The occurrence of dissolved methane in groundwater is not unusual—and it is not limited to areas of oil and gas production. Analyses from water wells throughout the U.S. show up to 60 percent of all water wells may contain detectable dissolved methane concentrations. Methane can be produced by certain geologic formations, decomposition of organic material in rocks, or microbes.
Subsurface methane and other light gases may occur dissolved in groundwater or as free gas. The presence of methane in a well may vary over time due to pumping or seasonality.
The exact concentration of dissolved methane in water capable of producing an explosion depends on the water temperature, ventilation of the well, percent composition of the gas, and air movement within the house or structure. Periodic monitoring may be prudent until seasonal variation and the effect of day-to-day water usage is understood.
Sampling for dissolved methane in groundwater requires proper methodology to ensure accurate results. It is recommended that sampling be done by appropriately trained professionals. The well owner may want to consider water testing laboratories that obtain certification or accreditation in the methods used in testing for methane.
Concentrations of between 5.3 percent of air volume and 15 percent of air volume can create the risk of an explosion hazard in poorly ventilated or confined areas.
When oxygen levels fall below 19.5 percent, hypoxia, or a lack of oxygen within the body’s organs, will occur. Symptoms of hypoxia can include headache, impaired attention and thought processes, decreased coordination, impaired vision, dizziness, nausea, impaired judgment, and unconsciousness or even death. A 1 percent concentration of methane in the air may cause dizziness, headaches, loss of judgment, and other symptoms.
If groundwater with methane is pumped into a pressurized tank, in rare circumstances when a faucet or similar valve is opened, the water can flame when ignited as the gases are released from the water. In this case, a venting system installed in the water tank components is required.
It may be possible to release methane outside of the building, using a specially configured pressurized water storage tank that vents the gas to the atmosphere. In such a system, the vent pipe needs to extend above the eave height of the well house or home where the tank is located. Using a combination of venting at the well casing, as well as installing aeration equipment in the water storage tank, will decrease the potential for methane.
When considering a water treatment device, make sure its specifications match the substances and concentrations to be treated. The Water Quality Association at www.wqa.org and NSF International at www.nsf.org may be able to advise if the treatment technology being considered has been performance tested.