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.� 30 <br />u General Engineering and Environmental Management Services <br />Stormwater permitting included compliance with City of Greensboro and State of North Carolina requirements. Design <br />criteria included 85- percent efficiency removal of total suspended solids (TSS), controlled release of the water quality <br />volume over 2 to 5 days, controlling post - development peak discharge rates to pre - development rates, and providing <br />permanent sediment control storage volumes. <br />A flow splitter structure located at the head of the SSF system distributes stormwater to two pretreatment sediment <br />chambers that have a permanent pool. Stormwater then flows through a perforated pipe manifold into the filter bed <br />areas. Attenuation in the sediment chambers is achieved by forcing attenuation of flows through the manifold system. <br />The control of transfer rates also acts as an energy dissipater as stormwater flows onto and over the filter media. Filter <br />media bed dimensions provide for a drawdown period of 40 hours after the runoff event. Filtered flow is collected in the <br />underlying collection system and flows to the outlet riser. <br />During significant (larger than the water quality volume) events, the independent filter beds are inundated and captured <br />runoff volumes overtop both filter beds. Attenuated flows are managed within the footprint of the SSF for events <br />including the 50- and 100 -year, 24 hour durations. The outlet riser is located in the pretreatment chambers, near the <br />flow splitter, to avoid disturbance of the filter media and mature media texture during the management of the larger storm <br />events. The client has reported the SSF provides better access for maintenance. <br />Page 15 l l <br />