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NQ FLO00 P cp ~ 2 e '~ z p < o o ~ y° ~bebn 1'\av Board of Directors Executive Committee: Cathy Reynolds Chauman City of Denver o Linda Morton p Chairman Pro-Tem p City of Lakewood ° Chris Christensen > Secretary ~ Douglas County ° John Stone • Treasurer ~ Jefferson County ~ Donaltl Hamslra i Member ~ City of Brighton ; Members: Bruce Alexantler m City of Denver m David A. Day Engineer S w Guillermo DeHerrera , Adams County o Joyce Foster ~ City of Denver N Wayne Gaston o City of Aurora ,^~ Jana L. Mentlez '~ Boulder Caunry John J. Nicholl Arapahoe County w Deborah Ortega City of Denver o Art Patton z Engineer ~ Mary Poe w Town of Morrison Dennis Reynolds Cary of Littleton Michael J. Romero City of Lafayette ~II ~I~~I~II~~~~~ ~I~ sss l_. $COH TBCkBr, Executive Director RFr~ tt,,- . DEC ~ ^ >,vy~. Division of I,,,,,_, „_ ,- December 11, 1995 Mr. Carl B. Mount, Senior Protection Specialist Division of Minerals and Geology 1313 Sherman Stree[, Room 215 Denver, CO 80203 Subject Dahlia North Resources Pit -Application to Amend Previously Approved 112 Regular Reclamation Permit Application Dear Carl: We have reviewed the subject application with respect to the South Platte River Technical Review Guidelines for Gravel Mining Activities Within or Adjacent to 100- year Floodplains. We continue to have the following concerns initially presented in our December 5, 1994 letter to Rick Mergens: No reference is made to a side channel spillway. Typically if the riverside berm is longer than 1,300 feet, two side channel spillways are required. However, due to the channel and bank geometry adjacent to this project, only one side channel spillway will be needed near the downstream end of the berm. See Section 2.4.5 of the Gravel Mining Guidelines to size spillway. We estimate a spillway length of 480 feet based on a final water surface area of 132 acres. In addition, the river side and pitside slopes of the spillway must be protected with very large rock. The crest of the spillway should not exceed the 5-year flood level and the adjacent berms shall not be higher than the 10-year flood level. A typical section of the spillway should be provided. 2. The proposed overburden and topsoil stockpiles are located within the South Platte River floodway area. This violates the floodplain regulations of the Federal Emergency Management Agency, Urban Drainage and Flood Control District, Adams County, and Commerce City. The location and size of these stockpiles as shown, especially if they are connected, will increase the flooding depths in this part of the South Platte River floodplain, causing other properties to be inundated more frequently and at greater depths.