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King County Post-Construction Soil Standard

Soil Standard Video View the Natural Networks show about King County‘s Post–construction Soil Standard. Choose your preferred format: Windows Media (download media player) Real Media (download media player)

The Natural Networks video is presented here in Windows Media variable speed format (free download). A Real Media version (free download) is also available.

 

This content will be made available in alternate formats for people with disabilities upon request.

King County's clearing and grading regulations include a post-construction soil standard for site development activities in unincorporated King County. Effective as of January 1, 2005, the soil standard is meant to preserve and restore healthy soils to better manage stormwater and reduce stormwater runoff and its negative effects. These regulations help prevent costly environmental and landscape problems by requiring permit holders to preserve topsoil, restore soils by adding compost after construction, or implement other measures to maintain the soil's moisture holding capacity.

Regulatory Requirements

Except for areas that will be covered by impervious surface or have been incorporated into a stormwater facility, areas that have been cleared and graded must have the soil moisture holding capacity restored to that of the original undisturbed soil native to the site to the maximum extent practicable.

Soil amendment is to take place between May 1 and October 1. Replaced topsoil shall be a minimum of eight inches thick and have an organic matter content of between 8 and 13 percent dry weight and a pH suitable for the proposed landscape plants.

It is recommended that compacted subsoils be tilled or plowed before placing amendments or topsoil and that planting beds be mulched with two inches of forest duff, ground bark, wood chips or other organic material after planting.

Surface mine operations are exempt from these requirements.

Soil Treatment Options

There are four soil treatment options permit holders can use to meet the soil standard:

• Option 1 – Leave native soil undisturbed, and protect from compaction during construction
• Option 2 – Amend existing soil in place
• Option 3 – Import topsoil mix with 8–13% soil organic matter content
• Option 4a – Native Soil: Stockpile site duff and topsoil, and reapply after grading and construction
• Option 4b – Disturbed Soil: Stockpile site soil, reapply, and amend in place.

A pre-approved amendment rate of 2.5 inches of compost or a custom amendment rate can be used for the options calling for soil amendment.

Learn more about the King County soil standard in the booklet, Achieving the Post-construction Soil Standard (PDF, 380 K). The booklet includes links to additional resources including the Online Compost and Topsoil calculator, which should be used in conjunction with the booklet. Other resources include:

• Soils for Salmon
• Composting and Soils – King County Solid Waste Division
• Natural Yard Care – King County Solid Waste Division
• Yard Talk episode two "It’s All About Dirt" – King County Water and Land Resources Division

For questions about the soil standard or how to implement it, contact:

Randy Sandin
Department of Development and Environmental Services
Land Use Services Division
Telephone: 206-296-6778 | Fax: 206-296-7055
TTY Relay: 711

Richelle Rose, Site Development Specialist
Department of Development and Environmental Services
Land Use Services Division
Telephone: 206-296-6608 | Fax: 206-296-7055
TTY Relay: 711

Kris Beatty, Project Manager
King County Solid Waste Division
Telephone: 206-296-3740 | Fax: 206-296-4475
TTY Relay: 711

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