Regional Variation of Chemical Groundwater Composition in Hessen, Germany, and Its Relation to the Aquifer Geology

Home , Buntsandstein, Hilders, Sensbachtal, Tephrite, Vogelsberg

Regional variation of chemical groundwater composition in Hessen, Germany, and its relation to the aquifer geology

INAUGURALDISSERTATION

zur Erlangung des Doktorgrades der Fakultät für Chemie, Pharmazie und Geowissenschaften der Albert-Ludwigs-Universität Freiburg im Breisgau

vorgelegt von

Florian Ludwig aus Koblenz

Freiburg 2011

Vorsitzender des Promotionsausschusses: Prof. Dr. Thorsten Koslowski Referent: Prof. Dr. Kurt Bucher Korreferentin: Prof. Dr. Ingrid Stober Datum der Promotion: 1. Dezember 2011

Drum hab ich mich der Magie ergeben, Ob mir durch Geistes Kraft und Mund Nicht manch Geheimnis würde kund; Daß ich nicht mehr, mit sauerm Schweiß, Zu sagen brauche, was ich nicht weiß; Daß ich erkenne, was die Welt, Im Innersten zusammenhält…

Faust – Johann Wolfgang von Goethe

Für meine Familie

Table of contents

Acknowledgements ...... 5

Abstract...... 7

Introduction ...... 9

Chapter 1: Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany – A Laboratory and Field Study

Abstract ...... 15 1. Introduction ...... 15 2. Study Area...... 17 2.1. Geography and Climate Data ...... 17 2.2. Geological Setting...... 17 2.3. Hydrogeology...... 21 3. Methods...... 22 4. Results and Discussion...... 26 4.1. Modal Mineral Composition and Analytical Rock Data...... 26 4.2. Composition of Leachates and Interpretation of Batch Experiments ...... 28 4.3. Groundwater Chemistry and Hydrochemical Evolution...... 34 4.3.1. Sulfate Adsorption...... 40 4.3.2. Hydraulic Properties...... 41 4.3.3. Stability Constraints ...... 42 5. Conclusions ...... 44 References ...... 45

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Chapter 2: Groundwater Evolution and Mineral Alteration Reactions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany - A Case Study

Abstract ...... 53 1. Introduction ...... 53 2. Study Area...... 55 2.1. Geography and Climate Data ...... 55 2.2. Geology ...... 55 2.3. Hydrogeology...... 59 3. Methods...... 60 4. Results and Discussion...... 64 4.1. Analytical Rock Data and Modal Mineral Composition...... 64 4.2. Groundwater Chemistry ...... 67 4.3. Composition of Leachates and Interpretation of Column Experiments..... 73 4.4. Hydrochemical Groundwater Evolution ...... 81 4.4.1. Near-surface Groundwater (Early-stage Weathering)...... 81 4.4.2. Groundwater at greater Depth (Late-stage Weathering)...... 82 4.4.3. Cation Exchange ...... 83 4.4.4. Interpretation of Hydrochemical Clusters...... 85 4.4.5. Stability Constraints ...... 87 5. Conclusions ...... 88 References ...... 89

- 2 - Table of contents

Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

Abstract ...... 97 1. Introduction ...... 97 2. Study Areas ...... 99 2.1. Devonian Shale, Idstein Depression, Middle Rhine Highlands...... 100 2.2. Permian Rotliegend Sedimentary Rocks, Lower Main Plain...... 100 2.3. Triassic Bunter Sandstone, Odenwald Mountain Range...... 102 2.4. Triassic Bunter Sandstone, Lower Hessian Depression...... 103 2.5. Tertiary Basaltic Rocks, Mt. Wasserkuppe, High Rhön ...... 103 2.6. Tertiary Basaltic Rocks, Vogelsberg Mountain Range...... 104 2.7. Quaternary Fluviatile Sediments, Upper Rhine Graben...... 105 3. Methods...... 105 4. Results and Discussion...... 113 4.1. Groundwater Composition and Input by Meteoric Water...... 113 4.2. Aquifer Lithologies ...... 114 4.3. Speciation and Mobility of Iron and Aluminium...... 115 4.4. Mobility Controls of Arsenic and Heavy Metals ...... 118 4.4.1. Arsenic ...... 120 4.4.2. Copper and Lead ...... 122 4.4.3. Cadmium, Cobalt, Nickel, and Zinc...... 124 4.4.4. Chromium...... 127 5. Conclusions ...... 129 References ...... 130

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General conclusions...... 135

Appendix App. 1 List of abbreviations ...... A-1 App. 2 Complete groundwater data...... A-3 App. 3 Complete rock data...... A-15 App. 4 Complete data leaching experiments...... A-17 App. 5 Analytical specimen images ...... A-21

Publications

Curriculum Vitae

- 4 - Acknowledgements

Acknowledgements Special thanks are due to my supervisor Prof. Dr. Kurt Bucher at the University of Freiburg for the competent mentoring of my PhD, for his patience and precious advice, for encouragement in critical moments, and gentle guidance throughout this study. I very much appreciate Prof. Dr. Ingrid Stober as second examiner for supporting and for contribution of valuable ideas. I am grateful to all colleagues at the University of Freiburg for their support during the lab experiments and sample conditioning, with special regard to Sigrid Hirth-Walther, Melanie Schrage, Dagmar Flemming, and Isolde Schmidt at the University of Freiburg. For exciting discussion, I would like to thank Dr. Ulrike Seelig, Dr. Sonia Ackermann and Dr. Fleurice Parat. This PhD thesis was initiated during my time as a freelance project hydrogeologist at the Hessian Agency for the Environment and Geology in Wiesbaden. I very much benefited from exciting discussion with numerous colleagues at the Department of Hydrogeology, and I would like to express deep thanks to the project leaders Dr. Bernd Leßmann, Dr. Dieter Käm- merer, and Dr. Georg Berthold. I would also like to thank Alexander Becht for his help during the field investigations and groundwater sampling. For valuable comments as well as for the interesting and constructive discussions I would like to thank Dr. Karl-Heinz Köppen and Achim Justen at Wasser und Boden Hydrogeologi- cal Consultants. Deep thanks are given to my family and also to my friends for their helpful support during all ups and downs of my PhD. Without their encouragement and motivation a lot of things would not have been possible within the last years.

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Abstract

Abstract Water-rock interactions of both low and high pH groundwaters in silicate fissured rock aquifers were studied in order to delineate the principal patterns of hydrochemical groundwater evolution. The investigations included both field studies and laboratory experiments. The fields of interest comprise the Triassic Bunter sandstone sequence of the Odenwald low mountain range and the Tertiary basaltic rock sequence of Mt. Wasserkuppe, Rhön mountain range, central Germany. Among the Bunter sandstone aquifer, groundwater composition comprises low pH, SO4-rich near-surface groundwaters issued by springs (Ca-Mg-SO4-type) grading to SO4-poor groundwaters at greater depth with near-neutral pH (Ca-HCO3-type). In the basaltic rock aquifer, the hydrochemical composition of near-surface groundwaters indicates a Ca/Mg-HCO3 type with near-neutral pH and evolves to a Na-HCO3 type with high pH at greater depth. In order to determine initial mineral alteration reactions and the origin of dissolved ions, short-term batch experiments of the original aquifer rocks were performed. The reactions were deduced from the leachate hydrochemical data calculating mass transfer as inverse modelling approach, balancing primary mineral dissolution and precipitation of secondary minerals. The definition of mineral reactions was also constrained to the saturation stages of the individual minerals and to reaction kinetics as mineral dissolution rates. Experimental mineral alteration reactions of the sandstone aquifer involve the decomposition of anorthite, K- feldspar, biotite, and jarosite as well as the mobilisation of Na-Cl-fluid inclusions in quartz grains. The basaltic rocks indicate the alteration of olivine, Ca-pyroxene, plagioclase, pyrrhotite, and feldspathoids. The transformation budgets were balanced by the formation of secondary clay minerals of the smectite group and iron hydroxides as low-T mineral phase. Natural groundwater evolution involves the mineral alteration reactions deduced from the batch experiments and also includes long-term reaction processes. Among the sandstone groundwaters, the dissolution of K-feldspar converts Ca-montmorillonite to illite (illitisation). The formation of Na-beidellite correlates with decreasing concentration of Na+ in solution during groundwater maturation. In the basaltic sequence, the conversion of secondary Na- beidellite to illite occurs at a later stage of groundwater evolution, reducing the concentrations of K+ and Mg2+. Among the mature high-pH basaltic groundwater at greater depth, water-rock interactions are basically limited to the dissolution of anorthite and albite. Sorption and exchange processes as a function of pH and the availability of sorptive matter (iron hydroxides, clay minerals) could be associated to both lithologies. As indicated for the sandstone sequence 2- by modelled adsorption curves, the decrease of SO4 concentrations during groundwater evo- 2- lution relates to the adsorption of SO4 at low-pH. Whereas near-surface groundwaters in the basaltic sequence do not indicate significant cation exchange, Na-alkalisation of the high-pH groundwaters at greater depth suggests the exchange of Na+ for Mg2+ and Ca2+ on secondary

- 7 - Abstract mineral phase. The concentrations of dissolved heavy metals and arsenic were referred to their mobility in the aquifer systems. Mobility of an ion is referred to its non-conservative transport in the aquifer system with possible effect by chemical (e.g. precipitation) or physical (e.g. sorption) processes. Prior to estimating the feasibility of demobilisation of dissolved species by sorption, speciation calculations were run to determine the individual element species. The mobility of iron could be basically related to the formation of solid ferrihydrite (Fe(OH)3) as a function of Eh and pH. Consequently, sorption curves were modelled for sorption of the metal ions and anionic As and Cr species on hydrous ferric oxide as a function of pH. With exception of Cu, the sorption mechanisms postulated were found to be consistent with the concentrations of the particular dissolved element species in the natural groundwaters. In addition, the concentrations of dissolved iron indicate positive linear correlation to dissolved arsenic and to several heavy metals such as Pb, Co, Ni, and Zn; suggesting co-precipitation and synchronous remobilisation of previously sorbed elements as a function of Eh. With regard to Cu, the formation of oxides has to be considered as an important mobility control.

- 8 - Introduction

Introduction Groundwater is the major resource for municipal water supply in central Europe as well as in many other locations around the world. Apart from availability and spatial distribution, groundwater quality is one of the key issues for sustainable groundwater management. Natu- ral weathering processes of rock-forming minerals affecting water quality of aquifers used for extensive groundwater extraction have been the issue of a great number of research papers. It is inevitable to know the principal patterns of natural groundwater evolution before delineat- ing possible anthropogenic influence on groundwater quality through agricultural land use, industrial emissions, or domestic waste in urban areas (Zhu and Schwartz 2011). Knowing the natural processes controlling baseline (unaffected) composition of groundwater (Postma et al. 2008) is essential to evaluate water quality problems and helps creating concepts for adequate use of groundwater resources. One method to describe the constraints of groundwater evolution is the approach of hydrochemical models. Principal contemplations by Garrels and Christ (1965) and Garrels and Mackenzie (1967) suggest that water composition can be explained by transformation budgets, balancing mineral dissolution and precipitation. With regard to energy budgets, Helgeson (1968) introduced a thermodynamic approach to describe mineral alteration reactions. He associated the feasibility of mineral dissolution or precipitation to the mineral saturation states in natural groundwaters. In relation to the groundwater composition, dissolved elements can be defined as immobile when incorporated into secondary mineral phase or as mobile when unaffected by chemical or physical processes (Drever 1997). Reactive transport models are currently used to explore groundwater evolution along the flow paths in aquifer systems. Some recent studies compiled by Edmunds and Shand (2008) focus on hydrochemical groundwater evolution in aquifers in Europe and significantly illustrate the variety of possible natural processes affecting groundwater composition. Zuddas (2010) defines water-rock interaction as the sum of chemical and physical exchanges which occur between groundwater and rocks. In addition to mineral dissolution and precipitation reactions, processes such as input of solutes by rainfall loads, sorption, ion exchange, or the Eh-pH-conditions of groundwater significantly affect groundwater quality. As suggested by White (2005), the grade of groundwater maturation can be described by the prevailing water- rock interactions. This study focuses on hydrochemical groundwater evolution in two fissured rock aquifers in Hessen, central Germany. The fields of investigation comprise the Bunter sandstone sequence of the Odenwald mountain range and the basaltic rock sequence at Mt. Wasserkuppe, High Rhön mountain range. The groundwater environments involve low and high pH groundwaters, respectively, and indicate small-scale variation of groundwater composition.

- 9 - PhD Thesis Florian Ludwig 2011

The key objectives of this study The investigations of this study aim at the interpretation of hydrochemical data with regard to weathering processes involved in natural groundwater evolution. Interpretation of the data is supported by the approach of the thermodynamic equilibrium model used to verify possible patterns of mineral alteration reactions. The key objectives are the verification of mineral alteration reactions suggested by mass transfer calculations, considering saturation states of the mineral phases involved and the individual mineral dissolution rates. The determination of the secondary mineral phase is an important issue of this study. Primarily, the secondary mineral phase is required to balance mineralogical transformations, but furthermore, the secondary mineral assemblage may subsequently affect groundwater quality. Thus, one basic issue of this research is the evaluation of the impact of physical processes such as surface complexation, sorption and ion exchange on groundwater composition. These processes are associated to the availability of iron hydroxides and smectites as the secondary mineral phase. The quantification of dissolved ions sorbed or exchanged as a function of pH is fundamental for the description of hydrochemical groundwater evolution. With regard to heavy metals and arsenic transported in natural groundwaters, the determination of the prevalent element species and the estimation of their affinity to sorption on iron hydroxides are essential to define mobility controls of theses elements.

Thesis layout The investigations of this report combine field studies and lab experiments. Mineral alteration processes associated to water-rock interaction of natural groundwater evolution are interpreted by comparing these reactions to reactions proceeding under laboratory conditions. Chapter 1 and 2 compile investigations on the hydrochemical groundwater evolution of near-surface to greater depth in the Bunter sandstone sequence of the Odenwald and in the basaltic sequence of Mt. Wasserkuppe, High Rhön. Contemplations are based on field data of groundwater composition, rock analysis data, hydrochemical composition of rainfall, and the results of short-term batch experiments involving the leaching of the original rocks. Solute compositions of both natural groundwaters and leachates are constrained to mineral alteration reactions calculated by inverse modelling. Dissolution-precipitation constraints are referred to the saturation stages of the minerals involved. The interpretation of the modelled mineral alteration reactions also includes a discussion of the limitations of laboratory experiments to simulate natural weathering processes. Calculated sorption curves allow the estimation of the influence of sorption and ion exchange processes on groundwater composition. The results are compiled as hydrochemical models for each aquifer lithology, describing the chemical and

- 10 - Introduction physical processes involved in natural groundwater maturation. The mobility of heavy metals and arsenic as potentially toxic or noxious dissolved elements in natural aquifer systems is discussed in chapter 3. Investigations are based on a data set of 130 samples from seven groundwater environments including those discussed in the previous course. The elements concerned are constrained to the Eh-pH conditions of the groundwaters and are classified in speciation diagrams. The mobility of dissolved element species is also referred to sorption on hydrous ferric oxides as precipitate during groundwater evolution. Modelled sorption curves allow the estimation of demobilisation of dissolved element species as a function of pH. The speciation diagrams illustrate the prevailing element species which allows the discussion of its solubility. The results of mobility investigations are assembled and discussed individually for each element.

References Drever JI (1997) The geochemistry of natural waters. 3rd edn. Prentice Hall, 686 New Jersey, 436 p Edmunds WM, Shand P (2008) Natural Groundwater Quality. Blackwell Publishing, p 469 Garrels RM, Christ CL (1965) Solutions, Minerals and Equilibria. Freeman, Cooper & Com- pany, p 450 Garrels RM, Mackenzie FT (1967) Origin of the chemical composition of some springs and lakes. In: Stumm W (ed) Equilibrium Concepts in Natural Water Systems. Advances in Chemistry 67:222-242 Helgeson HC (1968) Evaluation of irreversible reactions in geochemical processes involving minerals and aqueous solutions – I. Thermodynamics relations. Geochim Cosmochim Acta 32:853-877 Postma D, Kjøller C, Søgaard Andersen M, Condesso de Melo MT, Gaus I (2008) Geochemi- cal Modelling of Processes Controlling Baseline Composition of Groundwater. In. Ed- munds WM, Shand P (eds) Natural Groundwater Quality. Blackwell Publishing, p 469 White AF (2005) Natural Weathering Rates of Silicate minerals. In: Drever JI (ed) Surface and Groundwater, Weathering, and Soils. 5:133-168 Zhu C, Schwartz FW (2011) Hydrogeochemical Processes and Controls on Water Quality and Water Management. Elements 7:169-174 Zuddas P (2010) Water-Rock Interaction Processes Seen through Thermodynamics. Elements 6:305-308

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Chapter 1: Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany – A Laboratory and Field Study

Chapter 1: Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Moun- tain Range, Germany – A Laboratory and Field Study

Abstract

Field and laboratory investigations were performed to identify the principal mechanisms of the hydrochemical groundwater evolution among low mineralised groundwater in the Triassic Bunter sandstone aquifer of the Odenwald low mountain range, central Germany. Hydro- chemical composition comprises low pH, SO4-rich near-surface groundwaters issued by springs (Ca-Mg-SO4-type) grading to SO4-poor deep groundwaters with near-neutral pH (Ca-

HCO3-type). Batch experiments of the original rock were run to determine primary mineral alteration reactions and the origin of dissolved ions. Principal experimental reactions comprise the decomposition of anorthite, K-feldspar, biotite, and jarosite as mineral components of the original sandstone rock and the formation of clay minerals of the smectite group (Ca- montmorillonite, beidellite), and iron hydroxides as secondary minerals. Mobilisation of fluid inclusion in quartz grains contributes to Na+ and Cl- concentrations in the leachates. The evolution of deep groundwater circulation proceeds by mineral alteration reactions calculated by inverse modelling of both primary and secondary minerals to produce low-T mineral phases. The dissolution of K-feldspar converts Ca-montmorillonite to illite (illitisation). The formation of Na-beidellite correlates with decreasing concentration of Na+ in solution. Mineral reactions further proceed to the formation of kaolinite as stable mineral phase. As indicated by 2- modelled adsorption curves, the decrease of SO4 concentrations during groundwater evolu- 2- tion relates to the adsorption of SO4 on iron hydroxides. The leaching of calcite indicated for individual groundwaters relates to the distribution of loess in the appropriate catchment areas. Keywords: hydrochemical groundwater evolution, mineral alteration reactions, sulfate adsorption, illitisation, Triassic Bunter sandstone sequence, Germany

1 Introduction

Groundwater in the Bunter sandstone sequence (Buntsandstein) of the Odenwald low mountain range in Germany indicate a characteristic diversity of groundwater types. Ca-Mg-SO4- type waters prevail in shallow groundwaters produced by springs. Low pH values (4.5-5.5) allow high mobility of dissolved Al species with concentrations exceeding 800 µg l-1. Mobil- ity of an ion is referred to its non-conservative transport in the aquifer system with possible effect by chemical (e.g. precipitation) or physical (e.g. sorption) processes. With increasing depth, groundwaters grade to a Ca-HCO3-type with near-neutral pH and Al concentrations below detection limit. In contrast to increasing total of dissolved solids (TDS, mg l-1) and specific electric conductivity (SEC, µS cm-1) during groundwater evolution, the concentrations of 2- SO4 significantly decrease with increasing pH values. In general, groundwaters are poorly mineralised and the TDS rarely exceeds 100 mg l-1.

- 15 - PhD Thesis Florian Ludwig 2011

Some recently published research on groundwater evolution in siliceous, calcite-free or decalcified aquifers such as the Bunter sequence can be summarized as follows: in non- carbonate lithologies, Al-silicate mineral weathering determines groundwater composition (Appelo and Postma 2005). Here, the most rapid weathering reactions such as the decomposition of plagioclase will have the largest effect on groundwater composition (Van Camp and Walraevens 2008). The investigations of White et al. (1999, 2005) proved calcite, if present in the overburden (e. g. included in a loess cover), to react even more rapidly to initially domi- nate groundwater chemistry in a calcite-free aquifer lithology. Mineral reaction kinetics has also been an aspect of investigations of Coetsiers and Walraevens (2008) on groundwater evolution in a partly decalcified aquifer in Belgium. They identified that quartz, though com- prising the dominant component of the aquifer rock, does not contribute significantly to the groundwater composition due to its high resistance to weathering. Referring to Appelo and Postma (2005), Al-silicate weathering leads to the formation of secondary mineral phases such as clays (illite, montmorillonite, and kaolinite), and Fe oxides. With regard to the impact of rainfall loads on groundwater chemistry in a sandstone aquifer in France, Huneau and Travi (2008) identified meteoric water to be the major source of several solutes in the groundwater. Shand et al. (2002) identified chemical groundwater compositions similar to those in the Odenwald in a Triassic sandstone aquifer in the U.K. Concentrations of Ca2+, Mg2+, and - HCO3 partially exceed those of the Odenwald groundwaters and relate to calcite and dolo- mite leaching. The Bunter sequence of the Odenwald has already been the issue of numerous investigations focussing on hydrogeological aspects. Friedrich (2007) determined groundwater ages of near-surface groundwaters of 2-5 years, and increased groundwater ages of 10-20 years in 3 3 deeper-lying aquifers, using H- He- and SF6-dating methods. Quadflieg (1990) discussed the occurrence and evolution of shallow groundwater resources issued by springs in the Bunter of 2- Northern Hessen. He identified low pH values and high SO4 loads due to the impact of acidic rain. Balázs et al- (1992) and Balázs (1998) validated these findings for other areas of the Bunter sequence in Hessen, such as the Odenwald. He compiled findings about the long- 2- term monitoring of bulk deposition by rainfall, which suggest a decrease of SO4 and increasing pH values in meteoric water. Still, the geochemical processes involved in deep groundwater circulation in the Bunter sandstone sequence of the Odenwald have not been sufficiently described yet. This study concerns the hydrochemical evolution of groundwaters with depth, considering water-rock interaction processes in the Bunter sandstone sequence. Use is made of the hydrochemical data from natural groundwaters, X-ray fluorescence (XRF) analysis of rock samples and residual fillings of rock fractures, and thin-section analysis. In addition, batch experiments were run for samples of the Bunter sequence and for residual fracture fillings. The hydrochemical information acquired was then used for the hydrochemical modelling of dissolu-

- 16 - Chapter 1: Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Moun- tain Range, Germany – A Laboratory and Field Study

tion-precipitation constraints of the primary and secondary mineral phases and alteration products in the aquifer system. The key objectives of the study are: (i) a general description of the systematics of mineral alterations due to water-rock interaction in the Bunter rock sequence; (ii) to evaluate the con- 2- tribution of sulfate sorption on protonated FeOOH exchange sites to the decrease of SO4 concentrations in deep groundwaters; and (iii) to describe hydrochemical groundwater evolution according to groundwater flux from shallow to aquifers at greater depth.

2 Study Area

2.1 Geography and Climate Data The low mountain range of the Odenwald is located 60 km south-east of the city of Frankfurt in central Germany. The study area covers approximately 1,000 km² of the eastern part of the Odenwald between the longitudes 8°40’E and 9°10’E and the latitudes 49°25’N and 49°50’N. It is limited by the crystalline basement in the west and Tertiary and Quaternary deposits and basaltic intrusions of the Rheinheimer Bight in the north. The south-eastern limit is consti- tuted by the rivers Main and Neckar (Fig. 1). The area is predominantly covered with trees (spruce) and agricultural activity is very limited. Altitudes are up to 570 m in the south, with lower elevation values in the north. The climate is of moderate humid type with a mean annual rainfall of 800 mm in the north and 1200 mm in the south, and an average annual temperature of 10°C in the north and 9°C in the south. Evapotranspiration amounts to 500 mm per year in the north and 600 mm per year in the south. The climate data was provided by the Hessian Agency for the Environment and Geology (HLUG).

2.2 Geological Setting The Triassic Bunter sandstone of the central Odenwald predominantly comprises an interbedded sequence of beds of siliciclastic sandstone and thin layers of claystone with nearly horizontal stratification. Some recent publications by Backhaus et al. (2002, 2003) focus on the description of the lithostratigraphic series of the Bunter sandstone in the Odenwald and compile sedimentological interpretation of core samples. According to Backhaus and Schwarz (2003), the entire sequence builds up a total thickness of 450 m. The deposition of the Bunter sediments evolved at the northern rim of the Kraichgau basin between the northern Black Forest range to the south-east and the Odenwald range to the north-west (Karrenberg 1981). Sedimentation occurred as complex fluvial-lacustrine deposition under continental conditions in an arid-type climate. The detrital sediments derived from the disintegration of predominantly granitic crystalline rocks of the Black Forest highlands south-west of the basin (Kar-

- 17 - PhD Thesis Florian Ludwig 2011

renberg 1981; Geyer 2002). The strata of the Bunter sandstone rock sequence predominantly comprises quartz, K-feldspar and plagioclase, minor amounts of biotite and muscovite (K- mica) as lithic clasts. Interpreting core samples of the northern Odenwald, Dersch-Hansmann and Hug (2004) identified iron-bearing minerals, various amounts of syn-sedimentary clay minerals and authigenic chlorite in the intergranular pore space. The investigations of Möderl (1996) proved an intergranular mineral assemblage of jarosite, illite, kaolinite, and goethite as dominant Fe mineral in two Bunter core samples.

fluviatile deposits loess deposits Upper Bunter Middle Bunter Lower Bunter spring well

cross section

R R i

W_05 i v

W_03 v

e e

r r W_40 M nt a e A'' in m e s S_07 W_19 W_39 a W_31 b W_18 e A' n li W_01 W_30 l ne a t to S_02 s ys r S_32 d c A n a s S_27 n ei t W_12 s d n W_35 a s nt u B er N v e S_10 i c R k S_34 a r

05101520 km

Fig. 1 Location of the study area; detailed geological map of the Bunter sandstone (Buntsandstein) of the Odenwald, the Michelstädter Graben is the central tectonic structure, striking NNE-SSW; groundwater sampling sites are shown as triangles (springs) and squares (wells); map modified after HLUG (2003)

- 18 - Chapter 1: Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Moun- tain Range, Germany – A Laboratory and Field Study

During late Mesozoic and early Tertiary, the rift of the Upper Rhine Valley led to intense tectonic segmentation of the rock sequence and to the evolution of the Michelstädter Graben (Fig. 1; Fig. 2). In the central and northern parts of the investigation area, loess deposits with a thickness of up to several metres represent the latest geological, glacial evolution.

A 7.5 kmA' 15 km A'' 500 S_02

Ca-Mg-SO 400 4

W_01 W_19 L LB Ca-Mg-SO4

300 Ca-Mg-SO4 W_18 W_39 W_31 LB L Ca-HCO3 L y x L UB MB x Ca-HCO3 200 x x x MB LB MB x 100 x LB Ca-HCO x x LB 3

altitude (metres above sea level) crystalline basement x 0 LB

normal fault well spring groundwater flow path -100 LBLower Bunter MBMiddle Bunter UB Upper Bunter L loess deposits

Fig. 2 Cross-section of the investigation area with indication of groundwater flow paths and water types; the position of the cross-section is shown in Fig. 1

Table 1 Subdivision of the Bunter sandstone sequence in the Odenwald according to Backhaus and Schwarz (2003) Subsequence Formation Thickness of subformation Upper Bunter Röt formation 35 m Röt 4 Röt clay and quartzite approx. 95 m 28 m Röt 3 Röt sandstone 17 m Röt 2 Röt sandstone 6 m Röt 1 Röt siltstone Solling formation 9 m Solling sandstone Middle Bunter Hardegsen formation 16 m Fels sandstone approx. 150 m 14 m Hardegsen alternating sequence 23 m Hardegsen sandstone Detfurth formation 21 m Detfurth alternating sequence 12 m Detfurth sandstone Volpriehausen formation 25 m Upper Volpriehausen alternating sequence 22 m Lower Volpriehausen alternating sequence 17 m Volpriehausen sandstone Lower Bunter Miltenberg formation 60 m Miltenberg alternating sequence approx. 190 m 78 m Miltenberg sandstone Eck`scher Pebble horizon 52 m Eck`scher pebble sandstone

Investigations focus on the upper section of the subsequence of the Lower Bunter (LB) (Miltenberg Formation) and the Middle Bunter (MB) (Volpriehausen, Detfurth, and Hardegsen Formation). A subdivision of the different formations of the Bunter sandstone in - 19 - PhD Thesis Florian Ludwig 2011

the Odenwald is compiled in Table 1. As described by various authors, the LB generally comprises a more fine-grained spectrum of rock debris (Karrenberg 1981; Rosenberg 1999; Geyer 2002; Backhaus and Schwarz 2003). The LB sandstone is cemented by the inter- granular groundmass (clay minerals), contributed by secondary quartz growth. In contrast, the MB is composed predominantly of quartzitic sandstone. It comprises well-rounded mineral grains and only sparse amounts of inter-granular groundmass. The rock is silicate cemented by secondary quartz growth (Dersch-Hansmann and Hug 2004). In the investigation area, deposits of the Upper Bunter have been nearly completely eroded, and patches of minor extent remained along the eastern border of the field of investigation and in the central part of the Michelstädter Graben.

1.5 MB MB (Vogel) MB (Rosenberg) 1.0 Fe-shale LB Fe-sand LB (Vogel) LB (Rosenberg) 0.5 LB fracture #1

O) LB fracture #2

2 lith- shale sublitharenite

/K arenite 3 O 2 0 f#2 quartz f#1 arenite

log (Fe log wacke -0.5 arkose subarkose

-1.0

-1.5 012

log (SiO2/Al2O3) Fig. 3 Classification of rocks of the Lower (LB) and Middle Bunter (MB) and fracture fillings of the LB according to Herron (1988); data illustrated refer to the rock analysis of Vogel (1994) and Rosenberg (1999) in the Bunter of the Odenwald and rock analysis performed during this study

According to the geochemical classification after Herron (1988) the Bunter strata compiles K-feldspar-rich and clay-rich arkose and subarkose (LB) and quartz grain-dominated quartz arenite (MB) (Fig. 3). Examining various core samples of the LB (two samples) and the MB (eight samples), Meisl (1965) obtained information about the distribution of grain size. The core samples of the LB lacked the grain size fraction >0.5 mm and indicated the highest amounts of the clay grain size (<0.002 mm) of all samples. In general, all MB samples indicated a more coarse-grained distribution of grain size than the LB samples.

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2.3 Hydrogeology The Bunter sandstone builds up a fissured rock aquifer with silicate rock composition and cementation and medium to high fracture permeability. Dürbaum et al. (1969) obtained information about matrix permeability by measuring about 200 core samples of the Bunter Formation. Generally, matrix permeability decreased from coarse, poorly cemented quartzitic sandstones to fine-grained clay-rich dense sandstones. Compared to gross permeability (fracture and matrix permeability) derived from pumping test data, fracture permeability significantly exceeds matrix permeability. Well yields are predominantly due to fracture permeability and, thus, wells are usually associated to tectonic disruption, as along the Michelstädter Graben (Fig. 1). In the investigation area, groundwater discharge occurs as springs associated with near- surface groundwater circulation in the fissured sandstone. The occurrence of springs relates to stratification (contact springs) or to faults (border springs). Aquifers with deep groundwater circulation are made accessible by production wells extending up to 200 m below the surface. Groundwater flow paths are illustrated in Fig. 2. The catchment areas of the springs approxi- mate to the surface catchment areas and extend to less than 1 km². The surface catchment areas of the wells are larger, extending to several km². By gauging the runoff in surface catchment areas, Hölting (1978) determined values of groundwater recharge for the Bunter sandstone sequence. Thus, in the LB of the Odenwald, groundwater recharge amounts to 80 mm a- 1, in the MB to 65-130 mm a-1, and in the Upper Bunter to less than 15 mm a-1. Apparently, in the UB, groundwater recharge is very low. The high surface runoff in this sequence may be forwarded by rather impermeable, dense beds of clay- and siltstone (Table 1). Rainfall as throughfall is significantly reduced due to intense water uptake by leaves and interception (Balázs 1998). Information on the hydraulic properties of the rocks was obtained from pumping tests on the investigated production wells. Transmissibility (T) was estimated according to Logan (1964). He applied an approximation formula to the results of pumping tests as:

T = (2.43 Q m) (s (2m-s))-1 for unconfined conditions, if the available information is limited to discharge (Q), drawdown

(s), and aquifer thickness (m). Hydraulic conductivity (kf) was then calculated by the division -6 -5 - of T by the aquifer thickness. The kf-values for the LB range from 2.8 x 10 to 1.7 x 10 m s 1, and those for the MB from 9.3 x 10-7 to 3.3 x 10-4 m s-1 (Table 2). The ranges of hydraulic conductivities match data for the Bunter strata published by Matthess (1970). The kf values represent hydraulic conductivity of the fissured sandstone aquifer and combine both matrix and fracture permeability (Dürbaum et al. 1969, Stober and Bucher 2007). However, matrix

- 21 - PhD Thesis Florian Ludwig 2011

permeability in the Bunter sandstone sequence may be significantly reduced due to high amounts of fine-grained clay minerals in the matrix. The inter-granular pore space in the predominantly quartzitic sediments has also been reduced during diagenesis by secondary quartz growth. The dissolution of feldspar minerals can produce a secondary porosity. According to Dersch-Hansmann and Hug (2004), the inter-granular pore space in core samples of the northern Odenwald amounts to 10-15%. However, the secondary porosity is almost entirely refilled with a fine-grained matrix of clay minerals and authigenic chlorite.

3 Methods

The groundwater sampling was accomplished in June 2005. Seventeen samples were taken from production wells and springs in the Lower and Middle Bunter sequence. The sampling sites were chosen to represent groundwaters with minimal anthropogenic influence. The catchment areas are predominantly covered by forest (spruce). The groundwater samples were taken out from the running production process. At each sampling site, six samples were collected in 250-ml pre-washed polyethylene bottles and one in a 1-l glass bottle. An extra sample was filtered through a 0.45-µm Cellulose Acetate Millipore membrane filter to separate suspended sediments and added with 2 ml nitric acid to avoid the precipitation of dissolved material. Samples were kept refrigerated during transport to avoid changes in the chemical composition. Water temperature, specific electrical conductivity (SEC), the concentration of dissolved oxygen, and pH values were measured in the field. Major and minor cations (Ca2+, 2+ + + Mg , Na , K , Fetotal, Si) were analysed by inductively coupled plasma optical emission spec- - 2- - trometry (ICP-OES; Perkin Elmer Optima 3000 DV), and anions (Cl , SO4 , NO3 ) were detected by ion chromatography (Dionex DX 500). The detection of Al was performed by inductively coupled plasma mass spectrometry (ICP-MS; Perkin Elmer Elan 6100). The determination of alkalinity was gained by titration. An ion balance error of ±10% was deemed acceptable; most error values do not exceed ±5%. All analyses were accomplished at the state laboratory of the County of Hessen (LHL), Wiesbaden. To determine similarities and differences, individual correlation matrices were calculated for the spring and the well groundwaters. Since rainfall provides the primary input of solutes to recharge waters, it has to be accounted for the hydrochemical evolution of the groundwaters. The rainfall chemistry averaged for the hydrological cycle 2004-2005 is shown in Table 2. The data comprises values for throughfall under a forest canopy (spruce) and values for grassland. For the latter, the values have been multiplied by a factor of 2 to take into account the regional evapotranspiration. Long-term observations (1987-2005) of the rainfall input as throughfall are illustrated in Fig. 4.

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-1 2 SiO mg l -1 2 CO mg l -1 3 NO mg l -1 4 SO mg l 25.0 5.0 26.8 9.5 22.0 5.211.0 8.8 n/a n/a 6.5 7.5 3 -1 ere accomplished in June 2006; accomplished ere a a a 3.8 HCO 1.1 1.4 mg l -1 ion by a factor of two takes into account account into takes two of a factor by ion mg l -1 µg l µg -1 3300.5 µg l µg -1 mg l -1 mg l -1 not analysed not .3.6 2.7 2.7 1.6 1.6 b.d. b.d. b.d. b.d. 6.3 5.5 97.6 2.9 58.0 1.3 8.6 8.5 36.5 11.9 33.2 12.9 .5 3.1 1.4 b.d. b.d. 5.1 61.6 4.9 3.4 n/a 13.2 mg l n/a -1 mg l -1 SECpHCaMgNaKAlFeCl µS cm 952550 4.50 2.9 4.90 0.7 5.20 0.6 1.4 0.2 2.0 0.4 0.5 4.4 1.0 0.3 53 0.6 10 25 20 7 3.8 14 18.8 0.8 1.6 7.8 19.1 38.2 14.6 2.5 5.0 3.6 7.2 ll under a spruce canopy and grassland precipitation; multiplicat precipitation; grassland and canopy under a spruce ll -1 2 O mg l ta of 11 wells and six springs in the study area; groundwater testing and analysis w and analysis testing groundwater area; study in the springs and six 11 wells ta of central Odenwald; data provided by the HLUG) Odenwald;central by data provided Alkalinity calculated by difference by calculated Alkalinity Temp Eh ° C mV a -1 f k m s (m-m) sequ. Hydraulic properties and hydrochemical da and hydrochemical properties Hydraulic below detection limit detection below concentrations of solutes in precipitation represent throughfa represent precipitation in solutes of concentrations Fürth, station (gauging evapotranspiration the W_01W_03 LBW_05 LB 16-69W_12 LB 14-71 5.15E-06W_35 10.6 LB 65-117 1.70E-05 11.2 1.23E-05 LBW_18 335 25-48 11.7 9.0W_19 275 35-65 MB 2.79E-06 323 8.0 11.3 57 40-120 MB 8.4 4.28E-06 9.5 197 285 3.27E-06 130 8-12 11.2 11.6 6.02 239 5.7 6.53 57 3.28E-04 321 10.5 6.34 9.5 29.0 9.5 0.8 19.0 93 4 6.83 2 77 316 1.6 6.4 9.7 6.87 2.2 0.9 9.5 107 6.01 b.d. 9.6 1.6 2.8 5.13 b.d. 1.6 1.5 1.6 8.5 4.2 1.9 b.d. 1.8 2.6 12.2 1.6 b.d. b.d. 3.3 2.7 2.8 b.d. b.d. 2.6 6.6 b.d. 15.3 2.7 61 20.7 5.1 4.1 15.6 10.3 b.d. 3.4 27.5 19.0 6.6 1.8 5.2 7.0 6.8 n/a 9.6 24.2 6.0 12.9 Table 2 IDSite Sub- Screen detection limits W_30W_31 MBW_39 MB 59-148W_40 MB 62-200 8.71E-06 11.1 MB 55-132 9.25E-07S_02 11.8 292 71-102 1.73E-06S_07 8.9 10.9 276 LB 4.93E-06S_10 8.2 11.5 51 310 LBS_27 8.6 MB 73 242S_32 10.1 5.83 MB 55S_34 5.8 136 6.17 LB 9.8 0.8 2004/05 spruce Precip. 5.85 LB 6.31 5.9 2004/05 freeland Precip. 1.3 19.2 1.6 2004/05 x2, freeland Precip. 8.0 0.9 2 2.0 1.5 10.6 1.9 1.4 342 b.d. 8.7 371 10.8 1.6 b.d. b.d. 7.8 12.1 94 327 b.d. b.d. 2.9 104 8.1 10.3 414 b.d. 2.9 18.3 81 8.5 10.6 4.53 4.51 267 4.0 0.7 5.8 32.3 69 6.6 10.2 267 1.3 15.9 4.4 4.98 2.4 109 10.8 2.6 4.9 1.1 2.8 5.06 n/a 58 1.8 2.8 5.4 4.69 2.1 6.0 n/a 12.9 2.4 4.8 2.7 1.6 2.1 n/a 5.54 13.4 853 2.3 4.4 533 1.4 1.7 11.9 b.d. 6.5 b.d. 1.3 1.8 485 3.0 4.6 2.3 1.8 183 b.d. b.d. b.d. 878 1.6 b.d. 4.0 22.0 28.0 b.d. 2.3 190 b.d. 11,0 6.3 11.0 b.d. 11.0 b.d. 22.0 10.6 7.0 5.5 3.1 18.0 7.2 6.6 15.0 7.0 14.5 5.7 b.d.

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The chemical composition of rock samples of the Lower and Middle Bunter was detected by XRF analysis (Philips PW 2404) at the Mineralogical-Geochemical Institute, University of Freiburg. For preparation, all samples were ground to 10-µm grain size and then dried for 48 h at 50°C. One gram of sample powder was added to 4 g Spectromelt® as tableting agent for melt digestion. The samples represent a clay-rich arkose rock type and a quartz-dominated, K- poor quartz arenite. In order to compare original rock with the secondary mineral assemblage derived through weathering, additional chemical analysis was run for residual fracture fillings. Original and residual samples are from the same location. The fracture fillings were sampled at joint planes dissected in an active quarry.

20 5 Ca Mg Na K

Cl SO4 NO3 pH

15 4.5 ) -1

10 4 pH value concentrations (mg l

5 3.5

0 3 1986 1991 1996 2001 2006 Fig. 4 Long-term observations (1987-2005) of the rainfall input as throughfall, gauging station Fürth, central Odenwald

Information about the individual mineral assemblages as well as about the rock porosity and the occurrence of fluid inclusions was obtained by thin-section analysis. Point counting of the individual mineral grains allowed an estimation of the modal mineral composition of the rock samples of the Lower and Middle Bunter. In order to investigate mineral alteration reactions and to determine the origin of dissolved constituents, short-term batch experiments were conducted. It was not the aim to simulate long-term water-mineral reactions approaching near-equilibrium. The experiments focused on the variation of concentrations of dissolved ions in the leachates associated with the different rock samples. Rock samples of the Lower and Middle Bunter and two additional samples of fracture fillings of the Lower Bunter were ground to 40-µm grain size to increase the reactive surface. One hundred grammes of rock sample were allowed to react with 250 g of pure wa-

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ter. The experiments were run over periods of 30 min in contact with the atmosphere (PCO2 x 10-3.5 atmos) using a glass reaction vessel. A second run was performed isolated from the atmosphere with the addition of CO2 through a glass pipe into the leaching solution. Batch experiments of the fracture fillings were performed at atmospheric PCO2. The leaching solutions were kept in rotation by electric stirring during the experiments to avoid sedimentation of the reactive material. The final leaching solutions were centrifuged twice and filtered through 0.45-µm acetate membranes. The major cations and anions were determined at the University of Freiburg, the analysis of metals including Si was run at the LHL, Wiesbaden. Mineral alteration reactions related to natural groundwater evolution were calculated by application of the PHREEQC code (Parkhurst 1995) using an inverse modelling approach. Inverse modelling was chosen for the straightforward stoichiometric determination of mass transfers and to identify similar patterns of mineral reactions. The modelled mineral alteration reactions were constrained by the values of the saturation indices (SI) to verify the plausibility of precipitation or dissolution of the distinct minerals. For the calculations, the concentrations 2+ 2+ + + - - 2- 3+ of dissolved Ca , Mg , Na , K , Cl , HCO3 , SO4 , Al , Fetotal, Si, PCO2, and pH were considered. A maximum difference between calculated and observed values of 5% was accepted. The reactions involving the original rocks and the leaching waters to produce secondary minerals were deduced from interpretation of the batch experiments. As the modelling approach to investigate the natural groundwater evolution, acidic, poorly mineralised and SO4- rich spring water (sample S_27) was allowed to react with primary and secondary minerals to evolve to the groundwaters at greater depth. However, the modelling approach does not incorporate possible changes in near-surface groundwater composition. Thus, for interpretation of the modelling results, long-term changes in the composition of rainfall were taken into account.

2- Ion adsorption as the explanation for decreasing SO4 concentrations during groundwater evolution was found to be consistent with the filed concentrations. Low pH values of the initial solutions and the availability of iron in the Bunter rock sequence (goethite) as well as in the fracture fillings (hydrous ferric oxides as a precursor of goethite) favour the attraction of 2- SO4 to protonated exchange sites (Hingston et al. 1972; Drever 1997; Zhang and Peak

2007). A semi-quantification of SO4 sorption on FeOOH can be obtained by the calculation of adsorption curves. Calculations were run using the PHREEQC code and the thermodynamic data base of WATEQ4 (Ball and Nordstrom 1991). As modelling approach, the generalised two-layer model introduced by Dzombak and Morel (1990) without the calculation of the diffuse-layer composition was used. A value of 100 m² g-1 for the specific surface area was used to average the values of goethite (60-90 m² g-1, Gaboriaud and Erhardt, 2002) and of hydrous ferric oxides (200-750 m² g-1; Dzombak and Morel 1990). During modelling, a total amount of 1 g of iron hydroxide was reacted with 1 l of initial solution. This value relates to experi-

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mental studies of sulfate adsorption on goethite performed by Hingston et al. (1972) and 2- -4 Zhang and Peak (2007). SO4 was allowed to be attracted to a total of 4 x 10 mol of binding 2- sites, which equals the concentration of SO4 in the initial solution (S_27). Initially, all sur- 2- face sites were uncharged, to allow a maximum protonation and adsorption of SO4 . The cal- 2- culations considered the variation in sorption of SO4 on iron hydroxides as a function of pH 2- -1 -1 (4.5-7.0) for various initial SO4 concentrations (0.001-0.2 mmol l ) in 1.0 mmol l sodium nitrate background electrolyte. This value equals the total charge of dissolved constituents of 2- sample S_27 that was used as initial solution. At the time of groundwater recharge, the SO4 2- rainfall input as well as the SO4 concentrations in the shallow groundwaters exceeded present-day input values (Fig. 4). This follows from groundwater ages of 10-20 years at greater 2- depth (Friedrich 2007) and the associated water composition. The calculated amounts of SO4 adsorbed comprise both monovalent and bivalent bindings to the protonated binding sites. The sorption model is sensitive to various factors and some of them had to be estimated. It, thus, represents an approximation to the complexity of the aquifer system.

4 Results and Discussion

4.1 Modal Mineral Composition and Analytical Rock Data Thin-section analysis and point-counting proved quartz, feldspar minerals, biotite, and muscovite as lithic clasts of the original granitic rocks and opaque phases as the principal components of the sandstone. The data are compiled in Table 3. Compared with the Middle Bunter, the Lower Bunter contains less quartz (about 65%), but more K-feldspar, plagioclase, biotite, and muscovite. The mineral composition of the Middle Bunter is dominated by quartz (84%) and subordinate amounts of feldspar and K-mica (less than 6%).

Table 3 Thin-section analysis of rock samples of the Lower and Middle Bunter; opaque phase comprises an assemblage of clay minerals and oxides/hydroxides Sample #3, LB #5, LB #6, MB Subsequence Lower Bunter Lower Bunter Middle Bunter Formation Lower Miltenberg Upper Miltenberg Volpriehausen Location Quarry Schmelzer, Quarry Hintenlang, Quarry Zell- Sensbachtal Grasellenbach Langenbrombach Quartz 66.4 63.9 83.9 K-feldspar 16.0 13.7 3.1 Plagioclase 2.9 2.3 1.4 Opaque phase 7.1 10.7 2.5 Biotite 2.3 4.9 1.1 K-mica 1.9 2.9 0.3 Pore space 2.8 1.6 7.6 Σ counts 935 879 850

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Both samples of the Lower Bunter comprise a microcrystalline/opaque groundmass in the inter-granular space, significantly reducing rock porosity (pore space 1.6-2.8%). The sample of the Middle Bunter has a higher porosity (7.6%) due to only a sparse amount of a microcrystalline/opaque phase in the inter-granular space. The individual components of the microcrystalline/opaque phase could not be determined by microscopic analysis. Referring to scan- ning electron microscopy (SEM) analysis performed by Möderl (1996) of samples of the Lower Bunter, the fine-grained mineral assemblage comprises clay-minerals (illite, kaolinite) as well as goethite and jarosite. Fluid inclusions were found in quartz grains in all samples. They are present in many crustal rocks, including the Black Forest granite (Stober and Bucher 1999; Stober et al. 2002). Black Forest crystalline rocks represent the parent rock material of the sedimentary deposits of the Bunter sequence in the Odenwald. Fluid inclusions in metamorphic rocks investigated by Mullis and Stadler (1986) and Yardley et al. (1989) proved low-salinity NaCl fluids as well as high-salinity NaCl and CaCl fluid compositions. The XRF data confirm the mineral composition identified by thin-section analysis. A comparison of the Al2O3 concentrations indicates larger amounts of Al-silicate minerals in the Lower Bunter sample than in the Middle Bunter sample (Table 4). In addition, elevated amounts of Ca, Mg, Na, and K correlate with higher amounts of K-feldspar, plagioclase, and clay minerals in the sample of the Lower Bunter. The sample of Middle Bunter contains only limited amounts of both Al2O3 and the major cations, and SiO2 exceeds 98%. The total iron exceeds 1% in the Lower Bunter, with the value for the Middle Bunter being about seven times lower. Both analyses are similar to the data presented by Vogel (1994), who investigated core samples of the central Odenwald. The fracture fillings f#1 and f#2 can be related to the mineral alteration assemblage derived from natural rock weathering of the LB. In comparison with the original rock, the analytical data indicate comparable amounts of Ca, Na, and K and increased amounts of Mg. In addition, increased amounts of both Al2O3 and Fe2O3 contrast with decreased amounts of SiO2. As suggested by Singh et al. (1999) who studied natural systems, the iron accumulated in the water is likely to form hydrous ferric oxides, which may eventually transform to crystalline goethite. The LOI values (loss on ignition) of 2.17 and 3.3% indicate greater amounts of H2O in the mineral assemblage of the fracture fillings. The loss and gain of concentrations of elements in the mineral alteration assemblage is likely to correlate with distinct mineral alteration reactions and can, thus, be associated to groundwater evolution.

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4.2 Composition of Leachates and Interpretation of Batch Experiments The leaching solutions for the Lower and Middle Bunter rock samples indicate differences in their hydrochemical compositions (Table 5). The major ion compositions of the leachates are illustrated in the Schoeller plot of Fig. 5. The addition of CO2 as a weak acid results in higher values of dissolved anions and cations in the leachates. In all sandstone leachates, the Na:Cl 2+ 2- molar ratios are less than 1. There is no significant correlation between Ca and SO4 .

+ K is the dominant cation in both leachates of the LB rock sample. The addition of CO2 increases the K+ concentration by a factor of 3, similar to the increase in dissolved Na+ and Si. 2+ 2+ Ca and Mg concentrations are very low in the leachates at atmospheric PCO2, but the addition of CO2 significantly increases concentrations in the solution by factors of 70 and 11, re- - spectively. Cl is the major anion in samples at atmospheric PCO2. The addition of CO2 sig- - nificantly increases the concentration of HCO3 due to mineral alteration reactions, whereas - 2- the concentrations of Cl and SO4 remain at approximately constant values. Cl:Br molar ratios are 350 and 226, respectively, in the two LB leachates. The concentrations of dissolved 3+ Al and Fetotal both decrease with increasing PCO2.

At atmospheric PCO2, the leachate of the MB sample has approximately equal amounts of both alkali and alkali earth elements. Apart from K+ as the major cation, there are elevated 2+ 2+ - amounts of Ca and Mg . HCO3 is the major anion, and compared with the LB leachate, the - 2- concentration of Cl is lower and the concentration of SO4 higher. The addition of CO2 in- 2+ - + creases the concentrations of Ca and HCO3 by a factor of 2. The increase of K is less pro- 2+ 2- + - nounced and approximates that of Mg . There is no significant increase in SO4 , Na , Cl , Si or Cl/Br molar ratios (155 and 350, respectively). In contrast to the LB, the leachate of the 3+ MB indicates an increase in Al by a factor of 3 through the addition of CO2. Fetotal increases 3+ by a much smaller factor. For both samples, the concentration of dissolved Al and Fetotal are rather high with respect to the near-neutral pH. However, these values correlate with the findings of Zhu (2001), who performed batch experiments on samples of the LB of the Black For- est mountain range. The values derived through his experiments even exceed those of this study (Table 5). The hydrochemical compositions of the leachates of the fracture fillings (LB) contrast with those of the original rock. Most evidently, the initial pH of 5.5 (pure water) decreases to values of 4.53 and 4.63, respectively. During leaching of the original rock, the pH increased to 2+ 2+ 2- 7.23. The concentrations of Ca , Mg , and SO4 mobilised from the fracture filling samples significantly exceed those of the leachate of the original rock. Na:Cl molar ratios are close to 1. The amounts of dissolved Si indicate only limited dissolution of Al-silicate minerals. The concentrations of Fetotal are close to the detection limit.

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Mt. Konradsbuckel loss on ignition on loss LOI Quarry north of Seckmauern Quarry Hintenlang, Grasellenbach Quarry Hintenlang, Grasellenbach Quarry Zell- Quarry Langenbrombach Lower BunterUpper Miltenberg Quarry Hintenlang, Volpriehausen Grasellenbach Middle Bunter Upper Miltenberg Lower Bunter Upper Miltenberg Lower Bunter Upper Miltenberg Volpriehausen Lower Bunter Middle Bunter (%) 3.19 0.21 3.03 3.48 3.40 0.23 (%) 87.74(%) 0.17(%) 5.91(%) 1.06(%) 0.01(%) 98.11 0.16(%) 0.05 0.03 0.56 0.15(%) 0.04 0.00(%) 82.16 98.56 0.01(%) 0.78 0.02 0.27 8.92 2.39 0.02 0.04 75.63 99.13 0.40 0.20 0.06 0.27 12.59 3.53 0.08 86.90 0.04 97.59 0.61 2.17 0.07 6.62 1.35 94.46 0.10 96.55 0.00 0.30 3.30 0.00 1.85 2.00 99.75 0.19 0.17 0.25 0.14 99.20 0.73 (%) 0.13 0.01 0.15 0.12 0.21 0.16 XRF analysis data of rock samples of the Lower and Middle Bunter and fracture fillings of the Lower Bunter; Bunter; Lower the of fillings fracture and Bunter Middle and Lower the of samples rock of data analysis XRF 3 3 5 2 2 O O O 2 O 2 2 O 2 2 SiO P Table 4 4 Table SampleSubsequence Formation Location #5, LB #6, MB cleft#1 cleft#2LB* MB* TiO Al Fe MnO MgO CaO Na Sum LOI Data* Vogel by (1994) K

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-1 2 mg l -1 Brmg l SiO -1 4 SO mg l fer to the leachate data of the leachate fer to 3 -1 mg l -1 mg l -1 µg l µg -1 µg l µg -1 three (CL 30/98, CL 31/98, CL 32/98) re 32/98) 31/98, CL 30/98, CL three (CL mg l -1 mg l -1 mg l -1 mg l -1 µS cm µS ion of the leachates; the values in the last values the leachates; the ion of Temp pH SEC Ca Mg Na K Al Fe Cl HCO leaching min °C (final) sequ. liquid LB 2:5MB 30 2:5 30 20 7.76 20 266 7.29 218 7.1 5.5 15.4 4.2 6.2 2.8 105.0 112 25.7 82 1,800 249 21.8 8.9 186.7* 4.0 89.1* 0.22 8.8 26.1 0.08 11.7 2 2 Batch experiments, hydrochemical composit hydrochemical Batch experiments, Table 5 Table Leachate Sub- solid/#5, LB t CO #5, LB LB 2:5 30 20 7.23 78 0.1 0.2 2.5 31.8 855 327 20.2 12.2 5.4 0.13 8.2 Zhu (2001); solid/liquid ratios refer to the mass ratios of the rock sample and pure water as leachate water pure and sample the rock of ratios mass the to refer ratios solid/liquid (2001); Zhu #6, MB#6, MB CO cleft#1 MBcleft#2 2:5 30/98CL 30 LB 31/98CL LB 2:5 B 32/98CL 20 2:5 30 B 1:5 difference calc. by *alkalinity 30 B 6.54 1:5 88 60 d 20 1:5 60 d 20 22 4.53 60 d 7.5 271 22 4.63 6.30 91 48 22 2.4 6.60 10.6 56 6.67 2.6 10.2 2.7 36 1.3 1.5 6.9 18.5 2.6 0.3 2.1 584 0.5 6.6 1.9 2.0 0.5 185 1.8 640 3.9 11.4 3.6 6.9 30 11.4 20,090 54 5.7 2,150 1,156 48.2 8.8 2.3 30 520 30,960 9.1 2,481 5.8* 9.8 4.0 2.4 0.10 0.9 75.4 6.4 15.9 10.3 3.7* 17.1 2.3 19.7 <0.015 3.1 24.2 3.7 0.036 <0.015 14.2 21.6 5.0

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As a general assumption, both sandstone rock samples can be expected to react similarly, given their comparable mineral compositions. However, the variation in the hydrochemical evolution of the leaching solutions suggests that differing amounts of primary minerals and the associated formation of secondary minerals affects the ‘final’ composition of the leachate. Inverse modelling of the leachates rendered inappropriate results with respect to the mass transfers calculated. Most likely, the leachates were far off equilibrium with the mineral phases involved at the end of the short-term batch experiments. However, long-term batch experiments performed by Zhu (2001) indicate even higher Al and Fe concentrations at near- neutral pH at the end of the experiments (60 days).

#5, LB #5, LB CO2

#6, MB #6, MB CO2 leachates Zhu (2001)

1 ) -1 c (meq l

0.1

0.006 0.01

MgCa Mg+Ca Na+K Cl HCO3 SO4

Fig. 5 Schoeller plot of the leachate compositions #5 and #6 with and without the addition of CO2; the green lines refer to the leachate data of Zhu (2001)

A non-quantitative model of mineral alteration can be deduced by comparison of the leachates at atmospheric PCO2 with those with added CO2, using the saturation indices (SI) compiled in Table 6.

The concentrations of cations significantly increase with the addition of CO2, whereas the - 2- concentrations of Cl and SO4 are not affected. The investigations of Möderl (1996) proved tiny amounts of jarosite in association with goethite in the Bunter strata. As indicated in Table

6, all leachates are highly undersaturated with respect to jarosite. Independent of PCO2, 2- jarosite is likely to dissolve, releasing SO4 to the solution and forming e. g. goethite:

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- 2- + + KFe3(SO4)2(OH)6 + OH → 3FeOOH + 2SO4 + K + 2H + H2O.

2- - In a similar way to SO4 , the concentrations of Cl appear to be independent of PCO2. The Cl:Br molar ratios of the leachates are less than in seawater (approx. 650), but are similar to those determined in fluid inclusions in metamorphic rocks and quartz veins in the crystalline basement at different locations (Yardley et al. 1989, 1992, 1995). The values also are similar to those of leaching experiments on sandstone rocks of the Black Forest performed by Zhu (2001). Mineral fragments of crystalline rocks from the Black Forest are present in the strata of the Bunter sequence. The cracking, during grinding when the samples were being prepared, of these inclusions is likely to contribute to the concentrations of both Cl- and Na+ in the leachates. The Na:Cl molar ratios of the leachates are <1 (0.2-0.6). Since the Na:Cl molar ratios do not exceed 1:1, NaCl fluid inclusions appear to be the only source for dissolved Na+. With respect to the leachates, the origin of both Na+ and Cl- can be associated to the mobilisation of cracked fluid inclusions.

Table 6 Saturation indices of the leachates and the natural groundwaters; mineral abbreviations as recommended by Siivola and Schmid (2007); Bdl = beidellite, Jar = jarosite, Chal = chalcedony Leachate/ An Bt Hl Ill Jar Kln Kfs NaKMg- Na- Cal Ca- Chal Gt Gp groundwater Bdl Bdl Mnt sample

#5, LB -2.57 7.08 -8.80 5.38 -4.21 7.67 1.71 6.16 13.94 -4.13 6.04 -0.25 7.31 -5.32

#5, LB CO2 -1.70 12.51 -8.41 5.69 -6.97 6.84 2.80 6.04 13.76 -1.35 6.02 0.25 6.41 -3.83 #6, LB -0.97 10.34 -9.27 5.43 -5.00 7.49 1.57 6.12 13.86 -1.86 6.25 -0.16 6.98 -3.34

#6, LB CO2 0.43 11.83 -9.14 6.91 -4.72 8.60 2.37 7.52 13.23 -1.32 7.67 -0.10 7.07 -3.10 S_27 -10.55 -7.91 -9.98 -3.13 2.75 -4.08 -0.47 8.25 -4.90 -0.26 -0.30 -3.15 W_01 -9.66 -3.49 -0.04 -3.92 W_03 -9.28 -1.58 0.02 -3.32 W_05 -9.33 -2.14 0.05 -3.78 W_12 -9.84 -2.63 -0.07 -3.60 W_18 -9.61 -3.00 0.05 -3.90 W_19 -11.1 -7.11 -9.16 -3.57 2.02 -3.86 -0.96 7.81 -4.55 -0.79 -0.08 -2.84 W_30 -9.81 -3.59 0.05 -4.51 W_31 -9.73 -2.77 0.07 -4.02 W_35 -9.86 -2.35 -0.27 -2.91 W_39 -9.61 -3.51 0.02 -4.32 W_40 -9.30 -2.16 0.06 -3.22

The concentrations of dissolved Ca2+, Mg2+, and K+ can be related to the dissolution of anorthite, biotite, and K-feldspar. The addition of CO2 intensifies the leaching of the primary minerals. In the case of significant oversaturation (Table 6), a controlling factor on the cation concentrations including Na+ in the leachates is likely to derive from formation of secondary

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minerals of the smectite group. The formation of Ca-montmorillonite and NaKMg-beidellite results in the removal of dissolved ions; for example, Ca2+ and Mg2+ concentrations in the + atmospheric PCO2 LB experiment are low. The addition of CO2 increases H activity and this limits the formation of secondary minerals and increases the amounts of dissolved Ca2+ and Mg2+, as well of those of Na+ and K+.

2+ 2+ + The MB leachate at atmospheric PCO2 has concentrations of Ca , Mg , and K exceeding those of the LB leachate though the MB sandstone has less anorthite, biotite, and K-feldspar. Apparently, the formation of secondary minerals appears to be less distinctive in comparison to the LB. Mineral decomposition increases with the addition of CO2, though mineral alteration reactions are less intense in comparison with the LB sample.

Alkalinity in the leachates derives from the dissolution of CO2 as:

- + 2 CO2 + 2 H2O → 2 HCO3 + 2 H and the consumption of H+ through the alteration of feldspar minerals to minerals of the smectite group. The alteration of anorthite and the formation of Ca-montmorillonite proceeds as follows:

+ 2CaAl2Si2O8 + 6H → 2+ 3+ 4+ - Ca0.165Al2.33Si3.67O10(OH)2 + 1.835Ca + 1.67Al + 0.33Si + 4OH

with the consumption of CO2 and H2O. The formation of NaKMg-beidellite can either be described as the alteration of biotite:

+ 3+ 4+ KMg3AlSi3O10(OH)2 + 0.11Na + 1.33Al + 0.67Si → + 2+ (KNaMg0.5)0.11Al2.33Si3.67O10(OH)2 + 0.89K + 2.945Mg

or as the alteration of K-feldspar with the consumption of CO2 and H2O

+ 2+ 3+ + 2KAlSi3O8 + 0.11Na + 0.055Mg + 0.33Al + 6H → + 4+ - (KNaMg0.5)0.11Al2.33Si3.67O10(OH)2 + 1.89K + 2.33Si + 4OH .

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In general, the hydrochemical evolution of the leachates relates to leaching reactions with the particular mineral components in the rock samples and to the cracking and mobilisation of fluid inclusions as well. However, the reaction kinetics of the batch experiments do not parallel with the natural weathering conditions. The leaching of intact mineral grains with low reactive surface is likely to proceed more slowly than in the batch experiments. The comparison of the lifetimes of silicate minerals (Lasaga 1984) suggests low stability of Ca-feldspar (anorthite) but high stability of K-feldspar. Quartz can be considered as insoluble in the timescale of groundwater ages.

4.3 Groundwater Chemistry and Hydrochemical Evolution The analytical groundwater data compiled in Table 2 indicate that two principal hydrochemical facies are present. All spring groundwaters are Ca-Mg-SO4 in type, whereas groundwaters from deep wells are of a Ca-HCO3-type. Two samples of shallow wells (W_19, W_35) have a 2- - transition type with elevated concentrations of both SO4 and HCO3 (Fig. 6). The ranges of SEC of shallow and deep groundwaters predominantly comprise comparable values (58-109 and 51-107 µS cm-1 respectively). In the case of the well groundwaters, three samples indicate -1 2+ - elevated values (130-197 mS m ) due to high concentrations of Ca and HCO3 . The pH values significantly increase from shallow (4.5-5.5) to deeper (5.1-6.9) groundwaters, as well as the concentration of dissolved Si.

Mg SO4

80 20 80 20

W_19 60 40 60 40 W_35

40 60 40 60

W_35 20 80 20 80

W_19 Ca80 60 40 20 Na+K HCO 80 60 40 20 Cl 3 Fig. 6 Ternary plots of the major cations and anions of the springs (circles) and wells (squares) investigated; black symbols indicates LB, red symbols indicates MB; the grey fields indicate the dispersion of groundwater analysis data for the Bunter sequence of the Odenwald compiled by Berthold and Toussaint (1998)

Correlation matrices for the spring and well groundwaters are compiled in Table 7. The 2+ - well groundwaters indicate significant correlation of Ca and HCO3 (0.97), which are the 2- major dissolved constituents. With respect to SO4 , there is a significant inverse correlation (- + + 0.75) to SiO2. An inverse correlation is also suggested for K and SiO2 (-0.49). Na correlates

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to Cl-with a coefficient of 0.87, whereas the spring groundwaters indicate a perfect match of Na+ and Cl-(1.00). Both ions also show a high correlation to the total of dissolved solids 2+ + 2- (TDS) (0.90 and 0.89, respectively). Mg indicates correlation to both K (0.88) and SO4 (0.95).

Table 7 Correlation coefficients of major ion concentrations in the well and spring groundwaters

Mg Na K Cl HCO3 SO4 NO3 SiO2 TDS

Wells Ca 0.86 0.63 -0.25 0.63 0.97 -0.14 0.49 0.28 0.99 Mg 0.66 0.09 0.67 0.72 0.35 0.47 -0.13 0.88 Na 0.24 0.87 0.49 0.32 0.15 0.25 0.69 K 0.45 -0.43 0.68 0.20 -0.49 -0.20 Cl 0.49 0.24 0.55 0.18 0.68

HCO3 -0.37 0.45 0.44 0.95

SO4 -0.16 -0.75 -0.07

NO3 0.06 0.45

SiO2 0.29 Springs Ca 0.68 -0.19 0.77 -0.22 -0.71 0.77 0.11 -0.01 0.18 Mg 0.40 0.88 0.39 -0.49 0.95 -0.12 0.13 0.70 Na 0.42 1.00 0.42 0.30 -0.51 -0.09 0.90 K 0.38 -0.30 0.82 0.03 0.08 0.71 Cl 0.42 0.29 -0.53 -0.07 0.89

HCO3 -0.65 0.05 0.32 0.21

SO4 -0.32 -0.03 0.59

NO3 0.34 -0.40

SiO2 0.18

Fig. 7 illustrates the constraints of major cations and anions, indicating characteristic Ca:Mg molar ratios for both shallow and deep aquifers. While shallow groundwaters exhibit Ca:Mg molar ratios of 1.3-2.1 (average ~ 1.6), values of 3.7-4.8 (average ~ 4.5) indicate increasing concentration of Ca2+ relative to Mg2+ in the deeper groundwaters. Two exceptional 2- well samples (W_19 = 2.0; W_35 = 2.1) also have elevated concentrations of SO4 (19.0 and 25.0 mg l-1) comparable with those of the spring groundwaters (11.0-28.0 mg l-1). At greater 2- -1 -1 - depth, SO4 rarely exceeds 5 mg l (well groundwaters 0.7-5.1 mg l ). Cl concentrations indicate no significant increase or decrease with depth. The well samples, perhaps, have lower Na:Cl molar ratios than the spring samples. High concentrations of Al3+ are significantly correlated with low pH values. For all groundwater samples, the concentrations of Fetotal are below the detection limit (30 µg l-1). Data of the hydrochemical composition of meteoric water for the hydrological cycle 2004- 2005 are shown in Table 2. All dissolved constituents can be assumed to contribute to hydrochemical groundwater composition (Balázs 1998). The values of throughfall significantly - 35 - PhD Thesis Florian Ludwig 2011

exceed those of grassland rainfall. This correlates to the investigations of Moss and Edmunds (1992) on soil waters, who identified greater rates of assimilation of dissolved constituents in meteoric water by the woodland biome. Since the investigation area is covered with trees (spruce), groundwater recharge can be considered to derive predominantly from throughfall. + - - With the exception of K , HCO3 , and NO3 , all concentration values of dissolved ions in the + - recharge are below the values of the spring groundwaters. K and NO3 can be taken up by vegetation and may, therefore, be found at lower concentrations in recharge waters than in rainfall (Shand et al. 2002; Huneau and Travi 2008).

10 well, LB well, MB spring, LB spring, MB prec. forest prec. grassland x2

1 ) -1 c (meq l

0.1

0.01

Mg Ca Mg+Ca Na+K Cl HCO3 SO4 Fig. 7 Schoeller plot of the groundwater compositions of the springs and wells; the composition of rainfall is illustrated as green (grassland multiplied by a factor of 2) and blue (throughfall) line, respectively; for some spring groundwaters, HCO3 concentrations fall below detection limit and are thus not illustrated

Long-term hydrochemical data of throughfall (Fig. 4) indicate rather constant values for - 2- alkali and alkali earth elements and Cl , whereas concentrations of SO4 significantly decreased during the last decades (1987: 18.5 mg l-1; 2005: 6,5 mg l-1). Analogously, the pH - increased within a decade (1987-1997) from 3.78 to 4.32. The concentrations of NO3 do not -1 - show any trend and vary between 8 and 18 mg l . The concentrations of NO3 in the spring and well groundwaters are very likely to derive from atmospheric input, since agricultural land use in the catchment areas hardly occur. The calculation of mass transfers during groundwater evolution identified common mineral reactions for all groundwater samples (Table 8). All groundwater samples could be associated with the alteration of Ca-montmorillonite and K-feldspar and with rather limited mobilisation of NaCl fluid inclusions. The mobilisation of Na+ through alteration of the albite component

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of the plagioclase appears to be negligibly small, as albite could not be integrated into the modelling approach. The breakdown of biotite and the leaching of calcite from a loess cover could be occurring in a small group of groundwaters, and some groundwater samples indicate leaching of anorthite (W_35) and KNaMg-beidellite (W_39). Sample W_35 appears to be rather immature, with significant undersaturation of chalcedony (Table 6). Decreasing con- 2- centrations of SO4 with depth may be associated with sulfate adsorption on iron hydroxides (see below). In the natural groundwater system, jarosite does not appear to be a major source 2- of SO4 . Calculations were run without jarosite as the reactive phase, as it is likely to be exhausted due to low stability. The principal mineral reactions controlling the hydrochemical groundwater evolution can be summarised as illitisation of Ca-montmorillonite according to continued dissolution of K- feldspar:

2+ 3+ 4+ - Ca0.165Al2.33Si3.67O10(OH)2 + KAlSi3O8 + 0.5Mg + 1.33Al + 0.33Si + 4OH → 2+ + 2K0.5Mg0.25Al2.33Si3.5O10(OH)2 + 0.165Ca + 2H and the alteration of K-feldspar to Na-beidellite and subsequent sequestration of Na+

+ 3+ + 2KAlSi3O8 + 0.33Na + 0.33Al + 6H → + 4+ - Na0.33Al2.33Si3.67O10(OH)2 + 2K + 2.33Si + 4OH .

The dissolution of K-feldspar may then result in illitisation of Na-beidellite. Illitisation may well be associated with the hydrogeochemical environment of the Bunter sandstone strata. The dissolution of feldspar minerals (and biotite) in a humid climate at moderate temperatures proceed to the formation of secondary clay minerals of the smectite group (several authors, compiled in Heim 1990). Subsequent dissolution of K-feldspar at low rates issues a continuous source of K+ converting secondary smectite minerals to illite. Analogous to the Bunter strata, Singer and Stoffers (1980) described the illitisation of smectite clay minerals associated with K-feldspar-rich sandstone rocks. The formation of Na-beidellite associated with the dissolution of K-feldspar is consistent with the high degree of oversaturation in the initial solution (S_27, Table 6). Greater degrees of oversaturation favour the formation of Na- beidellite. The availability of biotite and the sequestration through illitisation are both likely to control the concentrations of Mg2+ in the groundwaters.

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gained 2 fixed CO 4 ) -1 (mmol l (mmol Ill Na-Bdl SO Formation 2 consumed An CO Bdl Bt Cal NaKMg- 4 mobilised ) -1 (mmol l (mmol Hl Kfs Ca-Mnt SO Decomposition sequence Calculated mass transfers during the hydrochemical evolution of the natural groundwaters natural the of evolution hydrochemical the during transfers mass Calculated W_01W_03 LBW_05 LBW_12 LBW_35 0.043 LBW_18 0.113 LB 0.068W_19 0.090 MB 0.023 0.177W_30 0.014 MB 0.054 0.255W_31 0.011 MB 0.052 0.205W_39 0.051 MB 0.052 0.095W_40 0.121 0.068 MB 0.020 0.013 0.030 MB 0.198 0.047 0.017 0.014 0.076 0.145 0.026 0.048 0.583 0.076 0.027 0.112 0.073 0.079 0.304 0.069 0.088 0.018 0.056 0.062 0.012 0.052 0.127 0.071 0.008 0.095 0.098 0.026 1.909 0.317 1.232 0.289 0.117 0.134 0.110 1.934 0.233 0.141 0.178 0.009 0.101 0.103 0.143 0.154 0.814 0.143 0.048 0.103 0.094 0.170 0.395 0.379 0.121 0.018 0.140 0.165 0.791 0.157 0.006 0.132 0.027 0.138 0.155 0.167 0.170 0.012 0.012 0.133 1.047 0.177 0.133 0.173 Table 8 Table Site ID Sub-

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In comparison with the original rock, XRF analysis data of the fracture fillings of the LB (Table 4) reflect the modelled mineral alteration processes. The increase of Mg can be linked with the formation of illite. Constant amounts of Na may result from its incorporation in Na- beidellite after the mobilisation of NaCl fluid inclusions, with Na:Cl molar ratios decreasing in the groundwaters with time. Constant amounts of Ca are likely to reflect the alteration of anorthite to Ca-montmorillonite prior to conversion to illite. In general, increasing amounts of

Al2O3 suggest the formation of clay minerals. The increasing amounts of Fe2O3 can be associated to the accumulation of Fe-hydroxides as poorly soluble mineral phase.

The concentration of Fetotal in the natural groundwaters is basically controlled by pH and Eh. Within the range of pH values of the natural groundwaters, the solubility of solid iron phase is at a minimum. High redox potentials as in the investigated groundwaters favour iron to exist as poorly soluble Fe3+ rather than as soluble Fe2+. Investigations performed by Liu and Millero (2000) on the solubility of iron hydroxides in low-salinity solutions proved that solubility of Fe-hydroxide is limited to values lower than 10-8 mol l-1 at a pH range of 5.5 – 7.0 in 0.7 mmol NaCl solution. The concentration of Al3+ in the natural groundwaters is controlled by pH and the activity of H4SiO4. At pH values of 5.5- 7.0, the concentrations of dissolved aluminium species does -8 -1 -1 -4 -1 not exceed 10 mol l (~0.3 µg l ), assuming the activity of H4SiO4 of 10 mol l and equilibrium with kaolinite. Increasing the activity of H4SiO4 further decreases solubility of solid phase, and Al3+ is incorporated within the structure of secondary minerals, as indicated for the mineral assemblages of the fracture fillings. Calcite as a dissolved component could be associated with groundwaters in the northern section of the Michelstädter Graben. In this area, loess deposits occur containing calcite to more than 10% (Vogel 1994). In contrast, in the southern part of the investigation area with the absence of a loess cover, groundwaters do not indicate calcite leaching. The saturation indices of all groundwaters indicate the undersaturation of calcite. Thus, the formation and leaching of secondary calcite is rather unlikely. The modelled values of CO2 are constrained to equal the concentrations of CO2 of individual groundwater samples. High concentrations relate to groundwaters associated to calcite leaching (W_03, W_05, W_19); CO2 has been transferred from the gas phase to replace the CO2 consumed by the dissolution of calcite (Drever 1997). Low concentrations (e.g. W_12) indicate groundwater evolution limited to the alteration of Al-silicate minerals. The mobilisation of fluid inclusions from quartz grains through weathering proceeds rather slowly due to very low dissolution rates of quartz. In comparison to the shallow groundwaters, the concentrations of Cl- increase only insignificantly in the groundwaters at greater depth. The concentrations of Cl- in rainfall suggest that a major amount of Cl- in the groundwaters relates to atmospheric input. This correlates with the findings of Huneau and Travi

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(2008), who identified Cl- in the groundwater largely to derive from rainfall. In the Odenwald, physical quartz weathering at shallow depth may contribute to the Cl- concentrations in the groundwater. In addition, and analogous to Huneau and Travi (2008), rainfall input appears to 2- be the major source of SO4 in the recharge and in the shallow groundwater. Therefore, the 2- concentrations of SO4 in the groundwater may predominantly be related to an atmospheric 2- origin and may, therefore, be sensitive to long-term changes of SO4 concentrations in meteoric water.

4.3.1 Sulfate Adsorption The calculated curves of sulfate adsorption on iron hydroxide suggest adsorption as a control- 2- ling factor on SO4 in the groundwaters. Several calculation runs were performed with varia- 2- -1 tion in pH and in the initial concentration of SO4 . The variation of total iron at values ≤1 g l did not affect the calculated sulfate adsorption curves. As displayed in Fig. 8, sorption will be 2- 2- favoured at low pH and high initial SO4 concentrations. At pH 4.5 and an initial SO4 concentration of 0.2 mmol l-1 in solution, 0.13 mmol l-1 would be fixed with mono- and bivalent 2- binding to protonated exchange sites. At pH 7.0, the amount of SO4 adsorbed would be reduced by a factor of 10. The calculated values are similar to the experimental studies of Zhang and Peak (2007), who determined sulfate adsorption isotherms at comparable pH values and 2- initial concentrations of SO4 .

) initial SO4 (S_27) -1 pH 4.5 pH 5.0 -1 pH 5.5 pH 6.0

pH 6.5 adsorbed (mmol l 2- 4 pH 7.0 -2 log c SO c log

-3 00.10.2

2- -1 c SO4 initial solution (mmol l )

2- Fig 8 Adsorption curves of sulfate on goethite at different pH values. The SO4 concentration of sample W_27 as initial groundwater is indicated by the dashed line; cSO4 = sulfate concentration

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Relating to groundwater evolution, sulfate sorption decreases with increasing pH values, caused by both Al-silicate mineral alteration reactions and protonation of exchange sites. Dur- ing protonation and adsorption, the loss of acidity (H+ activity in solution) equals half the loss 2- of sulfate (Drever 1997). At an early stage of evolution, SO4 may be significantly extracted 2- from groundwaters, whereas lower SO4 concentrations in mature groundwaters at near- 2- neutral pH can be considered as more stable. The occurrence of high SO4 concentrations in acid spring groundwaters is likely to reflect the depletion of free exchange sites in the near- 2- surface aquifers. This suggests that the adsorption of SO4 is related to groundwater circula- 2- tion to greater depth. Low pH and high SO4 concentrations at shallow wells (W_19, W35) indicate the progression of the acidification and sulfate breakthrough front to a greater depth. 2- Near-neutral pH and low SO4 concentrations of groundwaters at greater depth suggest effec- 2- tive SO4 adsorption. This correlates to the findings of Quadflieg (1990), who studied the impact of acid rain on groundwater in the Bunter sequence of Northern Hesse. Investigating soil solutions associated to a carbonate-free Triassic sandstone sequence in the U.K., Moss and Edmunds (1992) related acid-neutralising reactions to K-feldspar dissolution. The depletion of K-feldspar and other leachable Al-silicate minerals at shallow depth is, thus, likely to contribute to a shift of the sulfate breakthrough front. XRF analysis of the mineral alteration residue in the fracture space indicates significantly higher amounts of iron than the original rock (Table 4). This suggests that sulfate adsorption favours reactions with the fracture fillings and coatings on joint planes rather than to interaction with the original rocks. Batch solution reactions with pure water contrast with those of 2- the original rock. Low pH and high SO4 values of the leachates of the fracture fillings indi- + 2- cate remobilisation of H and SO4 from the exchange sites.

4.3.2 Hydraulic Properties Studies of the hydraulic properties of fissured rocks (e.g. Matthess 1971; Strayle et al. 1994;

Stober and Bucher 2007) identified decreasing hydraulic conductivity (kf value) due to decreasing joint aperture, which reduces with increasing depth. Decreasing aperture may also occur because of the generation of secondary minerals through rock weathering. The wells investigated indicate a notable exponential constraint of kf values and the average depths of the screened section (Fig. 9). The data is supplemented by seven wells from the area of investigation without further relation to either the LB or the MB. The distribution of points suggests a rapid decrease of hydraulic conductivity with depth for the shallow wells (average depth of screened section <40-50 m). At greater depth, the curve indicates a steeper gradient. The hydraulic conductivity appears to decrease only to minor extent with increasing depth.

- 41 - PhD Thesis Florian Ludwig 2011

-1 kf-values (m s ) 10-7 10-6 10-5 10-4 10-3 0 MB

20 R² = 0.63

LB 40

80 LB

100

120 MB average depth screened of section (mbs)

140

2 Fig. 9 Average screen depth plotted versus kf values, R of the trend line indicates a notable exponential constraint (black line), black squares indicate wells of the LB; red squares indicate wells of the MB; additional hydraulic data of wells in the Bunter sequence of the Odenwald without stratigraphic assignment derive from construction files and are illustrated as black crosses

The wells in the LB refer to average hydraulic conductivities (10-6-10-5 m s-1) at shallow depths, whereas the wells in the MB predominantly refer to average hydraulic conductivities (10-6-10-5 m s-1) at deep well depths. It appears, that in the LB, hydraulic conductivity is more poorly developed than in the strata of the MB. This might be explained by the fine-grained groundmass in the LB, causing a reduced rigidity of the rock sequence and a less developed degree of rock fracturing. In comparison, the MB strata indicates a more brittle deformation. Greater availability of reactive primary minerals in the LB is likely to contribute to higher transformation rates of primary to secondary minerals. This could explain the observations of a more intense formation of coatings on joint planes and a reduction of fracture aperture in the LB strata, contributing to a decrease of the hydraulic conductivity of the joint network.

4.3.3 Stability Constraints Stability relations among K-feldspar and alterations products are illustrated in Fig. 10. The standard state for the aqueous species corresponds to unit activity of the species in a hypothetical one molal solution referenced to infinite dilution at any pressure and temperature according to Helgeson et al. (1978). Whereas spring groundwaters plot along the line of quartz saturation, all well groundwa-

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ters reflect oversaturation with respect to quartz. Values increase with increasing aK+/aH+ ratios (a = ion activity). All groundwaters indicate kaolinite as the most stable mineral phase. Due to the subsequent release of K+, OH-, and silica through the alteration of K-feldspar, the chemical composition of the well groundwaters evolves towards the illite-montmorillonite stability field.

7 springs, LB wells, LB Quartz 6 K-mica springs, MB wells, MB

5 K-feldspar Illite ) + 4 amorphous silica /aH +

3 Kaolinite log (aK log Montmorillonite

2 Gibbsite

1 Pyrophyllite 0 -5 -4 -3 -2

log a H4SiO4 Fig. 10 Stability relations among K-feldspar and some alteration minerals; the saturation of quartz and amorphous silica are displayed as dashed lines (after Garrels 1984); a = ion activity

However, in the present system, montmorillonite and illite have to be considered as metastable mineral phases. Mineral alteration reactions further proceed to the formation of kaolinite. The decomposition of illite to kaolinite is as follows:

+ K0.5Mg0.25Al2.33Si3.5O10(OH)2 + 5H → + 2+ 3+ 4+ - Al2Si2O5(OH)4 + 0.5K + 0.25Mg + 0.33Al + 1.5Si + 3OH under consumption of H+. The release of K+, Mg2+ and silica into solution provokes further approach to the illite stability field.

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5 Conclusions

Groundwaters in the Bunter fissured rock sequence of the Odenwald originate from meteoric water. The hydrochemical evolution of the groundwaters derives from water-rock interaction during circulation in the joint network. The composition of dissolved constituents is basically controlled by the dissolution of K-feldspar, anorthite, (and biotite) and the formation of secondary minerals, e.g. Ca-montmorillonite and Na-beidellite. Leaching experiments of the original rocks contributed to the determination of the origin of dissolved constituents in the natural groundwaters. The leachate compositions suggest that the 2- - concentrations of SO4 and Cl in the near-surface groundwaters are not geogenic and predominantly relate to rainfall input. The mobilisation of fluid inclusions through the weathering of quartz grains may contribute to the concentrations of Na+ and Cl-. The dissolution of K- feldspar also results in the illitisation of secondary smectites. Sulfate adsorption on iron hy- 2- droxides is controlled by pH, the availability of free exchange sites and by SO4 activity. In the central part of the Michelstädter Graben, the leaching of calcite from a loess cover may contribute to hydrochemical groundwater evolution. All water-rock reactions can be comprised in the graduation of a Ca-Mg-SO4 groundwater type in poorly evolved near-surface waters to a Ca-HCO3 groundwater type at greater depth. Groundwater types were found to represent the grade of groundwater maturation. In the LB, mineral alteration reactions of primary to secondary minerals are more intense than in the MB and are likely to reduce hydraulic conductivity due to reduction of the fracture aperture.

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References

Appelo CAJ, Postma D (2005) Geochemistry, groundwater, and pollution. 2nd edn. Balkema Publishers, Rotterdam, 649 pp Backhaus E, Bähr R, Binding M (2002) Faziesbild und stratigraphische Einstufung des Mit- tleren und Oberen Buntsandsteins am unteren Neckar (TK 25, Blatt 6620 Mosbach) [Facies and stratigraphic classification of the Middle and Upper Bunter sandstone along the lower Neckar (TK 25, sheet 6620 Mosbach)]. Geol Jb Hessen 129:79-101 Backhaus E, Schwarz S (2003) Ein Sammelprofil des Buntsandsteins und Zechsteins im mitt- leren Odenwald anhand von Bohrungen und Gamma-Logs [An accumulative profile of the Bundsandstein and Zechstein rock formation on the basis of drillings and Gamma- logs]. Geol Jb Hessen 130:91-107 Balázs A (1998) 14 Jahre Niederschlagsdeposition in Hessischen Waldgebieten – Ergebnisse von den Meßstationen der Waldökosystemstudie Hessen [14 years rainfall deposition in Hessian forests – results of the gauging stations of the forest-ecosystem study in Hes- sen]. Forschungsberichte HLFWW 25, p 129 Balázs A, Brechtel HM, Führer H-W (1992) Saure atmosphärische Niederschlagsdepositionen und ihre Auswirkungen auf die chemische Qualität von Quellwasser im Hessischen Buntsandstein-Mittelgebirge [Acidic rain deposition and ist influences on the chemical quality of forest spring water in the Hessian highlands of Bunter sandstone]. Forstwis- senschaftliches Centralblatt, Hess Forstl Versuchsanst 111(3):156-168 Ball JW, Nordstrom DK (1991) WATEQ4F: user’s manual with revised thermodynamic data base and test cases for calculating speciation of major, trace, and redox elements in natural waters. US Geological Survey Open-File Report 90–129, 185 p Berthold G, Toussaint B (1998) Grundwasserbeschaffenheit in Hessen, Auswertung von Grund- und Rohwasseranalysen bis 1997 [Groundwater quality in Hessen, report on groundwater and raw water analysis data until 1997]. Hess L-Anst Umwelt 250:102 Coetsiers M, Walraevens K (2008) The neogene aquifer, Flanders, Belgium. In: Edmunds WM, Shand P (eds.) Natural groundwater quality. Blackwell Publishing, United King- dom, pp 263-286 Dersch-Hansmann M, Hug N (2004) Oberer und Mittlerer Buntsandstein im Untergrund des Dieburger Beckens [Upper and middle Bunter sandstone in the bedrock of the Dieburg basin]. Geol Jb Hessen 131:81-95

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Drever JI (1997) Adsorption. In: Drever JI (ed.) The geochemistry of Natural Waters. 3rd edn. Prentice Hall, New Jersey, pp 85-105 Dürbaum H-J, Matthess G, Rambow D (1969) Untersuchungen der Gesteins- und Gebirgs- durchlässigkeit des Buntsandsteins in Nordhessen [Investigations of the matrix and rock permeability of the Bunter sandstone in northern Hesse]. Notizbl Hess L-Amt Boden- forsch 97:258-274 Friedrich R (2007) Grundwassercharakterisierung mit Umwelttracern: Erkundung des Grundwassers der Odenwald-Region sowie Implementierung eines neuen Edelgas- Massenspektrometersystems [Characterisation of groundwater by environmental trac- ers: Groundwater investigation in the region of the Odenwald and implementation of a new system of noble gas mass spectrometry]. PhD Thesis, University of Heidelberg, 272pp Gaboriaud F, Erhardt J-J (2003) Effects of different crystal faces on the surface charge of col- loidal goethite (α-FeOOH) particles: an experimental and modeling study. Geochim Cosmochim Acta 67(5):967-983 Garrels RM (1984) Montmorillonite/illite stability diagrams. Clays Clay Min 32(3):161-166 Garrels RM, Mackenzie FT (1967) Origin of the chemical compositions of some springs and lakes. In: Gould RF (ed) Equilibrium concepts in natural water systems. Advances in Chemistry Series 67. Am Chem Soc, pp 222-242 Geyer G (2002) Buntsandstein [Bunter sandstone]. In: Geyer G (ed) Geologie von Unter- franken und angrenzenden Regionen [Geology of lower Frankonia and adjacent re- gions]. Klett-Perthes, Gotha and Stuttgart, pp 102-152 Heim D (1990) Tone und Tonminerale [Clays and clay minerals]. Enke, Stuttgart, 157 pp Helgeson HC, Delany JM, Nesbit HW, Bird DK (1978) Summary and critique of the thermodynamic properties of rock-forming minerals. Am J Sci, 278-A, pp 1-220 Herron MM (1988) Geochemical classification of terrigenous sands and shales from core or log data. J Sediment Res 58:820-829 Hingston FJ, Posner AM, Quirk PJ (1972) Anion adsorption by goethite and gibbsite. I. The role of the proton in determining adsorption envelopes. J Soil Sci 23(2):177-192 HLUG (2003) Geologische Karte von Hessen 1:200.000 [Geological Map of Hessen 1:200,000]. Hess L-Amt Umw Geol, Wiesbaden

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Hölting B (1978) Die Buntsandsteingebiete des Hessischen Berglandes [The areas of Bunter sandstone in the Hessian highlands]. In: Keller R (ed.) Hydrologischer Atlas der Bun- desrepublik Deutschland [Hydrological atlas of the federal republic of Germany]. Deut- sche Forschungsgem, Bonn Huneau F, Travi Y (2008) The miocene aquifer of Valréas, France. In: Edmunds WM, Shand P (eds) Natural groundwater quality. Blackwell Publishing, United Kingdom, pp 287- 305 Karrenberg H (1981) Buntsandstein in Deutschland [Bunter sandstone in Germany]. In: Kar- reberg H (ed) Hydrogeologie nichtverkarstungsfähiger Festgesteine [Hydrogeology of non-karstic bedrock]. Springer, Wien pp, 174-180 Lasaga AC (1984) Chemical kinetics of water-rock interactions. J Geophys Res 89(B6):4009- 4025 Liu X, Millero FJ (2000) Iron hydroxide solubility and morphology as examined by ESEM. Preliminary report, preprints of extended abstracts, Am Chem Soc 40(2):532-534 Logan J (1964) Estimating transmissibility from routine production tests of water wells. Ground Water 2:35-37 Matthess G (1970) Beziehungen zwischen geologischem Bau und Grundwasserbewegung in Festgesteinen [Relation of geology and groundwater flow in fissured rock aquifers]. Abh Geol L-Amt Bodenforsch 58:109 Meisl S (1965) Petrographie der Buntsandsteinsedimente [Petrography of the Bunter sediments]. In: Kupfahl H-G (ed) Erläuterungen zur Geologischen Karte 5323 [Annotations on the geological map 5323]. Hess L-Amt Bodenforsch, Wiesbaden, pp 105-122 Möderl T (1996) Mineralogische und geochemische Untersuchungen an zwei Bohrkernprofi- len im Buntsandstein [Mineralogical and geochemical investigations of two drilling core profiles of the Bunter sequence]. Erlanger Beitr Petr Min 6:1-22 Moss PD, Edmunds WM (1992) Processes controlling acid attenuation in the unsaturated zone of a Triassic sandstone aquifer (U.K.), in the absence of carbonate minerals. Ap- plied Geochemistry 6:573-583 Parkhurst DL (1995) User’s guide to PHREEQC: a computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations. US Geological Survey, Water-Resources Investigations Report 95-4227, 143 p Quadflieg A (1990) Zur Geohydrochemie der Kluftgrundwasserleiter des nord- und os- thessischen Buntsandsteingebietes und deren Beeinflussung durch saure Depositionen [About the geohydrochemistry of fissured rock quifers of the northern and eastern Hes- sian Bunter sequence and the influence of acidic rain]. Geol Abh Hessen 90:110 - 47 - PhD Thesis Florian Ludwig 2011

Rosenberg F (1999) Geochemie [Geochemistry]. In: Rosenberg F et al. (eds) Erläuterungen zur Geologischen Karte 4923 [Annotations on the geological map 4923]. Hess L-Amt Bodenforsch, Wiesbaden, pp 274-292 Shand P, Tyler-Whittle R, Morton M, Simpson E, Lawrence AR, Pacey J, Hargreaves R (2002) Baseline report series 1: The triassic sandstones of the Vale of York. British Geol Surv Comm Report CR/02/102N Siivola J, Schmid R (2007) List of Mineral Abbreviations – Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 01.02.07 Singer A, Stoffers P (1980) Clay mineral diagenesis in two East African lake sediments. Clay Min 15:291-307 Singh B, Wilson MJ, McHardy WJ, Fraser AR, Merrington G (1999) Mineralogy and chemistry of ochre sediments from an acid mine drainage near a disused mine in Cornwall, UK. Clay Min 34:301-317 Stober I, Bucher K (1999) Deep groundwater in the crystalline basement of the Black Forest region. Appl Geochem 14:237-254 Stober I, Bucher K (2007) Hydraulic properties of the crystalline basement. Hydrogeol J 15(2):213-224 Stober I, Zhu Y, Bucher K (2002) Water-rock reactions in a barite-fluorite underground mine, Black Forest (Germany). In: Stober I, Bucher K (eds) Water-rock interaction. Kluwer Academic Publishers, The Netherlands, pp 171-187 Strayle G, Stober I, Schloz W (1994) Ergiebigkeitsuntersuchungen in Festgesteinsaquiferen [Yield investigations in fissured rock aquifers]. Geol L-Amt Baden-Wuerttemberg, In- formationen 6/94, 114 pp Van Camp M, Walraevens K (2008) Identifying and interpreting baseline trends. In: Edmunds WM, Shand P (eds) Natural groundwater quality, Blackwell Publishing, United King- dom, pp 131-154 Vogel C (1994) Chemische Analysen [Chemical analysis]. In: Vogel C (ed) Erläuterungen zur Geologischen Karte 6220 [Annotaions on the geological map 6220]. Hess L-Amt Bodenforsch, Wiesbaden, pp 33-38 White AF, Bullen TD, Vivit DV, Schulz MS, Clow DW (1999) The role of disseminated calcite in the chemical weathering of granitoid rocks. Geochim Cosmochim Acta 63:1939- 1953

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White AF, Schulz MS, Lowenstern JB, Vivit DV, Bullen TD (2005) The ubiquitous nature of accessory calcite in granitoid rocks: implications for weathering, solute evolution, and petrogenesis. Geochim Cosmochim Acta 69:1455-1471 Yardley BWD, Banks DA, Davies GR, McCaig AM, Grant NT (1989) Chemistry and isotopic composition of fluid from a deep thrust zone, central Pyrenees. In: Miles JM (ed) Water-rock interaction symposium, Rotterdam, pp 789-792 Yardley BWD, Banks DA, Munz IA (1992) Halogen composition of fluid inclusions as trac- ers of crustal fluid behaviour. In: Kharaka YK, Meast P (eds.) Water-rock interaction Symposium, Rotterdam, pp 1137-1140 Zhang GY, Peak D (2007) Studies of Cd(II)-sulfate interactions at the gothite-water interface by ATR-FTIR spectroscopy. Geochim Cosmochim Acta 71:2158-2169 Zhu Y (2001) Hydrogeologie und Gestein-Wasser Reaktion in der Grube Clara (Schwarz- wald) [Hydrogeology and rock-water reactions in the Grube Clara, Black Forest]. Freiburger Geowiss Beitr 15, 145 pp

- 49 -

Chapter 2: Groundwater Evolution and Mineral Alteration Reactions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany – A Case Study

Chapter 2: Groundwater Evolution and Mineral Alteration Reactions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany - A Case Study

Abstract

Groundwater sampling was accomplished in the basaltic sequence of the Rhön mountain range, Germany, in order to investigate hydrochemical groundwater evolution and to delineate mineral alteration reactions involved in natural weathering. The hydrochemical compositions of near-surface groundwaters indicate a Ca/Mg-HCO3 type with near-neutral pH and evolve to a Na-HCO3 type with high pH at greater depth. Column experiments were performed with basaltic and phonolitic rock samples to determine individual mineral alteration reactions. The basic reactions could be related to the alteration of olivine, Ca-pyroxene, plagioclase, pyrrhotite, and feldspathoids under formation of secondary clay minerals (smectites, illite) and goethite. The mineral alteration reactions deduced from the leaching experiments by inverse modelling were found to be consistent with the mineral reactions associated with the natural groundwaters. The reactions calculated for groundwater evolution involve the alteration of primary and secondary minerals to produce low-T mineral phase. The conversion of secondary Na-beidellite to illite occurs at a later stage of groundwater evolution, reducing the concentrations of K+ and Mg2+. Near-surface groundwaters do not indicate significant cation exchange. Initial cation exchange requires elevated pH values, with Mg2+ removed from solution preferred to Ca2+. Na-alkalisation of the groundwaters at greater depth suggests the exchange of Na+ for Mg2+ and Ca2+ on Na-beidellite, supported by cation exchange on coatings of iron hydroxides as alteration products. Among the mature high-pH groundwater at greater depth, the dissolution of anorthite and albite has significant effect on groundwater composition. Keywords: hydrochemical groundwater evolution; mineral alteration reactions; cation exchange; Tertiary basaltic rock sequence; Germany

1 Introduction

Groundwater terrains build up by volcanic rock aquifers constitute important resources for domestic water supply in many locations around the world. Investigations on groundwater quality, hydraulic properties and groundwater flowpaths have been the issue of various studies on basaltic groundwater environments currently used for extensive groundwater extraction. Some recent studies describing hydrogeological constraints of volcanic terrains focused on the Vogelsberg volcanic complex, Germany (Leßmann 2001), the Snake River Plain aquifer, USA (Chapelle 2005), or the Deccan Volcanic Province, India (Pawar et al. 2008). With regard to global climate control, basaltic rock weathering plays an important role for sequestration of atmospheric CO2 (e. g. Berner 1995; Dessert et al. 2003; Oelkers et al. 2008). Sus- tainable groundwater management of volcanic rocks attaining fresh water of good quality and

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the understanding of constraints of CO2-consumption through silicate mineral weathering are of great relevance both in a local and global scale. The present study aims to contribute to the understanding of hydrochemical groundwater evolution in basaltic rocks. It focuses on processes involving water-rock interaction in the basaltic field of Mt. Wasserkuppe, Rhön mountain range, Germany. At Mt. Wasserkuppe, the hydrochemical groundwater evolution proceeds isolated from the associated non-magmatic basement, comparable to a large scale column experiment. The basaltic formation is delimited by the slopes of Mt. Wasserkuppe to all sides. Groundwater recharge exclusively derives from rainfall input. There is no horizontal or vertical groundwater inflow from the Triassic lime- and sandstones. Bioactivity in the poorly developed soil cover is limited and the effect of bulk deposition on groundwater composition is marginal due to low vegetation. Thus, this location is appropriate to study groundwater evolution in basaltic rocks in a local scale. Groundwaters at Mt. Wasserkuppe indicate significant variation in hydrochemical groundwater composition. Near-surface Ca/Mg-HCO3 type groundwaters associated with basaltic rocks indicate neutral to slightly basic pH values, low mineralisation (SEC 70-200 µS cm-1) and, for a near-surface environment, reduced concentrations of dissolved oxygen (4.5- -1 6.8 mg l ). Groundwater at greater depth (80-200 m) occurs as Na-HCO3 type with high pH (9.7) and low values of SEC (108 µS cm-1, variation of 107-125 µS cm-1 in the term 1998- 2006) and dissolved oxygen (4.3 mg l-1). Groundwater temperature (11.8°C) exceeds those of near-surface groundwaters (6.1-9.7°C) confirming groundwater circulation at greater depth.

Na-Ca-HCO3 type near-surface groundwaters occur in association with insular phonolitic domes northwest of Mt. Wasserkuppe. These groundwaters indicate neutral pH and saturation of dissolved oxygen. Research papers about silicate mineral weathering and groundwater evolution in basaltic rocks have been published by numerous authors. In non-carbonate lithologies, silicate mineral weathering is the main mechanism that determines groundwater composition (Appelo and Postma 2005). Huneau and Travi (2008) identified meteoric waters to be the major source of several solutes in near-surface groundwater. Pawar et al. (2008) published a study about hydrochemical groundwater evolution in the Deccan Trap basaltic sequence, India, including contemplations about cation exchange and progressive alkalisation of the groundwater. They proved olivine and pyroxene as the major source of dissolved ions, followed by dissolution of plagioclase. Investigations by Wood and Low (1988) on groundwaters in the basaltic lithology of the Snake River, Idaho, suggest that dissolved Mg predominantly relates to hydrolysis of olivine rather than to hydrolysis of pyroxene. The significance of reaction kinetics of primary minerals to groundwater evolution has been discussed by White (2005) comparing natural weathering rates of silicate minerals as well as describing initial and late-stage natural weathering. Investigations by Leßmann (2001) on groundwater evolution in the basaltic Vo-

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gelsberg mountain-range west of Mt. Wasserkuppe suggest correlation of groundwater ages and hydrochemical groundwater types. Using isotope dating methods (14C, 3H), in combination with δ18O data, Leßmann (2001) identified groundwater ages of few years of the near- surface Ca/Mg-HCO3 type groundwaters. Na-HCO3 type groundwaters at greater depth (approx. 100-500 m) indicate ages of hundreds to thousands of years. Several studies of the basaltic field of Mt. Wasserkuppe provide information about petrological aspects (Witt-Eickschen and Kramm 1997; Jung and Hoernes 2000), data about mineral composition of rocks and modal mineral composition (Ficke 1961; Ehrenberg et al. 1992, 1994; Ehrenberg and Hickethier 2002), and hydrochemical groundwater data (Stengel- Rutkowski 1994). Although there are some data on geology, mineral compounds, and groundwater, an overview of the interaction of these members still needs to be evaluated which is the aim of this study. The key objectives of this study are (i) the determination of the principle mineral alteration reactions involved in natural weathering, (ii) the quantification of mole mass transfers of the mineral alteration reactions, and (iii) to verify the plausibility of cation exchange during groundwater evolution.

2 Study area

2.1 Geography and Climate Data The Rhön mountain range is located 100 kilometres east of the city of Frankfurt, Germany. The range strikes northeast-southwest and extents to approximately 1,800 km² between the longitudes 9° 45’ E and 10° 20’ E and the latitudes 49° 15’ N and 50° 45’ N. The morphology is shaped by a chain of mounts built up of Tertiary volcanic rocks that overlay the pre- volcanic Mesozoic basement of sandstones and limestones. Erosion processes were promoted by the uplift of the Rhön shield in the latest Tertiary. As part of the UNESCO “Biosphere Reserve of the Central Rhön”, the area of investigation comprises the plateau and slopes of Mt. Wasserkuppe as the highest elevation of the Rhön (950 m ASL = above sea level). The area is located above the tree line and is predominantly covered with grassland without any agricultural activity. The climate is of moderate humid type with a mean annual rainfall (1991-2000) of 1,200 mm and an average annual temperature of 5°C. Grass reference evapotranspiration amounts to 400-450 mm per year. The climate data was provided online by the Hessian Agency for the Environment and Geology (HLUG).

2.2 Geology The Tertiary Rhön volcanism relates to the Cenozoic intraplate volcanism of central Europe which is associated with the tectonic stress field in the foreland of the Alpine orogenic belt

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(Illies 1975; Ziegler 1992), accompanied by extension of the continental crust. As Part of the Central European Volcanic Province, volcanic activity in the Rhön correlates with Tertiary volcanism of the Westerwald, the High Eifel and the Vogelsberg. The Rhön area is situated at the south-eastern margin of the Hessian Depression which can be interpreted as the northern extension of the Upper Rhine Graben (Jung and Hoernes 2000). Volcanic activity coincides with crustal thinning and the uplift of the Moho associated with the Cenozoic rifting (Ziegler 1990). Geophysical investigations by Prodehl (1981) and Prodehl et al. (1992) prove a crustal thickness of less than 30 km. Volcanic activity occurred from the Upper Oligocene to the Mid Miocene (25 – 11 Ma) with a maximum activity from 22 to 18 Ma (Lippolt 1982), accompanied by proceeding tectonic activity.

16 phonolite olivine nephelinite 14 trachy basalt Phonolite hornblende basalt 12 alkali olivine basalt

Trachyte 10 Foidite

8 O (weight %) 2

Basanite

O + K O + 6 2 Trachybasalt Na 4 Basalt 2

0 40 44 48 52 56 60 64 SiO2 (weight %) Fig. 1 Classification of the basaltic rock types located at Mt. Wasserkuppe and the phonolitic sample of Mt. Stellberg: TAS-diagram (after Le Bas et al. 1986) of the analysed rock samples; the grey-shaded fields illustrate the chemical variation of the particular rock types in the central Rhön according Ehrenberg et al. (1994)

The volcanic rocks of the Rhön represent an alkali basalt-trachyte-phonolite association related to mixing between partial melts of enriched and depleted mantle source components in the lithosphere and in the asthenospheric mantle (Wilson and Downes 1991). The magmatic rocks comprise a spectrum of primitive olivine-nephelinites and basanites including mantle xenoliths and highly differentiated, strongly silica undersaturated sodalite-nepheline- phonolites as illustrated in Fig. 1 (Ehrenberg et al. 1992). Spinel peridotite xenoliths are abundant in outcrops of alkali olivine basalt and olivine nephelinite (Witt-Eickschen and Kramm 1997). The significant change in magmatic evolution from highly-differentiated ex- plosive trachytic magmatism to eruptions of primitive nephelinites and basanites is accompa-

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nied by a phase of intense erosion and the deposition of fluviatile volcaniclastic sediments. The individual terms of the basaltic and phonolitic rocks used in this report refer to the nomenclature introduced by Ehrenberg et al. (1992). In the investigation area of Mt. Wasserkuppe, the basaltic magmas built up a sequence of 300 m of effusive layers and subaerial intrusions overlying the Triassic sedimentary basement (Ehrenberg et al. 1992). Table 1 compiles data of a 200 m drilling profile located 800 m east of the peak of Mt. Wasserkuppe (Fig. 2). Proceeding uplift generated the segmentation of both the pre-volcanic basement and the magmatic rock sequence into tectonic blocks. The highly-viscous phonolites (Ph, approx. 19-18 Ma) occur as endogenous domes which have been exposed by erosion. They are located northwest of Mt. Wasserkuppe (Fig. 2).

Table 1 Subdivision of the magmatic-volcaniclastic sequence of Mt. Wasserkuppe according to Ehrenberg and Hickethier (2002); data refers to the drilling cores of well W2 at Mt. Wasserkuppe

Stage Magmatic-volcaniclastic Sequence Thickness olivine nephelinite (oNe) 10 m tuff (Tu) 13 m Lower Miocene fluviatile volcaniclastic sediments (fvS) 12 m approx. 116 m alkali olivine basalt (aoB) 18 m ignimbrite (Ig) 33 m trachy basalt (TrB) 30 m hornblende basalt (hoB) 14 m tuff (Tu) 9 m Upper Oligocene hornblende basalt (hoB) 14 m approx. 84 m tuff (Tu) 21 m hornblende basalt (hoB) 17 m tuff (Tu) 9 m As described by Ehrenberg et al. (1992), the groundmass of the basaltic rocks basically comprises Ca-pyroxene and/or olivine, plagioclase, feldspathoids (nepheline, leucite, and sodalite), analcite, and traces of apatite. Feldspar microcrystals (0.1-1 mm) are embedded in the groundmass of the trachy basalt, hornblende basalt, and alkali olivine basalt. Olivine, Ca- pyroxene, and hornblende also occur as macrocrystals (>1 mm); olivine and Ca-pyroxene may also occur as mantle xenoliths. According to investigations by Ficke (1961), the chemical composition of olivine macrocrystals embedded in the alkali olivine basalt and olivine nephelinite can be averaged as Mg- rich forsterite86-fayalite14. There are two different types of pyroxene to be distinguished among the analysed rocks. Pyroxene in the phonolite can be classified as Na and Fe-rich aegirine-augite, whereas Ca-dominated augite occurs among the basaltic rocks. Plagioclase is prevalent in the groundmass and as microcrystals in all magmatic rocks investigated. Ehren- berg et al. (1992) compile data about the fraction of anorthite with hornblende basalt indicating the highest values (An52-65) and trachy basalt the lowest values (An26-47). As described by

Ficke (1961), the phonolite indicates dominance of the albite component (Ab40-42) and scar-

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city of anorthite (An7-10). The values correlate with studies by Ehrenberg et al. (1992, 1994), Ehrenberg and Hickethier (1994), and by Jung and Hoernes (2000) about major minerals compiled in basaltic rocks in the Rhön area.

10°E h c a b Hilders n e a p N p i

e r

h r e

c e

t + t

S g

s l

er l U

Mt. Hohlstein (684 m) v U n

i S16

r R r

i e

v v e i

i r

R R s u

s h S17 Mt. Tannenfels (669 m) e

+ Mt. Milseburg (835 m) T + H SX3 + + Mt. Stellberg (727 m) (779 m) SX2 58 B 4

S13 S15 + Mt. Steinwand S14

(646 m) a

Sieblos a

S18 v Wüstensachsen Mt. Wasserkuppe a W2 4 50°30’N (950 m) + S4 B 28 S3 B S19 S11 + (899 m) Poppenhausen S9 S10 S5 S6

phonolitic intrusions, domes

R R

i i

v v e

basalts and basanites e

r r

F F

u u

l l

d spring well d

a a fault (assumed) S1 0 1 2 km 8 7 + national roads 2 Mt. Heidelstein (923 m) B Fig. 2 Location of the study area: regional (a) and detailed geological (b) map of the Tertiary volcanic rocks and the volcaniclastic sediments in the Rhön area and at Mt. Wasserkuppe (after Ehrenberg and Hickethier 2002) and the spatial distribution of the groundwater sampling sites; in the detailed map, the position of the cross- section is indicated as red line, groundwater sampling sites are shown as triangles (springs) and as square (well); the cross section indicates tectonic segmentation and the vertical displacement of the individual tectonic blocks

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9°55’E

S18

7 7 7

9 9 9 0 0

50°30’N 0 8 8 8

0 0 0 0 0 0

0 0

0 W2

0 0 0

0 S3+4 0 8 S19

a ld u F

r 010.5 km e v i

R S5+6 WE W2 900

800

700 ? altitude (m)

600 ?

Quaternary oNe olivine nephelinite Te tephrite

clay/silt xeBs basanite, xenoliths

aoB alkali olivine basalt Triassic

Tertiary TrB trachy basalt sandstone/limestone Tu tuff Ig ignimbrite fault (assumed) vfS volcaniclastic hoB well / spring fluvaitile deposits hornlende basalt

Fig. 2 (continued)

2.3 Hydrogeology The basaltic sequence at Mt. Wasserkuppe builds up a fissured rock aquifer with medium -7 -5 permeability. Hydraulic conductivity of the basaltic rocks comprises kf values of 10 to 10 m s-1 (Büttner et al. 2003). Volcaniclastic fluviatile sediments (rock debris in pellitic matrix) may constitute porous aquifers of limited spatial extent and rather low permeability. The kf values of tuff layers do not exceed 10-9 m s-1 (Büttner et al. 2003). The debris of the phonolitic domes west of Mt. Wasserkuppe may as well be characterised as aquifers with local extent (Stengel-Rutkowski 1994). Rock weathering under formation of residual fine-grained assemblage of secondary clay minerals partially limits permeability of the volcanic rocks (Ehren- berg and Hickethier 2002). In addition, pelitic tuff layers may reduce vertical permeability and constitute hydraulic segmentation. However, tectonic disruption generated vertical groundwater pathways related to faults and, thus, contributes to groundwater recharge to greater depth. Groundwaters occur as lens-shaped reservoirs and groundwater recharged exclusively de- - 59 - PhD Thesis Florian Ludwig 2011

rives from rainfall. Discharge of near-surface groundwaters occurs as springs related to faults (border springs) or to stratification (contact springs). The discharge rates of most springs related to groundwater circulation in the basaltic sequence amount to 0.5–1.0 l s-1. Groundwater at greater depth (80-200 m) is made accessible by a production well (W2) associated with tectonic disruption (Fig. 2). The production rate of the well amounts to 4 l s-1. The recharge areas of the springs comply with the surface catchment areas and extent to less than 1 km². The catchment area of W2 extends to approximately 5 km² (Stengel- Rutkowski 1981) and includes the entire plateau of Mt. Wasserkuppe above 800 m ASL. Gauging the runoff in surface catchment areas in 1991, Stengel-Rutkowski (1994) determined an average groundwater recharge in the volcanic rocks of the Rhön of about 120 mm a-1. Re- ferring to previous studies by Diederich (1975) measuring surface runoff in basaltic rock catchments in the term 1971-1972, the recharge amounts to 135 mm a-1, respectively. Recent studies by Neumann (2009) of spatial distribution of groundwater recharge in Germany suggest recharge rates of 150 – 250 mm a-1 at Mt. Wasserkuppe (combined basaltic rocks and Triassic basement). Surface runoff, interflow, and near-surface groundwater issued by springs are drained by the River Fulda and subordinate rivers.

Data of the hydraulic conductivity (kf) of the rocks derives from pumping tests at two ob- servation wells (Bullermann and Schneble 1992) in the olivine nephelinite and alkali olivine basalt sequence 50 m south of the peak of Mt. Wasserkuppe. At shallow depth, the olivine nephelinite offers relatively low hydraulic conductivity (approx. 10-7 m s-1) due to a high grade of rock weathering and the formation of residual clays. The underlying alkali olivine -5 -1 basalt yields higher kf values of approximately 10 m s . Information on the hydraulic properties of the rocks at greater depth was obtained from pumping tests at well W2 (Fig. 2). A hydraulic conductivity of 3 x 10-6 m s-1 was estimated according to Logan (1964), taking into account discharge, drawdown, and aquifer thickness.

3 Methods

Groundwater sampling and analysis were accomplished similarly to investigations described in a companion study (Ludwig et al. 2011) about groundwater evolution in the Bunter sandstone sequence of the Odenwald, Germany. At Mt. Wasserkuppe and in the area northwest and east, 18 groundwater samples were taken of one deep production well and springs in Oc- tober 2006 (Fig. 2). The sampling sites were chosen to represent groundwaters with minimal anthropogenic influence. At each sampling site six samples were collected in 250 ml polyethylene bottles and one in a 1 l glass bottle. An extra sample was filtered through 0.45 µm Cel- lulose Acetate Millipore membrane filter and conditioned with 2 ml nitric acid. Water temperature, specific electrical conductivity (SEC), the concentration of dissolved oxygen, the

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redox potential (Eh), and pH-values were measured in the field. Major and minor cations 2+ 2+ + + (Ca , Mg , Na , K , Fetotal, Si) were determined by inductively coupled plasma optical emis- - 2- - sion spectrometry (ICP-OES; Perkin Elmer Optima 3000 DV), and anions (Cl , SO4 , NO3 ) were analysed by ion chromatography (Dionex DX 500). The detection of Al was performed by inductively coupled plasma mass spectroscopy (ICP-MS; Perkin Elmer Elan 6100). The determination of alkalinity was attained by titration. An ion balance error of ±10% was deemed acceptable. All analyses were accomplished at the state laboratory of the county of Hessen (LHL), Wiesbaden. Rainfall was accounted for the hydrochemical evolution of the groundwaters as it provides the primary input of solutes to recharge waters. The data comprise values for grassland, both as original data and multiplied by a factor of 1.5 to take into account the regional evapotranspiration. As some catchment areas are partly covered with forest, data is also given for bulk deposition (throughfall) under a spruce canopy. All data are compiled in Table 2. The chemical composition of rock samples of several magmatic events in the field of investigation area (trachy basalt, hornblende basalt, alkali olivine basalt, olivine nephelinite, and phonolite) was detected by XRF-analysis (Philips PW 2404) at the Mineralogical- Geochemical Institute, University of Freiburg. For preparation, all samples were ground to 10 µm grain size and then dried for 48 h at 50 °C. One gram of sample powder was added 4 grammes of Spectromelt® as tableting agent for melt digestion. Information about the individual mineral assemblages as well as about the rock porosity and mineral alteration reactions was obtained by thin section analysis. Point counting of the individual mineral grains allowed an estimation of the modal mineral composition of the magmatic rock samples. With exception of olivine nephelinite and hornblende basalt, the identification and quantification of minerals in the fine-grained groundmass (feldspathoids, olivine, pyroxenes, feldspars) could not be proceeded. The normative content of nepheline, olivine, diopside, and Fe-oxides as well as the composition of feldspars were calculated as CIPW-values. Calculations were run based of the XRF data and using an Excel calculation spreadsheet provided by White (2011). Epoxies and thin sections of the basaltic rocks were analysed by reflected light microscopy for inclusions of pyrrhotite in the Fe-oxide minerals. Mineral abbreviations used throughout the text refer to recommendations of the IUGS (Siivola and Schmid 2007).

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-1 2 SiO mg l -1 2 CO mg l -1 3 NO mg l -1 omplished in October in omplished 4 SO mg l 3 -1 HCO mg l e HLUG) -1 o account the regional the regional o account mg l -1 mg l -1 mg l -1 7 b.d. b.d. 2.1 39.7 10.0 9.1 7.9 17.7 canopy (data provided by th by provided (data canopy mg l -1 mg l -1 0.1 0.1 0.003 0.03 4.4 mg l -1 mg l on as throughfall under on as a forest throughfall grasslandrainfall; multiplication afactor by of 1.5 takes int -1 SECpHCaMgNaKAlFeCl cm µS -1 2 mg l O (m-m) C ° mV formation Hydrochemical data of 16 springs and one deep well in the field of Mt. Wasserkuppe: groundwater testing and analysis were acc were and analysis testing groundwater Wasserkuppe: Mt. of the field in well deep and one of 16 springs data Hydrochemical 2006; the concentrations of solutes in meteoric water represent water meteoric 2006;the concentrations of solutes in depositi bulk to relates “spruce” precipitation evapotranspiration; W2S1 hoB/TrB/aoBS3 80-200S4 11.8 aoB 197S5 oNe/vfS 4.3S6 oNe/vfS 108S9 aoBS10 aoB 9.72S11 3.6 oNe/aoB 7.4 6.1 oNe/aoBS13 <0.1 8.1 oNe/aoB 21.6 264S14 218 6.4 5.5 0.3 oNe 268S15 6.8 68 76 6.9 oNe 0.018S16 8.2 136 7.3 oNe b.d.S17 204 7.2 6.86 5.6 7.06 aoB 191S18 301 1.0 7.9 6.81 5.1 5.5 234 5.1 5.4 93 aoBS19 7.1 5.8 66.5 241 3.1 132 2.9 128 hoBSX2 6.1 4.9 5.2 118 8.5 2.9 7.21 2.6 oNe/Tu/vfSSX3 8.21 119 1.5 3.6 7.52 7.4 8.4 Ph 182 7.83 0.7 0.6 7.4 9.7 5.604/05 P. freeland 7.8 0.8 8.2 3.0 Ph 165 7.62 0.005 0.033 4.8 5.4 1.5 x 04/05 3.4P. freeland 217 8.3 8.8 0.009 5.3 177 4.5 b.d. b.d. 4.2 5.3 04/05 12.7 P. spruce 168 4.8 7.4 7.3 b.d. 5.0 217 5.6 0.7 7.62 1.2 1.7 4.5 177 0.8 6.6 0. 8.5 17.9 195 316 5.6 1.2 8.21 0.007 30.5 4.9 6.6 16.5 152 b.d. 9.4 181 13.1 30.5 1.3 7.75 b.d. b.d. 7.1 9.1 5.1 166 69 6.7 8.2 9.7 3.9 12.9 7.86 b.d. 0.003 2.1 2.4 10.0 99 6.7 b.d. 7.0 2.9 12.7 5.7 0.8 8.46 b.d. 1.9 b.d. 31.1 b.d. 6.58 8.6 3.0 2.9 0.7 13.5 b.d. 0.027 10.2 4.4 11.0 2.8 7.95 39.0 15.8 10.8 9.2 3.3 38.4 0.7 14.3 0.007 b.d. 9.2 9.3 12.0 3.2 37.2 11.1 15.0 4.7 0.8 0.012 5.8 b.d. 17.0 16.0 6.2 4.0 10.0 38 3.7 25 67.1 1.0 b.d. 0.026 11.0 2.5 b.d. 16.3 2.8 0.5 8.0 b.d. 6.67 b.d. 2.4 b.d. 19.9 70.2 5.08 0.5 6.0 19.0 0.011 7.32 4.90 8.7 19.9 6.5 3.5 1.1 69.5 95 3.4 0.007 0.7 b.d. 1.6 b.d. 9.2 6.4 4.4 67.1 0.3 b.d. b.d. 0.2 3.2 11.0 4.3 16.0 22.6 4.5 4.50 0.8 b.d. 12.7 1.7 0.5 6.1 72.6 2.9 27.5 b.d. b.d. 0.5 b.d. 14.0 43.9 4.9 0.3 4.4 0.6 20.2 19.9 0.010 14.0 8.5 0.008 2.3 b.d. 0.005 23.4 2.0 b.d. 0.011 6.0 0.007 b.d. 3.8 1.2 4.4 1.8 0.8 b.d. 17.2 24.1 24.0 28.7 0.053 11.0 18.2 19.1 12.4 3.8 16.0 0.025 2.5 14.8 3.8 13.0 5.4 11.7 3.6 4.1 18.8 10.1 7.8 8.2 14.6 Table 2 Table Site ID Geologicaldetection limits screen Temp Eh b.d. below detection limit detection b.d. below

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In order to determine principal mineral alteration reactions, column experiments with puri- fied water (0.05 µS cm-1) as substitute for meteoric water were carried out at the laboratory of the Mineralogical-Geochemical Institute at the University of Freiburg. The batch experiments were performed to deduce initial mineral alteration mechanisms by monitoring the hydrochemical evolution of the leachates through the experiments. However, equilibrium with secondary mineral phase was not expected to be attained due to short experimental run times. Comparable experiments were performed by Gislason and Eugster (1987) and Gislason et al. (1993). The necessity to extract fine-grained components as sample conditioning prior to leaching experiments has been discussed by Zorn et al. (2009). All rock samples were prepared to attain comparable experimental constraints including the elimination of weathering rinds and crushing of the rocks to create fresh mineral reaction surfaces. Wet sieving was performed to obtain comparable grain-size spectra (5.6–16 mm grain size) and to extract fine-grained components. Subsequently, the samples were dried for 48 h at 50°C. The experimental setup was designed to allow permanent solution flux through the rock sample substrate. The solution flux was generated by a rotary pump and the leaching solution flow proceeded from bottom to top in a 2 l glass reaction vessel (length 100 cm, diameter 5 -3.5 cm). The system was in contact with the atmosphere (PCO2 x 10 ) at 22°C. The prepared samples were embedded into the reactor as loose packaged beds without compaction. The pore volume of the sample beds was estimated to amount to about 60 %; porosity of the sample beds constitutes the preferential flow pathways. Solid:liquid mass ratios of the basaltic rock samples were 1:3, the ratio for the phonolite was 1:5.Pre-experiments were run in order to determine an appropriate solid-liquid ratio and to equilibrate the solution flux rate at about 20 l h-1 and a flow velocity in the probe package of approximately 15 m h-1. The experiments were run for periods of about 200 to 300 hours. Samples of 50 ml of leaching solution were taken after 2, 20, 48, 72 and 192 hours runtime. Additionally, the pH and the SEC were measured. The samples were centrifuged and filtered through 0.45 µm acetate membranes. Analyses were performed at the University of Freiburg. Mineral alteration reactions related to both leachate compositions and natural groundwater evolution were calculated by applying the PHREEQC code (Parkhurst 1995) and the thermodynamic data base of WATEQ4 (Ball and Nordstrom 1991) using an inverse modelling approach. Inverse modelling was chosen for stoichiometric determination of mass transfers and to identify similar patterns of mineral reactions. For calculations, the concentrations of dis- 2+ 2+ + + - - 2- 3+ solved Ca , Mg , Na , K , Cl , HCO3 , SO4 , Al , Si, PCO2, and pH were considered. A maximum difference between calculated and observed values of 5 % was deemed acceptable. The modelled mineral alteration reactions were constrained by the values of the saturation indices (SI) of primary and secondary minerals to verify the plausibility of precipitation or

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dissolution of these minerals. As modelling approach, the hydrochemical composition of rainfall as initial solution was allowed to react with the rock forming minerals to evolve to the compositions of the near- surface groundwaters issued by springs. Calculations were based on the rainfall composition of 2004/2005 amended for evapotranspiration. Groundwater at greater depth (well W2) was expected to evolve from a near-surface groundwater (S3) at Mt. Wasserkuppe. Cation exchange as the explanation for decreasing Mg and Ca concentrations and increasing Na concentrations during groundwater evolution was found to be consistent with the field concentrations. The availability of secondary clay minerals may favour the exchange of monovalent for bivalent cations (Drever 1997; Paces et al. 2008; Postma et al. 2008), promoted by high pH-values of the groundwater at greater depth. Consequently, cation exchange with Mg2+ (and Ca2+) attracted to the exchange matter and Na+ issued into solution was integrated into the hydrochemical modelling approach. Finally, to determine similarities and differences in groundwater composition in relation to the aquifer rocks, a cluster analysis was calculated for the variables Ca, Mg, Na and HCO3. The Euclidian distance of these parameters was determined using the software add-on Win- STAT® for Excel by Beneke and Schwippert (2001). Criterion for the grouping of clusters is minimal relative difference or highest relative similarity of the chosen variables. To separate individual clusters, a maximum dissimilarity of 0.5 was accepted and four individual hydrochemical clusters were grouped. The individual clusters were then compared to the associated aquifer rock types and to measured and modelled parameters to delineate systematic constraints in groundwater evolution. According to Drever (1997), statistical association does not necessarily establish any cause-and-effect relationship, but represents data in a way that cause-and-effect relationships can be deduced.

4 Results and discussion

4.1 Analytical Rock Data and Modal Mineral Composition Table 3 summarises analytical rock data obtained in this study. The values are similar to those published by Ehrenberg et al. (1992) for the same locations. It appears that rocks present relatively low amounts of alkali elements (< 6 weight %) and of SiO2 (< 47 weight %) and, thus, according to Le Bas et al. (1986), plot within the “Basanite” and “Trachybasalt” fields (Fig. 1). Mg and Ca occur as major cations. Though differing from the TAS-classification, the local rock-nomenclature is used as reference to prior studies. XRF-analysis of the phonolitic rock sample indicates scarcity of both MgO and CaO and the highest values of Na2O and K2O of all samples investigated. The variety in alkalinity and content of SiO2 reflects different stages

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of magmatic differentiation.

Table 3 XRF-analysis data of basaltic and phonolitic rock samples of Mt. Wasserkuppe and Mt. Stellberg given in weight%, the data significantly correlate with data published by Ehrenberg et al. (1992, 1994); LOI = loss on ignition

alkali olivine olivine hornblende trachy basalt phonolite Sample basalt nephelinite basalt Wasserkuppe, Wasserkuppe, W Wasserkuppe, Wasserkuppe, Stellberg, NW Location W slope slope NW slope SW slope Wasserkuppe

SiO2 46.92 41.34 42.65 45.96 56.50

TiO2 2.57 2.55 3.62 2.67 0.22

Al2O3 16.19 11.03 14.13 15.46 21.38

Fe2O3 5.87 7.09 9.80 7.14 1.92 FeO 5.60 6.20 3.70 5.00 0.40 MnO 0.22 0.23 0.21 0.29 0.42 MgO 5.86 14.42 7.73 3.73 0.21 CaO 8.37 11.39 12.08 9.27 0.47

Na2O 3.44 3.47 2.66 4.23 9.85

K2O 2.28 0.89 0.57 1.82 5.20

P2O5 0.83 0.94 0.69 1.28 0.03

sum 98.50 99.88 98.12 97.19 96.84 LOI 1.60 0.42 2.02 2.96 3.72 As identified by thin section analyses, macro- and microcrystals of olivine, Ca-pyroxene, plagioclase, and hornblende in the hornblende basalt constitute the mayor minerals in the basaltic rocks. The identification of single crystals also proved traces of sodalite and leucite in the groundmass of all rock samples (Table 4). As in the trachy basalt and olivine nephelinite, minor amounts of nepheline were detected in the hornblende basalt, indicating mineral alteration towards analcite. Analcite crystals could be proved in the alkali olivine basalt, olivine nephelinite and phonolite sample. Pyrrhotite (Fe1-xS2) was determined as inclusions in the opaque Fe-oxides (illmenite, magnetite) as well as in olivine and Ca-pyroxene. The pyrrhotite minerals build up to several percent of the particular surrounding mineral in all basaltic rocks, whereas the analysed phonolite sample is pyrrhotite-free. In the phonolite, crystals of nosean were identified. Direct light microscopy of epoxies of the alkali olivine basalt, olivine nephelinite, and trachy basalt could not identify volcanic glass. Normative CIPW calculations compiled in Table 4 suggest high amounts of feldspathoids (nepheline) within the basaltic rocks (15.6-23.5 %), predominantly as components of the fine- grained groundmass. The feldspars are anorthite-dominated (50-100 %), orthoclase and albite components are subordinate (0-31 % and 0-20 %, respectively). The phonolite comprises more than 50 % of normative nepheline component, the feldspars were calculated as anorthite-free orthoclase82-albite18. Investigations of Ficke (1961), however, suggest a subordinate

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modal anorthite feldspar component in the phonolites west of Mt. Wasserkuppe of less than 10 %.

Table 4 Thin section analysis of rock samples of different basaltic rocks in the investigation area and one phonolitic rock sample of Mt. Stellberg west of Mt. Wasserkuppe (in %); opaque phase comprises an assemblage of oxides and hydroxides; mic = microcrystals (<1 mm); mac = macrocrystals (> 1 mm); the modal mineral compositions calculated for the investigated rock samples correlate with data compiled by Ficke (1961); normative CIPW values given in weight%

Olivine 6.5 13.0 4.4

Olivinegm 6.9 5.2 Ca-pyroxene 19.9 21.1 12.8 33.6 1.2

Ca-pyroxenegm 4.2 14.4 10.0 12.3 Hornblende 9.2 Nepheline 13.2 1.1 Nosean 0.5 Opaque phase 8.8 6.0 21.2 8.3 4.4 Fsp mic+mac 22.1 28.4 11.8 25.7 groundmass 36.1 24.2 7.6 43.2 57.6

Σ counts 792 800 750 728 698 mac = macrocrystal, mic = microcrystal, gm = groundmass

CIPW noramtive calculation Orthoclase 13.7 0.0 3.4 11.1 31.8 Albite 8.8 0.0 1.8 5.8 7.1 Anorthite 22.4 11.9 25.4 18.4 0.0 Diopside 16.4 9.3 29.2 24.3 2.1 Olivine 14.5 34.0 14.3 8.6 2.8 Nepheline 16.6 21.3 15.6 23.5 56.7 Ilmenite 2.5 2.4 3.5 2.6 0.2 Magnetite 2.6 3.0 3.1 2.8 0.0 All basaltic rocks indicate fractures intersecting the rock structure. Fracture space often is partly resealed by secondary mineral phase. The rock surface indicates white and grey spots and cracks and a gritty disintegration of the rock (basaltic sunburn). Basaltic sunburn often is to the breakdown of nepheline and to the formation of analcite and the creation of capillary cracks during late-stage crystallisation as well as through chemical weathering. This parallels to findings of Ehrenberg et al. (1994), Bogaard et al. (2001), and Weiher et al. (2007) identifying basaltic sunburn in Tertiary basaltic volcanic sequences in central Germany. Thin section analysis proved rock weathering to be most effective along these fractures, preferentially leaching minerals compiled in the fine-grained groundmass. Macro- and micro-

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crystals indicate higher stability. As detected for individual olivine, Ca-pyroxene, and plagioclase mineral grains, mineral alteration is limited to the mineral rims exposed to the rock weathering surface.

4.2 Groundwater Chemistry The data compiled in Table 2 indicate individual hydrochemical groundwater types (Fig. 3). All spring groundwaters associated with basaltic rocks (alkali olivine basalt, olivine nephelinite, hornblende basalt) represent a Ca/Mg-HCO3 type with a wide range of pH values (6.58- 8.46) and SEC (68-218 µS cm-1). Individual groundwaters indicate Cl- concentrations that exceed those of Na++K+. With regard to the shallow groundwater environment, the concentra- -1 tions of dissolved oxygen (4.5-6.8 mg l ) are partially reduced in relation to atmospheric PO2.

Groundwater at greater depth (sample W2) indicates a Na-HCO3 type and high pH (9.7) and low values of SEC (108 µS cm-1) and dissolved oxygen (4.3 mg l-1). The concentration of Ca2+ (3.6 mg l-1) is diminished with regard to the concentration in the near-surface groundwa- 2- -1 2+ ters, as well as the concentration of SO4 (4.9 mg l ). The concentration of Mg is below the -1 detection limit of 0.1 mg l . The concentration of SiO2 falls below most values of the near- surface groundwaters.

1 ) -1 0.1 c (meq l

W2 (min-max) 0.01 springs basalts

SX2 phonolite

SX3 phonolite 0.001

Mg Ca Mg+Ca Na+K Cl HCO3 SO4 Fig. 3 Schoeller plot of the groundwater compositions: near-surface groundwaters associated with the basaltic rocks indicate a Mg/Ca-HCO3 type, whereas the groundwaters indicate a Na-Ca-HCO3-SO4 type; groundwater at greater depth relates to a Na-HCO3 type, the stability of values within the time period 1998-2006 is illustrated by min-max bars

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The groundwaters associated with phonolitic rocks represent a Na-Ca-HCO3/SO4 type. The concentrations of Na+ exceed those of the groundwaters of the basaltic rocks whereas the concentrations of Mg2+ and K+ are the lowest of all spring groundwater samples. High concentrations of dissolved oxygen (10.8 and 11.1 mg l-1, respectively) are close to equilibrium with the atmosphere. The constraints of dissolved cations and anions of all groundwater samples are illustrated in Fig. 4. The groundwater compositions analysed correlate with investigations on groundwaters in the basaltic sequence of the Rhön by Berthold and Toussaint (1998).

Mg SO4

80 20 80 20

60 40 60 40

40 60 40 60

20 80 20 80

Ca80 60 40 20 Na+K HCO 80 60 40 20 Cl 3 Fig. 4 Ternary plots of the major cations and anions of the groundwaters investigated: near-surface groundwaters of the basaltic sequence are indicated as black triangles, groundwaters associated with phonolitic rocks are indicated by blue (SX2) and green (SX3) triangles, groundwater at greater depth is indicated as red sqaures; the grey fields indicate the dispersion of previous groundwater analysis data for the basaltic sequence of the Rhön compiled by Berthold and Toussaint (1998); the grey arrows suggest maturation trends of the samples associated with basaltic rocks

With regard to groundwater recharge, groundwaters related to catchment areas partly covered with forest are affected by bulk deposition as throughfall under the forest canopy (S1, S10, S11, S17, SX2, SX3). As delineated in a companion study by Ludwig et al. (2011), the - concentration of NO3 in bulk deposition significantly exceeds the values in grassland rainfall - and, thus, may provoke higher concentrations of NO3 in the associated groundwaters. Conse- quently, as NO3 appears to predominantly derive from rainfall input and was excluded from the hydrochemical modelling approach.

As argued by White (2005), the quantification of mass transfers during water-rock interaction requires partitioning between sources of solutes produced by primary mineral dissolution and the sink of solutes created by secondary mineral precipitation. Considering the saturation states of a number of relevant minerals and taking into account reaction kinetics and relative mineral stability, basic mineral alteration reactions can be deduced. According to Gislason et al. (1993) and Nordstrom (2005), the saturation indices of the minerals involved provide in-

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formation about mineral stability and allow evaluation of the feasibility of mineral dissolution or of precipitation of these minerals from solution. Still, secondary minerals such as clay minerals of the smectite have to be considered as meta-stable phases in natural environments and might further disintegrate with proceeding reaction time (Gislason et al. 1993). Due to availability of thermodynamic data, ideal mineral phases were used to calculate saturation states. The binary system Forsterite86-Fayalite14 was simplified by the use of forsterite as primary mineral. The ternary system of the Ca-pyroxenes was introduced as diopside to the model, added by Na- and Fe-rich aegirine for the phonolite. For the ternary feldspar system, anorthite as least-stable phase was allowed to react. However, the mineral alteration reactions are balanced with effective mineral composition data of the particular volcanic rocks at Mt. Wasserkuppe determined by Ficke et al. (1961) and Ehrenberg et al. (1994). As primary minerals in the basaltic rocks, Mg-olivine, Ca-pyroxene, plagioclase and feldspatoids, analcite, and pyrrhotite indicate undersaturation in the groundwaters. With regard to secondary mineral phases, the groundwaters indicate oversaturation with respect to Na- and Mg- beidellite, Ca-montmorillonite, kaolinite, and goethite. Concerning oversaturation of laumontite, the formation of zeolites is not plausible due to the low-T groundwater regime. The saturation states are compiled in Table 5. As suggested by Gislason et al. (2001), the individual dissolution rates of minerals of crystalline basalt have great effect on the composition of leaching solutions. Investigating natural weathering rates of silicate minerals, White (2005) argues that quantitative rates of weathering are important in understanding mineral reaction mechanisms. Wogelius (1991) and Bernot (2004) compiled dissolution rates of several prominent silicate minerals included in the investigated rocks as a function of pH. Nepheline and forsterite offer low mineral stability indicating the highest dissolution rates. The stability of diopside exceeds that of anorthite at near- neutral pH, but indicates relative lower rates at pH values > 8.5. An albite component of plagioclase appears to be significantly less reactive relative to anorthite at all pH values concerned. As suggested by experimental studies of Blum and Stillings (1995), the plagioclase weathering rates increase with increasing anorthite content and decreasing pH. With regard to a K-feldspar component, White et al. (2001) suggest that the field weathering rate of plagioclase is much more rapid than that of K-feldspar. Blum (2004) emphasises, that the relative dissolution rates of minerals in experimental and natural systems are about similar, with K- feldspar < Ab-plagioclase < An-plagioclase < amphibols < pxroxenes < olivine < nepheline.

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0,27 -1,54 Ill Kln 1) -1.41 0.53 -0.73 6,20 1) Na-Bdl Mg-Bdl Ca-Mnt Lmt Prh ater samples; saturation indices SI = log (IAP K-1) (IAP = log indices SI saturation samples; ater -4,06 -4,27 -1,98 -27,90 -3,53 -1,68 - 0,30 0,53 -4,64 -4,81 - -31,04 -4,11 -2,79 - -2,32 4,48 10.64 2.97 0.25 -5.83 - 4,46 0,08 -9,22 1) 1) -6,71 -9,45 -5,19 -4,77 -5,73 -2,39 -42,02 -5,79 -5,86 7,26-8,71 -1,32 -3,09 0,47 - -8,57 7.09-9,64 - -2,80 -1.03-9,37 -2.16 -4,06 -3,37 - -5.36-7,05 -3,70 -3,27 -5,06 -1.40-9,30 -1,33 -2,25 -5,05 - -1,06 1,66 -3,68 -32,91 -4,44 -1,15 - - -33,53 -4,07 -3,86 -0,42 -29,01 -3,95 -5,38 -2,65 - - -3,21 -2,87 -1,66 - -35,87 -1,42 - - - -0,47 -4,33 -0,95 - -0,81 - -3,59 4,37 -0,80 4,75 - 10.58 - - 6,27 11.07 -0,94 2.77 - 12.51 - 2.24 3.19 3,52 -2.10 2.02 4.66 - - -2.79 9.80 3.42 2.01 -0,17 -1.53 - 2.16 3,80 1.94 3.69 1.15 4,28 - - -3.37 5,43 - 0.97 - 3,21 ------Fo Ca-Cpx An Ne Lct Sdl Anl Ntr Gt Cal -15,67 -13,59-11,31 -8,63-10,90 -6,10 -2,79 -6,29 -0,39 -4,70-14,25 -2,40 -3,46 -0,92 -9,61 -36,93 -4,33 0,52 -5,78 -4,17 -28,70 -0,78-13,94 -33,13 -6,00 -3,21 -2,78-14,49 -8,50 -3,87 -2,73 -0,58 6,86-13,97 -8,90 -3,25 -41,97 -2,54-13,33 -3,63 8,04 -8,68 -4,58 -4,85 -6,03-12,02 7,91 -2,34 -7,48 -4,34 -5,47 5,84 -1,18 -6,42 -2,59 -6,17 -32,08 -3,80 -5,36 -1,58 7,70 12.42-10,36 6,68 -36,03 -3,95 -4,99 5,15 -1,68 14.27-10,71 -3,07 - 4.33 -4,70 -34,13 -4,38 -2,53 -1,27 11.73-10,09 1.01 -5,18 -32,27 6.18 -4,14 1,32 -3,59 -5.04 - - 3.59 3.72 -4,46 - -4,67 -3,89 -3,65 7.79 -1.34 1.26 2.84 - -2,24 -2,37 -5,38 -2,61 - -3.61 - -0.25 5.13 - -2,50 -4,47 -1,56 5,9 6,75 -3.21 2.62 - -34,80 -2,41 - -0,63 7,15 - -8.37 5,86 12,92 -28,13 5,19 -1,99 -4,30 -1.39-15.62 5,63 12.01 - -3,32 - -3,55 5.10-15,55 6,02 -10.06 11.90 2,64 1,78 -1,66 4.19 -4.50 12,10 - -4,85 -9,97 - - 0.82 4.00 -5.29 -6.40 - -1,44 0.67 3.42 4,32 - - - -6.25 -1.60 -0,90 1,64 2.40 6,49 3,77 -1,53 -33.58 -4,79 2.22 5,59 6,31 - - -4.16 9.97 2.72 5,44 -1,32 - 12.62 -3.18 - 5,54 2.09 4.74 0.59 - - - 3.17 - -4.78 -2.91 -1.98 1.05 - - - 3.55 6.72 3,43 - 12.84 5,57 - - - 5.01 - - 0.98 - - -6.94 -2,48 2.90 - - - 6.31 ------1) 1) values calculated for Mg = 0,5 mg/l (half detection limit) detection (half = 0,5 Mg mg/l for calculated values 1) Saturation states of the leachates and the groundw the leachates and of states Saturation Table 5 Table leachate/ groundwater sample hoB oNe TrB Ph W2 S1 S3 S4 S5 S6 S9 S10 S11 S13 S14 S15 S16 S17 S18 S19 SX2 SX3 aoB

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The mineral dissolution or alteration reactions among the groundwaters are forwarded by + the consumption of H issued into solution by dissociation of CO2 as:

- + CO2 + H2O → HCO3 + H .

As suggested by the dissolution rates, feldspathoids offer low stability and are, thus, likely to initially contribute to groundwater composition with significant effect. The hydrolysis reactions of sodalite and nosean (limited to phonolite) to Na-beidellite may issue major amounts + 2- - of Na into solution and contribute to the concentrations of SO4 and Cl :

+ Na8Al6Si6O24Cl2 + H2O + 13H → + 3+ 4+ - - Na0.33Al2.33Si3.67O10(OH)2 + 7.67Na + 3.67Al + 2.33Si + 2Cl + 13OH

+ Na6.5K1.5Al6Si6O24(SO4)0.85|(Cl2)0.15 + H2O + 13H → + + 3+ 4+ 2- Na0.33Al2.33Si3.67O10(OH)2 + 6.17Na + 1.5K + 3.67Al + 2.33Si + 0.85SO4 + 0.3Cl- + 13OH-

with Al3+ and Si4+ issued into solution. The alteration reaction of nepheline suggests the consumption of Al3+ and Si4+ and the release of protons

3+ 4+ Na0.8K0.2AlSiO4 + 1.33Al + 2.67Si + 8H2O → + + + Na0.33Al2.33Si3.67O10(OH)2 + 0.47Na +0.2K + 14H .

With regard to the alteration of nepheline towards the formation of analcite, analcite has also to be considered as reactive primary mineral phase affecting groundwater composition. As K-rich feldspathoid, leucite may dissolve under formation of Na-beidellite and consumption of Na+:

3+ 4+ + KAlSi2O6 + 1.33Al + 1.67Si + 0.33Na + 6H2O → + + Na0.33Al2.33Si3.67O10(OH)2 + K + 10H .

The alteration of forsterite86-fayalite14 suggests the formation of Mg-beidellite and goethite

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as stable secondary mineral phases. This reaction requires availability of both Al3+ and Si4+ which may derive from the decomposition of feldspathoids. During this reaction, Fe(+II) is oxidised to Fe(+III):

3+ 4+ Mg1.72Fe0.28SiO4 + 2.33Al + 2.67Si + 8,56H2O → 2+ + - Mg0.165Al2.33Si3.67O10(OH)2 + 0.28FeOOH + 1.555Mg + 14.84H + 0.28e .

Analogous, the hydrolysis reaction of Ca-pyroxene suggests the formation of secondary Mg-beidellite and Ca-montmorillonite and goethite as stable mineral phases:

3+ 4+ Ca0.82Na0.07K0.02Mg0.68Fe0.38Si1.77Al0.23O6 + 4.43Al + 5.57Si + 18.76H2O →

Mg0.165Al2.33Si3.67O10(OH)2 + Ca0.165Al2.33Si3.67O10(OH)2 + 0.38FeOOH + 0.515Mg2+ + 0.655Ca2+ + 0.07Na+ + 0.02K+ + 33.14H+.

The alteration of anorthite as least stable feldspar component may react to Ca- montmorillonite as stable phases as:

3+ 4+ CaAl2Si2O8 + 0.33Al + 1.67Si + 4H2O → 2+ + Ca0.165Al2.33Si3.67O10(OH)2 + 0.835Ca + 6H .

2- With regard to the concentrations of SO4 in the groundwaters associated with the basaltic rocks (4.9-16.0 mg l-1), pyrrhotite is allowed to react to goethite. The oxidation of sulfide as major source for sulfate in crystalline rocks has been delineated in prior studies (e. g. Bucher and Stober 2010; Singhal and Gupta 2010). In contrast to pyrite, pyrrhotite may include other metals than Fe, indicated by “x”:

2- + - Fe(1-x)S2 + 10H2O → (1-x)FeOOH + 2SO4 + 19H + 15e

This reaction proceeds under consumption of H2O or the consumption of oxygen and the 2- release of protons, respectively, and the release of SO4 into solution. Reduced concentrations of dissolved oxygen in the basaltic groundwaters (4.3-6.8 mg l-1) might suggest consumption of oxygen through pyrrhotite oxidation. The flux of electrons relates to the oxidation of sulfur and iron, the iron released is deposited as Fe-hydroxide such as goethite. The formation of

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goethite is also contributed by the hydrolysis of olivine and Ca-pyroxene. With regard to the secondary mineral assemblage generated through basaltic rock chemical weathering, the alteration products proposed in the reactions above coincide with those proved in weathering covers of basaltic volcanic rock in central Germany. As reported by the HLUG (2006), the average secondary mineral assemblage comprises smectites (50 %), illite (13 %), Fe-oxides and hydroxides (12 %), and kaolinite (18 %) produced during late-stage weathering.

4.3 Composition of Leachates and Interpretation of Column Experiments As principal result of the column experiments, the increase in specific electric conductivity (SEC) of all leachates flattens with runtime (Fig. 5). During the leaching experiments, the initial pH-values of 5.5 levelled off at 7.1 - 7.9. As suggested Gislason and Eugster (1987), this might be due to the buffering effect of aqueous CO2, as the leaching solution is in contact to the atmosphere. The analytical data of the leaching solutions are compiled in Table 6.

70 phonolite alkali olivine basalt 60 olivine nephelinite trachy basalt hornblende basalt 50 ) -1 40

30 SEC (µS cm

0 0100200 time (h) Fig. 5 Scatter diagram of SEC vs. time: all samples indicate flattening of the excess of SEC during the experimental runs with exception of the trachy basalt which shows a near-linear relation of SEC and time

- All leachate compositions indicate HCO3 as major anion related to the consumption of

CO2 during mineral alteration reactions. Among the basaltic leachates, the concentrations of - 2- Cl and SO4 are subordinate (Fig. 6), which correlates with the composition of the associate groundwaters (Fig. 3).The proportion of alkali earth to alkali elements in the leachates is lower than in the groundwaters.

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-1 2 SiO mg l -1 4 SO mg l 3 -1 HCO mg l -1 mg l -1 mg l -1 mg l -1 mg l -1 mg l -1 lumn experiments: solid/liquidratios of experiments: ratios to mass refer lumn mg l -1 mg l -1 µS cm TempSECpHCaMgNaKAlFeCl leaching t (h) C ° liquid Hydrochemical compositions of the final leachates of the co compositions Hydrochemical Table 6 6 Table leachatebasalt olivine alkali 1:3 nepheliniteolivine solid/ 1:3phonolite 192 basalttrachy 192 22.0 basalthornblende 16 22.0 1:3 1:5 1:3 26 7.17 307 192 192 0.5 7.55 22.0 22.0 22.0 0.2 1.1 29 38 69 1.0 0.7 0.9 2.2 7.54 7.10 7.86 1.9 0.240 1.6 1.3 4.0 0.030 0.2 0.5 0.3 0.310 1.7 0.160 0.5 2.0 9.2 2.9 2.6 2.1 3.1 18.9 0.3 3.2 0.1 1.390 0.020 0.036 11.4 0.240 0.030 0.030 0.2 1.5 9.8 0.3 40.3 8.5 36.6 0.2 0.8 6.2 16.8 2.9 2.7 the rock sample and pure water asleachate sample the rock

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Due to the differing solid:liquid ratio, the leachate of the phonolite is not directly comparable to those of the basaltic rocks. It basically comprises the highest concentration of Na+ of all leachates and indicates the dominance of Ca2+ with respect to Mg2+. The concentrations of + 2- - Na as well as of SO4 and Cl notably exceed those of the basaltic rock leachates – though the solid:liquid mass ratio of the phonolite leachate effects even higher dilution. The steep initial increase of SEC during the leaching experiments might correlate with low stability of 3+ Na-rich sodalite and nosean. Low concentrations of Al and SiO2 in the final leachate might suggest formation of secondary minerals. As illustrated in Fig. 6, the leachate composition parallels to the composition of groundwaters from phonolitic rocks (Fig. 3).

10 alkali olivine basalt olivine nephelinite hornblende basalt trachy basalt 1 phonolite ) -1 0.1 c (meq l

0.01

0.001

Mg Ca Mg+Ca Na+K Cl HCO3 SO4 Fig. 6 Schoeller plot of the final leachate compositions at the end of the experimental runs; the data refers to values given in Table 6

3+ The concentrations of Al and Fetotal of the basaltic leachates are significantly higher than expected with regard to the mobility of dissolved Al- and Fe-species expected at near-neutral pH. However, these findings correlate with results of comparable leaching experiments on silicate minerals (Zhu 2001; Ludwig et al. 2011). Mobility of an ion is referred to its non- conservative transport in the aquifer system with possible effect by chemical (e.g. precipitation) or physical (e.g. sorption) processes. With regard to the concentrations of dissolved cations and H4SiO4 versus experimental runtime, the leachate compositions are not in equilibrium with solid phase. As illustrated in Fig. 7, the concentration curves still increase at the end of the experimental runs or slightly decrease as for Ca2+, Mg2+, and Al3+ in the alkali olivine basalt sample.

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0 0 alkali olivine basalt olivine nephelinite ) -1 -1 -1

-2 -2 log c (mmol l

-3 -3

-4 -4 0 50 100 150 200 hours 0 50 100 150 200 hours 0 hornblende basalt Ca2+ ) -1 -1 Mg2+ Na+

-2 K+ 2+

log c (mmol l Fe Al3+ -3

H4SiO4

-4 0 50 100 150 200 250 300 350 hours 0 0 trachy basalt phonolite ) -1 -1 -1

-2 -2 log c (mmol l

-3 -3

-4 -4 0 50 100 150 200 hours 0 50 100 150 200 hours

Fig. 7 Scatter diagram of concentrations of dissolved cations vs. experimental runtime: the concentration values indicate increasing trends at the end of the experiments suggesting the leachates not being in equilibrium with solid phase of primary and secondary minerals

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According to Gislason and Eugster (1987), the comparison of mass ratios of elements in solution to those in the original basaltic rock illustrates stoichiometric dissolution constraints. As displayed in Fig. 8, the mobilisation of Mg and Ca is incongruent, with exception of the trachy basalt sample. All other samples indicate mobility of dissolved Ca2+ enhanced to that of dissolved Mg2+ with respect to the element mass ratios in the rocks. Relating to the mineral composition of the basaltic rocks, it shows that the trachy basalt as the only sample with olivine exclusively occurring in the groundmass to react with the leachate, provokes congruent mobilisation of Mg and Ca. All other basaltic samples incorporate significant amounts of olivine macrocrystals and indicate incongruent mobilisation and domination of Ca2+ in solution.

0.6 1.2 aoB oNe

0.4 0.8 Ca ppm Ca ppm 0.2 0.4

0 0 00.10.20 0.2 0.4 0.6 0.8 Mg ppm Mg ppm 2 5 hoB TrB 4

3 1

Ca ppm Ca ppm 2

0 0 0 0.2 0.4 0.6 012 Mg ppm Mg ppm 2 Ph

1 Ca ppm

0 0 0.1 0.2 0.3 Mg ppm Fig. 8 Comparison of Mg-Ca mass ratios of the rock samples (straight lines, as weight%) and the leachates (crosses, as ppm): the trachy basalt indicates congruent mobility of dissolved Mg and Ca with respect to the mass ratio in the rock; all other leachates indicate incongruent dissolution with mobility of dissolved Ca favoured to mobility of dissolved Mg

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Comparatively, Na-K mass ratios of the leachates and the associated rocks indicate incongruent mobilisation with preferred mobility of dissolved K+ in relation to dissolved Na+ (Fig. 9). According to this, Ca2+ and K+ could be considered to be more intensively issued into solution, or Mg2+ and Na+ more strongly removed from solution by the formation of secondary minerals. Gislason et al. (1993) suggest, that secondary minerals may act as sinks for elements mobilised during the basalt alteration and, thus, control the hydrochemistry of the leaching solutions. It might also be suggested, that incongruent dissolution is affected by the mineral distribution in either the fine-grained, highly-reactive groundmass or their occurrence as rather stable macro-crystals.

1.2 3 aoB oNe

0.8 2 Na ppm Na ppm 0.4 1

0 0 0 0.2 0.4 0.6 0.8 1 00.511.5 K ppm K ppm 2 3 TrB

1 Na ppm Na ppm 1

hoB 0 0 00.511.522.5 01234 K ppm K ppm 3 Ph

2 Na ppm 1

0 01234 K ppm Fig. 9 Comparison of K-Na mass ratios of the rock samples (straight lines, as weight%) and the leachates (crosses, as ppm): all leachates indicate incongruent dissolution with mobility of dissolved K favoured to mobility of dissolved Na

Inverse modelling of the leachate compositions could be correlated to the mineral alteration reactions postulated for the natural groundwaters (Table 7). Still, the equations for the

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alkali olivine basalt, the olivine nephelinite, and the hornblende basalt had to be equilibrated by formation of meta-stable natrolite. This correlates with experimental studies of Gislason et al. (1993), who emphasised the importance of metastable phenomena in low-T weathering of crystalline basalt. The highest values of mineral dissolution were calculated for the feldspathoids analcite and leucite, followed by anorthite and Ca-pyroxene and only low values for the dissolution of olivine, sodalite, and pyrrhotite. Most reactions apparently evolve towards the formation of natrolite and only subordinately towards secondary Na- or Mg-beidellite. Aegirine and nosean as reactive components were exclusively related to the breakdown of the phonolite sample.

Laboratory experiments performed by Gislason et al. (2001) suggest that the dissolution rate of crystalline basalt is an integrated dissolution rate of the basaltic minerals. In undersaturated solutions, the stoichiometry of the dissolution of crystalline basalt is affected by the relative dissolution rates of the minerals. Furthermore, the saturation state of primary and secondary minerals is the most important variable for the dissolution and precipitation rates of minerals involved in natural weathering. The saturation states of the leachates predominantly parallel to those calculated for the groundwaters (Table 5). This suggests, that primary mineral stability associated with the leaching experiments is likely to be similar to those under natural weathering conditions. The leachates of the basaltic rock samples indicate dominance of the alkali elements (Fig. 7), which might relate to initially higher rates of dissolution of K- and Na-minerals such as leucite, nephelinite/analcite and sodalite during initial weathering of fresh mineral surfaces. The nonlinear rapid initial dissolution illustrated in Fig. 7 correlates with studies on experimental weathering of granites by White and Brantley (2003). They suggest, that the dissolution rates of the minerals mainly involved during the initial stages of weathering will then significantly decrease. This emphasises the importance of reaction kinetics and could explain the leachate composition as a function of mineral dissolution rates. In contrast, the dominance of alkali earth elements over alkali elements in the natural groundwaters might reflect the depletion of highly reactive primary K- and Na- silicate minerals on the reaction surface of the natural aquifer rocks. As suggested by White and Brantley (2003) and Navarre-Stichler and Brantley (2007), the depletion of primary minerals and the subsequent formation of secondary clay minerals and Fe-oxides is an important issue in natural groundwater systems.

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Ntr Po Gt Na-Bdl Mg-Bdl 2 CO 2 O ) -1 during the batch experiments batch the during -0.016 -0.027 -0.084 -0.080 -0.022 -0.206 -0.066 -0.114 0.433 0.109 -0.001 -0.014-0.011 -0.004-0.003 -0.044 -0.030-0.032 -0.020 -0.084 -0.054 -0.023 -0.003 -0.003 -0.437 -0.082 -0.310 -0.032 -0.004 -0.007 -0.143 -0.229 -0.004 -0.060 -0.203 -0.059 0.169 -0.015 0.143 -0.001 -0.002 -0.479 -0.002 -0.165 0.007 0.089 -0.001 0.089 -0.004 0.010 0.017 0.052 0.024 0.178 Mg-Ol Ca-Cpx An Aeg Lct Sdl Anl Nsn Decomposition (-) / Formation (+) (mmol l (+) (mmol / Formation (-) Decomposition Mineral abbreviations used as recomended by the USGS (2007) Calculated mass transfers mass Calculated Table 7 Table leachate aoB hoB oNe TrB Ph

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In contrast to the batch experiments, natural weathering involves much lower fluid:mineral ratios reacted over much longer terms of time. Flow velocities and pore volume of the packaged beds of the batch experiments exceed those values attained in natural systems. It might also be argued that, in contrast to natural groundwater environments, high concentrations of 3+ Al , Fetotal, (and H4SiO4) of the leachates at near-neutral pH reflect only limited formation of secondary mineral phase due to the short experimental runtimes. Limitations of comparability are also due to the availability of fresh mineral reaction surfaces in contrast to altered mineral surfaces in the field. Still, the calculated mass transfers suggest an approach to relate the leachate compositions to mineral alteration reactions.

4.4 Hydrochemical Groundwater Evolution

4.4.1 Near-surface Groundwater (Early-stage Weathering) The mineral alteration reactions deduced from the leaching experiments are consistent with the mineral reactions postulated for the natural groundwaters. Using inverse modelling and considering the mineral alteration reactions delineated, overall mass transfers during water- rock interaction of meteoric water to immature near-surface groundwater (S3) (coefficients in mmol l-1) were computed as:

0.014 Mg-olivine + 0.146 Ca-pyroxene + 0.002 leucite + 0.095 analcite

+ 0.017 pyrrhotite + 0,333 CO2 + 0.063 O2 → 0.020 Na-beidellite + 0.017 Mg-beidellite + 0.018 Ca-montmorillonite + 0.073 goethite

More intense water-rock reactions are indicated by higher rates of consumption of CO2 as for sample S14:

0.039 Mg-olivine + 0.296 Ca-pyroxene + 0.072 anorthite + 0.016 sodalite

+ 0.014 pyrrhotite + 0.849 CO2 + 0.052 O2 → 0.133 Na-beidellite + 0.133 goethite

During longer terms of groundwater maturation, the dissolution of anorthite may significantly contribute to groundwater composition. The modelled mass transfers of groundwaters with elevated Cl- concentrations (S4, S13, S16, S19) correlate with high conversion rates of Na-silicate minerals without the precipitation of Na-beidellite. This may suggest that at higher

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rates of alteration of sodalite, Na-rich natrolite has to be considered as meta-stable alteration product. Among the groundwaters associated with K-rich phonolitic rocks, Na-beidellite probably converts to illite (illitisation) as

+ 2+ Na0.33Al2.33Si3.67O10(OH)2 + 0.6K + 0.25Mg → + 3+ 4+ K0.6Mg0.25Al2.3Si3.5O10(OH)2 + 0.33Na + 0.33Al + 0.17Si with only little flux of Al and Si. This reaction correlates with the minor amounts of modelled secondary Na-beidellite and high amounts of Na+ remaining in solution. It suggests that Mg2+ and K+ are consequently removed from solution and remain fixed in secondary illite which correlates with the field values. The overall mole transfer was modelled for sample SX2 as:

0.062 Ca-pyroxene + 0.119 aegirine + 0.068 anorthite + 0.497 analcite

+ 0.037 sodalite + 0.082 nosean + 0.608 CO2 → 0.528 natrolite + 0.105 Na-beidellite + 0.020 illite with natrolite as metastable phase of the breakdown of Na-rich feldspathoids. Generally, the solubility of the particular Al and Fe solid species at near-neutral pH is at a minimum (Garrels & Christ 1965; Drever 1997). Both elements offer rather low mobility and will be conserved either in primary or in secondary minerals. Weathering trends of basaltic rocks under natural weathering conditions which show progressive enrichment of Al2O3 and

Fe2O3 in the alteration products have been described by Chesworth et al. (2004).

4.4.2 Groundwater at greater Depth (Late-stage Weathering)

Groundwater at greater depth indicates the lowest concentrations of SiO2 which suggests formation of secondary silicate minerals preferred to dissolution of silicate minerals. For mass transfer modelling, forsterite, Ca-pyroxene as well as feldspathoids were assumed to be un- available to water-rock interaction due to depletion (White and Brantley 2003) or due to the formation of rather nonreactive alteration rinds (Stichler-Navarre and Brantley 2007). Mineral alteration reactions were, thus, limited to the dissolution of anorthite and albite as primary minerals. The high pH value indicates subsequent consumption of H+ during long periods of water-rock interaction and, thus, reflects longer terms of groundwater maturation. In contrast to the basaltic near-surface groundwaters, low concentrations of K+ suggest illitisation of

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2- smectites such as Na-beidellite. The low concentration of SO4 might relate to the reduction 2- of SO4 to H2S. This also suggests that the oxidation of pyrrhotite would have stopped at an earlier stage of groundwater maturation due to scarcity of available dissolved oxygen or due to mineral depletion. With regard to the concentrations of Mg2+, Ca2+, and Na+, cation exchange, simplified as

Na─X─Na + Mg2+ → Mg═X + 2Na+ and and

Na─X─Na + Ca2+ → Ca═X + 2Na+

with X2- as exchange surface has to be considered. Assuming preferred formation of Na- beidellite >> Mg-beidellite and Ca-montmorillonite and cation exchange in high-pH groundwater, the groundwater evolution at greater depth evolving from near-surface groundwater composition (S3) can be described as follows:

0.244 anorthite + 0.160 albite + 0.415 Na─X─Na + 0,188 CO2 → 0.261 Na-beidellite + 0.017 illite + 0.282 Ca═X + 0.133 Mg═X

+ 0.046 O2 + 0.023 H2S

Calculations required a variation of input data and calculated values of 10 %, exceeding the maximum error of the near-surface groundwaters of 5 %. It may be argued that the accuracy of the modelled cation exchange charge balance is theoretical and is probably not attained in the complexity of a natural environment. This might suggest the need of variation of input parameter values during hydrochemical modelling.

4.4.3 Cation Exchange Cation exchange capacity (CEC) of exchange matter varies as a function of pH and as a function of the cation occupying the exchange sites (Drever 1997). In comparison to chlorite (<10 meq 100g-1), smectites such as beidellite or montmorillonite offer higher CEC values (80-150 meq 100g-1) and may contribute to the ion exchange of interlayer cations. The CEC of illite is rather limited (10-40 meq 100g-1), since K remains fixed in the interlayer position (Drever 1997). Iron hydroxides commonly form coatings on clay minerals (Jenne 1977) and may contribute to surface charge of the exchange matter (goethite approx. 100 meq 100g-1). Negative surface charge in a high pH system is due to high OH- activity favouring deprotonation of the

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hydroxyl groups of the exchange sites (Stumm 1992). This effect increases with increasing pH (Drever 1997; Singhal and Gupta 2010). Bivalent cations (e. g. Mg2+, Ca2+) indicate higher affinity for adsorption than monovalent cations such as Na+ (Drever 1997; Singhal and Gupta 2010). Hence, monovalent cations are bond less tightly to an adsorption surface than bivalent cations. As a simple approach to the constraint of cation adsorption and pH, sorption curves were modelled for the uptake of Ca2+ and Mg2+ on hydrous ferric oxide as a precursor of goethite for pH values of 6.0 – 10.0 (Fig. 10). For calculations, the generalised two layer model introduced by Dzombak and Morel (1990) without the calculation of the diffuse-layer composition was used. This particular sorption model itself as well as the chosen values of parameters (specific surface area 200 m² g-1, 1.0 gram of total hydrous ferric oxide to react, a total of 4 x 10-4 moles of weak binding sites) are arbitrary. Still, it illustrates the different sorption affinities of Ca2+ and Mg2+ to deprotonated exchange sites.

-3 Ca2+ in solution Ca2+ fixed on exchange surface Mg2+ in solution Mg2+ fixed on exchange surface

-4 ) -1 log c (mol l -5

-6 678910 pH Fig 10 Selective adsorption of Mg2+ and Ca2+ on hydrous ferric oxide as a function of pH: adsorption of Mg2+ initially proceeds at significantly lower pH values (approx. 7.5) than initial adsorption of Ca2+ (approx. 8.5) and increases with increasing pH; consequently, the amount of exchange sites occupied by fixed Mg2+ or Ca2+ increase with increasing pH

Initially, the concentrations of Ca2+ and Mg2+ in solution are equal (0.128 mmol l-1), as in sample S3 used for the modelling of mass transfers of groundwater at greater depth. At near- neutral pH, the surface charge of most iron oxides and hydroxides is zero, the amount of positive charge on the surface equals the negative charge on the surface (Drever 1997). Beyond this zero point of charge, the amount of negatively-charged, deprotonated exchange sites ex-

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ceeds that of positively charged exchange sites. Consequently, with increasing pH, the concentrations of dissolved Ca2+ and Mg2+ decrease and remain fixed on the exchange sites. The modelled values suggest selective adsorption of Mg2+ and Ca2+ with initial sorption of Mg2+ proceeding at lower pH values (approx. 7.5) than initial sorption of Ca2+ (approx. 8.5) (Fig. 10). Referring to the natural groundwaters, Mg2+ appears to be removed at an earlier stage of groundwater maturation from near-neutral to high pH. The demobilisation of Ca2+ through sorption on exchange sites might commence at higher pH. Inverse modelling of mass mole transfers during groundwater maturation (meteoric water Î near-surface groundwater Î groundwater at greater depth) suggests the formation of 0.316 mmol l-1 (Na)-beidellite and 0.073 mmol l-1 goethite. Referring to molar weight (Na- beidellite 353 g mol-1, goethite 88.8 g mol-1), the total of secondary mineral phase promoting cation exchange amounts to approx. 120 mg l-1. Assuming an average CEC of 100 meq 100g- 1, the sorption potential gained by formation of secondary minerals amounts to 0.120 meq l-1. This significantly falls below the modelled amount of 0.830 meq l-1 Na+ exchanged for Ca2+ and Mg2+ in the groundwater at greater depth. However, the given CEC values relate to neutral pH and increase with increasing pH (Fig. 10). This suggests, that at elevated pH, the secondary clay minerals may significantly contribute to cation exchange. In comparison, the near-surface groundwaters do not indicate cation exchange. This relates to comparably low pH values and, thus, limited availability of negatively charged exchange sites. With regard to the pH values, cation exchange does not significantly proceed at values below 8.5.

4.4.4 Interpretation of Hydrochemical Clusters

The Ca-Mg-Na-HCO3 clusters indicated for the groundwaters (Fig. 11) significantly correlate with the calculated amounts of CO2 consumed during the modelled mineral reactions. Sam- ples among the first cluster involve groundwaters with the lowest CO2 amounts calculated (0.15-0.30 mmol l-1). Cluster 2 and 3 both include groundwaters associated with elevated -1 amounts of CO2 (0.30-0.40 and 0.28-0.40 mmol l , respectively), whereas cluster 4 indicates -1 the highest amounts of CO2 (0.78-0.90 mmol l ) consumed by the modelled mineral alteration processes. Among the near-surface groundwaters, increasing amounts of CO2 consumed also parallel to increasing pH values. However, the groundwater composition at greater depth (W2) suggests rather little consumption of 0.188 mmol l-1 when evolving from a hydrochemical composition of cluster 1 (sample S3) due to the depletion of available CO2.

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Dissimilarity 4 2 0

S1 aoB S3 oNe/vfS

S19 oNe/Tu/vfS 1 Cluster

S4 oNe/vfS ) -1 S9 oNe/aoB S10 oNe/aoB Cluster 2 Cluster

S11 oNe/aoB l (mmol 3 S5 aoB S6 aoB

S18 hoB Cluster 3

SX2 Ph SX3 Ph S13 oNe S14 oNe Mg-Ca-Na-HCO Cluster S15 oNe S16 aoB Cluster 4 S17 aoB

Fig. 11 Ca-Mg-Na-HCO3 cluster analysis calculated for the 18 groundwater samples: clusters indicate groups of similar groundwater composition with a dissimilarity < 0.5; the groundwaters associated with phonolitic rocks (SX2; SX3) as well as groundwater at greater depth (W2, not illustrated in the figure) do not correlate with any of the four clusters; the composition of sample S13 approximately correlates with cluster 4

As the hydrochemical clusters do not represent groundwaters associated with particular basaltic rock types, it appears that theses clusters relate to different stages of groundwater maturation. Different groundwaters associated with a particular type of rock (e. g. alkali olivine basalt) relate to all four cluster types. Cluster 1 apparently represents poorly evolved low-pH groundwaters with low SEC values. Intermediate stages (cluster 2 and 3) further graduate to groundwaters of cluster 4 with elevated pH and SEC values. However, there is no change of groundwater type (Ca-Mg-HCO3 type). With regard to spatial distribution of the groundwaters (Fig. 2) and the associated rock type (Table 2), the conclusions derived from the hydrochemical clusters can be comprised as follows: - As there is no spatial constraint of the cluster formation, the similarity of a distinct cluster does not relate to surface mixing of groundwaters. - Groundwaters of a distinct cluster do not relate to a particular rock type. - Groundwaters associated with the same rock type may relate to different hydrochemical clusters.

As suggested by the modelling calculations, the evolution of a Na-HCO3 type groundwater (W2) through cation exchange requires further elevation of pH. Furthermore, sorption and desorption processes relate to prior transformation of primary minerals to secondary clay and

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iron hydroxides in order to create sufficient exchange surface. As argued by Leßmann (2001) for the basaltic Vogelsberg mountain range, the absence of a Na-HCO3 type among near- surface groundwaters relates to short residence time in the aquifer rock, whereas Bogaard et al. (2001) proved Na-HCO3 type groundwaters at greater depth (> 300 m) in an exploration drilling in the central Vogelsberg.

4.4.5 Stability Constraints Stability relations of solutions and solid mineral phases of the Ca-, Mg-, and Na-system are illustrated in Fig. 12 (a = ion activity). The standard state for the aqueous species corresponds to unit activity of the species in a hypothetical one molal solution referenced to infinite dilution at any pressure and temperature according to Helgeson et al. (1978).

20 20 12 Analcite silica Quartz 18 18 Quartz

Chalcedony Albite

10 Chalcedony Laumontite 16 16 Amorphous Amorphous silica ) Ch ) rys + Chlorite ot ile ) + satur ation + H 8 H 14 14 2 2 Na-beidellite Ta /a l /a c satu /a H ra + 2+ tio 2+ n 12 12 6 Ca- Mg-beidellite montmorillonite 10 10 Gibbsite Gibbsite log (a Na 4 Gibbsite log (a Ca log (a Mg log (a 8 8 Kaolinite Kaolinite silica 2 6 6 Kaolinite Pyrophyllite Amorphous Chalcedony Quartz 4 4 0 -5 -4 -3 -2 -5 -4 -3 -2 -5 -4 -3 -2 log a H SiO log a H SiO 4 4 4 4 log a H4SiO4 Fig. 12 Stability relations among the Ca-, Mg-, and Na-stability field system at 25°C and 0.1 MPa: the near- surface groundwaters of the basaltic sequence are indicated as black diamonds, groundwaters associated with phonolitic rocks are indicated by blue (SX2) and green (SX3) diamonds, groundwater at greater depth (W2) is indicated as red diamonds; stability diagrams modified from Helgeson et al. (1969) and Drever (1997); the posi- tions of boundaries of the clay mineral stability fields involve uncertainties, the chlorite and Mg-beidellite stability fields are limited by the lines of talc and chrysotile saturation, a = ion activity; zeolites might be more stable than albite but thermodynamic data was not available

As illustrated for the Ca- and Mg-stability diagrams, the near-surface groundwaters graduate from the kaolinite into the Ca-montmorillonite and Mg-beidellite stability fields. At greater depth, the groundwater plots close to the triple points of the kaolinite-clay mineral- zeolite/chlorite boundaries. In the Na-stability diagram, all samples plot within the kaolinite stability field. Na-beidellite does not appear as stable secondary mineral phase, though the near surface groundwaters indicate an approach of groundwater composition towards the Na- beidellite stability field. At greater depth, the groundwater sample as well plots below the Na- beidellite stability field, approaching the kaolinite-gibbsite boundary. With further increase of pH and proceeding mobilisation of Na+ and demobilisation of Mg2+ and Ca2+, the groundwater at greater depth might eventually evolve towards the stability

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field of gibbsite, intersecting the kaolinite stability field. This reaction path requires decreasing silica activity which could be associated with the incorporation during the formation of kaolinite and subsequent depletion of sources of alkali and alkali earth elements. This is, over long terms of reaction time, kaolinite and finally gibbsite appear to be the stable secondary mineral phases at greater depth, whereas secondary smectite has to be considered as metastable mineral phase over long terms of reaction time.

5 Conclusions

The basic mineral alteration reactions could be related to the alteration of Mg-rich olivine, Ca- pyroxene, plagioclase, pyrrhotite, and feldspathoids under formation of secondary clay minerals (smectite, illite) and goethite. The alteration of pyrrhotite significantly correlates with the reduced concentrations of dissolved oxygen in the near-surface groundwaters. Water-rock reactions preferentially affect the fine-grained mineral components in the groundmass, contributed by the leaching of micro- and macro-crystals. The hydrochemical clusters identified for Ca-Mg-Na-HCO3 constraints can be associated with different stages of groundwaters maturation and increasing modelled amounts of CO2 consumed through the alteration reactions. There is no constraint of spatial distribution or relation to particular rock types for the individual hydrochemical clusters proved for the groundwaters.

In the basaltic rock sequence, the low concentration of SiO2 in the groundwater at greater depth suggests subsequent incorporation in secondary silicate minerals. The calculations of mass transfers correlate with the formation of beidellite/montmorillonite and goethite at an early stage of groundwater evolution. The conversion of Na-beidellite to illite occurs at a later stage of groundwater evolution and effects as sink of K+ and Mg2+. Near-surface groundwaters (pH 6.8-8.5) do not indicate significant cation exchange. This suggests, that initial cation exchange requires elevated pH values, with Mg2+ removed from solution preferred to Ca2+. Na-alkalisation of the groundwaters at greater depth suggest the exchange of Na+ for Mg2+ on Na-beidellite, supported by cation exchange on coatings of iron hydroxides as alteration products. As indicated for high-pH groundwater at greater depth, the dissolution of anorthite and albite has significant effect on groundwater composition during late-stage weathering. The short-term batch experiments produced valuable data to balance mineral alteration reactions of fresh mineral surface weathering. However, this can only be seen as an approach to natural environments. Limitations are basically due to short experimental runtimes, high water-rock ratios, the lack of equilibrium to secondary solid phase, and to the availability of fresh mineral surfaces in contrast to altered mineral surfaces in natural systems. Still, the experiments emphasise the importance of reaction kinetics of the minerals involved and mineral dissolution rates when interpreting water-rock reactions.

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References

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Berner RA (1995) Chemical weathering and its effect on atmospheric CO2 and climate. In: White AF, Brantley SL (eds) Chemical weathering rates of silicate minerals. Review in Mineralogy, Min Soc Am 31:565-583 Bernot P (2004) Igneous Intrusion Impacts on Waste Packages and Waste Forms – A Process Model. U.S. Department of Energy, Las Vegas, 71 pp Berthold G, Toussaint B (1998) Grundwasserbeschaffenheit in Hessen, Auswertung von Grund- und Rohwasseranalysen bis 1997 [Groundwater Quality in Hessen, Report on Groundwater and Raw Water analysis data until 1997]. Hess L-Anst Umwelt 250, 102 pp Blum AE, Stillings LL (1995) Feldspar dissolution kinetics. In: White AF, Brantley SL (Eds) Chemical Weathering Rates of Silicate Minerals. Min Soc Am 31:291-351 Blum AE (2004) Determining Dissolution, Precipitation and Nucleation Rate Laws in Natural Systems. Conceptual Model Development for Subsurface Reactive Transport Modelling of Inorganic Contaminants, Radionuclides, and Nutrients, workshop, Albuquerque, pp 105-108 Boogard PJF, Jabri L, Wörner G (2001) Chemical Alteration of Basalts from the Drill Core „Forschungsbohrung Vogelsberg 1996“, Germany. In: Hoppe A, Schulz R (eds) Die Forschungsbohrung Vogelsberg – Einblicke in einen miozänen Vulkankomplex [The Vogelsberg Exploration Drilling – An Insight into a Miocene Volcanic Complex]. Geol Abh Hessen 107:101-118 Büttner G, Pamer R, Wagner B (2003) Hydrogeologische Raumgliederung von Bayern [Hy- drogeological spatial classification of Bavaria]. Bay L-Amt Umwelt, GLA-Fachbericht 20, 85 p Bucher K, Stober I (2010) Fluids in the upper continental crust. Geofluids 10:241-253 Bullermann M, Schneble H (1992) Dokumentation Messstellenbau [Construction report ob- servation wells]. Ingenieurgemeinschaft Umweltplanung Darmstadt, Darmstadt Chapelle FH (2005) Geochemistry of Groundwater. In: Drever JI (ed) Surface and Groundwa- ter, Weathering, and Soils. 5:425-449 Chesworth W, Dejou J, Larroque P, Rodeja GR (2004) Alteration of olivine in a basalt in France. CATENA 56:21-30 Dessert C, Dupré B, Gaillardet J, François LM, Allègre CJ (2003) Basalt weathering laws and

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the impact of basaltic weathering on the global carbon cycle. Chem Geol 202:257-273 Diederich G (1975) Hydrogeologie [Hydrogeology] In: Laemmlen (ed) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr, 5225 Geisa, 2. Auflage [Comments to the geological map, sheet 5225, Geisa, 2nd ed]. Hess L-Amt Umwelt Geol, Wiesbaden, pp 180-204 Drever JI (1997) The geochemistry of natural waters. 3rd edn. Prentice Hall, 686 New Jersey, 436 p Dzombak DA, Morel FMM (1990) Surface complexation modelling - Hydrous ferric oxide. John Wiley, New York, 393 p Ehrenberg K-H, Hickethier H (1994) Tertiärer Vulkanismus der Wasserkuppenrhön und der Kuppenrhön [Tertiary volcanism in the High Rhön Wasserkuppe and the Dome Rhön]. Jber Mitt oberrhein geol Ver 76:83-146 Ehrenberg K-H, Hickethier H (2002) Vulkanologische Karte der Wasserkuppenrhön 1:15000 mit Erläuterungen [Volcanologic map of the High Rhön 1:15000 with comments] Hess L-Amt Umwelt Geol, Wiesbaden, 28 p Ehrenberg K-H, Hansen R, Hickethier H, Laemmlen M (1994) Erläuterungen zur Geologi- schen Karte von Hessen, Blatt Nr, 5425 Kleinsassen, 2. Auflage [Comments to the geological map, sheet 5425, Kleinsassen, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, 385 pp Ehrenberg K-H, Hickethier H, Rosenberg F, Strecker G, Susic M, Wenzel G (1992) Neue Ergebnisse zum tertiären Vulkanismus der Rhön (Wasserkuppenrhön und Kuppenrhön) [Recent conclusions on tertiary volcanism in the Rhön (High Rhön and Dome Rhön)]. Beih z Eur J Mineral 4:47-102 Ficke B (1961) Petrologische Untersuchungen an tertiären basaltischen bis phonolithischen Vulkaniten der Rhön [Petrological Investigations on Tertiary basaltic and phonolitic volcanic rocks of the Rhön]. Miner and Petrol 7:337-436 Garrels RM, Christ CL (1965) Solutions, minerals, and equilibria. Harper and Row, New York, pp 450 Gislason SR, Eugster P (1987) Meteoric water-basalt interactions. A laboratory study. Geo- chim Cosmochim Acta 51:2827-2840 Gislason SR, Oelker EH, Steffansson A (2001) Controls on chemical weathering of basalt. Report on Goldschmidt Conference (2001) Gislason SR, Veblen DR, Livi KJT (1993) Experimental meteoric water-basalt interactions: Characterization and interpretation of alteration products. Geochim Cosmochim Acta 57:1459-1471 Helgeson HC, Brown TH, Leeper RH (1969) Handbook of theoretical activity diagrams de- picting chemical equilibria in geologic systems involving an aqueous phase at 1 atm. and 0 to 300 °C. Freeman Cooper & Co., San Francisco, CA Helgeson HC, Delany JM, Nesbit HW, Bird DK (1978) Summary and critique of the thermodynamic properties of rock-forming minerals. Am J Sci, 278-A:1-220 - 90 - Chapter 2: Groundwater Evolution and Mineral Alteration Reactions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany - A Case Study

HLUG (2006) Fachbericht Tonrohstoffe [Report on Clay Raw Material]. Hess L-Amt Umwelt Geol, Wiesbaden, p 76 Huneau F, Travi Y (2008) The Miocene Aquifer of Valréas, France. In: Edmunds WM, Shand P (eds) Natural groundwater quality. Blackwell Publishing, United Kingdom, pp 287– 305 Illies H (1975) Intraplate tectonics in stable Europe as related to plate tectonics in the Alpine system. Geol Rdsch 64:677-699 Jenne EA (1977) Trace element sorption by sediments and soils – Sites and processes. In: Chappel W, Petersen K (eds) Symposium on Molybdenum in the Environment, Vol. 2, Marcel Dekker, New York, pp 425-553 Jung S, Hoernes S (2000) The major- and trace-element and isotope (Sr, Nd, O) geochemistry of Cenozoic alkaline rift-type volcanic rocks from the Rhön area (central Germany): petrology, mantle source characteristics and implications for asthenosphere-lithosphere interactions. J Volc Geoth Res 99:27-53 Le Bas MJ, Le Maitre RW, Streckeisen A, Zanettin A (1986) A chemical classification of volcanic rocks based on the Total Alkali-Silica-Diagram. J Petrol 27:745-750 Leßmann B (2001) Hydrogeologie des vulkanischen Vogelsberges [Hydrogeology of the volcanic Vogelsberg]. Geol Abh Hessen 108, pp 144 Lippolt HJ (1982) K/Ar age determination and the correlation of Tertiary volcanic activity in Central Europe. Geol Jb, D52:113-135 Logan J (1964) Estimating Transmissibility from Routine Production Tests of Water Wells. Ground Water 2:35-37 Ludwig F, Stober I, Bucher K (2011) Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany: A Laboratory and Field Study. Aquat Geochem 17:165-193 Navarre-Stichler A, Brantley S (2007) Basalt weathering across scales. Earth and Planetary Science Letters 261:321-334 Neumann J (2009) Flächendifferenzierte Grundwasserneubildung von Deutschland [Spatial Distribution of Groundwater Recharge in Germany]. Geol Jb, Sonderhefte SC6:127 pp Nordstrom DK (2005) Modelling low-temperature Geochemical Processes. In: Drever JI (ed) Surface and Groundwater, Weathering, and Soils 5:37-72

Oelkers EH, Gislason SR, Matter J (2008) Mineral carbonation of CO2. Elements 4:333-337 Paces T, Corcho Alvarado JA, Herrmann Z, Kodes V, Muzak J, Novák J, Purtschert R, Re- menarova D, Valecka J (2008) The Cenomanian and Turonian Aquifers of the Bohe- mian Cretaceous Basin, Czech Republic. In: Edmunds WM, Shand P (eds) Natural Groundwater Quality. Blackwell Publishing, United Kingdom, pp 372–390 Parkhurst DL (1995) User’s guide to PHREEQC--A computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations. U.S. Geological Survey Water-Resources Investigations Report 95-4227, 143 pp

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Pawar NJ, Pawar JB, Kumar S, Supekar A (2008) Geochemical Eccentricity of Groundwater Allied to Weathering of Basalts from the Deccan Volcanic Province, India: Insinuation on CO2 Consumption. Aquat Geochem 14:41-71 Postma D, Kjøller M, Søgaard Andersen M, Condesso de Melo MT, Gaus I (2008) Geo- chemical Modelling of -Processes Controlling Baseline Compositions of Groundwater. In: Edmunds WM, Shand P (eds) Natural Groundwater Quality. Blackwell Publishing, United Kingdom, pp 71–90 Prodehl C (1981) Structure of the crust and the upper mantle beneath the Central European rift system. Tectonophysics 80:255-269 Prodehl C, Müller S, Glahn A, Gutsher M, Haak V (1992) Lithosphere cross-section of the European rift system. In: Ziegler PA (ed) Geodynamics of Rifting, Vol. 1. Case histories on rifts: Europe and Asia. Tectonophysics 208:113-138 Siivola J, Schmid R (2007) List of Mineral Abbreviations – Recommendations by the IUGS Subcommission on the Systematics of Metamorphic Rocks: Web version 01.02.07 Singhal BBS, Gupta RP (2010) Groundwater Quality. In: Singhal BBS, Gupta RP (eds) Ap- plied Hydrogeology of Fractured Rocks, 2nd edn. Springer, Dordrecht, pp 205-220 Smith KL, Milnes AR, Eggleton RA (1987) Weathering of Basalt: Formation of Iddingsite. Clays and Clay minerals 6:418-428 Stengel-Rutkowski W (1981) Hydrogeologisches Gutachten zur Festsetzung eines Wasser- schutzgebiets für den Bohrbrunnen auf der Wasserkuppe (Rhön) [Hydrogeological report about the designation of a sanctuary for the Mt. Wasserkuppe groundwater well (Rhön)] Expertise 5525/9, Hess L-Amt Umwelt Geol, Wiesbaden Stengel-Rutkowski W (1994) Hydrogeologie [Hydrogeology]. In: Ehrenberg K-H, Hansen R, Hickethier H, Laemmlen M (eds) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr, 5425 Kleinsassen, 2. Auflage [Comments to the geological map, sheet 5425, Kleinsassen, 2nd ed]. Hess L-Amt Umwelt Geol, Wiesbaden, pp 249-265 Stumm W (1992) Chemistry of the Solid-Water Interface. New York: Wiley-Interscience Weiher B, Lehrberger G, Thuro K (2007) Prüftechnischer Nachweis von Sonnenbrand an einem Basalt der Oberpfalz [Petrophysical Properties of sunburn basalt from the Upper Palatinate in north-eastern Bavaria]. In: Otto F (ed): Veröffentlichungen von der 16. Tagung für Ingenieurgeologie, 7.-10. März 2007, Bochum [Publications of the 16th Convention of Engineering Geology].Technische Fachhochschule Georg Agricola, Bo- chum, pp 77-85 White AF, Bullen TD, Schulz MS, Blum AE Huntington, TG, Peters NE (2001) Differential rates of feldspar weathering in granitic regoliths. Geochim Cosmochim Acta 65:847- 869 White AF, Brantley SL (2003) The effect of time on the weathering of silicate minerals: why do weathering rates differ in the laboratory and field? Chem Geol 202:479-506 White AF (2005) Natural weathering rates of silicate minerals. In: Drever JI (ed) Surface and Groundwater, Weathering, and Soils 5:37-72

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White JC (2011) Calculating CIPW Norms, Excel spreadsheet. Eastern Kentucky University, Department of Geography and Geology Wilson M, Downes H (1991) Tertiary-Quarternary extension-related alkaline magmatism in western and central Europe. J Petrol 31:811-850 Witt-Eickschen G, Kramm U (1997) Mantle Upwelling and Metasomatism beneath Central Europe: Geochemical and Isotopic Constraints from Mantle Xenoliths from the Rhön (Germany). Journal of Petrology 38(4):479-493 Wogelius RA, Walther JV (1991) Olivine dissolution at 25°C: Effects of pH, CO2, and organic acids. Geochim Cosmochim Acta 55:943-954 Wood WW, Low WH (1988) Solute geochemistry of the Snake River Plain Regional Aquifer System, Idaho and Eastern Oregon. US Geol Surv Prof Pap, 1408-D, 79 pp Ziegler PA (1990) Geological atlas of Eastern and Central Europe, 2nd ed. Shell Int Pet Mij Geol Soc Publ, Bath, pp 238 Ziegler PA (1992) European Cenozoic rift system. In: Ziegler PA (ed) Geodynamics of Rift- ing, Vol. 1. Case histories on rifts: Europe and Asia. Tectonophysics 208:91-111 Zhu Y (2001) Hydrogeologie und Gestein-Wasser Reaktion in der Grunde Clara (Schwarz- wald) [Hydrogeology and rock-water reactions in the Grube Clara, Black Forest]. Frei- burger Geowiss Beitr 15, pp 145 Zorn T, Küchler R, Noack K, Dittmar T, Worch E (2009) Dissolution of gypsum in batch and column experiments. – Grundwasser-Zeitschr Fachsekt Hydrogeol 14:287-295

Online: http://atlas.umwelt.hessen.de

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Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

Abstract

Groundwaters associated to seven different aquifer lithologies were analysed in order to investigate the constraints of concentrations of dissolved heavy metals and As and sorption affinity to Fe-hydroxides as solid phase. The dataset compiles a total number of 130 samples. Speciation calculations were run to determine the individual element species of Fe and Al as well as of heavy metals and As. The mobility of iron could be basically related to the formation of solid ferrihydrite (Fe(OH)3) as a function of Eh and pH. Mobility of an ion is referred to its non-conservative transport in the aquifer system with possible effect by chemical (e.g. precipitation) or physical (e.g. sorption) processes. Sorption curves were modelled for sorption of the metal ions and anionic As and Cr species on hydrous ferric oxide. Except for Cu, the sorption mechanisms postulated were found to be consistent with the concentrations of the particular elements in the natural groundwaters. Pb, Cd, Co, Zn, and Ni indicate low mobility at elevated pH, whereas Cr and As anionic species have low mobility at low pH. In addition, the concentrations of dissolved iron indicate positive linear correlation to dissolved arsenic and to several heavy metals such as Pb, Co, Ni, and Zn, suggesting co-precipitation and synchronous remobilisation of previously sorbed elements as a function of Eh. Sorption on Fe- oxides/hydroxides can be assumed to have major effect on the mobility of As and the heavy metals considered, contributed by co-precipitation and remobilisation with iron solid phase. The formation of metal precipitants (sulfides, carbonates) is rather unlikely with respect to the prevalent groundwater compositions and the Eh-pH conditions. However, the formation of oxides has to be considered as important mobility control of Cu. Keywords: groundwater quality, speciation heavy metals, arsenic, adsorption on oxides/hydroxides, Germany

1 Introduction

Regarding the mobility of heavy metals and arsenic in groundwater, samples associated to individual lithologies were collected from production wells and springs for domestic water supply. Analyses included mayor anions and cations as well as Fe, Al and a range of trace elements such as heavy metals and As. Prior studies about groundwater evolution by Ludwig et al. (2011) focused on general constraints of water-rock interaction and the concentrations of major elements in the associated groundwaters. However, these hydrochemical studies of the Bunter sandstone sequence of the Odenwald mountain range and the basaltic rocks of Mt. Wasserkuppe, High Rhön, Germany, did not include contemplations about trace element mobility in groundwater. In order to attain a sufficient database, additional groundwater samples were collected in the Bunter sandstone sequence along the Lower Hessian Depression and in

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the basaltic rock sequence of the Vogelsberg mountain range. Furthermore, groundwaters associated with clay shale of the Middle Rhine Highlands and the Rotliegend sedimentary rocks were analysed, both indicating high concentration values of Fe, As, and heavy metals in groundwater. Finally, the investigations included groundwaters in the sedimentary deposits of the Upper Rhine Graben. The origin of heavy metals and As can be associated, to some part, to rainfall loads as groundwater recharge. Huneau and Travi (2008) identified rainfall to be the major source of several solutes in near-surface groundwater. However, soils can be considered as sink for heavy metals and As as discussed in various studies. Investigations by McLean and Bledsoe (1992) suggest metals added to soil to be retained at the soil surface. They evaluate the feasibility of metals into other compartments such as groundwater to be minimal, as long as sufficient retention capacity of the soil is available. With regard to the fields of investigation of this study, the constraints of retention of heavy metals and As have been the issue of numerous reports. Consistently, soils were found to accumulate heavy metals and As with concentrations exceeding those of the original bedrock by factors of 10 to 100 (Müller et al. 1987, Sabel 1988, Rosenberg 1991, Emmerich 1994). Retention affinity of the soils is described as a function of pH and correlates to the availability of clay minerals, organic compounds, and Fe- oxides/hydroxides (Müller et al. 1987). Investigating fissured rock aquifers, Singhal and Gupta (2010) predominantly relate sorption as a controlling factor of mobility of dissolved constituents to water-rock interaction with (secondary) clay minerals, carbonates, and Fe-hydroxides. Further, they suggest sorption affinity as a function of pH and Eh of the groundwaters. With regard to water-rock interaction in basaltic aquifers, Flaathen and Gislason (2007) found heavy metals released during mineral alteration processes readily immobilised with increasing pH. This correlates to investigations of Bodin et al. (2003) describing solute transport in fractured aquifers. Prior studies of Hem (1977) focused on reactions of heavy metal ions and As at surfaces of hydrous iron oxides and found reaction affinities to relate to particular element species. Lahann (1976) investigated surface charge variation in ageing ferric hydroxide and suggests decreasing values with increasing age and the alteration of amorphous ferric hydroxides to goethite. Phillips (1999) suggests that solubilisation of Fe hydrous oxides causes a synchronous release of previously sorbed metals when introduced to reducing conditions. This parallels to findings of Overesch et al. (2008) who correlate the remobilisation of As to the dissolution of Fe-species. Contrary, the availability of free oxygen increases the precipitation of As with Fe-hydroxides. Field studies by Carrillo and Drever (1997) about adsorption of arsenic by natural aquifer material in the San Antonio-El Triunfo mining area, Baja California, Mexico, delineated sorption of As as a function of pH. The comparison of experimental and modelled results suggests that As is adsorbed mostly by oxyhydroxides surfaces in the natural environment.

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This study does not focus on the origin of heavy metals in groundwater but rather emphasises effects on heavy metal mobility in selected aquifers. The geochemistry of the aquifer rocks is considered as part of the discussion but without the attempt of a quantitative mass balance approach. The basic issues of this study are (i) the speciation of dissolved heavy metals and As, (ii) the estimation of sorption affinity to hydrous ferric oxides as one possible sorption mechanism, and (iii) to delineate possible constraints of iron de-/remobilisation and the concentrations of heavy metals and As in groundwater.

2 Study Areas

The fields of investigation focused on seven different groundwater landscapes with individual aquifer lithologies. All areas are located within the county of Hessen, Germany, and are introduced to concisely in the following.

8° 9° 10°E

Kassel

51°N 4

a ld u F

r e v i R n h a L iver R Fulda 6 5

1 Frankfurt am Main 2 Main er iv R 50° 2 R 7 i v e r

R h i n e 3

Fig. 1 Location of the seven individual groundwater lithologies in the county of Hessen: investigation focused on groundwater circulation in Devonian clay shales of the Idstein Depression (1), in the Permian Rotliegend sedimentary rocks of the Lower Main Plain (2), in the Triassic Bunter sandstone sequence of the Odenwald mountain range (3) as well as in the Triassic Bunter sandstone of the Lower Hessian Depression (4), in the Terti- ary basaltic rocks of the High Rhön mountain range (5) and in the Tertiary basaltic rocks of the Vogelsberg mountain range (6), and in the Quaternary sedimentary deposits of the Upper Rhine Graben

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2.1 Devonian Shale, Idstein Depression, Middle Rhine Highlands The Idstein Depression 40 km west of Frankfurt separates the western and eastern part of the Taunus mountain range as central section of the Devonian Middle Rhine Highlands (Fig. 1). The extension structure relates to the evolution of the Upper Rhine Graben in the South during early Tertiary. Extension forces lead to the separation of individual tectonic blocks with vertical displacement of several tens to 100 m (Anderle 1991). The rock sequence of the Id- stein Depression comprises quartzite and shale, which may indicate syn-tectonic hydrothermal alteration (Stengel-Rutkowski 1976). In the field of the Idstein Depression, the Devonian basement is covered by several metres of Quaternary calcareous loess deposits. The quartzite and shale sequence constitutes a fissured rock aquifer with low hydraulic -5 -6 -1 conductivity. The kf values fall within the range of 10 and 10 m s . (Stengel-Rutkowski 1991) Elevated hydraulic conductivities are associated with fault zones along the rim of the graben and along the intersections of the tectonic blocks. The aquifer is principally recharged by rainfall and tributary by the leakage of surface waters. The depth of wells tested ranges between 42 and 100 m. The hydrochemical composition of the groundwaters predominantly + - indicates a Ca-Mg-HCO3 type with sporadical elevated concentrations of Na and Cl . With absence of loess deposits, the groundwater indicates significantly lower values of Ca2+ and Mg2+ (spring groundwater sample, Fig. 2). The SEC varies in a range between 160 and 800 µS cm-1 at near-neutral pH values. All groundwaters exhibit reduced concentrations of dissolved oxygen and the Eh values basically range between +200 and -100 mV.

2.2 Permian Rotliegend Sedimentary Rocks, Lower Main Plain The Rotliegend sedimentary rocks in central Hessen outcrops 20-30 km southeast of Frankfurt (Fig. 1). It comprises a sequence of late Palaeozoic sedimentary rocks that constitute the overburden of the crystalline basement of the Odenwald, Spessart, and Taunus mountain ranges. Permian sedimentation occurred along the Hessain Trough as molasse basin of the Devonian-Carboniferous (variscian) orogeny. The rocks comprise conglomerates, arkoses, and claystone deposited under continental to shallow-marine conditions (Marell 1989). The sediments originate from erosion of the surrounding crystalline mountain ranges. They comprise rock clasts of shale, quartzite, phyllitc schist, granite, and rhyolite. The more fine- grained sandstones are build up by quartz grains and feldspars and are interbedded by layers of claystone (illite > kaolinite). The reddish colour of the rock sequence relates to a significant content of iron oxides. Rock cementation is attained by pelitic or carbonate binding material (Kowalczyk 1983). The formation of the Hanau-Seligenstadt Depression during Tertiary separated the Rotliegend Sprendlingen Horst in the West from the Rotliegend of the Wetterau in the East.

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100 100 clay shale, Idstein Depression Rotliegend sedimentary rocks, Lower Main Plain

10 10 ) ) -1 -1 1 1 c (meq l l c (meq l l

0.1 0.1

0.01 0.01

Mg Ca Ca+Mg Na+K Cl HCO3 SO4 Mg Ca Ca+Mg Na+K Cl HCO3 SO4

100 100 Bunter sandstone, Odenwald Bunter sandstone, Lower Hessian Depression

10 10 ) ) -1 -1 1 1 c (meq l c (meq l

0.1 0.1

0.01 0.01

Mg Ca Ca+Mg Na+K Cl HCO3 SO4 Mg Ca Ca+Mg Na+K Cl HCO3 SO4

100 100 basaltic rocks, High Rhön basaltic rocks, Vogelsberg

10 10 ) ) -1 -1 1 1 c (meq l c (meq l

0.1 0.1

0.01 0.01

Mg Ca Ca+Mg Na+K Cl HCO3 SO4 Mg Ca Ca+Mg Na+K Cl HCO3 SO4

100 sedimentary deposits, Upper Rhine Graben

10 ) -1 1 c (meq l l

0.1

0.01 Mg Ca Ca+Mg Na+K Cl HCO3 SO4 Fig. 2 Schoeller plots of groundwater compositions of the seven aquifer lithologies investigated: near-surface groundwaters issued by springs are drawn as red lines, samples taken off production wells associated to groundwater circulation at greater depth are drawn as blue lines; all samples predominantly relate to an Mg/Ca-HCO3 type, the concentrations of alkali elements, Cl, and SO4 are subordinate

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The Rotliegend sequence constitutes a fissured rock aquifer with heterogeneous spectrum of hydraulic conductivity (Renftel and Scharpff 1998). Whereas the claystone layers indicate rather low values, the sandstones and conglomerates provide higher hydraulic conductivity.

Tectonic disintegration of the rocks initiated groundwater flow paths with elevated kf values along fault zones. Groundwater recharge is generated by rainfall. The depth of production wells ranges from 50-150 m. Groundwaters predominantly indicate a Ca-Mg-HCO3 type (Fig. + 2- 2), in some cases associated to elevated concentrations of Na and/or SO4 . The SEC of the groundwaters analysed varies in a range of 500-1,000 µS cm-1, all samples show near-neutral pH values. With respect to dissolved oxygen, most groundwater samples are partly to significantly reduced and indicate Eh values between +220 and -200 mV.

2.3 Triassic Bunter Sandstone, Odenwald Mountain Range The Odenwald mountain range is located 60 kilometres southeast of the city of Frankfurt in central Germany (Fig. 1). The Triassic Bunter sandstone of the Odenwald comprises an alternating sequence of beds of arenitic sandstone and thin layers of claystone as caprock of the Palaeozoic crystalline basement. The entire sedimentary rock sequence builds up a total thickness of 450 m (Backhaus and Schwarz 2003). Sedimentation occurred as fluvial-lacustrine deposition under continental conditions in an arid-type climate. The sedimentary deposits derived from disintegration of predominantly granitic crystalline rocks of the Black Forest highlands south of the Odenwald. The strata of the Bunter sandstone predominantly comprises quartz, K-feldspar and plagioclase, minor amounts of biotite and muscovite (K-mica) as well as iron-bearing oxides (Dersch-Hansmann and Hug 2004). The Bunter sandstone builds up a fissured rock aquifer with silicate rock composition and cementation and medium to high fracture permeability. Well yields are predominantly due to fracture permeability and, thus, wells are usually associated to tectonic segmentation. ). Hy- draulic conductivity falls with in a range of 10-6 to 10-4 m s-1 (Ludwig et al. 2011). The occurrence of springs relates to stratification (contact springs) or to faults (border springs). Aquifers with deep groundwater circulation are made accessible by production wells; well depth spreads from 18 – 200 m. Near-surface groundwaters can be associated with a Ca-Mg-SO4 type and alkalinity values below the detection limit, whereas groundwaters at greater depth -1 relate to a Ca-HCO3 type (Fig. 2). The SEC amounts 50 – 200 µS cm , and pH values are acidic among the near-surface groundwaters and near-neutral at greater groundwater depth. The groundwaters are oxidised and indicate the highest concentrations of dissolved oxygen and of redox potential of the entire dataset.

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2.4 Triassic Bunter Sandstone, Lower Hessian Depression The Lower Hessian Depression extends between the city of Kassel in the North and the Vo- gelsberg volcanic complex in the South (Fig. 1). It constitutes the northern extension of the tertiary graben structure of the Upper Rhine Graben. During the orogeny, the central section of the graben was uncoupled from the adjacent Triassic Bunter sandstone sequence to the West and East. The vertical displacement amounts up to 200 m. In the central part of the graben, syn-tectonic limnic-fluviatile and marine sedimentation of clays and sands proceeded. During late Tertiary, basaltic magmas intruded the Triassic sandstone sequence and tertiary sediments along the displacement faults. The Middle Bunter comprises a sequence of 330 – 340 m (Becker and Kulick 1999) of middle to coarse grained sandstones interbedded with thin layers of clay- and siltstone. Ce- mentation of the sediments is predominantly quartzitic or ferro-pellitic. The granular structure is predominantly built up by quartz grains and subordinate amounts of feldspars and iron oxides. Cut-offs between sets of strata may also exhibit accumulations of mica. At the top, clay- and siltstones of the Upper Bunter sequence separate the strata of the Middle Bunter from the fine-grained tertiary deposits. Groundwater resources predominately relate to the fissured sandstone of the Middle Bunter. Groundwater recharge results from the western and eastern rims of the graben along the displacement faults. Within the graben, groundwater flow is favoured by elevated hydraulic conductivity along fault zones. Hydraulic conductivity yields values of 10-5 – 10-7 m s-1 (Pöschl 1999). The groundwaters are confined due to low hydraulic conductivity of the overburden of the Middle Bunter. Groundwater extraction was proceeded at 98 – 270 m well depth. The groundwaters analysed all refer to a Ca/Mg-HCO3 type with elevated concentrations of alkali elements and Cl- (Fig. 2). The SEC amounts 130 to 700 µS cm-1 and pH levels at near-neutral to light alkaline values. The groundwaters partly indicate low contents of dissolved oxygen and negative redox potentials.

2.5 Tertiary Basaltic Rocks, Mt. Wasserkuppe, High Rhön The Rhön mountain range with its highest peak, Mt. Wasserkuppe (950 m ASL), is located 100 kilometres east of the city of Frankfurt, Germany (Fig. 1). It is built up by a chain of mounts of Tertiary volcanic rocks that overlay the pre-volcanic Mesozoic basement of sandstones and limestones. At Mt. Wasserkuppe, the basaltic magmas built up a sequence of 300 m of effusive layers and subaerial intrusions. Volcanic activity occurred from the Upper Oli- gocene to the Mid Miocene (25 – 11 Ma) with a maximum activity from 22 to 18 Ma (Lippolt 1982). The magmatic rocks investigated comprise primitive olivine-nephelinites, basanites, and basalts (Ehrenberg et al. 1992). Spinel peridotite xenoliths are abundant in outcrops of

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alkali olivine basalt and olivine nephelinite (Witt-Eickschen and Kramm 1997). The basaltic rocks basically comprise Ca-pyroxene and/or olivine, plagioclase, feldspathoids (nepheline, leucite, and sodalite), analcite, and traces of apatite Ehrenberg et al. (1992). The basaltic sequence at Mt. Wasserkuppe builds up a fissured rock aquifer with medium -7 -5 -1 to high permeability. Hydraulic conductivity (kf) comprises values of 10 to 10 m s (Bütt- -9 -1 ner et al. 2003). Pelitic tuff layers (kf < 10 m s ) may constitute vertical hydraulic segmentation of the basaltic fissured rock aquifers. The groundwaters tested nearly exclusively represent near-surface circulation issued by springs. One single sample of groundwater circulation at greater depth was collected at a production well (depth 200 m). All samples can be associated with an Mg/Ca-HCO3 type with elevated alkali concentrations except for the well groundwater which relates to a Na-HCO3 type (Ludwig et al. 2011, Fig. 2). The SEC ranges at values of 70 – 220 µS cm-1, the pH values are neutral to alkaline. All groundwaters are partly oxygen reduced, the range of Eh comprises moderate positive values.

2.6 Tertiary Basaltic Rocks, Vogelsberg Mountain Range The Vogelsberg mountain range extends 50 km northeast of Frankfurt and constitutes the vast volcanic complex in Central Europe (Fig. 1). It is build up by an alternating sequence of volcanic and volcaniclastic basaltic rocks. Volcanic activity occurred from the upper Oligocene to late Miocene and was associated to the rift system of the Upper Rhine Graben. The volcanic rock sequence comprises up to 700 m of alkali and tholeiitic basalts and tuff layers (Wittenbecher 1992). The rock forming minerals are feldspars, Ca-pyroxene, amphibol, olivine, feldspathoids, and iron oxides (Ehrenberg and Hickethier 1988). The volcanic rocks constitute a multi aquifer sequence. The individual aquifers are separated by tuff layers as aquicludes. At grater depth, groundwaters are confined. According to Leßmann (2001), the Vogelsberg volcanic complex forms a radial system with groundwater recharge in the central part and groundwater flow at greater depth towards the rim of the basaltic sequence. Hydraulic conductivity decreases with increasing depth and comprises values of 10-5 – 10-7 m s-1.The depths of extraction wells range from 30 – 200 m, near-surface groundwaters can also be issued by springs. The groundwaters tested basically refer to a Mg- -1 Ca-HCO3 type (Fig. 2), the SEC amounts to 90 – 730 µS cm . The groundwaters indicate neutral to alkaline pH values. The concentrations of dissolved oxygen are only lightly reduced, with only few low values and a negative redox potential. Groundwater resources of the Vogelsberg are of great regional importance.

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2.7 Quaternary Fluviatile Sediments, Upper Rhine Graben The Upper Rhine Graben aquifer extents along the central graben structure between Frankfurt and Basel, Switzerland. It consists of unconsolidated clastic sediments of sand to gravel grain size and carboniferous fine-grained sediments. The field of investigation is girt by the rivers Main, Rhine, and Neckar and by the eastern flanking highland of the graben built up by the crystalline basement of the Odenwald mountain range and from the Triassic cap rocks of the Bunter sandstone and Muschalkalk limestone (Fig. 1). The sedimentary facies evolved from marine and limnic deposition of Oligocene to Miocene age to fluviatile sedimentation of braided rivers and loess deposits during Pleistocene. The quaternary psammitic and psephitic deposits constitute a sequence of several hundreds of meters, locally interbedded by fine- grained clay- und silt layers. These sediments originate from deposition of carboniferous rock debris from the Alps by the river Rhine. Rock clasts and mineral grains of granite and gneiss originate from the crystalline basement. Pebbles of limestone and iron-rich sandstone can be associated to the hinterland of the crystalline Odenwald (Kümmerle 1972). The fluvial deposits partly merge with aeolian sands related to glacial periods. Iron oxides and hydroxides as grain coatings are abundant among the Quaternary deposits and relate to the variation of oxygen content of groundwaters (Kümmerle 1972). The quaternary deposits constitute a multi aquifer formation with three principal aquifer -3 -4 -1 levels. Hydraulic conductivity (kf) comprises high values of 10 to 10 m s (Diederich and Matthess 1972). Groundwater flow proceeds in a western direction from the foot slope of the eastern limb of the graben towards the river Rhine in the East. The aquifer levels are recharged directly by rainfall and by vertical leakage of fine-grained beds of low hydraulic conductivity. Groundwater extraction occurred at 10 – 98 m well depth. The Groundwaters inves- 2- tigated all relate to a Ca-Mg-HCO3 type with partly elevated content of SO4 (Fig. 2). The SEC values of 400 – 1,200 µS m-1 indicate moderate to advanced mineralisation at near- neutral pH. Most groundwater samples indicate low concentrations of dissolved oxygen and, thus, negative redox potential (-70 - -270 mV). Groundwater resources of the Upper Rhine Graben obtain a major source of groundwater for domestic water supply.

3 Methods

Groundwater sampling in the individual fields of investigation was accomplished from 2005 to 2007 as separate campaigns. All samples of a particular aquifer lithology were collected within only few days to attain comparable meteoric and hydrological conditions. Principal patterns of groundwater evolution in the Bunter sandstone of the Odenwald and in the basaltic sequence at Mt. Wasserkuppe have been described in a companion study (Ludwig et al. 2011) and a forthcoming paper. In order to discuss the relevance of Fe-oxides and hydroxides for the

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mobility of As and heavy metals in groundwater, the dataset was extended to include a total of 130 samples from seven individual aquifer lithologies. Sampling was proceeded predominantly at production wells and tributary at springs for public water supply and were chosen to represent groundwaters with minimal anthropogenic influence. Water temperature, pH-values, specific electrical conductivity (SEC), the concentration of dissolved oxygen, and the redox potential (Eh) were measured at the sampling sites. Samples were taken in PE-bottles and 3+ conditioned for subsequent lab analysis. The detection of Al , Astotal, and the heavy metals Cd2+, Co2+, Cu2+, Cr2+, and Ni2+ was performed by inductively coupled plasma mass spectros- 2+ 2+ + + copy (ICP-MS; Perkin Elmer Elan 6100). Major and minor cations (Ca , Mg , Na , K , Feto- 2+ tal, Si, and Zn ) were detected by inductively coupled plasma optical emission spectrometry - 2- - (ICP-OES; Perkin Elmer Optima 3000 DV). Anions (Cl , SO4 , and NO3 ) were analysed by ion chromatography (Dionex DX 500). Alkalinity was determined by titration. A maximum error of ion balance of ±10% was tolerated. Analysis data are compiled in Table 1. All analyses were performed at the state laboratory of the county of Hessen (LHL), Wiesbaden. As possible sources of solutes with regard to arsenic and heavy metals various effects have to be considered. Loads of Cd2+, Cu2+, Pb2+, and Zn2+ in meteoric water measured at the gauging station Fürth/Odenwald for the term 1987 – 2005 are illustrated in Fig. 3. Soils tend to accumulate heavy metals and arsenic as discussed by numerous authors (e. g. McLean and Bledsoe 1992; Phillips 1999; Mellis et al. 2004). Since investigations focused on groundwater-rock reactions in the aquifer lithologies, the soil compartment was excluded from contemplations: Samples probed during the investigations do not interact with the soil matter and the contact is limited to a short-term passage of meteoric water as groundwater recharge. The geochemical properties of the aquifer rocks (volcanic rocks of the High Rhön and of the Bunter sandstone of the Odenwald) were detected by XRF-analysis (Philips PW 2404) at the Mineralogical-Geochemical Institute, University of Freiburg. All samples were ground to 10 µm grain size and then dried for 48 h at 50 °C. One gram of sample powder was added 4 grammes of Spectromelt® as tableting agent for melt digestion. Additionally, 4 grammes of the sample powder were added one gram of paraffin wax as binding agent for powder digestion. The geochemical data of the aquifer rocks are assembled in Table 2, completed by additional values published by Anderle (1991), Kümmerle and Seidenschwann (1993), Becker and Kulick (1999), and Bogaard et al. (2001). With regard to constraints of synchronous precipitation of Fe-oxides/hydroxides and the particular heavy metals and As, speciation calculations were performed for 25 °C and 1,000 hPa. In order to determine the feasibility of precipitation of Al-hydroxides, Al-species were also calculated. The calculations were performed using the thermodynamic data compiled by Drever (1997). Solute-solid boundaries of Fe-species with respect to pH-Eh-constraints were

- 106 - Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

-1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg nalysis were nalysis -1 µg l µg -1 µg l µg -1 µg l µg -1 As Cd l µg Cr Co Cu Ni Pb Zn -1 total Fe µg l µg -1 Al l µg -1 2 SiO mg l -1 2 CO mg l -1 4 SO mg l 3 -1 HCO mg l -1 seven individual aqui-fer lithologies: groundwater sampling and and a sampling groundwater aqui-fer lithologies: individual seven mg l -1 mg l -1 mg l -1 0.1 6.0 4.4 3.0 10.0 0.5 0.1 1.5 0.5 1.0 1.0 0.5 10.0 mg l -1 130 129 130 130 130 119 130 96 130 52 47 63 3 53 21 34 41 12 13 mg l -1 om August 2005 to February 2007 August 2005 to February om SEC pH cm µS Ca Mg Na K Cl -1 2 O mg l mbs °C mV Hydrochemical data of 130 groundwater samples associated to associated samples data of groundwater 130 Hydrochemical positive detections Table 1 accomplished during the period fr accomplished Σ Sample Depth Temp Eh Detection limits Depression Idstein shale, Clay ID 02 03ID ID 04 57ID 05 100 8.6 11.2ID 06 98ID 07 138 97 10.8 ID 08 1.4 51 79 8.2 1.3ID 09 10.6 43 744ID 10 1.0 10.3 42 223 383 123ID 12 10.4 60 7.45 -86 8.4 409 3.4 7.21ID 13 10.7 51 115.0 147ID 14 49.8 1.5 157 11.4 85 7.17 749 91 23.0 1.8ID 15 11.2 63 52.3 183 684 13.3 6.23ID 16 7.36 16.4 0.1 11.3 80 589 21 12.6 3.4 10.1ID 17 117.0 1.9 14.6 6.85 100 10.6 -27 566 10.4 Main Plain RotliegendLower 7.45 sedimentary rock, 1.0 112.0 26.7 0.6 88 12.5 797 24.0 5.7 133 01LMP 96.5 1.3 44 11.1 70 7.21 23.1 14.0 1.0 10.7 411.8 518 1.1 02LMP 6.64 6.8 10.2 91.8 60 67 483 1.3 18.1 170.2 9.4 10.0 0.3 03LMP 81.5 48.0 113 7.05 429 10.9 55 1.7 04LMP 9.5 39.0 17.6 12.1 7.28 46.0 206.2 1.9 152 0.7 563 62.9 19.8 22.9 141 05LMP 7.22 12.3 8.4 54.0 100 384.3 0.5 145 9.0 1.0 38.0 14.0 17.2 701 06LMP 7.56 61.3 12.9 44.9 18.2 5.6 13.2 151 197 4.4 42.0 22.0 23.3 361.1 449 1.2 20.0 07LMP 18.0 60.9 2.3 14.5 19.8 100 167 b.d. 6.72 15.4 791 17.6 5.1 08LMP 11.4 12.7 306.2 710 71.0 21.0 22.9 b.d. 157 7.19 20.3 54.4 1.4 85.0 59 24.0 27.9 2.4 09LMP 17.9 b.d 6.94 1.1 686 108 208 44.0 11.0 308.7 42.0 13.9 1.7 329.4 7.21 b.d. 48.8 27.0 10 117LMP 13.4 2.2 42.3 11.1 14.1 132.0 699 95 20.0 2.4 7.25 224 89.5 b.d. 29.0 11LMP 1.0 23.5 26.0 234.9 21.0 b.d. 9.5 572 100 171 144 26.9 23.1 16.0 12.4 10.6 7.46 77.1 223.3 0.7 12LMP 5.7 11.4 b.d. 850 148 12.3 33.3 13.5 3.3 24.0 30.8 44.0 b.d 1.4 77.0 204.4 7.64 9.8 117 65.8 42.5 b.d. 13LMP 2.7 b.d. 12.2 56.0 161 b.d. 22.2 1.0 85 651 268.4 7.13 17.3 b.d. 59.6 13.0 68.0 14LMP 10.6 b.d. 0.3 19.8 45.0 806 1.7 b.d. b.d b.d. 167 22.6 11.6 80 2,510 1.6 b.d. 49.6 124.0 1.6 14.1 23.0 15LMP b.d. 255.0 58.0 7.06 b.d. 1.1 b.d. b.d. b.d 18.1 21.8 11.0 50 702 26.0 3.3 b.d. 19.4 7.47 30.0 170 1.7 2.6 b.d. 16LMP 34.6 216.6 15.8 992 108.0 b.d. 27.0 b.d. b.d. 10.9 30 56.0 2.2 29.9 60.6 63 5.4 86.9 2.2 41 364.2 b.d. b.d 19.4 b.d. 3.2 7.41 b.d. 785 15.0 b.d. 9.5 b.d. 18.8 393.5 b.d. 11.2 82 36.0 b.d. 7.18 -25 1.6 b.d. b.d. 2.9 17.1 50.6 b.d. 88.5 30.0 b.d. 83.0 b.d. b.d. 31.9 392.2 2.3 10.7 b.d. 736 804 7.11 8.3 -12 b.d. 154.0 1.3 b.d. 26.0 b.d. 29.0 786 b.d. 5.4 b.d. 22.0 0.3 b.d. b.d. 18.4 2.1 303.8 b.d. 47.9 -232 89.3 24.1 25.5 37.0 b.d 33.7 783 b.d. b.d. b.d. 7.16 0.9 b.d. 0.5 38.0 b.d. 17.9 15.4 361.7 0.8 b.d. b.d. b.d. 875 2.7 0.4 21.0 1,180 3.3 b.d. 1.7 33.7 4.1 18.4 107.0 17.5 16.5 19.1 12.8 457.5 7.11 1.5 b.d. 21.0 b.d. b.d. 806 19.8 21.0 b.d. b.d. b.d. 1.8 b.d. 28.0 0.8 6.52 b.d. b.d. 685 2.1 1,270 22.4 10.1 11.5 110.0 b.d. 55.2 b.d. 16.8 36.0 353.8 b.d. b.d. 9.6 b.d. 6.6 b.d. 6.92 b.d. 105.0 1,020 3.2 9.7 376.4 31.0 b.d. b.d. b.d. 27.6 20.0 1.7 53.0 32.4 7.59 b.d 0.9 b.d. b.d. b.d. 24.0 b.d. 113.0 26.8 31.8 b.d. b.d. b.d. b.d. b.d. 3.1 300.7 93.0 83.0 b.d b.d. 448.4 18.6 b.d. 12.5 22.6 1.5 41.0 b.d. b.d. b.d. 29.9 b.d. b.d. b.d 16.2 23.8 25.1 b.d. 3.9 0.7 2.3 58.0 b.d. 110.0 b.d. 14.5 404.4 100.0 b.d. 9.8 b.d. b.d 40.9 2.5 b.d. 13.0 b.d. 2.8 15.9 4.3 21.4 b.d. b.d. 5.5 15.0 b.d. 344.7 3.2 28.6 48.0 1.1 18.1 16.4 b.d. 31.0 4.4 2.3 b.d. b.d. b.d. b.d 60.0 b.d. 11.9 b.d 17.4 b.d. 22.2 b.d. 276.3 41.0 12.0 2.1 15.2 b.d. b.d. b.d. b.d. 44.0 b.d. b.d. 19.8 266.6 b.d. 11.0 b.d b.d. b.d. 1.0 b.d. b.d. 92.0 5.4 b.d. 18.0 b.d. 63.5 283.7 b.d. 1.3 b.d 16.7 b.d. 180.0 1.4 b.d. b.d. b.d. b.d. b.d 21.7 b.d. 18.9 b.d 1.3 480.7 130.0 b.d. 0.9 83.2 b.d. b.d. b.d. 1.2 2.8 3.9 b.d. b.d. b.d. 25.5 b.d. 13.5 b.d. b.d. 1.7 b.d. 18.7 b.d 5.5 b.d. b.d. b.d. 0.6 2.8 b.d. b.d. b.d. 13.4 10.2 b.d 22.8 1.9 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 7.5 b.d. 3.1 130 b.d. b.d. b.d. 1.4 b.d. 0.6 17,200 16.7 b.d. b.d. b.d. b.d. 21.7 b.d. 74.9 b.d. b.d. 2,340 b.d. b.d. b.d. b.d. b.d. 30.3 b.d. 2.6 b.d. 9.9 b.d. 12.1 b.d. b.d. 0.7 2.4 b.d. b.d. 3.6 b.d. b.d. b.d. b.d. 1.9 b.d. 28.8 2,280 b.d. b.d. 2.3 b.d. 2.7 0.5 b.d. b.d. 5.0 10.4 b.d. 48.2 b.d. 2.8 b.d. b.d. b.d. 11.6 b.d. 1.6 b.d. 1950.0 7.3 b.d. b.d. 0.9 3.2 1.8 232.0 409.0 b.d. b.d. b.d.

- 107 - PhD Thesis Florian Ludwig 2011

-1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 As Cd l µg Cr Co Cu Ni Pb Zn -1 total Fe µg l µg -1 Al l µg -1 2 SiO mg l -1 2 CO mg l -1 4 SO mg l 3 -1 HCO mg l -1 mg l -1 mg l -1 mg l -1 0.1 6.0 4.4 3.0 10.0 0.5 0.1 1.5 0.5 1.0 1.0 0.5 10.0 mg l -1 130 129 130 130 130 119 130 96 130 52 47 63 3 53 21 34 41 12 13 mg l -1 SEC pH cm µS Ca Mg Na K Cl -1 2 O mg l mbs °C mV continued positive detections Table 1 Sample Depth Temp Eh Detection limits Σ 17LMP 18LMP 150 19LMP 11.4 54 20LMP 100 172 10.8 21LMP 10.9 62 4.5 185 22LMP 205 10.2 47 23LMP 6.2 676 10.7 44 4.6 91 24LMP 13.2 46 702 7.11 204mountain range Odenwald sandstone, Bunter 657 1.1 12.9 46 -152 101.0W_01 5.1 7.34 11.8 7.31 -195 0.2S_02 20.0 475 108.0 664 167 96.7 0.2W_03 75 17.6 816 19.7 6.77W_05 2.8 7.10 10.6 512 1.4 22.8 74.2 10.0 7.27S_06 111.0 72 335 747 9.3 1.1 24.0 7.64 68.1S_07 120 11.2 8.4 8.0 12.9 9.0 11.7 49.1S_09 359.9 6.78 63.0 1.3 275 27.6 11.4 13.6S_10 342 323 109.0 57 294.6 35.0 33.7 24.0 8.0 1.9 69.2W_12 1.7 10.8 9.2 8.4 23.7 32.0 5.5 335.5 9.7S_17 19.4 33.0 6.02 197 10.6 12.0 94 13.8 130W_18 354 48 29.0 5.7 4.4 21.1 8.7 32.0 14.1 295.2 371 170.2 3.1 6.53W_19 11.3 9.2 8.7 4.53 6.34 472.8 b.d. 17.3 23.0 18.9 46.0 29.0 12.1S_20 280 120 83.0 53.0 0.8 285 5.8 19.0 11.2 46S_23 327 251.9 14.0 104 b.d. 21.4 16 b.d 9.8 8.7 21.1 332.5 4.3 27.3 11.6S_25 321 1.6 2.6 9.5 10.3 34.0 b.d. 2.4 4.51 20.9 b.d 30.1 5.76 28.0 78 57S_27 24.0 265 2.7 9.5 9.1 81 2.2 6.6 2.7 316 3.9 18.0S_28 7.5 b.d. b.d 1.8 b.d. 10.3 8.7 b.d. 1.6 5.80 6.83 3.5 77W_30 4.2 9.7 b.d. 1.6 9.1 4.98 68 b.d. 2.6 2.4 b.d 42.9 5.2 6.4 0.9 111W_31 309 b.d. 6.3 1.5 8.5 4.9 b.d. 12.2 107 5.5 6.01 46S_32 b.d. 270 150 b.d. 3.0 14.9 10.4 7.8 5.77 2.8 b.d. 1.6 1.5 11.1 97.6 24.8 3.4 9.6 2.3 b.d. 0.9S_34 298 200 5.13 10.3 8.2 b.d. 58.0 2.7 4.4 100 2.1 b.d. b.d. b.d. 186 b.d. 11.8 2.7 b.d.W_35 414 292 b.d. 1.4 9.1 8.5 10.3 b.d. 159 8.0 b.d. 2.9 2.1 1.6 b.d. 1.6W_39 5.71 279 b.d. 276 b.d 1.3 2.1 4.6 b.d. 10.6 8.9 b.d. 20.7 71 2.0 2.9 b.d. 2.9 b.d. b.d. 22.0 0.6W_40 6.49 8.1 1.6 1.5 70 1.0 b.d. 9.8 8.1 2.6 8.2 69 36.5 1.9 b.d. 1.7 b.d. 10.3 b.d. 51 b.d. 137 16.5 b.d. 6.7 33.2 9.5 2.2 b.d. 3.5 8.5 11.0 5.89 b.d. 3.6 2.8 b.d. b.d. 10.9 92 73 11.9 267 107 b.d. 3.2 3.3 2.5 4.0 1.6 b.d. b.d. 5.06 5.4 b.d. 12.9 b.d. 3.6 7.0 b.d. 1.6 11.5 5.83 239 28.0 267 310 b.d. b.d. 15.3 b.d. b.d. 10.2 b.d. 4.9 5.4 b.d. 2.6 4.1 b.d. b.d b.d. 6.63 2.8 b.d. 6.17 5.8 242 2.8 b.d. b.d. 10.5 10.8 b.d. 8.6 5.4 853.0 109 1.7 10.6 b.d. 8.2 b.d 9.8 6.6 5.1 b.d. 18.0 27.5 2.5 93 b.d. 10.1 23.3 b.d 58 b.d 1.6 b.d. b.d. 22.0 7.2 b.d. 2.0 55 0.8 4.69 1.8 b.d. 136 b.d. b.d. 8.4 4.5 17.6 b.d. 2.7 1.3 7.0 b.d. 1.8 4.8 1.4 0.5 6.87 7.2 15.0 5.54 533.0 b.d. b.d. 1.6 2.1 b.d. 14.0 5.85 b.d. 6.31 7.3 9.5 b.d. 54.7 28.5 4.4 0.3 b.d. b.d 1.9 25.0 2.0 7.0 1.8 b.d. 9.6 5.9 b.d. 20.7 24.2 19.2 2.3 3.2 1.5 13.6 b.d. b.d. b.d. 259.0 b.d b.d. 2.1 2.3 1.4 26.8 12.9 2.8 27.0 485.0 b.d. b.d. 1.3 2.9 b.d. 2.0 7.3 2.5 35.0 b.d. b.d. 6.5 1.5 b.d 0.9 b.d. b.d 3.6 9.5 2.9 b.d. b.d. b.d. b.d. b.d. 14.1 b.d. b.d. 1.6 b.d 18.3 1.8 2.3 18.5 b.d. 68.0 3.1 b.d. 1.9 b.d. 4.7 17.0 b.d. b.d. b.d. 11.0 32.3 60.7 10.0 b.d b.d. 1.8 b.d. 1.7 13.8 1.6 11.0 18.0 b.d 1.4 b.d. b.d. b.d. b.d. 0.5 1.6 b.d. b.d. 15.0 b.d. 63.4 b.d 1.0 b.d. b.d. b.d. b.d. 7.2 2.7 19.0 1.3 3.1 b.d. 5.1 14.5 b.d. b.d. 4.0 6.9 b.d. 2.2 7.3 n/a b.d. b.d b.d. b.d. 2.5 11.9 15.6 5.7 b.d. 1.6 b.d b.d. 61.6 b.d. 22.0 n/a b.d. 1.4 b.d. 15.9 b.d. 91.9 b.d. 12.9 b.d. 6.7 b.d. b.d. 5.3 b.d. b.d. 33.1 b.d. 183.0 19.0 n/a 5.0 13.4 b.d. 4.9 11.0 b.d b.d. b.d. b.d. b.d. 1.1 b.d. b.d. b.d. b.d. b.d 56.4 b.d. b.d. b.d. b.d. b.d. n/a b.d. b.d. b.d. b.d. 6.5 n/a 1.4 b.d. b.d n/a 5.0 b.d. b.d. n/a b.d. b.d b.d. b.d. b.d. b.d 6.0 5.8 b.d. b.d. b.d. b.d. 878.0 7.5 b.d. 13.2 b.d. 11.9 b.d. b.d. b.d. b.d. 4.0 0.9 b.d 1.0 b.d. b.d. 2.0 b.d. b.d. 190.0 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d b.d. b.d. b.d b.d. b.d. b.d. b.d b.d. b.d 3.1 b.d. b.d. 0.3 b.d. 3.0 b.d. b.d. b.d. b.d. b.d. 0.9 b.d. b.d. b.d. b.d. 1.4 b.d. b.d. b.d. 1.5 2.6 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.9 b.d. b.d. 8.4 b.d. b.d. b.d. 1.1 b.d. b.d. b.d. 2.6 4.1 b.d. b.d. b.d. b.d. b.d. b.d. 0.8 b.d. b.d. b.d. b.d. b.d. Rotliegend sedimentary rock, Lower Main Plain RotliegendLower sedimentary rock,

- 108 - Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

-1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 As Cd l µg Cr Co Cu Ni Pb Zn -1 total Fe µg l µg -1 Al l µg -1 2 SiO mg l -1 2 CO mg l -1 4 SO mg l 3 -1 HCO mg l -1 mg l -1 mg l -1 mg l -1 0.1 6.0 4.4 3.0 10.0 0.5 0.1 1.5 0.5 1.0 1.0 0.5 10.0 mg l -1 130 129 130 130 130 119 130 96 130 52 47 63 3 53 21 34 41 12 13 mg l -1 SEC pH cm µS Ca Mg Na K Cl -1 2 O mg l mbs °C mV continued positive detections Table 1 Σ Sample Depth Temp Eh Detection limits Bunter sandstone, LowerHessian Depression 02LHD 03LHD 202 04LHD 12.5 220 11LHD 16.5 200 191 20LHD 15.5 160 -3 8.3 21LHD 11.4 240 93 22LHD 14.6 132 0.4 150 52 23LHD 0.4 13.5 221 195 6.57 364 24LHD 0.7 14.2 -197 98 355 2.1 10.8 25LHD 6.34 270 179 0.7 13.7 712 26LHD 18.5 6.50 547 125 33.8 6.6 2.4 -2 540 27LHD 11.0 6.99 39.2 112 275 7.36 28 12.1LHD 10.7 4.6 92.4 596 222 209 7.51 3.9 6.6 47.5 15.4 29LHD 15.4 6.4 169 199 45.5 1.5 8.8 7.46 24.2 30LHD 12.2 9.3 371 357 200 226 29.8 6.2 8.6 49.9 31LHD 3.4 11.9 28.2 33.6 228 160 117 5.6 1.8 8.73 29.5 7.95High Rhön mountainrocks, range Basaltic 12.2 4.6 3.6 212 210 80 31.9 19.1 1.9 73.8 6.57 26.2 3.7 30.0S1 5.3 12.1 249 83 4.3 48.0 6.48 30.7 27.7 122.6W2 5.6 575 12.0 9 22.0 18.6 1.4 197.0 6.39 23.3 4.0 281.8 9.4S3 1.2 74.0 8.2 296.5 607 19.1 7.08 16.9 26.2S4 21.0 17.0 90.0 8.2 22.0 0.5 312.9 688 1.5 59.2 1.3 67.3 200 41.0S5 7.12 4.8 10.5 294.6 11.8 40.0 22.9 26.8S6 32.0 574 12.6 7.09 6.8 6.1 14.0 64.0 10.0 25.1 9.7 1.7 7.2 197 58.0S9 29.7 b.d. 11.9 69.6 170.8 b.d. 159.2 7.02 6.6 1.8 22.6 28.5 218S10 8.3 14.5 7.4 4.3 3.7 15.4 8.4 b.d. 68.3 b.d 3.5 29.3 39.0 41.0S11 11.0 13,200 23.8 5.5 8.1 14.9 12.5 3.9 119.0 108 542 264S13 2.3 1,150 22.4 15.7 6.9 3.5 24.0 24.6 94.6 b.d. b.d. b.d. 76 268 b.d 0.9S14 5.8 6.4 b.d. 7.3 3.7 9.72 142.1 273.9 5.5 17.0 18.1 27.0 3.6 204 16.4 23.3S15 b.d. 11.0 2.2 6.8 8.2 926 3.6 3.7 27.0 b.d. 7.06 68 9.7 7.2 301 b.d. 46.0 286.7 b.dS16 1.5 b.d. 26.0 5.6 b.d. 2.0 11.8 3.9 29.0 5.1 136 7.9 3.7 191 309.3S17 b.d. 27.0 5.4 b.d. 4.2 48.0 b.d. 23.3 234 16.3 b.d. 6.86 39.6 93 b.d 4.6 8.5 17 0.7S18 29.7 2.6 b.d. b.d. 5.5 6.81 60.0 273.3 b.d. 8.9 241 5.1 128 19.3 2.9 14.8 5.8 7.4 15.0 21.6 b.d.S19 12.2 b.d. b.d. b.d. b.d. 7.1 b.d. 2.6 182 b.d. 7.21 49.0 132 6.1 7.8 7.8 17.6 3.0 0.3 3.7 b.d. b.d. 3.0 b.d. b.d 15.2 7.52 1.7 118 b.d. 165 2.6 b.d. 10.3 8.4 3.1 5.6 8.3 b.d b.d. 11.7 b.d. b.d. b.d. 14.5 8.21 b.d. 26.0 119 9.7 5.2 1.0 b.d. 177 b.d. b.d. b.d 5.4 7.4 7.83 0.6 b.d b.d. 1.9 b.d. b.d. b.d. 217 7.4 b.d. b.d. b.d. 217 2.9 b.d. 15.0 3.0 5.3 6.6 7.62 8.2 b.d. 66.5 3.6 b.d. 0.6 13 b.d. b.d. 168 b.d. 3.4 b.d. 1.7 195 4.5 7.3 7.62 8.8 1.8 43.4 0.7 b.d. b.d. b.d. 20 1.6 b.d. b.d. 177 b.d. 4.8 181 4.5 0.8 4.9 8.21 4.9 17.9 5.3 14.1 16.5 b.d. 4.8 b.d. b.d. b.d. b.d. 152 949 1.2 b.d. 316 1.6 5.1 7.75 13.1 5.0 0.7 8.5 3.4 2.5 b.d. 4.2 b.d. b.d. 166 1.1 2.1 9.4 0.7 5.6 b.d. 6.6 7.86 b.d. 9.1 12.9 b.d. 30.5 1.0 b.d. 1.6 b.d. 99 1.9 2.1 b.d. 6.7 0.8 4.4 30.5 5.6 b.d. 8.46 12.7 2.1 1.2 1.3 3.9 1.4 69 b.d. 12.7 b.d. b.d. 6.7 3.5 b.d. b.d. 7.1 13.5 1.9 31.1 1.3 2.9 7.95 1.9 1.3 b.d. 3.4 8.2 b.d. 8.6 3.0 39.7 18.2 0.8 b.d. b.d. 2.9 6.58 9.3 10.2 b.d. b.d. b.d. 9.2 2.8 2.2 39.0 1.7 0.7 b.d. b.d. 11.0 b.d 17.0 38.4 3.3 4.4 b.d. 12.4 b.d. 10.0 33.1 1.9 0.7 b.d. b.d. 2.5 37.2 4.7 15.8 4.0 67.1 6.2 12.0 3.9 0.8 b.d. b.d. 14.3 7.9 15.0 b.d 2.4 0.5 3.2 4.7 1.0 70.2 b.d. b.d. b.d. 16.0 2.8 3.5 16.3 8.0 8.8 b.d. b.d. 17.7 69.5 10.6 3.7 3.2 b.d. 1.7 6.7 b.d 19.9 0.5 b.d. 6.5 67.1 b.d. b.d 19.9 9.2 b.d. 0.5 b.d. 6.4 72.6 b.d. 1.7 19.0 1.8 b.d b.d. 1.1 b.d. 16.0 b.d. b.d 22.6 4.3 b.d. b.d. 3.3 b.d b.d. 14.0 b.d. 43.9 b.d. b.d 20.2 b.d. 26.8 b.d. b.d. b.d. b.d. b.d. 27.5 b.d. 19.9 b.d. b.d. 1.0 b.d 6.8 b.d. 8.5 b.d. b.d. b.d b.d. 23.4 b.d. b.d. b.d. b.d. b.d. 12.4 4.9 b.d. b.d. 24.1 b.d. 25.6 b.d. b.d. b.d b.d. b.d. b.d. b.d. b.d. 1.6 b.d. b.d. b.d b.d. b.d. b.d. b.d. 0.6 b.d. b.d. b.d b.d. b.d. b.d. 18.2 b.d. b.d. b.d. 1.7 b.d. b.d. b.d. b.d b.d. 2.4 17.2 b.d. b.d. b.d. b.d. 6.8 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 11.3 2.7 b.d. b.d. b.d. b.d. b.d. b.d. 2.8 b.d. b.d b.d. b.d. 2.3 b.d. b.d b.d. b.d. b.d. b.d. 0.7 b.d. b.d. 4.6 b.d. b.d. b.d. b.d. b.d. 1.0 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 2.0 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

- 109 - PhD Thesis Florian Ludwig 2011

-1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 µg l µg -1 As Cd l µg Cr Co Cu Ni Pb Zn -1 total Fe µg l µg -1 Al l µg -1 2 SiO mg l -1 2 CO mg l -1 4 120.0 15.4 15.740.0 b.d. n/a 2,530 21.2 5.1 b.d. b.d. 1.6 9,880 b.d. 7.3 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. SO mg l 3 -1 HCO mg l -1 mg l -1 mg l -1 mg l -1 0.1 6.0 4.4 3.0 10.0 0.5 0.1 1.5 0.5 1.0 1.0 0.5 10.0 mg l -1 130 129 130 130 130 119 130 96 130 52 47 63 3 53 21 34 41 12 13 mg l -1 SEC pH cm µS Ca Mg Na K Cl -1 2 O mg l mbs °C mV continued positive detections Table 1 Sample Depth Temp Eh Detection limits Σ VB 04VB 11VB 14 VB 16 11.8 140VB 25 9.3 8.3 186 130VB 32 12.1 103VB 34 7.5 242 230 12.9 208 252VB 35 5.5 205 8.7 11.4 285VB 37 68 6.9 251VB 39 137 11.1 62 8.03 129 6.1 170VB 40 11.1 16.8 6.1 263 7.63 8.10 405VB 41 35 8.10 179 9.9 10.4 7.3 9.3 215 11.2VB 50 11.9 40 8.15 15.7 6.7VB 52 12.0 69 6.3 213 200 7.3 8.25 -79 38.5 7.5 130VB 7.5 55 11.9 161 -101 19.1 7.4 1.1 9.8 8.14 1.6 3.7Graben Rhine Upper deposits, Sedimentary 23.8 217 0.8 3.2 8.35 4.9 13.8 03 12.3URG 493 5.5 11.6 198 738 0.6 12.0 2.0 14.2 788 04URG 1.0 1.0 5.2 1.4 10.1 24 8.28 6.5 105.5 159 2.9 7.59 8.3 05URG 733 10.4 5.2 7.65 11.4 80 50.5 4.3 4.3 0.8 19.0 68.5 10URG 6.3 4.6 191 12.1 56.7 67 64.9 313 7.36 4.4 -74 14URG 201.9 60.4 0.8 6.4 29.5 91.5 11.6 27 44.1 134 8.19 -60 70.2 5.1 27URG b.d. 49.1 0.9 0.1 3.4 15.0 10.4 56 10.1 3.2 -120 16.5 11.9 109.8 2.0 28URG 3.9 7.61 0.2 43.9 87 20.7 12.3 72 28.7 1.6 3.1 -223 1022 0.2 2.7 33URG b.d. 10.7 4.8 87.8 b.d. 11.3 12.7 18 15.6 15.6 -121 975 0.1 6.90 b.d. b.d. 34URG 13.0 b.d. 90.9 1018 50.0 7.13 11.1 29 27.0 27.9 4.3 -186 4.3 0.2 6.9 30.1 177.0 35URG 3.0 b.d. 7.03 194.6 555 26.7 6.6 6.95 10.7 13 b.d 372.1 22.4 -176 461.2 0.1 31.4 36URG 2.9 31.9 21.8 0.5 35.0 159.0 689 10.5 12 169.0 2.3 64.0 17.9 -160 25.5 0.1 7.43 3.1 38URG 27.0 b.d. 29.0 b.d 509 16.3 355.0 5.0 10.4 11 23.8 b.d 4.8 b.d. 22.5 -270 0.3 7.19 110.0 40URG 0.5 b.d. 9.7 b.d 11.9 780 12.2 12 2.7 7.5 27.0 b.d. -220 8.8 b.d 0.1 7.17 20.2 64.0 112.0 42URG 18.0 7.4 1.8 106.8 586 3.6 b.d. 11.3 70 48.8 27.6 3.8 b.d. -70 0.2 7.22 b.d. 91.0 3.8 42.0 b.d 51URG 3.1 18.3 31.1 b.d. 712 b.d. 14.1 31.1 11.7 10 0.7 3.2 b.d. -120 b.d. 7.49 6.8 b.d. b.d. b.d. 151.0 55URG 46.4 472.1 0.1 b.d. 646 40.0 4.0 18.6 11.5 24 43.0 11.2 b.d b.d. 2.6 -192 b.d. 38.6 18.7 0.1 7.32 b.d. 107.0 2.7 b.d. 13.0 5.8 1.1 10.2 75 2.9 b.d. b.d b.d 467.9 110.0 b.d. b.d. 1134 -141 474.0 0.3 b.d. 4.5 7.56 7.1 6.0 115.0 b.d. b.d. 9.4 490 769 1189 b.d. 15.3 b.d. 18.8 b.d. b.d. -97 34.8 4.5 6.7 49.3 0.1 7.18 117.0 21.0 b.d. 3.3 84.0 10.5 28.7 110.0 370 1.5 b.d. b.d. 7.05 1.8 b.d. b.d. 1.0 b.d b.d. -195 12.9 b.d. b.d. 216.0 b.d. 11.6 6.3 b.d. 359.9 2.9 0.2 b.d. b.d. 854 34.8 b.d. 281.8 19.3 14.0 208.0 5.3 40.0 5.7 b.d. 4.6 0.1 b.d. 7.42 b.d. b.d. 1.0 32.0 1.3 18.8 b.d. b.d. b.d. b.d. b.d. 22.3 13.6 55.0 5.7 12.7 36.9 475 b.d. 1.7 b.d. 63.0 b.d. 7.18 16.1 b.d. 14.5 67.0 b.d 2.7 359.9 b.d. b.d. 3.4 793 19.0 334.3 18.4 36.0 12.8 3.7 b.d. b.d. b.d. b.d. 1.7 129.0 b.d. b.d. 3,240 13.6 15.8 b.d. b.d. 7.50 b.d. 11.4 b.d. 2.7 5.2 247.1 100.0 b.d. b.d. 298.9 2.6 4.5 14.8 7.17 b.d. b.d. 2.3 21.2 b.d. b.d. 76.4 35.0 10.6 b.d. 19.2 b.d 2,880 b.d. b.d. 14.3 17.6 2,020 1.2 135.0 44.0 b.d. 94.0 b.d. b.d. 83.2 1.1 75.0 4.4 3.3 29.3 41.0 237.3 b.d. b.d. b.d. 14.5 b.d. 8.9 8.3 2.8 b.d. b.d. 10.5 b.d. 14.7 320.3 5.5 b.d. 1.4 b.d. 7.0 b.d. 45 b.d. 1.4 12.8 452.6 2.8 b.d. 97.0 b.d. b.d. 23.1 b.d. b.d. b.d. b.d. 3,850 20.1 b.d. 310.0 2,050 11.1 b.d. 49.0 b.d. b.d. 4.2 b.d. 1.6 8.3 260.0 11.1 b.d. b.d. 10.9 8.8 2.8 1.3 17.6 10.2 b.d. b.d. b.d. 2.5 b.d. 3,880 360.5 b.d. b.d. 27.3 39.0 b.d. b.d. b.d. b.d. 209.8 b.d. b.d. b.d. 16.9 2,260 18.0 b.d. b.d. b.d. 13.0 1.2 1.7 89.0 11.3 b.d. 310.5 62.8 2.3 b.d. b.d. b.d. b.d. 15.0 842 b.d. 176.3 0.7 712 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 22.9 b.d. b.d. b.d. b.d. 5.7 82.0 38.2 b.d. 3,300 1.4 b.d. 0.8 3,490 3.2 b.d. 11.7 1.8 b.d. b.d. 2,360 b.d. b.d. 0.5 b.d. 5.7 b.d. b.d. 16.1 b.d. 20.9 b.d. b.d. b.d. 3.7 2.4 b.d. b.d. b.d. b.d. 1.7 b.d. b.d. b.d. b.d. 17.5 b.d. b.d. b.d. b.d. b.d. 7,580 b.d. b.d. b.d. 1.9 b.d. b.d. b.d. b.d. b.d. 814 b.d. b.d. 11.2 b.d. b.d. b.d. b.d. b.d. b.d. 1.6 960 b.d. b.d. b.d. b.d. 3.1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.7 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.6 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Basaltic rocks, VogelsbergBasaltic mountain range 59URG 60URG 98 63URG 11.6 66 64URG 11.0 62 -104 12.0 54 -132 0.1 12.7 -110 0.2 693 -70 0.1 568 7.24 0.1 816 7.45 116.0 433 7.12 100.0 12.7 143.0 9.1 7.67 19.5 16.1 74.1 2.1 11.0 13.7 1.3 28.0 11.5 2.0 347.1 7.3 24.0 18.0 239.1 45.0 0.9 453.2 80.0 17.6 5.9 20.8 7.0 266.6 b.d. 7.3 16.1 3,700 b.d. n/a 2.0 1,310 b.d. 22.8 3.1 b.d. b.d. b.d. b.d. b.d. b.d. 360 b.d. b.d. b.d. b.d. 12.7 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

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-5 -1 -6.7 -1 related to the concentration of Fetotal at the detection limit of 10 g l or 10 mol l , respectively. The standard state for the aqueous species corresponds to unit activity of the species in a hypothetical one molal solution referenced to infinite dilution at any pressure and temperature according to Helgeson et al. (1978). The calculation of Al-species was associated to quartz oversaturation and a silica activity of 10-3.6 mol l-1, solute-solid boundaries were modelled for kaolinite, pyrophyllite, gibbsite, and amorphous Al(OH)3.

100 5.5

Cadmium Lead Copper Zinc pH

10 5 ) -1

1 4.5 pH Concentration (µg l Concentration (µg 0.1 4

0.01 3.5 1985 1990 1995 2000 2005 2010 Fig. 3 Loads of several heavy metals and pH values determined for freefall rainfall at the gauging station Fürth/Odenwald in the period 1987-2005

As approach to the demobilisation of solutes by adsorption, sorption on hydrous ferric oxide as sorptive matter was considered as a precursor of crystalline iron species such as goethite. Sorption curves as a function of pH were modelled for the cations Cd2+, Co2+, Cu2+, Ni2+, Pb2+, Zn2+, Ca2+ and Mg2+. Calculations were run using the PHREEQC (Parkhurst 1995) hydrochemical computer program in combination with the thermodynamic data of WATEQ4F by Ball and Nordstrom (1991, data for surface species published by Dzombak and Morel 1990) and MINTEQ.V4 (data refer to the database files of MINTEQA2 determined by Allison at al. (1990). Sorption curves for As- and Cr-species differ from those of the other cations due to formation of anion complexes (arsenate, arsenite, chromate). Calculations refer to a high ratio of hydrous ferric oxide to dissolved ions. A total of 1 g l-1 (10-1.7 mol l-1) dissolved iron (comparable values were used by Hingston et al. (1972) and Zhang and Peak (2007) during experimental studies of sulfate adsorption on goethite) was reacted with the particular ions at concentrations of 10-7 – 10-9 mol l-1 (detection limits). The dissolved ions

- 111 - PhD Thesis Florian Ludwig 2011

Upper Rhine Upper Graben q clsh,s gravel clay Depression ional data published by various authors various by data published ional ngl arkose clay clsh, Lower Main Plain Idstein and Seidenschwann 1993; data Idstein Depression: Anderle 1991; data Upper Upper data 1991; Anderle Depression: Idstein data 1993; Seidenschwann and B = Middle Bunter sandtone; Bnt = basanite; aB = alkali basalt; conl = conglomerate; conglomerate; = conl basalt; alkali = aB basanite; = Bnt sandtone; Bunter Middle = B 815 <310 2841858 <0.01 0.01 <0.05 <0.05 <0.05 <0.05 0.12 Depression weight%; the dataset also compiles addit also compiles the dataset weight%; lithologies investigated: values are given in given are values investigated: lithologies High RhönHigh Odenwald Vogelsberg Lower Hessian (%) 2.28 1.82 0.89 0.57 3.19 0.21 0.67 1.26 1.90 2.21 0.55 0.93 1.21 1.54 3.78 0.93 1.62 (%)(%) 46.92(%) 45.96 2.57(%) 41.34 16.19 2.67 42.65 11.47 15.46 2.55 87.74 12.14 11.03 98.11 13.29 14.13 3.62 40.76 13.50 5.91 0.17 44.91 1.06 0.56 0.03(%) 93.78 0.15 12.55 2.46 68.60 0.83 13.58 12.58 89.05 2.22 1.28 12.74 3.17 81.23 0.13 0.94 0.03 67.15 8.15 0.69 77.00 2.70 0.70 5.68 59.46 0.04 1.29 0.22 95.30 9.47 0.02 49.33 2.56 0.34 14.30 0.71 7.93 10.24 0.83 0.51 19.12 4.64 0.76 1.99 0.01 7.42 0.95 6.75 0.37 0.11 0.07 3.16 0.32 0.03 0.05 0.06 0.08 0.15 0.01 0.11 (%) 3.44 4.23 3.47 2.66 0.13 0.01 0.99 2.69 0.14 0.92 <0.3 <0.3 <0.3 1.27 0.47 0.56 0.37 XRF-analysis data of the seven aquifer aquifer seven of the data XRF-analysis 3 3total 2 5 2 O O O 2 O 2 2 O 2 2 Table 2 sampleSiO aoB TrB oNe hoB LB MB Bnt aB MB loess co P TiO Al Fe MnOMgOCaO (%)Na (%) 0.22 (%) 5.86 0.29 8.37LOI 3.73 0.23Sum 14.42 9.27 0.21As 7.73 11.39 (%) 0.01 12.08 (%) 0.16 1.60 0.00 0.05 98.15 0.01 2.96 0.19 96.86 0.02 12.52 99.54 0.42 0.18 11.60 10.94 97.84 10.92 2.02 0.06 0.00 98.47 0.02 0.78 99.12 1.62 0.05 96.03 0.20 5.97 0.11 98.95 0.00 0.05 99.24 0.20 0.00 0.18 91.03 0.41 0.05 0.41 96.98 1.25 0.09 94.96 0.10 2.24 0.07 92.35 0.39 96.97 0.25 0.01 94.05 0.44 1.00 0.04 99.93 11.96 74.66 Cd CrCuCo(ppm)32245948-1-25957 (ppm)Ni (ppm)Pb(ppm)78641642.842.3381338193021820 89Zn 35 (ppm) 4 23 78 (ppm) 570 63 131 16 140 157 99 424 21 121 90 4 13 112 18 -4 436 3 7 495 0 228 5 99 288 79 143 4 2 29 3 23 11 53 37 6 126 5 10 147 20 13 164 23 22 15 <8 29 66 10 66 69 87 35 95 3 4 9 23 14 44 K aoB = alkali olivine basalt; TrB = trachy basalt; oNe = olivine basalt; hoB = hornblende basalt; LB = Lower Bunter sandstone; M sandstone; Bunter Lower = LB basalt; hornblende = hoB basalt; = olivine oNe basalt; trachy = TrB basalt; olivine alkali = aoB clsh,q = quartzitic shale; clay clsh,sshale clay = silty Kümmerle Plain: Main Lower data 1999; Kulick and Becker Depression: Hessian Lower data 2001; Schulz and Hoppe Vogeslberg: Data andRhine Seidenschwann Graben: Kümmerle

- 112 - Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

Were allowed to be attracted to a total of 4 x 10-4 moles of binding sites. The model constraints were chosen to match those used in a companion study about the sorption of sulfate on hydrous ferric oxides (Ludwig et al. 2011). Speciation calculations for the elements expected to be attracted to Fe-oxides/hydroxides were performed using thermodynamic data compiled by Drever (1997) and Hem (1977). Calculations were run for 25°C and 1,000 hPa. Solute-solid boundaries were adjusted to the detection limits of the individual elements. For Co and Ni, speciation calculations could not be run due to lack of thermodynamic data.

4 Results and Discussion

4.1 Groundwater Composition and Input by Meteoric Water The groundwaters investigated indicate similar hydrochemical composition with Ca2+, Mg2+, - and HCO3 as principal dissolved constituents (Fig. 2). As discussed in companion studies (Ludwig et al. 2011) and by various authors (e. g. Appelo and Postma 2005), the character groundwater composition can be associated to the distinct mineral assemblage of the aquifer rocks and its disintegration by water-rock interactions; also attributed by the mobilisation of fluid inclusions (Bucher and Stober 2001). As delineated for the Bunter sandstone of the Odenwald and the basaltic rocks of the Rhön (Ludwig et al. 2011), groundwater composition may as well be affected by sorption processes or ion exchange. All 130 samples investigated were selected to represent groundwaters not influenced by ascending high saline Na-Cl type groundwaters. Thus, groundwater compositions can be suggested to derive predominantly from water-rock interaction. The dataset shows great variation of the pH and Eh values (4.53 – 9.72 and +414 – -270 mV, respectively) of the groundwaters. The most acidic groundwaters with high Eh values can be associated to near-surface groundwater circulation in the Odenwald Bunter sandstone sequence. The highest pH values can be related to the basic volcanic rock sequence of the High Rhön as well as to the basaltic rocks of the Vogelsberg. The most intensively reduced groundwaters fall within a range of near-neutral pH values (6.5 – 7.6) and predominantly associate with the sedimentary deposits in the Upper Rhine Graben and secondarily to the Rot- liegend sedimentary rock sequence. In comparison, the concentration range of the major cations Ca2+ (3.6 – 216 mg l-1) and Mg2+ (<0.1 – 49 mg l-1), the concentrations of minor elements indicate greater variation. The 1- -1 range of Altotal concentrations varies from detection limit (<3 µg l ) to 878 µg l ; the range of -1 Fetotal even exceeds a factor of 1,000 (<10 – 17,200 µg l ). The concentrations of heavy metals predominantly fall within the range of few µg l-1 and

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hardly exceed 10 µg l-1. Arsenic indicates a high range of values with a maximum of 74.9 µg l-1. Rainfall loads may be a significant source of major anions and cations as well as of heavy metals in groundwater recharge. Huneau and Travi (2008) identified rainfall to be the major source of several solutes in near-surface groundwater. As illustrated in Fig.3, the concentrations of Cu2+, Pb2+, and Zn2+ in rainfall amount to several to tens of µg l-1, whereas values of Cd2+ hardly exceed 0.1 µg -1. However, heavy metals and As are likely to be fixed during the soil passage. Studies by McLean and Bledsoe (1992) suggest, that metals added to soil (e. g. by meteoric water) tend to be effectively retained at the soil surface. The retention mechanisms include adsorption by soil solid surface and precipitation of solid phase as a function of pH and redox potential, cation exchange capacity, clay content, and iron content. Thus, further vertical movement to other environmental compartments such as groundwater should be minimal as long the retention capacity of the soil has not been exceeded. Furthermore, the concentration values of the rainfall loads decreased during the time period considered. In- creasing pH values in rainfall decrease the H+ input into the soil and, thus, improve retention ability. This suggests, that the activity of the heavy metals and As in the groundwaters predominantly relates to water-rock interaction, though mechanisms of metal fixation and redis- tribution may be similar to those described by McLean and Bledsoe (1992) and other authors for metal behaviour in soils.

4.2 Aquifer Lithologies The aquifer rocks considered by this study are basically built up by assemblages of silicate minerals but relate to different rock genesis. Whereas the Tertiary basaltic rock of the Vogels- berg and the High Rhön represent primary effusive rock sequences, all other aquifer rocks involve rock erosion of the crystalline basement and sedimentary processes. Rock formation either involved diagenetical compaction (Rotliegend sedimentary sequence and Bunter sandstone of the Odenwald and the Hessian Depression), metamorphism (clay shale of the Idstein Depression) or the absence of sediment compaction as for the Quaternary sedimentary deposits of the Upper Rhine Graben.

Geochemical data compiled in Table 2 indicates high variation of SiO2 with the lowest values in the basaltic volcanic rocks and the highest amounts in the Bunter quartz arenite and sedimentary deposits. The amounts of Al2O3 and SiO2 as well as those of alkali and alkali earth elements are likely to associate to the individual composition of silicate minerals proved in the rocks (Ehrenberg et al. 1992; Ludwig et al. 2011; several other authors). Low amounts of Al2O3 as proved for the quartz arenite (MB) of the Odenwald correlates with significantly low amounts of silicate minerals such as feldspars or mica. Subsequent silicate mineral decomposition through water-rock reactions has, consequently, significant effect on the hydro-

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chemical composition of the groundwaters (Appelo and Postma 2005). All rock samples analysed indicate the presence of iron. Values spread from 0.13 weight% in the Bunter sandstone to > 13 weight% in the basaltic volcanic rocks of the Vogelsberg and the High Rhön. In these rocks, iron may be either incorporated in the crystal structure of olivine, Ca-pyroxenes or amphibols (Ehrenberg et al. 1992; Ludwig et al. 2011) or may form iron oxides or sulfides (Ludwig et al. 2011). In the sedimentary rocks of the Rotliegend and Bunter sequence, Fe-oxides constitute coatings on grains of quartz and feldspars or incorporate within the clay beds (Renftel 1998; Kulick 1999; Ludwig et al. 2011). In the clay shale of the Idstein Depression, the presence of hydrothermal iron ores is associated to hydraulic effective rock fractures (Abel 1991). Iron also occurs in mica minerals as compound of the rock-forming minerals. Among the sedimentary deposits of the Upper Rhine Graben, iron is associated with grain coatings, clay minerals and accumulates in oxidising horizons. With exception of the basaltic rock samples, the amounts of heavy metals and As hardly exceed several tens of ppm. This suggest that activities of these elements might also be limited to low values in the associated groundwaters.

4.3 Speciation and Mobility of Iron and Aluminium

Iron

In the groundwaters investigated, the concentration of Fetotal varies within a range of <10 – 17,000 µg l-1. Among the oxidised groundwaters, values hardly exceed the detection limit.

The concentrations of Fetotal significantly increase with increasing stages of groundwater reduction. A positive effect of acidic pH on the concentration of dissolved iron can not be delineated (Fig. 4).

2+ All groundwater samples fall within the stability fields of Fe and solid Fe(OH)3 ferrihy- -6.7 -1 0 drite calculated for an activity of dissolved iron species of 10 mol l . Fe(OH)3 as dissolved species has no stability field, since equilibrium with solid ferrihydrite is attained at an activity of dissolved iron species of 10-7.67 mol l-1 which is smaller than the criterion of solubility of 10-6.7 mol l-1. Well-crystallised hematite is unlikely to precipitate at low temperatures, and the initial precipitate is likely to be amorphous solid phase such as ferrihydrite (Drever 1997).

FeCO3 might be of relevance as solute-solid boundary for reduced groundwaters and elevated concentrations of CO2. Iron sulfides as stable species were neglected, since formation requires highly reduced conditions which are not present in the groundwaters analysed. Fe3+ as dominant dissolved species is likely to be present among oxidised, highly acidic waters. However, the Eh-pH values of the groundwaters investigated plot far off the stability field of dissolved Fe3+. - 115 - PhD Thesis Florian Ludwig 2011

As indicated in the Eh-pH diagram (Fig. 4), groundwaters with high concentrations of Feto- 2+ tal fall within the stability field of dissolved Fe . Most samples plot parallel to the solute-solid 2+ boundary of Fe and Fe(OH)3. Moderate values of Fetotal plot closer to this line whereas Fetotal 2+ concentrations near the detection limit directly lie on the Fe /Fe(OH)3 boundary line or fall within the stability field of solid Fe(OH)3. At Fetotal concentrations below the detection limit, the samples plot within the Fe(OH)3 stability field or, in the acidic sector and at Eh values above + 100 mV, within the stability field of Fe2+. Among the oxidised groundwaters with acidic pH, the concentrations of Fetotal are below the detection limit. This parallels to investigations of Liu and Millero (2000), who determined low iron species solubility values of 10-6.5 – 10-7 mol l-1 at pH 4.5 – 5 and decreasing values with increasing pH. As illustrated in Fig. 4, the highest concentrations of dissolved Fe-species occur among reduced groundwaters at near neutral pH, which suggests, that the state of groundwater reduction significantly controls iron mobility in the aquifer.

1500 above 1000 µg l-1 100 to 1000 µg l-1 10 to 100 µg l-1 below detection limit 1000 3+ Fe 2+ Fe(OH) Fe(OH) + PO 2 2 = 1 atm

500 Fe(OH)3 ferrihydrite

Fe2+ Eh (mV) Eh Fe(OH) - 0 4

Fe CO 3 PH PC 2 = O 1 a 2 = tm 10 -3 a tm -500 Fe(OH)2

-1000 02468101214 pH Fig. 4 Simplified Eh-pH diagram of the distribution of iron species; solute-solid boundaries are calculated for -6.7 -1 a concentration of dissolved Fetotal at the detection limit (10 mol l ), higher concentrations effect a shift of the 2+ Fe /Fe(OH)3 boundary towards lower pH values, blue shading indicates solute species; calculations refer to thermodynamic data compiled by Drever (1997)

Aluminium

In the groundwaters analysed, the concentration of Altotal decreases with increasing pH. The highest concentration of 800 – 900 µg l-1 can be associated with acidic groundwaters with pH -1 < 5. At pH values above 8, Altotal does not exceed 50 µg l . The groundwater with the highest - 116 - Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

pH-value (9.72, Mt. Wasserkuppe, Rhön) indicates a comparatively low concentration of 18.2 µg l-1 (Fig. 5). 78 groundwater samples indicate values below the detection limit of 3 µg l-1. The highest values can be found among the predominantly acidic groundwaters of the Bunter of the Odenwald. All samples of the Upper Rhine Graben aquifer plot below the detection limit of Altotal. At low pH values, Al exists as Al3+. The occurrence of Al3+ as dominant dissolved species is limited to the acidic groundwaters of the Odenwald Bunter sandstone aquifer (range of pH 2+ + 4.5 – 5). With increasing pH, the hydrolysed forms Al(OH) and Al(OH)2 are the prevailing - species. Above a pH of 6.15, aluminium forms a negatively charged Al(OH)4 -complex. Most groundwater samples illustrated in Fig. 5, except those of the Odenwald Bunter sandstone, - plot in the Al(OH)4 -stability field.

0 basaltic rocks, High Rhön mountain range basaltic rocks, Vogelsberg mountain range Bunter sandstone, Odenwald mountain range Bunter sandstone, Lower Hessian Depression -2 Rotliegend sedimentary rocks, Lower Main Plain clay shale, Idstein Depression

s ou ph or -4 am H) 3 ite O yll Al( ph ro Py

Al(total) e sit ibb -6 G ite lin ao

log m m log K Al3+ -8

- Al(OH)4

-10 2+ + Al(OH) Al(OH)2

log αSi = -3.6 -12 2345678910 pH Fig. 5 Dissolved Al-species and equilibrium curves of Al-silicates and Al-hydroxides at a silica activity of 10- 3.6 mol l-1 as a function of pH; samples illustrated in the diagram indicate concentration values above the detection limit of 10-6.9 mol l-1; calculations refer to thermodynamic data compiled by Drever (1997)

The modelled curves of solute-solid boundaries drawn in Fig. 5 suggest elevated mobility of dissolved Al-species at very low and very high pH. As suggested by Eriksson (1981), solution equilibria with solid phase can be assumed to delimit the mobility of dissolved Al-species in natural environments. However, the values determined for the groundwaters (52 values above detection limit) do not fall systematically on any of the lines of calculated solute-solid equilibria of kaolinite, pyrophyllite, gibbsite and amorphous Al(OH)3. Since all groundwaters indicate saturation or oversaturation with respect to quartz, the calculations were adjusted to -3.6 an SIquartz of +0.4 or a silica activity of 10 , respectively. Despite increasing calculated val-

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ues of solubility of the solid Al-minerals considered above a solubility minimum at pH 6.15, the concentration values of dissolved Altotal do not increase with increasing pH. No increasing trend could be delineated; neither for one individual aquifer lithology, nor for the complete dataset. It might be suggested, that at alkaline pH-values, the groundwaters considered indicate oversaturation only with respect to gibbsite and kaolinite. At acidic pH, most samples also plot within the stability fields of pyrophyllite and amorphous Al(OH)3. At elevated pH- values, these solid species do not appear as stable phases with regard to the groundwaters investigated.

4.4 Mobility Controls of Arsenic and Heavy Metals Sorption mechanisms as controlling factor of ion mobility can be associated with charged surfaces of e. g. clay minerals, of oxides, hydroxides, and carbonates, and with organic matter as a function of pH (McLean and Bledsoe 1992). At low pH, positive surface charge due to protonation of the sorbent surface will attract anions. With increasing pH, the sorbent surface subsequently becomes deprotonated and preferentially attracts cations. At the pH value, where the number of protonated exchange sites equals the number of deprotonated exchange sites, the net charge will be zero (Drever 1997). For iron oxides and hydroxides such as hematite, magnetite, and goethite, these isoelectric points or points of zero charge fall within a range of pH of 6 to 7 (values of several authors compiled in Drever 1997). Heavy metals indicate a significant variety in affinity to sorptive matter. Sorption affinity of heavy metals to goethite has been described by Forbes et al. (1976); sorption affinity to Fe oxides has been the issue of studies by Benjamin and Leckis (1981). Generally, there is a higher affinity of iron oxides/hydroxides for Cu2+ and Pb2+ compared to Zn2+, Co2+, and Cd2+ (McLean and Bledsoe 1992). The sorption ability of hydrous ferric oxide may decrease with proceeding alteration of the original exchange matter. Investigating the surface charge of amorphous ferric hydroxide in aqueous suspension over time, Lahann (1976) found a decrease of surface charge of about 75% within 120 days and the formation of goethite from the ferric hydroxide. Over longer periods of time, the fracture coatings of fissured rocks tend to accumulate Fe- oxides/hydroxides with the amounts of Fetotal exceeding those of the original rock (Ludwig et al. 2011). Among the secondary mineral assemblage, clay minerals can be considered as stable, as their formation relates to slow geological processes (Bodin et al. 2003). Vandergraaf (1997) identified alteration minerals such as clay minerals to offer stronger sorption abilities than the original rock. As principle sorption mechanism, sorption curves of metals and anionic metal complexes on hydrous ferric oxides, Fig. 6 and Fig. 7 indicate the constraints of pH and the ion mobility.

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With regard to the distribution of iron species, ferrihydrite (Fe(OH)3) can be considered as poorly crystalline hydrous ferric oxide (Drever 1997) which might further evolve to form goethite (FeOOH) (Lahann 1976). In addition, primary iron minerals such as Fe-oxides, sulfates and carbonates might affect sorption mechanisms. However, sorption calculations were limited to secondary hydrous ferric oxides issuing fresh reaction surface to the dissolved ions in the groundwaters. Fig. 6 illustrates, that cation sorption affinity increases with increasing pH. At neutral to alkaline pH values, most heavy metals can be considered to be immobile as far as a sufficient amount of free exchange sites is available. Whereas sorption curves of Cu2+ and Pb2+ suggest demobilisation at acidic pH values, the calculated curves of Zn2+, Ni2+, Cd2+, and Co2+ fall within the field of near-neutral pH. For comparison, the sorption of Mg2+ and Ca2+ can be assumed to be limited to elevated alkaline pH values.

100

2+ 2+ 2+ 2+ 2+ Cu2+ Pb Zn Ni Mg Ca

adsorbed (%) adsorbed 40 Co2+

Cd2+ 20

0 4567891011 pH Fig. 6 Adsorption curves of bivalent metals on hydrous ferric oxides as a function of pH and a total of 4x10-4 exchange sites per litre; initial cation concentrations are adjusted to the particular detection limits; the curves of alkali earth elements Ca and Mg are given for comparison

The sorption curves calculated for the anionic complexes arsenate, arsenite, and chromate (Fig. 7) suggest efficient sorption at neutral to acidic pH, and high concentration values are limited to alkaline pH values. In comparison to sorption of arsenate, the demobilisation of arsenite as reduced As-species appears to be less effective. At smaller numbers of free exchange sites, arsenite can be assumed not to be entirely demobilised by adsorption.

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100 4 x 10-4 mol l-1 1 x 10-4 mol l-1

4 x 10-5 mol l-1 80

3- AsO3

adsorbed (%) adsorbed 40 2- AsO 3- CrO4 4

0 4567891011 pH Fig. 7 Adsorption curves of anionic complexes on hydrous ferric oxides as a function of pH and a total of 4x10-4 exchange sites per litre; initial concentrations of dissolved species are adjusted to the particular detection 3- limits; the sorption curves of trivalent arsenic as arsenite (AsO3 ) significantly vary with respect to the amounts of available exchange sites

As stated by numerous authours (e. g. Drever 1997; Singhal and Gupta 2010), it is neces- sary to know the chemical form in which a specific element is present prior to calculations of chemical equilibria or adsorption. Simplified speciation diagrams with relevant stability fields where calculated for the individual heavy metals and As. Carbonate species where not included to the Eh-pH diagrams, since solid species are far off equilibrium with the Eh-pH conditions and the PCO2 of the natural groundwaters. Under anaerobic conditions and high concentrations of sulfur, the elements considered may be transformed to sulfides (Drever 1997) which leads to immobilisation. In contact with oxygen, the sulfides are oxydised and the elements are re-released into solution. However, the formation of sulfides does not appear plausible at the present Eh-pH- constraints and the low concentrations of sulfur.

4.4.1 Arsenic Arsenic tends to form anionic complexes as heptavalent arsenate under oxidising conditions and as trivalent arsenite under reducing conditions (Hem 1977; Hem 1985; Nordstrom 2005; Henke 2009). Fig. 8 compiles the stability fields of both arsenate and arsenite, the associated hydrolysis products as well as the stability field of solid Asmetalloid as a function of Eh and pH.

The highest values of Astotal can be found within a small range of near-neutral pH values in both oxidised and reduced groundwaters. Concentrations of dissolved Astotal below the detec-

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tion limit can almost exclusively be associated to oxidised groundwaters.

1500 above 5 µg l-1 0.5 to 5 µg l-1 below detection limit 1000

H3AsO4 PO 2 = 1 a - tm H2 AsO4 500

2- HAsO4

Asmetalloid Eh (mV) Eh H3AsO3 3- 0 AsO4

PH 2 = 1 atm - H2AsO3 -500 2- HAsO3

-1000 0 2 4 6 8 10 12 14 pH Fig. 8 Simplified Eh-pH diagram of the distribution of As species; solute-solid boundaries are calculated for a concentration of dissolved As-species of 10-8.2 mol l-1 (detection limit), blue shading indicates solute species; calculations refer to thermodynamic data compiled by Nordstrom and Archer (2003)

2 With respect to co-precipitation, the correlation coefficients R of the Astotal and Fetotal concentrations associated to the particular aquifer lithologies partly suggest a notable linear constraint. Groundwaters of the Idstein Depression and the Rotliegend apparently approach to a linear constraint, with R2 values of 0.72 and 0.64, respectively. Among the groundwaters of 2 the Lower Hessian Depression, a linear correlation of Astotal and Fetotal is less evident with R = 0.27. Groundwaters in the sedimentary deposits of the Upper Rhine Graben do not indicate any correlation (R2 = 0.03). Linear correlation parallels to findings by Overesch et al. (2008) evaluating the mobilisation potential of arsenic in soils. They proved correlation of As and Fe in soils and synchronous remobilisation of As and Fe. For demobilisation, the availability of free O2 increases the precipitation of As-species with Fe-hydroxides. As suggested by Carrillo and Drever (1997), As-species is adsorbed mostly by oxyhydroxide surfaces in the natural environment. Recent studies of Nordstrom and Archer (2003) on speciation of As found hydrolysis of arsenite to be less distinctive than hydrolysis among the arsenate species. With regard to sorption of As-species on hydrous ferric oxides, they suggest bivalent arsenate to be more effectively adsorbed than uncharged or monovalent arsenite (Fig. 8). Another mechanism controlling As mobility among natural groundwaters may derive from co-precipitation of hydrous iron oxides and arsenate in oxidised waters (Hem 1977; Hem 1985). Demobilisation by the

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formation of As-sulfides as suggested by Hem (1985) is limited to a highly reduced environment and high sulfur concentrations or may occur as ore deposits in hydrothermal systems (O’Day 2006). Since the groundwaters tested do not match these conditions, the stability fields of As-sulfides were not calculated. The stability field of elemental As refers to the concentration of dissolved As-species at the detection limit of 0.5 µg l-1 (10-8.2 mol l-1). The groundwaters investigated in this study indicate mobility of dissolved As-species limited to pH values above 6.5, high concentrations preferentially occur in the field of reduced species. This correlates to As sorption under oxidising conditions and relative mobility under reduced conditions. Fig. 7 suggests complete adsorption of arsenate below pH 9, whereas arsenite can be assumed not to be adsorbed entirely. With a decreasing number of free exchange sites, mobility of reduced As-species increases. With regard to the mobility of As-species, the sorption affinity may be related to the Eh-pH conditions present in the groundwaters. The redox potential has double impact on the mobility of As-species in solution. Low Eh values effect high Fetotal mobility and potential As mobilisation and, additionally, suggest the formation of reduced As-species with higher mobility relative to oxidised As-species in the presence of sorptive matter. Increasing pH significantly increases hydrolysis of As and, thus, decreases sorption affinity.

4.4.2 Copper and Lead With regard to the mobility in groundwater, Cu and Pb indicate significant similarities. As suggested by McLean and Bledsoe (1992), precipitates of these metals such as carbonates can be assumed as important control of mobility. Sorption curves calculated for both Cu2+ and Pb2+ suggest similar sorption affinities with high mobility limited to acidic pH and complete fixation to hydrous ferric oxides above a pH of 6 (Fig. 6). Studies about competitive sorption of heavy metals found Cu2+ and Pb2+ to be attracted to sorptive matter to greater extent than other heavy metals (McLean and Bledsoe 1992). Lab experiments by Phillips (1999) found mobility of Cu- and Pb-species to correlate to the concentrations of dissolved Fetotal, which suggests the release of previously sorbed ions through dissolution of iron oxides/hydroxides. Among the groundwaters investigated, Cu predominantly occurs as Cu2+ species and hardly falls within the stability field of hydrolised CuOH+ (Fig. 9). The reduced groundwater samples fall within the stability field of solid Cu2O and Cumetal calculated for a concentration (detection limit) of 1.0 µg l-1 (10-7.8 mol l-1). Only few samples can be associated to the oxidised CuO solid species. Most Cu concentrations above the detection limit could be detected under oxidising conditions. Within the stability fields of solid Cu-species, concentration values above the detection limit fall near the solute-solid boundaries. At greater distance, Cu concentrations of waters

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within the solid phase fields are below the detection limit. This may suggest, that precipitation of Cu constitutes a relevant mechanism to control Cu mobility. In contrast to the calculated sorption curve, Cu mobility is not limited to low pH conditions. Dissolved Cu-species would be expected to be attracted to immobile iron oxides/hydroxides under oxidising conditions and to indicate greater mobility among reduced groundwaters. However, the groundwaters investigated indicate high mobility in oxidised groundwaters at pH exceeding 7, and low mobility in reduced groundwaters with high concentrations of dissolved iron.

1500 above 2 µg l-1 1 to 2 µg l-1 below detection limit 1000

PO 2 = 1 + atm 2+ 2+ Cu Cu 500 CuOH

CuOtenorite Eh (mV)

0 Cu 2O cu prite

PH 2 = 1 atm Cumetal -500

-1000 02468101214 pH Fig. 9 Simplified Eh-pH diagram of the distribution of Cu species; solute-solid boundaries are calculated for a concentration of dissolved Cu-species of 10-7.8 mol l-1 (detection limit), blue shading indicates solute species; calculations refer to thermodynamic data compiled by Drever (1997)

Only few groundwater samples indicate concentrations of Pb-species above the detection limit of 0.5 µg l-1 (10-8.6 mol l-1, Fig. 10). Pb mobility is limited to either acidic or reduced groundwater samples. All samples with values exceeding the detection limit fall within the stability field of dissolved Pb2+. The sorption curve calculated for sorption of Pb2+ on hydrous ferric oxide (Fig.6) suggests immobilisation of Pb2+ above a pH of 6 and mobility limited to a low-pH environment. This parallels to some acidic, oxidised groundwater samples. Mobility of Pb in reduced groundwaters at near-neutral pH might indicates co-remobilisation of Fe and previously sorbed Pb as suggested by Phillips (1999). With regard to the Pb concentration considered to calculate Pb stability fields, demobilisation by precipitation of Pb-oxide or Pbmetal is not likely among the groundwaters investigated.

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1500 above 1 µg l-1 0.5 to 1 µg l-1 below detection limit 1000

PO 2 = + 1 2+ atm Pb

500 PbOH Pb2+ Eh (mV) 0 PbOlitharge

PH 2 = 1 atm -500 Pbmetal

-1000 02468101214 pH Fig. 10 Simplified Eh-pH diagram of the distribution of Pb species; solute-solid boundaries are calculated for a concentration of dissolved Pb-species of 10-8.6 mol l-1 (detection limit), blue shading indicates solute species; calculations refer to thermodynamic data compiled by Drever (1997)

4.4.3 Cadmium, Cobalt, Nickel, and Zinc As suggested by McLean and Bledsoe (1992) and Mellis et al. (2004), sorption mechanisms constitute the most important controlling factor for mobility of Cd2+, Co2+, Ni2+, and Zn2+. Sorption curves calculated for metal sorption on hydrous ferric oxide suggest sorption initiat- ing above pH 6 and complete demobilisation above pH 8 (Fig. 6). Whereas precipitates of Ni and Zn are not a major mechanism for decreasing mobility due to high solubilities of the particular metal solid phases, Cd mobility may also be diminished by precipitation of Cd- carbonate. Wells and Gilkes (1998) also suggest the incorporation of Ni in lateritic hematite and goethite. The mobility of Cd appears to be significantly limited with only three samples exceeding the detection limit of 0.08 µg l-1 (10-9.2 mol l-1, Fig. 11). All groundwater samples fall within the stability field of Cd2+. Concentration values exceeding the detection limit can be related to oxidised acidic groundwaters or to partly reduced groundwater at neutral pH. Mobility of Cd might be correlated to lacking sorption affinity at low pH and remobilisation of Cd in reduced groundwaters. However, the number of relevant samples is too little to delineate certain constraints of Cd mobility. It might be suggested, that limited availability of Cd in the original aquifer rocks

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might be the limiting factor of Cd concentrations among the groundwaters considered.

1500 above 0.08 µg l-1 below detection limit

1000

PO 2 = 1 atm + 2+

500 Cd CdOH

Cd2+ Eh (mV)

0 CdOmonteponite

PH 2 = 1 atm -500

-1000 02468101214 pH Fig. 11 Simplified Eh-pH diagram of the distribution of Cd species; solute-solid boundaries are calculated for a concentration of dissolved Cd-species of 10-9.2 mol l-1 (detection limit), blue shading indicates solute species; calculations refer to thermodynamic data compiled by Drever (1997)

The mobility of Zn significantly parallels to that of Cd with the exception that more samples exceed the detection limit of 10 µg l-1 (10-6.8 mol l-1, Fig. 12) and that the detection limit differs by a factor of 250. Zn indicates relative mobility at low pH and in association with partly reduced groundwaters at pH 6 to 7. The mechanisms controlling Zn mobility are, thus, likely to be similar to those suggested for the mobility of Cd. Despite high availability of Zn in the basaltic volcanic rocks, the associated groundwaters do not indicate Zn2+ activities above the detection limit. This also suggests demobilisation of Zn2+ through effective adsorption at elevated pH values. The Eh-pH diagrams of Ni2+ and Co2+ (Fig. 13 and Fig. 14, respectively) reflect a similar pattern of ion activities as illustrated for Zn2+. However, the detection limits of Ni and Co of 1.0 and 0.5 µg l-1 (10-7.8 and 10-8.1 mol l-1) are significantly lower. Ion activities are limited to low-pH groundwaters and reduced groundwaters at near-neutral pH. Thus, sorption and remobilisation mechanisms might be expected to be similar to those suggested for Cd and Zn. As well as Zn, Ni does not exceed the detection limit among the high-pH groundwaters associated to the basalts despite high amounts of Ni determined in the aquifer rocks.

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1500 above 100 µg l-1 10 to 100 µg l-1 below detection limit 1000

PO 2 = 1 atm + 2+

500 Zn ZnOH Zn2+ Eh (mV) 0 ZnOzincite

PH 2 = 1 atm -500

-1000 02468101214 pH Fig. 12 Simplified Eh-pH diagram of the distribution of Zn species; solute-solid boundaries are calculated for a concentration of dissolved Zn-species of 10-6.8 mol l-1 (detection limit), blue shading indicates solute species; calculations refer to thermodynamic data compiled by Drever (1997)

1500 Nickel above 10 µg l-1 1 to 10 µg l-1 below detection limit 1000

PO 2 = 1 atm

500 Eh (mV) 0

PH 2 = 1 atm -500

-1000 02468101214 pH Fig. 13 Eh-pH diagram of the distribution of Ni activity at the detection limit of dissolved Ni of 10-7.8 mol l-1

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1500 Cobalt above 5 µg l-1 0.5 to 5 µg l-1 below detection limit 1000

PO 2 = 1 atm

500 Eh (mV) 0

PH 2 = 1 atm -500

-1000 02468101214 pH Fig. 14 Eh-pH diagram of the distribution of Co activity at the detection limit of dissolved Co of 10-8.1 mol l-1

4.4.4 Chromium Cr occurs in trivalent and hexavalent oxidation states in natural environments. According to Hem (1977), Cr forms anionic species when oxidised and cationic species when reduced. Therefore, the affinity to sorptive matter for hexavalent Cr6+ will be elevated at low pH (Fig.7) and sorption of trivalent Cr3+ will be favoured at high pH. However, anionic Cr- species may easily be desorbed. Cr2O3 is likely to occur as residual trivalent solid species, whereas amorphous Cr(OH)3 solid species may evolve as precipitate in natural reducing -8 -1 aqueous systems (Hem 1977). Solubility of Cr2O3 is limited to values below 10 mol l , whereas solubility of Cr(OH)3 yields higher values. As illustrated in Fig. 15, the groundwater samples investigated predominantly fall within + the field of reduced Cr(OH)2 species. At pH values below 6, the concentrations do not exceed the detection limit of 1.5 µg l-1 (10-7.6 mol l-1). The highest values plot close to the + 2- Cr(OH)2 /CrO4 stability field boundary. With regard to the low Cr concentrations determined it can be assumed, that concentrations are equilibrium controlled among the trivalent species. Solubility equilibrium with e. g. Cr2O3 could, thus, be considered as a limiting factor to Crtotal mobility. The Crtotal concentrations -6.9 -1 determined (Crmax = 10 mol l ) are to low to approach equilibrium with Fe(OH)3 solid spe-

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1500 above 3 µg l-1 1.5 to 3 µg l-1 below detection limit 1000

2- PO Cr2O7 2 = 1 atm

500 Cr3+ 2- CrO4

2+ Eh (mV) CrOH Cr 2 O 0 3

PH + - 2 = 1 Cr(OH) Cr(OH) atm 2 4 -500

-1000 02468101214 pH Fig. 15 Simplified Eh-pH diagram of the distribution of Cr species; solute-solid boundaries are calculated for a -7.6 -1 concentration of dissolved Cr-species of 10 mol l (detection limit), the stability field of residual Cr2O3 is drawn as solid line, blue shading indicates solute species; calculations refer to thermodynamic data compiled by Hem (1977) cies. Thus, the formation of Cr(OH)3 as controlling factor to mobility of trivalent Cr rather appears unlikely. Hexavalent Cr-species is hardly present among the groundwaters investi- 2- gated, though several samples plot close to the CrO4 stability field. This might suggest remobilisation of previously sorbed anionic hexavalent Cr combined with subsequent reduction to trivalent species. Furthermore, the high pH groundwaters can be associated to the basaltic aquifer rocks which incorporate high amounts of Cr. This suggests that high Crtotal mobility might be correlated to the dissolution of Cr-bearing primary minerals and mobility in high pH-groundwaters. As stated by Hem (1975), the reduction of hexavalent chromate to trivalent chromite can be coupled to ferrous iron oxidation. This would suggest low concentrations of dissolved iron which is evident for the partly reduced groundwaters at alkaline pH. Rather low Crtotal mobility at near-neutral pH among more intensively reduced groundwaters suggest competing sorption mechanisms, with divalent cations preferentially adsorbed (and remobi- + lised) than monovalent Cr(OH)2 species.

- 128 - Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

5 Conclusions

Under consideration of sorption on iron oxides/hydroxides, the mobility of As and the heavy metals considered by this study can be defined as constraint of species and the availability of sorptive matter as a function of pH and Eh. The feasibility of sorption on iron oxides/hydroxides to control ion activities in the groundwaters investigated can be suggested for several heavy metals and As. Fe(OH)3 was found to be the most likely solid iron species within the range Eh- and pH-values considered. Except for Cu2+, the activities of the cationic heavy metals in oxidised groundwaters could be correlated to the sorption curves calculated. For Cu, solute-solid boundaries are likely to have significant effect on Cu mobility. At near-neutral pH, reduced groundwaters may indicate elevated activities of cationic heavy metals suggesting synchronous remobilisation of iron and previously sorbed metals. Low values of dissolved Ni- and Zn-species in the high-pH groundwaters associated to the Ni-Zn-rich basaltic rocks significantly indicate effective demobilisation of these elements through sorption. Arsenic indicates mobility of As-species limited to pH values above 6.5 with arsenate pre- sumably fixed to sorptive matter below this values. The highest concentrations fall within the stability field of reduced arsenite. This suggests sorption affinity of the oxidised species to be more effective than sorption affinity of reduced arsenite, which correlates to the sorption curves calculated. The mobility of Astotal might also be related to high Fetotal mobility and potential As mobilisation under reducing conditions, indicated by positive linear correlation of

Fetotal and Astotal concentrations.

Crtotal predominantly occurs as mobile reduced trivalent chromite species among the groundwaters investigated. The highest values can be correlated to the high-pH groundwaters of the basaltic rocks and limited sorption affinity at high pH values. This also suggests that high Crtotal concentrations might be correlated to the dissolution of Cr-bearing primary minerals. Low Crtotal concentrations at near-neutral pH among reduced groundwaters suggests competing sorption mechanisms with divalent cations preferentially adsorbed and remobilised + than monovalent Cr(OH)2 species. This might suggest, that Crtotal concentrations are delimited under reduced conditions due to limited remobilisation with iron species. With regard to the Cr concentrations considered, the formation of solid Cr(OH)3 as controlling factor to mobility of trivalent Cr rather appears unlikely.

- 129 - PhD Thesis Florian Ludwig 2011

References

Abel H (1991) Lagerstätten [Ore deposits]. In: Anderle H-J (1991) Erläuterungen zur Geolo- gischen Karte von Hessen, Blatt Nr. 5715 Idstein, 2. Auflage [Comments to the geological map, sheet 5715, Idstein, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 148- 152 Appelo CAJ, Postma D (2005) Geochemistry, groundwater, and pollution. 2nd edn. Balkema Publishers, Rotterdam, 649 pp Backhaus E, Schwarz S (2003) Ein Sammelprofil des Buntsandsteins und Zechsteins im mitt- leren Odenwald anhand von Bohrungen und Gamma-Logs [An accumulative profile of the Bundsandstein and Zechstein rock formation on the basis of drillings and Gamma- logs]. Geol Jb Hessen 130:91-107 Becker RE, Kulick J (1999) Trias, Buntsandstein [Triassic, Bunter] In: Becker RE, Kulick J (1999) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 4923 Altmorschen, 2. Auflage [Comments to the geological map, sheet 4923, Altmorschen, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 64-99 Benjamin MM, Leckie OJ (1981) Multiple-site adsorption of Cd, Zn, and Pb on amorphous iron oxyhydroxide. J Colloid Interface Sci 79:209-221 Bodin J, Delay F, de Marsily G (2003) Solute transport in a single fracture with negligible matrix permeability: 1. fundamental mechanisms. Hydrogeol J 11:418-433 Bogaard PJF, Jabri L, Wörner G (2001) Chemical Alteration of Basalts from the Drill Core „Forschungsbohrung Vogelsberg 1996“, Germany. In: Hoppe A, Schulz R (eds) Die Forschungsbohrung Vogelsberg – Einblicke in einen miozänen Vulkankomplex [The Vogelsberg Exploration Drilling – An Insight into a Miocene Volcanic Complex]. Geol Abh Hessen 107:101-118 Bucher K, Stober I (2002) Water-rock reaction experiments with Black Forest gneiss and granite. In: Stober I, Bucher K (eds) Water-rock interaction. Kluwer Academic Publish- ers, p 61-95 Büttner G, Pamer R, Wagner B (2003) Hydrogeologische Raumgliederung von Bayern [Hy- drogeological spatial classification of Bavaria]. Bay L-Amt Umwelt, GLA-Fachbericht 20, 85 p Carrillo A, Drever JI (1997) Adsorption of arsenic by natural aquifer material in the San An- tonio-El Trifuno mining area, Baja California, Mexico. Environm Geol 35(4):251-257 Diederich G, Mattheß G (1972) Hydrogeologie [Hydrogeology] In: Kupfahl H-G, Meisl S, Kümmerle E (1972) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 6217

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Zwingenberg [Comments to the geological map, sheet 6217, Zwingenberg]. Hess L- Amt Umwelt Geol; Wiesbaden, p 193-214 Drever JI (1997) The geochemistry of natural waters. 3rd edn. Prentice Hall, 686 New Jersey, 436 p Ehrenberg K-H, Hickethier H (1988) Tertiär, Vulkanite [Tertiary, volcanic rocks] In: Diede- rich G, Ehrenberg K-H, Hickethier H (1988) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 5621 Wenings [Comments to the geological map, sheet 5621, We- nings]. Hess L-Amt Umwelt Geol; Wiesbaden, p 49-94 Ehrenberg K-H, Hickethier H, Rosenberg F, Strecker G, Susic M, Wenzel G (1992) Neue Ergebnisse zum tertiären Vulkanismus der Rhön (Wasserkuppenrhön und Kuppenrhön) [Recent conclusions on tertiary volcanism in the Rhön (High Rhön and Dome Rhön)]. Beih z Eur J Mineral 4:47-102 Emmerich K-H (1994) Podsole im Buntsandstein-Odenwald [Podsols of the Bunter sandstone, Odenwald]. Geol JB Hessen 122:173-184 Eriksson E (1981) Aluminium in Groundwater – Possible Solution Equilibria. Nordic Hydrol 12:43-50 Flaathen TK, Gislason SR (2007) The groundwater beneath Hekla Volcano, Iceland: A natu-

ral analogue for CO2 sequestration. Geochim Cosmochim Acta 71:A283 Forbes EA, Posner AM, Quick JP (1976) The specific adsorption of divalent Cd, Co, Pb, and Zn on goethite, J Soil Sci 27:154-166 Helgeson HC, Delany JM, Nesbit HW, Bird DK (1978) Summary and critique of the thermodynamic properties of rock-forming minerals. Am J Sci, 278-A:1-220 Hem JD (1975) Discussion of role of hydrous metal oxides in the transport of heavy metals in the environment. In: Progress in Water Technology 7:149-153 Hem JD (1977) Reactions of metal ions at surfaces of hydrous iron oxide. Geochim Cosmo- chim Acta 41:527-538 Hem JD (1985) Study and interpretation of the chemical characteristics of natural water. US Geol Survey Water Supply Pap 2254, 3rd ed, p 263 Henke KR (2009) Arsenic in natural environments. In: Henke KR (ed.) Arsenic: environmental chemistry, health threats, and waster treatment. John Wiley & Sons Ltd, pp 69- 235 Kowalczyk G (1983) Das Rotliegende zwischen Taunus und Spessart [The Rotliegend between Taunus and Spessart]. Geol Abh Hessen 84, p 99 Kümmerle E (1972) Quartär [Quaternary] In: Kupfahl H-G, Meisl S, Kümmerle E (1972) - 131 - PhD Thesis Florian Ludwig 2011

Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 6217 Zwingenberg [Com- ments to the geological map, sheet 6217, Zwingenberg]. Hess L-Amt Umwelt Geol; Wiesbaden, p 124-166 Lahann RW (1976) Surface Charge variation in aging Ferric Hydroxide. Clays Clay Min 24:320-356 Leßmann B (Die Hydrogeologie des vulkanischen Vogelsberges [Hydrogeology of the volcanic Vogelsberg]. Geol Abh Hessen 108, p 144 Lippolt HJ (1982) K/Ar age determination and the correlation of Tertiary volcanic activity in Central Europe. Geol Jb D52:113-135 Liu X, Millero FJ (2000) Iron hydroxide solubility and morphology as examined by ESEM. Symposium Chemical Speciation and Reactivity in Water Chemistry and Water Tech- nology, reprints of extended abstracts, Am Chem Soc 40(2):532-534 Ludwig F, Stober I, Bucher K (2011) Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany: A Laboratory and Field Study. Aquat Geochem 17:165-193 Ludwig F, Stober I, Bucher K (2011) Groundwater Evolution and Mineral Alteration Reac- tions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany - A Case Study. (forthcoming paper) Marell D (1989) Das Rotliegende zwischen Odenwald und Taunus [The Rotliegend between Odenwald and Taunus]. Geol Abh Hessen 89, p128 McLean JE, Bledsoe BE (1992) Behavior of metals in soils. Technology Innovation Office, Office of Solid Waste and Emergency Response, UA EPA, Washington, DC, p 25 Mellis EV, Cruz MCP, Casagrande JC (2004) Nickel adsorption by soils in relation to pH, organic matter, and iron oxides. Sci Agric 61(2):190-195 Müller G, Haamann L, Kubat R, Noë K (1987) Schwermetalle und Nährstoffe in den Böden des Rhein-Neckar-Raums: Ergebnisse flächendeckender Untersuchungen [Heavy metals and nutrient matter in soils of the Rhein-Main area: Results of comprehensive investigations]. Heidelberger Geowiss Abh 13, p 346 Nordstrom DK (2005) Modeling low-temperature Geochemical Processes. In: Drever JI (ed) Surface and Groundwater, Weathering, and Soils 5:37-72 Nordstrom DK, Archer DG (2003) Arsenic thermodynamic data and environmental geochemistry. In: Welch AH, Stollenwerk GK (eds) Arsenic in Ground Water. Kluwer, p 1-25 O’Day PA (2006) Chemistry and Mineralogy of Arsenic. Elements 2:77-83 Overesch M, Düster L, Greef K, Rinklebe J, Mansfeldt T (2008) Ermittlung und Beurteilung - 132 - Chapter 3: Estimating the Effect of pH, Eh, and Sorption on Iron Hydroxides on the Mobility of Arsenic and Heavy Metals in various Aquifer Lithologies in Hessen, Central Germany

des Mobilisierungspotentials von Arsen in Böden – Länderfinanzierungsprogramm “Wasser, Boden und Abfall”, Projekt B 4.07 [Determination and evaluation of the mobilisation potential of arsenic in soils – State finance program “Water, Soil and Waste”, Project B 4.07], 85 p Phillips IR (1999) Copper. Lead, Cadmium, and Zinc Sorption By Waterlogged and Air-Dry Soil. J Soil Contamin, 8(3):343-364 Pöschl W (1999) Hydrogeologie [Hydrogeology] In: Becker RE, Kulick J (1999) Erläuterun- gen zur Geologischen Karte von Hessen, Blatt Nr. 4923 Altmorschen, 2. Auflage [Com- ments to the geological map, sheet 4923, Altmorschen, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 293-330 Renftel L-O, Scharpff H-J (1998) Hydrogeologie [Hydrogeology]. In: Renftel L-O (1998) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 5819 Hanau, 2. Auflage [Comments to the geological map, sheet 5819, Hanau, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 139-212 Rosenberg F (1991) Geochemie [Geochemistry]. In: Anderle H-J (1991) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 5715 Idstein, 2. Auflage [Comments to the geological map, sheet 5715, Idstein, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 158-179 Rosenberg F (1993) Geochemie [Geochemistry] In: Kümmerle E, Seidenschwann G (1993) Erläuterungen zur Geologischen Karte von Hessen, Blatt Nr. 5818 Frankfurt a. M. Ost, 3. Auflage [Comments to the geological map, sheet 5818, Frankfurt a. M. East, 3rd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 136-151 Rosenberg F (1999) Geochemie [Geochemistry] In: Becker RE, Kulick J (1999) Erläuterun- gen zur Geologischen Karte von Hessen, Blatt Nr. 4923 Altmorschen, 2. Auflage [Com- ments to the geological map, sheet 4923, Altmorschen, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 274-292 Sabel K-J (1988) Böden [Soils]. In: Diederich G, Ehrenberg K-H, Hickethier H (1988) Erläu- terungen zur Geologischen Karte von Hessen, Blatt Nr. 5621 Wenings [Comments to the geological map, sheet 5621, Wenings]. Hess L-Amt Umwelt Geol; Wiesbaden, p 177-185 Singhal BBS, Gupta RP (2010) Groundwater Quality. In: Singhal BBS, Gupta RP (eds) Ap- plied Hydrogeology of Fractured Rocks, 2nd edn. Springer, Dordrecht, pp 205-220 Stengel-Rutkowski W (1976) Idsteiner Senke und Limburger Becken im Licht neuer Bohrer- gebnisse und Aufschlüsse (Rheinisches Schiefergebirge) [Idstein Depression and Lim- burg Basin at the sight of recent test drillings and outcrops]. Geol Jb Hessen 104:183- 224 - 133 - PhD Thesis Florian Ludwig 2011

Stengel-Rutkowski W (1991) Hydrogeologie [Hydrogeology] In: Anderle H-J (1991) Erläute- rungen zur Geologischen Karte von Hessen, Blatt Nr. 5715 Idstein, 2. Auflage [Com- ments to the geological map, sheet 5715, Idstein, 2nd ed]. Hess L-Amt Umwelt Geol; Wiesbaden, p 180-202 Vandergraaf, TT, Drew, DJ, Archambault D, Ticknor KV (1997) Transport of radionuclides in natural fractures: some aspects of laboratory migration experiments. J Contam Hy- drol 26(1-4):83-95 Wells M, Gilkes RJ (1998) Synthetic Ni goethite and hematite: reproducing hosts for nickel mineralization in Ni-laterites. Symposium Regolith '98, New Approaches to an Old Continent, Cooperative Research Centre for Landscape Evolution and Mineral Explora- tion (CRC LEME), Australia Witt-Eickschen G, Kramm U (1997) Mantle Upwelling and Metasomatism beneath Central Europe: Geochemical and Isotopic Constraints from Mantle Xenoliths from the Rhön (Germany). Journal of Petrology 38(4):479-493 Wittenbecher M (1992) Geochemie tholeiitischer und alkali-oivinbasaltischer Gesteine des Vogelsberges [Geochemistry of tholeiitic and alkali-olovine-basaltic rocks of the Vo- gelsberg]. Geol Abh Hessen 97, p 52

- 134 - General Conclusions

General Conclusions The hydrochemical compounds of the groundwaters investigated could be associated to mass transfers determined by the thermodynamic equilibrium model. The chemical and physical processes controlling groundwater composition in the groundwaters investigated are compiled in the following:

Bunter sandstone fissured rock aquifer, Odenwald mountain range

The evolution of Ca-Mg-SO4-type groundwater to SO4-poor groundwaters with near-neutral pH (Ca-HCO3-type) can be associated to mineral alteration reactions with anorthite, K- feldspar, biotite, and jarosite converted to secondary mineral phase. The alteration processes are attributed by the sorption of sulfate on protonated exchange sites. Exchange surfaces are provided by amorphous hydrous ferric oxides as secondary solid species, probably attributed by secondary clay minerals. The formation of secondary solid phase can be assumed to be the key factor for sorption processes, since the availability of exchange surface obtained by primary minerals such as iron oxides or primary clay minerals can be expected to be exhausted as a function of time. Low pH values in near-surface groundwater promote intense mineral weathering and the formation of secondary mineral phase. Solid iron phase can be expected to immediately precipitate due to rather low solubility constants of iron hydroxides such as ferrihydrite (Fe(OH)3) in oxidised groundwaters. The formation of secondary clay minerals can be expected to proceed over longer periods of time. The incorporation of previously released Al in secondary mineral phase can be expected to be a major control of the concentrations of dissolved Al-species. At an early stage of groundwater evolution, the exchange surfaces will be preferentially protonated due to high H+ activities in the associated near-surface groundwaters. Hence, sorption affinity will be improved and the ability to retain 2- dissolved anions such as SO4 can be expected to be highly efficient. At a later stage of groundwater maturation, the pH values approach near-neutral values. Thus, the conversion rates of primary to secondary minerals will decrease and exchange matter will approach to balanced surface charge. The transport of anions such as chloride or sulfate can thus be expected to be conservative without concentrations being affected by sorption processes.

Basaltic fissured rock aquifer, Mt. Wasserkuppe, High Rhön mountain range

The maturation of Ca/Mg-HCO3 type near-surface groundwater to a Na-HCO3 high-pH type at greater depth associates to the dissolution of olivine, Ca-pyroxene, plagioclase, pyrrhotite, and feldspathoids and to cation exchange. Secondary mineral phase comprises amorphous iron hydroxides as stable solid iron species and secondary clay minerals. The contribution of the primary minerals to hydrochemical groundwater maturation can be associated to the

- 135 - PhD Thesis Florian Ludwig 2011 mineral availability in the original rocks, to the mineral grain size, and to mineral stability in terms of mineral dissolution rates. Alkalinisation of groundwaters at greater depth relates to cation exchange on deprotonated exchange surfaces as a function of OH- activity. In near- surface groundwaters indicating neutral to slightly alkaline pH values, ion exchange does not proceed since potential exchange sites are nearly charge-balanced. High pH groundwater at greater depth consequently represents late-stage weathering, whereas near-surface groundwater can be associated to an early stage of groundwater maturation. With regard to reaction kinetics, late-stage groundwater evolution basically involves the dissolution of relative stable anorthite and albite. It appears, that the availability of reactive feldspathoids, olivine, Ca-pyroxene, and pyrrhotite is diminished in the altered basaltic aquifer rock.

Mobility controls of heavy metals and arsenic in groundwater The mobility of heavy metals and arsenic in groundwater could be associated to chemical and physical processes as a function of Eh, pH, and the availability of sorptive matter. Speciation calculations suggest ferrihydrite (Fe(OH)3) to be the stable prevailing solid iron species for the oxidised groundwaters. The calculation of sorption curves suggest amorphous hydrous ferric oxide to be of great relevance to control the mobility of dissolved trace elements. Sorption affinity basically depends on the pH of the groundwaters and on the prevailing species of the considered element. With exception of Cu, the sorption on hydrous ferric oxides was found to be consistent with the concentrations of the particular dissolved element species in the natural groundwaters. With regard to Cu, the formation of oxides has to be considered as most important mobility control for the investigated groundwater environments. Among reduced groundwaters, high concentrations of dissolved iron correlate with the concentrations of dissolved As-, Pb-, Co-, Ni-, and Zn- species. This might suggest co- precipitation and synchronous remobilisation of previously sorbed elements as a function of Eh.

Hydrochemical groundwater evolution in the natural environments considered has been outlined as complex combination of chemical and physical processes. Mineral alteration reactions as well as the effect of ion sorption and ion exchange could be determined by mass balance and thermodynamic equilibrium models. As principal result of this study, initial and comprehensive hydrochemical descriptions of two fissured rock aquifer systems were developed. The methods used illustrate both the benefits and the limitations of indirect modelling approaches. The combination of methods has been proven as valuable in order to investigate groundwater evolution and might, thus, be applied as template for hydrochemical investigations among other groundwater regimes. However, precise field investigations and

- 136 - General Conclusions general hydrogeological contemplations are inevitable prior to the implementation of a hydrochemical modelling approach. The numeric accuracy of calculations involved in mass transfer and thermodynamic modelling does not necessarily comply with the conditions in natural systems. Calculations should be evaluated as quantitative as well as qualitative approximation to the complexity of natural water-rock interaction processes. Still, the model conceptions evolved in this study may contribute to the understanding of natural mineral alteration processes and groundwater maturation through the application of numeric methods. Possible applications might involve the estimation of the CO2-sequestration potential of discrete groundwater regimes, referring to groundwater recharge, mineral conversion rates, and CO2 consumption. The model conceptions might also contribute to the estimation of the impact of low-pH recharge water on solutes in groundwaters with special regard to the mobility of noxious trace elements such as heavy metal and arsenic.

- 137 -

Appendix 1. Abbreviations

App. 1 Abbreviations

1. Analytic parameters and detection methods:

ASL altitude in meters above sea level T transmissibility in m2 s-1 -1 kf hydraulic conductivity in m s pH negative log of H+-activity Eh redox potential in mV Temp temperature in °C -1 O2 dissolved oxygen in mg l a activity of dissolved ion species SEC specific electric conductivity in µS cm-1 TDS total of dissolved solids in mg l-1

PCO2 atmospheric pressure of CO2

PO2 atmospheric pressure of O2 LOI loss on ignition tleaching runtime of leaching experiments SI saturation index of solid species CIPW calculated normative mineral content

ICP-MS inductively coupled plasma mass spectrometry ICP-OES inductively coupled plasma optical emission spectrometry XRF X-ray fluorescence analysis

2. Fields of groundwater investigations:

ID Idstein Depression LMP Lower Main Plain ODW Odenwald mountain range LHD Lower Hessian Depression HR High Rhön mountain range VB Vogelsberg mountain range URG Upper Rhine Graben

3. Lithologies:

LB Lower Bunter Sandstone MB Middle bunter Sandstone hoB hornblende basalt TrB trachy basalt aoB alkali olivine basalt oNe olivine nephelinite Ph phonolite

A-1 PhD Thesis Florian Ludwig 2011

App. 1 (followed)

4. Mineral abbreviations:

Ab albite Anl analcite An anorthite Bdl beidellite Bt biotite Cal calcite Chal chalcedony Cpx clinopyroxene Fo forsterite Gt goethite Gp gypsum Hl halite Ill illite Jar jarosite Kln kaolinite Kfs K-feldspar Lmt laumontite Lct leucite Mnt montmorillonite Ntr natrolite Ne nepheline Prh prehnite Po pyrrhotite Sdl sodalite

5. Abbreviations in mineral reaction reactions:

Na─X─Na exchange surface, monovalent binding site Mg═X exchange surface, bivalent binding site

6. Institutions:

HLUG Hessian Agency for the Environment and Geology, Wiesbaden LHL State laboratory of the County of Hessen, Wiesbaden

A-2 Appendix 2. Complete hydrochemical data groundwaters

App. 2 Complete hydrochemical data groudwaters

Sample ID 02 ID 03 ID 04 ID 05 ID 06 ID 07 ID 08 ID 09 ID 10 ID 12 ID 13 ID 14 Depth mbs 56.5 100 98 50.5 43 42 60 50.7 85 63 80 Field parameters Temp °C 8.611.210.88.210.610.310.410.711.411.211.310.6 Eh mV 138 97 79 223 123 -86 147 91 183 21 -27 133 -1 O2 mg l 1.43 1.27 0.98 8.44 3.36 1.51 1.81 0.10 3.44 0.56 1.31 1.13 SEC µS cm-1 744.0 383.0 409.0 156.5 749.0 684.0 589.0 566.0 797.0 518.0 483.0 429.0 pH 7.45 7.21 7.17 6.23 7.36 6.85 7.45 7.21 6.64 7.05 7.28 7.22 Laboratory parameters Ca mg l-1 115.049.852.312.6117.0112.096.591.881.562.954.044.9 Mg mg l-1 23.0 13.3 14.6 5.7 26.7 23.1 18.1 17.6 19.8 18.2 23.3 17.6 Na mg l-1 16.4 10.1 12.5 6.8 10.7 9.4 9.5 9.0 61.3 15.4 12.7 17.9 K mg l-1 1.91.01.01.71.31.91.01.22.31.41.12.2 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 270 163 244 49 312 300 241 316 294 277 188 137 Ba µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Li µg l-1 11.7 17.1 21.6 4.1 7.2 13.0 17.8 15.9 40.4 22.2 22.0 27.5 Rb µg l-1 0.90.71.20.62.63.10.61.54.02.62.31.8

Cl mg l-1 24.0 14.0 10.0 8.4 39.0 14.0 20.0 21.0 85.0 27.0 20.0 16.0 -1 HCO3 mg l 411.8 170.2 206.2 22.0 384.3 361.1 306.2 308.7 329.4 234.9 223.3 204.4 -1 SO4 mg l 48.0 46.0 38.0 24.0 42.0 71.0 42.0 29.0 21.0 44.0 56.0 45.0 -1 NO3 mg l 7.6 4.6 1.2 20.0 8.7 b.d. 5.3 1.2 13.0 b.d. 0.3 0.2 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 180 130 110 46 140 200 140 130 110 120 160 150 Br µg l-1 40 40 50 b.d. 50 60 30 40 80 40 40 50 -1 CO2 mg l 22.9 17.2 19.8 14.1 22.9 48.8 26.0 30.8 77.0 19.8 14.1 19.4 -1 SiO2 mg l 12.9 18.0 20.3 12.4 13.9 9.5 13.5 13.0 10.6 21.8 15.8 19.4

Al µg l-1 b.d. b.d. b.d. 42.5 b.d. b.d. b.d. b.d. b.d. 5.4 b.d. b.d. -1 Fetotal µg l b.d 117 144 b.d b.d 2,510 b.d 41 b.d 736 786 b.d As µg l-1 b.d. 0.7 b.d. b.d. b.d. 2.6 b.d. b.d. b.d. 0.8 b.d. b.d. Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 2.7 b.d. b.d. b.d. 2.2 2.9 2.1 1.7 3.3 b.d. b.d. b.d. Co µg l-1 b.d. b.d. b.d. b.d. b.d. 5.4 b.d. 0.8 b.d. b.d. 0.9 b.d. Cu µg l-1 1.1 b.d. b.d. b.d. b.d. b.d. 1.5 3.2 6.6 b.d. b.d. b.d. Ni µg l-1 b.d. b.d. b.d. 4.1 b.d. 17.5 b.d. b.d. b.d. b.d. 3.9 b.d. Pb µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 0.6b.d.b.d.b.d.b.d.b.d.b.d.1.1b.d.b.d.b.d.b.d. Ti µg l-1 1.71.92.13.21.81.41.61.61.52.71.72.0 U µg l-1 1.1 1.1 b.d. b.d. 1.3 0.6 2.1 0.9 0.8 b.d. b.d. 0.8 V µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

A-3 PhD Thesis Florian Ludwig 2011

App. 2 (followed)

Sample ID 15 ID 16 ID 17 LMP 01 LMP 02 LMP 03 LMP 04 LMP 05 LMP 06 LMP 07 Depth mbs 100 88 70 60 113 152 100 151 100 58.6 Field parameters Temp °C 10.4 11.1 10.2 10.9 12.1 12.3 13.2 14.5 11.4 11.0 Eh mV 44 67 55 141 145 197 167 157 208 224 -1 O2 mg l 0.26 0.74 0.45 5.56 4.38 5.11 2.35 1.68 2.40 5.69 SEC µS cm-1 563.0 701.0 449.0 791.0 710.0 686.0 699.0 572.0 850.0 651.0 pH 7.56 6.72 7.19 6.94 7.21 7.25 7.46 7.64 7.13 7.06 Laboratory parameters Ca mg l-1 60.9 54.4 44.0 132.0 89.5 77.1 65.8 59.6 124.0 108.0 Mg mg l-1 27.9 42.3 23.5 23.1 33.3 22.2 22.6 18.1 34.6 18.8 Na mg l-1 13.4 26.9 12.3 9.8 17.3 49.6 30.0 60.6 9.5 8.3 K mg l-1 1.0 3.3 1.0 1.7 1.6 1.7 2.2 1.6 1.3 0.9 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 199 197 178 751 448 290 672 684 435 290 Ba µg l-1 b.d. b.d. b.d. 89 350 191 299 526 227 230 Li µg l-1 22.8 25.2 18.3 52.4 58.8 102.0 126.0 118.0 43.5 33.1 Rb µg l-1 1.4 3.6 1.5 2.4 3.1 3.6 1.7 1.6 2.6 1.5

Cl mg l-1 24.0 68.0 23.0 26.0 27.0 15.0 30.0 22.0 38.0 21.0 -1 HCO3 mg l 268.4 255.0 216.6 364.2 393.5 392.2 303.8 361.7 457.5 353.8 -1 SO4 mg l 58.0 56.0 36.0 83.0 26.0 37.0 21.0 21.0 36.0 24.0 -1 NO3 mg l b.d. 2.7 b.d. 27.0 14.0 6.7 16.0 8.7 20.0 18.0 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 110 180 83 150 140 120 80 90 170 120 Br µg l-1 70 60 50 b.d. 40 40 30 30 30 30 -1 CO2 mg l 29.9 50.6 29.0 25.5 15.4 12.8 10.1 9.7 26.8 23.8 -1 SiO2 mg l 17.1 18.4 17.9 18.4 19.8 16.8 20.0 22.6 16.2 21.4

Al µg l-1 b.d. b.d. b.d. 11.5 9.6 b.d. 18.6 9.8 15.9 11.9 -1 Fetotal µg l 1,180 1,270 1,020 b.d b.d b.d b.d b.d b.d b.d As µg l-1 b.d. b.d. b.d. 0.7 4.3 4.4 17.4 63.5 1.3 0.9 Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 2.8 b.d. Co µg l-1 1.5 2.5 3.2 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 b.d. 1.1 b.d. 1.0 1.4 1.3 1.2 2.8 1.9 1.4 Ni µg l-1 5.5 12.0 11.0 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Pb µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.6 b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.1 b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 9.2 8.7 b.d. b.d. Sn µg l-1 b.d. b.d. b.d. 0.7 b.d. 0.5 b.d. b.d. 1.3 b.d. Ti µg l-1 1.9 2.1 2.1 3.4 3.5 2.9 3.5 3.9 3.2 4.2 U µg l-1 b.d. b.d. b.d. 5.2 6.4 14.5 13.0 12.2 5.4 1.9 V µg l-1 b.d. b.d. b.d. 3.3 b.d. b.d. b.d. 0.8 b.d. 1.2 Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 30 b.d.

A-4 Appendix 2. Complete hydrochemical data groundwaters

App. 2 (followed)

Sample LMP 08 LMP 09 LMP 10 LMP 11 LMP 12 LMP 13 LMP 14 LMP 15 LMP 16 LMP 17 Depth mbs 108 95 100 148 85.1 80 50 30 82.2 150 Field parameters Temp °C 11.1 10.6 11.4 12.2 11.6 11.0 10.9 11.2 10.7 11.4 Eh mV 171 117 161 167 170 63 -25 -12 -232 172 -1 O2 mg l 1.44 0.28 1.56 3.30 3.20 2.30 0.30 0.50 0.36 4.48 SEC µS cm-1 806.0 702.0 992.0 785.0 804.0 783.0 875.0 806.0 685.0 676.0 pH 7.47 7.41 7.18 7.11 7.16 7.11 6.52 6.92 7.59 7.11 Laboratory parameters Ca mg l-1 86.9 88.5 154.0 89.3 107.0 110.0 105.0 113.0 83.0 101.0 Mg mg l-1 31.9 24.1 33.7 19.1 22.4 32.4 31.8 29.9 40.9 20.0 Na mg l-1 47.9 33.7 16.5 55.2 27.6 12.5 25.1 13.0 16.4 17.6 K mg l-1 2.7 1.8 2.1 1.7 3.1 2.3 2.8 2.3 2.1 1.4 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 439 347 804 700 603 180 184 285 602 587 Ba µg l-1 103 115 120 275 278 b.d. 56 121 518 367 Li µg l-1 150.0 85.2 55.8 108.0 72.3 11.8 20.7 18.2 49.9 53.4 Rb µg l-1 5.6 5.2 4.4 1.6 3.1 2.2 4.6 2.4 2.7 2.0

Cl mg l-1 28.0 31.0 53.0 41.0 58.0 48.0 60.0 44.0 5.4 24.0 -1 HCO3 mg l 376.4 300.7 448.4 404.4 344.7 276.3 266.6 283.7 480.7 359.9 -1 SO4 mg l 93.0 110.0 100.0 31.0 41.0 92.0 180.0 130.0 1.7 35.0 -1 NO3 mg l 10.0 0.4 24.0 12.0 29.0 42.0 b.d. b.d. b.d. 22.0 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 220 140 180 120 99 67 99 88 80 120 Br µg l-1 50 70 90 70 80 80 130 80 30 40 -1 CO2 mg l 14.5 15.0 28.6 19.8 18.0 18.9 83.2 25.5 7.5 19.4 -1 SiO2 mg l 18.1 22.2 15.2 16.7 21.7 13.5 18.7 13.4 21.7 21.1

Al µg l-1 b.d. b.d. b.d. b.d. b.d. 10.2 22.8 b.d. 9.9 b.d. -1 Fetotal µg l b.d b.d b.d b.d b.d 130 17,200 2,340 2,280 b.d As µg l-1 3.9 5.5 0.6 3.1 16.7 b.d. 74.9 12.1 10.4 9.1 Cd µg l-1 b.d. b.d. b.d. b.d. b.d. 0.7 b.d. b.d. b.d. b.d. Cr µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 2.4 b.d. b.d. b.d. Co µg l-1 b.d. b.d. b.d. b.d. b.d. 0.5 28.8 5.0 b.d. b.d. Cu µg l-1 b.d. b.d. 2.6 1.9 2.3 2.8 2.7 b.d. 1.8 1.6 Ni µg l-1 b.d. b.d. 3.6 b.d. b.d. 1.6 48.2 7.3 b.d. b.d. Pb µg l-1 b.d. b.d. b.d. b.d. b.d. 0.9 11.6 3.2 b.d. b.d. Sn µg l-1 b.d. b.d. b.d. 0.8 0.8 b.d. b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. 9.0 b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. 0.6 b.d. 1.6 b.d. 0.7 b.d. b.d. Ti µg l-1 2.6 3.3 2.2 2.8 3.4 2.2 4.7 2.4 4.2 3.1 U µg l-1 5.4 2.4 12.1 13.9 8.8 6.7 1.0 1.6 1.4 2.8 V µg l-1 b.d. 0.5 b.d. 2.3 1.9 b.d. 3.5 b.d. b.d. 0.6 Zn µg l-1 b.d. b.d. b.d. b.d. b.d. 232 1,950 409 b.d. b.d.

A-5 PhD Thesis Florian Ludwig 2011

App. 2 (followed)

Sample LMP 18 LMP 19 LMP 20 LMP 21 LMP 22 LMP 23 LMP 24 W_01 S_02 W_03 Depth mbs 53.5 100 62.25 47 44 45.8 46 74.5 72 Field parameters Temp °C 10.8 10.9 10.2 10.7 13.2 12.9 11.8 10.6 8.0 11.2 Eh mV 185 205 91 204 -152 -195 167 335 342 275 -1 O2 mg l 6.16 4.59 1.10 5.10 0.20 0.20 2.81 9.00 10.80 8.00 SEC µS cm-1 702.0 657.0 475.0 664.0 816.0 512.0 747.0 57.0 93.9 196.6 pH 7.34 7.31 6.77 7.10 7.27 7.64 6.78 6.02 4.53 6.53 Laboratory parameters Ca mg l-1 108.0 96.7 74.2 111.0 68.1 49.1 109.0 5.7 5.8 29.0 Mg mg l-1 19.7 22.8 8.4 12.9 27.6 33.7 23.7 0.8 2.4 4.3 Na mg l-1 10.0 9.3 13.6 11.4 69.2 5.5 13.8 1.6 1.8 2.7 K mg l-1 1.1 1.3 1.7 1.9 9.7 4.4 3.1 2.2 2.4 1.6 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 2.9 b.d. Sr µg l-1 266 545 162 272 1640 731 292 44 57 83 Ba µg l-1 540 294 124 643 1020 b.d. 654 116 91 60 Li µg l-1 28.3 34.1 24.5 20.9 477.0 25.2 23.3 b.d. b.d. b.d. Rb µg l-1 1.3 1.7 6.0 3.7 8.2 7.8 3.1 6.1 3.9 4.5

Cl mg l-1 63.0 24.0 12.0 33.0 32.0 23.0 53.0 4.2 3.0 6.3 -1 HCO3 mg l 294.6 335.5 170.2 295.2 472.8 251.9 332.5 12.2 b.d. 97.6 -1 SO4 mg l 32.0 29.0 83.0 46.0 14.0 34.0 28.0 2.7 22.0 2.9 -1 NO3 mg l 28.0 24.0 2.8 21.0 1.2 b.d. 19.0 6.6 11.0 8.6 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 150 130 76 110 75 99 69 b.d. 63 40 Br µg l-1 40 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. -1 CO2 mg l 14.1 18.9 27.3 21.1 20.9 7.5 20.7 11.0 36.5 -1 SiO2 mg l 17.3 21.4 24.0 30.1 18.0 42.9 14.9 10.3 7.0 11.9

Al µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 853.0 b.d. -1 Fetotal µg l b.d b.d 111 b.d 46 186 b.d b.d b.d b.d As µg l-1 3.5 1.5 3.4 24.8 9.1 2.9 3.5 b.d. b.d. b.d. Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.3 b.d. Cr µg l-1 b.d. b.d. b.d. 8.0 b.d. b.d. b.d. b.d. b.d. b.d. Co µg l-1 b.d. b.d. 0.6 b.d. b.d. b.d. b.d. b.d. 2.0 b.d. Cu µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.5 Ni µg l-1 b.d. 1.0 3.2 b.d. b.d. b.d. b.d. b.d. 4.7 b.d. Pb µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 0.5 b.d. b.d. b.d. Sn µg l-1 b.d. b.d. 0.6 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. 1.0 b.d. b.d. 0.6 b.d. 0.8 1.3 b.d. 0.9 Ti µg l-1 2.6 3.0 2.0 2.9 1.7 3.6 1.7 b.d. b.d. 1.0 U µg l-1 3.4 3.2 6.2 1.4 61.1 b.d. 2.8 b.d. b.d. b.d. V µg l-1 1.6 0.8 1.4 8.9 b.d. b.d. 4.3 b.d. b.d. b.d. Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 55 b.d. b.d. b.d.

A-6 Appendix 2. Complete hydrochemical data groundwaters

App. 2 (followed)

Sample W_05 S_06 S_07 S_09 S_10 W_12 S_17 W_18 W_19 S_20 S_23 S_25 Depth mbs 120 48 120 16 Field parameters Temp °C 11.7 9.2 10.6 8.7 8.7 11.3 8.7 11.2 9.5 8.7 9.1 8.5 Eh mV 323 354 371 280 327 285 265 321 316 309 270 298 -1 O2 mg l 8.40 9.20 12.10 9.80 10.30 11.60 10.30 9.50 9.70 10.40 10.30 10.30 SEC µS cm-1 130.1 46.4 103.5 77.8 81.2 56.6 67.7 77.4 107.1 99.7 158.5 71.0 pH 6.34 5.76 4.51 5.80 4.98 6.83 5.77 6.01 5.13 5.71 6.49 5.89 Laboratory parameters Ca mg l-1 19.0 3.9 6.6 5.2 4.9 6.4 4.4 9.6 8.5 8.1 16.5 5.4 Mg mg l-1 2.6 0.9 2.6 2.3 2.1 0.9 2.0 1.6 2.6 2.5 3.6 1.7 Na mg l-1 2.7 1.5 2.8 2.1 2.1 1.6 2.2 1.9 3.3 2.8 5.4 1.8 K mg l-1 1.6 1.4 2.7 1.6 1.7 1.5 1.6 1.6 2.6 2.5 2.0 2.1 Be µg l-1 b.d. b.d. 2.4 1.1 1.1 b.d. b.d. b.d. 1.4 1.3 b.d. b.d. Sr µg l-1 73 44 67 49 62 51 47 51 56 53 63 37 Ba µg l-1 57 b.d. 78 64 66 b.d. 77 b.d. 71 56 b.d. 76 Li µg l-1 b.d. b.d. b.d. 1.1 b.d. b.d. b.d. 3.0 1.4 1.4 1.7 b.d. Rb µg l-1 4.5 2.5 4.3 2.5 2.3 2.6 2.2 4.5 2.7 2.0 1.3 3.0

Cl mg l-1 5.5 2.9 4.6 3.6 4.0 2.8 2.8 4.1 6.6 4.5 7.2 3.2 -1 HCO3 mg l 58.0 6.7 b.d. b.d. b.d. 15.3 b.d. 27.5 b.d. b.d. 20.7 b.d. -1 SO4 mg l 1.3 4.9 28.0 18.0 22.0 5.1 14.0 1.8 25.0 27.0 35.0 17.0 -1 NO3 mg l 8.5 5.5 6.3 7.5 5.5 3.4 7.9 6.8 5.0 4.9 9.7 6.6 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 32 b.d. 55 69 84 b.d. 30 29 56 53 48 35 Br µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. -1 CO2 mg l 33.2 23.3 10.6 17.6 15.0 7.0 13.6 24.2 26.8 14.1 18.5 15.0 -1 SiO2 mg l 12.9 8.4 7.2 7.3 7.0 9.6 7.3 12.9 9.5 10.0 13.8 6.9

Al µg l-1 b.d. 28.5 533.0 259.0 485.0 b.d. 68.0 b.d. 60.7 63.4 7.2 91.9 -1 Fetotal µg l b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d As µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Co µg l-1 b.d. b.d. 1.7 2.2 2.5 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 b.d. b.d. 1.0 b.d. b.d. b.d. b.d. b.d. 1.4 b.d. b.d. b.d. Ni µg l-1 b.d. 1.6 7.3 5.3 5.0 b.d. 5.0 b.d. 5.8 4.0 2.0 3.1 Pb µg l-1 b.d. b.d. 1.4 b.d. b.d. b.d. b.d. b.d. 0.9 b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 0.8 1.3 1.9 b.d. b.d. 1.6 b.d. 0.5 0.7 b.d. b.d. b.d. Ti µg l-1 b.d. b.d. b.d. b.d. b.d. 1.0 b.d. 1.1 b.d. b.d. 1.0 b.d. U µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. V µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Zn µg l-1 b.d. b.d. 33 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

A-7 PhD Thesis Florian Ludwig 2011

App. 2 (followed)

Sample S_27 S_28 W_30 W_31 S_32 S_34 W_35 W_39 W_40 LHD 02 LHD 03 Depth mbs 150 200 70.3 136.5 107 202 220 Field parameters Temp °C 7.8 8.2 11.1 11.8 8.1 8.5 9.5 10.9 11.5 12.5 16.5 Eh mV 414 279 292 276 267 267 239 310 242 191 -3 -1 O2 mg l 10.60 9.80 8.91 8.21 10.19 10.78 10.49 8.59 10.12 8.30 0.40 SEC µS cm-1 68.7 91.5 51.2 73.1 109.2 57.5 93.4 54.6 136.4 131.5 364.0 pH 5.06 6.63 5.83 6.17 4.69 5.54 6.87 5.85 6.31 6.57 6.34 Laboratory parameters Ca mg l-1 5.4 8.2 5.8 9.8 4.8 4.4 9.5 5.9 19.2 10.8 33.8 Mg mg l-1 1.6 2.7 0.8 1.3 2.3 1.3 2.8 0.9 2.5 6.6 12.1 Na mg l-1 1.4 1.9 1.6 2.0 6.5 1.8 1.6 1.9 3.1 4.6 6.4 K mg l-1 1.8 2.1 1.5 1.4 2.3 1.6 1.8 1.6 1.4 1.5 8.6 Be µg l-1 b.d. b.d. b.d. b.d. 3.5 b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 67 41 29 39 41 33 38 29 600 29 259 Ba µg l-1 76 52 b.d. b.d. 79 53 97 b.d. 121 b.d. b.d. Li µg l-1 b.d. b.d. 1.2 1.2 b.d. b.d. b.d. 1.2 b.d. 3.7 50.8 Rb µg l-1 2.3 3.5 4.7 4.0 3.6 2.6 1.7 3.7 4.4 1.1 16.2

Cl mg l-1 2.3 3.6 2.9 2.9 11.0 3.1 2.7 4.0 5.1 3.4 4.6 -1 HCO3 mg l b.d. 11.0 18.3 32.3 b.d. b.d. 15.6 15.9 61.6 73.8 122.6 -1 SO4 mg l 18.0 19.0 0.5 1.3 22.0 11.0 19.0 1.1 4.9 1.4 74.0 -1 NO3 mg l 6.6 9.0 4.4 2.8 5.2 8.8 5.2 6.0 3.4 3.2 b.d. -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 37 38 21 28 79 52 50 22 31 80 60 Br µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 20 -1 CO2 mg l 14.5 11.9 n/a n/a n/a n/a n/a n/a n/a 22.0 67.3 -1 SiO2 mg l 5.7 6.7 12.9 13.4 6.5 7.5 6.0 11.9 13.2 22.9 12.6

Al µg l-1 183.0 56.4 b.d. b.d. 878.0 190.0 b.d. b.d. b.d. b.d. b.d. -1 Fetotal µg l b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d 13,200 As µg l-1 b.d. 1.0 b.d. b.d. b.d. b.d. 0.9 b.d. b.d. 0.9 2.3 Cd µg l-1 b.d. b.d. b.d. b.d. 0.3 b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.5 2.2 Co µg l-1 b.d. b.d. b.d. b.d. 2.6 0.9 b.d. b.d. b.d. b.d. 2.0 Cu µg l-1 b.d. b.d. b.d. 1.4 b.d. 1.1 b.d. 2.6 b.d. b.d. b.d. Ni µg l-1 3.0 1.5 b.d. b.d. 8.4 4.1 b.d. b.d. b.d. b.d. 8.9 Pb µg l-1 b.d. b.d. b.d. b.d. b.d. 0.8 b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. 1.4 b.d. b.d. b.d. b.d. b.d. Ti µg l-1 b.d. b.d. 1.5 1.4 b.d. 1.1 b.d. 1.1 1.4 2.4 2.3 U µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. V µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.8 b.d. Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 12 10

A-8 Appendix 2. Complete hydrochemical data groundwaters

App. 2 (followed)

Sample LHD 04 LHD 11 LHD 20 LHD 21 LHD 22 LHD 23 LHD 24 LHD 25 LHD 26 LHD 27 Depth mbs 200 160 240 150 221 98 270 125 112 222 Field parameters Temp °C 15.5 11.4 14.6 13.5 14.2 13.7 18.5 11.0 10.7 15.4 Eh mV 93 52 195 -197 179 -2 275 209 199 226 -1 O2 mg l 0.40 0.70 2.10 0.70 2.40 3.90 6.60 8.80 6.20 1.80 SEC µS cm-1 355.0 712.0 547.0 540.0 596.0 371.0 357.0 228.0 212.0 249.0 pH 6.50 6.99 7.36 7.51 7.46 8.73 7.95 6.57 6.48 6.39 Laboratory parameters Ca mg l-1 39.2 92.4 47.5 45.5 49.9 26.2 30.0 27.7 23.3 26.2 Mg mg l-1 15.4 24.2 29.8 33.6 31.9 22.0 18.6 8.2 8.2 10.5 Na mg l-1 9.3 28.2 29.5 19.1 30.7 19.1 16.9 4.8 6.8 7.2 K mg l-1 5.6 3.6 3.7 4.3 4.0 1.5 1.3 1.7 1.8 3.7 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 287 645 600 669 664 407 479 126 150 184 Ba µg l-1 110 137 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Li µg l-1 11.7 22.2 24.5 23.4 25.2 21.6 10.5 1.9 3.2 5.2 Rb µg l-1 8.0 7.0 5.3 3.8 4.9 2.2 1.9 1.3 3.6 11.6

Cl mg l-1 5.3 48.0 12.0 9.4 17.0 14.0 10.0 8.3 11.0 3.9 -1 HCO3 mg l 197.0 281.8 296.5 312.9 294.6 170.8 159.2 119.0 94.6 142.1 -1 SO4 mg l 21.0 90.0 41.0 32.0 58.0 39.0 41.0 5.8 11.0 9.7 -1 NO3 mg l b.d. b.d. 0.3 b.d. 0.8 0.3 2.2 4.2 8.2 0.9 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 130 100 180 240 170 80 100 120 100 70 Br µg l-1 30 40 30 30 20 20 20 30 40 20 -1 CO2 mg l 40.0 26.8 9.7 6.6 8.4 b.d. b.d. 26.0 29.0 39.6 -1 SiO2 mg l 29.7 11.9 14.5 14.9 15.7 16.4 23.3 23.3 29.7 12.2

Al µg l-1 15.4b.d.12.5b.d.17.0b.d.11.819.3b.d.b.d. -1 Fetotal µg l 542 1,150 b.d 926 b.d 17 b.d b.d b.d b.d As µg l-1 3.6 5.5 b.d. 4.2 b.d. 1.7 3.0 b.d. 0.6 b.d. Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 3.7 3.9 2.6 2.6 3.7 b.d. 1.9 1.6 b.d. 2.5 Co µg l-1 0.7 4.6 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.1 1.0 1.3 Ni µg l-1 3.0 7.8 b.d. b.d. b.d. b.d. b.d. b.d. 1.4 1.3 Pb µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. 0.6 b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 1.0 b.d. b.d. b.d. Ti µg l-1 3.4 1.6 1.7 1.6 1.8 1.4 2.3 2.8 3.0 1.4 U µg l-1 b.d. 8.9 6.6 b.d. 5.6 2.4 3.7 b.d. b.d. b.d. V µg l-1 b.d. b.d. b.d. b.d. b.d. 0.6 3.3 0.8 1.7 0.6 Zn µg l-1 b.d. b.d. b.d. b.d. 14 b.d. b.d. b.d. b.d. 12

A-9 PhD Thesis Florian Ludwig 2011

App. 2 (followed)

Sample LHD 28 LHD 29 LHD 30 LHD 31 S1 W2 S3 S4 S5 S6 S9 S10 Depth mbs 169 200.19 160 210 200 Field parameters Temp °C 12.2 11.9 12.2 12.1 6.1 11.8 7.4 8.1 6.9 7.3 8.2 7.2 Eh mV 117 80 83 9 218 197 264 268 204 301 191 234 -1 O2 mg l 1.90 5.60 1.20 0.50 5.50 4.27 6.39 6.83 5.55 5.35 5.51 5.80 SEC µS cm-1 575.0 607.0 688.0 574.0 76.3 107.7 68.1 136.2 93.2 127.9 132.0 118.1 pH 7.08 7.12 7.09 7.02 7.06 9.72 6.86 6.81 7.21 7.52 8.21 7.83 Laboratory parameters Ca mg l-1 59.2 64.0 69.6 68.3 5.1 3.6 5.1 7.1 8.4 9.7 7.4 8.2 Mg mg l-1 25.1 28.5 29.3 24.6 2.9 b.d. 3.1 5.2 3.0 3.4 4.8 5.3 Na mg l-1 22.6 23.8 22.4 18.1 2.6 21.6 2.9 3.6 4.5 4.8 4.2 5.6 K mg l-1 3.5 3.5 3.7 3.7 0.6 0.3 0.7 0.8 0.7 0.7 0.8 1.2 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 621 727 726 554 89 29 36 70 76 77 76 66 Ba µg l-1 101 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Li µg l-1 19.6 22.5 24.7 22.8 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Rb µg l-1 5.0 4.8 4.7 6.5 2.7 1.8 1.9 2.3 2.8 2.2 2.8 3.2

Cl mg l-1 24.0 27.0 27.0 27.0 1.7 1.0 1.2 8.5 2.1 2.1 1.9 3.0 -1 HCO3 mg l 273.9 286.7 309.3 273.3 16.5 66.5 30.5 30.5 31.1 39.7 39.0 38.4 -1 SO4 mg l 46.0 48.0 60.0 49.0 9.1 4.9 7.1 8.2 11.0 10.0 12.0 15.0 -1 NO3 mg l 2.8 6.2 4.0 b.d. 10.0 1.5 2.4 5.7 9.2 9.1 5.8 10.0 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 130 130 140 140 b.d. b.d. b.d. b.d. b.d. b.d. 80 70 Br µg l-1 50 30 30 30 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. -1 CO2 mg l 16.3 15.0 17.6 26.0 b.d. b.d. b.d. b.d. 6.2 7.9 b.d. b.d. -1 SiO2 mg l 14.8 15.2 14.5 15.0 10.2 12.7 15.8 14.3 16.3 17.7 19.9 19.9

Al µg l-1 b.d. b.d. b.d. 43.4 33.1 18.2 4.7 8.8 6.7 b.d. b.d. b.d. -1 Fetotal µg l b.d 13 20 949 b.d b.d b.d b.d b.d b.d b.d b.d As µg l-1 1.8 1.6 2.1 1.9 b.d. 0.5 b.d. b.d. b.d. b.d. b.d. b.d. Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 3.4 4.4 3.5 3.4 1.8 1.7 b.d. b.d. b.d. b.d. 1.6 b.d. Co µg l-1 1.6 b.d. b.d. 2.2 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 b.d. b.d. b.d. b.d. b.d. 1.1 b.d. b.d. b.d. b.d. b.d. b.d. Ni µg l-1 1.9 1.7 1.9 3.9 1.0 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Pb µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 0.6 b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Se µg l-1 6.8 10.2 5.4 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. 2.1 b.d. b.d. b.d. b.d. b.d. b.d. Ti µg l-1 1.5 1.6 1.5 2.0 2.2 1.5 2.1 1.9 2.1 2.2 2.8 2.6 U µg l-1 7.6 8.6 7.6 7.5 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. V µg l-1 b.d. b.d. b.d. b.d. b.d. 10.2 1.3 0.5 1.4 1.8 0.9 0.7 Zn µg l-1 b.d. b.d. b.d. 11 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

A-10 Appendix 2. Complete hydrochemical data groundwaters

App. 2 (followed)

Sample S11 S13 S14 S15 S16 S17 S18 S19 VB 04 VB 11 VB 14 VB 16 VB 25 Depth mbs 140 130 103.1 Field parameters Temp °C 7.9 8.5 7.4 7.8 8.3 7.4 6.6 7.3 11.8 9.3 8.3 12.1 12.9 Eh mV 241 182 165 177 217 195 181 316 186 242 230 252 285 -1 O2 mg l 6.14 5.56 5.42 5.28 4.50 4.90 5.10 6.60 7.53 5.48 8.71 6.87 6.08 SEC µS cm-1 118.9 217.0 168.1 176.6 151.5 166.2 98.8 69.3 205.0 137.2 128.5 169.9 405.0 pH 7.62 7.62 8.21 7.75 7.86 8.46 7.95 6.58 8.03 7.63 8.10 8.10 8.15 Laboratory parameters Ca mg l-1 8.8 17.9 13.1 12.9 12.7 13.5 9.3 4.4 16.8 10.4 9.3 15.7 38.5 Mg mg l-1 5.0 9.4 6.7 6.7 8.6 9.2 4.0 3.2 11.2 7.3 7.5 7.5 23.8 Na mg l-1 5.6 3.9 2.9 2.9 3.3 4.7 2.8 3.7 6.3 3.7 3.2 4.9 11.6 K mg l-1 1.3 0.8 0.7 0.7 0.8 1.0 0.5 0.5 1.1 0.6 1.0 1.0 1.4 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 67 160 138 126 119 141 43 47 133 92 60 70 246 Ba µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Li µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Rb µg l-1 4.3 1.5 1.2 1.2 1.7 3.2 1.8 2.2 3.5 3.2 1.8 1.8 2.9

Cl mg l-1 2.8 17.0 2.5 2.4 3.5 3.2 1.7 4.3 5.5 2.9 5.2 4.3 19.0 -1 HCO3 mg l 37.2 67.1 70.2 69.5 67.1 72.6 43.9 27.5 105.5 56.7 60.4 91.5 201.9 -1 SO4 mg l 16.0 8.0 6.5 6.4 16.0 14.0 8.5 4.9 4.6 3.4 2.0 3.9 15.0 -1 NO3 mg l 11.0 8.7 4.4 4.5 6.1 14.0 6.0 2.3 9.5 16.0 10.0 5.7 13.0 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 70 80 90 90 19 80 b.d. b.d. 86 130 86 b.d. 110 Br µg l-1 b.d. b.d. b.d. b.d. b.d. 30 b.d. b.d. b.d. b.d. b.d. b.d. b.d. -1 CO2 mg l b.d. 9.2 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. -1 SiO2 mg l 19.0 22.6 20.2 19.9 23.4 24.1 18.2 17.2 28.7 30.1 26.7 22.4 27.9

Al µg l-1 3.3 26.8 6.8 12.4 25.6 b.d. 6.8 11.3 b.d. 31.9 17.9 3.1 31.4 -1 Fetotal µg l b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d b.d As µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 1.7 2.4 2.7 2.8 2.3 4.6 b.d. 2.0 3.8 2.6 5.8 4.5 4.0 Co µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 b.d. b.d. b.d. b.d. 1.0 b.d. b.d. b.d. b.d. 4.5 b.d. b.d. b.d. Ni µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Pb µg l-1 0.7 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.5 b.d. b.d. b.d. b.d. b.d. Ti µg l-1 2.7 5.6 3.7 4.0 4.7 3.4 3.1 2.5 1.7 3.4 1.4 1.4 2.2 U µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. V µg l-1 0.9 3.1 3.7 3.6 5.9 3.1 2.8 1.7 6.9 3.1 3.3 7.1 5.5 Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

A-11 PhD Thesis Florian Ludwig 2011

App. 2 (followed)

Sample VB 32 VB 34 VB 35 VB 37 VB 39 VB 40 VB 41 VB 50 VB 52 VB 55 URG 03 Depth mbs 208.2 67.5 62 35 40 69 129.8 24.4 Field parameters Temp °C 11.4 11.1 11.1 9.9 11.9 12.0 11.9 9.8 12.0 8.3 11.4 Eh mV 251 263 179 213 -79 -101 217 198 159 313 -74 -1 O2 mg l 6.06 7.28 6.68 7.38 1.60 0.83 1.99 6.53 6.34 5.13 0.10 SEC µS cm-1 215.0 200.0 160.5 493.0 738.0 788.0 733.0 190.9 134.2 86.6 1022.0 pH 8.25 8.14 8.35 8.28 7.59 7.65 7.36 8.19 7.61 7.13 6.90 Laboratory parameters Ca mg l-1 19.1 13.8 14.2 50.5 68.5 64.9 70.2 16.5 10.7 6.6 177.0 Mg mg l-1 12.3 10.1 10.4 29.5 44.1 49.1 43.9 11.3 6.9 5.0 21.8 Na mg l-1 5.2 4.3 4.4 10.1 11.9 20.7 15.6 4.3 2.3 1.8 16.3 K mg l-1 0.8 0.8 0.9 1.6 2.7 15.6 4.3 0.5 0.5 0.7 2.7 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 147 98 96 76 181 536 843 656 126 81 462 Ba µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. 124 b.d. b.d. b.d. 254 Li µg l-1 b.d. b.d. b.d. b.d. 3.4 16.4 33.4 15.1 b.d. b.d. 12.3 Rb µg l-1 2.2 2.0 1.9 3.2 1.9 4.3 19.9 7.5 2.9 2.0 6.4

Cl mg l-1 6.4 3.2 3.1 13.0 50.0 27.0 35.0 4.8 3.6 2.7 42.0 -1 HCO3 mg l 109.8 87.8 90.9 194.6 372.1 461.2 355.0 106.8 46.4 34.8 472.1 -1 SO4 mg l 4.8 3.0 2.9 64.0 27.0 29.0 64.0 3.2 6.0 5.3 110.0 -1 NO3 mg l 10.0 5.6 5.6 8.2 13.0 b.d. b.d. 6.5 3.8 17.0 b.d. -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 b.d. b.d. 110 80 140 230 520 140 b.d. b.d. 170 Br µg l-1 b.d. b.d. b.d. b.d. 50 60 b.d. 50 b.d. b.d. b.d. -1 CO2 mg l b.d. b.d. b.d. 11.9 7.5 8.8 14.1 b.d. b.d. 12.8 49.3 -1 SiO2 mg l 25.5 27.0 27.6 48.8 31.1 31.1 38.6 28.7 22.3 14.8 11.6

Al µg l-1 9.7 b.d. b.d. b.d. b.d. 18.7 b.d. 14.0 3.7 83.2 b.d. -1 Fetotal µg l b.d b.d b.d b.d 769 490 b.d b.d b.d 45 3,240 As µg l-1 b.d. b.d. b.d. 1.0 b.d. 2.9 b.d. b.d. b.d. b.d. 10.6 Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 3.3 5.7 5.7 1.7 2.7 3.4 2.6 2.8 2.8 2.3 b.d. Co µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 1.3 b.d. b.d. b.d. b.d. b.d. b.d. 1.6 b.d. b.d. b.d. Ni µg l-1 b.d. b.d. b.d. 1.2 1.1 3.3 2.8 b.d. b.d. b.d. b.d. Pb µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.8 Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 1.1 b.d. 2.8 b.d. b.d. 0.5 b.d. 1.3 b.d. b.d. 1.2 Ti µg l-1 1.7 1.6 1.9 5.6 2.8 2.7 3.0 2.8 1.7 1.3 1.6 U µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 4.7 V µg l-1 5.1 6.1 6.2 0.8 5.8 b.d. b.d. 1.2 6.5 2.8 b.d. Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 63

A-12 Appendix 2. Complete hydrochemical data groundwaters

App. 2 (followed)

Sample URG 04 URG 05 URG 10 URG 14 URG 27 URG 28 URG 33 URG 34 URG 35 URG 36 Depth mbs 80 67 27 56 71.6 18 28.9 13 12 10.9 Field parameters Temp °C 12.1 11.6 10.4 12.3 12.7 11.1 10.7 10.5 10.4 12.2 Eh mV -60 -120 -223 -121 -186 -176 -160 -270 -220 -70 -1 O2 mg l 0.20 0.20 0.14 0.15 0.10 0.11 0.29 0.14 0.17 0.14 SEC µS cm-1 975.0 1018.0 555.0 689.0 509.0 780.0 586.0 712.0 646.0 1134.0 pH 7.03 6.95 7.43 7.19 7.17 7.22 7.49 7.32 7.56 7.18 Laboratory parameters Ca mg l-1 159.0 169.0 110.0 112.0 91.0 151.0 107.0 115.0 117.0 216.0 Mg mg l-1 23.8 22.5 7.4 18.3 11.2 13.0 9.4 10.5 6.3 18.8 Na mg l-1 20.2 18.0 6.8 18.6 7.1 15.3 12.9 19.3 16.1 18.4 K mg l-1 3.8 3.1 1.1 2.9 1.5 1.8 1.0 13.6 1.7 2.7 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sr µg l-1 552 483 291 322 266 348 238 349 284 654 Ba µg l-1 261 253 138 173 197 337 140 88 139 155 Li µg l-1 30.4 19.6 2.8 7.3 4.2 2.7 3.0 b.d. 1.8 6.2 Rb µg l-1 5.4 5.9 b.d 3.7 b.d b.d b.d 3.5 0.7 0.7

Cl mg l-1 40.0 43.0 6.7 21.0 4.6 32.0 19.0 36.0 35.0 44.0 -1 HCO3 mg l 467.9 474.0 281.8 359.9 334.3 359.9 247.1 298.9 237.3 320.3 -1 SO4 mg l 84.0 110.0 63.0 55.0 4.5 100.0 94.0 75.0 97.0 310.0 -1 NO3 mg l 5.9 b.d. 0.7 0.2 2.2 b.d. b.d. 2.3 1.7 1.2 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. F µg l-1 120 170 49 110 110 41 31 82 67 44 Br µg l-1 b.d. b.d. b.d. 50 b.d. 60 b.d. 70 70 60 -1 CO2 mg l 40.0 34.8 11.4 15.8 14.5 17.6 7.0 12.8 8.8 17.6 -1 SiO2 mg l 14.5 12.7 14.3 19.2 23.1 10.5 11.1 4.2 13.0 16.9

Al µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. -1 Fetotal µg l 2,020 2,880 2,050 3,850 2,260 3,880 842 712 3,490 3,300 As µg l-1 5.5 8.3 2.5 10.2 0.7 1.2 0.8 3.2 20.9 0.5 Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cr µg l-1 b.d. b.d. b.d. 1.7 1.8 b.d. b.d. 1.7 b.d. b.d. Co µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Cu µg l-1 b.d. b.d. 1.4 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Ni µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.6 b.d. b.d. Pb µg l-1 b.d. b.d. 2.4 b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 0.7 0.6 b.d. b.d. 0.6 0.6 b.d. b.d. b.d. b.d. Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. Sn µg l-1 0.5 b.d. b.d. b.d. b.d. 0.6 0.6 b.d. b.d. 0.5 Ti µg l-1 1.3 1.4 1.8 2.9 3.0 1.2 1.4 1.4 1.7 2.1 U µg l-1 2.8 3.9 0.7 b.d. b.d. b.d. 1.3 3.1 b.d. 0.5 V µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.5 b.d. b.d. Zn µg l-1 b.d. 38 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d.

A-13 PhD Thesis Florian Ludwig 2011

App. 2 (followed)

Sample URG 38 URG 40 URG 42 URG 51 URG 55 URG 59 URG 60 URG 63 URG 64 detection Depth mbs11.670102475986661.554limit Field parameters Temp °C 11.3 11.7 11.5 10.2 18.8 11.6 11.0 12.0 12.7 Eh mV -120 -192 -141 -97 -195 -104 -132 -110 -70 -1 O2 mg l 0.14 0.28 0.11 0.24 0.13 0.13 0.18 0.10 0.10 SEC µS cm-1 1189.0 370.0 854.0 475.0 793.0 693.0 568.0 816.0 433.0 pH 7.05 7.42 7.18 7.50 7.17 7.24 7.45 7.12 7.67 Laboratory parameters Ca mg l-1 208.0 67.0 129.0 76.4 135.0 116.0 100.0 143.0 74.1 Mg mg l-1 36.9 5.2 21.2 8.9 14.7 12.7 9.1 16.1 11.5 0.1 Na mg l-1 13.6 4.4 29.3 11.1 20.1 19.5 11.0 13.7 7.3 K mg l-1 2.3 1.4 1.4 1.3 10.9 2.1 1.3 2.0 0.9 Be µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.0 Sr µg l-1 604 128 549 205 346 317 254 340 200 30 Ba µg l-1 63 66 208 199 215 209 90 183 b.d. 50 Li µg l-1 8.9 1.9 4.6 2.8 6.7 13.3 2.1 5.9 4.4 1.0 Rb µg l-1 b.d b.d 0.8 b.d 0.9 1.5 b.d 0.7 0.8 0.5

Cl mg l-1 41.0 8.3 49.0 18.0 39.0 28.0 24.0 18.0 5.9 -1 HCO3 mg l 452.6 209.8 360.5 176.3 310.5 347.1 239.1 453.2 266.6 6.0 -1 SO4 mg l 260.0 15.0 89.0 82.0 120.0 45.0 80.0 40.0 7.3 -1 NO3 mg l b.d. b.d. 0.6 b.d. b.d. b.d. b.d. b.d. b.d. 0.0 -1 HPO4 mg l b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.07 F µg l-1 32 120 63 87 110 150 100 140 180 20 Br µg l-1 50 30 80 40 70 70 50 b.d. b.d. 20 -1 CO2 mg l 27.3 5.7 22.9 5.7 15.4 17.6 7.0 n/a n/a 4.4 -1 SiO2 mg l 11.3 16.1 11.7 17.5 15.7 20.8 16.1 21.2 22.8

Al µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 3.0 -1 Fetotal µg l 2,360 814 7,580 960 2,530 3,700 1,310 9,880 360 10 As µg l-1 3.7 3.1 11.2 1.7 5.1 2.0 3.1 7.3 12.7 0.5 Cd µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.1 Cr µg l-1 1.9 b.d. b.d. b.d. 1.6 b.d. b.d. b.d. b.d. 1.5 Co µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.5 Cu µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.0 Ni µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 1.0 Pb µg l-1 b.d. b.d. 0.6 b.d. b.d. b.d. b.d. b.d. b.d. 0.5 Sn µg l-1 b.d. b.d. b.d. b.d. b.d. 0.6 b.d. b.d. b.d. 0.5 Se µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 5.0 Sn µg l-1 b.d. b.d. 0.9 0.5 0.7 b.d. b.d. b.d. 0.6 0.5 Ti µg l-1 1.3 2.3 3.6 2.3 2.2 3.0 2.1 3.7 2.0 1.0 U µg l-1 86.2 b.d. b.d. b.d. 0.7 b.d. 0.9 b.d. 1.3 0.5 V µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. 0.8 b.d. 0.5 Zn µg l-1 b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. b.d. 10

A-14 Appendix 3. Complete rock data

App. 3 Complete rock data

detection Bunter sandstone, Odenwald Volcanic rocks, High Rhön - - 136 35236399 - 5 - 35236399 - - 136 - - 17 28 131 157 121 112 261 5 162118 - 13 772 39 38 24 10 58 50 35 57 196 89 78 218 57 4 238 16 1282 570 1287 361 424 140 907 - 90 9 1033 5 12 47 108 6 141 189 78 88 124 71 266 127486 32 85 185 492 174 461 336 1211 525 1019 292 696 272 694 1766 52 0.13 0.01 0.15 0.12 3.44 4.23 3.47 2.66 9.85 1.060.010.16 0.150.05 0.00 0.01 2.39 0.02 0.04 0.4 3.53 0.06 0.04 11.47 0.61 0.07 0.22 12.14 5.86 8.37 0.29 13.29 3.73 9.27 0.23 13.50 14.42 11.39 0.21 2.32 7.73 12.08 0.42 0.21 0.47 0.175.91 0.03 0.56 0.27 8.92 0.270.04 12.59 2.570.78 16.19 0.02 2.67 0.20 15.46 0.08 11.03 2.55 2.17 0.10 14.13 3.62 3.30 0.83 21.38 0.22 1.60 1.28 2.96 0.94 0.42 0.69 2.02 0.03 3.72 3.19 0.21 3.03 3.48 2.28 1.82 0.89 0.57 5.20 87.74 98.11 82.16 75.63 46.92 45.96 41.34 42.65 56.50 98.47 99.12 97.49 96.44 98.15 96.86 99.54 97.84 96.60 #5, LB #6, MB cleft#1 cleft#2 aoB TrB oNe hoB Ph limit tot 3 3 5 2 2 O O O 2 2 O O 2 2 2 TiO K Sample weight% SiO MnO MgO CaO Na Al Fe Sum ppm V Zn Rb Sr LOI Cr Ni Cu Zr Ba Melt digestion: sample 1 g + 4 g Spectromelt® powder P

A-15 PhD Thesis Florian Ludwig 2011

App. 3 (followed)

detection Bunter sandstone, Odenwald Volcanic rocks, High Rhön 3 298 28 45 15 3 17 25 2 1212 54 24 21 4 8117730 27 34 24 374 91410752 231113 98 0 44 16 64 126 29 19 5 90 29 46 71 68 467 - 16 31 - - 14 - - 61 77 - 834 5 451 556 737 639 816 149 857 953 - 100 200 26 71068 8 8 209164 232 116 786425 244 128 1223 369 1206 102 10 862 90 982 229 44 <5 <5<5<5 796230 32 24 59 48 1 102114 8523 27 115 74 314 84 1268 471 117 1007 268 726 66 248 722 247 1631 56 213 93 71 - 512 103 - 10 <100 <100 298 221 205 - - 100 #5, LB #6, MB cleft#1 cleft#2 aoB TrB oNe hoB Ph limit Sample ppm Sc V Cu Zn Rb Sr Zr Nb Ba Hf Ta U Cl F S digestion:Powder 4 g sample + 1 g paraffin powder Cr Ni Ga Y Pb Th Co

A-16 Appendix 4. Complete data leaching experiments

App. 4 Complete data leaching experiments

5.6-16 mm cleft#1 cleft#2 Ph Ph Ph Ph Ph 2 #6, MB CO 2:5 1:5 40 µm #6, MB 2 Bunter sandstone, Odenwald Volcanic rocks, High Rhön #5, LB CO 78 266 88 218 271 91 16 24 29 32 38 7.23 7.76 6.54 7.29 4.53 4.63 7.10 0.120.17 7.102.52 5.48 7.50 6.20 2.37 15.40 2.58 4.22 10.60 2.75 2.66 10.22 0.80 2.62 6.92 1.03 0.10 1.91 1.24 0.16 0.65 1.34 0.20 1.58 1.64 0.21 1.87 0.27 2.20 2.85 5.44 3.960.410.13 9.10 0.050.87 0.228.20 8.82 0.07 0.71 0.08 26.10 75.40 0.19 0.22 19.70 10.30 0.10 0.10 0.34 11.70 0.19 13.20 3.73 4.88 4.97 0.08 0.53 1.26 1.52 2.74 6.17 0.16 12.20 48.21 8.54 31.80 105.00 18.50 25.70 6.63 3.87 1.80 2.45 2.69 2.86 3.11 20.20 21.80 6.86 8.88 8.84 2.40 1.54 30 min 30 min 30 min 30 min 30 min 30 min 2 h 24 h 48 h 72 h 192 h 0.020.02 ------0.03 - 0.03 0.03 0.64 - 0.05 0.02 - 0.03 - 0.03 0.03 - - 0.02 limit #5, LB 3 -1 2 3 4 leaching grain size grain solid/liquid t pH SEC mg l mg SO sample detection Ca Mg Na K Al HCO Fe Cl Br NO SiO F

A-17 PhD Thesis Florian Ludwig 2011

App. 4 (followed)

1:3 5.6-16 mm 7.86 7.01 6.11 6.88 7.26 7.17 0.770.250.05 0.31 0.19 0.07 36.61 9.15 1:3 5.6-16 mm Volcanic rocks, High Rhön Volcanic rocks, High Rhön 6779 10131516 5 162737695 2 h20 h48 h72 h192 h2 h20 h48 h72 h192 h h192 h72 h48 h20 h2 h192 h72 h48 h20 2 0.33 1.26 1.58 1.92 2.93 1.18 4.59 7.25 8.56 11.44 0.080.02 0.500.33 0.19 1.130.58 0.90 0.44 1.77 1.32 1.38 0.71 4.04 1.87 1.63 1.67 0.20 2.22 2.61 0.02 0.29 3.22 0.36 0.09 0.44 0.42 0.66 0.14 0.56 0.72 0.86 0.19 0.51 0.88 0.96 0.16 0.96 1.04 0.91 0.020.02 0.02 0.03 0.03 0.03 0.03 0.02 0.03 0.03 0.03 0.04 - 0.06 0.10 - 0.12 - 0.28 0.03 0.24 0.03 detection 3 -1 2 3 4 leaching sample size grain solid/liquid limitt TrB TrB TrB TrB TrB aoB aoB aoB aoB aoB pH SEC l mg Al HCO Ca Mg Na K Fe SiO SO Cl F Br NO

A-18 Appendix 4. Complete data leaching experiments

App. 4 (followed)

5.6-16 mm 0.160.200.00 0.13 0.51 0.00 40.27 18.92 1:3 1:3 5.6-16 mm Volcanic rocks, High Rhön Volcanic rocks, High Rhön 7.38 7.38 7.42 7.48 7.59 7.54 7.55 4 11 16 18 23 27 29 8 12 16 17 26 2 h h 20 48 h 72 h 144 h 216 h 240 h 307 h 20 h h 48 72 h 96 h 132 h 192 h 0.170.00 0.450.55 0.08 0.760.44 1.10 0.15 0.98 1.01 1.50 0.19 1.36 1.32 1.58 0.28 1.48 1.44 1.95 0.38 1.86 1.66 1.86 0.49 1.93 2.01 2.01 0.50 0.21 2.10 1.98 0.10 0.38 2.10 0.84 0.20 0.50 0.58 1.22 0.28 0.64 0.81 1.49 0.36 1.13 0.93 1.69 0.67 1.09 1.02 2.36 0.65 1.41 2.24 1.33 1.09 4.71 7.20 8.79 12.01 13.54 15.83 16.33 2.21 5.42 3.88 5.94 10.05 9.74 0.020.02 - 0.06 0.08 - 0.13 - 0.15 0.02 0.30 0.05 0.43 0.11 0.78 0.22 1.39 0.24 0.08 0.05 0.07 0.06 0.09 0.07 0.15 0.06 0.23 0.16 0.31 0.16 detection 3 -1 2 3 4 leaching pH SEC l mg sample size grain solid/liquid limitt hoB hoB hoB hoB hoB hoB hoB hoB oNe oNe oNe oNe oNe oNe Ca SiO Mg Na K Fe Al HCO SO Cl F Br NO

A-19

Appendix 5. Analytical specimen images

App. 5: Analytical specimen images

Lower Bunter sandstone, Lower Miltenberg formation, Miltenberg sandstone Sample: #3 Location: Quarry Schmelzer, Sensbachtal

Outcrop of Lower Bunter, exposed Macroscopic view, reflected light fissure plane Thin section, plane-polarised light

Fissure, partly filled with fine- Thin section, cross-polarised light grained mineral assemblage

A-21 PhD Thesis Florian Ludwig 2011

App. 5: (followed)

Lower Bunter sandstone, Upper Miltenberg formation, Miltenberg alternating sequence Sample: #5 Location: Quarry Hintenlang, Grasellenbach

Outcrop of Lower Bunter, view rectangular to Macroscopic view, reflected light fissure plane

Thin section, plane-polarised light Thin section, cross-polarised light

A-22 Appendix 5. Analytical specimen images

App. 5: (followed)

Middle Bunter sandstone, Volpriehausen formation, Volpriehausen sandstone Sample: #6 Location: Quarry Zell-Langenbrombach

Outcrop of Middle Bunter, view rectangular to Macroscopic view, reflected light cleavage

Thin section, plane-polarised light Thin section, cross-polarised light

A-23 PhD Thesis Florian Ludwig 2011

App. 5: (followed)

Upper Oligocene, hornblende basalt Sample: hoB Location: Mt. Wasserkuppe, north-western slope

Hornblende basalt, specimen, reflected light Thin section, plane-polarised light

Lower Miocene, trachy basalt Sample: TrB Location: Mt. Wasserkuppe, south-western slope

Trachy basalt, specimen, reflected light Thin section, plane-polarised light

Epoxy compound, direct light, pyrrhotite Epoxy compound, direct light, pyrrhotite indicated by red arrow indicated by red arrow A-24 Appendix 5. Analytical specimen images

App. 5: (followed)

Lower Miocene, alkali olivine basalt Sample: aoB Location: Mt. Wasserkuppe, western slope

Alkali olivine basalt, specimen, reflected light Epoxy compound, direct light, pyrrhotite indicated by red arrow

Thin section, plane-polarised light Thin section, plane-polarised light

Lower Miocene, phonolite Sample: Ph Location: Mt. Stellberg, northwest of Mt. Wasserkuppe

Phonolite, specimen, reflected light Thin section, plane-polarised light

A-25 PhD Thesis Florian Ludwig 2011

App. 5: (followed)

Lower Miocene, olivine nephelinite Sample: oNe Location: Mt. Wasserkuppe, western slope

Phonolite, specimen, reflected light Thin section, plane-polarised light

Epoxy compound, direct light, pyrrhotite indicated by red arrow

A-26

Publications

Ludwig F, Stober I, Bucher K (2011) Hydrochemical Groundwater Evolution in the Bunter Sandstone Sequence of the Odenwald Mountain Range, Germany: A Laboratory and Field Study. Aquat Geochem, 17, pp 165-193

Ludwig F, Berthold G, Kämmerer D, Leßmann B (2007) Ermittlung geogener Hintergrundwerte von Spurenstoffen in hessischen Grundwässern. – HLUG Jahresbericht 2006, pp 27-33

Peer-review Ludwig F, Stober I, Bucher K (2011) Hydrochemical Groundwater Evolution and Mineral Alteration Reactions in the Basaltic Rock Sequence of Mt. Wasserkuppe, Germany - A Case Study. Aquat Geochem (forthcoming)

Abstracts and Presentations Ludwig F, Berthold G (2009) Urangehalte in hessischen Grund- und Rohwässern. – Landesbetrieb Landwirtschaft Hessen – Hydrogeologie und Grundwasserbeschaffenheit unter besonderer Berücksichtigung von Spurenelementen, 16.09.2009, Rauischoldshausen (oral presentation)

Ludwig F (2009) Uran in hessischen Grund- und Rohwässern. – DVGW – Uran und Radioaktivitätsparameter im Roh- und Grundwasser, 12.05.2009, Mainz (oral presentation)

Ludwig F, Berthold G, Kämmerer D, Leßmann B (2008) Uran, Arsen und Co. - Spurenstoffe in hessischen Grundwässern. – FH-DGG-Tagung 2008, Göttingen (abstract, oral presentation)

Ludwig F, Stober I, Bucher K (2007) Genesis of low-mineralised groundwater in a fissured sandstone aquifer, Odenwald, Germany – Where has all the sulfate gone? – Goldschmidt Conference Cologne, Geochim. Cosmochim. Acta, Vol. 71, 15S, p. A600, St. Louis (abstract, poster presentation)

Ludwig F, Stober I, Bucher K (2006) Regionale Variation der Grundwasserbeschaffenheit in Hessen und ihre geogenen Ursachen. - FH-DGG-Tagung 2006, Cottbus (oral presentation)

Ludwig F, Berthold G, Kämmerer D, Leßmann B (2006) Ermittlung geogener Hintergrundwerte von Spurenstoffen in hessischen Grundwässern. - FH-DGG-Tagung 2006, Cottbus (poster presentation)

Curriculum Vitae

Name Florian Ludwig Date of birth 23 August 1975 Place of birth Einbeck, Germany Nationality German

Professional Experience

Since August 2009 Consultant for applied hydrogeology at Wasser und Boden Hydrogeological Consultants, Boppard-Buchholz, Germany August 2004 to June 2009 Freelance hydrogeologist at the Hessian Agency for the Environment and Geology, Wiesbaden, Germany May 2004 to July 2004 Fixed-term consultant at ARCADIS Engineering Consultants Agency, Karlsruhe, Germany November 2000 to March 2004 Student assistant at GTC Geophysical and Hydraulic Engineering, Karlsruhe, Germany June 2000 to September 2000 Internship at Erdbaulabor Geotechnical Consultants, Göttingen, Germany November 1996 to May 1998 Student assistant at GGU Geophysical Investigations, Karlsruhe, Germany

Education

Since July 2005 External PhD student at the Institute of Geoscience, University of Freiburg, Germany PhD Thesis: Regional variation of chemical groundwater composition in Hessen, Germany, and its relation to the aquifer geology (supervising tutor: Prof. Dr. Kurt Bucher) October 1996 to February 2004 Diploma in Geology at the Institute of Applied Geology, University of Karlsruhe, Germany Diploma Thesis: Tectonic and Karst groundwater drainage at Hirschberg-Gopfberg mountain range, Community of Schnepfau, Vorarlberg, Austria (in German; supervising tutor: Prof. Dr. Heinz Hötzl) September 1999 to June 2000 Applied Engineering Geology and Applied Hydrogeology, University of Wales, Cardiff, United Kingdom August 1988 to May 1995 Abitur at Roswitha-Gymnasium, Bad Gandersheim, Germany