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Appendix B <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 stern 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 S 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 <br /> Delta or a subcontractor to the nearest 0.01-foot relative to mean sea level (MSL) or a site <br /> datum. <br /> Exploratory boring'logs and'well construction details will be prepared for the final <br /> written report. <br />