Fact Sheet: Methane Gas Migration and Mitigation

Methane gas has been a “hidden” problem in Northeastern Pennsylvania.  The gas is typically associated with wetlands, bogs, landfills, coal-producing formations, natural saline seeps, some glacial deposits, and gas storage areas.  Because of the development of the Marcellus Shale, the presence of methane gas and the potential for methane gas migration is a growing concern.   Methane is a colorless, odorless gas that is lighter than air.   Natural gas is mostly methane (70 – 90 % CH₄), carbon dioxide (0 to 8 % CO₂), plus other gases.  The other gases may include ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and hydrogen sulfide (H₂S) as well as small amounts of helium.

Methane gas is highly flammable between a lower explosion limit (LEL) of 5.53 percent by volume in air and an upper explosion limit (UEL) of 15 percent.  These percentages are equivalent to a methane concentration of 50,000 and 150,000 parts per million (ppm) in air.  The minimum concentration level at which the gas has the potential to explode is called the lower explosive limit (LEL); below the LEL level there is not enough gas to cause an explosion.  Above the UEL, there is inadequate oxygen to fuel combustion, but if the space is vented and the gas concentration drops below the UEL, the gas can become diluted enough to explode (it would require an ignition source).  Methane is not considered toxic, but it is an asphyxiant at a concentration of over 50 percent in air (it displaces oxygen).  Therefore, the primary risks for methane would be asphyxiation in a confined or poorly vented area or a potential explosion hazard.   As a safety measure, the natural gas industry adds mercaptans to the produced methane gas that enters the pipeline and your home. The mercaptans produce a very pungent odor so that gas leaks will be noticed, but unprocessed methane gas tends to have NO ODOR.  It is critical to note that some unprocessed methane gas may contain long chain hydrocarbon molecules that can create an odor.

From the available data in the Citizen Groundwater/Surfacewater Database, it would appear that the natural background level of methane in private wells in Northeastern Pennsylvania ranges from not detectable or trace levels to over 28 mg/L.  You may suspect the presence of methane gas in your water if you hear a “gurgling noise”, sputtering at the tap, the water has a lot of gas bubbles, is effervescent or fizzy.  

Note: If the pumping level of water in your well starts to fall below your pump intake, ordinary air may mix with the water and produce similar symptoms. When in doubt, contact a professional to determine the nature of the observed gas.

For more on this topic – Methane Gas Migration
Citizen Groundwater and Surfacewater Database