The Determination of the Influential Parameters in Hydrochemistry of Hard Rocks and Karstic Groundwater in the West of Urmia, Iran

The investigation into water resources of hard rocks and limestone, is very important because of their quality and role in the supply of the portable water. More than 10 percent of Iran is covered with hard rocks formations which increases up to 25% in the northwest of Iran. Because of the high quality of hard rock and karstic aquifers and their suitable location for supplying the drinking water of rural areas, the exploration and exploitation of groundwater from these formations are of interest. In quantitative terms, while the frequency of springs in hard rocks is normally more than that of karstic aquifers, the discharge of karstic springs is normally higher. The hydrochemistry of groundwater in hard rocks and limestone is influenced by aquifer body material, groundwater flow velocity, and residential time of water in aquifer. The study area was located in the west of Urmia City, northwest of Iran as a part of Lake Urmia watershed. The geological units is mainly carbonate rocks (limestone and dolomite).
In order to investigate the quality of groundwater resources, 15 samples of springs were collected and analyzed for the major ions (HCO3, CL, SO4, Mg, Ca, Na, K). Other parameters such as TDS, PH and EC were also measured. Various diagrams and techniques like Durov and Gibbs diagrams, saturation index, and ion ratios were employed to determine the water type and faces and the source of ions. Also some diagrams were used to check water quality for agricultural and drinking usages. Pie diagrams of SO4, Na, and EC showed that the basin area located in young alluviums bearing gypsum caused an increase in SO4 and EC. Marls of Miocene formation in the area also had increased the concentration of Na in some water samples
Based on the samples position in the Piper, Durov, and Gibbs diagrams, most types of groundwater was bicarbonate and calcic types.
The main factors which controled the groundwater chemistry were processes such as ion exchange (due to the presence of clay minerals), weathering, and dissolution of limestone and dolomite formations. It was also found that the watersheds of the large number of springs were located in Permian limestone and detrital Miocene units.
Wilcox diagram showed that most of the samples were in the class C2-S1, which indicated their low salinity and their appropriateness for agriculture. Schoeller diagram also showed that the groundwater region had good and acceptable quality for drinking. Saturation index survey showed a highest value of unsaturity related to dolomites for the samples which is influenced by Silvana dolomitic formation. Under saturity of samples related to gypsum, halite, and anhydrate was expected because of the absence of saline gypsiferous formations in the area. The results of this research showed that the groundwater of the study area has a water with calcic and bicarbonate types with a high hydrochemical quality, which is appropriate for agriculture and drinking uses. It was also found that lithology has a major role in the hydrochemistry and quality of the groundwater. Weathering and solution of Routeh and Tertiary limestone karstic formations, and Silvana dolomitic formation have more impact on the groundwater quality of the study area. However, alluvial gypsiferous and Miocene formations with marl beds have a little impact on the quality of groundwater in the north, center and east of the area.