Mechanisms of arsenic contamination of a surfacial aquifer in Turkey

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1 (Proc. 6th International Groundwater Quality Conference held in Fremantle, Western Australia, 2 7 December 2007). 1 Mechanisms of arsenic contamination of a surfacial aquifer in Turkey O. GUNDUZ 1 & C. SIMSEK 2 1 Department of Environmental Engineering, Dokuz Eylul University, Tinaztepe Campus, Buca, 35160, Izmir, Turkey orhan.gunduz@deu.edu.tr 2 Department of Drilling, Torbali Vocational School of Higher Education, Dokuz Eylul University, Torbali, 35860, Izmir, Turkey Abstract In this study, possible sources of extremely high concentrations of arsenic (reaching as high as µg/l) in the shallow groundwater of Simav plain, Turkey is studied in order to understand probable mechanisms of contamination. It has been found out that the major source of arsenic in groundwater is arsenic containing geological formations in and around the vicinity of the plain. However, this otherwise-contained arsenic in lower strata is mobilized by the help of geothermal fluid that is present underneath the tectonically active faulty graben zone. Overexploitation of groundwater in surfacial aquifer is also found to be a factor effective in high levels of arsenic in water supply wells. Furthermore, the uncontrolled disposal of the wastes an abandoned Cu-Pb-Zn mine that also contains lenses of arsenic and antimony is another mechanism of arsenic contamination in the surface and subsurface waters of the plain. Further research is currently under way to characterize the details of arsenic in the area. Key words arsenic contaminated groundwater; geothermal area; old mine; Simav Plain; Turkey INTRODUCTION Arsenic is one of the elements that has proven detrimental effects to humans. Particularly, arsenic in drinking water supply has been reported to cause numerous cases of cancer in many parts of the world (Cantor, 1997; Tapio & Grosche, 2006). It has been further documented that the majority of these reported cases are related to arsenic originating from local geological formations (O Shea et al., 2007). Being situated in a tectonically active area of complex geology, Turkey is one of these areas where arsenic containing layers are widespread (Colak et al., 2003). The Province of Kutahya located in western Anatolia is one such area with high arsenic concentrations and several episodes of arsenic poisoning (Col et al., 1999). The Simav plain is one of the areas in Kutahya where high arsenic levels are detected (Simsek & Gunduz, 2007). Simav plain demonstrates a complex geological structure in a tectonically active area. The metamorphic, magmatic and sedimentary rocks in and around the plain contain sulfuric mineralization with high arsenic contents (Gunduz et al., 2008). This geological structure has also created an active geothermal system within which arsenic is transformed to dissolved form. Based on these fundamentals, this research is aimed

2 2 O. Gunduz & C. Simsek to detect and quantify the presence of arsenic in the groundwater and understand the mechanisms of arsenic contamination within Simav Plain surfacial aquifer. DESCRIPTION OF PROJECT AREA The project area (Figure 1) is formed at the base of a graben system and is surrounded by Ak Mountain to the north, Egrigoz Mountain to the east and Simav Mountains to the south. This graben system was filled by the alluvial sediments of the surrounding mountains. The Simav Plain was mostly covered by a shallow lake which was then drained in 1960s to create agricultural lands. With a population of 55000, the district of Simav is the largest population center within the project area. Agricultural production and thermal tourism are among the major economical activities in the region. Three geothermal fields located at Eynal, Nasa and Citgol (as denoted by H1, H2 and H3 in Figure 1) are utilized in serving the requirements of the thermal hotels and the central heating system of the city of Simav. Simav Plain and its vicinity is considered to be situated in Central Aegean climate, which shows attributes of a transition zone from Mediterranean climate to Central Anatolian climate (Simsek & Gunduz, 2007). Based on data from Simav Meteorological Station collected between , the region receives an average precipitation of 723 mm. Monthly averages of highest and lowest precipitation occur in December and August with totals of mm and 11.2 mm, respectively (DMI, 2005). The prevailing climatic conditions of the area triggers land erosion. The hot and dry summers followed by cold and wet winters results in significant sediment transport from the highlands to Simav Plain. The rate of this process depends on the seasonal vegetation cover and precipitation amounts as well as the local topography. In particular, the southern slopes of the area have steep grades that creates flash floods and high sediment transport. The relatively thick alluvial layer in the plain (i.e., up to 90 m in thickness) is a clue for the rapid deposition of transported sediments. From a geological point of view, five major units (Figure 1) are observed in the study area including (i) Paleozoic-aged Menderes Metamorphics, (ii) Paleocene-aged Egrigoz Granite, (iii) Neogene-aged Kizilbuk Formation, (iv) Lower Quaternary-aged Basalt; and (v) Quaternary-aged Alluvium (Akdeniz & Kocak, 1979; Hasozbek, 2003). The metamorphic rocks of the area are mainly composed of schist, gneiss and marble that experienced medium to high metamorphism. Pb-Zn and Sb type sulfite minerals are developed in schist units due to hydrothermal alteration. An old Cu-Pb-Zn mine was operated in the schist located to the south of Degirmenciler Village near Simav district center (Figure 1). This mine was primarily used for copper and lead production and was abandoned in The magmatic rocks of the area belong to Egrigoz Magmatic Complex and mainly consist of granite. Egrigoz granite surfaces out by cutting Menderes Metamorphics and is frequently observed in northwestern parts of the study area (Figure 1). Being considered as the primary cover rock of the project area, Kizilbuk Formation overlies Menderes Metamorphics and Egrigoz Granite. It consists of claystone, conglomerate, sandstone, agglomerates and tuff. Nasa Basalt is the youngest volcanic formation that is also considered to be the heat source for the geothermal fields of the study area (Ercan et al., 1984). Finally, an alluvium layer

3 Mechanisms of arsenic contamination of a surfacial aquifer in Turkey 3 overlies these units and forms the uppermost unit in Simav Graben Plain (Gunduz et al., 2008). Fig. 1 Local geology and water quality sampling locations (Gunduz et al., 2008). Fig. 2 Cross-sectional schematic (A-A' plane) of Simav Plain (Gunduz et al., 2008).

4 4 O. Gunduz & C. Simsek Based on these geological formations, the hydrogeology of the study area is governed by two major aquifer systems. The first one of these aquifer systems is the alluvial surfacial aquifer that supplies fresh cold water. This system provides the majority of groundwater extracted for drinking, irrigation and industrial use within the plain. The second aquifer, on the other hand, is a part of the local geothermal system formed along major fault lines that pass underneath Simav graben area (Figure 2). In this system, hot geothermal waters surface out from the fault line and mix with surface and subsurface waters of the plain. This system resulted in three major geothermal fields located at Nasa, Eynal and Citgol (Figure 2). Currently, these fields are used as thermal spas and further supply hot water for the central heating system of the city of Simav. The alluvial surfacial aquifer is mainly composed of sedimentary sands and gravels. The aquifer reaches up to 90 m in thickness and provides the biggest portion of extracted groundwater. The sediments of old Simav Lake demonstrate the characteristics of this alluvial layer. These sediments originate from different lithology rocks found in the vicinity of the project area. In particular, significant sediment influx is found to originate from highly-weathered Menderes Metamorphics located in higher elevations to the southwestern parts of the study area. Thus, the geochemical characteristics of samples collected from the alluvium layer are shown to be quite similar to the characteristics of sampled from Menderes Metamorphics, particularly with regards to trace elements and heavy metals (Gunduz et al., 2008). The reservoir rocks of geothermal field found underneath Simav Plain are composed of conglomerates, sandstones, limestones, schists and marbles that belong to Kizilbuk Formation and Menderes Metamorphics. These rocks are broken with the movement of Simav graben faults and are transformed into a fractured structure that play an important role in the formation and storage of hot waters. These units reveal a productive aquifer, which shows confined aquifer characteristics in many parts of the plain (Gunduz et al., 2008). MATERIALS AND METHODS Upon continuous health-related complains from locals, the municipalities of Citgol and Kelemyenice have decided to initiate a water quality assessment study in order to detect and quantify the presence of arsenic and other toxic minerals in the surface and subsurface waters of Simav plain. A total of 33 monitoring stations (i.e., 3 geothermal wells, 27 groundwater wells and 3 surface water) were selected and sampled within the plain in order to understand the characteristics of arsenic presence in the unconfined aquifer. Within the scope of field sampling campaign, two sets of samples are collected from each sampling station (i.e., 1000 ml for standard anion and cation analysis and 50 ml for trace element and heavy metal analysis). All samples are filtered (0.45 µm) and stored at 4 ºC in polyethylene bottles until analyzed for the physicochemical parameters. All 50 ml samples collected for trace element and heavy metal analysis are then acidified to achieve ph value of less than 2. The ph (WTW-pH330), temperature (WTWpH330) and electrical conductivity (EC) (WTW-EC330) measurements are conducted on the field. The cation analyses are performed with ICP-MS in ACME Laboratories (Canada). Chloride and bicarbonate ions are analyzed with volumetric methods; nitrate

5 Mechanisms of arsenic contamination of a surfacial aquifer in Turkey 5 measurements are done by photometric methods and sulfate analysis are conducted with gravimetric methods in Dokuz Eylul University laboratories. The Aquachem v3.70 computer program are then used to conduct primary computations of water chemistry and correlation analysis between the parameters. Accordingly, the error in anion-cation balance are computed to be less than 2.5%. A water quality database is then formed on a geographic information system (GIS) platform (ArcGIS v9.1) for further analysis and data visualization. RESULTS AND DISCUSSIONS A statistical summary of the results of Simav Plain water quality monitoring program is presented in Table 1. Based on these results, it could be seen that not only geothermal water samples but also surface and groundwater samples contain high levels of trace elements that are typically found in hot geothermal fluids (Gemici & Tarcan, 2004; Demirel & Yildirim, 2002) in western Anatolia. Among these, arsenic, boron and lithium are particularly high with values reaching 594.0, and µg/l, respectively for geothermal water samples; 561.5, and µg/l, respectively for groundwater water samples; and, 179.2, and µg/l, respectively for surface water samples. Elevated temperature with values as high as 114 ºC and long contact times with the reservoir rock resulting in electrical conductivity values reaching 2357 µs/cm are believed to be among the major causes for these high concentrations in geothermal water samples. In particular, high arsenic concentrations are found to be related to the presence of arsenic containing geological formations around the plain as revealed by the soil-rock sampling program (Gunduz et al., 2008). High arsenic concentrations in surface and subsurface waters are related to a number of contamination mechanisms. One of these mechanisms is associated with the uncontrolled discharge of waste geothermal fluid to the surface water drainage network as no re-injection application is implemented in the three geothermal fields of Simav plain. Thus, high arsenic and boron levels are detected in surface water sampling stations despite the dilution effect within the stream and in groundwater sampling stations close to the discharge points along the stream (Figure 3). Another mechanism is related to the dispersion of hot geothermal fluid towards the bottom of the unconfined alluvial aquifer. The fault zone in plain allows an opening for pressurized geothermal fluid to ascend and disperse within the bottom of the alluvial aquifer where it mixes with cold groundwater. It has also been found out that poorly constructed geothermal boreholes leak and contaminate the alluvial aquifer as a result of the corrosive nature of geothermal fluid. In addition, some of the deep cold water wells drilled in the alluvial aquifer are over-pumped resulting in the accelerated mixing of hot and cold waters at the bottom of the alluvial layer. This phenomenon creates an hot water wedge that exhibits similar characteristics to salt water intrusion. In consequence, a number of cold water wells around the geothermal fields have elevated temperature values. Table 1 Statistical summary of water quality monitoring in Simav Plain Parameter Unit Surface Water Samples (N=3) Ground Water Samples (N=27) Geothermal Water

6 6 O. Gunduz & C. Simsek Min Max Mean Std. Std. Min Max Mean Dev. Dev. Min Max Temp ºC ph EC µs/cm Ca +2 mg/l Mg +2 mg/l Na + mg/l K + mg/l Cl - mg/l NO 3 mg/l SO 4 mg/l HCO 3 mg/l Al µg/l As µg/l B µg/l Cu µg/l Fe µg/l Li µg/l Mn µg/l Pb µg/l Sb µg/l Zn µg/l ITASHY(2005) 2 EPA (2003) 3 WHO (2004)

7 Mechanisms of arsenic contamination of a surfacial aquifer in Turkey 7 Fig. 3 Arsenic distribution in the alluvial aquifer. Finally, Gunduz et al. (2008) have found out high arsenic levels in the geochemical structure of the parent metamorphic rocks in and around the plain. The steep topography of the area has resulted intense weathering of these rocks and Simav Plain has essentially been created as a result of the deposition of these eroded material. Thus, a similar geochemical structure with high arsenic levels have also been detected in the alluvial material samples collected from the plain. The water-rock interaction within this alluvial layers is another source for the presence of arsenic in groundwater samples. Last but not the least, it has been found out that arsenic/antimony containing waste materials of the abandoned Cu-Pb-Zn mine was deposited in an uncontrolled manner near Simav district center (Figure 1). It is believed that these chemicals have leached from the waste disposal area and mobilized towards the plain and contaminated the groundwater as could be seen from extremely high arsenic value (561.5 µg/l) detected at sampling point G-4 in Figure 3. CONCLUSIONS Detailed studies on the local and regional geology, hydrogeology and tectonics of the area has revealed that high arsenic values in surface and subsurface waters of Simav plain are mainly related to the naturally occurring arsenic containing strata (i.e., arseno-pyrites) found within the lower geological units of the plain. It has been found out that one of the major mechanisms of arsenic contamination in the plain is related to the mobility associated with the hot geothermal fluid. When hot geothermal waters with high arsenic concentrations are extracted from relatively lower strata, the otherwise-contained arsenic is introduced to the surface and mix with the cold water reserves of the surfacial aquifer. Thus, geothermal water production and its uncontrolled discharge to the highly permeable river bed is found to be an important mechanism for arsenic contamination of the surfacial aquifer. Furthermore, arsenic containing mining wastes of an abandoned copper-lead-zinc mine located to the southern parts of the plain is another potential source of arsenic in the aquifer. The uncontrolled disposal of the wastes of this old mine has created an alternative pathway for the mobility of arsenic towards the plain. Last but not the least, the improperly constructed water supply wells that are utilized for agricultural irrigation and drinking water supply are drilled to deeper levels (and sometimes beyond the extend) of the surfacial aquifer and extract water from deeper layers where arsenic concentrations are higher. As a consequence of these factors combined with the over exploitation of groundwater, it could be concluded that Simav Plain and its immediate vicinity is under severe risk with regards to increased cancer (i.e., gastro-intestinal cancers) mortality, that is possibly related to arsenic toxicity. However, further research on source identification and health risk assessment studies are required to confirm this outcome. Acknowledgements The authors would like to express their gratitude to the municipalities of Citgol and Kelemyenice for their support throughout the study. The authors also thank the

8 8 O. Gunduz & C. Simsek Scientific and Technological Research Council of Turkey. This paper is a part of a more comprehensive research conducted on Simav Plain. REFERENCES Akdeniz, N. & Konak, N. (1979) The situation of rocky units of Menderes Massive around Simav and metabasic, metaultramafic rocks. Bull. Turkish Geol. Assoc. 22, (in Turkish). Cantor, K. P. (1997). Drinking water and cancer. Cancer Causes Control 8, Col, M., Col, C., Soran, A., Sayli, B.S. & Ozturk S. (1999) Arsenic-related Bowen s disease, Palmar keratosis and skin cancer. Env. Health Persp. 107, Colak, M., Gemici, U. & Tarcan, G. (2003) The effects of colemanite deposits on the arsenic concentration of soil and groundwater in Igdekoy-Emet, Kutahya, Turkey. Water Air Soil Pollut. 149, Demirel, Z. & Yildirim, N. (2002) Boron pollution due to geothermal wastewater discharge in to the Buyuk Menderes River, Turkey. Int. J. Env. Pollut. 18, DMI (2005) Simav Meteorological Report. State Meteorological Organization, Simav (in Turkish). EPA (2003). Environmental Protection Agency Office of Water National Primary Drinking Water Standards. Ercan, T., Gunay, E. & Savascin, Y. (1984) Regional evaluation of Cenozoic-aged volcanism in Simav and its environs. MTA J. 97/98, (in Turkish). Gemici, U. & Tarcan, G. (2004) Hydrogeological and hydrochemical feature of the Heybeli Spa, Afyon Turkey: arsenic and the other contaminants in the thermal waters. Bull. Env. Con. Tox. 72, Gunduz, O., Simsek, C. & Hasozbek, A. (2008) The assessment of arsenic contamination in Simav Plain, Turkey. Sci. Tot. Environ. (in preparation). Hasozbek, A. (2003) Geology, petrology and the evolution of the Egrigoz magmatic complex. MSc Thesis, Dokuz Eylul University, Izmir, Turkey. ITASHY (2005). Regulation on waters for human consumption, Official Gazette dated 17/02/2005, No.25730, Ankara. O Shea, B., Jankowski, J. & Sammut, J. (2007) The sources of naturally occurring arsenic in coastal sand aquifer of eastern Australia, Sci. Tot. Environ. 379, Simsek, C. & Gunduz, O. (2007) IWQ Index: A GIS-integrated technique to assess irrigation water quality. Environ Monit. Assess. 128, Tapio, S. & Grosche, B. (2006) Arsenic in the aetiology of cancer. Mutation Res. 612, WHO (2004) World Health Organization Guidelines for Drinking Water Quality Third Edition, Vol. 1., Geneva.

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