Well water in Merrimack, New Hampshire

In Merrimack, 3% of 242 private wells tested between 2006 and 2020 had arsenic above the New Hampshire guidance level (5 ug/L), according to NH DHHS.

The strongest signal is PFOA: 50% of 204 local samples were above the limit, too few samples to carry the headline but first on the test list below.

269 private wells tested 2006 to 2020 in state summaries; 889 test results across 13 contaminants from at least 98 wells, 1963 to 2025; PFOA has the most at 204. Data refreshed September 3, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

NHDES samples private wells near known or suspected PFAS sources (industrial sites, airports, landfills, fire training areas), and wells with a detection are resampled over time. PFAS shares describe wells that were tested for a reason, not every well in the area. In that targeted sampling, 50% of 204 PFOA results in Merrimack were above the EPA limit of 4 ng/L. In that targeted sampling, 9% of 204 PFOS results in Merrimack were above the EPA limit of 4 ng/L.

Separately, a USGS and NHDES statistical model puts the chance that a bedrock well in Merrimack exceeds 5 ug/L of arsenic at 20% (as low as 0% in parts of town), based on geology rather than tests.

What homeowner tests found

NH DHHS WISDOM private well summaries: private wells tested and reported to the state, 2006 to 2020. Shares are against the level the state applies to each contaminant, named in the last column; several are stricter than EPA.

Contaminant	Above state level	Wells tested	Median	95th pct	Highest	State level
Sodium	37%	241	15	71	160	20 mg/L
Lead (stagnant)	21%	24	4.1	25.1	30.4	15 ug/L
Iron	8%	241	0	800	18,000	300 ug/L
Copper (stagnant)	8%	24	0.1	1.3	3.6	1.3 mg/L
Manganese	3%	241	0	200	1,000	300 ug/L
Arsenic	3%	242	0.2	2.8	15	5 ug/L
Uranium	2%	241	1.9	15	81	30 ug/L
Chloride	2%	243	27	119	380	250 mg/L
Fluoride	<1%	269	0.1	1.1	7	4 mg/L
Nitrate	0%	31	0.5	3.3	5.9	10 mg/L
Nitrite	0%	31	0	0	0.1	1 mg/L

What individual samples found

Each row summarizes every public sample for that contaminant inside Merrimack. 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	Above limit	Samples	Detected	Median	Highest	Limit
PFOA 2020 to 2025	50%	204	91%	3.95	45	4 ng/L EPA limit
PFOS 2020 to 2025	9%	204	67%	0.69	24	4 ng/L EPA limit
PFHxS 2020 to 2025	<1%	204	64%	0.425	19	10 ng/L EPA limit
PFNA 2020 to 2025	0%	194	12%	0	0.67	10 ng/L EPA limit
Iron 1963 to 2012	no limit	21	86%	40	3,000	300 ug/L nuisance level
Chloride 1963 to 1970	no limit	20	100%	7.65	259	250 mg/L nuisance level
Manganese 1963 to 2012	no limit	10	90%	30	240	300 ug/L health guideline

Sampled fewer than 10 times, too few to summarize: Nitrate (7), Fluoride (7), Lead (3), Uranium (3), Arsenic (3), Sodium (9).

Closer than the town

See the sampled wells near your address

The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.

Check my address

What this means

Among homeowners in Merrimack who sent a sample to the state lab, the health-based limits most often exceeded were lead (21% of 24 wells), copper (8% of 24 wells), and arsenic (3% of 242 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.

Sodium 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 Merrimack

1
PFOA
50% of 204 local samples were above the limit.
2
Lead
21% of 24 local wells tested were above the New Hampshire guidance level.
3
PFOS
9% of 204 local samples were above the limit.
4
Copper
8% of 24 local wells tested were above the New Hampshire guidance level.
5
Arsenic
3% of 242 local wells tested were above the New Hampshire guidance level.
6
Uranium
2% of 241 local wells tested were above the New Hampshire guidance level.
7
Fluoride
<1% of 269 local wells tested were above the New Hampshire guidance level.
8
PFHxS
<1% of 204 local samples were above the limit.
9
Volatile organic compounds (VOCs)
13 leaking underground storage tank sites on record locally.
10
PFAS
2 unlined landfills on record locally.
11
Metals panel
15 hazardous waste sites on record locally.

Test your Merrimack well for PFOA, lead and PFOS

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209 Already tested? Upload the report

Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.

Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.

Where to get a well tested in New Hampshire: certified labs, state programs and prices.

Already have results back? Get your lab report read against the Merrimack numbers, $29. Every line explained, ranked by what matters, with the fix for each.

Wells in Merrimack

569 domestic wells in Merrimack are on record with the state since 1984. 99% are drilled into bedrock, and the typical well is 305 feet deep (one in ten goes past 668 feet).

In a typical Merrimack well, bedrock starts about 16 feet down, the median yield is 6 gallons per minute, 24% of wells yield under 3 gallons per minute and usually need a storage tank.

Bedrock wells are where arsenic, uranium and radon come from: the water sits in fractures in granite and metamorphic rock and picks up whatever the rock carries. That is why testing for those three matters more here than in a dug or gravel well.

256

1980s

149

1990s

2000s

2010s

2020s

Find your own well's report

The state keeps the driller's report for most wells drilled since 1984. It tells you how deep your well is, where bedrock starts, and how much water it makes, which decides what treatment can work.

Open NHDES OneStop and choose Water Well.
Enter your town and one word of your street name. Leave out the house number and the Road or Street part; a short search matches more.
In the results, click Show for your address to see the report: total depth, depth to bedrock, casing, yield in gallons per minute, static water level, and the driller.
Save Results exports the whole list to a spreadsheet.

Reports exist only for wells drilled since January 1984, when reporting became mandatory, and street names are as they were when the well was drilled.

The rock under Merrimack

Not a principal aquifer

The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the town centroid. A single well can sit in a different unit, especially near a boundary.

Official help in New Hampshire

Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.

Private Wells, NHDES
New Hampshire Environmental Laboratory Accreditation Program, NHDES

Contamination sources on record in Merrimack

NHDES records 13 leaking underground storage tank sites, 2 unlined landfills, 15 hazardous waste sites, and 17 reported spills and releases in Merrimack, among 199 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.

13: leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
2: unlined landfillsOlder unlined landfills are a leading source of PFAS, VOCs and metals in nearby wells.
15: hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
17: reported spills and releasesMost spills are fuel; a few are solvents or chemicals that reach the water table.
52: registered underground storage tank sitesRegistered tanks are regulated and inspected; they matter most when they are old or near a shallow well.
28: locally identified potential contamination sourcesTowns inventory these (vehicle repair, labs, salt piles, farms) when they draw wellhead protection maps.
69: other remediation projects
3: other solid waste facilities

Treatment that fits the local profile

Lead

Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching

Copper

Neutralizing filter to raise pH; Point-of-use reverse osmosis

Sodium

Point-of-use reverse osmosis; Distillation

Iron

Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration

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

Systems we would look at first

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For lead

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For lead

Acid neutralizing filter

whole-house, at the point of entry, about $1,200

Raises pH so plumbing stops leaching lead and copper.

For lead

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

For iron

Iron and manganese oxidizing filter

whole-house, at the point of entry, about $1,800

Air-injection or greensand media; fixes staining at the source.

For PFOA

Aquasana Claryum 3-Stage under-sink filter

under-sink or countertop, about $175

Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.

For PFOA

Whole-house PFAS carbon system

whole-house, at the point of entry, about $3,000

Granular activated carbon certified to NSF/ANSI 53 for PFOA and PFOS; replace media on schedule.

For PFOA

Aquasana HealthShield whole-house filter

whole-house, at the point of entry, about $2,099

Whole-house carbon system the maker certifies to reduce PFAS (PFOA and PFOS) and VOCs at every tap; a UV option adds bacteria protection.

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Common questions

How deep are wells in Merrimack?

The typical domestic well in Merrimack is 305 feet deep, based on 569 wells reported to the state since 1984. One in ten is deeper than 668 feet. 99% are drilled into bedrock.

How often should I test a private well in Merrimack?

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 near Merrimack

Closest first. Groundwater does not stop at a line on a map, so the next town over is a fair second opinion.

Want the numbers themselves? Download the New Hampshire dataset as CSV, every county and town, with the sources named.

Sources

NHDES PFAS sampling: 806 samples in Merrimack. PFAS results for private wells from the New Hampshire Department of Environmental Services Environmental Monitoring Database. Retrieved September 3, 2026.
USGS Water Quality Portal: 83 samples in Merrimack. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
NH DHHS WISDOM private well summaries: summaries for 11 contaminants in Merrimack, up to 269 wells each. Town summaries of private well tests run by the New Hampshire Public Health Laboratories, published by NH DHHS through the WISDOM environmental public health tracking portal. Exceedance shares use New Hampshire guidance levels, which are stricter than EPA for arsenic (5 ug/L), manganese (0.3 mg/L), radon (2,000 pCi/L) and sodium (20 mg/L). Statistics for small counts are suppressed (*). Retrieved September 3, 2026.
NH DHHS WISDOM private well summaries: modeled chance (20%) that a well in Merrimack exceeds 5 ug/L of arsenic, from geology rather than tests. Town summaries of private well tests run by the New Hampshire Public Health Laboratories, published by NH DHHS through the WISDOM environmental public health tracking portal. Retrieved September 3, 2026.
NHDES Water Well Inventory: 701 well records in Merrimack, 569 domestic. Well construction records reported to the New Hampshire Department of Environmental Services Water Well Board. Only aggregates are shown; owner names and addresses are never stored. Retrieved September 3, 2026.
NHDES OneStop regulated sites: 199 regulated sites located in Merrimack. Remediation sites, underground storage tanks, solid waste facilities and potential contamination sources from the New Hampshire Department of Environmental Services OneStop database. Retrieved September 3, 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.