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i ERI 205503,RQ3 Town 76 Servigg Station 5886.Stockton,California June 2.122 • Surveying well locations relative to a permanent datum and well casing elevations relative to mean sea level, • Evaluating the groundwater flow direction and gradient, and, ' • Preparing and submitting this report summarizing the data collected and presenting recommendations for work at this site 1 BACKGROUND The site is located immediately west of Interstate 1-5 on the northwestern corner of West March Lane and the I-5 offramp in Stockton, California, as shown on the Site Vicinity Map (PIate 1) The location 1 of the existing underground storage tank (UST) field, dispenser islands, other selected site features, and surrounding properties are shown on the Generalized Site Plan (Plate 2) Properties in the vicinity of the site are generally occupied by commercial developments 1 It is ERI's understanding that Union Oil Company of California (Union Oil) purchased the land in 1967, at which time the property was vacant In 1982, Unocal constructed a service station at the site and installed three 12,000-gallon USTs to store gasoline and diesel fuels (Delta 1996) To date, environmental work at the site included the following • Removal and replacement of USTs, product lines, and dispensers • Removal and disposal of approximately 1,200 cubic yards of soil at Forward Landfill in Manteca, California • Completion of a well survey within a 1/a-irule radius of the site • Drilling 44 soil borings (21 GeoprobeO borings, 20 soil borings, and 3 hand-auger borings), and ' installing three single-casing groundwater monitoring wells and four dual-casing groundwater monitoring wells • Performing a tank integrity test • Obtaining access agreements from property owners south and southwest of the subject site • Performing an underground utility search in the vicinity of the subject site • Performing quarterly groundwater monitoring and sampling ' The results of the preceding work indicate that dissolved petroleum hydrocarbons and select oxygenated compounds are present in groundwater, beneath and in the vicinity of the site PRESENT INVESTIGATION ERI performed the work in accordance with a Site Safety Plan (which was kept on site during field operations) and ERI's field protocol (Attachment B) ERI obtained an encroachment permit from the City and a well installation permit from the County prior to initiating the field work Copies of these permits are provided in Attachment C On April 8, 1999, ERI observed the drilling of nine off-site soil borings (B 11 through B19) by Woodward Drilling, Inc (Woodward) of Rio Vista, California Three borings were drilled at each ' location a shallow boring (approximately 15 feet below ground surface [bgs]), an intermediate boring (approximately 22 feet bgs) and a deep boring (approximately 36 feet bgs) Drilling was performed 2