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Groundwater Monitoring Well Installation Section 2 2.5 MONITORING WELL DESIGN The monitoring wells will be drilled using a truck mounted hollow stem auger drilling rig advancing an 8-inch nominal diameter borehole to the target depth. Soil samples will be collected from the boring as a"continuous core",where site conditions permit, and logged according to the Unified Soil Classification System. The borings for the wells will be advanced ten(10)to fifteen (15) feet below first encountered shallow groundwater(shallow groundwater is expected to occur within the upper twenty to thirty feet) in order to characterize the lithology underlying the site. A fifteen (15) foot well screen is proposed at these monitoring locations,the length and depth of which will be confirmed in the field and based on observed lithology. Cement grout or bentonite chips/pellets will be used to backfill the boring, should it be advanced further than the field determined well completion depth. Additionally, the monitoring wells will be designed and installed according to the California Well Standards and permit conditions of the San Joaquin County Environmental Health Department with the following details: Borehole Diameter—Nominal 8-inch diameter. Borehole Depth —Estimated to be approximately 45 feet below ground surface, depending on first occurrence of groundwater. Well depths will allow for normal fluctuations of the shallow groundwater table and will be based on lithology. Casing Diameter—Nominal 2-inches. Casing Materials—ASTM F480 Schedule 40 flush threaded PVC blank casing. Top of casing shall be approximately two feet above ground surface, for above ground completions and just below ground surface for at grade completions. Well Screen —Factory slotted ASTM F480 Schedule 40 PVC well screens. Approximately 15 linear feet of flush threaded well screen will be placed in the boreholes. All reasonable attempts shall be made to assure that the well screens are a minimum of 24 feet below ground surface, assuring an annular seal of no less than 20 feet in length. As these wells will only be used for environmental monitoring and not potable supply, a shallower sanitary seal is justified, should it be required. Filter Pack—The filter pack proposed is a 2/12 type (12 x 20 mesh)Monterey Silica Sand, or equivalent. The proposed monitoring wells are intended for sensitive water quality determinations;therefore all filter pack material shall be handled to avoid contact with contaminants as discussed in Section 11 of the California Well Standards. The filter packs will extend approximately two feet above the top of the screened interval. Slot Aperture Width—The well screens will be installed with a 0.020-inch aperture width. The gradation is based on the initial selection of the filter pack and is sized to retain, at a minimum, the D90 of the filter pack. Protective Surface Casing—For above ground completions, six linear feet of nominal 6-inch diameter '/4-inch wall steel casing, or 6 x 6-inch square tubing, equipped with a lockable, April 2008Woodbridge Sanitary District WBSD07-002 2-4 Groundwater Monitoring Well Installation Workplan