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EXHIBIT D <br /> HAHN WATER RESOURCES, LLC <br /> July 8, 2020 <br /> Angie Fowler, PE <br /> SGM <br /> 118 W Sixth St, Suite 200 <br /> Glenwood Springs, CO 81601 <br /> Supplement to Hahn Water Resources Letter Report of August 2, 2019 on an Evaluation of <br /> the Impacts of Dewatering at Rifle Pit No. 1 <br /> This report presents supplemental findings to those in my August 2, 2019 letter report to you on <br /> the impacts of dewatering at the Rifle Pit No. 1. The Rifle Pit No. 1 is a proposed sand and <br /> gravel mine located in Garfield County, Colorado within the alluvial channel of the Colorado <br /> River. <br /> SGM filed a permit application to the Colorado Division of Reclamation, Mining and Safety <br /> (DRMS) entitled "Construction Materials Regular (112) Operation Reclamation Permit <br /> Application" (Application) in January 2020. SGM received comments to the Application from <br /> DRMS (through Scott Contracting, Inc.) and from Garfield County. Those comments included <br /> questions related to the proposed dewatering activities. This report is intended to address <br /> questions and requests for additional information contained in the DRMS and Garfield County <br /> responses to the Application. <br /> Dewatering Concepts <br /> The initial goal of my investigation was to evaluate the expected changes in on-site and off-site <br /> groundwater levels that would accompany the dewatering activities. Changes in groundwater <br /> levels were of particular interest in terms of their impacts to on-site wetlands. <br /> A numerical groundwater flow model (MODFLOW) was used to estimate water level impacts <br /> from pit dewatering with an emphasis on water level change that would result from dewatering <br /> rather than on a specific dewatering system and its performance. Site-specific data available for <br /> this analysis was extremely limited. That data included drilling logs and water level <br /> measurements for 5 exploratory borings (HP Geotech, 2008), a site elevation survey, preliminary <br /> mapping of on-site wetlands, mapping of various ditches and laterals surrounding and traversing <br /> the property, a decree for water rights on an adjacent parcel that included a discussion of aquifer <br /> properties, and aerial imagery. The dewatering was modeled as if it were accomplished with a <br /> fully penetrating perimeter drain. The model predicted a pit inflow rate of about 7 cubic feet per <br /> second (cfs) or about 3,000 gallons per minute (gpm) under steady-state conditions. In this case, <br /> steady state conditions represent the point in time following an extended period of dewatering <br /> when inflow rates have leveled off. Given the absence of site-specific information on aquifer <br /> properties,there is significant uncertainty in these predicted inflow rates. <br /> 1 <br /> 6589 Elaine Road -Evergreen,Colorado 80439 • office 720.242.8639 • cell: 303.870.5757 <br /> hahnwaterresources@gmail.com • www.hahnwaterresources.com <br />