Memorandum <br />Page 1 of 2 <br />lqjff <br />DATE: September 2, 2021 <br />PROJECT: 2100102-2. M 0 <br />TO: Colin McArthur <br />Cameron McCarthy <br />PHONE: 458-234-6354 <br />EMAIL: cmcarthur@cameronmccarthy.com <br />SUBJECT: Stormwater Treatment <br />FROM: Kim Dorr <br />KPFF Consulting Engineers <br />PHONE: 503-664-3951 <br />EMAIL: Kim.dorr@kpff.com <br />This memo has been prepared to address Willamette Greenway Permit requirements for the proposed <br />indoor football practice facility on the University of Oregon's Autzen Stadium site, west of the Hatfield Dowlin <br />Complex. This memo describes how the proposed design meets the requirements of the City of Eugene <br />Stormwater Management Manual and Eugene City Code, including stormwater quality, flood control, flow <br />control, oil control, and source control. <br />Existing Conditions <br />The 10-acre development site consists of two turfed football practice fields and one grass practice field <br />utilized by the University of Oregon (UO) football team. The three outdoor practice fields are bound by Martin <br />Luther King Jr. Blvd to the north, Leo Harris Pkwy to the west and south, and the Moshofksy Athletic Center <br />and Hatfield Dowlin Complex to the east. The development site soil composition is characterized as <br />Hydrologic Soil Group Type A based on the United States Department of Agriculture (USDA) Web Soil Survey <br />for the project area. Soils of this group type typically have a high infiltration rate with low runoff potential. <br />The overall site is served by a private 15-inch storm main that belongs to the University and discharges to an <br />existing public 42-inch storm main in Leo Harris Pkwy. The 42-inch line flows west where it eventually outfalls <br />to the Q Street Channel. At the northern, downstream end of the private 15-inch main, there is a water <br />quality manhole that provides treatment for all drainage collected on the development site. <br />Proposed Conditions <br />The proposed conditions include an indoor football practice facility with connection to the Hatfield Dowlin <br />Complex and new drainage infrastructure that includes roof drains and stormwater treatment. The proposed <br />development will drain to a water quality manhole at the northwest corner of the site before discharging to <br />the public main in Leo Harris Pkwy. <br />Stormwater Quality <br />The city of Eugene requires water quality treatment of an equivalent area for all new or replaced impervious <br />surfaces. <br />The 2014 City of Eugene Stormwater Management Manual (SWMM) implements a hierarchy system in which <br />infiltration facilities must be considered first. If infiltration is not possible, filtration facilities must be sized; <br />and finally, if the site has insufficient room for filtration facilities, a greatly increased SDC fee may be paid. <br />800 Willamette Street, Suite 400, Eugene, OR 97401 541.684.4902 FAX 541.684.4909 <br />Eugene, OR Portland, OR <br />