Worrisome levels of crude oil persist in a cove of Lake Conway eight months after ExxonMobil's Pegasus pipeline ruptured in Mayflower. But state authorities charged with monitoring the cleanup say the lingering oil is more of a threat to the area's ecology than it is to human health.
Those same state officials also say that they are confident the main body of Lake Conway was spared direct damage from the Pegasus pipeline disaster on March 29. To confirm that conclusion, further water sampling of the main body of the lake will continue.
Authorities reached those conclusions after reviewing data released Oct. 11 by Arcadis, a contractor hired by Exxon to gather and analyze soil and underwater sediment samples from dozens of sites the spill affected. An independent expert consulted by the Arkansas Times and InsideClimate News reviewed the data from Arcadis and agreed with the broad conclusions drawn by the Arkansas Department of Environmental Quality (ADEQ), the Arkansas Game and Fish Commission and the Arkansas Department of Health.
Soon after the pipeline break spewed at least 210,000 gallons of a heavy type of Canadian crude called diluted bitumen (or dilbit) into a neighborhood, as well as adjacent wetlands and Lake Conway's Dawson Cove, tanker trucks vacuumed up over a million gallons of oil and contaminated water. In addition, crews scraped over 8,000 tons of crude-saturated plants, soil and debris from the land around the cove.
A remediation plan for contaminated sections of Dawson Cove will likely be designed early next year after Exxon makes a follow-up set of soil and sediment tests available. The cove is a nearly 12-acre section of Lake Conway that drains an 11,000-acre watershed. It is separated from the main body of lake by a man-made dike, built to carry traffic on Highway 89.
When news of the spill broke on March 29, city and county workers sprang into action to contain the oil, creating a makeshift dam to block Dawson Cove from the rest of the lake. Using gravel, dirt and plywood, they plugged the culverts under Highway 89 that allow water to flow from the cove to the lake. (The culverts are no longer blocked.) Soon afterwards, a response team deployed booms and weirs, floating structures that contain the spread of oil in water.
It appears they were successful: Six samples drawn from underwater sediment in Lake Conway just beyond Highway 89 show no evidence of major contamination. The culverts are roughly a mile from where oil poured into the Northwoods subdivision.
Several days after the spill, rainfall caused the water level in the cove to rise. Cleanup organizers were forced to pump water from the cove into the lake to prevent it from flooding a nearby neighborhood. Ryan Benefield, deputy director of ADEQ, said this was done only after determining that the oil had been successfully contained farther back in the cove.
"We had stopped the progression of oil far from that point and we were testing the water on either side of Highway 89," Benefield said. "We had repetitive, dozens of booms and surface-to-bottom weirs throughout the cove, and free oil didn't penetrate past the first couple of booms."
Still, he said, chemicals in the oil may have been carried into the main lake as water was pumped over Highway 89, adding that "water comes in the top of the cove and it goes out into the lake. So, water that had been in the cove when we had free oil, we were pumping into the main body of the lake. But we weren't seeing levels of concern from our testing." So it seems likely that some amount of the Pegasus oil did flow past Highway 89 and into the lake — the question is just how much.
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