Methodology
How each number on this site is made.
Arsenic
The arsenic numbers are modeled estimates from the U.S. Geological Survey, published in 2017, using 2010 population. The source gives a best estimate and a 95 percent range for how many people using domestic wells were predicted to have arsenic above 10 micrograms per liter. The page shows that best estimate and the likely range, rounded to the nearest hundred. They're county-wide statistics, not tests of any well.
Source: Estimated county-level domestic well population with arsenic greater than 10 micrograms per liter, U.S. Geological Survey, 2017.
Last checked October 26, 2026.
Radon
County zones from the U.S. Environmental Protection Agency predict indoor air radon potential. They don't measure radon in well water. Zone 1 is the highest potential, zone 2 is moderate, and zone 3 is lower. This site shows those zones as High, Moderate, and Lower. The map was developed in 1993. The spreadsheet is labeled EPA 402/A-16/001.
Source: EPA Map of Radon Zones, U.S. Environmental Protection Agency, 1993.
Last checked October 26, 2026.
Labs
The labs come from the Connecticut Department of Public Health list of in-state laboratories certified to test drinking water, dated October 9, 2026. Only labs that accept private well samples are shown. A yes on a grouped test means the lab is certified for some or all of the tests in that group.
Source: In-state laboratories certified to test drinking water, Connecticut Department of Public Health, 2026.
Last checked October 26, 2026.
Testing schedule
The testing schedule comes from Connecticut Department of Public Health guidance on which private well tests to run and how often. The materials were updated May 2026.
Source: Educational Materials on private well testing (updated May 2026), Connecticut Department of Public Health, 2026.
Last checked October 26, 2026.
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