Journal of Groundwater Science and Engineering

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Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).

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Heat transfer performance and dynamic effects of middle-shallow U-tube ground heat exchangers under geological stratification

Chang-zhe Wang, Feng Liu, Li-juan Yuan, Hua-jun Wang

, Available online , doi: 10.26599/JGSE.2026.9280101

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Abstract:
Previous research has lacked sufficient attention to the heat exchange performance of middle-shallow U-tube ground heat exchangers (GHEs), particularly regarding the impact of vertical lithology heterogeneity. In this study, a heat transfer model of GHEs coupling vertical lithological variations and ground temperature distribution is established, based on field test data of middle-shallow boreholes in Langfang, Hebei Province. The heat transfer characteristics of GHEs within the depth of 200–300 m and their influencing factors are analyzed. Results show that the flow velocity and wall thickness strongly affect the heat transfer of middle-shallow GHEs. Increasing the flow rate helps to enhance heat transfer, but is not conducive to improving energy efficiency of the system due to higher power consumption of circulating pumps. There is an optimal flow rate range of 2–3 m³/h for PE-RT GHEs. Furthermore, reducing the wall thickness from 8 mm to 3 mm can significantly improve the heat transfer per unit depth by 10–12% for PE-RT GHEs. The thermal influence distance (TID) of GHEs exhibits significant lithological differences and seasonal variations along the depth. As the depth increases, the TID in winter and summer exhibits increasing and decreasing trends, respectively. Especially, the TID of sandy layers due to a high thermal conductivity is greater than that of clay layers under the same conditions. For 250–300 m deep GHEs, the maximum TID reaches 5.8 m in winter and 7.3 m in summer, respectively, after running for five years. The heat transfer performance of middle-shallow GHEs has an attenuation risk of up to 33–35% during long-term operation, which can be alleviated using an intermittent operation strategy. The present findings can offer a useful reference for the design and optimization of middle-shallow GHEs in similar geological conditions.

New Insights into Soda Water in Shallow Groundwater of the North China Plain

Bo Gao, Jiang-tao He, Bao-nan He, Yan-jia Chu, Zhen Chen, Ji-chao Sun

, Available online , doi: 10.26599/JGSE.2026.9280103

Abstract(432) FullText HTML (161) PDF(0)

Abstract:
Soda water in shallow aquifers represents a unique hydrochemical type, often enriched in arsenic (As), fluorine (F), iodine (I), and other components, while also acting as a critical driver of soil salinization. However, existing studies have failed to effectively distinguish between salinization (characterized by soluble salt accumulation) and alkalization (characterized by soda-alkali enrichment). The "New Insights" of this study do not rely on new data but derive from an in-depth excavation and interpretation of the 2006–2009 National Groundwater Pollution Survey dataset—the only authoritative background dataset covering the entire North China Plain. Focusing on shallow groundwater in the North China Plain, this study refines the identification criteria for soda water based on existing concepts, analyzes its spatial distribution characteristics, delineates typical zones, and conducts a preliminary investigation into the genetic differences across regions. Results show that when using the criterion—"HCO₃⁻ + CO₃²⁻ as dominant anions with [(HCO₃⁻ + CO₃²⁻) - (Ca²⁺ + Mg²⁺)] > 0 meq%"—combined with hydrochemical cluster analysis, soda water is primarily concentrated in two zones: The mountain-front discharge zone (Area A) and the runoff-ancient Yellow River channel zone (Area B). These two zones account for 88.48% of all soda water samples and exhibit distinct hydrochemical features. In Area A, groundwater has a simple anion composition dominated by HCO₃⁻, a median total dissolved solids (TDS) content of 501.15 mg/L, and elevated concentrations of F⁻ and NO₃⁻. In contrast, Area B is characterized by diverse anions (HCO₃⁻, SO₄²⁻, and Cl⁻), a higher median TDS (863.56 mg/L), and enrichment of reductive components including As, F⁻, I⁻, Fe, and Mn. Genetic analysis reveals that soda water in Area A forms through the combined effects of mineral weathering, dissolution, and calcite-dolomite precipitation. In contrast, groundwater in Area B evolves under calcite-dolomite precipitation controlled by evaporative concentration, with further modifications by microbial geochemical processes and agricultural activities. This study clarifies the spatial distribution patterns and genetic mechanisms of soda water in the North China Plain, laying a foundation for further research on its formation processes.

Identification of the effects of shallow-buried mining on the hydrochemical evolution of phreatic groundwater in arid and semi-arid regions: A case study of the Ten Tributaries Basin

Zhuang Wang, Jun-nan Li, Ge-su Tao, Chao-zhu Li

, Available online , doi: 10.26599/JGSE.2026.9280095

Abstract(273) FullText HTML (119) PDF(5)

Abstract:
Revealing the evolution of phreatic water hydrochemistry under natural processes and mining activities in shallowly buried mining areas of arid and semi-arid regions is key to identifying the impacts of mining on groundwater. Taking the Ten Tributaries Basin in the upper Yellow River as the study area, this study combined ion ratios, stable isotope tracing, and the Chemical Mass Balance (CMB) model to reveal and quantify the effects of coal mining (recharge area) and mirabilite mining (discharge area) on phreatic water chemistry. Results show that mining activities are the key anthropogenic factor driving the spatial differentiation of phreatic water chemistry, with influence intensity exhibiting significant spatial heterogeneity. In undisturbed areas, natural dissolution processes contribute more than 80% of the hydrochemical composition, dominated by carbonate dissolution. However, in mining-affected areas, groundwater chemistry deviates from natural evolutionary pathways, characterized by enhanced dissolved-ion input and more complex ionic compositions. In recharge areas, coal mining mainly promotes carbonate dissolution and vadose-zone disturbance, increasing TDS by factors of 1.96 and 1.88, respectively, relative to natural conditions. In discharge areas, mirabilite mining is dominated by evaporite dissolution and deep saline-water mixing, leading to TDS increases by the factors of 4.41 and 3.24, respectively. These mining effects are superimposed on the pathway-controlled groundwater flow system, resulting in distinct spatial differentiation of groundwater hydrochemistry. The improved CMB model effectively quantifies the impacts of mining disturbances on groundwater chemistry. The results provide scientific support for groundwater resource management and ecological protection in shallowly buried mining areas of arid and semi-arid regions.