Your well water test comes back with arsenic at 8 parts per billion. The report says "below MCL," meaning below the maximum contaminant level. The implication is that you're fine. The water is safe.
Here is what the EPA said when it set that 10 ppb arsenic limit back in 2001. The agency estimated that drinking water at exactly 10 ppb over a lifetime carries a cancer risk of approximately 1 in 300. For comparison, the EPA typically triggers regulatory action at a cancer risk of 1 in 10,000 or lower. It landed on 10 ppb not because 10 ppb is safe, but because getting water systems below that was not considered cost-effective at the time.
That's straight from the EPA's own regulatory history, not a fringe reading of it. The 10 ppb limit is a feasibility standard. It is not a health standard.
Arsenic in Connecticut's Geology
Arsenic sits naturally in Connecticut's bedrock, especially in the metamorphic and igneous rock of central and eastern Connecticut. Groundwater moves through those formations and dissolves some of the arsenic out of the rock. The process is slow, and concentrations are usually low. But in some areas, and in some individual wells, arsenic reaches or passes the federal limit.
The CT Department of Public Health has documented arsenic in private wells across the state. There's no single hot zone to point at. The risk follows the geology, so it shows up wherever the rock formations favor it.
What Does the Research Say About Low-Level Arsenic?
Most of what we know comes from places where natural arsenic contamination is severe: Bangladesh, Taiwan, Chile. At high levels (above 100 ppb) arsenic causes skin lesions, nerve damage in the hands and feet, and sharply higher cancer rates.
The range that matters for Connecticut wells is lower, roughly 5 to 50 ppb. There the evidence gets murkier, though it's still worrying. Studies have found associations between long-term exposure at these levels and higher rates of bladder, lung, and skin cancer. One 2011 study in Environmental Health Perspectives found that arsenic below the federal limit was associated with increased bladder cancer risk in a U.S. population.
Back in 1999, the National Academy of Sciences reviewed the evidence and concluded the standard of the day, 50 ppb, was "not adequately protective of public health." Dropping to 10 ppb in 2001 was an improvement. It was not a fix.
What Should CT Well Owners Do About Arsenic?
If your well test comes back at 8 ppb, you are below the federal limit and in violation of nothing. Your water meets the standard. You also carry a lifetime cancer risk from that arsenic which the EPA estimates at roughly 1 in 375.
Want ZIP-level context before deciding whether to test? Enter your ZIP code at CheckYourTap.com to see available public-system or regional monitoring records associated with the ZIP. This is not a test of a tap, well, or property. Free, in 30 seconds.
Whether that risk is acceptable is your call to make. What matters is knowing it exists, and knowing that "below MCL" does not mean zero risk.
Treatment, at least, is settled science. Reverse osmosis removes arsenic effectively, typically down to below 1 ppb. Activated alumina and iron-based media filters work too. A point-of-use reverse osmosis system runs $300 to $800 installed.
So if you're sitting between 5 and 10 ppb, technically "safe" by federal standards, the real question is whether you'd rather accept the leftover risk or spend a few hundred dollars to remove it. The risk is small in absolute terms. It is also real. And arsenic is only one of the contaminants that the standard mortgage water test doesn't adequately cover. If your well is in eastern Connecticut, uranium from the granite bedrock is worth testing for as well.
Keep Reading
- The Water Test You Got When You Bought Your House Is Worthless Now
- There's Uranium in Some Eastern Connecticut Wells. It's Not from a Nuclear Plant.
- The Rotten Egg Smell in Your Well Water Is Telling You Something. Listen to It.
- Connecticut's Crumbling Foundation Crisis Taught Us One Thing. The Well Water Crisis Is Next.
Sources: EPA Arsenic Rule History, 2001; EPA Risk Assessment for Arsenic in Drinking Water; Environmental Health Perspectives, arsenic and bladder cancer, 2011; National Academy of Sciences, Arsenic in Drinking Water, 1999; CT DPH Private Well Testing Data.
