Methane contamination of drinking water is associated with gas-well drilling and hydraulic fracturing, as shown by studies in northeastern Pennsylvania and upstate New York. The research found that methane concentrations in drinking water wells increased with proximity to gas wells, reaching up to 64 mg CH₄ L⁻¹ in active extraction areas, which is a potential explosion hazard. In contrast, nonactive areas had much lower methane concentrations, averaging 1.1 mg L⁻¹. Isotopic analysis of methane (δ¹³C-CH₄) and ratios of methane to higher-chain hydrocarbons indicated that the methane in active areas originated from deeper thermogenic sources, such as the Marcellus and Utica shales, while nonactive areas had more biogenic or mixed sources. No evidence of contamination from deep saline brines or fracturing fluids was found. The study highlights the need for greater oversight, data collection, and regulation to ensure the sustainable development of shale-gas extraction and to build public confidence in its use. The findings suggest that methane contamination is a significant environmental risk associated with shale-gas exploration worldwide. The study also examined the potential mechanisms of methane migration into shallow groundwater, including physical displacement of gas-rich fluids, leaks from gas-well casings, and fracturing activities that create new fractures. The results emphasize the importance of long-term monitoring and baseline data collection to assess the environmental impact of shale-gas extraction.Methane contamination of drinking water is associated with gas-well drilling and hydraulic fracturing, as shown by studies in northeastern Pennsylvania and upstate New York. The research found that methane concentrations in drinking water wells increased with proximity to gas wells, reaching up to 64 mg CH₄ L⁻¹ in active extraction areas, which is a potential explosion hazard. In contrast, nonactive areas had much lower methane concentrations, averaging 1.1 mg L⁻¹. Isotopic analysis of methane (δ¹³C-CH₄) and ratios of methane to higher-chain hydrocarbons indicated that the methane in active areas originated from deeper thermogenic sources, such as the Marcellus and Utica shales, while nonactive areas had more biogenic or mixed sources. No evidence of contamination from deep saline brines or fracturing fluids was found. The study highlights the need for greater oversight, data collection, and regulation to ensure the sustainable development of shale-gas extraction and to build public confidence in its use. The findings suggest that methane contamination is a significant environmental risk associated with shale-gas exploration worldwide. The study also examined the potential mechanisms of methane migration into shallow groundwater, including physical displacement of gas-rich fluids, leaks from gas-well casings, and fracturing activities that create new fractures. The results emphasize the importance of long-term monitoring and baseline data collection to assess the environmental impact of shale-gas extraction.