OSS professional certifications

Only individuals with Certificates of Competency are authorized to perform work and maintenance on on-site sewage systems.

On-site sewage system designers are licensed through the Washington State Department of Licensing. Visit the Board of Registration for Professional Engineers & Land Surveyors' website for more information.

King County certifies liquid waste pumper/haulers, on-site system maintainers, associate installers, and master installers. The requirements for these certifications include these three steps. More details about requirements for each step (PDF).

Examination: Exams that cover the necessary knowledge for the desired certification are offered by Washington On-site Sewage System Association (WOSSA) and Public Health.

IF YOU PASS THE EXAM, orientation interviews will be scheduled for successful candidates for the Associate Installer, Master Installer and Onsite System Maintainer Certificates of Competency.

IF YOU FAIL THE EXAM, you may re-take the exam. A new application and exam fee will be required.
Initial certification: After an applicant passes the required exam, the applicant must submit an application with proof that all requirements for certification have been met and a certification fee.
Certification renewal: All certifications expire on December 31st of each year. If a certified professionals wishes to renew their certification for the following year, a certification renewal application and fee must be submitted by December 31st.

Reference/study materials for the Certification Exams

King County On-Site Sewage Code, Title 13, Code of the King County Board of Health
Chapter 246-272A WAC: On-site Sewage Systems
Technical Information and References and Recommended Standards and Guidance documents (Washington State Dept. of Health)
Basic Principles of On-Site Sewage This document was prepared prior to the adoption of the 1995 on-site sewage rules. For items specific to Washington State rules see Chapter 246-272A WAC.
USEPA, Onsite Wastewater Treatment and Disposal Systems-Design Manual
USEPA, The Onsite Wastewater Treatment and Disposal Systems Manual
King County Site Development Process Flow Chart (Master Installer exam only)

Recommended courses for Continuing Education Units

Liquid waste vehicle inspections

Every vehicle in use for pumping or hauling of liquid waste must be inspected before a Pumper Business Owner certification or certification renewal is approved. Pre-scheduled inspections are offered at the Eastgate Environmental Health office. Please contact the Eastgate Environmental office for scheduling. Please review the inspection checklist to ensure that each vehicle will receive a satisfactory inspection.

Each fall, inspections are also offered at the Renton septage disposal facility and Brightwater treatment plant. Certified liquid waste pumper/haulers will receive a notification via email about these inspection days.

Certification renewal deadlines and late fees

Current fees for certification applications can be found on our current fee schedule.

All certificates of competency expire DECEMBER 31st of EACH YEAR.
Applications for renewal will be accepted annually beginning in November. Exam re-take is NOT required.
FOR LIQUID WASTE PUMPER/ HAULER: A late fee of 50% of the renewal amount will be charged for a renewal application received after January 15th. After January 31st, double the renewal fee will be charged. The applicant may be required to re-take the exam if the renewal application is not submitted by February 10th.
FOR MASTER/ASSOCIATE INSTALLER AND OSMs: A late fee of 25% of the renewal amount will be charged for a renewal application received after January 15th. The applicant may be required to re-take the exam if the renewal application is not submitted by January 15th.
All fees are non-refundable.