Assessment of the dynamics of changes in the physical and chemical properties and morphological composition of the filling mixture as well as the identification of the elements capable of migrating into the environment is an important part of assessing the environmental efficiency of such an environmental measure during the filling of mined-out space of an ore deposit. During scientific research, the environmental safety mined-out space filling technology at the gold ore deposit by the mixture of rock waste, cement and crushed car tires was investigated. The authors carried out a set of laboratory studies and created a physical model of groundwater infiltration. Under laboratory conditions, this model allowed the experiment to evaluate the migration of elements and substances from the filling mixture into the environment to assess the risks of secondary pollution. The potential hazard of element migration from the backfill mixture into the environment was determined as a result of testing the backfill mixture on a bench with washing using the model solution that emits drainage water. During research, it was revealed that under the conditions of an ore deposit, the filling mixture components transformation would not lead to hazardous hydrochemical and hydrogeochemical areas or pollution stream formation.