Modified DRASTIC method for groundwater vulnerability assessment in areas with diverse Quaternary deposits

Abstract

Developing accurate groundwater vulnerability maps is necessary for environmental planning and protection of groundwater resources. The DRASTIC method is one of the most widely used groundwater vulnerability assessment techniques. To achieve a more precise vulnerability estimation in areas where aquifers are covered with an extra layer of diverse sediments and thus, have more complex hydrogeology, e.g. in formerly glaciated regions, a further modification of the DRASTIC method is required. In such areas, the thickness of deposits can vary from thin layers with a high pollution potential to thick Quaternary layers making the groundwater protected against contamination. Therefore, the purpose of this study is to modify the DRASTIC method to be successfully applied in the areas characterized by a layer of diverse Quaternary sediments, which remarkably influence the nature of the infiltration conditions. First, the D-, S-, and I-parameters were modified, considering the nature of the Quaternary layer. To help the process, a model was created, which takes as input all necessary files for vulnerability assessment and creates a map using all parameters with weights assigned to them. Later, both the original and the modified DRASTIC methodology was applied in an area with glacial sediments located in Central Estonia. For the validation of methods, the comparison of results from existing vulnerability maps, which were produced by methodology specifically developed for local geological conditions, was used. In conclusion, the results generated by the modified DRASTIC method showed significantly more similarities with the existing maps than the original DRASTIC method. Thus, the modified DRASTIC method is successfully applicable in areas where the aquifer is covered with an extra layer of diverse Quaternary sediments.