Application of DRASTIC Model for Groundwater Vulnerability Assessment of the Ghaen Aquifer

1- Since the share of precipitation in Iran as the dry and semi-dry country is about a third of the global average (mm 250), actually in many parts of Iran including South Khorasan province and Ghaen plain, the main source of water for agriculture, drinking and the industry is groundwater. Groundwater sources because of being beneath underlying soil, are less sensitive and vulnerable than surface water from extensively and spot pollution sources caused by human activity but because of the ease of purification in case of contamination require proper management (Babiker et all. 2005). In order to prevent pollution of water resources, we need to identify an area that is high potential to contamination and high vulnerability to pollution sources. Vulnerability index is dimensionless and depends on properties of geological, hydrological and hydro geological of aquifer (Antonakos & Lambrakis, 2007). One of the most common methods used to estimate aquifer vulnerability is DRASTIC method that is provided by the US Environmental Protection Agency (Aller et al., 1987). Lots of studies in the literature was performed about groundwater vulnerability assessment with DRASTIC method in the world such as Jyangyn area located around the Yangtze River (You-Hailin et al. 2011), Romania (Gabriela Breabăn & Paiu, 2012), the aquifer Vdykvfrynja located in Jordan (Rakad Taany et al. 2013), Tunisia (Hamza et al. 2007), Brazil (Nober et al. 2007) Syria (Katta et al. 2010) America (Evans, 1990) and Italy (Vias et al. 2006). Also in Iran DRASTIC method is used for evaluating groundwater vulnerability in case of bazargan & poldasht (Asghari Moghaddam et al., 1388), Hashtgerd (Azad shahraki, et al., 1389), Davarzan (Amir Ahmadi et al., 1390), Neyshabur (Amirahmadi et al., 1392).
In this study, According to the importance of Ghaen ain plain in agriculture and saffron production, and also in line with sustainable development of groundwater resources in the plain, vulnerability assessment and determining the areas at risk in the region is considered. For this purpose, according to acceptable performance model DRASTIC, this model was used to determine the vulnerability of the Plains.
2- Materials and Methods study area
Ghaen plain is Sub-basins of KHAF- Petregan salt (Code 51) in South Khorasan Province which is located between Longitude 59ú 11ʹ to 58 úú 34ʹ east and latitudes between 33ú 3ʹ to 33 úú 26ʹ north. Figure 1 shows position of Ghaen aquifer into the country.
3- DRASTIC model
DRASTIC model is a descriptive method (index-overlapping) for aquifer vulnerability assessment. DRASTIC model basically gives the necessary information about the area can be used as theoretical background For the use of different methods to assess the risk of aquifer vulnerability.
The advantage of this method is that provides relatively simple algorithms that can be able to integrate a large amount of spatial data and Presented maps for the index and vulnerability classification. The basis of these methods is based on potential sources of contamination in the aquifer.
4- In this regard, by collecting input parameters of DRASTIC model in the area include depth of water, net recharge, aquifer and soil media, topography, impact of the vadose zone media and Hydraulic conductivity, the Ghaen Plain vulnerability assessment was carried out. According to Equation 1 aquifer vulnerability map was prepared in GIS software.
Equation (1)
The results of this study showed that the index of vulnerability DRASTIC model for Ghaen plain is between 75 and 152. Figure 2 shows the vulnerability of Ghaen plain.
The DRASTIC results indicated As seen in Figure 3 using the Baloosha classification (2006) in the range of about 0.44 percent of the area without risk of contamination, so low vulnerability in the range of 10.88 percent, less vulnerability in the area 80.52 percent, 6.42 percent have mild to moderate vulnerability and 1.71 percent of potential vulnerabilities within the region is moderate to high.
Also according to the Baloosha (2006) and Aller (1987) classification DRASTIC index was calculated. That about 6.29, 91.34 and 2.36 percent of the aquifer area was located in low, medium, and high vulnerable classes, respectively. Noted the high vulnerable zones were located in northeastern part of the area. The results can be applied for making management decisions in line with the sustainable use of groundwater resources in the Ghaen plain.