Dissolved-methane concentrations in well water in the Appalachian Plateau physiographic province of Maryland
2013, Bolton, D.W., and Pham, Minh Phung T.
Administrative Report 14-02-01
Methane in well water has been reported anecdotally over the years in the Appalachian Plateau of Maryland; however, no systematic study has been conducted regarding methane occurrence and distribution. The potential development of natural gas reserves in the Marcellus Shale in western Maryland has raised concerns about whether these activities could result in methane contamination of the water-supply aquifers in the region. Well water is not routinely tested for methane in Maryland, since it does not have an established Primary or Secondary Maximum Contaminant Level (MCL). Because of the concern over possible methane contamination of water wells resulting from Marcellus Shale gas-development activities, the Maryland Geological Survey (MGS) evaluated methane samples from 49 wells in 2012 and an additional 28 wells in 2013 in Garrett County and western Allegany County. The purpose of this study was to measure ambient methane concentrations in water wells in the region, and to begin to gain an understanding of the occurrence and distribution of methane in water wells. This report discusses the methane data collected in both years.
Situated in the westernmost part of Maryland, Garrett County and the western section of Allegany County are located within the Appalachian Plateau Physiographic Province, which is characterized by outcrops of sedimentary rocks of Carboniferous (Pennsylvanian and Mississippian) and Devonian periods. The gently folded strata form synclines and anticlines that are the source regions for coal and natural gas, respectively (Nutter and others, 1980). The five major coal basins in the region are the Lower Youghiogheny Basin, Upper Youghiogheny Basin, Castleman Basin, Upper Potomac Basin, and Georges Creek Basin.
Natural gas production and coal mining were once a large part of the economy in this region. The Accident Dome used to be an area of intensive natural gas extraction. Currently, the Accident Dome is used as a gas-storage facility (fig. 2). The other anticlinal structure, the Deer Park Anticline, contains several active natural gas-producing wells (Gregory Day, Maryland Department of the Environment, oral commun., 2012).
From an economic standpoint, coal mining is not as prominent today as it was in the past in Garrett County; however, both strip- and deep-mining operations still exist. There are several economically viable coal seams within the Pennsylvanian System that underlie the basins. Among them are the Upper Freeport coal, Waynesburg coal, Pittsburgh coal, Kittanning coal group, and Bakerstown coal (fig. 3). From a water-quality standpoint, coal seams are among significant sources of methane production (Eltschlager and others, 2001).
Methane is a colorless, odorless, flammable gas that can occur naturally in well water. Methane has a solubility of about 28 milligrams per liter (mg/L) (28,000 micrograms per liter [μg/L]) in water. Even though methane is not a regulated constituent in drinking water, it is recommended that methane levels above 10 mg/L (10,000 μg/L) need to be addressed to prevent asphyxiation and explosive conditions in confined spaces (Eltschlager and others, 2001). Prior to the present study, no quantitative measurements for methane have been done for well waters in Maryland on a regional basis, although methane has occasionally been detected in wells in western Maryland using a simple qualitative test (a flame test using well water placed in a jar) (Steve Sherrard, Garrett County Health Department, oral commun., 2012).
Methane has been identified in ground water in neighboring West Virginia and Pennsylvania. A study conducted in West Virginia from 1997 to 2005 by the U.S. Geological Survey (USGS) sampled 170 water wells for methane (Mathes and White, 2006) (fig. 4). They concluded that higher methane concentrations (greater than 10,000 μg/L) were found in wells completed in Pennsylvanian-age rock formations as well as those located in valleys and on hillsides. These findings suggest that topography and geology are contributing factors in the occurrence of methane. From sampling more than 1,700 wells in Susquehanna County, Pennsylvania, Molofsky and others (2011) also found that methane detection was linked to topography. A study conducted by Stoner and others (1987) in southwestern Pennsylvania showed that, particularly in Greene County, methane in ground water is ubiquitous with concentrations commonly exceeding 25,000 μg/L and as high as 74,000 μg/L.