Admin Order 58-12-14 - Laserfiche WebLink

Home Browse Search

ISA for industrial land use is 60 %, as compared to 35% for low density residential land use (see Volume I, Appendix B for ISA factors by land use category), which significantly increases the overall basin buildout ISA. Overall, however, the buildout ISA for RR -SC is similar to that projected for the other basins: Bethel - Danebo (increases from 35% in 2006 to 50% at buildout), Willakenzie (37% in 2006 to 47% at buildout), Amazon (33% to 44 %), Willamette River (40% to 44 %), Laurel Hill (20% to 43 %), and Willow Creek (14% to 42 %). As with the other basins, now that stormwater development standards are in place (since mid - 2006), it is expected that the actual buildout ISA will be lower than the 50% calculated since the ISA factors used in the calculations assume buildout using traditional development practices. As described previously, this is appropriately conservative for use in modeling the major stormwater system for purposes of ensuring adequate conveyance and flood control. Topic; Underground Injection Controls or UICs (Drywells) It seems that rain garden projects proposed for drywell decommissioning are not needed for flood control, and may not be needed for pollution control either. Is it necessary to replace the lost capacity of drywells since they do not appear to have much of an effect on the overall drainage of the area? Instead of conveying UIC runoff to surface waterways (as part of decommissioning), infiltrate. [RR -7j, [RR -16j, [SC -121 Existing UICs must be decommissioned to meet Safe Drinking Water Act regulations. These facilities manage stormwater runoff primarily generated by impervious surfaces in the existing rights of way with an average contributing area of approximately 2.7 acres per drywell. There are approximately 150 total in RR -SC, with roughly equal numbers owned and managed by Eugene and Lane County. The County and the City must provide alternative means to convey the runoff currently managed by the existing drywells to meet the City and County's goals and policies related to flood control and water quality protection, and to remain in compliance with Oregon Drainage Law. Surface infiltration via rain gardens will be employed in decommissioning isolated drywells where there is no piped system with capacity nearby to connect to. In addition to managing the runoff for flood control, rain gardens provide the added benefit of surface water treatment and groundwater recharge. For the instances where there is capacity in the municipal system and the system is in close enough proximity for connection, the RR -SC plan assumes the runoff originally going to the drywell will be directed to the municipal system. In that case, pre- treatment of runoff utilizing a structural water quality facility prior to discharging to the municipal system will be incorporated. RR -SC Stormwater Basin Plan Comments Pg.12 of 17