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annual fluctuations in ground water levels. Care should be <br />exercised in depth placement of the screens to accommodate for the <br />above criteria. Normally, spring installations would place a <br />majority of the well screen below the water table. Due to the <br />unusually dry winter of 1986-87, local ground water levels should <br />be researched to determine how much of the well screen should be <br />placed below the water table. <br />Page 2. It is recommended that if field and siting conditions are <br />acceptable, the southern -most up -gradient monitoring wells should <br />be sited approximately 50 to 100 feet farther to the south. This <br />distance will further remove any potential recharge influence of <br />Little Johns Creek to these wells. All other well locations <br />appear appropriate for Phase 1 installation. <br />New Monitoring Wells -Phase 2: <br />Page 2. Phase 2 wells should be <br />horizons available. Wells that screen <br />should be avoided if possible. <br />Drilling and Sampling: <br />sited in the most permeable <br />low permeability materials <br />Page 2. DHS recommends that geophysical logging include S -P, <br />resistivity (short and long normal), natural gamma, and a caliper. <br />Monitoring Well Construction -Well Casing: <br />DHS approves the use of PVC well screens (wire wrap) and casing. <br />However, it is here noted that solvents detected during routine <br />ground water monitoring will require re-evaluation for acceptance <br />of water quality data. Solvents in ground water do not provide an <br />acceptable environment for using PVC monitoring installations. <br />Well Seals: <br />Page 3. The use of bentonite pellets for sealing filter packs <br />below the water table should not require using water for <br />,hiydration. If water must be added for this purpose, formation <br />wate-r is recommended. Approximately 30 to 45 minutes should be <br />ailowed for hydrating 1/4" bentonite pellets; further, tamping <br />pellets with the tremie pipe assists in their disassociation. <br />Page 3. As described in the section for "Monitoring Well <br />Abandonment," unless Forward, Inc. requests using a specific <br />commercially produced bentonite as a cement additive, Halliburton <br />ratios of ingredients should be used. Grouting should be <br />accomplished using a tremie pipe whose bottom is a few feet above <br />the bentonite seal. Grout should then be pumped into the borehole <br />until it appears at the surface. <br />cc: Dave Wang <br />Ray LeClerc <br />2 <br />