Laserfiche WebLink
GANSER LUOYAN & ASSOCIATES <br />Nydrogeological and Environmental Consultants <br />toward the northeast and discharge into the South Platte River adjacent to the <br />Bachofer property. This discharge will increase surface flows in the channel. <br />The results of Deere and Ault's HEC -RAS surface model and appear to be unreliable <br />and unrealistic when compared to actual stream flow data measured at the nearby <br />Fort Lupton gauging station. Peak flows during recent flooding measured 9,200 cfs <br />at this station on 9/13/2013, while the water level was at 4877.6 feet. The model <br />results produced a 100 year level at 4876.5 feet with flows of 29,000 cfs. The model <br />results should not be used as a basis to re- establish a new 100 -year flood plain map. <br />• Groundwater mounding that occurs on the west side due to the impermeable slurry <br />wall around L.G. Everist pits has created a higher heads in this area and as a <br />consequence, the alluvial aquifer is discharging and contributing more water to <br />surface flows in the river than what was occurring prior to the slurry wall <br />construction. <br />Deere & Ault have misconstrued the results of the USGS Report 2010 -5019. The <br />presence of mounding 2 to 4 feet above normal levels means that in addition to the <br />actual length of the slurry wall, a hydraulic barrier to flow has formed beyond the <br />edges of the slurry wall that will block nearly all alluvial flow. This means that <br />essentially no alluvial groundwater can flow northward to discharge areas as in the <br />past. As a result, nearly all of this flow will be routed into the river channel as either <br />alluvial or surface flow ultimately increasing the base -flow and stage level in the <br />river in this area. <br />• There is some evidence to suggest that higher groundwater levels exist on the east of <br />the river at or about the time that the pits were lined. Data obtained from the <br />Colorado Division of Water Resources well listing report shows two wells in the <br />vicinity of the Bachofer property with a continuous monitoring record that dates <br />back to 1989 and 1994. <br />• Historic aerial photos from Google Earth from 2002 to 2012 show that the river <br />morphology has changed. A noticeable increase in the formation of sand bars has <br />occurred in a reach of the river from approximately `/z mile upstream of the Bachofer <br />property to the Fort Lupton gauging station `/s mile downstream meaning that the <br />river stage has increased and caused flooding of the subject property. <br />• There is ample evidence that indicates construction of the sand and gravel pits <br />located on the west of the South Platte River from the Bachofer property has <br />disturbed the natural topographic surface of the area. Prior to construction of the <br />Golden cell, the land was below the 100 year flood plain elevation of 4874 and thus <br />could mitigate a flood swell or higher stage in the river that was above this value. <br />Based on a pre- mining topographic map developed by Deere and Ault (11/25/2008) <br />and a survey of the Golden Cell by King Surveyors (5/19/2009), approximately 60 <br />percent of this area that was once part of the flood fringe that could mitigate flood <br />stage levels has been removed. More importantly, the Golden Cell together with <br />19 <br />