Laserfiche WebLink
STORMWATER SITE PLAN May 10,2017 <br /> OAKES AVENUE APARTMENTS PAGE 17 <br /> A7.12 Maintenance of Stormwater Drainage and Treatment Facilities. This project is subject to <br /> MR 1-5. MR-10, A stormwater Operations and Maintenance manual, has not been produced. <br /> MR 4: PRESERVATION OF NATURAL DRAINAGE <br /> Runoff from the site currently flows towards the City streets and into the City's combined <br /> sewer system.The flow patterns and basins are preserved. <br /> MR 5: ON-SITE STORMWATER MANAGEMENT <br /> This site shall be constructed on Alderwood soils described as Vashon Till or hardpan. Vashon <br /> Till has nearly no infiltration abilities and is expected to perch flow over the hardpan during <br /> rainstorms. Given the impermeable soils found on-site, infiltration is not recommended per the <br /> geotech. Impervious soils combined with proximity to structures and property lines make <br /> dispersion infeasible. <br /> Lawn, landscaping and planter areas shall be treated with BMP T5.13 amended topsoil to assist <br /> in retaining runoff. <br /> City codes require pavers for the drive courtyard of this project. The pavers themselves are not <br /> permeable, but the paver system will allow water to pass between the pavers and into the <br /> subsurface below. The paver section is graded to drain towards a catchbasin, and the subgrade <br /> is graded to match. The subgrade also contains a perf pipe underdrain in a trench that follows <br /> and approximates the flow line of the paver surface and is expected to pick up all stormwater <br /> from the pavers, although a statistically small amount may infiltrate. <br /> Footing drains and roof downspout drains also connect to the storm discharge into the <br /> combined sewer system. <br /> P:\Work(Sharefi.le)\Proiects`2016\16i-208 Rainier Building Co\CE\DOCS\\Drain\2017 05 10 16-20S Oakes Drain Rpt.doe <br />