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r 4.0 WELL INSTALLATION During this investigation,two groundwater monitoring wells will be installed. All field procedures will be overseen by a geologist, under the direction of a California registered geologist. Procedures for drilling soil borings, well installation, well development, and groundwater sampling are outlined in the following sections. The on-site geologist will be present at all times during drilling in order to: • Direct and observe the drilling subcontractor; • Maintain a lithologic log of the borehole in accordance with the United Soil Classification System(USCS); • Screen drilling cuttings and atmospheric conditions within the work place with a PID; 4 • Oversee the implementation of the Health and Safety Plan. 4.1 Well Installation Permit and Utility Clearance • Following the approval of this work plan, a San Joaquin County well installation permit will be obtained for the proposed monitoring wells. Site access will be coordinated with the current site operator. The well locations will be marked and Underground Service Alert (USA)will be contacted to obtain clearance of underground utilities prior to the advancement of the borings. 4.2 Soil Sampling The boreholes will be advanced using a truck-mounted drilling rig equipped with an 8-inch- diameter hollow-stem auger. Soil samples will be collected at 5-foot intervals using a California modified drive sampler. The samples will be screened with a PID and examined for lithologic identification. Laboratory analyses will not be performed. 4.3 Monitoring Well Installation Two-inch-diameter groundwater monitoring wells will be installed in borings drilled at the proposed locations of MW-8 and MW-9 shown on Figure 2.The locations have been selected to ' be downgradient of the area at the northwestern corner of the former maintenance shop where groundwater monitoring data and the 2002 1,2-DCA investigation data show the presence of 1,2- DCA. MW-8 will be installed at the location closest(approximately 40 feet)to HP-1, where 1,2- DCA was reported in discrete groundwater samples collected at depths of 50 and 65 feet bgs at �►. concentrations of 170 and 130µg/L,respectively. A soil boring will be completed to a depth of approximately 90 feet bgs. A well will be constructed with a 10-foot screen incorporating the ` first permeable zone encountered below 80 feet bgs. The well will be installed through the hollow-stem augers. 1t will be completed with flush threaded,2-inch inner diameter schedule 40 PVC casing and well screen.The purpose of MW-8 will be to assess the presence of 1,2-DCA at the depth of historic low groundwater levels. MW-9 will be installed slightly further downgradient in a boring completed to a depth of 70 feet bgs.The well will be screened from 60 to 70 feet bgs. The purpose of MW-9 is to assess the downgradient extent of 1,2-DCA and variations in its concentration with time. The screened intervals will be filter packed with pre-washed No. 3 filter sand from the total depth to approximately 2 feet above the top of the screened interval.The screen size will be assessed L. r 3