Groundwater quality and geothermal energy. The case of Cerro Prieto Geothermal Field, México Maria Aurora Armienta a, * , R. Rodríguez a , N. Ceniceros a , O. Cruz a , A. Aguayo a , P. Morales b , E. Cienfuegos b a Universidad Nacional Autónoma de México, Instituto de Geofísica, Circuito Exterior, C.U., México D.F. 04510, Mexico b Universidad Nacional Autónoma de México, Instituto de Geología, Circuito Exterior, C.U., México D.F. 04510, Mexico article info Article history: Received 14 August 2013 Accepted 14 September 2013 Available online 8 October 2013 Keywords: Water quality Arsenic Heavy metals Isotopes Agriculture Geothermal water abstract The influence of the Cerro Prieto Geothermal Field (CPGF) on groundwater quality of the close-by agricultural area was evaluated by means of chemical and isotopic determinations. According to irri- gation standards, concentrations of As, Cd, Pb, Crtot, Cr(VI), Cu, Cd, Hg, B in agricultural wells showed the suitability of the water for irrigation. Iron was below irrigation limits in all but one well. However, chloride levels were above those limits in 83 out of 87 collected samples. Isotopic determinations of d 2 H, d 18 O, d 34 S, d 13 C, and spatial concentration trends of elements related with geothermal brines and toxic metals and metalloids did not indicate an influence of the CPGF to groundwater in the nearby agricul- tural area. Isotopic values of d 2 H, d 18 O showed the occurrence of evaporation processes and infiltration of canal’s irrigation water to geothermal water reservoirs and to groundwater in the agricultural zone. High chloride concentrations might be associated with these processes. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Geothermal energy has been claimed to be one of the most environmental friendly energies [1,2] mainly because of its lower emission of greenhouse gases [3e5] and especially before the world spread use of solar and wind energies. In spite of providing less MW than other energy supplies, it is still relevant, with an installed capacity of 10715 MW in 2010 [5]. However, geothermal power plants have been pinpointed as pollution sources, mainly owing to the release of H 2 S and other toxic chemicals usually emanated in geothermal zones [6e9]. Nevertheless, although some studies have reported pollution of water bodies from geothermal plants [10,11], their impact to the quality of waters and soils has been brought up less. Toxic elements like Cd, Hg, As, Cd, Mn, F and boron are usually enriched in geothermal fluids [12e18]. These elements may pollute the environment through spills and interaction of deep geothermal brines with shallow aquifers and surface waters. In México, electrical energy is mainly provided by thermal plants (oil, natural gas and charcoal) with about 75% of the gener- ation capacity in 2010 [19]. Yet, Mexico is the fourth ranked country generating geothermal energy with an installed capacity of 958 MW [5]. Furthermore, the geothermal power plant of Cerro Prieto, located northwest of the country (Fig. 1) is the second largest of the world, with a capacity of 720 MWe provided by 13 power units [20,21]. While being in continuous operation for almost 40 years, it has been seen by nearby dwellers as an environmental hazard to the surrounding area. However, irrigation with agricul- tural wash-off water flowing from the USA through the Mexican border collected by a dam, and distributed to an irrigation-canals net, constitutes a contaminating source of shallow groundwater that cannot be overseen. The aim of this work is to evaluate the groundwater quality in the agricultural area adjacent to Cerro Prieto power plant, to determine the actual influence of the geothermal plant in water chemistry, focused on arsenic, heavy metals, fluoride, and boron. To Accomplish this objective geochemical and stable isotopic determinations ( 18 O, D, 13 C, 34 S) were carried out. 2. Local geological and hydrogeological framework The study area is located in the Salton Sea Basin which is mostly placed in the North-American territory. The basin was filled with sediments (clay, sands, clayey sands) reaching a thickness of 2000 m [22]. Three sedimentary environments have been identi- fied: fluvial, lacustrine and alluvial. * Corresponding author. Tel.: þ52 5556224114; fax: þ52 5555502486. E-mail addresses: victoria@geofisica.unam.mx, aurora.armienta@gmail.com (M.A. Armienta). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.renene.2013.09.018 Renewable Energy 63 (2014) 236e254