The source of oil sheen on the North Platte River that appeared last month between Casper and Evansville is still being sought. Keith Guille, for the Wyoming Department of Environmental Quality says, the DEQ, along with BP, are focusing on a wall that was installed about 10 years ago at the sight of the old Amoco refinery where the Three Crowns Golf Course is now located. That wall, described as very long and very deep, was installed and monitored to prevent contaminants from flowing into the river.

"For ten years that monitoring has worked and they have not seen any type of constituents reaching the river. Last year they started seeing small oil sheens and it was around the springtime."

Guille says by last August they were no longer finding evidence of  sheen, but come this April they returned.

"and it seemed like they were a little bit more frequent. At that point we thought it was important to notify of course the media and the public, but also Evansville and let them know, "This is what we're seeing".

Guille says BP has tested the water quality where the oil sheen was sighted and near the Evansville intake valve. No public health risk is believed to be present. High springtime water levels have also helped to move the sheen past the intake valves.

To date, he says, DEQ continues to work with BP to come up  with two action plans.

"One to investigate where these oil sheens are coming from and then after the investigation is done, and they determine what is the source, then go out and actually have a plan to remediate that issue."

He says, they want to determine, first, if the wall has been compromised.

While there remain some unknowns, Guille maintains that the oil sheens are very small and that water quality is not threatened.

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