Wilton, CT Well Water Testing: What the Public Record Shows

Wilton's public well record looks different from its neighbor Weston's. In a USGS report on 2013 to 2015 samples, 2.5% of 81 Wilton samples exceeded the EPA arsenic limit, but 7.5% of 80 exceeded the uranium limit, about twice the 3.9% rate in the statewide dataset (USGS Open-File Report 2017-1046). CT DPH recommends testing every private well for arsenic, uranium and radon at least once (CT DPH).

What Rock Is Under Wilton?

The largest unit on the CT DEEP map is the Ordovician(?) granitic gneiss, followed by the Harrison Gneiss, the undivided Trap Falls Formation and granitic gneiss, and the Pumpkin Ground Member of the Harrison Gneiss.

The share of town is the area of each unit inside Wilton's boundary on the CT DEEP bedrock map (CT DEEP); units under 1% are left out. The percentages are from USGS Table 4 and describe wells in that rock unit statewide, not wells in Wilton (USGS Open-File Report 2020-1111). Units with only a handful of samples tell you very little.

The Harrison Gneiss had the highest uranium rate of any rock unit in the USGS study with at least 10 uranium samples: 7 of its 15 samples exceeded the limit. Only Greenwich and Stamford have more of it than Wilton. The granitic gneiss had elevated arsenic and uranium rates statewide. USGS's 2017 report described Wilton's dominant units as the Harrison Gneiss, its Pumpkin Ground Member, and the undivided Trap Falls Formation and granitic gneiss, and noted that none of the statewide-dataset wells in those units had high arsenic.

What Has Testing Found in Wilton?

USGS's 2017 report looked at every available result from three towns with unusually many samples. In Wilton, 2.5% of 81 samples had arsenic above 10 µg/L and 7.5% of 80 had uranium above 30 µg/L. Next door in Weston, 47.3% of 110 samples exceeded the arsenic limit, and USGS attributed the contrast to the towns' different geology (USGS Open-File Report 2017-1046).

The results are from 2013 to 2015 and describe the wells that were sampled, not every home in Wilton. A low town-wide arsenic rate does not clear any single well. The uranium result is also a reason to test radon: CT DPH pairs uranium above 30 µg/L with tests for radium and radon (CT DPH).

What Should Wilton Well Owners Test, and How Often?

CT DPH's schedule applies to every private well in Connecticut, whatever the town (CT DPH, updated May 2026):

• Basic indicators every year (bacteria, nitrate, nitrite, sodium, chloride, iron, manganese, hardness, pH and others), and after any well, pump or pipe repair or a flooded wellhead.
• Arsenic, uranium and radon at least once, ideally every 5 years. Levels can fluctuate.
• Lead and volatile organic compounds at least once, and lead again when planning a pregnancy or with a child under 6.
• Fluoride every 5 years when a child under 12 lives in the home.

Since October 1, 2022, new wells have been tested for arsenic and uranium when drilled (CT DPH arsenic; CT DPH uranium). If your well is older and has no arsenic or uranium result on file, that is the gap to close first. CT DPH also recommends a radon in water test for every home on a well, even if indoor air tested low (CT DPH, revised February 2025).

Use a laboratory certified by CT DPH for the tests you need, and compare results with CT DPH Action Levels and EPA limits: 10 µg/L for arsenic, 30 µg/L for uranium, and CT DPH's recommended 5,000 pCi/L action level for radon in water. If a result is high, CT DPH says to retest, stop drinking the water until it is resolved, and contact your local health department (find yours) or the CT DPH Private Well Program at (860) 509-8401. The full schedule, lab tips and how to read a report are in our Connecticut private well testing guide.

What This Page Does Not Tell You

It does not tell you what is in your well. USGS cautions that rock-unit exceedance rates "may not represent the actual hazard for existing and future wells," and the study's lead author said bedrock geology "is not always predictive" (USGS Open-File Report 2020-1111; USGS, April 2021). Even neighboring towns can differ sharply, as Weston and Wilton do in USGS's 2013 to 2015 data. Only a certified lab test of your water answers the question.

Keep Reading

• Private well testing in Connecticut: the complete guide
• Arsenic and uranium in Connecticut wells, by region
• Radon in Connecticut well water
• Weston well water testing
• Redding well water testing

How we built this page: rock unit shares come from overlaying the CT DEEP bedrock geology map (Rodgers, 1985, digitized at 1:50,000) on the CTDOT municipal boundary for Wilton. Exceedance percentages and sample counts are copied from USGS Open-File Report 2020-1111, Table 4. Wilton's town-level results are from USGS Open-File Report 2017-1046, Table 4. This page describes geology and published sampling. It is not a measurement or rating of any home's well.

Sources: Gross and Brown, USGS Open-File Report 2020-1111; Flanagan and Brown, USGS Open-File Report 2017-1046; USGS news release (April 2021); CT DEEP, Bedrock Geology of Connecticut; CTDOT Municipalities; CT DPH, Educational materials: testing recommendations for private wells (updated May 2026); CT DPH, Arsenic in private well water; CT DPH, Uranium in Private Well Water (April 2024); CT DPH, Radon in Your Well Water (revised February 2025).

About this guide: CheckYourTap is an independent water-quality service funded by Valiant Energy Solutions, a Connecticut water quality and energy services company established in 1930. Valiant offers paid well testing and treatment, which is what the request button on this page connects you with. You can also contact any CT DPH-certified laboratory directly. The facts on this page come from the public sources cited above.