Geohydrology and susceptibility of major aquifers to surface contamination in Alabama; area 13

The geohydrology and susceptibility to surface contamination of the major aquifers in Area 13--Baldwin and Mobile Counties Alabama--are described. Within this area are two major aquifers. The Pliocene-Miocene aquifer occurs throughout the study area. The Alluvial-Coastal aquifer is found near the major rivers and coastal areas and overlies the Pliocene-Miocene aquifer. There is no continuous confining unit between these two aquifers, thus , they are hydraulically connected and act as a single hydrologic unit. The entire study area is susceptible to surface contamination. The sediments are highly permeable, which allows rapid infiltration of water. Areas around some of the large pumping centers are highly susceptible to contamination, not only because of permeable sediments and flat terrain, but also because of depressions created in the potentiometric surface by large withdrawals of water from the aquifers. These depressions act as funnels to direct groundwater flow toward pumping centers; this increases the possibility of a contaminant migrating into the groundwater system. Other areas of high susceptibility are regions characterized by flat terrain and highly permeable soils, which increase the rate of infiltration from the surface. (USGS)