Spatial and Temporal Variability of Quality Parameters of the Dehloran Plain Groundwater, Ilam, based on sedimentary rocks formations

Groundwater has important role to supply fresh water in the world. In this study, chemical quality parameters of the Dehloran plain groundwater including: cations, anions, the electrical conductivity (EC), concentration of total dissolved solids (TDS), total hardness (TH), sodium absorption ratio (SAR), percent of sodium (Na%) and PH were studied in a 5-years period (2010-2014) in the 10 wells and 100 samples of Water Organization of the Ilam Province. Cations concentrations is as Ca2> Na> Mg2> K and Anions concentration is as Cl- > SO42- > HCO3-. In the five years period (2010-2014). The maximum and minimum of groundwater quality in the Dehloran Plain are as: EC = 946-7811 (μmohs/cm), TDS = 614-5233 (mg/l), TH = 246-3020 (mg/l), SAR= 1.19-11.64, percent of sodium (Na %) = 7.38-65.02 % and PH = 6.89-7.95. According standard indexes of Shoeller and Wilcoks, the Dehloran plain groundwater about some quality parameters such as: the electrical conductivity (EC), concentration of total dissolved solids (TDS) and total hardness (TH) is not appropriate for potable and agriculture, but it have not any problem about sodium absorption ratio (SAR) and PH, can be considered as appropriate for potable and agriculture consumption. Results show that the SAR having high correlation coefficient (0.69) with sodium ion. This correlation shows sodium ion emplace calcium and magnesium ions in colloidal soils. The sedimentary rocks formations have effective role in variation of quality of groundwater in the Dehloran Plain. The gypsum and evaporated rocks (Gachsaran formation) and carbonate rocks (Asmari formation) have caused to decrease groundwater quality. Correlation between HCO3- with Mg2 (45%) and with Ca2 (16%) show that the carbonate – dolomitic Asmari formation may be has been more effective role in produce of Mg2 than to Ca. We can suppose that origin of major cations (Ca2, Na) and major anions (Cl- , SO4) of the Dehloran plain groundwater are evaporatic Gachsaran formation and origin of anions and cations with low abundance (Mg and HCO3-) are carbonate – dolomitic Asmari formation. Origin of some parts of the Mg cations can be marly and shaly members of the Pabdeh and Gorpy formation. The detrital rocks (Bakhtiari conglomerate) have been not effective role in decrease Dehloran plain groundwater quality.