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On-Site Sewage System (OSS) Designers and King County Certified Installers and Maintainers
Lynn Schneider, Supervisor, On-site Sewage Program

Updated addendum to OSS repair design and submission

We continue to experience problems with unpermitted work of drainfield remediation and/or repairs. This Memorandum is intended to provide clarity to activities related to remediation and/or repair of drainfields. The purpose of this memo is to up-date the March 4, 2016 and June 20, 2016 Industry Memorandums. As noted, this will be a "living document" to address issues either previously not addressed or to provide clarification to current issues.

Drainfield "jetting" and/or "vacuuming"

There has been a proliferation of "jetting" and/or vacuuming of older OSS as observed in Routine Operation and Maintenance and time-of-sale reports. In most cases, "jetting"/"vacuuming" appears to be used to facilitate property transfer reports to mollify interested parties where an older OSS is failing or pre-failing. Also, sometimes more work is done to the OSS than is being reported included replacing deteriorating concrete or clay tiles. Simply put, this practice is not allowed without securing proper permits through Public Health — Seattle & King County.

The net result of this practice only serves to temporarily extend the life of an aging drainfield for the sole purpose of a time-of-sale report. It is the next property owner that then has to deal with a failing OSS and the cost of replacing it. This practice dilutes the purpose of the time-of-sale requirement, which reflects poorly on the OSS Industry.

Effective immediately, the only circumstances where "jetting" and/or "vacuuming" will be considered are as follows:

  • For pressurized systems using small diameter PVC pipe —this is considered an optional and acceptable maintenance activity. Please document the activity in the comments box of the Inspection Report, if one is being submitted to PHSKC. This will help us document the effectiveness of this activity.
  • For gravity systems with rigid 4" diameter PVC pipe. In order for "jetting" and/or "vacuuming" to be considered for gravity systems, a repair proposal must be submitted by a master installer, designer, or professional engineer with a comprehensive evaluation of the conditions of the system.

"Jetting" and/or "vacuuming" will not be allowed for the following:

  • Concrete or clay tiles.
  • Flexible PVC or other plastic pipe.
  • For systems without a record drawing.
  • For older systems at the end of their expected lifespan.


There appears to be some confusion as to design and permitting fees.

  • Site designs for repairs to failing OSS require a two-hour fee of $369.60. Note: the repair must be completed ASAP to address the failing OSS.
  • Repair installation permit fee for all failed systems is $691.
  • Repair installation permits are valid for 2 years from the date of issuance.
  • Site designs that are submitted to support residential or commercial expansions, alterations or otherwise serves to extend the lifespan of the structure, even when also replacing a failing OSS, require full design fee based on system type and drinking water source.

Notice on Title

For non-conforming systems, the Notice on Title must reflect the operational capacity of the system based on whatever site or design limitations there are for the particular property. The number of bedrooms notation is to be replaced with design capacity to more accurately reflect the system limitations.

Repair applications

  • For all time-of-sale and operation and maintenance based repair applications, a copy of the report must be provided or the application will be sent back.
  • Operation-Performance Monitoring Reports should be provided on all site investigations. It appears that some homeowners are "fishing" for good reports and that some members of the OSS Industry are accommodating them. Without the initial report it is difficult to determine if some reports are indeed legitimate.
  • Investigations of OSS do not require permits; however, the results of the investigations shall be reported.
  • For sewage tank and/or d-box replacements, it is expected that a comprehensive evaluation of the rest of the system be provided or the application may be sent back as incomplete.
  • To document consideration for the contributing factors related to the failure and to ensure that the repair addresses ALL causes, an O&M report that specifies all "contributing factors" is required to be submitted with all repair applications. Please refer to:

    • WAC 246-272A-0280 Repair of failures.
      (5) Prior to designing the repair system, the designer shall consider the contributing factors to enable the repair to address identified causes.

    • KCBOH Title 13, 13.64.010 Repairs of failing OSS
      1. This title shall be applied to maximum extent permitted by the site for any repair necessitated by the failure of an existing OSS.
      1. It is unlawful to repair an OSS without an OSS limited repair or repair permit.