Attachment B <br />City of Eugene • 180 W 8th Avenue, Suite 200 • Eugene, OR 97401 • 541-682-5291 • www.eugene-or.gov <br />Memorandum Date: November 6, 2024 To: Eugene Planning Commission From: Doug Singer, PE, Development Service Manager, Public Works Engineering Subject: Stormwater Development Standards The purpose of this memo is to provide the Planning Commission with City staff’s responses to written testimony received since the September 24, 2024 Planning Commission public hearing regarding the proposed amendments to the Stormwater Development Standards. This recent testimony (CA 24-3 Testimony Batch 2) was provided to the Planning Commission via email on November 5, 2024. An October 15, 2024, staff memo provided staff responses to the written testimony received prior to the September 24, 2024 public hearing and spoken testimony from the public hearing. Written testimony from Eric Favreau (of Favreau Engineering) via email October 24, 2024, raises concerns about the proposal to require an “infiltration stormwater quality facility” (infiltration facility) on sites that have an infiltration rate of “less than 0.6 inches per hour.” The current code requires an infiltration system when infiltration rates on the site are “less than 2 inches per hour.” Favreau expressed that requiring infiltration facilities where a development site’s infiltration rates are lower than 2 inches per hour are likely to result in perpetual standing water because an infiltration-only facility does not include drains to prevent standing water. Favreau noted that “extended filtration facilities” provide some infiltration and also have underdrains that send excess water to the city stormwater system or other approved destination to prevent perpetual standing water. As a refresher, treatment of stormwater generally falls into a hierarchy of three priorities, ranging from on-site treatment being the first priority and discharge off-site being the lowest priority. Under this tiered system, the “infiltration facility” is considered a first tier priority, and the “extended filtration facility” is a second tier priority. This is explained in more detail in Staff’s memorandum to the Planning Commission from October 15, 2024. After internal discussions between staff, and with Favreau, staff agrees that the current code provisions are the more appropriate standard. Allowing a development to use extended filtration (rather than requiring an infiltration facility) on sites that infiltrate at rates of less than 2 inches per hour can still achieve the City’s desired outcome given the extent of infiltration-limited areas in Eugene. Therefore, staff recommend that the Planning Commission make no change to the current code’s standard for requiring full infiltration of the water quality design storm volume; it should remain at the 2 inches per hour infiltration rate and not be reduced to 0.6 inches per hour. This addresses Favreau’s concerns, and still meets the City’s NPDES permit requirements to maximize infiltration. This staff recommendation is reflected in Section 9.6792(3)(b)1.a in the attached Ordinance, proposed for Planning Commission’s recommendation. <br />Agenda Page 26 of 27