Who makes Loop?

King County

King County Wastewater Treatment Division recovers and recycles beneficial resources from the wastewater treatment process, namely biosolids, reclaimed water and biogas. Biosolids produced by King County are called Loop. Loop is a safe and effective soil amendment that grows healthy and lush crops, forests, and gardens.

Visit King County for more information or to schedule a tour of a treatment plant.

Who turns their dirt around with Loop?

Boulder Park Inc.

Thanks to Boulder Park, Inc., many farmers and landowners have already reaped the benefits of Loop. Boulder Park is a farmer-owned company managing the distribution and use of Loop in Douglas County. Since 1991, farmers who’ve amended their soil with Loop have increased crop yields, decreased fertilizer costs, reduced erosion, stored carbon, and helped replenish the soil for thousands of acres of dryland grain crops.

Visit Boulder Park for more information.

Natural Selection Farms, Inc.

Natural Selection Farms, Inc. is a third generation family farming operation on the southern side of Snipes Mountain in Yakima County, WA. They believe holistic farm management practices should be used to promote crop growth and maintain harmony with nature. Natural Selection Farms has been committed to returning carbon and nutrients in biosolids to soils since 1980. Their use of Loop has reduced the use of synthetic fertilizers and pesticides on thousands of acres of canola, hops, alfalfa, wheat, orchards and managed rangeland.

Visit Natural Selections Farm for more information.

Hancock Forest Management

Hancock’s Snoqualmie Forest has been fertilized with Loop since 1987. Every year, Loop supplies about 1,000 acres of timberlands with nitrogen and other essential nutrients to help trees grow. Loop substitutes for commercial fertilizers while enhancing soils and wildlife habitat. Learn more.

Washington State Department of Natural Resources (DNR)

Loop is used to improve soils and fertilize trees in state forests in King County, primarily in Marckworth Forest near Duvall. King County partnered with DNR in 1995 as part of the Mountains to Sound Greenway biosolids forestry program. Loop helps store carbon in wood and forest soils. Learn more. 

Alleycat Acres

Alleycat Acres is a Seattle-based urban farming collective that converts vacant lots into community-run farms. By farming the cityscape Alleycat Acres is addressing a number of issues facing our communities. Members of the collective agree that it makes sense to use GroCo compost made with Loop to condition and fertilize city dirt into fertile soil. Not only does GroCo help them grow lots of nutritious fruits and vegetables, Alleycat Acres is doing their part to close the nutrient loop.

Visit Alleycat Acres for more information.

Seattle University

As part of the Sustainable Urban Agriculture Program, Seattle University manages a demonstration garden at the South Treatment Plant in Renton. They have also transformed an unused area of the treatment plant’s grounds into a teaching farm. These projects showcase the benefits gained with use of GroCo compost made with Loop in sustainable farming. The program educates students and citizens on growing food locally. They have partnered with local agencies to contribute nutritious produce to neighboring communities.

Visit Seattle University for more information.

Who can help you turn your dirt around?

GroCo, Inc.

GroCo, Inc. has been recycling carbon and nutrients by composting Loop with sawdust since 1976. GroCo compost made with Loop is composted for over a year resulting in a mature, clean, weed- and pathogen-free soil amendment that looks and smells earthy, much like a forest floor. GroCo compost is ideal for use in residential and commercial landscaping, home vegetable gardens, and soil restoration.

Visit Sawdust Supply, Inc. for more information.

Who are friends of Loop?

Northwest Biosolids 

Northwest Biosolids is a cooperative of public wastewater agencies, sewer districts, and private companies in Washington, Oregon, Idaho, Alaska, and British Columbia. Northwest Biosolids’ mission is to advance environmental sustainability through the beneficial use of biosolids. With the support of its members, Northwest Biosolids provides continuing education and networking opportunities, produces publications, reviews biosolids regulations and funds university involvement and research.

Visit Northwest Biosolids for more information.

Mountains to Sound Greenway Trust

The Mountains to Sound Greenway connects natural areas, trails, working farms and forests, historic towns and communities, wildlife habitat and recreation opportunities from Seattle across the Cascade Mountains to Central Washington. The Mountains to Sound Greenway Trust facilitated an agreement between King County and private and public forestland owners to use Loop to fertilize and preserve Greenway forests, as well as restore degraded natural lands. The Trust provides outdoor science education – featuring Loop – for forest field study trips to students.

Visit Mountain to Sound Greenway Trust for more information.


Founded in 1999, IslandWood is a nationally recognized outdoor education center connecting thousands of children and adults every year to the natural world in communities throughout the Puget Sound region. IslandWood’s mission is to provide exceptional learning experiences and to inspire lifelong environmental and community stewardship. The partnership between King County’s Brightwater Center and IslandWood is leading the way to new and enhanced educational programs for area students, teachers, and community members. The partnership enables the expansion of educational programs currently offered at the Brightwater Center to students in the third through eighth grades, including teacher trainings, adult workshops, family programs, and summer camps.

Visit Islandwood for more information.

Northwest Biocarbon Initiative (NBI)

The Northwest Biocarbon Initiative seeks to make the Northwest a living laboratory for biocarbon solutions, promoting the use of natural systems to mitigate climate-destabilizing pollution. From forestry to stormwater management, composting to ecosystem restoration, biocarbon innovators like Loop are finding new ways to cultivate healthy soils, plants, and communities while reducing our dependence on fossil fuels. NBI works to build momentum for these approaches by showcasing successes, raising support from elected leaders and the public, and developing sustainable business models for biocarbon.

Visit The Northwest Biocarbon Initiative for more information.