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SECTION 3 – STORMWATER <br />25 <br />iv.It is preferred that runoff from upstream tributary areas (off-site land areas) be <br />bypassed around the storage facility of a site. If this is not feasible, the off-site runoff <br />can be routed through the storage facility but would be subject to the storage release <br />rate requirements as if it were part of the development in question. <br />a.) If the inlet invert is below expected storage facility water elevations, the <br />contributing storm network’s hydraulic grade line shall be reevaluated to ensure <br />there are no negative impacts. <br />v.Infiltration Routing (dry storage facilities only) <br />a.) If the Engineer wishes to consider the release of runoff through the infiltration <br />process in a dry storage facility, the infiltration rate shall be as recommended in a <br />geotechnical report, certified by a Professional Engineer based upon site specific <br />soil borings. The number of soil borings shall be adequate to represent the storage <br />facility infiltration characteristics. The soil boring(s) shall be positioned at the <br />proposed storage facility location and in-situ soils shall be used with the proposed <br />storage facility. <br />b.) The infiltration discharge shall be the area of inundation along the side slopes of <br />the storage facility for a given elevation. The storage facility bottom shall be <br />excluded from infiltration release calculations. <br />c.) If there is both a proposed concentrated flow outlet (ex. Discharge pipe) and <br />infiltration considered in the elevation-release rate calculations, the total release <br />from the storage facility at a given elevation would be the summation of the <br />infiltration release rate and the concentrated outlet (pipe) release rate. While the <br />routing should consider the total release in order to size the storage facility, the <br />calculations shall clearly provide a tabulation of infiltration release and <br />concentrated pipe release rates for each elevation considered in the routing analysis <br />to ensure that the allowable concentrated release rates have not been exceeded at <br />any outlet. <br />3-1.4 (b) ALTERNATIVES TO REQUIRED STORAGE <br />1.) For a project site that does not lend itself well for stormwater storage or to the entire <br />calculated required storage volume, the engineer shall propose alternative methods to control <br />the release rate and avoid downstream impacts. Any alternative methods shall require the <br />approval of the City Engineer. <br />2.) When the City Engineer approves an alternative method, a fee computed for each acre-foot or <br />part thereof of stormwater storage volume as required but not provided shall be paid as <br />established and allowed by City Ordinance.