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(CNN) —  

The Department of Homeland Security has requested assistance from the Defense Department to mount approximately 218 miles of new and replacement barriers along the US-Mexico border, according to documents released by the Sierra Club, a grassroots environmental organization.

In a February 25 memo to the Defense Department, the Department of Homeland Security identifies four sectors along the southern border that require reinforcement through barriers, light installation and other measures. Combined, the mileage amounts to approximately 218 miles of new or replacement barrier, just shy of the White House’s January request of approximately 234 miles.

The memo largely focuses on vehicle and pedestrian barriers – the former is intended to stop vehicles, but people can easily climb over it, and the latter is designed to keep both vehicles and pedestrians from crossing. The request, which will be funded through counterdrug monies, also cites the number of drug seizures in each region.

“DHS requests that DoD assist in the execution of projects, within the Project Areas set forth below, to: (1) replace existing vehicle barriers or dilapidated pedestrian fencing with new pedestrian fencing; (2) construct roads; and (3) install lighting,” the memo reads.

The four sectors listed are: El Centro, Yuma, Tucson and El Paso. In addition to new replacement barriers, the Department of Homeland Security has also requested assistance with road construction and light installation.

  • In the El Centro sector, the Department of Homeland Security requests the replacement of around 15 miles of existing vehicle barrier with new pedestrian fencing, in addition to light installation. The project is located in Imperial County, California.
  • In the Yuma sector, the Department of Homeland Security has asked for assistance to replace around 36 miles of existing vehicle barrier and approximately six miles of “dilapidated pedestrian fencing with new pedestrian fencing,” in addition to light installation. The areas are located in Yuma County, Arizona.
  • In the Tucson sector, the Department of Homeland Security requests replacing around 86 miles of existing vehicle barrier with new pedestrian fencing, in addition to light installation. The areas are located in Pima, Cochise, and Santa Cruz Counties, Arizona.
  • In the El Paso Sector, which includes New Mexico, the Department of Homeland Security requests replacing approximately 70 miles of existing vehicle barrier with new pedestrian fencing, in addition to light installation. Areas are located in Luna, Hidalgo and Doña Ana Counties, New Mexico.

The memo notes that the projects are on federal property. In areas where that’s not the case, the onus is on the Department of Homeland Security to secure the land.

Acting Defense Secretary Patrick Shanahan wrote a response to the request on March 25, saying that that the Pentagon would use $1 billion to fund border barriers at two of the four requested sectors.

“At this time I have decided to undertake Yuma Sector Projects 1 and 2 and El Paso Sector Project 1 by constructing 57 miles of 18-foot high pedestrian fencing, constructing and improving roads, and installing lighting as described in your February 25, 2019 request,” Shanahan wrote.

“Additional support may be available in the future, subject to the availability and other factors,” he added.

CNN reported this week that the Defense Department has begun scouting sites along the US-Mexico border to erect new physical barriers.

Small teams of engineers and experts, comprised of about 10 personnel, are on the ground in Yuma, Arizona, and the New Mexico part of the El Paso sector, which also includes Texas, looking at sites, according to two department officials.

President Donald Trump has repeatedly aired his grievances about the situation along the southern border, going so far as to threaten closing it entirely Friday.

In February, he also declared a national emergency in order to funnel billions of dollars to wall construction. As part of his announcement, he directed the use of counterdrug monies to partially fund new wall construction. Under the declaration, other funds can also be dedicated to building the wall and related infrastructure, including military construction funds.

The national emergency declaration prompted a slew of lawsuits and received pushback from Democrats and Republicans. The Sierra Club, which released the Department of Homeland Security memo, is among the groups challenging the declaration, citing potential damage to the environment.

The Pentagon notified Congress that it authorized the transfer of $1 billion. The funds are set to go toward building 57 miles fencing along the southwest border, in addition to improving roads and other measures in the region.

The Army Corps of Engineers was allowed to begin planning and construction for the project Monday night, though construction isn’t expected to start before the end of May. The department will direct the funds toward 18-foot-high fencing along the Yuma and El Paso sections of the border, according to a letter Shanahan sent to Secretary of Homeland Security Kirstjen Nielsen.

The administration has previously said it plans to shift an additional $1.5 billion using counterdrug monies at some point in the future. The Department of Homeland Security has also made a separate request to tap into $3.6 billion of military construction funds, but that request is still being reviewed by the Defense Department and has yet to be approved.

CNN’s Ryan Browne contributed to this report.