TEMPORAL PATTERN OF NATURALLY OCCURRING METHANE LEVELS IN DOMESTIC WATER WELLS, OVERLYING THE MARCELLUS SHALE IN NEW YORK
In 2014 and again in 2016 we resampled 26 wells with among the highest methane concentrations (>0.01 mg/L) in the original sample of 137 wells. Using the 2013, 2014, and 2016 methane concentrations, we developed a time series of methane levels as a baseline record prior to unconventional drilling in New York. Methane concentrations between 2013, 2014 and 2016 were all positively correlated with correlation coefficients > 0.8. In all three years, >10% of observed methane concentrations (in the subsample of 26) were above warning levels (>10 mg/L).
The classification system and time series can be used to predict natural methane occurrence in New York state as well as regions with similar hydrogeologic settings, such as Pennsylvania, where unconventional natural gas extraction is common and expanding. Understanding the natural conditions favorable to methane occurrence will help identify the differences between methane migration due to unconventional drilling versus natural occurrence.