2506 MELVIN AVE 2018-01-02 MF Import

� Willows ApaRmenu Drainage Smdy 09/162009 DOWNSTREAM CONDITIONS � The proposed development site currently drains by sheet flow to the east down the public right of way of Melvin Avenue into the I-5 corridor. There is no public stom drain system currently available along the south edge of Melvin Avenue. A twenty-five foot � concrete sound suppression wall has been recently constructed along the I-5 ROW line. It appears that the wall, which was mounted on spaced pilings tather than a conventional full length footing, was constructed over the historical cobble filled drainage swale I joining the Melvin sub-basin into the I-5 drainage system. The pre-existence of the cobble filled drainage swale is indicated in the aerial photograph obtained from the Snohomish County property web site. M old downsueam drainage map, Figure 3,which + was obtained from the Everett project archives, indicates that the rock filled swale � connects to a storm CB located at the edge of the I-5 travel lanes. Fmm there, runoff � enters the piped public conveyance. This rock filled trench appears to be the sole downstream convey and provided for this sub-drainage area. Unfortunately, the WASHDOT plans do not ofticially document the conveyance or iYs capacity. However, I since all releases from the site will either be restricted within detention or infiltrated thtough the previous pavements, no new impacts on the downsueam are expected as a result of this project. � A Preliminary BiologicaUEcological Evaluation for the Willows at Melvin Place was prepazed by LFR on August 18, 2009. This report evaluated the pmposed site for environmental impacu to the downstream basin. The report concludes that rhe site is not Ihydrologically connected to the Snohomish River or it's tributaries. No sensitive species i or habitats were identified which would be impacted by this project. � tiPSTREAM CONDITIONS IUpstream to the west of the site there aze two residential parcels which share che comm�n access easement, which will serve as the driveway for the subject ptoject. The front ( properry contains the original SFR with roof drains to the lawn. The density of � impervious is considered minor with frequent storms absorbed into the lawn azea. Larger winter events can result in some sheet flows to the north and eas;. The reaz lot contains a small apartment building facing Broadway with a gravel pazking area in the reaz and I. sloping to the east. However, the roof drains undoubtedly aze directed to the public storm drain in Broadway. The pazking azea is collected into a local catch basin located in the � northeast lot corner of the lot. Pipes indicate that the stormwater is conveyed due west to the Broadway storm system. There is no indication that there will be a significant stormwater contribution from the upstream propeRies which will impact the proposed � project. Therefore, we do not expect to see any significant surface contributions from the south onto the development. However, the poten:ial for subsurface tlows does exist and absent a geotechnical report may need to be addressed in the footing drains. 1 � �� PROIECT:05812 I