The use of hydraulic fracturing in the US to release natural gas from shale formations has raised concerns with water-well owners and water-resource managers across the Marcellus and Utica Shale regions. A new from report from the USGS documents data on dissolved methane concentrations in New York's groundwater.
New York is recovering from a state of shock caused by storm Sandy, ripping across the East Coast of the US. Costs for clearing up the damage have been estimated at $30-40 billion, with the city's subway system sustaining the worst damage in its 108-year history. Reports cite that Sandy brought a record storm surge of almost 14ft to central Manhattan, with Maryland reported to have suffered the worst rain and snow - 12.5 inches and 28 inches, respectively.
While climate change and global warming will be inevitably blamed, another environmental concern in the region has come under scrutiny by a recent report: increasing methane in groundwater as a result of hydraulic fracking activity.
New York State is underlain by numerous bedrock formations of Cambrian to Devonian age that produce natural gas and to a lesser extent oil. The first commercial gas well in the US was dug in the early 1820s in Fredonia, south of Buffalo, New York and produced methane from Devonian-age black shale.
Methane occurs locally in the groundwater of New York. As a result, it may be present in drinking-water wells, in the water produced from those wells, and in the associated water-supply systems.
The natural gas in low-permeability bedrock formations has not been accessible by traditional extraction techniques, which have been used to tap more permeable sandstone and carbonate bedrock reservoirs. However, newly developed techniques involving horizontal drilling and high-volume hydraulic fracturing have made it possible to extract previously inaccessible natural gas from low-permeability bedrock, such as the Marcellus and Utica Shales.
Methane reaches saturation in water at 28 milligrams per liter (mg/L) at atmospheric pressure and becomes flammable in air at about 5% by volume. The Office of Surface Mining recommends that methane concentrations greater than 28 mg/L in well water should be addressed immediately by removing any potential ignition source and venting the gas away from confined spaces.
Dissolved methane concentration data in New York - results
Since 2002, the US Geological Survey (USGS), in cooperation with New York State Department of Environmental Conservation (NYSDEC), has conducted groundwater-quality monitoring assessments in major river basins in New York. Since 2009, these assessments have included sampling for dissolved gases, including methane
By 2011, methane had been sampled in eight of the 14 major river basins in the State, says USGS. This data, combined with those from groundwater age-dating analyses, yielded dissolved methane concentrations from water wells at 239 locations in New York from 1999 to 2011. Samples collected through 2011 indicate that concentrations of methane in groundwater from most wells measured (91%) were at or below the Office of Surface Mining action level of 10 mg/L and a large number of wells (47%) had no detectable methane.
However, methane concentrations from several wells exceeded 10 mg/L (9%); in five cases, the measured concentrations were greater than 28 mg/L (2%). Methane was detected in both unconsolidated and bedrock aquifers across New York. In unconsolidated aquifers, 93% of the wells had non-detect to low-level methane concentrations (methane concentrations <1 mg/L), and less than 1% of the wells (one well) was greater than the saturation value of 28 mg/L.
The greater methane concentrations are most likely associated with confined glacial aquifers over black shale bedrock. In bedrock formation aquifers, 73% of the methane concentrations were less than 1 mg/L, while nearly 4% had concentrations greater than 28 mg/L across the State. Three of the four highest methane values in bedrock wells were associated with Devonian-aged black shale bedrock. In total, many of the greater methane concentrations were most likely associated with wells drilled into these shales.
The 1999-2011 analysis of dissolved methane in groundwater in New York is meant to document the natural occurrence of methane in the State's aquifers. While many of the greater concentrations of dissolved methane appear to be associated with wells drilled in black shale bedrock or in unconsolidated deposits overlying black shale bedrock, the limited set of existing data does not allow a more concise analysis at this time, according to USGS.
The organization added that the study does indicate the need for continued collection of methane data and analysis for individual and public water-supply wells to document methane concentrations for water wells in New York State.
Author's note: This article was taken from the USGS report analysis of dissolved methane in groundwater in New York. It was prepared in cooperation with the New York State Department of Environmental Conservation. More information and the report from the U.S. Geological Survey (USGS) can be found at http://waterdata.usgs.gov/nwis.
