Black Creek and Middendorf Aquifer: Fluoride, Radium, and What SC Coastal Plain Well Owners Should Know

Two major aquifers underlie much of the South Carolina Coastal Plain: the Black Creek aquifer and the Middendorf aquifer. Together they supply drinking water to private wells and some municipal systems across Florence, Williamsburg, Berkeley, Charleston, Horry, and Georgetown Counties. Both aquifers have documented water quality characteristics that differ from typical shallow groundwater, most notably, elevated fluoride in certain areas, and concerns about radium at depth. This article covers what the geological data actually shows and what it means for homeowners.

The Geology

Black Creek and Middendorf are major Coastal Plain aquifers, confined, deep, and extensively used across the Pee Dee region and coastal counties. USGS has documented significant head declines and cones of depression in both aquifers, concentrated in areas of heavy municipal and industrial pumping. Myrtle Beach and Florence in particular have driven major pumping-induced pressure declines over the past half-century.

Fluoride: The Fossil Shark Teeth Effect

USGS Water-Supply Paper 2067 documented fluoride concentrations of 0.5 to 5.5 mg/L in Black Creek aquifer wells across Horry and Georgetown Counties. The source is geologically specific: fossil shark teeth (fluorapatite) embedded in the aquifer sediments release fluoride through anion exchange with groundwater.

Dental fluorosis, the cosmetic discoloration and mottling of tooth enamel caused by excess fluoride during tooth development, has been historically documented in areas with elevated well water fluoride. The risk is specifically for children whose teeth are still forming, not adults.

Fluoride Regulatory Standards

• EPA Primary MCL: 4.0 mg/L (health-based)
• EPA Secondary MCL: 2.0 mg/L (cosmetic/dental fluorosis concern; utilities must provide special notice if exceeded)
• Optimal for dental health: ~0.7 mg/L (community water fluoridation target)

Water at 3.0 mg/L fluoride is technically below the primary MCL but well above the secondary. A family using a private well at this level without knowing has a meaningful risk of dental fluorosis in children.

Radium

Radium is a naturally occurring radionuclide that accumulates in certain deep Coastal Plain groundwater. The EPA's combined radium MCL is 5 pCi/L (Ra-226 + Ra-228) under the 2000 Radionuclides Rule.

Black Creek and Middendorf are part of broader SC deep Coastal Plain aquifer systems known regionally for elevated radium in some locations. Direct confirmed radium numbers for these two specific aquifers are not publicly centralized; USGS and SCDNR publications provide the best general documentation. For any specific well, test results are the only reliable data.

Who Should Test, and for What

If you are on a private well in any of these SC counties:

• Fluoride: Test once and document. If below 2 mg/L, re-test every 3–5 years. If between 2 and 4 mg/L, treat or use bottled water for children during tooth development. If above 4 mg/L, treat regardless of household composition.
• Radium (combined Ra-226 + Ra-228): Test once. If well below 5 pCi/L, re-test every 5 years. If near or above, treat.
• Uranium: Often co-occurs with radium. EPA MCL: 30 ppb.
• Standard panel: Annual coliform, nitrate, iron, manganese, hardness, pH.

Treatment

Fluoride removal:

• Activated alumina filtration (whole-house or point-of-use)
• Reverse osmosis (point-of-use), 85–95% reduction
• Distillation (slow, point-of-use)

Standard activated carbon, softeners, and sediment filters do NOT reduce fluoride.

Radium removal:

• Ion exchange (cation softener), removes radium as a side benefit of softening
• Reverse osmosis, effective for residual drinking water protection

A softener properly sized and configured for radium removal can be a dual-purpose investment, addressing both hardness and radionuclides in one system.

Free Well Testing

Solomon Home Water Solutions arranges well water testing for SC Coastal Plain homeowners, Horry, Georgetown, Florence, Williamsburg, Berkeley, Charleston, Dorchester Counties. We coordinate with certified labs for fluoride, radium, and standard parameters, and recommend treatment specifically sized to your results. Call (843) 890-0511.