The Trump administration could potentially waste billions of dollars on a border wall because it failed to fully account for factors like varying terrain and land ownership along the Southwest border, according to a new report.

The report, conducted by the Government Accountability Office, found that Customs and Border Protection, the agency responsible for construction of the wall, did not consider the cost of building along each segment of the border, which can vary depending on factors such as topography and land ownership.

The report also found that the agency selected locations for barriers without fully assessing where they were needed to prevent illegal border crossings.

“Without assessing costs, consistent with leading practices for capital decision making, C.B.P. does not have complete information for prioritizing locations to use its resources in the most cost-effective manner,” the report said.