**1. Introduction**

The gypsum unit is one of the evaporite units that can be easily dissolved when it contacts with water in nature. Furthermore, gypsum units are geological environments with karstic characteristics as limestone unit, and all karstic structures can also develop in gypsum units. Therefore, gypsum areas are the sources for pollutants with inorganic characteristics, and geologically they also include geological structures that develop specifically to karstic areas. Moreover, gypsum areas are risky geological environments where natural hazards may occur in the case of the presence of settlement areas or human-made structures (building, road, substructure systems, etc.) on them [1–3]. For these reasons, gypsum is an important evaporite unit that should be taken into account in terms of both natural hazards and environmental problems and urbanization. Therefore, gypsum units cause negative effects on soil infertility and ground/surface water quality due to problems such as dissolution, salinization,

erosion, and corrosion that directly occur in nature [4–6]. On the other hand, the rapid construction that comes with urbanization requires new settlement areas. Therefore, there are also constructions on gypsum units [3]. The reason why it is considered that gypsum areas will cause significant environmental problems in the future is natural hazards and environmental problems that will arise in the event when gypsum is mainly surfaced or very close to the surface especially in new places opened for settlement, as required by karst geology. This also suggests that there will be risks for the life of humans and living beings and that these risks will increase, especially in these kinds of areas in the future, along with the opening of an area consisting of evaporite units for construction. Geological structures specific to gypsum karst lead to the formation of caves/areas causing the danger of collapse under the ground of the building and also collapses along with the fact that dissolution caves and dissolution channels are merged over time and create large galleries. As a result of these events, concrete materials, pipes, and cable systems of buildings and substructure systems are damaged. This also means that substances that may leak liquid and gas are mixed into the soil, water, and even into the atmosphere or that there are energy losses. Thus, there will also be economic losses. For this reason, it was considered necessary to draw attention to the problems originating from gypsum, while they are examined with environmental problems and soil and water pollutions on the issues for environmental monitoring purposes, and these problems should not be ignored [5].

When natural-origin environmental problems described above are considered, it is essential to reveal the geological, engineering, hydrogeological, and environmental impact models of the environment in the site selection for settlement purposes and in the site selection of other human-made constructional areas [7, 8]. Therefore, various maps on different topics and scales that define the gypsum area from all aspects and geological/geophysical sections of various sizes are prepared by the relevant experts and scientists [3, 9–16]. Thus, gypsum areas can be defined in detail by using mineralogical-petrographic and structural properties of geologically lithological units, their degree of weathering, geophysical-hydrological-physicomechanical properties, and meteorological status, and other surface and underground research methods. With these studies, risky areas at the horizontal-vertical or shallow-deep dimensions can be determined by preparing reports and maps to take precaution for natural hazards and environmental impacts. According to the results found, new and future sustainable planning and preparations can be made for these issues. Then, human/plant/animal health and their living environments can be maintained in a sustainable manner. Therefore, the problems of erosion and pollution may be reduced more effectively with the measures to be taken. In conclusion, all these issues were examined in this study.
