The Department of Homeland Security will send four vendors to a site in San Diego in the next few weeks to begin construction on a variety of concrete prototypes that could become the model for President Trump's promised border wall, agency officials announced Thursday.

"These prototypes will help us refine the design standards and security requirements that will meet the needs of U.S. Border Protection," U.S. Border Patrol Chief Ronald Vitiello told reporters during a presentation.

The vendors whose designs were selected for construction were chosen from a pool of approximately 400 defense contractors and concrete manufacturing companies who submitted their own proposals earlier this spring. U.S. Customs and Border Protection had originally intended to notify awardees by May 8 and begin prototype construction in late June, but the process dragged on for months while officials refused to provide reasons for the numerous delays.

Agency officials posted two solicitations for proposals earlier this year: one that requested designs for a 30-foot concrete wall that could withstand severe weather and prevent people from "climbing it [or] digging beneath it," and another that sought alternative ideas such as a see-through barrier.

Vitiello said vendors will have one month to build prototypes that are 30-feet wide and 30-feet tall, with an average budget of $450,000 for each. Depending on how the structures withstand testing, they may remain in place when actual construction of the border wall begins.

The four vendors who received contracts are based in Arizona, Texas, Alabama and Mississippi. A final design will be selected after each prototype has been tested for aesthetics, weather resistance, penetrability, and cost.

"We're going to build four prototypes for concrete and then we're going to build four prototypes with other materials and then we're going to make a decision about which is best appropriate," Vitiello said.

Two bidders whose proposals were initially rejected by CBP dealt a blow to the procurement process when they filed protests against the agency earlier this summer. Though both protests were dismissed by the Government Accountability Office last week, CBP could face new protests following Thursday's announcement.

The agency has yet to announce which of the vendors that responded to its request for non-concrete wall designs have been tapped for prototype construction.

Thursday's big reveal comes nearly a month after DHS issued a waiver to bypass environmental laws and regulations that could have prevented vendors from drilling or building their prototypes on the designated construction site in Southern California.

"This waiver is pursuant to authority granted to the Secretary of Homeland Security by Congress and covers a variety of environmental, natural resource, and land management laws," the department said in an Aug. 1 statement.