3 <br />Potential impacts from the proposed site on existing drainage: New single family houses will <br />increase the runoff. <br /> <br />Techniques for mitigating potential conflicts or problems: Individual soakage trenches will be <br />constructed on each lot to mitigate any increased runoff. A soakage trench will be constructed to <br />accommodate the runoff from the proposed driveway. The calculations for sizing the soakage trench are <br />attached. <br /> <br />Infiltration Test Results: One test hole was dug onsite at the south side of the property. The test hole <br />was dug to approximately 9 feet deep. No ground water was encountered. The test hole was into bar run <br />material. It is my opinion that these infiltration test results are substantially in conformance with the City <br />of Eugene’s Presumptive Infiltration Testing for an Open Pit Falling Head Procedure. An infiltration rate <br />of just over 5” per hour was observed and therefore 2.5" per hour can be used for the design rate, giving <br />a safety factor of 2. <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 trenches have <br />been designed to accommodate the new impervious areas for the 5-year storm per the City of Eugene <br />requirements. <br /> <br />Stormwater hierarchy category justification: Does not apply. <br /> <br /> <br /> <br /> <br />