What’s actually in NJ private well water — a contaminant guide for homeowners

Published by NJ Clean Stream  |  Private Well Contamination Series, Article 2 of 3

If you own a home served by a private well in New Jersey, the single most important thing you can do for your family’s health is test your water — thoroughly, with a certified laboratory, for the right contaminants. This guide explains which contaminants pose the greatest risks in your area, what the results mean, and what to do when problems are found.

Understanding the units

Milligrams per liter (mg/L) equals parts per million. Used primarily for nitrate. Micrograms per liter (μg/L) equals parts per billion (ppb). Used for most chemical contaminants — arsenic, PFAS, VOCs. Picocuries per liter (pCi/L) measures radioactivity. Used for radon. Colony-forming units per 100 milliliters (CFU/100mL) expresses bacteria concentrations. The regulatory standard for public water is zero detectable coliform per 100 milliliters.

Nitrates: the most widespread risk

Nitrate enters groundwater primarily from synthetic nitrogen fertilizers, animal manures, and septic system effluent. In South Jersey’s well-drained, sandy Coastal Plain soils, nitrate moves rapidly from the surface to the water table. The federal MCL for nitrate in public water is 10 mg/L (as nitrogen).

Health effects: Methemoglobinemia (“blue baby syndrome”) in infants under six months — potentially life-threatening. Increased colorectal cancer risk in adults at chronic elevated exposure. Particular concern for pregnant women, immunocompromised individuals, and the elderly.

Below 5 mg/L: Generally low risk. Annual testing appropriate.

5–10 mg/L: Elevated, approaching the MCL. Infants, pregnant women, and immunocompromised individuals should use alternative water or certified treatment.

Above 10 mg/L: Exceeds MCL. Infants must not drink this water or be fed formula prepared with it. All household members should use alternative water or certified treatment immediately.

Treatment: Reverse osmosis (RO) achieves greater than 90 percent nitrate removal. Ion exchange systems are also effective for whole-house treatment. Activated carbon and standard pitcher filters do not remove nitrate.

Arsenic: the silent carcinogen

Arsenic occurs naturally in New Jersey’s geological formations — in Highlands crystalline bedrock, certain Coastal Plain sedimentary units, and specific glacial deposits. It is released from minerals into groundwater through natural geochemical processes. The federal MCL is 10 ppb, but at this concentration the excess lifetime cancer risk is approximately 4 per 1,000 — far higher than the one-in-one-million benchmark used for most contaminants.

Health effects: Bladder cancer, lung cancer, and skin cancer at chronic exposure. Also causes cardiovascular disease, diabetes, and peripheral neuropathy. No threshold below which exposure is entirely safe. Particularly harmful to fetuses and young children.

Below 5 ppb: Relatively low risk, though not zero. Annual testing recommended.

5–10 ppb: Significant cancer risk over a lifetime. Consider treatment, particularly for children, pregnant women, and long-term residents.

Above 10 ppb: Exceeds the public water MCL. Treatment strongly recommended.

Above 50 ppb: High cancer risk. Immediate alternative water source or treatment required. Do not use for drinking or cooking without treatment.

Treatment: Point-of-use reverse osmosis achieves greater than 95 percent arsenic removal. Whole-house adsorptive media systems (iron oxide-based) are also effective. All systems require regular maintenance and media replacement. Have treated water tested annually to confirm performance.

Radon: the invisible gas from your well

Radon is produced by uranium decay in bedrock and dissolves in groundwater. When water is used indoors — showering, dishwashing, laundry — dissolved radon is released into indoor air. New Jersey’s Highlands region has among the highest radon concentrations in indoor air of any state, reflecting the uranium content of its bedrock aquifers. Radon is the second-leading cause of lung cancer in the United States — approximately 21,000 deaths annually.

Below 1,000 pCi/L: Relatively low contribution to indoor radon from water. Focus on air entry through foundation as the primary radon concern.

1,000–4,000 pCi/L: Moderate contribution to indoor radon. Test your home’s indoor air; if air levels exceed 4 pCi/L, water treatment may be warranted.

Above 4,000 pCi/L: Significant radon in water. Point-of-entry treatment is recommended, particularly for homes with indoor air radon levels above 4 pCi/L.

Treatment: Point-of-entry aeration systems — which bubble air through water to strip dissolved radon before it enters the home — achieve greater than 99 percent removal. Granular activated carbon can also adsorb radon but accumulates radioactive decay products requiring specialized disposal.

Coliform bacteria: the indicator of fecal contamination

Total coliform and E. coli are indicator organisms for fecal contamination. Their presence signals the water may contain pathogenic bacteria, viruses, or parasites. Sources in private wells include failing septic systems, agricultural animals, surface water infiltration through deteriorated well casings, and flooding. E. coli specifically confirms recent fecal contamination from warm-blooded animals.

Total coliform absent, E. coli absent: No evidence of fecal contamination. Retest annually and after any flooding or well work.

Total coliform present, E. coli absent: Possible contamination. Resample immediately. If confirmed, investigate the source and consider shock chlorination.

E. coli present: Confirmed fecal contamination. Do not drink without treatment. Boil water immediately. Shock chlorinate the well. Investigate the source. If contamination recurs, structural well repair or replacement may be necessary.

Treatment: Ultraviolet disinfection systems at the point of entry effectively inactivate bacteria, viruses, and protozoa without adding chemicals. Continuous chlorination is also effective. Neither addresses chemical contamination — combined treatment trains are needed if both microbiological and chemical contamination are present.

PFAS: the emerging well water threat

PFAS contamination from military installations and industrial sources has affected private wells in multiple New Jersey communities. The aquifer contamination from PFAS use at military airfields does not stop at public water service area boundaries. Private well users in communities surrounding military installations in Burlington and Ocean counties have documented PFAS contamination with no regulatory requirement to test, no notification, and no mandatory remediation.

The EPA finalized MCLs for PFAS in public drinking water in 2024 at 4 parts per trillion for PFOA and PFOS. New Jersey had previously set its own standards at 13 parts per trillion. For private wells near potential PFAS sources, test using EPA Method 533 or 537.1 and treat any detectable PFAS using certified treatment systems. Treatment: Granular activated carbon and reverse osmosis are both effective for PFAS removal. Filter media must be replaced on schedule to maintain effectiveness.

Volatile organic compounds: industrial sources

Solvents like PCE, TCE, TCA, and benzene have been used extensively in dry cleaning, manufacturing, metal degreasing, and automotive repair. When released to the environment, they move through soil into groundwater, forming plumes that extend far from the source. Most VOCs of concern are classified as possible or probable human carcinogens. Treatment: Granular activated carbon at the point of entry is effective for most VOC removal. Point-of-use activated carbon filters provide treatment at drinking taps but do not address inhalation exposure from showering.

A practical testing strategy for NJ private well owners

  • Annual baseline testing: Total coliform bacteria, E. coli, nitrate, and pH. Cost typically $50–$150 at a certified laboratory. Provides early detection of the most common and immediately actionable problems.
  • Every 3–5 years: Expand to include arsenic, lead, iron, manganese, hardness, and the standard VOC panel. Add radon if you are in the Highlands or northern NJ counties.
  • Location-based testing: PFAS if near a military installation or airport. 1,4-dioxane if near an industrial site, dry cleaner cluster, or Superfund site. Pesticides if in an agricultural area.
  • After any flood event: Retest for coliform bacteria before resuming well water use. After any nearby industrial incident or spill, contact the NJ DEP for guidance on what to test for.

Always use a NJ DEP-certified laboratory. A list of certified laboratories is available from the NJ DEP’s Division of Environmental Measurement and Site Assessment.

This is Article 2 of 3. Article 1 explains the scope of private well use in NJ and the regulatory vacuum. Article 3 examines the gaps in New Jersey’s Private Well Testing Act and the policy changes needed to protect well owners.