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Soil Restoration at Preston Mill Park

By December 15, 2022July 26th, 2023No Comments

Cross-posted from

Loop® trucks delivering fertilizer replacement to amend soil at Preston Mill Historical Park

World Soil Day takes place on December 5 each year and serves as an opportunity to focus attention on the critical importance of healthy soil and sustainable management of soil resources. Soil is a critical piece of our natural systems and contributes to producing sufficient, safe, and more nourishing food for healthier plants, animals, and people. Soil also helps counteract biodiversity loss and climate change.

In 2016, King County Parks partnered with the county’s Wastewater Treatment Division Biosolids Program on a soil amendment project at Preston Mill Historical Park. As the former site of a working lumber mill for nearly 100 years, the soil at Preston Mill had been compacted and severely degraded over years of industrial neglect. Feedback gathered from the local community indicated interest in seeing the land redeveloped for recreational use.

Preston Mill Historical Park in 2016 before soil amendment

King County Wastewater Treatment Division Biosolids Program oversees agriculture and forestry projects and product development for Loop®, the nutrient-rich organic fertilizer alternative and a natural soil builder created from King County’s wastewater. The County produces approximately 120,000 wet tons of biosolids each year, most of which is used for agricultural crops in Central Washington or state forests in King County, like Marckworth Forest, a working forest near Duvall.

But the program wanted to conduct a successful demonstration in the western part of the state. The Biosolids Program transported trucks full of Loop to Preston Mill, where the biosolids were blown onto a large area of the property where nothing was growing. Grass was then seeded onto the lawn. Within months, the soil sprouted healthy bright green grass from land that had been previously unusable. To this day, the Preston Mill meadow remains a source of enjoyment and pride for area residents.

Grass meadow at Preston Mill Historical Park after soil amendment. Photo credit: Eli Brownell

More improvements to Preston Mill Historical Park are under development.

To learn more about how King County treats wastewater to create nutrient-rich biosolids that support healthy soil, check out The poop-Loop scoop: How King County recycles waste and water.