Relationship between north Ji’nan geothermal water and Ji’nan spring water revealed by hydrogeochemical characteristics

The north Ji’nan geothermal field is located in the northern part of Ji’nan City, Shandong Province. It also lies to the north of the Ji’nan spring region boundary and Bai spring region boundary. The north Ji’nan geothermal field, Ji’nan spring region and Bai spring region all belong to the first-class karst groundwater system of Ji’nan monocline structure hydrogeological division. The geothermal reservoir types in the north Ji’nan geothermal field are dominated by Ordovician limestone fractured karst stratified and zoned reservoirs, which are controlled by fault structures. Geothermal water mainly occurs in the Ordovician limestone thermal reservoirs. Based on analyzing the conventional chemical components, trace elements and isotopes, this paper studied the genesis mechanism of geothermal water in the north Ji’nan geothermal field, Shandong Province, as well as its recharge, runoff and discharge. The relationships between geothermal water, karst groundwater and spring water are also discussed. The methods used in this paper include the ion component rose diagram, hydrogeochemical stratigraphic section, Piper diagram, hydrogeochemical characteristic coefficient, Tritium isotope dating, and 14C dating. Research indicates that geothermal water, karst groundwater and spring water have the same supply source. Geothermal water has characteristics of dissolved water and belongs to marine sedimentary rock dissolved water. The analysis results of stable isotopes of hydrogen-oxygen and Tritium dating show that geothermal water is modern water, and modern atmospheric precipitation is its main recharge source. According to 14C dating, geothermal water was recharged by Pleistocene precipitation and attributed to the mixture of modernistic and ancient atmospheric precipitation. Research indicates that north Ji’nan geothermal field geothermal water and Ji’nan spring water are closely linked, both of which receive the southern mountain precipitation recharge. The runoff conditions and the sealing degree of hydrological geochemical environment have great difference between the eastern and western parts of the north Ji’nan geothermal field.