Chao Zhuang

Groundwater depletion constitutes a critical global challenge. Exploitation of deep aquifers leads to nonnegligible depletion of water stored in adjacent aquitards (termed aquitard depletion). Although aquitards generally exhibit lower permeability than aquifers, they possess significantly higher storativity. Accurately quantifying aquitard depletion remains a methodological challenge. This study develops a new methodology, based on the analytical well hydraulics model for a classical leaky aquifer system, to estimate aquitard depletion at a regional scale. Specifically, a formulation for the regional average completion degree of aquitard depletion is derived. Theoretically, when the pumping duration reaches the hydraulic response time of the aquitard, approximately 97% of its ultimate depletion is achieved. Furthermore, applying the frequently used step‐drawdown model with half the actual pumping time yields a regionally representative estimate of aquitard depletion. Applications to the Su‐Xi‐Chang (China) and the Virginia Coastal Plain (United States) aquifer systems show that aquitards contribute dominantly to total depletion (~96% and ~94%, respectively), most of which is irreversible due to inelastic compaction. These findings underscore the predominant role of aquitards in groundwater storage loss and highlight the necessity of incorporating aquitard dynamics into assessments for sustainable groundwater management.

Many hydrogeological processes are intricately linked to both the spatial heterogeneity and temporal dynamics of the involved parameters. The variability in hydrogeological parameters across both space and time domains is defined as the spatiotemporal heterogeneity. This study introduces a partitioning geostatistical inversion approach to characterize the spatiotemporal heterogeneity, and further applies this methodology to the long‐term multi‐extensometer data from the second aquitard beneath Qingliang Primary School, Changzhou City, China. The Principal Component Geostatistical Approach (PCGA) is used to capture the temporal variability in the hydraulic conductivity ( K ) and specific storage ( S _s ) across the three sub‐layers of the aquitard of interest. Comparative analysis reveals that models accounting for spatiotemporal heterogeneity achieve significantly higher accuracy than those considering only spatial heterogeneity. PCGA effectively captures the temporal variations in aquitard K and S _s , with sub‐layer 3 dominating the temporal dynamics. Additionally, neglecting the initial delayed drainage within the aquitard leads to a notable overestimation of K . Moreover, utilizing a stage‐wise distribution of parameters as an initial guess significantly enhances inversion accuracy. The proposed methodology not only deepens the understanding of aquitard deformation but also holds broad potential for advancing the characterization of spatiotemporal heterogeneity in 4D hydrogeological modeling.

The microbially-induced calcium carbonate precipitation (MICP) technique has shown great robustness in dealing with soil and groundwater contamination problems. A typical result of the implementation of MICP technique is a change in the pore structure. In this study, the effects of MICP on the pore structure of yellow sandstone from the Zigong area, Sichuan, China under different conditions, (e.g., temperature, pH, and calcium ion concentration) are investigated using LF-NMR resonance. The pore network of yellow sandstone is accurately measured using the peak area of the T₂ spectral signal. The distribution of calcium carbonate in the pores of the yellow sandstone is characterized by the magnitude of the T₂ signal variation. The results show that the precipitation of calcium carbonate caused by MICP tends to be deposited in relatively large pores. However, the calcium carbonate precipitates in the smaller pores at a higher temperature. A higher pH considerably enhances the precipitation, and the alkaline environment tends to cause the precipitation of the calcium carbonate in the large pores. Although the amount of produced calcium carbonate continuously increases as the MCIP process continues, which is expected, the production efficiency decreases steadily.