the buried tanks, as shown on Plates VII & VIII. rive (5) soil samples were taken after tank removal; one from each and of the tank locations, and one beneath the pump island, where discolored soil and odors were noted. Plate VIII shows the locations of the samples. Laboratory analysis revealed that the samples from the north and of the two tanks, (85-1 & SS-2,) were clean, but the other samples revealed varying amounts of contamination. Table I lists that data in tabular form for ease of review. g As a result of the above work, Jim Thorpe Oil submitted a resampie/rewxcavation workplan to the SJCLHD on April 4, 1990, proposing to excavate additional spoil to remove the remaining contamination. A copy of that workplan is attached as Exhibit C. ` CHRQtj LOGY QF_ WaRK TS[ihlF_ After receiving approval from the SJCLHD, work commenced on August 17 1990, using Thorpe Oil Co. equipment and personel under the direction and supervision of William Hunter, R8, and Harlen Knoll, EHS, from the County Environmental Health Division. The sediments consisted primarily of tan-to-buff colored, very fine-to-fine grained, friable, sandy loam, with occasional lenses of grayish--tan clay. No distinc bedding was noted, (typical of flood plan deposits,) and the sail was fairly loose and poorly indurated. No xree water was --- - --- - - noted;-portions---of-the-excavation- were da;np, buE quickly dried j' out upon exposure to air. - , . �r A definiie petroleum odor was rioted from the tipper portion of the sy excavation, but became fainter as spoil removal continued. Some Discoloration was evident, especially in the area beneath the - site of the pump island. No .free product or color was noted in any of samples placed in water, although some showed a slight 2 _.