Nebraska has objected to a proposal from TransCanada to build Keystone XL through the state's Sandhills, an area containing the Ogallala Aquifer.
Mike Linder, director of the Nebraska Department of Environmental Quality, said his agency delineated what it considers the Sandhills area.
"Obviously, the applicant cannot propose the route without knowing the area to be avoided," he said in a statement. "NDEQ has been reviewing available information and has selected a map of ecoregions which was finalized in 2001 as best depicting the Sandhills region."
A NDEQ spokesman told the Platts news service that a supplemental environmental impact study of Keystone XL has a Sept. 1 deadline.
Republican lawmakers presented U.S. President Barack Obama a measure to extend payroll tax benefits that included a rider on Keystone XL. That section gives the president about two months to announce a decision on the pipeline, a time frame the executive branch questions.
Environmental critics of the project claim tar sands oil pipelines like Keystone XL are risky.
U.S. Rep. Louie Gohmert, R-Texas, told Fox News that, with Iran threatening to block the Strait of Hormuz, a key oil shipping lane, projects like Keystone XL were vital to national security.
"This president has got to take a strong stand and let Iran know that blocking the Strait of Hormuz would be a provocation for a military strike, in addition to getting the Keystone pipeline done," he said.