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Rate Control To Liden Drive 24-HR, Event Existing Runoff(cfs) Proposed Runoff(cfs) 2-YR 4.68 > 1.42 10-YR 9.16 > 2.18 100-YR 15.57 > 8.65 *See Attached HydroCAD Report for Details To 694 Service Road 24-HR, Event Existing Runoff(cfs) Proposed Runoff(cfs) 2-YR 6.08 > 0.89 10-YR 10.57 > 1.93 100-YR 18.83 > 4.16 *See Attached HydroCAD Report for Details Total Site 24-HR, Event Existing Runoff(cfs) Proposed Runoff(cfs) 2-YR 10.76 > 2.31 10-YR 19.73 > 4.11 100-YR 34.40 > 12.81 *See Attached HydroCAD Report for Details Water Quality Treatment The site was permitted by the watershed district in 2004 as part of improvements to the property which included new pavement for a site entry and drive thru off of Black Oak Drive and some hardscape improvements on the east and north sides of the property. At that time, stormwater was routed to a pre- treatment pond and then passed thru a limited filtration basin. The basin was designed under old guidelines that required the volume from the Minneapolis-St. Paul Median Storm Rainfall event to be infiltrated for the impervious surfaces being proposed at that time. Current rules require water quality treatment volume for 1.1 inches of runoff over the area of new or reconstructed impervious surface. Considering the layout of the site, it is not reasonable to differentiate between the existing stormwater runoff and the need for additional stormwater treatment. Therefore, a volume for 1.1 inches of runoff over all impervious surfaces will be used for water quality treatment. Soil survey information for the area doesn't yield favorable soil groups on the property. Given the limited remaining open space on the site and the amount of additional impervious surface being proposed with this construction project, it is unreasonable that the project can meet water quality treatment through infiltration methods as outlined by the Watershed District Rules 6.c. The proposed development will utilize two filtration basins for water quality treatment due to the physical limitations that restricts infiltration. The filtration method requires drawdown within 48-hours