Methane (CH4) is a colorless, odorless, and tasteless gas that is the primary component of natural gas. When found in water, it is dissolved under pressure, similar to carbonation. While dissolved methane is not toxic when ingested, its presence indicates a significant safety concern. The danger arises when the gas separates from the water and accumulates in a confined space, creating a risk of fire, explosion, or asphyxiation.
The Immediate Physical Hazard of Methane Gas in Water
The most serious risk associated with methane in water occurs when the gas “comes out” of solution, a process known as degassing. This happens naturally when water pressure drops, such as when water is pumped from a well into a home’s plumbing system or agitated during use. The methane, being lighter than air, then rises and concentrates in enclosed areas like well houses, basements, or utility rooms.
Methane becomes highly flammable when its concentration in the air falls within a specific range, known as the explosive limits. The Lower Explosive Limit (LEL) is about 5% by volume, while the Upper Explosive Limit (UEL) is around 15% to 17%. Any ignition source, such as a pilot light, electrical spark, or switch, can cause a fire or explosion if the concentration is between the LEL and UEL.
In extremely high concentrations, particularly in small or poorly ventilated enclosures, methane presents a secondary hazard. It can displace the oxygen necessary for breathing, creating an asphyxiation risk. This risk is less common than the explosion hazard but remains a possibility in tightly sealed spaces. The main concern is the invisible, flammable air mixture the water can create, not the water itself.
Health Effects of Ingesting Methane-Contaminated Water
Dissolved methane is considered non-toxic, and drinking water containing it has not been linked to direct health effects. Once consumed, the gas is not absorbed by the body but is expelled naturally. Consequently, there is no federal drinking water standard for dissolved methane based on ingestion toxicity.
The concern with ingestion is often indirect, as methane contamination can correlate with the presence of other harmful substances. Depending on the source, the water may contain regulated co-contaminants like metals, salts, or bacteria. These other compounds, not the methane itself, typically pose the genuine health risk.
Determining the Origin of Methane Contamination
Methane enters groundwater through two primary pathways, and knowing the source is necessary for understanding the long-term risk. Natural sources are categorized as biogenic or thermogenic. Biogenic methane is produced by microbes that break down decaying organic matter, such as in wetlands or peat deposits, and this process usually yields relatively pure methane.
Thermogenic methane originates from deep underground, created by the heat and pressure acting on ancient organic material over geologic time. This type is associated with natural gas reserves and can migrate into groundwater through fissures or faults in the rock. The presence of other gases like ethane or propane suggests a thermogenic origin.
Human activities can also introduce methane into water, making the source anthropogenic. Common examples include leaks from landfills, compromised septic systems, or the migration of gas from underground storage fields or pipelines. Oil and gas drilling, particularly hydraulic fracturing, has also been shown to be a source of methane migration into water supplies.
Testing and Remediation Strategies for Methane in Water
Determining the concentration of methane in a private well requires professional water testing, with results typically reported in milligrams per liter (mg/L). The United States Department of the Interior suggests action levels to guide homeowners on the necessary response. Concentrations below 10 mg/L are viewed as safe, though monitoring may be recommended.
Immediate action is needed when concentrations reach or exceed 28 mg/L. At this level, the water is likely saturated and the air space in the well or home is approaching the explosive limit. For concentrations between 10 mg/L and 28 mg/L, mitigation is advised, and homeowners should remove all potential ignition sources from confined spaces.
The most effective method for removing dissolved methane from water is aeration, often achieved using an air-stripping system. This process exposes the water to air, forcing the dissolved methane to escape into the atmosphere before the water enters the home’s plumbing. As a low-cost solution, proper ventilation of all confined spaces, such as installing a vent on the wellhead, allows the lighter-than-air gas to disperse safely.