Groundwater is a vital water source for human survival and regulates the hydrological cycle within the uppermost strata. Through the processes of recharge and discharge, as well as solute exchange, it interacts with surface water systems in Zhengzhou, e.g., the Yellow River and the Jialu River. Therefore, systematically assessing its hydrochemical characteristics, driving factors, and health risks is crucial for ensuring the safety of public drinking water and regional development. This study focuses on shallow (45~55 m), medium-deep (80~350 m), deep (350~800 m), and ultra-deep (800~1200 m) groundwater in Zhengzhou City. A descriptive statistical analysis was employed to identify the primary chemical constituents of groundwater at various depths within the study area. Piper diagrams and the Shukarev classification method were employed to determine the hydrochemical types of the groundwater. Additionally, Gibbs diagrams, correlation coefficient methods, ion ratio coefficient methods and chlorine–alkali indices were employed to investigate the formation mechanisms of the chemical components of the groundwater, and the health risks in the study area were evaluated. Results: Ca²⁺ dominates the shallow/medium-deep groundwater, Na⁺ dominates the deep/ultra-deep groundwater; HCO₃⁻ (70~82%) is the dominant anion. Water chemistry shifts from HCO₃-Ca to HCO₃-Na with depth. Solubilisation, cation exchange, counter-cation exchange, and mixed processes primarily govern the formation of the groundwater’s chemical composition in the study area. Nitrate health risk assessments indicate significant differences in non-carcinogenic risks across four population groups (infants, children, young adults, and adults). Medium-depth groundwater poses a potential risk to all groups, while shallow and deep groundwater threaten only infants. Ultra-deep groundwater carries the lowest risk.

To evaluate the impacts of the Middle Route of the South-to-North Water Diversion Project on groundwater depth in the water-receiving areas of Henan Province, this study systematically investigated the spatiotemporal evolution of groundwater depth and its influencing factors before and after project operation, based on monitoring data from 2004 to 2024, using geostatistical methods and principal component analysis. The results indicate that following project operation, the ratio of groundwater supply to allowable groundwater withdrawal decreased from 216.50% to 175.09%, representing a reduction of 41.41 percentage points and indicating an alleviation of groundwater overexploitation pressure. After project operation, the areal proportion of the 0–8 m groundwater depth interval decreased by 14 percentage points relative to the pre-operation period, that of the 8–28 m interval increased by 14.2 percentage points, and that of the >28 m interval decreased slightly. After project operation, the spatial variability of groundwater depth changed, and the nugget-to-sill ratio exhibited fluctuating behavior: it decreased during 2015–2021, indicating a stage-wise strengthening of spatial dependence; in 2022, the nugget-to-sill ratio increased sharply and spatial autocorrelation weakened; and overall, the ratio fluctuated within the strong to moderate spatial autocorrelation range. The PLSR-VIP analysis identified surface water supply and domestic water consumption as the two highest-ranked factors associated with groundwater depth. Although diverted water volume had a full-sample VIP of 1.010, its VIP exceeded 1 in only 38.1% of leave-one-year-out refits and decreased to 0.825 after detrending, with a non-significant detrended correlation (r = −0.228, q = 0.356). These findings indicate that its statistical importance was sensitive to sample composition and temporal trends. During 2015–2024, groundwater depth exhibited a decreasing trend, indicating groundwater-level recovery, coinciding with changes in the regional water supply structure. However, the independent contribution of the diversion project to this recovery could not be established from the present analyses.

Understanding the crack development and rainfall infiltration in loess under wetting–drying cycles is crucial for assessing slope stability and promoting sustainable land management in ecologically vulnerable regions. This study employed a three-dimensional column model (Φ₂₄ × 50 cm) with 64 buried electrodes to simulate short-term heavy rainfall by changing the light duration (10 h/d and 5 h/d) and using 100 mm rainfall water. Results indicate that dry–wet cycles cause cumulative damage, significantly altering soil infiltration properties. After four cycles, the rainfall infiltration recharge coefficient increased from an initial 0.44% to 45.58%, a more than 100-fold rise. Resistivity imaging revealed a shift in water transport mode: from uniform matrix flow initially to preferential flow dominated by crack networks as cracks developed. During drying, crack zones exhibited high resistivity (ρ > 150 Ω·m), while water-filled cracks during infiltration showed low resistivity (ρ < 50 Ω·m). Resistivity is an excellent comprehensive index to quantify multi-field coupling damage, and its change (ρ∝ 1/w^1.86 × 1/(1 + 0.032 width)) synchronously responds to water content, crack development and dry–wet process. Low water content (w < 15%) and medium crack width (4–6 mm) are the most sensitive states. Longer illumination (10 h/d) promoted greater crack development and higher infiltration capacity compared to shorter cycles (5 h/d). The developed resistivity–moisture relationship provides a non-destructive monitoring tool for slope moisture dynamics, supporting not only geotechnical stability assessment but also optimized irrigation scheduling and adaptive land-use planning. These insights contribute directly to the sustainable management of soil and water resources in loess landscapes, aligning with sustainability goals in fragile ecosystems.

A thorough understanding of the resistivity response characteristics of ethanol-contaminated soil is of great significance for the development of non-destructive geophysical detection techniques and for supporting contaminated site investigation and assessment. This experimental study aims to systematically investigate the resistivity behavior of ethanol-contaminated sandy soils, with a focus on the coupled mechanisms of multiple factors, including water content, ethanol concentration, particle size distribution, and contamination time. It is hypothesized that water content serves as the dominant factor controlling resistivity, whereas ethanol concentration and contamination time regulate resistivity by altering the physicochemical properties of the pore fluid. Under laboratory conditions, silt, fine sand, and medium sand were selected as the test materials. Resistivity was systematically measured using a Miller Soil Box with increasing water content, Wenner array configuration across varying water contents (3–24%), ethanol concentrations (40–98%), and contamination durations (0–144 h). The experimental results indicate the following: (1) Regardless of the presence of ethanol contamination, the resistivity of sandy soil decreases with increasing water content following a power-law relationship. The decrease is most pronounced at low water contents (3–9%), and gradually stabilizes at higher water contents. The results show that, at a constant water content, resistivity systematically and consistently follows the order: silt > medium sand > fine sand. (2) The influence of ethanol concentration on resistivity is constrained by water content levels, and the overall increase in resistivity is primarily attributed to ion dilution and the obstruction of conductive pathways. (3) Over time, resistivity exhibits a two-stage increasing trend, associated with ethanol volatilization and water loss. Resistivity changes in fine sand samples contaminated with ethanol at concentrations ranging from 75% to 95% follow a two-stage pattern. The initial phase of growth is characterized by a gradual increase over a period of 0–48 h, followed by a more rapid increase during the subsequent phase, which extends from 48 to 144 h. The results show that higher initial ethanol concentrations enhance the sensitivity of resistivity to temporal changes. Comprehensive analysis indicates that the resistivity variation mechanism under multi-factor coupling conditions can be summarized as follows: the water content is the dominant factor in the regulation of the conductive pathways; the particle size distribution determines pore structure and the characteristics of the particle interface; ethanol concentration and contamination time dynamically alter pore fluid properties, collectively regulating the resistivity response. Although the experiments were conducted under controlled laboratory conditions and the results have certain limitations, they provide a preliminary reference for interpreting resistivity responses in relatively homogeneous sandy contaminated sites and offer theoretical support for the application of resistivity methods in contamination identification and dynamic monitoring.