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Compost enhances soil texture, increases the ability of the soil to absorb air and water, suppresses weed growth, prevents erosion, and reduces the need for water, fertilizers, and pesticides. It is beneficial for many uses, including agriculture, erosion control, stormwater management and land restoration.

In the King County region, municipal food and yard waste, manure, and biosolids are all used to make compost products. Compost made with King County’s Loop® biosolids is made by composting woody material with Loop—the nutrient-rich organic material made by cleaning and recycling human waste and food at our wastewater treatment plants.


Policy and Goals:

The use of compost is required by King County KCC Title 18.30 – Compost Procurement and Use and in accordance with Washington State RCW 42.19A. 150

  • Departments shall plan for the use of compost in any of the following categories that are applicable to the departments’ operations and project types:
    • Landscaping projects;
    • Construction and postconstruction soil amendments;
    • Applications to prevent erosion, filter stormwater runoff, promote vegetation growth, or improve the stability and longevity of roadways in accordance with K.C.C. Title 9; and
    • Low-impact development and green infrastructure to filter pollutants or keep water on-site, or both in accordance with K.C.C. Title 9.

Supporting policies:
As stated in King County's Sustainable Purchasing Executive Policy (CON 7-22-EP),

  • Use biosolids compost

As stated in Washington State RCW 43.19A.120 - Use of compost products in projects,

  • If compost products can be utilized in the project, the state agency or local government must use compost products

As outlined in King County’s 2020 Strategic Climate Action Plan,

  • Build markets for compost and other recycled content materials
  • Deliver regional organics plan
  • Explore compost benefits on King County–owned farms

As stated in the King County Code (KCC 28.86.090),

  • Biosolids-derived products should be used as a soil amendment in landscaping projects funded by King County

As stated in the King County Comprehensive Plan,

  • King County agencies shall use recycled organic products, such as compost, whenever feasible and promote the application of organic material to compensate for historic losses of organic content in soil caused by development, agricultural practices, and resource extraction.


  • compost‑amended topsoil
  • biosolids-derived products


  • conventional soil with no compost additive

End of Life

  • compost yard waste, clean wood, mixed loads, and non-organic material with vendor

An EPA checkmark indicates a certification or standard is recommended by the U.S. Environmental Protection Agency (EPA).

Recommended Material


A product of King Country, Loop biosolids is made from cleaning and recycling all the water that comes from homes and businesses, producing a nutrient-rich soil builder.


Technical Specification Language

King County's CompostWise Program

Washington Organic Recycling Council

U.S. Composting Council

Washington State Department of Ecology: Composting Guide

EPA: Reducing the Impact of Wasted Food by Feeding the Soil and Composting

Contact Us

Phone: 206-263-9400

TTY Relay: 711

Fax: 206-296-7676