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2019 Municipal Plaza and Center Street Concept Stormwater Reuse <br />06/26/2019 <br />Page: 4 <br />Additional Considerations <br />A simplified estimate of stormwater runoff expected from the street section was assembled to <br />ensure the watershed can produce enough runoff to adequately fill the tanks. Table 1 is a summary <br />expected runoff volumes for a variety of events. A rainfall event producing between 3.6 and 4.3 <br />inches in 24 hours (5-year to 10-year return interval) can completely fill the tank. <br />Table 1: Summary of expected runoff volumes. <br />Wen <br />1 ' Event <br />1-Year <br />2-Year <br />5-Year <br />10-Year <br />' of ii,11i , U II Il <br />II J u� PUUu 3J11pI)io� u <br />�)I�III,I <br />II I ((� ,�II1 ! <br />IIy o �I !uuuw5lw <br />1 00 <br />2.46 <br />2.86 <br />3.58 <br />4.26 <br />5 500 <br />14,700 <br />17,600 <br />22,700 <br />27,500 <br />41,140 <br />109,956 <br />131,648 <br />169,796 <br />205,700 <br />During final design, additional hydraulic information will be provided to provide an effective high <br />flow bypass system. In other words, if the tank is full and the City experiences a 100-year rainfall <br />event, there will be adequate bypass capacity to reduce local flooding and protect the tank(s). Also, <br />since the COR trunk storm sewer system is already designed to accommodate a 100-year rainfall <br />event with discharge to regional flood storage areas, the bypass system will effectively mimic the <br />originally designed scenario. In between events when irrigation is occurring, or the tanks is being <br />filled, there will be hydraulic relief on the trunk system and volume control provided. <br />Since the reuse water will pass through a filter and UV treatment system, the impact to groundwater <br />resources through the infiltration of irrigation water is expected to be very minimal. Impacts to <br />groundwater resources in the ERA are not anticipated. <br />Sincerely, <br />IE'. twn & Menk, Illnc, <br />Timothy J. Olson, PE, CFM <br />Water Resources Project Manager <br />