Using Discriminant Analysis to Determine Sources of Salinity in Shallow Groundwater Prior to Hydraulic Fracturing

Lautz, Laura K.; Hoke, G. D.; Lu, Zunli; Siegel, Donald I.; Christian, Kayla; Kessler, J. D.; Teale, Natalie

doi:10.1021/es502244v

Cited by 36 publications

(27 citation statements)

References 32 publications

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“…While groundwater from the current study in New York State resembles previous results documented in Pennsylvania, West Virginia, and New York (Heisig and Scott ; Darrah et al , ; Lautz et al ; Harkness et al ), the magnitude of chemical variation is much higher in Pennsylvania groundwater than that in New York. For example, the highest concentrations of helium documented in New York are 37,090 × 10 −6 ccSTP/L, which is nearly an order of magnitude lower than Pennsylvania (403,035 × 10 −6 ccSTP/L) (Darrah et al , ).…”

Section: Discussionsupporting

confidence: 78%

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Kreuzer

Darrah²,

Grove

et al. 2018

Groundwater

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Environmental concerns regarding the potential for drinking water contamination in shallow aquifers have accompanied unconventional energy development in the northern Appalachian Basin. These activities have also raised several critical questions about the hydrogeological parameters that control the naturally occurring presence and migration of hydrocarbon gases in shallow aquifers within petroliferous basins. To interrogate these factors, we analyzed the noble gas, dissolved ion, and hydrocarbon gas (molecular and isotopic composition) geochemistry of 98 groundwater samples from south-central New York. All samples were collected ≫1km from unconventional drilling activities and sample locations were intentionally targeted based on their proximity to various types of documented fault systems. In agreement with studies from other petroliferous basins, our results show significant correlations between elevated levels of radiogenic [ He], thermogenic [CH ], and dissolved ions (e.g., Cl, Br, Sr, Ba). In combination, our data suggest that faults have facilitated the transport of exogenous hydrocarbon-rich brines from Devonian source rocks into overlying Upper Devonian aquifer lithologies over geologic time. These data conflict with previous reports, which conclude that hydrodynamic focusing regulates the occurrence of methane and salt in shallow aquifers and leads to elevated levels of these species in restricted flow zones within valley bottoms. Instead, our data suggest that faults in Paleozoic rocks play a fundamental role in gas and brine transport from depth, regulate the distribution of their occurrence in shallow aquifers, and influence the geochemistry of shallow groundwater in this petroliferous basin.

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Section: Discussionsupporting

confidence: 78%

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Kreuzer

Darrah²,

Grove

et al. 2018

Groundwater

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“…In this case, we would expect coincidence of Na‐rich waters that reflect mixing of fresh and saline water and elevated thermogenic methane concentrations. Other prior studies have also found strong associations between basin brine mixing with shallow groundwater and occurrence of methane [ Lautz et al ., ; Warner et al ., ].…”

Section: Discussionmentioning

confidence: 99%

Methane occurrence is associated with sodium‐rich valley waters in domestic wells overlying the Marcellus shale in New York State

Christian

Lautz

Hoke

et al. 2016

Water Resources Research

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Prior work suggests spatial parameters (e.g., landscape position, distance to nearest gas well)can be used to estimate the amount of dissolved methane in domestic drinking water wells overlying the deep Marcellus Shale. New York (NY) provides an opportunity to investigate methane occurrence prior to expansion of high-volume hydraulic fracturing because unconventional gas production is currently banned in the state. We sampled domestic groundwater wells for methane in 2013 (n 5 137) across five counties of NY bordering Pennsylvania, and then resampled a subset of those wells in 2014 for methane concentrations and d 13 C-CH 4 and dD-CH 4 . The majority of waters from wells sampled (77%) had low concentrations of methane (<0.1 mg/L), and only 5% (n 5 7) had actionable levels of methane (>10 mg/L). Dissolved methane concentrations did not change as a function of proximity to existing vertical gas wells, nor other parameters indicating subsurface planes of weakness (i.e., faults or lineaments). Methane levels were significantly higher in wells closer to hydrography flow lines, and most strongly correlated to Na-HCO 3 water type. The distribution of methane between Ca-HCO 3 (n 5 76) and Na-HCO 3 (n 5 23) water types significantly differed (p < 0.01), with median methane concentrations of 0.002 and 0.78 mg/L, respectively. Combined classification of sampled waters based on the dominant water cation, well topographic position, and geologic unit of well completion effectively identified wells with a greater than 50% probability of having methane concentrations exceeding 1 mg/L. Such classification schemes may be useful as a screening tool to assess natural versus gas production-related sources of methane in domestic wells.

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“…Previous applications of inorganic and isotopic tracers of dissolved salts and hydrocarbon and noble gas geochemical tracers have revealed the influence of the tectonic and hydrogeological setting on water quality and natural contamination in areas of oil and gas development both in the NAB and elsewhere (Darrah et al, 2015b;Engle and Rowan, 2014;Llewellyn, 2014, Lautz et al, 2014Molofsky et al, 2013;Mortiz, 2015;Revesz et al, 2010;Schon, 2011;Sharma and Baggett, 2011;Siegel et al, 2015a;Siegel et al, 2015b;Warner et al, 2012, Warner et al, 2013b, Wunsch, 1992.…”

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confidence: 99%

The geochemistry of naturally occurring methane and saline groundwater in an area of unconventional shale gas development

Harkness

Darrah

Warner

et al. 2017

Geochimica et Cosmochimica Acta

128

167

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Since naturally occurring methane and saline groundwater are nearly ubiquitous in many sedimentary basins, delineating the effects of anthropogenic contamination sources is a major challenge for evaluating the impact of unconventional shale gas development on water quality. This study investigates the geochemical variations of groundwater and surface water before, during, and after hydraulic fracturing and in relation to various geospatial parameters in an area of shale gas development in northwestern West Virginia, United States. To our knowledge, we are the first to report a broadly integrated study of various geochemical techniques designed to apportion natural and anthropogenic sources of natural gas and salt contaminants both before and after drilling. These measurements include inorganic geochemistry (major cations and anions), stable isotopes of select inorganic constituents including strontium (87 Sr/ 86 Sr), boron (δ 11 B), lithium (δ 7 Li), and carbon (δ 13 C-DIC), select hydrocarbon molecular (methane, ethane, propane, butane, and pentane) and isotopic tracers (δ 13 C-CH 4 , δ 13 CC 2 H 6), tritium (3 H), and noble gas elemental and isotopic composition (He, Ne, Ar) in 112 drinking-water wells, with repeat testing in 33 of the wells (total samples=145). In a subset of wells (n=20), we investigated the variations in water quality before and after the installation of nearby (<1 km) shale-gas wells. Methane occurred above 1 ccSTP/L in 37% of the groundwater samples and in 79% of the samples with elevated salinity (chloride >50 mg/L). The integrated geochemical data indicate that the saline groundwater originated via naturally occurring processes, presumably from the migration of deeper methane-rich brines that have interacted extensively with coal lithologies. These observations were consistent with the lack of changes in water quality observed in drinkingwater wells following the installation of nearby shale-gas wells. In contrast to groundwater samples that showed no evidence of anthropogenic contamination, the chemistry and isotope ratios of surface waters near known spills or leaks occurring at disposal sites (n=8) mimicked the composition of the Marcellus flowback fluids, and show direct evidence for impact on surface water by fluids accidentally released from nearby shale-gas well pads and oil and gas wastewater disposal sites. Overall this study presents a comprehensive geochemical framework that can be

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Using Discriminant Analysis to Determine Sources of Salinity in Shallow Groundwater Prior to Hydraulic Fracturing

Cited by 36 publications

References 32 publications

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Structural and Hydrogeological Controls on Hydrocarbon and Brine Migration into Drinking Water Aquifers in Southern New York

Methane occurrence is associated with sodium‐rich valley waters in domestic wells overlying the Marcellus shale in New York State

The geochemistry of naturally occurring methane and saline groundwater in an area of unconventional shale gas development

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