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• • • C. MONITORING WELL DESIGN • • Proposed monitoring well construction materials (e.g., well casing, screen, filter pack, • seal, grout, and well protection) are described in this section. • 1. Well Casing and Screen As indicated in Figure 5, well casing and screen sections will be 10 feet in length and will be flush couple threaded polyvinyl chloride(PVC) (ASTM F480), Schedule 40, four-inch • nominal inside diameter. No PVC solvent will be used. It is anticipated that a well • screen size of 0.020-inch will be used. The well bottom will be closed, and the bottom • cap will either be threaded or attached with stainless steel screws. The well screen and • casing will be kept clean and free of foreign matter and washed with approved water prior to use. Well centralizers, if deemed necessary to maintain the appropriate plumb, • will be PVC or stainless steel, and will be connected to the casing using stainless steel • attachments. The top of the well casing will have a removable Schedule 40 oversized cap • to prevent well contamination. • The contractor will install the screen and casing using the materials described previously. • The contractor and onsite geologist will record the well construction details on "as-built" • plans, a copy of which will be given to the City. A well installation record will be included with the well log as indicated above. • • Care will betaken to install the protective casing and well casing plumb. All joints will • be constructed to provide a straight, non-constricting, and watertight fit. Any casing or • screen deformation or bending will be minimal to the point of allowing the insertion and retrieval of the pump and/or bailer optimally designed for that size casing. • • The contractor will provide means of protecting the well bore and casing assemblies, • when installed, from the entrance of foreign objects. The entry of nuisance water, such as rainfall runoff or construction water from other construction activities, into the borehole • will be prevented. The contractor will protect the work from damage and take all • measures necessary to prevent delays. • 2. Filter Pack, Bentonite Seal, and Grout • • As shown in Figure 5, well backfill materials (e.g., filter pack, bentonite, and grout) will • form a continuous annular filling around the well casing. The filter pack will be sand composed of sound durable particles and will be free of organic matter, clay balls, and • other deleterious substances. Sand material used in the pack around the well screen will • be selected to be compatible with both the screen slot size and aquifer materials. Based • on the 0.020-inch slot well screen, the anticipated filter pack size will be RMC No. 3 sand. The filter pack size may be modified based on the results of the formation sample • sieve analysis. The pack will have a uniformity coefficient less than 2.5. The pack will • be properly cleaned and bagged by the supplier. The filter pack will be installed a • minimum of 6 inches below the screen, and from 2 to 5 feet above the screen. • • Riverbank WWTP Workplan Nolte Associates,Inc. • March 2005 3 \\SasO\project\SA1542\mon_well\new\gwmwiwp\wp.doc •