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' therefore a groundwater investigation is warranted. <br /> 2 .3 Depth to groundwater <br />' According to Mr. Knoll, the seasonal high groundwater depth (1986) <br /> was between 15 and 20 feet below grade. According to the Fall, <br />' 19900 Depth to Groundwater map prepared by San Joaquin county <br /> Public Works Department, Flood Control Section, the present depth <br /> to groundwater in the vicinity of the site is currently between 30 <br /> and 40 feet. According to the map, groundwater in the area flows to <br />' the northeast. <br /> 3 .0 PROCEDURES <br /> 3.1 Drilling and Sampling <br /> IOn April 9, 1993 , four soil borings were drilled at the site. <br /> Borings #1 through #3 were advanced to a depth of 38 feet and <br /> completed as groundwater monitoring wells. Boring #4 was terminated <br /> at a depth of 28 feet. <br /> The borings were drilled with a truck--mounted drilling rig equipped <br /> with 8-inch outside-diameter hollow-stem augers. The B-57 drill rig <br /> and two-man crew were supplied by Woodward Drilling. During <br /> drilling, auger returns were monitored for the presence of organic <br />' vapors using a photo-ionization detector (PID: Thermo Environmental <br /> 580A, 10. 0 eV, calibrated to isobutylene) . <br /> Discrete soil samples were collected ahead of the drill bit using <br />' a split-tube sampler loaded with three pre-cleaned 2-inch by 6-inch <br /> brass sleeves. The samples were collected at five-foot intervals, <br /> using a 140 pound hammer to advance the sampler 18 inches. The <br /> number of blows required to advance the sampler in 6-inch <br /> increments was recorded on the boring logs. To avoid cross <br /> contamination, the sampling equipment was washed in a tri-sodium <br /> phosphate (TSP) solution and rinsed twice with water prior to each <br />' sampling run. <br /> For each sample, both ends of the lead tube were covered with <br /> aluminum sheets, capped and sealed with tape. A single soil sample <br /> was also collected from the previously excavated soil, which had <br /> been stockpiled on-site. The sample (SP-1) was collected using a <br /> metric soil sampler pre-loaded with two 2-inch by 3-inch brass <br /> sleeves. The ends of the lead tube were covered with aluminum <br /> sheets, capped and sealed with tape. The soil samples were stored <br /> on ice and transmitted under chain of custody to WEST Laboratories <br /> in Davis. <br /> 3.2 Logging <br />' Soil was extruded from the second brass tube and screened for the <br /> 2 <br />