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Applied Geochemistry 65 (2016) 1e13

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Applied Geochemistry

journal homepage: www.elsevier .com/locate/apgeochem

Linking groundwater quality to residence times and regional geologyin the St. Lawrence Lowlands, southern Quebec, Canada

Marion Saby a, *, Marie Larocque a, Daniele L. Pinti a, b, Florent Barbecot a, Yuji Sano b,Maria Clara Castro c

a GEOTOP and D�epartement des sciences de la Terre et de l'atmosph�ere, Universit�e du Quebec �a Montr�eal, CP8888 succ, Centre-Ville, Montr�eal, QC, Canadab Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, 277-8564, Japanc Dept. of Earth and Environmental Sciences, University of Michigan, 1100 N. University, Ann Arbor, MI, 48109-1005, USA

a r t i c l e i n f o

Article history:Received 16 January 2015Received in revised form26 October 2015Accepted 27 October 2015Available online 4 November 2015

Keywords:Groundwater qualityGroundwater residence timesRegional geologySt. Lawrence LowlandsQuebec (Canada)

* Corresponding author.E-mail address: marion.saby23@gmail.com (M. Sa

http://dx.doi.org/10.1016/j.apgeochem.2015.10.0110883-2927/© 2015 Elsevier Ltd. All rights reserved.

a b s t r a c t

The assessment of groundwater quality in shallow aquifers is of high societal relevance given that largepopulations depend directly on these water resources. The purpose of this study was to establish linksbetween groundwater quality, groundwater residence times, and regional geology in the St. LawrenceLowlands fractured bedrock aquifer. The study focuses on a 4500 km2 watershed located in the St.Lawrence Lowlands of the province of Quebec in eastern Canada. A total of 150 wells were sampled formajor, minor, and trace ions. Tritium (3H) and its daughter element, 3He, as well as radiocarbon activity(A14C) were measured in a subset of wells to estimate groundwater residence times. Results show thatgroundwater evolves from a CaeHCO3 water type in recharge zones (i.e., the Appalachian piedmont) to aNaeHCO3 water type downgradient, toward the St. Lawrence River. Locally, barium (Ba), fluoride (F), iron(Fe), and manganese (Mn) concentrations reach 90, 2, 18, and 5.9 mg/L respectively, all exceeding theirrespective Canadian drinking water limits of 1, 1.5, 0.3, and 0.05 mg/L. Release of these elements intogroundwater is mainly controlled by the groundwater redox state and pH conditions, as well as by thegeology and the duration of rockewater interactions. This evolution is accompanied by increasing 3H/3Heages, from 4.78 ± 0.44 years upgradient to more than 60 years downgradient. Discrepancies betweencalculated 3H/3He and 14C water ages (the latter ranging from 280 ± 56 to 17,050 ± 3410 years) suggestmixing between modern water and paleo-groundwater infiltrated through subglacial recharge when theLaurentide Ice Sheet covered the study area, and during the following deglaciation period. A linearrelationship between 3H activity and corrected 14C versus Mg/Ca and Ba support a direct link betweenwater residence time and the chemical evolution of these waters. The Ba, F, Fe, and Mn concentrations ingroundwater originate from Paleozoic rocks from both the St. Lawrence Platform and the AppalachianMountains. These elements have been brought to the surface by rising hydrothermal fluids alongregional faults, and trapped in sediment during their deposition and diagenesis due to reactions withhighly sulfurous and organic matter-rich water. Large-scale flow of meltwater during subglacial rechargeand during the subsequent retreat of the Laurentide Ice Sheet might have contributed to the leaching ofthese deposits and their enrichment in the present aquifers. This study brings a new and original un-derstanding of the St. Lawrence Lowlands groundwater system within the context of its geologicalevolution.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Anthropogenic activity and climate change are arguably thelargest threats to groundwater quality in the 21st century

by).

(Aeschbach-Hertig and Gleeson, 2012), however local geology canalso have a significant impact (e.g., Nickson et al., 1998; Marimonet al., 2012). Groundwater quality assessment has primarily beencarried out using either statistical approaches applied togeochemical data (Li et al., 2012; Mahlknecht et al., 2004; Maclearet al., 2003; Pacheco, 1998; Paralta and Ribeiro, 2001), geochemicalmodeling (Carrillo-Rivera et al., 2002; Homoncik et al., 2010;

M. Saby et al. / Applied Geochemistry 65 (2016) 1e132

Marimon et al., 2012), or by tracing groundwater flow using stableand radioactive isotopes (Clark and Fritz, 1997; Barbecot et al.,2000). These approaches require an understanding of the presentgeological context, but not of the geological evolution of the region.However, knowledge of the geological evolution of a particularregionmight prove critical to understandwhich individual elementor set of elements are present and how they interact with eachother and with the host media, in addition to their spatial distri-bution in a particular area. Very few studies consider the diverserelationships between the past and present hydrogeological con-texts and the geological evolution of the studied area, thegroundwater residence time, the occurrence of highly mineralizedfluids, and their role in the formation of economic deposits (e.g.,Aquilina and De Dreuzy, 2011; Kloppmann et al., 2002).

With more than five million inhabitants, the St. LawrenceLowlands is the most densely populated region in the Canadianprovince of Quebec. This region hosts most of the agricultural andindustrial activities of the province. Approximately 5% of thegroundwater extracted in this area is used as drinking water(MDDELCC, 2012). The region is characterized by a regional frac-tured bedrock aquifer of CambroeOrdovician age, overlain bydiscontinuous and often perched Quaternary granular aquifers.Several studies carried out in southern Quebec have highlighted thepresence of high barium (Ba), fluorine (F), iron (Fe), and manganese(Mn) concentrations (Lacasse, 2013) in fresh and brackishgroundwater (Cloutier et al., 2010). High concentrations of theseelements have been observed in the Becancour (Meyzonnat et al.,2015) and Eastern Monteregie (Beaudry, 2013) watersheds inparticular, but their origins (i.e., anthropogenic or natural) andrelease mechanisms into groundwater are not yet fully understood.

The purpose of this study was to establish links betweengroundwater quality, groundwater residence times, and regionalgeology in the St. Lawrence Lowlands fractured bedrock aquifer.This study focused on the Nicolet-St. François watershed (hence-forth referred to as NSF), which is located between the previouslymentioned Becancour and Eastern Monteregie watersheds (Fig. 1).Understanding the regional geology and the emplacement ofgeological units over time is extremely important to understandingpast fluid circulation and the impact of thesemineralized fluids androcks on the current groundwater chemical signature. Here,groundwater contains relatively high levels of F, Ba, Mn, and Fe. Tounderstand the spatial distributions of these ions and their originsin groundwater, the groundwater chemistry and regional flowweretraced using major and trace elements measured in 150 wells, andresidence times were estimated with the 3H/3He and 14C methodsin a few select wells. Geochemical analyses were also made on rockcuttings to constrain concentrations of anomalous elements in thebedrock aquifer. These were compared with the correspondingconcentrations in the groundwater.

2. Geology and hydrogeology of the study area

2.1. Geology

The study area corresponds to the Nicolet River Basin and thelower part of the Saint-François River watershed, in the Centre-du-Qu�ebec region (Fig. 1a). The regional fractured aquifer is composedof rocks belonging to two geological provinces: the AppalachianMountains in the southeastern part of the basin, and the St. Law-rence Platform in the northwestern part (Fig. 1a). Geographically,the area is part of the St. Lawrence Lowlands.

The St. Lawrence Platform is a Cambrian-Lower Ordovician sil-iciclastic and carbonate platform, formed in an extensional contextrelated to the opening of the Iapetus Ocean, and overlain byMiddle-Late Ordovician foreland carbonate-clastic deposits, which

were deposited during the closure of Iapetus and the AppalachianMountains buildup. Cambrian Potsdam Group quarztitic sandstone,Early Ordovician dolostone of the Beekmantown and Chazy Groups,Middle-Late Ordovician carbonates of the Black River and TrentonGroups, carbonate-rich Utica shale and the silty-shale of theLorraine/Sainte-Rosalie Groups, and molassic shales of the Queen-ston Group are unconformably deposited on the gneiss graniteanorthosite terrains of the Proterozoic Grenville Province(Globensky, 1987). Cambrian green and red shales of the SilleryGroup, slate, limestone, and sandstone conglomerate of the BourretFm, schists of the Drummondville Olistostrome, calcareous slate ofthe Bulstrode and Melbourne Fm, and schists, shales, sandstoneand conglomerates of the Shefford, Oak Hill, and SuttoneBennettGroups outcrop in the Appalachian piedmont (Globensky, 1993).

Unconsolidated Quaternary fluvio-glacial deposits cover thefractured Paleozoic aquifer (Lamothe, 1989). Basal deposits are tillsfrom the last two Quaternary deglaciation episodes (45 and13 ka BP), followed by glacio-lacustrine sandy and organic deposits.A thick clay layer deposited during the Champlain Sea episode(12e9 ka BP; Bolduc and Ross, 2001) covers sandy deposits over a30 km strip along the St. Lawrence River (Lamothe and St-Jacques,2014). This thick clay layer led to the confinement of the underlyingfractured bedrock aquifer and Quaternary deposit aquifers in thisnarrow area. Further upgradient, the clay layer is no longer uni-form, creating a flat area composed of sand, patches of clay, andshale, which led to a heterogeneous and semi-confined hydro-geological context. Upgradient, reworked till and bedrock outcropsleave the fractured aquifer unconfined in its main recharge zone(Fig. 1b).

2.2. Hydrogeology

The study area is divided into two main aquifer systems(Larocque et al., 2015). The first corresponds to superficial uncon-solidated Quaternary aquifers of relatively limited thickness(1e80 m), and the second system is the underlying Paleozoicfractured bedrock aquifer. Hydraulic conductivities in the fracturedbedrock aquifer are heterogeneous and range from 5 � 10�9 m/s to7 � 10�6 m/s (Larocque et al., 2015). Hydraulic conductivities in theQuaternary units range from 1.2 � 10�5 m/s for sand to5.8 � 10�7 m/s for till. Groundwater flows from recharge zones inthe Appalachian piedmont toward the St. Lawrence River, and themain tributaries, the Nicolet and Saint-François rivers. The meandepth of the water table is 4.4 m. The annual volume of abstractedgroundwater is 23.4 Mm3, corresponding to 3% of the annualrecharge (152 mm; Larocque et al., 2015). Most of the study area iseither cultivated (48%, mainly along the St. Lawrence River) orforested (45%, mainly in the Appalachian piedmont) (Larocqueet al., 2015). Urbanized zones, surface water, and wetlands occupy2, 1.1, and 3.7% of the study area respectively. Agriculture is domi-nated by corn (27%), hay (22.4%), and soybean (19.8%) production(Larocque et al., 2015). The 1961e2010 average annual temperaturefor the study area is 5.6 �C, and the average annual precipitation is1018 mm/yr (25% as snowfall; Nicolet and Drummondville stations,Environment Canada, 2014).

3. Sampling and analytical methods

Between June and August 2013, 150 groundwater samples (147in the fractured bedrock aquifer, and 3 in the granular deposits;designated by NSF in Table 1 and Table A1) were collected fromprivate and municipal open bedrock wells with depths rangingbetween 1 and 250 m (Fig. 2). Ten additional observation wells andfive piezometers were drilled and instrumented as part of thisproject (designated by NSF-R in Table 1 and Table A1). The five

Fig. 1. a) Geological map of the St. Lawrence Lowlands (southern Quebec, Canada) and location of the Nicolet-Saint-François study area and b) geological profile along the regionalflow line.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e13 3

piezometers are 2.5 cm in diameter, have a 1 m screen at theirlower end, and reach between 2 and 10 m depth. The ten drilledbedrock wells and all the other private bedrock wells are casedalong the section crossing the unconsolidated Quaternary depositsand are open in the bedrock aquifer (depths ranging between 52and 91 m). Domestic and observation wells were purged of a vol-ume equivalent to three times the borehole volume (GRIES, 2011)and water was sampled once its chemoephysical parameters hadstabilized (pH, temperature, redox potential, and electric conduc-tivity, measured with an air-tight cell). Continuously pumpedmunicipal wells were sampled directly. Groundwater was collectedat the observation wells using a submersible pump with speedcontrol (Redi-Flo2®), maintaining the whole sampling line underpressure to prevent water degassing. All samples were filtered to

0.45 mm in the field and analyzed for chemoephysical parametersin situ. A subset of twenty samples was also analyzed for 3H andhelium isotopic ratios (3He/4He). Ten of these were also analyzedfor 14C and d13C of the total dissolved inorganic carbon (TDIC). Thislast subset of samples was selected such that the wells would berepresentative of the general flow gradient, spanning the Appala-chian recharge zone to the St. Lawrence River. A further 14 watersamples (Fig. 2) were collected for noble gas analysis using 3/8 inchrefrigeration-type copper tubes (Weiss, 1968). Water was allowedto flow for several minutes prior to sealing the copper tubes withstainless steel clamps. All water samples were kept at 4 �C duringstorage and transport. Rock samples were taken from drillingwastes of the seven bedrock wells drilled during the study in orderto quantify the amount and distribution of different elements found

Table 13He3He and14C ages of groundwater from the Nicolet Saint-François study area.

Well name 3H ± 3Hetri ± 3He3He ± A14C ± d13C 14C 14C

TU ccSTP/g � 10�13 Age pMC ‰ Ages (yrs) ±0.5% Ages (yrs) ±20%

yrs V-PDB Uncorrected Corrected

NSF134 8.8 1.0 1.10 0.10 30.90 1.66 60.8 0.2 �10.7 4113 2140NSF137 5.2 0.8 7.92 0.61 >60NSF140 9.8 1.0 0.23 0.11 12.17 0.90NSF144 1.4 0.6 1.57 0.06 56.10 7.29 56.1 0.20 �16.3 4778 6280NSF148 8.3 0.7 2.63 0.08 46.80 1.39NSF149 4.5 0.5 5.19 0.50 >60NSF150 10.9 0.9 13.50 1.32 >60NSF152 4.8 0.6 1.82 0.13 50.24 2.09NSF215 10.5 1.1 0.08 0.05 4.78 0.44 94.7 0.4 �20 450 1310NSF216 9.8 0.8 5.93 1.29 58.28 1.40 90.6 0.3 �22.1 816 4860NSF218a 11.9 1.0 5.83 0.72 54.06 1.42 85.2 0.3 �18.6 1324 2880NSF219a 12.7 1.0 6.51 3.36 55.70 1.34 97.3 0.4 �20.3 226 280NSF220 5.1 0.6 1.78 0.10 48.25 1.95 43.5 0.2 �16 6881 8200NSF221 5 0.6 6.39 1.95 >60 24.3 0.2 �12.3 11,695 10210NSF224 0.8 0.3 1.39 0.18 >60NSF242 10.2 1.0 0.14 0.06 7.94 0.63NSF244 10 1.0 0.47 0.06 19.28 1.18NSFR1 0.8 0.6 �0.58 1.38 >60 6.5 0.1 1.9 22,596 17,050NSFR4 3.2 0.6 2.12 0.12 60.02 3.22NSFR7 9.8 1.0 0.67 0.10 23.55 1.33 65.4 0.2 �17.7 3510 3690

All 14C ages corrected using the Fontes and Garnier equilibrium model (Fontes, 1992), except for NSFR1 (Tamers, 1975).a Granular wells.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e134

in excess of drinking water limits in the aquifer material. Thesesamples have been selected to follow the regional groundwaterflow path, from the recharge zone to the discharge zone (cf. Fig. 2).

A certified laboratory (ISO/CEI 17025) analyzed major, minor(±0.5%) and trace (±2%) solute ions and alkalinity using the ICP-MSmethod for ion analysis and titration at pH 4.5 for alkalinity. HCO3was computed from alkalinity using Diagramme® software (avail-able at http://www.lha.univ-avignon.fr/LHA-Logiciels.htm). Heliumisotopes were analyzed at the Noble Gas Laboratory of the Uni-versity of Michigan and at the Atmospheric and Ocean ResearchInstitute (AORI) of the University of Tokyo. At the Noble Gas Lab-oratory of the University of Michigan, noble gas isotopes weremeasured on aMAP-215mass spectrometer. Elemental abundances

Fig. 2. Sampling sites for geochemical, 3H, 14C, d13C, and noble gas analyses overlain on th

of He and Ne are associated with uncertainties of 1.5 and 1.3%respectively, at ± 1s level. Details on the noble gas analytical pro-cedure of the University of Michigan can be found in Ma et al.(2005) and Castro et al. (2009). Samples analyzed at AORI of theUniversity of Tokyo were degassed offline and subsequently puri-fied in a line connected to a Helix SFT. Helium isotopes wereanalyzed and compared to the Helium Standard of Japan (HESJ)standard (Matsuda et al., 2002), with a 2s precision of ±0.2% (Sanoet al., 2008). 4He and 20Ne concentrations were measured on aPfeiffer QMS Prisma™ connected to the purification line. Details onthe analytical procedure of the University of Tokyo can be found inSano et al. (2008). Tritium was analyzed at the EnvironmentalIsotope Laboratory (EIL) of the University of Waterloo using liquid

e spatial distribution of confinement conditions (modified from Larocque et al., 2015).

Table 2Chemical analyses of rocks from the Nicolet Saint-François study area.

Well name CaO MgO Na2O K2O TOT/S TOT/C Ba F Fe2O3 MnO

% % % % % % ppm ppm % %

NSF-R1 6.62 3.25 1.05 3.3 0.13 1.68 345 896 6.1 0.12NSF-R2 35.81 1.45 0.4 1 0.35 8.53 244 650 1.7 0.03NSF-R3 2.76 2.64 1.74 1.04 0.79 1.17 1055 905 4.87 0.16NSF-R7 1.05 1.7 1.21 3.2 <0.02 0.15 692 717 8.55 0.11NSF-R8 3.33 3.64 0.99 3.16 0.35 0.82 485 794 5.81 0.18NSF-R9 39.22 3.14 0.38 0.36 0.1 10.09 124 386 1.27 0.03NSF-R10 10.69 3.1 0.97 3.68 0.81 3.16 223 955 4.91 0.07

M. Saby et al. / Applied Geochemistry 65 (2016) 1e13 5

scintillation counting (LSC). Samples analyzed for tritium wereconcentrated 15 times by electrolysis prior to counting. Thedetection limit for enriched samples is 0.8 TU (Heemskerk andJohnson, 1998). Groundwater for 3H/3He and 14C age determina-tion was sampled from wells along what was expected to be themain groundwater flow directions (Fig. 2; Table 1).14C activity andd13C in groundwater were analyzed at the Beta Analytic Inc. Labo-ratory, Florida, using a Single Stage Accelerator Mass Spectrometer(SSAMS). 14C measured activity (A14C) was expressed in percent ofmodern carbon (pMC). The 13C content of TDIC is reported usingd (‰) notation, as a deviation from the Vienna-Belemnite from thePee Dee formation (V-PDB, North Carolina, USA).

Seven rock samples were analyzed for whole rock geochemistry(Fig. 2; Table 2) at ACME Lab in Vancouver. The samples werecrushed to 80% passing 10 mesh (2 mm) and pulverized to 85%passing 200 mesh (75 mm). The powders were mixed with LiBO2/Li2B4O7 flux in the laboratory, fused, and dissolved in ACS-gradenitric acid, and analyzed by ICP for major elements and ICP-MSfor minor elements. Total carbon and sulfur were measured usingthe Leco method (LECO Corporation, 2007).

4. Results

Table A1 (in the Appendix) reports the main physicoechemicalparameters of the 150 sampled wells measured in the field,together with the major ion concentrations, and those of Ba, F, Fe,Mn, and Sr. Table 1 shows the tritiogenic 3He concentrations (3Hetriin cm3STP/gH2O) and tritium (3H in TU), used for calculating 3H/3Heages in the selected wells. The measured 14C activities (A14C inpMC) and the d13C of soil CO2 are also reported as uncorrected 14Cages (A0 ¼ 100 pMC) and corrected 14C ages, using the Fontes andGranier equilibrium model (henceforth the F&G equil; Fontes,1992). Uncertainties on the 14C uncorrected ages are estimated to

Table 3Chemical interpretation for each cluster from the results of a hierarchical cluster analysi

Clusters C1 C2 C3

Number of samples 34 18 9Ca 67,82 84,72 114,44Mg 12,80 15,76 24,21Na 17,14 147,50 24,22K 2,19 4,12 6,48HCO3 188,24 252,39 343,33Cl 22,07 214,63 22,81SO4 32,00 60,28 48,11F 0,11 0,44 0,12Mn 0,26 0,41 0,64Fe 0,10 0,17 2,64Ba 0,09 0,60 0,72

Groups CaeHCO3 NaeHCO3 CaeHCO3

Dominant trace elements Mn Ba, F, Fe, Mn, Ba

Bold values: highest values of all clusters for the given element; underlined values: low

be ±0.5% of the reported value, and are related to the analyticaluncertainties of the measured A14C (Table 2). Uncertainties of ±20%of the reported value for the corrected 14C ages depend essentiallyon the assumed d13C of the soil CO2 for the F&G equil (see Section4.2 for details).

Table 2 reports major oxides and trace elements of the rockcuttings. Table 3 reports the results of a Hierarchical Cluster Anal-ysis (HCA) applied to all 150 samples, performed using the com-mercial software package JUMP®. This HCA highlights the statisticalrobustness of the relationship between water chemistry types(determined based on the major ions) and the relative enrichmentsof trace ions in groundwater.

4.1. Groundwater chemistry

92.5% of all water samples from the current study are ofCa,MgeHCO3 and NaeHCO3 type (Fig. 3). The Ca,MgeHCO3 typerepresents modern freshwater, where the dissolution of Quater-nary calcareous tills and Ordovician calcareous shales of the frac-tured aquifer is the dominant process (Cloutier et al., 2010;Meyzonnat et al., 2015). This water circulates mainly in the un-confined aquifers of the Appalachian piedmont (Fig. 2). TheNaeHCO3 group represents more evolved groundwater, thechemistry of which is mainly controlled by Ca2þeNaþ ion exchange,whereby Ca2þwater exchanges with Naþmineral (e.g., Cloutier et al.,2010). This water type occurs downgradient in the study area,both in semi-confined and confined environments. A few watersamples close to the St. Lawrence River are of NaeCl, NaeSO4, andCaeCl water types (Fig. 3). The NaeCl water type representsgroundwater with salinity derived frommixing with pore seawatertrapped in the Champlain Sea clays or in the fractured rock aquifers(Meyzonnat et al., 2015). Two samples, NSF-R7 and NSF165(Table A1), located upgradient in the study area, have abnormally

s.

C4 C5 C6 C7

13 26 45 713,89 30,56 36,91 0,335,52 11,32 6,25 0,06146,23 22,84 8,15 185,712,17 4,23 1,71 2,38256,15 159,42 98,07 275,7172,37 3,93 11,72 43,008,54 7,00 12,22 48,571,00 0,24 0,04 0,110,03 0,13 0,02 0,000,16 0,28 0,00 0,000,47 0,29 0,02 0,00

NaeHCO3 Mix-HCO3 CaeHCO3 NaeHCO3

F

est values of all clusters for the given element.

Fig. 3. Piper diagram of groundwater hydrogeochemistry representing groundwatertypes of the study area.

Fig. 4. Evidence of groundwater geochemistry evolution; a) cationic exchange be-tween Ca2þ and Naþ in groundwater and evidence of salt water (the arrow representsthe general groundwater flow path), and b) evolution of the Mg/Ca ratio plottedagainst pH, indicating the dissolution of carbonates along the flow line.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e136

high NaCl concentrations, of 3500 and 260 mg/L respectively. Suchhigh Na/Cl ratios are likely the result of local pollution from roaddeicing salt.

Plots of Mg/Ca ratios versus pH can provide information oncarbonate dissolution processes (Cloutier et al., 2010). AMg/Ca ratioof between 0.5 and 1 is representative of young, Ca,MgeHCO3 typegroundwater in equilibriumwith calcite and dolomite. In the studyarea, this diagram shows a positive trend between Mg/Ca and pH,suggesting incongruent-dissolution of Mg-calcite or dolomite alongthe regional flow path (Fig. 4a), and is concordant with thegeochemical downgradient groundwater evolution. A plot of(Ca þ Mg)/(Na þ K) ratios versus total cations (Fig. 4b) suggestscationic exchange between Ca and Na (Appelo and Postma, 2005;Cloutier et al., 2006). Calcium derived from CaeHCO3 type waterreplaces the sodium from clay or iron minerals. This process en-riches the water in Naþ compared to Ca2þ, confirming the ion ex-change. A similar process depletes Ca2þ from downgradientgroundwater. A saline water end-member is identified by the shiftof the NaeCl and NaeSO4 water groups. This shift is thought toindicate mixing between fresh and saline water (Fig. 4b).

Ten wells show Ba concentrations above the drinking waterthreshold value of 1 mg/L (Table A1), and twelve wells show Baconcentrations of between 0.5 and 1mg/L. F exceedances are rare inthe study area, with only two wells exceeding the drinking waterquality standard of 1.5 mg/L (Health Canada, 2014), and eight wellswith concentrations of between 1 and 1.5 mg/L (Table A1). Feconcentrations are as high as 18 mg/L in 32 wells, compared withthe Canadian esthetic quality standard of 0.3 mg/L (Health Canada,2014), and Mn concentrations are as high as 5.9 mg/L, comparedwith the Canadian esthetic quality standard of 0.05 mg/L (HealthCanada, 2014; Table A1).

Rock analyses from seven locations (Fig. 2) show that Ba con-centrations range from 124 to 1055 ppm, F concentrations from 386to 955 ppm, and Fe2O3 concentrations from 1.27 to 8.55%. MnOconcentrations vary between 0.03 and 0.18% in both the St. Law-rence Lowlands and the Appalachian Mountains (Table 2). Otheranalyses performed as part of previous studies in the area showeven higher maximum values: greater than 1500 ppm Ba and F,

greater than 20% Fe2O3, and greater than 0.25% MnO (SIGEOM,2014).

4.2. 3H/3He and 14C groundwater residence times

The calculation of 3H/3He ages requires the separation of heliumderived from the decay of post-bomb tritium (3Hetri) from all otherhelium components potentially present in groundwater. Theseadditional components may include 1) atmospheric helium insolubility equilibrium with water (Heeq), 2) excess air helium(Heea), which results from air bubbles entering the water table, and3) terrigenic helium (Heterr), produced by U and Th decay in thecrust and/or derived from a mantle component. The Weise-plotdiagram (Fig. 5) shows helium isotopic ratios, for which bothnumerator and denominator have been corrected for air contami-nation by substracting the 3He and the 4He amounts derived fromexcess air (ea)) (3Hetot�3Heea)/(4Hetot�4Heea). The corrected excessair 3He/4He ration (here normalized to the 3He/4He ratio in the

Fig. 5. Measured 3He/4He ratios corrected for helium air excess (Heea) (and normalizedto the 3He/4He atmospheric ratio) versus the relative amount of 4He due to solubility(4Heeq) with respect to total helium corrected for air excess. The dashed line representsthe mixing line between recharge water (air saturated water conditions, or ASW, with3He/4He ratio ¼ Req) and water enriched in terrigenic 4He (RTerr). Dashed and dottedlines represent the addition of helium, and mixing with a terrigenic component of ratioRterr.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e13 7

atmosphere Ra ¼ 1.386 � 10�6, is plotted against the inverse of thenormalized helium concentration corrected for excess-air (4Heeq/(4Hetot�4Heea)) (Weise and Moser, 1987). Mixing between thedifferent end-members is represented by a linear equation,Y ¼ mX þ b (Weise and Moser, 1987), as per Eqn. (1):

ð3Hetot � 3HeeaÞð4Hetot � 4HeeaÞ|fflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

Y

¼�Req � Rterr þ

3Hetri4Heeq

�|fflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflfflffl}

m

$4Heeq

4Hetot � 4Heea|fflfflfflfflfflfflfflfflfflfflfflffl{zfflfflfflfflfflfflfflfflfflfflfflffl}X

þ Rterr|ffl{zffl}b

(1)

where Hetot is the total measured helium, Req is the 3He/4He ratio ofthe atmospheric helium in solubility equilibrium with water(0.984 Ra; Benson and Krause, 1980), and Rterr corresponds to thetime-integrated ratio of 3He and 4He radiogenic production of thecrust and/or mantle He addition. Straight lines traced along groupsof samples represent mixing of post-bomb groundwater accumu-lating 3Hetri and pre-bomb radiogenic 4He enriched groundwater(Fig. 5). The slope, “m”, of Eqn. (1) is associated with the amount oftritium that completely decayed into 3Hetri and the Y-intercept, Rterr(the “b” term in Eqn. (1)). Groundwater helium can be explained bythe decay of 4e67 TU of tritium mixed with terrigenic heliumcharacterized by Rterr ranging from 0.05 to 0.70Ra. This Rterr value ishigher than that expected for local production from Li (3He), U andTh (4He) present in local formations (0.012Ra; Pinti et al., 2011;M�ejean et al., 2015) and suggests a mantle helium contributionon the order of 0.5e8.6%. This mantle helium is derived from theleaching of plutonic intrusions of the Cretaceous Monteregian Hills(Pinti et al., 2011). 3Hetri can be estimated following the equation ofSchlosser et al., 1989:

3Hetrit ¼ 4Hetot$ðRtot � RterrÞ � 4Heeq$�Req � Rterr

��� 4He20Ne

�ea$�20Netot � 20Neeq

�$ðRea � RterrÞ (2)

where R is the measured 3He/4He ratio in groundwater; Ratm and(4He/20Ne)ea are generally assumed to be atmospheric(Ratm ¼ 1.382 � 10�6; Sano and Fischer, 2013;[4He/20Ne]exc ¼ 0.3185; Ozima and Podosek, 1983). Measuredtritium in the current study ranges from the detection limit value of0.8 TU (NSF224 and NSF-R1) to 12.7 TU (NSF219) (Table 1).

Calculated 3H/3He ages vary between 4.8 ± 0.4 years in wellNSF215, upgradient, and 60.0 ± 3.2 years in well NSF-R4, down-gradient, in the fractured bedrock aquifer (Table 1; Fig. 2). 3H/3Heages cannot be calculated for sample NSF-R1, located down-gradient. The tritium content for this well is below the detectionlimit of 0.8 TU, indicating that water recharged prior to the bombpeak (background 3H of 5e6 TU; Clark and Fritz, 1997) and that anydetectable tritium has completely decayed since then. This samplealso contains very high amounts of radiogenic 4He, 5.29 � 10�6

cm3STP/gH2O, two orders of magnitude higher than the atmo-spheric amount of helium in solubility equilibrium with water (Airsaturated Value or ASW; i.e. 4.6� 10�8 cm3STP/gH2O at 10 �C; Smithand Kennedy, 1983). This high amount of radiogenic 4He indicatesthe presence of paleo-water, possibly tens of thousands of years old,as also indicated by uncorrected 14C ages (see below). Calculated3H/3He ages for samples NSF137, 149, 150, 221 and 224 (Table 1) areolder than 60 years, and are therefore at the limit of the datingmethod. This is due to the fact that their measured 3He/4He ratiosare very radiogenic, i.e. close to the Rterr end-member (Fig. 5). Thecalculation of 3Hetri can be difficult to assess because it is over-shadowed by the 3Heterr and this can easily lead to an under- oroverestimation of the 3Hetri and so of the ages.

Measured 14C activities (A14C) plotted against the d13C of TDICgenerally show an inverse trend (R2 ¼ 0.74), suggesting the evo-lution of groundwater carbon content with age (Fig. 6a). Post-bombtritium-rich groundwater dissolves biogenic soil CO2(A14C ¼ 120 pMC; d13C ~ �23‰), evolving with time and accu-mulating dead carbon from carbonate dissolution (A14C ¼ 0 pMC;d13C ¼ 0‰; sample NSF-R1). Uncorrected 14C ages range from230 ± 56 years for well NSF219, located in themain recharge area ofthe Appalachians piedmont, to 17,050 ± 3410 years for well NSF-R1,located downgradient in a semi-confined zone (Table 1; Fig. 2). 14Cactivities were corrected for carbonate dissolution (A0

14C) using theF&G equil model (Fontes, 1992). This is the only 14C age modeladapted to carbonate-dominated aquifers which takes into accountboth the dissolution of carbonates and the CaeNa exchange pro-cesses (Fontes,1992; Plummer and Glynn, 2013). Corrected 14C agesrange from 280 ± 2 yrs for well NSF219 to 10,210 ± 80 years for wellNSF221 which is located in the plain at the base of the Appalachianpiedmont, in a semi-confined aquifer (Fig. 2). The F&G equil modelfails to provide a corrected 14C age for well NSF-R1, probablybecause of its high levels of dead carbon (A14C ¼ 6.5 pMC andd13C ¼ 1.9‰). Other well-known 14C correction models of Pearson(1992), Mook (1972), IAEA (Salem et al., 1980), Evans et al. (1979),and Eichinger (1983) are not able to calculate a 14C age for NSF-R1groundwater. Only 14C activities corrected with the model ofTamers (1967) allow the calculation of a corrected 14C age, of17,050 ± 3410 years (Table 1).

The apparent contradiction between calculated 3H/3He and 14Cages (Table 1) is often observed in aquifers (i.e., Andrews, 1985;Patriarche et al., 2004; Castro and Goblet, 2005) and is thought toresult from the mixing of water masses having different ages andorigins. This is apparent from the significant relationship

Fig. 6. a) Inverse trends between the measured 14C activity (A14C) and the measuredd13C of the TDC (b). Dead carbon reservoir isotopic composition and 14C activities arefrom Taupin (1990) (soil CO2) and Le Gal Lasalle et al. (2001) (carbonates) and b)measured 3H activity against the uncorrected 14C activity (A14C). Numbers on thetheoretical mixing line represent the percentage of the older component in themixture.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e138

(R2 ¼ 0.80) between measured 14C and 3H activities (Fig. 6b).Samples from the current study area (NSF) have been compared tothose from the neighboring Becancour watershed (BEC; data fromVautour et al., 2015) to show that such mixing is a commonoccurrence and dominant process in the St. Lawrence Lowlandsaquifers. The first end-member represents recently rechargedfreshwater containing some post-bomb 14C (A14C ¼ 97.3 pMC) andtritium (3H ¼ 12.7 TU). The second end-member is an oldergroundwater, recharged prior to 1952, and thus containing pre-bomb tritium (<0.8 TU; Clark and Fritz, 1997) as well asA14C � 6.5 pMC, the latter derived by the addition of dead carbon

from the carbonate pool. Most modern water (well NSF219) is ofCaeHCO3 type at a depth of 6.1m, while the oldest water (well NSF-R1) is of NaeCl type under entirely confined conditions at a depthof 84.4 m. This mixing could have taken place in the wells or in theaquifer itself. The first hypothesis is unlikely, because the totality ofthe sampled wells from the fractured aquifer are equipped withcasing that prevents water from the unconsolidated granularaquifer to flow into the fractured one. Thus the observed mixingbetween freshwater and fossil water is expected to have occurred inthe fractured aquifer itself.

5. Discussion

5.1. Trace elements and groundwater quality

HCA applied to the major and trace ions of the 150 sampledwells (Table 3) allows the relationship between the chemical evo-lution of groundwater in the watershed and their trace elementconcentrations, such as those of Ba, F, Fe, and Mn, to be highlighted.The HCA indicates that the more evolved waters are those enrichedin Ba, F, Fe, and Mn. These are 1) CaeHCO3 groundwater, mainlylocated downgradient, far from the main recharge zone of theAppalachian Mountains, and in a semi-confined environment; 2)evolved NaeHCO3 waters which underwent CaeNa ionic exchange(Table 3).

Calculated 14C ages support the occurrence of prolongedwatererock interactions, which could have led to the release oftrace elements such as Ba, F, Fe, and Mn into groundwater. Thiswater evolved chemically with time, as shown by the Mg/Ca ratio,which inversely correlates with 3H activities (Fig. 7a) and positivelycorrelates with corrected 14C ages (Fig. 7b). It is also apparent thatwater types tend to follow this pattern by evolving downgradientfrom CaeHCO3 to NaeHCO3 (Fig. 7b).

Ba concentrations tend to increase from upgradient to down-gradient along the general flow path (Fig. 8). Ba increases signifi-cantly when water flows through the Sillery group, the Bourret Fmand the Olistotrome of Drummondville, which correspond to thesame type of rocks as those which host barium economic deposits(see Fig. 8 and Section 5.2). A second increase in Ba occurs in theLorraine and Ste-Rosalie Groups. Concentrations finally decrease inthe Queenston Group.

Fluorine has been reported as problematic in other basins of theSt. Lawrence Lowlands, particularly in the Eastern Monteregie(Beaudry, 2013). Plotting Ca versus F concentrations (Fig. 9a) yieldsa saturation curve which highlights the precipitation of calcium-fluorine by groundwater circulation as a result of the release of Finto groundwater. However, results also show a clear relationshipbetween pH and F in groundwater (Fig. 9b), which can signify anexchange between F� and OH�, a process called desorption(Savenko, 2001). Desorption of F tends to occur above a pH of 7(Hounslow, 1995), increasing with pH and OH� availability.

Fe and Mn sources in groundwater are known to be related topH and redox conditions (Homoncik et al., 2010). Fig. 10a showsthat Fe2þ and Mn2þ can be mobilized in groundwater over a largerange of pH and Eh values. Generally, Fe is more soluble under theFe2þ form in weakly oxidizing water and reducing water than Mn.Mn will be more soluble under the Mn2þ form in more stronglyoxidizing water. Some samples have very low Fe and Mn concen-trations despite the fact that conditions are favorable for theirrelease into groundwater, implying that these elements are notfully available in the matrix. Reducing water conditions seem tobetter explain Fe availability in water than does pH (Fig. 10a). ForMn, the relationship with Eh and pH is less clear than for Fe, butreducing water is still the main factor controlling the concentrationof dissolved Mn in groundwater. In near-neutral pH conditions,

Fig. 7. a) 14C ages as a function of the corresponding Mg/Ca ratio, b) evolution of the 3Hactivity as a function of the Mg/Ca ratio, and c) relationship between 14C ages andbarium (Ba) concentrations.

Fig. 8. Relationship between barium (Ba) concentrations and the distance along theflow line, with geology superposed in the background.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e13 9

interactions between Fe and Mn can occur (Collins and Buol, 1970).The scatterplot of Fe versus Mn (Fig. 10b) shows that high Fe

concentrations are found only with high Mn concentrations, while

high Mn concentrations can occur in the presence of a wide rangeof Fe concentrations, probably because of its greater availability inthe host rock. The high affinity of Mn to ferric oxides could lead toits removal by occlusion and sorption to precipitated Fe (Morganand Stumm, 1965; Collins and Buol, 1970). Conversely, when Feoxides are reduced by the flow of reducing groundwater, Fe2þ andMn2þ are released. Moreover, Fe is more likely to adsorb or formcomplexes with organic matter than is Mn (Hem, 1972). Theoccurrence of Mn in the upgradient portions of the study area canbe explained by its occurrence coinciding with a larger range of Ehvalues than Fe, and because it is less reactive with organic matterand thus does not form complexes with it.

5.2. Origin and evolution of trace elements in rocks and theirrelease into groundwater

Ba is mostly found in host rock in the form of the barite mineral(BaSO4). This mineral formed chemically when Ba2þ, originatingfrom rising hydrothermal fluids across the Grenville shield(Carignan et al., 1997) to the surface, encountered sulfate-richwater, such as seawater. The precipitation of barite mainly de-pends on the availability of sulfate (from seawater) and barium(mainly from crystalline rocks), these two elements not beingtransported together (Machel, 2001; Aquilina and De Dreuzy, 2011;Aquilina et al., 2011, 1997). Barite is then trapped in carbonate rocksduring diagenesis (Paradis and Lavoie, 1996). The direct relation-ship between Ba and corrected 14C ages (Fig. 7c) also suggests that along watererock interaction time, as well as the quasi-absence ofrecharge downgradient, is critical in the release of this element intogroundwater, and leads to an increase in Ba concentrations alongthe flow path.

Similarly, F� has a hydrothermal origin and can precipitate un-der the form of fluorite (CaF2) in carbonate rocks during diagenesis,

Fig. 9. a) Relationship between F and Ca (the dashed line represents the dissolutioncurve of calcium fluorine), and b) evolution of F as a function of pH.

Fig. 10. Relationships between a) pH and Eh, compared to the Fe/Mn ratio representedby the size of the circles, and b) Mn concentrations and Fe concentrations, illustratedfor the different water types.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e1310

when it is in contact with calcium-rich water, such as seawater. F�

can also be adsorbed in clays by exchange with OH� under acidicconditions (Savenko, 2001), as in the volcanic activity of thePaleozoic. Reactivation of the St. Lawrence rift system occurredduring the Devonian and Mesozoic (Carignan et al., 1997; Tremblayet al., 2013; Bouvier et al., 2012) bringing additional hydrothermalfluids and leading to F and FeBa veins hosted in Cam-broeOrdovician rocks (Carignan, 1989; Carignan et al., 1997).Dissolution of these veins might be a secondary source of dissolvedF and Ba in modern groundwater, but it is unlikely to be the mainsource because of their low presence and distribution in the area(more to be considered as recorders of past events).

The main process leading to Fe- and Mn- sulfide precipitation inrocks is the sulfide biogenic or thermochemical reduction (Machel,2001). Lorraine shales contain up to 1.5% Total Organic Carbon(Lavoie et al., 2013). The availability of reactive sulfate and organic

matter is the main factor underlying the transport/concentration ofeither Fe or Mn sulfides (Eqn. (3) And (4)) in anoxic/high temper-ature conditions (Eqn. (5)), or oxides (Fe2O3 and MnO) in cooler/oxidant conditions.

Fe2þ þ H2S/FeSþ 2Hþ (3)

FeSþ H2S/FeS2 þ H2 (4)

2CH2Oþ SO2�4 /2HCO�

3 þ H2S (5)

The presence of pyrite (FeS2) has been observed in Appalachianmetasediments (Sassano and Schrijver, 1989; and in the NSF-R7drilled well of this study) and in the Utica and Lorraine shales(B�erub�e et al., 1986), confirming the formation of Fe sulfides in the

M. Saby et al. / Applied Geochemistry 65 (2016) 1e13 11

region during the Paleozoic. Mn nodules from the Ordovician werefound in the Appalachians, close to the study area, in the St. DanielFm (Trottier et al., 1991). Major weathering episodes driven bymassive groundwater recharge during the Devonian last stage ofAppalachian orogeny (Lavoie, 2008) led to the oxidation of Fe andMn sulfides (FeS2 andMnS) present in rocks, the release of Fe2þ andMn2þ into the aqueous media, and precipitation in the form of Feand Mn oxides (Fe2O3 and MnO; Appelo and Postma, 2005). Thelater confinement provided by the Champlain Sea clay deposits ledto the progressive reduction of groundwater which triggered thereduction of Fe and Mn oxides and sulfurs in the rock, and therelease of Fe2þ and Mn2þ into groundwater.

The potential sources of Ba, F, Fe, andMn are thus the Ordovicianrocks of the St. Lawrence Platform and the Appalachian Mountains.Enrichment of these elements could be related to Paleozoic epi-sodes of Mississippi Valley Type (MVT) ore deposition (Ingebritsenand Sanford,1998; Machel, 2001), as observed in the BeekmantownGroup dolostones in New York State and in Ontario (Benison andLowenstein, 1997). Macro-evidence of MVT-related deposits is abarite ore exploited near the town of Upton, 20 km west of thestudy area in the Drummondville Olistostrome of mid-Ordovicianage (Paradis and Lavoie, 1996). Migration of NaeCaeCl andNaeCleBr brines (Bethke and Marshak, 1990; Sverjenski andGarven, 1992) is believed to be the main mechanism of MVT oreconcentration. Primary fluid inclusions in quartz, calcite, and saddledolomite of the Beekmantown dolostones indicate that themineralizing fluids were NaeCaeCl brines (Benison andLowenstein, 1997; Aquilina and De Dreuzy, 2011; Aquilina et al.,2011). Pinti et al. (2011) studied the origin of NaeCaeCl brines(up to 350 g/L TDS) in the Beekmantown and Chazy Groups atBecancour. They concluded that these brines could be of Devonianage, one of the most prolific periods of MVT ore deposition in NorthAmerica (Garven et al., 1993).

5.3. Groundwater residence times and their relationship withexcess trace ion concentrations

Corrected 14C ages range from 17,050 ± 3410 yrs for NSF-R1 to283± 57 yrs for NSF219 (Table 1). The older 14C age corresponds to aperiod when the Laurentide Ice Sheet covered the study area.However, as a result of the geothermal gradient, as well as the heatgenerated by friction, meltwater was present at the base of thecontinental glaciers (e.g., Gilkeson et al., 1981). There is compellingevidence that the magnitude of subglacial recharge into confinedaquifer systems covered by the Laurentide Ice Sheet was up to 10times greater than at present (e.g., McIntosh and Walter, 2005;Person et al., 2007). The other corrected 14C ages obtained in theNSF watershed range between 12,000 and modern (Table 1),similar to the 14C ages found in the neighboring watersheds ofBecancour (corrected 14C from 9200 to modern; Vautour et al.,2015) and Eastern Monteregie (uncorrected 14C ages from 13,800to modern; Beaudry, 2013). This period roughly corresponds to theice retreat of the Laurentide Ice Sheet, followed by a glacio-isostaticmarine transgression, known as the Champlain Sea, which invadedthe study area 12,800e12,300 yrs ago (Parent et al., 1985). Between10,600 and 6700 yrs before present, the main phase of isostaticrebound lowered the St. Lawrence River base level from þ60 m aslto ca. 16 m asl (Lamarche et al., 2007). At 6.7 kyrs, the hydrographicnetwork of the St. Lawrence Valley reached a configuration close tothat observed at present. It is expected that during this acceleratedisostatic rebound period, new emerging recharge zones andincreased potentiometric heads favored a large invasion of melt-water into the shallower Quaternary aquifers (e.g., Person et al.,2007) and the confined aquifers of the St. Lawrence Lowlands.

In the Michigan basin, large amounts of meltwater resulted inthe dissolution of Devonian evaporites, which increased thegroundwater salinity (e.g., McIntosh et al., 2011). In a broad regionof the Cambrian-Ordovician aquifer system of northeastern Illinois,dissolution of secondary barite, driven by meltwater infiltration,led to high dissolved barium concentrations in groundwater(Gilkeson et al., 1981). In the St. Lawrence Lowlands, a similarprocess could have taken place. During subglacial recharge underthe Laurentide Ice Sheet at around 20,000 yrs (Person et al., 2007), alarge amount of meltwater could have favored the dissolution ofsecondary barite, which was subsequently diluted by the lastepisode of meltwater formation during the Laurentide Ice Sheetretreat (12,000 yrs), and the reorganization of the hydrographicnetwork of the St. Lawrence Lowlands (6700 yrs and younger)(Fig. 7c).

Similar results have been recently showed in the Armoricanbasement in terms of ages and links between elements dissolved inold groundwater and glacial transport which supports thegroundwater evolution model presented in this study (Aquilinaet al., 2015).

6. Conclusions

The objective of this study was to establish links betweengroundwater quality, groundwater residence times, and regionalgeology on the scale of the St. Lawrence Platform and the Appala-chian Mountains aquifers in southern Quebec (Canada). To attainthis objective, the study combined groundwater chemistry andgroundwater residence times with an economic geology model andhistorical geology.

Results have shown that major ion concentrations highlightregional groundwater flow directions and the evolution ofgroundwater from a young water end-member, characterized bythe CaeHCO3 water type in the piedmont of the Appalachiansrecharge area, to an old water end-member, characterized by theNaeHCO3 type downgradient in the study area. Two distinct watermasses were identified, with 3H/3He ages pointing to water lessthan 60 years, and 14C ages of several thousand years, likely infil-trated in the CambroeOrdovician aquifers by subglacial recharge orimmediately following the last deglaciation. This long interactiontime between rock and groundwater is likely an important factor inthe release of anomalous concentrations of Ba, F, Fe, and Mn intogroundwater. Their concentrations in the rock can be explained bytheir deposition as mineral phases (barite, sulfates, etc.) in thesedimentary rocks of the CambroeOrdovician St. Lawrence Plat-form and Appalachians. Their recent release in post-glacialgroundwater might be favored by the redox state, geology, pH,interaction with organic matter, and availability of reactive dis-solved compounds, such as SO4

2�. This work shows that the releaseof hydrothermal fluids along regional faults in the sedimentarybasin, combined with marine water, has likely triggered thedeposition of sulfides in reducing environments and the depositionof oxides in oxidizing environments.

This study brings a new and original understanding of thegroundwater system within the context of its geological history. Itnot only characterizes the natural groundwater quality of the studyarea, but also contributes to better understanding groundwaterquality problems in the St. Lawrence Lowlands. A similar approachto understanding natural groundwater quality problems could beused in similar geological settings, such as in the Paleozoic sedi-mentary basins of Michigan or Mississippi, for example, but mayalso be applied in different geological contexts, such as volcanic orplutonic settings.

M. Saby et al. / Applied Geochemistry 65 (2016) 1e1312

Acknowledgments

The authors would like to thank the Quebec Ministry of Envi-ronment (Minist�ere du D�eveloppement durable, de l’Environne-ment et de la Lutte contre les changements climatiques), theQuebec Research Fund (“Fonds de recherche du Qu�ebec - Nature etTechnologies”), as well as the “Municipalit�es r�egionales de comt�es-MRC”, the “Conseil r�egional des �elus-CRE”, the municipalities, andthe well owners who contributed funding to this research and ac-cess to sampling locations. We wish to thank Chris Hall of theUniversity of Michigan (USA) for analyzing helium isotopes, andPauline M�ejean for helping with the analyses during her stay atAORI, University of Tokyo (Japan). Michelle Laithier (UQAM) isthanked for having redrawn the figures of this manuscript.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.apgeochem.2015.10.011.

References

Aeschbach-Hertig, W., Gleeson, T., 2012. Regional strategies for the acceleratingglobal problem of groundwater depletion. Nat. Geosci. 5, 853e861.

Andrews, J.N., 1985. The isotopic composition of radiogenic helium and its use tostudy groundwater movement in confined aquifers. Chem. Geol. 49, 339e351.

Appelo, C.A.J., Postma, D., 2005. Geochemistry, Groundwater and Pollution, seconded. CRC Press, Boca Raton, Florida, USA.

Aquilina, L., De Dreuzy, J.R., 2011. Relationship of present saline fluid with paleo-migration of basinal brines at the basement/sediment interface (Southeastbasin e France). Appl. Geochem 26, 1933e1945.

Aquilina, L., Pauwels, H., Fouillac, C., 1997. Water-rock interaction processes in theTriassic sandstone and the granitic basement of the Rhine graben : geochemicalinvestigation of a geothermal reservoir. Geochim. Cosmochim. Acta 4281e4295,61-20.

Aquilina, L., Boulvais, P., Mossmann, J.R., 2011. Fluid migration at the basement/sediment interface along the marginof the South-East Basin (France): impli-cations for Pb-Zn ore formation. Min. Depos. 46e8, 959e979.

Aquilina, L., Vergnaud-Ayraud, V., Armandine Les Landes, A., Pauwels, H., Davy, P.,P�etelet-Giraud, E.T., Roques, C., Chatton, E., Bour, O., Ben Maamar, S.,Dufresne, A., Khaska, M., Le Gal La Salle, C., Barbecot, F., 2015. Impact of climatechanges during the last 5 million years on groundwater in basement aquifers.Sci. Rep. 5, 14132.

Barbecot, F., Marlin, C., Gibert, E., Dever, L., 2000. Hydrochemical and isotopiccharacterisation of the Bathonian and Bajocian coastal aquifer of the Caen area(northern France). Appl. Geochem 15, 791e805.

Beaudry, C., 2013. Hydrog�eochimie de l'aquif�ere rocheux r�egional en Mont�er�egieest, Qu�ebec. MS Thesis. Institut national de la recherche scientifique (INRS).Canada, Quebec.

Benison, K.C., Lowenstein, T.K., 1997. Carbonate-hosted mineralization of the lowerOrdovician Ogdensburg Formation: evidence for a Paleozoic thermal anomalyin the St. Lawrence Lowlands of New York and Ontario. In: Montenez, I.,Shelton, K., Gregg, J. (Eds.), Basin-wide Fluid Flow and Associated DiageneticPatterns: Integrated Petrologic, Geochemical, and Hydrologic Considerations,SEPM Spec. Publ, 57, pp. 207e218.

Benson, B.B., Krause, D., 1980. Isotopic fractionation of helium during solution: aprobe for the liquid state. J. Sol. Chem. 9, 895e909.

B�erub�e, M.-A., Locat, J., G�elinas, P., Chagnon, J.-Y., Lefrançois, P., 1986. Black shaleheaving at Sainte-Foy, quebec, Canada. Can. J. Earth Sci. 23, 1774e1781.

Bethke, C.M., Marshak, S., 1990. Brine migrations across North America d the platetectonics of groundwater. Annu. Rev. Earth Planet. Sci. 18, 287e315.

Bolduc, A.M., Ross, M., 2001. Surficial geology, Lachute-Oka, qu�ebec. Geol. Surv. Can.http://dx.doi.org/10.4095/212599. Open File 3520.

Bouvier, L., Pinti, D.L., Tremblay, A., Minarik, W., Roden-Tice, M., 2012. Late Jurassicreactivation of the St. Lawrence rift system, Qu�ebec, Canada: evidence fromapatite (U-Th)/He dating. In: Proc. 3rd INQUA-igcp-567 Inter. Workshop ActiveTectonics, Paleoseismology & Archaeoseismology, pp. 25e28.

Carignan, J., 1989. Caract�erisations isotopiques (C, O, Sr, Pb) et gen�ese de filons�epithermaux associ�es au rift du Saint-Laurent. Universit�e du Qu�ebec �a Mon-tr�eal, Quebec, Canada. MS thesis.

Carignan, J., Gari�epy, C., Hillaire-Marcel, C., 1997. Hydrothermal fluids duringMesozoic reactivation of the St. Lawrence rift system: C, O, Sr and Pb isotopiccharacterization. Chem. Geol. 137, 1e21.

Carrillo-Rivera, J.J., Cardona, A., Edmunds, W.M., 2002. Use of abstraction regimeand knowledge of hydrogeological conditions to control high-fluoride con-centration in abstracted groundwater: San Luis Potosì basin, Mexico. J. Hydrol.261, 24e47.

Castro, M.C., Goblet, P., 2005. Calculation of groundwater ages e a comparative

analysis. Ground Water 43, 368e380.Castro, M.C., Ma, L., Hall, C.M., 2009. A primordial, solar He-Ne signature in crustal

fluids of a stable continental region. Earth Planet. Sci. Lett. 279, 174e184.Clark, I.D., Fritz, P., 1997. Environmental Isotopes in Hydrogeology. CRC Press, Boca

Raton, Florida, USA.Cloutier, V., Lefebvre, R., Savard, M.M., Bourque, �E., Therrien, R., 2006. Hydro-

geochemistry and groundwater origin of the Basses-Laurentides sedimentaryrock aquifer system, St. Lawrence Lowlands, Quebec, Canada. Hydrogeol. J. 14,573e590.

Cloutier, V., Lefebvre, R., Savard, M.M., Therrien, R., 2010. Desalination of a sedi-mentary rock aquifer system invaded by Pleistocene Champlain Sea water andprocesses controlling groundwater geochemistry. Environ. Earth Sci. 59,977e994.

Collins, J.F., Buol, S.W., 1970. Effects of fluctuations in the EhepH environment oniron and/or manganese equilibria. Soil Sci. 110, 111e118.

Corporation, L.E.C.O., 2007. Carbon and Sulfur Determination e LECO InductionFurnace Instruments, 48.

Eichinger, L., 1983. A contribution to the interpretation of 14C groundwater agesconsidering the example of a partially confined sandstone aquifer: Radiocarbon25, 347e356.

Environment Canada, 2014. Canadian climate Normals 1961-2010. http://climat.meteo.gc.ca/climate_normals/results_1981_2010_f.html?stnID¼5426&autofwd¼1.

Evans, G.V., Otlet, R.L., Downing, A., Monkhouse, R.A., Rae, G., 1979. Some problemsin the interpretation of isotope measurements in United Kingdom aquifers. In:Isotope Hydrology II. International Atomic Energy Agency, Vienna,pp. 679e708.

Fontes, C.H., 1992. Chemical and isotopic constraints on 14C dating of groundwater.In: Taylor, R.E., Long, A., Kra, R.S. (Eds.), Radiocarbon Dating after Four Decades:an Interdisciplinary Perspective, Springer, New York, pp. 242e326.

Garven, G., Ge, S., Person, M.A., Sverjensky, D.A., 1993. Genesis of stratabound oredeposits in the midcontinent basins of North America. 1. The role of regionalgroundwater flow. Am. J. Sci. 293, 497e568.

Gilkeson, R.H., Perry Jr., E., Cartwright, K., 1981. Isotopic and Geologic Studies toIdentify the Sources of Sulfate in Groundwater Containing High Barium Con-centrations. University of Illinois Water Resour, p. 39. Center Report 81-0165.

Globensky, Y., 1987. G�eologie des Basses-Terres du Saint-Laurent, Quebec. Minist�eredes Richesses Naturelles du Quebec 63 (v. MM 85e02).

Globensky, Y., 1993. Lexique stratigraphique canadien. Volume V-B: r�egion desAppalaches, des Basses-Terres du Saint-Laurent et des Iles de la Madeleine.Minist�ere de l’�Energie et des Ressources et Direction G�en�erale de l’Explorationg�eologique et min�erale. DV 91e23.

GRIES, 2011. Protocole de pr�el�evement d’�echantillons d’eau souterraine pour lePACES, p. 9. Juin 2010.

Health Canada, 2014. Guidelines for Canadian Drinking Water Quality: SummaryTable. FederaleProvincialeTerritorial Committee on Drinking Water. http://www.hc-sc.gc.ca/ewh-semt/water-eau/drink-potab/guide/index-eng.php.

Heemskerk, A.R., Johnson, J., 1998. Tritium Analysis: Technical Procedure 1.0. Uni-versity of Waterloo, Waterloo, Ontario, Canada.

Hem, J.D., 1972. Chemical factors that influence the availability of iron and man-ganese in aqueous systems. Geol. Soc. Am. Bull. 83, 443e450.

Homoncik, S.C., MacDonald, A.M., Heal, K.V., Dochartaigh, B.E.O., Ngwenya, B.T.,2010. Manganese concentrations in Scottish groundwater. Sci. Total Environ.408, 2467e2473.

Hounslow, A.W., 1995. Water Quality Data: Analysis and Interpretation. CRC Press,Boca Raton, Florida, USA.

Ingebritsen, S.E., Sanford, W.E., 1998. Groundwater in Geologic Processes. Cam-bridge University Press, Cambridge, United Kingdom.

Kloppmann, W., Girard, J.P., N�egrel, P., 2002. Exotic stable isotope compositions ofsaline waters and brines from crystalline basement. Chem. Geol. 184, 49e70.

Lacasse, K., 2013. Caract�erisation g�eochimique et isotopique des aquif�eres du sud-ouest de la Mauricie. MS thesis. Universit�e du Qu�ebec �a Trois-Rivi�eres,Quebec, Canada.

Lamarche, L., Bondue, V., Lemelin, J.-M., Lamothe, M., Roy, M., 2007. Deciphering theHolocene evolution of the St. Lawrence River drainage system using lumines-cence and radiocarbon dating. Quart. Geochronol. 2, 155e161. http://dx.doi.org/10.1016/j.quageo.2006.04.002.

Lamothe, M., 1989. A new framework for the Pleistocene stratigraphy of the centralSt. Lawrence Lowland, southern Quebec. G�eogr. Phys. Quart. 43, 119e129.

Lamothe, M., St-Jacques, G., 2014. G�eologie du Quaternaire des bassins versant desrivi�eres Nicolet et Saint-François, Qu�ebec, p. 34. Minist�ere Energies etRessources Naturelles Report.

Larocque, M., Gagn�e, S., Tremblay, L., Meyzonnat, G., 2015. Rapport d’�etape Phase III.Projet de connaissance des eaux souterraines de la zone Nicolet et de la partiebasse de la zone Saint-François, p. 261. Report presented to the MDDELCC.

Lavoie, D., 2008. Appalachian foreland basin in Canada. In: Hsü, K.J., Miall, A.D.(Eds.), Sedimentary Basins of the World, Series Ed, Sedimentary Basins of theWorld d USA and Canada, vol. 5. Elsevier, Amsterdam, pp. 65e103.

Lavoie, D., Rivard, C., Lefebvre, R., Sejourne, S., Theriault, R., Duchesne, M.J.,Ahad, J.M.E., Wang, B., Benoit, N., Lamontagne, C., 2013. The Utica shale and gasplay in southern Quebec: geological and hydrogeological syntheses andmethodological approaches to groundwater risk evaluation. Inter. J. Coal Geol.126, 77e91.

Le Gal Lasalle, C., Marlin, C., Leduc, C., Taupin, J.D., Massault, M., Favreau, G., 2001.Renewal rate estimation of groundwater based on radioactive tracers (3 H, 14C)

M. Saby et al. / Applied Geochemistry 65 (2016) 1e13 13

in an uncon- fined aquifer in a semi-arid area, Iullemeden Basin. Niger. J.Hydrol. 254, 145e156. http://dx.doi.org/10.1016/S0022-1694(01)00491-7.

Li, J., Wang, Y., Xie, X., Su, C., 2012. Hierarchical cluster analysis of arsenic andfluoride enrichments in groundwater from the Datong basin, Northern China.J. Geochem. Explor. http://dx.doi.org/10.1016/j.gexplo.2012.05.002.

Ma, L., Castro, M.C., Hall, C.M., Lohmann, W.M., 2005. Cross-formational flow andsalinity sources inferred from a combined study of helium concentrations,isotopic ratios and major elements in the Marshall aquifer, southern Michigan.Geochem. Geophys. Geosyst. 6, Q10004. http://dx.doi.org/10.1029/2005GC001010.

Machel, H.G., 2001. Bacterial and thermochemical sulfate reduction in diageneticsettingsdold and new insights. Sediment. Geol. 140, 143e175.

Maclear, L.G.A., Adlem, M., Libala, M.B., 2003. Trend Analysis of Fluoride Concen-trations in Surface Water and Groundwater: 2000e2003. Coelga Devel. Co.Report 258047/6.

Mahlknecht, J., Steinich, B., Leon, I.N., 2004. Groundwater chemistry and masstransfers in the independence aquifer, central Mexico, by using multivariatestatistics and mass balance models. Environ. Geol. 45, 781e795.

Marimon, M.P.C., Roisenberg, A., Suhogusoff, A.V., Viero, A.P., 2012. Hydro-geochemistry and statistical analysis applied to understand fluoride prove-nance in the guarani aquifer system, Southern Brazil. Environ. Geochem. Health35, 391e403.

Matsuda, J., Matsumoto, T., Sumino, H., Nagao, K., Yamamoto, J., Miura, Y.,Kaneoka, I., Takahata, N., Sano, Y., 2002. The 3He/4He ratio of the new internalHe standard of Japan (HESJ). Geochem. J. 36, 191e195.

McIntosh, J.C., Walter, L.M., 2005. Volumetrically significant recharge of Pleistoceneglacial meltwaters into epicratonic basins: constraints imposed by solute massbalances. Chem. Geol. 222, 292e309.

McIntosh, J.C., Garven, G., Hanor, J.S., 2011. Impacts of Pleistocene glaciation onlarge-scale groundwater flow and salinity in the Michigan Basin. Geofluids 11,18e33.

MDDELCC, 2012. Strat�egie de protection et de conservation des sources destin�ees �al’alimentation en eau potable. Available at: http://www.mddelcc.gouv.qc.ca/eau/potable/strategie/strategie.pdf.

M�ejean, P., Pinti, D.L., Larocque, M., Sano, Y., 2015. Noble gas, carbon and nitrogen ina St. Lawrence Lowlands bedrock aquifer (eastern Canada). In: Abstract 34178Presented at AGU Joint Assembly, Montr�eal, QC, 3e7 May.

Meyzonnat, G., Larocque, M., Barbecot, F., Gagn�e, S., Pinti, D.L., 2015. The potential ofmajor ion chemistry to assess groundwater vulnerability of a regional aquifer insouthern Quebec (Canada). Environ. Earth Sci. (in press).

Mook, W.G., 1972. On the reconstruction of the initial 14C content of groundwaterfrom the chemical and isotopic composition. In: Rafter, T.A., Grant Taylor, T.(Eds.), Proceedings of the 8th International 14C Conference. Wellington, RoyalSociety of New Zealand, pp. 342e352.

Morgan, J.J., Stumm, W., 1965. The role of multivalent metal oxides in limnologicaltransformations, as exemplified by iron and manganese. In: Jaag, O. (Ed.), Proc.Second Intern. Conf. August 1964, Tokyo. Advances in Water Pollution Research.Pergamon Press, pp. 103e131.

Nickson, R.T., McArthur, J.M., Burgess, W.G., Ahmed, K.M., Ravenscroft, P.,Rahman, M., 1998. Arsenic poisoning of Bangladesh groundwater. Nature 395,338.

Ozima, M., Podosek, F.A., 1983. Noble Gas Geochemistry. Cambridge UniversityPress, Cambridge, United Kingdom.

Pacheco, F.A.L., 1998. Application of correspondence analysis in the assessment ofgroundwater chemistry. Math. Geol. 30, 129e161.

Paradis, S., Lavoie, D., 1996. Multiple-stage diagenetic alteration and fluid history ofOrdovician carbonate-hosted barite mineralization. South. Quebec Appala-chians Sediment. Geol. 107, 121e139.

Paralta, E., Ribeiro, L., 2001. Stochastic modeling and probabilistic risk maps of ni-trate pollution in the vicinities of Beja (Alentejo, South Portugal). In: Proc. 3rdInternational Conference on Future Groundwater Resources at Risk, Lisbon,pp. 251e261.

Parent, M., Dubois, J.M.M., Bail, P., Larocque, A., Larocque, G., 1985. Pal�eog�eographiedu Quebec m�eridional entre 12 500 et 8000 ans BP. Rech. Am�erindiennes au

Quebec 15, 17e37.Patriarche, D., Castro, M.C., Goblet, P., 2004. Large-scale hydraulic conductivities

inferred from three dimensional groundwater flow and 4He transport modelingin the Carrizo aquifer. Texas. J. Geophys. Res. 109, B11202. http://dx.doi.org/10.1029/2004JB003173.

Pearson, F.J., 1992. Effects of parameter uncertainty in modeling 14C in groundwater.In: Taylor, R.E., Long, A., Kra, R.S. (Eds.), Radiocarbon dating After Four Decades:An Interdisciplinary Perspective, Springer, New York, pp. 262e275.

Person, M., McIntosh, J., Bense, V., Remenda, V.H., 2007. Pleistocene hydrology ofNorth America: the role of ice sheets in reorganizing groundwater flow sys-tems. Rev. Geophys. 45, 1e28.

Pinti, D.L., B�eland-Otis, C., Tremblay, A., Castro, M.C., Hall, C.M., Marcil, J.-S.,Lavoie, J.-Y., Lapointe, R., 2011. Fossil brines preserved in the St-LawrenceLowlands, Quebec, Canada as revealed by their chemistry and noble gas iso-topes. Geochim. Cosmochim. Acta 75, 4228e4243.

Plummer, L.N., Glynn, P.D., 2013. Radiocarbon dating in groundwater systems. In:Isotope Methods for Dating Old Groundwater. International Atomic EnergyAgency, Vienna, pp. 33e89.

Salem, O., Visser, J.H., Dray, M., Gonfiantini, R., 1980. Groundwater flow patterns inthe western Lybian Arab Jamahiriaya. In: Arid-zone Hydrology: Investigationswith Isotope Techniques. International Atomic Energy Agency, Vienna,pp. 165e179.

Sano, Y., Fischer, T., 2013. The analysis and interpretation of noble gases in modernhydrothermal systems. In: Burnard, P. (Ed.), The Noble Gases as GeochemicalTracers, Advances in Isotope Geochemistry Series, Springer, New York,pp. 249e317.

Sano, Y., Tokutake, T., Takahata, N., 2008. Accurate measurement of atmospherichelium isotopes. Anal. Sci. 24, 521e525.

Sassano, G.P., Schrijver, K., 1989. Framboidal pyrite early-diagenetic, late-diageneticand hydrothermal occurrences from the Acton Vale Quarry, Cambro-Ordovician, Qc. Am. J. Sci. 289, 167e179.

Savenko, A.V., 2001. Interaction between clay minerals and fluoride-containingsolutions. Water Resour. Res. 28, 274e277.

Schlosser, P., Stute, M., Sonntag, C., Munnich, K.O., 1989. Tritiogenic 3He in shallowgroundwaters. Earth Planet. Sci. Lett. 94, 245e256.

SIGEOM, 2014. Carte Int�eractive. Minist�ere des Ressources Naturelles du Qu�ebec.Available at: http://sigeom.mrn.gouv.qc.ca/signet/classes/I1108_afchCarteIntr?l¼f.

Smith, S.P., Kennedy, B.M., 1983. The solubility of noble gases in water and NaClbrine. Geochim. Cosmochim. Acta 47, 503e515.

Sverjenski, D.A., Garven, G., 1992. Tracing great fluid migrations. Nature 356,481e482.

Tamers, M.A., 1967. Radiocarbon ages of groundwater in an arid zone unconfinedaquifer. In isotope techniques in the hydrological cycle. AGU Geophys. Monogr.11, 143e152.

Tamers, M.A., 1975. The validity of radiocarbon dates on groundwater. Geophys.Surv. 2, 217e239.

Tremblay, A., Roden-Tice, M.K., Brandt, J.A., Megan, T.W., 2013. Mesozoic faultreactivation along the St. Lawrence rift system, Eastern Canada: thermochro-nologic evidence from apatite fission-track dating. Geol. Soc. Am. Bull. 125,794e810.

Trottier, J., Brown, A.C., Gauthier, M., 1991. An ordovician rift environment for thememphremagog polymetallic massive sulphide deposit, Appalachian Ophiolitebelt, Quebec. Can. J. Earth Sci. 28, 1887e1904.

Vautour, G., Pinti, D.L., M�ejean, P., Saby, M., Meyzonnat, G., Larocque, M.,Castro, M.C., Hall, C.M., Boucher, C., Roulleau, E., Barbecot, F., Takahata, N.,Sano, Y., 2015. 3H/3He, 14C and (U-Th)/He groundwater ages in the st. LawrenceLowlands, quebec. East. Can. Chem. Geol. 413, 94e106, 10.1016/j.chemgeo.2015.08.003.

Weise, S., Moser, H., 1987. Groundwater dating with helium isotopes. In: Techniquesin Water Resource Development. International Atomic Energy Agency, Vienna,pp. 105e126.

Weiss, R.F., 1968. Piggybacks sampler for dissolved gas studies on sealed watertubes. Deep Sea Res. 15, 695e699.