The EPA regulates the monitoring and testing of underground storage tanks (USTs), that were or are used to store petroleum or other hazardous substances, which could impact the environment and human health. Currently, there are over half a million registered underground storage tanks in the US alone. Many tanks installed prior to the mid-80s were composed of steel, which can corrode over time allowing for leakage into the surrounding groundwater and soil. The Hazardous and Solid Waste Amendments to the Resource Conservation and Recovery Act (RCRA), passed in 1984, required the US Environmental Protection Agency (EPA) to develop regulations for the underground storage of motor fuels. The EPA requires owners and operators of USTs to maintain and clean up sites damaged by petroleum contamination.