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Work Plan to Install Additional Monitoring ARCADIS Wells Former OCC Lathrop Facility PW21, PW25, and PW30). Each borehole will be advanced by a C-57 licensed drilling contractor using mud rotary drilling methodology(unless an alternative method is deemed more appropriate) under the supervision of ARCADIS staff working under the direction of an ARCADIS Professional Geologist.The drill rig will be equipped with a minimum 12-inch-diameter drill bit for the proposed 2-inch nested wells or minimum 8- inch-diameter drill bit for the proposed single 2-inch wells. Borings will be continuously logged,and the lithology encountered will be recorded using the Unified Soil Classification System by an ARCADIS field geologist.After each boring has been advanced to its proposed total depth,wells will be constructed using a five foot long 2- inch-diameter PVC sump, 0.020 slot PVC screen, and blank Schedule 80 PVC casing. In addition, centralizers will be placed above and below the screen and in 50 foot intervals above the screen. 3.2.3 Filter Pack Installation and Grouting After the screen and blank casing have been placed inside the open borehole,the well annulus materials will be added by pumping the materials through a tremie pipe.The well annulus in the screened intervals will be filled with number 3 sand to a minimum of 2 feet above the screen.A minimum of 3 feet of bentonite chips will be placed and hydrated above the sand pack to isolate the screened interval and to prevent the entrance of grout into the sand pack. In boreholes containing a nested pair of wells, the annulus from 2 feet above the deeper screen to 5 feet below the shallower screen will be filled with bentonite.Typical proposed single and nested well construction details are presented on Figures 3 and 4, respectively. After the bentonite seal has hydrated, neat cement grout will be placed in the annular space above the bentonite seal to the ground surface to seal the remainder of the borehole. The SJCEHD will be notified before the wells are sealed so that a field inspector can witness this activity. 3.2.4 Well Development Grout will be allowed to cure for a minimum of 48 hours before development activities are conducted. Each well will be developed using one or more of the following methods: air development,water jetting, and mechanical surging.The specific methods and duration of well development will be determined in the field based on professional judgment. Water quality parameters, including pH, conductivity, and turbidity,will be monitored to track and document progress during development. 2014.03.13 mw installation work plan_fnal.doc 3