Hydrogeological and hydrogeochemical study of the Gediz spas, Kütahya, Turkey

The Kütahya Gediz spas are located in the eastern part of the Simav Graben, which is oneof the Western Turkey grabens. Gediz geothermal systems have been physically divided intotwo main groups; the Ilıca and Muratdağı geothermal areas. The reservoir rocks of thegeothermal systems are Paleozoic metamorphic rocks in the Ilıca area and Jurassic toCretaceous Muratdağı Melange, which consists of marble, cherty limestones, schist,ultramafic rocks and their complexes, in the Muratdağı area. Since the clayey levels of theoverlying Miocene - Pliocene sedimentary rocks, they are the cap rocks of the systems. Theheat sources are the high geothermal gradient caused by graben tectonics of the area. Thermalwaters in the Ilıca and Muratdağı areas are generally sodium, sulfate and bicarbonate andcalcium, sulfate types, respectively. Cold waters in the areas are mainly dominated bymagnesium and bicarbonate ions. Assessments of chemical geothermometers and mixingmodels applied to the thermal waters, which have measured discharge temperatures rangingfrom 31.2°C to 77°C in Ilıca area and 20.3°C to 43°C in Muratdağı area, suggest that reservoirtemperatures 162°C in Ilıca area and 84°C in Muratdağı area. The important environmentalproblems in Ilıca area are boron and total dissolved solids contaminations in cold aquifers andsoils. To prevent these environmental impacts of thermal waters used for spas and districtheating in the area, re-injection of produced thermal waters into the geothermal reservoirs isnecessary.