KING

Eight to 10 percent of the dirt used to cover disturbed ground must be organic matter.

RENTON, Wash. - Before you build, you have to scrape away the dirt. That's how construction works.

In King County, post-construction rules require workers to leave the dirt cleaner than they found it.

"The soil will be rich, deep and able to sustain plant life," said Kris Beatty, of King County Solid Waste.

Just covering the yards of new housing developments with a thin layer of common dirt won't do.

Contractors have to put down eight inches of it - and they have to make it healthy.

"They'll bring compost in and bring enough of it to meet the required organic matter content," Beatty said.

Eight to 10 percent of the dirt used to cover disturbed ground must be organic matter. In other words – it has to be alive.

"We all know the importance of clean air, and water and the organisms in it, but soil is just as important," Beatty said. "In fact scientists say, in a single teaspoon of the stuff there are 4 billion organisms in there."

The organisms grow healthy lawns and gardens and help prevent damage to water quality.

Storm water runoff often whisks away nasty toxins that build up on the streets and sends them into storm drains. Much of it ends up dripping right into Puget Sound.

Construction crews work hard keep their dirt out of this nasty stream, but some of it usually gets through.

That's why King County leaders created some of the strictest solid requirements in the nation, and has possibly laid the groundwork for other agencies to follow.