Investigating the qualitative changes of groundwater in Quaternary sediments of Jovin plain using statistical and hydrochemical methods

It is very important to study the quality of groundwater and the zoning of qualitative parameters for different uses. In some cases, this related to composition and Quaternary deposits. Groundwater is considered as an important source of water resources due to its low pollution potential as well as its high storage capacity compared to surface water. The chemical composition of water-soluble ions is affected by various reactions that occur between water and aquifers. Numerous factors, such as poor recharge and nutrition, reactions between water and rock, such as the dissolution of evaporative rocks and the phenomenon of cation exchange from groundwater, mixing of waters such as the infiltration of saline seawater into coastal aquifers, agricultural return water can control the salinity of groundwater. This study aims to evaluate the quality of groundwater in Quaternary sediments of Jovin plain located in northeastern Iran, which includes the study of spatial changes in groundwater quality in different sectors and determining the factors affecting it.

In this study, a combination of statistical methods such as cluster analysis and correlation coefficients and hydrochemical methods such as ionic ratios and compound diagrams have been used to evaluate the chemical quality of groundwater. In this plain, three large zones can be seen as follows from the south to the north: A. Coarse-grained alluvial fans, the materials of these deposits are mostly gravel and sand, but they also contain coarse-grained and fine-grained layers and lenses. The physical properties of this unit, such as porosity, skewness and lack of cement, rate of weathering, are similar to very coarse-grained alluvial units. B. The young alluvial fan structures, this unit are mostly made of fine-grained materials such as sand, silt, along with horizons of gravel. They are a concentrated location for agriculture activities. From a morphological point of view, the aforementioned fan structures have not yet lost their morphology. Therefore, due to the lack of erosion and erosion grooves, the age of young alluvium has been attributed to the Holocene. C. Flood zone deposits in the northern part of the study area, two zones throughout, have formed parallel to the heights of Mount Jovin. To check the chemical quality of groundwater in Jovin plain, 29 water samples were collected from agricultural wells located in plain. The samples were then analyzed to measure cations (Na +, Mg2 +, Ca2 + and anion (SO42-, HCO3-, Cl-) and other chemical parameters including EC, TDS, TH and pH.

Based on the results of cluster analysis, the aquifer can be divided into 4 zones, each group having a different chemical composition. According to the matching of the information layers (grouping the groundwater quality with the quaternary outcrops of the region), the wells that make up zone one in terms of water quality are geologically in the structural area of ​​large foothill alluvial alluvium, zone wells. 2 In young alluvial fan structures, zone 3 and 4 wells are located in floodplain deposits. The type of water in the direction of groundwater movement varies from the southern heights of the plain to the north of the plain to the Kal-Shoor River (from zone 1 to zone 4) from sodium bicarbonate to sodium sulfate and finally to sodium chloride.

This process was based on the matching of the sodium cation diagram with the sulfate and chloride anions. In the study of ionic ratios, the origin of sodium is from the weathering of plagioclase-albite and ion exchange, magnesium from upstream granites, calcium due to ion exchange with quaternary sediments of the aquifer. The concentration of groundwater-soluble ions increases from the first group to the fourth group. In the first and second groups, the water type is bicarbonate-sodic, in the third group, sulfate-sodic and finally, in the fourth group, the water type is chloride-sodium. This indicates the series of anionic evolution and from the south to the north of the plain in the direction of groundwater flow. The high correlation between chlorine and sodium (R2 = 0.93) indicates the presence of a linear relationship between these elements and the role of the dissolution of halite in the chemical composition of groundwater in the region. However, the unequal concentration of chlorine and sodium in the analyzed samples of Jovin aquifer indicates the existence of another source (albite degradation or ion exchange) for these two ions and the Na / Cl ion ratio in all samples is more than 0.5, which also emphasizes this point. By examining the concentration of groundwater aqueous solution of TDS in groups 1 and 2, it is below 500 mg / l and indicates the weathering of silicates. Groups 3 and 4, located at the low stream of the plain, are above 500 mg / l, indicating the weathering of carbonates.