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Groundwater Monitoring Well Construction Workplan <br /> February 2024 <br /> Groundwater Levels <br /> The Corcoran Clay is a hydraulic barrier to groundwater movement in the Subbasin. <br /> Groundwater aquifers above the clay are generally confined where groundwater levels below the <br /> clay are confined. The aquifers were grouped together into an Upper Aquifer(above the clay) <br /> and a Lower Aquifer(below the clay). <br /> Upper Aquifer <br /> The depths to groundwater and trends vary based on location in the Subbasin. Groundwater <br /> levels are much deeper in the non-Delta upland portions of the Subbasin where groundwater <br /> levels are affected by pumping, discontinuous recharge disconnect from streams and channels, <br /> and deep percolation of water from agricultural fields. <br /> Groundwater is projected to be about 20 to 30 below ground surface (bgs) at the well sites. <br /> Lower Aquifer <br /> The depths to groundwater in the Lower Aquifer(where the water is confined) are typically <br /> deeper than those in the Upper Aquifer. Groundwater levels (piezometric heads')range from <br /> about 20 to 270 feet bgs and in some locations, are below sea level. Groundwater elevations in <br /> the Lower Aquifer at the well sites are projected to be about 50 feet below ground surface. <br /> 1 Piezometric head(or hydraulic head)is a specific measurement of liquid pressure above a vertical datum. It is usually <br /> measured as a liquid surface elevation,expressed in units of length,at the entrance of a piezometer. <br /> GEI Consultants, Inc. 12 <br />