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Laura Seitz, Deseret News
James Holland, hydrologist/geologist with the Kanab Field Office of the United States Bureau of Land Management, examines an oil-covered rock with the Forest Service's Joe Harris and BLM's Sarah Schlanger in Little Valley Wash in the Upper Valley region of Grand Staircase-Escalante National Monument on Friday, April 4, 2014. There is oily residue on plants and rocks, tar balls and intermittent exposures of asphalt-like patches along a 3- to 4-mile stretch of the wash.

ESCALANTE, Garfield County — Remnants from at least one large oil spill found by hikers on March 23 in Grand Staircase-Escalante National Monument has officials wondering how and when the damage occurred.

As many as 4 miles in the Little Valley Wash now contain the aftermath of the spill, with about 1.5 miles of 6-inch thick oil flows contained in the mostly dry stream bed. Bureau of Land Management officials who manage the monument say it's likely the leak happened decades ago.

BLM officials hypothesize that the spill became encased in sediment deposits over time, making it difficult or impossible to see in most areas. Last September, intense floods washed down the drainage, possibly unburying the oil deposit and carrying parts of it downstream for 2.5 miles.

Boulders and tree trunks in the drainage now demonstrate the depth of the initial oil flows, with steady black lines as many as 2 feet above the stream bed. Black splotches are found in other areas, with vegetation collecting the oil as it flowed along with the flood waters.

Long stretches of oil patches not mixed with sediment have liquified in regions exposed to the sun.

"It's not what we want to see here," associate monument manager Sarah Schlanger said during an examination of the area Friday.

Aerial photos of the area were taken last June and didn't reveal any evidence of the spill, according to BLM geologist and hydrologist James Holland.

"It's pretty plain that it was buried," Holland said. "With the (color) contrast with the sand, we should have been able to see it from the aerial photo. When the flood came crashing down through here, things changed."

Citation Oil and Gas Corp. purchased the oil extraction lease for the area from Tenneco in 1987, following the estimated time frame of the spill. The 1996 monument designation allowed existing leases to continue but has since prohibited new leases from being signed.

Hikers who discovered the spill also found an exposed pipeline in the same area. Citation had made recent repairs on the pipe for a "pinhole" leak, which reportedly lost less than 10 barrels of oil and 400 barrels of saline water, BLM spokesman Larry Crutchfield said. It remains unclear how, if at all, that leak and others have contributed to current conditions in Little Valley Wash.

Mark Bing, central region manager for Citation, was present during Friday's examination.

"We're here to help wherever we can," Bing said.

Schlanger said she was unsure if Tenneco will become involved.

While it's likely the larger spill occurred under regulatory conditions different from today, policies have always been in place for leaseholders to inform the BLM of leaks at certain threshold amounts. As of recently, the BLM now requires leaseholders in the area to report spills of any size, Schlanger said.

BLM wildlife biologist Terry Tolbert said the harm done to plants and wildlife is difficult to determine.

"Some of the little shrubs that have been covered up are still flexible, still alive," Tolbert said. "When the shrubs come out of dormancy, we'll be able to tell better" how they have been affected.

Water samples in the oil-ridden drainage were taken to test for total dissolved solids and hydrocarbons, which will indicate how invertebrates and larger wildlife may be affected by altered water quality. Soil samples were also taken.

Until more can be learned about how and when the spill occurred, BLM officials are still unsure if removing the oil deposit would be beneficial for the ecosystem.

"There's a lot of things to weigh," Holland said. "You weigh what it would take to get equipment in here, how much damage it would do, whether it would be worth it."

Managers will also look at ways to prevent the deposit from spreading farther down the drainage.

"The good thing is it's not moving right now," Schlanger said.

Email: mjacobsen@deseretnews.com