Federal agencies have so far not decided whether to undertake an assessment of the ecological harm caused by ExxonMobil's pipeline break, which spewed a tarry oil slick into yards, streets and creeks in a central Arkansas town.

For now, they're leaving it to state agencies to decide whether and how to quantify and counteract the environmental damage.

The rupture in the Pegasus pipeline on March 29 dumped up to an estimated 294,000 gallons of Canadian heavy crude in Mayflower, Ark.—including in a cove that flows into Lake Conway, a major fishing lake. If that estimate turns out to be correct, the Arkansas spill would be one-third the size of a 2010 Michigan pipeline spill, the worst accident of its kind in U.S. history.

Experts say that after oil spills, hydrocarbons and toxins leech into the soil and sediment and travel up the food chain as fish and animals eat contaminated species. The oil can also kill crucial erosion-protecting vegetation.

It can take years and millions of dollars to restore the environment.

"Ecosystems provide the most basic forms of sustenance for us: our food supply, our drinking water, protection against floods and natural disasters," said John Kostyack, vice president for wildlife conservation at the National Wildlife Federation. "When you start breaking down those ecosystems, you start losing that."

The Arkansas Department of Environmental Quality and the Arkansas Game and Fish Commission are in charge of surveying the damage to oil-hit wildlife, wetlands, soil and groundwater along the mile-long spill site.

The two agencies told InsideClimate News they have little experience in handling a major oil spill like the one in Mayflower.

When major oil or chemical accidents hit, federal and state agencies have the option to do a damage assessment together through a legal process called the Natural Resource Damage Assessment and Restoration Program, or NRDA (pronounced nerd-ah). Through a NRDA, agencies determine the cost of ecological destruction from spills and develop a plan to restore the ecosystem that must be paid for by the responsible parties. States cannot do a NRDA on their own.

Federal agencies that can conduct a NRDA are the National Oceanic and Atmospheric Administration (NOAA), the five Interior department bureaus—including the Fish and Wildlife Service—plus the U.S. Departments of Agriculture, Energy and Defense, as well as federal Indian tribes.

NOAA, which manages marine ecosystems, said it has no plans to take a NRDA approach in Mayflower. "We don't think [the oil] is impacting NOAA trust resources," said spokeswoman Keeley Belva.

The Fish and Wildlife Service, the only federal agency directly involved in the Mayflower spill that does NRDA work, said it hasn't made a decision yet.

"The state's got the lead," said Jim Boggs, a field supervisor at the service's Arkansas office.

What the State Is Doing

The state Game and Fish Commission plans to hire a private consultant in the next few weeks to quantity the damage to wildlife and Lake Conway and create a plan to restore the ecosystem. The work to restore the environment is expected to be paid for by Exxon, according to commission spokesman Keith Stephens. He said neither Exxon nor federal agencies would have a say in the decision on the consultant.

The Department of Environmental Quality will do its own damage assessment. Ryan Benefield, the agency's deputy director, said about 10 engineers, geologists and water scientists will soon begin "extensive sampling" of sediment, soil, groundwater and surface water in areas where much of the oil has been cleaned up.

Time is not on their side, however.

Collecting data on oil-damaged areas is critical in the first days after a spill because the oil is still visible, said Jeffrey Short, a scientist at Oceana, a conservation organization.



"You lose information at an exponential rate after an incident occurs" as oil settles and is absorbed in the surrounding ecosystem, said Short, who worked for 31 years as a NOAA research chemist. For much of that time he was involved in damage assessment for the Exxon Valdez oil spill.

Not long after the oil spills, "there's a blackout period where things are happening in the environment and you can't see them," he said.

The Challenge of Dilbit



Short said the problem is especially worrisome for diluted bitumen, or dilbit, the type of oil that spilled from Exxon's pipeline in Arkansas. The heavy bitumen crude is diluted with chemicals and light hydrocarbons so that it's thin enough to flow through pipelines. When it hits the water, and the diluents evaporate, the bitumen sinks to the bottom and accumulates in the sediment.



"Once it sinks, how do you tell where it went ... unless you have a means of evaluating it in the field?" Short said.

The crude that was flowing through the Pegasus pipeline is called Wabasca Heavy. According to industry, Wabasca contains at least 10 types of hazardous constituents, including benzene, a known human carcinogen, as well as polyaromatic hydrocarbons that can disrupt the hormone systems in animals and humans.

After the oil is cleaned up, "there will be these residual chemicals in the environment ... and nobody really knows [for] how long," said Ben Cash, the biology department chair at the University of Central Arkansas who is leading snake rescue efforts in Mayflower.



"It's a little more difficult to put a value" on those types of impacts, Cash said.



Three years ago it was dilbit that spilled out of Enbridge's pipeline and into Michigan's Kalamazoo River. Sunken oil is still being removed from the bottom of the river today. Dilbit is also the same type of oil that would flow through the proposed Keystone XL pipeline.



Stephanie Millsap, a contaminant specialist with the Fish and Wildlife Service in Michigan, said the service put her in charge of NRDA activities one day after Enbridge reported the million-gallon spill. "We realized that given the magnitude of the volume of the oil spill ... there was a definite potential for NRDA issues," she said.



Millsap said the agencies involved in the NRDA process there are studying the bitumen that has settled with the river bottom sediment. She said researchers are examining the toxicity of the crude to the ecosystem; how harmful it is to fish and invertebrate; and the impacts of dredging oil and soil from the Kalamazoo River.



"I don't think any one of us had ever dealt with sinking oil before," she said.

Benefield of the Arkansas Department of Environmental Quality said his agency is taking water samples twice a week "at elevation and at depth" in the swampy cove and in the main body of Lake Conway to see if any oil has traveled or sunk, in addition to Exxon's daily samples. The 6,700-acre fishing area, which is stocked with bass, catfish and crappie, lies nine-tenths of a mile from the Mayflower spill site.



"So far, we've seen non-detect or low levels [of oil] that would more likely be associated with motor boat activity," he said.



So Far, Wildlife the Priority

Removing the oil and rescuing wildlife has been the top priority of federal, state and Exxon officials.

Contractors hired by Exxon have been leading most of the rescue and recovery operations. Wildlife specialists have collected more than 160 animals and transferred them to a rehabilitation center. About 100 of them have been released back into the wild, according to Exxon.

More than 200 animals have died as a result of the spill, more than half of which were euthanized snakes. Ducks, turtles, beavers, lizards and nutria have also been harmed, mainly in the streams and swamp areas that lead into the cove of Lake Conway.

The Game and Fish Commission said it is is gathering the data from Exxon and the federal Fish and Wildlife Service. It will hand the information to the private consultant to help calcuate the wildlife damage and devise a rehabilitation plan.

The agency said that while it believes the spill hasn't harmed the fish in the main body of Lake Conway, it is concerned about reputational damage to the treasured lake.

"You're always going to have folks who are concerned about health reasons, and they might not ever come back to the lake," said Chris Racey, assistant chief of fisheries management at the commission. "Long-term, we want to carefully consider any impacts to recreation. That's a difficult thing to measure. That may be a challenge down the road for us."

Kostyack of the National Wildlife Federation said he believes a NRDA process will become inevitable in Mayflower, simply because it is a major oil spill and the ecosystem damage is extensive.

The NRDA process for oil spills was established as part of the federal Oil Pollution Act of 1990. Congress passed the law one year after the 11-million gallon Exxon Valdez spill to give government agencies more authority and funding to respond to major oil accidents and to enforce rehabilitation work. More than 80 oil-related NRDA processes have been launched.

"Any time you have natural resources impacted like [in Mayflower], you're going to have an NRDA situation," Kostyack said. "Whenever you have an oil spill, the obligation falls upon the oil company to clean it up, as well as to restore it back to the conditions that existed [before] the spill. So you need agencies to supervise that process."