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4.0 Installation of Piezometers The geotechnical investigation will include installation of four standpipe piezometers. A drill rig with a hollow stem auger with a minimum diameter of 5" shall be used to advance the boreholes and install the piezometers to depths of approximately 50 feet below existing ground. A two-inch diameter PVC pipe will be installed in each of the borings upon completion. A 10-foot long screened section will be located between depths of approximately 10 to 25 feet below ground surface. A 3/8"minus rounded gravel filter pack will be placed around the lower 20 feet of pipe and grout will be used as a seal from the existing ground surface to a minimum depth of 5 feet below existing ground surface. The piezometers will be developed by removing sediment and water by air lifting and by surging the screened section with a surge block. This process shall be repeated at least 3 times or greater until the discharge is free of sediment. The top of the piezometer pipe shall have a removable cap or plug. The solid section of the PVC pipe will be extended to a height of approximately 5 feet above ground surface. A 6" diameter steel casing shall be placed around the PVC pipe to protect it from damage. The steel casing shall extend to a depth of 3 feet below existing ground surface and to a height of 3" greater than the height of the PVC pipe. A lockable lid with hinge shall be installed on the top of the casing and the casing shall be painted white or silver color. Any piezometer that is located within the traffic area of the O&M road shall be installed within a 2'x2' 8" thick concrete pad with a 6" circular vault with a cover secured by stainless steel bolts (see Figure 2). 5.0 Estimated Depths to Groundwater and Monitoring Appendix A contains logs for borings done in November of 2018 by WallaceKuhl for use in the designing of the Pumping Station No. 4. The groundwater elevations for these borings ranged from 63 feet to 73 feet (MSEL NAVD88) with depths to groundwater averaging 32 feet. Pumping Station No. 4 is approximately 4,800 feet to the west of Pumping Station No. 3 with land surfaces 20 feet higher than at Pumping Station No. 3. P g g p I,I The San Joaquin River is located approximately 22,000 feet to the east of Pumping Station No. 3, and has a river stage that ranges from 10 to 20 feet above MSEL. There are no nearby open excavations or ponds exhibiting groundwater ponding. The closest gravel pits i I