CHS Engineers provided stormwater facility design, site grading, a looping water main, side sewer connections and local road improvements for the expansion of the five acre Doxon Toyota site.

In order to mitigate a high groundwater table within the flat Auburn valley, the low part of the site was raised an average of two feet and a shallow arch-pipe Stormtech detention system installed.  A BayFilter manhole provides water quality treatment downstream of detention.  A duplex pump system then discharges the controlled flow to the City’s drainage system, which is too shallow for gravity flow.

Also associated with the project were improvements to the sub-standard 35th Street NE, adjacent to the site.  This included new paving, grading, signage, striping, stormwater collection and conveyance, and realignment of the connection to Auburn Way.  Design challenges in 35th Street included existing utility conflicts with sewer and water, a shallow storm main in Auburn Way and grading a nearly flat existing gravel right-of-way while maintaining multiple existing driveway cuts.