GSA's Public Buildings Service issued this Notice of Availability for a Final Supplemental Environmental Impact Statement (Final SEIS) covering flood control and utility upgrades at the Raul Hector Castro Land Port of Entry in Douglas, Arizona, and construction water supply provisions for the adjacent proposed Commercial Land Port of Entry. The Final SEIS adds a Floodplain Assessment with a Finding of No Practicable Alternative for construction in floodplains, and addresses a newly identified need to truck treated wastewater from the City of Douglas Wastewater Treatment Plant. GSA's preferred alternative is Alternative 1 (Flood Control, Utility Upgrades, and Construction Water Supply). A 30-day wait period closes July 20, 2025, after which GSA will issue a Record of Decision.1