By TOM LUTEY Of The Gazette Staff
Long after the Yellowstone River cleanup ends, there will likely be crude oil residue balled up on the river bottom and traces of the black bathtub ring now lining the banks, officials said last week.
When ExxonMobil’s Silvertip pipeline broke July 1 beneath the flood-swollen river, an estimated 1,200 barrels of crude were swept into the runoff. As cleanup continued last week, officials acknowledged only a fraction of the oil would be recovered. The rest would slowly break down over time, though no one would speculate how long the process would take.
“Generally, petroleum breaks down, attenuates is what we call it, but that doesn’t happen overnight, I’m not going to lie to you,” said Mary Ann Dunwell, of the state Department of Environmental Quality’s Remediation Division.
Landowners along the oil spill’s path were getting a feel for that long-term breakdown last week. Crude oil coating pasture and river grasses along the Yellowstone was becoming sticky and thick while lighter chemicals in the substance slowly evaporated in the sun.
People speak of crude oil as if it is a single substance, but that’s not the case, said Mike Trombetta, chief of the hazardous waste site cleanup bureau of the Montana DEQ.
“Petroleum is not one chemical. It’s a mixture of hundreds of chemicals and every crude is different,” Trombetta said. “All petroleum over time will naturally degrade. The lighter ends volatize off, evaporate in the air. Oil will degrade over time, depending on where it is.”
In the river, microbes will break the petroleum down when conditions are right, Trombetta said. In some cases the oil will bind with sediment and form tar balls, settling in deep, slow-moving channels. Cleanup crews will be collecting tar balls when possible, but others will be left behind.
ExxonMobil has an expert in the area working on issues such as how the petroleum might degrade. The company declined to make him available for comment last week.
On land, the petroleum should steadily degrade with the help of air and sun exposure, Trombetta said.
River land is often hay country, and the state Department of Agriculture has been getting inquiries about whether hay from the oil spill area is safe. Spokesman Ron Zellar said the department has been taking cues from other states such as Texas and Oklahoma where oil spills on crops are more common.
Ag officials have been advising farmers not to feed oil-contaminated hay to dairy cattle, but other livestock can eat the hay with no ill effect, Zellar said. If the hay is truly bad, cattle probably won’t eat it, Zellar said.
Hay is a murky area for the state ag officials, who regulate animal feed, but not hay.
The acceptability of the hay is something agreed upon by the buyer and seller in Montana. The message to hay customers is buyer beware.
Contact Tom Lutey at tlutey@billingsgazette.com or 657-1288.
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