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Groundwater Afonitoring Work Plan 1950[fest Fremont Street,Stockton, Cali brnia 2.2.1 Soil Borings During the PEA field work in January 2005, groundwater was first encountered at depth ranging from approximately 12 feet bgs to as deep as 20 feet bgs. The groundwater level stabilized at approximately 4.5 to 9.5 feet bgs following the drilling. In this Work Plan, the proposed depth of new boreholes(MW-1 through MW-3) is 20 feet bgs. However,the final depth will be determined by professional judgment of the on-site personnel based on the actual depth of groundwater encountered in the field. A subcontractor with a valid C-57 license will be used for advancement of the soil borings and well installations. A hollow-stem auger drill rig will be utilized to advance and install the groundwater monitoring wells. Three 8-inch diameter boreholes(MW-I through MW-3)will be advanced at the proposed monitoring well locations presented on Figure 3. Although no soil samples will be submitted for laboratory analysis,continuous soil samples will be collected for lithologic logging in accordance with the Unified Soil Classification System(USCS). All work will be performed by or under the direction of a professional geologist,certified engineering geologist,or professional civil engineer. 2.2.2 Well Installation The proposed monitoring wells(MW-1 through MW-3)will be installed to approximately 20 feet bgs and constructed with 2-inch diameter schedule 40 polyvinyl chloride(PVC)flush thread casing. The wells will be constructed with 10-foot long, 0.010-inch slot, schedule 40 PVC well screen typically placed from approximately 10 to 20 feet bgs. The exact depth of each well and the depth interval of screen will be determined in the field upon completion of each boring. The length of screened intervals may vary due to the locations where water-bearing features are encountered in each borehole. All wells will have a filter pack of Lonestar#1C or#2/12 sand placed to I foot above the top of the screen interval and a 1 to 2-foot-thick zone of li_ydrated bentonite pellets.The remainder of the annulus will be sealed with a cement grout to approximately 6 feet bgs and then further filled with concrete to 1 foot bgs. Both cement grout and concrete will contain 3 percent to 5 percent by weight of powdered sodium bentonite. A 2-inch lockable well cap will be installed on the top of the well casing. A flush- mounted well box with concrete collar and covered by a lid with waterproof gasket will be installed for each well. After completion of the fieldwork, the well locations will be surveyed for northings and castings using California Coordinate System NAD 83 and elevation(NAVD 1988). A California-licensed surveyor will conduct the surveying task. Project 102790 5 December 2007