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SECTION 3 – STORMWATER <br />28 <br />3-1.8 STORAGE FACILITY REQUIREMENTS <br />1.) Detention Basins Design <br />i.Minimum longitudinal and transverse bottom slopes of 1.0% unless underdrains are <br />provided <br />ii.Vegetated side slopes of the basin shall not exceed 4 foot horizontal to 1 foot vertical <br />(4:1) <br />iii.Storage depth shall not exceed 4 feet without approval <br />2.) Retention Basins Design <br />i.A maintenance ledge at least 6 foot in width placed 1 foot vertically above the normal <br />pool elevation <br />ii.A safety ledge of at least 6 foot in width placed 1.5 feet vertically below the normal <br />pool elevation <br />iii.Side slopes below the safety ledge shall not exceed two foot horizontal to 1 foot vertical <br />(2:1) <br />iv.Vegetated side slopes above the maintenance ledge shall not exceed 4:1 <br />v.The average permanent pool elevation of the basin shall be at least 4 feet in depth with <br />at least 25% of the basin being 8 feet in depth <br />vi.Fencing or a barrier is recommended around the perimeter <br />3.) Outlet control structures shall be designed to operate as simply as possible without manual <br />operation and shall require little or no maintenance and/or attention for proper operation. <br />4.) The storage facility owner shall be responsible for storage facility access and maintenance, <br />including the removal of accumulated sediment and debris. The owner shall maintain records <br />of storage facility maintenance operations and provide them to the City upon request. The City <br />may perform periodic inspection of storage facilities and require sediment removal and <br />associated storage facility maintenance at the owner’s expense. <br />5.) A geotechnical investigation should be performed to determine the anticipated soil conditions <br />at the site. If infiltration release is considered in the calculation the geotechnical investigation <br />should provide recommended infiltration rates. At a minimum, soil maps from USGS should <br />be provided, along with the anticipated soil infiltration rates to be encountered. If soils within <br />Soil Groups C or D are indicated, infiltration may not be a viable option. <br />6.) A storage facility located adjacent to a roadway should be provided with an adequate <br />recoverable slope or clear zone offset from the AASHTO Roadside Design Guide to minimize