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Amy Eschberger Reference No. 20144265-REV1 <br /> Colorado Division of Reclamation, Mining and Safety September 4,2020 <br /> 1.0 PROPOSED LOCATIONS <br /> The proposed locations for both wells are shown in Figure 1. The locations are approximate and may be shifted <br /> slightly (less than 50 feet) prior to drilling. The locations were selected to be near current access roads on the Site <br /> and will allow access using a truck mounted drill rig. <br /> A suitable location does not exist for a hydraulically-upgradient background well that would also intercept the <br /> same geologic units as those intercepted by the existing monitoring wells. Therefore, MW-8 will be located side <br /> gradient to the north of the CKD disposal areas and on the east side of the access road. Based on information <br /> from monitoring wells MW-1 through MW-7 installed at the Site and our understanding of the Site geology, Golder <br /> anticipates that well MW-8 will be completed at depths of between approximately 230 and 270 feet. <br /> Following monitoring at MW-8 and assessment of results, MW-9 may be installed. However, if water quality observed in <br /> MW-8 is similar to existing downgradient wells(specifically MW-4, MW-6, and MW-7),well MW-9 will not need to be <br /> installed. Instead, a demonstration can be made that the concentrations in groundwater in samples collected from <br /> existing wells reflect natural conditions.The evaluation criteria are outlined in Section 3.2. The location for MW-9 was <br /> selected because it is geologically down-dip and hydrogeologically downgradient from the CKD disposal area and the <br /> existing monitoring wells.The proposed location is the farthest downgradient location that could be identified within the <br /> permit boundary that is accessible and feasible for drilling without the need for major earthworks. Golder anticipates <br /> that well MW-9, if needed,will be completed at depths of between approximately 310 and 360 feet. <br /> 2.0 DRILLING AND WELL INSTALLATION <br /> 2.1 Utilities <br /> Prior to drilling activities, Golder or the drilling subcontractor will request a utility locate and Golder will file a notice <br /> of intent(NOI)to drill monitoring holes with the Colorado Division of Water Resources. <br /> 2.2 Drilling Methods <br /> The following drilling methods will be used: <br /> ■ Hollow stem auger though overburden/fill, anticipated to be no more than 30 feet. The hollow stem augers <br /> casing will remain in place during the remainder of drilling. <br /> ■ Air-Rotary (open hole drilling) in competent bedrock to within 10 to 30 feet of anticipated contact between the <br /> Niobrara Formation and the Codell sandstone. <br /> ■ Air-Coring (open hole drilling)to contact between the Niobrara Formation and the Codell sandstone. <br /> The reason for the switch from air-rotary to air-coring is to allow for better sample retrieval and more accurate <br /> identification of the lithologic contact. Collection of rock samples for analytical testing or hydrologic testing is not <br /> planned. <br /> To the extent practical, air will be used as the drilling fluid until first groundwater is encountered. Limited water <br /> may be needed for coring and to help facilitate cutting removal. The volume of water, if used, will be recorded. <br /> Prior to monitoring well installation, described below, the core holes will be reamed (using air-rotary methods)to <br /> an 8-inch diameter. Drilling and sampling will be performed by a qualified drilling firm, subcontracted to Golder, <br /> under the supervision of a Golder hydrogeologist/engineer. <br /> GOLDER 2 <br />