Determination of the pollution of underground caves at the level of Slovenia, their priority remediation and monitoring of the condition of caves

In Slovenia, caves are the most affected by pollution, especially in the 20th century (Gams, 2004; Prelovšek, 2011; Tičar, 2021). The problem of cave pollution became particularly acute after World War II when the amount of waste increased dramatically due to economic development. In the absence of regulated municipal waste management, the population in karst areas used caves and shafts for illegal waste dumps (Prelovšek, 2011; Tičar, 2021). Pollution primarily degrades the diverse and vulnerable groundwater environment, while also affecting the health of the population by reducing the quality of groundwater. Karst aquifers are extremely sensitive to pollution, mainly due to the thin soil, point discharge in dolines and ponors, and the concentration of water flows in the epikarst and vadose zones (Zwahlen, 2004). Slovenia obtains about 43% of its total drinking water from karst aquifers, mainly in the Alpine and Dinaric regions (Lah, 1998, Brečko Grubar and Plut, 2001). Karst caves are protected from pollution by numerous laws, in Slovenia directly by the Underground Caves Protection Act, which came into force in 2004. The Act defines caves as natural values of national importance and a public good and affirms state ownership of them. However, at the level of Slovenia, data on cave pollution are unreliable and incomplete, despite the legal basis for monitoring the condition of caves. According to Cave Registry (2018), 657 caves or 5.2% of all caves are classified as polluted caves. Based on the results of four projects, Čekada (2015) estimated that a good third (35%) of the 517 caves are contaminated. Taking into account the method of linear extrapolation, up to 2,700 caves in Slovenia would be polluted. The Ministry of Environment and Spatial Planning (2015) estimates that between 15 and 20% of karst caves in the lowlands are polluted, and at the same time, it has data on 153 destroyed and 385 polluted caves (Ministry of Environment and Spatial Planning, 2017). Recent research, based on a study of the condition of 6,965 caves based on the records in the Cave Registry, defines that 20.0% or 1,390 of them are polluted caves (Tičar, 2021). The project contributes to the regulation of cave pollution in Slovenia and is based on three objectives. The first objective focuses on the inventory of cave pollution at the level of Slovenia. A uniform methodology for assessment will be established and an inventory of all caves will be carried out based on data from the Cave Registry. The data obtained will be the basis for the study of cave pollution at the regional level, where the main factors influencing cave pollution will be defined and a comparison of pollution between individual regions will be carried out. The second objective focuses on the preparation of a priority remediation plan in Slovenia. Based on the method of analytical hierarchical process and influencing factors, a list of priority remediation measures will be prepared for all polluted caves. At the same time, a protocol for the implementation of cave remediation in Slovenia will be developed, which will guide contractors to a systematic approach to solving problems in the field. The third objective focuses on improving the monitoring of the condition of caves. An improved protocol for collecting data on the condition of caves in Slovenia will be prepared and implemented by updating the existing records of the Cave Registry. In addition, the project also focuses on developing methods for estimating the amount of waste in polluted caves. At the same time, a sample of 100 polluted caves will be monitored, which will provide key information for the implementation of other activities and the evaluation of the reliability of the data obtained on the Cave Registry. The results of the project will be presented in the form of reports, monographs and scientific papers and will be presented at conferences and a panel of experts at the end of the project.