Evaluating Quality Variation of Groundwater Resources in Marand Plain Using Unsupervised Combination Approach (GQI and GWQI Index)

Marand aquifer is one of the large plains with extensive agricultural and industrial activities and it is categorized in critical aquifer class. One of the problems of groundwater decline is groundwater quality changes that affect how they are used and managed. Therefore, in this study, using 46 water samples from wells, qanats and springs in June 2014 and June 2017 and analyzing the parameters of main, secondary and rare ions to calculate the GQI and GWQI groundwater quality indices. According to the output maps of these two indicators, which show the difference in determining the quality of drinking water in the region, it was not possible to choose one of these two indicators to determine the drinking water capacity of the region. The two indicators used, in order to achieve a single map, the method of unsupervised combination was introduced and used. The results indicate that a higher CI than the results of the two indicators. The results showed that Marand plain is in the middle and acceptable classes in terms of GWQI and GQI index. The highest and lowest GWQI and GQI indices were observed in the south and northwest of the plain, respectively. Comparison of drinking water quality index maps of the study area in 2014 and 2017 shows that in 2017 the area of plain, indicates a decrease in water quality over the last 5 years.