Moritz-_Methane_baseline

Methane Baseline Concentrations and Sources in Shallow Aquifersfrom the Shale Gas-Prone Region of the St. Lawrence Lowlands(Quebec, Canada)Anja Moritz,† Jean-Francois Helie,‡ Daniele L. Pinti,‡ Marie Larocque,‡ Diogo Barnetche,‡

Sophie Retailleau,‡ Rene Lefebvre,§ and Yves Gelinas*,†

†GEOTOP and Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke West, Montreal, Quebec,Canada, H4B 1R6‡GEOTOP and Departement des sciences de la Terre et de l’atmosphere, Universite du Quebec a Montreal, C.P. 8888, succursaleCentre-ville, Montreal, Quebec, Canada, H3C 3P8§INRS-ETE, 490 de la Couronne, Quebec, Quebec, Canada, G1K 9A9

*S Supporting Information

ABSTRACT: Hydraulic fracturing is becoming an importanttechnique worldwide to recover hydrocarbons from unconven-tional sources such as shale gas. In Quebec (Canada), theUtica Shale has been identified as having unconventional gasproduction potential. However, there has been a moratoriumon shale gas exploration since 2010. The work reported herewas aimed at defining baseline concentrations of methane inshallow aquifers of the St. Lawrence Lowlands and its sourcesusing δ13C methane signatures. Since this study was performedprior to large-scale fracturing activities, it provides backgrounddata prior to the eventual exploitation of shale gas throughhydraulic fracturing. Groundwater was sampled from private (n= 81), municipal (n = 34), and observation (n = 15) wellsbetween August 2012 and May 2013. Methane was detected in80% of the wells with an average concentration of 3.8 ± 8.8mg/L, and a range of <0.0006 to 45.9 mg/L. Methaneconcentrations were linked to groundwater chemistry anddistance to the major faults in the studied area. The methaneδ13C signature of 19 samples was > −50‰, indicating apotential thermogenic source. Localized areas of high methaneconcentrations from predominantly biogenic sources werefound throughout the study area. In several samples, mixing,migration, and oxidation processes likely affected the chemicaland isotopic composition of the gases, making it difficult topinpoint their origin. Energy companies should respect a safedistance from major natural faults in the bedrock whenplanning the localization of hydraulic fracturation activities tominimize the risk of contaminating the surrounding ground-water since natural faults are likely to be a preferentialmigration pathway for methane.

■ INTRODUCTIONThe interest in shale gas extraction and exploitation has beenincreasing worldwide during the past decade.1 In 2010, shale gasaccounted for 23% of the total dry natural gas production in theUnited States, a proportion projected to increase to 49% by2035.2,3

Received: January 25, 2015Revised: February 23, 2015Accepted: March 9, 2015Published: March 9, 2015

Article

pubs.acs.org/est

© 2015 American Chemical Society 4765 DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

Shale gas extraction utilizes hydraulic fracturing, or “fracking”,to release the entrapped gas by fracturing the source rock. This isdone by pumping large amounts of a mixture of water, sand andadditives into the well at high pressure.4,5 Some have suggestedthat hydraulic fracturing of the rock could induce methanemigration toward the surface, potentially contaminating ground-water resources.6−10 Yet, the most probable pathways ofgroundwater contamination by methane or flow-back waters(i.e., fracking fluids and recovered saline groundwater) are leaksthrough badly cemented well casings, and flow-back watersspillage on the surface.5−11 Studies carried out in the Marcellusshale have reported high thermogenic methane concentrations ingroundwater located within a distance of 1 km from frackedwells, as suggested by carbon (δ13C) and hydrogen (δ2H) stableisotope analyses.8−12 It is unclear however whether the gasmigrated through fracking-induced fractures or leaky casings.7−11

Li and Carlson (2014) found no correlation between dissolvedmethane concentration and distance to oil/gas well or welldensity in Northeastern Colorado. However, these authors haveshown that the number of shallow groundwater wells withmethane concentrations >5mg/L decreased as the distance to anoil/gas well became greater than 700 m.13 Darrah et al. (2014)recently reported that contaminated wells in the Barnett andMarcellus shales were linked to gas leakage from intermediate-depth strata through failures of annulus cement, faultyproduction casings, or an underground gas well failure, ruling

out upward migration from depth through overlying geologicalstrata.7

Few studies worldwide report methane concentrations andsources before hydraulic fracturing, although local legislationsrequiring companies to assess local baseline methane concen-trations before drilling are progressively being implemented.14 InNew York State, Kappell et al. (2012) reported natural methanelevels in groundwater but did not assess its source,15 whileMcPhillips et al. (2014) found that methane concentrations weremostly correlated to groundwater chemistry, with little influencefrom valleys versus upslope location of the wells, distance from aconventional gas well, or geohydrologic units.16 McIntosh et al.(2014) reported that dissolved methane in groundwater ofsouthwesternOntario (Canada) was almost exclusively microbialin origin and that its concentration was linked to bedrockgeology.17 To our knowledge, the only study reporting theanalysis of groundwater quality before and after hydraulicfracturing is that of Boyer et al. (2011).18 These authors reportedno statistical difference in groundwater−methane concentrationsbefore and after drilling with or without hydraulic fracturing(approximately 50% of the wells were fracked). The dissolvedmethane concentration was higher in one well following drilling,but this well had not been hydraulically fractured.18 Longermonitoring periods maybe required to understand potential risksto shallow groundwater owing to the slow migration rate ofcontaminants (gas and fluid) through the well casing, the

Figure 1.Map of sampled area and the St. Lawrence Lowlands geology and tectonic structures. Methane concentrations are represented with the size ofthe circles and methane δ13C signatures by their color. Note that the “fracked” wells (orange stars) appearing on the map are private exploration wellsfracked before the moratorium in 2010. They are sealed and cannot be accessed to collect gas samples.

Environmental Science & Technology Article

DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

4766

sedimentary sequence or natural preferential flow paths.19 Toassess whether methane contamination is associated withfracking, it is therefore important to monitor both the baselineconcentrations of methane and its isotopic signature prior toshale gas extraction.8,10,12,15−17,20

Discriminating between deep thermogenic and shallowbacterial sources of methane using stable carbon isotopesignatures is crucial to distinguish between the natural presenceof methane in groundwater and potential contaminationsources.18,21−24 Furthermore, it is important to assess whethera relationship exists between the natural occurrence/concen-tration of thermogenic methane and the main geological featuresof the study area, such as the presence of faults and the lithology.In the St. Lawrence Lowlands (Quebec, Canada), the Utica

Shale has been targeted by energy companies because of itspotential for shale gas production, but total recoverable reservesstill have to be fully assessed.25 Since 2010, there has been amoratorium on shale gas exploration and exploitation. Recently,the Quebec government has launched scientific, societal, andeconomic studies on the risks and benefits of potential futureshale gas exploitation.26 These studies offered a uniqueopportunity to measure hydrocarbon gas concentrations andδ13C signatures in shallow aquifers in an area not yet affected byshale gas exploitation, and hence to document baselineconcentrations and sources of dissolved hydrocarbon gases.27

This paper presents methane, ethane and propane concen-trations as well as the δ13C signature of methane from 130municipal, private and observation wells sampled in the area ofthe St. Lawrence Lowlands. Approximately 1.9 million peoplelive in this region, which is the most important and fertileagricultural area of the Quebec Province (Canada), and whichhas recently been assessed for the shale gas potential from theUtica Shale.25,28

■ MATERIALS AND METHODSGeology and Hydrogeology. Located within the St.

Lawrence Lowlands, the study area corresponds to a 15 435km2 corridor between Montreal and Quebec City, bordered bythe Appalachian Mountains (southeast) and the north shore ofthe St. Lawrence River (northwest) (Figure 1). This corridorcorresponds to the main exploration area of the Utica Shale gas.25

The area overlaps two geological provinces: the St. LawrencePlatform, a Cambrian−Ordovician carbonate and siliciclasticplatform, and the Cambrian−Devonian orogeny of theAppalachian Mountains. The Ordovician sedimentary units ofthe St. Lawrence Platform crossed by the sampled wells are instratigraphic order:29 (1) 30−300 m thick calcareous mudstoneof the Utica Shale with a total organic carbon content (TOC)between 1 and 1.5% and the facies- and time-equivalent Stony

Point Formation;28 (2) the Sainte-Rosalie Group, a typical flyschconsisting of a succession of siltstone, mudstone, silty shale andrare dolomitic units; (3) a turbiditic unit dominated bymudstones with subordinate alternating sandstone and siltstoneof the Lorraine Group with TOC between 0.5 and 1%. Thisgroup is the most exposed in the St. Lawrence Lowlands (Figure1); and finally (4) shale, sandstone and conglomerates of the“molasse”-type Queenston Group. The Ordovician sedimentarysequence of the St. Lawrence Platform is directly overlain byQuaternary sediments made of glacial tills, marine and lacustrinesilt, and from Champlain Sea silty clays and glacio-fluvial sands(11 200−9800 yrs).30 In the Appalachian Mountains, thefractured bedrock aquifer is composed of metasediments, mainlyshales, schists, slates, and phyllades belonging to several units ofCambrian−Ordovician age. A detailed stratigraphy of the studyarea is reported in Pinti et al. (2014).31

The study area is marked by multiple faults, with the mostimportant ones being the Yamaska normal fault bordering the St.Lawrence River and the Logan line, a thrust fault that marks thetransition between the St. Lawrence Platform and theAppalachian Mountains (Figure 1). A regional semiconfined orconfined aquifer is located in the Ordovician fractured bedrock ofmoderate hydraulic conductivity (∼10−6−10−5 m/s). Limitedextent granular aquifers are found also in the superficial coarse-grained Quaternary sediments, such as the glacio-fluvial or fluvialsands. The main groundwater flow directions in the bedrockaquifer are SE-NW and follow the general topography, withrecharge occurring mostly in the Appalachian Mountains anddischarge to the St. Lawrence River or its main tributaries.32

Aquifer confinement increases gradually from the highestelevations toward the St. Lawrence Platform.Groundwater chemistry shows the occurrence of low-salinity

water, dominantly of Ca−Mg−HCO3− type, close to the

recharge areas of the Appalachian Mountains. This water evolvesby ion exchange into a Na-HCO3 type downstream, withelectrical conductivity ranging from 88 to 4,466 μS/cm in thestudy area. Saline groundwater (conductivity from 717 to 31,500μS/cm) is found in a 10 km wide zone bordering the St.Lawrence River close to the Chambly-Fortierville syncline.32,33

Groundwater is clearly brackish in a 2,200 km2 area to the northof the Monteregie-Est basin in the fractured Queenston Group,where salinity reaches 5 g/L locally.34 The source of salinityderives from exchanges of freshwater with pore seawater trappedinto the thick Champlain Sea silty-clays that confine partially ortotally the aquifer fractured bedrock aquifer.35

Sampling and analysis. Water samples were collectedthroughout the St. Lawrence Lowlands (Figure 1). A total of 130wells were visited on private properties (n = 81), municipalities(n = 34), as well as at groundwater observation stations (n = 15).

Table 1. Average, Median, Range of Methane, Ethane and Propane Concentrations (in mg/L), and Methane δ13C Signatures (in‰ vs. VPDB)a

methane (mg/L) ethane (mg/L) propane (mg/L) methane (‰)

average 3.8 ± 8.8 0.010 ± 0.018 0.003 ± 0.002 −62.3Nb 117 42 10 73median 0.1 0.003 0.002 −60.0maximum 45.9 ± 0.8 0.086 ± 0.003 0.006 ± 0.004 −24.8minimum <0.0006 <0.0004 <0.0010 −105.1limit of detectionc 0.0006 0.0004 0.0010 N/Alimit of quantificationc 0.0020 0.0010 0.0030 N/A

aThe NBS19 and LSVEC international standards were used to anchor δ13C signatures to the VPDB scale. The experimental detection/quantificationlimits are also provided. bNumber of samples measured (above the limit of detection). c3 standard deviations (3 σ). d10 standard deviations (10 σ).

Environmental Science & Technology Article

DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

4767

All the wells were open borehole bedrock and their depthsranged from 6 to 120 m. A volume equivalent to three times thewater volume in the wellbore was purged for observation wellsthat are not used for human consumption. Water was sampledonce the physicochemical parameters of the water (pH,conductivity and temperature) had stabilized. Water wassampled at the wellhead in municipal wells and before anywater treatment or filtration unit in domestic wells. Sampling andanalysis were performed following established methods, asdescribed in the Supporting Information section.

■ RESULTS AND DISCUSSIONHydrocarbon Gas Concentrations. Dissolved methane

was detected in 117 of the 130 wells. The average methaneconcentration was 3.8± 8.8mg/L, themedian was 0.1mg/L, andthe range was <0.0006 to 45.9 mg/L (Table 1; the complete dataset is available in the Supporting Information section, Table S1).In 84 samples with detectable methane levels (65% of allsamples), the measured concentration was below 1 mg/L(Figure 2). Ethane and propane concentrations were detected in

a limited number of wells with maximum concentrations of 0.086mg/L for ethane (42 wells) and 0.006 mg/L for propane (10wells) (Table 1).In May 2013, the Quebec Ministry of Environment approved

new regulations for the protection of groundwater that set analert level for methane concentration in groundwater used fordrinking purposes to 7 mg/L.36 Above this level, well ownershave to take measures to avoid the accumulation of gaseousmethane in water pipes. As an example, the U.S. Department ofEnergy considers methane concentrations between 10 and 28mg/L as non problematic; direct actions are required only at 28mg/L.37 The 7 mg/L concentration level was exceeded for 18wells where it averaged 21.8 ± 11.0 mg/L. At four of these wells,methane concentrations were higher than 28 mg/L, whichcorresponds to the solubility of methane in water at 1 atm and 15°C. The maximum measured concentration was 45.9 ± 0.8 mg/L. These high concentrations indicate that methane sponta-neously degasses and can be problematic if it accumulates inclosed, unventilated spaces such as the well casing. These resultsare comparable to methane concentrations in groundwatermeasured by Kappel et al. (2012), McPhillips et al. (2014) as well

as McIntosh et al. (2014) in drinking water wells from New YorkState (United States) and southwestern Ontario (Canada).15−17

The higher concentrations of methane were found along theYamaska, Logan and d’Aston faults on the south shore oppositeto Trois-Rivieres, around the city of Chambly and northeast ofMontreal (Figure 1). Dissolved methane concentrations in theseareas were approximately 10 times higher than the averagegroundwater−methane concentrations in the St. LawrenceLowlands. The Logan line, which corresponds to the boundarybetween the St. Lawrence Platform Ordovician terrains and theCambrian-Ordovician metasediments of the Appalachians,marks the transition between high and low dissolved methaneconcentrations. The majority of wells with high methaneconcentrations fall within the Lorraine Group Shales (Figure1), which is also a hydrocarbon source rock. The CH4 medianconcentrationmeasured in wells tapping into the Lorraine Groupis 1.92 mg/L, against 0.34, 0.003, and 0.075 mg/L for the Sainte-Rosalie, Utica Shale and Queenston Groups, respectively.Noteworthy, methane concentrations are highest in wells locatedclosest to major fault accidents (Figure 3), suggesting facilitatedmigration of gases through natural faults in the bedrock. This isespecially clear for wells taping the bedrock aquifer in theLorraine formation.

Methane Sources. The δ13C signature of methane wasdetermined for the 73 samples with methane concentrationshigher than 0.03 mg/L allowing accurate δ13C measurement,with isotopic ratios ranging from −105.1 to −24.8‰. Methaneδ13CC signatures below −64‰ are usually indicative of abiogenic (bacteriogenic) source if minimal methane oxidationhas occurred,24,38 although less depleted δ13C values are alsopossible depending on the methane precursor.39,40 For instance,methane produced in freshwater sediments, where precursorscan be more enriched than in groundwater, showδ13Csignaturesranging from −65 to −50‰.40 In contrast, methane δ13Csignatures ranging between −50 and −20‰ suggest athermogenic source,24,39 although slightly more negative valueshave also been observed.38

In this work, δ13C values lower than −64‰ were used toindicate a predominantly biogenic origin and δ13C signatureshigher than −50‰ a predominantly thermogenic origin. Out ofthe 73 samples with CH4 concentrations greater than 0.03 mg/L,31 had δ13C signatures more depleted than −64‰, while 19

Figure 2. Distribution of methane concentrations from 0 to 50 mg/Land from 7 to 50 mg/L (insert) for samples with detectable CH4concentrations.

Figure 3. Relationship between methane concentrations and distance ofthe groundwater well from the major bedrock faults.

Environmental Science & Technology Article

DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

4768

others had δ13C signatures less depleted than −50‰ (Figure 4).The majority of samples with less depleted δ13C signatures were

characterized by lowmethane concentrations (<1 mg/L). Out ofthese 19 samples with a δ13C signature > −50‰, three hadmethane concentrations >7 mg/L, with one sample having aconcentration of 26.4 ± 1.9 mg/L, close to the solubility ofmethane at 1 atm and 15 °C (28 mg/L). These three well werelocated close to the Logan line (Figure 1). The five samples witha δ13C signature < −64‰ and a concentration >7 mg/L werealso close to the Logan line and associated with the Lorrainegroup. The vast majority of samples with methane concen-trations >7 mg/L showed isotopic signatures between −64 and−50‰ (Figure 4).Thermogenic gases normally contain ethane, propane and

other higher hydrocarbon gases at varying concentrations.Biogenic gases contain mostly methane and possibly very lowlevels of ethane.43 The concentration ratios between methaneand the sum of these higher hydrocarbon gases (C1/(C2+C3)),also referred to as gas wetness, can thus be used as a sourceindicator. Ratios greater than 1000 indicate a biogenic sourcewhile ratios lower than 100 indicate a thermogenicsource38,39,41−43 Figure 5 shows that the majority of the samplesplot outside the thermogenic gas window. The only samplefalling within the thermogenic window (δ13C > −50‰) had alow methane concentration (<1 mg/L). Thus, none of thesamples with high methane concentrations (>7 mg/L) and lessdepleted in 13C (δ13C > −50‰) appears to be of thermogenicorigin.There were nine cases where the gas wetness ratio suggested a

nonthermogenic source whereas the δ13C signature of methanewas typical of a thermogenic one. Three processes can alter thegas wetness and/or the δ13C signature of methane: (1) mixing ofdifferent sources; (2) oxidation of methane; and (3) migration ordiffusion of gas.38−43 Mixing of biogenic and thermogenic gasescan be represented with different mixing curves that varyaccording to the gas wetness ratio and the δ13C signature of theend-members. Two such theoretical mixing curves arerepresented in Figure 5 with different thermogenic and biogenicend-members.

Oxidation of methane results in an enrichment in 13C of theresidual methane. It also results in a decreasing C1/(C2+C3)ratio39−42,44 since the oxidation kinetics of 12C−CH4 are higherthan those of 13C−CH4, and the oxidation kinetics of methaneare higher than those of ethane and propane.39 On the otherhand, the migration of gas mainly results in a higher C1/(C2+C3) ratio since the diffusion rate through the bedrock ishigher for the lighter methane compared to heavier ethane andpropane. In most studies published so far, migration was found toonly slightly affect the δ13C signature of methane compared tothe C1/(C2+C3) ratio.

41,42

Samples that plot outside of the biogenic or thermogenicwindow could have been affected by one of more of theseprocesses (i.e., mixing, oxidation and migration). For example,three wells showed high concentrations of methane with a δ13C >−50‰ (Figure 2) although their C1/(C2+C3) ratio was >100(Figure 5), suggesting an alteration of the original gascomposition. The available data is however insufficient to drawdefinitive conclusions on the processes taking place for eachsample. Methane in samples falling within the thermogenic andbiogenic windows could also have been affected by theseprocesses to some extent. The determination of the δ13Csignature of ethane and/or the δ2H signature of methane wouldbe necessary to determine the exact processes that affected thegas wetness or δ13C signature of methane in these samples.Despite the fact that most of the gas measured in the samples

was biogenic in origin, thermogenic sources also contributed tosome extent to the groundwater pool of light hydrocarbons in thearea. This thermogenic gas could be mostly associated with theLorraine silty shale outcrops. Here, biogenic gases formed atshallower depths in anoxic environments, likely in semiconfinedor confined fractured aquifers where methanogens canproliferate,45,46 possibly mix with thermogenic gases formed inthe deeper horizons of the Lorraine Shale or even the Utica Shale.Although speculative at this point, major faults could be apreferential path for this deeper thermogenic component tomigrate upward7 and mix with biogenic shallower methane(Figure 2).

Figure 4. Relationship between methane concentrations and δ13Csignatures by geological formations. Gray areas depict the delimitationsbetween biogenic (left gray area) and thermogenic (right gray area)methane.

Figure 5. Bernard plot of methane/(ethane+propane) ratio versus δ13Cof methane for the samples analyzed in this study. Gray areas depictapproximate delimitations for biogenic and thermogenic methane.Mixing curves A and B are theoretical mixing curves modified fromWhiticar.39 The arrows indicate the general direction of the methane/(ethane + propane) ratios and the δ13C of methane upon oxidation ormigration. Modified from refs 48 and49

Environmental Science & Technology Article

DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

4769

The hypothesis of an increased methane concentration inconfined aquifers is supported by the relation found between themeasured concentration of methane and well water chemistry(Figure 6). Freshwater recently recharged in nonconfined

aquifers having a Ca,Mg(HCO3) and Na-SO4-type chemistryare extremely depleted in methane (CH4 median values of 0.06and 0.02 mg/L, respectively). Methane concentration increasesrapidly in more evolved groundwater affected by ion Ca−Naexchange (Na-HCO3) and exchange with saline waters (Na−Cl-type) in confined aquifers (CH4median values of 0.34 to 7.6 mg/L, respectively). This net increases of methane concentration isprobably related to the change from oxygenated shallowenvironments to deeper and anoxic ones where methanogenscan proliferate and methane oxidation and loss is stronglylimited.45−47

Methane is thus a natural component of groundwater in the St.Lawrence Lowlands and can be present at concentrations thatexceed solubility under conditions encountered in the wells.Depleted δ13C measurements suggest that methane found inthese shallow fractured bedrock aquifers is mostly produced bymethanogenic bacteria, although the gas composition may havebeen altered by processes such as migration and/or mixing withdeeper-seated thermogenic sources and bacterial oxidation.Additional analyses such as the δ13C signature of ethane andpropane as well as δ2H of methane are required to pinpoint theexact sources of this gas and the processes that may have alteredit. The relationship between methane concentrations andgroundwater chemistry suggests that methane levels arecontrolled to a large extent by the composition of the bedrock,local redox conditions, as well as water flow patterns andconfinement (residence time). Natural faults in the bedrock arelikely to be a preferential migration pathway for methane,especially in the Lorraine formation, as shown by the inversetrend between methane concentrations and distance from thefaults. This is an important finding as a faulty fracked well locatedin the vicinity of natural faults could lead to much greatercontamination of the groundwater compared to wells operated incompact intermediate bedrock. Energy companies, which targetthe area where the bedrock of the Lorraine group is located,should thus respect a safe distance from major natural faults inthe intermediate and superficial bedrock when locating frackedwells. In view of the current study, this is a reasonable precaution

to minimize the risk of contaminating the surroundinggroundwater in case a fracked well becomes faulty.

■ ASSOCIATED CONTENT*S Supporting InformationSampling and analysis of methane, ethane and propane dissolvedin groundwater, plus a table listing all the data acquired in thiswork. This material is available free of charge via the Internet athttp://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*Phone: 514-848-2424 ×3337; fax: 514-848-2868; e-mail: [email protected] ContributionsSampling was carried out by A.M., D.B., and S.R., while theconcentration and isotopic analyses were done by AM.Calibration of the reference gases for isotopic analysis wasdone by A.M. and J.F.H. A.M. and Y.G. wrote the first draft of themanuscript with inputs from D.P., J.F.H., M.L., and R.L.. Allauthors have given approval to the final version of themanuscript.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe thank the Strategic Environmental Assessment Committeeon Shale Gas and the Quebec Government for entrusting us thisproject (Project CEES no. E3-9 and FQRNT “InitiativesStrategiques d’Innovation” Project no. 171083). This researchwas funded by grants from the FRQ-NT, NSERC, and CFI.

■ REFERENCES(1) Kerr, R. A. Natural Gas From Shale Bursts Onto the Scene. Science2010, 328, 1624−1626.(2) United States Energy Information Administration. Annual EnergyOutlook 2012 with Projections to 2035; 2012.(3) Wang, Q.; Chen, X.; Jha, A. N.; Rogers, H. Natural gas from shaleformation − The evolution, evidences and challenges of shale gasrevolution in United States. Renewable Sustainable Energy Rev. 2014, 30,1−28.(4) Kargbo, D. M.; Wilhelm, R. G.; Campbell, D. J. Natural gas plays inthe Marcellus Shale: Challenges and potential opportunities. Environ.Sci. Technol. 2010, 44, 5679−5684.(5) Vidic, R. D.; Brantley, S. L.; Vandenbossche, J. M.; Yoxtheimer, D.;Abad, J. D. Impact of shale gas development on regional water quality.Science 2013, 340, 1−9.(6) Warner, N. R.; Jackson, R. B.; Darrah, T. H.; Osborn, S. G.; Down,A.; Zhao, K.; White, A.; Vengosh, A. Geochemical evidence for possiblenatural migration of Marcellus Formation brine to shallow aquifers inPennsylvania. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 11961−11966.(7) Darrah, T. H.; Vengosha, A.; Jackson, R. B.; Warner, N. R.; Poreda,R. J. Noble gases identify the mechanisms of fugitive gas contaminationin drinking-water wells overlying the Marcellus and Barnett Shales. Proc.Natl. Acad. Sci. U. S. A. 2014, 111, 14076−14081.(8) Osborn, S. G.; Vengosh, A.; Warner, N. R.; Jackson, R. B. Methanecontamination of drinking water accompanying gas-well drilling andhydraulic fracturing. Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 8172−8176.(9)Molofsky, L. J.; Connor, J. A.; Farhat, S. K.; Wylie, A. S., Jr Methanein Pennsylvania water wells unrelated to Marcellus shale fracturing. OilGas J. 2011, December 5, 54−67.(10) Jackson, R. E.; Gorody, A. W.; Mayer, B.; Roy, J. W.; Ryan, M. C.;Van Stempvoort, D. R. Groundwater protection and unconventional gasextraction: The critical need for field-based hydrogeological research.Ground Water 2013, 51, 488−510.

Figure 6.Methane concentrations measured in groundwater of differentchemical types.

Environmental Science & Technology Article

DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

4770

(11) Stokstad, E. Will fracking put too much fizz in your water? Science2014, 344, 1468−1471.(12) Jackson, R. B.; Vengosh, A.; Darrah, T. H.; Warner, N. R.; Down,A.; Poreda, R. J.; Osborn, S. G.; Zhao, K.; Karr, J. D. Increased stray gasabundance in a subset of drinking water wells near Marcellus shale gasextraction. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 11250−11255.(13) Li, H.; Carlson, K. H. Distribution and origin of groundwatermethane in the Wattenberg Oil and Gas Field of Northern Colorado.Environ. Sci. Technol. 2014, 48, 1484−1491.(14) Wyoming Oil and Gas Conservation Commission (WOGCC).Wyoming Oil and Gas Regulations, Chapter 3. Operational and DrillingRules, 2014.(15) Kappel, W. M.; Nystrom, E. A. Dissolved Methane in New YorkGroundwater, U.S. Geological Survey Open File Rep. 2012-1162, 2012;pp 1−6.(16) McPhillips, L. E.; Creamer, A. E.; Rahmb, B. G.; Walter, M. T.Assessing dissolved methane patterns in central New York groundwater.J. Hydrol.: Reg. Stud. 2014, 1, 57−73.(17) McIntosh, J. C.; Grasby, S. E.; Hamilton, S. M.; Osborn, S. G.Origin, distribution and hydrogeochemical controls on methaneoccurrences in shallow aquifers, southwestern Ontario, Canada. Appl.Geochem. 2014, DOI: 10.1016/j.apgeochem.2014.08.001.(18) Boyer, E. W.; Swistock, B. R.; Clark, J.; Madden, M.; Rizzo, D. E.The Impact of Marcellus Gas Drilling on Rural Drinking Water Supplies;The Center for Rural Pennsylvania, 2011; p 29.(19) Myers, T. Potential contaminant pathways from hydraulicallyfractured shale to aquifers. Ground Water 2012, 50, 872−882.(20) Gorody, A. Factors affecting the variability of stray gasconcentration and composition in groundwater. Environ. Geosci. 2012,19, 17−31.(21) Chafin, D. T.; Swanson, D. M.; Grey, D. W.Methane-Isotope Datafor Ground Water and Soil Gas in the Animas River Valley, Colorado andNew Mexico, 1990−91. , U.S. Geological Survey Water ResouceInvesigations. Report 93−4007, 1996.(22) Sloto, R. A. Baseline Groundwater Quality from 20DomesticWells inSullivan County, Pennsylvania, 2012 Scientific Investigations Report2013 − 5085. 2013.(23) Barker, J. F.; Fritz, P. Carbon isotope fractionation duringmicrobial methane oxidation. Nature 1981, 293, 289−291.(24) Stolper, D. A.; Lawson, M.; Davis, C. L.; Ferreira, A. A.; SantosNeto, E. V.; Ellis, G. S.; Lewan, M. D.; Martini, A. M.; Tang, Y.; Schoell,M.; Sessions, A. L.; Eiler, J. M. Gas formation. Formation temperaturesof thermogenic and biogenic methane. Science 2014, 344, 1500−1503.(25) Rivard, C.; Lavoie, D.; Lefebvre, R.; Sejourne, S.; Lamontagne, C.;Duchesne, M. An overview of Canadian shale gas production andenvironmental concerns. Int. J. Coal Geol. 2014, 121, 64−76.(26) Commite de l’evaluation environnementale strategique sur le gazde schiste. Plan de Realisation de l’Evaluation EnvironnementaleStrategique sur le gaz de Schiste; 2012.(27) Pinti, D. L.; Gelinas, Y.; Larocque, M.; Barnetche, D.; Retailleau,S.; Moritz, A.; Helie, J. F.; Lefebvre, R. Concentrations, Sources EtMecanismes De Migration Preferentielle Des Gaz D’Origine Naturelle(Methane, Helium, Radon) Dans Les Eaux Souterraines Des Basses- TerresDu Saint-Laurent, 2013; p 94.(28) Lavoie, D.; Rivard, C.; Lefebvre, R.; Sejourne, S.; Theriault, R.;Duchesne, M. J.; Ahad, J. M. E.; Wang, B.; Benoit, N.; Lamontagne, C.The Utica Shale and gas play in southern Quebec: Geological andhydrogeological syntheses and methodological approaches to ground-water risk evaluation. Int. J. Coal Geol. 2013.(29) Lavoie, D.; Theriault, R. Upper Ordovician shale gas and oil inQuebec: Sedimentological, geochemical and thermal frameworks.Search Discovery 2014, 9.(30) Lamothe, M. A new framework for the pleistocene stratigraphy ofthe Central St. Lawrence Lowland, Southern Quebec. Geographie Phys.Quat. 1989, 43, 119.(31) Pinti, D. L.; Retailleau, S.; Barnetche, D.; Moreira, F.; Moritz, A.M.; Larocque, M.; Gelinas, Y.; Lefebvre, R.; Helie, J. F.; Valadez, A.222Rn activity in groundwater of the St. Lawrence Lowlands, Quebec,

eastern Canada: Relation with local geology and health hazard. J.Environ. Radioact. 2014, 136, 206−217.(32) Larocque, M.; Gagne, S.; Tremblay, L.; Meyzonnat, G. Projet deconnaissance des eaux souterraines du bassin versant de la riviere Becancouret de la MRC de Becancour - Rapport scientifique, Rapport depose auministere du Developpement durable, de l’Environnement, de la Fauneet des Parcs, 2013; p 213,(33) Larocque, M.; Meyzonnat, G.; Gagne, S. Rapport d’etape phase I:Projet de connaissance des eaux souterraines de la zone Nicolet et de la partiebasse de la zone Saint-Francois, Rapport depose au ministere duDeveloppement durable, de l’Environnement, de la Faune et des Parcs,m2013; p 106.(34) Carrier, M. A.; Lefebvre, R.; Rivard, C.; Parent, M.; Ballard, J. M.;Benoit, N.; Vigneault, H.; Beaudry, C.; Malet, X.; Laurencelle, M.Portrait des ressources en eau souterraine en Monteregie Est, Quebec,Canada. Projet realise conjointement par l’INRS, la CGC, l’OBV Yamaskaet l’IRDA dans le cadre du Programme d’acquisition de connaissances sur leseaux souterraines, rapport final I, 2013.(35) Cloutier, V.; Lefebvre, R.; Savard, M. M.; Therrien, R.Desalination of a sedimentary rock aquifer system invaded byPleistocene Champlain Sea water and processes controlling ground-water geochemistry. Environ. Earth Sci. 2009, 59, 977−994.(36) MDDEFP. Reglement sur le prelevement des eaux et leurprotection. Gaz. Off. du Quebec 2013, 145, 2184−2215.(37) Technical Measures for the Investigation and Mitigation of FugitiveMethane Hazards in Areas of Coal Mining; Department of Energy. U.S.Department of the Interior. Office of Surface Mining Reclamation andEnforcement2001; p 129.(38) Schoell, M. The hydrogen and carbon isotopic composition ofmethane from natural gases of various origins.Geochim. Cosmochim. Acta1980, 44, 649−661.(39) Whiticar, M. J. Carbon and hydrogen isotope systematics ofbacterial formation and oxidation of methane. Chem. Geol. 1999, 161,291−314.(40) Whiticar, M.; Faber, E.; Schoell, M. Biogenic methane formationin marine and freshwater environments: CO2 reduction vs. acetatefermentationIsotope evidence. Geochim. Cosmochim. Acta 1986, 50,693−709.(41) Schoell, M. Genetic characterization of natural gases. Am. Assoc.Pet. Geol. Bull. 1983, 67, 2225−2238.(42) Stahl,W. J. Carbon and nitrogen isotopes in hydrocarbon researchand exploration. Chem. Geol. 1977, 20, 121−149.(43) Whiticar, M. J. Stable isotope geochemistry of coals, humickerogens and related natural gases. Int. J. Coal Geol. 1996, 32, 191−215.(44) Whiticar, M. J.; Faber, E. Methane oxidation in sediments andwater column environmentsIsotope evidence. Org. Geochem. 1986,10, 759−768.(45) Coleman, D. D.; Liu, C.; Riley, K. M. Microbial methane in theshallow Paleozoic sediments and glacial deposits of the Illinois, USA.Chem. Geol. 1988, 71, 23−40.(46) Aravena, R.; Wassenaar, L. I. Dissolved organic carbon andmethane in a regional confined aquifer, southern Ontario, Canada:Carbon isotope evidence for associated subsurface sources. Appl.Geochem. 1993, 8, 483−493.(47) Aravena, R.; Wassenaar, L. I.; Plummer, L. N. Estimating 14Cgroundwater ages in a methanogenic aquifer. Water Resour. Res. 1995,31, 2307−2317.(48) Faber, E.; Stahl, W. Geochemical Surface Exploration forHydrocarbons in North Sea. Am. Assoc. Pet. Geol. Bull. 1984, 68, 363−386.(49) Bernard, B. B.; Brooks, J. M.; Sackett, W. M. Natural gas seepagein the Gulf of Mexico. Earth Planet. Sci. Lett. 1976, 31, 48−54.

Environmental Science & Technology Article

DOI: 10.1021/acs.est.5b00443Environ. Sci. Technol. 2015, 49, 4765−4771

4771