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ithe annular space is filled, thereby preventing the undesirable <br /> mixing if annular material with caved material from above. <br /> EMCON suggests that the wells be constructed of 4-1/2-inch-diameter, <br /> flush-threaded, Schedule 80 PVC casing. The design of a typical moni- <br /> toring well is shown on Figure 6. On the basis of available data and <br /> experience at this and other disposal sites, PVC is considered to be a <br /> relatively inert and structurally sound casing material for this <br /> application. There is presently no evidence that landfill leachate <br /> contaminants are harmful to PVC casing. Machine-slotted screen will <br /> be placed from the bottom of the borehole to 5 to 10 feet above static <br /> water level . It is anticipated that 0.020-inch slotted screen will be <br /> used. If subsurface materials that are finer or coarser-grained than <br /> anticipated are encountered, appropriately sized screen will be used. <br /> Placement of annular materials shall be completed in a manner that <br /> maintains the structural integrity of the well . Filter pack will con- <br /> sist of sand compatible with the well screen and will be placed from <br /> the bottom of the borehole to approximately 5 feet above the top of <br /> the screened interval . If the well is not being constructed within <br /> conductor casing, and borehole bridging problems are expected, annual <br /> materials will be placed at appropriate depths using a tremmie pipe. <br /> Approximately 2 feet of bentonite pellets will be placed over the <br /> filter pack as a seal , with sufficient water added to "charge" the <br /> pellets. The remainder of the annular space will be filled with a <br /> cement-bentonite grout using a pressure-delivery technique and grout <br /> mixture approved by the local county health district. <br /> Prior to pump installation, the monitoring wells will be developed to <br /> prevent the movement of sediment into the casing. Acceptable methods . <br /> include pumping or air lifting with filtered compressed air. <br /> The monitoring wells will be completed by installing individual , dedi- <br /> cated <br /> cated pumps and locking protective covers. EMCON recommends that Well <br /> Wizard pneumatic bladder pumps be installed in both the new and <br /> PJ9 9390207.00D 12 <br />