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September 29, 2014 Monitoring Well Abandonment and Installation Workplan clay,clay,and sand deposits6.Soils are derived from mixed Sierran and Coast Range source materials,and are characterized by poor drainage7. The Lathrop area groundwater basin is comprised of an approximately 150-feet thick upper water-bearing zone overlying a 75 to 1,000 feet thick lower water-bearing zone.The lower water-bearing zone provides drinking water to the City of Lathrop.The hydraulic connection between the upper and lower zones appears limited due to extensive low permeability strataa. Depth to groundwater varies depending on location,season,and local influences.The shallowest groundwater levels are generally observed adjacent to the San Joaquin River, and groundwater depths tend to increase with distance from the river.In the alluvial flood plain deposits,groundwater is typically within 12 feet of land surface.Median water levels in the WWTF and WRP-1 MBR monitoring wells,groundwater elevation contours are shown on Figure 2. 1.4. Proposed Monitoring Well Destruction Four piezometers (PZ-1,-2,-3,and-4) are identified for destruction because they currently are located within the boundaries of the proposed percolation ponds (Figure 1).The construction information for these piezometers is summarized below in Table 1.Available construction permits are included in Appendix A,and available well boring logs are included in Appendix B.The four piezometers were installed to monitor groundwater conditions during a percolation disposal capacity assessment conducted within LAA 3.9 TableConstruction Information for Wells . Piezometers Proposed for Destruction. Diameter Depth Screened Proposed Well ID Year Drilled Interval (inches) (feet bls) Action (feet bls) KMW-7 2002 4 27.40a Unknown Destroy PZ-1 2012 2 2S 10-25 Destroy PZ-2 2012 2 20 10-20 Destroy PZ-3 2012 2 20 10-20 Destroy PZ-4 2013 1 15 10-15 Destroy a:Well depth from top of casing,measured on 4/28/2014. 6 Kleinfelder,"Hydrogeology of the Mossdale and Reiter Property,Lathrop,California', November 24, 2004. Soil Conservation Service,1992,Soil Survey of San Joaquin County. a Page,R.W., 1985,Geology of the fresh groundwater basin of the Central Valley,California,with texture maps and sections.U.S.Geological Survey Professional Paper 1401-C. 9 City of Lathrop—Crossroads WWTP Expansion Percolation Disposal Capacity Assessment: Land Application Area 3 Draft,Stantec,August 2013. HydroFocus, Inc. 3