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Volume 31 Issue 5
Oct.  2020
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Janete Moran-Ramírez, José Iván Morales-Arredondo, Maria Aurora Armienta-Hernández, José Alfredo Ramos-Leal. Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys. Journal of Earth Science, 2020, 31(5): 1007-1015. doi: 10.1007/s12583-020-1294-x
Citation: Janete Moran-Ramírez, José Iván Morales-Arredondo, Maria Aurora Armienta-Hernández, José Alfredo Ramos-Leal. Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys. Journal of Earth Science, 2020, 31(5): 1007-1015. doi: 10.1007/s12583-020-1294-x

Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys

doi: 10.1007/s12583-020-1294-x
More Information
  • This study was conducted to identify the origin, hydrogeochemical processes and evolution of groundwater in a tectonic valley. This study was carried out with the aim of quantifying the proportions of groundwater flows contributing to the water chemistry abstracted in a zone of convergence favored by the presence of active faults. The study area is located in the Trans-Mexican Volcanic Belt. End members methodology was applied to identify the mixing of hydrothermal with fresh groundwater, where changes in the aquifer geology result in distinct groundwater chemical signatures. Ternary mixing was quantified using conservative elements. Moreover, other evolutionary processes, such as ion exchange and silicate weathering occur due to changes in the geology of the area. In ternary mixing, each of the end members is associated with the lithology through which it circulates. The local flow contributes 70% of the water to the system, the intermediate flow contributes 14%, and the regional flow contributes 16%. Three types of water are produced:Na-HCO3, due to the interaction of water with volcanic rocks of rhyolitic composition, Na-Mg-HCO3, due to the interaction of water with volcanic rocks of basaltic-andesite composition, and Ca-HCO3, due to the interaction of water with sedimentary calcareous rocks.
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  • Alaniz-Álvarez, S. A., Nieto-Samaniego, A., Reyes-Zaragoza, M. A., et al., 2001. Estratigrafía y Deformación Extensional en la Región San Miguel Allende-Querétaro. México. Rev. Mexicana de Ciencias Geológicas, 18(2): 129-148 (in Spanish) http://www.wanfangdata.com.cn/details/detail.do?_type=perio&id=Open J-Gate000000879196
    American Public Health Association, AWWA (American Water Works Association), Water Environment Federation), 2005. Standard Methods for the Examination of Water and Wastewater, Amer. Public Health Assn., 21: 258-259 http://www.researchgate.net/publication/224945621_Standard_Methods_for_the_Examination_of_Water_and_Wastewater
    Aranda-Gómez, J. J., Levresse, G., Acheco Martínez, J., et al., 2013. Active Sinking at the Bottom of the Rincón de Parangueo Maar (Guanajuato, México) and Its Probable Relation with Subsidence Faults at Salamanca and Celaya. Boletín de la Sociedad Geológica Mexicana, 65(1): 169-188. https://doi.org/10.18268/bsgm2013v65n1a13 doi:  10.18268/bsgm2013v65n1a13
    Barbieri, M., Nigro, A., Petitta, M., 2017. Groundwater Mixing in the Discharge Area of San Vittorino Plain (Central Italy): Geochemical Characterization and Implication for Drinking Uses. Environmental Earth Sciences, 76(11): 393. https://doi.org/10.1007/s12665-017-6719-1 doi:  10.1007/s12665-017-6719-1
    Carrera, M. L., Higgins, R. W., Kousky, V. E., 2004. Downstream Weather Impacts Associated with Atmospheric Blocking over the Northeast Pacific. Journal of Climate, 17: 4823-4839. https://doi.org/10.1175/jcli-3237.1 doi:  10.1175/jcli-3237.1
    Carranco-Lozada, S. E., Ramos-Leal, J. A., Noyola-Medrano, C., et al., 2013. Effects of Change of Use of Land on an Aquifer in a Tectonically Active Region. Natural Science, 05(2): 259-267. https://doi.org/10.4236/ns.2013.52a038 doi:  10.4236/ns.2013.52a038
    Carrasco-Núñez, G., Milány, M. C., Verma, S. P., 1989. Geology of the Zamorano Volcano, State of Querétaro. Mexican Journal of Geological Sciences, 8(2): 194-201
    CEAG, 2000. Follow-up of the Hydrogeological Study and Mathematical Model of the Aquifer of the Irapuato Valley-Valle de Santiago-Huanimaro, Gto. Technical Report, State Water Commission of Guanajuato, Guanajuato. 72
    Chae, G. T., Yun, S. T., Kim, K., et al., 2006. Hydrogeochemistry of Sodium-Bicarbonate Type Bedrock Groundwater in the Pocheon Spa Area, South Korea: Water-Rock Interaction and Hydrologic Mixing. Journal of Hydrology, 321(1/2/3/4): 326-343. https://doi.org/10.1016/j.jhydrol.2005.08.006 doi:  10.1016/j.jhydrol.2005.08.006
    Cook, P. G., 2003. A Guide to Regional Groundwater Flow in Fractured Rock Aquifers. CSIRO Land and Water, Glen Osmond. 151
    Douglas, M., Clark, I. D., Raven, K., et al., 2000. Groundwater Mixing Dynamics at a Canadian Shield Mine. Journal of Hydrology, 235(1/2): 88-103. https://doi.org/10.1016/s0022-1694(00)00265-1 doi:  10.1016/s0022-1694(00)00265-1
    Han, D. M., Liang, X., Jin, M. G., et al., 2010. Evaluation of Groundwater Hydrochemical Characteristics and Mixing Behavior in the Daying and Qicun Geothermal Systems, Xinzhou Basin. Journal of Volcanology and Geothermal Research, 189(1/2): 92-104. https://doi.org/10.1016/j.jvolgeores.2009.10.011 doi:  10.1016/j.jvolgeores.2009.10.011
    Huizar-Álvarez, R., Mitre-Salazar L. M., Marín-Córdova, S., et al., 2011. Subsidence in Celaya, Guanajuato, Central Mexico: Implications for Groundwater Extraction and the Neotectonic Regime. Geofísica Internacional, 50(3): 255-270 http://www.scielo.org.mx/scielo.php?script=sci_abstract&pid=S0016-71692011000300001&lng=en&nrm=iso&tlng=en
    Mifflin, M. D., 1968. Delineation of Groundwater Flow Systems in Nevada, Report series H-W., Desert Research Institute Technical, 4: 111
    Morales-Arredondo, J. I., Armienta, M. A., et al., 2018. Estimación de la Exposición a Elevados Contenidos de Fluoruro en Agua Potable en Distintas Comunidades de Guanajuato, México. Tecnología y Ciencias del Agua, 9(3): 156-179. https://doi.org/10.24850/j-tyca-2018-03-07 (in Spanish) doi:  10.24850/j-tyca-2018-03-07(inSpanish)
    Morales-Arredondo, J. I., Esteller-Alberich, M. V., Armienta Hernández, M. A., et al., 2018. Characterizing the Hydrogeochemistry of Two Low-Temperature Thermal Systems in Central Mexico. Journal of Geochemical Exploration, 185: 93-104. https://doi.org/10.1016/j.gexplo.2017.11.006 doi:  10.1016/j.gexplo.2017.11.006
    Morán-Ramírez, J., Ramos-Leal, J. A., 2014. The VISHMOD Methodology with Hydrochemical Modeling in Intermountain (Karstic) Aquifers: Case of the Sierra Madre Oriental, Mexico. Journal of Geography and Geology, 6(2): 132-144. https://doi.org/10.5539/jgg.v6n2p132 doi:  10.5539/jgg.v6n2p132
    Ortega-Gutiérrez, F., Mitre-Salazar, L. M., Roldan, Q. J., et al., 1992. Mapa Geológico de la República Mexicana y Texto Explicativo de la Quinta Edición de la Carta Geológica de la República Mexicana. Esc. 1 : 200 000 UNAM. México
    Pérez-Venzor, J. A., Aranda-Gómez, J. J., McDowell, F., et al., 1996. Geology of the Palo Huérfano Volcano, Guanajuato, Mexico. National Autonomous University of Mexico. Institute of Geology, 13(2): 174-183
    Povară, I., Simion, G., Marin, C., 2008. Thermo-Mineral Waters from the Cerna Valley Basin (Romania). Studia Universitatis Babes-Bolyai, Geologia, 53(2): 41-54. https://doi.org/10.5038/1937-8602.53.2.4 doi:  10.5038/1937-8602.53.2.4
    Ramos-Leal, J. A., Martínez-Ruiz, V. J., Rangel-Mendez, J. R., et al., 2007. Hydrogeological and Mixing Process of Waters in Aquifers in Arid Regions: A Case Study in San Luis Potosi Valley, Mexico. Environmental Geology, 53(2): 325-337. https://doi.org/10.1007/s00254-007-0648-3 doi:  10.1007/s00254-007-0648-3
    Rodríguez, R., Morales-Arredondo, I., Rodríguez, I., 2016. Geological Differentiation of Groundwater Threshold Concentrations of Arsenic, Vanadium and Fluorine in el Bajio Guanajuatense, Mexico. Geofísica Internacional, 55(1): 5-15 http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S0016-71692016000100005
    Trujillo-Candelaria, J. A., 1985. Subsidencia de Terrenos en la Ciudad de Celaya, Gto. Reunión SOBRE ASENTAMIENTOS Regionales: México, DF, Sociedad Mexicana de Suelos, Asociación Geohidrólogica Mexicana, 1-2 (in Spanish)
    Tubau, I., Vázquez-Suñé, E., Jurado, A., et al., 2014. Using EMMA and MIX Analysis to Assess Mixing Ratios and to Identify Hydrochemical Reactions in Groundwater. Science of the Total Environment, 470-471: 1120-1131 doi:  10.1016/j.scitotenv.2013.10.121
    Valentino, G. M., Stanzione, D., 2003. Source Processes of the Thermal Waters from the Phlegraean Fields (Naples, Italy) by Means of the Study of Selected Minor and Trace Elements Distribution. Chemical Geology, 194(4): 245-274. https://doi.org/10.1016/s0009-2541(02)00196-1 doi:  10.1016/s0009-2541(02)00196-1
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Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys

doi: 10.1007/s12583-020-1294-x

Abstract: This study was conducted to identify the origin, hydrogeochemical processes and evolution of groundwater in a tectonic valley. This study was carried out with the aim of quantifying the proportions of groundwater flows contributing to the water chemistry abstracted in a zone of convergence favored by the presence of active faults. The study area is located in the Trans-Mexican Volcanic Belt. End members methodology was applied to identify the mixing of hydrothermal with fresh groundwater, where changes in the aquifer geology result in distinct groundwater chemical signatures. Ternary mixing was quantified using conservative elements. Moreover, other evolutionary processes, such as ion exchange and silicate weathering occur due to changes in the geology of the area. In ternary mixing, each of the end members is associated with the lithology through which it circulates. The local flow contributes 70% of the water to the system, the intermediate flow contributes 14%, and the regional flow contributes 16%. Three types of water are produced:Na-HCO3, due to the interaction of water with volcanic rocks of rhyolitic composition, Na-Mg-HCO3, due to the interaction of water with volcanic rocks of basaltic-andesite composition, and Ca-HCO3, due to the interaction of water with sedimentary calcareous rocks.

Janete Moran-Ramírez, José Iván Morales-Arredondo, Maria Aurora Armienta-Hernández, José Alfredo Ramos-Leal. Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys. Journal of Earth Science, 2020, 31(5): 1007-1015. doi: 10.1007/s12583-020-1294-x
Citation: Janete Moran-Ramírez, José Iván Morales-Arredondo, Maria Aurora Armienta-Hernández, José Alfredo Ramos-Leal. Quantification of the Mixture of Hydrothermal and Fresh Water in Tectonic Valleys. Journal of Earth Science, 2020, 31(5): 1007-1015. doi: 10.1007/s12583-020-1294-x
  • tectonics favor the mixing of recharged groundwater with upwelling hydrothermal fluids that influence the hydrogeochemistry of groundwater (Barbieri et al., 2017). In the Leon Valley, Guanajuato State, Mexico, hydrochemical analysis showed that the abstracted groundwater is the product of a sequential process of binary mixing involving three end members (Ramos-Leal et al., 2007).

    Mix models allow identifying the contribution of distinct groundwater sources to the aquifer of a certain zone. There are different mix models, such as M3 (Multivariate Mixing and Mass balance calculations) that uses principal component analysis code, which approaches the modeling of mixtures and mass balance from a purely geometric perspective (Laaksoharju et al., 1999). The Mix model that involves computing the ratios by which two or more end-members are mixed in a sample. The MIX software, a maximum likelihood method to estimate mixing ratios, allows recognizing the uncertainty in the concentrations of the final members (Tubau et al., 2014; Carrera et al., 2004). In the present work we applied the methodology, of relating the concentrations of conservative elements as proposed by Douglas et al. (2000).

    The investigated area is located in the State of Guanajuato, Mexico, which is recognized worldwide for its industrial, mining, and agricultural activities, where the use of groundwater is of paramount importance (CEAG, 2000). Severe problems associated with water quality and availability have been reported in all the aquifers in this area (Rodríguez et al., 2016). In the townships of Villagran and Juventino Rosas, groundwater is abstracted from two different aquifers. The first is a shallow granular aquifer with an irregular alternation of fine-to-coarse material that, in some areas, is interspersed with fractured basaltic rocks or with ignimbrites at a depth ranging, approximately, from 50 to 150 m, and an average temperature of 24 ℃. The second is a deep aquifer hosted in fractured felsic rocks interspersed with sedimentary strata, located at a depth ranging from 200 to 350 m, and regional flow with temperature ranging from 29 to 50 ℃ (Morales-Arredondo et al., 2018).

    In both municipalities, the shallow aquifer is over-exploited, and the groundwater level has been depleted, generating the accelerated subsidence of the terrain. Currently, wells must be drilled at greater depths to extract the groundwater. Furthermore, recent studies have reported that the deep aquifer has low-temperature geothermal characteristics, with a high content of As and F- (Morales-Arredondo et al., 2018; Rodríguez et al., 2016). Due to over-exploitation, it has been reported that faults act as preferential conduits for the migration of deep geothermal fluids (Morales-Arredondo et al., 2018).

    The present study based on previous publications on this area (Morales-Arredondo et al., 2018) aims to get insight on the physicochemical changes occurring along the groundwater flowpath that is controlled by the geological faults, which is produced by the contact of different geological materials. This manuscript provides hydrogeochemical evidences (by using conservative elements concentration) about the proportions of water mixing from three flow systems resulting on the water types determined in the study area. The mixing model justifies the hydrogeochemical characteristics previously reported in the active tectonic volcano sedimentary environment of Juventino Rosas and Villagrán, central Mexico. The role of active geological faults in the mixing processes between fresh and geothermal water is also discussed. This can be achieved by applying diverse hydrogeochemical methods and considering mixing of end members. Results of this study contribute to improve the understanding of sedimentary volcanic aquifers. In addition, the methodology could be applied to study the hydrogeology and hydrogeochemistry of similar aquifers worldwide. The main objective of this study is the identification of hydrogeochemical processes and mixing that are responsible for the chemical composition of groundwater in a tectonic valley.

  • The municipalities of Juventino Rosas and Villagran are located in the State of Guanajuato, and they belong to the hydrogeological province of Valle de Celaya (Fig. 1). The study area is located between the physiographic regions of the TransMexican Volcanic Belt and Mesa Central (Ortega-Gutierrez et al., 1992). Most of the area contains rocks that vary in age from the Early Cretaceous to the Quaternary. A carbonate sequence from Early Cretaceous of marine origin with a low metamorphic grade (greenschist facies), evidenced by the presence of Muscovite-rich phyllites, slates and mineral paragenesis of albite-chlorite-epidote (Huizar-Álvarez et al., 2011). The Soyatal Formation of the late Cretaceous is composed of interstratified limestones with shales (Carranco-Lozada et al., 2013). An Eocene red polymictic conglomerate of continental origin is observed lying discordantly on Mesozoic rocks (Huizar-Álvarez et al., 2011). In the northern part of the valley, rhyolite and Early Miocene ignimbrites are wide-spread. These rhyolites and ignimbrites are overlaid by Middle Miocene extensional-related basaltic and andesitic rocks (Alaniz-Álvarez et al., 2001). The basement is composed of sedimentary rocks with low-grade metamorphism, with a transmissivity of 1.2×10-4 m2/s (Rodríguez et al., 2016).

    Figure 1.  Location of the Valle de Celaya Aquifer, regional geology of the study area, and sampling points.

  • In the Celaya Valley, an intense agricultural activity is developed, which is supplied by groundwater through extraction wells. The density of wells in 2009 (Carranco-Lozada et al., 2013), reached 1 well/km2. The Celaya aquifer is classified as an over-exploited aquifer, which has resulted in the generation of a big drawdown cone, around which the groundwater mixture occurs in the valley (Fig. 1).

    Two-thousand wells exploit the aquifer; the total extraction of groundwater amounts to 600 Mm3/year (Aranda-Gómez et al., 2013), of which 67% is used in agriculture, 4% in industry, and 23% as the source of drinking water. The depth of the static level ranges between 80 to 100 m, with an average annual depletion ranging between 2.5 and 3.5 m (Huizar-Álvarez et al., 2011). The depth of the wells varies from 100 to 300 m (Huizar-Álvarez et al., 2011).

    The basement shows low hydraulic conductivity. This unit is overlaid by low conductivity sedimentary rocks of marine origin, which act as an aquitard. Pumping tests in this material indicated a transmissivity of 1.2×10-4 m2/s (Huizar-Álvarez et al., 2011).

    Recharge zones are located in the topographically highest and more distant parts of the valley, to the north (Sierra el Patol) and to the south in the Cerro de la Gavia (Carranco-Lozada et al., 2013). In the first case, the recharge water infiltrates through volcanic rocks of rhyolitic composition dominated by minerals, such as quartz, sanidine, oligoclase, traces of biotite, hematite and zircon (Carrasco-Núñez et al., 1988). In the southern zone, the infiltration area is formed by rocks of basalt-andesitic composition presenting as main mineralogy labradorite, andesine, oligoclase, orthopyroxenes, clinopyroxenes and olivine (Carrasco-Núñez et al., 1989). A transmissivity of 106×10-4 m2/s has been reported for rocks of medium-to-mafic composition (Pérez-Venzor, 1996).

    The filling of the valley acts as an aquitard; it is composed of a complex sequence of inter-stratified layers of sand, tuffs, and fine-grained clays (Fig. 2). The northern part of the valley is dominated by felsic volcanic rocks. The southern part of the valley is composed of basic and intermediate rocks. The center of the valley is composed of alternations of lava flows with sands and conglomerates, with thicknesses ranging between 30-130 m of clays, 20-100 m of tuffs, and 30 m of sand, and a lava presence in some areas. In general, the aquitard has a hydraulic conductivity of 1×10-6 m2/s, with a storage coefficient of 0.003 (Huizar-Álvarez et al., 2011).

    Figure 2.  Hydrogeological conceptual model with the northern flowpath (local flow), southwest flowpath (intermediate flow) and thermal flow (regional flow). These flows converge in the big drawdown. It can also be seen that the presence of geological faults facilitate the flow of thermal water.

  • Thirty-two groundwater samples were collected from the Celaya Valley, State of Guanajuato, central Mexico. Sampling and preservation were done following the methodology established in APHA-AWWA (2005). Immediately after being collected, samples for major cations were acidified with nitric acid (HNO3) ACS until a pH < 2. All samples collected in polyethilene bottles were stored at a temperature of 4 ℃. Temperature, pH and conductivity were measured in the field and calibrated to the water temperature at each site. The chemical analyses for the major elements, boron (B) and silicon dioxide (SiO2), were performed at the Analytical Chemistry Laboratory, Institute of Geophysics, National Autonomous University of Mexico (UNAM) (the laboratory participates in international calibration exercises of chemical analyzes of geothermal waters). The presence of B was determined by colorimetry through reactions with carminic acid (Method 4500-BC) APHA-AWWA. The presence of SiO2 was determined by atomic absorption spectrophotometry with flame and ultraviolet-visible (UV-vis) spectroscopy (molybdosilicic acid method). Major ions were analyzed using standard methods (APHA-AWWA, 2005). Volumetry was used to determine HCO3- and CO32-(titrating with HCl) and Ca2+ and Mg2+ (titrating with EDTA). Cl- was analyzed by potentiometry with selective electrodes (4500-Cl-) (APHA-AWWA, 2005), Na+ and K+ were determined by atomic emission spectrophotometry (3500-Na+ and K+), and SO42- was determined by turbidimetry (4500-SO42-). Analytical quality was assessed through ionic balance (less than 8%) and the use of certified (NIST traceable) reference solutions. Measured concentrations are included in the supplementary material (Table 1).

    ID T (℃) pH EC (mS/cm) TDS (ppm) HCO3-(ppm) Cl- (ppm) SO42- (ppm) F- (ppm) Ca2+ (ppm) K+ (ppm) Mg2+ (ppm) Na+ (ppm) Error (%)
    1 8.2 665.0 475.0 231.6 34.3 57.2 2.6 14.1 15.6 1.9 108.5 0.1
    2 23.8 7.7 729.0 520.7 266.4 27.0 78.8 1.6 33.8 19.2 3.3 76.3 -8.0
    3 23.4 7.9 872.0 622.9 303.8 49.5 97.9 1.5 56.2 22.7 1.9 145.2 7.8
    4 21.2 7.2 1414.0 1010.0 607.5 51.6 118.0 0.6 103.5 27.1 16.1 193.3 5.8
    5 25.5 7.6 1116.0 797.1 443.2 68.1 120.0 0.6 59.2 23.5 23.6 152.0 1.8
    6 23.1 7.7 1253.0 895.0 443.2 111.6 104.8 0.5 74.7 25.6 23.6 158.3 2.3
    7 26.0 7.5 1056.0 754.3 435.7 49.6 119.6 0.7 53.4 22.4 21.9 114.7 -4.7
    8 42.2 8.3 621.0 443.6 278.9 25.1 32.8 7.1 4.7 11.0 1.9 131.2 3.3
    9 8.0 688.0 491.4 318.7 33.6 41.9 0.9 25.2 18.0 5.7 86.9 -8.3
    10 42.9 8.4 462.0 330.0 209.1 13.5 28.2 1.7 10.9 9.1 2.4 91.2 5.8
    11 47.8 8.2 426.0 304.3 203.3 11.2 23.1 1.7 10.1 7.3 2.4 83.8 4.6
    12 40.8 7.9 534.0 381.4 244.0 16.8 38.1 1.1 20.4 16.1 4.8 92.4 5.1
    13 29.4 8.1 559.0 399.3 249.0 22.8 46.0 0.9 25.9 11.5 10.0 74.1 -0.4
    14 7.6 753.0 537.9 313.7 29.8 70.0 1.0 36.2 15.3 3.8 123.4 2.8
    15 26.5 7.8 624.0 445.7 268.9 20.8 50.9 1.8 15.7 14.4 2.9 118.8 3.9
    16 36.0 6.8 590.0 421.4 286.3 6.7 26.8 2.9 16.2 3.7 1.5 99.3 -0.8
    17 37.0 7.3 595.0 425.0 280.2 8.4 26.6 1.1 19.1 6.8 6.5 83.5 -0.8
    18 48.0 7.1 648.0 462.9 280.2 6.3 40.3 1.7 18.1 4.8 3.6 84.8 -5.6
    19 38.0 8.0 577.0 412.1 258.5 9.8 29.1 1.8 4.5 1.7 0.6 102.5 -3.5
    20 47.0 7.5 494.0 352.9 257.3 9.4 21.8 3.0 10.8 9.4 2.2 85.2 -2.8
    21 30.0 7.4 576.0 411.4 265.7 9.7 34.0 1.4 16.4 15.9 1.9 87.0 -1.6
    22 42.3 7.3 517.0 369.3 270.6 11.7 22.9 2.8 12.4 10.4 2.2 95.4 -0.3
    23 33.0 7.1 660.0 471.4 275.4 9.0 25.7 2.7 13.8 11.3 2.9 88.0 -2.5
    24 34.5 6.3 459.0 327.9 218.6 3.7 23.1 1.0 28.7 10.8 7.4 37.6 -2.5
    25 34.5 7.3 751.0 536.4 289.9 21.5 38.8 2.2 35.8 8.1 6.1 89.5 1.7
    26 28.0 6.9 629.0 449.3 346.7 2.6 8.6 0.8 44.7 26.0 10.0 49.4 -0.5
    27 32.0 6.7 660.0 471.4 343.0 3.9 12.9 0.6 43.4 11.8 8.4 62.7 -0.9
    28 33.5 6.6 594.0 424.3 294.7 5.2 23.9 2.1 32.4 9.5 7.8 66.7 -0.6
    29 24.0 7.2 646.0 461.4 323.7 17.1 46.4 0.6 37.3 14.2 6.1 76.0 -5.7
    30 34.0 6.4 473.0 337.9 207.8 6.2 32.7 1.0 33.6 11.3 10.4 31.5 -0.7
    31 29.5 6.8 696.0 497.1 352.7 4.4 46.2 0.8 62.9 3.4 21.4 40.0 -0.8
    32 29.0 6.8 955.0 682.1 314.1 26.5 183.0 0.9 118.5 4.5 26.7 22.1 -2.6

    Table 1.  Physicochemical data of the samples of groundwater in Santa Cruz de Juventino Rosas and Villagrán, Guanajuato, Mexico

  • End-members (EM) methodology was used to quantify the mixture in the alluvium region. This method consists of identifying the samples that contain the maximum and minimum concentrations of conservative ions (that do not interact with the solid matrix) in the hydrogeological basin (Morán-Ramírez and Ramos-Leal, 2014; Ramos-Leal et al., 2007).

    The methodology for the qualitative and quantitative analysis of a ternary mixture consists of identifying the three end members that represent the evolution of the aquifer under study. The quantitative representation of each of the samples is delimited by the chemical composition of the end members, which are expressed as fractions. A ternary mixture is analyzed with the calculation of the fractions that are obtained when approaching a system with three equations and three unknowns. The sum of the three mixing fractions according to the volumetric balance equation is obtained using the following equations

    where CW is the total sum of the three mixing fractions of the EM (End-members). CFL is local flow, CFI is intermediate flow and CFR is regional flow concentration.

    where ClW is the total concentration of chlorides. ClFL is the concentration of chlorides local flow, ClFI is the concentration of chlorides intermediate flow and ClFR is the concentration of chlorides regional flow.

    where Fw is the total concentration of fluorides. FFL is the concentration of fluorides local flow, FFI is the total concentration of fluorides intermediate flow and FFR is the concentration of fluorides regional flow.

    Solving CFL and simplifying we obtain

    Solving CFR and simplifying

    The only solution for CFI is when CW=1. The other two components are calculated by replacing CFL and CFR in Eq. 1.

  • Initially the flow was going from northeast to southwest. However, due to the formation of a big drawdown, the southwest flows have been reversed and now they are directed towards the big drawdown in the center of the valley (Trujillo-Candelaria, 1985).

    The presence of faults in the tectonic valley favor thermal flow (regional flow), which mixes with the intermediate flow of the system. It is worth mentioning that in the northern part of the valley, groundwater interacts with sedimentary rocks of calcareous composition (Figs. 1, 2).

    In the aquifer of the Celaya Valley, electrical conductivity ranged between 426 and 1 414 μS/cm, with a mean of 696 μS/cm, this variation indicates that low values are influenced by local recharge and high values have a greater evolution. A mean pH of 7.4 was measured in the study area, with a maximum pH of 8.35 and a minimum pH of 6.3, indicating that the samples are slightly acidic to alkaline. The groundwater temperature ranged from 21.2 to 48 ℃, with an average of 33.2 ℃, showing an above average environmental air temperature.

    The concentration of Na ranged between 22.1 and 193.3 mg/L, with an average of 92.2 mg/L. Sodium was the dominant cation, followed by Ca2+, Mg2+, and K+; the presence of Na+ results from the interaction of water with volcanic rocks of Na+ rich rhyolitic composition; although, the lowest value is found in the sample that interacts with limestone rocks.

    The concentrations of Ca2+ and Mg2+ oscillated between 4.5 and 118.5 mg/L and between 0.64 and 26.7 mg/L, respectively, with an average concentration of 7.8 to 34.1 mg/L, respectively. In the case of Ca, this variation indicates that the low values are related to the interaction with volcanic rocks, while the high values result from the interaction with limestone rocks. This is the result of water flow through volcanic rocks of intermediate to mafic composition.

    The concentrations of HCO3-, Cl- and SO42-ranged from 203.2 to 607.5 mg/L, 2.6 to 111.6 mg/L, and 8.6 to 183 mg/L, respectively, with an average of 302.6, 22.7, and 52.2 mg/L, respectively. The abundance of major anions in the groundwater was in the order HCO3- > SO42- > Cl-.

    Figure 3 shows the drawdown cone, the northern flow path, southwest flow path and thermal flow and the distribution of major ions and physicochemical parameters in the valley.

    Figure 3.  Distribution of the main major ions and physicochemical parameters of the groundwater of the Celaya Valley.

    In the case of Mg2+ and Ca2+, the lowest values of less than 5 mg/L are distributed in the center of the valley. This may be related to two processes, ionic exchange due to the presence of clay materials and/or precipitation of dolomite.

    The lowest values of Na+, K+ and Cl- are found in the recharge zone north of the valley and the highest concentrations of the most evolved water are found in the southwest.

    The lowest values of HCO3-, SO42-and TDS are located in the drawdown cone and the highest values are located to the southwest, which corresponds to the area of greatest evolution except for SO42-whose highest concentrations are found northeast.

    The areas with the highest temperature are close to the geological faults that cross the large drawdown cone.

  • The chemical evolution of groundwater results from water-rock interactions during the infiltration and circulation processes. These interactions produce different hydrogeochemical signatures, known as water families, which are represented in the Durov diagram. In this diagram, the water-rock interaction processes in the studied area were recognized, including ion exchange in some cases (Fig. 4). Five families of water were identified; the Ca-HCO3 type was identified in a sample located northeast of the study area in carbonate rocks of the Soyatal Formation (local flow). The Ca-Na-HCO3 family originates from the interaction of water with rhyolites, and it is distributed throughout the valley (northern zone). The Na-Ca-HCO3-Cl type is mainly found in the southwest part of the valley (Southwest flowpath or intermediate flow). It results from the circulation of water through volcanic rocks (basalts and andesites). The water mixing processes are indicated by a green ellipse (Mixing zone) where the family type is Mixed Ca-Na-Mg-HCO3-SO4, and in the drawdown cone we have a dominant water family Na-HCO3. The Durov diagram shows the occurrence of cation exchange, which is consistent with the presence of clays in the center of the big drawdown (Figs. 1, 2). The conceptual model indicates that the Na-Mg-Ca-HCO3 family results from the cation exchange between the Na-HCO3 and Mg-Ca-HCO3 families (Fig. 2). Although the latter was not identified in the present study, it has been reported in an area located to the west of the valley (CEAG, 2000).

    Figure 4.  Durov diagram represents the water families and the hydrogeochemical processes of the Celaya Valley.

    In general, water-rock interaction begins with the infiltration of water in the subsoil, and the concentration of the chemical species increases with distance along the flow path and /or as the residence time increases. This process is represented in Fig. 5. This diagram is a modification of the Mifflin diagram (1968), where the sum of the main cations versus the main anions enables identification of the evolution of groundwater and establishes the different types of water flows in the system. The area closest to the origin has lower concentrations of anions and cations, due to the short circulation and residence time of the water. The samples in this area are associated with a local flow. In the middle zone of the graph, the concentrations are associated with a greater distance or a longer residence time, and an intermediate flow (drawdown cone). In the last zone, the concentrations are higher; the samples in this area correspond to a longer residence time, which increases the water-rock interactions and results in a higher evolution of groundwater (Fig. 5).

    Figure 5.  Modified Mifflin diagram representing the evolution of the groundwater and flows in the Celaya Valley.

    As can be seen in Fig. 5, the northern flowpath (local flow) and southwest flowpath (intermediate flow) converge in the big drawdown cone, which is consistent with what was previously indicated with respect to the inversion of the flow of the southwest zone.

    Figure 6a shows the relationship between Ca2++Mg2+ and HCO3-+SO42-. The 1 : 1 correlation line divides two regions: (a) silicate weathering region and (b) a region with alteration of carbonate rocks. As seen, the samples are located in the region of silicate weathering, in different proportions. The end member that is more evolved represents a greater proportion of this process. The end member C2 has an intermediate alteration, and the end member C1 represents the lowest alteration with constant concentrations of Ca2+ and Mg2+, which is consistent with the distribution of volcanic rocks in the area. This graph identifies the local flow, intermediate flow and mixing zone. Those samples reflecting the greatest alteration of silicates belong to the southwest flowpaths (3, 7, 5, 4, and 6). The Northern flowpaths (32, 31, 26, 24, 30, 27, and 7) near the 1 : 1 line interacted with carbonates.

    Figure 6.  Diagrams showing (a) the interaction with silicates (b) cation exchange and (c) convergence of both flows in the center of the valley.

    Figure 6b displays the ratio of (Ca2++Mg2+)-(HCO3-+SO42-) versus (Na++K+)-Cl-. In Fig. 6b, the black line is related to the process of cation exchange. In the study area, the samples are distributed along this line, evidencing the occurrence of this process. The tectonic valley is composed by clay material, originated by the silicate weathering process, which facilitates ion exchange that is an important process in the evolution of groundwater in the study area. The ratio of (Ca2++Mg2+)-(HCO3- +SO42-) versus (Na++K+)-Cl- is lower in the local flow, while the largest ion exchange occurs in the intermediate flow, both flows coincide in the mixing area located in the big drawdown cone.

    Figure 6c shows the relationship between Na+/(Na++Ca2+) versus Na++K+ mol/mol. This graph indicates three evolutionary trends. The main trend is limited by three extremes; the groundwater local flow from the north with the presence of carbonate rocks towards the center (black line). Another intermediate flow that comes from the interaction with rhyolitic rocks (blue line) is mixed with hydrothermal waters (regional flow) identified with red arrow. Both flows converge in the mixing zone in the big drawdown cone (Figs. 1, 2, 4, 6c).

  • The final members represent the highest and lowest concentrations of the system. The mixtures can be binary or ternary. Binary mixtures have been used to quantify mixtures of fresh and marine waters (Valentino and Stanzione, 2003; Douglas et al., 2000). The involvement of three types of water corresponds to a ternary mixture.

    In the study area, a triangle is shown, whose vertices are the end members (Fig. 7). The remaining samples plot in the area limited by the mixing lines; they are considered to be a mixture of the fractions of the end members. Any sample of water in the system may be generated by combining the three end members. Based on the scatter plot (for example, Cl- and F-) of the conservative elements (that is, those that do not react chemically with the environment during the evolution of groundwater), three end members (C1, C2, and C3) were identified; thus, the mixture is a ternary mixture. The first end member belongs to the local flow. The second end member is more evolved and correspond to intermediate flows, showing a different origin of groundwater. The third end member is associated with regional recharge.

    Figure 7.  Ternary diagram shows the ternary mixture resulting in the hydrogeochemical characteristics of the groundwater in the studied area; samples 26, 6, and 8 correspond to end members C1, C2, and C3, respectively.

    The end member C1 is represented by Sample 26, located in the northern section of the study area (Figs. 1, 7). This water sample is associated with local recharge, and it has low values of Cl-, SO42-and F-. The lowest values in the sample were found for Cl- 0.08 meq/L and 0.04 meq/L of F- (Fig. 7), with a temperature of 28 ℃ and a pH of 6.86; this water type is Ca-Na-HCO3.

    The end member C2 is represented by sample 6; it corresponds to an intermediate flow. The well is located in the center of the study area (Figs. 1, 7), with a temperature of 23.1 ℃, a pH of 7.65, a Cl- concentration of 3.19 meq/L, and an F- concentration of 0.03 meq/L (Fig. 4). The water type of this sample is Na-Ca-HCO3-Cl.

    End member C3 is represented by sample 8. This water sample represents a regional flow of hydrothermal origin. It is located towards the southern section of the study area, (Figs. 1, 7), with a temperature of 42.2 ℃, a pH of 8.34, a Cl- concentration of 0.72 meq/L, and a high concentration of F- 0.37 meq/L (Fig. 7). This type of water is Na-HCO3.

    Spatially the members C2 (Sample 6) and C3 (Sample 8) are very close. However, the flows are different. C3 comes from an upward vertical flow through geological faults and C2 comes from a lateral flow.

    As seen in Fig. 7, the end Member C1 contributes 70% of the water to the system, end Member C2 contributes 14% and end Member C3 contributes 16%.

  • In the western portion of the Celaya Valley aquifer, the water families are mainly Na-HCO3, due to the interaction of water with volcanic rocks of rhyolitic composition, Na-Mg-HCO3, due to the interaction of water with composition of basaltic-andesite volcanic rocks and Ca-HCO3, due to the interaction of water with calcareous sedimentary rocks. The family Ca-Na-Mg-HCO3-SO4 and Na-Ca-HCO3-Cl mixed type corresponds to the most evolved southwest flow. Silicate weathering due to the hydrothermal influence is a process that is identified in the aquifer, and the ion exchange is a result of the water that circulates through the clay materials in the valley. Three flow systems were identified (local, intermediate and regional), which are mixed in the center of the Valley. The local flow originates in the mountainous area, south and north of the valley, the intermediate flow comes from the southwest of the valley, and the presence of geological faults facilitates mixing with the thermal flow (regional flow). The local flow contributes to 70% of the water in the system, the regional flow contributes to 16% of the water in the system, and the intermediate flow only contributes to 14% of the water in the system. The relationship of Ca2++Mg2+ and HCO3-+SO42- is consistent with the type of geological environment present in the Celaya Valley. In general the hydrogeochemistry shows the convergence of groundwater flows to a big drawdown.

  • The authors are thankful for the support Olivia Cruz and Alejandra Aguayo from the Analytical Chemistry Laboratory at the Instituto de Geofisica, National Autonomous University of Mexico. We also thank Itzamna Flores-Ocampo and Ricardo Flores Vargas for their help in the field campaigns. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1294-x.

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