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

The DRASTIC method is one of the most widely used groundwater vulnerability assessment techniques. In areas where the main useful aquifers are covered with an extra layer of diverse sediments, a further modification of the DRASTIC method is required for a more precise vulnerability estimation. In this article, the DRASTIC method was improved in areas characterized by a layer of diverse Quaternary deposits remarkably influencing the infiltration conditions. Three parameters were modified: (1) the D-parameter was adjusted to consider the overlying Quaternary deposits that, in some cases, make the aquifer confined, (2) the S-parameter was replaced by the Quaternary sediment-type parameter to assess the hydraulic characteristics of the highly variable deposits, and (3) the I-parameter was replaced by the thickness of the Quaternary deposits parameter to describe the distance from the ground surface to the main useful aquifer. The original and modified DRASTIC methodology was applied in an area with glacial sediments in Central Estonia. Comparing the results using the original and the modified DRASTIC method to a former Estonian groundwater vulnerability method showed that the DRASTIC method was significantly improved and could, thus, be successfully applied in other areas characterized by a heterogenous Quaternary sediment cover.