## 2 Geoenvironmental Setting  
The area of Inowroclaw is in fact a post-mining area, where the last mining operations were carried out over 30 years ago, but there are still ground deformations that can be detected via surveying methods. This area, which is located just over the salt diapir--one of the many in the North European Plain--has become a survey field for several generations of geologists and geophysicists. Thus, the salt structure of Inowroclaw has been the subject of comprehensive studies for several generations of geologists and geophysicists. These studies were carried out based on the needs of geological exploration and mining works in the past. Nowadays, these studies are conducted for geohazard assessment, which is important to the community in terms of planning and development, as well as for infrastructure management. While the large number research studies undertaken over the past one hundred years is awe-inspiring, there are still key knowledge gaps to be filled. A particularly important issue is the need to obtain information on the characteristics of ground surface displacements in the area of the old borehole mining in the western part of the town. Hence, a large area of the site is excluded from built development. Potential reasons for the observed displacements, which have positive and negative values, are as follows. Firstly, there has been suberosional deposition of soluble minerals; secondly, a diapiric uplift movement of the dome has been observed; and lastly, we are left with the post-mining effects of abandoned mine workings. Although they are only small vertical displacements occurring at the rate of several mm a year, the displacement of negative values should be assumed as the result of karst development, which is one of the most hazardous phenomena that can cause the collapse of the ground surface. A combination of the aforementioned sources affecting the stability of the ground surface generates quite complex spatial characteristics of ground movements, and their suitable analysis and interpretation requires in-depth knowledge of the underground conditions(geological setting, geotechnical properties, hydrogeological regime, localization of natural or post-mining cavities, etc.). The geological structure of the Inowroclaw salt dome is one of many salt structures which appear in the Polish part of the North European Plain (mostly in the Kujawy region). It has clearly affected the surface topography. An example of this is the fact that the town that has developed right above the salt structure is also located on a small hill that is only 12 m high, yet quite clearly stands out in the flat area of Kujawy. The depth of the salt surface in Inowroclaw is one of the shallowest salt structures in the Polish province of Zechstein salt formation: in some areas, its gypsum cap rock lies only a few meters below the surface. The gypsum cap is at a depth of 6-221 m, while the top surface of the salt structure is situated at a depth of 122-272 m (Figures 1 and 2). The local geology follows a simple pattern with a salt dome which consists of a core of salt and an envelope of surrounding strata. The Inowroclaw salt dome consists of Zechstein salt sediments sloping almost vertically, and the dome is also covered by steeply deposited Jurassic sediments. Its overburden consists of Quaternary sediments, and in the northern part of the deposit, these are also joined by strata. The Jurassic formations surrounding the deposit consist of sand deposits in the western part and deposits of the Lower Jurassic sandstones with poor diagenesis, while in the eastern part, in the middle and in the Upper Jurassic formations, we find marks, limestones and dolomites. Quaternary formations with a thickness of 3 m to 47.5 m are represented by unsorted glacial sediments (glacial till), glacial sands, and gravel [12; 13; 14; 15; 16; 17; 18; 19].