located to the west of the proposed street improvements for stormwater treatment and <br />retention. In order to mimic existing drainage patterns, discharge from the proposed rain gardens <br />will be controlled by an orifice outlet and directed to a level spreader. The calculated outflow of <br />0.130 cfs, will be less than the pre-development rate of 0.539 cfs. <br />Runoff from impervious surfaces of the newly created lots will also be retained onsite at pre- <br />development levels. Per the stormwater report, the impervious surfaces will drain to an <br />underground holding tank with an orificed outlet to a level spreader in order to mimic existing <br />drainage patterns. <br />Based on the above findings, the proposed partition complies with this standard. <br />With respect to EC 9.6792 Stormwater Quality, in order to reduce runoff pollution and mitigate <br />the volume, duration, time of concentration and rate of stormwater runoff from the <br />development, the applicant must select, size, and locate infiltration or filtration type stormwater <br />quality facilities from the Stormwater Management Manual to treat the stormwater runoff from <br />the shared driveway. <br />Because the applicant proposes the construction of a public street, the proposed development is <br />subject to the standards at EC 9.6792(3)(b),(e-g). Subsection (b) requires that the treatment of the <br />public street be based on the following priority order: infiltration, filtration, mechanical. Since the <br />site is characterized by of Type D Dixonville-Philomath-Hazelair and Panther soils which are not <br />suitable for infiltration without further testing, filtration is the appropriate method for water <br />quality treatment of the public street. Since a significant portion of the roadside rain gardens are <br />proposed to be located in the area of future sidewalks, the specific proposal is not acceptable. <br />However, staff agrees with the applicant's engineer that other options are available that would <br />comply with the stormwater standards at subsections (e-f), which requires that the selected <br />stormwater quality facilities treat all stormwater runoff from new or replaced impervious surface <br />areas and that the facilities be sited designed and constructed according to the water quality <br />provisions and the facility design requirements set forth in the Stormwater Management Manual. <br />Therefore, for compliance with these standards the following condition is warranted: <br />• Prior to final plat approval, the applicant shall submit a revised storm drainage plan which <br />demonstrates compliance with EC 9.6792(e-f) for water quality treatment of runoff from <br />the impervious surfaces of the newly constructed portions of Spring Boulevard. <br />Because the proposed water quality facility is sized to treat only the stormwater runoff from the <br />public street, pursuant to EC 9.6792(2)(d) all lots in the proposed subdivision shall comply with EC <br />9.6792 (3) (d)-(g) at the time of the development permit applications for each lot. <br />EC 9.6793 Stormwater Flow Control Headwaters <br />PT17-07 Furtick - PW Referral Page 8 of 11 <br />