Hydrogeochemical characteristics of Eskişehir-Sivrihisar-Günyüzü basin

Abstract

Groundwater is mostly the unique water source in semiarid regions of Turkey. The aim of this study is to define aquifer characteristics by using hydrogeochemical and hydrogeological data obtained from the Günyüzü Basin located in the Sakarya River catchment area at the SW of Eskişehir-Sivrihisar. The study area covers an area of543 km2 with an annual average precipitation of393 mm/year. The study area comprises Mesozoic metamorphic rocks. Eocene granite, Neogene sedimentary rocks and recent alluvium where different hydrogeological properties such as unconfined-confined-partly karstic, fractured and granular aquifers having thermal component can be observed. The metamorphic basement begins with radiolarite, serpantinite, splitic basalt and diabases which are overlain by micaschist, quartzite, calcschist and marble. The thickness of brown, beige, light gray marble is more than 100 meters and seen at the top of metamorphic series. The metamorphic series are cut by magmatic rocks, where the main marble aquifer is bordered by these impermeable intrusions at sides and by impermeable schists at the bottom within the studied areaThe geological units in the study area are hydro-geologically classified as local rich, medium, poor aquifers and aquicludes. Paleozoic marbles have been jointed and faulted and evaluated as local permeable units. They contain and conduct significant amount of groundwater. According to data obtained from pumping tests at wells drilled in the marbles, the hydraulic conductivity ranges between 1.19 and 98.9 m/day and specific capacity is between 0.64 and 75 l/sec/m. Although these figures do not represent the whole aquifer, they provide an idea of the heterogeneity of the system. Most of the spring discharge from this aquifer. Marbles also play an important role on recharge of the basin, because the thickness of marbles is more than 100 meters and seen at the top of metamorphic series at higher altitudes of basin. Short and heavy rainfalls and snow-melts directly affect the recharge in this karstic area where response of these events has been observed in the spring discharges. Quaternary alluvium and Neogene conglomerates and limestones are secondary important aquifers. According to data obtained from the pumping experiments carried out at the wells drilled in the basin, the hydraulic conductivity of the Neogene limestones varies between 1,39 and 4.1 m/day and specific capacity varies betw&m 'İ.8 and 2.9 l/sec/m. The hydraulic conductivity of the Neogene conglomerates varies between 0.27 and 0.39 m/day and specific capacity is between 0.38 and 0.55/sec/m. The ophiolite, schists of the metamorphic complex, Eocene granites, Neogene marl, clays and diabases are the other impermeable levels in basin. Samples obtained from springs and wells within the research area from 9 locations, choosen in order to represent aquifer characteristics, have been examined. The groundwaters have pH values ranging from 6.59 to7.56, and temperatures changes 14 -35"C. Piper and Schoeller semilogaritmic diagrams are both used in order to specify the dominant lithology in the formation of chemical composition, and to classify water samples with respect to their chemical composition. Results indicate that they generally have Ca++>Mg++>Na+>K+ and HCO_3 >SO_4-2>Cr anions and cations which show that carbonate rocks are dominant in the formation of chemical composition. The chemical composition of water samples consist with the lithological properties of the researched area. Only Hamamkarahisar spring (K7) is characterised by Ca++> Na+> Mg++>K+ and HCO_3>C1>SO_4-2. anions and cations.=delta 18 O (%o-11.2 - %o-8.9) and =delta 2H (%o-79 - %o-60) isotope values show that all water (thermal and cold) samples except for Çukurçeşme spring are located in between the Ankara meteoric line =delta2H = 8.=delta 18 O + 14.5 ) and Global meteoric line (=delta2H = 8 =delta 18 O + 10) This shows that all waters (thermal and cold) are of meteoric in origin. The elevation-oxygen-18 plot of precipitation is found to be -0.32 %o/ 100 m. The EC-Tritium relationship indicates the existence of groups with different origins. These groups that have high EC ( 590-1216 mg/1 ) and low 3H (0 - 4 TU) values represent the deep circulating waters (Kl, K4, K5, K7), low EC ( 309-440 mg/1 ) and high SH (4-10 TU) values represent the shallow circulating waters (K2, K3, K6, K8, K9) where these waters mix in various proportions.

Özet

Yeraltısuları Türkiyenin yarı kurak bölgelerinde çoğu zaman tek su kaynağıdır. Yarı kurak iklim özelliğindeki Günyüzü Havzası, Eskişehir-Sivrihisar ilçesi güneydoğusunda, Sakarya nehri ana drenaj alanı içerisinde yer almaktadır. Havzada, geçirimsiz ortam olarak sınıflandırılan metamorfık şistler, granitik kayaçlar ve diyabaz dayklarıyla sınırlanan Paleozoyik yaşlı mermerler, sıcak ve soğuk sular için ana rezervuar kayaç niteliğindedir. Aynı zamanda havza içindeki Neojen yaşlı kireçtaşları, konglomeralar ve Kuvaterner yaşlı alüvyonlar da diğer önemli akiferlerdir. Çalışma kapsamında 9 su noktasından kurak (Temmuz-Eylül 2005) ve yağışlı (Mart-Mayıs 2006) dönemlerde sistematik örnekler alınmıştır. Örneklerin analizleri kurak ve yağışlı dönemde sularınCa++ >Mg ++ >Na +>K + ve HC0_3 >S0_4= >Cl-şeklinde bir iyon dizilimine sahip olduğunu göstermiştir. İncelenen sular içinde ortalama 35"C sıcaklık değeri ile termal su niteliğinde olan Çardak Hamamı kaynağı (K7) ise Ca ++> Na +> Mg ++>K+ ve HCO_3>C1 >SO_1= şeklinde bir dizilim sergilemiştir. Elde edilen tüm bu iyon dağılımı, bölgedeki karbonatlı kayaçların, suların ana bileşenlerinin oluşumunda belirleyici olduğu ve suların nispeten yüksek magnezyum içeriğinden dolayı da akifer kayaçların dolomitik bileşen içerdiğini işaret etmiştir. Sularda ölçülen =delta 18 O (%o —11.2 - %o-8.9) ve =delta 2H (%o -79 - %o -60) izotop değerleri, suların atmosferik kökenli olduğunu, 3H (0 - 8 TU) değerleri ise suların sığ, (Musluk çeşmesi kaynağı (K2), Çukurçeşme kaynağı (K3), Atlas kaynağı (K6'•), Nasrettin Hoca kaynağı (K8'), Babadat kaynağı (K9)) ve derin (Yeniçıkrı kaynağı (Kİ), Subaşı kaynağı (K5), 55886/A (K4), Çardak Hamamı kaynağı (K7)) dolaşımlı olduğunu ortaya koymuştur.