Resolution 3284 - Laserfiche WebLink

The Applicant's proposed storm drainage system would utilize on-site retention and infiltration to the maximum extent feasible, but would include a combination of infiltration and stormwater detention systems. Detailed soils analysis would be submitted with detailed engineering and building plans at time of submittal for Building permits and SEPA reviews for the individual phases of development. Based on those reports, Public Works would determine where infiltration would be acceptable. An infiltration system would collect storm drainage in a perforated conveyance pipe which would allow storm drainage to drain into the ground directly. The portion of the storm drainage which is not absorbed into the ground through the perforated pipe conveyance system would be collected in a series of open ditches, percolation trenches or percolation structures which would infiltrate the remainder of the storm drainage water into the ground. Biofiltration would occur naturally via the percolation process. Where infiltration is not feasible, on-site detention would be provided. Drainage from the site would be conveyed via a tightlined storm drainage system to a surface pond or underground vault where it would be detained for a time and released at a rate not exceeding that of the predeveloped site. The overall storm drainage volume would increase, but the rate of release would be the same or less than the predeveloped site. Biofiltration through grass lined swales would be provided. Storm drainage conveyance from the tops of slopes would incorporate a tightlined system to convey water down steep slopes. Energy dissipaters would be utilized to minimize water velocities in the system. CONCLUSIONS The South Everett Drainage Basins Plan is the appropriate policy document which applies to storm drainage 28