Man pumping septic tank

There are over 26,000 Onsite Sewage Systems in Mason County. The Goal of the On-Site Sewage System Program is to protect public health and the environment by minimizing the threat of surface and ground water contamination from failing or improperly designed, installed or maintained onsite sewage systems.

On-site sewage system (OSS) means an integrated system of components, located on or nearby the property it serves, that conveys, stores, treats, and/or provides subsurface soil treatment and dispersal of sewage. It consists of a collection system, a treatment component or treatment sequence, and a soil dispersal component. An on-site sewage system also refers to a holding tank sewage system or other system that does not have a soil dispersal component.

Sewage Program Activities:
  • Onsite Sewage System Permit Review (New, Repair, Modification Reviews and Inspections)
  • Certification of Onsite Sewage System Professionals (Installers, Operation and Maintenance Specialists, and Pumpers)
  • Building Permit Review (Residential and Commercial) for Sewage review and Water Adequacy review
  • Platting Permit Review (Short Plats, Large Plats, BLA’s, etc…) for Sewage review and Water Adequacy review
  • Property Evaluations and Winter Observations for site suitability for Onsite Septic Systems.
  • Existing Septic Reviews/ “Health Letters” for property transfers or loan certifications.
  • Onsite Sewage System enforcement activities (complaints and other sewage related violations)
  • Homeowner Education (mail outs, events, homeowner classes, etc…)
  • Promote Onsite Septic System maintenance and maintain the OSS Maintenance database (OnlineRME).


Mason County Community Services, Environmental Health is located at Building 8 within the downtown Shelton county campus.

Physical and Mailing Address:
Mason County Community Services
Environmental Health
415 N. 6th Street
Shelton, WA 98584

Environmental Health Contact numbers:
Shelton: 360-427-9670, Ext. 400
Belfair: 360-275-4467, Ext. 400