Baseline Groundwater Quality Studies Find Naturally Occurring Methane in Northeastern Pennsylvania

Two reports are posted online (Wayne County and Pike County).

NEW CUMBERLAND, Pa. – Well-water tested in Wayne and Pike counties contains low-to-moderate concentrations of naturally occurring methane, according to new studies by the U.S. Geological Survey.

None of the water tested in these two studies exceeded the Pennsylvania Department of Environmental Resources action level of 7 milligrams per liter for methane in well water.

The agency recommends periodic monitoring for wells with detectable methane up to 7 milligrams per liter. Corrective action, such as well venting, is recommended for wells with methane concentrations equal to or greater than 7 milligrams per liter.

In Wayne County, about 65 percent, or 22 of the 34 private drinking-water supply wells tested-contained concentrations of dissolved methane high enough to detect in laboratory testing, but most methane concentrations were low, less than 0.1 milligrams per liter. Three -- or about 10 percent -- of the 34 tested wells in Wayne County produced groundwater with dissolved methane concentrations near or greater than 1 milligram per liter and as high as 3.3 milligrams per liter; these relatively elevated concentrations are at least 10 times greater than methane concentrations in the other well-water samples.

In the Pike County study, about 80 percent -- or 16 of 20 tested wells -- contained detectable concentrations of methane, with two wells having methane concentrations greater than 1 milligram per liter and as high as 5.8 milligrams per liter. The concentrations of dissolved methane in about 10 percent of well-water samples in both studies were high enough to allow for isotopic analysis to identify the type of natural gas in the water. 

The source of methane can be thermogenic, which is typical of shale-gas methane; or biogenic, which is typical of methane produced by microbial activity at or near the surface such as in marshes or in alluvial deposits. In Pike County, the isotopic composition of two methane samples indicated that methane was predominantly microbial in origin, and in Wayne County, the isotopic composition of three methane samples indicated a thermogenic origin and (or) mixture of microbial and thermogenic types.

None of the wells tested in either study were located near currently producing natural gas wells.  Both Wayne and Pike counties are within the Delaware River Basin, where a moratorium on shale-gas drilling is in place.

The Wayne County and Pike County samples were collected in 2012 and 2013 to assess baseline groundwater quality in areas underlain by the Marcellus Shale but where no extensive shale-gas development has occurred.  The Wayne County study was conducted by USGS in cooperation with the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geological Survey, and the Pike County study was conducted by USGS in cooperation with the Pike County Conservation District. In both studies, the water samples were analyzed for methane and about 45 other constituents, including dissolved salts such as sodium and chloride; metals and trace elements such as arsenic, barium, iron, and manganese; and radon. All of the well owners were notified of the results.

“Water-quality data were lacking in Wayne County,” said USGS scientist Ronald Sloto, who led the Wayne County study. “Without baseline water-quality data, it would be difficult to determine whether a relationship exists between gas production activities and the well-water chemistry in the area. This study provides a pre-gas well drilling groundwater-quality baseline for Wayne County. Although the number of water samples was small, the analytical results show the presence of naturally occurring methane in some private drinking water wells.”

Similarly, data on occurrence of methane and other constituents potentially related to shale-gas development were not available or were limited in Pike County, according to USGS scientist Lisa Senior, who led the Pike County study. She said that the Pike County study included sampling four wells monthly over the course of one year because “little is known about variability in groundwater quality through time, but this variability is important in interpreting baseline assessments. Many baseline assessments consist of one-time sampling.”

Methane is the primary component of natural gas produced from the Marcellus Shale in Pennsylvania. One of the societal concerns with unconventional gas production is the possible migration of methane into drinking water aquifers because it can be flammable or even explosive

These studies show that naturally occurring methane can be found in drinking water wells in areas where no unconventional natural gas development is occurring. The studies also provide background information on other aspects of groundwater quality, such as arsenic, barium, chloride, and radon concentrations that may be of concern in areas of shale-gas development.  Because the number of samples in Wayne County and Pike County were relatively small, additional sampling would be necessary to provide a broader picture of naturally occurring methane in the region. Currently, the USGS is continuing to collect data on baseline groundwater quality in areas in Pennsylvania underlain by the Marcellus Shale by conducting an expanded study in Wayne County in cooperation with the Wayne Conservation District and in a new study in Lycoming County in the north-central part of the state in cooperation with Lycoming County. The results will be available online at the USGS National Water Information System website.