POLLUTION POTENTIAL OF GROUND- WATER RESOURCES IN ANTALYA CITY

Transcription

1 POLLUTION POTENTIAL OF GROUND- WATER RESOURCES IN ANTALYA CITY Mustafa Yildirim and Bulent Topkaya Akdeniz University, Department of Environmental Engineering, Topcular, Antalya, Turkey Presented at the 13 th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region (MESAEP), Thessaloniki, Greece, Oct SUMMARY Antalya is the largest city at the Turkish Mediterranean coast with high population increase rates. During the last 25 years, the population has increased five fold, whereas the residential areas expanded by 25 times. One of the main consequences of this development is the stress placed on the local environment, water supply resources and waste disposal infrastructure. It is clear that degradation of any of these assets would have a negative effect on tourism, which is the city s most important source of income. In the recent years the pollution threat especially on the groundwater resources is worsened. As the whole drinking water demand of Antalya is supplied by groundwater resources, the vulnerability of groundwater to contamination around Antalya City is the main focus of this study. The parameters are calculated by using the geological, soil and topographical maps, in addition to the groundwater level data of the study area. The prepared thematic maps are integrated by the DRASTIC method to determine the vulnerable zones in the study area. Finally, DRASTIC indices for industrial and municipal pollutants are derived and vulnerability maps prepared. It is determined that the study area is highly vulnerable to industrial and municipal pollutants. KEYWORDS: Antalya, groundwater, vulnerability maps, DRASTIC method, Geographical Information Systems (GIS). INTRODUCTION The main residential areas of Antalya are located on groundwater-rich travertine formation, where precipitation and surface runoff can easily and rapidly penetrate through the ground. The porous rock forms the water bearing stratum, from which the whole city and the surrounding settlements obtain their drinking water via springs and wells that are drilled in the karstic limestone. It is assummed that the groundwater flows through three main duden channels (rivers in the subterranean), and then reaches the Mediterranean Sea. Tracer tests have demonstrated that flow velocity in the travertine is about 200 m/ day [1]. The study area which extends to approximately 758 km 2 consists of two travertine plateaus, separated by a 100 m- high cliff. The city of Antalya is located on the lower plateau. It is terminated by a cliff (on average 40 m high), and thus separated from the sea (Figure 1). The population increase rate of Antalya is considerably higher than the Turkish overall increase rate. Table 1 sets out the effects of the population increase more clearly: Between the years 1975 and 2002, the population has increased five-fold, whereas the residential areas have expanded 25-fold and the population density decreased fivefold (Figure 2). According to the results of the population census and projections, it can be forecasted that the number of residents will increase to more than two millions until the year 2030 [2]. It is an incredible increase with enormous environmental impacts on the groundwater resources of this area. On the other hand, only a part of the city has a modern sewerage system. In the remaining majority of the inhabited areas the wastewater is disposed via percolating septic tanks. Historically, the porous travertine formation, on which the major part of the city is settled, has been a convenient and inexpensive disposal option for wastewater and storm water, by simply percolating into the porous rock. Although numerous projects on amendment of the sewer system are ongoing, the rate of urbanization shadows these efforts. Therefore, it is most probable that, in the near future, septic tanks would be the major disposal system [1]. This study will mainly focus on the protection of the groundwater resources, which are under serious pollution threat. In Figure 2, it can be observed that the groundwater protection zones, as well as the extraction wells and some parts of the groundwater recharge area, are already 981

2 surrounded by settlements. Due to the topographic conditions and the existing land-use plans in the region, the city can only expand to the northern direction, and it is expected in the near future that the recharge areas of the groundwater sources and the extraction wells will be surrounded by settlements which have no sewer systems (Figure 2). In this study, the vulnerability of groundwater resources to contamination and possible impacts of various pollution sources on the groundwater are determined by using Geographic Information Systems (GIS), Remote Sensing data and the DRASTIC method. FIGURE 1-3D model of Antalya City. TABLE 1 - Development of population and the expansion of the residential areas in Antalya. Years Population Area (km²) Population/km² , , , Landsat-MSS 1987 Landsat-TM 2002 Landsat-ETM+ FIGURE 2 - Expansion of the residential areas of Antalya City. 982

3 MATERIALS AND METHODS The main pollution sources considered in this study are: Percolating septic tanks (settlements without sewer system) In 2002, new sewer systems for the western part of Antalya were completed, and the main domestic wastewater treatment plant with a deep-sea outfall system became operational. However, the new sewer system covers only less than 40 % of the city area and wastewater generated in the remaining residential areas, without sewer systems, is still disposed off by percolating septic tanks (Figure 3). As these settlements are located directly over the groundwater recharge area, percolating septic tanks are considered to be the main pollution sources of groundwater. Duden Holes Duden holes (sink holes) are openings in the travertine upper plateau, where water can easily move to underground. They are the most important systems for the transportation of contaminants (Figure 4). A cross section of a duden hole in Varsak region is illustrated in Figure 5. Industrial districts and abandoned landfill areas Two of the three industrial districts in the study area are located within the city boundaries and connected with the sewer system. The remaining main industrial site, Antalya Organized Industrial District (O.S.B.), is located directly on the duden channels and has an operational wastewater treatment facility with a capacity of m³/day. However, the treated effluents are discharged to areas near the duden channels and can easily reach the groundwater (Figure 3). In case of a malfunction in the wastewater treatment facility, the groundwater quality can be affected inversely. The abandoned landfill, within the catchment area of the duden channels, is out of operation, but due to lack of adequate impermeable bottom layers, it is possible that the leachate can also reach the groundwater (Figure 3). Petrol stations Parts of the main highways, connecting Antalya with other provinces of the country, are crossing the duden channels and passing near the extraction wells. Numerous petrol stations, located along these highways, are also considered as groundwater pollution sources, as leakages from underground storage tanks and losses during fuel transfers may reach the groundwater resources. The locations of the petrol stations can be observed in Figure 4. DRASTIC Model DRASTIC is a groundwater quality index for evaluating the pollution potential of large areas by using the hydro-geologic settings (factors) of the region. This method was firstly developed by EPA in the 1980s [3]. DRASTIC evaluates pollution potential based on seven hydro-geological factors, which make up the acronym DRASTIC: Depth of the water table, net Recharge, Aquifer media, Soil type, Topography, Impact of the vadose zone, and hydraulic Conductivity (Figure 6,Table 2) [3-5]. FIGURE 3 - Areas covered by the sewer system, location of the industrial areas and settlements. FIGURE 4 - Locations of highways, petrol stations and duden holes (GWPZ: Groundwater Protection Zone). 983

4 FIGURE 5 - Profile of a duden hole in Varsak region. DRASTIC Index (DI) = D r D w + R r R w + A r A w + S r S w + T r T w + I r I w + C r C w FIGURE 6 - Hydrogeological settings (elements of DRASTIC method). TABLE 2 - Hydrogeological settings (factors) and weights [6, 8]. DRASTIC factors Weights (D) Depth of the water table 5 (R) Net recharge 4 (A) Aquifer media 3 (S) Soil type 2 (T) Topography 1 (I) Impact of the vadose zone 5 (C) Hydraulic conductivity 3 Each factor is assigned a weight (1-5), based on its relative significance regarding the pollution potential. Each factor is further assigned a rating value between 1 and 10, depending on local conditions. High values correspond to high vulnerability. The attributed values are obtained from tables, which give the correspondence between local hydrogeological characteristics and the parameter value [6]. The DRASTIC index, a measure of the pollution potential, is computed by summation of the products of rating and weights of each factor as follows [6, 7]: where D r = Ratings to the depth to water table D w = Weights assigned to the depth to water table R r = Ratings for ranges of aquifer recharge R w = Weights for the aquifer recharge A r = Ratings assigned to aquifer media A w = Weights assigned to aquifer media S r = Ratings for the soil media S w = Weights for soil media T r = Ratings for topography (slope) T w = Weights assigned to topography I r = Ratings assigned to vadose zone I w = Weights assigned to vadose zone C r = Ratings for rates of hydraulic conductivity C w = Weights given to hydraulic conductivity The higher the DRASTIC index, the greater is the relative pollution potential. While the minimum value of the DRASTIC index is 23, its maximum is 226. It should be noted that such extreme values are very rare, and the most common values range between 50 and 200 [6]. The DRAS- TIC index can be further divided into four categories: low, moderate, high, and very high. The sites with high and very high categories are more vulnerable to contamination and, consequently, need to be managed more carefully [9]. The weights assigned are relative, therefore, a site with a low pollution potential may still be susceptible to groundwater contamination, but is less susceptible to contamination compared with the sites with high DRASTIC ratings [4]. In the framework of this study, the generalized DRASTIC index is divided into seven categories, in order to classify the vulnerability of the study area more accurately. 984

5 TABLE 3 - DRASTIC Index (DI) ratings [3,6,7]. Pollution potential Index Ratings Index Ratings in this study Low DI Moderate 100 < DI High 140 < DI Very High 180 < DI 180 < RESULTS AND DISCUSSION In order to create the vulnerability maps of groundwater resources, seven DRASTIC factors (Table 2) are transferred by using GIS software. Additionally, rating ratios for each setting are assigned and using the GIS map calculator, spatial results are calculated. These results are interpolated by using Inverse Distance Weighted (IDW) interpolation method and, finally, the vulnerability map for the study area is obtained (Figure 7) [10]. The vulnerability map shows that the pollution potential of groundwater sources in Topcular Airport zone is rated as very high, whereas the entire coastal zone of the city has a high-very high pollution potential. In order to take adequate measures against the pollution threat, the locations of each pollution source are overlapped on the vulnerability maps (Figures 8-10). The main results are: The entire study area (758 km 2 ) is located on highvery high rated zones (Figure 7). In the western part of the city, the sewer system is completed and under operation. In the remaining part of the city (covering 60 %), construction of the sewerage system should be completed immediately (Figure 8). Almost all of the scattered settlements in the surroundings of the city area are located directly on the duden channels. In these areas, wastewater disposal via percolating septic tanks should be avoided (Figure 8). The treatment plant of the Organized Industrial District should be amended with impermeable layered lagoons with adequate capacity sufficient for several days in order to achieve a degree of safety in case of malfunction in the plant operation (Figure 8). Due to the ability of direct access to groundwater flow, special care should be given to duden holes which are almost completely located in high - very high vulnerable-rated areas (Figure 9). Attention should be given to highways crossing the duden channels with many petrol stations located along them, as urban runoff can transport contaminants, such as zinc on the tires, metallic and synthetic machine oils, as well as other materials containing heavy metals, into groundwater (Figure 10). FIGURE 7 - Vulnerability map of the study area. 985

6 FIGURE 8 - Vulnerability map and locations of the scattered settlements, existing sewer system industrial districts, abandoned landfill, and duden channels. FIGURE 9 - Vulnerability map and locations of the duden holes. 986

7 FIGURE 10 - Vulnerability map and locations of petrol stations and highways. CONCLUSION In this study, the DRASTIC method is presented as a tool for the assessment of pollution potential of groundwater affected by various sources, and applied to Antalya city area. The vulnerability map shows that the activities take place in the study area represent serious threat for the groundwater sources where immediate measures should be taken. It is possible for the local authorities to assign groundwater protection zones and to create groundwater monitoring programs regarding areas of the highest contamination potential determined by the vulnerability maps. ACKNOWLEDGEMENTS The authors are grateful to Akdeniz University for financial support of this project (No: ). REFERENCES [1] Tractabel, Black & Veatch, Su-Yapi (1996) Antalya Metropolitan City, Antalya Water Supply and Sanitation Project, Environmental Impact Assessment Report, [2] DIE (2001) Result Census of 2000, [3] Aller, L., Bennett, T., Lehr, J.H., and Petty, R.J. (1985) DRAS- TIC: A Standardized System for Evaluating Groundwater Pollution Potential Using Hydrogeologic Settings, U.S. EPA, Robert S. Kerr Environmental Research Laboratory, Ada, OK, EPA/600/2-85/0108, [4] Aller, L., Bennett, T., Lehr, J. H., Petty, R. J., and Hackett, G. (1987) DRASTIC: A standardized system for evaluating groundwater pollution potential using hydrogeologic settings, EPA-600/ [5] USGS (1999) Improvements to the DRASTIC Groundwater vulnerability mapping method, U.S. Department of the Interior USGS Fact Sheet FS [6] Lobo-Ferreira, J.P. (1999) The European Union Experience on Groundwater Vulnerability Assessment and Mapping. static.teriin.org/teri-wr/coastin/papers/paper1.htm. [7] Thirumalaivasan, D., Karmegam, M., and Venugopal, K. (2003) AHP-DRASTIC: Software for Specific Aquifer Vulnerability Assessment Using DRASTIC Model and GIS. Environmental Modelling & Software, Volume 18,

8 [8] Lee, S., Lee, D.H., Choi, S.H., Kim, W.Y., and Lee, S.G. (1998) Regional Groundwater Pollution Susceptibility Analysis Using DRASTIC System and Lineament Density. gis.esri.com/library/userconf/proc98/proceed/to200/ PA- P171/ P171.htm. [9] Engel, B., Cooper, B., Navulur, K., and Hahn, L. (1997) Groundwater Vulnerability Evaluation to Pesticide and Nitrate Pollution on a Regional Scale Using GIS. ecn.purdue. edu/~aggrass/groundwater/ [10] Arslanoglu, M., Ozcelik, M. (2005) Improvement of Digital Terrain Elevation Data. Proceedings book of 10 th Turkish Scientific and Technical Surveying Symposium, Ankara, Received: January 31, 2006 Revised: April 18, 2006 Accepted: May 18, 2006 CORRESPONDING AUTHOR Mustafa Yildirim Akdeniz University Department of Environmental Engineering Topcular, Antalya Turkey Phone: Fax: m.yildirim@ttnet.net.tr FEB/ Vol 15/ No 9a/ 2006 pages