Redding has no town-level results in the USGS reports, but its bedrock is well mapped. Nearly half the town sits on the same Ordovician(?) granitic gneiss that underlies most of Weston, a unit where USGS found 14.2% of statewide well samples above the arsenic limit and 25.6% above the uranium limit (USGS Open-File Report 2020-1111; CT DEEP). CT DPH recommends testing every private well for arsenic, uranium and radon at least once (CT DPH).
● Key Takeaways
About 45% of Redding is mapped on Ordovician(?) granitic gneiss (statewide: 14.2% of samples over the 10 µg/L arsenic limit, 25.6% over the 30 µg/L uranium limit). About 29% is Ratlum Mountain Schist (0% of 114 over the arsenic limit, 9.6% of 104 over the uranium limit). No town-level results are published for Redding. Test for arsenic, uranium and radon at least once.
What Rock Is Under Redding?
Redding's bedrock is a patchwork. The two largest units are the Ordovician(?) granitic gneiss and the Ratlum Mountain Schist, and only Weston has a larger area of that granitic gneiss.
| Rock unit | Share of town (CT DEEP map) | USGS samples above 10 µg/L arsenic | USGS samples above 30 µg/L uranium |
|---|---|---|---|
| Ordovician(?) granitic gneiss | About 45% | 14.2% of 106 | 25.6% of 86 |
| Ratlum Mountain Schist | About 29% | 0% of 114 | 9.6% of 104 |
| Rowe Schist | About 8% | 1.9% of 54 | 1.8% of 55 |
| Gneiss of the Highlands massifs | About 5% | 0% of 17 | 5.9% of 17 |
| Stockbridge Marble | About 5% | 7.1% of 14 | 0% of 13 |
| Amphibolite unit in Ratlum Mountain Schist | About 3% | 0% of 2 | 0% of 2 |
| Ratlum Mountain Schist (queried on the map) | About 2% | 8.3% of 12 | 0% of 6 |
| Harrison Gneiss | About 2% | 14.3% of 7 | 46.7% of 15 |
The share of town is the area of each unit inside Redding'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 Redding (USGS Open-File Report 2020-1111). Units with only a handful of samples tell you very little.
The two main units point in different directions. The granitic gneiss had elevated rates for both arsenic and uranium statewide. In the Ratlum Mountain Schist, none of 114 statewide samples exceeded the arsenic limit, but 9.6% of 104 exceeded the uranium limit. Smaller areas of Rowe Schist, Highlands gneiss and Stockbridge Marble had lower rates or few samples. Which unit your well is drilled into matters more than the town line.
What Has Testing Found in Redding?
Neither USGS report breaks out Redding. The 2017 report gave town-level figures only for Stamford, Weston and Wilton, the three towns with unusually many samples. The nearby published figures are Weston's, where 47.3% of 110 samples exceeded the arsenic limit, and Wilton's, where 2.5% of 81 did (USGS Open-File Report 2017-1046).
Redding shares its most extensive rock unit with Weston. That is a reason to test, not a prediction for any Redding well.
What Should Redding 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.
Test your Redding well
A water specialist can arrange certified lab testing for your well, starting with arsenic, uranium, radon and a basic indicators panel.
CheckYourTap is an independent water-quality service, not your town or utility. We connect you with a vetted local partner. Your online report is free. Testing and treatment are paid services, and there's no cost to talk.
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
- Newtown 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 Redding. Exceedance percentages and sample counts are copied from USGS Open-File Report 2020-1111, 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.
