On his way to Lake Tahoe earlier this month, Greg Service pulled into an eastbound rest stop along Interstate 80 about 40 miles west of Truckee.

The Santa Rosa resident tossed a ball to his dog at the Gold Run Safety Area, but was soon in for a nasty surprise.

"He came out of the bushes covered with slime," Service said. "It smelled like sewage."

Behind the bushes, Service said he saw a stream covered with a foamy, orange, foul-smelling substance.

"It was about 5 feet across in some places and almost 3 feet deep in some places," he said. "It was full of what appeared to be sewage."

He cleaned up his dog – "fortunately, I had the truck, so he could ride in back," he said – and continued on.

But he was so concerned about the incident, he took photos of the stream and called the state Department of Transportation. Dissatisfied with the agency's response, he checked the westbound Gold Run rest stop on his way home, where he found more of the substance, and later called The Bee.

"It was right after the Fourth of July holiday," Service said, adding that he suspected that the rest stop's sewage system had backed up or they flushed it "right into an open trench about 100 feet away."

"It starts right below the westbound rest stop's restroom facility, in a marsh area, then runs into a culvert and under the parking lot for trucks, then in an open ditch for about 200 feet along I-80, then under I-80, where it ends up in a creek near the eastbound rest stop," he said.

Service said he drives to Tahoe often and stopped by the next weekend in both directions again and "it was just as ugly."

Rochelle Jenkins, a Sierra-area spokeswoman for Caltrans, said the substance is not sewage.

At first, she said it was likely arsenic. "Our haz mat crews say it's arsenic from past gold-mining activities in the area," she said. "They see it a lot in summer.

It's naturally occurring in the ground, but dredging stirred it up and caused a higher concentration in the creeks as the water carried it down to them, she said.

"Minerals can have a sulfur smell," Jenkins added. "We're almost positive (it's arsenic), but are testing to be sure."

The stream Service's dog got into is a "naturally occurring creek that comes out of a spring," Jenkins said. "It's partly fenced, so no vehicle dumped anything into it. You'd have to walk to it."

And, she added, "dogs off-leash are a no-no," as Placer County has a strict leash law.

Test results that came back July 20 showed the foamy, orange, foul-smelling water was indeed caused by a mineral – but primarily iron, Jenkins said.

"Iron is naturally occurring in rocks in the area," she explained. "Dredging washed it into the creeks.

"In summer, combined with stagnant water and air, it can grow bacteria," Jenkins said. "That would account for the foaming, color and smell."

The tests were also positive for arsenic, she added, "but that was pretty low."

© Copyright The Sacramento Bee. All rights reserved.

• Read more articles by Barbara Barte Osborn

Order Reprint