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u � <br /> Field Practices and Procedures <br /> Page 4 <br /> 2-inch-diameter flush-threaded casing is generally used for wells dedicated for <br /> groundwater monitoring purposes. <br /> A monitoring well is typically cased with threaded, factory-perforated and blank <br /> Schedule 40 PVC. The perforated interval consists of slotted casing, generally with 0.01 <br /> or 0.02 inch-wide by 1.5-inch-long slots, with 42 slots per foot. The screened sections of <br /> casing are factory machine slotted and will be installed approximately 5 feet above and <br /> 10 feet below first-encountered water level. The screened interval will allow for seasonal <br /> fluctuation in water level and for monitoring floating product. A threaded or slip PVC <br /> cap is secured to the bottom of the casing. The slip cap can be secured with stainless <br /> steel screws or friction; no solvents or cements are used. Centering devices may be <br /> fastened to the casing to ensure even distribution of filter material and grout within the <br /> borehole annulus. The well casing is thoroughly washed and/or steam cleaned, or may be <br /> purchased as pre-cleaned, prior to completion. <br /> A filter pack of graded sand will be placed in the annular space between the PVC casing <br /> and the borehole wall. Sand will be added to the borehole through the hollow stem of the <br /> augers to provide a uniform filter pack around the casing and to stabilize the borehole. <br /> The sand pack will be placed to a maximum of 2 feet above the screens, followed by a <br /> minimum 1-foot seal consisting of bentonite pellets. <br /> Cement grout containing 5 percent bentonite or concrete will be placed above the <br /> bentonite seal to the ground surface. A concrete traffic-rated vault box will be installed <br /> over the monitoring well(s). A watertight locking cap will be installed over the top of the <br /> well casing. Reference elevations for each monitoring well will be surveyed when more <br /> than two wells will be located on site. Monitoring well elevations will be surveyed by a <br /> California licensed surveyor to the nearest 0.01-foot relative to mean sea level (MSL). <br /> Horizontal coordinates of the wells will be measured at the same time. <br /> Exploratory boring logs and well construction details will be prepared for the final <br /> written report. <br /> M:\Field Practices\Field Practices and Procedures-revised 07-2004.doc <br />