South Magnolia CSO Control Project

King County Department of Natural Resources and Parks, Wastewater Treatment Division

This is an update on King County’s South Magnolia Combined Sewer Overflow (CSO) Project. Please call the construction hotline at 206-205-0968 or use the contact information below for questions, concerns and complaints.

King County’s contractor, Walsh Construction Company, is continuing work on 32nd Avenue West to prepare for installation of a new gravity sewer pipeline that is one component of CSO control facility in Magnolia.  The gravity sewer pipeline will convey excess stormwater and sewage during heavy rains to a 1.5-million gallon underground tank under construction in the Smith Cove area.   The new facility will reduce untreated overflows to Puget Sound from an outfall extending from 32nd Avenue West.

 On Tuesday, September 2, King County’s contractor will begin installing shoring for a drill pit on the east side of 32nd Avenue West. This work can be noisy, and will last 3-5 days.  People will hear noise from drill pit preparation work, and may feel some vibration near the site.  The contractor will be monitoring vibration levels.  People are more sensitive to vibration than structures, and while you may feel vibration, it does not mean that problems will occur as a result.

The week of September 8, the contractor expects to begin delivering equipment for the Horizontal Directional Drilling operation.

What you can expect during this work

  • Oversized loads with equipment are arriving today (Friday, August 29)
  • Work will be carried out during normal working hours beginning at 7:00 a.m. and may extend up until 8:00 p.m.
  • Flaggers will direct traffic through the work zone.
  • Increased traffic activity as trucks haul excavated material.
  • Drivers should proceed slowly through the project area and watch for workers, other pedestrians, bikes, and cars.

For more information

24-hour construction hotline: 206-205-0968

 Or contact Leslie Rankin at or Kristine Cramer at