Natural Gas and Your Drinking Water System
What to consider if you have natural gas in your water supply
by Dave Clark, Director of Environmental Programs (RCAP)
Between coliform, nitrates, arsenic, and the rest, water operators have a tough job keeping our drinking water safe. But what about the contaminants we don’t have a maximum contaminant level (MCL) for like natural gas? What threats does gas in our water system pose to the operator and the consumer? In today’s world, in which there is a resurgence of underground disturbances due to various man-made activities, it pays to understand natural gas and how it might affect your water system.
Methane does not have a Safe Drinking Water Act (SDWA) MCL in water because it is considered non-toxic. Natural gas is comprised mostly of methane and gets into water either naturally or through various outside forces. Natural gas is odorless, has low solubility and high volatility, so it doesn’t tend to stay in water. Methane can also cause problems with the operation of the well pump and water system due to dissolved gases in the water.
The main concern with natural gas is explosion potential. In elevated concentrations it can escape quickly from water, causing an explosive hazard in poorly ventilated or confined areas. Escaping gas may seep into confined areas where it may reach dangerous concentrations. At explosive levels, a spark from a control switch in a well house or a flame from a water heater in a basement could ignite the methane with disastrous results. There have been rare cases in Pennsylvania where houses, camps, or wells have exploded due to methane accumulation.
How much methane is too much?
Explosive level for methane is 5 to 15 percent of volume in air. The US Department of the Interior estimates that water with methane concentrations above 28 mg/L may create explosive conditions. Well owners with methane concentrations between 10 – 28 mg/L should routinely monitor their well for methane to make sure concentrations are not increasing to a dangerous level. Wells with methane concentrations below 10 mg/L are considered safe for use.
Even though the main concern for methane is the potential for explosion it is important to remember that methane could also displace oxygen in an enclosed space, so there is also a danger of asphyxiation.
How do I measure methane?
Gas bubbling or hissing in the water is not necessarily an indication of methane; it could be other gases or air entering the water system. Gas detectors and meters are available for measuring methane in water. Methane escapes quickly from water, so it is often hard to measure. Methane is lighter than air, so meters need to be installed at a ceiling height to capture areas of highest concentration. Detecting methane in water is difficult, since it is odorless, tasteless, and colorless, therefore testing for methane in water requires a specialized sample collection process.
What can I do to remove methane?
If you are in a natural gas prone area, it may prove beneficial to simply vent your well caps and enclosed areas such as sheds. Once water reaches surface pressure and warms above 58 degrees, methane escapes from the water and rises in the well and accumulates under the well cap. A vent tube at the well cap can release methane from the well. For wells in basements or inside a building, the well cap needs to be tightly sealed, and the vent tube must be extended to release to the outside of the building.
Air stripping can be effective in removing methane as well as other constituents such as hydrogen sulfide and radon. Aeration can be as simple as spray aeration inside a storage tank or packed tower aerators. Water with iron, manganese, and some other contaminants may need to be pre-treated before aeration to avoid clogging the aeration units.
The simplest aeration method uses a pressure tank without a bladder or diaphragm (with an air release valve), but this is not effective for treating large volumes of water. Aeration of water as it enters a storage tank is more effective, but more expensive, often involving an air pump or compressor.
These simple methods could keep your drinking water treatment plant and your customers safe.