About Aquifer Susceptibility Maps

Aquifer Susceptibility

Aquifer Susceptibility

             Aquifer susceptibility is a measure of the ease with which water enters and moves through an aquifer.  This considers only the physical factors that affect flow into and through an aquifer, without regard to threats to ground water from human sources or natural sources of contamination.  Aquifer susceptibility sometimes is called sensitivity.

             In order to rate the susceptibility of aquifers, a weighting and ranking system has been developed.  This system considers factors such as rock type, fractures, faulting, development of caves and other dissolution features, depth to water, recharge, overlying materials, and permeability.

             In general, groundwater reservoirs such as the Madison aquifer have high to very high susceptibility because of cave development that allows very fast ground-water velocities and little filtering of water.  Some sandstone aquifers have medium to high susceptibility, depending on various factors.  Rock formations with low permeability and fine-grained materials, such as silt, typically have low susceptibility.

             The map at the left shows the outcrop of the Madison aquifer in red, with a very high susceptibility, largely because of the following factors:  1) the ease with which recharge water from streams or the land surface can reach the aquifer, and 2) the development of karst features such as caves and sinkholes, which result in high permeability, fast ground-water movement, and very limited filtering of water.