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f <br /> t <br /> 1 EEnW16-NERKENHOM INC. <br /> SITE INVESTIGATION: GROUNDWATER <br /> 4. 1 MONITORING WELL INSTALLATION <br /> As described in Section 3. 1, three 6-inch diameter hollow-stem angered boreholes <br /> were drilled for subsequent conversion to monitoring wells (MW1, MW2, and MW3) <br /> on September 20 and 21 , 1990 (see Figure 3) . After soil samples were obtained. <br /> each borehole was reamed with a 10-inch diameter auger. During drilling, <br /> saturated soil samples were encountered at a depth of 37 feet in each borehole. <br /> The three monitoring wells were constructed of nominal 4-inch diameter, flush <br /> joint, Schedule 40 PVC as follows: <br /> Well Construction Details (feet) <br /> Annular Annular <br /> Well Cased Well Grout Bentonite Sand <br /> Number Dem Screen Seal Seal Pack <br /> MW1 42 27-42 0-24 24-25.5 25.5-45 <br /> MW2 43 28-43 0-24.5 24.5-26 26-43 <br /> MW3 43 28-43 0-24.5 24.5-26 26-44 <br /> Well screen, with a slot size of 0.010-inch was installed in each monitoring <br /> well . A uniform grain size (Monterey No. 3) sand pack was extended from the <br /> bottom of the boring to approximately 2 feet above the top of the highest screen <br /> perforation. A 1 1/2-foot bentonite pellet seal was placed above the sand pack, <br /> and a grout-cement mixture was place in the remaining annular space to the ground <br /> surface. <br /> All drilling was conducted dry with no fluids added to the borehole or <br /> lubrication to the drilling equipment. All drilling equipment was thoroughly <br /> cleaned with high-pressure, hot water prior to use to prevent potential cross- <br /> contamination. The PVC casings were capped with water-tight locking caps and the <br /> wells were installed with flush-mounted, water-tight covers . The drill cuttings <br /> produced from each of the boreholes were containerized in 55-gallon drums with <br /> lids and stored on-site to await disposal based on the results of the analytical <br /> testing. <br /> The monitoring wells were developed using surge/block bailing techniques on <br /> September 24, 1990, to remove the fine-grained and/or suspended material from the <br /> well and/or well screens. Each well was developed for a period of approximately <br /> 2 hours during which 110 gallons of water were removed from each well . The <br /> development water produced from each of the monitoring wells was containerized <br /> in 55-gallon drums with lids and stored on-site to await disposal based on the <br /> results of the analytical testing. <br /> 1J 17 <br /> l <br />