Effect of geological formations on the quality and geochemical characteristics of groundwater Shiyan plain aquifer, Kermanshah

The plain of Shiyan, with an area of 207 km2,is one of the most important plains of the Kermanshah province, Iran. However, the framework of hydrogeochemistry of this plain has not been studied yet. This study investigated the hydrogeochemical characteristics of this aquifer through groundwater sampling, geological survey while considering the direction of groundwater flow. Hence, the geological map of the study area was prepared through aerial photographs and field investigation, and then a sampling of groundwater was carried out. After the chemical analysis of the samples, the dominant hydrogeochemical processes in the groundwater system were studied and interpreted according to the geological environment. According to the results, the most abundant process in the aquifer is ion exchange and the groundwater evolves hydrogeochemical as it flows from north-west to east and south-east. The electrical conductivity of the samples taken from the input and output borders of the plain is higher than that of its central zones due to the presence of the Amiran and Kashkan marly formations and maybe the elimination of dolomite from the broke-down zones. The results of the Piper, Stiff, Durov diagrams are consistent and indicate that the dominant water type in this aquifer is the bicarbonate with high magnesium. The Shahbazan Formation has the most influence of terrigenous agents on groundwater quality. Meanwhile, the Amiran and Kashkan formations are responsible for the high concentration of the chemicals found in the groundwater of the east and north of the Shiyan plain. Also, since the plain is entirely under irrigated cultivation and application of chemical fertilizers for increasing agricultural productivity is common in this region, the high level of nitrate in the aquifer should have a human-made origin.