Source: https://www.usgs.gov, March 6, 2017

Tests of 75 private drinking water wells in Lycoming County, in north-central Pennsylvania, found water from most of the sampled wells contained concentrations of radon that exceeded a proposed, nonbinding health standard for drinking water. Smaller percentages of the wells contained concentrations of arsenic or methane that exceed existing drinking water standards.

The US Geological Survey carried out the tests in 2014 to assess the natural characteristics of local groundwater and the potential effects of land uses such as mining, natural gas production, agriculture, and sewage and septic systems on local water supplies. Property owners participated voluntarily in the testing and were notified of the results.
Some of the randomly-selected wells tested in this study were located near natural gas production sites that use unconventional methods such as hydraulic fracturing. However, the findings were very similar to those of an earlier study in northeastern Pennsylvania’s Wayne County, where unconventional gas drilling is not permitted, the researchers said.
Radon, arsenic, and methane carry potential health risks, but property owners can test and treat their wells to control these risks. Pennsylvania does not regulate private wells, but the Pennsylvania Department of Environmental Protection and Penn State Extension provide testing and treatment guidance for private well owners. The first step is getting information about potential contaminants, said USGS scientist Eliza Gross, who led the Lycoming County study.
“As in many parts of the state, water quality data were lacking in Lycoming County,” said Gross, a physical scientist with the USGS’ Pennsylvania Water Science Center.  “This study provides much-needed information. The number of water samples was relatively small, so we can’t draw definitive conclusions about water quality throughout the county. But we want residents who get their water from private wells to know about our results, and to be aware that the EPA recommends regular testing of private drinking water wells.”
The USGS researchers analyzed the water samples for arsenic, radon, methane, and over 170 other constituents, including dissolved salts; metals and trace elements; and bacteria.
Among substances with potential health risks, the most commonly found one was radon-222, a radioactive gas that occurs naturally in some types of rock, and can seep into basements and is dissolved in some groundwater supplies. Radon-222 in indoor air is the second leading cause of lung cancer. Radon in drinking water is not currently regulated, but the US Environmental Protection Agency has proposed standards that provide guidelines for community water systems.
Two-thirds of the Lycoming County samples, 50 out of 75, contained levels of radon-222 that exceeded the proposed drinking-water standard of 300 picocuries per liter. (A picocurie is a measure of radioactive decay; the more picocuries per liter, the more radioactivity is emitted.)
These levels are consistent with those found in groundwater tests statewide, and may indicate naturally occurring radon. Three samples contained radon levels higher than a less protective proposed standard of 4,000 picocuries per liter.
Nine out of the 75 samples contained arsenic concentrations higher than the EPA’s maximum contaminant level – the highest level allowed in public drinking water supplies –  of 10 micrograms per liter. One sample contained 23.6 micrograms of arsenic per liter, the highest concentration found in this study. When people drink water containing high concentrations of arsenic over many years, they may experience health effects such as skin damage, circulatory problems and an increased risk of developing cancer.
Two of the 75 samples had methane concentrations exceeding the Pennsylvania Department of Environmental Protection’s action level of 7 milligrams per liter for methane in well water. One water sample had 13.1 milligrams per liter of methane, and one had 16.8 milligrams per liter. The state agency recommends periodic monitoring for wells with methane up to 7 milligrams per liter, and corrective action such as well venting for wells with methane concentrations of 7 milligrams per liter or more.
Methane is the primary component of natural gas. The migration of methane into groundwater aquifers is a concern, because methane in tap water can be flammable or explosive. In this study, 15 out of the 75 wells, or 20 percent, had methane levels high enough to be detected in laboratory tests.
“One of our goals was to collect baseline information, so future studies can determine whether there is a relationship between human activities and well water chemistry,” Gross said. “The variations in water quality that we saw can generally be explained by natural processes. In some instances human activities may play a role. For example, we found a wide range of levels of chloride, or salt, from less than 1 milligram per liter to nearly 1,000 milligrams per liter. The higher levels could be from road de-icing salts.”
The testing was done in cooperation with the Lycoming County Department of Planning and Community Development, the Pennsylvania Department of Environmental Protection, and other local partners. The USGS Pennsylvania Water Science Center has done similar studies in Wayne, Pike and Bradford counties, and plans are underway to assess groundwater in neighboring Clinton and Potter counties. All results will be online at the USGS National Water Information System website.
The study, “Groundwater Quality for 75 Domestic Wells in Lycoming County, Pennsylvania, 2014,” is online at https://pubs.er.usgs.gov/publication/sir20165143 .