DEVELOPMENT OF THE MATHEMATICAL MODEL SET FOR UNSATURATED AND SATURATED ZONES FOR PREDICTING CONTAMINANT TRANSPORT FROM A NEAR-SURFACE SOURCE TO A DISCHARGE AREA    

E. V. Kononchenko^#, A. B. Petrash^##

FSBI "Gidrospetzgeologiya”, ul. Marshala Rybalko 4, Moscow, 123060 Russia

^#E-mail:lena.konon@mail.ru
^##E-mail:A.B.Petrash@yandex.ru

The paper describes the development procedure of the model set for unsaturated and saturated zones. These models permit characterizing quantitatively the solute transport from a near-surface source to the groundwater table and a discharge area. The method application has been considered by the example of the area showing chloride groundwater contamination. A salt storage site having been in operation in the period of 1967-2007 serves as a source of pollution. In 2016, a network of monitoring wells was installed at a distance of 300 m to the northwest of the storage site. According to observations, the permanent excess in chloride concentrations in groundwater over the threshold for drinking water has been registered. At present, no decrease in contaminant concentrations after the removal of the contamination source is observed. That is probably connected with the developing of the secondary contamination source (salinization zone) in the unsaturated zone. The models for the unsaturated and saturated zones have been developed for this investigation site. The saturated zone model has been calibrated on the basis of monitoring data that include groundwater table levels and chloride concentrations. A chloride plume in the groundwater flow has been simulated in absolute concentrations. Solute transport in the unsaturated zone has been calculated in relative concentrations. Based on the simulation results, the time intervals have been defined that characterize the steps of contamination plume formation during the salt storage use, as well as the steps of its degradation after its the salt storage removal. Sensitivity analysis of both zones model parameters has been made and the most important of them have been identified. As a result of sensitivity analysis, a number of model scenarios (both conservative and softer) have been considered in order to study the variability of model forecasts. Proceeding from the complex model retrospective calculations and monitoring data, the more accurate parameters have been obtained for the properties of unsaturated zone sediments.

Keywords: numerical modeling, unsaturated and saturated zones, groundwater, solute transport model

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