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the 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 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 />