FACT SHEET
METHANE IN PRIVATE GROUNDWATER SYSTEMS
JUNE 2015
WHAT IS METHANE? Methane (CH4) is a colorless,
odorless, tasteless, and combustible gas that typically
makes up 70 to 98 percent of the mixture known as
natural gas. Methane is a naturally occurring hydrocarbon
that can be found underground in both shallow and deep
rock formations, including coal beds, and is also commonly
associated with marshes and landfills. Methane can
be created by thermogenic processes under heat and
pressure typical of deep formations; or by methanogenic
processes that include carbon dioxide (CO2) reduction
(to produce sub-surface microbial gas), and fermentation
(to produce near-surface microbial gas) that is typical of
shallow formations, landfills, or marshes.
HOW DOES METHANE GET INTO GROUNDWATER? The
presence of methane in water wells is relatively common.
It may occur naturally, generated within an aquifer (i.e.,
groundwater) source rock formation, or as the result of
migration through natural pathways. However, it may also
be present when current or historical human activities such
as landfills, coal mining and drilling for oil and gas create
conditions for gas migration. Methane can be present
in a water well as a gas dissolved within the groundwater
(dissolved gas) or as free gas.
WHAT ARE THE HEALTH AND SAFETY ISSUES RELATED
TO METHANE? Methane is classified as a simple
asphyxiant (impairs normal breathing) and explosion
hazard. Methane is not known to be toxic and consuming
water that contains methane does not present a health
hazard. Exposure to methane does not cause cancer.
Methane is lighter than air and free methane gas may
accumulate within an enclosed space such as a wellhead,
subsurface well vault, or within a poorly ventilated
basement or crawl space where it could present a risk
of explosion if allowed to build up to concentrations
above the Lower Explosion Limit (LEL). The LEL is the
lowest concentration capable of producing a flash, fire
or explosion. This concentration in air for methane is
approximately 5.0% (50,000 parts per million (ppm)).
When oxygen levels fall below 18% due to displacement
by methane, methane can result in asphyxiation (i.e.,
impairs normal breathing). Methane dissolved in
groundwater below its solubility (~28 milligrams per liter
(mg/l)), is not flammable, however, at concentrations that
exceed solubility, it can be ignited.
HOW IS METHANE CONCENTRATION MEASURED?
• Free Methane: Because methane is colorless, odorless,
and tasteless it cannot be readily detected without
a combustible gas detector or meter. This is why an
odorant that can be smelled at very low leakage
is added to natural gas sold to the public. Using a
meter, the presence of methane in air is commonly
measured as a percent of the LEL. It is important to
understand the units being used and how they relate
to each other. For example, a meter reading of 10%
LEL is equivalent to 0.5 % methane in air, or 5,000
ppm.
• Dissolved Methane: Laboratory analysis of a water
sample is required to determine the concentration of
methane dissolved in water. The resulting laboratory
report will provide the concentration of dissolved
methane as mg/l, or micrograms per liter (µg/l).
Again, it is important to understand the units being
used: 1 mg/l is equal to 1,000 µg/l; the unit “µg/l”
can also be expressed as parts per billion (ppb).
The maximum concentration of methane dissolved in
water varies with temperature and pressure. At 68oF
and standard atmospheric pressure, the maximum
dissolved concentration of methane in water is 28
mg/l; but when water is removed from a deep
formation under higher pressure conditions, the
concentrations can be higher.
WHAT LEVELS OF METHANE CONCENTRATION ARE
CONSIDERED A CAUSE FOR CONCERN?
• Free Methane: The U.S. Department of the
Interior, Office of Surface Mining Reclamation and
Enforcement (OSMRE) suggests the following action
levels for detections of free methane (based on
percentage in air):
For unoccupiable spaces, such as a well head:
• No Immediate Action – < 1%;
• Warning: investigate/vent – >1% to <3%; and
• Immediate Action: active venting/treatment –
>3%.
For occupiable spaces of a home:
• No Immediate Action – < 0.25%;
• Monitor trends – >0.25% to <0.5%;
• Warning: investigate/vent – >0.5% to <1%;
and
• Immediate Action: active venting/treatment –
>1%.
State and local regulations should be consulted if
free methane is detected in air at the warning levels
indicated by the OSMRE guidelines. Likewise, the
installation of an appropriate gas venting system is
advisable if methane is present.
•
Dissolved Methane: Generally, when dissolved
methane is present at concentrations of less than 10
mg/l, it isn’t necessary to take immediate action.
State and local regulations should be consulted
if dissolved methane is present in a water well
at 10 mg/l or greater. However, even at lower
concentrations, the installation of an appropriate gas
venting well cap is an inexpensive precaution. When
dissolved methane concentrations exceed 10 mg/l,
or in accordance with state and local requirements,
a properly qualified private water system contractor
should be consulted to carefully select and install
appropriate methane mitigation measures. This
may include the use of a vented well cap; or the
installation of a cistern, with or without an aeration
device, to further reduce the concentrations of
dissolved methane.
REFERENCES AND ADDITIONAL RESOURCES
•
Ohio Department of Health, Fact Sheet – Methane.
www.odh.ohio.gov/~/media/ODH/ASSETS/Files/eh/
HAS/Methane.ashx
•
Ohio Watershed Network, Well Water Interpretation
Tool. http://ohiowatersheds.osu.edu/well-educatedohio/well-water-interpretation-tool
•
Pennsylvania DEP Fact Sheet – Methane Gas and your
water well. www.dep.state.pa.us/dep/deputate/
minres/Districts/homepage/California/SSA/5600-FSDEP2690.pdf
•
Penn State Extension, Water Facts #24; Methane Gas
and Its Removal from Water Wells in Pennsylvania,
Rev 10/8/12. http://www.ourenergypolicy.org/wpcontent/uploads/2013/10/XH0010.pdf
•
Kentucky Department for Environmental Protection
– Division of Water, Methane Gas and Your Water
Well – A Fact Sheet for Domestic Water Well Owners
August 2003, Rev. May 2011. http://water.ky.gov/
groundwater/Lists/Helpful%20Publications%20
for%20Water%20Wells/Attachments/1/GWMethaneGasAndYourWaterWell.pdf
•
Technical Measures for the Investigation and Mitigation
of Fugitive Methane Hazards in Areas of Coal Mining.
US Dept. Int. Office of Surface Mining Reclamation and
Enforcement. http://www.osmre.gov/resources/library/
ghm/methane.pdf
STATE AGENCIES:
Michigan
Michigan Department of Environmental Quality
Office of Drinking Water and Municipal Assistance
Constitution Hall
525 West Allegan Street | P.O. Box 30473
Lansing, MI 48909-7973 | Telephone: 1-800-662-9278
http://www.michigan.gov/deq/0,1607,7-135-3306_332912306--,00.html
Ohio
Residential Water and Sewage Program
Bureau of Environmental Health
Ohio Department of Health | 35 Chestnut Street-7th Floor
Columbus, Ohio 43215 | Telephone: 614-644-7551
Fax: 614-466-4556
http://www.odh.ohio.gov/odhprograms/eh/sewage/
sewage1.aspx
Pennsylvania
Pennsylvania Department of Environmental Protection
Bureau of Safe Drinking Water
Rachel Carson State Office Building
400 Market Street | Harrisburg, PA 17101
Telephone: 1-717-783-2300
http://www.portal.state.pa.us/portal/server.pt/community/
about_dep/13464/office_locations/585263
West Virginia
West Virginia Bureau for Public Health
Office of Environmental Health Services
Environmental Engineering Division
350 Capitol Street, Room 313 | Charleston, WV 25301
Telephone: (304) 356-4272 | Fax: (304) 558-0289
http://www.wvdhhr.org/oehs/eed/contact.asp
Disclaimer: This fact sheet was created for general information
purposes only. Refer to the references provided herein for more
detailed information or contact Matthew Hammer at Hull &
Associates, Inc.
6397 EMERALD PARKWAY | SUITE 200 | DUBLIN, OHIO 43016