No Residential Explosive Hazard from Present Natural Gas Drilling Techniques

The May 16 issue of C&E News has an article entitled, "Methane Fouls Well Water". The basic question is whether present drilling methods for natural gas are leading to contamination of water wells. A Duke University group sampled a number of wells in the vicinity of natural gas drilling and found no drilling fluids in the well water. However they did find an increased concentration of methane in the well water. The level was 19.2 mg per liter on average   
The secondary question was then whether this is a dangerous level of methane in well water. Most seemed to agree that methane is not a physiological poison. The only open question was whether the release of methane from the contaminated water within a domicile could lead to a concentration of methane, which would be dangerously explosive.
   
Fortunately, we always have at our disposal some simple mathematics, which can bring out the perspective of most problems. Let's do it now.
   
19.2 Mg of methane in a liter water is 0.0012 moles. Since a mole of gas occupies 22.4 L volume, the 19.2 mg of methane in one liter water would be 0.027 L of methane. Converting liters to ft.³ , gives 0.00094 ft.³ of methane, if all of it is released from one liter of water.
   
A small house might be 2000 ft.². With an 8 foot ceiling, the total volume would be 16,000 ft.³.
   
The lower explosive limit for methane in air is 5%. That is, an explosion could occur only if the methane concentration is at least 5%, with 95% air. In a 16,000 ft.³ house, that would require 800 ft.³ of methane.
   
If well water containing 19.2 mg per liter of methane were allowed to release all its methane within the house, it would require 850,000 L of well water to give 800 ft.³ of methane. That is also 224,000 gallons. No single household uses 224,000 gallons of well water in a reasonable time, and the concern about explosive possibility is not significant.