Department of Geology, University of Cincinnati, 500 Geology-Physics Building, Cincinnati, OH, 45221-0013, USA.
Department of Earth System Science, University of California, Irvine, Irvine, CA, 92697-4675, USA.
Environ Monit Assess. 2018 May 3;190(6):322. doi: 10.1007/s10661-018-6696-1.
Degradation of groundwater quality is a primary public concern in rural hydraulic fracturing areas. Previous studies have shown that natural gas methane (CH) is present in groundwater near shale gas wells in the Marcellus Shale of Pennsylvania, but did not have pre-drilling baseline measurements. Here, we present the results of a free public water testing program in the Utica Shale of Ohio, where we measured CH concentration, CH stable isotopic composition, and pH and conductivity along temporal and spatial gradients of hydraulic fracturing activity. Dissolved CH ranged from 0.2 μg/L to 25 mg/L, and stable isotopic measurements indicated a predominantly biogenic carbonate reduction CH source. Radiocarbon dating of CH in combination with stable isotopic analysis of CH in three samples indicated that fossil C substrates are the source of CH in groundwater, with one C date indicative of modern biogenic carbonate reduction. We found no relationship between CH concentration or source in groundwater and proximity to active gas well sites. No significant changes in CH concentration, CH isotopic composition, pH, or conductivity in water wells were observed during the study period. These data indicate that high levels of biogenic CH can be present in groundwater wells independent of hydraulic fracturing activity and affirm the need for isotopic or other fingerprinting techniques for CH source identification. Continued monitoring of private drinking water wells is critical to ensure that groundwater quality is not altered as hydraulic fracturing activity continues in the region. Graphical abstract A shale gas well in rural Appalachian Ohio. Photo credit: Claire Botner.
地下水水质恶化是农村水力压裂地区的主要公众关切。先前的研究表明，在宾夕法尼亚州马塞勒斯页岩的页岩气井附近的地下水中存在天然气甲烷（CH），但没有钻井前的基线测量。在这里，我们展示了俄亥俄州尤蒂卡页岩免费公共水质测试计划的结果，我们在水力压裂活动的时间和空间梯度上测量了 CH 浓度、CH 稳定同位素组成以及 pH 值和电导率。溶解的 CH 浓度范围从 0.2μg/L 到 25mg/L，稳定同位素测量表明主要是生物成因碳酸盐还原 CH 源。CH 的放射性碳测年与三个样品中 CH 的稳定同位素分析相结合表明，化石 C 底物是地下水 CH 的来源，一个 C 日期表明是现代生物成因碳酸盐还原。我们发现地下水 CH 浓度或来源与活跃的气井场地之间没有关系。在研究期间，水井中 CH 浓度、CH 同位素组成、pH 值或电导率没有明显变化。这些数据表明，在不受水力压裂活动影响的情况下，地下水中可能存在高水平的生物成因 CH，并证实需要同位素或其他 CH 源识别指纹技术。继续监测私人饮用水井对于确保地下水质量在该地区继续进行水力压裂活动时不会发生变化至关重要。
