Table 1.

Mean values ± standard deviation of methane concentrations (as milligrams of CH₄ L^-1) and carbon isotope composition in methane in shallow groundwater δ¹³C-CH₄ sorted by aquifers and proximity to gas wells (active vs. nonactive)

Water source, n	milligrams CH4 L-1	δ13C-CH4, ‰
Nonactive Catskill, 5	1.9 ± 6.3	−52.5 ± 7.5
Active Catskill, 13	26.8 ± 30.3	−33.5 ± 3.5
Nonactive Genesee, 8	1.5 ± 3.0	−57.5 ± 9.5
Active Genesee, 1	0.3	−34.1
Active Lockhaven, 7	50.4 ± 36.1	−40.7 ± 6.7
Total active wells, 21	19.2	−37 ± 7
Total nonactive wells, 13	1.1	−54 ± 11

The variable n refers to the number of samples.