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1 <br /> Amy Eschberger Protect No 20144265 ' <br /> Colorado Division of Reclamation, Mining and Safety July 24,2020 <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 sub-contractor will request a utility locate and Golder will file a t <br /> notice 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. ' <br /> ■ Air-Rotary in competent bedrock to within 10 to 30 feet of anticipated contact between the Niobrara <br /> Formation and the Codell sandstone. <br /> ■ Air-Coring 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. Prior to monitoring well installation, described <br /> below, the core holes will be reamed (using air-rotary methods)to an 8-inch diameter. Drilling and sampling will <br /> be performed by a qualified drilling firm, subcontracted to Golder, under the supervision of a Golder ' <br /> hydrogeologist/engineer. <br /> It is assumed that excess drill cuttings will be non-hazardous and can be disposed at a nearby solid waste landfill. <br /> However, this disposal method may require sampling and chemical analysis of the cuttings prior to disposal. If , <br /> necessary, the cuttings may be temporarily stockpiled on Site pending the laboratory analysis. <br /> The Golder hydrogeologist/engineer will prepare a Iithologic log of each borehole as drilling progresses. In addition ' <br /> to this geologic information, the Golder hydrogeologisUengineer will pay close attention to the depth at which <br /> groundwater is first encountered, if discrete intervals of saturation exist at various depths, and changes in lithology. <br /> 1 <br /> GOLDER 2 ' <br />