gol-e-gohar iron ore mine of sirjan in southern part of iran is a large open pit that operates below the groundwater table and during mining operation, dewatering is required to prevent operation processes from flooding. current operation is going on by digging wells in or out of the pit and pumping to prevent flooding. as a result of the former dewatering operation a vast deep cone of depression has been formed and water from all around the area is flowing into the pit. salinity of discharged groundwater is very high and may affect on the ground water quality and environment. on other hand, until now, tailings of mine activities have been disposed of without proper environmental safeguards. to address this problem, a tailings dam is proposed to be constructed in accordance with environmental standards. study of hydrochemistry and chemical processes involved in conjunction with isotopes study are applied to investigate the dewatering effects on the groundwater quality and their origins. for this, ground water samples were collected for hydrochemistry, trace elements and isotopes 18o and 2h studies. based on the results of chemical analysis, water types were categorized into four groups (na-cl, ca-cl, na-so4 and na-hco3) and based on water types, various ion ratios and isotope studies, it is concluded that groundwater of the pit area is affected by deep saline groundwater which is related to the northern salt marsh through the saltwater intrusion happening. while, distant ground waters are related to meteoric water containing dissolved minerals in contact. based on trace elements studies, mean concentration of elements for all water samples in descending order are: sr > fe > b > mn > ba > al > zn > as > pb > cu > mo > ni > co > u. evaluation of the results is done by comparing “heavy metal pollution index” (hpi), “heavy metal evaluation index” (hei) and “degree of contamination” (cd). the indices show that most of the water samples are counted as low contaminated according to who standards of drinking water and contamination levels are not dangerous. low concentration of the heavy metals in the groundwater of the area is mainly due to geochemical conditions and hydrogeochemical properties of the soil and its minerals contents. presence of calcite (caco3) in the area neutralizes the acid generated from sulfide oxidation and reduces the metals availabilities. in addition, high adsorption potential of heavy metals by soil also helps this situation. furthermore, in order to assess the effect of tailings waste disposal behind the proposed tailings dam and predict the risk of metals contaminant release from the tailings into the environment, laboratory batch and sorption isotherm tests and a field experiment were conducted on the soil of the area. results of experiments showed that although the concentration of trace elements in the tailings waste is very high, their adsorption in the soil profile (below tailings dam site) is generally strong indicating that the soils in the study area can restrain some of the elements from entering the groundwater. however, even metals that adsorb well to the soil may eventually enter the groundwater after a long time. therefore, the use of a 2.0 mm thick high-density polyethylene geotextile layer covered with clay to protect the geomembrane is suggested in the tailings dam system design.