Memorandum <br />Page 2 of 2 <br />May 13, 2026 <br /> <br /> <br />At this phase of design, the site has been divided into two drainage basins, as shown in Appendix 1, Exhibit <br />1 - Stormwater Basin Map. Both basins are treated with vegetated swales, though this approach and the <br />exact basin divisions may change during the PEPI and Building Permit design. For this analysis, both basins <br />are assumed to be 80% impervious. See Appendix 2 for the Proposed Runoff and Water Quality Calculations. <br /> <br />Basin 1 consists of the west private road and the adjacent driveways, sidewalks and residential structures. <br />The runoff at this stage in the design is entirely private, though that may change during development of the <br />PEPI plans. The water quality swale treating Basin 1 may be maintained by either the developer or the City <br />of Eugene. <br /> <br />Basin 2 consists of the public road, the eastern private road and the adjacent private residential <br />development. The runoff from this area is directed to a second water quality swale that will be maintained <br />by the City of Eugene. <br />Flood Control & Flow Control <br />All stormwater runoff from the site will be directed to an existing 42 -inch stormwater main. Although the <br />Eugene Stormwater Masterplan shows capacity issues on the downstream end of this main, those were <br />previously addressed by a Capital Improvement Project performed by the City of Eugene. Therefore, no <br />detention or retention is required to meet flood control standards on this site. <br /> <br />Flow control standards apply to projects that discharge to a headwaters stream at over 500 feet in elevation. <br />The site is over 500 feet, but it does not discharge to a headwaters stream. Therefore, flow control standards <br />do not apply. <br />Source Control and Oil Control <br />Source control is required for facilities that are highly likely to generate pollutants that are not addressed <br />through the implementation of vegetated stormwater facilities. None of these higher -risk facilities are <br />proposed as part of this development, so source control is not required. <br /> <br />Oil control standards are triggered with large parking lots, vehicle storage, or a high number of additional <br />daily trips. None of these triggers apply to the proposed development, so oil control is not required. <br /> <br /> <br />Appendices: 1 – Basin Maps <br /> 2 – Calculations <br /> <br />2500261-kg