Well water in Mendham township, New Jersey
In Mendham township, 22% of 532 private wells tested between 2002 and 2024 had total coliform above the New Jersey limit (any detection), according to NJDEP.
532 private wells tested 2002 to 2024 in state summaries; 7 individual samples from 5 wells, 1990 to 2007. 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.
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What this means
Among homeowners in Mendham township who sent a sample to the state lab, the health-based limits most often exceeded were total coliform (22% of 532 wells), PFOS (4% of 70 wells), and PFOA (3% of 70 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 exceeds the state's advisory level in a sizable share of wells; this is mostly a taste, staining or diet issue rather than a toxicity one.
What to test for in Mendham township
- Iron23% of 532 local wells tested were above the New Jersey nuisance level.
- Total coliform22% of 532 local wells tested were above the New Jersey limit (any detection).
- Manganese9% of 532 local wells tested were above the New Jersey nuisance level.
- Gross alpha7% of 176 local wells tested were above the New Jersey limit.
- PFOS4% of 70 local wells tested were above the New Jersey limit.
- PFOA3% of 70 local wells tested were above the New Jersey limit.
- E. coli2% of 532 local wells tested were above the New Jersey limit (any detection).
- Arsenic<1% of 532 local wells tested were above the New Jersey limit.
Contamination sources on record in Mendham township
NJDEP records 15 regulated sites in Mendham township, among 15 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.
- 14
- registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
- 1
- other remediation project
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
- Gross alpha
- Point-of-use reverse osmosis; Water softener (cation exchange) for radium; Anion exchange for uranium
- 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
- Radon
- Aeration (bubble-up or diffused) whole-house; Granular activated carbon whole-house (lower levels only)
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Common questions
Is there arsenic in well water in Mendham township?
Arsenic was detected in 0% of 7 public well samples in Mendham township, 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 Mendham township?
The median radon level across 3 public samples in Mendham township was 2,360 pCi/L, with a high of 2,470 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Mendham township?
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.
Sources
- USGS Water Quality Portal: 15 samples in Mendham township. 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 11 contaminants in Mendham township, up to 532 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: 15 regulated sites located in Mendham township. 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.