- - - Institute of Technology and Engineering, Standard Research Institute, Karaj, Iran
- - - Department of Geology Engineering, Imam Khomeini International University, Qazvin, Iran

Excessive exploitation of groundwater resources has negatively affected their equilibrium and the groundwater level in several aquifers. Naghade plain (one of Urmia lake aquifers) requires a proper and qualitative management which has suffered a decline in recent years. One of the most important indicators for assessing and zoning the quality of groundwater is to measure the concentration of water ions and determine the groundwater quality index (GQI) by combining the concentration of ions and their relationship with safe standards. The purpose of this study is to apply GQI and FGQI methods for assessing groundwater quality in Naghade plain, based on the World Health Organization (WHO) and the National Standard of Iran (INSO). For this purpose, the chemical parameters were used for sampling and analysis of hydro geochemical parameters and compared with the WHO and INSO standards. Due to the uncertainty that exists, the ability of the fuzzy set in the decision making process with the Fuzzy GQI method and the water quality of the area were studied based on the FGQI method. The results of FGQI were based on two WHO and INSO standards of between ۰ and ۱۰۰ variables and groundwater quality in terms of the totally undesirable levels. Finally, the FGQI method in threshold values is considered better than the GQI method and gradual changes in groundwater quality are considered and is a useful method for assessing groundwater quality in the area.