Assessment and validation of groundwater vulnerability to nitrate and TDS using based on a modified DRASTIC model: a case study in the Erbil Central Sub-Basin, Iraq.

In recent years, groundwater vulnerability assessment has become a crucial step in effectively protecting groundwater resources against increasing groundwater pollution in recent years. Sustainable effectual management of groundwater sources in terms of quality has become a critical factor in the development of unplanned urbanization areas, especially in regions with intensive agricultural and industrial activities in the land use/land cover (LULC) models. In this study, the GIS-based DRASTIC model was used by modified to estimate the groundwater vulnerability of porous aquifers to nitrate and total dissolved solids (TDS). The DRASTIC and the modified DRASTIC models generate four different groundwater vulnerability zones: high (33.6, 37.8%), moderate (45.9, 42.3%), low (18.7, 18.3%), and very low (1.8,1.6%). DRASTIC_LULC index map provides four different vulnerability zones: low, moderate, high, and very high, covering 0.1%, 7.6%, 83.6%, and 8.7% of the Erbil Central Sub-Basin, respectively. The most important hydrogeological factors determining the DRASTIC vulnerability obtained from sensitivity analyses are depth to the water table and impact of vadose zone parameters with average effective weight values of 23.7% and 22.6%. For validating the DRASTIC_LULC model, the water quality parameters, nitrate and TDS, have been used with an accuracy of 68% and 79%, which indicates that the validation accuracy for this model is quite high. Maps obtained as a result of this study can be used to create a baseline map for the sustainable management of groundwater quality in vulnerable areas of the Erbil Central Sub-Basin and its planning.