A new round in the fight over the Keystone XL pipeline has begun, as TransCanada reapplied for a U.S. permit to build the controversial $7.6-billion, 1,600-mile-long project, which would carry crude oil from Alberta's tar sands to the Gulf of Mexico.

The Calgary-based energy company's application, received by the State Dept. on May 4, is different from its initial submission, which President Obama rejected in January. For one thing, the new application only applies to the 1,179-mi. section from Hardisty, Alberta, to Steele City, Nebraska.

TransCanada said in February that it would proceed to build the pipeline section running from Cushing, Okla., to Nederland, Texas. That segment does not need a presidential permit to begin construction because it does not cross an international border.

Work on that $2.3-billion portion is expected to begin this summer; company officials anticipate that it will be operational by mid- to late- 2013.

The State Dept. said it was committed to a "rigorous, transparent and thorough review" of TransCanada's new application. The department said it plans to hire an outside contractor to review the Environmental Impact Statement from the earlier Keystone XL proposal and also identify and assist with new analysis.

A key sticking point in the earlier discussions over the pipeline was its original route, which was to cut directly through Nebraska's environmentally sensitive Sand Hills region.

TransCanada has changed that plan. On April 18, it submitted alternative Nebraska routes to the state's Dept. of Environmental Quality. DEQ will help determine a specific alignment and oversee the public comment and review process. TransCanada said on May 4 that it ihas been working with Nebraska officials on a route that would avoid the Sand Hills region.

Once a final Nebraska route is determined, TransCanada will incorporate that as part of its application with the State Dept.

The project has become a hot political issue in the U.S. Congressional Republicans have repeatedly called on Obama to approve the plan.

Energy-industry officials also want to see the project started quickly. Marty Durbin, American Petroleum Institute executive vice president, said, "The earth hasn’t moved, the geology hasn’t changed, the information remains the same, so there should be no reason for a re-review of KXL." He added, "The pipeline will be state-of-the art and has already been thoroughly examined for more than three years, including three environmental assessments.”

But environmental groups, including the Natural Resources Defense Council, are concerned that although the alternative Nebraska routes do avoid the Sand Hills, a spill anywhere along the pipeline’s route could be environmentally destructive.

If the pipeline is approved, TransCanada says it plans to begin construction in the first quarter of 2013, with completion slated for late 2014 or early 2015.