On-site Sewage System Technical Correction Rulemaking

WAC 246-272A-0110, Table I, Category 2, On-site Sewage Systems

Affected and Interested Parties

Companies that manufacture proprietary treatment products and other interested parties.

What’s Happening?

The State Board of Health (Board) has rulemaking authority for on-site sewage systems with design flows less than 3,500 gallons per day. Chapter 246-272A WAC, On-Site Sewage Systems, sets standards for the siting, design, installation, use, care, and management of these small on-site sewage systems. At the March 2024 board meeting, the Board delegated rulemaking to the department under RCW 43.20.050(4).

The Department of Health (Department) is considering amending WAC 246-272A-0110, Table 1, Category 2, to add NSF/ANSI 40 testing for Category 2 products. On May 13, 2024 the Department filed a CR-101 Preproposal Statement of Inquiry (PDF) to initiate rulemaking.

WAC 246-272A-0110 states manufacturers of proprietary treatment products used in on-site sewage systems must test their products with the EPA and register their products with the department based on EPA test results before the product is allowed to be permitted or installed in Washington. This allows the Department to ensure that products used in on-site sewage systems can provide the appropriate level of treatment needed to protect public health and the environment such as drinking water sources and shellfish sites. Proprietary treatment products are required to be installed and operated as they were tested and registered to ensure they continue to perform as needed.


Category 2 products treat high-strength sewage from restaurants and other facilities that generate high levels of oil and grease. Prior to the recent rule revision, the rule required testing for Category 2 products under the EPA/NSF Protocol for the Verification of Wastewater Treatment Technologies/EPA Environmental Technology Verification (April 2001). This protocol tested for organic sewage strength (CBOD5), suspended solids (TSS), and oil and grease. EPA archived this testing protocol in 2013. During the recent rule revision, the EPA Method 1664, Revision B (February 2010) testing was adopted for Category 2 systems to treat oil and grease. This recommendation, however, neglected to assure that Category 2 products are also tested for organic sewage strength (CBOD5) and suspended solids (TSS). 

The Department will consider if Category 2 products should be tested by both EPA Method 1664, Revision B (February 2010) and NSF/ANSI 40 -Residential Wastewater Treatment Systems (versions dated between January 2009 and May 31, 2021). 

For more information about the recent rule revision on chapter 246-272A WAC, visit the On-site Sewage System Rule Revision webpage.

Get Involved and Stay Informed

Informal Public Comment Period Planned

The department will hold an informal comment period asking for your input on the draft rule. Subscribe to Wastewater Rules and Regulations Email Updates.

Rulemaking Timeline 

May 2024 – Start rulemaking

July 2024 – Informal comment period

August 2024 – Formal comment period

September - Public hearing

October 2024 – Rulemaking complete

Rulemaking Resources

Documents What's This Date Filed/Released
CR-101 Preproposal Statement of Inquiry (PDF) Announces intent of rulemaking. May 13, 2024

Rule Revision Contacts

Peter Beaton, Rule Coordinator

Jeremy Simmons, Wastewater Section Manager