Groundwater contamination mechanism in a geothermal field: A case study of Balcova, Turkey

Journal of Contaminant Hydrology 103 (2009) 13–28

Contents lists available at ScienceDirect

Journal of Contaminant Hydrology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j c o n h yd

Groundwater contamination mechanism in a geothermal field: A case study of Balcova, Turkey Niyazi Aksoy a,⁎, Celalettin Şimşek a, Orhan Gunduz b a b

Dokuz Eylül University, Torbali Technical Vocational School of Higher Education, 35120 Torbali-Izmir, Turkey Dokuz Eylul University, Faculty of Engineering, Department of Environmental Engineering, 35160 Buca-Izmir, Turkey

a r t i c l e

i n f o

Article history: Received 31 January 2008 Received in revised form 21 August 2008 Accepted 25 August 2008 Available online 13 September 2008 Keywords: Geothermal pollution Arsenic Boron Balcova geothermal field Izmir-Turkey

a b s t r a c t The Balcova Geothermal Field (BGF) located in Izmir, Turkey is situated on an east-west directed graben plain within which the hot waters surface from a fault zone that cuts the Mesozoic aged Bornova Flysch. Due to the low permeability and porosity of the Bornova Flysch, the geothermal water cycles along the immediate vicinity of the Agamemnon fault and mixes with cold waters at different depths of this fractured zone. Within the scope of this study, the mixing patterns and the groundwater contamination mechanisms are analyzed by, hydrogeological and hydrogeochemical methods. Based on the results of this research, it has been found out that the hot geothermal water and the cold regional groundwater resources of the surficial aquifer mix within the fractured zone in Bornova Flysch and within the Quaternary alluvium aquifer due to natural and anthropogenic activities including (i) the natural upward movement of geothermal fluid along the fault line, (ii) the accelerated upward seepage of geothermal fluid from faulty constructed boreholes drilled in the area, (iii) the faulty reinjection applications; and, (iv) the uncontrolled discharge of waste geothermal fluid to the natural drainage network. As a result of these activities, the cold groundwater reserves of the alluvial aquifer are contaminated thermally and chemically in such a way that various toxic chemicals including arsenic, antimony and boron are introduced to the heavily used surficial aquifer waters hindering their use for human consumption and agricultural irrigation. Furthermore, the excessive pumping from the surficial aquifer as well as the reduced surface water inflow into BGF due to the dam constructed on Ilica Creek intensify the detrimental effects of this contamination. Based on the results of this study, it can be concluded that the groundwater pollution in BGF will expand and reach to the levels of no return unless a series of preventive measures is taken immediately. © 2008 Elsevier B.V. All rights reserved.

1. Introduction Geothermal energy has become an important energy source in China, Japan, United States, Iceland and Turkey where major tectonic activity exists (Lund and Freeston, 2000; Fridleifsson, 2001). There are 200 geothermal systems in Turkey, most are located in the Aegean region (Aksoy et al., 2008). The geothermal systems of the region are generally of low to moderate enthalpy and are mostly situated in horstgraben systems. The most significant of these fields include

⁎ Corresponding author. Tel.: +90 232 853 1828; fax: +90 232 853 1606. E-mail address: [email protected] (N. Aksoy). 0169-7722/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jconhyd.2008.08.006

Kizildere (242 °C), Germencik (232 °C), Seferihisar (153 °C), Balcova (140 °C) and Alasehir (213 °C) (Fig. 1). With geothermal energy becoming increasing popular in Turkey, the environmental impacts of geothermal energy have become a key research topic (Celik and Sabah, 2002; Cakin, 2003; Serpen, 2005; Tarcan and Gemici, 2005; Dogdu and Bayari, 2005). Contamination of surface and subsurface waters with toxic heavy metals is the most severe environmental impact of geothermal energy. These contamination problems are mainly attributed to flawed well construction, faulty reinjection applications and uncontrolled discharge of waste geothermal fluids to surface waters. As a consequence, surface and subsurface waters become chemically and thermally polluted. Arsenic and boron occur in high

14

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

Fig. 1. General geology of the Aegean Region, locations of geothermal fields and a general overview of the study area.

concentrations in the geothermal waters of Turkey (Gemici and Tarcan, 2004). High levels of arsenic have contaminated some cold water resources near geothermal fields and high boron concentrations degraded water quality in many aquifers that are used for irrigation (Gemici and Tarcan, 2002; Demirel and Yildirim, 2002; Cakın, 2003; Dogdu and Bayari, 2005). In order to assess the potential negative impacts, the groundwater pollution mechanisms of the specific geothermal field must be determined in order to propose possible mitigation measures. Sampling the cold water aquifers in the vicinity of geothermal fields provides valuable data on how the geothermal fluid mixes with cold waters and to what extent it influences the general water quality pattern. Our

research is mainly focused on groundwater temperatures and the concentrations of some toxic chemicals and tracer compounds that are specific to hot geothermal waters. Based on this fundamental knowledge, the flow mechanisms of the hot geothermal fluid and the associated groundwater pollution risk in BGF are analyzed. We address key parameters that include but are not limited to groundwater temperature and arsenic, antimony, boron and lithium concentrations. The potential impacts of these contaminants on the quality of drinking and irrigation water resources are investigated and possible mitigation measures are discussed. The results obtained are believed to be applicable to many geothermal fields in the Aegean Region, Turkey that have similar geological characteristics and contamination patterns.

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

2. Balcova geothermal field 2.1. General characteristics The BGF is situated 10 km west of the city of Izmir in the Balcova district (Fig. 1). It is only a few kilometers from the coastline and the Bay of Izmir on the Aegean Sea. Since Hellenistic times, the hot springs in BGF have been used as thermal spas. The Greek poet Homer mentions the hot springs of the BGF in his epic ‘The Illiad’. Today, the BGF is one of the most significant geothermal areas of the Aegean Region and its hot waters are widely used for thermal tourism and domestic heating purposes. The 26 geothermal wells (including 15 production wells, 2 reinjection wells and 9 monitoring wells) in BGF range from 104 °C to 141 °C. The locations of 13 production wells used in this study are shown on Fig. 2. The geothermal fluid rises along the Agamemnon fault and flows within the fault zone developed inside the low porosity and low hydraulic conductivity Bornova Flysch (Serpen, 2004). The northern portions of the field are an important citrus and vegetable growing area. There exist numerous greenhouses distributed

15

within the citrus orchards. The greenhouses and the citrus orchards are protected by legislation against residential and commercial development. Irrigation waters for these fields are mostly obtained from the shallow aquifer in the alluvial deposits of Ilica Creek (Fig. 2). The eastern and western portions of the geothermal field, on the other hand, are densely populated residential areas. BGF is located within the Ilica Creek watershed that covers a total area of 130 km2. Based on 1979–2005 climate data collected at the Guzelyali Meteorological Station located 5 km away from the watershed, the long-term average annual temperature is 17.9 °C. The months with the highest and lowest average temperature values are July (28.1 °C) and January (8.9 °C), respectively. The watershed receives an average annual precipitation of 682 mm with the highest monthly average (150 mm) in December and the lowest monthly average (1.9 mm) in August. Based on these data, this area has a typical Mediterranean climate with hot, dry summers and warm rainy winters. The total amount of mean annual precipitation over the Ilica Creek watershed is calculated to be 88.7 × 106 m3; 33.4% of the total precipitation is lost by evaporation and

Fig. 2. Locations of sampling stations and local geology of the study area.

16

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

Fig. 3. General stratigraphy of the study area (modified from Serpen, 2004).

evapotranspiration, and 46.6% is surface runoff. The remaining 20.0% infiltrates to recharge the shallow aquifer (Serpen and Kayan, 2001). The rock-filled Balcova Dam constructed on Ilica Creek controls the natural flow of the Creek and provides water to the Balcova Plain (Figs. 1 and 2). Currently, the water held by the dam is only used for drinking water for the city; no water is allocated for irrigation. The first production well in BGF was drilled in 1963; 124 °C geothermal waters were found at 125 m depth. Today, a total of 15 wells are used for production and 2 wells for reinjection. Since 1996, the hot geothermal fluid has been used in heating residences. Currently, about 2.1 million m2 of closed area and 10 ha of greenhouses are heated by geothermal energy. A 75 MWt (megawatt thermal) capacity heating center provides heat for homes, university buildings, hospitals, thermal treatment centers, hotels and greenhouses. The total production from the BGF is about 300 L/s during the October–April period and about 50 L/s during the May– September period when the central heating system is taken off line. In winter, about 60–70% of the produced geothermal fluid is reinjected to the reservoir rock by BD-8 and BD10 reinjection wells. The remaining waste fluid is discharged to the Ilica Creek.

Fig. 4. A schematic hydrogeological cross-section of the study area.

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

2.2. Geological characteristics The Izmir–Ankara zone (Fig. 1) is a complex unit that includes meta-sandstones, shales, volcanic and magmatic rocks, ophiolites and allochthonous limestones. Within the study area, this unit is mostly characterized by Menderes Metamorphics, Bornova Flysch and alluvium as shown in Figs. 2 and 3. Stratigraphically, the Menderes Metamorphics of Paleozoic age form the basement of the Izmir region. This unit is primarily composed of schists and marbles but does not crop out in the study area. The Bornova Flysch of Mesozoic age overlies the Menderes Metamorphics via a detachment fault formed as a result of the east-west oriented tectonics (Erdogan and Gungor, 1992; Genc et al., 2001; Sozbilir, 2002). The Bornova Flysch is mainly composed of meta-sandstones, ophiolites, serpentinites, diabases, shales, phyllites and limestones (Fig. 3). This surrounds the allochthonous limestones of upper Cretaceous age, which are a member of the Karaburun Carbonate Platform (see Fig. 1) (Erdogan and Gungor, 1992). Although not observed in BGF, it should also be mentioned that there are Neogene series that unconformably

17

overlie the Bornova Flysch in other areas. The Neogene series are composed of sandstone, conglomerate, claystone and limestone as well as tuffs and andesites. The studies conducted by Ongur (2001) revealed that the Bornova Flysch is as much as 2000 m thick. Based on the thin sections obtained from core samples of several boreholes drilled in the area, the meta-sandstones are mostly quartz with extensive Fe-oxidation and siderite alteration (Satman et al., 2002). The thin sections also document the presence of the Agamemnon fault zone. In another study conducted on shales of the area, Gemici (2001) found quartz, muscovite, biotite, feldspar, chlorite and opaque minerals. Finally, unconsolidated sediments of Quaternary age cover these units throughout the region (Fig. 3). This alluvial material consists mostly of clayey-sands with clay ratios ranging between 7% and 33%. Particularly around the southern portions of the study area, the alluvial material demonstrates higher hydraulic conductivity rates as it consists of comparably larger particles and less clay. As a result of dense graben tectonics developed between the Upper Cretaceous and the Upper Miocene, the units that

Fig. 5. Groundwater levels in the unconfined surficial aquifer.

18

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

form the Menderes Massive have moved up and E–W oriented graben basins have developed within the region (Kaya, 1999). The Izmir graben area where BGF is situated is a perfect example of these E–W oriented systems. The graben tectonics in the region have created active normal faults where hot water could discharge. Within the study area, the Agamemnon fault is the most significant normal fault. The heat source of the Balcova geothermal system has not been clearly identified. In order to understand the heat source of geothermal fields in Western Anatolia, one should focus on the general geology of the region. Almost all of these fields are located in E–W directed graben systems. Due to this graben tectonics, the thickness of the crust is believed to reduce to less than 25 km (Maden et al., 2005). The heat flux around these grabens in Western Anatolia are several times higher than the normal level due to this relatively small crust thickness. Taking into account that the flysch is known to be over 2000 m thick and it may even reach 4000 m or more (Ongur, 2001), ground water circulation is assumed to reach to a depth of minimum 2000 m. The heat could simply be extracted from rocks at depth in a local framework characterized by the anomalous regional gradient of 110 mW/m2 (Ilkışık, 1992; Serpen and Mihcakan, 1999). The Balcova geothermal system represents “fracture zone systems with high temperatures at sweep base” as described by Serpen (2004). A higher water table beneath the mountainous terrain to the south of the fracture zone (the Agamemnon Fault) likely creates terrain-induced forced convection in the Balcova geothermal system (Serpen, 2004).

2.3. Hydrogeological characteristics Two geological units discussed in the previous section determine the overall hydrogeology of the system in the BGF. The alluvial layer supplies fresh water and demonstrates unconfined aquifer properties. The Bornova Flysch is a complex formation including permeable meta-sandstones, allochthonous limestones and impermeable shales (Figs. 3 and 4). As the allochthonous limestone units are not intersected in any of the wells drilled in the study area, the metasandstones are considered to be the main aquifer for the hot water and they demonstrate confined aquifer properties. The unconfined alluvial aquifer is extremely permeable and transmits significant amounts of water. It is primarily used to supply drinking and irrigation water to the Balcova plain. It is mainly recharged by direct infiltration of precipitation and seepage from Ilica Creek. The thickness of the shallow aquifer ranges from 50 m to 150 m. The cold water of this aquifer is pumped via wells that are about 30 m deep. The groundwater table in the shallow surficial aquifer is between 5 and 20 m from the ground surface (Fig. 5). Variations in groundwater table in the unconfined aquifer are less than 5 m, annually. The discharge rates of the non-artesian geothermal wells in the BGF range from 20 L/s to 100 L/s. As the general conductivity of the Bornova Flysch is fairly low, these wells are thought to be fed mainly from the meta-sandstones and the fault zone. The water circulation in the BGF is thought to be confined to the fault zone and to a minimum depth of 2000 m (Serpen, 2004).

Fig. 6. Isotopic composition of some samples from the study area.

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

As seen from the cross-section view of the BGF and its vicinity (Fig. 4), the geothermal water of the BGF discharges from the Agamemnon fault zone that cuts the low permeability Bornova Flysch. Therefore, the geothermal fluid is confined to a very narrow region within the fault. It is believed that the general water inflow to the system takes place from either the main fault or from the meta-sandstone and allochthonous limestone layers that recharge from outcrops in the far-south parts of the study area. 3. Materials and methods As a part of the field studies, a hydrogeochemical sampling campaign was completed in the summer months of 2004. The hydrogeochemical sampling program included a total of 39 sampling stations representing geothermal waters, surface waters, groundwaters and sea water. The locations of these stations are shown on Fig. 2. The samples collected from 39 stations were analyzed for physical and chemical parameters as well as for some isotopic properties. Before the samples were collected, both hot and cold water wells were operated for 20–25 min and scaling inhibitor pumps in hot water wells were shut down. Three sets of samples were taken from each sampling station; a 1000 mL sample for anions, a 1000 mL sample for isotopes and a 50 mL sample for cations. Two geothermal wells, seawater, a sample from Balcova Dam Lake and two groundwater samples were collected for isotope analysis. All water samples were filtered through 0.45 µm filter paper and stored in polyethylene bottles. Nitric acid is then added to samples that were to be analyzed for cations in order to obtain a pH value of less than 2. The pH, temperature and electrical conductivity (EC) values were measured in the field with portable equipments (WTW-pH330 and WTW-EC330). Cations were analyzed by ICP-MS spectrophotometry, Cl and HCO3 were analyzed by volumetric methods and the SO4 by gravimetric methods. The analytical errors in anion analysis were determined to be less than 2.5%. The AquaChem computer code was then used to assess the water chemistry of the samples. Deuterium, Oxygen-18 and Tritium isotopes were analyzed to determine the origin of hot and cold waters within the geothermal system. 1000 mL samples were sent to the Isotope Laboratory of the State Hydraulic Works (DSI) in Ankara, Turkey. The analysis was carried out in accordance with the standards defined by the International Atomic Energy Agency (IAEA). In this regard, Oxygen-18 and Deuterium analyses were conducted with the mass spectroscopy technique that had an uncertainty of ±0.05‰ and ±1.0‰, respectively. On the contrary, Tritium analysis was performed with the liquid scintillation counting technique with a detection limit of ±0.25 TU. 4. Results and discussions The extend of groundwater pollution was assessed using physical and chemical indicators. The physical indicators mainly include the overall mixing patterns of hot and cold waters as well as the amount of thermal pollution. The chemical indicators include the geochemical composition of hot and cold waters of the area as well as the distribution of particular constituents

19

(i.e., antimony, arsenic, boron and lithium) Finally, a number of preventive measures that should be taken to protect and sustain the quality of cold water reserves are discussed. A geographic information system (GIS) platform is developed to provide a tool that allows spatial analysis of parameter distributions within the study area. The parameter distribution maps are generated by implementing the built-in interpolation algorithm (i.e., inverse distance weighing) of the GIS platform used in this study (i.e., ArcGIS v9.0 package of ESRI Inc.). The specific domain of interest for this study is the shallow aquifer around the BGF Although the domain of interest does not contain three sampling stations (i.e., BC-8, BC-10 and BC-11), their parameter values are still used in generating the parameter distribution maps given in the following sections. 4.1. Physical indicators of groundwater pollution 4.1.1. Mixing patterns of hot and cold waters The isotope composition of the hot and cold waters of BGF are of meteoric origin and plot on a line parallel to waters of the general Mediterranean Region precipitation (Fig. 6). However, there are some differences between cold groundwater and deep geothermal water isotope chemistry (Table 1). The cold water oxygen-18 and deuterium values ranged from −6.1 to −6.4, −35.8 to 39.8, respectively. The oxygen-18 value of the geothermal water were found to be higher than the cold water due to the water-rock interaction. Tritium values range from 1.1–2.0 TU for deep geothermal waters, but cold groundwater has 4.70 TU. This indicates that the cold groundwater has a shorter circulation time than the deep geothermal waters. It is, however, suspicious to find high tritium values in geothermal waters. If the geothermal waters are assumed to be older than 50–60 years, no tritium levels should have been measured in these waters. Thus, this finding could only be explained by the fact that young cold waters are mixed with old geothermal waters. In the water samples excluding the sea water, there is a strong linear relationship (r = 0.98) between tritium levels and Cl concentrations. Based on this relationship, a value of 330 mg/L Cl should have been measured in geothermal waters. However, the highest Cl value in geothermal samples were measured to be 276 mg/L, which is an indication that geothermal waters are mixed with young cold waters. Based on the tracer tests reported by Aksoy (2001) and Aksoy et al. (2008) the reinjected geothermal water flow velocity was calculated to be between 2.7 m/h and 4.3 m/h in shallow wells (up to 100 m). B9 is a shallow well that intersects the highly permeable alluvium layer and the flysch. This well is

Table 1 Isotope composition of some water samples Sampling number

δ18O (o%)

δ2H(o%)

Tritium (TU)

B4 BD-3⁎ BD-7 BC-22 SW5 Balcova Dam

−8.0 −5.7 −5.9 −6.1 2.5 −6.4

−47.4 − 42.2 − 38.6 − 35.8 12.2 − 39.8

2.0 1.1 1.3 4.7 3.7 4.7

⁎Simsek (2001).

20

X

Well depth m

T °C

pH

Geothermal fluid samples B1 503,115 4,248,997 B4 503,462 4,248,980 B5 503,015 4,248,996 B7 503,172 4,249,033 B10 502,765 4,249,032 BD1 502,864 4,249,196 BD2 503,482 4,249,219 BD3 503,706 4,249,187 BD4 503,065 4,249,240 BD5 502,599 4,249,492 BD7 502,804 4,249,221 BD9 504,219 4,249,217 BD10 502,724 4,248,998

104 125 110 100 125 564 677 750 630 1100 600 776 750

115 117 124 115 114 135 137 128 132 117 115 138 104

7.2 7.4 7.4 7.0 7.5 8.2 8.4 8.2 8.3 8.2 7.0 8.9 7.6

Surface water samples SW-1 502,832 4,248,526 SW-2 502,962 4,249,038 SW-3 502,463 4,251,118 SW-5⁎ 506,200 4,250,880

– – – –

7.9 7.8 9.8 8.2

⁎Sea water.

Y

19.0 40.1 23.1 23.0

Mg+ 2 mg/L

Na+ mg/L

HCO−3 mg/L

SO−4 2 mg/L

Ca+ 2 mg/L

K+ mg/L

1925 1950 1813 1948 1948 1632 2010 1926 2020 1853 2190 2020 1473

23.3 21.2 31.4 22.7 26.9 19.1 15.2 22.2 20.1 17.6 26.8 14.5 22.3

26.2 24.8 21.6 27.6 26.5 29.7 30.1 27.9 32.5 31.8 32.0 35.1 27.7

4.9 5.1 6.2 7.6 8.0 2.7 2.5 3.0 2.4 2.5 9.1 4.9 9.0

345.1 347.3 323.1 402.0 400.5 417.1 508.5 435.5 460.3 399.1 382.9 476.4 345.4

550 661 610 611 650 698 664 680 682 690 575 390 690

219 186 165 198 192 168 186 205 231 189 213 228 159

684 2236 1384 55,600

64.1 22.1 34.3 570.4

1.6 35.5 35.4 415.0

33.6 5.4 13.6 1565.1

10.3 392.8 284.3 14420.5

225 595 413 180

117 296 164 2450

EC µS/cm

Cl− mg/L

Al µg/L

As µg/L

B µg/L

Ba µg/L

Be µg/L

190 172 178 216 205 194 260 241 250 227 220 276 138

51 21 29 20 40 30 42 53 68 40 30 5050 127

197.7 173.2 242.7 384.2 363.7 298.4 1419.8 674.6 776.8 163.5 357.2 278.1 261.6

9950 9224 9804 15904 15079 13756 21333 20483 20822 12935 18270 20453 7806

129.13 100.19 528.27 125.92 128.91 124.48 102.16 116.54 125.59 109.5 135.35 125.48 107.25

0.75 0.42 0.74 0.66 0.7 0.89 0.7 1.09 0.9 1 0.55 1.38 0.68

17 180 208 30406

21 26 126 1034

1.5 182.4 63.7 231.0

b20 9499 3354 5046

20.7 121.5 35.3 87.7

Br µg/L

Cd µg/L

Cr µg/L

273 242 262 270 262 266 352 318 326 276 291 364 211

0.32 0.27 0.24 b .05 b .05 b .05 b .05 b .05 b .05 0.19 b .05 b .05 b .05

2.7 0.9 1.3 28.2 30.1 25.5 30.6 30.3 31 1.5 31.2 24.2 1.5

b .05 22 0.82 271 b .05 278 b .05 83061

b .05 b .05 b .05 2.26

0.9 0.6 1.7 15.2

Cu µg/L

Fe µg/L

Li µg/L

Mn µg/L

Ni µg/L

Pb µg/L

Sb µg/L

Zn µg/L

6.9 15.7 6.5 13 23.8 10.3 26.6 13 11.9 4.3 12.9 19.2 58.8

570 138 419 146 126 99 24 31 24 262 95 4886 747

1126 1080 999 1465 1442.4 1417.2 1873.9 1652.8 1706.4 1101.4 1555.9 1615.2 851.9

64.38 43.62 44.68 44.58 45.7 31.1 15.01 21.69 19.33 21.53 23.16 83.28 47.69

3.3 14.7 b .2 b .2 3.7 b .2 b .2 b .2 0.4 0.8 b .2 14 40.8

2.3 4.7 1.2 0.6 0.6 0.3 0.5 0.4 0.5 0.8 0.4 9.5 2.5

124.8 38.9 688.5 234.0 52.6 26.0 104.4 109.0 114.8 193.9 152.3 58.0 169.3

20.7 39.6 9.1 5.3 14.7 7.1 7.6 8.3 7.6 6.8 7.2 14.0 37.0

6.3 1.7 5.1 184.2

10 323 563 1876

5.3 1014.2 281.6 0.2

15.57 52.38 99.50 2.39

5.3 b .2 20.1 b .2

0.2 0.3 2.8 3.5

0.8 23.7 14.6 0.1

4.9 5.8 10.1 0.8

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

Table 2 Chemical analysis results for geothermal water and surface water samples

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

equipped with a perforated casing that extends across the contact between the flysch and alluvium. The reinjected waste geothermal fluid pumped down this well unfortunately escaped to the alluvial zone through these perforations. The reinjection operation continued from 1996 to 2002, during which, 1.5 to 2 million m3 of geothermal fluid are pumped into the aquifer annually. The remaining (40–100 L/s) waste geothermal fluid was discharged to the Ilica Creek bed where it infiltrated to the highly permeable alluvial aquifer. 4.1.2. Thermal pollution of cold waters The temperature of the regional groundwater is a physical parameter that directly influences the quality of water for drinking and irrigation purposes, particularly in the vicinity of geothermal areas such as the BGF. Typically, when the temperature of water is above 25 °C, it is considered to be a heated resource and is not suitable for drinking. In geothermal waters (Table 2), there is a strong link between temperature and B (r = 0.70) and Li (r = 0.67) concentrations. There also exists a weak linear correlation between boron concentrations and water temperature in cold water samples

21

and well depth. On the other hand, well depth demonstrates a weak negative correlation with Cl concentration and EC values. These results show that elevated temperatures and boron indicate the presence of a thermal water component. The BGF system is mainly controlled by the steeply dipping Agamemnon fault zone. Thus, the depths of geothermal wells depend on their proximity to the fault line. The heated waters quickly rise and discharge into the alluvium along the fault line. Hence, the temperatures of shallow and deep geothermal wells are similar. Hot waters in the study area range between 104 °C and 138 °C and are saline (Tables 2 and 4). The water temperature of wells drilled in the shallow aquifer ranges from 21.6 °C to 42 °C, which clearly shows that it is thermally polluted (Table 5). The thermal pollution occurs principally near and to the northwest of the Agamemnon Fault. Particularly, cold water sampling stations BC-16, BC-19, BC-20 and BC-21 are thermally polluted (Fig. 7). Moreover, water samples with temperatures higher than 35 °C could only be used for irrigational purposes with caution (IWQC,1991). It must be noted that the detrimental effects of these waters are not only related to their heat content but also to their chemical composition.

Fig. 7. Groundwater temperature in the unconfined surficial aquifer.

22

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

Table 3 Chemical analysis results for cold groundwater samples X

Y

Groundwater samples BC-1 505,513 4,250,951 BC-2 504,632 4,250,484 BC-3 503,140 4,250,695 BC-4 503,067 4,251,319 BC-5 502,311 4,250,964 BC-6 502,476 4251332 BC-7 501,628 4,250,964 BC-8 500,139 4,250,514 BC-9 502,140 4,249,702 BC-10 501,503 4,248,664 BC-11 502,816 4,248,583 BC-12 505,329 4,248,065 BC-13 503,948 4,249,801 BC-14 505,158 4,249,913 BC-15 502,849 4,250,082 BC-16 502,666 4,249,860 BC-17 502,338 4,249,878 BC-18 502,397 4,249,656 BC-19 502,101 4,249,676 BC-20 502,219 4,249,755 BC-21 502,811 4,249,926 BC-22 504,246 4,248,976

Water Level m

WellDepth m

T °C

Ph -

EC µS/cm

Ca+ 2 mg/L

K+mg/L

Mg+ 2 mg/L

Na+ mg/L

HCO3- mg/L

SO−4 2 mg/L

1.2 3.7 6 2.4 5.4 N.D. N.D. 2 19 – 11 6.3 N.D. 7.8 20.5 N.D. N.D. 19.3 N.D. N.D. 21 –

8 28 25 21 35 N.D. 18 9 20 – 72 N.D. 17 N.D. 21 25 27 80 60 75 60 –

21.8 25.7 26.6 26.3 23.5 22.6 22.6 22.8 28.5 22.4 21.6 22.1 24.6 23.8 30.0 29.1 29.0 42.0 39.5 37.5 35.0 18.0

7.1 7.4 7.0 7.0 7.3 6.0 7.0 6.9 6.9 6.9 7.7 7.5 6.8 6.4 6.7 7.3 7.2 6.3 6.8 6.9 6.6 7.5

5540 1374 1872 1873 1401 1560 1707 1707 1053 1053 873 1310 960 823 1029 467 1182 1815 1725 1627 1653 695

267.7 127.0 113.8 146.9 121.8 92.3 216.7 143.8 72.0 92.0 75.4 78.5 99.6 63.9 76.3 61.5 66.0 20.8 64.4 86.8 48.2 8.8

62.5 5.2 11.2 12.4 12.9 13.0 17.2 16.5 22.1 1.0 3.6 42.2 1.2 6.0 8.2 10.4 9.8 27.6 16.9 15.8 20.7 1.3

160.8 28.1 32.7 48.2 45.1 65.6 71.2 56.3 38.9 68.3 54.0 51.3 24.7 31.1 31.8 27.5 28.5 7.7 19.9 39.2 19.5 3.8

815.6 67.6 180.4 208.0 142.6 365.0 152.1 170.8 167.6 53.6 12.9 93.5 83.3 74.6 127.0 154.4 189.1 346.9 205.0 131.6 262.2 12.8

639 457 530 518 468 422 470 396 432 432 364 298 412 307 518 401 456 436 451 467 518 110

888 112 296 256 221 222 185 214 123 102 82 164 82 42 123 123 205 288 246 164 168 15

N.D. no data.

4.2. Chemical indicators of groundwater pollution Chemical analysis of hot geothermal water and cold samples in BGF are presented in Tables 2 and 3 and their descriptive statistics are given in Tables 4 and 5. For this particular study, all water samples besides the geothermal fluid samples are considered to be cold waters. These include the wells drilled into the shallow aquifer for water supply purposes and the samples collected from the surface waters in and around BGF (i.e., Ilica Creek and Izmir Bay). The hot geothermal waters of the BGF are Na–HCO−3 type waters (Fig. 8). The cold groundwaters, on the other hand, are characterized to be Mg–Ca–HCO3, Na–HCO3 and Na–Cl type waters (Fig. 8). The hot waters have a pH range of 7.0–8.9, whereas the cold waters have a pH range of 6.0–7.7. The electrical conductivity (EC) values range from 1473 to 2190 μS/ cm for hot waters and from 467 to 5540 µS/cm for cold waters (Tables 4 and 5). The maximum EC value is recorded in a cold water well (BC-1) that is close to the seashore (Fig. 2). This particular well is influenced by salt water intrusion and is a Na–Cl type water. When this well is excluded, the maximum EC value becomes 1873 µS/cm. The Ca+ 2 and Mg+ 2 ions that are generally present in high concentrations in cold waters are usually low in hot waters (Nicholson, 1993). In BGF, Ca+ 2 values range from 14.5 to 31.4 mg/L, Mg+ 2 values range from 2.4 to 9.1 mg/L, and Na+ values range from 323 to 508 mg/L (Table 4). SO−4 2 and Cl− concentrations range from 159 to 231 mg/L and 138 to 276 mg/L, respectively, in hot geothermal waters of the BGF (Table 2). On the other hand, the concentrations of SO−4 2 and Cl− in cold waters range from 15 to 296 mg/L and from 10 to 495 mg/L, respectively, when sea water intruded BC-1 well is excluded. The SO−4 2 and Cl− concentrations in hot waters are relatively low compared to cold waters.

Mn concentration in geothermal waters range from 15.01 to 83.28 µg/L whereas it reaches to 2382 µg/L in cold waters. BC-1, BC-11, BC-14, BC-18 and BC-21 contain Mn levels above the drinking water standard, which is believed to be related to local lithology (ITASHY, 2005). The hot waters contain high concentrations of As, B, Br, Li and Sb. In particular, As, B and Sb concentrations reach levels as high as 1420 µg/L, 21333 µg/L and 688.5 µg/L, respectively, making the geothermal fluid of the BGF extremely toxic for human and plant life. The correlation coefficients between temperature and As (r = 0.53), B (r = 0.67), Br (r = 0.81) and Li (r = 0.69) are typical for hot geothermal fluids. The toxic element levels in cold waters are low under normal conditions. With maximum levels of 170.1 µg/L, 8463 µg/L, 711.9 µg/L and 25.6 µg/L for As, B, Li and Sb, respectively, it is clear that the cold waters of the BGF are contaminated by the geothermal water as well as sea water. Antimony is a rare element that typically originates from hydrothermal alteration of rocks (Inan and Tanyolu, 1982). It is a highly carcinogenic chemical and its toxicity shows similar characteristics to arsenic poisoning. The U.S. Environmental Protection Agency (EPA) has set a national limit of 6 µg/L antimony for drinking waters (EPA, 2003). The maximum permissible antimony concentration in drinking water has been set as 5 µg/L in the Turkish Drinking Water Quality Standard (ITASHY, 2005). In the BGF, the antimony concentrations are between 26 and 689 µg/L in hot geothermal waters; between 0 and 26 µg/L in groundwaters; and, between 0 and 24 µg/L in surface waters. SW-2 and SW-3 also have high levels of antimony, attributed to the discharge of waste geothermal fluid into the Ilica Creek bed. Moreover, the antimony concentration of the BC-11 water is also high. Arsenic is a typically high in geothermal waters. It mostly originates from pyrite and arsenopyrite. High arsenic

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

23

Table 3 (continued) Cl− mg/L Al µg/L As µg/L B µg/L Ba µg/L Be µg/L Br µg/L Cd µg/L Cr µg/L Cu µg/L Fe µg/L Li µg/L Mn µg/L Ni µg/L Pb µg/L Sb µg/L Zn µg/L Cl− mg/L Al µg/L As µg/L B µg/L Ba µg/L Be µg/L Br µg/L Cd µg/L Cr µg/L Cu µg/L Fe µg/L Li µg/L Mn µg/L Ni µg/L Pb µg/L Sb µg/L Zn µg/L Groundwater samples 1356 61 5.7 106 12 0.7 120 9 1.1 193 12 1.2 153 28 4.3 495 24 2.6 484 8 3.3 263 8 1.9 145 13 16.3 95 10 1.1 24 10 26.5 134 14 5.1 104 8 1.1 85 6 1.8 70 10 1.7 86 56 2.2 101 17 3.2 170 306 170.1 117 31 11.5 113 71 10.8 182 19 17.9 10 314 12.9

1511 410 4423 5244 2889 4108 643 2117 3179 70 49 494 1220 580 2988 4149 4505 8463 4349 1416 5168 b 20

19.60 36.89 19.22 71.47 75.34 34.73 96.03 24.71 17.43 4.27 24.64 30.99 30.95 49.36 35.12 46.97 56.74 66.45 41.52 25.49 44.16 48.28

0.67 b.05 b.05 b.05 b.05 b.05 b.05 b.05 0.11 b.05 b.05 b.05 b.05 b.05 b.05 0.08 b.05 0.53 0.12 b.05 0.09 0.08

4210 240 462 1075 357 1231 1211 666 352 345 39 277 173 93 127 163 504 217 179 228 252 44

0.7 0.06 0.06 b .05 b .05 b .05 b .05 b .05 0.11 0.16 0.08 b .05 b .05 0.1 b .05 0.06 b .05 b .05 b .05 b .05 b .05 0.25

concentrations in drinking waters are now known to increase cancer risk in humans (Chatterjee and Mukherjee, 1999). The EPA and Turkish standards for arsenic in drinking water have been set at 10 µg/L. In addition to human health effects, high arsenic concentrations in irrigation waters are also toxic to plants and cultivated crops. It has the tendency to accumulate

Table 4 Descriptive statistics for geothermal fluid samples (n = 13)

T pH EC Ca+ 2 K+ Mg+ 2 Na+ HCO−3 SO−4 2 Cl− Al As B Ba Be Br Cd Cr Cu Fe Li Mn Ni Pb Sb Zn

Unit

Maximum

Minimum

Mean

Median

Std. Dev

°C – µS/cm mg/L mg/L mg/L mg/L mg/L mg/L mg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L

138.00 8.90 2190.00 31.40 35.10 9.10 508.50 698.00 231.00 276.00 5050.00 1419.80 21333.00 528.27 1.38 364.00 0.32 31.20 58.80 4886.00 1873.90 83.28 40.80 9.50 688.46 39.60

104.00 7.00 1473.00 14.50 21.60 2.40 323.10 390.00 159.00 138.00 20.00 163.50 7806.00 100.19 0.42 211.00 0.05 0.90 4.30 24.00 851.90 15.01 0.20 0.30 25.95 5.30

122.38 7.79 1900.62 21.79 28.73 5.22 403.32 627.00 195.31 212.85 430.85 430.12 15063.00 150.67 0.80 285.62 0.11 18.38 17.15 582.08 1375.93 38.90 6.07 1.87 158.95 14.23

117.00 7.60 1948.00 22.20 27.90 4.90 400.50 661.00 192.00 216.00 40.00 298.40 15079.00 125.48 0.74 273.00 0.05 25.50 13.00 138.00 1442.40 43.62 0.40 0.60 114.79 8.30

10.70 0.60 181.96 4.76 3.63 2.55 56.00 85.25 23.32 38.80 1388.16 349.57 4904.88 114.00 0.25 43.52 0.10 13.98 14.10 1312.53 313.53 19.77 11.63 2.62 170.67 11.51

2.3 3.1 1.2 3.5 3.4 4.2 5.6 3.5 0.6 2.7 0.8 1.3 1.9 0.6 3.1 2.8 3.5 3.7 1.8 2.0 3.6 1.8

5.8 5.4 10.2 15.5 2.6 3.8 5.6 1.9 3.4 4.7 0.8 2.6 3.0 2.2 0.7 8.4 11.9 10.6 5.8 4.3 12.0 2.7

1743 b10 b10 b10 b10 b10 b10 488 b10 b10 55 b10 b10 b10 b10 22 13 1219 223 46 71 140

52.7 36.7 377.6 321.1 136.8 65.1 62.4 187.1 466.0 19.7 11.4 30.8 14.5 12.6 178.9 244.2 186.1 711.9 401.5 292.6 456.8 5.7

2382 1.5 3.8 3.3 1.7 3.0 0.5 5.9 5.6 0.4 63 2.1 6.2 460 1.3 4.6 1.7 623 33.3 7.9 413 4.4

b .2 b .2 1 b .2 0.6 b .2 1.3 b .2 0.2 1.5 17.2 77.9 0.2 16.2 b .2 1.7 0.7 3.2 41.4 4.1 3.3 5

4.2 0.4 0.5 0.7 1.0 0.9 1.5 0.1 0.5 0.2 0.8 0.5 0.2 0.2 0.3 1.4 1.0 1.3 4.1 0.7 1.2 0.3

0.36 0.13 0.13 0.09 1.19 0.15 0.14 0.06 4.68 0.13 25.59 0.66 0.09 0.12 0.59 0.79 1.32 1.48 5.82 2.54 0.44 3.00

219.7 8.5 169.7 40.0 5.7 7.1 32.9 10.4 379.5 48.4 308.8 59.3 49.3 6.8 28.7 13.2 148.5 13.1 347.0 58.0 4.9 9.1

in plant tissues when arsenic contaminated waters are used for irrigation purposes (Badruk, 2003; Zhang et al., 2002). Within the study area, arsenic concentrations in geothermal waters are between 164 µg/L and 1420 µg/L, similar concentrations (i.e., 1471 µg/L) observed in other geothermal fields of the Aegean (Gemici and Tarcan, 2004). It is important to note that all these values are above the drinking water standard value of 10 µg/L (ITASHY, 2005) and hence possesses serious health risks to humans. Arsenic correlates strongly with boron (r = 0.68) and lithium (r = 0.74). High correlations observed between arsenic, boron and lithium indicate that arsenic is introduced to the environment via geothermal fluid. The arsenic concentrations in groundwater samples are between 0.7 and 170.1 µg/L. Particularly, the samples from BC-9, BC-11, BC-18, BC-19, BC-20, BC-21 and BC-22 have arsenic concentrations exceeding the EPA limits. The BC-18 well contains the highest arsenic concentration in any groundwater and is clearly contaminated by geothermal fluid. Surface water samples collected from SW-2 (182.4 µg/L) and SW-3 (63.7 µg/L) also contain high levels of arsenic due to the discharge of waste geothermal fluid to Ilica Creek. Boron is another contaminant present in geothermal fluids. High boron concentrations are known to create health problems in humans, animals and plants (Mastromatteo and Sullivan, 1994; Col and Col, 2003). The boron limit in Turkish standards has been set at 1 mg/L for drinking waters (ITASHY, 2005). Similarly, boron concentrations of 1.0 mg/L or less are considered to be suitable for irrigation purposes for sensitive crops. In the geothermal fluids of the BGF, the boron concentrations are between 7.8 mg/L and 21.3 mg/L (Table 4); and boron ranges between 0.0 mg/L and 9.5 mg/L in surface waters (Table 2). The spatial distribution of boron concentration in the shallow aquifer is presented in Fig. 9. The majority of plain has values above the irrigation water standard

24

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

Table 5 Descriptive statistics for groundwater samples (n = 22)

Temperature pH EC Ca+ 2 K+ Mg+ 2 Na+ HCO−3 SO−4 2 Cl− Al As B Ba Be Br Cd Cr Cu Fe Li Mn Ni Pb Sb Zn

Unit

Maximum

Minimum

Mean

Median

Std. Dev

Turkish water standard (ITASHY, 2005)

US water standard (EPA, 2003)

% exceedance in 22 samples based on Turkish standard

°C – µS/cm mg/L mg/L mg/L mg/L mg/L mg/L mg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L µg/L

42.00 7.70 5540.00 267.70 62.50 160.80 815.60 639.00 888.00 1356.00 314.00 170.10 8463.00 96.03 0.67 4210.00 0.70 5.60 15.50 1743.00 711.90 2382.29 77.90 4.20 25.59 379.50

18.00 6.00 467.00 8.78 1.00 3.77 12.80 110.00 15.00 10.00 6.00 0.70 20.00 4.27 0.05 39.00 0.05 0.60 0.70 10.00 5.70 0.44 0.20 0.10 0.06 4.90

27.05 6.96 1513.59 97.46 15.35 43.37 182.57 431.91 196.41 209.36 47.59 13.77 2636.14 40.93 0.11 565.68 0.10 2.59 5.63 188.18 194.19 183.08 8.03 1.00 2.25 89.48

25.15 6.95 1387.50 82.65 12.65 35.80 153.25 443.50 166.00 118.50 13.50 3.25 2503.00 36.01 0.05 264.50 0.05 2.75 4.50 10.00 157.85 4.51 1.15 0.70 0.52 36.45

6.34 0.41 988.42 58.68 14.23 32.00 168.30 103.47 172.16 283.42 86.89 35.58 2231.99 21.93 0.16 886.86 0.14 1.28 4.08 439.94 193.91 521.59 18.25 1.10 5.44 119.26

– 6.5 ≤ pH ≤ 9.5 2500 200 10 50 200 – 250 250 200 10 1000 300 – – 5 50 2000 200 – 50 20 10 5 –

– 6.5 ≤ pH ≤ 8.5 – – – – – – 250 250 200 10 – 2000 4 – 5 100 1300 300 – 50 – 15 6 5000

– 14 5 9 64 32 27 – 18 18 9 32 68 0 – – 0 0 0 18 – 23 9 0 9 –

(see Fig. 9) and irrigating crops with these waters represents significant risks for plants such as the mandarins, tomatoes and flowers that are commonly cultivated in and around the BGF.

Some of the agricultural fields and greenhouses of the study area have been abandoned as a result of high boron content in irrigation waters. The groundwater resources of the Balcova

Fig. 8. Distribution of water samples on a Piper diagram.

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

25

Fig. 9. Boron concentrations in the surficial aquifer water.

basin are being polluted by boron due to geothermal water seepage from the south and sea water intrusion from the north. The high levels of Br and Cl observed in BC-1 is an indication for sea water intrusion to the alluvial aquifer. Lithium is another trace element found in geothermal fluids that originates in silicate minerals (Inan and Tanyolu, 1982). It is commonly used as a tracer to trace the distribution of geothermal fluid. Within the study area, lithium and boron have shown a relatively high correlation (r = 0.69) in all waters sampled. The lithium concentrations of hot water samples range from 0.85 mg/L to 1.87 mg/L whereas they range between 0.01 mg/L and 0.71 mg/L in cold groundwater samples and from 0.002 mg/L to 1.01 mg/L in surface waters. Lithium concentrations exceed the limits of typical fresh groundwater in many wells around the BGF including BC-3, BC-4, BC-9, BC-18, BC-19, BC-20 and BC-21. Lithium concentration of SW-2 water is very close to the lithium concentrations observed in hot waters, further demonstrating the impact of waste geothermal fluid discharge to the Ilica Creek. According to Cl-20B-200Li plot, the effect of geothermal and sea water on some water wells are clearly observed (Fig. 10) where BC-9, BC-18, BC-19, BC-20 and BC-21 are influenced by

geothermal pollution and BC-1, BC-4, BC-6 and BC-7 are influenced by sea water intrusion. 4.3. Preventive measures for the protection of cold water resources Our results show that groundwater contamination in Balcova Plain is a function of several factors including but not limited to geothermal water originating from the Agamemnon fault zone. Although geothermal activity has been in existence for centuries, its detrimental effects were spatially limited to an area in the immediate vicinity of hot water springs. It is now known that the natural discharge of hot geothermal fluid from these springs is to some extent responsible for the contamination of cold water resources of the area (i.e., the Ilica Creek and regional groundwater in the shallow aquifer). The recent developments in BGF have dramatically accelerated the influence of geothermal waters on local fresh water resources. We conclude that both natural and anthropogenic mechanisms are responsible for the contamination of cold water resources of the area. A schematic representation of

26

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

Fig. 10. CI-20B-200Li plot for mixing system.

these contamination mechanisms is presented in Fig. 11. There is a natural contamination mechanism, wherein the geothermal fluid discharges from the fault zone and is dispersed at the bottom of the alluvial aquifer. Without human intervention, the extent of this dispersion would have been limited to the immediate vicinity of the natural groundwater pathway. However, the over-exploitation of groundwater in this aquifer has resulted in the spread of geothermal fluid in vertical and lateral directions. This overexploitation pattern is not only a function of the total water extracted from the aquifer but also to the depths of the boreholes drilled in the alluvium. Deep water wells trigger the mobilization of geothermal fluid that otherwise would stay deep within the shallow aquifer. Thus, construction of deep cold water wells (i.e., N50 m) must be avoided to minimize the intrusion of geothermal fluid into their capture zones. Furthermore, it is crucial to minimize the amount of water pumped from these wells in order not to overexploit the aquifer. Finally, cold water wells that are chemically and thermally polluted by the geothermal fluid must be sealed up and abandoned as soon as possible. Another reason for the contamination of the shallow aquifer is the failure in some geothermal well casings. Both production and reinjection wells are constructed in such a

way that filter zones are not properly situated. There are a number of wells in the BGF where the shallow aquifer is not properly isolated from production and reinjection fluids. Furthermore, geothermal fluid has resulted in severe corrosion problems in well casings, which in turn failed to contain the fluid inside the well during its ascent to the surface. In this regard, proper maintenance of production and reinjection wells should be carried out on a regular basis together with routine monitoring of the physicochemical characteristics of the geothermal fluid produced. Moreover, future development in the BGF with regard to the construction of new geothermal wells (i.e., location and production rates) must be carefully planed and implemented to minimize their impacts on groundwater quality. A strategic environmental impact assessment study would need to be conducted prior to any major developments. Faulty reinjection practices are probably the most important factor in the deterioration of groundwater quality in the shallow aquifer. Unfortunately, the reinjection operation conducted from well B9 (a shallow well of less than 50 m that is mainly drilled into the highly permeable alluvium layer) has resulted in excessive contamination of shallow cold water aquifer. This situation further deteriorated as a result of the reduced fresh water inflow to the aquifer due to droughts in late 1990s and of

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

27

Fig. 11. A schematic representation of groundwater pollution in the BGF.

the reduced surface water influx to the plain from Ilica Creek due to Balcova Dam. The discharge of waste geothermal fluid into Ilica Creek is another reason for the accelerated dispersion of geothermal fluid. The highly permeable sediments in the creek bed has given ample opportunities for the geothermal fluid to seep into the shallow aquifer. Thus, the discharge of waste geothermal fluid to the Creek bed must be stopped. A possible solution would be to construct a concrete channel that directly discharges to the sea. In addition, fresh water inflow to the plain must be increased by properly scheduled water releases from the dam. Finally, sea water intrusion to the aquifer is another important aspect of the deteriorating groundwater quality in the plain. Being mostly related to overexploitation of the aquifer's water for irrigational purposes, sea water has started to intrude towards the plain in BC-1, BC-4, BC-6 and BC-7. Thus, these areas must be monitored closely and the farmers in the coastal zone should be educated as to the proper use of irrigation water. They should be clearly advised not to use waste geothermal fluid for irrigation. Moreover, some water from the Balcova Dam reservoir should be allocated to satisfy the demands of the farmers for irrigation water. 5. Conclusions Hot geothermal fluids contaminate the shallow groundwater at the Balcova geothermal field near Izmir, Turkey by

both natural and anthropogenic mechanisms. The anthropogenic mechanisms are the most important cause for the contamination of cold surface and subsurface water resources in and around the BGF. The anthropogenic contamination is due to faulty reinjection of waste geothermal fluid, failures in geothermal well casings, discharge of waste geothermal fluid to Ilica Creek, construction of deep cold water wells and overexploitation of the shallow aquifer. Concentrations of arsenic, antimony and boron are extremely high and are a danger to human health and agricultural production. Arsenic is believed to be the most important environmental pollution parameter within BGF due to its carcinogenicity; and boron is the most detrimental chemical for agricultural crop production. Fortunately, the Balcova Plain is served by the water distribution system of Izmir City and the contaminated groundwater is generally not used for human consumption. However, boron pollution in groundwater has damaged agricultural production in the region. The reduction in citrus production and abandonment of several greenhouses are due to the elevated boron concentrations in irrigation waters withdrawn from the shallow aquifer. Concentrations of several parameters decrease from the geothermal field in the south to the Aegean Sea in the north. Furthermore, it has also been found that geothermal fluid influences the composition of the shallow aquifer from a depth of about 60 m from the ground surface. Considering

28

N. Aksoy et al. / Journal of Contaminant Hydrology 103 (2009) 13–28

that the shallow aquifer has a thickness ranging between 50 m to 150 m and thickens towards the sea, hot geothermal fluid disperses towards the northern parts of the BGF area from the bottom of the aquifer. Excessive pumping of deep wells in the shallow aquifer is the main reason for rapid dispersion of hot geothermal fluid into the shallow aquifer. In addition, shallow reinjection operations performed in the past as well as the discharge of waste geothermal fluid to the Ilica Creek bed have created further problems. Finally, the reduced fresh water inflow to the plain due to Balcova Dam is also responsible for the reduction in groundwater levels and higher dissolved solids in the unconfined aquifer. Although geothermal waters are an alternative energy source to fossil fuels, they have their own environmental impacts that need to be addressed before they are used extensively. In this regard, it is of utmost importance that geothermal fields are planned carefully and their environmental impacts mitigated properly. Mineral contents of geothermal fluid in many fields are extremely high and thus, improper disposal of these waters can pollute dilute shallow water resources. Therefore, appropriate disposal of waste geothermal fluids is critical to protecting the shallow groundwater resource. Acknowledgements The authors would like to express their gratitude to the excellent comments made by the anonymous reviewers that improved the quality of the manuscript. References Aksoy, N., 2001. Monitoring the Balcova-Narlidere geothermal system using tracers. Ph.D. dissertation, Dokuz Eylul University Graduate School, Izmir, Turkey, 150 pp., (In Turkish). Aksoy, N., Serpen, U., Filiz, Ş., 2008. Management of the Balcova-Narlidere geothermal reservoir, Turkey. Geothermics 37, 444–466. Badruk, M., 2003. Environmental problems in geothermal energy applications. Proceedings of the Geothermal Energy Seminar-TESKON 2003, 811 October, Izmir, Turkey, pp. 345–358 (In Turkish). Cakın, A., 2003. Environmental effects of geothermal applications, case study: Balcova geothermal field. MS Thesis, Izmir Institute of Technology, Turkey, 97 pp. Celik, M., Sabah, E., 2002. The geological and technical characterization of Ömer–Gecek geothermal area and the environmental impact assessment of geothermal heating system in Afyon, Turkey. Environmental Geology 41, 942–953. Chatterjee, A., Mukherjee, A., 1999. Hydrogeological investigation of groundwater arsenic contamination in South Calcuta. Science of the Total Environment 225, 249–262. Col, M., Col, C., 2003. Environmental boron contamination in waters of Hisarcik area in Kutahya province of Turkey. Food and Chemical Toxicology 41, 1417–1420. Demirel, Z., Yildirim, N., 2002. Boron pollution due to geothermal wastewater discharge into the Buyuk Menderes River, Turkey. International Journal of Environment and Pollution 18, 602–608. Dogdu, M.S., Bayari, C.S., 2005. Environmental impact of geothermal fluids on surface water, groundwater and streambed sediments in the Akarcay Basin, Turkey. Environmental Geology 47, 325–340.

EPA, 2003. National Primary Drinking Water Standards. Office of Water, United States Environmental Protection Agency. EPA 816-F-03-016. Erdogan, B., Gungor, T.,1992. Stratigraphy and tectonic evolution of the northern margin of Menderes massive. TPTJ Bulletin C 4/1, Ankara. (In Turkish). Fridleifsson, I.B., 2001. Geothermal energy for the benefit of the people. Renewable and Sustainable Energy Reviews 5, 299–312. Gemici, U., 2001. Durability of shales in Narlidere, Izmir, Turkey, with an emphasis on the impact of water on slaking behavior. Environmental Geology 41, 430–439. Gemici, U., Tarcan, G., 2002. Distribution of boron in thermal waters of western Anatolia, Turkey, and examples of their environmental impacts. Environmental Geology 43, 87–98. Gemici, U., Tarcan, G., 2004. Hydrogeological and hydrochemical feature of the Heybeli Spa, Afyon Turkey: arsenic and the other contaminants in the thermal waters. Bulletin of Environmental Contamination and Toxicology 72, 1107–1114. Genc, C.S., Altunkaynak, S., Karacik, Z., Yazman, M., Yilmaz, Y., 2001. The Cubukludag graben, south of Izmir: its tectonic significance in the Neogene geological evolution of the western Anatolia. Geodinamica Acta 14, 45–55. Ilkışık, O.M., 1992. Silica heat flow estimates and lithospheric temperature. Proceedings of Anatolia XI. Congress of World Hydrothermal Organization, May 13-18, Istanbul-Pamukkale, Turkey, pp. 92–106. Inan, K., Tanyolu, E., 1982. Mineralogy, 2th edition. Doyuran Publication, Istanbul. 315 pp. ITASHY, 2005. Regulation on waters for human consumption. Official Gazette dated 17/02/2005, No.25730, Ankara (in Turkish). IWQC, 1991. Irrigation water quality criteria. Technical Procedures Act, Amendment to Water Pollution Control Regulation, Official Gazette Date: 7.1.1991, No: 20748, Ankara (in Turkish). Kaya, O., 1999. Fault composition of western Anatolia: assessment with regards to petroleum and geothermal potential. Symposium on the industrial raw materials of western Anatolia (BAKSEM), Izmir, 8–14 March 1999 (In Turkish). Lund, J.W., Freeston, D.H., 2000. World-wide direct uses of geothermal energy 2000. Geothermics 30, 29–68. Maden, N., Gelisli, K., Bektas, O., Eyuboglu, Y., 2005. The relationship between crust structure and tectonics in Anatolia. 2nd Engineering Science and Young Investigators Congress, Istanbul, 17–19 November 2005 (In Turkish). Mastromatteo, E., Sullivan, F., 1994. Summary: international symposium on the health effects of boron and its compounds. Environmental Health Perspectives 102, 139–141. Nicholson, K., 1993. Geothermal Fluids: Chemistry and Exploration Techniques. Springer-Verlag, NewYork. 263pp. Ongur, T., 2001. Geology of Izmir Agamemnon Hot Springs-Balcova Geothermal Area and new conceptual geological model. Report for Balcova Geothermal Ltd., Izmir, Turkey. 24 pp. (In Turkish). Satman, A., Onur, M., Serpen, U., 2002. Production Performance Project of Balcova-Narlıdere Geothermal Field, Project Report, Balcova Geothermal Inc. Department of Petroleum and Natural Gas, Istanbul Technical Univ. Istanbul, Turkey. 512 pp. (In Turkish). Serpen, U., Mihcakan, M., 1999. Heat flow and related geothermal potential of Turkey. Geothermal Resource Council Transactions 23, 485–490. Serpen, U., Kayan, I., 2001. Hydraulic balance of Balcova geothermal field. Proceeding of 13th International Petroleum Congress and Exhibition of Turkey, Ankara. 8 pp. Serpen, U., 2004. Hydrogeological investigations on Balcova geothermal system in Turkey. Geothermics 33, 309–335. Serpen, U., 2005. Geothermal energy and its utilization in World and Turkey. Proceedings of the Geothermal Energy Seminar-TESKON 2005, 23-26 November, Izmir, Turkey, pp. 435–447 (In Turkish). Simsek, S., 2001. Personel Cmmunication. Izmir. Sozbilir, H., 2002. Geometry and origin of folding in the Neogene sediments of the Gediz Graben, western Anatolia, Turkey. Geodinamica Acta 15, 277–288. Tarcan, G., Gemici, U., 2005. Effects of the contaminants from Turgutlu– Urganlı thermomineral waters on cold ground and surface waters. Bulletin of Environmental Contamination and Toxicology 74, 485–492. Zhang, H., Ma, D.S., Hu, X.X., 2002. Arsenic pollution in groundwater from Hetao Area, China. Environmental Geology 41, 638–643.