When your well water test comes back with arsenic at 8 parts per billion, the report says "below MCL" — 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 the 10 ppb arsenic limit in 2001: the agency estimated that drinking water at exactly 10 ppb over a lifetime carries a cancer risk of approximately 1 in 300. The EPA's standard for triggering regulatory action is typically a cancer risk of 1 in 10,000 or lower. The agency set the arsenic limit at 10 ppb not because 10 ppb is safe, but because achieving lower levels was not considered cost-effective at the time.
This is documented in the EPA's own regulatory history. It is not a fringe interpretation. The 10 ppb limit is a feasibility standard, not a health standard.
Arsenic in Connecticut's Geology
Arsenic occurs naturally in Connecticut's bedrock — particularly in the metamorphic and igneous rocks of central and eastern Connecticut. As groundwater moves through these formations, it can dissolve arsenic from the rock. The process is slow and the concentrations are generally low, but in some areas and some wells, arsenic levels can reach or exceed the federal limit.
The CT Department of Public Health has documented arsenic in private wells across the state. The risk is not concentrated in one area — it's distributed across the state's geology, with higher concentrations in areas with specific rock formations.
What Does the Research Say About Low-Level Arsenic?
The health effects of arsenic in drinking water have been studied extensively, primarily in populations in Bangladesh, Taiwan, and Chile where naturally occurring arsenic contamination is severe. At high levels — above 100 ppb — arsenic causes skin lesions, peripheral neuropathy, and dramatically increased cancer risk.
At lower levels — in the range of 5–50 ppb, which is the range relevant to Connecticut wells — the evidence is more nuanced but still concerning. Studies have found associations between long-term exposure in this range and increased risk of bladder cancer, lung cancer, and skin cancer. A 2011 study in Environmental Health Perspectives found that exposure to arsenic at levels below the federal limit was associated with increased risk of bladder cancer in a U.S. population.
The National Academy of Sciences reviewed the arsenic evidence in 1999 and concluded that the then-current 50 ppb standard was "not adequately protective of public health." The 2001 revision to 10 ppb was an improvement. It was not a solution.
What Should CT Well Owners Do About Arsenic?
If your well water arsenic test comes back at 8 ppb — below the federal limit — you are not in violation of any regulation. Your water meets the standard. You also have a lifetime cancer risk from arsenic exposure that the EPA estimates at roughly 1 in 375.
When was the last time you tested your well water? Enter your ZIP code at CheckYourTap.com to see what's in your tap water — free, in 30 seconds.
Whether that risk is acceptable is a personal decision. What matters is that you know the risk exists and that the "below MCL" designation doesn't mean zero risk.
The treatment for arsenic in well water is well-established. Reverse osmosis removes arsenic effectively — typically to below 1 ppb. Activated alumina and iron-based media filters are also effective. The cost of a point-of-use reverse osmosis system runs $300–$800 installed.
If your arsenic level is between 5 and 10 ppb — technically "safe" by federal standards — the question is whether you want to accept the residual risk or eliminate it. The cost of elimination is modest. The risk, while small in absolute terms, is real. Arsenic is just one of the contaminants that the standard mortgage water test doesn't adequately cover — and if your well is in eastern Connecticut, uranium from the granite bedrock may be another concern worth testing for.
Frequently Asked Questions
Is arsenic at 8 ppb in well water safe to drink?
Technically, 8 ppb is below the EPA's legal limit of 10 ppb, so your water is in compliance. However, the EPA estimates that drinking water at 10 ppb carries a lifetime cancer risk of approximately 1 in 300 — far above the agency's typical 1-in-10,000 action threshold. The 10 ppb limit is a feasibility standard, not a health standard.
Where in Connecticut is arsenic most common in well water?
Arsenic occurs naturally in Connecticut's bedrock, particularly in the metamorphic and igneous rocks of central and eastern Connecticut. As groundwater moves through these formations, it dissolves arsenic from the rock. The risk is distributed across the state's geology, not concentrated in one area.
How do you remove arsenic from well water?
Reverse osmosis is the most effective and affordable option, typically reducing arsenic to below 1 ppb. Activated alumina and iron-based media filters also work well. A point-of-use reverse osmosis system costs $300 to $800 installed.
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.