King County's post-construction soil standard first in western Washington

Other Washington communities to adopt similar standards by 2009

Builders and developers with projects in unincorporated King County are now meeting a new post-construction soil standard—the first of its kind adopted in western Washington. The standard helps protect the environment from the negative effects of stormwater runoff.

King County’s post-construction soil standard, which has been a part of the construction-permitting process since 2005, requires a minimum of eight inches of soil containing 8-13 percent of the soil organic matter that provides food for worms and other soil life.

While King County’s requirements for proper soil management are some of the first of their kind in western Washington, they are certainly not the last. In fact, the Washington State Department of Ecology is requiring western Washington counties and cities with municipal stormwater permits to adopt similar soil standards by 2009.

“Like clean air and clean water, healthy soil is vital for a healthy environment,” said Theresa Jennings, acting director of the King County Department of Natural Resources and Parks. “Preserving soil or restoring it in disturbed areas such as construction sites is essential to managing stormwater runoff and preventing water pollution.”

“King County has developed tools to help developers meet this standard, such as a guidance booklet and online compost and topsoil calculator to help determine the amount of soil or compost that’s needed for a specific site,” said Stephanie Warden, director of King County’s Department of Development and Environmental Services. “We can also offer expert advice to help builders and developers meet soil-management requirements so that building permits won’t be delayed.”

King County has developed four different options that developers can use to meet the post-construction soil standard:

• Leaving native soil undisturbed and protected from compaction during construction;
• Amending existing soil in place;
• Importing topsoil with 8-13 percent soil organic matter content; or
• Stockpiling native site duff and topsoil, and reapplying after grading and construction.

“These soil management practices will improve stormwater management and create a foundation for healthy and beautiful landscapes, which can be a strong selling point to homebuyers,” Warden said.

Healthy soil not only allows vegetation to flourish, but protects the environment by absorbing excess rainwater and preventing flooding. Acting like a sponge, deep, rich soil releases water to plants between rainfalls. Water is filtered as it percolates through the soil, preserving water quality and protecting the people and wildlife that depend on it.