4418 RUCKER AVE MEDICAL BLDG 2018-01-02 MF Import

Schmidt Development Drainage Study 12/20/07 DOWNSTREAM CONDITIONS ]'he proposed development site currently drains by sheet flow to the public catch basin at the intersection of Rucker Avenue with 44' Street. It is unlikely that all existing street runoff is captured in this partial system. It seems probable that surface sheet flow bypasses the CB and flows further to the north through a private parking lot to the parking area of the Chinese Restaurant. Storm CB's do not appear to occur in significant numbers As previously indicated, the downtown area is a Combined Sewer area where the public storm water is combined with the local sewapQ flows. The water is accumulated at the sewage treatment plant, where it is treated prior to discharge to Puget Sound in the Snohomish River estuary. The flow calculations indicate that the contributions from the new development will not increase significantly above the existing flow because the areas are largely impervious already. Consequently, the development of the project is not expected to impact the downstream capacity of the existing sewers. UPSTREAM CONDITIONS The curb on Evergreen Way serves as a barrier to prevent upstream flows from draining down onto the property. The result is that Evergreen runoff has no impact on the proposed building site and is collected into the existing Public Storm Drain system. The SFR immediately south of the Schmidt property may add modest surface flows to the proposed building site but none were observed in the field. The lot contains an older home and is predominantly lawn so it seems likely that most runoff is absorbed into the groundwater regime. 'file Church south of the SFR in contrast is predominately impervious but from the grading it would appear that surface flows not absorbed within the site or possibly directed to the drains in Evergreen Way would sheet flow onto Rucker via the Driveway access rather than flowing north onto the project. Therefore, we do not expect to see any significant surface contributions from the south onto the development. llowever, the potential for subsurface flows does exist and absent a geotechnical report may need to be addressed in the footing drains. PROJELT:05780