Metal release in shallow aquifers impacted by deep CO2 fluxes

Available online at www.sciencedirect.com Available online at www.sciencedirect.com

ScienceDirect  ScienceDirect 

Energy Procedia 00 (2018) 000–000 Available online www.sciencedirect.com Available online atatwww.sciencedirect.com Energy Procedia 00 (2018) 000–000

ScienceDirect ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Energy Procedia Procedia 00 146(2017) (2018)000–000 38–46 Energy www.elsevier.com/locate/procedia

International Carbon Conference 2018, ICC 2018, 10–14 September 2018, Reykjavik, Iceland International Carbon Conference 2018, ICC 2018, 10–14 September 2018, Reykjavik, Iceland

Metal release in shallow aquifers impacted by deep CO2 fluxes Metal release in shallow aquifers impacted by deep CO2 fluxes

Thea 15th International b District Heating and Cooling Marco Agnelli , Fidel Grandiaa,* , Symposium David Soleron , Alvaro Sáinz-Garcíaaa, David Brusibb, a,* b Marco Agnellia, Fidel Grandia , David Soler , Alvaro Sáinz-García , David Brusi , b Manel Zamoranobb, Anna Menció b Assessing the feasibility of using the heat demand-outdoor Manel Zamorano , Anna Menció a

Amphos21 Consulting S.L., Passeig de Garcia-Fària 49, Barcelona 08019, Spain

Amphos21 Consulting Garcia-Fària 49,Aurèlia Barcelona 08019,69, Spain GEOCAMB, Dept. Ciències Ambientals, Universitat dedeGirona, C/ Maria Capmany Girona 17003, Spain temperature function forS.L., a Passeig long-term district heat demand forecast b b

a

GEOCAMB, Dept. Ciències Ambientals, Universitat de Girona, C/ Maria Aurèlia Capmany 69, Girona 17003, Spain

I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc

Abstract a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France from underground formations- IMT on shallow water resources is a concerning aspect in CO2 capture The impact ofcDépartement CO2 leakageSystèmes Énergétiquesstorage et Environnement Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France The impact of CO2 risk leakage from underground storage formations shallow waterCO resources a concerning in interact CO2 capture and storage (CCS) assessment. In Campo de Calatrava region on (Spain), natural from the Earth’saspect mantle with 2 fluxes is fromresultant the Earth’s mantle interactacidic with and storage (CCS)resulting risk assessment. In Campo de Calatrava region (Spain), natural properties. CO2 fluxes The shallow aquifers, in significant changes in their physical and chemical water is slightly -4 molꞏL shallow aquifers, resulting in enriched significant physical and-1)chemical The resultant slightly acidic and otherproperties. metals usually found atwater traceisconcentrations. (pH 5.9-6.4), oxidizing, and in changes iron (upintotheir 6.1×10 -4 molꞏL-1) and other metals usually found at trace concentrations. (pH 5.9-6.4), oxidizing, and reveal enriched iron (upFe(III) to 6.1×10 Thermodynamic calculations thatinaqueous carbonate complexes play an important role in the persistence of this high Abstract Thermodynamic calculations reveal that aqueous Fe(III) carbonate complexes play an important role in the persistence of this high concentration of iron and trace metals in solution. concentration of iron and trace metals in solution. District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the Copyright © gas 2018emissions Elsevier Ltd. All rights reserved. greenhouse fromAll therights building sector. These systems require high investments which are returned through the heat Copyright © 2018 Elsevier Ltd. reserved. Copyright © to 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the the publication committee policies, of the the International International Carbon Conference 2018.decrease, sales. Due the changed climate conditions andpublication building renovation heat demand in the future could Selection and peer-review under responsibility of committee of Carbon Conference 2018. Selection andthe peer-review of the publication committee of the International Carbon Conference 2018. prolonging investmentunder returnresponsibility period. Keywords: Leakage; Electrical resistivityof tomography The mainCCS; scope of this Metal papertransport; is to assess the feasibility using the heat demand – outdoor temperature function for heat demand Keywords: Metal transport;located Electrical tomography was used as a case study. The district is consisted of 665 forecast. CCS; The Leakage; district of Alvalade, in resistivity Lisbon (Portugal), buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district 1.renovation Introduction scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were 1.compared Introduction with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is storage considered, the margin of erroriscould be the acceptable for some of applications The impact of CO from underground on shallow aquifers one of main concerns Carbon 2 leakage The impact of CO leakage from storage oninshallow aquifers is one of the main concerns of Carbon (the error in annual demand was lowerunderground than 20% all weather scenarios considered). However, after introducing renovation 2(CCS) dissolution water would promote chemical interactions with both Capture and Storage projects since CO2for scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). dissolution in water would promote chemical interactions with both Capture and Storage (CCS) projects since CO 2 water and host rock. Among these reactions, metal release and mobilization can jeopardize the quality of an aquifer The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the water and host rock. Among these reactions, metal release and mobilization can jeopardize the quality of an aquifer preventing its further use as water resource. Dissolution of the host rock minerals may lead, also, to alteration in the decrease in its thefurther numberuse of heating hours of 22-139h during the heating season (depending onlead, the combination of weather and preventing as water resource. Dissolution of the host rock minerals may also, to alteration in the hydrodynamics of the aquifer. renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the hydrodynamics of the aquifer. Underscenarios). the conditions usually found incould shallow aquifers, i.e. elevated redox and circumneutral pH, the mobility and of coupled The values suggested be used to modify the function parameters for the scenarios considered, Under the conditions usually found in shallow aquifers, i.e. elevated redox and Fe(III) circumneutral pH, the mobility of most trace metals is very low since their solubility is controlled by sorption onto oxi-hydroxides. In case of improve the accuracy of heat demand estimations.

most trace metals is very low since their solubility is controlled by sorption onto Fe(III) oxi-hydroxides. In case of © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +34 935830500. * Corresponding Tel.: +34 935830500. E-mail address:author. [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]

1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the International Carbon Conference 2018. Selection and peer-review under responsibility the publication Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the publication committee of the International Carbon Conference 2018. 10.1016/j.egypro.2018.07.006

2

Marco Agnelli et al. / Energy Procedia 146 (2018) 38–46 Author name / Energy Procedia 00 (2018) 000–000

39

CO2 leakage, their release and mobility would be initially promoted by the dissolution of the Fe(III) minerals as a response to the pH decrease in the aquifer. However, the buffering effect should prevent long-term conditions of low pH, especially in carbonate-bearing rocks. Recent laboratory experiments and evidence from natural analogues [1, 2, 3, 4, 5, 6] suggests that metal solubilization could be more persistent than previously expected. For example, Grivé et al. showed that Fe(III) solubility in CO2-bearing fluids can significantly increase due to the formation of Fe(III) carbonate complexes that are stable at circumneutral pH and, therefore, more persistent in time and space in geological media [7]. The enhanced solubility of Fe(III) would prevent the formation of Fe (III) oxi-hydroxides, and promote high concentrations of metals usually found as trace and minor amounts in solution. Although laboratory experiments provide a first evidence of metal-CO2-rock interaction, the long-term, aquiferscale conditions can be better observed studying natural systems. In this study, the impact of CO2 fluxes from mantle degassing on a shallow, freshwater aquifer was investigated in the Campo de Calatrava region, in central Spain. The use of natural systems as analogues of processes potentially occurring in man-made activities has been long debated since conditions could be different. In this work, a detailed geological and geophysical investigation at Cañada Real degassing site was performed to ensure that the samples collected were the product of the reaction of CO2 from deep sources with very shallow aquifers. The occurrence of sinkhole features in this site suggested underground dissolution of the carbonate-rich aquifer. To better understand the processes occurring there, an electrical resistivity tomography (ERT) survey was carried out. The objectives were i) to delineate the geometry of the geological formations that host the local shallow aquifer and the bedrock, ii) to determine depth and width of the fault zone that presumably acts as main pathway for the gas release, and iii) to identify geo-electric anomalies related to the presence and dynamics of CO2-rich waters. Finally, from the analysis of the collected samples and the use of thermodynamic calculations of solute speciation in these waters, the role and importance of aqueous Fe(III) carbonate complexes in metal mobility was assessed. 2. CO2 emission from the Campo de Calatrava Volcanic field The Volcanic Field of Campo de Calatrava covers over 5000 km2 in the Tajo-La Mancha Tertiary basin in central Spain. It consists of around 240 volcanic structures related to a Plio-Quaternary strombolian and hydromagmatic activity. This field is thought to be the area with highest natural CO2 emission from underground in the Iberian Peninsula and it has been recently tested to determine the impact of CO2 degassing in ecosystems [8, 9, 10]. The main aquifers in the region are found at shallow depths (less than 50 meters deep), hosted by the Miocene-Pliocene sedimentary cover, which overlie a fractured Paleozoic basement.

Fig. 1. (A) Cold, CO2-rich geyser near Almagro town; (B) Cañada Real site; intense CO2 degassing is observed.

40

Marco Agnelli et al. / Energy Procedia 146 (2018) 38–46 Author name / Energy Procedia 00 (2018) 000–000

3

These waters are commonly fresh and with a neutral pH in absence of deep gases, with conductivities below 500 μSꞏcm-1, and alkalinity around 5×10-3 molꞏL-1. Where impacted by CO2 gas flows, their pH decreases, and their metal content significantly increases (conductivity up to 3910 μSꞏcm-1 and alkalinity up to 4×10-2 molꞏL-1). CO2-rich groundwaters flow out through springs and cold geysers (Fig. 1a) and this causes changes in the biogeochemistry of the surface ecosystems. The Cañada Real site, the largest emission point source of CO2-rich groundwater in the area, is an almost circular pool of 10 m diameter with maximum depth of around 6 m (Fig. 1b). Its present-day shape was previously interpreted to be a sinkhole due to the dissolution and collapse of the Upper Pliocene calcarenitic formation, but no conclusive data from underground existed to confirm it. The pool shows a continuous gas bubbling due to high CO2 flux (>20,000 gꞏm−2ꞏd−1), totaling a daily degassing over 2.5 tons of CO2. 3. Methods Three ERT profiles between 200 and 600 m long (ERT#1 to ERT#3) were carried out at Cañada Real in May 2014 (Fig. 2). Apparent resistivity data acquisition was implemented with a Lund Imaging System (ABEM Instrument AB, Sweden), following the Wenner-Schlumberger array. A sequence of two correlative protocols involving all the possible quadripoles from up to 41 available electrodes connected to the ground at the same time was followed. A first (“long”) batch considered the full transect length at a constant electrode spacing (i.e. 10 m for ERT#1 and ERT#3, 20 m for ERT#2). A second (“short”) batch comprised only the two central multicore cable coils and an electrode separation half of the previous one. Measurements were done once again in the central segment of lines ERT#1 and ERT#2 where the spring and/or the fault zone are present, by overlapping the same array with a reduced electrode spacing of 5 and 2.5 m in ERT#1, and 10 and 5 m in ERT#2, for “long” and “short” configuration, respectively. This design allowed for higher resolution coverage of the most interesting areas of the profiles. Data inversion was performed with Res2DInv package (Geotomo Software, Malaysia). After a pre-processing manual deletion of noisy data points and a preliminary default inversion to discard some records with excessive difference between measured and calculated values, 96-98% of the data remained valid for the analysis. Iterative least squares inversion and finiteelement forward modelling [11] was applied to apparent resistivity pseudo-sections to get the final resistivity sections, giving a bulk root mean square error (RMS) of 7.3 to 9.2%, which reflects an acceptable quality for the models. The maximum investigation depths from the surface ranged between 40 and 91 m. 4. Impacts on shallow aquifer hydrodynamics: Clues from electrical resistivity tomography The ERT survey results provide indications on the subsurface features of shallow aquifers impacted by CO2 flows, and on their hydrodynamics. Three resistivity units may be distinguished with regard to the resistivity distribution along these profiles (Fig. 2a), consistently with the available geological maps covering the area [12]. The uppermost resistive unit defines a roughly continuous level parallel to the surface in all the profiles, with a minimum thickness of 5-7 m and a maximum of 15 m. This unit is attributed to Upper Pliocene calcarenites. The groundwater table is located within this unit at depths mostly ranging between 4.5 and 5.5 m from the surface. Beneath, a second resistive unit is characterized by very low to low resistivity values with some low-medium resistivity patches in its eastern upper zones. It is formed by Upper Pliocene clastic alluvial sediments cropping out in nearby river cuts. In accordance with the low resistivity values, it may be assumed that the unit is saturated with groundwater. The bottom of the geoelectrical sections forms a third, highly resistive unit attributed to the Ordovician quartzite basement. However, this third unit is cut by an area with low-medium resistivity values, which is interpreted to be a fracture zone with WSWENE orientation and up to 50 m wide. This fractured area is consistent with the main fault pattern in the region and would be the conduit for the ascent of CO2 flows in this area. Upward migration of gas would cause a progressive decrease in resistivity of the Neogene sediments as it gradually dissolves into groundwater, increasing its electrical conductivity, and giving rise to very low resistivity areas. The size and distribution of these most conductive lenses probably reflect the stratigraphic position of patches of higher porosity (e.g., sand-gravel lenses with lesser fine content), which represent preferential pathways for the CO2-bearing water to spread across the aquifer.

4

Marco Agnelli et al.Procedia / Energy00 Procedia 146 (2018) 38–46 Author name / Energy (2018) 000–000

41

Fig. 2. (a) Location and model sections of the three electrical resistivity tomography profiles measured at Cañada Real. The sinkhole emitting CO2 is located inside a green grassy rectangular area, surrounded by brown vineyard’s terrain. The inferred cartographic trace of a fault zone is also indicated in the map. Resistivity scale in the sections is divided into four classes only for descriptive clarity. Black dashed lines delineate contacts between resistivity units 1, 2 and 3, whereas dotted lines indicate different resistivity areas within Unit 3. (b) Zoomed view of the resistivity section ERT#1 along the spring zone. Color scheme is adjusted to four discrete resistivity intervals in order to emphasize different features related to the CO2 dynamics: (b1) uses the same scale as in Fig. 2a for a more detailed general view; (b2) highlights very low and low resistivity values in Unit 2; (b3) shows the convex shape defined by the ascending CO2-bearing water plume across Unit 1; and (b4) illustrates horizontal spreading of gas and water in the near-surface.

42

Marconame Agnelli et al. Procedia / Energy Procedia (2018) 38–46 Author / Energy 00 (2018)146 000–000

5

Fig. 3. Interpretative model of CO2 migration on profile ERT#1. CO2 gas ascending across the fractured, fine-grained materials of the main fault zone and other minor faults flows into the water-saturated Neogene sands and gravels, causing dissolution of the carbonate-rich seal formation. Emission into the atmosphere at the bubbling spring may be linked to a stationary upward water-gas plume beneath.

A detailed inspection of the resistivity distribution in the vicinity of the spring zone (X coordinates 20 to 40 m in line ERT#1) reveals distinctive features that can be directly linked to the process of groundwater upward migration and gas release (Fig. 2b). Here, the uppermost calcarenitic unit hosts a negative anomaly that suddenly disrupts the horizontal continuity of prevailing high resistivity values. Below the first 3-4 m from the surface (18-30 Ωꞏm), resistivity rapidly decreases to 4-16 Ωꞏm, depicting a sort of hemispherical convex shape up to about 8-9 m depth. The anomaly extends even deeper inside the underlying detrital sediments, where it becomes a nearly vertical neck-shaped positive anomaly of low-medium values (8-20 Ωꞏm) horizontally surrounded at both sides by two very low resistivity elliptical zones (<4 Ωꞏm). No more distortion of the resistivity isolines is detected below 20-22 m deep, so the Paleozoic basement does not seem to be involved here in the dynamics that causes this particular anomaly. The interpretation of the underground structure from ERT data has been represented in Fig. 3. ERT data suggest that the gas flows in this site are strong enough to modify water flow and create a preferential path upwards causing dissolution in the seal formation, which is carbonate rich. This prolonged reaction has led to the formation of the sinkhole and an area of intense gas outflow to the atmosphere [9]. 5. Water and gas geochemistry 5.1. Major ions and dissolved gases The water and gas chemistry from 12 springs and cold geysers in Campo de Calatrava has been analyzed (Table 1). Spring waters are characterized by a circumneutral pH in the range of 5.9 to 6.4, an electrical conductivity ranging from 1345 µSꞏcm-1 up to 3910 µSꞏcm-1, and Eh values in the range of 167.2 mV to 360.2 mV. Only in one sampling point, Baño Chiquillo, a more reduced Eh value is measured (-52 mV). Temperature at the sampling points is between 16.9 and 27 ºC. Major ion composition is characterised by Mg, Ca, and HCO3, with minor concentrations of Na, Cl, and SO4 (Fig. 4 and Table 1). Dissolved CO2 (mainly as bicarbonate) is the main anion in solution (up to 0.041 molꞏL1 ) (Fig. 4). These data are quite similar to the compositions from the CO2-free aquifers in the region (Table 1, “Pozuelo de Calatrava” sample), although a general increase in solute content is observed when CO2 is present, suggesting some degree of water-gas-rock interaction. Concerning the chemical composition of dissolved gases (Table 2), CO2 is by far the most abundant gas, ranging from 85.77% to 99.92%, followed by N2 and Ar. H2S content was always below the detection limit. These compositions are consistent with those reported in a previous study [13]. The authors suggested that a mantle-sourced signature of these volcanic products is preserved in many CO2-rich gas discharges in the Calatrava Volcanic Province,

6

Marco Agnelli et al. / Energy Procedia 146 (2018) 38–46 Author name / Energy Procedia 00 (2018) 000–000

43

whose carbon and helium isotopic signature is characterized by values between -6.8 and -3.2 ‰ (V-PDB) and up to 2.7 R/Ra, respectively.

Fig. 4. Triangular diagrams showing the chemical composition of the major elements in CO2-bearing water samples, and in non-impacted aquifers in the Campo de Calatrava region. See Tables 1 and 3 for complete chemistry of these waters. Table 1. Chemistry of the CO2-bearing springs sampled in the Campo de Calatrava area. All the concentrations are expressed as molꞏL-1. Eh in mV and electrical conductivity in (µSꞏcm-1). Data from a spring not affected by CO2 flows (“Pozuelo de Calatrava”) are the mean values of the samples collected by Confederación Hidrográfica del Guadiana between 2009 and 2014 [14]. T pH Eh Elec. HCO3FClSO42Ca2+ Mg2+ Na+ K+ Sample (°C) Cond. Chorro Glicerio 2.2×10-5 4.9×10-3 1.9×10-3 5.9×10-3 1.3×10-2 1.0×10-2 1.7×10-3 16.9 6.2 181 3660 0.041 Chorro Villa Elena

18.8

6.1

180

2390

0.026

2.7×10-5

2.2×10-3

6.5×10-4

4.1×10-3

8.3×10-3

4.2×10-3

1.2×10-3

Fontecha 1

18.4

5.9

207

2430

0.016

3.1×10

5.0×10

2.6×10

1.6×10

4.5×10

1.3×10

-2

1.1×10-3

Fontecha 2

22.4

5.9

295

2310

0.017

3.8×10-5

5.3×10-3

2.8×10-3

1.6×10-3

4.6×10-3

1.4×10-2

1.1×10-3

Fontecha 3

21.5

6.2

313

2440

0.017

4.5×10

5.8×10

2.7×10

1.7×10

4.7×10

1.4×10

-2

1.1×10-3

Fontecha 4

27.1

5.9

17

1720

0.014

2.5×10-5

3.1×10-3

1.5×10-3

1.4×10-3

3.5×10-3

8.7×10-3

9.2×10-4

Cañada Real

21.8

6.1

282

3910

0.035

2.5×10

7.9×10

3.2×10

3.8×10

9.6×10

2.0×10

-2

2.1×10-3

Baño Chico

21.6

6.1

360

1600

0.017

3.0×10-5

1.3×10-3

5.8×10-4

1.8×10-3

5.3×10-3

3.4×10-3

7.0×10-4

Baño Chiquillo

25.2

6.4

-53

1714

0.018

4.1×10

1.4×10

6.4×10

3.1×10

4.7×10

3.7×10

-3

8.0×10-4

Codo Jabalon

-5

-5

-5

-5

-3

-3

-3

-3

-3

-3

-3

-4

-3

-3

-3

-3

-3

-3

-3

-3

18.2

5.9

211

1345

0.016

3.2×10-5

3.8×10-3

1.9×10-3

1.7×10-3

4.7×10-3

9.2×10-3

8.2×10-4

Barranco Grande

21

6.1

167

2000

0.017

3.0×10

2.9×10

1.4×10

1.9×10

5.3×10

7.2×10

-3

1.0×10-3

Hervidero Nuevo

21

6.0

213

1626

0.011

3.8×10-5

2.2×10-3

9.6×10-4

1.4×10-3

2.8×10-3

4.8×10-3

6.8×10-4

Pozuelo de Calatrava

n.a.

7.3

n.a.

n.a.

0.003

n.a.

9.9×10

1.5×10

1.1×10

8.4×10

1.2×10

9.5×10-5

-5

-3

-4

-3

-4

-3

-3

-3

-4

-3

5.2. Minor and trace metals All the studied samples are enriched in trace metals compared to CO2-free aquifers (Table 3). Iron is by far the most abundant, ranging from 4.5×10-7 molꞏL-1 to 6.1×10-4 molꞏL-1 (Table 3). Samples also show high concentrations of Mn (up to 8.0×10-5 molꞏL-1), Zn (up to 1.5×10-6 molꞏL-1), Ni (up to 1.2×10-6 molꞏL-1), Co (up to 7.1×10-7 molꞏL-1), Cu (up to 3.3×10-7 molꞏL-1) and As (up to 1.4×10-7 molꞏL-1). The increase of iron and trace metals in solution is neither directly correlated with pH or CO2 pressure. In contrast, a good linear correlation between Ni, Zn and Co concentrations is observed, suggesting a similar geochemical behavior and source for all of them (Fig. 5).

Marco Agnelli et al. / Energy Procedia 146 (2018) 38–46 Author name / Energy Procedia 00 (2018) 000–000

44

Table 2. Chemical composition of the dissolved gases in the studied samples. CO2 (%) N2 (%) Ar (%) Sample

7

O2 (%)

Chorro Glicerio

91.16

8.23

0.20

0.40

Chorro Villa Elena

88.35

11.25

0.16

0.30

Fontecha 1

92.00

7.66

0.17

0.16

Fontecha 2

91.40

8.50

0.01

0.01

Fontecha 3

80.40

18.66

0.18

0.66

Fontecha 4

83.22

15.89

0.14

0.68

Cañada Real

99.53

0.42

0.01

0.01

Baño Chico

82.30

16.92

0.14

0.40

Baño Chiquillo

93.30

6.20

0.05

0.28

Barranco Grande

85.77

13.41

0.32

0.48

Hervidero Nuevo

88.50

11.12

0.23

0.14

Table 3. Minor and trace metal concentration (in molꞏL-1) in the studied water samples. “Pozuelo de Calatrava” sample is representative of non-impacted aquifers. Fe Mn Zn Cr Ni Co Cu Sample Chorro Glicerio

1.3×10-4

8.0×10-5

1.5×10-6

7.8×10-8

1.2×10-6

7.1×10-7

<5.0×10-9

Chorro Villa Elena

2.9×10

2.2×10

7.4×10

1.3×10

7.0×10

2.4×10

<5.0×10-9

Fontecha 1

6.1×10-4

1.5×10-5

9.2×10-7

4.0×10-8

9.5×10-7

2.7×10-7

3.2×10-7

Fontecha 2

5.2×10

1.3×10

3.8×10

4.3×10

5.8×10

1.7×10

-7

3.3×10-7

Fontecha 3

1.4×10-6

4.7×10-6

4.0×10-7

4.2×10-8

4.6×10-7

6.3×10-8

3.3×10-7

Fontecha 4

4.7×10

1.8×10

1.2×10

2.1×10

7.8×10

3.4×10

1.5×10-7

Cañada Real

1.6×10-5

7.3×10-6

4.4×10-7

1.0×10-7

2.9×10-7

9.7×10-8

<5.0×10-9

Baño Chico

2.5×10

1.6×10

6.9×10

2.3×10

6.1×10

3.7×10

-7

2.0×10-7

Baño Chiquillo

3.6×10-7

1.1×10-5

5.2×10-7

2.8×10-8

9.7×10-7

2.9×10-7

1.7×10-7

Codo Jabalon

3.9×10

1.1×10

7.4×10

3.9×10

7.3×10

2.2×10

-7

3.2×10-7

Barranco Grande

6.1×10-4

2.6×10-5

1.0×10-6

3.7×10-8

6.3×10-7

3.4×10-7

3.0×10-7

Hervidero Nuevo

3.8×10

1.8×10

3.8×10

3.5×10

8.2×10

3.2×10

2.7×10-7

Pozuelo de Calatrava

<1.0×10-6

-4

-4

-5

-5

-4

-4

-5

-5

-5

-5

-5

-5

<1.0×10-6

-7

-7

-6

-7

-7

-7

<1×10-10

-7

-8

-8

-8

-8

-8

<5×10-10

-7

-7

-7

-7

-7

-7

<1.0×10-9

-7

-7

-7

<1.0×10-9

<1.0×10-9

Fig. 5. Correlation diagram of Ni, Zn and Co concentrations in the CO2-rich waters in Campo de Calatrava.

8

Marco Agnelli et al. / Energy Procedia 146 (2018) 38–46 Author name / Energy Procedia 00 (2018) 000–000

45

6. Discussion The electrical tomography profiles in Cañada Real site revealed that CO2 in the Campo de Calatrava region migrates from deep sources, through faults towards the surface, reaching very shallow aquifers or being directly released to the atmosphere. In the aquifers, the gas dissolves in groundwater decreasing the pH, and dissolving minerals from the host rock. In some cases, such dissolution is able to make the ground unstable and create sinkholes as in the Cañada Real site. This dissolution has also a significant impact on the chemistry of the groundwaters, resulting in high metal content, especially iron. The mobility of iron in low-CO2, surface waters and shallow groundwaters is very limited due to the low solubility of Fe(III) at circumneutral pH and oxidizing conditions. In general, iron concentration under these conditions is lower than 1×10-6 molꞏL-1 due to the equilibrium with Fe(III) oxi-hydroxides. Higher concentrations are commonly observed in acidic environments from oxidative Fe-sulphide dissolution (e.g., acid mine drainage) or in anoxic waters due to the higher solubility of Fe(II). In CO2-rich waters, however, the formation of Fe(III) carbonate complexes can explain their observed enhanced solubility [7] (Fig. 6). Considering these species, thermodynamic calculations using ThermoChimie v9 database predict that Fe in solution is found as FeCO3OH(aq) between 75 to 95% in mol basis in the studied samples from Campo de Calatrava. Other metals found enriched in solution are Zn, Co, Ni and Cu. Unlike iron, whose enhanced concentration is a combination of that released from iron minerals and the formation of soluble Fe (III) aqueous carbonate complexes, the high concentration of trace metals seems to not be greatly influenced by aqueous speciation. Thermodynamic calculations predict that Zn, Co and Ni will be mainly solubilized as free divalent cations and only carbonate aqueous species may be significant for Cu. The sources of these metals are likely to be the Fe (III) oxi-hydroxides, which are dissolved due to the CO2 inflow. These minerals are believed to be the main solubility limiting phases through surface adsorption, and their dissolution leads to the release of all adsorbed ions.

FeCO� OH���� � H� ↔ Fe�� � CO�� �� � H� O �� Fe�CO� ��� � �CO�� �� ������ ↔ Fe �� Fe�CO� ��� � �CO�� �� ������ ↔ Fe

Fe�OH������� � �H� ↔ Fe�� � �H� O

Fe�OH������� � �H � ↔ Fe�� � �H� O FeCO������ ↔ Fe�� � CO�� ��

Campo de Calatrava CO2-rich waters

Fig. 6. pH-Eh diagram of the aqueous speciation of iron considering the pCO2 found in shallow groundwaters in Campo de Calatrava. Main reactions affecting such speciation are shown. Aqueous Fe(III) carbonate complex is predominant in all samples.

7. Conclusions The commonly observed increase in metals, especially iron, in laboratory and field experiments on CO2 injection as well as in natural systems had long been discussed in the risk assessment of underground carbon storage strategies. In particular, very high metal concentrations in shallow, oxidizing aquifers could not be satisfactorily explained without invoking local changes in pH or Eh (e.g., due to occurrence of reduced gases within the CO2 flow) since a change in the iron speciation is necessary to overcome the solubility limit of Fe (III) oxi-hydroxides. In this study, and based on data from previous laboratory experiments [7], the iron concentration in shallow aquifers impacted by CO2

46

Marco Agnelli et al. / Energy Procedia 146 (2018) 38–46 Author name / Energy Procedia 00 (2018) 000–000

9

flows in Campo de Calatrava region has been explained by considering the formation of aqueous Fe (III) carbonate species. The studied waters have circumneutral pH and are oxidizing. This finding is especially relevant when dealing with the environmental impact of CO2 leakage since impacted waters can be more persistent in both time and space because an increase of pH due to water-rock buffering does not have a significant effect. Acknowledgements This research was supported by the Met-Trans and CO2-React Marie Curie Initial Training networks funded by the European Commission. References [1] Kharaka Yousif K., James J. Thordsen, Susan D. Hovorka, H. Seay Nance, David R. Cole, Tommy J. Phelps, and Kevin G. Knauss. “Potential environmental issues of CO2 storage in deep saline aquifers: geochemical results from the Frio-I Brine pilot test, Texas, USA” Applied Geochemistry 24(6) (2009): 1106-1112. [2] Little Mark G., and Robert B. Jackson. “Potential impacts of leakage from deep CO2 geosequestration on overlying freshwater aquifers” Environmental Science and Technology 44 (2010): 9225-9232. [3] Lu Jiemin, Judson W. Partin, Susan D. Hovorka, and Corinne Wong. “Potential risks to freshwater resources as a result of leakage from CO2 geological storage: a batch-reaction experiment” Environmental Earth Science 60 (2010): 335-348. [4] Trautz Robert C., John D. Pugh, Charuleka Varadharajan, Liange Zheng, Marco Bianchi, Peter S. Nico, Nicolas F. Spycher, Dennis L. Newell, Richard A. Esposito, Yuxin Wu, Baptiste Dafflon, Susan S. Hubbard, and Jens T. Birkholzer. “Effect of dissolved CO2 on a shallow groundwater system: a controlled release field experiment” Environmental Science and Technology 47 (2013): 298-305. [5] Lions Julie, Nicolas Devau, Louis de Lary, Sebastien Dupraz, Marc Parmentier, Philippe Gombert, and Marie-Christine Dictor. “Potential impacts of leakage from CO2 geological storage on geochemical processes controlling fresh groundwater quality: A review” International Journal of Greenhouse Gas Control 22 (2014): 165–175. doi: 10.1016/j.ijggc.2013.12.019. [6] Menció Anna, Helena Guasch, David Soler, Arnau Canelles, Manel Zamorano and David Brusi. “Influence of regional hydrogeological systems at a local scale: Analyzing the coupled effects of hydrochemistry and biological activity in a Fe and CO2 rich spring” Science of the Total Environment 569-570 (2016): 700-715, doi: 10.1016/j.scitotenv.2016.06.185. [7] Grivé Mireia, Lara Duro, and Jordi Bruno. “Fe(III) mobilisation by carbonate in low temperature environments: Study of the solubility of ferrihydrite in carbonate media and the formation of Fe(III) carbonate complexes” Applied Geochemistry 49 (2014): 47-57. [8] Elío Javier, Marcelo F. Ortega, Barbara Nisi, Luis F. Mazadiego, Orlando Vaselli, Juan Caballero, and Fidel Grandia. “CO2 and Rn degassing from the natural analog of Campo de Calatrava (Spain): Implications for monitoring of CO2 storage sites” International Journal of Greenhouse Gas Control 32 (2015): 1-14, doi: 10.1016/j.ijggc.2014.10.014. [9] Gasparini Andrea, Alvaro Sainz-García, Fidel Grandia, and Jordi Bruno. “Atmospheric dispersion modelling of a natural CO2 degassing pool from Campo de Calatrava (northeast Spain) natural analogue. Implications for carbon storage risk assessment” International Journal of Greenhouse Gas Control 47 (2016): 38–47. [10] Fernández-Montiel Irena, Anna Pedescoll, and Eloy Bécares. “Microbial communities in a range of carbon dioxide fluxes from a natural volcanic vent in Campo de Calatrava, Spain” International Journal of Greenhouse Gas Control 50 (2016): 70-79. [11] Loke M.H. “Tutorial: 2D and 3D electrical imaging surveys. Geotomo Software” Gelugor, Malaysia (2014), pp. 169. http://www.geotomosoft.com. [12] IGME. “Mapa Geológico de España 1:50,000. Sheets 784 Ciudad Real and 785 Almagro” Instituto Geológico y Minero de España, Madrid (1988). [13] Vaselli Orlando, Barbara Nisi, Franco Tassi, Luciano Giannini, Fidel Grandia, Tom Darrah, Francesco Capecchiacci, and Luis Perez del Villar. “Water and gas geochemistry of the Calatrava Volcanic Province (CVP) hydrothermal system (Ciudad Real, central Spain)” Geophysical Research Abstracts 15 (2013): 11102. [14] Confederación Hidrográfica del Guadiana. https://www.chguadiana.es/cuenca-hidrografica/calidad-y-estado-de-las-masas-de-agua/aguassubterraneas.