Those actions were aimed to mitigate the risks agents might face at firing ranges, which have long been seen as potential danger spots for lead exposure. That's because most bullets are made of lead, and shooting them results in lead dust that can only be controlled with proper ventilation and personal hygiene.

The lead levels at the Niagara Gun Range were too much, though, for the Customs agency at the time.

"As of Feb. 23, 2006, use of the Niagara Gun Range by CBP personnel was discontinued," Engleman told Armenia in that 2006 letter.

All that changed at the end of 2006, said Bowker, the Customs spokesman. The Niagara Gun Range moved to a new facility about a half mile from its old one, and it bid on the contract the Customs agency was offering for a training facility.

"They successfully competed again for the CBP contract which was awarded in 2007," Bowker said.

The gun range bid again for the Customs contract when it came up for renewal in 2011 and 2016, and it won both times for a simple reason: The facility "was the sole bidder and subsequently won the contracts," Bowker said.

The Customs spokesman also stressed that lead exposure was by no means a constant issue for Customs agents working at the gun range.