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area of the proposed infiltration facility is anticipated to be approximately 2-feet below the bottom of the facility located at 407-ft. Infiltration testing was not performed as part of the Geotechnical investigation. However, an infiltration rate of 2 in/hr was assumed based on the infiltration rate of the stormwater facility growing medium and the Ksat value of the native soil from the NRCS Soil Survey. See Appendix B. The following table summarizes the calculated runoff for pre- and post-construction peak flow rates for the water quality and flood control (5-year) design storms. Supporting HydroCAD calculations are provided in Appendix A. ***Flow is retained on-site for the water quality event due to the rim of the overflow structure being set above the maximum water surface elevation. 2.3 STORMWATER FLOW CONTROL The standards set forth in EC 9.6793 only apply to development sites in Headwaters areas. The site is not located within a Headwaters area based on the Headwaters Streams Map in Appendix J of the Eugene Stormwater Management Manual. Therefore, flow control is not required. 2.4 STORMWATER OIL CONTROL The standards set forth in EC 9.6794 apply to development sites that store wrecked or impounded vehicles, have an expected daily traffic count greater than 100 vehicles per 1,000 SF of gross building area, development resulting in 100 or more off-street parking spaces, or development approving 125 percent or more of the minimum required off-street parking. None of the above criteria apply to the proposed development. 2.5 STORMWATER SOURCE CONTROLS The standards set forth in EC 9.6795(a)-(g) do not apply to the proposed development. A mid-rise multi- family development is not listed as one of the uses that trigger source control requirements. EC 9.6795(h) applies to covered vehicle parking structures. Some of the proposed parking is located underneath the proposed building. However, it does not fall under the definition set forth in Section 3.9 of the Eugene Stormwater Management Manual, which defines a covered parking structure as an enclosed building. The parking area underneath the proposed building is not enclosed and is designed to allow flood events to pass underneath the structure. Therefore, source control measures do not apply. However, the proposed private stormwater facility will serve as source control for the project. 2.6 DEDICATION OF STORMWATER EASEMENTS EC 9.6796 applies to city-maintained stormwater management facilities. The proposed facility will be privately owned and maintained. Therefore, an easement for the facility is not required. The Alton Baker May 3, 2019 Preliminary Stormwater Report Page 2