Table 50. Summary of geologic units, and availability and quality of ground 

 water in Mobile County (modified from O'Neil and Mettee 1982). 



Series 



Geologic unit 



Thickness 

 m (ft) 



Availability of water 



Qual ity of water 



Holocene 



and 

 Plei stocene 



Alluvium, low 

 terrace, and coast- 

 al deposits 



0-46 (0-150) 



Will yield 38 1pm (10 

 gpm) where saturated 

 sands are of sufficient 

 thickness. Potential 

 sources of 1,325 to 2,650 

 lpm (350 to 700 gpm) 

 well in the Mobile River 



Water generally suitable 

 for most uses but common- 

 ly contains iron in excess 

 of 0.3 mg/1 and may be suf- 

 ficiently acidic to be 

 corrosive. Locally, in 

 areas close to Mobile Bay 

 and Mississippi Sound, water 

 is very hard, has high 

 chloride and dissolved- 

 solids contents, and con- 

 tains iron in excess of 

 0.3 mg/1 



High-terrace 

 deposits 



ttT'UFm Will yield 38 1pm 



( 10 gpm) or more where 

 saturated sands are of 

 sufficient thickness 



Probably soft and low in 

 dissolved solids. May con- 

 tain iron in excess of 0.3 mg/1. 



Water generally is soft and low 

 in dissolved solids but may con- 

 tain iron in excess of 0.3 mg/1 

 and may be sufficiently acidic to 

 be corrosive. In areas adjacent 

 to Mobile River, Mobile Bay, and 

 Mississippi Sound, water may have 

 a dissolved-sol ids content that 

 exceeds 1,000 mg/1, a sul furous 

 odor, and a chloride content that 

 exceeds 500 mg/1 . 



PI iocene 



Miocene 



Ci tronel le 

 Formation 



Micocene Series 

 undi f ferentiated 



0-61 (0-200) Will yield 2,650 lpm 

 (700 gpm) or more per 

 well . 



120-1,030 

 (400-3,400) 



GROUND WATER QUALITY 



The following discussion is taken primarily from Reed and McCain (1971 

 and 1972). Most of the wells tapping the Miocene-Pliocene aquifer yield 

 water that is good for most uses. The water is generally soft, with a 

 dissolved solids content of only 250 mg/1. In localized areas, the water may 

 be too acidic for some uses. Wells in areas near the major waterways may 

 produce objectionable amounts of iron. Some wells on Dauphin Island (Biloxi 

 quadrangle) produce water that is high in chloride and dissolved solids 

 content and has a sulfurous odor. Recently, some wells in the vicinity of 

 the Mobile (Mobile quadrangle) waterfront have shown an increase in chloride 

 content, indicating an increase in saltwater encroachment. At Gulf Shores 

 (Pensacola quadrangle) in Baldwin County, saltwater encroachment has also 

 occurred. 



The water produced from alluvium and low terrace deposits is similar to 

 that from the Miocene-Pliocene aquifer in that it is mostly soft and is low 

 in dissolved solids. It differs in that it frequently has iron in excess of 

 0.3 mg/1 and is acidic enough to be corrosive. As these deposits are much 

 shallower than the Miocene-Pliocene aquifer, they are more immediately 



169 



