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STORMWATER SITE PLAN <br />COMPASS HEALTH SUPPORTIVE HOUSING <br />NOVEMBER 7, 2019 <br />PAGE 11 <br />MR 6: RUNOFF TREATMENT <br />Runoff treatment is not required in the combined sewer area per Public Works Policy #2-11 <br />Storm water Control in the Combined Sewer Area. <br />MR 7: FLOW CONTROL <br />The site redevelopment will result in more than 5,000 sf of new and new or replaced <br />impervious surface and will require construction of a flow control facility. Per Public Works <br />Policy #2-11, Flow Control shall be provided except that "a forested land cover" shall be <br />replaced with "the existing site conditions" provided that there are no downstream issues like <br />increased CSO's and /or basement flooding. There are no known basement flooding issues in <br />the area. Public Works has been contacted but did not respond. The site is set to match <br />existing conditions and therefore should have a neutral effect to flow rates. WWHM2012 by <br />DOE has been used to perform drainage basin, flow frequency and detention pipe flow <br />duration calculations. <br />The development area contains the building, the landscaping (hard and soft) in the right of way <br />of Lombard Avenue, and site walkways and patios. The frontage along 33`d is excluded. It is <br />being redeveloped to remove the angle parking and provide a planter strip. This will reduce <br />impervious surface in a basin where the existing ground cover is used for calculations. The <br />existing basin contains 0.32 acres and in the existing condition the basin has the following land <br />uses: <br />Impervious 0.05 ac <br />Lawn 0.27 ac <br />In the developed condition, the site has a detained basin and a bypass basin. <br />The detained basin has the following land uses: <br />Impervious 0.25 ac <br />Landscaping 0.03 ac <br />The bypass basin has the following land uses: <br />Impervious 0.04 ac <br />An underground detention pipe will be used to provide flow control. The pipe will be located to <br />the southeast of the building in the courtyard and will discharge to the sewer system in the <br />alley. <br />The pipe has the following design parameters: <br />Diameter = 8 foot <br />Length 35 lineal feet (in a U pattern) <br />50 year depth = 7.50 feet <br />Peak Storage Volume = 1,655 cf <br />P:\Work\Projects\2017\17-125 Environmental Works\CE\DOCS\Final SSP 17-125.doc <br />