Gas in Groundwater
by Darrel Dunn, Ph.D., PG, Hydrogeologist
This web page is a brief, non-technical discussion of gas dissolved in groundwater that is apropos to a question from a viewer of this website. It deals with dissolved methane and hydrogen sulfide, and is not a comprehensive treatment of gas dissolved in groundwater.
Methane and hydrogen sulfide are common dissolved gasses in groundwater. Methane can produce an explosive atmosphere if concentrated in an enclosed space in a house or other enclosure. The web pages on this site titled Subsurface Methane West US and Subsurface Methane New Mexico contain much information on the occurrence of methane in groundwater.
Low concentrations of hydrogen sulfide may impart an unpleasant odor often described as a "rotten egg" smell. Hydrogen sulfide may be produced by reduction of sulfate in groundwater that has a low oxygen concentration. Such chemical reduction may be augmented by the action of anaerobic bacteria if organic material is present. Hydrogen sulfide in the low concentrations associated with the foul odor may cause health effects. An OSHA Fact Sheet says that "repeated or prolonged exposures may cause eye inflammation, headache, fatigue, irritability, insomnia, digestive disturbances and weight loss." A CDC Fact Sheet says that hydrogen sulfide has not been shown to cause cancer in humans. This fact sheet also states that the EPA has determined that data for hydrogen sulfide are inadequate for carcinogenic assessments. Hydrogen sulfide is corrosive to metals, can cause yellow or black stains on kitchen and bathroom fixtures, and can discolor and affect taste of beverages and cooked foods.
Two ways to deal with gas in water from a well are (1) explore for productive layers in the aquifer that do not contain gas, and (2) remove the gas from the water produced by the existing well. One way to remove gas from water is by aeration. There are various ways to aerate the water. Some are installed within the well, others treat the produced water.
Some additional information on gas in groundwater is in the web page on groundwater quality.