Investigation of geothermal waters effect on groundwater quality in Alaşehir Plain

Gediz Basin is one of big graben system in Aegean region in Turkey. Alasehir basin is very important geothermal site which islocated in the southern part of the Gediz Graben. Many geothermal wells are drilled and this application causes some problems associated with not only waste geothermal fluid disposal but also uncontrolled surface eruptions during drilling operations. A main objective of this study is to investigate the geothermal fluid effects on groundwater chemistry where geothermal drill was collapsed and to cause significant thermal and chemical contamination. The Paleozoic-aged Menderes metamorphic rocks form the basement of the Alasehir plain and are observed outcropping in the eastern and western parts of the plain. The Menderes metamorphic rocks consist of mica and chloriteschist in their lower levels and marble in their upper sections. This marble is geothermal water reservoir rock in the study area. The Neogene sedimentary Formation, formed of limestone, claystone and sandstone, overlies basement rock. This formation is widely observed along the Alasehir plain. Finally, Quaternary alluvial layers overlie the basement and the Neogene Formation in the study area. The thickness of the alluvial layer ranges from 30 to 120 m in the Alasehir plain. This alluvial layer is very important groundwater aquifer and big portion of drinking and irrigation water demand are supplied this aquifer. During the sampling study, a total of 16 groundwater sampling points were selected among the drilling data to represent the conditions of groundwater. As monitoring procedure, field parameters, major anion and cation and heavy metal concentration were analyzed in water samples taken from geothermal fluid and observation groundwater wells during dry and wet season in 2014. As a result, the chemical composition of the geothermal water contains highly level of arsenic and boron contaminants contend to the environment and the water sources. Based on the long term groundwater level, temperature and electrical conductivity values show that the groundwater is effected geothermal intrusion which is came from near geothermal activities. This geothermal intrusion cause the groundwater contamination with respect to arsenic and boron and this contamination deteriorate the groundwater drinking and irrigation water quality.