METHANE: HOW IS CONCENTRATION MEASURED AND WHAT LEVELS ARE CAUSE FOR CONCERN?
By Matt Hammer  |   July 10th, 2015
   
MEASUREMENT
 
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.   
 
WHEN SHOULD YOU BE CONCERNED?
 
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.   
 
For more information and resources you can download our Methane Fact Sheet HERE
Matt Hammer, Senior Project Manager
Matt has nearly 20 years of consulting experience in water resources and environmental investigation and remediation.  He has worked with clients in the oil and gas sector, the industrial sector, and with state and federal agencies.  His experience includes site characterization, predictive numerical modeling, data management and emergency response.  Matt’s training and specialization is in quantitative hydrogeology, including aquifer test design, and in numerical and analytical groundwater modeling.
 
He holds a Master of Science, Geological Sciences (Specializing in Hydrogeology) from The Ohio State University and a Bachelor of Science, Geology from Miami University.
 
 
Add a Comment
Name
 
     
Email
 
     
Comment*
 
 
 
 
 
Categories
 
Archive
 
2016
2015
Visit us