Methane and Other Gases in Drinking Water and Groundwater
Migration of Gas, Cuttings, or Mud During Drilling
Possible Pathways for Gas Migration Along Casing or Formation Cement Bounding and Cracking Issues
This is a free resource that is being provided by Mr. Brian Oram, Professional Geologist and owner of B.F. Environmental Consultants Inc. and the Water-Research Center. This fact sheet is part of our on-going education program for private well homeowners, i.e., as The Homeowner Outreach Program. B.F. Environmental Consultants, Inc. and Mr. Brian Oram support the Citizens Groundwater/Surfacewater Database, which is a grassroots effort to compile the water quality data for Northeastern Pennsylvania. To learn more, please contact the Water-Research Center- http://www.water-research.net.
Methane gas has been a “hidden” problem in Northeastern Pennsylvania. The gas is typically associated with wetlands, bogs, landfills, coal-producing formations, natural saline seeps, some glacial deposits, and gas storage areas.
Because of the development of the Marcellus Shale, the presence of methane gas and the potential for methane gas migration is a growing concern. Methane is a colorless, odorless gas that is lighter than air. Natural gas is mostly methane (70 – 90 % CH4), carbon dioxide (0 to 8 % CO2), plus other gases. The other gases may include ethane (C2H6), propane (C3H8), butane (C4H10), and hydrogen sulfide (H2S) as well as small amounts of helium.
1. Thermogenic methane, which is formed from buried organic matter at considerable depths where the rocks are compressed and heated; this includes the methane found in coal, gas from some Devonian sandstones/shales, and gas from the Marcellus and Utica Formations. Methane is produced by the inorganic breakdown of organic matter (heat and pressure).
2. Microbial (previous terme biogenic or bacterial methane) forms closer to the surface by the action of bacteria (methanogens- “bacteria that produce methane and cannot live in an environment with oxygen). This would include methane generated in landfills, lake sediments, wetlands/swamps, organic-rich glacial deposits, other recently buried organic deposits, and other carbon rich environments that are without oxygen. Microbial methane gas typically contains 20 percent to 30 percent less methane than is found in thermogenic natural gas.
Methane Gas Concerns and Concentrations
Just like radon gas, methane gas migrates naturally up through the soil, geological materials, and through the groundwater and into your home or well. Some gas naturally enters houses through the foundation, which is why some homes can have a radon problem if the gas entering the home happens to have a relatively high concentration of radon. When your water well is pumped, the drop in the level of the water in the wellbore reduces the pressure within the formation and permits more gas to migrate toward the wellbore. If the well is not properly vented and there happens to be substantial amounts of methane, the gas could accumulate under the well cap near the electrical connections for your well or the methane could enter with the well water and outgas in your home. The US Department of the Interior, Office of Surface Mining, suggests that when the level of methane gas in the water is less than 10 mg/L it is safe, but monitoring is required at 10 to 28 mg/L, and immediate action is needed above 28 mg/L. At a level of 28 mg/L, the water is fully saturated with methane and it is likely that any air space in the well is at or approaching the LEL. The air and out-gassing methane, not the water, is now flammable.
Based on a review of regulations and guidance from other states, the following are our professional recommendations related to suggested actions for your well depending on the level of methane gas detected in the water:
< 2 mg/L – Make sure your well is fitted with a passive venting system using a vented sanitary well cap.
> 2 to 7 mg/L – Monitor quarterly for one year and install a passive venting system using a vented pipe and vented sanitary well cap.
> 7 mg/L to < 10 mg/L – Corrective Action is Needed! – Seek help from a professional. Install active venting and monitor quarterly for one year. Consider Isotopic Analysis – “Like fingerprinting the source of the gas.” Remove ignition sources - if the well is in a well pit or basement, corrective action is needed and you should seek guidance from a licensed professional.
> 10 mg/L to < 20 mg/L – Corrective Action and Additional Testing are Needed! – Seek help from a professional.
> 20 mg/L – Immediate Corrective Action is Needed! – Seek help from a professional.
It would be advisable to test for methane, ethane, and propane by a certified testing laboratory. With respect to baseline testing, it would be wise to test for all three gases but if you’re on a budget at least test for methane and ethane and seek guidance from a professional.
Note: Corrective action is recommended if the well is in a well pit or in the basement and the initial methane in water concentration is above 2 mg/L.
Regarding the construction of Natural Gas Wells - it is not only important to properly case and cement, but it is critical that centralizers are used to aid in the development of uniform cement layers.
When to Test for Methane?
This is a common question and to be honest all we can say is that the level of methane in well water is controlled by many factors and conditions and it can be highly variable. If you want to test under the conditions most favorable to methane gas migration or leakage, it would be advisable to conduct testing when one or more of the following conditions exist:
a. barometric pressure is low and soils are saturated;
The variability in methane gas concentrations may require you to sample the well three to four times per year to establish a realistic baseline and provide some insight into background levels of methane gas. You can visually monitor the quality of the water, if the amount of dissolved gases increase, i.e., if there are more bubbles and fizz, maybe it is time to check the water. If you see foam, you would want to test the water for surfactants.
Taking Action – Based on Your Level of Methane
Level 1- Passive Venting: Methane Levels < 2 mg/L
Level 2 – Monitoring, Source Identification, and Passive Venting: Methane Levels 2 to < 7 mg/L
At this stage, a passive venting system should be installed. At this level, the venting system would consist of a vented well cap using a vented piping approach. The vent piping should have an inside diameter of 0.5 inches , extend 6 to 12 inches below the sanitary well cap, at least 12 inches above the well cap, and the end of the pipe that extends above grade should be turned down and fitted with a corrosion resistant fine screen. The screen should have a mesh size of 25 mesh or less. The vent piping should use watertight connections that extend above flood level and local ignition sources. A screen is added so insects cannot enter or clog the pipe and the pipe is turned down to prevent precipitation from directly entering the well. The well casing should extend at least 3 feet above the local flood stage for your area.
Level 3 – Active Venting, Removing Ignition Sources, and Seasonal Monitoring: Methane Level 7 to < 10 mg/L
Because the level of methane gas in the well water will fluctuate as the water level in the well changes, it would be advisable to conduct seasonal monitoring to better understand the variation in the gas concentration. In addition, this level of action would also include installing additional monitoring devices, an active venting system on the well, and an evaluation of the well to determine if a modification to the well would reduce the level of methane gas. The main goals are to attempt to understand the natural variation in methane levels, provide a venting system that will ensure your family and home is safe, and to proactively manage the potential risk. At this concentration, the venting system should vent the gas above local ignition sources, above flood level, and above a human exposure level, i.e., at least 6 feet or more.
Level 4 – Aggressive, Potentially Long-Term Treatment: Methane Levels > 10 mg/L to < 20 mg/L.
At this level, it is most likely that a treatment system will be needed and it would be necessary to install intrinsically safe equipment, i.e., switches, pumps, fixtures, etc. Intrinsic safety is a requirement that applies to devices that are being operated in areas with flammable gases or fuels. It means that the device is incapable of igniting those gases. In short, an intrinsically safe piece of equipment won't ignite flammable gases even if the unit is in a flammable environment. Additional real-time monitoring equipment and a gas shroud should be installed around the pump.
An immediate response and action is needed. At this level, it is likely the water has a number of aesthetic and safety issues and concerns and it may be advisable check if the water is also influenced by elevated levels of pH, ORP (oxidation/reduction potential), barium, strontium, chloride, iron, manganese, bromide, total dissolved solids, and other elements associated with saline water. Your first response should be to contact the PADEP and the local Natural Gas Company so they can conduct an investigation and seek the advice of a licensed professional.
1. Seek advice from a licensed professional.
2. Conduct an assessment of the methane level in the water, space under the well cap, and methane level in the air in your home or other confined spaces.
3. Mitigate any immediate hazards that could result in an explosion.
4. If possible, modify the wellhead to properly vent the gas and upgrade electrical connections to reduce the level of methane in the water to less than 7 mg/L.
5. This modification may include raising the well pump, installing a pump shroud, installing an active venting system, cement sealing a portion of the well, and any other modifications to make sure the well is properly and safely vented.
6. Conduct biological and chemical analysis to determine the source of the methane gas and general quality of the water.
7. If necessary, install a long-term treatment system. This should include some type of aeration and degasing system. Special precautions and additional testing will be needed if disinfection will be a component of the system.
If the water is saturated with methane, i.e., > 28 mg/L, it may be advisable to retest the water/air using the IsoBag sampling method recommended by Isotech Laboratories, Inc. and conducting an isotropic analysis of the gas/water and seek the assistance of a professional.
Well/ System Modifications
The Gas Shroud- In some cases, well contractors have reduced or eliminated methane or other gas problems in the well by installing a gas “shroud” on a submersible pump. This involves placing a pipe or tube, often a thin-walled plastic pipe, from the top of the submersible pump motor, a distance of 10 or more feet above the pump. The shroud is sealed at the top of the submersible pump motor below the pump intake. The top of the shroud is open and set below the pumping water level. Methane rises through the water column in the well, reducing the amount of methane in the water in the shroud. This method only works with 6-inch or larger diameter wells with standard well pumps, and wells that pump relatively small quantities of water at one time. Because the gas shroud may interfere with cooling the motor, this modification to your system should be done under the supervision of a licensed professional.
Cementing – If the source of the methane gas is from a formation near the base of the well, it may be advisable to consider abandoning a portion of the well. To make this decision, it would be advisable to have a copy of the well drillers log, so you have some idea of the type of rock units and location of water bearing zones; you don’t want to seal off the source of most of your well water. For this option, it may be necessary to camera survey the well and use other tools to evaluate the change in water quality with depth in the well.
Raise the Pump – Because the amount of gas dissolved in the water is a function of pressure, it may be advisable to consider raising the pumping setting. If the well is deep and the pump is set near the base of the well, it may be advisable to raise the pump intake level. It is likely that the amount of methane dissolved in the water will get lower as you decrease the water pressure in the borehole. Do not raise the pump intake above its pumping level because you will then start to pump air along with the water (air bubbles in the water). If the problem was related to lose of circulation, it may be possible to line the upper portion of the private well.
Install a Dole Flow Control Valve- This modification has been successful in preventing gas locking in submersible pumps. This modification would include the installation of a dole flow valve with by-pass to divert 1/3 of the pumped water back to the well. In addition, the check valve would removed from the pump. The bypass, dole flow value, and a new check valve should be installed at least 20 feet above the pump. The bypass should be located at a point where the water will cascade back to the well.
Maintenance and Monitoring
After you have taken the necessary corrective action, it will be necessary to maintain the equipment and monitor your drinking water quality. If you hire a water treatment specialist, you may want to consider a licensed or approved contractor who is certified by the Water Quality Association (WQA) and someone that is using an NSF Approved Process or components. For water quality monitoring, there is some self-monitoring equipment for this task. You should also conduct an annual water analysis and annual assessment of your system.
We want to take this opportunity to thank Dr. Brian Redmond, Professional Geologist at Wilkes University; Mr. Burt Waite, Professional Geologist at Moody and Associates, Inc., Mr. Bob Pirkle, President of Microseeps, Inc.; Mr. Tom Reilly, Jr. , Reilly Associates for providing a technical review of this factsheet.
© 2011 by B.F. Environmental Consultants Inc.
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