Manganese in Coastal SC Well Water: A 2026 County Risk Guide from USGS Aquifer Data

What manganese is and why coastal SC aquifers have it

Manganese is a naturally occurring trace metal found in the minerals and sedimentary rocks that make up aquifer formations throughout the South Carolina Coastal Plain. Under normal aerobic (oxygen-rich) conditions, manganese forms insoluble oxides and stays bound to soil particles. The problem for well owners is that many of the aquifers supplying private water wells across coastal SC are not aerobic.

The coastal plain geology from Myrtle Beach south through Beaufort and Jasper Counties includes thick layers of organic material: peat deposits, dark organic clays, and marsh sediments that formed over thousands of years in low-lying coastal environments. When groundwater moves through these sediments, microbial activity consumes the available dissolved oxygen, and the environment becomes reducing (anaerobic). Under reducing conditions, manganese minerals dissolve and enter the water as soluble ionic manganese. This process is well-documented in USGS groundwater quality literature covering coastal plain aquifer systems, including the South Atlantic Coastal Plain aquifer systems that underlie South Carolina.

The USGS National Water Information System (NWIS) holds decades of groundwater quality measurements from monitoring wells and domestic wells across South Carolina. Data from this system, combined with USGS NAWQA coastal plain aquifer assessments, forms the basis for the county risk classifications in this guide.

Manganese in coastal SC well water is not a contamination event or a spill. It is geochemistry. That distinction matters for treatment: you cannot fix it by changing anything at the surface. The source is in the aquifer, and treatment happens at the point of use.

EPA and WHO standards for manganese in drinking water

The regulatory picture for manganese is more complicated than for contaminants like nitrate or PFAS, where a single enforceable Maximum Contaminant Level governs public water systems and sets the benchmark for private wells. Manganese has two separate standards, and neither is enforceable for private wells, which are not regulated under the Safe Drinking Water Act. Private well owners are responsible for their own testing and treatment.

• EPA Secondary MCL: 0.05 mg/L. The Secondary Maximum Contaminant Level is an aesthetic guideline, not a health standard. At concentrations above 0.05 mg/L, manganese causes black or dark brown staining on fixtures and laundry, a metallic or musty taste, and dark sediment in toilet tanks. The SMCL is the threshold at which most people begin noticing water quality problems. Source: EPA Secondary Drinking Water Standards.
• EPA 2004 Health Advisory: 0.3 mg/L. The EPA issued a lifetime health advisory in 2004 recommending 0.3 mg/L as a protective benchmark for adults. The advisory specifically flags concern for infants under one year of age whose formula is mixed with well water: developing neurological systems are more sensitive to manganese than adult systems. Source: ATSDR Toxicological Profile for Manganese.
• WHO Guideline Value: 0.4 mg/L. The World Health Organization sets a guideline value of 0.4 mg/L based on neurological endpoints in adults. This is a health-based guideline rather than an enforceable limit.

In practice: well water at 0.05 to 0.3 mg/L will stain and taste off, and merits treatment. Well water above 0.3 mg/L should be treated before use for drinking or cooking, particularly if infants or young children live in the home. Well water above 0.4 mg/L warrants prompt treatment for any occupant.

For reference, USGS Circular 1360 (DeSimone et al., 2014, Water Quality in Principal Aquifers of the United States) found that 37 percent of domestic wells nationally had manganese detections above the 0.05 mg/L secondary MCL. Coastal plain aquifer systems, where reducing conditions are common, run above that national average.

How to identify manganese problems in your home

Manganese leaves a distinctive signature in a household that is often mistaken for iron or mold. Knowing which staining pattern you are looking at helps narrow the treatment approach before you spend money on the wrong system.

• Black or dark brown staining on fixtures. Iron staining is orange or reddish-brown. Manganese staining is distinctly dark: black rings in toilets, dark brown or black streaks in sinks, and grayish-black buildup on faucet aerators. If you are seeing black, manganese is the first thing to test for.
• Black flecks in the toilet tank. The still water in a toilet tank oxidizes dissolved manganese over time, depositing black particulate on the tank interior. Homeowners often call this "black mold," but the pattern is distinct: gritty black sediment, not fuzzy growth.
• Dark laundry staining. Gray or black streaks on white laundry after washing with well water containing elevated manganese. The staining is worse when the water heater is involved because heat can accelerate oxidation.
• Metallic or astringent taste. Water with manganese above 0.05 mg/L often has a distinct metallic or slightly bitter taste, particularly noticeable in coffee or ice cubes. Iron produces a more pronounced metallic taste; manganese is often described as astringent or earthy.
• Filter plugging. Sediment cartridge filters on well systems turning black or dark gray within a few weeks of installation suggest oxidized manganese particulate in the water.

Visual symptoms point you toward the problem, but a certified lab test is the only way to confirm concentration and size treatment correctly. Our SCDES private well testing guide covers which labs are certified in South Carolina and what a standard panel costs.

County-level manganese risk across coastal SC

The table below classifies manganese risk by county based on the documented geology and reducing conditions of the aquifer systems most commonly used for private well water supply in Solomon's coastal SC service area. Risk ratings represent the geological potential for elevated manganese, not a measured average for any county as a whole. Individual wells vary, and testing your specific well is the only way to know your concentration.

The county classifications above align with the broader USGS finding that reducing conditions in coastal plain aquifer sediments are a primary driver of manganese in domestic wells nationally. The specific organic-rich geology of Horry and Georgetown Counties, combined with high rates of private well use in rural and suburban Grand Strand and Pee Dee areas, makes those two counties the highest-priority targets for manganese testing among SC well owners.

Which wells carry the highest manganese risk by aquifer type

County geography tells part of the story. Aquifer type tells the rest. In coastal SC, private wells draw from several distinct aquifer systems, each with different manganese characteristics.

• Surficial aquifer (shallow, unconfined). The surficial aquifer is the shallowest groundwater zone, often 10 to 60 feet below land surface across the coastal counties. Wells in this aquifer in areas with significant organic soil cover, marshland adjacency, or peat layers are at highest manganese risk. The water table fluctuates with rainfall, which can cause manganese concentrations to vary seasonally. These wells also carry higher bacteria and nitrate risk (see our bacteria risk by county guide and nitrate county risk guide).
• Black Creek aquifer (confined, 200 to 500 ft). The Black Creek is a major confined aquifer supplying private wells and some municipal systems across Horry, Georgetown, Florence, and Williamsburg Counties. Confined aquifers are isolated from surface recharge and typically have anoxic (low oxygen) conditions because the water has been in the ground for a very long time. Manganese and iron are both commonly elevated in the Black Creek. It also carries documented elevated fluoride in Horry and Georgetown Counties, covered in our Black Creek and Middendorf aquifer guide.
• Charleston and Gramling aquifers (confined). The Charleston aquifer serves much of Charleston County's private well population. Manganese in this system varies by location. The 2020 USGS assessment of the Charleston aquifer (referenced in our saltwater intrusion guide) mapped chloride distribution but also documented variable secondary contaminants including iron and manganese in some monitoring wells.
• Floridan aquifer (deep, limestone). The Floridan is a deep karstic limestone aquifer that supplies some wells in Beaufort, Jasper, and parts of Colleton County. Manganese is less commonly elevated in the Floridan than in the shallower coastal plain units because limestone systems are less organic. However, Floridan wells in SC are not uniform; local conditions matter, and testing is still warranted.
• Alluvial deposits near river corridors. Wells drilled into alluvial sands and gravels adjacent to the Waccamaw, Pee Dee, Black, and Edisto Rivers often encounter high iron and manganese because these floodplain deposits are organically rich and strongly reducing. Georgetown County well owners near river corridors fall into this category.

Our coastal SC well water treatment pillar covers the full spectrum of contaminants by aquifer type for homeowners who want a single reference on the wells in this region.

What removes manganese from well water

Manganese treatment is chemistry-dependent in a way that iron treatment is not always. The treatment path depends on whether manganese is dissolved (ionic, clear water) or oxidized (particulate, discolored water), and on the concentration, pH, and iron levels present. A free in-home test before any equipment selection is not optional: the wrong system for the chemistry will fail quickly or not work at all.

• Oxidation filtration (greensand, birm, or catalytic carbon). Manganese above about 0.05 mg/L is most reliably removed with an oxidation media filter. Greensand (coated glauconite) and birm (diatomite-based media) oxidize dissolved manganese to the insoluble form and then filter it out. Catalytic carbon media can also oxidize manganese while simultaneously addressing chlorine and organics. These systems are the standard whole-house solution for moderate to high manganese. We size them based on the measured manganese concentration and flow rate demand for your household. See our overview of whole-house water filtration for system types.
• Air injection oxidation. For wells with high combined iron and manganese, an air injection system introduces oxygen directly into the pressure tank to oxidize both metals before they enter the home's plumbing. The oxidized particles are then trapped by a downstream filter media tank. Our iron removal guide and the iron in well water article cover the air injection approach for combined iron and manganese situations.
• Cation exchange softener (limited). A water softener will remove dissolved (ionic) manganese below about 0.3 to 0.5 mg/L as a side effect of softening. Above that level, or where manganese is already partially oxidized to particulate form, the softener resin will foul. If you have a softener installed and it is fouling faster than expected, manganese in the incoming water is one of the first things to check. Our water softening service page covers when softeners are and are not the right first step.
• Reverse osmosis (point-of-use). An NSF/ANSI 58-certified RO system at the kitchen tap reduces dissolved manganese to very low levels at the point of drinking and cooking. RO is most useful as a second stage when the whole- house system handles the bulk manganese load and you want an extra reduction step at the kitchen sink. Our RO drinking water pillar covers system selection and certification. Under-sink drinking water systems are a common add-on for well households that install a whole-house filter for manganese and iron but want verified kitchen-tap quality for drinking and baby formula.

pH matters in manganese treatment. Most oxidation media systems work best at pH 7.0 or above. Coastal SC well water is often on the acidic side (pH 6.0 to 6.8) due to high organic acid content from the same organic sediments that drive reducing conditions. An acidic well may need pH adjustment (calcite neutralizer or soda ash injection) upstream of the manganese filter for the media to perform correctly.

When and how to test for manganese

Private wells in South Carolina are not tested automatically. Testing is the owner's responsibility. There is no state requirement to test a private well on any schedule, though SCDES recommends annual testing for standard parameters.

The SCDES private well testing framework, explained in detail in our SCDES well testing guide, identifies manganese as part of the secondary contaminant panel recommended for coastal plain wells in areas with known reducing conditions. If you are in Horry, Georgetown, Beaufort, or Jasper County and have a private well, include manganese in your next test order.

When to trigger a manganese test:

• You are new to a property with an existing well and have not seen the most recent test results.
• You are seeing black or dark brown staining that you have not traced to a confirmed source.
• A sediment filter on your system is turning black within weeks of installation.
• Laundry is coming out with grayish discoloration that does not respond to increased detergent.
• You have an infant in the household whose formula is mixed with well water.
• You have made any changes to the well, pressure tank, or wellhead that could affect water quality.

What to test for alongside manganese:

Manganese in reducing-condition well water rarely appears alone. A complete panel for coastal SC well water should include manganese, iron, pH, total hardness, total dissolved solids, coliform bacteria, nitrate, and sulfide. For wells in high-risk areas for secondary contaminants, add fluoride (Horry and Georgetown Counties specifically, given the Black Creek and Middendorf aquifer elevated fluoride documented in our aquifer fluoride and radium guide) and arsenic.

For context on what USGS has found in SC domestic well water more broadly, the USGS National Water-Quality Assessment Program (NAWQA, usgs.gov NAWQA) publishes assessment data for coastal plain aquifer systems that is publicly searchable through the NWIS portal. This data is the backbone of the county risk classifications in this article.

Our complete coastal SC well water treatment guide and the well vs. city water comparison are useful reference points if you are deciding whether to treat your well water or connect to municipal service where it is available in your area. The Solomon service area covers all 20 cities across coastal SC where we perform free water tests and system installations.