CURTISS, Wis. (AP) -- Crews have recovered thousands of gallons of crude oil that leaked in a farm field from an underground pipeline, officials said Wednesday. The Clark County accident happened only two weeks after an environmental group went to court trying o block plans for another, larger pipeline along the same route across Wisconsin.

"There is oil penetrated about an inch into the ground," said Dave Weitz, a spokesman for the Department of Natural Resources. "They are moving quite rapidly to clean that surface up."

The spill, discovered Tuesday, covered about one-half acre of the field, and the environmental damage is marginal, he said.

A 4-foot crack in the Enbridge Energy Co. pipeline caused the spill, but what caused the crack remains under investigation, said Denise Hamsher, spokeswoman for the Houston-based company.

She said in a telephone interview Wednesday evening that an estimated 52,500 gallons spilled.

"We have recovered the vast majority of the crude oil," Hamsher said. "We don't expect an environmental impact. No rivers or drinking water or the public were affected."

The spill occurred about five miles southwest of Curtiss in a pipeline that began carrying crude oil from Alberta, Canada, and elsewhere to refineries near Chicago in 1998, Hamsher said.

The damaged section was cut out and replaced, and the line reopened by Wednesday evening, she said. But she said it was being kept at reduced operating pressure, pending the investigation into the cause.

She said the 24-inch-diameter pipe normally carries about 300,000 barrels a day. It is one of two pipelines buried at least 3 feet underground at the site of the spill, Hamsher said.

The oil spewed into a drainage area of a farm field in northeast Clark County and then flowed about a half mile before a drop in pressure shut the pipeline down and recovery crews arrived, she said.

The drainage area helped prevent the oil from spreading over more of the field, Hamsher said.

Weitz said the ground's frozen state helped minimize damage, too.

"There is no surface water impacted. No wetlands. No flowing water," he said. "It is not an environmental disaster."

Hamsher said the last rupture of one of Enbridge Energy's major pipelines occurred four years ago. The company transports 1.5 million barrels of crude oil -- or 63 million gallons -- a day through its pipeline network in the Upper Midwest, she said.

Two weeks ago, Midwest Environmental Advocates in Madison sued the DNR to challenge its decision to allow Enbridge Energy to install a third crude oil pipeline, this one 42 inches in diameter, along the same right- of-way through Wisconsin.

The lawsuit, filed in Dane County Circuit Court, contends the DNR failed to adequately address the risk of pipeline corrosion and rupture and properly review the effect the construction would have on wetlands and riverways, said Brent Denzin, an attorney for Midwest Environmental Advocates.

"Tuesday's spill highlights the need to study the threat posed by additional Enbridge pipelines before we remove wetlands and grade riverbanks to construct them," Denzin said in a statement.

Preliminary construction work on the project has started, but the lawsuit seeks an injunction to halt the work, Denzin said.

The DNR has not yet responded to the lawsuit, so no court dates have been set, he said.

Hamsher said the company has received the necessary permits for the new pipeline and had worked with environmental agencies on the plans, which call for the line to be operational in the first quarter of 2008.

As for Tuesday's accident, "I think it showed that the system works," Hamsher said. "The leak detection system immediately detected the pressure drop and the pipeline was shut down."

There won't be any impact on waterways, and the company will work with the landowner on any damage to the land, she said.

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