2013-10-04_GENERAL DOCUMENTS - M1999120

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C;ANSUM LUJAN & ASSOCIATES Hydrogeological and Environmental Consullanls Response to Deere and Ault Comment #3 Deere & Ault have misconstrued the results of the USGS Report 2010 -5019. The USGS report shows on Figure 29 report the direction of the hydraulic gradient in the alluvial aquifer under steady -state conditions for the 2000 irrigation and non - irrigation seasons without lined or unlined pits. Based on the orientation of the equipotential lines drawn on this figure, less than half of the total alluvial flow would discharge into the river by the Bachofer property while the remaining proportion of flow would discharge further north. With the presence of lined pits, the configuration of the groundwater surface would be significantly different. The outline of the lined pits as shown on Figure 34 of the USGS report is located directly across the river from the Bachofer property and extends approximately 4,000 feet westward across the flood plain to nearly the edge of the alluvial valley. The lined pits physically extend across approximately 80 percent of the total width of the alluvial floodplain. Although the report does not include a figure with model simulations showing a hydraulic head configuration due to the lined pits, the report does illustrate the change in groundwater levels. The presence of mounding 2 to 4 feet above normal levels means that in addition to the actual length of the slurry wall, a hydraulic barrier to flow has formed beyond the edges of the slurry wall that will block nearly all alluvial flow. The length of this barrier can be seen on Figure 34, which is denoted by the color blue and delineates the total extent of the mounding. The blue shading covers the entire width of the river alluvium from the southwest bank of the river to the western edge of the valley. This means that essentially no alluvial groundwater can flow northward to discharge areas as in the past. As a result, nearly all of this flow will be routed into the river channel as either alluvial or surface flow ultimately increasing the base -flow and stage level in the river in this area. Given the above scenario, it may also be possible that groundwater levels on the east side of the river by the Bachofer property have increased due to mounding on the west side of the river. Frequent flooding has resulted from higher groundwater levels on the west side of the river may have caused higher water levels on the east with recharge to the alluvial aquifer occurring from the flood waters. As illuminated in the USGS report, mounding has and will occur due to lining mine pits with low permeability barriers such as slurry walls. Another factor that is contributing to flooding of the Bachofer property is the elevation of the top of L.G. Everist's Golden cell located directly across the river from the Bachofer property. The elevation, as shown by a topographic survey performed by King Surveyors, Inc in 2009, shows that the elevation of the rim of the pit is 4877 feet. This elevation is 3 feet above the 100 year elevation at 4874 that was determined by Weld County for obtaining a Flood Hazard Permit on 5/19/1987 on the Bachofer property. The surface elevation of this pit precludes the use of this portion of the flood plain to mitigate a flood swell thus, causing higher flood levels in the river and on adjacent areas such as the Bachofer property.