2015-10-16_GENERAL DOCUMENTS - M1999120

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GA\ SER LUJAN &- ASSOCIATES Hvdrogeological and Environmental Consultants In addition, the present model results by GL&A differ significantly from previous modeling results conducted by Deere and Ault Consultants, Inc.(D&A, 2008) that were submitted to Weld County Public Works Department. These previous results by D&A showed negligible impact of mining operations on the water level surface from the 100 year event when compared to pre -mining conditions. Modeling results from GL&A indicate a significant difference (approximately 2 feet) in surface water elevations between pre -mining and existing mining surface topography. In addition, model simulations using the 5 -year event (7,900 cfs) are close to the 100 year event determined by the Flood Insurance Study (FIS) for the Town of Fort Lupton (U.S. DH&UD FIA, 1978). As part of this modeling work to demonstrate the causal link between mining development and subsequent flooding of the Bachofer property, GL&A performed the following tasks: Simulated surface water flow through a series of 7 cross-sections that extend east - west across the South Platte River from the Everist property to the eastern side of river approximately 1500 feet upgradient and 3000 feet downgradient of Bachofer property. Developed cross-sections from existing topographical surveys presented in a Deere and Ault report submitted to Weld County dated December 9, 2008. Data from this period was used to develop cross-sections representative of current mining topography. Pre -mining data were obtained from the USGS digital elevation model with a 2 -foot contour resolution based on the 1950 Fort Lupton 7.5 minute quadrangle map. • Simulated peak discharges of 7,900, 10,000 and 29,000 cfs for the 5, 10, and 100 year events, respectively. • Prepared a summary report describing results of the HEC -RAS model and rebuttal of Deere and Ault report. Bachofer Property The Bachofer property is located on Lot 6 in the SW 1/4 of the NE 1/4 Section 30, T2N, and R66W adjacent to and along the east side of the South Platte River. The property is situated between the river and Highway 85 and %2 mile south of WCR 18. The property (Figure 1) is triangularly shaped and primarily wedged between the river on the west and the Plateville Irrigation and Milling Company Ditch to the east. The house sits on a flat area on the eastern edge of the trees as shown in Figure 1 below. This flat area forms the post -Piney Creek alluvial terrace deposit and is comprised of interbedded sand and gravel. The area is heavily vegetated with cottonwood, willow, and occasional elm trees, tall bushes, and grass that extend from the house to the bank of the river. -2-