Southeastern Coastal Plain

The aquifer between the Floridan and the Piedmont — supplying inland Georgia, Alabama, and the Carolinas without much fanfare

States

GA, AL, SC, MS, TN, NC

Type

Multi-layered Cretaceous-Tertiary confined sandy aquifers

Status

Stable in most of the system; localized declines at major pumping centers; arsenic and radium in specific sub-regions

The Southeastern Coastal Plain Aquifer System fills a quiet middle position in US private-well geography. Inland from the more dramatic Floridan coastal system, upland from the rapidly-growing Piedmont and Blue Ridge crystalline aquifer of the inner Southeast, this system supplies drinking water to a substantial swath of inland Georgia, Alabama, the Carolinas, eastern Mississippi, and parts of Tennessee. It rarely makes news. Its problems are mostly local rather than regional. Its productivity is moderate rather than extraordinary. It is, in many ways, the median US private-well aquifer — and a substantial fraction of inland-Southeast private wells tap it.

What it is, geologically

The aquifer system is a stack of Cretaceous and Tertiary sandy aquifers and intervening clay confining units, deposited as the Atlantic and Gulf coastal plains built outward through the Mesozoic and Cenozoic. The principal aquifer units, generally from oldest/deepest to youngest/shallowest:

• Tuscaloosa aquifer (Cretaceous) — the deep regional aquifer; heavily used in central Alabama and east-central Mississippi.
• Eutaw and McShan aquifers (Cretaceous) — additional Cretaceous units.
• Black Creek and Middendorf aquifers (Cretaceous) — important in the Carolinas.
• Selma Group / Ripley aquifer (Cretaceous-Tertiary) — Alabama, Mississippi.
• Various Tertiary units — Wilcox, Claiborne, Jackson Group equivalents.

The aquifer is generally confined in the deeper sub-basins (toward the coast) and unconfined where the formations outcrop along the inland fall line. Recharge happens at the outcrop areas; transit times to the deep confined zones are measured in centuries.

Major populations served

• Macon, GA — long history of Tuscaloosa aquifer use.
• Augusta, GA / Aiken, SC — fall-line cities on the inner edge of the system.
• Columbia, SC — Black Creek and Middendorf aquifers.
• Tuscaloosa, AL — namesake for the deep aquifer; mixed groundwater and surface water.
• Montgomery, AL — primarily groundwater from this system.
• Birmingham metro fringes — northern edge of the system overlaps with Valley and Ridge geology.
• Smaller cities and rural areas across central and southern AL, MS, GA, SC, NC — the bulk of the private-well population.

Water quality

Water quality in the Southeastern Coastal Plain aquifer is generally good — moderate hardness, moderate TDS, lower iron and manganese than many sedimentary systems. Most of the localized concerns are sub-regional:

• Arsenic — pockets, particularly in some Tertiary sand sub-regions of central Alabama and central Mississippi. Less universal than Mississippi Alluvial or New England crystalline. See arsenic.
• Radium — naturally elevated in some Cretaceous sands, especially in parts of central Georgia and South Carolina. Not as severe as the eastern Wisconsin Cambrian-Ordovician situation but locally significant. See radium.
• Iron and manganese — common in deeper confined wells with reducing conditions. See iron and manganese.
• Hydrogen sulfide — common in deeper wells. See hydrogen sulfide.
• Bacteria — risk depends on well depth and casing integrity. Shallow rural wells in agricultural areas (poultry country in Alabama and Georgia) are vulnerable. See bacteria.
• Nitrates — agricultural source; less pervasive than in the corn belt but real in poultry-concentrated and row-crop sub-regions.
• Hardness — generally moderate.

Long-term decline at pumping centers

The deep Tuscaloosa and Black Creek aquifers have shown long-term water-level declines at the heaviest-pumped centers — particularly in the Albany, Georgia area and parts of the South Carolina coastal plain. The declines are modest by Western US standards (tens of feet over decades, not hundreds) but they are continuing trends. State agencies in GA, SC, AL maintain monitoring data.

Known contaminant concerns

Communities on this aquifer