Story highlights The moves by the transition team show how seriously Trump is taking his promise

Trump could use a 2005 law to remove legal barriers to building the wall

Washington (CNN) President-elect Donald Trump's transition team is engaged in active discussions with the US Army Corps of Engineers and Interior Department to begin planning a wall along the Mexican border, including how specific environmental laws could get in the way, CNN has learned.

A US official with knowledge of a visit last last month to the Interior Department -- which oversees most federal lands and major environmental laws -- said the transition team was particularly interested in finding out "how long it would take" to build the wall given potential legal obstacles.

"It seems clear they were trying to size up the environmental laws that may be obstacles to building the wall," the source said.

Another US official told CNN the Trump transition team has also reached out to the Army Corps of Engineers' Southwest Division, that has previously built border security fencing, to determine what previous fencing cost and how it was constructed. The team also asked Interior several questions, including how much wall would be needed, in an effort to determine a solid number of miles of wall necessary to secure the southern border.

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The moves by the transition team, including previously reported questions to the Department of Homeland Security, show how seriously Trump is taking his promise to build a massive physical barrier between the US and Mexico. The idea energized backers at this rallies but was dismissed by opponents as expensive and unfeasible.

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