3 <br /> <br /> <br /> <br />METHODOLOGY <br /> <br />Drainage at existing site: Currently the property drains to the north. <br /> <br />Potential impacts on the proposed site from existing conditions: Two new triplexes will be built on <br />site. There are no impacts from the proposed site on the existing conditions. <br /> <br />Potential impacts from the proposed site on existing drainage: The two new triplexes will increase <br />the runoff. <br /> <br />Techniques for mitigating potential conflicts or problems: a soakage trench will be constructed on <br />the north end of the site to mitigate any increased runoff. The calculations for sizing the soakage trench <br />are attached. <br /> <br />Infiltration Test Results: Two test holes were dug onsite in the approximate location of the proposed <br />soakage trench. The test holes were dug to approximately 6 feet deep. Sandy bar run material was <br />encountered at approximately 3.5 feet deep. The holes were presoaked for 20 minutes and the holes <br />drained completely within 5 minutes. The estimated infiltration rate for these holes is about 40 inches per <br />hour. No ground water was encountered. For purposes of determining the infiltration rate, 20” per hour <br />should be used, giving it a safety factor of over 2. <br /> <br /> <br />Narrative that defines the proposed stormwater management techniques, including discharge <br />point(s) for runoff from private and public impervious areas: The proposed soakage trench has been <br />designed to accommodate the new impervious areas per the City of Eugene requirements. <br /> <br />Stormwater hierarchy category justification: Does not apply. <br /> <br /> <br /> <br /> <br />