Well water in Monmouth County, New Jersey
In Monmouth County, 11% of 7,572 private wells tested between 2002 and 2024 had total coliform above the New Jersey limit (any detection), according to NJDEP.
7,586 private wells tested 2002 to 2024 in state summaries; 153 individual samples from 58 wells, 1951 to 2025. Data refreshed September 9, 2026.
What homeowner tests found
NJDEP Private Well Testing Act summaries: private wells tested and reported to the state, 2002 to 2024. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.
| Contaminant | Wells tested | Above state level | Median | 95th pct | Highest | State level | |
|---|---|---|---|---|---|---|---|
| Iron | 7,582 | 74% | 300 ug/L | ||||
| Manganese | 7,582 | 39% | 50 ug/L | ||||
| Total coliform | 7,572 | 11% | |||||
| Gross alpha | 6,917 | 2% | 15 pCi/L | ||||
| PFOA | 677 | 1% | 14 ng/L | ||||
| E. coli Fecal coliform or | 7,568 | <1% | |||||
| Nitrate | 7,586 | <1% | 10 mg/L | ||||
| Arsenic | 2,136 | <1% | 5 ug/L | ||||
| PFOS | 677 | <1% | 13 ng/L | ||||
| PFNA | 677 | <1% | 13 ng/L |
What individual samples found
Each row summarizes every public sample for that contaminant inside Monmouth County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| PFOA 2021 to 2024 | 24 | 58% | 46% | 2.55 | 16 | 4 ng/L EPA limit | |
| PFOS 2021 to 2024 | 23 | 48% | 13% | 0 | 10 | 4 ng/L EPA limit | |
| Radium (226 + 228) 2000 to 2012 | 26 | 92% | 4% | 0 | 5.1 | 5 pCi/L EPA limit | |
| Arsenic 1977 to 2025 | 153 | 45% | 0% | 0 | 2.6 | 10 ug/L EPA limit | |
| Uranium 2008 to 2012 | 12 | 67% | 0% | 0.01 | 0.145 | 30 ug/L EPA limit |
Sampled fewer than 10 times, too few to summarize: Fluoride (3), Lead (3), Copper (3), Nitrate (3), Manganese (7), Radon (6), Chloride (5), Sodium (4), Iron (1).
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What this means
Among homeowners in Monmouth County who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (11% of 7,572 wells), PFOA (1% of 677 wells), and E. coli (<1% of 7,568 wells). These are ordinary wells tested by their owners, so the shares are the best available picture of a typical well here, with one caveat: people test more often when they suspect a problem.
Iron and manganese exceed the state's advisory level in a sizable share of wells; these are mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Monmouth County
- Volatile organic compounds (VOCs)9 hazardous waste sites on record locally.
- Metals panel9 hazardous waste sites on record locally.
- Iron74% of 7,582 local wells tested were above the New Jersey nuisance level.
- Manganese39% of 7,582 local wells tested were above the New Jersey nuisance level.
- Total coliform11% of 7,572 local wells tested were above the New Jersey limit (any detection).
- Radium (226 + 228)4% of 26 local samples were above the limit.
- Gross alpha2% of 6,917 local wells tested were above the New Jersey limit.
- E. coli<1% of 7,568 local wells tested were above the New Jersey limit (any detection).
- Nitrate<1% of 7,586 local wells tested were above the New Jersey limit.
- Arsenic<1% of 2,136 local wells tested were above the New Jersey limit.
Contamination sources on record in Monmouth County
NJDEP records 9 hazardous waste sites in Monmouth County, among 3,319 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 9
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 2,546
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 26
- lined landfills and transfer facilities
- 738
- other remediation projects
Treatment that fits the local profile
- Total coliform
- Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
- Manganese
- Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
- PFOA
- Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
- PFOS
- Granular activated carbon whole-house; Point-of-use reverse osmosis; Anion exchange
- Radium (226 + 228)
- Water softener (cation exchange); Point-of-use reverse osmosis
Get your Monmouth County water tested at home
A licensed local water treatment company tests your tap water in your home, walks you through the numbers, and quotes treatment only if something needs fixing. Free, about 30 minutes, no obligation. Tell us what you need and we match you with a company that serves Monmouth County.
Common questions
Is there arsenic in well water in Monmouth County?
Arsenic was detected in 45% of 153 public well samples in Monmouth County, and 0% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Monmouth County?
The median radon level across 6 public samples in Monmouth County was 92.5 pCi/L, with a high of 170 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Monmouth County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Towns in Monmouth County
- Colts Neck township10% total coliform
- Freehold township8% total coliform
- Howell township9% total coliform
- Manalapan township9% total coliform
- Marlboro township12% total coliform
- Middletown township10% total coliform
- Millstone township13% total coliform
- Tinton Falls borough9% total coliform
- Upper Freehold township14% total coliform
- Wall township8% total coliform
43 towns have fewer than 30 public samples and are included in the Monmouth County totals above rather than shown separately: Aberdeen township, Allenhurst borough, Allentown borough, Asbury Park, Atlantic Highlands borough, Avon-by-the-Sea borough, Belmar borough, Bradley Beach borough, Brielle borough, Deal borough, Eatontown borough, Englishtown borough, Fair Haven borough, Farmingdale borough, Freehold borough, Hazlet township, Highlands borough, Holmdel township, Interlaken borough, Keansburg borough, Keyport borough, Lake Como borough, Little Silver borough, Loch Arbour village, Long Branch, Manasquan borough, Matawan borough, Monmouth Beach borough, Neptune City borough, Neptune township, Oceanport borough, Ocean township, Red Bank borough, Roosevelt borough, Rumson borough, Sea Bright borough, Sea Girt borough, Shrewsbury borough, Shrewsbury township, Spring Lake borough, Spring Lake Heights borough, Union Beach borough, West Long Branch borough.
Sources
- USGS Water Quality Portal: 273 samples in Monmouth County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- NJDEP Private Well Testing Act summaries: summaries for 10 contaminants in Monmouth County, up to 7,586 wells each. Share of private wells exceeding each standard in tests required at sale or lease under the New Jersey Private Well Testing Act, September 2002 to December 2024, published by NJDEP. Tests are untreated water at the time of sale or lease, so every well is counted once per transaction. Municipalities with fewer than ten wells are suppressed. Standards are New Jersey's: arsenic 5 ug/L, PFOA 14 ng/L, PFOS 13 ng/L, PFNA 13 ng/L, manganese and iron secondary standards. Uranium and PFAS were added to the required panel in 2021 and 2020, so their well counts are smaller. Retrieved September 9, 2026.
- NJDEP regulated sites: 3,319 regulated sites located in Monmouth County. Known Contaminated Sites, regulated underground storage tank facilities and solid waste landfills from the New Jersey Department of Environmental Protection (NJ-GeoWeb). Retrieved September 9, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.