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On-site Sewage System (OSS) Program

On-site Sewage System (OSS) Program


The Public Health On-site Sewage System (OSS) Program helps to ensure that over 85,000 septic systems including 192 septic systems in Seattle are safe. Septic systems treat wastewater when homes and buildings are not connected to public sewer systems. The OSS Program provides educational, advisory and permitting services for owners of septic systems and certifications for several septic professionals.
Septics 101 — Learn the basics

Current focus areas:

Healthy Beach Project

Healthy Beach Project

Public Health continues to work with Vashon-Maury Island residents to document improvements to water quality, find sources of excessive bacteria, and, where possible, eliminate these sources. During the 2018-2020 Pollution Identification and Correction Project, we are sampling water quality, performing visual surveys, and providing technical support and education.

Marine Recovery Area

Marine Recovery Area

A Marine Recovery Area (MRA) was established to protect especially sensitive marine waters from pollution from poorly functioning or failing on-site sewage systems (OSS). A 2006 state law (RCW 70.118A) required Puget Sound counties (including King County) to designate MRAs where shellfish growing areas are closed due to bacterial pollution (or if closure is likely), or where bacteria or nitrogen are seriously affecting water quality.

2016 On-Site Sewage System (OSS) Plan Update

2016 On-Site Sewage System (OSS) Plan Update

Public Health – Seattle and King County completed a stakeholder process to update its Onsite Sewage Systems Management Plan to incorporate new information, highlight current problems, confront new critical issues and more thoroughly address all OSS throughout King County.

Spring Beach Community

Spring Beach community

Spring Beach is a beautiful community area overlooking Colvos Passage on the west shore of Vashon Island. View Spring Beach map to see the area in greater detail. Spring Beach has about 12 properties, mostly of seasonal occupancy, all of which over a number of years discharge untreated sewage directly to Puget Sound. The Spring Beach community is making great progress and is working with professional designers and the county to install systems that meet current codes for on-site sewage systems.

Contact us

Environmental Health Services
14350 SE Eastgate Way
Bellevue, WA 98007

Phone: 206-477-8050 (answered until 4:00 pm)

Fax: 206-296-9792

Office hours:

  • Monday, Tuesday, Wednesday & Friday:
    8:00 am – 4:00 pm

  • Thursday:
    9:00 am – 4:00 pm

New office hours effective February 3, 2020:

  • Mondays, Wednesdays and Fridays
    8:00 am to 3:00 pm


  • Tuesdays and Thursdays
    10:30 am to 3:00 pm

Link/share our site at www.kingcounty.gov/oss