EL PASO, Texas (Border Report) — The Department of Homeland Security is investigating how materials used to build the border wall in Arizona allegedly ended up on the market in Mexico, CBS 5 Investigates reports.

Steel posts as well as construction waste have been advertised as being for sale in scrap yards in Sonoyta, Sonora.

A CBS 5 Investigates producer spotted an ad in an internet forum. The ad, titled “Steel For Sale Arizona,” said “We have an amazing amount of steel left over from the border (sp) wall Trump built. Government-issued steel for sale. They are basically giving it away.”

The seller reportedly sold posts for $50 each post or $800 to deliver a truckload, and the seller stated that the steel came from the border wall project near Naco, Arizona.

CBS 5 Investigates reports that Southwest Valley Constructors is the company contracted to build the border wall near Naco and replace the old vehicle barriers and border fence near Lukeville. And it is that project that appears to be the source of the steel posts found in Sonoyta.

DHS told CBS 5 Investigates that CBP is aware of the allegations and that they involve subcontractors.

CBP is looking into allegations that border-wall crews used bulldozers and front-end loaders to push the scrap metal onto the Mexican side.

CBS 5 Investigates traveled into Mexico and spotted several locations that were selling the steel posts and the scrap metal from the barriers that are being replaced.

One business owner, who tells the reporter that the U.S. is giving the steel to Mexico for free, says he’ll his pieces of scrap metal for $4 apiece.

CBS 5 Investigates also visited construction the sites and found countless pieces of scrap metal on the Mexican side.