Using factor analysis and cluster analysis for hydro geochemical analysis of Gorgan water sources, the related data of two sampling periods in spring and winter is used. According to correlation matrix, in spring and winter, Po4-3, HCo3- and K+ much of the groundwater is correlated with electrical conductivity. Cl- has more combination with Mg-2 in spring, while there is the most combination between the Ca+2 and So4-2 in winter. The cluster diagrams show that there is similarity between Cl ions and Mg-2 in groundwater more than 88%, and 80% between So4-2 and Ca+2 ions in spring while there are the most similarity between So4-2 and Ca+2 in winter, and then Cl- and Mg-2, according to this and correlation matrix, the dominated type of groundwater is Mg-2- Cl- in spring and is Ca+2- So4-2 in winter. According to the analysis method, three factors which are effective on chemical combination of groundwater include: 1- Aquifer hydro geochemical Process, because most of the cations and onions have factor-load in high level. 2-Feeding by surface water (river, runoff,) because of increase of HCo3-, s concentration and groundwater’s Po4-3. 3- Human activity (seepage of wastewater, absorbing wells and…) because nitrate is showing the highest load in third factor. The nitrate’s concentration in groundwater is more influenced by wastewater and irrigation of agriculture fertilizers. In the third factor, the concentrations of Na+ and Cl- are considerably increased.
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