From the Document: "The U.S. Army Corps of Engineers (USACE) is performing work on border barriers, roads, and lighting along the U.S. southern border on behalf of the Departments of Homeland Security (DHS) and Defense (DOD). In addition to USACE's military and civil works responsibilities, a variety of entities--federal agencies (including DOD entities) and tribal, state, local and foreign governments--may access USACE's engineering and contracting expertise through the agency's Interagency and International Support (IIS) program. Typically the requesting entity reimburses USACE's IIS work. Pursuant to IIS agreements, DHS has tasked USACE with managing various construction activities to meet border security requirements of DHS's Customs and Border Protection (CBP)."
CRS In Focus, IF11224
Congressional Research Service: https://crsreports.congress.gov/