(CNN) -- Frozen winter conditions are helping slow the spread of a pipeline leak on Alaska's North Slope, an environmental official said.





An estimated 46,000 gallons of a water-and-oil mixture was spilled before the source of the leak -- a pipe rupture -- was identified Monday, according to the Alaska Department of Environmental Conservation (ADEC).





The ruptured 18-inch line, owned by oil company BP and which usually carries a mixture of 75 percent water and 25 percent oil, has been repaired.





The frozen conditions make the spill less mobile, Matthew Carr of the U.S. Environmental Protection Agency said late Wednesday.





"Any spill is regrettable," Steve Reinhart, a BP spokesman in Anchorage, told CNN. "We will clean this up thoroughly and our investigation will find out what happened so that we can ensure this doesn't happen again."





Reinhart said the spill, which occurred entirely on land, has had no impact on production or wildlife in the area, and is contained to a small fraction of the much larger Prudhoe Bay oil field.





"It is not a pool of oil spreading out across the ground," Reinhart said, comparing its consistency to that of a snow cone. "It's a partially solidified mass that's piled up in one area, and as we speak, truckloads of this material is being moved off this site and to a collection depot."





According to officials, the rupture was approximately 24 inches lengthwise, running along the bottom of the pipeline.





In an incident report on its Web site Wednesday, ADEC described the rupture as being "consistent with an overpressure scenario," caused by ice inside the pipe.





The leak was discovered early November 29 by a BP worker conducting a routine inspection.





The North Slope's biggest spill to date happened in 2006 when a corroded pipeline dumped 200,000 gallons of crude oil.





CNN's Nick Valencia contributed to this report.
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