Walt Baker, director of the Utah Division of Water Quality, said Wednesday that samples from the discharge, which created a significant amount of foam on the river and what observers described as a "bad odor," were being analyzed, with results expected Thursday morning.
Sand Wash, located about 40 miles south of Vernal, is the primary put-in area for Green River rafters to access Desolation Canyon, which lies farther to the south.
Initial tests, according to Michael Zucker, a response and remediation specialist with the Department of Environmental Quality, indicated the presence of montmorillonite clay minerals and aluminum chloride.
"This could be from natural runoff of clay formations and alkali. It could also be from drilling mud used in oil production," he said.
In other words, the discharge could be from an unreported dump, or some kind of release from oil and gas drilling operations located in the general vicinity of Sand Wash - or even farther upstream.
The foamy conditions could also be the result of an unusually early and high spring runoff. Green River flows at the U.S. Geological Survey's Jensen monitoring station were running 85 percent above normal this week.
Baker declined to speculate on the cause of the spill until the test results are in. But David Jackson, a Colorado-based whitewater guide who has extensive experience on the Green River, says he doubts the conditions currently seen on the river have a natural explanation.
Initial observations of foam and odor on the river were made on March 9. The initial incident report filed by the state says the foamy substance covered "100 percent" of the river channel by this past weekend.
"If this were a natural phenomenon, it would be seen every year," Jackson said.
"I can say that I have never seen the river covered in foam like described here. Neither have I ever heard anyone else describe the river similarly covered."
Baker said said state water analysts are currently combing the river from Sand Wash down to the city of Green River taking additional samples.
Jerry Kenczka, assistant manager for the BLM's Vernal Field Office, said agency officials were dispatched to the area Monday, and initial foam and water samples were taken. It is possible, he said, that the release may have occurred above Sand Wash.
"One of the guys who went down there yesterday saw some foam farther upstream, perhaps from the Ouray crossing or the Jensen crossing," he said. "It could have come from upstream. We just don't know right now."
But Kenczka said observers sent to the scene did not find any immediate impacts to fish and wildlife.
"Nobody has seen any dead fish or dead animals," he said.
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