Gulf Coast Regional Aquifer-System Analysis — A Mississippi perspective

Abstract

The Gulf Coast Regional Aquifer-System Analysis is a study of regional aquifers in sediments of mostly Cenozoic age in an area of about 230,000 square miles in the Coastal Plain of Alabama, Arkansas, Florida, Illinois, Kentucky, Louisiana, Mississippi, Missouri, Tennessee, and Texas, and an additional 60,000 square miles offshore. Three aquifer systems have been identified: two in sediments of mostly Eocene age, the Mississippi embayment aquifer system and the Texas coastal uplands aquifer system, and one in sediments of Miocene and younger age, the coastal lowlands aquifer system. These aquifer systems thicken from less than 100 feet near their updip limit to thousands of feet gulfward toward their downdip limits. Two of these aquifer systems occur in Mississippi. The Mississippi embayment aquifer system is present in about 90 percent of the State and the coastal lowlands aquifer system is present in the southern one-third of the State. The Mississippi embayment aquifer system exceeds 5,000 feet in thickness in central Louisiana and in southwestern Mississippi. The thickest area in southwestern Mississippi underlies most of six Mississippi counties, centered around Jefferson County. The coastal lowlands aquifer system is more than 10,000 feet thick in southern Texas and southern Louisiana. The greatest thickness of the coastal lowlands aquifer system in Mississippi occurs in southern Hancock County where the system is slightly more than 5,000 feet thick. Each of the three aquifer systems is composed of several individual aquifers and confining units. There are seven aquifers and three confining units in the Mississippi embayment aquifer system, five aquifers and two confining units in the Texas coastal uplands aquifer system, and five aquifers and two confining units in the coastal lowlands aquifer system. Most of the thicker parts of each aquifer system contain moderately saline to very saline water. Water in the Mississippi embayment aquifer system is moderately saline to very saline in most of a seven county area in southwestern Mississippi. Water in the coastal lowlands aquifer system is moderately saline to very saline in parts of three counties in south western Mississippi and in parts of the three counties along the Gulf Coast. About 9,600 million gallons per day of ground water was pumped from the aquifers in the study area during 1980. About 15 percent of that pumpage (or about 1,400 million gallons per day) was in Mississippi, mostly from the Mississippi River Valley alluvial aquifer of the Mississippi embayment aquifer system. About 10 percent of the Mississippi pumpage, or 140 million gallons per day, was from the coastal lowlands aquifer system. Preliminary results from simulation of ground-water flow indicates that parts of Mississippi are major regional recharge areas for both the Mississippi embayment aquifer system and the coastal lowlands aquifer system. The Mississippi River alluvial plain or fDelta' area of Mississippi is part of a much larger regional discharge area that extends westward into parts of eastern Arkansas and northeastern Louisiana.