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Mr: Besharah Najjar <br />Re: Brighton Mine Floodplain Use Permit <br />July 18, 1002 <br />Page 2 of 2 <br />DFA 6 will be picked up close to Riverdale Road and channeled to the North Pond, or <br />wetland area. A channel with several drop structures has been designed to take this flow <br />from the east side of Brantner Ditch to a grouted boulder mndown channel into the <br />wetland azea. <br />DFA 7 will be picked up close to Riverdale Road and channeled to the edge of the <br />wetland area. A channel has been designed to carry this flow as well, and will-include <br />four drop structures, because of the steep grade. The flow will be tamed from the east <br />side of Brantner Ditch to a grouted boulder rundown channel irito the wetland area. <br />Specifically addressing the outstanding Urban Drainage issues presented in a letter to <br />Carolyn Archuleta dated March 18, 2002: <br />1: Request for more detail in the grouted boulder rundown channels, including crest <br />elevations, toe elevations, and cross sections; structures limited to a 4:1 slope <br />Crest and toe elevations are d~cult to show because they will change depending <br />on the final location of the rundown channels. The detail specifies that the <br />channel will extend from existing ground at the top of the pit slope to three feet <br />below the pit invert. We believe this is enough detail to be able to construct the <br />channel accordingly once the final pit confrguration and exact location of the <br />rundown channel are known. <br />A cross section of a typical grouted boulder rundown channel has been included <br />on the revised Reclamation Plan. <br />The 4.•1 maximum slope for the grouted boulders is presented in Section 2.4.3 <br />Grouted Sloping Boulder Drops of the Urban Storm Drainage Criteria Manual. <br />This section focuses primarily on grouted boulder drops in grass-lined channels. <br />Section 7.6 Grouted Riprap Rundowns does not specify a maximum allowable <br />slope for the rundown channels. We feel a 3:1 slope is reasonable for the <br />rundown channels into the mining pits in this case. All grouted boulder rundowns <br />and protection will be constructed according to Section 4.4.1.2 of the Urban <br />Storm Drainage Criteria Manual. <br />2. Channels from property boundary to mining pits need to be designed and <br />constructed during the mining operation <br />Please refer to the above discussion regarding the design of the offsite tributary <br />channels. These channels will be constructed in a phased manner as mining and <br />reclamation progress from one end of the mining cell to the other. <br />3. Offsite tributary channels must be constructed during the mining operation <br />Please refer to the above comment. <br />