Sin-DRASTIC: A Modified Vulnerability Mapping Method for Alluvial Aquifer Hosted by Karst in the North of Hamadan Province, West of Iran

Since 1987, just after introduction of DRASTIC model by the committee of Environmental Protection Agency (EPA) of USA, this method has become highly popular for mapping the aquifer vulnerability analyses all around the world. Despite the criticisms raised against the selected factors' weights of the DRASTIC method in different cases, it still utilizes as a privilege method for groundwater vulnerability assessments in alluvial aquifers. However, sometimes the DRASTIC method is subjectively modified to be more compatible with the new conditions and assumptions (modified DRASTIC). Feasibility and accessibility of data gathering for running the DRASTIC method are the reasons that made it popular for groundwater studies. By using this method, an overview of aquifer vulnerability to pollution could be drawn. In karst aquifers, methods like GOD, EPIK, PaPRIKa, LEPT, and so on are all among the highly acceptable methods used for aquifer vulnerability evaluation. However, when an alluvial and a karst aquifer are adjacent, it will cause a major concern. In this case, overall vulnerability assessments would be complicated and difficult. Regarding this fact, finding and employing a comprehensive method to evaluate this critical condition will have a great importance. In northern territories of Hamadan Province, Western Iran, thick quaternary sediments cover deep karst aquifers and formations of Miocene. Occurrences of many collapse sinkholes in the overburden alluvial section and the karst bedrock made it possible for pollutants to enter the deep aquifers of the region more easily. Therefore, it is essential to consider the role of cover-collapsed sinkholes in any try towards conducting vulnerability assessments for the region. In this study, a modified version of the DRASTIC method, in which an extra layer containing the spatial distribution of sinkholes is included, has been used. This modified version is called the Sin-DRASTIC. Results of this study showed that adding the sinkhole distribution layer to the other main layers, commonly used for running DRASTIC method, will produce more reliable results.