Immigration and Customs Enforcement (ICE) says it is expecting a "historic" surge in migration at the border, and the number of those arriving at the border is expected to triple -- as the Biden administration prepares to lift the Title 42 public health order.

In a filing in a case on family detention, ICE’s Juvenile Coordinator painted a grim picture of what the months ahead look like for the agency.

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"ICE is preparing to utilize its limited resources to respond to an historic border surge, with projections forecasted to triple current arrivals," the April 8 filing in the Flores v Garland case says.

The agency said that it is currently seeing border enrollments (which are separate from migrant encounters by Customs and Border Protection) ranging from between 1,000-2,000 arrivals a day. As a result, it says it will need resources for up to 3,000 people a day being released into the U.S. under the non-detained docket and via monitoring under the Alternatives to Detention (ATD) program.

"Given these forecasts and the recently announced decision to end Title 42 next month, ICE must shift its focus and prepare to manage its resources for a population of up to 600,000 by the end of the fiscal year," the official said. The Washington Times first reported on the filing.

While ICE did not comment to Fox News on the filing, the 600,000 appears to be specifically about the number of those enrolled in ATD -- by which a small percentage of illegal immigrants released in the non-detained docket are monitored via GPS, phone calls or a smart phone app. There are currently just over 215,000 enrolled in the program.

ICE’s predictions are the latest acknowledgement by the Biden administration of fears expressed by both Republicans and Democrats in Congress that the lifting of the order, combined with a seasonal increase in number, will lead to an overwhelming number. 

There were more than 221,000 migrant encounters at the border in March, and CBP has been encountering about 7,000 migrants a day -- DHS has said it has been planning for up to 18,000 migrants a day. 

Border Security migrant

Immigrant men from many countries are taken into custody by U.S. Border Patrol agents at the U.S.-Mexico border on December 07, 2021 in Yuma, Arizona. Governors from 26 states have formed a strike force to address the crisis at the border. (John Moore/Getty Images)

Republican states have sued to block the lifting of the order, while Republicans and Democrats in Congress have signed onto legislation that would extend the lifting of the order by at least 60 days.

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ICE, meanwhile, said that toward the end of 2021, "ICE chose to shift its usage of the family facilities to focus on single adults, consistent with the administration’s goal of addressing irregular migration while supporting a system of border management that is orderly, safe and humane."

An ICE spokesperson told Fox News Digital that: "As a matter of policy, U.S. Immigration and Customs Enforcement does not comment on ongoing or pending litigation. However, lack of comment should not be construed as agreement with, or stipulation to, any allegations."

Thomas Homan, a former Immigration and Customs Enforcement acting director, said the Trump administration was detaining many more illegal immigrants than the Biden administration is, with more than 55,000 detained compared to just over 20,000 under Biden.

"There’s plenty of space, they shouldn’t be releasing them unless they’re out of resources, and they're not there yet," he said.

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He said that when illegal immigrants are released into the country, it is much harder to remove them than if they are detained.

"When you’re detained you have a hearing in front of a judge in 28-32 days, when you're not detained it can be years," he said.

"The Homeland Security lifecycle report, which the Homeland Security secretary has the same data I had, will tell you that you release them, the chances are they'll never leave, and that is the whole purpose of this administration, not only let millions in the country, but making sure they stay here."