A half-ton of river rock and a bucket full of starter plants are Adam DeCoste's way of showing the world how nature can help keep Interstate 5 motorists' oil out of wild salmon's drinking glass.

A half-ton of river rock and a bucket full of starter plants are Adam DeCoste's way of showing the world how nature can help keep Interstate 5 motorists' oil out of wild salmon's drinking glass.

The plants and rocks actually are tools DeCoste hopes will filter petroleum and other contaminants from runoff that now flows from I-5's viaduct into Bear Creek in downtown Medford.

After every gully-washer or the lightest of rains, the runoff collects contaminants as it drains directly into a sliver of Bear Creek that is home to wild chinook salmon, steelhead and even threatened coho salmon.

DeCoste has planted the sage, red-twig dogwood and choke cherry amid the rocks at the base of one of 34 downspouts running from the viaduct to the creek. It will demonstrate what environmental studies across the country have shown — native plants can filter contaminants.

"I see it as an incremental process," said DeCoste, a 24-year-old Medford man who is studying the viaduct's role in Bear Creek water quality as part of his pursuit of an environmental studies degree at Southern Oregon University.

"We can only be doing good any time we keep any pollution from flowing into Bear Creek," DeCoste said. "We want this to set a precedent, show an example that we can take to the powers-that-be and see if they want to do more of this."

The Oregon Department of Transportation certainly is interested in seeing runoff from the viaduct and other highways thinned of the inevitable oil, gas and other contaminants forever present on roadways.

But that has posed a problem on the viaduct, where runoff is funneled straight down in pipes that bend and eventually drain into the stream.

"We've tried other methods of absorbing that (runoff)," said Eryca McCartin, ODOT's project manager in Medford.

"What we find is they plug up within days from material coming off the surface."

Over time, ODOT workers systematically have cut many of the viaduct's downspouts just above the elbow, providing a perfect spot for oil-grabbing plants to cleanse the runoff before it hits the actual creek.

"That's what we try to do in most places — have it filter naturally," McCartin said.

The insidious sloughing of petroleum products straight into urban streams is a nationwide problem that has seen some solutions in larger municipalities, and those practices are slowly filtering into smaller communities, said Greg Stalpach, a project manager at the Rogue Valley Council of Governments involved with Bear Creek cleanup efforts.

"After a rain, you look into a street and you see oil everywhere," Stalpach said. "There are a lot of people who don't realize that what goes down storm drains goes straight into that creek."

DeCoste will follow up last week's planting Tuesday by helping run a demonstration drill with city engineers, firefighters and state transportation officials simulating a large-scale traffic accident gas spill there.

"Our focus is to try to figure out what our response is and what the protocols are, let alone how to do it," DeCoste said.

The plan is to practice stringing a hot-dog-like set of booms across the creek at Hawthorne Park to curb the flow of gas downstream.

"It's just like firefighters," said Jim Hutchins, a Medford naturalist and Bear Creek caretaker who has helped DeCoste this past year on the viaduct efforts. "If you don't practice, you're not going to be ready."

McCartin said ODOT has procedures in place to curtail road spills at the accident scene, regardless of whether that be on the viaduct or elsewhere.

"We've really focused on keeping the materials from leaving the surface," McCartin said. "It's always good to be prepared."

Also, ODOT does not plan on stopping any I-5 traffic on the viaduct during Tuesday's spill drill, McCartin said.

Reach reporter Mark Freeman at 776-4470, or e-mail mfreeman@mailtribune.com.