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Four additional groundwater monitoring wells are proposed to obtain data to assess the data yaps; DEW0 and DMW-1 l downs adient to the north, and DMW-12 and�� laterally to the cast and west, respectively. A detailed scope of'work for installation and sampling of these wells is presented in the following sections. 4.0 SCOPE OF WORK The proposed scope of work for the additional 1,21-DCA field investigation includes the following tasks: • Coordination with regulatory agencies to finalize this work plan, and preparation of an updated health and salety plan. • Sol] boring and installation of four new monitoring wells downgradient and laterally with respect to DMW-9. A 10-foot screened interval will be selected based on lithology of'the individual borings, but will be within the range of the approximately 45 to 70 foot bgs interval. • Sampling and analysis of the four new monitoring wells. • Preparation of a report containing the field investigation results. Details ofd these tasks and the methods to be used are presented in the following sections. 5.0 SOIL BORING AND WELL INSTALLATION Four borings will he advanced and groundwater-monitoring wells will be installed in the boreholes with total depths and screen intervals similar to DMW-9. The borings will be advanced using a hollow-stem auger (HSA)equipped drill rig. The monitoring wells will be installed in the approximate locations shown on Figure 10. All field procedures will be overseen by an on-site geologist under the direction of a California-registered geologist. The on-site geologist will be present at all tithes 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 using a photo ionization detector (PID); • Oversee implementation of the Health and Safety plan. 5.1 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. 5.2 Drilling and Sample Collection Two 8.25-inch diameter soil borings will be drilled for the purpose of constructing 2-inch diameter groundwater monitoring wells. To reach the groundwater zone screened by DMW-9, the borings will be advanced to a depth of approximately 70 feet bgs. 6