Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities
Elevated levels of diesel range organic compounds in groundwater near Marcellus gas operations are derived from surface activities
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DOI：
10.1073/pnas.1511474112
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发表时间：
2015-10-27
影响因子：
11.1
通讯作者：
Plata, Desiree L.
中科院分区：
文献类型：
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作者：
Drollette, Brian D.;Hoelzer, Kathrin;Plata, Desiree L.
在通过大流量水力压裂(HVHF)开采天然气的过程中，使用了数百种有机化学品。然而，目前尚不清楚这些注入深层页岩层的化学物质是否会到达浅层地下水含水层，并影响当地水质，无论是从这些深层高压注入点，还是从地表或浅层地下。在这里，我们报告了宾夕法尼亚州东北部马塞卢斯页岩上的私人住宅井中浅层地下水样本中可检测到的有机化合物水平。地下水样品的可净化和可提取有机化合物分析显示，痕量挥发性有机化合物远低于环境保护局的最高污染物水平，汽油范围(0-8 ppb)和柴油范围(DRO；0-157 ppb)的挥发性有机化合物含量较低。特定化合物的分析表明，邻苯二甲酸二(2-乙基己基)酯的存在，这是一种公开的HVHF添加剂，值得注意的是，在典型的地源水样和野外空白中没有这种添加剂。将这些分析与(I)深层咸水地下水的无机化学指纹，(Ii)特征惰性气体同位素，以及(Iii)活跃的页岩气开采井和已披露的违反环境健康和安全规定的井之间的空间关系进行配对，我们区分了与自然形成的咸水地下水有关的化学特征和与地表的替代人为途径(如意外溢出或泄漏)有关的化学特征。这些数据支持一种DRO向地下水的输送机制，即从地表意外释放压裂液化学物质，而不是这些流体从下面的页岩地层地下流动。
Hundreds of organic chemicals are used during natural gas extraction via high-volume hydraulic fracturing (HVHF). However, it is unclear whether these chemicals, injected into deep shale horizons, reach shallow groundwater aquifers and affect local water quality, either from those deep HVHF injection sites or from the surface or shallow subsurface. Here, we report detectable levels of organic compounds in shallow groundwater samples from private residential wells overlying the Marcellus Shale in northeastern Pennsylvania. Analyses of purgeable and extractable organic compounds from 64 groundwater samples revealed trace levels of volatile organic compounds, well below the Environmental Protection Agency's maximum contaminant levels, and low levels of both gasoline range (0-8 ppb) and diesel range organic compounds (DRO; 0-157 ppb). A compound-specific analysis revealed the presence of bis(2-ethylhexyl) phthalate, which is a disclosed HVHF additive, that was notably absent in a representative geogenic water sample and field blanks. Pairing these analyses with (i) inorganic chemical fingerprinting of deep saline groundwater, (ii) characteristic noble gas isotopes, and (iii) spatial relationships between active shale gas extraction wells and wells with disclosed environmental health and safety violations, we differentiate between a chemical signature associated with naturally occurring saline groundwater and one associated with alternative anthropogenic routes from the surface (e.g., accidental spills or leaks). The data support a transport mechanism of DRO to groundwater via accidental release of fracturing fluid chemicals derived from the surface rather than subsurface flow of these fluids from the underlying shale formation.