Well Water in Merrimack, New Hampshire
Hillsborough County · Population ~26,000 · Aquifer: Glacial Till / Bedrock
Hardness: Moderate to Hard
Merrimack is the epicenter of New Hampshire's PFAS crisis. Saint-Gobain Performance Plastics has operated here since 1985, releasing PFAS compounds that contaminated groundwater across a massive plume affecting thousands of private wells. The state has been testing and providing bottled water and treatment systems to affected residents, but the contamination is ongoing and widespread.
The PFAS Crisis
In 2016, NH DES confirmed that Saint-Gobain Performance Plastics had contaminated groundwater across Merrimack with PFAS (per- and polyfluoroalkyl substances). The contamination plume extends for miles, affecting residential wells throughout the town.
New Hampshire has some of the strictest PFAS standards in the country:
- PFOA: 12 parts per trillion (ppt) — the EPA guideline was 70 ppt until 2024
- PFOS: 15 ppt
- PFHxS: 18 ppt
- PFNA: 11 ppt
At these strict levels, 27% of tested wells near contamination sites exceed NH standards. If you're on a well in Merrimack, PFAS testing is not optional — it's essential.
What the State Is Doing
NH DES has been actively responding to the Merrimack PFAS contamination:
- Free PFAS testing for wells within the investigation area
- Bottled water provided to homes exceeding NH PFAS standards
- Whole-house treatment systems installed at state expense for affected homes
- Ongoing monitoring of the contamination plume
Saint-Gobain has been required to fund much of the response, but the process is slow and not every affected well has been identified yet.
Beyond PFAS: Other Concerns
PFAS dominates the headlines, but Merrimack wells face other issues common to NH's granitic geology:
- Arsenic — naturally occurring in bedrock. ~30% of NH wells exceed the EPA standard. See our arsenic guide.
- Radon — dissolved in groundwater from granite. Can off-gas during showering. See our radon guide.
- Manganese — causes black staining, metallic taste
A comprehensive test should cover PFAS and the standard suite of contaminants.
What Merrimack Residents Should Do
If you haven't had your well tested for PFAS, contact NH DES immediately — testing may be free if you're within the investigation area. Even if you're outside the known plume, PFAS can travel farther than initial models predict.
Also test for arsenic, radon, bacteria, nitrates, manganese, and hardness. See our testing guide for labs and costs.
If your water exceeds any standards, you may be eligible for NH's well water treatment rebate program — up to $5,000-$10,000 toward a treatment system.
NH Treatment Rebates: If your well water exceeds any health-based standards, you may be eligible for $5,000-$10,000 in state rebates toward a treatment system. Check your eligibility.
Every well is different. Two wells on the same street can produce completely different water. The data on this page reflects documented conditions in the Merrimack area, but the only way to know what's in your water is to test it.
Sources
- NH DES — Saint-Gobain PFAS Investigation
- NH DES — PFAS Standards and Testing Program
- USGS — Groundwater Quality in Southern New Hampshire
- EPA — PFAS in Merrimack, NH