Underground storage refers to the practice of storing various materials, such as natural gas, petroleum, or water, in subterranean facilities. This method is often used to ensure a reliable supply of resources, protect them from environmental factors, and reduce surface land use. Common types of underground storage include salt caverns, aquifers, and depleted oil and gas reservoirs. These storage solutions are designed to maintain the integrity of the stored materials while minimizing risks associated with leaks or contamination.