Ground water最新文献

Mechanical dispersion is driven by a variance in velocity rather than by the concentration gradient in the classical Fickian model. The groundwater community needs a theoretical development for this that offers a practical way to implement it (Konikow 2025). The method of Advective Transport Phenomena (De Lange 2020) describes mechanical dispersion based on the spread of water particles generated at sub-model scale by advective flow through zones with conductivity different from that of the overall aquifer, leading to a new parameter in the dispersive mass flux which is added to the advective mass flux computed at model scale similar to the existing approach in numerical modeling. The new parameter, called dispersive volume shift, is determined only by the traveled distance and the aquifer heterogeneity described by the horizontal and the vertical characteristic length and the log conductivity variance. The dispersive mass flux combines the dispersive volume shift and the concentration difference which is proportional to the traveled distance per time step. Using a spreadsheet model, the longitudinal concentration distribution in a traveling plume is simulated in a homogeneous aquifer and in a heterogeneous aquifer. The latter case shows asymmetry in the plume growth which is not produced by a classical Fickian model. Developments are still needed for application in general numerical modeling.

Long-term monitoring at landfills and impoundments containing coal combustion products (CCPs) or other industrial wastes is essential for detecting possible leachate releases to groundwater and mapping contamination plumes. This study evaluates a novel, non-invasive geophysical approach-towed time-domain electromagnetic (TEM) surveys-for non-invasive and rapid assessment of groundwater quality near landfills and impoundments that have the potential to release plumes with higher total dissolved solids (TDS) than groundwater. CCPs are one such example where releases can have relatively high sulfate, sodium, and/or calcium concentrations resulting in high TDS and, therefore, high electrical conductivity. This makes electromagnetic (EM) methods suitable for their detection and monitoring. Recent advancements in TEM technology enable efficient subsurface imaging over extensive areas using antennas towed by vehicles on land or boats on water bodies. TEM surveys provide valuable information about overburden thickness, geological structures, lithology, and pore-fluid TDS. We conducted integrated ground-based and waterborne TEM surveys at a CCP complex adjacent to a river in the eastern United States. Despite challenging site conditions, including railroad tracks, high-voltage power lines, and power-generation infrastructure, high-quality TEM data were collected. Over 20 line-km of data were acquired and inverted using laterally constrained two-dimensional (2D) and spatially constrained three-dimensional (3D) inversions. Results successfully delineated geological boundaries and identified conductive anomalies consistent with elevated TDS indicative of potential leachate plumes. Geophysical interpretations agreed well with water-quality data from nearby monitoring wells. This work highlights the effectiveness of integrated ground-based and floating TEM surveys for high-resolution characterization around CCP impoundments.

Regulatory agencies in humid temperate environments rely on timely evaluations of streamflow depletion and drawdown to protect aquatic ecosystems and existing water users. Numerical models offer detailed insights, but their complexity and time demands often preclude their practical use in rapid decision-making. We present pycap-dss, an open-source Python package that implements a suite of analytical solutions for estimating streamflow depletion and drawdown. The tool supports superposition of multiple wells and time-varying pumping, enabling cumulative impact assessments in situations with multiple wells and streams. The software is modular and extensible, allowing users to interchange solutions or add new analytical methods. A YAML-based configuration supports batch processing of multiple wells, and an optional AnalysisProject class facilitates integration with regulatory workflows. Rigorous unit and regression testing ensures computational reliability, and continuous integration supports ongoing development. We demonstrate deterministic examples of drawdown where multiple solutions are readily compared and streamflow depletion with multiple wells in the Central Sands region of Wisconsin. We also show the value of Monte Carlo analyses of streamflow depletion in the same Central Sands example, leveraging computational efficiency to evaluate the uncertainty of individual and cumulative streamflow depletion calculations from over 200 high-capacity wells.

Aquifer Storage and Recovery (ASR) is a managed aquifer recharge method where water is injected and later extracted using wells. In saline aquifers, ASR performance is often limited by dispersive mixing, which creates a transition zone at the edge of the injected freshwater and buoyancy-driven flow, which causes the freshwater to rise and deform during storage-both reducing recovery efficiency. This study investigates whether horizontal wells can improve ASR performance in saline, low-transmissivity aquifers by achieving acceptable recovery efficiencies and outperforming conventional vertical wells. Three configurations were evaluated numerically with MODFLOW 6: a horizontal well, a fully penetrating vertical well, and a dual well system with a fully penetrating injection well and a partially penetrating extraction well. Models were tested on a large set of parameter combinations from Latin Hypercube Sampling, targeting conditions where vertical wells perform poorly. The horizontal well generally achieved higher recovery efficiencies, with a median of 45% after five ASR cycles, compared to 6% and 16% for the fully and partially penetrating vertical wells. Its advantage was greatest under strong buoyancy conditions, where vertical wells failed to recover any freshwater. While dispersive mixing reduced horizontal well performance by causing earlier saltwater breakthrough, it improved vertical well recovery by stabilizing the injected freshwater. In conclusion, horizontal wells are promising for ASR when hydraulic conditions require multiple vertical wells and when buoyancy-driven flow significantly limits vertical well performance.

Reliable mapping and delineation of contaminant plumes and accurate estimation of contaminant mass discharge (CMD) are critical for groundwater risk assessment and planning of remedial actions at contaminated sites. However, traditional interpolation methods are often challenged by low-density sampling resulting in improper plume delineation. This study introduces a probabilistic censoring method that enhances geostatistical interpolation by incorporating comparably cheap, high-resolution, but semi-quantitative data collected from direct push-probes in the subsurface. The method converts halogen-specific detector signals into binary presence-absence indicators, which are interpolated using indicator kriging to generate a probability field of contaminant distribution. The probability field is then used to censor a spatial concentration field derived from traditional groundwater sampling, retaining interpolated concentration values only in areas where contamination is likely. We apply the method to a site contaminated with chlorinated solvents using two datasets with different sampling densities. Results show that, using our new method, plume fringes became more clearly defined and the total area with low concentrations (<10 μg L^-1) increased by 41-85%. CMD estimates were reduced by 13-18%, while relative uncertainty remained largely unchanged. The method integrates seamlessly with traditional interpolation methods and our censoring workflow can be applied to other forms of direct-push data (e.g., relative permeability). As such, the framework offers a useful method for incorporating semi-quantitative field measurements into concentration interpolation and CMD estimation at contaminated sites.

The Macrodispersion Experiment (MADE) at Columbus Air Force Base (MS, USA) was initiated in the mid-1980s and aimed to study solute transport in highly heterogeneous porous media by conducting large-scale natural-gradient tracer experiments. A review of the original field tracer experiments reveals several issues that were not addressed in most modeling efforts. These issues include: non-stationary flow; significant questions regarding the reliability of reported hydraulic conductivity values; a significant mass imbalance (23-50%) between the injected and observed tracer; a three-dimensional architecture based on sedimentological information; and vertical hydraulic head gradients. This paper demonstrates how these issues can be integrated into a knowledge framework that systematically assesses the knowns, unknowns, and confidence levels. Using the knowledge framework, we generate a set of multi-conceptual models as a way forward for a holistic approach for an improved understanding of the processes that affect the interpretation of measured tracer concentrations at the MADE site. Our purpose for applying the workflow at the MADE site is twofold. First, to provide a constructive dialogue towards untangling several unresolved issues associated with modeling the MADE tracer experiments. Second, to illustrate how the application of a knowledge framework coupled with multi-conceptual models can support a holistic approach for understanding flow and transport at highly heterogeneous sites.

In the past decade the groundwater modeling industry has trended toward more computationally intensive methods that necessarily require more parallel computing power due to the number of model runs required for these methods. Groundwater modeling that requires many parallel model runs is often limited by numerical burden or by the modeler's access to computational resources. Over the last 15 years the evolution of the cloud in accelerating groundwater model solutions has progressed; however, there are no apparent literature reviews of MODFLOW and PEST cloud implementation, specifically with regards to open-source and efficient scalable solutions. Here we describe infrastructure as code used to develop the architecture for running PEST++ in parallel on the cloud using Docker containers and open-source software to allow simple and repeatable cloud execution. The architecture utilizes Amazon Web Services and Terraform to facilitate cloud deployment and monitoring. A publicly available MODFLOW-6 model was used to evaluate parallel performance locally and in the cloud. Local model runs were found to have a linear 12 s increase in model run time per agent on a typical office computer compared to the cloud implementation's 0.02 s per model, indicating near perfect scaling even at up to 200 concurrent model runs. A consulting groundwater model was calibrated with the cloud infrastructure, which enabled acceleration of project completion at minimal cost.

The objective of this article is to analyze the influence of clay zones on subsidence from groundwater pumping. Finite element analyses were conducted on a sand-only aquifer and a sand aquifer with two clay zones located at different distances from the well face. A model that accounts for recoverable and nonrecoverable strains was used to simulate the sand and clay. This model couples the groundwater flow with the stress-deformation response of the aquifer materials. Each aquifer was pumped from a single well for a period of 6 months, and then the groundwater level was lowered gradually to an elevation below the elevation of the clay zones and kept there for 10 years. The groundwater level was then raised gradually back to the original elevation over a period of 10 years. The results of the analyses show that the ground surface subsidence profile is strongly influenced by the presence of the clays zones. The ground surface sags where these clay zones are present resulting in a wavy ground surface profile. Subsidence continued when pumping is stopped, albeit at a much slower rate than during pumping, and when the groundwater level is below the elevation of the clay zones. Clay zones further away from the well face lag the subsidence of clay zones nearer the well face because of lower changes in hydrostatic head. Sags in ground surface subsidence profile from groundwater pumping are indicators of the presence of low hydraulic conductive geological materials.

Groundwater is a main source of drinking water for some rural areas. People in these rural areas are potentially at risk from elevated levels of arsenic (As) due to a lack of water treatment facilities. The objectives of this study were to (1) measure As concentrations in approximately 50 groundwater samples from rural domestic wells in the western United States, (2) explore the potential of cupric oxide (CuO) particles in removal of As from groundwater samples under natural conditions (i.e., without adding competing anions and adjusting the pH or oxidation state), and (3) determine the effects of As removal on the chemistry of groundwater samples. Forty-six groundwater well samples from rural domestic areas were tested in this study. More than 50% of these samples exceeded the U.S. Environmental Protection Agency Maximum Contaminant Limit (US EPA MCL) of 10 µg/L for As. CuO particles effectively removed As from groundwater samples across a wide range of pH (7.11 and 8.95) and concentrations of competing anions including phosphate (<0.05 to 3.06 mg/L), silica (<1 to 54.5 mg/L), and sulfate (1.3 to 735 mg/L). Removal of As showed minor effects on the chemistry of groundwater samples, therefore most of the water quality parameters remained within the US EPA MCLs. Overall, results of this study could help develop a simple one-step process to remove As from groundwater.