Twana O. Abdullah, Salahalddin S. Ali & Nadhir A. Al-Ansari
Halabja Saidsadiq Basin is located in the northeastern part of Iraq covering an area of about 1278 km2 with a population of about 190,727. Groundwater is the principal source of water in this area. Agricultural practices within the basin are widespread and located close to groundwater wells. This poses imminent threat to these resources. DRASTIC model integrated with GIS tool has been used to evaluate the groundwater vulnerability of this area. In addition, the DRASTIC model was modified using nitrate concentrations and sensitivity analysis to modify the recommended weighting value to get accurate results. The modified rates were calculated using the relations between each parameter and the nitrate concentration in the groundwater based on the Wilcoxon rank-sum non-parametric statistical test. While, to calibrate all types of modifications, the Pearson’s correlation coefficient was applied. The standard vulnerability map of the studied basin classified the basin into four zones of vulnerability index including very low (34 %), low(13 %), moderate (48 %), and high (5 %) vulnerability index, while the combined modification classified the area into five classes: very low (7 %), low (35 %), moderate (19 %), high (35 %), and very high (4 %). The results demonstrate that both modified DRASTIC rate and weight were dramatically superior to the standard model; therefore, the most appropriate method to apply is the combination of modified rate-weight.[1]

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