Methane

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.

Is my private well at risk?
Methane in the air can create the risk of an explosion hazard in poorly ventilated or confined areas. Methane also can cause unconsciousness or death by suffocation when encountered in enclosed spaces.
What is the measurement of methane?
Dissolved methane in drinking water is not currently classified as a health hazard and escapes quickly from water at low concentrations. In general, dissolved methane concentrations less than about 10 mg/L require no immediate action. Levels greater than 10 mg/L are a possible indication that methane may be of concern. Regulatory action levels for dissolved methane concentrations vary by state and should be reviewed.

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.

What are the health risks from methane?
In addition to any explosion hazard that might exist, prolonged exposure to methane must be avoided in places where it can displace breathable oxygen, such as basements or enclosed well houses.

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.

How can I address unsafe levels of methane?
Any water well with methane present should have a gas venting system installed at the well to vent gas to the atmosphere. This may allow a portion of methane gas to escape before it can accumulate in the water distribution lines, pressure tanks, water heaters, water treatment equipment, or well houses. This option is most effective for dealing with free gas bubbling through the water. However, this method is unlikely to be fully effective against the portion of gas dissolved in groundwater.

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.

Water treatment options for methane
Aeration at the point of water entry into the house can also help remove methane gas. Aeration releases gas from suspension in the water so it can be vented into the atmosphere through a pipe. Aeration equipment must be specially designed or modified by the manufacturer to safely remove methane gas. A totally closed system should be provided to prevent any methane gas from leaking out of the system and into the building interior.

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.