Which RCRA amendment strengthened the EPA's authority to enforce regulations at federal facilities?

The Federal Facilities Compliance Act is the correct answer because it specifically enhances the authority of the Environmental Protection Agency (EPA) to enforce hazardous waste regulations at federal facilities. This amendment was enacted to ensure that federal facilities are held to the same standards as private sector organizations in terms of compliance with hazardous waste laws. It addresses the unique challenges associated with regulating federal properties, allowing for effective oversight and accountability in managing hazardous waste.

The other options do not have the same focus on federal facilities' compliance. The Hazardous and Solid Waste Amendments are more about modifying waste management procedures and increasing regulatory controls, especially concerning land disposal practices. The Land Disposal Program Flexibility Act pertains to the management of waste disposal methods rather than regulation enforcement at specific facility types. Finally, the Hazardous Waste Management Act generally regulates hazardous waste but does not specifically bolster enforcement powers at federal sites like the Federal Facilities Compliance Act does.