The Environmental Protection Agency (EPA) estimates that hundreds of thousands of underground storage tanks containing petroleum or hazardous chemicals are leaking and pose a threat to public health and the environment. Most of DOD's underground storage tanks are single-walled steel tanks that do not have corrosion protection and have an average life expectancy of 16 to 20 years. Most were installed prior to 1965 and are now beyond their average life expectancy. Leaking tanks can contaminate nearby groundwater, which is the primary source of drinking water for half of the population of the United States. They can also cause fires and explosions. Regulations require the following: (1) Ensure that new underground storage tanks have automatic leak detection, corrosion protection, and spill and overflow protection; (2) By 1998 upgrade all existing tanks to meet the new-tank standards and, until they do, annually test nonupgraded tanks for leaks; (3) Clean up damages caused by leaking tanks; and (4) Close inactive substandard tanks after 12 months after being taken out of service.