We present a model of the spread of an evaporating aerosol impurity from a model high-altitude source. Based on this model, the inverse problem for evaluating the fields of the locality contamination is considered. Analysis of the data obtained is performed for the case of direct experimental detection of the rocket fuel in a number of lakes located in the area where the second stages of rockets descend. The predominance of the kinematical spread of the rocket fuel toward the underlying surface is shown, taking into account the current meteorological conditions, hydrological characteristics of lakes, the trajectory of the rocket stage descent, and the limitations on the guaranteed fuel supply.