Water samples were collected from 20 domestic wells during August and September 2012 and analyzed for 47 constituents and properties, including nutrients, major ions, metals and trace elements, radioactivity, and dissolved gases, including methane and radon-222. This study, done in cooperation with the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey (Pennsylvania Geological Survey), provides a groundwater-quality baseline for central and southern Sullivan County prior to drilling for natural gas in the Marcellus Shale.

The analytical results for the 20 groundwater samples collected during this study indicate that only one constituent (gross-alpha radioactivity) in one sample was found to exceed the U.S. Environmental Protection Agency (USEPA) primary drinking water maximum contaminant level (MCL). Water samples from 85 percent of the sampled wells exceeded the proposed USEPA MCL of 300 picocuries per liter (pCi/L) for radon-222; however, only two water samples (10 percent of sampled wells) exceeded the proposed USEPA alternate maximum contaminant level (AMCL) of 4,000 pCi/L for radon-222. In a few samples, the concentrations of total dissolved solids, iron, manganese, and chloride exceeded USEPA secondary maximum contaminant levels (SMCL). In addition, water samples from two wells contained methane concentrations greater than 1 milligram per liter (mg/L).

In general, most of the water-quality problems involve aesthetic considerations, such as taste or odor from elevated concentrations of total dissolved solids, iron, manganese, and chloride that develop from natural interactions of water and rock minerals in the subsurface. The total dissolved solids concentration ranged from 31 to 664 mg/L; the median was 130 mg/L. The total dissolved solids concentration in one water sample exceeded the USEPA SMCL of 500 mg/L. Chloride concentrations ranged from 0.59 to 342 mg/L; the median was 12.9 mg/L. The concentration of chloride in one water sample exceeded the USEPA SMCL of 250 mg/L. Concentrations of dissolved iron ranged from less than 3.2 to 6,590 micrograms per liter (µg/L); the median was 11.5 µg/L. The iron concentration in samples from 20 percent of the sampled wells exceeded the USEPA SMCL of 300 µg/L. Concentrations of dissolved manganese ranged from less than 0.13 to 1,710 µg/L; the median was 38.5 µg/L. The manganese concentration in samples from 35 percent of the sampled wells exceeded the USEPA SMCL of 50 µg/L.

Activities of radon-222 ranged from 169 to 15,300 picocuries per liter (pCi/L); the median was 990 pCi/L. The gross alpha-particle radioactivity ranged from below detection to 33 pCi/L; the median was 1.5 pCi/L. The gross alpha-particle radioactivity of one water sample exceeded the USEPA MCL of 15 pCi/L.

Concentrations of dissolved methane ranged from less than 0.001 to 51.1 mg/L. Methane was not detected in water samples from 13 wells, and the methane concentration was less than 0.07 mg/L in samples from five wells. The highest dissolved methane concentrations were 4.1 and 51.1 mg/L, and the pH of the water from both wells was greater than 8. Water samples from these wells were analyzed for isotopes of carbon and hydrogen in the methane. The isotopic ratio values fell in the range for a thermogenic (natural gas) source. The water samples from these two wells had the highest concentrations of arsenic, boron, bromide, chloride, fluoride, lithium, molybdenum, and sodium of the 20 wells sampled.