SciELO - Scientific Electronic Library Online

 
vol.17 número1Applying DC resistivity imaging to investigating the relationship between water quality and transpiration beneath circular islands in the Okavango Delta, Botswana: a case study of Thata IslandMetal speciation in sediments from crude oil prospecting in the coastal area of Ondo State, Nigeria índice de autoresíndice de materiabúsqueda de artículos
Home Pagelista alfabética de revistas  

Servicios Personalizados

Revista

Articulo

Indicadores

Links relacionados

  • En proceso de indezaciónCitado por Google
  • No hay articulos similaresSimilares en SciELO
  • En proceso de indezaciónSimilares en Google

Compartir


Earth Sciences Research Journal

versión impresa ISSN 1794-6190

Earth Sci. Res. J. vol.17 no.1 Bogotá ene./jun. 2013

 

DRASTIC-based methodology for assessing groundwater vulnerability in the Gümüshaciköy and Merzifon basin (Amasya, Turkey)

Arzu Firat Ersoy* and Fatma Gültekin*

*Karadeniz Technical University, Engineering Faculty, Geological Engineering Department, 61080, Trabzon, Turkey Corresponding author: Arzu FIRAT ERSOY e-mail:arzufirat@gmail.com phone: + 90 462 377 20 63 fax: + 90 462 325 74 05

Recibido: 23/10/2012 - Aceptado: 04/042013


ABSTRACT

Preparing aquifer vulnerability maps has become crucial during recent years for preventing adding new ones to aquifers which have been contaminated due to environmental effects and been out of use. GIS techniques and DRASTIC method were used when preparing vulnerability maps for the basin in which the Gümüshaciköy and Merzifon aquifers are located. Groundwater flow is approximately directed west-east and many villages are located across the aquifer in the basin which contains two sub-provinces and is characterised by intensive agricultural activity. DRASTIC layers were created when preparing vulnerability map, using parameters such as groundwater level, recharge, aquifer environment, topography and hydraulic conductivity. The aquifer vulnerability map was prepared by overlapping the layers by means of GIS. , three different vulnerability zones were determined in the Gümüshaciköy basin according to DRASTIC scores low (<100), medium (100-140) and high (>140). Based on the vulnerability map, it was found that the Gümüshaciköy Basin had a low contamination potential. It was established that 16% of the basin had high vulnerability and 47% low vulnerability. Areas having high vulnerability generally overlapped areas where the slope was gentle soil above the aquifer was permeable.

Key words: Vulnerability Mapping, DRASTIC, Geographic Information System (GIS), Turkey


RESUMEN

La preparación de mapas de vulnerabilidad acuífera se ha convertido en una actividad crucial en los últimos años para prevenir la contaminación por efectos ambientales de un afluente y su posterior inutilización. Técnicas GIS y el método DRASTIC fueron utilizados en la preparación de mapas de vulnerabilidad en la cuenca donde están localizados los acuíferos Gümüshaciköy y Merzifon, en Turquía. El flujo de las aguas subterráneas corre aproximadamente Oeste-Este y varias poblaciones están ubicadas al paso del acuífero por dos subprovincias que se caracterizan por la actividad agrícola. Se crearon capas en el método DRASTIC cuando se preparó el mapa de vulnerabilidad con parámetros como nivel, recarga, ambiente del acuífero, topografía y conductividad hidráulica. La representación de vulnerabilidad se logró al sobreponer estas capas a través de técnicas GIS, lo que permitió determinar tres zonas diferentes de vulnerabilidad en la cuenca de Gümüshaciköy basado en los puntajes del método DRASTIC: baja (<100), medio (100-140) y alta (>140). Con base en este mapa, se concluye que la cuenca de Gümüshaciköy tiene un bajo potencial de contaminación. Se estableció que el 16 % de la cuenca es altamente vulnerable y el 47 % de baja vulnerabilidad. En aquellos lugares identificados con alto potencial de contaminación se suelen sobreponer áreas donde la inclinación de tierra sobre el acuífero es permeable.

Palabras clave: Mapa de vulnerabilidad, DRASTIC, Sistema de información Geográfica (GIS), Turquía.


Introduction

Groundwater has been considered as an important source of water supply due to its relatively low susceptibility to pollution compare to surface water. Groundwater quality is usually subject to contamination especially in agriculture-dominated areas having intensive activity involving the use of fertilisers and pesticides. Vulnerability assessment has been recognised for its ability to delineate areas which are more easily contaminated than others as a result of anthropogenic activity on/or near the earth's surface. Vulnerability studies can thus provide valuable information for stakeholders working on preventing further deterioration of the environment (Mendoza and Barmen 2006). 

The concept of groundwater vulnerability to contamination was introduced in the 1960s in France by Margat (1968). Several approaches for developing aquifer vulnerability assessment maps were adopted such as DRASTIC (Aller et al. 1987), GOD (Foster 1987), AVI (Van Stempvoort et al 1993), and SINTACS (Civita 1994). Conventional methods (i.e. DRASTIC, AVI, GOD, SINTACS) can distinguish degrees of vulnerability on a regional scale involving different lithology (Vias et al 2005). DRASTIC is a familiar method developed for the US Environmental Protection Agency (EPA) by Aller et al (1987) it has been used in several regions (Merchant 1994; Melloul and Collin 1998; Cameron and Peloso 2001; Al-Adamat et al 2003; Baalousha 2006; Jamrah et al 2007; Sener et al 2009; Massone et al 2010). 

The area studied in this research is located in Amasya (mid Black Sea region), namely the Gümüshaciköy-Merzifon Basin (GMB) (Figure 1). Groundwater is the major source of irrigation in the Amasya District in Turkey. Surface water has been the main source of water supply for irrigation during the last few decades (Firat Ersoy and Gültekin 2008). However, water demand has increased and groundwater is now used as a secondary source. Annual groundwater exploitation yield was only 3.5x106m3 during the 1970s, and rose to 5.5x106 m3 in 2005 (Firat Ersoy, 2007). Due to the excessive exploitation of groundwater, water levels have significantly decreased. Groundwater quality has also been affected by over exploitation. The town of, Gümüshaciköy is located in this basin. Some well water's nitrate concentration has reached 15.6 mg/l in the Gümüshaciköy Basin. Nitrite and ammonium concentration have reached 0.03 and 0.3 mg/l respectively, around the town (Firat Ersoy et al, 2006). 

This paper was aimed at assessing groundwater vulnerability to pollution in a shallow aquifer using the DRASTIC model and geographical information system (GIS) techniques combined with hydro-geological data layers, i.e. depth of water, net recharge, aquifer media, soil media, topography, impact of vadose zone and hydraulic conductivity. A vulnerability map, showing high, medium and low vulnerability areas was produced for the mentioned basin. 

Study area 

The GMB covers a 1,060 km2 area elevation ranging from 550- 1,873 m (Figure 1). Average annual rainfall is 458 mm average annual temperature is 13.6°C (URL-1) and the average annual potential evaporation is 680 mm (Firat Ersoy, 2007). The most important body of surface water flowing through the basin is the Gümüssuyu River, which discharges 8.5x106m3/year (Firat Ersoy, 2007). Groundwater in the basin draws from both alluvium aquifers, one being confined, (the Gümüshaciköy aquifer) and the other unconfined (Merzifon). Agriculture is widespread in the basin, and fertiliser and pesticide application have caused groundwater contamination through leaching. 193 wells had been drilled in the GMB up to 2006, 173 wells were aimed at irrigation, and 20 well for domestic purposes. 

Geology 

The Paleozoic metamorphic rocks in the study area, represent the oldest formation. These rocks consist of clayey schist, chlorite schist and green schist, marble and re-crystallised limestone. Upper Jurassic-Lower Cretaceous limestone, in the area has fossils which are generally compact, thick-bedded, very hard and fissured lower Cretaceous limestone is pink, very hard, thick bedded and micritic, overlying Jurassic limestone. Cretaceous limestone outcrops on the plain. The flysch series having mixed volcanic material composed of conglomerate, green and black sandstone, shale, marl, limestone, andesite, tuff and tuffite are deposited in the Upper Cretaceous limestone. Cenozoic beds started with the Middle Eocene age flysch series in the study area. Flysch consists of sandstone, shale, sandy limestone, marl, local conglomerate, tuff and agglomerate. The Miocene series consist of thick blue claystone and marl and the Pliocene beds of micro conglomerate, sandstone, sand, clay, gravel and a mixture of these layer thickness ranges from 10 to 50 cm in these series. The very loose layers are not continuous and change their lithology over short distances. This unit gradually become harder as one goes deeper and turns out to be conglomerate. Some blocks of the gravels are 50 cm thick and about 5-10 cm-in diameter 95% of such gravel and blocks are usually rounded and are composed of volcanic material. The Quaternary is characterised by alluvium and an alluvium cone consisting of detrical material that comes from north and south with the flood waters. Alluvium and cone (10-60 m thick) take the form of gravel, sand, clay and a mixture of these, along the Gümüssuyu, Köseler and Salhan Rivers. 

Hydrogeology 

The GMB's hydrogeological setting has been outlined by Firat Ersoy (2007). The most impotant geological units for groundwater transport in the basin are Quaternary alluvium and Pliocene clay, sand, gravel and a mixture of these. Unconsolidated Quaternary and Pliocene sediments are around 350 m thick. The other units underlying the alluvium do not bear significant amounts of groundwater. The GMB can be divided into discrete hydrogeological units, including permeable (alluvium), semi-permeable (weak cemented pebble and sandstone, silty clay and volcanic rocks) and impermeable (massive marble and limestone, silty clay and schist). Alluvial materials and the Pliocene units consisting loosely cemented pebbles, sand and clayey-silt materials outcrop in most parts of the basin. Known as the Gümüshaciköy aquifer, this part is crucial to groundwater storage and transfer since it is characterised by high conductivity and storage capacity. Deposits have a heterogeneous structure, being formed as alluvial cones at the end of tributary rivers. The alluvial cone formed by the alluvial unit of the Pasa and Yakacik river is called the Merzifon aquifer. Well logs show that the cone's middle sections consist of clayey levels between pebble and sand layers and that level becomes thin along the eastern edge, dominated by clay and silt. Since the section between the east of the Gümüshaciköy aquifer and the south of the Merzifon aquifer consists of Miocene clay and marl, it is not important in terms of groundwater. 

The Late Eocene volcanic rocks outcropping across the north, northwest and northeast of the basin form a catchment area with their fractured and fissured structure. Natural discharge in the basin is provided by a stream flowing through it from west to east. The Gümüshaciköy aquifer naturally discharges into the Gümüssuyu river, located in the east of basin. The basin contains numerous springs discharging from geological units, faults and fractures. Some are exploited as potable for drinking water and others are used for irrigation, consequently recharging the groundwater. The springs' total flow rate is 720 l/sec. Three ponds in the basin are used for irrigation. Infiltration into the groundwater from these ponds has been estimated as being 41.5 m3/year on average (Firat Ersoy, 2007). The basin contains 193 wells, 167 in the Gümüshaciköy aquifer and 26 in the Merzifon aquifer (DSÄ°, 2006). Well depth varies from 39 to 290 m and pump flow-rates from 5 to 60 l/sec (DSÄ°, 2006). As most of these wells are used for irrigation, pumps operate from May to October. The increased number of wells drilled in the aquifer during recent years and accordingly, the increased amount of water pumped from the aquifer has resulted in a decrease in groundwater level by 15 to 20 m (DSI, 2006). Several pumping tests have been performed at existing wells in the Gümüshaciköy and Merzifon aquifers. Data interpretation has indicated 89.7- 1727 m2/day transmissivity, 0.76- 19.17 m/day hydraulic conductivity and 1.5x10-5- 7.9x10-3 storage coefficient for the basin (Firat Ersoy, 2007). 

Materials and Methods 

DRASTIC, proposed by the US Environmental Protection Agency (Aller et al., 1987) and its modification termed SINTACS (Civita, 1994), are two methods for evaluating vertical vulnerability based on the following seven parameters: depth to water (D), net recharge (R), aquifer media (A), soil media (S), topography (T), vadose zone impact (I), and hydraulic conductivity (C) Figure 2). Each mapped factor is classified into ranges (continuous variables) or significant media types (thematic data) having an impact on pollution potential. Weighting multipliers are then used for each factor to balance and enhance their importance, the typical rating ranging from 1 to 10 (Table 1). The final vulnerability index is a weighted sum of the seven factors. 

Results 

Depth to water (D) 

Depth to water is defined as the distance (in meters) from the ground surface to the water table. Groundwater table depth in the GMB has been measured since 1976. This present study, has used the 2005 values for groundwater table depth. The 167 wells' location was digitised from the accompanying digital elevation model (DEM).Groundwater table depth changed between 9-40 m in the GMB the Merzifon aquifer has the lowest groundwater depth in the GMB. The deepest groundwater occurred at the end of the impermeable layer over the aquifer media in the mostly confined Gümüshaciköy aquifer. The depth to water table map was then classified into ranges defined by the DRASTIC model and assigned rates ranging from 1 (minimum impact on vulnerability) to 10 (maximum impact on vulnerability) (Figure 3). 

Net recharge (R) 

Net recharge is the total quantity of water infiltrating from ground surface to an aquifer on an annual basis. Local recharge in the study area comes from inflow by the Gümüssuyu river and its branches, irrigation return flow and direct recharge. The main groundwater recharge source are the Gümüssuyu River, springs, located high in the basin, and irrigation leakage. The average direct annual volume of recharge into the aquifer from the surface of the basin and from the springs is about 11334316 m3 (Firat Ersoy, 2007). Irrigation pond canals contribute 41.5 m3 recharge in the area (Firat Ersoy, 2007) the recharge map was then classified into ranges and assigned ratings from 1 to 8 (Figure 4). 

Aquifer media (A) 

Aquifer media refers to consolidated or unconsolidated rock which serves as an aquifer. The main aquifer being exploited and that most vulnerable to contamination is partially confined, here called the Gümüshaciköy aquifer the central and northern parts of the Gümüshaciköy aquifer are confined. The clayey layer over high permeability uncemented sediments is 2- 10 m thick from the drilling data. Clayey layer thickness of gradually changes from the centre to the north of the basin. The Merzifon aquifer is unconfined. The aquifer media was obtained using a subsurface geology map, geological sections, and drilling profiles of the Gümüshaciköy and Merzifon aquifers. The main aquifer includes Quaternary alluvium and Pliocene gravel, sand and clayey levels. The Merzifon aquifer's alluvial fan is relatively thin, consisting of coarse-grained gravel and sand with silt and clay interbeds. The aquifer media were mapped as shown in Figure 5

Soil media (S) 

Soil media refers to the uppermost portion of the vadose zone characterised by significant biological activity. Soil plays a significant role in the amount of recharge which can infiltrate into the ground and hence on a contaminant's ability to move vertically into the vadose zone. A soil's pollution potential is largely affected by the type of clay present, such clay's shrink/swell potential, and soil grain size. Soil media in the GMB was determined using drilling profiles. The Gümüshaciköy and Merzifon aquifers are covered by clayey gravel and sand and alluvial plains. Fractured volcanic rocks are located west and south-west of the GMB and limestone outcrops south of the basin. Thickness over the volcanic rock and limestone gradually changes form bottom to top, the hills especially, having little or no soil. The soil media map was then classified into ranges and assigned ratings from 3 to 10 (Figure 6). 

Topography (T) 

Topography refers to land surface slope variability. Slope degree will determine the extent of pollutant runoff and settling long enough to infiltrate. A digital elevation model (DEM) was used to extract the slope of the study area, while 27% of the GMB has a gentle slope, most of the basin has a steep slope. The areas in the extreme east and south consist of ridges which may reach 1050 m.. The topography has been mapped as shown in Figure 7

Vadose zone impact (I) 

The vadose zone is defined as the zone above the water table which is unsaturated. Unconsolidated clayey gravel and sand represents the vadose zone in the plain, volcanic rocks and limestone is the vadose zone in the mountain areas. The map of vadose zone impact is shown in Figure 8

The aquifer's hydraulic conductivity (C) 

Hydraulic conductivity is important because it controls the rate of groundwater movement in the saturated zone, thereby controlling the degree and fate of contaminants. Hydraulic conductivity values used in this study were derived from pumping test data. Hydraulic conductivity varied from 8.79 × 10−6 to 2.21 × 10−4 m/s in alluvium (Firat Ersoy, 2007). The hydraulic conductivity of the other rock in the basin was available from the pertinent literature. Hydraulic conductivity values for various rock types have been proposed by Domenico and Schwartz, (1990). The hydraulic conductivity of the limestone and fractured volcanic rocks, located in the west and south part of the basin, were 10-3 m/s and 3x10-4 m/s, respectively. Clayey unit permeability is 10−9 to 10−10 m/s. Hydraulic conductivity rating distribution is shown in Figure 9

The aquifer vulnerability map 

The vulnerability map was obtained using the seven hydro-geological data layers in the ArcView GIS software environment. DRASTIC scores ranged from 58 to 177, taking into consideration the determined ratings and weightings. These values were reclassified into three classes using the Natural Breaks (Jenks) classification method. The study area's vulnerability was classed as low (<100), medium (100-140) and high (>140) according to data obtained from hydrogeological investigations (Figure 10). 

The GMB's high groundwater vulnerability risk zones were mainly located in the centre of the basin where some villages are located and also in the northern and southern parts of the basin. These vulnerable zones covered around 16% of the studied area. Four springs in the southern area had as high vulnerability risk. 

The GMB's middle groundwater vulnerability risk zones were mainly located in the groundwater recharge area (Figure 10), these vulnerable zones covered around 37% of the studied area. The GMB's low groundwater vulnerability risk zones were mainly located in the west and south-east of the study area (Figure 10), these vulnerable zones covered 47 % of the studied area. 

The resulting vulnerability map indicated that the highest potential areas for contamination were the central part of the basin where the slope is gentle. In the southern area where karstic limestone outcropped, the high DRASTIC index probably represented the effects of aquifer media and hydraulic conductivity. Impermeable volcanic rocks and clay, silty-clay units located in the west and east respectively had low DRASTIC index. 

Conclusions 

The Merzifon-Gümüshaciköy (Amasya-Turkey) Basin is an important agricultural centre for the central Black Sea section groundwater is a major water source for such activity. Groundwater quality has deteriorated due to excessive abstraction of groundwater. This study involved using a GIS model and the DRASTIC method for determining the vulnerability of the groundwater in the basin. The aquifer vulnerability map was prepared using depth to water, net recharge, aquifer media, soil media, topography, vadose zone impact, and hydraulic conductivity. The study area was divided into three zones according to groundwater vulnerability assessment results: low (risk index <100); middle (risk index 100- 140) and high groundwater vulnerability risk (risk index >140). 

The DRASTIC method results should be useful in designing aquifer protection and management strategies. The DRASTIC index map indicated that overall potential for groundwater becoming polluted was low for the GMB. Low sensitivity areas lay outside the agricultural areas in the basin. The alluvium and most Pliocene sediments were used for agriculture in the GMB. The town of Gümüshaciköy is located on an aquifer recharge area. Areas determined by the DRASTIC method should thus be given priority in research in terms of contamination. High nitrate concentrations were mainly near urban areas according to the the study area's analysis (Firat Ersoy et al, 2006). High nitrate concentration was likely to be related to wastewater leakage from industrial activities, urbanisation and agricultural practices. 

Two towns and many villages were situated in the study area involving agricultural activities many wells were used for springs. The prevention of groundwater pollution caused by waste and wastewater in Gümüshaciköy's recharge area was significant owing to groundwater flow being west to east in the basin. Regarding urban planning and organisation of agricultural activities in the Merzifon and Gümüshaciköy districts, the vulnerability risk map prepared in the study could be most important when considering protection off groundwater quality  

Acknowledgements 

This work was supported by the Karadeniz Technical University's Scientific Research Fund Project number: 2008.112.005.14. The authors are grateful to Geomatics Engineer Dr. R. Nisanci and Y. S. Erbas for training in GIS mapping. 

References 

Al-Adamat. RAN., Foster. IDL., Baban. SMJ. (2003). Groundwater vulnerability and risk mapping for the Basaltic aquifer of the Azraq basin of Jordan using GIS, remote sensing and DRASTIC. Appl Geogr. 23:303- 324.         [ Links ]

Aller. L., Bennett. T., Lehr. JH., Petty. RH., Hackett. G. (1987). DRASTIC: a standardized system for evaluating groundwater pollution potential using hydrogeologic settings. USEPA Report 600/2- 87/035, Robert S. Kerr Environmental Research Laboratory, Ada, Oklahoma.         [ Links ]

Baalousha. H. (2006). Vulnerability assessment for the Gaza Strip, Palestine using DRASTIC. Env Geol 50:405- 414.         [ Links ]

Cameron. E., Peloso. GF. (2001). An application of fuzzy logic to the assessment of aquifers' pollution potential. Env Geol 40:1305- 1315.         [ Links ]

Civita. M (1994). Le carte della vulnerabilit'a degli acquiferi all'inquinamiento: teoria e pratica [Contamination vulnerability mapping of the aquifer: theory and practice]. Quaderni di Tecniche di Protezione Ambientale, Pitagora, Italy.         [ Links ]

Domenico. P. A., and Schwartz. F. W. (1990). Physical and Chemical Hydrogeology, John Wiley and Sons, New York, 506 pp.         [ Links ]

DSI. (2006). Yil Sonu Faaliyet Raporu, Ä°sletme Bakim Sube Müdürlüğü, Samsun (in Turkish).         [ Links ]

Firat Ersoy A., Ersoy H. and Gültekin F. (2006). Nitrate, Nitrite and Ammonia Contamination in Groundwater: A Case Study from Gümüshaciköy Plain. Turkey, Asian Journal of Water, Environment and Pollution, Vol. 4, No. 1, pp. 107-118.         [ Links ]

Firat Ersoy A. (2007). Gümüshaciköy (Amasya) Akiferi'nin Yeraltisuyu Akim Modeli. PhD Thesis, KTU Graduate School of Natural and Applied Sciences, Trabzon, Turkey (in Turkish with English Abstract).         [ Links ]

Firat Ersoy A., Gültekin F. (2008). Modeling Groundwater Flow In The Agricultural Area of Gümüshaciköy (Amasya, Turkey). Bulletin of Engineering Geology and the Environment, Vol. 67, No. 4, pp. 529-535.         [ Links ]

Foster S. (1987). Fundamental concepts in aquifer vulnerability, pollution risk and protection strategy. In: Van Duijvenbooden W, Van Waegeningh HG (eds) Vulnerability of soil and groundwater to pollutants. Committee on Hydrological Research, The Hague, pp 69- 86.         [ Links ]

Jamrah A., Futaisi AA., Rajmohan N., Al-Yaroubi S. (2007). Assessment of groundwater vulnerability in the coastal region of Oman using DRASTIC index method in GIS environment. Environ Monit Assess. doi:10.1007/s10661-007-0104-6.         [ Links ]

Margat J. (1968). Vulnerabilite des nappes d'eau souterraine a la pollution [Groundwater vulnerability to contamination]. Bases de al cartographie, (Doc.) 68 SGC 198 HYD, BRGM, Orleans, France.         [ Links ]

Massone H, Mauricio MQ, Martínez D. (2010.) Enhanced groundwater vulnerability assessment in geological homogeneous areas: a case study from the Argentine Pampas. Hydrogeology Journal, 18: 371- 379.         [ Links ]

Melloul AJ., Collin M. (1998). A proposed index for aquifer waterquality assessment: the case of Israel's Sharon region. J Environ Manage 54(2):131- 142.         [ Links ]

Mendoza JA. Barmen G. (2006). Assessment of groundwater vulnerability in the Río Artiguas basin, Nicaragua. Env Geol 50:569- 580.         [ Links ]

Merchant JW. (1994). GIS-based groundwater pollution hazard assessment: a critical review of the DRASTIC model. Photogramm Eng Remote Sens 60(9):1117- 1127.         [ Links ]

Sener E., Sener S., Davraz A. (2009). Assessment of aquifer vulnerability based on GIS and DRASTIC methods: a case study of the Senirkent-Uluborlu Basin (Isparta, Turkey). Hydrogeology Journal, 17: 2023- 2035. URL-1.,http://www.dmi.gov.tr/verideğerlendirme/yillik-toplam-yagis-verileri-AMASYA,15 March 2011.         [ Links ]

Van Stempvoort D., Ewert L., Wassenaar L. (1993). Aquifer vulnerability index (AVI): a GIS compatible method for groundwater vulnerability mapping. Can Water Resour J 18:25- 37.         [ Links ]

Vias JM., Andreo B., Perles MJ., Carrasco F. (2005). A comparative study of four schemes for groundwater vulnerability mapping in a diffuse flow carbonate aquifer under Mediterranean climatic conditions. Env Geol 47:586- 595.         [ Links ]