Groundwater provides more than 40 percent of California's drinking water. To protect this vital resource, the State of California created the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The Priority Basin Project of the GAMA Program provides a comprehensive assessment of the State's groundwater quality and increases public access to groundwater-quality information. Selected groundwater basins of the San Francisco Bay area constitute one of the study units being evaluated.
Underground injection wells, where water and/or other substances are injected into the Earth, are used for a wide variety of purposes. The U.S. Environmental Protection Agency (EPA) regulates around 850,000 underground injection wells through its Underground Injection Control program under the Safe Drinking Water Act. The EPA defines six classes of wells based on their use:
"A sinkhole is a depression in the ground that has no natural external surface drainage. Basically this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface.