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Field Practices and Procedures <br /> Page 4 <br /> environmental assessment and remediation projects. Wells are normally constructed <br /> using Schedule 40 polyvinyl chloride (PVC) casing. The borehole diameter will be a <br /> minimum of four inches larger than the outside diameter of the casing. <br /> Wells installed for environmental assessment and remediation projects are typically cased <br /> with threaded, factory-perforated and blank Schedule 40 PVC. The perforated interval <br /> consists of slotted casing, generally with 0.01, 0.02, or 0.03-inch-wide by 1.5-inch-long <br /> slots, with 42 slots per foot. A threaded or slip PVC cap is secured to the bottom of the <br /> casing. The slip cap can be secured with stainless steel screws or friction; no solvents or <br /> cements are used. Centering devices may be fastened to the casing to ensure even <br /> distribution of filter material and grout within the borehole annulus. The well casing is <br /> thoroughly washed and/or steam cleaned, or may be purchased as pre-cleaned, prior to <br /> 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. Well elevations will be surveyed by a California <br /> licensed surveyor to the nearest 0.01-foot relative to mean sea level (MSL). Horizontal <br /> coordinates of the wells will be measured at the same time. Horizontal coordinates are <br /> normally measured in California State Plane Coordinates. Latitudes and longitudes are <br /> normally calculated for each well, per California Assembly Bill 2886 (Geotracker) <br /> requirements. <br /> Exploratory boring logs and well construction details will be prepared for the final <br /> written report. <br /> M:\Field Practices\Field P&P-With Air Rotary Drilling-revised 02-2005 by SGB.doc <br />