Groundwater quality deterioration has become an environmental problem of widespread concern. In this study, we used a water quality index (WQI) and multivariate statistical techniques to assess groundwater quality and to trace pollution sources in the Hutuo River alluvial-pluvial fan, China. Measurement data of 17 variables in 27 monitoring sites from three field surveys were obtained and pretreated. Results showed that there were 53.09% of NO₃⁻, 18.52% of SO₄²⁻ and 83.95% of total hardness (TH) in samples that exceeded the Grade III standard for groundwater quality in China (GB/T 14848-2017). Based on WQI results, sampling sites were divided into three types: high-polluted sites, medium-polluted sites and low-polluted sites. The spatial variation in groundwater quality revealed that concentrations of total dissolved solids (TDS), Cl⁻, TH and NO₃⁻ were the highest in high-polluted sites, followed by medium-polluted and low-polluted sites. The temporal variation in groundwater quality was controlled by the dilution of rainwater. A principal component analysis (PCA) revealed that the primary pollution sources of groundwater were domestic sewage, industrial sewage and water–rock interactions in the dry season. However, in the rainy and transition seasons, the main pollution sources shifted to domestic sewage and water–rock interactions, nonpoint pollution and industrial sewage. According to the absolute principal component scores-multivariate linear regression (APCS-MLR), most water quality parameters were primarily influenced by domestic sewage. Therefore, in order to prevent the continuous deterioration of groundwater quality, the discharge of domestic sewage in the Hutuo River alluvial-pluvial fan region should be controlled.

Medium-low temperature geothermal resources in the Wumishan Formation, which is the geothermal reservoir, are local enrichment resources in Xiong’an New Area, North China. In this study, 35 water samples were collected from the bedrock of Taihang Mountains and Wumishan Formation in Xiong’an New Area and display the chemical compositions of water samples as well as the stable isotope compositions for hydrogen, oxygen, carbon, sulfur, and strontium. Hydrogeochemical characteristics and isotope compositions of water samples are analyzed to understand the origin and circulation processes of these geothermal fluids. Our results of cold groundwaters in the bedrock of Taihang Mountain indicate a more open oxidation environment, and the HCO₃-Ca·Mg-type groundwater also indicates a prevailing carbonate dissolution condition. The deep geothermal fluids in the Wumishan Formation beneath Xiong’an New Area indicate a closed reduction condition, and their hydrochemical types are mainly Cl·HCO₃-Na type. The diagram of hydrogen vs. oxygen isotope indicates that the recharge for the deep geothermal fluids in the Wumishan Formation of Xiong’an New Area is mainly from atmospheric precipitation. The high δ¹³C values (-3.4‰−-4.9‰) are notably controlled by the eluviation of the carbonate rock layers. The δ³⁴S values vary from 18.02‰ to 27.01‰; the relatively high values indicate the eluviation of sedimentary rock layers. The high ⁸⁷Sr/⁸⁶Sr ratios (0.70806−0.71270) and the high Sr²⁺ concentrations (0.69−2.92 mg/L) suggest that the Sr in the deep geothermal fluids originates from the eluviation of both silicates and carbonates. According to the multimineral equilibrium diagram, chalcedony is saturated at the measured temperature of geothermal wells; therefore, we chose chalcedony as a geothermal thermometer for the calculation of the reservoir temperature of the Wumishan Formation, and the results vary from 68.63 to 89.10°C. Our study identifies the geothermal type of the deep medium-low temperature hydrothermal systems and also recognizes their water-rock interaction processes. We get a comprehensive understanding that the geothermal resources in the Wumishan Formation beneath Xiong’an New Area is convection-conduction type, for which potential of geothermal development and utilization is enormous.

The study of geothermal field characteristics and the mechanisms involved in the hydrogeochemical evolution of geothermal fluids is an effective means to understand the formation, reservoir conditions and circulation mechanics of geothermal resources. Documenting these parameters within the Rongcheng Bulge of Xiong’an New Area, China, is of great significance to its future development and utilization as a geothermal resource. In this paper, we investigate the hydrochemical characteristics of geothermal fluids and the rock thermal properties of the Rongcheng Bulge Reservoir and the surrounding rocks to identify the mechanisms of geothermal fluid genesis within the geothermal field. The results show that the geothermal water in the Rongcheng Bulge is mainly recharged by atmospheric rainfall. The thermal storage temperature at which the deep geothermal fluid is located ranges between 63 and 105 °C, whereas the depth of geothermal water circulation is between 1500 and 2700 m. Fluid exchange is weak during deep circulation, but as the geothermal fluid rises, the proportion of cold water mixed with the geothermal waters is 75–95%. The overall geothermal gradient of the carbonate thermal reservoir is significantly lower than that within the overburden and basement rocks, probably due to convection during the upward transport of groundwater in the reservoir. The geothermal fluid in the area of the Rongcheng Bulge is recharged by the Taihang Mountains and atmospheric precipitation. Following recharge and deep circulation, the fluids rise along fractures and by interlayer convection and are mixed with cold water to form the current, accessible geothermal water.

The Xiong’an New Area is one of the areas with the richest geothermal resources in the east-central part of China. However, the genesis of the geothermal water in Jixianian carbonate reservoirs in this area is still unclear. This study conducted systematical geochemical and isotopic analyses of the geothermal water in the Jixianian carbonate reservoirs in the Rongcheng geothermal field and summed up the genetic mechanisms of geothermal fluids in deep geothermal reservoirs. The results are as follows: the geothermal water in the study area has a hydrochemical type of Cl·HCO₃-Na and originates from meteoric water in the Taihang Mountains. The age of the geothermal water increases from 22 ka in the west to 45 ka in the east, and its transport rate is approximately 1.02 m/a. The Sr concentration and ⁸⁷Sr/⁸⁶Sr ratio of the geothermal fluids increase along their runoff direction and are related to the dissolution and filtration of minerals such as dolomite and gypsum and the decay of ⁸⁷Rb in the Earth’s crust. The geothermal water is involved in deep circulation and occurs in a closed system. These results are consistent with those obtained using the PHREEQC inverse model. The reverse hydrogeochemical simulation results exhibited the precipitation of gypsum and halite, the dissolution of anorthite and quartz, and desulfurization. The geothermal reservoir temperatures were estimated to be 92–113 °C using a SiO₂ geothermometer, and the thermal groundwater may have undergone deep circulation, with a prolonged retention time. Moreover, the groundwater occurs in a closed environment, strong water-rock interactions occur between the groundwater and related minerals, and the groundwater absorbs the heat from the deep heat source, thus forming geothermal water.

Geothermal resources are abundant in China and are distributed mainly in the eastern region where energy demand is high, especially in Tianjin. However, a significant disparity remains between the actual heating area and the potential heatable area of geothermal resources in Tianjin, which indicates the vast untapped potential for development and utilization in the region. In this study, we reviewed the history and current status of geothermal development in Tianjin. We further analyzed the factors affecting the development and utilization of geothermal heat in Tianjin. Subsequently, we constructed a system dynamics (SD) model of geothermal development and utilization in Tianjin. We developed four scenarios, including baseline, policy incentives, technological progress, and economic inputs. The results of the multiscenario forecasts and sensitivity analyses of the SD model showed the following: Tianjin will go through four stages of geothermal development and utilization in the future. Policy support and economic investment were the two main factors influencing the development of geothermal energy, and the influence of technological progress was comparatively smaller. Based on the above results, we proposed recommendations to promote sustainable development of geothermal energy in Tianjin according to three aspects: policy mechanism, economic investment, and technological progress.

Xiong'an New Area boasts abundant geothermal resources, with widespread Jixianian geothermal reservoirs serving as key targets for exploration and development. Zoning geothermal resources helps characterize their distribution and attributes, offering critical guidance for their sustainable exploitation and utilization. This study integrates data from drilling and production tests across 21 geothermal wells to analyze the Jixianian strata, including depth, thickness, temperature, single-well water yield, Groundwater Level Depth (GWD), and Total Dissolved Solids (TDS). Employing fuzzy mathematics, a zoning analysis was performed, yielding quantitative evaluation scores and delineating favorable zones for development. Key findings include: (1) Geothermal reservoirs in the Rongcheng and Niutuozhen uplifts exhibit shallow burial depths, substantial thicknesses, high productivity, and relatively low temperatures, making them highly suitable for large-scale geothermal exploitation; (2) Zones with high resource potential but uncertain conditions require further exploration to mitigate development risks; (3) Areas near the Rongcheng fault or Jixianian strata buried deeper than 4,000 m are recommended for deferred exploitation; (4) Comprehensive evaluation reveals that the Jixianian carbonate geothermal reservoirs in Xiong'an New Area manifest geothermal resources of 5,370.31×10¹⁶ J, geothermal fluid reserves of 101.17×10⁸ m³, and recoverable fluid reserves of 93.41×10⁴ m³/d under balanced extraction and reinjection. Recoverable geothermal heat amounts to 9.36×10¹⁶ J/a, equivalent to 319.4×10⁴ t/a of standard coal. This study provides valuable insights into the exploration and sustainable exploitation of deep geothermal reservoirs in Xiong'an New Area, enhancing resource utilization and contributing to the development of a green and sustainable Xiong'an New Area.