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GL&A <br />October 6, 2015 <br />Ross Bachofer <br />P.O. Box 652 <br />LaSalle, Colorado 80645 <br />GANSER 1,1"JAN &C ASSO('IATES <br />1tvdroaeoloaical and Environmental Consultants <br />RE: HEC RAS Model Results of the Hydrologic Impact of LG Everist Mine on <br />Bachofer Property; 7525 Highway 85, Fort Lupton, Colorado <br />Ganser Lujan and Associates (GL&A) has quantitatively evaluated, using the HEC RAS <br />model, hydrologic flood impacts on the Bachofer Property caused by aggregate mining at <br />the adjacent LG Everist Mine site. The Bachofer property is located on Lot 6 in the SW <br />1/4 of the NE 1/4 Section 30, T2N, and R66W adjacent to and along the east side of the <br />South Platte River directly across from the open -pit mine site. The property is situated <br />between the river and Highway 85 and % mile south of Weld County Road (WCR) 18. <br />The property �s triangularly shaped and wedged between the river on the west and the <br />Plateville Irrigation and Milling Company Ditch to the east. The house sits on a flat area <br />on the eastern edge of the trees as shown in Figure 1 below. <br />Summary <br />Flooding of the lower level of the Bachofer residence has occurred repeatedly since 2004 <br />when an underground slurry wall, soil berms, and soil mounds were constructed in and <br />around the open -pit cells at the mine site. Since that time, flood events on the Bachofer <br />property have occurred fairly regularly with flows greater than approximately 6,400 cubic <br />feet per second (cfs) (GL&A, 2013). In the past, prior to installation of the slurry walls <br />and berms and creation of soil mounds in the mined areas, the flows reached over 10,000 <br />cfs and no flooding occurred. Discharges of 10,000 cfs and less that have caused <br />flooding since 2004 are significantly below the 100 year flow event of 29,000 cfs as <br />determined by the US Army Corps of Engineers for the Flood Insurance Study for the <br />Town of Fort Lupton (U.S. DH&UD FIA, 1978). The lower level of the house sits <br />approximately 1 foot above the 100 year flood plain level of 4874.0 feet as determined by <br />Weld County for obtaining a Flood Hazard Permit. As such, the homeowner was not <br />required to have a permit because his land was above the 100 year floodplain level. <br />There was also no history of flooding on this property prior to that time. <br />The results of these model simulations appear to support the historical and current <br />observations that construction activities at the Everist mine have not only altered the <br />hydrologic regime of the South Platte River but have also changed the morphology and <br />topography of the original floodplain on the west side of the river causing a constriction <br />and restriction of flood flows. As a result, flood flows, which in the past could spread <br />and dissipate across the pre -mining flood plain with no effect on the Bachofer property <br />on the east side, now flood his land and house. <br />6692 TV. 96`x' Place, Westminster, CO 80021, 720-272-2306, caluian("omcast.net <br />