Methane migration
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April 3, 2012 My drinking water catches fire - now what?
In areas where it occurs, gas migration refers to the movement of natural gas (mostly methane) through bedrock and soil. It can leak from a variety of sources, including reservoir rock, coal seams, landfill, gas wells, or pipelines. It is very common in regions of North America that are undergirded by hydrocarbon deposits, such as in southwestern and northeastern Pennsylvania.
Gas_mig
Source: The Pittsburgh Geological Society, Natural Gas Migration Problems In Western Pennsylvania (Pamphlet).
Barometric pressure or temperature contrasts can cause diffuse natural gas molecules to migrate from areas of high concentration, such as gas escaping from coal seams, to areas of low concentration, such as in buildings or water wells. Methane gas typically crawls along bedrock fractures, semi-compact and loose soil, and may become dissolved in ground water. It can enter a building through basement walls, cracks in the foundation, or a water well. As it moves through highly permeable material such as soil, it can essentially be "here today and gone tomorrow". When it does build up in a basement or water well with poor air circulation, it can be an explosion risk. All it takes is one spark from a faulty wire or furnace to ignite it.
Methane is lighter than air, colorless, and difficult to detect without the aid of a small electronic device called a "gas sniffer". Like helium in a balloon, methane rises. When methane gets in a water well, the gas bubbles in the water that gets pumped out may be strong enough in concentration to burn when lit by a match. For people with methane in their water, lighting it on fire from a faucet makes an entertaining parlor trick--one that was used to amaze those unfamiliar with this phenomenon in the film, Gasland. Methane is rarely dangerous unless there is an accumulation of it in a confined space.
Without a doubt, hydraulic fracturing and horizontal drilling do release natural gas into the atmosphere. Most of this occurs during the flowback stage after a well has been fractured. That is often when you will see a well being flared as excess methane gets burned off. Methane is also present as dissolved gas in flowback water. Since it is lighter than air, when dissolved methane is exposed, it simply bubbles out of solution and dissipates into the atmosphere. It presents no risk to public health as it is only present in the air in extremely dilute amounts. Methane gas separation technology actually exists to capture methane before it leaves the well bore, yet so far this has generally been considered only an extra cost with little benefit. That may in part be due to the prevailing depressed prices of natural gas which make the captured product of little monetary value.
Homeowners who live in areas where gas migration is an issue generally realize that they need to avoid dangerous build-ups of methane gas. The two most common methods of getting rid of it are through venting and aeration.
Gas_vent
Source: Penn State, School of Forest Resources, Water Facts #24, Methane Gas and Its Removal from Wells in Pennsylvania
Venting can be aided by use of a fan to pump the methane outside or via an airstream to dilute the methane at the point of entry into a confined space. A water well's casing and cap may be vented to avoid accumulation in distribution lines, pressure tanks, water treatment equipment, water heaters, or in a well house. However, venting is less effective than aeration in dealing with dissolved methane in groundwater. The basic idea of aeration is when air gets pumped into the water, methane gas is forced out, and it generally is the only way to reduce methane concentrations to lower than 3 to 5 ppm (parts per million). These may consist of spray aerators that mist the well water into an enclosed tank, but may range at the high end to tower units that collect and disburse the accumulated gas.
One caveat must be added to the prescription of venting and/or aeration, to remove methane from drinking water. That is that anytime you open a sealed water system you introduce the possibility of bacterial contamination. Water is generally sanitized in a tank through chlorination. And here may be the rub. When chlorine interacts with organic matter, such as hydrocarbons, it can produce trihalomethanes in drinking water as a byproduct. These substances are considered carcinogens, and may produce kidney, liver and/or central nervous system issues. Trihalomethanes can be filtered out, or else the homeowner can try a disinfectant other than chlorine that doesn't have trihalomethanes as a byproduct. That will need to be the subject of another post.
Resources
Burckhardt, Tate A., "The Fine Points of Methane Removal", WaterTechOnline.com, Latham, NY, June, 2009, Accessed 2012-04-03.
Lidji, Eric, "A Way To Get That Gas Out of the Water", GreeningofOil.com, Anchorage, Alaska, 28 July, 2010, Accessed 2012-04-03.
Osborna, Stephen G. , Avner Vengoshb, Nathaniel R. Warnerb, and Robert B. Jackson, Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing, PNAS Journal, Washington, DC, 14 April, 2011, Accessed 2012-04-03.
Penn State, College of Agricultural Sciences, Cooperative Extension, School of Forest Resources, Water Facts #24, Methane Gas and Its Removal from Wells in Pennsylvania. (PDF) University Park, PA.
The Pittsburgh Geological Society, Natural Gas Migration Problems In Western Pennsylvania, (PDF), Pittsburgh, PA
Steingraber, Sandra, "On the Health Crisis Surrounding Natural Gas Extraction", Democracy Now hosted by Amy Goodman & Juan González, New York, NY, 27 May, 2011 (video), accessed 2012-04-03.
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