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[Display omitted] • Groundwater vulnerability zonation investigation is conducted for GHM Greater Bay Area. • Three different perspectives are comprehensively considered in this study. • Groundwater risk, function value and contamination status are superposed using the AHP method. • Quantification and visualization of groundwater contamination prevention regionalization. • The AHP-DRASTICH model is an effective method to evaluate the groundwater risk in shallow aquifers. The groundwater contamination assessment and prevention regionalization are an important part of groundwater investigation, which is of great significance to groundwater environmental management and contamination control. Although the Guangdong-Hong Kong-Macao Greater Bay Area (GHM Greater Bay Area) has faced significant groundwater contamination since 2020, there's been no investigation into its vulnerability zonation. In this paper, groundwater in a typical area of south China was taken as the research object. We analyzed groundwater contamination risk by considering both the groundwater vulnerability and the load from contamination sources. Using the analytic hierarchy process (AHP) method, we superposed the groundwater risk, function value and contamination status, and realized the quantification and visualization of groundwater contamination prevention regionalization. Based on the DRASTIC model, the zones of low, moderate, high, and very high vulnerability are respectively 14.2 %, 24.28 %, 37.67 %, and 20.45 % of the study area. Results show that the groundwater vulnerability grade in the area is III-IV, which means it is easy to be polluted. The functional value of groundwater in the south-central part of the region is relatively high. Most of the areas with high prevention and control levels are located in plain areas and the Piedmont plain area with an area of 460 km2. The secondary control levels (key protection area) are mainly located in the middle, southwest, and northeast of the plain, with an area of 6944 square kilometers. Consequently, the ideas and contamination prevention zone maps might provide a scientific foundation for long-term planning and management and groundwater conservation in the Guangdong-Hong Kong-Macao Greater Bay Area and peripheral zones. [ABSTRACT FROM AUTHOR]

Two separate groups of geothermal waters have been identified in the coastal region of Guangdong, China. One is Xinzhou thermal water of regional groundwater flow system in a granite batholith and the other is thermal water derived from shallow coastal aquifers in Shenzao geothermal field, characterized by high salinity. The hydrochemical characteristics of the thermal waters were examined and characterized as Na-Cl and Ca-Na-Cl types, which are very similar to that of seawater. The hydrochemical evolution is revealed by analyzing the correlations of components versus Cl and their relative changes for different water samples, reflecting different extents of water-rock interactions and clear mixing trends with seawaters. Nevertheless, isotopic data indicate that thermal waters are all of the meteoric origins. Isotopic data also allowed determination of different recharge elevations and presentation of different mixing proportions of seawater with thermal waters. The reservoir temperatures were estimated by chemical geothermometries and validated by fluid-mineral equilibrium calculations. The most reliable estimates of reservoir temperature lie in the range of 148–162°C for Xinzhou and the range of 135–144°C for Shenzao thermal waters, based on the retrograde and prograde solubilities of anhydrite and chalcedony. Finally, a schematic cross-sectional fault-hydrology conceptual model was proposed. [ABSTRACT FROM AUTHOR]