Hydrogeologic Investigation of Fractured Karst Aquifers in an Urban Alabama Valley and Ridge Setting

The Geological Survey of Alabama Groundwater Assessment Program (GSAGAP) is working with public water supply systems and the State Legislature to develop hydrogeologic data for development of new local groundwater sources and state-wide groundwater policy initiatives. Over the past ten years many groundwater sourced public water systems in Alabama interconnected with larger surface-water systems to avoid additional groundwater source development. However, recent extreme droughts and more stringent disinfection byproducts regulations have threatened the reliability of treated water delivery from surface-water systems. Therefore, Alabama is experiencing renewed interest in development of groundwater sources, especially by systems in the Appalachian Valley and Ridge geologic province in northeast Alabama, where population growth and increasing water demands are straining the capability of water systems to provide adequate water supplies.

The Valley and Ridge is characterized by complex stratigraphy and geologic structure that makes the development of groundwater sources difficult.  Lacking adequate hydrogeologic data, most wells in the past were constructed in the most convenient areas, in and near population centers and recharge areas, where aquifers were at or near the land surface. However, population growth accompanied by increased impervious surfaces, storm water runoff, contaminants, subsidence, and pumping rates have rendered many groundwater production areas inadequate.

An ongoing hydrogeologic investigation by the GSAGAP in the Valley and Ridge in central Alabama is evaluating potential well locations, pathways of groundwater recharge, and strategies for protection of vital aquifers in this rapidly growing area. A number of geologic mapping techniques are used to identify potential aquifers, confining units, and recharge areas. Geochemical analytes and isotopes, including chlorofluorocarbons, oxygen-18, deuterium, and carbon-13 are being evaluated to determine anthropogenic impacts, residence times, and pathways of recharge movement. Trends of land-use change using geographic information systems data are also being assessed.