Biosolids laws & rules

We regulate biosolids under the state biosolids rule, although we partner with local health districts on a variety of biosolids management issues. The following information provides an overview of key sections of the biosolids rule, but it is not a complete description of regulatory requirements.

Biosolids rule - Chapter 173-308 WAC

The biosolids rule was drafted in 1998 and updated in 2007. It sets the requirements for permitting and plans that anyone who produces or uses biosolids must follow. Our state rule incorporates all the legal requirements in the federal rule, but goes further to require specific plans for land application and additional public notice requirements.

The biosolids rule establishes:

  • Standards and frequency for analysis of biosolids.
  • Agronomic rate requirement and beneficial use.
  • Rules for septage.
  • Permitting requirements and fees.
  • Access restrictions to land application areas.

Standards and frequency for biosolids analysis

Biosolids are sampled and analyzed for both pathogens and pollutants. There are four sections that deal with biosolids analysis:

  • Section 140 lists the required sampling and analytical methods for pollutants. These methods were scientifically established by the Environmental Protection Agency (EPA) as the appropriate method for obtaining accurate and consistent results.
  • Section 150 establishes the minimum frequencies of sample analysis for those who make biosolids. It’s important to note that these are minimums. We can, and often do, require more frequent sampling.
  • Section 160 lists both the pollutants and their concentration limits established through the EPA risk assessment process. These limits have been reviewed and confirmed as protective of human health and the environment by the National Academy of Sciences.
  • Section 170 describes the procedures for establishing pathogen reduction in biosolids production. This section describes pathogen reduction processes and sampling methods. Pathogen reduction can be accomplished when treatment plants use specific processes of time and temperature. They can also be met by sampling and analyzing for pathogen surrogates like fecal coliform or salmonella.

Agronomic rate requirement and beneficial use

Washington law requires biosolids be put to a beneficial use. This means using biosolids for the purposes of improving soil quality and growing crops. Spreading biosolids on the landscape without harvesting crops is not allowed.

  • Section 190 requires that biosolids applied to land must be at approved agronomic rates. This means that we must review proposed rates in advance of land application and provide an approval. Any approved rate must be based on the needs of a crop to be grown. The application rate must be “agronomic," meaning that the nitrogen in the biosolids must match the crop needs for that growing season.

Septage rules

  • Section 270 regulates septage. Septage is liquid and solids removed from septic tanks that hold primarily domestic sewage. This section of the rule describes procedures for pathogen reduction, site management and access restrictions, and application rates.


  • Section 310 sets permitting requirements under the biosolids rule.
  • See Permitting & Forms if you:
    • Already have permit coverage, but have questions or need forms / templates.
    • Want to apply for permit coverage under the biosolids rule.

Contact your regional Ecology biosolids coordinator, listed below, to inquire about new permit applications.

Notes on reading a state rule

Trying to make sense of a technical rule can be confusing. The biosolids rule has 36 sections and five appendices. Each section is numbered starting with 173-308 and then adding another 3-digit number, such as 173-308-310. Each section is also named, so 173-308-310 is the section on permitting. If you’re interested in what’s required to get permit coverage, you would look in this section. The table of contents lists the different section numbers and names. The appendices provide specific lists of what’s needed for submitting a permit application (Appendix 1), and what’s needed for land application plans (Appendices 3 and 4).

The difference between a law and a rule

  • State legislatures and national congress pass laws. An agency is often named in the law to develop and implement a rule. For biosolids, the law (Chapter 70A.226 RCW) instructed Ecology to develop and implement the rule (Chapter 173-308 WAC).

Compliance with federal biosolids regulations

The requirements of the federal rule are included in Washington's biosolids rule. Compliance with Washington permit requirements ensures compliance with the federal rule.

Federal reporting requirement for major treatment works

  • Major treatment works (those serving 10,000 customers or treating 1 million gallons per day design flow) must also file an electronic annual report with EPA. This is in addition to any requirements under state permit coverage.