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% <br /> The borehole for each observation well was advanced with 10-inch hollow <br /> stem augers. When the augers had been advanced to the desired depth of the <br /> well (approximately 25 feet) , the PVC well casing was lowered down the <br /> center of the augers and set to the appropriate depth. The annular space <br /> between the augers and the screened portion of the well was then backfilled <br /> with filter pack. As the filter pack was placed, the augers were withdrawn <br /> from the hole so the sand would flow out of the augers and fill the annular <br /> space of the borehole. The filter pack extended to approximately 1 foot <br /> above the top of the screen. A 1-foot seal of bentonite pellets was <br /> placed in the annular space above the filter pack. Since the bentonite seal <br /> was above the water table, approximately 3 gallons of potable water were <br /> added to allow swelling of the bentonite. After sufficient time had passed <br /> for the bentonite to swell (at least 1 hour) , the remaining annular space <br /> was backfilled to surface with a cement-bentonite grout. Representatives of <br /> ,.. the County Environmental Health Department were onsite to inspect and approve <br /> the grouting of each observation well. <br /> Each observation well was finished with a tamper-resistant, watertight <br /> street box set into concrete. The street boxes were set slightly above the <br /> existing ground surface to provide additional protection against <br /> infiltration of surface water. A threaded water-tight brass cap with a cork <br /> liner (2-inch wells) or rubber clamp-on cap (4-inch wells) was placed over <br /> the end of each well casing inside the street box. <br /> a.. <br /> Each observation well was developed by surging with a surge block and <br /> pumping with a centrifugal pump. Due to the fine texture of the soil <br /> material surrounding the wells, none of the wells produced clear water, even <br /> after extensive developing. However, turbidity was reduced significantly in <br /> all wells. With the exception of well OW-2, all wells produced water <br /> continuously throughout the development process. Well OW-2 was pumped dry <br /> twice during development. Development water from each well was retained in <br /> labeled drums pending chemical analysis. <br /> V <br /> 3286a/BAV100 15 <br />