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File No. 20-3937-01 <br /> June 21, 1996 <br /> A-3 GROJINDWATER WELL INSTALLATION <br /> A-3.1 Monitoring Well Construction <br /> Construction details for shallow groundwater monitoring wells are as follows: <br /> 0 The monitoring wells will have casings consisting of 2-inch inside <br /> diameter, flush-threaded joint, Schedule 40 PVC pipe. These wells will be <br /> constructed in 8-inch diameter borings. <br /> • Well screen sections will be perforated with 0.010- or 0.020-inch factory- <br /> cut slots. The perforation sieve openings are assessed (and modified if <br /> required) after the borings are logged, and if warranted, a sieve test has been <br /> performed and the results received. <br /> • The wells are generally screened from 5 feet above to 15 feet below first <br /> groundwater. If an apparent aquitard is encountered, the well is usually <br /> terminated to 2 feet into the aquitard. Effort is made not to screen across <br /> two aquifers. If confined aquifer conditions or high vadose zone <br /> contamination is encountered, the well screen in usually not set above the <br /> depth of first encountered groundwater. Wells are usually not set in areas <br /> of suspected significant soil contamination. <br /> hry <br /> • The PVC pipe and end caps will be steam cleaned prior to installation. <br /> • The annular space between the screen and the wall of the boring is <br /> backfilled with the appropriate clean Lone Star Industries 0130 or 2112 <br /> Monterey sand to approximately 2 feet above the top of the perforated <br /> sections. Based on soil logs or a sieve test, modifications may be made <br /> regarding the size of sand to be used. Installation of the 0130 sand may <br /> require that the sand be tremmied, using clean water. In this event, a <br /> sample of the tremie water is collected, unless the source is thought to be <br /> clean. <br /> • A 3- to 5-foot bentonite plug is placed above the sand pack to provide an <br /> annular seal against surface water infiltration and to reduce the potential for <br /> cement grout to infiltrate into the water. <br /> • The remaining annular space is filled to the surface with tremmied <br /> cement/bentonite grout(surface seal)to the surface. <br /> 20-3937-011UP960068 Page A-3 01996,Kleinfelder,Inc. <br /> KLEINFELDER 2825 East Myrtle Street,Stockton,_CA 95205-4794 (209)948-1345 (209)948-0621 fax <br />