Jan. 28 (UPI) -- For the first time in 38 days, the full federal government will begin to reopen Monday after Congress and President Donald Trump reached a deal to end the longest shutdown in U.S. history.
Parks, museums and agencies that have been shuttered or working with skeleton staffs are set to reopen this week, although some may take longer to ramp up.
The Internal Revenue Service is buried in millions of unanswered letters from taxpayers and is weeks behind in training an influx of workers for tax season.
Forbes estimated Monday backlogged IRS mail is about five million pieces, three times the amount it received over 10 days prior. The mail surge was prompted by taxpayers who couldn't find help at federal assistance centers and phone services that were closed by the shutdown.
The National Taxpayer Advocate, the government watchdog group for the IRS, told congressional staffers it could take as long as 12 to 18 months to return operations to normal, despite the Trump administration ordering 30,000 back to work during the shutdown without pay. Of those workers, 8,000 took hardship exemptions not to return and another 5,700 couldn't be found.
While places like the Smithsonian museums and the National Zoo in Washington, D.C., are expected to take visitors, federal prosecutors, air-traffic controllers and airport screeners could receive back pay as early as this week. Those workers, deemed essential, were ordered to continue working during the shutdown.
"There's a couple different payroll providers in the federal government and how an employee gets paid or which payroll provider covers their agency will dictate how long it takes," acting White House chief of staff Mick Mulvaney told CBS News Face the Nation Sunday.
"Some of them could be early this week. Some of them may be later this week but we hope that by the end of this week all of the back pay will be made up and of course the next payroll will go out on time."
Some of those workers have their hands full with a month's worth of email and backlog issues to work through. The U.S. Food and Drug Administration, for example, will start taking new drug and medical device applications again, but it may take months to catch up.
Employees at other agencies had to suspend various projects during the shutdown and now must work to reboot them.
"It may take days to get started," David Berteau, president and chief executive of the Professional Services Council, which represents workers at roughly 400 private government contractors, told The Washington Post.
"We have no experience at starting back up after five weeks," he added. "You have to make sure that the funds are still available before you can start the contract again. And everybody's going to be trying to do it at once."
U.S. Forest Service engineer Carl Houtman said many federal employees will be happy for things to return to normal, regardless of what needs to be done
"It's great for everybody, Houtman told USA Today. "In three weeks, we may be playing this game of chicken again, but at least everyone is getting a paycheck."
The shutdown officially ended Friday when Trump signed a federal spending measure. He'd unsuccessfully demanded billions for a wall along the U.S. southern border, and ultimately decided to end the impasse when the shutdown began to affect air traffic in New York City. While Trump did not get the wall, he has threatened to close the government again next month if a deal with Congress on border security is not reached.