U.S. EPA defines a Sole Source Aquifer (SSA) as an aquifer that supplies at least 50 percent of the drinking water consumed in the area overlying the aquifer. These areas may have no alternative drinking water source(s) that could physically, legally and economically supply all those who depend on the aquifer for drinking water.The SSA designation protects an area's ground water resource by requiring U.S. EPA to review certain proposed projects within the designated area. All proposed projects receiving federal funds are subject to review to ensure that they do not endanger the water source.For more information on SSAs,including GIS data, visithttp://water.epa.gov/infrastructure/drinkingwater/sourcewater/protection/solesourceaquifer.cfm.