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January 25, 2016 Monitoring Well Abandonment Workplan • The wells located within CLSP and River Islands (CLSP-2, CLSP-4, CLSP-10,MWR-6, MWR-13, MWR-15, and MWR-20) should be abandoned by over-drilling to remove all the material within the original borehole including the well casing, screen,filter pack and annular seal per San Joaquin County well standards.This is necessary when well construction is unknown,or when obstructions are found in the well. The material extracted from the original borehole should be removed under direction of a SJCEHD inspector, and the excavated well boring should be filled with sealing materials by free-fall at depths shallower than 30 feet or tremie pipe or equivalent at deeper depths,proceeding upward from the bottom of the well or boring. Sealing materials should be placed in one continuous operation,and the pressure required for the placement of sealing material should be maintained long enough for sealing materials to properly set.After the sealing operation is completed and the sealing material has set,the remaining excavation should be filled with clean soil. • Per the San Joaquin County well standards,if well construction is known and the well was installed and maintained according to the County well standards,the well can be abandoned by pressure-grouting. Therefore,the wells located within Mossdale (MWM-14,MWM-16,and MWM-26) should be abandoned by pressure-grouting. Pressure for grout emplacement should be maintained long enough for the grout to properly set.The well casing should be left in place during sealing operations.A hole at least one foot larger in diameter than the originally drilled hole should be excavated around the outside of the well casing to a depth of three feet below the ground surface,and the well casing should then be cut off six inches above the bottom of this excavation and removed.The grout used to fill the well should be allowed to spill over into the excavation during the sealing operation,and fill the excavation up to a thickness of one foot forming a"cap"which has a diameter of at least one foot greater than the diameter of the originally drilled hole.After the sealing operation is completed and the sealing material has set, the remaining excavation should be filled with clean soil to just below street grade.The surface should be re-paved to match the surrounding street grade using either black stained concrete or hot asphalt.The surface completion should be approved by the City of Lathrop Public Works department. • Sealing material will be selected based on the required structural,handling,and sealing properties, and the chemical environment into which it is placed. Sealing materials should have such low permeability that the volume of water passing through them is of little consequence. Suitable materials can include neat cement and sand-cement grout.Used drilling mud or cuttings from drilling should not be used for any part of the sealing material. For abandonment of these wells,neat cement should be used. Potable water should be used for sealing mixtures. 3. Schedule for Completion of Work and Reporting Submission of this Monitoring Well Abandonment Workplan is required prior to the scheduled construction or abandonment of any groundwater monitoring well. For wells currently located in the City right-of-way or on City owned property,abandonment will occur by November 30, 2016. For wells that are on private property,the City will work with land owners to explain the well abandonment procedure and develop a plan to complete work.Abandonment of wells located on Hydro Focus, Inc. 5