Large On-site Sewage Systems (LOSS)

LOSS - What are they?

Designer/Installer/Operator Qualifications

Fees for Project Review and Operating Permits

Program Staff

Information and Guidance


LOSS - What are they?

Large On-site Sewage Systems (LOSS) convey, store, treat, and provide subsurface soil treatment and disposal of domestic sewage. Their design flow is between 3,500 to 100,000 gallons per day.

LOSS offer an alternative to centralized municipal sewage treatment plants and can serve from 10 to about 370 individual residences, or equivalent flows from schools and churches, campgrounds and recreation vehicle parks, resorts or state park sites, or smaller cities or towns.

Our staff review and approve LOSS project applications state-wide. The LOSS rule is Chapter 246-272B WAC, developed under authority of Chapter 70A.115 RCW. The revised rule became effective July 1, 2011.

All existing LOSS are required to obtain and renew annual operating permits from the Department of Health. Some LOSS were previously regulated and permitted by either the Washington State Department of Ecology or local health jurisdictions. The regulatory authority for these LOSS transferred to us when the revised rule became effective.

Traditionally, on-site treatment occurs through a septic tank and drainfield, located on or near the property where the sewage is produced. Other higher level treatment methods, in combination with a drainfield, are becoming more common, particularly when there is a concern about nutrients such as nitrates in the groundwater or when a drainfield is less able to provide adequate treatment.

Certain types of wastewater and sewage are not allowed to be treated by or flow into a LOSS, including industrial wastewater and stormwater. The Department of Ecology reviews, permits, and regulates systems that treat industrial wastewater and stormwater.

LOSS Designer, Installer, and Operator Qualifications


A professional engineer, licensed in the State of Washington, must prepare and stamp all LOSS design documents and reports submitted to the Department of Health (Department) for review and approval. On-site designers may not submit documents for LOSS. (Chapter 18.210.010(3) and (9) RCW)


The LOSS installer must be approved by local health jurisdiction in the county where the LOSS is being constructed. The installer also must have three or more years experience installing on-site sewage systems or must have successfully completed at least one similar installation that includes a pressure drainfield. (Chapter 246-272B-05000 WAC)


The LOSS operator is responsible for ensuring the LOSS consistently and reliably treats sewage to meet the operating permit conditions. Depending on the type of LOSS, the operator may need to hold a Department of Ecology wastewater certification (Chapter 173-230 WAC), be approved by a local health jurisdiction, or be qualified to operate a LOSS using proprietary technology. (Chapter 246-272B-07200 WAC)

Fees for LOSS Project Review and Operating Permits

Fees for LOSS project review, inspections and operating permits were adopted March 2, 2020. The base fee is required at the time of first document submittal. Any hourly fees for additional review time must be paid in full before approvals are granted.

Large on-site sewage systems fees recently increased.

  1. Plan review and inspection. The following fees apply for the Department's review of LOSS design documents and evaluations, and for Department inspections:

Category Base Fee Hourly Fee
New Project Review
Major Modification or Expansion
$848.00 $106.00 per hour if the application requires more than eight hours review time
Minor Modification or Expansion $424.00 $106.00 per hour if the application requires more than four hours review time
Site and Environmental Inspections $1000.00 per visit N/A
Final (post construction) Inspection $500.00 per visit N/A
  1. Operating permits The following fees apply for annual LOSS operating permits and renewals.

Category Base Fee System Volume Fee
Initial operating permit and annual renewal $608.00 $.0405 for each gallon of approved daily design flow
LATE application processing fee $94.00 N/A
Review of documents in response to permit conditions (hourly charge) $106.00 N/A
Inspection related to an enforcement event $1000.00 N/A

Statutory Authorities: RCW 43.20.050, 43.70.110; 43.70.250, 70A.115, and WAC 246-272-3000

Join our LOSS Email Lists

Large On-site Sewage System Email List

LOSS Engineer Email List

LOSS Operators and System Managers Email List

LOSS Owner Email List

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For questions, please contact the Wastewater Management Section at or call 360-236-3330.