Zoning of Drinking Water Quality Using Entropy Method and Its Relationship with the Drought (Case Study: Abdalan Aquifer, Gachsaran)

The reduction of water quality in groundwater resources over the last half century has attracted increased amounts of attention from hydrogeologists. Therefore, different methods called quality indicators of ground water have been used to check the quality status of these vital resources. However, the use of expert judgments is one of the weaknesses of these qualitative models. In this research, it has been tried to use the entropy theory to evaluate the quality of ground water and reduce such judgments of taste. Sixteen water well samples were extracted along the Abdalan aquifer for physical and chemical analyses in 18 months.The results of the application of the entropy method showed that chlorine has the highest rate of influence on the quality of underground water in the region and is the main factor in the reduction of water quality. Also, the results of the entropy method showed that sodium and potassium have the most instability and constant changes. The highest entropy weight is related to magnesium and it shows that there are stable and uniform changes in the underground water of the studied area. In general, the results showed that 74% of the groundwater samples in the study area have good quality, 13% have average quality, and the other 13% have poor quality. Also, the inverse relationship between the drought index (SIAP) and the groundwater resources quality index (EWQI) in the 18-month period shows the leaching effect of evaporative formations in the conditions of increased precipitation.