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generation of the Phase t permits, the next permits will include performance standards for water <br />quality treatment. <br />Anticipated Permit Language <br />For new development that creates 5,000 square feet or more of impervious surtace, the permits <br />will have a minimum pertormance standard of capturing and treating 80 percent of the average <br />annual rainfall, calculated based on site runoff estimates and using rain event characteristics <br />appropriate for the region or locality. The permits will also contain a minimum water quality <br />treatment performance standard of 70 percent removal of Total Suspended Solids (TSS), as <br />compared with uncontrolled runoff. DEQ is considering similar (though likely less stringent) <br />requirements for redevelopment projects. These minimum standards will apply to all of the <br />permittees except Johnson City, which is a 40-acre mobile home park in Clackamas County. <br />Many states and municipalities, both in Oregon and across the nation, are already achieving <br />these performance standards.2 These minimum performance standards are simple, straight <br />forward and give permittees maximum flexibility in how they design their program requirements.3 <br />These performance standards accommodate the approaches currently used in existing, effective <br />programs and will require some permittees to either demonstrate how tlieir existing programs <br />(treatment BMPs, site design, LID, etc.) achieve the pertormance standards or adopt more <br />stringent requirements. <br />Stormwater Quantitv Requirements <br />Increases in stormwater runoff rates and volume have been shown to have a detrimental effect <br />on receiving water quality and habitat. Stormwater control techniques that preserve or mirriic <br />natural hydrology - often referred to as "Green Infrastructure" or "Low Impact DevelopmenY' - are ~5 `~- <br />becoming increasingly prevalent in Oregon and across the country.~These techniques attempt.to ~4 ~ <br />mimic the predevelopment hydrology through runoff volume control, peak runoff rate control, flow ~ <br />f~equency/duration control, and water quality control. DEQ intends to incorporate per.mit <br />conditions related to volume and hydrologic pertormance into MS4 permits. DEQ is consulting <br />with EPA on potential permit approaches and researching the approaches currently used by <br />communities in Oregon and nationally. The goal of the permit language proposed below is to <br />provide a significant incentive for permittees to adopt and/or refine volume and hydrologic <br />performance requirements that are appropriate for local municipalities. <br />Anticipated Permit Language <br />Discussions with EPA and DEQ's research on specific permit requirements are ongoing. Specific <br />performance requirements will be considered over the coming weeks, but the permifs will include <br />the following general requirements: <br />Review codes and development standards and, where possible, remove barriers to low <br />impact development practices. <br />Develop a program to protect water resources by requiring all new and redevelopment <br />projects that result in creation or replacement of 5,000 square feet or more of impervious <br />surface to control stormwater discharge rates,, volumes, velocities and durations. <br />. Maintain or restore, to the maximum extent practicable, the site's <br />predevelopment hydrology with regard to rate, volume and duration of flow. <br />•_Require onsite retention (flow volume control) facilities and infiltration to the <br />maximum extent practicable. Where onsite retention and infiltration is infeasible, <br />2 Portland, Salem (Mill Creek),.North Carolina, Michigan, Maryland, New Jersey, Washington. <br />3 Virginia Stormwater Management: Nutrient Design System, Appendix B. Center for Watershed Z <br />Protection and Virginia Department of Conservation and Recreation. Version 1.0. 5/14/2007 `' <br />2 <br />