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py. E Quik Stop Market No, 120 Project No. 349120-31 Ucrober 9, 1992 '-' Page 2 - FIELD INVESTIGATION Exceltech installed three groundwater monitoring ;yells around the underground tank complex during this investigation (see Figure 2). Field work began on June 28, 1990 with the construction of monitoring well mw-I. Following analysis of soil and groundwater samples collected from MW-1, Exceltech installed two additional monitoring wells NW-2 and MW-3) between July 30 and August 1, 1990. Exploratory Drilling and Soil Sampling The exploratory borings were drilled at the locations shown on Figure 2 using a Mobile B S3 truck-mounted drill rig. Before drilling, concrete pavement which overlaid the locations of wells MW-2 and MW-3 was cored by Cai-West Concrete Cutting of Manteca, Californi,. Pre-cleaned, hollow-stem augers were then used to advance the hole to the desired depth. Soil samples were collected by driving a pre-cleaned modified California split-spoon sampler ahead of the auger. The sampler, containing three 2-inch.Jmmeter, 5-inch-long brass liners, was driven 18 inches with a rig- operated, 140-pound hammer. It was then retrieved and disassembled into its component parts. The lowermost brass liner corrtzining the soil sample was sealed with foil, capped, labeled_ and stored in a chilled cooler for transportation to a state-certified laboratory. An Exceltech geologist logged the borings and characterized the sediments using the Unified Soil Classification System and M-unsell Soil Color Charts. A copy of the well installation permit issued by the San Joaquin Local Health District and boring logs are located in Appendix A. All soil cuttings were placed on and covered with plastic sheeting and left on-site. Groundwater Monitoring Well Construction tion, Exceltech cc 1certed the exploratory boreholes to groundwater Upon comple monitoring wells by installing 2-inch-diameter, schedule 40 polyvinyl chloride (PVC) _- blank and factory-slotted (.02 inch) casing with flush-threaded couplings. No solvents or cements were used during well construction. An Excelt ;r ge;;iogist determined the placeM--Dt of the screened interval. Once the casing was placed, the auger was pulled out of the ground a few feet at a time _ while No. 2/12 sand was slowly poured down the annular space between the auger and the casing. This was done to make the desired continuous gravel pack around the screen. The rest of the auger was then removed. A bentonite seal approximately 2 feet thick was Ehen placed on top of the sand and hydrated. The remainder of the boring was filled with a cement slurry under the supervision of an environmental health specialist from the San Joaquin County Public Health Service. When the hole had been filled to grade, a pre-cast, traffic-rated, watertight vault box was placed to approximately I inch above grade. A plastic locking cap and lock were placed on top h NEIt n,.