Groundwater that forms part of the water cycle. Temporal and spatial characterization of groundwater pollution is an important issue in the effective remediation of groundwater aquifers and the assessment of health risks. Uncertainty analysis is an integral step in the hydrological modeling process. Quantitative evaluation of uncertainty in the outputs of the simulation model and estimation of its parameters increase the confidence in the modeling results and correct knowledge of the sources of uncertainty. Due to the increasing use of groundwater models in the management and prediction of aquifer behavior, this study seeks to analyze the uncertainty in quantitative modeling of alluvial aquifers in Garmsar plain in Semnan province. Description of the contaminated source includes identification of the location and source, injection rate and release periods. It is recommended to study the construction of concrete road tanks for mixing groundwater and drinking water in the area and diluting heavy metals and reducing water hardness (TDS). Combining the use of MODFLOW method in groundwater and artificial feeding of groundwater aquifers due to flood spreading as well as mixing surface water from rain and snow collection with groundwater in water reservoirs, the effects of heavy metals and toxins in the drinking water of the region can be expected to be significantly reduced. The results showed that the feeding parameter has less detection capability in the calibration process than other parameters (in other words, its posterior distribution function has not changed much compared to the previous distribution function) and has more uncertainty.