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Q NIATO:lIX <br /> may be moderated by the presence of low permeability clay layers and because of the possible <br /> influence of infiltration from the unlined stormwater pond to the north. <br /> The PW-1, PW-2, and PW-3 sites each comprise a group of three wells screened at varying <br /> depths. Historically, a negative vertical gradient (groundwater head decreases with depth) <br /> exists between the two shallowest screened intervals at each site (Figure 8). The vertical <br /> gradient implies that groundwater in a well screened in the uppermost portion of the aquifer <br /> may occur closer to the ground surface than groundwater in a monitoring well with a deeper <br /> screen. <br /> 4.0 NEW DMP WELLS <br /> Proposed locations for the new DMP wells (LP-4, LP-5, LP-6, and LP-7) are shown on <br /> Figure 7. LP-7 will serve as the background well, and the others will be compliance wells. <br /> The gradient in the uppermost aquifer is not well defined from the existing monitoring network. <br /> Based on the regional gradient, we anticipate that LP-4 will be the downgradient compliance <br /> well and LP-7 will be the upgradient background well. However, if recharge from the unlined <br /> storm-water pond is important locally, LP-6 may be a downgradient compliance well and LP-7 <br /> may be a cross-gradient background well. <br /> The deepest historical water level in the existing LP wells is about 20 feet bgs. Each DMP well <br /> will be drilled to about 25 feet bgs. Long screened intervals will be needed because of the <br /> historically large fluctuations in water levels in existing wells. Each new well will be screened <br /> from about 10 to 25 feet bgs. <br /> 5.0 SCOPE OF WORK <br /> The scope of work consists of drilling, installing, developing, and sampling four groundwater <br /> monitoring wells, and preparing a report documenting these DMP activities. <br /> 5.1 MONITORING WELL DRILLING <br /> Geomatrix protocols for the installation and development of monitoring wells are presented in <br /> Appendix A. A Health and Safety Plan for conducting these activities at the Lathrop site is <br /> included in Appendix B. Simplot's Contractor Safety Plan for the Lathrop site is included in <br /> Appendix C. Each boring will be advanced using hollow-stem auger methods to about 25 feet <br /> bgs. While drilling, the contractor will attempt to collect a continuous soil sample. Soil <br /> samples will be described using the Unified Soil Classification System (USCS) as presented in <br /> IAPROJECM741.000\6741-06.doc 3 <br />