ORIGINAL PAPER Effect of irrigation on a deep aquifer: a case study from the semi-arid Harran Plain, GAP Project, Turkey M. Irfan Yesilnacar • Ibrahim Yenigun Received: 2 December 2009 / Accepted: 16 April 2010 / Published online: 21 May 2010 Ó Springer-Verlag 2010 Abstract Inappropriate irrigation practices are responsi- ble for the deterioration of groundwater quality in a great number of developing countries, particularly in semi-arid and arid regions. The study was undertaken to determine the variation in groundwater quality of a deep aquifer after surface irrigation was started in the semi-arid Harran Plain, southeast Turkey. Physical and chemical parameters of the groundwater, including pH, temperature, electrical con- ductivity, sodium, potassium, calcium, magnesium, chlo- ride, bicarbonate, sulphate and nitrate, were determined on a monthly basis from November 2008 to July 2009. The quality of the deep aquifer was assessed hydrochemically in order to determine its suitability for human consumption and agricultural purposes. With the exception of two wells, the measured and analyzed parameters in all the ground- water samples were below the internationally accepted maximum concentrations for human consumption and for agricultural purposes. The study identified a local con- tamination as a consequence of excess irrigation, high evaporation rates and drainage. It is hoped that the results will assist planners in the proper design and control of irrigation schemes to avoid further deterioration of these important aquifers. Keywords Groundwater quality Á Irrigation Á Deep aquifer Á Harran Plain Á GAP project Á Turkey Re ´sume ´ Des pratiques d’irrigation inapproprie ´es sont responsables de la de ´te ´rioration de la qualite ´ des eaux souterraines dans un grand nombre de pays en de ´velopp- ement, particulie `rement dans les re ´gions de climat semi- aride et aride. L’e ´tude a e ´te ´ entreprise afin de de ´terminer l’e ´volution de la qualite ´ de l’eau souterraine d’un aquife `re profond apre `s que des travaux d’irrigation aient de ´bute ´ dans la plaine semi-aride de Harran dans le sud-est de la Turquie. Des parame `tres physiques et chimiques de l’eau souterraine, comportant le pH, la tempe ´rature, la con- ductivite ´ e ´lectrique, les teneurs en sodium, potassium, calcium, magne ´sium, chlorures, bicarbonates, sulfates et nitrates ont e ´te ´ de ´termine ´s sur un base mensuelle de no- vembre 2008 a ` juillet 2009. La qualite ´ de l’eau de l’aqui- fe `re profond a e ´te ´e ´value ´e sur le plan hydrochimique afin de de ´terminer son utilisation possible pour la consomma- tion humaine et des usages agricoles. Avec l’exception de deux puits, les parame `tres mesure ´s et analyse ´s dans tous les e ´chantillons d’eau ont e ´te ´ infe ´rieurs aux concentrations maximum accepte ´es internationalement pour la consom- mation humaine et les usages agricoles. L’e ´tude a identifie ´ une contamination locale due a ` une irrigation excessive, des taux d’e ´vaporation e ´leve ´s et des pratiques de drainage particulie `res. On espe `re que les re ´sultats obtenus aideront les planificateurs responsables de la conception et du contro ˆle des sche ´mas d’irrigation et permettront d’e ´viter de futures alte ´rations de ces importants aquife `res. Mots cle ´s Qualite ´ des eaux souterraines Á Irrigation Á Aquife `re profond Á Plaine d’Harran Á Projet GAP Á Turquie Introduction Groundwater is an important natural resource. Worldwide, more than two billion people depend on groundwater for M. I. Yesilnacar (&) Á I. Yenigun Department of Environmental Engineering, Harran University, Osmanbey Campus, 63190 S ¸ anlıurfa, Turkey e-mail: iyesilnacar@yahoo.com; mirfan@harran.edu.tr 123 Bull Eng Geol Environ (2011) 70:213–221 DOI 10.1007/s10064-010-0299-6