The role of geological formations lithology on surface and groundwater quality of Shirin Darreh dam watershed

Assessment of drinking water resources quality and determination of natural and anthropogenic effective factors on their chemical composition has an important role in sustainability of ecosystems depending on these resources. In this study, aimed at assessing water quality of rivers and springs in Shirin Darreh dam watershed and the reservoir and investigating the effect of formations lithology on their quality, water quality data in 2018-2019 water year for 33 samples of the rivers, 6 samples of springs and one sample collected from the reservoir were used. Three water quality indices including WQIB, WQIMT, and WQIDD were calculated for these samples. 10 sediment samples were collected from the study area and their mineral content were determined to study the lithology effect on water quality. The results of Gibbs diagram showed that rock weathering was more important than evaporation and precipitation in determining the chemical composition of the study water resources. Also, the major type and face in the collected water samples, and gypsum, shale and marl were detected as the most important source of these ions. The results reflect the effect of the lithology on the chemical composition of the study water resources. Gypsum and the various clay minerals that were in accordance with the hydrogeochemical studies.The stored water in the reservoir had higher quality for drinking that can be contributed to the springs joining in adjacent to the reservoir. The higher quality of these springs can be due to their origin in the Tirgan karstic Formation.