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September 30, 2015 Monitoring Well Abandonment and Installation Workplan grout used to fill the well shall be allowed to spill over into the excavation during the sealing operation,and fill the excavation up to a thickness f 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 shall be filled with clean soil. • Sealing material will be selected based on the required structu al,handling,and sealing properties,and the chemical environment into which it is placed.Sealing materials shall have such low permeability that the volume of ivater passing through them is of little consequence.Suitable materials can include neat cement, sand-cement grout,and bentonite clay.Used drilling mud or ct ttings from drilling shall not be used for any part of the sealing material. For abandonment of these wells,neat cement shall be used. Potable water shall be used for sealing mixtures. 3. Drilling Details 3.1. Drilling Equipment and Techniques A C-57 licensed well driller will employ an approved mechanical means (i.e.,auger,rotary, or cable tool methods)to bore the holes and construct the well to a maximum depth of about 1 foot below the bottom of the designed well screen depth.The borehole diameter will be selected so there is a minimum 2-inch radial thickness of sealing material between the well casing and borehole wall. For the prevailing subsurface conditions encountered in the Lathrop area(i.e.,unconsolidated sediment),a hollow-stem auger has successfully been used to drill monitoring well boreholes. 3.2. Borehole Logging and Soil Sampling California Department of Water Resources and San Joaquin County require completion and submittal of Water Well Drillers' Reports.In the Lathrop area,the nea surface deposits are composed of discontinuous inter-bedded silty sand,sandy silt,silty ch y,clay,and sand. Continuous-core samples will be collected using a split-spoon samplei driven ahead of the drilling tool. Core samples will be removed from the split-spoon samp er and examined to describe their texture,moisture content,grain size,and color using th Unified Soil Classification System.The core samples will be bagged and kept chille i for pore-water extraction. Pore water from select core samples shall be extracted usi ig a vacuum pump and filter,and the electrical conductivity of the pore water measured. In addition to core sample descriptions,the borehole log will also report any changes in the drilling rate, caving of the borehole,or changes in water temperature or water levels.All observations will be recorded and reported on a well boring and construction form (an example boring and construction form is provided in Appendix Q. HydroFocus, Inc. 6