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New stormwater rules ahead By Tony Boom Sep 26, 2022 12:15 AM A A New stormwater regulations emphasizing retention — the practice of capturing the water and releasing it via infiltrations into the ground, evaporation or reuse at the site — will be coming to cities and areas of the Rogue Valley. The new regulations will affect new developments and redevelopment of properties that would have more than 5,000 square feet of impervious surfaces. They will be contained in a Rogue Valley Stormwater Design Manual prepared by Rogue Valley Sewer Services. A RVSS working group is refining the standards following a public comment period on the proposed regulations. Those standards will need to be approved by the agency’s Storm Water Advisory Team in January and be in place by February to meet requirements of a stormwater permit issued to RVSS in 2019 by Oregon Department of Environmental Quality. RVSS is the designated stormwater permit holder for the municipalities of Ashland, Central Point, Medford, Phoenix, Talent and urbanized, unincorporated areas of Jackson County. It also provides stormwater quality services for Phoenix, Talent and some unincorporated areas including White City. Under the current manual, detention is used as the primary means to deal with stormwater, said Carl Tappert, RVSS manager. Detention is the practice of capturing, holding and slowly releasing runoff downstream. Bioswales are one way of implementing the detention strategy. “Detention will still be required. The change that we are doing is adding retention. We will likely see fewer bioswales,” said Tappert. “The permit registrant must establish a site performance standard with a numeric stormwater retention requirement to target natural surface or predevelopment hydrologic function to retain rain on-site and minimize the offsite discharge of precipitation,” the 2019 permit states. It calls for utilizing stormwater controls that infiltrate, capture and/or evaporate stormwater. Typical urban development interferes with the hydrologic process of filtering rain through soil, recharging ground water and slowly reaching streams. Rooftops, parking lots, roadways and other impervious surfaces that collect rainwater increase the amount of pollution in the water and hasten the flow into water bodies. This can have detrimental effects on aquatic life, ecosystems, recreation and drinking water quality. The new regulations will decrease work by homebuilders in some areas as it will increase the minimum impervious surface area requiring measures. The new standards would only impact larger-sized new home construction, said Tappert. Stormwater provisions for sites with 2,500 square feet of impervious surface is the current standard, but that will go to 5,000 square feet under the new rules. Those regulations will apply in all areas except Medford, which adopted its own code allowing the 5,000-square-foot standard. DEQ established the 5,000-square-foot figure in its 2019 permit. The regulations also will bring a lower threshold for rainfall in a 24-hour period that must be treated. It will drop from the current 1-inch level to .46 of an inch. That’s because retention is seen as a better way to treat runoff. “DEQ’s view it that it is a more effective treatment method. It’s a better treatment than going in a swale, which is most of the time what is happening currently,” RVSS Stormwater Program Manager Jennie Morgan told Phoenix City Council during a presentation. “That is the prime reason why the working group decided to lower the standard.” The new manual will make meeting stormwater regulations easier because it clarifies what the requirements are and the language is cleaner, said Tappert. “We think it’s good progress. This is an improvement over what has been done in the past.” A simplified approach that doesn’t require an engineer’s certification can be used for development with up to 10,000 square feet of impervious surface. Sites over 10,000 square feet still will use detention, and those plans will need engineering approval and must use a performance approach. Under the simplified method, ponded retention, pervious surface retention, vegetation filter strips and disconnected downspouts are approved approaches. For the performance method, underground retention, soil filtration, swales, basins, proprietary treatment and vegetated roofs also would be allowed. Detention would be allowed if no soil filtration is available. Alternatives are available if the new standards can’t be met due to site conditions. They might appear in some areas of the valley that have high clay content in the soil, said Tappert. Each jurisdiction and RVSS will have one vote when considering adoption of the new manual. Only five comments were received on the draft, and none came from any of the jurisdictions. Reach Ashland freelance writer Tony Boom at [email protected].