Opponents of the Trump administration’s plan to break up the Washington, D.C., headquarters of the country’s public lands bureau are warning of a brain drain, saying many staffers who are being reassigned are opting to quit rather than move out West.

U.S. Interior Secretary David Bernhardt defended the move Friday. Opponents have projected that the number of Bureau of Land Management staffers agreeing to move from headquarters could be as low as 15%, which Bernhardt said was “not consistent with what I’ve seen.”

Speaking at a Las Vegas conference on Colorado River water supplies, Bernhardt said he did not immediately have firmer figures, however.

“A year from now … you’re going to find out that it worked really well,” Bernhardt told reporters.