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<br />Provided Treatment Volume <br /> <br />Provided Filtration Volume: <br />(FB1) – 0.088 ac-ft x 43,560 cf/ac-ft = 3,830 cf <br /> <br />(see attached HydroCad calculations) <br /> <br />Draw Down Time – FB1 <br /> <br />Assumed Infiltration Rate of Filter Media (SP): 0.80 in/hr <br />(Based on MN storm water manual) <br /> <br />Maximum Time of Infiltration = 48 hrs, 0 min <br /> <br />Design Time of Infiltration = 36 in (3.0-ft) / 0.80 in/hr = 45 hrs, 00 min <br />(assuming full system to basin outlet) <br /> <br /> <br />RATE CONTROL <br /> <br />Existing Drainage <br /> <br />The existing site consists of two drainage areas (EXIST). EXIST1 drains off site to the <br />northeast regional pond via surface drainage and existing storm sewer. EXIST2 drains <br />to Foss Road via surface drainage. The existing drainage areas have the following <br />calculated runoff rates from 2, 10, and 100-year storm events: <br /> <br />EXISTING DRAINAGE <br />Drainage <br />Area <br />2-Year Runoff <br />(cfs) <br />10-Year Runoff <br />(cfs) <br />100-Year Runoff <br />(cfs) <br />EXIST1 1.15 2.60 6.41 <br />EXIST2 0.04 0.09 0.23 <br /> <br /> <br />Proposed Drainage <br /> <br />The proposed site consists of twelve drainage areas (DA). DA1-DA4C drain to the <br />proposed filtration basin (FB1) via proposed storm sewer. DA5 drains directly to FB1 <br />via surface drainage. DA6 consists almost entirely of green areas which drain <br />directly to the northeast regional pond via surface drainage and existing storm <br />sewer. DA7 consists almost entirely of green areas which drain directly to Foss Road <br />via surface drainage. The proposed drainage areas have the following calculated <br />runoff rates from 2, 10, and 100-year storm events: <br />60