Dynamics of Pollution in the Hyporheic Zone during Industrial Processing Brine Discharge

The industrial production of chemicals, including the manufacture of mineral fertilizers, is often associated with the need for the disposal of highly mineralized brines through their discharge into surface water bodies or an underground water-bearing layer. When dealing with surface water bodies, the problem of the hyporheic zone effect could substantially influence the process and, thus, must be examined. We consider a two-layer system (liquid–porous medium) for a detailed assessment of the importance of considering the hyporheic zone during the modeling of brine discharge. A three-dimensional numerical simulation of brine transport is performed for parameters close to the characteristics of the media and flows typical for natural water bodies. The dynamics of a saturated brine in a two-layer system are studied for the period of brine discharging and after the cessation of the disposal, and the accumulation of salts in the bottom porous layer is assessed. Calculations show that a significant amount of impurities is observed not only near the water body bottom but also throughout the entire thickness of the porous layer. Moreover, the obtained data reveal that the effect of vertical stratification dramatically influences the brine discharge process and leads to propagation of the brine into the porous medium with a velocity that is three orders of magnitude higher than the filtration rate in the horizontal direction. As a result, the heterogeneity in the depth distribution of the impurity concentration is significant. In particular, the maximum concentration of salt in the hyporheic zone exceeds those near the river surface by hundreds of times. Impurities accumulated in the water-bearing layer of the river bottom are nonhazardous at low- and medium-flow rates. However, with an increase in the river flow intensity—for example, during the flood period or caused by operating regime of a hydroelectric power plant—the accumulated contamination may become an intensive source of pollution, which significantly limits the water use regime.