Groundwater Contaminantion Analysis Using Fuzzy-Topsis, Case Study: ZANJAN Plain

Assessing the quality of available water is especially important to meet drinking needs. Therefore, it is important to prepare and formulate an approach that can provide a more appropriate evaluation with higher accuracy and taking into account the inaccuracies caused by instrumental errors and measurements. The aim of this study was to evaluate the groundwater quality of Zanjan plain based on a method similar to fuzzy ideal solution.

To achieve this goal,  57 and 59 groundwater quality samples in dry and wet seasons were used and the 28 quality parameters were analyzed in each sample. The relative closeness coefficient of each samples were determined based on fuzzy weight specified by the opinions of experts in this field for each quality parameters and the fuzzy decision matrix based on drinkable water quality standards. By calculating the relative closeness coefficient of each samples, the contamination ranking for each sample was determined.

The results show that the more polluted areas are mainly concentrated in the center and northwest of the plain and this is in complete harmony with the location of industrial centers (such as lead and zinc complexes) and the hydrogeological characteristics of the aquifer. In order to evaluate the accuracy of the ranking, the results of the proposed method were compared with the definite case of the method similar to the ideal solution. Examination of the qualitative parameters related to rank 1 (lowest pollution rate) shows that most of the parameters in this rank, which should represent the lowest pollution rate, have high values ​​in the definite method compared to the fuzzy method (for example, the amoun of the arsenic parameter located in rank 1 of the definite and fuzzy methods is equal to 0.4 and 0 micrograms per liter, respectively) and this has been repeated in reverse regarding the 59th rank (maximum pollution rate), which indicates the reliability of the rankings and the high accuracy of the proposed method.

The results showed that the pollution is concentrated in the central plains and partly in the North and Northwest plain due to the significant polluting industries, pesticides, and manure storage depot in these areas. Based on proposed approach can be calculated the rank pollution of groundwater quality samples with high accuracy, especially in cases where the assessment of water quality for drinking purposes must be considered.