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Atlantic Richfield Company 4 ARCO 595 6100 North Highway 99,Stockton California September 13,2002 • wells MW-8 through MW-10 were installed at depths of 74 feet, 70 5 feet, and 70 5 feet bgs, respectively Shallow wells MW-8 through MW-10 were completed with 20-foot screens, extending from 53 feet to 73 feet bgs, 50 feet to 70 feet bgs, and 50 feet to 70 feet bgs, respectively Well completion details are included in Table 1 Bonng logs and well construction details are included in Attachment C Field procedures are described in Attachment D Subsurface Conditions Soil encountered during drilling activities generally consisted of interbedded layers of sands, slits, and clays A continuous clay layer is present beneath the site and site vicinity and ranges in thickness from ground surface to approximately 18 feet bgs Discontinuous sand and clay interbeds were present to the depth explored The most continuous sand interbeds were water-bearing zones encountered between the approximate depths of 60 and 70 feet and at about 98 feet deep Boring logs are presented in Attachment C Geologic cross-sections are included as Figures 3 and 4 Groundwater was first encountered in borings for shallow wells MW-8 through MW-10 and deep wells DMW-1 through DMW-3 at depths ranging from approximately 60 feet to 79 5 feet bgs Groundwater was again encountered at depths of 98 to 99 feet in the deeper borings Stabilized groundwater levels in the shallow wells ranged from • approximately 61 to 63 feet bgs during groundwater monitoring activities on July 17, 2002 (Table 2) Shallow groundwater appears to be under unconfined to semi-confined conditions within layers of sand, silty sand, and sandy silt Stabilized groundwater levels in the deeper wells ranged from 63 to 73 feet bgs This groundwater appears to be under semi-confined to confined conditions Stabilized water levels suggest some communication between the shallow and deep water-bearing zones Soil Sampling and Analysis Soil samples for logging were collected at 5-foot intervals from the borings for shallow wells MW-8, MW-9, and MW-10, from the ground surface to the total depths explored Soil samples for logging were collected at 5-foot intervals from the borings for deep wells DMW-1 through DMW-3 from approximately 49 feet bgs to the total depth explored Soils encountered during the advancement of the borings for deep wells DMW-1 through DMW-3 were not logged from ground surface to approximately 49 feet bgs, due to the close proximity of borings PSB-2, PSB-1, and the boring for well MW-7, respectively Selected soil samples were analyzed for TPHg, BTEX, and TPHd by the California Department of Health Services/Leaking Underground Fuel Tank (DHS/LUFT) method, and fuel oxygenates (MtBE, TAME, DIPE, EtBE, TBA, 1,2- DCA, and EDB) by EPA Method 8260B TPHg, BTEX, TPHd, MtBE, and other fuel oxygenates were not detected in soil samples Soil analytical results are presented in Table 3 Field and laboratory 11ARCOW5451Reportslwell tnstall3 doc