Laserfiche WebLink
f <br /> ' Drainage Channels <br /> ' Besides the drainage swales between retention ponds described above, the reclamation <br /> plan calls for a 200-foot wide bottom width drainage channel to be located adjacent to and <br /> west (inside) of the site perimeter berm. This channel is both a redundant flood protection <br /> ' facility and an internal drainage channel. If a breach were to occur in the site perimeter <br /> berm (if it is not brought in to compliance with FEMA requirements), then flood flows <br /> ' would be conveyed along the channel, according to the design criteria, and be dumped <br /> into the flood pool at the north end of the Flatiron Property. We believe that this flood <br /> protection redundancy will not be justified after the site perimeter berm is certified as a <br /> flood levee by FEMA. If the site perimeter berm is constructed to FEMA standards, then <br /> this intemal channel could be reduced in size to serve only drainage purposes (although <br /> this would require the land contours to be modified to balance cuts and fills), possibly a <br /> maximum 50-wide, shallow, meandering swale. <br /> Groundwater Issues <br /> ' Based upon available data at the beginning of this study, we found that groundwater levels <br /> currently vary in depth across the site from 1 to 5 feet below the existing ground surface. <br /> Recharge from precipitation, streamflow and irrigation, may cause the water table to rise <br /> from 2 or more feet during the late spring and early summer months. The Pierre shale <br /> underlying the alluvial sand and gravel forms an impervious barrier to downward <br /> groundwater flow. Water moving into the groundwater system percolates vertically until <br /> contacting the existing water table or the Pierre shale bedrock surface. Groundwater then <br /> moves laterally downgradient towards the location of surface discharge into ponds and <br /> swales on the site. Groundwater in the sands and gravels within the site may be in direct <br /> ' hydraulic connection with the surface water flowing in South Boulder Creek and the <br /> irrigation water in the ditch. Upon completion of the operator's reclamation plans the <br /> groundwater will likely be within three feet of the surface in most areas. Groundwater <br /> control measures, such as the installation of french drains, underdrain pipelines, and <br /> -14- <br />