February 12, 2025

Attention OSS Professionals,

This is a special edition newsletter. As many of you are aware, revisions to WAC 246-272A are coming soon. Please review our highlighted rules and regulation changes to WAC 246-272A below. This notification is not all-inclusive of the revisions to WAC 246-272A effective April 1, 2025 but is intended to highlight some of the key changes to the rule.

The complete Chapter 246-272A WAC, as well as a Summary of Rule Changes, Significant Analysis, and other supporting documents can be found by visiting the Washington State Department of Health on-site sewage system rule revision webpage.

Please keep an eye out for our regularly scheduled newsletter to come later this month.

WAC 246-272A-0025 

Highlights: Connection to Public Sewer System Distance Specifics 

• Clarification of where to measure 200 feet from to determine requirements for connection to sewer.
• The 200’ measurement from adequate public sewer will be measured from where the existing building drain connects to the existing building sewer, or where no building drain exists, within 200 feet from where the sewer line begins, as measured along the usual or most feasible route of access.
• As defined by WAC 246-272A-0010 Definitions:
  • Building drain means that part of the lowest piping of a building’s drainage system that receives the discharge of sewage from pipes inside the walls of the building and conveys it to the building sewer beginning two feet outside the building wall.
  • Building sewer means that part of the horizontal piping of a drainage system extending from the building drain, which collects sewage from all the drainage pipes inside a building, to an OSS. It begins two feet outside the building wall and conveys sewage from the building drain to the OSS.

WAC 246-272A-0230 

Highlights: Changes to Table VI to Include Bacteria Levels and Subsequent Updates to DS&G

Click here to view: Updated Table VI

• Systems with ≥24<36” of vertical separation must have timed dosing (36”+ vertical separation does not require timed dosing in soil types 2-6)
  • Will require elapsed time meters (refer to pressure distribution systems DS&G)
• Bacteria levels are now included in Table VI
• Required treatment levels and disinfection levels from Treatment Level B & BL2 reduced to TLC & BL3 for soil types 2-6 when vertical separation is ≥18 <24

Note: The term “Departmental Standards & Guidance (DS&G)” will replace “Recommended Standards & Guidance (RS&G)” as of April 1, 2025 with the new WAC revisions.

WAC 246-272A-0210 

Highlights: Table IV Setback changes

Refer to WAC 246-272A-0210, Table IV for the following horizontal setback changes to on-site septic system components:

Table IV:

• Removed “suction line” from existing well setback
• Added “non-public drinking water well”
• Added “non-public, in ground, drinking water containment vessel”
• Added “easement for water supply line” to existing pressured water supply line setback
• Added “closed geothermal loop or pressurized non-potable water line”
• Added “lined stormwater detention pond”
• Added “unlined stormwater detention pond
• Added “irrigation canal or irrigation pond (up or down gradient)”
• Added “subsurface stormwater infiltration or dispersion component

Other Changes in Section:

• Added statement that OSS components take precedence to stormwater components
• Removed option for LHO to reduce horizontal setbacks to 2ft for OSS components to inground swimming pools.

WAC 246-272A-0233 

Highlights: Pump Chamber Requirement Changes 

(1) All pump chambers, except pump basins, must be designed to meet the following requirements:

(a) Have a minimum volume of 1,000 gallons;

(b) Provide an internal volume to account for the design flow, full-time pump submergence, space for sludge accumulation below the pump inlet and emergency storage volume of at least 75 percent of the design flow;

(c) Follow any applicable DS&G or proprietary product design manual for all OSS components included in the pump chamber; and

(d) Comply with chapter 246-272C WAC.

This section identifies “pump basin” to mean a water-tight receptacle that contains a pump to convey sewage from a limited use area that is separate from the main wastewater sewer pipe leaving a structure, to the main treatment component of an OSS; typically, much smaller than a pump chamber and separate from the main sewer pipe due to elevation restrictions. Pump basins are intended for limited, specialized uses, and not intended as a replacement or substitute for a pump chamber. Pump basins must be in compliance with chapter 246-272C WAC.

WAC 246-272A-0234 

Highlights: Changes to Loading Rates

In accordance with WAC 246-272A-0234, modifications were made to Table VIII (Hydraulic Loading Rates), which includes the creation of a new optional Column B (Loading Rate for Residential Effluent Meeting Treatment Level C & BL3 or Higher Effluent Quality Using Pressure Distribution gal./sq. ft./day). 

This allows higher loading rates (smaller drainfields) for effluent treated to a higher treatment level.

WAC 246-272A-0238 

Highlights: Observation and Sampling Ports

• Requires each SSAS lateral to include at least one observation port
  • Includes gravity systems
  • Allows for sampling & monitoring
  • SSD excluded
• Disinfection units must include an easy access, freefall sampling port

Questions? Contact us!

Email: SHD-EHQ@snoco.org

Call: (425) 339-5250