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overland onto the site from the southwest. Overland flow <br /> 'r <br /> patterns in the area are complicated by the extensive system <br /> ' of irrigation ditches and laterals . These channels convey <br /> flood waters over a portion of the area, causing shallow <br /> flooding. Isolated areas that are above the flood water <br /> ' elevation are not inundated but are nevertheless included <br /> within the floodplain. The Urban Drainage and Flood Control <br /> ' District is in the process of revising the floodplain in <br /> ' this area. <br /> The South Boulder Creek channel capacity of 1700 cfs is <br /> about equal to the 5-year recurrence interval discharge at <br /> ' the site. Flows in excess of 1700 cfs cause local flooding <br /> from overflow of the creek and from overland flow from the <br /> south. <br /> A recently-constructed flood control berm and channel directs <br /> ' flood waters away from much of the proposed mining area so <br /> that only lands east of the berm (see Figure C-1) will now be <br /> subjected to flooding. <br /> Water Quality. Ground water is generally of higher quality <br /> ' than surface water because of the natural filtration and <br /> ' purification offered by water percolating through the alluvial <br /> sands and gravels. Ground water at the site is well within <br /> ' the state water quality standards . The pH is approximately 7. 5. <br /> ' C-5 <br />