A federal border agency has been given permission to bypass environmental laws to build 18 miles of new wall on the U.S.-Mexico border in the Rio Grande Valley of South Texas.

The Department of Homeland Security announced in the Federal Register on Thursday that it has given U.S. Customs and Border Protection permission to ignore environmental and land regulations so it can speed up the process of building miles of new barrier in Hidalgo County.

CBP will move forward on six projects in the southern border's busiest of its nine U.S. Border Patrol sectors, according to details outlined in the announcement. The largest portion of wall construction is 8 miles long and will stretch from near Goodwin and Abraham Roads east to near the International Boundary Water Commission levee.

The announcement comes a day after DHS said Secretary Kirstjen Nielsen waived regulations for two miles of other border projects in the Rio Grande Valley's Cameron County.

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In Wednesday and Thursday's decisions, the memos stated Nielsen had the authority to make the exceptions under the Illegal Immigration Reform and Immigrant Responsibility Act of 1996, which states a chief can waive all legal requirements if a wall, road, or other infrastructure is immediately needed.

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"There is presently an acute and immediate need to construct physical barriers and roads in the vicinity of the border of the United States in order to prevent unlawful entries into the United States in the project area. In order to ensure the expeditious construction of the barriers and roads in the project area, I have determined that it is necessary that I exercise the authority that is vested in me by section 102(c) of IIRIRA," Nielsen wrote.

In fiscal year 2017, U.S. Border Patrol apprehended 137,000 people in the Rio Grande Valley Sector, almost half of the 310,000 taken into custody nationwide.

DHS did not say when the project will start or how long construction is expected to last.

The Center for Biological Diversity slammed the department's use of waivers and said the administration is ignoring 28 relevant laws to build a wall and issued the Thursday waiver despite having been in the midst of collecting comments from local residents on the plan.

“The Trump administration is ignoring thousands of people in Hidalgo County who don’t want these disastrous border walls,” Laiken Jordahl, borderlands campaigner at the Center for Biological Diversity, said in a statement. “The Rio Grande Valley is one of the most spectacular and biologically important landscapes in the country. Every acre is irreplaceable."

The organization has not decided whether it will sue over the matter.

President Trump campaigned in 2016 to build a "beautiful" wall between the U.S. and Mexico. When he took office in January 2017, the barrier between both countries' 1,954-mile border covered approximately one-third of that space.

In April, CBP announced several projects that would replace and build new barriers on 100 miles.