A development program was performed successfully to develop and test a prototype system for temporarily stopping the flow of hazardous materials spilling on land or underwater from ruptured or damaged containers. The prototype system is portable, integrated, and field-operable by one man. It uses foamed-in-place polyurethane rigid foam plugs surrounded by a flexible protective membrane for sealing leaks. An applicator tip attached to a long handle is placed into the leak. The foam delivery system then is actuated and the foam chemicals, which are stored in a backpack, are automatically mixed and forced through a delivery tube and into the applicator tip expanding it both inside and outside the tank. The foam hardens in a few minutes and locks the plug in place. The applicator is then detached from the delivery system, which then can be refilled with foam chemicals and reused with a new applicator. The prototype leak-plugging system from this project has been developed to the point that it is now realistic to project practical field use of such a system. A preliminary implementation plan, including recommendations for additional work needed, is outlined.