1125 80TH ST SW 2016-01-01 MF Import

Cf G PUBLIC WORKS Ev Err MEMORANDUM la 1' I� (/0� C t ,4-r TO: Kirk Brooks/AI Locke FROM: lane Zimmerman ` I i t 1 , DATE: July 14, 1995 SUB.IECT: Drainage Calculation Review, Dennis Petroleum ' General: The MDNS states that "if an infiltration basin is not constructed for treatment of stormwater, a portion of the building rooftop runoff shall be routed to roof downspout systems designed and constructed to City standards, if suitable soils exist on the site. The portion of the roof runoff routed to these ,ystems shall be designed so that the volume of water infiltratw.q into the ground on the site after development matches, as closely as is feasible, the i olume of water infiltrating into the ground under existing conditions." If suitable s.ils do exist on the site some roof-top infiltration will be required. The applicant should consult the City's Design and Construction Standards and Specifications for more details on design of infiltration systems. The attached table can be used to size any systems provided for this site. The pond calculations can be changed to account fot any reduction in roof-top impervious surface routed to the pond... The MDNS also states that "this project shall design a storm line and connection point, for future stormwater discharge from lot 1, that bypasses.the stormwater retention/detcntion and runoff treatment facilities on this project site and that ties into the storm line extension from the Washington Natural Gas site. This storm line and connection point shall be contained within the existing storm ch •,nage easement on this site." Calculations are needed for this line and the calcs for the size of the WNG extension need to account for existing rates of runoff from lot 1. The calculation package needs to state whether or not the calculations include the access drivt. If the access drive is not included, it needs to be.