The Geochemistry of Saline Springs in the Athabasca Oil Sands Region and Their Impact on the Clearwater and Athabasca Rivers

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2013-01-08 The geochemistry of saline springs in the Athabasca oil sands region and their impact on the Clearwater and Athabasca rivers

Gue, Anita

Gue, A. (2013). The geochemistry of saline springs in the Athabasca oil sands region and their impact on the Clearwater and Athabasca rivers (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/28159 http://hdl.handle.net/11023/400 master thesis

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UNIVERSITY OF CALGARY

The geochemistry of saline springs in the Athabasca oil sands region and their impact on the Clearwater and Athabasca rivers

Anita Eleanor Gue

A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

DEPARTMENT OF GEOSCIENCE CALGARY, ALBERTA DECEMBER, 2012

UNIVERSITY OF CALGARY

FACULTY OF GRADUATE STUDIES

The undersigned certify that they have read, and recommend to the Faculty of Graduate Studies for acceptance, a thesis entitled “The geochemistry of saline springs in the Athabasca oil sands region and their impact on the Clearwater and Athabasca rivers” submitted by Anita Eleanor Gue in partial fulfilment of the requirements for the degree of Master of Science.

______Co-supervisor, Bernhard Mayer, Geoscience

______Co-supervisor, Stephen Grasby, Geoscience

______Edwin Cey, Geoscience

______Michael Wieser, Physics & Astronomy

17 December 2012 Date iii Abstract

The geochemistry of saline springs discharging from Devonian carbonate rocks into the Clearwater and Athabasca rivers in northeastern Alberta was characterized using major ions, trace elements, dissolved gases, and PAHs. In addition, stable isotope analyses of H2O, SO4, DIC, Sr, and Cl were used to trace the provenance of spring waters, dissolved solutes, and subsurface processes affecting water chemistry. Spring waters were found to contain Laurentide glacial meltwater, which was supported by radioisotope analyses. The high salinity of the springs was found to be mainly due to evaporite and carbonate dissolution in the subsurface. Spring waters have been affected by bacterial sulfate reduction, methanogenesis, and methane oxidation. Trace elements and some PAHs were present in low concentrations, the origins of which did not seem to be weathering of bitumen. The total discharge of saline groundwater into the rivers over the study reach was estimated using a Cl isotope mass balance approach, which revealed that saline groundwater accounts for only a very small proportion of the annual mass flux in the rivers of trace elements and PAHs, but accounts for a higher proportion of major ions, particularly in the Clearwater River. iv Acknowledgements

Many thanks to my two supervisors, Bernhard Mayer and Stephen Grasby, for providing me with such an interesting project and for your generous support along the way. Thanks also for the patience and trust you showed when I left to work in Yellowknife partway through writing this thesis.

Thanks also to the fine folks at the Applied Geochemistry Group (Mike, Maurice, Jack) and the Isotope Science Laboratory (Mike, Steve, Jesusa, Nenita) at the University of Calgary for your assistance with lab analyses and your cheerful question answering.

Thanks to Bernadette Prömse for assistance in the field and for many laughs.

I would also like to acknowledge my colleagues at Environment Canada for their support during my education leave and their encouragement when I returned to work with a thesis to finish.

My sisters in geochemistry - Leslie, Leanne, Bernadette – thanks for making my time in Calgary so fun, for the moral support, and for all the adventures both at the university and beyond. Katie, sister on this crazy journey of life, your friendship made all the difference. My dear friends in Yellowknife, your support along the way kept me going through the thick and the thin.

Finally, a big thanks to my family for loving encouragement throughout. v Dedication

In memory of Aunty Lillian, not because she cared about geochemistry but because she cared about me. Our two years together in Calgary was a blessing. vi Table of Contents

Approvals Page...... ii Abstract ...... iii Acknowledgements...... iv Dedication...... v Table of Contents ...... vi List of Tables...... ix List of Figures and Illustrations...... xi List of Plates...... xiv

CHAPTER ONE: INTRODUCTION ...... 1 1.1 Objective...... 3 1.2 Oil sands background ...... 3 1.3 Study area ...... 5 1.3.1 Climate and vegetation...... 7 1.3.2 Quaternary geomorphology...... 7 1.3.3 Geologic setting ...... 9 1.3.4 Hydrogeologic setting ...... 13 1.4 Previous studies of springs ...... 16

CHAPTER TWO: METHODS ...... 19 2.1 Sampling locations ...... 19 2.2 Field methods...... 20 2.3 Chemical analyses ...... 21 2.3.1 Major ions...... 21 2.3.2 Dissolved organic carbon (DOC) ...... 22 2.3.3 Trace elements ...... 22 2.3.4 Polycyclic aromatic hydrocarbons (PAHs)...... 23 2.3.5 Dissolved gas composition ...... 23 2.4 Stable isotope analyses...... 24 2.4.1 δ18O and δ2H of water ...... 24 2.4.2 34S and δ18O of sulfate...... 24 2.4.3 13C of dissolved inorganic carbon (DIC) ...... 25 2.4.4 δ13C and 2H of dissolved methane...... 25 2.4.5 37Cl ...... 26 2.4.6 87Sr/86Sr...... 26 2.5 Radioisotope analyses...... 26 2.5.1 Tritium (3H) ...... 27 2.5.2 Radiocarbon (14C) ...... 27 2.6 QA/QC ...... 27

CHAPTER THREE: RESULTS ...... 29 3.1 Field measurements ...... 29 3.1.1 Spring waters ...... 29 3.1.2 River waters ...... 30 3.2 Chemical analyses ...... 31 vii 3.2.1 Major ion chemistry ...... 31 3.2.1.1 Spring waters...... 31 3.2.1.2 River waters...... 32 3.2.1.3 Temporal changes in TDS in select springs ...... 34 3.2.2 Trace elements ...... 36 3.2.2.1 Spring waters...... 36 3.2.2.2 River waters...... 37 3.2.3 PAHs ...... 39 3.2.3.1 Spring waters...... 39 3.2.3.2 River waters...... 39 3.3 Stable isotope ratios of water and dissolved constituents...... 41 3.3.1 δ18O and 2H of water ...... 41 3.3.2 δ34S and δ18O of sulfate...... 41 3.3.3 13C of DIC...... 42 3.3.4 87Sr/86Sr...... 42 3.3.5 37 Cl...... 42 3.4 Gas geochemistry in spring waters...... 44 3.4.1 Chemical composition of gases ...... 44 3.4.2 Isotopic composition of methane...... 44 14 3 3.5 Radioisotopes CDIC and H in spring waters...... 45

CHAPTER FOUR: SOURCES OF SPRING WATERS ...... 47 4.1 Temperature ...... 47 4.2 Isotopic evidence of glacial meltwater ...... 49 4.2.1 δ18O and 2H of water ...... 49 4.2.2 Quantification of glacial meltwater proportion...... 54 3 14 4.2.3 Age-dating of spring waters using H and CDIC...... 57

CHAPTER FIVE: SOURCES OF SOLUTES...... 61 5.1 Water types...... 61 5.1.1 Spring waters ...... 61 5.1.2 River waters ...... 64 5.2 Halite dissolution...... 65 5.2.1 Na/Cl ratios ...... 66 5.2.2 Cl/Br ratios ...... 68 5.2.2.1 Spring waters...... 69 5.2.2.2 River waters...... 70 5.2.3 Cl isotopes ...... 71 5.2.3.1 Spring waters...... 71 5.2.3.2 River waters...... 72 5.3 Carbonate and gypsum dissolution...... 73 5.3.1 Major ion ratios...... 73 5.3.2 δ34S and δ18O: sulfate dissolution...... 77 5.3.2.1 Bacterial sulfate reduction...... 78 5.3.3 δ13C of DIC: carbonate dissolution and methanogenesis...... 82 5.3.4 87Sr/86Sr ratios: carbonate dissolution...... 85 5.3.4.1 Spring waters...... 87 5.3.4.2 River waters...... 90 viii 5.4 Water-mineral equilibria in spring waters...... 90 5.4.1 Computer modeling setup...... 90 5.4.2 Mineral saturation...... 91 5.4.3 Mineral equilibria...... 93

CHAPTER SIX: TRACE COMPONENTS IN SPRING WATERS...... 97 6.1 Trace Elements ...... 97 6.1.1 Trace elements with water quality guidelines ...... 98 6.1.2 EPA Priority Pollutants ...... 100 6.1.3 Elements associated with oil sands...... 102 6.2 PAHs...... 104 6.2.1 Spring waters ...... 107 6.2.2 River waters ...... 108 6.3 Dissolved gases in spring waters ...... 110 6.3.1 Composition...... 110

6.3.2 Isotopic composition of CH4 ...... 112

CHAPTER SEVEN: INFLUENCE OF SALINE GROUNDWATER ON RIVER WATER QUALITY ...... 117 7.1 Cl isotope mass balance...... 117 7.1.1 Clearwater River...... 119 7.1.2 Athabasca River...... 121 7.2 Total discharge of saline groundwater...... 122 7.2.1 Clearwater River...... 123 7.2.2 Athabasca River...... 124 7.3 Annual mass flux of major ions from saline groundwater...... 125 7.3.1 Clearwater River...... 126 7.3.2 Athabasca River...... 127 7.4 Annual mass flux of trace elements from saline groundwater...... 128 7.4.1 Clearwater River...... 128 7.4.2 Athabasca River...... 129 7.5 Annual mass flux of PAHs from saline groundwater...... 132 7.5.1 Clearwater River...... 132 7.5.2 Athabasca River...... 133

CHAPTER EIGHT: CONCLUSIONS AND FUTURE RESEARCH ...... 135 8.1 Sources of spring water ...... 135 8.2 Sources of solutes in springs...... 136 8.3 Trace elements, PAHs, gases...... 137 8.4 Influence on river water quality...... 138 8.5 Future work...... 139

REFERENCES...... 142

Appendix A: Photos and descriptions of sampling sites...... 156

ix List of Tables

Table 2-1: Spring descriptions and locations ...... 20

Table 3-1: Field measurements at springs and rivers sites ...... 33

Table 3-2: Major ion concentrations in spring and river waters sampled in October 2010 ...... 33

Table 3-3: Concentrations of select major ions through time...... 35

Table 3-4: Total metal concentrations in springs and rivers...... 38

Table 3-5: Results of PAH analyses in spring and river waters...... 40

Table 3-6: Stable isotopic composition of spring and river waters and dissolved constituents...... 43

Table 3-7: Chemical and isotopic composition of dissolved gases in spring waters...... 43

Table 3-8: Results for samples taken in May 2011: radiocarbon age (uncorrected), 14C activity as percent modern carbon (pmc), alkalinity, 13 18 2 CDIC, δ O and H of water, and tritium content...... 46

Table 4-2: Radiocarbon and tritium concentrations in spring waters measured in May 2011 and calibrated calendar ages ...... 59

Table 5-1: Water classification based on TDS concentration...... 61

Table 5-2: Saturation indices of spring waters with respect to common rock- forming minerals...... 92

Table 6-1: Concentrations of metals for which PAL water quality guidelines have been developed (CCME, 2007) ...... 99

Table 6-2: Concentrations of elements on the EPA list of priority pollutants (PPE) ...... 100

Table 6-3: Concentrations of detectable PAHs in spring and river waters ...... 107

Table 7-1: Contribution of major ions from saline groundwater to the Clearwater River over the study reach, calculated using Cl isotope mass balance...... 120 x Table 7-2: Contribution of major ions from saline groundwater to the Athabasca River over the study reach, calculated using Cl isotope mass balance...... 122

Table 7-3: Discharge and total annual mass flux of major ions from individual springs, total saline groundwater over the study reach, and in the Clearwater River...... 127

Table 7-4: Discharge and annual mass flux of major ions in the Athabasca River, spring AR03, and total saline groundwater over the study reach. ....128

Table 7-5: Annual mass fluxes of trace elements from saline groundwater and in the Clearwater River...... 130

Table 7-6: Annual mass fluxes of trace elements from saline groundwater and in the Athabasca River...... 131

Table 7-7: Annual mass fluxes of PAHs in the Clearwater River and saline groundwater over the study reach...... 133

Table 7-8: Annual mass fluxes of PAHs in the Athabasca River and saline groundwater over the study reach...... 134

xi List of Figures and Illustrations

Figure 1-1: The three designated Oil Sands Areas (OSAs) in Alberta correspond with the Peace River, Athabasca, and Cold Lake deposits...... 2

Figure 1-2: Location of the study area in northeast Alberta with sampling locations, rivers, and oil sands developments...... 5

Figure 1-3: Routing of the Clearwater-Athabasca Spillway (CLAS) from Glacial Lake Agassiz during the retreat of the Laurentide Ice Sheet approximately 10,000 ya...... 8

Figure 1-4: Generalized stratigraphic and hydrostratigraphic units in NE Alberta...... 10

Figure 1-5: Cross-section of hydrostratigraphic units in NE Alberta at the edge of the Alberta Basin...... 11

Figure 1-6: Simplified map of bedrock geology with spring and river sampling locations...... 15

Figure 1-7: Electromagnetic survey of the Athabasca River bed with surrounding geology...... 18

Figure 3-1: Calculated TDS from values reported in the literature in various years compared with values from this study...... 36

Figure 4-1: Relationship between temperature of spring waters and total dissolved solids...... 48

Figure 4-2: Temperature versus δ18O of spring waters...... 49

Figure 4-3: Stable isotopic composition of spring and river waters with the LMWL for Fort Smith, NT...... 50

Figure 4-4: Semi-log plot of chloride concentration against δ18O values for spring waters...... 53

Figure 5-1: Piper plot of spring and river waters...... 62

Figure 5-2: Major ion concentrations versus TDS for spring waters...... 63

Figure 5-3: TDS versus δ18O of spring waters...... 64 xii Figure 5-4: Na/Cl ratios of springs from this study compared with those of formation waters from Upper Devonian units deeper in the WCSB ...... 67

Figure 5-5: Spring locations with subsurface extent of the Prairie Evaporite Formation and dissolution area ...... 68

Figure 5-6: Cl/Br ratios of spring and river waters, plotted with Cl/Br ratios of: formation waters from Upper Devonian units in the WCSB and Cretaceous units near the study area, saline fens near the study area, and Elk Point dissolution brines in WCSB...... 70

Figure 5-7: δ37Cl values of spring and river waters versus Cl concentration...... 73

Figure 5-8: Concentrations of Ca plus Mg versus HCO3 in spring waters...... 74

Figure 5-9: Ratios of Ca:Mg concentrations versus TDS for spring waters from this study and saline fens near the study area ...... 75

Figure 5-10: Cation versus anion concentration for the ions that would be liberated into solution by the dissolution of carbonates and gypsum: Ca,

Mg, SO4 and HCO3...... 76

Figure 5-11: δ34S and δ18O values of sulfate in spring river waters, plotted with ranges for various sources of sulfate; evaporitic source ranges identified by age...... 78

Figure 5-12: δ34S versus concentration of dissolved sulfate in all spring waters, excluding AR01...... 79

Figure 5-13: δ34S of dissolved sulfate vs. dissolved sulfide concentration in springs waters, excluding AR01...... 80

Figure 5-14: δ18O of dissolved sulfate versus dissolved sulfate in spring waters, excluding AR01...... 81

18 18 Figure 5-15: δ OSO4 versus δ OH2O in spring waters (excluding spring AR01)...... 82

Figure 5-16: 13C of DIC in spring waters as a function of alkalinity...... 84

Figure 5-17: δ13C of DIC versus methane concentration in spring waters...... 85

Figure 5-18: 87Sr/86Sr ratios in spring waters and river waters ...... 87

Figure 5-19: Concentrations of strontium vs. calcium in spring waters...... 88

Figure 5-20: 87Sr/86Sr ratios vs. 1/Sr concentration for spring waters and for Upper Devonian formation waters in the WCSB...... 89 xiii Figure 5-21: Calculated saturation indices of spring waters for common minerals...... 92

Figure 5-22: Spring waters plotted in terms of Mg and Ca activities, with

stability fields for carbonate minerals in the system CaO-MgO-CO2-H2O at atmospheric pressure and 2°C...... 94

Figure 5-23: Spring waters plotted in terms of Mg and Ca activity ratios, with

stability fields for smectite clays in the system CaO-MgO-SiO2-Al2O3-H2O at atmospheric pressure and 2 °C...... 95

Figure 5-24: Stability fields for aluminosilicate clays gibbsite, kaolinite, and

Ca-Beidellite in the system CaO-MgO-SiO2-Al2O3-H2O at atmospheric pressure and 2°C...... 96

Figure 6-1: Concentrations of PPE in spring and river waters...... 102

Figure 6-2: Concentrations of metals associated with bitumen in spring and river waters...... 104

Figure 6-3: Concentration of total PAHs in spring and river waters...... 106

Figure 6-4: Concentrations of individual PAHs in spring and river waters...... 109

Figure 6-5: Dissolved gas composition of spring waters ...... 112

Figure 6-6: Isotopic composition of methane in spring waters plotted with possible source ranges...... 114

Figure 6-7: 2H values of methane and co-existing spring waters...... 115

xiv List of Plates

Spring CW01...... 156

Spring CW02...... 156

Spring CW03...... 156

Spring CW05...... 157

Spring CW07...... 157

Spring CW08...... 157

Spring CW09...... 158

Spring AR01...... 158

Spring AR02...... 159

Spring AR03...... 159

1 Chapter One: Introduction

The oil sands deposits located in northeastern Alberta are one of the largest proven reserves of crude oil in the world. Three oil sands areas cover an area of 142,200 km2 (Figure 1-1) and contain an estimated 169 billion barrels of recoverable reserves (Energy Resources Conservation Board (ERCB), 2011). A non-conventional source of oil, this resource is gaining attention as global energy demands increase and conventional sources become depleted (Giesy et al., 2010). The pace of oil sands development in Alberta is rapid, with production expected to increase from the current 1.5 million barrels per day to 3.5 million barrels per day by 2020 (ERCB, 2011). However, the development of Alberta's oil sands has become controversial, with local, national, and international attention on environmental and health issues associated with their development (Gosselin et al., 2010). Concerns over the water quality of the Athabasca River, which runs through the oil sands area, have been increasing in prominence in recent years as studies on the effects of oil sands development on local river ecosystems have been published (Kelly et al., 2009; Timoney and Lee, 2009; Kelly et al., 2010). New monitoring plans created by the federal and provincial governments are designed to further the understanding of natural baseline conditions and potential impacts from oil sands development on water quantity, water quality, and ecosystem health in the Athabasca Basin (Environment Canada, 2011a; Government of Canada and Government of Alberta (GOC and GOA, 2012)). Key issues to be addressed include baseline water quality conditions and surface water – groundwater interactions (Environment Canada, 2011a). This study addresses a portion of these concerns through enhancing the understanding of the baseline geochemistry of saline groundwater discharging to the Athabasca River and its major tributary, the Clearwater River. Devonian carbonate rocks naturally outcrop in these river valleys in the Athabasca oil sands region. From these rocks saline groundwater discharges into the river systems as seeps and springs. This groundwater contains some compounds similar to those of concern from oil sands development; therefore, these saline

2 groundwater contributions to rivers need to be considered when assessing potential industrial impacts on river water quality. Understanding the baseline chemistry and origins of these spring waters contributes to the overall understanding of surface water – groundwater interactions in the Athabasca oil sands region, which in turn supports monitoring efforts focused on the effects of oil sands development on water resources. The Clearwater River system offers the opportunity to study the water quality of these natural saline springs in a minimally impacted river system in the Athabasca oil sands region. This provides a valuable baseline for comparison with saline groundwater nearer to oil sands development and for temporal trends as development continues.

Figure 1-1: The three designated Oil Sands Areas (OSAs) in Alberta correspond with the Peace River, Athabasca, and Cold Lake deposits (image from http://oilsands.alberta.ca/reclamation.html#JM-OilSandsArea).

3 1.1 Objective

The objective of this study was to characterize the baseline chemistry and isotopic composition of saline springs discharging from Devonian carbonates into the Clearwater and Athabasca rivers. This provides insight into the origin of the spring waters, the sources of salinity, sub-surface processes that have affected spring waters, and the impact of saline groundwater discharge on river water quality. This baseline information will contribute to the understanding of surface water – groundwater interactions in the Athabasca oil sands region.

1.2 Oil sands background

Oil sands are a combination of bitumen (viscous, heavy crude oil), and the rock material in which it is found. Bitumen is recovered by two techniques: surface mining, which occurs in the Athabasca OSA and in-situ recovery, which occurs in all three OSAs. Open-pit mining is used where oil sands ore is found at depths of ≤ 65 m (ERCB, 2011). After mining, bitumen is extracted from the ore using a hot water process. About 20% of the reserves are recoverable in this way. The remaining 80% of reserves are too deep to be mined, but may be developed using in-situ techniques (Canadian Association of Petroleum Producers (CAPP), 2011a). This can be through either primary development, similar to conventional crude oil production, or through enhanced recovery where the reserves are heated to increase the viscosity. In 2010, 53% of oil sands production was from surface-mining, but by 2015 in-situ production is expected to exceed that of mining (ERCB, 2011). Both surface mining and in-situ production can have potential effects on surface and groundwater resources. Both require large quantities of water and produce large quantities of wastewater. For example, the extraction of bitumen from mined ore requires an average of 3.4 barrels of freshwater per barrel of oil, the majority of which is sourced from the Athabasca River (CAPP, 2011b). Under a zero-discharge policy, much of this water is reused, and the remaining wastewater is stored in large tailings ponds that contain process-affected water, fine silts, left-over bitumen, salts, organic compounds, and solvents (Government

4 of Alberta (GOA), 2011). Tailings waters are highly saline and contain toxic naphthenic acids and polycyclic aromatic hydrocarbons, released during processing (Allen, 2008). Currently, industry is required to capture any detected seepage from tailings ponds (GOA, 2011); however, seepage from tailings ponds into groundwater and surface water may still be a concern for water quality (Timoney and Lee, 2009). Tailings ponds in the Athabasca OSA occupy approximately 170 km2 of the landscape (CAPP, 2011c) and hold an estimated 720 million m3 of tailings (Gosselin et al., 2010). In-situ development also requires water, but the use of saline groundwater reduces freshwater consumption to 0.5 barrels per barrel of oil produced (CAPP, 2011b). Wastewater from this process is either injected into the subsurface or transported to a treatment facility (CAPP, 2011b). Water withdrawals from deep aquifers, as well as deep well injection of wastewater into the subsurface, has the potential to affect groundwater regimes. The interplay between surface water and groundwater systems means that processes affecting groundwater may affect surface water regimes, and vice- versa. In addition to issues directly related to water consumption and disposal, both surface mining and in-situ development require the removal of the boreal forest for infrastructure. In the case of mining, 662 km2 of boreal forest has been disturbed to date due to surface mining in the Athabasca OSA (CAPP, 2011b). More than 65% of the boreal forest in this area is comprised of wetlands, defined as areas permanently or temporarily submerged or permeated by water (Natural Resources Canada, 2003). Wetlands perform several functions, including water storage, and groundwater recharge or discharge (Harris, 2008). Their large-scale removal raises questions surrounding possible effects on groundwater regimes in the area. This study of springs, which are natural discharge areas for groundwater, will contribute to the understanding of groundwater regimes in the oil sands area.

5 1.3 Study area

The study area is located in the Athabasca oil sands region in northeastern Alberta and extends into western Saskatchewan. It is defined by the Clearwater River to the south, the edge of the Canadian Shield to the east, the Athabasca River to the west, and the Firebag River to the north (Figure 1-2).

Figure 1-2: Location of the study area in northeast Alberta (greyed area), with sampling locations, rivers, and oil sands developments (Oil sands shapefiles from www.esri.com).

6 The boreal plains topography of the area is interrupted by the Athabasca and the Clearwater river valleys, incised 60 to 150 m below the plains. In addition, four major uplands rise up to 1500 m above the surrounding plains: Muskeg Mountain in the northeast, the Birch Mountains in the northwest, Thickwood Hills in the west, and Stony Mountain in the south (Hamilton and Mellon, 1973) (Figure 1-3). Within the study area the only settlements are the municipality of Fort McMurray and the hamlet of Fort McKay, located 60 km north of Fort McMurray on the Athabasca River. Road access is possible from Fort McMurray to Fort McKay on the west side of the Athabasca River, but there is no road access along the Clearwater River beyond Fort McMurray. The Clearwater River is a major tributary of the Athabasca River, Alberta's longest waterway. These rivers are part of the Mackenzie River Basin, Canada’s second-largest watershed, which drains one fifth of the country’s landmass north into the Arctic Ocean (Mackenzie River Basin Board (MRBB), 2004). The Clearwater River flows west from Broach Lake in Saskatchewan for 295 km to its confluence with the Athabasca River at Fort McMurray. The entire Clearwater River has been named a Canadian Heritage River in recognition of its natural value, historical importance as a trade route, and recreational potential (GOA and SEC, 2003). This designation is meant to promote responsible river stewardship and includes a management plan created by various stakeholders that expresses the need for ongoing inventories to expand the knowledge base for the river and its corridor (GOA and SEC, 2003). The Clearwater River corridor is considered to be relatively undisturbed and anthropogenic activities are limited, though in addition to the municipality of Fort McMurray at its mouth, there are some commercial and industrial land uses along its length including tourism, forestry, oil and gas developments, trapping, and agriculture (GOA and SEC, 2003). Historically there have also been salt mining operations along its reaches to exploit the thick Middle Devonian evaporite salt deposits located beneath the Paleozoic carbonates (Allan, 1943). The Athabasca River, in contrast, flows through many settled and developed areas on its 1375 km path from the Columbia Icefields in the Rocky Mountains to Lake Athabasca in northeast Alberta. The upper reach of the river

7 in Jasper National Park is also designated as a Canadian Heritage river (Canadian Heritage Rivers Board Secretariat, 2011). Conventional oil and gas, forestry, coal mining, agriculture, commercial fishing, and trapping all occur within the Athabasca sub-basin upstream of Fort McMurray (MRBB, 2004). Extensive oil sands mining operations are located along the river downstream of Fort McMurray. The river ends in the Peace Athabasca Delta, one of the world’s largest freshwater deltas, recognized as a Unesco World Heritage site and as a wetland of international significance by the Ramsar Convention (MRBB, 2004).

1.3.1 Climate and vegetation

The study area falls within the mid-Boreal Uplands ecoregion, as defined in the National Ecological Framework for Canada (Ecological Stratification Working Group (ESWG), 1996). This uplands ecoregion is part of the continuous mid-Boreal forest that extends from Ontario to the Rocky Mountains. In this ecoregion summers are short and cool, and winters are cold. Monthly average temperatures at Fort McMurray are 16.8 °C in July and -18.8 °C in January (Environment Canada, 2010a) Mean annual precipitation ranges from 400 to 500 mm, and more than 70% falls as rain in the summer with July being the wettest month (Corkum, 1985). The most common trees in this mixed deciduous and coniferous forest are aspen, balsam poplar, spruce, and balsam fir. Poorly drained, cold fens support tamarack and black spruce (ESWG, 1996). Waterlogged muskeg or peat bogs ranging in depth from one to several meters cover 60 - 75% of the surface, and discontinuous permafrost is present below a depth of 0.25 - 0.75 m (Hamilton and Mellon, 1973).

1.3.2 Quaternary geomorphology

The Clearwater River is an underfit stream. The valley was proposed to be spillway for Glacial Lake Agassiz by Smith (1989). During the melting of the Laurentide Ice Sheet, Lake Agassiz formed as a proglacial lake covering much of the eastern prairie provinces and extending into the United States (Figure 1-3). The Clearwater-Athabasca Spillway (CLAS) connected Lake Agassiz and the

8 Mackenzie valley as a northwestern drainage route for catastrophic discharge from the lake (Smith and Fisher, 1993). Murton et al. (2010) described evidence of two catastrophic floods that drained through the CLAS to the Arctic Ocean, the first near the onset of the Younger Dryas around 13,000 years ago, and the second between 11,700 and 9,360 years ago. These floods carved the deep valley through which the Clearwater River now flows to the Athabasca River.

Figure 1-3: Routing of the Clearwater-Athabasca Spillway (CLAS) from Glacial Lake Agassiz during the retreat of the Laurentide Ice Sheet approximately 10,000 years ago. Major uplands in the study area are also shown. Modified from Fisher (2007).

9 1.3.3 Geologic setting

The study area is situated on the northeastern edge of the Alberta Basin within the Western Canada Sedimentary Basin (WCSB). The southwest-dipping wedge of sediments of the WSCB lies unconformably on the crystalline Precambrian rocks of the Canadian Shield (Norris, 1973). An erosional unconformity truncates Paleozoic strata, above which lie Cretaceous sediments, including those that host the Athabasca oil sand deposits. A veneer of Pleistocene glacial drift overlies almost the entire area, which is in turn covered by muskeg and boreal forest (Carrigy, 1973). The stratigraphy and hydrostratigraphy of the study area has been described by Bachu et al. (1993) and is summarized in Figure 1-4. A cross section through the study area is shown in Figure 1-5. The oldest sedimentary succession in the WCSB in the study area is the early- to mid-Devonian Elk Point Group, which overlies the Precambrian basement. Deposited within the Elk Point sub-basin, the northern edge of these sediments extends to the Clearwater River. The group is divided into a lower dolomitic and an upper evaporitic subgroup. Only two units of the Lower Elk Point sub-group exist in the study area, probably due both to the depositional edge of the Elk Point Basin, and also to dissolution along the edge (Meijer-Drees, 1986). The oldest is the Basal Red Beds Formation, a unit of arkosic sandstone with sandy dolomite and shales that fills in Precambrian depressions. It is overlain by the Contact Rapids Formation, a unit of dolomitic siltstone with scattered beds of anhydrite and gypsum that outcrops at Contact Rapids on the Clearwater River (Norris, 1973). South and downdip of the study area several evaporitic formations lie in between these two units, which include beds of almost pure halite up to 76 m thick (Meijer-Drees, 1986). The Upper Elk Point sub-group is represented by three formations in the study area. The oldest is the Winnipegosis Formation (aka Methy or Keg River Formation), which consists of dolomite with minor anhydrite and outcrops along the Clearwater River upstream of the sampled springs. The overlying Prairie Evaporite Formation consists of relatively pure halite interbedded with anhydrite and dolostone. The only member of this formation in the study area is the Leofnard Member, which reaches a thickness of 240 m in the subsurface near

10 the mouth of the Clearwater River (Norris, 1973). The feather edge of this salt unit would be expected just west of the Winnipegosis outcrop on the Clearwater; however, it is absent due to salt dissolution, which has caused a swath of

Figure 1-4: Generalized stratigraphic and hydrostratigraphic units in NE Alberta. Devonian carbonates that host the saline springs of this study are shaded. Modified from Bachu and Undershultz (1993).

Figure 1-5: Cross-section of hydrostratigraphic units in NE Alberta and through the study area. Modified from Bachu et al. (1993). 11

12 collapse structures along the margins of this group (Hitchon et al., 1969). Norris (1973) suggested the presence of saline springs along the Clearwater River is evidence that dissolution is still occurring. The final unit in the Upper Elk Point sub-group in the area is the Watt Mountain Formation, consisting of dolomite shales overlying the Prairie Evaporites (Bachu and Underschultz, 1993). An erosional disconformity separates the Elk Point Group from the overlying upper-Devonian units of the Beaverhill Lake Group. Several carbonate formations make up this unit. The oldest is the Slave Lake Formation, a thin limestone unit that oversteps the edge of the Prairie Evaporites and lies directly over the Winnepegosis Formation (Norris, 1973). Above this is the alternating succession of shale and argillaceous limestone of the Waterways Formation, which reaches a thickness of up to 200 m in the Clearwater River area. Collapse structures from the dissolution of underlying Prairie Evaporites are evidenced in this unit (Norris, 1973). The Waterways formation outcrops along the Clearwater River west of Contact Rapids, and along the Athabasca River from Fort McMurray to Fort McKay, and again further north (Figure 1-6). It is from this formation that saline springs emerge in the river valleys. The Paleozoic succession is intersected by the sub-Cretaceous unconformity and Cretaceous sediments fill in paleotopography created by collapse structures (Carrigy and Mellon, 1959). The Lower Cretaceous Mannville Group includes the McMurray Formation, a sandstone unit that crops out along both the Athabasca and Clearwater rivers and which is mined extensively for bitumen on both sides of the Athabasca River. The overlying Clearwater and

Grand Rapids formations are dominated by sandstone and also outcrop in the study area. The Colorado Group shales and thin sandstones lie discontinuously over the Mannville Group. Unconsolidated glacial and post-glacial deposits of sands and gravels up to 50 m thick blanket most of the Cretaceous succession, with localized paleovalley fill deposits up to 100 m thick (Bachu et al., 1993).

13 1.3.4 Hydrogeologic setting

The hydrostratigraphy of the study area (Figure 1-4) was described by Bachu et al. (1993) using the following definitions from Marsily (1986): aquifers are water-saturated units from which water can be pumped; aquitards are less permeable units from which water cannot be produced, but which permit vertical leakage between aquifers; and aquicludes are units of very low permeability that do not permit vertical leakage. Bachu et al. (1993) noted that in the eastern part of the WCSB, where the study area is located, many of the aquitards become more arenaceous and less effective, thereby allowing some cross-formational flow. Three main aquifer systems crop out in the study area. From the oldest to youngest they are: 1) the Contact Rapids-Winnipegosis carbonate aquifer system, bounded below by Lower Elk Point evaporites and above by the Prairie-Watt Mountain aquiclude; 2) the Beaverhill-Cooking Lake carbonate aquifer system, bounded below by the Prairie-Watt Mountain aquiclude and overlain directly in the study area by, 3) the McMurray Wabiskaw sandstone aquifer/aquitard system, which is bounded above by the Clearwater aquitard. The saline springs that form the basis of this study emerge from the Waterways Formation of the Beaverhill Lake - Cooking Lake karstic aquifer system (Bachu et al., 1993). Varying scales of groundwater flow regimes are found in this complex area at the edge of the WCSB. By definition, basin-scale flow occurs from regional recharge at topographic highs to regional discharge at topographic lows, local-scale flow systems are created by local topographic highs and lows, and intermediate-scale flow regimes exist in the transition between regional and local scale (Toth, 1963). Regional recharge areas for the WCSB have been generally described as the mountains of Alberta and Montana, with overall flow direction from the southwest towards the northeast to regional discharge areas in the Clearwater and Athabasca river valleys (e.g. Hitchon et al., 1969; Bachu et al., 1993). Accordingly, Bachu et al. (1993) classified the Contact Rapids – Winnipegosis system as a regional flow system. The Beaverhill - Cooking Lake aquifer system was classified as an intermediate to local flow system within the study area, meaning underlying regional trends are affected by local topography.

14 The overlying Cretaceous aquifer, the McMurray Wabiskaw system, was considered by Bachu et al. (1993) to be a local flow system, completely driven by local topography. However, other research has shown that the WCSB has never been fully flushed by meteoric water as would be expected from a regional flow system (Michael et al., 2003). Grasby and Chen (2005) suggested that the topography- driven basin-scale flow regime in the WCSB was reversed during Pleistocene glaciations and has not yet reached equilibrium. Further, Grasby and Chen (2005) suggested that subglacial meltwater was forced into the subsurface during the last glacial period and that it is Laurentide glacial meltwater, as opposed to regional basin brines or local modern recharge, emerging as saline springs from the Devonian carbonates of the Beaverhill-Cooking Lake aquifer in the Clearwater and Athabasca river valleys.

112°0'0"W 111°0'0"W 110°0'0"W Bedrock Geology E Populated Place AR03 ! River sampling site ! ! RAR02 Saline Spring [_ Water Survey of Canada Gauge Station

r e Mesozoic iv R Devonian, Waterways Formation a c s Devonian a

a Proterozoic-Archean 57°30'0"N h

Fort MacKay ! AR02

AR01 ! A l b e r t a Saskatchewan

CW05 [_ CW03 57°0'0"N RCW02 River Fort McMurray ! ! CW02 water ! lear ! RAR01 ! CW09 !! CW01 C [_ ! ! RCW01 [_ ! CW07 CW08 a River basc ha At

05 10 20 30 40 Kilometres

Figure 1-6: Simplified map of bedrock geology with spring and river sampling locations. Geology basemaps modified from Hamilton et al. (2004) and Government of Saskatchewan (2012). Naming conventions for this study: CW = Clearwater River spring, RCW = Clearwater River sample, AR = Athabasca River spring, RAR = Athabasca River sample.

16 1.4 Previous studies of springs

Saline springs in the study area have been known for over a century, although they have been the focus of few scientific studies. Bell (1884) wrote of cold mineral springs along the Clearwater River and suggested that “copious” springs and seeps of varying sizes may have an effect on the river water chemistry. Bell (1884) also described the salt deposits at La Saline, a spring on the east bank of the Athabasca River labelled AR01 in this study. The saline springs have been mentioned in several subsequent geological survey reports since (Carrigy and Mellon, 1959; Norris, 1973; Hitchon et al., 1969; Grasby 2006). Hitchon et al. (1969) suggested that the springs’ major ion composition was the result of dissolution of Elk Point evaporites by meteoric water. Grasby and Chen (2005) postulated that the water source of the springs was Pleistocene glacial meltwater and showed that the salinity source was Devonian evaporate deposits. Additionally, Grasby (2006) presented stable isotope data of sulfate, which supported a Devonian evaporite source of salinity and showed evidence of bacterial sulfate reduction. Stewart and Lemay (2011) reported on the general chemistry and isotopic data for saline fens along Salt Creek, just south of the study area, which showed some similarities to the springs of this study. Gibson et al. (2011) reported on the geochemistry and isotopic composition of riverbed groundwater seeps along the Athabasca River within the study area, which were identified through a waterborne electromagnetic (EM) terrain conductivity survey conducted by WorleyParsons (2010). Ten areas of high conductivity, interpreted to be zones of high pore water salinity, were identified in the riverbed, six of which were sampled for groundwater seepage (Figure 1-7). Five of these groundwater seeps were located where the river has incised to the Waterways Formation, but were less saline than the springs discussed in the current study (Gibson et al., 2011). The electromagnetic survey indicated that in addition to springs and seeps located on the riverbanks, saline groundwater is entering the river system through riverbed seeps. No electromagnetic imaging is available for the Clearwater River, but it is reasonable to expect similar riverbed seepage in this river. Recently, Jasechko et al. (2012) used previously reported data to quantify the combined saline groundwater

17 seepage from Devonian and Cretaceous formations into the Athabasca River over reaches extending north and south of the present study area. None of the previous work discussed above has included all of the springs investigated in this study. In addition, this project included the most comprehensive suite of analyses that has yet been conducted on saline springs emerging from the Beaverhill-Cooking Lake aquifer, including major ions, trace elements, polycyclic aromatic hydrocarbons, various stable isotope compositions, as well as tritium and radiocarbon. Building upon previous work, this study furthers the understanding of the provenance of the spring waters and the subsurface processes that have influenced their chemistry, as well as their effect on river water quality. This will enhance knowledge of natural baseline conditions of groundwater in the Athabasca oil sands region and contribute to the understanding of groundwater-surface water interactions in the Clearwater and Athabasca rivers.

Figure 1-7: Electromagnetic survey of the Athabasca River bed with surrounding geology; numbered sites are zones of high riverbed conductivity presumed to be saline groundwater seeps. Modified from Gibson et al. (2011).

19 Chapter Two: Methods

In this chapter the locations and types of springs that were sampled are described. Methods used in field sampling as well as laboratory analyses for chemical and isotopic parameters are presented. The quality assurance and quality control (QA/QC) program for the study is also outlined.

2.1 Sampling locations

Throughout this study sites where groundwater emerges at the surface are all referred to as ‘springs’; however, the sampling sites had many different forms and some may also be referred to as seeps, salt marshes, or meadows with multiple seeps and pools. Descriptions for each spring are given in Table 2-1 and photos of each spring are provided in Appendix A. Ten springs in total were sampled: seven in the Clearwater River valley and three in the Athabasca River valley. The sample sites are remote and most springs were accessed by helicopter, except for spring AR02, which is located near Fort McKay and is accessible by road. Nine springs were sampled in October 2010 to obtain sufficient water for a full suite of chemical and isotopic analyses (Figure 1-6). In May 2011, four springs were re-sampled and one new spring was added (AR02) for radiocarbon and tritium analyses for age-dating the water. Water isotopes and a simplified major ion suite were also analyzed in samples obtained in May 2011 in order to detect any temporal changes in spring chemistry between October 2010 and May

2011. Two samples from each river were also taken, upstream and downstream of the sampled springs (Figure 1-6). The Clearwater River upstream site was located on the south shore at the edge of the Canadian Shield in Saskatchewan just before the river begins to incise through Devonian carbonate rocks. The downstream site was located on the north shore at the mouth of the Clearwater River before the confluence with the Athabasca River. Both Clearwater River sites were accessed by helicopter. On the Athabasca River, the upstream site was located on the west shore just before the town of Fort McMurray, and was

20 accessed by road. The downstream site was just north of the most northern spring (AR03) on the southern tip of an island in the middle of the river and was accessed by helicopter.

Table 2-1: Spring descriptions and locations. Datum is WGS84.

Site River Latitude Longitude Type of spring

AR01 Athabasca 57.07286 -111.51138 La Saline spring: multiple discharge points running into La Saline Lake on east side of river. AR02 Athabasca 57.18967 -111.62715 Seep below dry well on west side of river. AR03 Athabasca 57.66597 -111.42915 Discrete spring on west bank of river. CW01 Clearwater 56.70965 -110.35622 Discrete spring and pool on south side of river.

CW02 Clearwater 56.71982 -110.41514 Several seeps and springs running into one main channel on north side of river. CW03 Clearwater 56.73471 -110.47091 Discrete spring and pool on south side of river. CW05 Clearwater 56.74869 -110.53017 Small seep in a meadow of pools and seeps on south side of river. CW07 Clearwater 56.68799 -110.78003 Small spring in a meadow of pools and seeps on south side of river. CW08 Clearwater 56.66081 -110.83073 Small seep beside a meadow of pools on south side of river. CW09 Clearwater 56.68252 -111.16472 Meadow of pools on south side of river.

2.2 Field methods

Springs were sampled as close to the source as possible. If the site was a seep or meadow with multiple pools the pool with the highest electrical conductivity was sampled because to minimize sampling of waters diluted by runoff or shallow groundwater. At river sites, a grab sample was taken by hand at about 20 cm depth after wading from shore as far as possible into the main flow. Field measurements of temperature, dissolved oxygen, pH, and electrical conductivity were made directly in the springs and rivers using a YSI multi- parameter sonde which was calibrated daily. Flow velocity of the springs was measured where possible using a Swoffer 2100 open stream velocity meter with a 2-inch diameter propeller. Cross-sectional measurements were made to calculate discharge. Where water levels were insufficient to use the flow meter, flow was roughly estimated by timing the filling of a 125 mL sample bottle in a discrete channel.

21 At each site, a total of sixteen sample bottles were filled with spring water for laboratory analyses of various chemical and isotopic parameters. Nitrile gloves were worn while sampling. Bottles were either glass or high-density polyethylene (HDPE), according to the lab requirements described in Sections 2.3 and 2.4. Bottles were rinsed three times with sample water before filling, with the exception of bottles for sulfide analysis as the bottles contained a pre-treatment of preservative. Samples requiring filtration were passed through 0.45 m nitrocellulose membrane filters using a hand vacuum pump filtration unit. When necessary, samples were preserved or ions were precipitated before tightly capping the bottles. All samples were transported and stored in cool, dark conditions.

2.3 Chemical analyses

The following sections describe the methods of collection and analyses for chemical parameters in waters, the laboratories used, and the measurement uncertainties associated with the reported data.

2.3.1 Major ions

Most major ion concentrations were determined at the University of Calgary Applied Geochemistry Group (AGg) laboratory. For cation analyses, samples were filtered and acidified to pH < 2 with ultra pure nitric acid to prevent the formation of metal oxides. HDPE bottles were used. Cation concentrations were determined using atomic absorption spectrometry on a

Perkin Elmer Flame Absorption spectrometer. Detection limits were 1 mg/L or better, and measurement uncertainty was ±5%. For most anion analyses, samples were filtered and stored unpreserved in HDPE bottles. Dissolved sulfate and chloride concentrations were measured using a Dionex Ion Chromatograph instrument with detection limit of 1 mg/L or less, and measurement uncertainty of ±5%. Dissolved bromide concentrations were determined at the University of Alberta by neutron activation analysis at the Slowpoke facility with a measurement uncertainty of < 5%. Dissolved sulfide

22 was sampled in glass bottles, pretreated with an anti-oxidizing buffer consisting of NaOH, ascorbic acid, and disodium EDTA in water. Sulfide concentration was then measured in the lab using an Orion model 290A meter with an Ag/S ISE probe calibrated to laboratory standards. Measurement uncertainty was ±16%. Samples for alkalinity measurements were collected in glass jars. Alkalinity titrations were conducted at the University of Calgary as soon as possible, within 4 to 7 days after sampling, using an Orion 960 automated titrator. Forward titrations were done with H2SO4 of 0.1M for spring waters and 0.01M for river waters. Reverse titrations were conducted with 0.1 N NaOH for all samples. Samples for alkalinity in spring waters were unfiltered, which was determined to be acceptable due to the low suspended sediment in the spring waters. Charge balance calculations confirmed that the resultant alkalinity concentrations were reasonable. Alkalinity is expressed throughout this thesis as mg/L of bicarbonate ion. Measurement uncertainty was ±5%. The detection limit was 1 mg/L.

2.3.2 Dissolved organic carbon (DOC)

Filtered samples for analysis of dissolved organic carbon content (DOC) were collected in glass bottles. Samples were acidified to pH 2 with HCl to eliminate inorganic carbon by driving it out as CO2 gas. DOC content was analyzed at the U of C Environmental Science Laboratory on a Shimadzu total organic carbon analyzer (model TOC-VCPN). Standard methods for TOC analysis by high temperature combustion with automatic purging of acidified samples were followed (Eaton et al., 2005). Measurement uncertainty was ±0.1 mg/L. The detection limit was 1.0 mg/L.

2.3.3 Trace elements

Unfiltered samples for analysis of total metals were collected in HDPE bottles and acidified with ultra pure nitric acid to a pH of < 2 in the field to prevent precipitation of metal ions. Concentrations of 34 elements were determined at Environment Canada’s National Laboratory for Environmental

23 Testing (NLET) in Burlington, Ontario using an inductively coupled argon plasma- collision/reaction cell mass spectrometer (CRC-ICP-MS) following 16 hours of in-bottle digestion to liberate all metals (NLET, unpublished-a). Detection limits ranged from 0.01 to 0.5 g/L and are listed by element in Table 3-4.

2.3.4 Polycyclic aromatic hydrocarbons (PAHs)

Unfiltered samples were taken in amber glass bottles for analysis of concentrations of 25 PAHs. Analysis was completed at NLET in Burlington, Ontario. Samples were extracted using dichloromethane and fractionated on a silica gel column, then analyzed for PAH using single column capillary gas- liquid chromatography (NLET, unpublished-b). Detection limits varied from 2.95 to 25.1 ng/L and are listed by PAH in Table 3-4. Four surrogates (fluorene-d10, naphthalene-d8, d-perylene, pyrene-d10) were also analyzed in each sample and are listed by percent recovery in Table 3-4. Surrogates are chemical standards not expected to occur in the samples, and are added to each sample to assess unusual effects or processing errors. The acceptable range of % recovery for surrogates is from 60 to 120% (US Environmental Protection Agency (EPA), 1999).

2.3.5 Dissolved gas composition

Unfiltered samples were taken in teflon bottles with septum tops for analysis of dissolved gas composition. Samples were sent to Isotech Laboratories in Champaign, Illinois, where dissolved gas compositions were determined by headspace equilibration and gas chromatography with a Shimadzu 2010 instrument. The mole fractions of the following nine dissolved gases were determined: helium, hydrogen, argon, oxygen, carbon dioxide, nitrogen, carbon monoxide, methane, and ethane. Mole fractions were normalized to 100% and are approximately equal to volume percent. Measurement uncertainty was ± 2%.

24 2.4 Stable isotope analyses

Stable isotope ratios were determined for the following elements: hydrogen and oxygen in water, sulfur and oxygen in sulfate, carbon in dissolved inorganic carbon (DIC), carbon and hydrogen in dissolved methane, dissolved strontium, and chloride. All measured isotope ratios, except those of strontium, are expressed in delta notation with respect to internationally accepted standards according to Equation 2-1, where R is the ratio of the heavy isotope to the light isotope of the two most abundant isotopes of an element.

(2-1) Positive delta values reflect an enrichment in the heavier isotope while negative values reflect a depletion in comparison with the internationally accepted reference material. Strontium isotope values are expressed as a simple ratio between the heavy and light isotopes of 87Sr and 86Sr. Analyses were completed at the U of C Isotope Science Laboratory unless otherwise stated.

2.4.1 δ 18O and δ 2H of water

Filtered samples for isotopic analysis of water were taken in HDPE bottles. The 2H/1H and 18O/16O ratios in water were determined by laser spectroscopy using a Los Gatos Research DLT-100 instrument, following procedures outlined by Lis et al. (2008). This method measures the isotopic ratios directly on water vapour molecules using off-axis integrated-cavity output spectroscopy (ICOS) rather than converting water to H2 and CO2 gas as in conventional mass spectrometry techniques. Results are reported relative to Vienna Standard Mean Ocean Water (V-SMOW). Measurement uncertainty was ±0.1‰ for 18O and ±1.0‰ for 2H.

2.4.2 δ34S and δ 18O of sulfate

Filtered samples were taken in HDPE bottles and treated with barium chloride to precipitate sulfate as BaSO4. Samples were preserved in the field with

25 hydrochloric acid to lower the pH to < 4 to inhibit precipitation of BaCO3. The 34 32 18 16 S/ S and O/ O ratios of BaSO4 were determined by continuous flow isotope ratio mass spectrometry (CF-IRMS) with an elemental analyser for S and a pyrolysis reactor for O using He as a carrier gas. 34 32 For S/ S analysis, BaSO4 was converted to SO2 by combustion at 1020 °C following the procedures outlined by Giesemann et al. (1994). Measurements were made with a Carlo Erba NA 1500 elemental analyzer interfaced to a VG PRISM II mass spectrometer. Values are reported relative to Vienna Canyon Diablo Troilite (V-CDT) with a measurement uncertainty of ±0.3‰. 18 16 For O/ O analysis, BaSO4 was converted to CO by pyrolysis at temperatures between 1350 and 1500 °C using a high temperature reactor coupled to a continuous flow isotope ratio mass spectrometer. Procedures followed those described by Kornexl et al. (1999). Measurements were made with a Heka HT Oxygen analyzer interfaced to a Thermo DeltaV-Plus mass spectrometer via a Thermo Conflo-IV open split/interface. Results are expressed with respect to V-SMOW with a measurement uncertainty of ±0.5‰.

2.4.3 δ13C of dissolved inorganic carbon (DIC)

Filtered samples were taken in glass bottles for analysis of 13C in DIC. In the laboratory, anhydrous phosphoric acid was used to convert DIC to CO2, which was cryogenically purified and distilled on a glass vacuum extraction line before being analysed for 13C/12C on a VG 903 dual-inlet IRMS instrument. Results are reported relative to the Vienna Pee Dee Belemnite (V-PDB) standard with a measurement uncertainty of ±0.2‰.

2.4.4 δ 13C and δ2H of dissolved methane

The same samples used for dissolved gas composition were used for isotopic analysis of dissolved methane at Isotech Laboratories in Champaign, Illinois. Gases were extracted from water by headspace equilibration. Methane was isolated in a gas chromatography column then analysed using CF-IRMS 13 with combustion to produce CO2 for the analysis of C, and with pyrolysis to

26 2 produce H2 for the analysis of H (Isotech, unpublished). The isotopic composition of carbon is reported relative to V-PDB, with a measurement uncertainty of 0.3‰. The isotopic composition of hydrogen is reported relative to V-SMOW with a measurement uncertainty ±5‰.

2.4.5 δ37Cl

Filtered samples for chloride isotopic analysis were collected in HDPE bottles. Silver chloride was precipitated from the waters at the University of Calgary. This precipitate was converted to methyl chloride, from which 37Cl/35Cl was determined at the National Water Research Institute (NWRI) in Saskatoon, Saskatchewan, using CF-IRMS as described by Wassenaar and Koehler (2004). An area-peak linear correction was applied to correct for preferential ionization of 35Cl. Results are reported relative to standard mean ocean chloride (SMOC). Measurement uncertainty was ±0.1‰.

2.4.6 87Sr/86Sr

Filtered samples were collected in HDPE bottles for strontium isotopic analysis, which was conducted at the Department of Physics and Astronomy at the University of Calgary. Strontium was extracted from the samples using ion exchange resin columns, eluted with deionized water, evaporated, and then analysed using positive ion thermal ionization mass spectrometry (PTIMS) with a Thermo Electron Triton instrument. The methods followed those described by Burton et al. (2002). The reference material used in the laboratory was SRM987.

Measurement uncertainty in the 87Sr/86Sr ratio ranged from 2x10-6 to 5x10-6.

2.5 Radioisotope analyses

The radioactive isotopes 3H in water, and 14C in DIC were analyzed at GNS Science laboratories in Lower Hutt, New Zealand.

27 2.5.1 Tritium (3H)

Samples for tritium were unfiltered and collected in 1 L HDPE bottles with no head space. Tritium was measured following procedures described by Morgenstern and Taylor (2009) for electrolytic enrichment and liquid scintillation counting, using Quantulus low-level counters. Tritium is reported in Tritium Units (TU); one TU represents a 3H/1H ratio of 1x10-18. The detection limit was 0.03 TU and measurement error ranged from 0.017 to 0.067 TU.

2.5.2 Radiocarbon (14C)

Samples for radiocarbon analysis were unfiltered and collected in 100 mL amber glass bottles with no headspace. Mercuric chloride solution was added in the field to suppress biological activity. In the laboratory, DIC was converted to

CO2 through the addition of phosphoric acid and cryogenically purified. CO2 was then converted into elemental carbon (graphite) by reaction with hydrogen gas at 700 °C, using iron as a catalyst. Measurement of radiocarbon was done using accelerator mass spectrometry (AMS). Following Stuiver and Polach (1977), radiocarbon results are expressed in percent modern carbon (pmc), meaning the absolute percent of modern carbon in the sample relative to the standard NBS oxalic acid corrected for decay since 1950. Measurement uncertainty ranged from 0.06 to 0.18 pmc . Uncorrected radiocarbon ages are reported as conventional ages before present, as defined by Stuiver and Polach (1977).

2.6 QA/QC

The quality control program followed in October 2010 included field duplicates, field blanks, and lab split samples. Duplicate samples for all parameters were taken at one out of the nine springs sampled to assess consistency in sampling, storage, and analyses methods. Field blanks of deionized water were collected for all parameters at one site, following the same procedures of filtering and preservation to assess any effects on sample chemistry caused by sample handling, transport, or processing. Lab split

28 samples, consisting of two analyses of sample water from the same sample bottle, were completed for most parameters to detect any variations in laboratory analysis. In addition to sampling and lab QA/QC samples, the electrical charge balance was calculated for each sample in order to estimate the accuracy of major ion analyses. Generally a charge balance of ≤5% is considered acceptable (Appelo and Postma, 2005). The charge balance of all springs samples was ≤3%, and that of river samples was ≤5%.

29 Chapter Three: Results

The results of all analyses are presented in this chapter. Measurements made in the field in October 2010 are reported, followed by laboratory analyses for chemical and isotopic compositions of the waters and dissolved constituents. Temporal differences in chemistry and isotopic compositions between October 2010 and May 2011 at these springs are compared with historical data for the springs from the literature. Tritium and 14C data for spring waters sampled in May 2011 are also presented.

3.1 Field measurements

Parameters measured in the field during sampling in October 2010 included temperature, pH, electrical conductivity, dissolved oxygen, and estimated discharge of springs (Table 3-1).

3.1.1 Spring waters

The temperature of spring waters ranged from 1.0 to 4.8 °C, with the exception of spring AR01 which had a temperature of 10.5 °C. Daily mean air temperature in Fort McMurray on the four sampling days ranged from 8.2 to 13.6 °C (Environment Canada, 2011b). The spring with the highest temperature, AR01 (La Saline), had very low discharge, and flowed for several meters on the surface before the measuring point. Therefore, the relatively high temperature may be partially due to surface warming. The pH of the spring waters was slightly acidic to neutral, ranging from 6.4 to 7.1. Both Athabasca springs had a pH below 7, with values of 6.9 at AR01 and 6.7 at AR03. Most Clearwater springs had near-neutral pH, with the exception of spring CW09, which was a saline pool in a meadow rather than a flowing spring and had a pH of 6.4. Electrical conductivity of spring waters ranged from 11,280 to 46,810 S/cm, with the exception of spring AR01 (La Saline), which had a much higher conductivity of 70,340 S/cm.

30 The concentration of dissolved oxygen in the spring water at the surface ranged from 0.1 mg/L to 3.0 mg/L. Dissolved oxygen was not correlated with spring water temperature. Approximate discharge of the springs, where flow measurement was possible, ranged from 0.02 to 15 L/s. Spring AR03, on the Athabasca River, had the highest discharge. The discharge of all other springs was below 7 L/s. Spring CW09 was a pool with no obvious inflow or outflow so discharge was not measured.

3.1.2 River waters

River water temperatures were higher than spring water temperatures, ranging from 5.2 to 7.3 °C. The temperatures of both rivers increased downstream: the Clearwater increased from 5.2 to 7.3 °C and the Athabasca River increased from 6.3 to 7.2 °C. Upstream and downstream temperatures were measured at different times of day; therefore different upstream and downstream temperatures may reflect ambient air temperature differences at the time of sampling. The pH of the river waters was slightly higher than that of spring waters, ranging from 7.7 to 8.1. The pH of the Clearwater increased downstream from 7.7 to 8.1. The pH of the Athabasca River was constant at 8.1. The rivers ranged in electrical conductivity from 60 to 280 S/cm. The Clearwater increased in conductivity downstream from 60 to 200 S/cm. The Athabasca decreased in conductivity downstream from 280 to 210 S/cm.

Dissolved oxygen concentration in the rivers ranged from 11.5 to 13.3 mg/L. The site with the lowest temperature, the upstream Clearwater site, had the highest dissolved oxygen content and higher temperatures in the Athabasca River corresponded to the lower dissolved oxygen content. Discharge for the rivers was obtained from historical average daily and monthly flow values available online from Environment Canada (2010b). Flow varies widely throughout the year in both rivers. Monthly mean discharge of the Clearwater varies from 29 to 488 m3/s throughout the year, while that of the Athabasca varies from 99 to 2740 m3/s. In the sampling month of October, the

31 historical monthly mean discharge of the Clearwater River near its mouth at Draper is 125 m3/s; on the days the upstream and downstream river samples were taken, flow was estimated to be 134 and 130 m3/s, respectively (Environment Canada, 2010b). For the Athabasca River near Fort McMurray, the historical monthly mean flow in October is 540 m3/s; on the days the upstream and downstream river samples were taken, flow was recorded as 681 and 931 m3/s, respectively.

3.2 Chemical analyses

Water samples taken in October 2010 were analysed for the concentrations of major ions, trace elements, and polycyclic aromatic hydrocarbons. Some springs were re-sampled in May 2011; these were sampled for concentrations of select major ions in addition to radioisotopes. The major ion chemistry of these springs was compared between October 2010 and May 2011, and was also compared with historical data for these springs.

3.2.1 Major ion chemistry

Major ion chemistry of spring and river waters collected in October 2010 is summarized in Table 3-2. The total dissolved solids (TDS) of the samples was calculated from the sum of the ions listed in Table 3-2 with the exception of SiO2 and DOC.

3.2.1.1 Spring waters

The main dissolved ions in spring waters were sodium and chloride, found at concentrations ranging from 2,320 to 17,900 mg/L, and 3,690 to 27,400 mg/L, respectively. Other major ions present at appreciable concentrations were sulfate (520 to 4,280 mg/L), calcium (174 to 1,200 mg/L), and magnesium (79 to 374 mg/L). Major ions present in the spring waters at low concentrations included potassium (13 to 52 mg/L), sulfide (0 to 60 mg/L), bromide (2 to 14 mg/L), dissolved organic carbon (DOC) (2.4 to 31.4 mg/L), strontium (4.35 to 23.4 mg/L), and dissolved silica (3 to 10 mg/L). Barium, lithium, manganese,

32 and iron were present at concentrations below 1 mg/L. Alkalinity in the springs ranged from 206 to 752 mg/L. The TDS of the spring waters ranged from 7,210 to 51,800 mg/L. The charge balance of major ion analyses in the springs was better than 3%.

3.2.1.2 River waters

The main dissolved ions in both rivers were calcium and bicarbonate. Both calcium and bicarbonate increased downstream in the Clearwater, from 7.1 to 18.8 mg/L and from 34 to 78 mg/L, respectively. In contrast, calcium and bicarbonate decreased in the Athabasca from 38 to 32 mg/L and from 146 to 126 mg/L, respectively. Other major ions were present in low concentrations. Chloride increased downstream from 2.3 to 23.1 mg/L in the Clearwater, and from 2.8 to 11.0 mg/L in the Athabasca. Sodium also increased downstream in both rivers, from 2.5 to 18.0 mg/L in the Clearwater, and from 10.6 to 14.3 mg/L in the Athabasca. Magnesium increased in the Clearwater from 2.8 to 5.8 mg/L, but decreased slightly downstream in the Athabasca from 10.6 to 9.2 mg/L. Sulfate increased in the Clearwater from 1.6 to 4.7 mg/L, but decreased in the Athabasca from 30.0 to 23.6 mg/L. Silica decreased in the Clearwater from 5.9 to

4.6 mg/L, but increased in the Athabasca from 2.2 to 3.0 mg/L. All other major ions (K, Ba, Sr, Li, Mn, Fe, S) were present at concentrations ≤ 1 mg/L or below detection limits in both rivers (Table 3-2). Overall, TDS increased downstream in the Clearwater, from 67 to 175 mg/L and decreased slightly downstream in the Athabasca, from 262 to 242 mg/L. The charge balance of all river samples was better than 5%.

Table 3-1: Field measurements at springs and rivers sites. (-) denotes that the measurement was not possible.

Field Measurement AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 CW09 RAR01 RAR02 RCW01 RCW02 Site type spring spring spring spring spring spring spring spring spring river river river river

Temperature (°C) 10.5 1.7 1.5 2.0 2.8 1.0 1.5 4.8 4.6 6.3 7.2 5.2 7.3 pH 6.9 6.7 7.0 6.8 6.8 7.1 7.1 6.9 6.4 8.1 8.1 7.7 8.1 Conductivity (μS/cm) 70,340 20,820 11,280 22,050 29,730 24,000 28,670 35,610 46,810 280 210 60 200

Dissolved O2 (mg/L) - 1.5 1.6 3.0 0.4 0.9 0.9 0.1 0.9 11.8 11.5 13.3 - Discharge estimate (L/s) 0.02 15 7 3 0.2 0.04 0.04 0.04 - - - - -

Table 3-2: Major ion concentrations in spring and river waters sampled in October 2010. LTD denotes a value less than the detection limit. TDS and charge balance were calculated from all major ions except for SiO2 and DOC.

Parameter (mg/L) AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 RAR01 RAR02 RCW01 RCW02 Na 17,900 3,990 2,320 4,800 6,720 5,390 6,310 8,340 10.6 14.3 2.5 18.0 Ca 1,200 867 174 375 577 396 408 555 38.6 32.9 7.1 18.8 Mg 374 130 79 147 207 204 177 233 10.6 9.2 2.8 5.8 K 52 13 13 17 23 32 26 29 1.1 1.0 0.7 1.3 Ba 0.02 0.01 0.04 0.05 0.01 0.02 0.04 0.02 0.06 0.04 0.01 0.02 Sr 23.4 13.2 4.4 8.2 12.8 11.6 12.1 15.7 0.28 0.22 0.03 0.09 Li 0.83 0.14 0.17 0.23 0.33 0.54 0.59 0.62 0.006 0.007 0.002 0.006 Mn 0.03 0.03 0.02 0.04 0.04 0.71 0.4 0.22 0.02 0.01 0.02 0.02 Fe LTD 0.05 LTD LTD LTD 1.71 LTD LTD 0.11 0.24 0.28 0.39 Cl 27,400 6,170 3,690 7,500 10,400 8,100 9,800 12,600 2.8 11.0 2.3 23.1

Alkalinity as HCO3 526 206 389 332 505 486 752 565 146 126 34 78

SO4 4,280 2,500 520 1,080 1,760 1,130 1,290 1,760 30.0 23.6 1.6 4.7 S2- LTD 59.7 16.2 16.5 22.6 0.2 13.5 8.2 LTD LTD LTD LTD Br 13.7 1.5 3.7 3.6 5.5 4.7 5.3 6.3 0.007 0.011 0.011 0.026

SiO2 7.5 9.6 3.4 5.0 5.1 3.8 3.3 5.2 2.2 3.0 5.9 4.6 DOC 5.3 5.8 4.1 3.5 4.4 2.4 7.1 8.2 8.5 11.1 7.0 14.4

TDS (calc.) 51,800 14,000 7,210 14,300 20,200 15,800 18,800 24,100 240 219 51 150 33

charge balance (%) 0.1 -1.1 -2.5 0.0 0.0 2.3 -1.0 0.9 3.2 3.3 5.3 5.1 34 3.2.1.3 Temporal changes in TDS in select springs

Sampling of spring waters was repeated in May 2011 at four sites: CW03, CW05, CW08, and AR01. Another spring, AR02 on the Athabasca River near Fort McKay, not visited in 2010, was also sampled in May 2011. The purpose of repeating the analysis of major ions was to assess potential temporal changes in spring water chemistry, and to obtain concurrent analyses of major ions and the age-dating radioisotopes 14C and 3H. Data from 2010 and 2011 is compiled in Table 3-3 along with literature values for samples collected from the same springs in 2001 (Grasby, 2006), the 1990's by R. Stern of the Alberta Geological Society (Grasby, pers. com.), and 1965 (Hitchon et al., 1999). The TDS values calculated from this simplified list of major ions through time is represented graphically in Figure 3-1. The spring with the greatest variability in TDS over time was spring AR02 at Fort McKay, decreasing from 214,000 mg/L in 2001 to 5320 mg/L in 2011. This site was a flowing well in 2001 but in 2011 was a small trickle. Located near intense oil sands development, this may suggest a change in groundwater flow patterns at this location. The change in TDS may indicate a different source or mixture of water sources. The TDS of spring AR01 (La Saline) also decreased from 73,200 to 44,700 mg/L in four samples taken between 1965 and 2011. The changes in TDS may reflect different contributions of dilute shallow groundwater due to the different times of year that samples were taken. The rest of the springs had similar TDS concentrations throughout the years (Figure 3-1). In general, the chemistry of these springs seems to be relatively consistent through time, although further sampling at different times of the year and over consecutive years would be necessary to confirm this.

Table 3-3: Concentrations of select major ions through time, with TDS calculated as the sum of these ions. (-) indicates no measurement was made. Reference column refers to the data sources: (1) this study (2) Grasby (2006), (3) Hitchon et al. (1999), (4) Stern, R. obtained from Grasby (pers. com. 2010).

Sample date Ref. Temp pH Ca Mg Na K SO4 HCO3 Cl Br TDS (this study id) ID sampled °C mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/L La Saline Sep-1965 3 8.0 7.8 1,830 456 25,600 64 4,780 227 40,200 14.0 73,200 AR01 RS96-19 1996 4 - 5.8 1,820 491 26,000 82 4,860 625 32,900 109.0 66,800 AR01-2010 Oct-2010 1 10.5 6.9 1,200 374 17,900 52 4,280 526 27,400 13.7 51,700 AR01-2011 May-2011 1 - 7.9 1,330 305 15,400 50 4,500 253 22,900 - 44,700 AR02 A01-05 Oct-2001 2 7.2 5.9 1,730 447 79,200 57 5,730 155 126,300 30.0 214,000 AR02-2011 May-2011 1 - 8.2 59 17 1,870 4 396 336 2,640 - 5,320 RS97-35 1997 4 6.7 7.0 39 123 4,510 9 2,610 448 5,530 - 13,300 AR03 A01-06 Oct-2001 2 5.1 6.8 858 111 4,030 10 2,500 243 6,420 <0.5 14,200 AR03 Oct-2010 1 1.7 6.7 867 130 3,990 13 2,500 206 6,170 1.5 13,900 CW01 RS94-01 1994 4 5.0 7.3 190 86 2,460 12 378 388 3,560 4.8 7,070 CW01 Oct-2010 1 1.5 7.0 174 79 2,320 13 522 389 3,690 3.7 7,290 CW02 RS94-02 1994 4 5.1 7.0 427 162 5,570 16 1,080 332 9,160 3.4 16,700 CW02 Oct-2010 1 2.0 6.8 375 147 4,800 17 1,080 332 7,500 3.6 14,300 RS94-03A 1994 4 6.3 6.8 730 263 8,190 23 2,170 439 11,300 5.0 23,100 CW03 A01-01 Oct-2001 2 6.1 6.7 537 182 6,200 15 1,770 358 9,850 4.9 18,900 CWO3-2010 Oct-2010 1 2.8 6.8 577 207 6,720 23 1,760 505 10,400 5.5 20,200 CWO3-2011 May-2011 1 7.8 554 217 6,630 26 1,680 498 10,400 - 20,000 RS94-05A 1994 4 4.0 7.1 400 206 5,060 31 958 525 7,750 4.9 14,900 CW05 A01-03 Oct-2001 2 2.3 7.1 333 171 4,130 22 928 393 7,220 4.4 13,200 CW05A-2010 Oct-2010 1 1.0 7.1 396 204 5,390 32 1,130 486 8,090 4.7 15,700 CW05-2011 May-2011 1 - 7.8 376 219 5,140 36 1,070 482 8,370 - 15,700 CW07 RS94-07A 1994 4 4.0 7.0 443 185 6,620 24 1,180 739 7,930 4.0 17,100 CW07A Oct-2010 1 1.5 7.1 408 177 6,310 26 1,290 752 9,830 5.3 18,800 CW08 CW08-2010 Oct-2010 1 4.8 6.9 555 233 8,340 29 1,760 565 12,600 6.3 24,100 CW08-2011 May-2011 1 - 7.4 538 245 8,230 27 1,700 596 13,100 - 24,400 CW09 RS96-20B 1996 4 30.4 7.5 233 155 6,410 10 1,320 819 9,070 <0.02 18,000 CW09 Oct-2010 1 4.6 6.4 607 245 7,280 22 1,680 538 10,700 5.3 21,100 35

Figure 3-1: Calculated TDS from values reported in the literature in various years compared with values from this study. References are the same as for Table 3-3.

3.2.2 Trace elements

Water samples from October 2010 were analyzed for concentrations of 29 trace elements, mostly metals, as listed in Table 3-4.

3.2.2.1 Spring waters

In the spring waters, only boron was present at concentrations above 1 mg/L, with concentrations of 989 and 5210 !g/L in the Athabasca springs, and between 1040 and 2570 !g/L in the Clearwater springs. The following nine elements were present at concentrations above 1 !g/L in one or more springs, with the highest concentrations in !g/L in brackets: Al (411), As (9.63), Cr (1.83), Cu (8.96), Ni (2.39), Rb (58.7), Se (2.98), and Zn (22.8). Two metals, Nb and V, were not detected in any of the spring waters. Of the elements detected in the springs, the following twelve are on the EPA list of priority pollutants (EPA,

37 2012), a compilation of regulated toxic compounds in US: Ag, As, Be, Cd, Cr, Cu, Ni, Pb, Sb, Se, Tl, Zn.

3.2.2.2 River waters

In most cases trace element concentrations were lower in river samples than in spring water samples. Eleven metals listed by the EPA as priority pollutants were detected in at least one sample from each river (Ag, As, Be, Cd, Cr, Cu, Ni, Pb, Sb, Tl, Zn). These are the same priority pollutants found in the spring waters, with the exception of Se, which was undetected in the river waters. In the Clearwater River most trace elements increased in concentration downstream. No trace element was present in concentrations above 1 mg/L. The following seven elements were present in concentrations above 1 ! g/L at the downstream site (concentrations in !g/L given in brackets): Al (151), B (28.1), Cu (1.30), Ni (1.31), Rb (1.05), V (1.06), Zn (2.5). Two elements, Pt and Se, were undetected in the Clearwater River. In the Athabasca River trace element concentrations were generally higher than in the Clearwater River. All elements that were detected decreased in concentration downstream. Aluminum was present both upstream (1050 !g/L) and downstream (174 !g/L) at concentrations two orders of magnitude higher than other metals. The following elements were present at concentrations higher than 1 !g/L at the upstream site (concentrations in !g/L given in brackets): As (1.22), B (8.8), Co (1.30), Cr (2.17), Cu (3.57), La (1.73), Ni (4.16), Pb (1.62), Rb (3.04), V (3.38), Zn (11.1). Three metals, Se, Sn, and W, were not detected at either Athabasca River site.

Table 3-4: Total metal concentrations in springs and rivers (!g/L). 'LTD' denotes less than detection limit (DL), which is listed in the second column. Metals that are shaded are listed by the EPA (2012) as priority pollutants.

μg/L DL AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 CW09 RAR01 RAR02 RCW01 RCW02 Ag 0.001 0.033 LTD LTD 0.031 LTD 0.011 0.009 0.006 0.004 0.009 LTD 0.004 LTD Al 0.5 79.9 LTD LTD 11.4 LTD 13.7 LTD 411.0 7.4 1,050 174 15 151 As 0.01 0.09 LTD LTD 0.14 LTD 9.63 0.04 0.16 0.31 1.22 0.49 0.23 0.56 B 0.5 5,210 989 1,080 1,040 1,720 1,400 2,570 2,470 2,000 8.8 16.6 7.7 28.1 Be 0.001 0.204 0.047 0.032 0.045 0.092 0.064 0.118 0.110 0.066 0.081 0.005 0.004 0.005 Bi 0.001 LTD LTD LTD 0.022 LTD LTD LTD LTD LTD 0.012 LTD 0.008 LTD Cd 0.001 0.168 0.015 0.029 0.041 0.099 0.047 0.017 0.180 0.081 0.075 0.017 0.111 LTD Ce 0.001 0.006 0.001 LTD 0.002 LTD 0.023 0.001 0.061 0.001 0.191 0.029 0.109 0.035 Co 0.002 0.886 0.080 0.047 0.044 0.054 0.944 0.058 0.212 0.062 1.300 0.280 0.042 0.218 Cr 0.01 1.53 1.15 0.59 1.72 1.13 0.86 0.18 1.83 1.27 2.17 0.58 0.35 0.86 Cs 0.001 0.016 0.004 0.004 0.005 0.007 0.006 0.010 0.015 0.007 0.013 0.002 0.002 0.002 Cu 0.02 1.17 0.92 0.68 8.96 0.83 1.25 1.0 1.38 1.02 3.57 1.67 0.87 1.3 Ga 0.001 0.048 LTD LTD LTD LTD LTD LTD 0.085 LTD 0.318 LTD 0.002 LTD La 0.001 0.043 0.008 0.001 0.018 0.004 0.298 0.013 0.628 0.009 1.730 0.281 0.056 0.327 Mo 0.005 0.033 LTD LTD 0.109 LTD 0.106 LTD LTD LTD 0.567 0.817 0.089 0.178 Nb 0.001 LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD 0.001 LTD Ni 0.02 2.16 0.75 0.43 2.39 0.68 2.02 0.54 1.43 0.83 4.16 1.8 0.24 1.31 Pb 0.005 0.141 0.132 0.209 0.920 0.159 0.182 0.142 0.604 0.173 1.620 0.276 0.037 0.220 Pt 0.001 LTD LTD 0.002 0.028 0.001 0.007 0.007 0.002 LTD LTD LTD LTD LTD Rb 0.001 58.7 10.9 10.1 12.4 17.7 15.6 19.3 23.8 20.2 3.04 1.04 0.68 1.05 Sb 0.001 0.158 0.076 0.028 0.203 0.066 0.058 0.068 0.068 0.084 0.102 0.068 0.013 0.050 Se 0.01 2.98 LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD Sn 0.005 0.002 LTD LTD 0.012 LTD LTD LTD LTD LTD LTD LTD 0.027 LTD Tl 0.001 LTD LTD 0.016 0.012 0.001 LTD 0.009 LTD LTD 0.020 LTD 0.002 0.013 U 0.0005 0.0718 0.0242 0.0454 0.0428 0.0500 0.0599 0.0668 0.0914 0.0172 0.5200 0.3040 0.0101 0.0615 V 0.005 LTD LTD LTD LTD LTD LTD LTD LTD LTD 3.380 1.530 0.273 1.060 W 0.001 0.001 0.002 LTD LTD LTD LTD 0.001 LTD LTD LTD LTD 0.006 LTD Y 0.001 0.010 0.004 LTD 0.002 0.004 0.028 0.005 0.032 0.004 0.080 0.015 0.043 0.014 Zn 0.2 2.5 1.3 1.2 22.8 1.4 4.0 1.3 5.7 1.7 11.1 2.9 1.9 2.5 38

39 3.2.3 PAHs

Water samples were analyzed for 25 polycyclic aromatic hydrocarbons (PAHs) and the results are summarized in Table 3-5. The majority of surrogate recovery in the analyses was within acceptable range of 60 to 120% (EPA, 1999). Results were not corrected for percent recovery of surrogates.

3.2.3.1 Spring waters

Seven PAHs were detected at low concentrations in the spring waters. Total PAH concentration in the Athabasca springs ranged from 106 to 274 ng/L, and from 7.3 to 35.2 ng/L in the Clearwater springs. The suite of PAHs present in Athabasca springs was more diverse, with up to 7 detected, than the suite of PAHs present in Clearwater springs, with a maximum of 3 detected. Phenanthrene was the only PAH present in all spring waters and ranged in concentration from 7.3 to 32.9 ng/L. Naphthalene was also present in all but two spring waters at concentrations from 6 to 170 ng/L in spring AR01. Fluoranthene, fluorene, and 2-methylnapthalene were also present in Athabasca springs at concentrations up to 32.8 ng/L.

3.2.3.2 River waters

More PAHs were detected in the river samples than in the spring samples. In the Clearwater River, the number of PAHs detected increased downstream from 2 to 8, and the concentration of total PAHs increased from 18 to 363 ng/L. In the Athabasca River, the number of detected PAHs decreased downstream from 11 to 8, and the concentration of total PAHs decreased from 338 to 230 ng/L. The two most common PAHs in the springs were also present in all river samples: naphthalene (9 to 227 ng/L) and phenanthrene (9.0 to 38.6 ng/L). Chrysene (3.86 to 8.28 ng/L), fluoranthene (12.10 to 17.80 ng/L), fluorene (23.50 to 22.10 ng/L), 1- and 2-methylnapthalene (9.55 to 29.90 ng/L) were present in both Athabasca samples and the downstream Clearwater sample.

Table 3-5: Results of PAH analyses in spring and river waters. 'LTD' denotes a value less than the detection limit (DL) listed in the second column. PAH listed in % recovery are surrogates added to samples. PAHs that were not detected in any samples are listed at bottom of the table.

PAH DL (ng/L) AR01 AR03 CW01 CW02 CW03 CW05 CW08 CW09 RAR01 RAR02 RCW01 RCW02 TOTAL PAH 274 106 19 7 16 19 35 10 338 230 18 363 chrysene 2.95 5.81 LTD LTD LTD LTD LTD LTD LTD 8.28 3.86 LTD 4.27 fluoranthene 4.08 13.40 9.73 LTD LTD LTD LTD LTD LTD 17.80 12.10 LTD 17.70 fluorene 6.38 17.90 10.10 LTD LTD LTD LTD LTD LTD 18.30 12.50 LTD 22.10 indene 5.05 LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD 5.22 naphthalene 5.8 170 57 10 LTD 6 10 18 LTD 168 145 9 227 1-methylnaphthalene 6.73 12.70 LTD LTD LTD LTD LTD LTD LTD 16.70 9.55 LTD 18.70 2-methylnaphthalene 7.59 21.00 8.41 LTD LTD LTD LTD 7.62 LTD 27.30 15.20 LTD 29.90 1,2,3,4-tetrahydronaphthalene 5.71 LTD LTD LTD LTD LTD LTD LTD LTD 8.53 6.34 LTD LTD perylene 13.40 LTD LTD LTD LTD LTD LTD LTD LTD 15.20 LTD LTD LTD phenanthrene 6.2 32.8 21.0 9.3 7.3 9.3 8.9 9.4 10.0 38.5 25.5 9.0 38.6 pyrene 3.93 LTD LTD LTD LTD LTD LTD LTD LTD 4.55 LTD LTD LTD retene 13.6 LTD LTD LTD LTD LTD LTD LTD LTD 14.4 LTD LTD LTD surrogates recovery: pyrene-d10 1% 94 76 109 103 102 113 97 89 110 86 93 117 fluorene-d10 1% 84 48 85 68 94 104 68 52 87 65 93 104 naphthalene-d8 1% 114 44 105 82 93 143 71 38 137 105 131 142 d-perylene 1% 65 50 85 73 65 90 73 12 89 67 12 97 PAHs below detection in all samples: 2LTDchloronaphthalene 6.65 acenaphthene 5.17 acenaphthylene 6.53 anthracene 6.12 benzo(a)anthracene 9.96 benzo(a)pyrene 9.42 benzo(b)fluoranthene 10 benzo(e)pyrene 8.7 benzo(g,h,i)perylene 17.1 benzo(k)fluoranthene 8.63 dibenz(a,h)anthracene 25.1 dibenzothiopene 8.16 indeno(1,2,3LTDcd)pyrene 18 40

41 3.3 Stable isotope ratios of water and dissolved constituents

The following stable isotope ratios were analyzed in spring and river waters: δ18O and δ2H of water, δ13C of dissolved inorganic carbon (DIC), δ34S and δ18O of sulfate, and δ 37Cl. The isotope ratio of dissolved strontium (87Sr/86Sr), which includes the radiogenic isotope 87Sr, was also determined. Results are tabulated in Table 3-6.

3.3.1 δ 18O and δ2H of water

The δ18O values of water ranged from -23.5 to -18.8‰ in the spring samples. The spring waters with the highest δ18O values were CW09 (-18.8‰) and AR03 (-19.2‰), while the lowest δ18O value was observed at CW05 (-23.5‰). The δ2H values of water ranged from -178 to -149‰ in the spring waters. Again, the highest δ2H values were found in springs CW09 (-149‰) and AR03 (-152‰), and the lowest δ2H value was found in spring CW05 (-178‰). The values of both δ18O and δ2H increased downstream in the Clearwater River, δ18O from -15.8 to -12.1‰, and δ2H from -129 to -114‰. The Athabasca River samples had constant δ18O and δ2H values of approximately -17.8‰ and -140‰ respectively.

3.3.2 δ 34S and δ 18O of sulfate

The δ34S values of dissolved sulfate in most spring waters ranged from 22.4 to 27.6‰ while δ18O values ranged from 6.7 to 13.7‰. Dissolved sulfate in one spring, AR01 (La Saline), had a lower δ34S value of 7.0‰ and a lower δ18O value of 2.3‰. The concentration of dissolved sulfate in river waters was low. In the Clearwater samples, there was insufficient sulfate to measure δ18O, and only enough sulfate to measure δ34S in the downstream sample (9.9‰). The δ34S of both Athabasca River samples was constant from upstream (6.6‰) to downstream (6.9‰) while the δ18O values decreased slightly (from 0.3‰ to -1.0‰).

42 3.3.3 δ13C of DIC

The δ13C values of DIC in most spring waters ranged from -14.5 to -1.1‰. 13 Two springs had positive δ CDIC values: CW03 (5.0‰) and AR01 (33.7‰). The δ13C of DIC in the river samples remained fairly constant from upstream to 13 downstream, with the Clearwater samples having slightly lower δ CDIC (~-8‰) than the Athabasca samples (~-7‰).

3.3.4 87Sr/86Sr

In spring waters, the 87Sr/86Sr ratio of dissolved strontium ranged from 0.708553 to 0.709044. In the Clearwater River samples, the 87Sr/86Sr ratio decreased downstream, from 0.715775 to 0.711151. In the Athabasca River waters, the 87Sr/86Sr ratio increased downstream, from 0.710296 to 0.710459.

3.3.5 δ37 Cl

The δ37Cl value of dissolved chloride was positive in all spring waters, ranging from 0.2 to 1.0‰. In the river waters, the δ37Cl value was negative, ranging from -2.3 to -1.4‰. In both rivers, the δ37Cl value increased downstream, by 0.8‰ in the Clearwater River (from -2.3 to -1.4‰) and by 0.3‰ in the Athabasca River (from -1.8 to -1.5‰).

Table 3-6: Stable isotopic composition of spring and river waters and dissolved constituents. (-) denotes insufficient quantity for analysis.

Isotope ratio AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 CW09 RAR01 RAR02 RCW01 RCW02 2 δ H (H2O) ‰ -169 -152 -168 -163 -170 -178 -171 -172 -149 -140 -139 -129 -114 18 δ O (H2O) ‰ -21.8 -19.2 -21.9 -21.3 -22.3 -23.5 -22.4 -22.7 -18.8 -17.8 -17.7 -15.8 -12.1 34 δ S (SO4) ‰ 7.0 24.1 27.6 22.4 24.1 25.4 26.3 24.7 23.8 6.6 6.9 - 9.9 18 δ O (SO4) ‰ 2.3 13.7 8.5 11.0 11.7 9.2 9.6 6.7 9.4 0.3 -1.0 - - δ13C (DIC) ‰ -1.1 33.7 -14.2 -10.3 5.0 -14.5 -13.5 -11.6 -4.9 -7.1 -7.3 -8.3 -8.2 δ37Cl ‰ 0.61 0.34 0.97 1.04 0.91 0.18 0.61 0.75 0.54 -1.79 -1.50 -2.25 -1.43 87Sr/86Sr 0.708742 0.708553 0.709044 0.708929 0.708812 0.708833 0.708701 0.708646 0.708773 0.710296 0.710459 0.715775 0.711151

Table 3-7: Chemical and isotopic composition of dissolved gases in spring waters. 'LTD' denotes a value less than detection limit.

Gas unit CW01 CW02 CW03 CW05 CW07 CW08 CW09 AR03

N2 % 96.15 95.58 94.52 92.31 89.57 94.90 70.24 80.48

CO2 % 2.02 2.39 3.69 5.54 8.87 3.44 26.81 13.96 Ar % 1.53 1.36 1.26 1.84 1.29 1.12 1.68 1.46

CH4 % 0.24 0.20 0.47 0.06 0.19 0.42 1.13 3.98

O2 % 0.07 0.47 0.04 0.22 0.04 0.02 0.09 0.07

C2H6 % 0.002 0.003 0.014 LTD 0.002 0.011 0.043 0.058 CO % LTD LTD LTD 0.029 LTD 0.011 LTD LTD He % LTD LTD LTD LTD LTD 0.081 LTD LTD

H2 % LTD LTD LTD LTD 0.044 LTD LTD LTD

Dissolved CH4 mg/L 0.063 0.063 0.160 0.015 0.067 0.530 0.210 1.030 13 δ CCH4 ‰ -44.4 -47.8 -44.7 LTD -48.0 -44.8 -62.6 -56.2 2 δ HCH4 ‰ -67 LTD -65 LTD LTD -65 -219 -160 43

44 3.4 Gas geochemistry in spring waters

The chemical composition of dissolved gases as well as the isotopic composition of dissolved methane was determined for most spring waters. Results are listed in Table 3-7.

3.4.1 Chemical composition of gases

The most dominant dissolved gas in all springs was nitrogen, which comprised 70.2 to 96.2% of the gas. The next most common gas was carbon dioxide, which comprised 2.0 to 26.8% of dissolved gases, with the highest CO2 fraction in AR03 and CW09. Argon made up 1.1 to 1.8% of the dissolved gas content in all springs. Only two hydrocarbon gases were dissolved in the spring waters in detectable quantities: methane and ethane. Methane comprised usually <1% of the dissolved gas, but in springs AR03 and CW09 comprised up to 4.0%. Ethane made up <0.06% of dissolved gas content, with the highest proportions found in AR03 and CW09. Oxygen was present in all springs as <0.5% of dissolved gas. Other gases - carbon monoxide, helium, and hydrogen - were present in only some springs at fractions of <0.1%. Although hydrogen sulfide gas was not detected by dissolved gas analysis, several springs had a distinct sulfur odour and dissolved sulfide concentrations ranged from 0 to 60 mg/L, with the highest values being found in springs CW09 and AR03 (Table 3-2).

3.4.2 Isotopic composition of methane

The 13C value of methane was determined for 7 spring waters and ranged from -62.6 to -43.7‰. The 2H value of methane was determined in 4 of these spring waters and ranged from -219 to -65‰. The lowest δ13C and 2H values were found in methane from springs AR03 and CW09, which also had the highest proportions of methane.

45 14 3 3.5 Radioisotopes CDIC and H in spring waters

18 The four springs with the lowest δ OH2O values in fall 2010 were 14 3 resampled in May 2011 for radiocarbon ( CDIC) and tritium ( HH2O) analyses for age-dating. One spring was sampled on the Athabasca (AR01 - La Saline), and three on the Clearwater River (CW03, CW05, CW08). In addition to 14C and tritium content, the concentration of DIC and its 13C value were determined, as well as δ18O and 2H values of water. All results are tabulated in Table 3-8. 13 The CDIC values obtained in May 2011 differed from those obtained in 13 October 2010: CDIC increased in AR01 by 6‰ (from -1.1 to 5.1‰) and in CW05 by 1.4‰ (from -14.5 to -13.1‰), but decreased in CW03 by 17.3‰ (from 5.0 to -12.3‰), and in CW08 by 5.4‰ (from -11.6 to -17.0‰). Alkalinity also varied in the spring waters between October 2010 and May 2011. Springs AR01, CW03, and CW05 decreased in alkalinity by 7 to 23 mg/L between the two sampling trips while spring CW08 increased in alkalinity by 30 mg/L. With the exception of spring CW03, decreases in alkalinity between the trips corresponded with 13 increases in δ CDIC values. The δ18O and 2H values of water were slightly higher in May 2011 than those measured in October 2010 in springs AR01 and CW05 (by ≤1.1‰ for δ18O and ≤5‰ for 2H), but remained constant in springs CW03 and CW08. All values 18 2 for the four re-sampled springs were ≤-20.7‰ for δ OH2O ≤-164‰ for HH2O in May 2011. The 14C content of these four spring waters ranged from 1.6 to 28.9 pmc (Table 3-8). Raw radiocarbon ages before present ranged from 9902 ± 50 to 33,130 ± 310, though to be meaningful these must be corrected for dilution by "dead" carbon, and for varying levels of radiocarbon in the atmosphere throughout time (see Chapter 4). The tritium concentration in spring waters ranged from 0.11 ± 0.02 to 4.52 ± 0.07 TU, with the highest concentration found in spring AR01 and the lowest in CW05. By comparison, current modern precipitation containing tritium from nuclear bomb testing contains approximately 10 TU of tritium (Froelich, 2009). Waters with appreciable 3H concentrations are considered to be ≤60 years old (Clark and Fritz, 1997). No relationship between tritium concentration and raw

46 radiocarbon age was immediately apparent, but after corrections and calibration, radiocarbon age and groundwater ages inferred from 3H concentrations were consistent (Chapter 4).

Table 3-8: Results for samples taken in May 2011: radiocarbon age (uncorrected), 14 13 18 2 C activity as percent modern carbon (pmc), alkalinity, CDIC, δ O and H of water, and tritium content.

Raw % 14 13 18 2 radiocarbon modern δ C δ C Alk as HCO3 δ O δ H Tritium Spring age (ybp) carbon (‰) (‰) (mg/L) (‰) (‰) (TU) AR01 13,885 ± 45 17.6 -812.7 5.1 253 -20.7 -164 4.52 ± 0.07 CW03 27,920 ± 170 3.1 -968.5 -12.3 498 -22.4 -171 0.29 ± 0.02 CW05 33,130 ± 310 1.6 -983.5 -13.1 482 -23.6 -180 0.11 ± 0.02 CW08 9902 ± 50 28.9 -705.9 -17.0 596 -22.1 -171 1.66 ± 0.04

47 Chapter Four: Sources of spring waters

In this chapter, the temperature of the spring waters is used to interpret the scale of the groundwater flow system discharging at the springs. The origins of the spring waters are investigated using the stable isotope ratios of water, 18O/16O and 2H/1H, as well as the radioisotopes 14C and 3H.

4.1 Temperature

The temperature of all spring waters was below 4.8 °C, with the exception of spring AR01 at 10.5 °C. The mean surface temperature of all springs, excluding AR01, was 2.5 °C. Spring AR01 (La Saline) had very low flow that increased within a few metres from the outlet to a channel depth appropriate for sampling. Its high temperature and high TDS may be due to surface warming and evaporative effects along the flow path before the sampling point. There is a general positive correlation between TDS and temperature of all the springs (Figure 4-1). However, if surface warming and evaporative effects were the cause of higher TDS, a positive correlation between δ18O values and spring water temperature would be expected, similar to surface-warmed springs described by Grasby and Londry (2007). But no trend between δ18O and TDS is evident (Figure 4-2). Thus, the high temperature and TDS of spring AR01 is likely not due to surface warming and may be representative of subsurface temperatures that increase with increasing depth. The temperature of all springs was above 0.7 °C, the mean annual surface air temperature at Fort McMurray (Environment Canada, 2010a). The relationship between spring temperature and the scale of groundwater flow is complex. The temperature of springs discharging from a shallow flow system will be near the mean annual air temperature, or the temperature of the main recharge events (Hackbarth, 1978). Springs discharging from deeper flow systems may be expected to reflect the geothermal thermal gradient of the area, assuming low volumes of water discharging rapidly enough that heat is not lost (Manga, 2001). In the WCSB, the flow of groundwater has been found to be too low to transmit heat advectively on a regional scale (Bachu and Burwash, 1991;

48 Corbet and Bethke, 1992); therefore, the local geothermal gradient of 40 to 50 °C/km (Hitchon, 1984) cannot be simply used to relate the temperatures of the springs to the depth of flow. However, the Devonian carbonate unit from which these springs emerge is a karst system and preferential flow in fractures may occur at a higher rate than general groundwater flow in the WCSB, which could allow the transport of some heat advectively. If the springs discharge from such preferential flowpaths, the springs with higher temperatures (CW03, CW08, CW09) would be discharging waters that were warmed at greater depths. Springs with temperatures nearer the mean annual air temperature (AR03, CW01, CW02, CW05, CW07) may be part of more shallow local flow regimes, or may have lost any heat acquired from depths by dissipation in the subsurface. Consideration of other parameters is necessary for further interpretation of the scale of the groundwater flow system that is discharging at the springs.

Figure 4-1: Relationship between temperature of spring waters and total dissolved solids. Mean annual air temperature of 0.7 °C (Environment Canada, 2010a) is represented by the solid line.

Figure 4-2: Temperature versus δ18O of spring waters.

4.2 Isotopic evidence of glacial meltwater

A few lines of evidence suggest that these spring waters are sourced at least partially from glacial meltwater. The stable isotope ratios of water, 18O/16O and 2H/1H, indicate precipitation as a source of water, as opposed to formation waters from deeper in the basin. In addition, radioactive isotopes 3H and 14C indicate ages of the spring waters that are compatible with being sourced at least partially from meltwater from the last glacial maximum.

4.2.1 δ 18O and δ2H of water

The stable isotope ratios of oxygen and hydrogen in water vary according to the water source and any isotope fractionation processes that have occurred in the water cycle. Local precipitation displays a linear relationship between the δ2H and δ18O of water, which can be plotted to form a local meteoric water line (LMWL) (Clark and Fritz, 1997). A LMWL (Figure 4-3) was constructed for Fort Smith, NT, located 365 km north of Fort McMurray and 260 km from the

50 northern-most spring, using historical data from the Global Network for Isotopes in Precipitation (IAEA and WMO, 2006). Groundwater recharged by modern local precipitation should plot on the LMWL near, or slightly below, the amount-weighted average precipitation. At Fort Smith, the amount-weighted average δ18O and δ2H values in precipitation are -19.0‰ and -148‰ respectively (Birks et al., 2003). In Figure 4-3, the isotopic composition of spring and river waters are plotted with the LMWL, as well as literature values for δ2H and δ18O of formation waters from elsewhere in the WCSB, and the amount-weighted average precipitation at Fort Smith.

Figure 4-3: Stable isotopic composition of spring and river waters with the LMWL for Fort Smith, NT, with the mean amount-weighted annual precipitation at Fort Smith (Birks et al., 2003), and deep basin brines (Connolly et al., 1990b). The LMWL for Fort Smith, calculated using data from IAEA and WMO (2006), follows the relationship δ2H=6.87δ18O + 18.0.

51 The isotopic compositions of the river waters plot on or near the LMWL in Figure 4-3. This is expected for surface waters that have undergone little evaporation, which reflect the isotopic composition of precipitation in the catchment basin (Gonfiantini et al., 1998). However, the isotopic compositions of the waters from both rivers plot above the amount-weighted mean precipitation for Fort Smith. The catchment areas for these rivers extend south and east from Fort Smith, hence this LMWL might not be representative over the whole river basins. The isotopic compositions of river waters represent a mixing of meteoric water from the entire upstream river basin. The Athabasca River has a larger basin than the Clearwater with glacial headwaters and generally higher elevation overall, which is reflected in lower 2H and δ18O values in the Athabasca samples. The isotopic compositions of the spring waters also plot on or near the LMWL in Figure 4-3, indicating water of meteoric origin that has not been altered isotopically by evaporation or water-rock interaction. However, most spring waters had lower δ18O and 2H values than the regional amount-weighted average precipitation. This is similar to brine springs found in other locations on the eastern fringe of the WCSB (Grasby et al., 2000; Grasby and Chen, 2005). Springs AR03 and CW09 had δ18O and 2H values closest to those of average annual precipitation, falling within 1.5‰ for δ18O and 4‰ for 2H. The δ18O and 2H values of the rest of the springs were lower than average precipitation by up to 4.5‰ in δ18O and up to 30‰ in 2H. The isotopic compositions of the spring waters are distinct from Alberta Basin brines, which plot to the right of the LMWL and above the average isotopic composition for Fort Smith precipitation. Thus, although the NE edge of the WCSB has been described as the discharge area for basin brines (e.g. Hitchon et al., 1969), these springs apparently do not discharge Devonian formation waters from deeper in the basin. The low δ18O and 2H values of the spring waters along the LMWL indicate that although the water has a meteoric origin, it has a different isotopic composition than average precipitation in the region. The main factor controlling the isotopic composition of precipitation is the temperature of condensation, which is correlated to ground temperature, altitude, and seasonality (Gonfiantini

52 et al., 1998). As a result the δ18O and 2H values of precipitation are generally higher than average in the summer and lower in the winter. In the Prairies, recharge of shallow groundwater occurs predominantly after snowmelt (Hayashi et al., 2003; Grasby et al., 2010), which would cause the δ18O and 2H values of groundwater to be slightly lower than those of average precipitation. However, Ferone and Devito (2004) found that the water budget in peat-pond complexes of the Boreal Plains differed from surface depressions in the Prairies in part due to storage of water in peat. Although precipitation patterns are similar in the two regions, snow did not accumulate to the same degree in the treed Boreal Plains and runoff was not sufficient to overcome peat storage and contribute to shallow groundwater recharge (Ferone and Devito, 2004). Since the present study area is located in a similar ecoregion, the low δ18O and 2H values of the spring waters are probably not due to a bias towards snowmelt in groundwater recharge. The formation of permafrost or methane hydrates is another process known to impart low δ18O and 2H values into groundwater (Stotler et al., 2012). During this process, solutes are excluded from permafrost or methane hydrates as they freeze and concentrate in the residual fluid. 18O is preferentially accumulated in the ice, resulting in lower δ18O values in the remaining water. In a semi-log plot of chloride concentrations and δ18O values, freezing-out processes can be identified by a linear trend (Stotler et al., 2012). The spring waters do not exhibit a linear trend in Figure 4-4. Thus, although the springs occur in the zone of discontinuous permafrost, the low δ18O and 2H values do not seem to be caused by permafrost formation.

Figure 4-4: Semi-log plot of chloride concentration versus δ18O values for spring waters.

Latitude and continental fractionation effects on the isotopic composition of precipitation are thought to have been constant in the study area since the Laramide orogeny (Connolly et al., 1990a). However, precipitation that occurred in a climate colder than today would have lower δ18O and δ2H values than modern precipitation. Groundwater depleted in 18O and 2H on the eastern fringe of the WCSB has previously been attributed to subglacial Laurentide meltwater forced into the Devonian carbonates by subglacial pressure, causing a regional reversal in the groundwater flow system (Grasby and Chen, 2005). According to this model, regional groundwater flow in the WCSB has not yet reached equilibrium after deglaciation (Grasby and Chen, 2005). Many studies have described glacial meltwater recharge in other locations in North America (e.g. Clark et al., 2000; Desaulniers et al., 1981; Grasby et al., 2000; McIntosh et al., 2011; Person et al., 2007). In total, Person et al. (2007) estimated that about 3.7 x 104 km3 of meltwater from the Laurentide Ice Sheet has been emplaced in confined aquifers across North America. The isotopic composition of the springs

54 in this study, with δ18O and 2H values lower than mean annual modern precipitation, suggests they may be comprised at least partially of Laurentide glacial meltwater. The isotopic composition of glacial meltwater during the Late Pleistocene has been estimated (e.g. Clark et al., 2000; Hillaire-Marcel et al., 1979; Remenda et al., 1994). Remenda et al. (1994) concluded from various literature values for melting Pleistocene ice across Canada that, for a latitudinal zone from 48° to 50°N, meltwater had an average δ18O value of -24 to -25‰. In a more northerly study at Yellowknife, NT (latitude 62°N), Clark et al. (2000) estimated a δ18O value of -28‰ for Laurentide glacial meltwater mixed with precipitation at the edge of the ablating ice sheet in this area. Considering either estimate for the isotopic composition of Pleistocene meltwater, the isotopic compositions of most spring waters in the current study are not low enough to be sourced entirely from Laurentide glacial meltwater. Rather, the isotopic compositions of the spring waters fall along a mixing line, coincident with the LMWL, between glacial meltwater and modern precipitation. The terms 'modern' and 'recent' here refer to precipitation that has fallen in the current climate regime over the last 10,000 years since the last glacial period. Mixing of glacial meltwater and modern precipitation is consistent with a groundwater flow system that is local to intermediate in scale as suggested by Bachu and Undershultz (1993) for this area, which should show influence of both shallow groundwater (recent precipitation) and deeper flow systems (glacial meltwater recharge still discharging from Devonian carbonates).

4.2.2 Quantification of glacial meltwater proportion

The hydrogen and oxygen isotope ratios of the springs fall along the LMWL for Fort Smith, suggesting that they can be attributed to linear mixing between modern precipitation and Laurentide glacial meltwater. The following two end-member mixing model was employed to estimate relative contributions of these two water sources to the spring waters:

18 18 18 δ Ospring = fmeltwaterδ Omeltwater + fppt δ Oppt (4-1)

55 where fmeltwater and fppt represent the fractions of spring water originating from Laurentide meltwater and modern precipitation, the sum of which is unity. The calculations were conducted using two estimated values for the δ18O of glacial meltwater: -25‰ (Remenda et al., 1994) and -28‰ (Clark et al., 2000). In both cases the δ18O value for modern amount-weighted precipitation at Fort Smith (-19.0‰) was used in the calculations (Birks et al., 2003). The results of the isotope mass balance calculations suggest that glacial meltwater may account for a large proportion, up to 75%, of the spring waters, with the balance being sourced from modern precipitation (Table 4-1). The higher δ18O value of -25‰ for glacial meltwater (Remenda et al., 1994) results in larger estimated proportions for a glacial source, with a maximum of 75% in spring CW05. The lower δ18O value of -28‰ estimated for more northerly glacial meltwater (Clark et al., 2000), results in a maximum contribution of 50% from this source in spring CW05. With the exception of springs AR03 and CW09, using either glacial δ18O value, the springs are composed of at least 26% glacial meltwater. Spring CW09 is sourced entirely from recent precipitation, and spring AR03 is sourced almost entirely from recent precipitation in both calculations (97 or 98%). These springs plot near the mean amount-weighted precipitation for Fort Smith on the LMWL (Figure 4-3), which supports the notion of modern recharge being the sole source of water. Although Laurentide meltwater is often characterized by its δ18O value in the literature, the constant relationship between hydrogen and oxygen isotopes in meteoric waters provides a check on the validity of the assumption of a glacial end-member in this linear mixing. An estimate of the deuterium content of the meltwater can be obtained using the relative fractions of Laurentide meltwater and modern precipitation in spring waters as calculated from oxygen isotopes. The isotope mass balance expressed for hydrogen and rearranged for the 2H of glacial meltwater gives:

2 2 2 δ H meltwater = ( H spring – fppt H ppt)/fmeltwater (4-2)

56 Springs AR03 and CW09 were not included in the 2H calculations because of the very low contribution of glacial meltwater to these springs. For all other springs, the calculated 2H values for glacial meltwater are relatively uniform, 18 with a mean value of -189 ± 2‰ using a δ Omeltwater value of -25‰ or 18 2 -209 ± 3‰ using a δ Omeltwater value of -28‰ (Table 4-1). The H value obtained from the higher δ18O estimate (-25‰) is close to the 2H value of -180‰ for Laurentide meltwaters from Glacial Lake Agassiz (Remenda et al., 1994), which 18 was located southeast of the study area. This supports using the δ Omeltwater value of -25‰ to estimate proportions of glacial meltwater, which results in glacial meltwater accounting for higher percentages of spring waters, from 39% in spring CW02 to 75% in spring CW05.

Table 4-1: Relative proportions of Laurentide glacial meltwater and recent precipitation in spring waters, based on linear two component mixing for two estimates for the δ18O of glacial meltwater, -25‰ (Remenda et al., 1995) and -28‰ (Clark et al., 2000). 2H values for glacial meltwater were calculated from resulting proportions using Equation 4-2.

spring water (Oct.2010) glacial meltwater δ18O = -25‰ glacial meltwater δ18O = -28‰ δ18O δ2 H % % δ2 H % % δ2 H spring meltwater meltwater (‰) (‰) meltwater ppt (‰) meltwater ppt (‰) AR01 -21.8 -169 46% 54% -194 31% 69% -216 AR03 -19.2 -152 3% 97% - 2% 98% - CW01 -21.9 -168 49% 51% -189 32% 68% -209 CW02 -21.3 -163 39% 61% -187 26% 74% -206 CW03 -22.3 -170 55% 46% -188 36% 64% -208 CW05 -23.5 -178 75% 25% -188 50% 50% -208 CW07 -22.4 -171 56% 44% -189 37% 63% -209 CW08 -22.7 -172 61% 39% -188 41% 59% -208 CW09 -18.8 -149 0% 100% - 0% 100% -

2 mean δ H meltwater (‰) -189 -209

2 standard deviation δ H meltwater (‰) 2 3

57 3 14 4.2.3 Age-dating of spring waters using H and CDIC Four springs were revisited in May 2011 for sampling of radiocarbon and tritium to determine the age of the waters. These springs were chosen due to their low δ18O values in October 2010 samples and corresponding higher estimated proportions of glacial meltwater. The δ18O values analyzed in 2011 varied slightly from 2010 values, particularly that of spring AR01, which increased by 1.1‰. However, δ18O values of these springs remained much below that of mean average precipitation (-19‰). Radiocarbon dating of the spring waters is based on the decay of 14C in DIC. Uncalibrated ages are reported as conventional radiocarbon ages, as defined by Stuiver and Polach (1977). This approach uses the Libby half-life of 5568 years in the following decay equation to determine the age of a sample:

(4-3)

14 where t is the radiocarbon age in years before present (ybp), at C is the activity of 14C in DIC in percent modern carbon (pmc) after t years of decay and normalized for δ13C fractionation to -25‰, 100 represents the activity of 14C in the standard (NBS oxalic acid) in the year 1950, and y is the year of measurement. The 14C activity in DIC is dependent on the sources and sinks of DIC in the system. The main source of 14C to the DIC in groundwater is the soil zone, where root respiration and decay of organic matter produce high concentrations of CO2 with 14C activity near 100 pmc, similar to that of vegetation (Hackley et al., 2006). However, the 14C activity of DIC may be diluted by any process that adds "dead" carbon (carbon with no measurable 14C) or that causes a loss of 14C. If not accounted for, this results in falsely old radiocarbon ages. A dilution factor, q, was calculated for the spring waters to account for the process of carbonate dissolution in the Devonian carbonate aquifer, which would add dead carbon to DIC. The revised equation for radiocarbon age, incorporating q, becomes:

(4-4)

The dilution factor for carbonate dissolution was calculated according to Tamers’ (1975) alkalinity correction. This is based on the initial and final DIC concentrations during calcite dissolution in a closed system. This dissolution is described by Equation 4-5 whereby carbonic acid, formed from soil zone CO2 and water, containing active 14C mixes with 14C-dead carbonate rocks, resulting in an even mixture of 14C-active and 14C-dead bicarbonate.

- 2+ H2CO3 + CaCO3 à 2HCO3 + Ca (4-5)

The dilution factor is calculated from initial and final molar concentrations of DIC (Clark and Fritz, 1997):

(4-6)

Assuming all carbonic acid dissociates and is consumed in the dissolution of limestone, this results in a dilution factor of 0.5 for all spring waters. In this case 14 half of the carbon in the resulting bicarbonate comes from soil CO2 (active C) and half comes from the Devonian carbonates (dead 14C). This simple model of the geochemical reaction was used because it does not require knowledge of recharge conditions, which are not known for this system. Tritium can be used to trace very recent recharge and, if present, may negate the assumption of closed system carbonate dissolution described above. Waters with appreciable tritium concentrations have recharged since nuclear bomb tests in the 1950s and 1960s, and modern precipitation has a tritium content of approximately 10 TU (Froelich, 2009). In spring AR01 the high tritium concentration (4.52 TU) indicated a significant proportion of water that has recharged in the last 60 years. The higher δ18O value measured in 2011

59 (-20.7‰) also resulted in a low estimated proportion of glacial meltwater in this spring water. For these reasons, a corrected radiocarbon age was not pursued for this spring. For springs CW03, CW05, and CW08, corrected radiocarbon ages calculated with Equation 4-4 ranged from 4330 to 27,540 radiocarbon ybp (Table 4-2). However, as radiocarbon concentration in the atmosphere has not been constant through time, radiocarbon ages must be calibrated to give dates in calendar years (Clark and Fritz, 1997). Calibration was performed using the 14C- calibration curve IntCal09 (Reimer et al., 2009) and the online calibration tool Calib 6.0 (Stuiver and Reimer, 1993; Stuiver et al., 2011). The resultant calendar ages were 2880 to 3090 ypb for spring CW08, 24,300 to 25,700 for spring CW03, and 29,270 to 30,650 ybp for CW05. The relative calendar ages calculated from 14C concentrations correspond with both the relative proportion of glacial meltwater calculated from 2011 δ18O values and the relative tritium concentrations in spring waters.

Table 4-2: Radiocarbon and tritium concentrations in spring waters measured in May 2011. The dilution factor, q, was used to correct the radiocarbon age for carbonate dissolution. Calibrated calendar ages calculated from Stuiver et al. (2011).

uncorrected corrected calibrated 14 3 spring at C H q radiocarbon age radiocarbon age calendar age (pmc) (TU) (ybp) (ybp) (ybp) AR01 17.6 4.52 ± 0.07 - 13,885 ± 45 - - CW03 3.1 0.29 ± 0.02 0.5 27,920 ± 170 22,360 ± 310 24,300 - 25,700 CW05 1.6 0.11 ± 0.02 0.5 33,130 ± 310 27,540 ± 50 29,270 - 30,650

CW08 28.9 1.66 ± 0.04 0.5 9900 ± 50 4330 ± 50 2880 - 3090

The radiocarbon ages of spring waters from CW03 and CW05 coincide with the last glacial period, which endured from approximately 110,000 to 10,000 years ago, supporting the notion of glacial meltwater as a water source. The calendar age of CW08 is more recent than the last glaciation; however, this does not preclude glacial meltwater as a partial water source to this spring. The tritium content of 1.66 TU indicates the presence of at least some water that was

60 recharged within the last 60 years. This means that the DIC pool in this spring has been influenced by some amount of very recent recharge. The addition of 'young' DIC from the soil zone would contribute active 14C to the system, thus influencing radiocarbon ages to more recent values. Also, the assumption of closed-system carbonate dissolution used to correct radiocarbon ages may not be entirely accurate for this spring. In general, the mixing of glacial meltwater and Holocene recharge in all the springs would have the overall effect of introducing active 14C into the DIC reservoir and reducing the radiocarbon age of spring waters. Therefore, the radiocarbon ages presented here are conservative estimates giving the more recent age boundary for DIC from a glacial source of water. Older ages are possible, particularly for those springs containing lower calculated proportions of glacial meltwater and even more so for springs containing tritium, indicating some component of very recent recharge. The simple alkalinity correction of 14C activity for carbonate dilution performed here resulted in estimates of the calendar ages of spring waters. However, isotopic exchange between carbonate minerals and DIC has not been taken into account in the corrections. More detailed estimates for carbonate dilution may have been achieved through chemical mass-balance modeling or δ13C mixing models; but the required knowledge of recharge conditions was unavailable. Nonetheless, the relative water ages for these three springs obtained through simple alkalinity corrections and calibration are consistent with both tritium concentrations and proportions of glacial origins calculated from δ18O 18 values of the spring waters. This supports the interpretation of δ OH2O values as an indicator of water source, with lower δ18O values (around -22‰) found in spring waters with partial glacial origins, and higher δ18O values (around -19‰) found in spring waters recharged predominantly by modern precipitation.

61 Chapter Five: Sources of solutes

In this chapter the chemistry of spring waters is used to classify water types. Differences in major ion chemistry distinguish the spring waters from shallow groundwater, river water, and deep basin brines. The isotopic compositions of spring waters and dissolved ions give insights into subsurface processes that have contributed to the salinity of the springs. Mineral dissolution/precipitation reactions are investigated using stoichiometric calculations. Potential water-mineral equilibria in the springs are explored using thermodynamic models.

5.1 Water types

The total dissolved solids (TDS) in spring and river waters was calculated as the sum of the concentrations of the following dissolved ions: HCO3, Cl, SO4, S2-, Br, Ba, Sr, Li, Na, Ca, Mg, Mn, Fe, K (Table 3-2). The TDS of spring waters was two to three orders of magnitude higher than that of river waters. Relative concentrations of ions were used to classify water types.

5.1.1 Spring waters

The TDS of the springs ranged from 7,210 to 51,770 mg/L. According to Davis’ (1964) classification system based on the TDS of waters, all springs were saline except for CW01, which was brackish (Table 5-1). The spring waters had a Na-Cl water type and cluster closely together but distinctly from river waters on a Piper plot in Figure 5-1.

Table 5-1: Water classification based on TDS concentration (Davis, 1964). classification TDS (mg/L) samples fresh < 1000 all river samples brackish 1000 - 10,000 CW01 saline 10,000 - 100,000 all springs except CW01 brine > 100,000 none

Figure 5-1: Piper plot of spring and river waters. Upstream river samples are indicated by solid symbols, downstream river samples by hollow symbols.

63 Major ion concentrations in spring waters are plotted against TDS in

Figure 5-2. With the exception of HCO3, most major ion concentrations fall along a linear mixing line with intercepts close to 0, indicating a fresh, low-TDS water as one end-member, and a high-TDS water as the other end-member. The fact that Athabasca and Clearwater springs fall along the same mixing lines in Figure 5-2 suggests that all spring waters are mixtures of the same two end-members.

Figure 5-2: Major ion concentrations versus TDS for spring waters, in meq/L.

In Chapter 4, mixing between glacial meltwater and modern recharge was discussed. It might be surmised that these were the two end-members for the TDS mixing lines, i.e. glacial meltwater that has dissolved minerals as the high- TDS water and recent recharge as the low-TDS water. However, no trend is 18 apparent between the δ OH2O value and TDS of spring waters (Figure 5-3), suggesting that the proportion of glacial meltwater in each spring is not an indicator of its salinity. TDS is likely affected by the solubility of minerals along the groundwater flowpath as well as the residence time of waters, not only of glacial meltwater but also of the modern component of spring waters which has

64 recharged since glacial times. The tritium concentrations in spring waters indicated varying proportions of very recent recharge (<60 ypb) in spring waters (Chapter 4).

Figure 5-3: TDS versus δ18O of spring waters.

5.1.2 River waters

The TDS of all river samples was below 240 mg/L. The river waters had a

Ca-HCO3 water type with the composition being slightly more influenced by Na- Cl in the downstream samples (Figure 5-1). In the Clearwater River, TDS increased threefold downstream from 51 to 150 mg/L. Some of the increase in Ca and HCO3 may be attributed to surface runoff and weathering of bedrock as the river channel enters the Devonian carbonates from the Canadian Shield. The increases in concentration of Na, Cl, SO4, and Ca (Table 3-2) may be at least partially attributed to solutes contributed from springs and seeps along the river and its tributaries. However, the downstream Clearwater River site is also downstream of a portion of Fort McMurray, and the increase in TDS in the Clearwater River may also be at least partially due to influences of the municipality.

65 The Athabasca River decreased slightly in TDS downstream from 240 mg/L to 219 mg/L. Water quality data from the Regional Aquatics Monitoring Program (RAMP) at similar sites sampled in the fall from 2002 – 2007 do not show a downstream decrease in TDS (RAMP, 2012) which suggests this may be an anomalous occurrence. There are a few possible reasons for the downstream decrease in TDS. One may be the proximity of the upstream site to the municipality of Fort McMurray. The site was chosen for road access, and was located upstream of most of the town, but downstream of a golf course. Inputs from the town and golf course such as wastewater, stormwater, and runoff may have influenced the upstream site. Another possible reason for the decrease in TDS may be dilution by additional flow contributed from tributaries over the study reach (e.g. Minshall et al., 1985). While concentrations of most ions decreased downstream in the Athabasca River, concentrations of Na increased from 10.6 to 14.3 mg/L and concentrations of Cl increased from 2.8 to 11.0 mg/L (Table 3-2). This may be at least partially attributed to the input saline water from springs and seeps along the Athabasca River. This is supported by the findings by Jasechko et al. (2012) that saline groundwater accounts for 0.1 to 3% of the discharge of the Athabasca River over a similar reach (Fort McMurray to Old Fort). The uncertainties surrounding anthropogenic effects from Fort McMurray on the water quality of the Athabasca River suggest this upstream site may not be ideal for determining effects of the saline springs on Athabasca river water chemistry. However, it does serve for a comparison of water chemistry between the rivers and springs.

5.2 Halite dissolution

Underlying the Devonian carbonates from which the springs emerge is the Prairie Evaporite Formation. Near the study area, it consists of relatively pure halite interbedded with anhydrite and minor anhydrite dolostone (Grobe, 2000). The dissolution of halite was investigated using ion ratios and stable isotope ratios.

66 5.2.1 Na/Cl ratios

Halite is very soluble in water, producing equal molar concentrations of sodium and chloride ions following the reaction:

NaCl à Na+ + Cl- (5-1)

The molar ratio of Na/Cl is approximately one in all the spring waters, as expected from halite dissolution (Figure 5-4). This is distinct from formation waters from Devonian carbonate units deeper in the WCSB, which have an average Na/Cl molar ratio between 0.7 and 0.8 (calculated from Michael et al., 2003 and Connolly, 1990). The lower Na/Cl ratio of formation waters was interpreted as the result of the evaporation of seawater and subsequent water- rock reactions (Michael et al., 2003), as opposed to halite dissolution. No halite exists in the Devonian carbonates or overlying Cretaceous sedimentary strata, only in the underlying evaporites. The springs are mostly located beyond the dissolution edge of the Prairie Evaporite Formation, which occurs just east of Fort McMurray (Grobe, 2000) (Figure 5-5). For halite dissolution to be the source of salinity, the spring waters must have traveled at least from the dissolution edge of these evaporites, located between 5 and 30 km west of most of the springs. This gives an indication of the scale of groundwater flow discharging at the springs, and is consistent with the intermediate scale of flow described in Chapter 4, with deeper glacial meltwaters mixing with more recently recharged local waters.

Figure 5-4: Na/Cl ratios of springs from this study compared with those of formation waters from Upper Devonian units deeper in the Western Canada Sedimentary Basin (WCSB).

Figure 5-5: Spring locations compared with subsurface extent of the Prairie Evaporite Formation and dissolution area. Modified from Grobe (2000).

5.2.2 Cl/Br ratios

Bromide and chloride are considered to be generally conservative tracers in natural waters. Chemically, the two halides are very similar, differing mainly in solubility with bromide compounds being more soluble (Davis et al., 1998). During precipitation of halite, bromide is excluded from the crystal structure,

69 imparting higher Cl/Br ratios in halite minerals and any subsequent dissolution brines. The Cl/Br ratio in halite generally is greater than 3000, but can be an order of magnitude higher depending on re-dissolution/re- precipitation cycles. In contrast, the Cl/Br ratio of atmospheric deposition is generally less than 200, while that of seawater is around 290 (Davis et al., 1998).

5.2.2.1 Spring waters

The mass ratio of chloride to bromide in the spring waters ranged from 989 to 4086 (Figure 5-6). The average reported Cl/Br ratio in shallow groundwater in Quaternary sediments near the study area was 242 (calculated from Lemay, 2002); and in Cretaceous formation waters was 325 (calculated from Lemay, 2002). Formation waters from Upper Devonian carbonate units downdip in the WCSB had an average Cl/Br ratio of 213 (calculated from Connolly, 1990). In contrast, halite dissolution brines originating from Devonian Elk Point evaporites further south in the basin had reported Cl/Br ratios in excess of 20,000 (Freeman, 2007). When the Cl/Br ratios of spring waters are compared to other values from the literature, the springs plot in an intermediate zone between Elk Point halite dissolution brines, fresh shallow groundwaters, and Cretaceous formation waters (Figure 5-6). The Cl/Br ratios of saline fens near the study area reported by Stewart and Lemay (2011) are slightly higher than most of the springs investigated in this study but similar to that of spring AR03. The higher Cl/Br ratios found in these fens suggest they contain a halite-dissolution brine that have not been as diluted by other waters as the springs. This may be explained by their locations: the fens are located within the current extent of the Prairie Evaporite Formation, therefore the waters have not traveled as far from the source of halite and have been less diluted by other waters. The same may be true for spring AR03, which is located close to the outcrop area of Elk Point evaporites, which contain halite (Figure 5-5). The rest of the springs are located beyond the dissolution edge of the Prairie Evaporite Formation (Figure 5-5), allowing for a longer flowpath from the source of halite and a greater possibility of mixing with other waters before discharging.

Figure 5-6: Cl/Br mass ratios of spring and river waters, formation waters from Upper Devonian units in the WCSB and Cretaceous units near the study area, saline fens near the study area, and Elk Point dissolution brines in WCSB.

5.2.2.2 River waters

The Cl/Br ratio in the river waters increased downstream, from 203 to 877 in the Clearwater, and from 389 to 1033 in the Athabasca. These values fall together with those of shallow Quaternary groundwater (Lemay, 2002) in Figure 5-6. The range of shallow Quaternary Cl/Br ratios may be considered representative of water in the region that originated as precipitation and has not come into contact with evaporite beds. The downstream increase of the Cl/Br ratio in river samples may be, however, at least partially due to the input of

71 halite dissolution brines from these saline springs and other saline groundwater inputs along their reaches.

5.2.3 Cl isotopes

The natural variation in the stable isotope ratio of chloride is much smaller than other common isotopic tracers. The global range of δ37Cl in seawater, groundwater, and evaporites reported in several studies ranges from -1.4 to 1.5‰, while reported δ37Cl values of rainwater range from -4 to 1.8‰ (Koehler and Wassenaar, 2010 and references therein). Fractionation of Cl isotopes does not occur biologically, but only through physical processes such as ion filtration, diffusion, brine evaporation, and salt deposit formation (Clark and Fritz, 1997). Remnant seawater should preserve a δ37Cl value of 0‰, unless affected by diffusion during infiltration (Clark and Fritz, 1997). Halites precipitated from seawater can have δ37Cl values higher than 0‰ (Kaufman et al., 1984; Eggenkamp et al., 1995). During halite precipitation from seawater, 37Cl is slightly enriched in the mineral, resulting in δ37Cl ranging from 0.4 to 0.6‰ (Eastoe and Peryt, 1999). δ37Cl values higher than 0.6‰ in halite require repeated cycles of evaporation and precipitation, resulting in a significant depletion of the original volume of halite (Eastoe and Peryt, 1999). Atmospheric deposition, on the other hand, which contains Cl largely sourced from marine aerosols, has been observed to have δ37Cl values less than 0‰; this has been attributed to fractionation through acidification of sea-salt aerosols (Volpe et al., 1998; Koehler and Wassenaar, 2010).

5.2.3.1 Spring waters

The δ37Cl of dissolved chloride in all the spring waters was positive and ranged from 0.2 to 1.0‰ (Figure 5-7). All springs except CW05 and AR03 had δ37Cl values that were equal to or greater than the maximum δ37Cl value of 0.6‰ for halite precipitated from seawater. Meijer Drees (1986) suggested that almost all the evaporitic rocks of the Elk Point Group are partly or completely recrystallized, including the Prairie Evaporite Formation, which showed signs of

72 having undergone many cycles of evaporation and dissolution. Such cycles of re-precipitation would have increased the δ37Cl of the remaining halite, which is consistent with the positive values seen in the spring waters. The distinct δ37Cl values of spring waters enables an isotope mass balance calculation to determine the percentage of Cl and other major ions in the Clearwater River that are sourced from saline springs (Chapter 7).

5.2.3.2 River waters

The δ37Cl values of all river samples were negative. The Clearwater upstream sample had the lowest δ37Cl value (-2.3‰) but increased downstream to -1.4‰. These values are consistent with previous observations in Canadian rivers, that δ37Cl values increased downstream from approximately -3.0‰ at the headwaters, reflecting the negative δ37Cl values in precipitation, to higher values downstream following the addition of Cl with positive δ37Cl values from diffuse and point sources of Cl (Koehler and Wassenaar, 2010). The downstream increases in δ37Cl values and Cl concentration in the Clearwater River may be at least partially attributed to saline groundwater point sources along this reach. Inputs of Cl from Fort McMurray through runoff or stormwater near the downstream site could also be partially responsible for the increase. The δ37Cl values of the Athabasca River samples increased slightly downstream from -1.8‰ to -1.5‰. The river flows for 1140 km from its glacial headwaters to the study area; anthropogenic and natural sources of Cl along this path likely result in the δ37Cl value in the river at study area being higher than at the headwaters. Within in the study area, the slight increase in δ37Cl values may be due in part to input of Cl from saline springs. Any influence of halite dissolution spring waters on δ37Cl values would be less dramatic in the Athabasca than in the Clearwater because the upstream Athabasca δ37Cl value has already increased from expected headwater values, whereas the lower upstream δ37Cl value in the Clearwater reflects the proximity to the headwaters and fewer point sources of Cl to the river. Thus, Cl derived from halite dissolution with positive δ37Cl values in saline spring waters has more of an

73 effect on δ37Cl values and Cl concentration in the Clearwater River than the Athabasca River.

Figure 5-7: δ37Cl values of spring and river waters versus Cl concentration. Symbols for upstream river sites are solid; downstream sites are hollow.

5.3 Carbonate and gypsum dissolution

Although the springs had a Na-Cl water type, sulfate, magnesium, calcium, and bicarbonate ions were also present in appreciable concentrations. Major ion ratios show the dissolution of carbonates and gypsum can account for the concentrations of these ions.

5.3.1 Major ion ratios

The Devonian carbonates in the study area belong mainly to the Waterways Formation, an alternating sequence of shales and limestone (Norris, 1973). The dissolution of calcite, the dominant mineral in limestone, and of dolomite, which is often associated with calcite (Deer et al., 1966), are described by the following reactions:

2+ - CaCO3 + CO2 + H2O à Ca + 2HCO3 (5-2) (calcite)

2+ 2+ - CaMg(CO3)2 + 2CO2 + 2H2O à Ca + Mg + 4HCO3 (5-3) (dolomite)

As these reactions proceed, the total concentration in meq/L of cations released by dissolution (Ca and Mg), is balanced by that of HCO3. This was not the case in most of the spring waters, where meq/L concentrations of Ca plus Mg were much higher than that of HCO3 (Figure 5-8). The ratio of Ca:Mg (meq/L) was approximately 1.5 in Clearwater springs (Figure 5-9). This is similar to the Ca:Mg ratio in saline fens near the study area reported by Stewart and Lemay (2002) of approximately 1. Springs on the Athabasca River had higher Ca excess, with Ca:Mg ratios of approximately 2 (AR01) and 4 (AR03).

Figure 5-8: Concentrations of Ca plus Mg versus HCO3 in spring waters in meq/L.

Figure 5-9: Ratios of Ca:Mg concentrations (meq/L) versus TDS (g/L) for spring waters from this study and saline fens near the study area reported by Stewart and Lemay (2011).

Sulfate minerals are a possible source of excess Ca in the spring waters. Both gypsum and anhydrite are present in the Prairie Evaporite Formation underlying the Devonian carbonates. The solubility of anhydrite is low in water, but its hydration product, gypsum, is soluble and increasingly so in the presence of calcite or halite (Deer et al, 1966); therefore, gypsum dissolution will be considered here. The dissolution of gypsum produces equal molar concentrations of calcium and sulfate ions, and is described by the reaction:

2+ 2- CaSO4•2H2O à Ca + SO4 + 2H2O (5-4)

When the dissolution of gypsum (Equation 5-4) is considered in conjunction with carbonate dissolution (Equations 5-2 and 5-3), additional Ca and SO4 ions are added to solution. The molar concentration of (Ca + Mg) should equal that of (HCO3 + SO4) ions in solution. Figure 5-10 shows that this is the case for the spring waters, indicating that the concentrations of these ions can be

76 explained by the dissolution of gypsum in addition to the dissolution of carbonates. Since Mg is present in dolomite but not gypsum, the higher Ca:Mg ratio in the Athabasca springs, particularly in AR03, suggests a larger influence of sulfate mineral dissolution than carbonate dissolution. In spring AR03, the larger influence of sulfate dissolution may be explained by its location. In contrast to the Clearwater springs, which are located beyond the dissolution edge of Prairie Evaporite deposits, this spring is located near an outcrop area of the Elk Point Group. Dissolution of gypsum in these evaporite deposits by local recharge can occur near spring AR03 with minimal dilution or mixing with other waters before being discharged at the springs.

Figure 5-10: Cation versus anion concentration (meq/L) for the ions that would be liberated into solution by the dissolution of carbonates and gypsum: Ca, Mg,

SO4 and HCO3.

77 5.3.2 δ 34S and δ 18O: sulfate dissolution

Potential sources of sulfate, such as marine evaporite minerals, oxidation of sulfide minerals, or atmospheric deposition can be identified through the δ34S and δ18O values of dissolved sulfate. In Figure 5-11, δ18O and δ34S values of sulfate in spring waters and Athabasca River waters are plotted with those of potential sulfate sources from Clark and Fritz (1997). With the exception of spring AR01 (La Saline), the isotopic compositions of sulfate in spring waters plot together but outside the ranges of most sulfate sources. Only springs CW03 and AR03 fell within the defined range for Devonian evaporites which would be expected for sulfate derived from the Prairie Evaporite Formation. In all springs but AR01, the 34 δ SSO4 values ranged from 22.4 to 27.6‰, within the range expected for 18 evaporites, but δ OSO4 values ranged from 6.7 to 13.7‰, falling slightly below the range expected for this source. In spring AR01, the concentration of sulfate was 2 to 8 times higher than 34 18 in the rest of the springs. The δ SSO4 and δ OSO4 values were 7.0‰ and 2.3‰, respectively. The isotopic signature of dissolved sulfate in the Athabasca River was similar, with δ34S values of 6.6 and 9.9‰, and δ18O values of 0.3 and -1.0‰. 34 34 The δ SSO4 value in spring AR01 is similar to the δ SSO4 value found in groundwater in the overlying McMurray Formation of 6.4‰ (Lemay, 2002). These values fall clearly within the expected values for the oxidation of sulfide minerals found in soils and sediments. Spring AR01 contains a large proportion of modern recharge (as shown in Chapter 4), which would have infiltrated through the soil and overlying units.

Figure 5-11: δ34S and δ18O values of sulfate in spring river waters, plotted with ranges for various sources of sulfate; evaporitic source ranges identified by age. Modified from Clark and Fritz (1997).

5.3.2.1 Bacterial sulfate reduction

34 When δ SSO4 is plotted against SO4 concentration for all springs but AR01, 34 a general trend of increasing δ S with decreasing SO4 concentration is apparent (Figure 5-12). This inverse relationship may be indicative of bacterial sulfate reduction (BSR), during which the light isotopes of S and O in sulfate are preferentially metabolized by bacteria, thus enriching the residual sulfate in heavy isotopes as SO4 concentrations decrease (Kaplan and Rittenberg, 1964). 34 The δ SSO4 value of gypsum in the Prairie Formation would be expected to be similar to that of anhydrite from the Elk Point evaporites elsewhere in the WCSB, which has reported values ranging from 18.2 to 22.6‰ (Sasaki and Krouse, 1969; 34 Hitchon and Krouse, 1972; Horita et al., 1996). The δ S of spring water sulfate is higher than this in all springs except CW02, suggesting that some degree of bacterial sulfate reduction has occurred in most spring waters.

Figure 5-12: δ34S versus concentration of dissolved sulfate in all spring waters except AR01. Grey area indicates expected range of δ34S for Elk Point Formation anhydrite (Sasaki and Krouse, 1969; Hitchon and Krouse, 1972; Horita et al., 1996).

The bacterial reduction of sulfate requires an organic substrate, either fixed or reduced, and produces hydrogen sulfide and mineralized carbon (Clark and Fritz, 1997). These reactions include several intermediary steps with sulfide compounds (e.g. Rees, 1973), but in simplified terms these reactions can be represented by (Clark and Fritz, 1997):

2- - 2CH2O + SO4 à 2HCO3 + H2S (5-5) (fixed carbon)

2- - - CH4 + SO4 à HCO3 + HS + H2O (5-6) (reduced carbon)

Both methane and dissolved organic carbon (DOC) were present in the springs and could have provided the substrate for BSR. Hydrogen sulfide, a product of BSR, gives a distinctive sulfur-odour that was observed at some of the springs. Concentrations of dissolved sulfide measured in these spring waters

80 ranged from 0.2 to 60 mg/L (Table 3-2). However, the occurrence of dissolved sulfide depends on pH and the availability of metals that may precipitate sulfide minerals (Clark and Fritz, 1997). Thus, concentrations of dissolved sulfide in some spring waters may have been affected by mineral precipitation or dissipation, as has been noted for other groundwaters where BSR has been identified (e.g. Van Stempvoort et al., 2005). This may explain why, although BSR 34 would be expected to increase both δ SSO4 and dissolved sulfide concentrations, 34 is no apparent correlation between dissolved sulfide concentration and δ SSO4 (Figure 5-13).

Figure 5-13: δ34S of dissolved sulfate vs. dissolved sulfide concentration in springs waters, excluding AR01.

The effect of BSR on the δ18O value of residual sulfate is more variable and 34 less well understood than its effect on δ SSO4 (Mangalo et al., 2007). Some researchers have found that kinetic isotope fractionation controlled δ18O values in 18 residual sulfate (e.g. Aharon and Fu, 2000), while others have found δ OSO4 values were controlled by equilibrium isotope exchange between water and

81 intermediate sulfur compounds (e.g. Fritz et al., 1989; Brunner and Bernasconi, 2005). Some studies have found that the δ18O value of residual sulfate approached a constant value as sulfate was consumed by BSR (e.g. Mitzutani and Rafter, 1973; Fritz et al., 1989; Aharon and Fu, 2000). In the springs, there is an 18 trend of decreasing δ OSO4 values with decreasing sulfate concentrations (Figure 5-14). A similar trend was reported by Fritz et al. (1989) and Mangalo et al. (2007) 18 for SO4 altered by BSR in water with low δ O values and was attributed predominantly to oxygen isotope equilibrium exchange between sulfur intermediates and water during BSR. Similar oxygen isotope equilibrium exchange in the low δ18O spring waters is a possibility in the springs, where 18 18 lower δ OH2O values generally corresponded with lower δ OSO4 values (Figure 5- 15).

Figure 5-14: δ18O of dissolved sulfate versus dissolved sulfate concentrations in spring waters (excluding spring AR01).

18 18 Figure 5-15: δ OSO4 versus δ OH2O in spring waters (excluding spring AR01). Arrow indicates general trend of lower δ18O values of sulfate with lower δ18O values of water, suggesting equilibrium isotope exchange during BSR between sulfur compounds and water. The isotopic separation between δ18O values of sulfate and water is approximately 30‰.

5.3.3 δ 13C of DIC: carbonate dissolution and methanogenesis

Dissolved inorganic carbon (DIC) in carbonate aquifers is derived from the dissolution of CO2 into the waters, sourced either from the atmosphere or from the soil zone, and the subsequent dissolution of carbonate minerals (Clark and Fritz, 1997). Organic carbon processed through microbially-mediated reactions, such as bacterial sulfate reduction or methanogenesis, may also contribute CO2 to the DIC pool (Aravena et al., 1995). DIC can be found in three 2- - forms, depending on the pH of the water: CO3 , HCO3 , and H2CO3 (Appelo and Postma, 2005). In most natural waters near neutral pH, DIC exists predominantly as HCO3 (Appelo and Postma, 2005). The sources of DIC can be traced through its δ13C value. In the dissolution of carbonates following Equations 5-2 and 5-3, carbon is sourced equally from carbonate minerals and carbon dioxide. The δ13C value of the resulting

83 bicarbonate, under equilibrium conditions in a closed system, reflects an even mixture of the two sources and equals the mean of the δ13C values of carbon sources (Apello and Postma, 2005). The Beaverhill Lake carbonates have a reported 13C value of 0.1‰ (Carrigy and Mellon 1959), which falls in the expected δ13C range of 0 to 2‰ for ancient marine rocks (Gonfiantini and Zuppi,

2003). The CO2 in most groundwaters is derived from respiration in the soil zone, and has a δ13C value around -23‰ in landscapes dominated by C3 plants (Clark and Fritz, 2007), as is the case in the study area. Thus, at equilibrium the 13C value of DIC produced from dissolution of the Devonian carbonates by soil CO2 under closed system conditions should be around -12‰, reflecting equal contributions of C from these two sources. 13 The C values of DIC in five springs along the Clearwater River (CW01, CW02, CW05, CW07, and CW08) were within 2.5‰ of the predicted value of -12‰. This suggests that the DIC in these waters can be explained by equilibrium carbonate dissolution by soil CO2. Calculations of saturation indices in Section 5.4 support carbonate equilibrium in these springs. The slight variations observed from the expected 13C of -12‰ may be due to differences from 13 13 literature values for the C of soil CO2 and for Devonian carbonates. The δ CDIC values in the two Athabasca springs as well as CW03 and CW09 were 7.1 to 13 45.7‰ higher than expected for carbonate dissolution (Figure 5-16). δ CDIC values can be increased through microbial processes that preferentially use 12C, 13 enriching the remaining DIC pool in C. Methanogenesis through the CO2- 13 reduction pathway is one such process, which results in an increase in δ CDIC values corresponding with a decrease in alkalinity (Whiticar et al., 1986), as seen 13 in Figure 5-16. Higher δ CDIC values would thus be expected in springs with higher methane concentrations. This is confirmed for springs AR03, CW03, and CW09 in Figure 5-17 (AR01 was not analyzed for methane concentration and is excluded). Methanogenesis and BSR are generally considered to be mutually exclusive processes because sulfate-reducing bacteria outcompete methanogens for the organic substrates necessary for both processes (Appelo and Postma, 2005). However, the isotopic compositions of sulfate and DIC in springs AR03,

84 CW03, and CW09 show evidence of both processes having occurred. Generally methanogenesis does not occur until all sulfate has been consumed by BSR. However, sulfate remains in all spring waters. This implies that the waters discharging at the springs are a mixture of waters from different zones in the aquifer. Waters from springs AR03, CW03, and CW09 may have reached conditions adequate for methanogenesis after sulfate was consumed by BSR but subsequently mixed with waters still containing some sulfate. This would result in the isotope fractionation effects of both processes being preserved in the waters.

Figure 5-16: 13C of DIC in spring waters as a function of alkalinity. The dashed line at δ13C of -12‰ represents the expected δ13C value resulting from carbonate dissolution by soil CO2.

Figure 5-17: δ13C of DIC versus methane concentration in spring waters (methane was not analyzed in spring AR01).

5.3.4 87Sr/86Sr ratios: carbonate dissolution

Strontium is a trace element found in a wide variety of rocks. The four stable isotopes of Sr are not greatly affected by fractionation or biological processes (McNutt, 2000). This makes it an ideal tracer of groundwater movement, water-rock interactions, and salinity (Clark and Fritz, 1997). The heavier isotope, 87Sr, is the radiogenic daughter of 87Rb, thus the 87Sr/86Sr ratio of a mineral can increase over time as a result of the decay of 87Rb which has a half- life of 4.88 × 1010 years (McNutt, 2000). Rb substitutes for potassium in crystal structures, which can result in higher 87Sr/86Sr ratios in K-rich minerals, such as feldspars, micas, and clays. Conversely, Sr substitutes for Ca in Ca-rich minerals, such as carbonates and gypsum, resulting in lower 87Sr/86Sr ratios. Generally, silicate minerals have low Sr concentrations but high 87Sr/86Sr ratios while carbonates and sulfates have high Sr concentrations with low 87Sr/86Sr ratios. The 87Sr/86Sr of carbonates and evaporites will dominate in groundwaters exposed to these minerals, due to their high concentrations of Ca and Sr. Any influence of

86 low-concentration, high 87Sr/86Sr from overlying sandstones or shallow groundwaters would be overpowered by the low 87Sr/86Sr carbonate and evaporite signature (McNutt, 2000). In Figure 5-18 the 87Sr/86Sr ratios of spring and river waters are plotted with reported 87Sr/86Sr ratios of relevant rocks and waters for comparison. 87Sr/86Sr ratios range from 0.7078 to 0.7083 for Middle to Upper-Devonian seawater (Burke et al., 1982) and from 0.70781 to 0.70789 for anhydrite from the Prairie Formation in Saskatchewan (Horita et al., 1996). 87Sr/86Sr ratios range from 0.7082 to 0.7094 for Middle to Upper Devonian carbonate rocks of the WCSB and 0.7094 to 0.7121 for formation waters found within (Connolly et al., 1990b). Near the study area, Cretaceous formation waters have 87Sr/86Sr ratios ranging from 0.70754 to 0.71002 (Lemay, 2002). Formation waters in the Canadian Shield have a wide reported range of 87Sr/86Sr ratios between 0.7100 and 0.7380 (Frape et al., 1984; McNutt et al., 1990).

Figure 5-18: 87Sr/86Sr ratios in spring waters (grey bar) and river waters (squares and triangles; solid symbols represent upstream river samples, hollow symbols represent downstream samples). Ranges of 87Sr/86Sr ratios of other materials are shown for comparison (references in text).

5.3.4.1 Spring waters

The concentration of strontium ranged from 4.4 to 23.4 mg/L in the spring waters. The good correlation between strontium and calcium concentrations (Figure 5-19) suggests they have the same source(s) (McNutt, 2000). From the major ion analyses, carbonate dissolution was found to be the main source of Ca springs, although not the sole source. Excess Ca was determined to be sourced from gypsum dissolution, particularly in the Athabasca springs (Section 5.3.1).

Figure 5-19: Concentrations of strontium vs. calcium in spring waters.

The 87Sr/86Sr ratios in the Clearwater spring waters ranged from 0.708647 to 0.709044. The 87Sr/86Sr ratios in the Athabasca springs were lower, with values of 0.708742 and 0.708553 in AR03 and AR01, respectively. These ratios all fit within the reported range of 87Sr/86Sr ratios in mid- to upper-Devonian carbonate rocks in the WCSB of 0.7082 to 0.7094 (Connolly et al., 1990b), supporting the notion that dissolution of Devonian carbonates is the main source of Ca and Sr to the springs. The lower 87Sr/86Sr ratio in the Athabasca springs, however, is consistent with a greater proportion of Ca sourced from gypsum dissolution in these springs. Anhydrite from the Prairie Formation has a 87Sr/86Sr ratio between 0.70781 to 0.70789 in Saskatchewan (Horita et al., 1996), which is consistent with estimates for mid-Devonian seawater of 0.7078 to 0.7083 (Burke et al., 1982). Increased dissolution of Prairie Evaporite gypsum would lower 87Sr/86Sr values. A Keeling plot of reciprocal strontium concentration versus 87Sr/86Sr ratios in the spring waters and Upper Devonian Formation waters (Connolly et al., 1990b) is presented in Figure 5-20. The spring waters are distinct from formation waters from downdip in the WCSB, which have higher strontium concentrations and 87Sr/86Sr ratios, interpreted to be acquired by meteoric water passing through

89 volcanic sediments (Connolly et al., 1990b). The lower 87Sr/86Sr ratios of the spring waters match more closely the 87Sr/86Sr ratios of Devonian carbonates in the WCSB. However, although the range of 87Sr/86Sr in spring waters is small, there is a general trend of higher Sr concentrations with lower 87Sr/86Sr ratios in the spring waters (Figure 5-20). This suggests two component mixing, with one end-member having a low Sr concentration and a slightly elevated 87Sr/86Sr ratio, and the other end-member having a high Sr concentration and low 87Sr/86Sr ratio, as might be expected from Devonian carbonate or sulfate minerals. The y-axis of a Keeling plot gives the Sr isotopic ratio of the end-member with high Sr concentration, 0.7086. This is slightly higher than values reported for Prairie Evaporite Formation gypsum in Saskatchewan (Horita et al., 1996), but within the range of Devonian carbonate rocks in the WCSB (Connolly et al., 1990b).

Figure 5-20: 87Sr/86Sr ratios vs. 1/Sr concentration for spring waters and for Upper Devonian formation waters in the WCSB reported by Connolly et al. (1990b).

90 5.3.4.2 River waters

Globally, river waters have high 87Sr/86Sr ratios, from 0.704 to 0.922, reflecting the weathering of common silicate minerals (Capo et al., 1998, and references therein). The 87Sr/86Sr ratio of river waters in this study was higher than that of the springs, indicating a different source of strontium, and Ca, in these waters. The 87Sr/86Sr ratios in both the Clearwater and Athabasca rivers decreased downstream. In the Clearwater River, the higher 87Sr/86Sr ratios of 0.715775 and 0.711151 reflect its flow through ancient Precambrian Shield rocks, in which the decay of Rb in K-bearing minerals imparts a high 87Sr/86Sr ratio (Capo et al., 1998). The values for the Clearwater fall within the 87Sr/86Sr range reported for Shield waters from 0.7100 to 0.7380 (Frape et al., 1984; McNutt et al., 1990). In the Athabasca River, the lower 87Sr/86Sr ratios of 0.710459 and 0.710296 reflect the influence of carbonate rocks in its headwaters in the Rocky Mountains and its flowpath through younger rocks. The downstream decrease in the 87Sr/86Sr ratio in the rivers, particularly the Clearwater, indicates the addition of waters with lower 87Sr/86Sr ratios, such as the saline springs of this study.

5.4 Water-mineral equilibria in spring waters

The high solubility of the carbonate and sulfate minerals present in the system allows the possibility that equilibrium has been achieved between these minerals and the spring waters. At equilibrium with a mineral, water is considered saturated with respect to that mineral. The saturation states of minerals in spring waters were determined using the activities of major ions through geochemical computer modeling. In addition, thermodynamic modeling was used to investigate if equilibrium processes between minerals are a control on water chemistry.

5.4.1 Computer modeling setup

All calculations of activities, saturation indices, and mineral equilibria were done using SpecE8 and Act2 programs within The Geochemist’s Workbench® software. Activities of dissolved ions (Ca2+, Mg2+, Na+, K+, Cl-,

91 - 2- 2- HCO3 , SO4 , Sr ) were calculated using the extended Debye-Hückel (B-dot) equation. This equation is suitable for waters of ionic strengths up to 3, but is less reliable above ionic strengths of 0.5. The ionic strength of all spring waters was less than 0.4 with the exception of AR01 (I=0.9), therefore this equation was deemed suitable. The default “thermo.dat” file was used for thermodynamic data, which is based mainly on the SUPRCT data compilation by Johnson et al. (1991). For all calculations, temperature was set to 2 °C and pressure was set to 1 bar. The activities of water and solid minerals were set to 1; calculated values for the activity of water confirm this assumption is reasonable.

5.4.2 Mineral saturation

The saturation index (SI) of a mineral is the logarithm of the ratio of the activity product of ions released by dissolution and the solubility product for the mineral dissolving, which is calculated from thermodynamic data. An SI of 0 indicates the water is saturated, or at equilibrium, with respect to that mineral, although due to uncertainties in thermodynamic data, a range from -0.5 to 0.5 is considered acceptable (Paces, 1976). Undersaturation (SI < -0.5) indicates that a mineral will not precipitate from solution and should dissolve. Oversaturation (SI > 0.5) indicates that the mineral has the potential to precipitate, or that it is not reactive in the system because if there are no kinetic barriers to its precipitation, activities of its constituents would be limited to saturation values (Deutsch, 1997). Carbonate minerals, however, can achieve an oversaturated state through an increase of temperature, the addition of a common ion, or through the loss of CO2 (Langmuir, 1997). The SI of spring waters with respect to many common rock-forming minerals was calculated (Table 5-3 and Figure 5-21). Many spring waters were at equilibrium with the carbonate minerals calcite, dolomite, and witherite; quartz; and the sulfate mineral barite. The Athabasca springs were also saturated with the sulfate minerals celestite, and gypsum, although the Clearwater springs were not. Only the carbonate mineral strontianite was oversaturated in nearly all springs.

Figure 5-21: Calculated saturation indices of spring waters for common minerals. Dotted lines indicate ±0.5, the range of SI indicating water-mineral equilibrium based on ion activities.

Table 5-2: Saturation indices of spring waters with respect to common rock- forming minerals. Shaded values are within the range of saturation (-0.5 to 0.5).

Mineral Formula Type AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 CW09

Anhydrite CaSO4 sulfate -0.77 -0.66 -1.72 -1.37 -1.12 -1.38 -1.37 -1.19 -1.12

Barite BaSO4 sulfate 0.22 0.30 0.52 0.67 0.14 0.26 0.53 0.24 0.46

Calcite CaCO3 carbonate -0.06 -0.61 -0.46 -0.63 -0.35 -0.14 0.02 -0.22 -0.80

Celestite SrSO4 sulfate -0.28 -0.29 -1.15 -0.81 -0.55 -0.68 -0.65 -0.53 -0.58

Dolomite CaMg(CO3)2 carbonate 0.69 -0.91 -0.17 -0.50 0.04 0.60 0.86 0.41 -0.78

Gypsum CaSO4•2H2O sulfate -0.47 -0.25 -1.31 -0.96 -0.72 -0.96 -0.96 -0.82 -0.74 Halite NaCl halide -2.19 -3.37 -3.76 -3.20 -2.95 -3.12 -2.99 -2.79 -2.91

Quartz SiO2 silicate 0.47 0.68 0.22 0.39 0.40 0.30 0.23 0.37 0.50

Strontianite SrCO3 carbonate 1.11 0.47 0.82 0.63 0.92 1.28 1.45 1.15 0.44 Witherite BaCO carbonate -0.08 -0.69 0.73 0.37 -0.13 0.46 0.88 0.18 -0.25 3

93 5.4.3 Mineral equilibria

If water is assumed to be in equilibrium with the minerals of an aquifer, the stability fields of those minerals can be described as functions of the activities of dissolved ions in the water (Garrels and Christ, 1965). Comparison between modeled equilibria and actual spring water ion activities reveals whether equilibrium reactions between minerals may control the concentrations of dissolved ions and the extent of dissolution/precipitation reactions. This method is used to investigate the processes controlling Ca and Mg concentrations in spring waters. Given the high abundance of calcite and dolomite in the Devonian carbonates, equilibrium between these minerals is considered first. Dolomitization is the process through which dolomite is formed through the alteration of calcite, following the reaction (Deer et al., 1966):

2+ 2+ 2CaCO3 + Mg à CaMg(CO3)2 + Ca (5-7)

To represent the Devonian carbonates, a simplified system containing CaO-

MgO-CO2-H2O was modeled. The equilibrium state in terms of the activities of Ca2+, Mg2+, and H+ is shown in Figure 5-22 with the stability fields for carbonate minerals. Although the spring waters closely follow a parallel slope of one, they plot above the stability line between calcite and dolomite, indicating that the activities of Ca and Mg in spring waters are not strongly controlled by equilibrium between these two pure end members. However, variations in the Ca/Mg ratio in both minerals could affect the position of the equilibrium line.

Figure 5-22: Spring waters plotted in terms of Mg and Ca activities, with stability fields for carbonate minerals in the system CaO-MgO-CO2-H2O at atmospheric pressure and 2 °C.

Another factor controlling Ca and Mg activities may be ion-exchange reactions on clay minerals, which exert an important control on water chemistry (Drever, 1997). Equilibrium exchange reactions between the aluminosilicate clays Ca- and Mg-smectite have been shown to control the activities of these ions in natural surface waters even when they are not the main constituents (e.g. Abercrombie, 1989; Grasby et al., 1999). The identification of argillaceous shales in the Waterways Formation (Norris, 1973) indicates that clay minerals are present in the host rock. However, Al, a common element in these clays, has low solubility in natural waters and its concentration is difficult to measure accurately (Hitchon et al., 1999). Therefore, the equilibrium reactions between the smectite clay end-members Ca- and Mg-beidellite expressed in Equation 5-8 was balanced on Al.

2+ 2+ 3Ca + 20[Mg0.165Al2.33Si3.67O10(OH)2] à 3Mg + 20[Ca0.165Al2.33Si3.67O10(OH)2] (5-8)

This cation exchange reaction was used in the equilibrium modeling of a system containing CaO-MgO-SiO2-Al2O3-H2O, to represent the Devonian carbonates with aluminosilicate clays present (Figure 5-23). The ion activities of Ca and Mg in the springs lie directly on the equilibrium boundary of these end- member clays. Therefore, despite the fact that these are not the major minerals in the system, exchange reactions between Ca- and Mg-smectites appear to control Ca and Mg activity ratios in the spring waters.

Figure 5-23: Spring waters plotted in terms of Mg and Ca activity ratios, with stability fields for smectite clays in the system CaO-MgO-SiO2-Al203-H2O at atmospheric pressure and 2 °C.

96 Further investigation into equilibrium cation exchange reactions between Na-, K-, Ca-, and Mg-beidellites, and into equilibrium between these smectites and the common clay minerals kaolinite and gibbsite did not reveal any further insight into other equilibrium processes controlling spring water chemistry. An example is given in Figure 5-24 for the system CaO-MgO-SiO2-

Al2O3-H2O, where none of the springs plot along equilibrium lines between stability fields for gibbsite, kaolinite, and Ca-beidellite. Thus, equilibrium cation exchange reactions between these clay minerals do not appear to control the concentrations of Ca and Mg in the springs. No further mineral equilibria were found, other than that between Ca- and Mg-smectite, that could account for major ion activity ratios in the spring waters.

Figure 5-24: Stability fields for aluminosilicate clays gibbsite, kaolinite, and Ca-

Beidellite in the system CaO-MgO-SiO2-Al2O3-H2O at atmospheric pressure and 2 °C.

97 Chapter Six: Trace components in spring waters

Understanding the trace concentrations of PAHs and elements introduced to river systems from saline groundwater in the Athabasca oil sands region is important for the mass balance approach to assessing potential impacts of development favoured in current monitoring plans (e.g. GOA and GOC, 2011). In this chapter, the concentrations of trace elements and PAHs, as well as the composition of dissolved gases, in spring waters are presented. The isotopic composition of methane is examined to determine its source and biogeochemical fate.

6.1 Trace Elements

Many elements were present in spring and river waters at trace concentrations (Table 3-4). Mostly metals, as well as some metalloids and non- metals, these were examined in three groupings: those with designated freshwater quality guidelines for the protection of aquatic life (PAL) determined by the Canadian Council of Ministers of the Environment (CCME, 2007), those listed as priority pollutants by the US Environmental Protection Agency (EPA, 2012), and those commonly associated with Athabasca oil sands bitumen. Generally, total concentrations of metals are not considered a reliable indicator of the environmental fate of metals, since the mobility and consumption of a metal in the water column is affected by both its phase and speciation (Guéguen et al., 2011). Parameters affecting the partitioning of metals into dissolved, adsorbed, and complexed phases include pH and the presence of other compounds such as suspended sediments and dissolved organic matter (Drever, 1997). These conditions will change as the spring waters mix with river waters, thus their fate in the rivers may not be predicted by their speciation and partitioning in the spring waters. Thus, for the purpose of this study, to quantify substances contributed to the river systems from these springs, total metal concentrations are adequate. Natural and anthropogenic effects on the trace metal concentrations in water and sediments of the Athabasca River and its tributaries have been the

98 subject of several studies (e.g. Conly et al., 2007; Headley et al., 2007; Kelly et al. 2010; Timoney and Lee, 2009). Bitumen is known to contain heavy metals (Allan and Jackson, 1977), therefore erosion caused by the Athabasca River and its tributaries incising through the bituminous McMurray Formation may be a natural source of metals to the rivers. However, in a study of three tributaries, Conly et al. (2007) found no effect of natural erosion of oil sands on the concentrations of metals in suspended and bed sediments. Kelly et al. (2010) also reported that oil sands erosion could not fully account for trace element concentrations in the Athabasca River and some tributaries. Potential anthropogenic influences on metal concentrations in the rivers include seepage from tailings ponds (e.g. Allan and Jackson, 1977; Timoney and Lee, 2009), air deposition from mining dust and oil sands processing (Kelly et al., 2010), and changes in phase partitioning due to increased DOC as a result of the bulk disturbance of peatlands (Guéguen et al., 2011). The saline springs of this study may be an additional source of trace elements to the Clearwater and Athabasca rivers that should be taken into account in the balance of natural versus anthropogenic effects on metal concentrations in the rivers.

6.1.1 Trace elements with water quality guidelines

Canadian water quality guidelines for the protection of aquatic life have not been developed for all metals that were analysed. Those for which CCME guidelines have been developed are listed in Table 6-1. Several guidelines were exceeded, both in spring and river samples. The springs with the most metals present at concentrations above guideline values were AR01 and CW08, with three exceedances each. Springs CW05 and CW08 had two metals above guideline concentrations. Springs AR03, CW01, and CW02 contained no metals above guideline concentrations. The concentration of boron was 1.1 to 3.5 times higher than the guideline value in five springs (AR01, CW03, CW07, CW08, CW09). The concentration of iron was 1.5 to 37 times higher than the guideline value in springs CW08, CW05, and AR01. Aluminum concentration was 1.5 times higher than the guideline value in spring CW09 and 4.1 times higher in spring CW08. Arsenic concentration was

99 twice the guideline value in spring CW05. Selenium was present only in spring AR01 and concentration was triple the guideline value. In the river samples, several metals were present above guideline values. It should be noted that PAL guidelines are broad and can be exceeded naturally in some systems (e.g. Caron et al., 2008), necessitating site-specific objectives (CCME, 2003). Local baseline conditions in the rivers need to be considered when examining these exceedances. For example, Headley et al. (2007) found high concentration of metals in the sediments of other tributaries to the Athabasca River in the region, and concluded the metals were naturally derived from sediment erosion. In the upstream Clearwater sample, only Cd and Fe concentrations exceeded guideline values, by 2.5 and 1.8 times, respectively. In the downstream Clearwater sample guideline concentrations were exceed for Fe by 3 times and for Al by 1.5 times. In the upstream Athabasca sample, concentrations exceeded guideline values for Al by 10 times, Cd by 6.8 times, Cu by 1.8 times, and Fe by 8.9 times. In the downstream Athabasca sample, only Al and Fe concentrations exceeded guideline values, by 1.7 and 2.1 times, respectively.

Table 6-1: Concentrations of metals (g/L) for which PAL water quality guidelines have been developed (CCME, 2007), listed in second column in g/L (WQG). Some guidelines depend on other parameters such as hardness or pH and therefore varied for each sample; these guidelines were determined for each sample using an online calculator (CCME, 2007) and are indicated by (**). Greyed values exceed guidelines. Less-than-detect values are indicated by 'LTD'.

WQG AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 CW09 RAR01 RAR02 RCW01 RCW02 Ag 0.1 0.033 LTD LTD 0.031 LTD 0.011 0.009 0.006 0.004 0.009 LTD 0.004 LTD Al ** 79.9 LTD LTD 11.4 LTD 13.7 LTD 411 7.4 1050 174 15 151 As 5 0.09 LTD LTD 0.14 LTD 9.63 0.04 0.16 0.31 1.22 0.49 0.23 0.56 B 1500 5210 989 1080 1040 1720 1400 2570 2470 2000 8.8 16.6 7.7 28.1 Cd ** 0.168 0.015 0.029 0.041 0.099 0.047 0.017 0.18 0.081 0.075 0.017 0.111 LTD Cu ** 1.17 0.92 0.68 8.96 0.83 1.25 1 1.38 1.02 3.57 1.67 0.87 1.3 Fe 300 11200 5.2 LTD 165 LTD 9170 6.3 443 10.8 2620 625 529 947 Mo 73 0.033 LTD LTD 0.109 LTD 0.106 LTD LTD LTD 0.567 0.817 0.089 0.178 Pb ** 0.141 0.132 0.209 0.92 0.159 0.182 0.142 0.604 0.173 1.62 0.276 0.037 0.22 Se 1 2.98 LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD Tl 0.8 LTD LTD 0.016 0.012 0.001 LTD 0.009 LTD LTD 0.02 LTD 0.002 0.013 U 15 0.0718 0.0242 0.0454 0.0428 0.05 0.0599 0.0668 0.0914 0.0172 0.52 0.304 0.0101 0.0615 Zn 30 2.5 1.3 1.2 22.8 1.4 4 1.3 5.7 1.7 11.1 2.9 1.9 2.5

100 6.1.2 EPA Priority Pollutants

The EPA list of priority pollutants (PPE) under the US Clean Water Act includes 13 elements that may endanger the environment or human health: Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl, and Zn (EPA, 2012). In a study of these PPE in the Athabasca River and tributaries as well as the snowpack, Kelly et al. (2010) concluded their concentrations were affected by air deposition from oil sands processing. Kelly et al. (2010) also suggested that sediment erosion and seepage from tailings ponds may contribute some of these elements to the river systems. Groundwater inputs, such as the saline springs in this study, could be another source of these priority pollutants to the rivers. All PPE, with the exception of Hg, were measured in spring and river waters (Table 6-2).

Table 6-2: Concentrations of elements on the EPA list of priority pollutants (PPE) in g/L. Shaded values indicate an exceedance of CCME PAL water quality guideline values (WQG), also in g/L. Less-than-detect values are indicated by 'LTD'.

PPE WQG AR01 AR03 CW01 CW02 CW03 CW05 CW07 CW08 CW09 RAR01 RAR02 RCW01 RCW02 Ag 0.1 0.033 LTD LTD 0.031 LTD 0.011 0.009 0.006 0.004 0.009 LTD 0.004 LTD As 5.0 0.09 LTD LTD 0.14 LTD 9.63 0.04 0.16 0.31 1.22 0.49 0.23 0.56 Be - 0.204 0.047 0.032 0.045 0.092 0.064 0.118 0.11 0.066 0.081 0.005 0.004 0.005 Cd ** 0.168 0.015 0.029 0.041 0.099 0.047 0.017 0.18 0.081 0.075 0.017 0.111 LTD Cr 1 53 1.15 0.59 1.72 1.13 0.86 0.18 1.83 1.27 2.17 0.58 0.35 0.86 Cu ** 1.17 0.92 0.68 8.96 0.83 1.25 1.0 1 38 1.02 3.57 1.67 0.87 1.3 Ni 2.16 0.75 0.43 2.39 0.68 2.02 0.54 1.43 0.83 4.16 1.8 0.24 1.31 Pb 0.141 0.132 0.209 0.92 0.159 0.182 0.142 0.604 0.173 1.62 0.276 0.037 0.22 Sb 0.158 0.076 0.028 0.203 0.066 0.058 0.068 0.068 0.084 0.102 0.068 0.013 0.05 Se 1.0 2.98 LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD Tl 0.8 LTD LTD 0.016 0.012 0.001 LTD 0.009 LTD LTD 0.02 LTD 0.002 0.013 Zn 30.0 2.5 1.3 1.2 22.8 1.4 4.0 1.3 5.7 1.7 11.1 2.9 1.9 2.5

Most PPE were found in similar concentrations in many springs, suggesting a common origin in the spring waters. Weathering of rocks is a common natural source of metals in groundwater (Drever, 1997), and the weathering of Devonian carbonates and evaporites discussed in Chapter 5 is a likely source of trace metals in the spring waters. However, a few differences between springs were evident (Figure 6-1). Spring CW02 had higher concentrations of Cu (8.96 g/L), Zn (22.8 g/L), Pb (0.920 g/L), and Cd (0.041 g/L) than other springs. Spring CW08 also had higher concentrations of Zn (5.7 g/L), Pb (0.604 g/L), and Cd (0.180 g/L) than most spring waters. Spring

101 CW05 had a relatively high concentration of As (3.01 g/L), exceeding PAL guidelines, but otherwise had a similar PPE composition to the other springs. Spring AR01 was the only spring containing Se, and at 2.98 g/L it exceeded PAL guidelines. Spring AR01 also had among the highest concentrations of Cr, Ni, Be, Cd, and Sb. As discussed in Chapter 5, the sulfate in this spring is sourced from sulfide oxidation as opposed to evaporite dissolution; this process can be accompanied by the release of metals from sulfide minerals (Clark and Fritz, 1997) and may account for some differences in metal concentrations between spring AR01 and the rest of the springs. Differences in PPE concentrations between springs are not consistent among elements and do not correlate with TDS, therefore cannot be explained by dilution by fresh waters. Overall, the difference in PPE composition in springs AR01, CW02, CW05, and CW08 from the other springs may indicate a different or additional source of PPE to these springs. The river samples had varying concentrations of PPE. Zn, Ni, and Pb were higher in both Athabasca samples than most spring waters. All PPE concentrations decreased downstream in the Athabasca River. This may be due to dilution by increased flow downstream in the watershed (Minshall et al., 1985). However, this trend should be treated with caution, because as discussed in Chapter 4, this site may not have been representative of upstream conditions due to its proximity to Fort McMurray and a golf course. In the Clearwater River, concentrations of most PPE were similar to those in spring waters and increased downstream with the exception of Cd and Ag, which were not detectable in the downstream samples. Contributions of PPE from the springs may be responsible for at least part of the increase in concentrations in the Clearwater River. Other inputs from tributaries, groundwater, overland flow, sediment, and aerial deposition may also influence PPE concentrations in the rivers.

102

Figure 6-1: Concentrations of PPE in spring and river waters in !g/L. Black bars represent spring waters, grey bars represent river waters.

6.1.3 Elements associated with oil sands

Oil sands deposits overly the Devonian carbonates from which these springs emerge. If shallow groundwater contributions to spring waters flows through or along oil sands deposits, the trace elements present in bitumen may also be present in spring waters. Shallow groundwater may also be influenced by the air deposition of metals from mining dust and oil sands processing. The predominant heavy metals in oil sands are nickel, vanadium, and iron (Allan and Jackson, 1997). Other minor elements found in oil sands include As, Hg, Se, and

103 Zn (Hitchon, 1993). No spring contained measurable concentrations of V. However, Ni was present in all springs and Fe was present in most springs (Figure 6-2). Spring AR01 contained several metals found in bitumen (Fe, Ni, Zn, and Se) suggesting oil sands are a possible source of metals to this spring. This is consistent with visual observations at the sampling site of an oily sheen on waters and pieces of bituminous McMurray Formation present at the surface. Spring CW05 also contained four metals (Ni, Zn, As, Fe) common to bitumen suggesting possible interaction with oil sands. No other spring contained more than two metals common to the oil sands in appreciable concentrations. Thus, the trace element chemistry in most spring waters do not seem to be affected by the overlying bitumen deposits. All river samples contained the three predominant oil sands metals (Ni, V, Fe) as well as As and Zn. In the Clearwater River, the concentrations increased downstream with increased proximity to the oil sands developments. In the Athabasca River, concentrations decreased downstream. There are many potential sources of these metals to the river systems including input from groundwater, sediment erosion, tributaries, and air deposition of dust and emissions from mining developments. True background concentrations of oil sands-related metals are not known in these river systems, because widespread air deposition of PPE over the landscape over the last ~40 years of mining and upgrading has likely influenced shallow groundwater and runoff and therefore river concentrations (Kelly et al., 2010).

104

Figure 6-2: Concentrations of metals associated with bitumen in spring and river waters, in ! g/L. Black bars represent spring waters, grey bars represent river waters.

6.2 PAHs

Nearly ubiquitous in nature, PAHs are non-polar organic compounds containing two or more fused benzene rings (Neff, 1979). Compounds with less than 4 benzene rings (e.g. naphthalene, fluorene, phenanthrene) are considered to be low molecular weight PAHs, while compounds with 4 or more rings are considered to be of high molecular weight (e.g. chrysene, perylene). PAHs usually occur in complex assemblages of hundreds of related compounds, spanning a wide range of properties (Neff et al., 2005). As a trace contaminant, PAHs are of concern because some are carcinogenic, mutagenic, or toxic (Walker, 2001). Of the hundreds of PAH compounds, 16 appear on the EPA list of priority pollutants (EPA, 2012). Hydrophobic by nature, the solubility of PAHs decreases with increasing molecular weight and increases with the presence of alkyl groups in the molecular structure (Neff, 2002). High molecular weight PAHs have a tendency to bind to DOC, thereby increasing in solubility in the presence of DOC (Youngblood and Blumer, 1975). The increase of DOC caused by peatland

105 disturbance in oil mining (Guéguen et al., 2011) could influence the solubility of PAHs in the Athabasca River and its tributaries. Removal of PAHs from the water column occurs via sorption to particulates, volatization for low molecular weight compounds, photodegredation for high molecular weight compounds, and biodegradation (CCME, 1999). The sources of PAHs, either natural or anthropogenic, can be classified into three groups: fossil fuels (petrogenic), burning of organic matter (pyrogenic), and transformations of organic matter through diagenic processes (biogenic) (Neff, 1979; Neff et al., 2005). Pyrogenic and petrogenic sources can be distinguished by the distribution of alkylated versus non-alkylated (parent) PAHs (Stout et al., 2001). These two sources may also be distinguished by the dominant compounds present: petrogenic PAHs are dominated by low molecular weight compounds, while pyrogenic PAHs are dominated by heavy molecular weight compounds (Neff et al., 2005). In addition, alkylated compounds dominate petrogenic PAHs, while parent compounds dominate pyrogenic PAHs (Neff et al., 2005). Kelly et al. (2009) analyzed bitumen from the Athabasca oil sands and found it to be dominated by alkylated low molecular weight PAHs (phenanthrenes, dibenzothiphenes, and fluorenes), which is consistent with a petrogenic source. In the Athabasca oil sands region, natural erosion of the McMurray formation has distributed hydrocarbons throughout the rivers in the area (Headley et al., 2001). The sources of PAHs in water and sediments of the Athabasca River and its tributaries have been investigated by several researchers (Headley et al., 2001; Conly et al., 2002; Akre et al., 2004; Timoney and Lee, 2009; Kelly et al., 2009). Headley et al. (2001) found the total concentration of PAHs in sediment to be higher in tributaries than in the Athabasca River main stem, and identified a petrogenic source, likely natural erosion of oil sands. In tributaries affected by oil sands development, both Timoney and Lee (2009) and Kelly et al. (2009) found a relationship between increased oil sands development and dissolved PAH concentrations, with PAH assemblages reflecting a petrogenic source. Kelly et al. (2009) also found air deposition of pyrogenic PAHs from oil sands upgrading to be a significant source of pollution to the landscape. Seepage

106 from tailings ponds is another possible source of PAHs in the rivers (Timoney and Lee, 2009). The contribution of PAHs from saline groundwater to the Athabasca River and its tributaries has not yet been considered. The analysis suite of PAHs did not contain many alkylated PAHs making the identification of source difficult. However, the assemblage of parent PAHs is useful to characterize the contribution of PAHs from saline groundwater to the river systems. The concentration of total PAHs in spring waters ranged from 7.3 ng/L to 273.6 ng/L and in river waters from 18.0 to 337.6 ng/L (Figure 6-3). Of the twelve PAHs detected, six are listed as EPA priority pollutants: chrysene, fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene (EPA, 2012). Five have been assigned interim PAL water quality guidelines (CCME, 1999), none of which was exceeded (Table 6-3).

Figure 6-3: Concentration of total PAHs in spring and river waters, in ng/L.

107 Table 6-3: Concentrations of detectable PAHs in spring and river waters (ng/L). PAHs were not analyzed in spring CW07. PAHs on the EPA priority pollutant list are marked with (*) in the second column (EPA). Interim PAL water quality guidelines (ng/L) are listed in the third column (WQG) (CCME, 1999). Non-detect values are indicated by 'LTD'.

PAH (ng/L) EPA WQG AR01 AR03 CW01 CW02 CW03 CW05 CW08 CW09 RAR01 RAR02 RCW01 RCW02 chrysene * 5.8 LTD LTD LTD LTD LTD LTD LTD 8.3 3 9 LTD 4.3 fluoranthene * 40 13.4 9.7 LTD LTD LTD LTD LTD LTD 17.8 12.1 LTD 17.7 fluorene * 3000 17.9 10.1 LTD LTD LTD LTD LTD LTD 18.3 12.5 LTD 22.1 indene LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD LTD 5.2 naphthalene * 1100 170 57 10 LTD 6 10 18 LTD 168 145 9 227 1-methylnaphthalene 12.7 LTD LTD LTD LTD LTD LTD LTD 16.7 9.6 LTD 18.7 2-methylnaphthalene 21.0 8.4 LTD LTD LTD LTD 7.6 LTD 27.3 15.2 LTD 29.9 1,2,3,4- tetrahydronaphthalene LTD LTD LTD LTD LTD LTD LTD LTD 8.5 6 3 LTD LTD perylene LTD LTD LTD LTD LTD LTD LTD LTD 15.2 LTD LTD LTD phenanthrene * 400 32.8 21.0 9 3 7.3 9.3 8.9 9.4 10.0 38.5 25.5 9.0 38.6 pyrene * 25 LTD LTD LTD LTD LTD LTD LTD LTD 4.6 LTD LTD LTD retene LTD LTD LTD LTD LTD LTD LTD LTD 14.4 LTD LTD LTD total PAH concentration 273.6 105.9 19.0 7.3 15.5 19.1 35.2 10.0 337.6 230.1 18.0 363.5

6.2.1 Spring waters

The Athabasca spring waters contained more individual PAHs at higher concentrations than the Clearwater springs (Table 6-3). Phenanthrene was the only PAH present in all spring samples, while naphthalene was present in four Clearwater springs and both Athabasca springs. The Athabasca springs also contained the light PAHs fluoranthene, fluorene, and methylnaphthalenes. In addition, AR01 contained chrysene, a high molecular weight PAH. The difference in PAH assemblages suggest that the Athabasca springs may have a different or additional source of PAHs than the Clearwater springs. The dominance of phenanthrene in the spring waters is consistent with its dominance in tributary sediments (Headley et al., 2001), bitumen, and air deposited PAHs (Kelly et al., 2009). However, naphthalene, dominant in several springs, is nearly absent in bitumen but is present in air deposited PAHs (Kelly et al., 2009). The same is true for fluorene and methylnapthalenes, light molecular weight PAHs found in the Athabasca springs. This suggests that air deposition of PAHs from upgrading emissions, rather than oil sands weathering, may be the source of PAHs to the spring waters. Air-deposited PAHs could be introduced to the springs through infiltration and shallow groundwater contributions to the springs. The lower concentrations of PAHs in the Clearwater

108 springs may reflect the greater distance from emission sources than the Clearwater springs, resulting in less deposition. However, dibenzothiopene, a sulfur-containing PAH which is present in air deposition (Kelly et al., 2009), is absent in the springs. If PAHs in the springs are due to air deposition on the surface, this compound must have been attenuated in the subsurface. In order to identify the source of PAHs with more certainty, alkylated PAH concentrations would need to be determined and compared with parent PAHs to determine a pyrogenic or petrogenic source.

6.2.2 River waters

In general, the river samples contained more individual PAHs than the spring waters, with the exception of the upstream Clearwater sample, which contained only naphthalene and phenanthrene. The total PAH concentration increased downstream in the Clearwater from 18 to 363 ng/L with an additional 6 PAHs in the downstream sample. Naphthalene and phenanthrene concentrations increased from 9 to 227 ng/L and from 9 to 39 ng/L respectively. Given that the Clearwater springs contained only naphthalene and phenanthrene, and 1-methylnaphthalene (in CW08 only), the increase in river concentrations of these compounds may be partially attributed to the springs, but they cannot be the sole source of total PAHs to the Clearwater River. Conly et al. (2001) determined that it is unlikely that oil sands material is added to the Clearwater River, nor its main tributary the Christina River, through erosion of the McMurray Formation. This leaves air deposition of PAHs onto the landscape and their eventual release into the river through runoff and shallow groundwater recharge as a possible source of increased PAHs in the downstream Clearwater site. The Athabasca River decreased in total PAH concentration downstream. Perylene, pyrene, and retene, PAHs that were found only in the Athabasca upstream site, decreased to below detection in the downstream site. All other detectable PAHs decreased in concentration between the two sites (Figure 6-4). Four PAHs were present in the Athabasca upstream sample and one in the downstream sample that were not present not in the springs, indicating that the

109 saline springs are not the sole source of total PAHs to the Athabasca River, particularly at the upstream end of the study area. The decrease in total PAH concentration over the study reach may be due to the proximity of the upstream site to Fort McMurray and oil sands mining and upgrading activity. However, as previously discussed, the upstream Athabasca site may not be ideal for identifying downstream trends.

Figure 6-4: Concentration of individual PAHs in spring and river waters (ng/L).

110 6.3 Dissolved gases in spring waters

The composition of dissolved gases was measured only in the spring waters. The δ13C value of methane was determined in 7 spring waters but, due to 2 the small quantities of dissolved methane, the HCH4 value was measured in only 5 samples. The relative concentrations of gases and the isotopic composition of methane give insights to subsurface processes that have affected spring waters.

6.3.1 Composition

The three main components of the dissolved gas in the springs were nitrogen, carbon dioxide, and methane (Figure 6-5). Potential contamination of samples by atmospheric gases can be identified by the N2/Ar ratio (Littke et al.,

1995). In dry atmosphere the N2:Ar ratio is around 83; in the spring waters this ratio ranged from 42 to 85. Only spring CW08 had a N2:Ar ratio near that of atmosphere, indicating possible contamination. Nitrogen dominated the dissolved gasses in all springs, accounting for 70 to 96% of all dissolved gas content. With the exception of spring CW09 (70%), N2 was present in higher proportions in spring waters than in the atmosphere, which contains 78% N2. Though nitrogen-rich gas is ubiquitous in oil and gas bearing basins, determination of its origin has been controversial (Zor’kin et al., 1977). There are many potential sources for nitrogen gas in natural gas accumulations such as atmospheric N2, mantle degassing, radiogenic processes, volcanoes, and rock weathering, but the most important source may be the decomposition of mature organic matter (Littke et al., 1995). This source is plausible for the springs, being on the edge of the WCSB, a major oil and gas bearing basin. Carbon dioxide was the second most dominant dissolved gas in the spring waters. Ranging from approximately 2 to 27% of dissolved gas, it accounted for particularly high proportions of the gases found in AR03 (14%) and CW09 (27%).

The partial pressure of CO2 is often higher than in the atmosphere in limestone aquifers, and is controlled by the soil CO2 in the recharge area (Drever, 1997). In the carbonate aquifer hosting the springs, modern recharge through the soil zone

111 is a source of dissolved CO2. Springs CW09 and AR03 contained almost no glacial meltwater according to H and O isotopes (Chapter 4), and also had the highest proportion of CO2. It is possible that the high proportion of modern recharge in these springs has provided more soil CO2 to these springs, although 13 δ CDIC values indicate it has been affected by fractionation likely through methanogenesis (Chapter 5). Methane was the third most common dissolved gas in the spring waters, although it was present at low concentrations of less than 0.06 mmol/L. It usually accounted for <1% of dissolved gases, with the exceptions of springs CW09 (1.1%) and AR03 (4.0%). Methane has a low solubility (~2mmol/L at 0°C), which decreases with increasing salinity (Clark & Fritz, 1997), therefore high concentrations would not be expected in these saline springs. In addition, methane is often present at only trace levels when sulfate is present or BSR is occurring (Whiticar, 1999), unless it has migrated from a different source area. One source of methane can be microbial, through either fermentation of organic matter or carbonate reduction, summarized simply as (Clark and Fritz, 1997):

2Corganic + 2H2O à CH4 + CO2 (6-1)

Methanogenesis in the subsurface is a process that can add CO2 to the system. So dissolved CO2 in spring waters is likely a mixture of soil water CO2 from modern recharge and CO2 produced through methanogenesis in the subsurface.

112

Figure 6-5: Dissolved gas composition of spring waters in mole percent. The composition of dry air is included for reference.

6.3.2 Isotopic composition of CH4 There are two main formation pathways of methane in the subsurface: microbial production and thermogenic production (Horita & Bernt, 1999). Whiticar (1999) demonstrated that the isotopic composition of methane could be used to distinguish between thermogenic, bacterial carbonate reduction, and 13 bacterial fermentation pathways. δ CCH4 values were determined in seven 2 samples, but δ HCH4 values were determined in only five samples, due to the low 13 concentration of methane available for analyses. The δ CCH4 values ranged from 2 -62.6 to -44.4‰, and the δ H CH4 values ranged from -219 to -65‰ (Table 3-7). The isotopic composition of methane in spring waters was plotted with the isotopic signature of methane sources on Whiticar’s (1999) diagram of δ13C versus δ2H (Figure 6-6). Of the five springs that had enough data to be plotted,

113 only CW09 fell clearly in a defined source zone, that of bacterial carbonate reduction. During this processes, the reduction of CO2 to produce methane requires an organic substrate and can be described by the following reaction (Whiticar, 1999):

+ CO2 + 8H à CH4 + 2H2O (6-3)

The isotopic composition of produced methane depends partially on the δ13C 2 values of the CO2 and the organic substrate, and the H value of co-existing water, and isotope fractionation (Kotelnikova, 2002). Therefore, the delineations in Whiticar's (1999) source diagram may not be universal. For example, 13C- enriched sources of CO2 have been reported to produce biogenic methane with δ13C values as high as -40‰ (Kotelnikova, 2002, and references therein), which is 13 near the δ CCH4 of several springs (CW01, CW03, CW08). However, there is a 13 2 trend of increasing CCH4 with increasing HCH4 values in the spring waters (Figure 6-6). This may indicate that a secondary process, such as methane oxidation, has altered the original methane produced via CO2 reduction. Methane oxidation is a microbial process that preferentially consumes 12C, 13 leaving the residual CH4 enriched in C (Barker & Fritz, 1981). This process can 2 2 also enrich residual methane in H (Whiticar, 1999). The HCH4 values in springs CW01, CW03, and CW08 ranged from -65 to -67‰, which is higher than 2H values expected from any of the source ranges given by Whiticar (1999). If the methane in all the springs was created by bacterial carbonate reduction, with methane from spring CW09 as the least-altered, methane oxidation could cause the observed increase in 13C and 2H values seen in Figure 6-6.

114

Figure 6-6: Isotopic composition of methane in spring waters plotted with sources ranges. Modified from Whiticar (1999).

13 Comparison of the δ CCH4 value in spring waters to that of methane found in other parts of the WCSB reveals some similarities. Methane from other Upper Devonian formations in the WCSB had reported δ13C values around -45.0‰ (James, 1990). Methane coexisting with bitumen in Cretaceous sediments in the oil sands region had reported δ 13C values varying from -49 to -32‰ (Jha et al., 13 1979). The δ CCH4 values in springs CW01, CW02, CW03, CW07, and CW08 13 ranged from -44.4 to -48.0‰, within the range of δ CCH4 values found in Cretaceous geologic units that overly the Devonian carbonates hosting the springs. This may suggest that methane in these springs is from the same source, or that methane in these overlying geologic units has undergone the same amount of oxidation.

115 The water used in methane production can be identified through 2 hydrogen isotopes. The HCH4 value is derived from only two sources, organic matter or water (Schoell, 1980). In the case of bacterial carbonate reduction, all the hydrogen is sourced from co-existing formation water and the relationship 2 2 between HH2O and HCH4 is relatively consistent in various environments with the 2H value of methane being 160 to 180‰ lower than that of the water 2 (Whiticar, 1999). Comparing the H values of methane and spring water, no clear relationship is apparent (Figure 6-7). The 2H value of methane ranged from 70‰ lower to 107‰ higher than that of coexisting spring waters, suggesting either that it was not formed from these waters, or that it has been substantially altered by isotope fractionation. Methane is a highly mobile molecule (Schoell, 1980), therefore it is possible that the methane found in the spring waters was formed from other waters and has migrated from elsewhere in the WCSB to discharge with the spring waters.

Figure 6-7: 2H values of methane and co-existing spring waters.

116 Formation waters in the upper Devonian units of the WCSB have an average 2H value of -82‰ (Connolly et al., 1990b), which would produce methane with expected 2H values between -242‰ and -262‰. However, the 2 lowest HCH4 value in the springs was -219‰ in spring CW09; therefore, even in this spring a secondary processes such as oxidation must have increased the 2 HCH4 value. Further oxidation of methane in the rest of the spring waters would 13 2 be necessary to account for the higher δ CCH4 and HCH4 values in these springs. Methane oxidation has been shown to be coupled with bacterial sulfate reduction under anaerobic conditions in marine sediments (eg. Claypool and Kvenvolden, 1983) as well as in groundwater (Van Stempvoort et al., 2005). There is evidence of both processes in the spring waters, although determination of whether they are coupled would require further investigation. Further clarity on the source of methane and the similarity or difference with methane found elsewhere in the WCSB could be achieved through further isotopic analyses of dissolved gases. The isotopic composition of CO2 and its isotopic separation from methane can be diagnostic of bacterial CO2 reduction as a methane source (Whiticar, 1999). In addition, isotopic ratios of ethane, the only other hydrocarbon gas present in the spring waters, could be used to further decipher the source of methane (James, 1990), and to identify bacterial methane oxidation (James & Burns, 1984).

117 Chapter Seven: Influence of saline groundwater on river water quality

One issue to be addressed by water quality monitoring efforts in the Athabasca oil sands region is the quantification of natural inputs of substances to the river systems from groundwater discharge. The mass fluxes of major ions, trace elements, and PAHs from saline groundwater from Devonian carbonate rocks into the Clearwater and Athabasca rivers are estimated in this chapter. A chloride isotope mass balance calculation enables the determination of average groundwater flow rates in the study area. Average flow rates are used in conjunction with historical water quality data as well as data from this study to estimate the annual mass flux of constituents from saline groundwater into the rivers. Fluxes are expressed as percentages of the average mass flux of constituents in the rivers to quantify the impact of saline groundwater on the water quality of these rivers.

7.1 Cl isotope mass balance

The conservative nature of chloride stable isotopes (Clark and Fritz, 1997) allows the fraction of Cl in the river sourced from saline springs to be determined through an isotopic mixing model. Precipitation contributes Cl to rivers (Volpe et al., 1998; Koehler and Wassenaar, 2010), but the major sources of Cl to most rivers are groundwater contributions and anthropogenic influences such as road salt and industrial process water (Jasechko et al., 2012). If anthropogenic influences are minimal, as is the case on the Clearwater River, a two-end member mixing model can be employed between Cl sourced from precipitation with negative δ37Cl values (Volpe et al., 1998; Koehler and Wassenaar, 2010), and Cl from groundwater influenced by evaporite dissolution with positive δ37Cl values (Kaufman et al., 1984; Eggenkamp et al., 1995). In this scenario, Cl found in the river upstream of the study area as well as in runoff, shallow groundwater, and tributaries is considered to have a similar negative δ37Cl value which is close to that of precipitation because of proximity to the headwaters and the absence of Cl sources to these waters. On the other hand, groundwater affected by evaporite

118 dissolution, such as that discharging at the saline springs, is expected to have a positive δ37Cl value that reflects the isotopic composition of the evaporites. In Equation 7-1, the total mass flux of Cl in the downstream river sample,

Fds, is considered to be the sum of the flux of Cl from these two sources: saline groundwater affected by evaporite dissolution (Fgw), and precipitation in the upstream sample, tributaries, shallow groundwater, and throughflow, all of 37 which should have similar δ Cl values (Fus):

Fds = Fus + Fgw (7-1)

Given linear mixing and no isotopic fractionation, the Cl isotope ratio in the 37 downstream river sample (δ Clds) can thus be represented by the following 37 isotope mass balance equation, where δ Clus is the isotopic value of Cl in the 37 upstream river sample and δ Clgw is the isotopic value of Cl in evaporite- dissolution groundwaters:

37 37 37 Fdsδ Clds = Fusδ Cl us + Fgwδ Cl gw (7-2)

Combining equations 7-1 and 7-2, the fraction of Cl sourced from evaporite dissolution over the study reach (Fgw) can represented by:

(7-3)

The fraction of Cl in the river attributable to saline groundwater in the downstream river samples can then be used to calculate the proportions of other major ions in the river that may be attributed to saline groundwater inputs. This is shown in Equation 7-4, where the ratio of the average concentrations in spring waters of a major ion (Mgw) to Cl (Clgw) is multiplied by the downstream Cl concentration in the river (Clds) and Fgw to determine the concentration of the major ion in the river contributed from saline groundwater (Mds-gw):

119

(7-4)

Uncertainties imbedded in individual parameters may be compounded in these mass balance calculations. The parameter with the largest impact is the δ37Cl measurements, with an uncertainty of 0.1‰. When comparing two δ37Cl measurements, as in Equation 7-3, the uncertainty increases to 0.14‰. The relative uncertainty in the fraction of Cl attributable to groundwater in the rivers 37 (Fgw) is dependent on the values of δ Cl in the river samples and the difference between them, which in the Athabasca River is not much larger than the uncertainty of the measurements. The relative uncertainty in the measurement of major ion concentrations is low by comparison at 5%. Therefore, the uncertainties in the concentrations of major ions Mds-gw calculated from Equation 7-4 vary between the two rivers, and are dominated by the magnitude of the difference between upstream and downstream δ37Cl values compared with the measurement uncertainty of δ37Cl.

7.1.1 Clearwater River

On the Clearwater River there are no point sources of industrial process water and very few roads that may be a source of road salt. Therefore the assumption made in Equation 7-1 is upheld; that is, there are only two main sources of Cl: precipitation and saline groundwater affected by evaporite dissolution. The fraction of Cl sourced from evaporite dissolution was calculated according to Equation 7-3, using the average δ37Cl value of all spring waters of 37 37 0.7‰ (δ Clgw), and the measured upstream and downstream δ Cl values in the river of -2.3‰ and -1.4‰ respectively. The resulting fraction of Cl in the downstream sample sourced from saline groundwater is approximately 30 ± 5%. The downstream Clearwater sample in October 2010 contained 23.1 mg/L of Cl, therefore approximately 6.9 ± 1.3 mg/L of Cl in this sample was sourced from saline groundwater discharging into the river or tributaries along the study reach.

120 In order to determine the fraction of other major ions in the downstream Clearwater sample attributable to saline groundwater using Equation 7-4, the average molar ratio of each major ion to Cl was first calculated for all spring waters. However, the mean SO4:Cl ratio excluded spring AR01 because the isotopic composition of SO4 in this spring revealed a different source of SO4 than the rest of the springs (see Chapter 5). The resulting calculated concentration in mg/L of each major ion attributable to saline groundwater (Table 7-1) has a relative uncertainty of 20%. The proportion of each ion attributable to saline groundwater is also expressed as a percentage of the concentration in the downstream sample. These calculations reveal that an estimated 25% of Na, 26% of SO4, and 10% of Sr in the Clearwater River may be attributed to saline groundwater input over the study reach. Saline groundwater also accounts for approximately 2% each of Ca and Mg, 1% of K, and 0.5% of

HCO3 in the river.

Table 7-1: Contribution of major ions from saline groundwater to the Clearwater River over the study reach, calculated using Cl isotope mass balance. Relative uncertainty in the calculated concentration in river from saline groundwater is 20%.

concentration mean ratio concentration in concentration in proportion in river ion:Cl river from river from in river from major downstream in saline saline saline ion sample all springs groundwater groundwater groundwater (mmol/L) (mol/mol) (mmol/L) (mg/L) Cl 6.5E-01 1 2.0E-01 6.9 30% Na 7.8E-01 1 2.0E-01 4.5 25%

SO4 4.9E-02 0.07 1.1E-02 1.0 26% Sr 1.0E-03 0.001 9.8E-05 0.01 10% Ca 4.7E-01 0.05 8.5E-03 0.3 2% Mg 2.4E-01 0.03 5.9E-03 0.1 2%

HCO3 1.3E+00 0.03 7.0E-03 0.4 0.5% K 3.4E-02 0.002 4.8E-04 0.02 1%

121 7.1.2 Athabasca River

Calculations of a Cl isotope mass balance were repeated for the Athabasca River using Equation 7-3. The average δ37Cl value of spring waters of 0.7‰ 37 37 (δ Clgw) was used with the δ Cl values of the upstream and downstream Athabasca River samples of -1.8‰ and -1.5‰, respectively. The resulting fraction of Cl in the downstream sample sourced from saline groundwater is approximately 12 ± 6%. The relative uncertainty for this estimate is high at 50% and is due to the very small difference between upstream and downstream δ37Cl values in the Athabasca River which was only twice the standard measurement error of δ37Cl. In addition, this estimate should be treated with caution due to the assumptions made in Equation 7-1. The assumption of no point sources of Cl may not be valid; possible anthropogenic sources of Cl on this stretch of the Athabasca River include road salt, as there are more roads near the Athabasca River than the Clearwater River, and potential seepage of saline water from tailings ponds along the river. Unfortunately the δ37Cl values of anthropogenic sources of Cl are often indistinguishable from the δ37Cl values from halite dissolution in saline groundwaters (Koehler and Wassenaar, 2010). If present, anthropogenic sources of Cl would result in an overestimate of saline groundwater input using Equation 7-3. Conversely, the assumption made in Equation 7-2 that the δ37Cl value of the upstream sample would be similar to that of precipitation, tributaries, runoff, and shallow groundwater may not be valid. The upstream Athabasca sample has a higher δ37Cl value than the upstream Clearwater sample (and than that expected in precipitation) due to the great distance from the headwaters and input of Cl to the river upstream of the study area. If tributaries, runoff, and shallow groundwater in fact have similar δ37Cl values to precipitation as assumed for the Clearwater River, these sources would introduce Cl with lower δ37Cl values than that of the upstream sample, and disregarding them in Equation 7-2 would lead an underestimate of saline groundwater input. Ideally, additional terms would be added to Equations 7-1, 7-2, and 7-3 to eliminate these uncertainties. However, for the purposes of this study, the contribution of saline

122 groundwater input to the Athabasca River over the study reach is estimated at 12 ± 6%. This proportion of saline groundwater input to the river was employed in Equation 7-4 to determine the concentrations of major ions present in the downstream river sample attributable to saline groundwater inputs (Table 7-2). The calculated concentrations of ions sourced from saline groundwater and the calculated percentage of downstream concentrations carry a relative uncertainty of 50%. An estimated 6% of Na, 1% each of SO4 and Sr, and ≤ 0.3% of Ca, Mg,

HCO3, and K in the Athabasca River can be attributed to saline groundwater input over the study reach. The proportions of major ions sourced from saline groundwater over the study reach are much smaller in the Athabasca River than in the Clearwater River. This is due to differences in both river discharge, which is roughly 1.5 times higher in the Athabasca River, and saline groundwater discharge over the study reach, which is calculated below.

Table 7-2: Contribution of major ions from saline groundwater to the Athabasca River over the study reach, calculated using Cl isotope mass balance.

concentration mean ratio concentration in concentration in proportion in river ion:Cl river from river from in river from major downstream in saline saline saline ion sample all springs groundwater groundwater groundwater (mmol/L) (mol/mol) (mmol/L) (mg/L) Cl 3.1E-01 1 3.7E-05 1.3 12% Na 6.2E-01 1 3.7E-05 0.9 6%

SO4 2.5E-01 0.07 2.4E-06 0.2 1% Sr 2.5E-03 0.001 1.9E-08 0.002 1% Ca 8.2E-01 0.05 1.9E-06 0.1 0.2% Mg 3.8E-01 0.03 1.1E-06 0.03 0.3%

HCO3 2.1E+00 0.03 1.2E-06 0.1 0.1% K 2.5E-02 0.002 8.6E-08 0.003 0.3%

7.2 Total discharge of saline groundwater

It was proposed in Chapter 1 that there are likely more discharge points of saline groundwater from Devonian carbonates into the rivers than just the springs sampled in this study. Visual observations were made of more surface seeps, and riverbed seeps such as those described by Gibson et al. (2011) would

123 also contribute saline groundwater to both rivers. The Cl isotope mass balance calculations in Section 7.1 enable the estimation of a total discharge of saline groundwater into the rivers over the study reach. Using the average Cl concentration in the spring waters (Clgw) and the average annual Cl mass flux in the river (QCl), the annual flowrate of groundwater (Qgw) can be determined from the fraction of the annual Cl flux attributed to saline groundwater inputs (Fgw), as described by:

Qgw = FgwQCl/Clgw (7-5)

This assumes constant spring chemistry and discharge over the year. This assumption is supported by Jasechko et al. (2012) who found that saline groundwater discharge to the Athabasca River from Cretaceous and Devonian units has remained near constant over the last 15 years. Uncertainties in this discharge calculation are dominated by the relative uncertainty in the estimate of the fraction of Cl in the river sourced from groundwater (Fgw). This uncertainty is 20% for the Clearwater River and 50% for the Athabasca River.

7.2.1 Clearwater River

The average annual discharge of the Clearwater River was 3.8 x 109 m3/yr over the period of 2001-2010, as calculated from daily discharge data for a hydrometric station at Draper, located near the downstream sampling site on the Clearwater River (Environment Canada, 2010b). The average annual mass flux of Cl in the river was 1.1 x 108 kg/yr (not flow-weighted) as calculated from discharge and publically reported water quality data from 2001-2010 (RAMP, 2012). Approximately 30 ± 5% of this was sourced from saline groundwater, as determined from Cl isotopes in Section 7.1. Using the mean concentration of Cl in spring waters (10,707 mg/L) in Equation 7-5 results in an estimate of saline groundwater discharge over this reach of 3.2 x 109 L/yr, or approximately 100 ± 20 L/s. This is about 0.1% of the flow in the Clearwater River. In comparison, the total discharge of the 6 springs on the Clearwater River with measureable flow in this study was approximately 10 L/s, with individual flowrates ranging from

124 0.04 to 7 L/s. The Cl isotope mass balance thus reveals that the springs sampled in this study represent only one tenth of the volume of saline groundwater entering the Clearwater River over the study reach.

7.2.2 Athabasca River

No value for discharge of the Athabasca River is available at the northern downstream end of the study area. However, discharge was measured at a station 65 km further downstream of the study area at the Embarass Airstrip over the period 1971-1984, though not continuously. Monthly mean discharge reports give a range of flow from 198 to 1640 m3/s with a mean discharge of 784 m3/s over the entire year, which gives an average annual discharge of 2.47x1010 m3/yr (Environment Canada, 2010b). There is no publically-available water quality data for this site or nearby, so the Cl concentration measured in the downstream Athabasca sample in this study (11 mg/L) was used with the mean discharge to give an estimated annual Cl flux of 2.7x 108 kg. From the Cl isotope mass balance, approximately 12 ± 6% of this is attributable to saline groundwater input over the study reach. Employing Equation 7-5 with the mean Cl concentration in spring waters (10,707 mg/L) gives a flowrate of saline groundwater in the study area of 3.1 x 109 L/yr, or approximately 97 ± 47 L/s, which is between 0.01 and 0.02% of the annual discharge of the river. This is lower than the estimate by Jasechko et al. (2012) for saline groundwater discharge from both Cretaceous and Devonian rocks into the Athabasca River over a similar reach of between 500 and 3400 L/s. The lower flowrates calculated in this study reflect the fact that only saline water from the Devonian carbonates was considered which has higher Cl concentration than Cretaceous groundwater in the area. However, uncertainties arise in these calculations from possible changes in river discharge since 1984 and potential seasonal variations in Cl concentrations in the river since only the single downstream sample was available. Of the three springs sampled on the Athabasca River, only one (AR03) had measurable discharge into the Athabasca River; at 15 L/s this spring had the highest discharge of all springs in this study. Of the other two springs, the flow

125 of AR02 was too low to measure, and the flow of AR01, while measureable at 0.02 L/s, did not discharge directly into the Athabasca River but into Saline Lake on the shore of the river. The flow of spring AR01 accounts only for approximately 10 to 30% of the estimated discharge of saline groundwater over the study reach, supporting the assumption of additional discharge of saline groundwater into the river.

7.3 Annual mass flux of major ions from saline groundwater

In order to characterize the effect of the springs on river water chemistry, the annual mass flux of major ions to the river systems was calculated for two scenarios. First, the mass flux from individual springs was calculated using spring discharge measurements, assuming constant flow and chemistry throughout the year. This was compared to the total annual mass flux over the study reach calculated from total saline groundwater discharge (Section 7.2) and average spring water chemistry. These two estimates give lower and upper bounds of estimated contributions to the rivers from saline groundwater. The mass flux from individual springs, calculated from primary measurements, may be considered the lower boundary of spring water contributions to the rivers and has a lower uncertainty stemming mainly from flow measurements and the assumption of constant flow. Visual differences in flow were in fact noted between October 2010 and May 2011 in four springs, with three springs having slightly lower flow (AR01, CW08, CW03) and one spring having higher flow (CW05), suggesting that flow is not necessarily constant throughout the year. However, in the absence of detailed flow measurements through time, a rough estimate of annual loadings from these springs was calculated assuming a constant flowrate. The total mass flux from saline groundwater over the study reach, calculated from estimates of total discharge and average concentrations, gives a rough upper boundary to spring water contributions to the rivers over the study reach. This mass flux estimate is associated with higher uncertainty, stemming mainly from uncertainty in the calculations of total saline groundwater discharge into the Clearwater and Athabasca rivers.

126 7.3.1 Clearwater River

The mass flux of TDS from the 6 individual springs with measurable flow on the Clearwater River is approximately 3,100,000 kg/yr. Annually, these springs contribute to the river approximately 1,600,000 kg of Cl; 1,000,000 kg of

Na; 231,000 kg of SO4; 122,000 kg of HCO3; 78,000 kg of Ca; and 33,000 kg of Mg. These fluxes are compared with the average annual mass flux in the Clearwater River, calculated from daily discharge data at Draper (Environment Canada, 2010b) and publically available river water chemistry data (RAMP, 2012) for the time period 2001 to 2010 in Table 7-3. Major ion contributions from only these springs range from 0.04% of bicarbonate in the river to 1% of Cl, Na, and SO4 in the river (Table 7-3). The total annual mass flux of major ions from saline groundwater over the study reach was calculated using the estimated total saline groundwater discharge of 3,200,000 m3/yr and the mean concentrations of major ions in spring waters (Table 7-3). The total flux of TDS from saline groundwater from Devonian carbonates into the Clearwater River is approximately 66,000,000 kg/yr. Annually, saline groundwater contributes to the river approximately 34,000,000 kg of Cl; 22,000,000 kg of Na; 5,600,000 kg of SO4; 1,500,000 kg of HCO3; 1,800,000 kg of Ca; and 630,000 kg of Mg. These represent similar percentages of annual mass fluxes in the river as arrived at in Section 7.1, but slight differences arise from using the 10-year average river chemistry here, versus only the downstream river sample from this study in Section 7.1. There is an order of magnitude difference between the mass flux of ions from just the springs studied and the estimated total mass flux from saline groundwater over the study reach. Without the isotope mass balance approach to determine groundwater discharge, the major ion contributions to the river would be underestimated. This highlights the utility of isotopic analyses in addition to physical and chemical analyses in determining groundwater contributions to the river system.

127 Table 7-3: Discharge and total annual mass flux of major ions from individual springs, total saline groundwater over the study reach, and in the Clearwater River. Spring CW09 is excluded because discharge was not measurable.

River Springs annual mass flux Springs Proportion Total saline Proportion annual sum mass of river groundwater of river unit mass flux CW01 CW02 CW03 CW05 CW07 CW08 flux mass flux mass flux mass flux flow m3/yr 3.8E+09 220,000 95,000 5,000 1,100 1,300 1,300 3.2E+05 0.01% 3.2E+06 0.1% Na kg/yr 8.8E+07 510,000 450,000 34,000 6,100 8,000 11,000 1.0E+06 1% 2.2E+07 25% Cl kg/yr 1.1E+08 810,000 710,000 52,000 9,200 12,000 16,000 1.6E+06 1% 3.4E+07 30% Ca kg/yr 6.2E+07 38,000 35,000 2,900 450 500 700 7.8E+04 0.1% 1.8E+06 3%

HCO3 kg/yr 2.9E+08 86,000 31,000 2,500 550 950 710 1.2E+05 0.04% 1.5E+06 1% SO kg/yr 2.7E+07 110,000 100,000 8,900 1,300 1,600 2,200 2.2E+05 1% 5.6E+06 21% Mg kg/yr 2.0E+07 17,000 14,000 1,000 230 220 300 3.3E+04 0.2% 6.3E+05 3% K kg/yr 4.1E+06 2,900 1,600 120 40 30 40 4.7E+03 0.1% 8.0E+04 2% TDS kg/yr 6.0E+08 1,600,000 1,300,000 100,000 18,000 23,000 31,000 3.1E+06 1% 6.6E+07 11%

7.3.2 Athabasca River

The annual mass fluxes of ions from individual springs versus total saline groundwater discharge are not compared in detail for the Athabasca River since only spring AR03 had measureable flow directly into the river. However, the annual mass flux of major ions from this spring are listed in Table 7-4, along with the total mass flux of ions over the study reach from saline groundwater. Total saline groundwater discharge into the Athabasca over the study area was estimated to be 97 ± 47 L/s (Section 7.2), which is approximately 0.01% of the annual river discharge of 784,000 L/s. The total mass flux of TDS from saline groundwater from Devonian carbonates into the Clearwater River is approximately 64,000,000 kg/yr, or 1% of the annual mass flux of TDS in the river. Annually, saline groundwater contributes to the river approximately

33,000,000 kg of Cl; 21,000,000 kg of Na; 5,400,000 kg of SO4; 1,500,000 kg of

HCO3; 1,800,000 kg of Ca; and 610,000 kg of Mg. Because long-term river water chemistry was not available, the downstream river water sample was used to calculate the river mass flux, and the proportions of the river mass flux of ions attributed to saline groundwater are the same as those from the isotope mass balance approach in Section 7.1.

128 Table 7-4: Discharge and annual mass flux of major ions in the Athabasca River, spring AR03, and total saline groundwater over the study reach. Mass flux from total saline groundwater discharge is also expressed as a proportion of the annual mass flux in the river.

River AR03 Saline Proportion of annual annual groundwater river annual unit mass flux mass flux annual mass flux mass flux flow m3/yr 2.5E+10 1.5E+01 3.1E+06 0.01% Na kg/yr 3.5E+08 1.9E+06 2.1E+07 6% Cl kg/yr 2.7E+08 2.9E+06 3.3E+07 12% Ca kg/yr 8.1E+08 4.1E+05 1.8E+06 0.2%

HCO3 kg/yr 3.1E+09 9.7E+04 1.5E+06 0.05%

SO4 kg/yr 5.8E+08 1.2E+06 5.4E+06 1% Mg kg/yr 2.3E+08 6.1E+04 6.1E+05 0.3% K kg/yr 2.4E+07 6.4E+03 7.8E+04 0.3% TDS kg/yr 5.4E+09 6.6E+06 6.4E+07 1%

7.4 Annual mass flux of trace elements from saline groundwater

The proportions of trace elements in river waters attributable to the individual springs of this study were very small. However, the total annual mass flux of trace elements into the rivers from saline groundwater was calculated using the total saline groundwater discharge estimated in Section 7.2 and mean concentrations of elements in spring waters. This was compared with mean annual mass fluxes of these elements calculated from discharge data (Environment Canada, 2010b) and water quality data (RAMP, 2012) for the period 2001 to 2010. Some elements (Bi, Ce, Cs, Ga, Nb, Pt, Rb, W, and Y) in the rivers were not reported by RAMP (2012); for these elements the annual mass flux in rivers was calculated using the concentration in the downstream sample taken in this study. Again, the uncertainty in these mass flux estimates is dominated by the relative uncertainty in groundwater discharge over the study reach which was ±20% for the Clearwater and ±50% for the Athabasca.

7.4.1 Clearwater River

Of the 34 elements measured in spring waters, only boron and rubidium account for greater than 1% of the annual mass flux in the river. The average annual mass flux of B from saline groundwater is 6500 kg/yr, or 5% of the annual load in the river. Boron is commonly found in clay-rich marine sediments and forms highly soluble compounds in water (CCME, 2009). The Devonian

129 carbonates from which the springs emerge contain clays which could be the source of boron in spring waters. The average annual mass flux of Rb is 66 kg/yr, or 2% of the annual load in the river. Rb is also a common element that substitutes for K in many minerals (Clark and Fritz, 1997), and the source is also likely the clays that are present in the Devonian carbonate rocks. The annual fluxes of all other elements from saline groundwater over the study reach are much lower, and account for ≤0.5% of the annual mass fluxes in the Clearwater River (Table 7-5). Saline groundwater from the Devonian carbonates is thus not a major source of trace elements to the Clearwater River in the study reach.

7.4.2 Athabasca River

Of the 34 elements measured, only boron accounts for ≥ 1% of mass flux found in the Athabasca River. The annual mass flux of boron from saline groundwater in the study area is 6300 kg, or 1% of the annual load in the river. Rb from saline groundwater accounts for only 0.2% of the annual mass flux in the Athabasca River. The annual mass fluxes of all other elements from saline groundwater over the study reach are much lower, and account ≤ 0.1% of the fluxes of trace elements in the Athabasca River (Table 7-6). Saline groundwater from the Devonian carbonates is thus not a major source of trace elements to the Athabasca River over the study reach.

130 Table 7-5: Annual mass fluxes of trace elements from saline groundwater and in the Clearwater River. Elements marked by * were not reported by RAMP, so mean concentrations were calculated from the downstream river sample (RCW02). 'LTD' represents concentrations less than detection limits and (-) indicates the value could not be calculated due to values being LTD.

Clearwater River Q = 3.76 x 109 m3/yr estimated saline groundwater discharge = 3.17 x 106 m3/yr Mean Annual Mean Annual mass Proportion of concentration mass flux in concentration flux from saline river mass in river river all springs groundwater flux (g/L) (g/yr) (g/L) (g/yr) (%) Ag 1.8E-08 6.6E+04 1.6E-08 5.0E+01 0.07 Al 8.5E-04 3.2E+09 1.0E-04 3.3E+05 0.01 As 8.4E-07 3.1E+06 1.7E-06 5.5E+03 0.2 B 3.5E-05 1.3E+08 2.1E-03 6.5E+06 5 Be 9.0E-05 3.4E+08 8.6E-08 2.7E+02 0.0001 Bi* LTD - 2.2E-08 7.0E+01 - Cd 2.0E-08 7.4E+04 7.5E-08 2.4E+02 0.3 Ce* 3.5E-08 1.3E+05 1.3E-08 4.3E+01 0.03 Co 5.0E-07 1.9E+06 2.7E-07 8.4E+02 0.04 Cr 1.5E-06 5.7E+06 1.1E-06 3.6E+03 0.06 Cs* 1.6E-09 5.9E+03 8.1E-09 2.6E+01 0.4 Cu 1.4E-06 5.1E+06 1.9E-06 6.1E+03 0.1 Fe 1.5E-03 5.6E+09 3.0E-03 9.5E+06 0.2 Ga* LTD - 6.7E-08 2.1E+02 - La* 3.3E-07 1.2E+06 1.1E-07 3.6E+02 0.03 Mo 2.3E-07 8.7E+05 8.3E-08 2.6E+02 0.03 Nb* LTD - LTD - - Ni 1.3E-06 5.1E+06 1.2E-06 4.0E+03 0.08 Pb 5.8E-07 2.2E+06 3.0E-07 9.4E+02 0.04 Pt* LTD - 7.9E-09 2.5E+01 - Rb* 1.1E-06 3.9E+06 2.1E-05 6.6E+04 2 Sb 5.6E-08 2.1E+05 9.0E-08 2.8E+02 0.1 Se 5.6E-07 2.1E+06 3.0E-06 9.4E+03 0.4 Sn 9.8E-08 3.7E+05 7.0E-09 2.2E+01 0.01 Tl 4.8E-08 1.8E+05 9.5E-09 3.0E+01 0.02 U 1.1E-07 4.3E+05 5.2E-08 1.7E+02 0.04 V* 1.1E-06 4.0E+06 LTD - - W* LTD - 1.2E-09 3.6E+00 - Y* 1.4E-08 5.1E+04 1.1E-08 3.6E+01 0.07 Zn 1.2E-05 4.6E+07 4.7E-06 1.5E+04 0.03

131 Table 7-6: Annual mass fluxes of trace elements from saline groundwater and in the Athabasca River. Elements marked by * were not reported by RAMP, so mean concentrations were calculated from the downstream river sample (RAR02). 'LTD' represents concentrations less than detection limits and (-) indicates the value could not be calculated due to values being LTD.

Athabasca River Q = 2.47 x 1010 m3/yr estimated saline groundwater discharge = 3.05 x 106 m3/yr Mean Annual Mean Annual mass Proportion of concentration mass flux in concentration flux from saline river mass in river river all springs groundwater flux (g/L) (g/yr) (g/L) (g/yr) (%) Ag 1.1E-08 2.6E+05 1.6E-08 4.8E+01 0.02 Al 8.3E-04 2.0E+10 1.0E-04 3.2E+05 0.002 As 8.1E-07 2.0E+07 1.7E-06 5.3E+03 0.03 B 2.5E-05 6.1E+08 2.1E-03 6.3E+06 1 Be 7.7E-08 1.9E+06 8.6E-08 2.6E+02 0.01 Bi* LTD - 2.2E-08 6.7E+01 - Cd 2.9E-08 7.1E+05 7.5E-08 2.3E+02 0.03 Ce* 2.9E-08 7.1E+05 1.3E-08 4.1E+01 0.01 Co 3.9E-07 9.6E+06 2.7E-07 8.1E+02 0.01 Cr 1.3E-06 3.2E+07 1.1E-06 3.5E+03 0.01 Cs* 2.0E-09 4.9E+04 8.1E-09 2.5E+01 0.05 Cu 1.5E-06 3.8E+07 1.9E-06 5.8E+03 0.02 Fe 9.8E-04 2.4E+10 3.0E-03 9.1E+06 0.04 Ga* LTD - 6.7E-08 2.0E+02 - La* 2.8E-07 6.9E+06 1.1E-07 3.5E+02 0.005 Mo 6.0E-07 1.5E+07 8.3E-08 2.5E+02 0.002 Nb* LTD - LTD - - Ni 1.3E-06 3.3E+07 1.2E-06 3.8E+03 0.01 Pb 6.0E-07 1.5E+07 3.0E-07 9.0E+02 0.01 Pt* LTD - 7.9E-09 2.4E+01 - Rb* 1.0E-06 2.6E+07 2.1E-05 6.4E+04 0.2 Sb 6.7E-08 1.7E+06 9.0E-08 2.7E+02 0.02 Se 3.5E-07 8.5E+06 3.0E-06 9.1E+03 0.1 Sn 1.5E-07 3.7E+06 7.0E-09 2.1E+01 0.001 Tl 3.0E-08 7.4E+05 9.5E-09 2.9E+01 0.004 U 3.4E-07 8.3E+06 5.2E-08 1.6E+02 0.002 V* 1.5E-06 3.8E+07 LTD - - W* LTD - 1.2E-09 3.5E+00 - Y* 1.5E-08 3.7E+05 1.1E-08 3.4E+01 0.01 Zn 5.7E-06 1.4E+08 4.7E-06 1.4E+04 0.01

132 7.5 Annual mass flux of PAHs from saline groundwater

The proportion of PAHs attributable to the individual springs of this study was minimal. However, the total annual mass flux of PAHs from saline groundwater into the rivers in the study area was calculated in a manner similar to that used for trace elements (Section 7.4) using mean saline groundwater discharge (Section 7.2) and mean PAH concentrations in the spring waters. Since the composition of PAHs differed in the Clearwater and Athabasca springs, the mean concentrations were calculated separately for the springs on each river. For the determination of annual mass flux of PAHs in the rivers, a consistent record of concentrations over time was not available, thus concentrations in the downstream river samples were used in conjunction with the mean annual river discharges (calculated from Environment Canada, 2010b).

7.5.1 Clearwater River

The annual mass flux of total PAHs in the Clearwater River is approximately 1400 kg, whereas the average annual mass flux of total PAHs from saline groundwater is 70 g/yr, or 0.01% of the flux in the river. Only 3 of the 8 PAHs found in the Clearwater River were found in the Clearwater springs. The annual mass fluxes from saline groundwater of phenanthrene and 2- methylnaphthalene accounts for 0.02% of the fluxes of these compounds in the river. The annual mass flux of naphthalene from saline groundwater accounts for 0.004% of the flux in the river (Table 7-7). Saline groundwater discharge from Devonian carbonates thus does not make a major contribution to the mass flux of PAHs in the Clearwater River.

133 Table 7-7: Annual mass fluxes of PAHs (ng/yr) in the Clearwater River and saline groundwater over the study reach, expressed in ng/L and as a proportion of mass flux in the river. 'LTD' represents concentrations less than detection limits and (-) indicates a value that could not be calculated due to a LTD value.

Clearwater River Q = 3.76 x 109 m3/yr estimated saline groundwater discharge = 3.17 x 106 m3/yr Mean Annual mass Proportion of Concentration Annual mass concentration flux from saline river in river flux in river CW springs groundwater mass flux (ng/L) (ng/yr) (ng/L) (ng/yr) (%) chrysene 4.3 1.6E+13 LTD - - fluoranthene 17.7 6.7E+13 LTD - - fluorene 22.1 8.3E+13 LTD - - indene 5.2 2.0E+13 LTD - - naphthalene 227.0 8.5E+14 11.1 3.5E+10 0.004 1-methylnaphthalene 18.7 7.0E+13 LTD - - 2-methylnaphthalene 29.9 1.1E+14 7.6 2.4E+10 0.02 phenanthrene 38.6 1.5E+14 9.2 2.9E+10 0.02 total PAH concentration 363.5 1.4E+15 22.2 7.0E+10 0.005

7.5.2 Athabasca River

The annual mass flux of total PAHs in the Athabasca River is approximately 4400 kg, whereas the average annual mass flux of total PAHs from saline groundwater is 580 g/yr, or 0.01% of the flux in the river. All but one of the 8 PAHs found in the Athabasca River downstream sample were found in the Athabasca springs. An additional 3 PAHs were found in the upstream Athabasca sample that were not present in the downstream river sample or the spring water samples (see Chapter 6). The annual flux from saline groundwater accounts for 0.01 to 0.02% of the annual mass flux in the river of each PAH (Table 7-8). Although saline groundwater does not contribute a great fraction of the PAHs found in the Athabasca River at the downstream end of the study area, the suite of PAHs found in both are similar, as are the proportions of each contributed by saline groundwater. This suggests that the springs and the river are affected by the same source of PAHs. In Chapter 6, it was proposed that the suite of PAHs present in the Athabasca spring waters may be sourced from air deposition from upgrading activity.

134 Table 7-8: Annual mass fluxes of PAHs (ng/yr) in the Athabasca River and saline groundwater over the study reach, expressed in ng/L and as a proportion of mass flux in the river. 'LTD' represents concentrations less than detection limits and (-) indicates a value that could not be calculated due to a LTD value.

Athabasca River Q = 2.47 x 1010 m3/yr estimated saline groundwater discharge = 3.05 x 106 m3/yr Mean Annual mass Proportion of Concentration Annual mass concentration flux from saline river in river flux in river AR springs groundwater mass flux (ng/L) (ng/yr) (ng/L) (ng/yr) (%) chrysene 3.9 7.4E+13 5.8 1.8E+10 0.02 fluoranthene 12.1 2.3E+14 11.6 3.5E+10 0.02 fluorene 12.5 2.4E+14 14.0 4.3E+10 0.02 naphthalene 145.0 2.8E+15 113.4 3.5E+11 0.01 1-methylnaphthalene 9.6 1.8E+14 12.7 3.9E+10 0.02 2-methylnaphthalene 15.2 2.9E+14 14.7 4.5E+10 0.02 1,2,3,4-tetrahydronaphthalene 6.3 1.2E+14 LTD - - phenanthrene 25.5 4.9E+14 26.9 8.2E+10 0.02 total PAH concentration 230.1 4.4E+15 189.8 5.8E+11 0.01

135 Chapter Eight: Conclusions and future research

In this study, the geochemistry and origins of saline spring waters discharging into the Clearwater and Athabasca rivers were investigated. Located in the Athabasca oil sands area on the northeastern edge of the Western Canadian Sedimentary Basin (WCSB), the springs emerge from Devonian carbonate rocks that underlie bitumen-bearing Cretaceous units. Stable isotope techniques enabled the identification of sources of water and radioisotopes allowed the age-dating of spring waters. Spring waters were characterized by concentrations of dissolved ions, trace elements, PAHs, and dissolved gases. Mineral saturation and equilibria were explored through geochemical modeling. Sources of solutes, as well as subsurface processes that have affected water chemistry, were identified using stable isotope ratios. Annual mass fluxes of solutes, trace elements, and PAHs into the rivers from these springs were estimated and compared with annual mass fluxes of these compounds in the rivers. This information contributes to the understanding of surface water - groundwater interactions in the Athabasca oil sands area and is necessary for consideration in the mass balance approach for assessing potential impacts of oil sands development on river systems.

8.1 Sources of spring water

The δ18O and 2H values of the spring waters indicated the source of spring waters was meteoric. In most spring waters, however, δ18O and 2H values were considerably lower than expected for modern recharge, suggesting that the spring waters contain some proportion of glacial meltwater. Radiocarbon dating of DIC in three spring waters was compatible with glacial meltwater from the last glacial period and this interpretation was supported by very low tritium concentrations. With the exception of springs CW09 and AR03, which were sourced almost entirely from modern recharge, the proportion of glacial meltwater in the springs ranged from 39 to 75%, using a δ18O value for 18 2 meltwater of -25‰ (Remenda et al., 1994). δ OH2O and HH2O values, Cl/Br ratios, and 87Sr/86Sr ratios indicated that spring waters were distinct from both

136 shallow groundwaters and formation waters deeper in the WCSB. Thus, the springs do not discharge water from the regional-scale groundwater flow system in the basin, nor from strictly local shallow flow systems, but rather from an intermediate-scale flow system.

8.2 Sources of solutes in springs

The springs were classified as brackish or saline, with TDS between 7,210 and 51,800 mg/L. All springs had a Na/Cl water type. Ion ratios of Na/Cl and Cl/Br identified halite dissolution as the main source of Na and Cl, which was supported by positive δ37Cl values in spring waters. The most likely source of halite is the Middle Devonian Prairie Evaporite Formation. Although the spring locations are beyond the dissolution edge of this formation, close to the study area these salts underlie the Devonian carbonates that host the springs. Major ion ratios indicated gypsum dissolution as an important source of

Ca and SO4 in the spring waters. With the exception of spring AR01, where the 34 oxidation of sulfide minerals was identified as the source of sulfate, δ SSO4 and 18 δ OSO4 values indicated an evaporitic source of sulfate in all spring waters that had been altered through bacterial sulfate reduction. The most likely source of gypsum to the spring waters is again the Prairie Evaporite Formation. Major ion ratios and mineral saturation indices indicated that the chemistry of the Athabasca springs was more influenced by gypsum dissolution than the Clearwater springs. This is explained by their closer proximity to the dissolution edge of the Prairie Evaporites and to an outcrop edge of the Elk Point Group. The dissolution of carbonate minerals in the Devonian aquifer was - identified as the main source of HCO3 to the springs through major ion ratios 87 86 13 and Sr/ Sr ratios in spring waters. δ C values in DIC supported the dissolution of carbonates by soil CO2, although in both Athabasca springs and two Clearwater springs, δ13C values were elevated due to methanogenesis. Most spring waters were saturated with respect to the carbonate minerals calcite and dolomite; however, geochemical modeling showed that equilibrium between these two minerals does not control the concentrations of Ca and Mg in the

137 spring waters. Rather, equilibrium exchange between Ca- and Mg-smectite was found to be a more likely control on the concentrations of these ions. This means that although gypsum and carbonate dissolution contribute Ca to the waters, it may be equilibrium exchange between clay minerals that controls the concentration of each in the waters.

8.3 Trace elements, PAHs, gases

Twelve metals listed by the EPA (2012) as priority pollutants (PPE) were detected in spring waters at trace concentrations. Two PPE, Se and As, were at concentrations higher than CCME (2007) guidelines for the protection of aquatic life (PAL) in separate springs. B, Fe, and Al were also present in some spring waters at concentrations exceeding PAL guidelines. Of the dominant heavy metals associated with bitumen, V was not present in any spring waters. Springs AR01 and CW05 contained both Ni and Zn, as well as other metals associated with the oil sands (As, Fe, Se, As). Most of the springs, however, did not contain the assemblage of trace elements expected from weathering of bitumen. The concentration of total PAHs ranged from 7.3 to 273 ng/L in spring waters. Twelve PAH compounds, including six listed as PPE (EPA, 2012), were detected in the Athabasca springs but only naphthalene and phenanthrene were detected in the Clearwater springs. The assemblage of PAHs present in Athabasca springs was similar to those found in the Athabasca River, suggesting a similar source; however, the assemblage of PAHs in the Clearwater springs contained fewer compounds than found in the Clearwater River. Some PAHs that were present in the springs (naphthalene, fluorene, and methylnaphthalenes) are not found in raw bitumen but could have a pyrogenic source and are found in air deposition from oil sands upgrading facilities (Kelly et al., 2009). This suggests that a source of PAHs, and possibly trace elements, to spring waters may be air deposition and subsequent infiltration of shallow groundwater. Of the dissolved gases present in the springs, nitrogen was the most abundant, followed by CO2. Methane was the third most common gas in the springs. The isotopic composition of methane indicated that it was sourced from

138 methanogenesis through carbonate reduction and altered through partial methane oxidation. The isotopic composition of methane also indicated some similarities with methane found in Cretaceous units which overlie the Devonian carbonates.

8.4 Influence on river water quality

The total discharge of the nine springs sampled in this study was shown through Cl isotope mass balance calculations to account for only a small portion of saline groundwater discharge over the study area into the rivers. This highlights the utility of isotopic analyses in addition to traditional physical and chemical water quality analyses in determining groundwater input and subsequently the mass balance of substances entering the rivers. The total discharge of saline groundwater along each river was determined from the Cl isotope mass balance, average annual discharge of the rivers, and average Cl concentrations in the rivers. This revealed similar saline groundwater discharge along both rivers of 100 ± 20 L/s on the Clearwater and 97 ± 47 L/s on the Athabasca. High relative uncertainties in groundwater discharge stemmed from uncertainties in the Cl isotope mass balance calculations and the small differences in δ37Cl values over the study reaches, particularly in the Athabasca River. These discharge estimates enabled estimates of the mean annual mass flux of substances from saline groundwater into the rivers over the study area, assuming constant flow and chemistry in the springs throughout the year. Along the Clearwater River, the average annual discharge of saline groundwater amounts to approximately 3.2 x 106 m3/yr, or 0.1% of the average annual river discharge. The annual mass flux of TDS from saline groundwater is approximately 66,000,000 kg/yr. This consists primarily of approximately 22,000,000 kg of Na, or 25% of the annual mass flux in the river, 34,000,000 kg of

Cl, or 30% of the annual mass flux in the river, and 560,000 kg of SO4, or 21% of the annual mass flux in the river. The average annual mass fluxes of trace elements and PAHs from saline groundwater accounted for a much smaller proportion of the annual mass flux of these substances in the Clearwater River. The metals contributed in the highest proportion to the river are boron at 6500

139 kg/yr, or 5% of the annual mass flux, and rubidium at 66 kg/yr, or 2% of annual mass flux. All other trace elements contributed from spring waters account for ≤0.5% of the annual mass flux in the river. Annual mass flux of total PAHs from saline groundwater is approximately 70 g/yr. Only 3 of the 8 PAHs detected in the river were found in the Clearwater springs, each of which account for ≤0.02% of the annual mass flux in the river. Therefore, saline groundwater from the Devonian carbonates contributes relatively large proportions of the annual flux of major ions in the Clearwater River, but only very small proportions of trace elements and PAHs found in the river. Along the Athabasca River, the average annual discharge of saline groundwater amounts to approximately 3.1 x 106 m3/yr or about 0.01% of the average annual river discharge. The annual mass flux of TDS from saline groundwater is approximately 64,000,000 kg/yr. This consists primarily of approximately 21,000,000 kg of Na, or 6% of the annual mass flux in the river, 33,000,000 kg of Cl, or 12% of the annual mass flux in the river, and 540,000 kg of

SO4, or 1% of the annual mass flux in the river. Trace elements from saline groundwater account for ≤1% of the annual mass fluxes in the river. The suite of 8 PAHs found in the Athabasca springs is similar to those found in the river, although with a flux of 580 g/yr, saline groundwater accounts for only 0.01% of the mass flux of PAHs in the river. Therefore, saline groundwater from the Devonian carbonates contributes a moderate proportion of the annual flux of Na and Cl in the Athabasca River, but only very small proportions the annual flux of trace elements and PAHs.

8.5 Future work

The ten springs sampled in this study were not a comprehensive inventory of all saline groundwater discharge into the Clearwater and Athabasca rivers from Devonian carbonates in the study area. Visual observations indicated many more salt marshes and possible springs along the Clearwater River. In addition, riverbed seeps, such as those identified by Gibson et al. (2011) in the Athabasca River, likely also contribute saline groundwater from the Devonian carbonates to these rivers and their tributaries. A complete inventory of these

140 saline groundwater contributions to the rivers would be necessary to quantify the total effect of Devonian discharge on river water chemistry and confirm the mass fluxes calculated from the Cl isotope mass balance in this study. Variations in the discharge of the springs were assumed to be negligible in the calculation of mass fluxes of substances to the rivers. Discharge measurements throughout the year could test this assumption, and would allow more accurate mass flux calculations. In addition, chemical and isotopic analyses of spring waters at various times throughout the year could give further insight into temporal variations in chemistry, sources of water and solutes, subsurface processes affecting spring waters, and influence on river water chemistry. Further understanding of the source of methane requires additional isotopic analyses of dissolved gases. The determination of the isotopic compositions of dissolved CO2 and ethane in spring waters, in addition to that of methane which was done in this study, could help identify the source of gases. The PAHs and some trace elements present in the Clearwater springs may be sourced from air deposition over the landscape and infiltration of shallow groundwater. Analysis of PAHs and trace elements in wet and dry deposition, as well as in shallow groundwater in the area is necessary to test this hypothesis. Further analysis of alkylated PAHs in spring waters would also help narrow down their source. The isotopic composition of spring waters was compared to that of precipitation in Fort Smith, NWT, the closest location to the study for which this information was available. A local meteoric water line (LMWL) for Fort McMurray would be very beneficial for further research on many topics in the Athabasca oil sands area. This would require the collection and isotopic analysis of precipitation throughout the year over several years. The Clearwater springs are located relatively far from the areas of oil sands mining and would likely not be affected by surface mining, other than by air deposition from upgrading. The Athabasca springs are located closer to areas of mining development. Repeated sampling of these springs could be used to monitor for any effects caused by altered groundwater regimes due to removal of the boreal forest and surface mining. In addition, the Clearwater springs are

141 located updip of in-situ oil sands development areas. Although the springs were not discharging basin brines from the WCSB, repeated sampling of these springs could be useful to monitor for any potential effects of in-situ development on groundwater chemistry and flow in the Devonian carbonates.

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156 Appendix A: Photos and descriptions of sampling sites

CW01: Discrete spring and pool on the south side of the Clearwater River, effervescent in places. Smelled of sulfur.

CW02: Several spring discharge points flowing into one channel, which flowed into Clearwater River on the north side. Some effervescence and sulfur odour.

CW03: Discreet spring and pool on the south side of the Clearwater River with one deeper effervescent portion where sample was taken (2nd picture). Smelled strongly of sulfur.

157

CW05: A meadow with multiple pools and seeps on the south side of the Clearwater River (visible in upper left corner of picture). Seep that was sampled had red biological slime. A slight oily sheen was visible on the spring water.

CW07: A discrete seep in a meadow of fresher pools on the south side of the Clearwater River that ran for approximately 9m then abruptly ended. White precipitate was present near the flow.

CW08: A meadow of saline pools and seeps on the south side of the Clearwater River, sampled seep was small.

158

CW09: Large meadow of saline pools on north side of Clearwater River; one pool was sampled. There was no obvious inflow or outflow. Some bubbles were present.

AR01 (La Saline): A spring with several discharge points, all with very low flow, running into La Saline Lake on the east side of Athabasca River from a large mound of mineral deposits. In October 2010 only one small trickle was found and sampled (left picture); in May 2011 it was dry so a different discharge point was sampled (right picture). Bitumen present at surface.

159

AR02 (near Fort McKay on west bank of Athabasca River): Previously described as a flowing well (Grasby, pers. com. 2010), the well was dry in May 2011. There was a small discrete discharge into the Athabasca River from below the well casing.

AR03: A discrete spring on the west bank of the Athabasca River. There was some effervescence and a strong smell of sulfur.