Hydrogeology Journal最新文献

The Mississippi Embayment aquifer system (MEAS) and the Coastal Lowlands aquifer system (CLAS) are two principal aquifers in the US Gulf Coastal Plain. Despite their importance to the region, a comprehensive characterization of these aquifers has not been achieved yet. In this study, the horizon-assisted lithologic modeling (HALM) method is introduced to integrate horizon structures and well log data for aquifer characterization. By employing horizon restorations, the HALM method proves to be versatile in incorporating various geologic features into lithologic models. The HALM method was applied to characterize both the MEAS and the CLAS in the Louisiana and southwestern Mississippi regions. The resulting large-scale high-resolution hydrostratigraphic model provides a highly accurate representation of aquifer structures in regionally extensive hydrogeologic units, including synclines, angular unconformities, and faulting. Notably, the model highlights the presence of surficial coarse sediments, indicating significant groundwater recharge zones for the Southern Hills aquifer system, the Chicot aquifer, and the Sparta aquifer. Additionally, the Mississippi River alluvial aquifer and the Chicot aquifer are found to be thick and shallow, making them easily accessible for irrigation purposes. Furthermore, the model reveals significant connections between rivers and alluvial aquifers in northern Louisiana, with reduced river–aquifer contact as one approaches the Gulf of Mexico. Comparing the two aquifer systems, the CLAS exhibits relatively thick and extensive aquifers compared to the MEAS. This study not only contributes to advancements in geologic modeling techniques but also enhances the understanding of regional hydrogeology in the US Gulf Coastal Plain.

Investigations focusing on the impacts of mining on groundwater systems typically provide a qualitative analysis of groundwater flow and chemistry, whereas relatively few studies quantitatively analyze groundwater temperature perturbations induced by mining. This study aims to identify the hydrogeological mechanism responsible for changes to groundwater temperature associated with longwall coal mining. Here, the extreme gradient boosting (XGBoost) method was used to construct three models at different phases of mining disturbance to identify the factors governing groundwater temperature dynamics: (1) a pre-disturbance model; (2) an in-disturbance model; and (3) a post-disturbance model. The feature relative importance (FRI) of input variables contributing to groundwater temperature dynamics was quantified for a long-term groundwater monitoring dataset collected from the Ningtiaota Coalfield, Ordos Basin, China. Pre-mining disturbance groundwater temperatures were stable, and the XGBoost model identified the groundwater level of the respective monitoring wells to be the greatest predictor for variation in groundwater temperature. During mining disturbance, proximal monitoring wells exhibited a decline in groundwater temperature, where the FRI of groundwater temperature in an upgradient monitoring well increased by 151–662% relative to the pre-mining disturbance model. The monitoring of aquifer properties and stable isotope composition of groundwaters provided additional evidence to suggest groundwater temperature decreases were associated with increased recharge contributions from surficial Quaternary aquifers. Post-mining disturbance, groundwater temperature and aquifer specific storage demonstrated recovered to pre-mining conditions. This study provides insights into mining-induced groundwater temperature dynamics as a result of changes to hydraulic connection between aquifers.

Groundwater recharge estimation is important for groundwater resource management especially in arid and semiarid areas, such as Loess Plateau, China. Here, loess deposits form regionally important aquifers, typified by a thick unsaturated zone, facilitating the application of environmental tracers to estimate groundwater recharge rates. In this study, the chloride mass balance (CMB) method was used to estimate groundwater recharge from precipitation for two sites in Inner Mongolia, China. Due to the uncertainty in determining the prerequisite chloride input flux for the CMB method, three different techniques (artificial ³H tracer method, the measured chloride concentration in precipitation, and 1963 tritium peak method) were used to determine the chloride input flux to increase the reliability of the calculated groundwater recharge rates. The different chloride input flux results obtained from the different techniques were found to be consistent. The average groundwater recharge rate calculated from the chloride mass balance method is 0.038 m/year. The groundwater recharge rate obtained in this study was found to be consistent with groundwater recharge rates derived from similar studies in the Loess Plateau.

Mine-water geothermal resources have potential to provide low-carbon heating and cooling in many areas; however, this potential has not been fully realised due to technical, economic and policy challenges. The UK Geoenergy Observatory (UKGEOS) in Glasgow was developed to provide an at-scale research facility designed to help de-risk mine-water geothermal usage. The limited knowledge of the hydrogeological systems altered by former mining activities is a key determinant of the long-term sustainability of water and heat abstraction/reinjection. This work presents a hydrogeological conceptual model developed using groundwater monitoring data obtained during the construction of the Observatory between 2020 and 2022, results from initial pumping tests performed in 2020, and results of hydrochemistry analysis from 25 sampling rounds collected between 2019 and 2022. The analysis of the data provides evidence of the dominant role of mine workings in controlling groundwater flow, with high intra-mine connectivity; increased fracturing in sandstones above mine workings; and limited inter-mine connectivity. Groundwater recharge is meteoric, mean residence times are >50 years, and there is a general upwards circulation from the deeper mine levels to the superficial deposits and the River Clyde. Faults play a significant role in limiting the extent of the highly transmissive mine workings, but there remains uncertainty surrounding the role of the faults in connecting different mine workings and their hydraulic behaviour in nonmined units. The conceptual model, that will be refined as new data become available, will be used to help guide monitoring and sampling programs and plan research activities in the Observatory.

Research on the hydrogeology of andesitic volcanic aquifers in subduction areas is reviewed. Andesitic aquifers are of high interest in volcanic arc islands and subduction zones, where they constitute a strategic water resource. This review gathers a compilation of worldwide results and case studies to propose a generic hydrogeological conceptual model (GHCM). It is based on the geological conceptual model splitting the volcanic edifice, from upstream to downstream, into central, proximal, medial and distal zones. In this geological structure, the GHCM identifies where the main aquifer types (fractured lava, pyroclastic flows, and the volcano-sedimentary basins downstream) and the typical aquitards (lahars, fine pyroclastic falls and surges, indurated pyroclastic flow, and weathered rocks) are structured and organized. To integrate the evolution of volcanoes and some specific volcanic activities, a specific GHCM for old andesitic volcanoes or andesitic shield volcanoes is detailed. The paper also describes how the GHCM results are of use to hydrogeologists in terms of scale (from the lithological units to the regional scale), to effectively site water wells, and to sustainably manage groundwater resources in such aquifers. Among these various scales, the volcanic “flank continuum” is presented as the most adapted to support groundwater resources management. Several ways to improve this GHCM are suggested, notably to better consider the geological complexity of these aquifers.

Karst aquifers are complex systems characterized by high heterogeneity and anisotropy. Karst hydrological duality is evident in processes such as recharge, storage, and flow. The MODFLOW Conduit Flow Process (CFP) simulates this flow duality. In this study, CFP version 2 (CFPv2) was applied to the Yucatan karst in Mexico, known for its well-developed karst features, including subsurface conduits. Given the sparse data regarding the three-dimensional location and connectivity of conduits and underwater coastal springs, the theoretical conduit pathways were inferred from geology or geophysics. CFPv2 was utilized to evaluate these theoretical conduit network arrangements based on indirect data from gravimetry, geophysics, and geological information from the second-largest impact crater on Earth. The Merida Metropolitan Area (a densely populated region in the Mexican state of Yucatan) was selected as the study area. Piezometric data from 43 monitoring wells (collected during the monitoring period 1996–2001) formed the basis for model inversion. Recharge volumes were derived from precipitation data collected from 14 climatic stations. Results were compared with a previous groundwater flow model applied in the same area utilizing the CFP Mode 2, a turbulent flow-enabled single continuum model. Results of this study support the hypothesis of multirings of preferential flow influencing groundwater dynamics, providing important insights regarding the sub-surface in this karst region.

Agent-based models (ABMs) have long been applied in economics and social science research. The combination or coupling of these models with those of natural systems is a more recent application, and their use in conjunction with groundwater flow and transport models can be considered an innovative way to take advantage of their potential. In the Latin American region, sustainable management of groundwater resources can still be considered understudied. Among other characteristics, the existence of large transboundary aquifers in the region adds a further complication for addressing the sustainability of groundwater resource use. In this type of system, the impacts of joint regulations for utilization by different countries, the diversity of socioeconomic drivers and the conservation interests of each group of users might be consistently represented and explored through flow models coupled with ABMs. This review of the scientific literature aims to compile up-to-date information regarding the application of hydrogeological models coupled with agent-based models, focusing on their contributions to the sustainable management of groundwater resources and analyzing their potential for the Latin American region.

The effect of subsurface structures in blocking groundwater seepage has a long-term influence on groundwater level (GWL). A finite difference method (FDM) model considering the actual distribution of subsurface structures in an urban area of Shanghai (China) was established to predict GWL in the phreatic aquifer (Aq0) and the first confined aquifer (AqI). The equivalent hydraulic conductivity (K_eq) of model elements containing subsurface structures, calculated by the effective medium theory, was applied to the model. The predicted GWL fitted the monitored value in Aq0 well. Additional subsurface structures were added to the model to analyze the influence of the distribution type and the proportion (%) of the volume of subsurface structures that occupy the aquifer (V_u). Four scenarios with different distribution types (concentrated, subconcentrated, subscattered, and scattered) and ten scenarios with V_u varying from 5 to 50%, were analyzed. In all scenarios, the regional average GWL in AqI increased compared to the actual conditions because of the decrease in K_eq and the blockage effect on groundwater flow. The influence of scattered distribution on the regional GWL distribution was the smallest, and the subscattered distribution resulted in the most nonuniform GWL redistribution. The blockage effect of the subsurface structures gradually increased with increasing V_u. The increasing rate of ΔL_av (difference in regional average GWL between the predicted and actual scenarios) becomes considerable when V_u is ~29%. Hence, the projected increase in volume of subsurface structures in AqI under the assumed subscattered distribution is suggested to be <29%.

The key factors determining the operational cost and carbon footprint of public water supplies derived from groundwater are identified. Both remain low compared to alternative sources while groundwater levels remain stable and water quality potable, but can increase markedly if derived from overexploited and/or polluted aquifers. Thus, ‘potable source protection zones’ are strongly advocated, and examples from England (UK) and Spain are illustrated. The concept of minimising the carbon footprint of groundwater use for potable water supply is novel, and deserves greater attention.

Saline pans are environments with ephemeral to persistent evaporite crusts, surface and groundwater brine, little to no vegetation, and low topographic gradients. These characteristics make them sensitive to diverse hydrological processes. This research provides guidance on assessing and interpreting fluctuations in saline pan groundwater levels. Observations from the center of the Bonneville Salt Flats, Utah, USA, focused on meteorological and groundwater level fluctuations and were used to quantify evaporation and identify natural environmental controls on saline pan groundwater level variation. Primary water fluxes consist of precipitation and evaporation. Eddy-covariance evaporation measurements, spanning over 1.5 years and capturing diverse surface conditions, were collected. An artificial neural network, trained on meteorological measurements and eddy-covariance-measured evaporation, estimated evaporation over a 6-year period. The saline pan has two states: (1) dry, when water availability rather than evaporative potential limits evaporation, and (2) wet, when evaporative potential limits evaporation. In dry conditions, characterized by evaporation rates of ~0.1 mm/day, groundwater levels with daily average depths ≥5 cm below the surface, demonstrated daily variations >6 cm during summer and seasonal fluctuations >50 cm in response to temperature changes. Groundwater levels did not respond to temperature changes when there was surface water. Groundwater levels rose to the surface under wet conditions. Over multiple years, the system is in balance, with evaporation equaling precipitation.