A Houston-based pipeline company continued cleanup Tuesday at the site of a nearly 19,000 gallon oil spill in northwest Oklahoma that threatened a local water supply over the weekend.

Crews from Plains All American Pipeline were at the site in rural Loyal, about 60 miles (97 kilometers) northwest of Oklahoma City. The 450-barrel leak was reported Friday, but it's unclear when it started.

Oklahoma Corporation Commission spokesman Matt Skinner said roughly 70 acres of farmland are affected and that the spill reached a small creek at one point. But he says the leak was contained before it flowed into a second creek that flows into the Cimarron River about 16 miles (26 kilometers) away.

The state's Department of Environmental Quality also sent a specialist to the site last week, who confirmed there was no contamination in the second creek, agency spokeswoman Erin Hatfield said. A regional spokesman for the EPA didn't return a message seeking comment.

A statement issued by the company Tuesday said the oil was contained to farmland and part of an unpaved county road and stated that it continues to investigate the cause of the leak. Skinner said officials believe corrosion caused a hole in the line.

"Our current priorities are to ensure the safety of all involved and limit the environmental impact of the release," the company said in the statement.

Severe thunderstorms are possible in the area throughout the week, but Skinner said booms are already in place to hold back any potentially heavy rainfall.

The corporation commission and the EPA will test the water in the nearby creek for its salt content — saltwater is found in barrels of crude — and must ensure the site is remediated before they sign off on the cleanup, Skinner said.

"They have to bring the site back to beneficial use, which in this case is farmland, and it's farmland that's growing a crop," he said.

The spill happened on wheat farmer and cattle rancher Steve Pope's land, and he and his wife are now trying to survey the damage by collecting oily water and photographing the fields.

"Luckily, we hadn't put (cattle) out here yet. We were fixing to turn cattle out on this grass," the 58-year-old Pope told KFOR-TV.

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Associated Press reporter Ken Miller contributed to this report from Oklahoma City.