A study of displacements relating to geodynamical processes involves a use of accurate measurement equipment. Better and better accuracy of field surveys neglecting a survey environment can be insufficient in a reliable study. One of the environmental aspects is discussed in the paper. That is a geotechnical condition of a ground - an environment of benchmarks, which changes of position are observed in geodetic surveys. The conditions determine a ground stability affected by weather or geological processes. The main idea of the paper is to consider geotechnical and geological aspects in geodetic reasoning carried on the base of displacement analysis within a study of geodynamics. There are presented examples illustrating the problem. The first relates to former levelling observations carried in an area of Wieliczka, well geologically surveyed due to mining activity in a salt deposit. There are presented results obtained on the base of a numerical analysis. The seasonal variations of benchmarks’ heights are explained in a background of geology. The changes of ground properties induced by atmospheric conditions are suggested as the main cause of the displacements. The survey data processing provided values of displacements caused by seasonally expanding grounds. The second examples concerns ongoing observations in the area of Inowroclaw (located above the salt dome) bring similar variations of heights that can not be related to that cause. The estimated linear trend of height changes proves an uplift process of the salt dome. Derived conclusions suggest a certain methodology helpful in reliable analysis of geodetic surveys. The conclusions prove that geodetic surveys carried out for investigations of displacements in geodynamics require quite extensive geological data., Zbigniew Szczerbowski., and Obsahuje bibliografii