Washington (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.

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