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South Platte Decision Support System Groundwater Component Task 33 Field Study Work Plan <br />for Alluvial and Bedrock Well Installation, Testing, and Water Level Monitoring <br />well's total depth. At locations where HSA is required, borings will be terminated at <br />the well's total depth. Wells installed during Phase 2 will not be drilled with the <br />primary goal of determining the depth to bedrock due to the sufficiency of bedrock <br />surface data obtained during Phase 1. <br />3.1.3 Alluvial Well Installation <br />As described in Section 3.1.2, alluvial wells will be constructed using direct push <br />technology (DPT) or, if conditions are not suitable for DPT, hollow-stem auger <br />equipment. If additional existing wells are identified that can be used to accomplish <br />the objectives of the Phase 2 field data collection, as described in Section 2.0, then <br />these existing wells will be used instead of installing new wells pending approval by <br />the State. <br />Wells installed using DPT will be constructed of nominal l-inch inside diameter (ID) <br />schedule 40 polyvinyl chloride (PVC) as shown in the figures in Appendices C1 and <br />C4. Piezometers will be constructed by advancing a temporary casing to target <br />completion depth and up to a 20-foot length of 0.010-inch-slot well screen with an <br />end-cap will be installed. A filter pack consisting of 10-20 sand will be installed <br />adjacent to and extending to approximately 2 feet above the well screen. If lithologic <br />conditions warrant, natural formation collapse will be allowed instead of an installed <br />filter pack, or pre-pack screens maybe used. The installation method and description <br />of pre-pack screens is presented in Appendix C4. The remaining casing will be <br />constructed of blank PVC casing and grouted in place. <br />A steel protective casing with hinged lid and locking hasp will be installed over the <br />PVC well casing to provide well security. If mutually agreed upon by the Contractor <br />and the State, up to three protective steel bollards will be installed around the well. If <br />site-conditions warrant, atraffic-rated flush-mount protective surface casing will be <br />installed. Drawings of well completions using a steel protective casing and aflush- <br />mountcompletion are presented in Figure 1 of Appendix C1, and in Figure 5.13 of <br />Appendix C4, respectively. The respective numbers of locations requiring a simple <br />steel protective casing, protective bollards, or flush mount completions will be <br />determined during field verification of observation well sites. <br />In the event that conditions are not suitable for DPT, well installation, drilling, and <br />lithologic sampling will be performed using HSA methods. Use of drilling fluids is <br />not anticipated but may be required if heaving sands are encountered in the borehole <br />or if other conditions warrant. A drawing of a typical HSA well completion is <br />presented in Figure 1 of Appendix D. Wells constructed using hollow-stem auger <br />equipment will be constructed of 2-inch ID schedule 40 PVC with up to 20 feet of <br />0.020-inch slot factory-milled screen with the remaining casing consisting of flush- <br />threaded blank casing. A 10-20 filter pack will be installed in the annulus to a <br />minimum of 2-feet above the screened interval and a minimum of 2 feet of bentonite <br />seal will be installed above the filter pack. The remaining annulus will be grouted <br />~.~.-~ <br />11 <br />Z:\SPDSS\10-CDM DELIVERABLES\PHASE 2 FIELD WORKPLAN\FINAL DRAFT\FINAL SPDSS TASK 33 2 WORK PLAN.DOC <br />