Private Well Bacteria Risk in Coastal SC: An Aquifer-by-County Guide for 2026

Why does aquifer depth determine bacteria risk in my SC well?

Bacteria in drinking water almost always enter from the surface: animal waste, septic effluent, agricultural runoff, or floodwater carrying soil organisms. The critical variable is how many feet of soil and rock separate a well's intake from that surface source, and whether the aquifer formation is confined (sealed above and below by clay or rock) or unconfined (open to surface water percolation).

The USGS National Water Quality Assessment Program (NAWQA), which has studied SC coastal plain groundwater for decades, identifies three distinct aquifer systems relevant to private wells in Solomon's service area:

• Surficial aquifer: Shallow unconfined sand and gravel, typically 10 to 80 feet deep. No confining layer above it. Rainwater and surface runoff recharge it directly. Highest inherent bacteria vulnerability. Common in coastal Horry, Georgetown, and low-lying areas of Beaufort, Colleton, and Berkeley counties.
• Black Creek aquifer: Confined sand unit, typically 150 to 400 feet below surface in the Grand Strand and Pee Dee region. The overlying clay layer substantially reduces bacteria infiltration risk, though iron and hydrogen sulfide are common quality issues. Prevalent in Horry, Georgetown, and Williamsburg counties.
• Floridan Aquifer System: Deep carbonate and sand formation, 200 to 600 feet in coastal SC. Artesian pressure in many zones pushes water upward, which means the well casing operates under positive pressure that resists surface infiltration. Predominant source in Beaufort, Jasper, Hampton, and Colleton counties. Bacteria risk is primarily a well casing and grouting issue, not an aquifer quality issue, at this depth.

Sources: USGS Water Resources Investigations Report 03-4256 "Hydrogeology of the Coastal Plain of South Carolina"; USGS NAWQA Coastal Plain Principal Aquifer Systems data portal (https://water.usgs.gov/nawqa/); SCDES Private Drinking Water Wells program (https://www.scdhec.gov/environment/water/private-drinking-water-wells).

What does the county-level bacteria risk look like across Solomon's service area?

The table below compiles USGS aquifer system mapping, published well depth ranges from SC DHEC/SCDES permitting data, and SCDES testing guidance into a county-level reference. Risk ratings reflect inherent aquifer vulnerability based on confinement and depth, not measured contamination rates in any specific year. An individual well's actual risk also depends on construction quality, casing integrity, and proximity to contamination sources.

Note: Many cities in Solomon's 20-city service area (Charleston, North Charleston, Mount Pleasant, Summerville, Goose Creek, Hanahan, Bluffton, Hilton Head Island, Myrtle Beach, North Myrtle Beach, Surfside Beach, Pawleys Island, Conway, Georgetown city, Port Royal, Beaufort city) are served by BJWSA, Charleston Water System, Mount Pleasant Waterworks, or GSWSA municipal water and do not use private wells. This table covers outlying and rural private well customers within those same counties and surrounding areas.

How was this data compiled?

This analysis draws on three primary public sources. USGS National Water Quality Assessment (NAWQA) Program reports on coastal plain aquifer systems in the Carolinas, Georgia, and Virginia provide the aquifer system classifications, typical depth ranges, and confinement characteristics. SC DHEC (now SCDES) private well permitting statistics and technical guidance documents (available at scdhec.gov) provide depth ranges observed in permitted SC wells and the annual testing recommendations. EPA's Ground Water Rule (2006) background documentation provides the framework for understanding how aquifer type relates to microbial contamination risk for groundwater systems (https://www.epa.gov/dwreginfo/ground-water-rule).

The relative risk ratings in Table 1 are qualitative assessments based on hydrogeological factors, specifically aquifer confinement status, depth to water, and proximity to known contamination pathways. They are not county-averaged measured coliform detection rates, because no such consolidated county-level private well coliform dataset is publicly available for SC. Individual well test results from a certified laboratory are always more reliable than generalized risk assessments.

How does hurricane season raise bacteria risk for SC coastal wells?

Flooding is the single most reliable way to spike bacteria counts in a shallow well in a short period of time. When floodwater overtops a wellhead or pools around the casing, contaminated surface water enters directly. SCDES and FEMA both note that wells flooded during a hurricane or tropical storm should be treated as contaminated until tested and cleared (https://www.scdhec.gov, SC Emergency Management Division well recovery guidance).

The critical threshold is whether floodwater reached the well cap or vent opening. A wellhead elevated on a concrete pad with a sealed pitless adapter significantly reduces flood intrusion risk; a buried steel casing with a simple threaded cap at grade in a low-lying coastal yard does not.

Horry and Georgetown counties, which routinely experience tropical storm and hurricane-related flooding given their flat coastal plain topography and proximity to the Grand Strand and Waccamaw River basin, have the highest post-storm recontamination exposure among Solomon's private well service counties. After any named storm, those customers should follow SCDES shock chlorination guidance before resuming use.

See also: Post-Flood Well Disinfection for SC Homeowners and Preparing Your Water System for Hurricane Season.

What does a total coliform test actually measure?

Total coliform is a group of bacteria used as an indicator of whether surface water or soil organisms have entered a water supply. Coliform bacteria themselves may not cause illness, but their presence signals that a contamination pathway exists. The EPA Maximum Contaminant Level for total coliform in public water systems is zero detectable per 100 mL sample (https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations). Private wells are not regulated under the Safe Drinking Water Act, so there is no federal MCL that applies, but SCDES uses the same zero-tolerance standard as a practical guide.

E. coli is a subset of total coliform that specifically indicates fecal contamination. A positive E. coli result is more serious than a positive total coliform result alone and requires immediate action: stop drinking the water, identify the contamination source, shock chlorinate, and retest. SCDES guidance on E. coli in private wells is at scdhec.gov.

Standard certified-lab bacteria testing panels for private wells include total coliform and E. coli. Many SC environmental labs offer this as a basic well water panel. Solomon can refer you to current SC-certified laboratories.

Can UV disinfection permanently protect my well water from bacteria?

UV disinfection systems certified to NSF/ANSI Standard 55 Class A deliver a minimum UV dose of 40 millijoules per square centimeter, sufficient to inactivate E. coli, Giardia, Cryptosporidium, and most waterborne viruses without adding a chemical residual (NSF International, https://www.nsf.org/consumer-resources/articles/uv-water-treatment). Solomon installs systems that achieve 99.99% elimination of bacteria and viruses.

UV is not a substitute for identifying and eliminating the contamination source. A cracked casing, a compromised well cap, or a flooding event that has introduced sediment and organic matter needs to be addressed at the source. But for private well customers in the surficial aquifer zones of Horry and Georgetown counties, where the contamination pathway is geologically inherent, UV adds a permanent disinfection backstop that operates continuously between annual tests.

One technical prerequisite: UV lamp effectiveness drops sharply when UV transmittance is reduced by iron, manganese, tannins, or turbidity in the source water. Coastal SC well water commonly contains iron. Installing a whole-house iron filter before the UV chamber ensures the lamp operates within its rated performance range. See Does a Water Softener Remove Iron from Well Water for background on iron treatment options.

Frequently asked questions about SC well bacteria risk