Exxon Mobil Corp. violated a state water-use permit while constructing an ice road across the North Slope, state officials said Tuesday.

The company is building the 50-mile ice road to support development of its remote Point Thomson oil and gas field.

Such roads are made by laying down a strip of ice, typically at least 6 inches thick, using ice chips and water drawn from lakes, rivers and flooded gravel mines on the Slope.

Ice roads, which typically melt away in summer, provide a safe way to haul heavy equipment such as drilling rigs across the delicate tundra.

An Exxon contractor, Alaska Frontier Constructors Inc., last week pumped water from the broad Sagavanirktok River delta as part of work to build the road east to Point Thomson.

But a work crew failed to first test the water to make sure it was brackish and not fresh water, said Gary Prokosch of the state Department of Natural Resources.

Taking fresh water from the river isn't allowed because it's important for winter survival of whitefish and other species, said Bill Morris, a habitat biologist with the state Department of Fish and Game.

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