The implementation of managed aquifer recharge (MAR) systems in the Midwest has been limited, likely due to a relative abundance of water, land use requirements, and cost. Despite limited use in the Midwest, MAR systems that source from stormwater can provide benefits in reducing flooding, while also improving shallow groundwater quality if high-quality water is infiltrated into the subsurface. We hypothesize that recharge may be safely and economically enhanced by installing shallow, small-diameter drywells that allow deeper infiltration. These installations can benefit areas where groundwater recharge is naturally low, including regions with high evapotranspirative demand and areas with lower-permeability surficial soils. In this study we assess the benefit of drywells through direct field monitoring of recharge quantity and quality via a drywell and by comparison with estimated rates of natural recharge using a one-dimensional model. Over 1 year, we found the 3.2 cm-diameter drywell to passively infiltrate an additional 30.2 to 52.2 L (best estimate 35.3) of water from rainfall, runoff, and snow melt. Compared to a model-estimated natural recharge of 177 L per year, per 1 m2 of landcover, implementation of a drywell can increase infiltration by 17 to 29%. Results suggest no need for pretreatment, as a large majority of the drywell water quality samples had concentrations below associated EPA limits. Additionally, this study discusses the longevity and the required installation and maintenance costs of implementing small-diameter drywells. This study builds on other studies that have assessed small-diameter drywells by assessing performance under natural runoff conditions and water quality impacts.
Climate change and human activities increasingly affect interconnected stream-aquifer systems, motivating continued evaluation of how stream-aquifer interactions are represented in integrated groundwater-surface water models. Most groundwater models quantify stream-aquifer exchange using an empirical riverbed leakance parameter that is predefined or calibrated from observed head differences between the stream and aquifer. Here, we describe the numerical implementation of the analytical stream aquifer flow exchange (SAFE) formulation (Morel-Seytoux et al., 2018) within the finite-element-based Integrated Water Flow Model (IWFM). SAFE represents stream-aquifer exchange using physically based parameters and provides an alternative to commonly used first order exchange (FOE) formulations, such as the MODFLOW River Package (RIV). A key extension is the ability to quantify asymmetric stream-aquifer exchange arising from different groundwater heads on opposing sides of a stream, a capability not available in standard stream-aquifer interaction packages. Numerical experiments using hypothetical test cases and a large-scale regional application demonstrate that differences in conductance and connectivity parameterizations produce distinct spatial and temporal patterns of simulated exchange. Compared with FOE, the SAFE formulation produces smoother temporal transitions and reduced short-term variability in simulated exchange. These results demonstrate the importance of conceptual model formulation when interpreting simulated stream-aquifer exchange and provide a physically based alternative for large-scale integrated groundwater-surface water modeling.
Groundwater occurrence in the Deccan basalt is highly uncertain. Non-invasive hydro-geophysical techniques, when integrated with a priori geological information, can aid in delineating saturated zones. This study uses electrical resistivity anisotropy with direct current (DC) resistivity and time-domain induced polarization (IP) for delineating groundwater prospects. We utilized the geophysical responses of DC resistivity, induced polarization, anisotropy and available borehole litholog data to locate the potential aquifers. Anisotropic inversion of DC resistivity data enables the identification of fractured basalt. We observed shallow saturation zones where fractured basalt overlies less permeable layers and deeper confined zones below the intertrappeans within fractured amygdaloidal basalts. The most productive shallow aquifers exhibit low to moderate resistivity (1 to 36 Ωm), and moderate to low chargeability (1.1 to 8 mV/V) and anisotropy (1.1 to 1.21). Finally, we conducted aquifer tests in different wells in the study area to quantify the aquifer parameters. This study offers a strong scientific basis for the assessment of groundwater potential zones and their management in the complex basaltic terrains of the Deccan province.
Abstract The Humboldt River, in Northern Nevada, USA, is a source of water for agricultural, municipal, and industrial uses. Mining has been active in Nevada since the 1800s. The recognition that groundwater withdrawal for many purposes—including mining—has the potential to deplete streamflow has prompted studies of the Humboldt River Basin. Nevada Gold Mines (NGM) operates several mine complexes in the Middle Humboldt River Basin. Although dewatering rates have reached about 3.9 cubic meters per second or greater (m 3 /s: 100,000 acre‐feet per year [afy]), most water was not consumed by mine operations. Rather, most water was returned to groundwater, used to augment surface water, or used to offset other groundwater withdrawals. The objective of this study is to evaluate the effect of groundwater use and management by NGM on surface water in the Middle Humboldt River Basin, emphasizing the Humboldt River and spanning mine development through post‐closure and pit lake formation. The study proceeds by first estimating historical and potential future net groundwater uses; then identifying features that control the propagation of pumping effects toward surface water bodies; and then using expedient calculations to estimate the locations, timing, and quantities of surface‐water depletion. The study yields a best estimate and an ensemble of results illustrating a range of potential outcomes. As a result of water management practices and identified factors that delay and diminish stream depletion versus the mine dewatering, the study finds that the peak stream depletion is likely to be on the order of 0.25 m 3 /s (about 6000 afy), a rate which may be challenging to discern for much of the stream hydrograph.
Braided river systems are an important source for groundwater recharge, but their complex morphology makes river-groundwater exchange fluxes difficult to estimate. Their river channel morphology changes frequently after floods, which has effects on recharge rates that have rarely been studied in the past. This work aims to isolate the effects of changes in braided river morphology on groundwater recharge for two sections of the Wairau River and Waikirikiri River in New Zealand. For each study site, two different river morphology variants of a fully coupled surface water-groundwater model utilizing high-resolution DEMs of river bathymetry before and after a major flood event were set up while keeping parameterization and boundary conditions the same. The models demonstrate that flood-induced morphology changes in braided river systems alter groundwater recharge. We identify features, both simulated and observed, that explain the direction of change. Features that increase groundwater recharge are a larger braidplain aquifer extent and volume, larger wetted area and, specifically, an increase of areas with high exchange rates in locations of larger gradients between braidplain aquifer and regional aquifer. These factors influence groundwater recharge independent of connection (Wairau River) or disconnection (Waikirikiri River) of the system to the regional aquifer, albeit with different magnitudes. An extension of our research to other braided rivers is needed to more broadly generalize our findings.
Direct measurements of groundwater velocity made with borehole flowmeters in screened wells must be compensated for the effects of flow-field distortion (also known as borehole acceleration). A theoretical equation developed by Drost et al. (1968) and simple inputs describing hydraulic properties of well construction and geologic formation were programmed into an Excel workbook to facilitate computation by groundwater-flowmeter users. Tables describing the physical and hydraulic properties for well constructions and gravel pack media are provided with an example to facilitate use of the workbook. Groundwater flowlines converge or diverge as they pass from a geologic formation, through a gravel pack and well screen. The extent of flowline convergence or divergence and the value of the flow-field distortion coefficient is related to the relative changes in hydraulic conductivity of the well screen, gravel pack, and geologic formation. Convergence or divergence is accompanied by acceleration or deceleration of groundwater. Direct measurements of groundwater velocity at the center of the monitoring well can be adjusted to provide a more accurate estimate of velocity in the formation by applying a correction for flow-field distortion. Variables required to compute the flow-field distortion coefficient include the hydraulic conductivity of the gravel pack, well screen, and the geologic formation surrounding the well screen; the borehole radius, and the inside radius and outside radius of the well screen.
Leakage from aging sewer and stormwater pipes into the subsurface poses significant environmental risks and threatens the integrity of urban infrastructure, primarily through the degradation of groundwater quality and the alteration of urban water balances. While the presence of defects within pipe networks is well-documented, accurately quantifying volumetric exchange fluxes remains a challenge due to the complex, nonlinear interactions between the pipe, the surrounding variably saturated soil, and the fluctuating groundwater level. Current modeling approaches often overlook the threshold behaviors of these systems, leading to potential inaccuracies in leakage estimation. In this study, we show for the first time that leaky pipes can become hydraulically disconnected from the underlying groundwater, a phenomenon analogous to well-known river-groundwater interactions that include disconnection. In a sewer-groundwater context, hydraulic disconnection is restricted to point sources and is strongly influenced by colmation/clogging. Through numerical modeling of a hypothetical case study, we show that the leakage flux from the pipe (in absolute terms) initially increases with declining groundwater levels, until a critical depth below the leaky pipe is reached. After this point, the hydraulic communication from the groundwater to the leaky pipe stops and the leakage flux can be considered constant. In a sensitivity analysis, we demonstrate the impact of the individual hydraulic parameters of the leaky-pipe-groundwater system on the hydraulic disconnection. We further modify the properties of the aquifer material, resulting in a hydraulic disconnection depth of 0.89 m, 1.77 m and 4.00 m below pipe for sand, loamy sand and sandy loam aquifers, respectively. This insight has important implications for leakage modeling: once hydraulic disconnection occurs, the leakage flux becomes independent of groundwater dynamics. The present study provides a proof-of-concept for the mechanism by which leaky sewers hydraulically disconnect from groundwater.
Computational demands for uncertainty quantification and optimization often exceed available resources for high-fidelity environmental models. While surrogate modeling (or model emulation) offers a pragmatic solution, widespread adoption is hindered by a significant "implementation gap": practitioners often lack standardized, robust tools to integrate emulation techniques directly into existing modeling workflows, relying instead on bespoke implementations. To bridge this gap, we present the Emulator module within the open-source pyEMU package. This framework provides a "plug-and-play" architecture for deploying Gaussian Process Regression (GPR), Data-Space Inversion (DSI) and other model emulation approaches. The framework automates the complex "plumbing" of emulation-based workflows, including non-Gaussian data transformation and the generation of PEST interface files, allowing trained surrogates to serve as drop-in replacements for physics-based models. We believe this one-to-one correspondence between physics-based model and emulator-based workflows will facilitate direct comparisons between the two so that the community in general can build up the knowledge of when and how to effectively and appropriately deploy emulation. We demonstrate the utility of these tools through a benchmarking optimization problem and a history-matching application on a synthetic groundwater model.
Data centers are energy end users with the fastest growing need for electricity in the United States, mainly because of the rapid expansion of cloud computing and artificial intelligence (AI). A substantial portion of this electricity, between 10% and 40%, is used for cooling. As the number of data centers increases and the sector's energy demand continues to rise exponentially, there is an urgent need to explore the use of alternative energy systems that are more efficient and sustainable. This article explores aquifer thermal energy storage (ATES) as a technically feasible and currently underutilized solution for data center cooling in the United States. Previous case studies from Europe and assessments based in the United States are considered, and the potential of ATES for reducing electricity usage for data centers, which would reduce overall greenhouse gas emissions and support sustainable energy operations.
Numerical modeling has been widely used to assess the feasibility of geothermal energy development at sites across the world, but modeling applications simulating the potential impacts on shallow hydrothermal resources and surface water are relatively scarce. In this study, we apply the MODFLOW 6 groundwater energy (GWE) code to simulate fully coupled groundwater flow and heat transport in a Rocky Mountain rift valley. The site features a moderate temperature hydrothermal system with steeply dipping normal faults, fractures, and shear zones that convey upwelling geothermal water to the shallow subsurface and facilitate interaction between deep geothermal pumping and the shallow subsurface. Following calibration against a set of publicly available well water levels, streamflow observations, well and spring water temperatures, and thermal gradients, the model is used to simulate the impacts of deep geothermal development on surface water supplies and shallow hydrothermal resources, including a hot spring system. The model simulates significant hydrologic and thermal impacts of deep geothermal pumping on the shallow hydrothermal system, including large changes in groundwater levels (-1.2 to +3.1 m), temperatures (-5.6°C to +8.7°C), and groundwater flow to springs (-10.7% to +15.4%). Depletion of tributary groundwater is simulated in three scenarios (0.8-10.7% of the geothermal extraction rate), demonstrating that deep geothermal pumping can infringe upon surface water rights. Results broadly demonstrate that in rift valley systems, geologic structures conveying upwelling geothermal water can lead to surficial thermal and hydrologic impacts in response to deep geothermal pumping, highlighting the need for regulatory frameworks that integrate geothermal energy and water resources.
Quantifying and localizing groundwater discharge is inherently difficult. It requires knowledge about hydraulic conductivity and the hydraulic gradient on the scale of interest. Conventional hydraulic testing, such as pumping tests, may fail in the presence of heterogeneity and complex structural boundaries. While advanced 2D and 3D hydraulic tomography may resolve small-scale heterogeneity, it is typically limited to small spatial scales and requires costly field installations. We propose a simplified tomographic approach using a limited number of pumping and observation wells spatially distributed over a well profile in the order of 100 m transverse to the direction of ambient flow. To infer the spatially variable hydraulic-conductivity field from drawdown data with its uncertainty, we apply an iterative ensemble smoother. Subsequently, the posterior ensemble of hydraulic-conductivity fields is used to calculate total and specific discharge based on the observed ambient hydraulic heads in the same wells. We test our approach in a synthetic scenario mimicking a channel-like aquifer such as the quaternary fill in a small river valley. The results demonstrate that multiple spatially distributed pumping tests are suitable to quantify total discharge and its associated uncertainty. The approach is more reliable than a conventional one that estimates effective transmissivity from fitting analytical solutions to pumping-test data. The tomographic analysis additionally allows locating spatial patterns of specific discharge at a resolution similar to the spacing of the wells, which may be important when assessing and remediating contaminant plumes.
Modern methods of aquifer hydraulic testing estimate subsurface properties by creating frequency-dependent variations in groundwater well levels. These methods are variously known as periodic, harmonic, or oscillatory hydraulic testing, of which sinusoidal testing is a specific case. Periodic testing provides several potential advantages over traditional methods, including larger signal-to-noise ratios, larger distances over which hydraulic disturbances propagate, and the ability to undertake zero net water extraction. One of three approaches are used to induce groundwater pressure fluctuations: (1) extraction/reinjection of water using motorized pumps, (2) pressurization/depressurization using compressed air, and (3) transient displacement of the water column by slug testing. The latter was the focus of the present study; specifically, how to improve sinusoidal slug testing methods by ensuring accurate generation of sinusoidal variations in well water levels. Two previously published sinusoidal testing designs were evaluated in terms of the ratio of effective transfer link length, L $$ L $$ , to effective flywheel radius, r e $$ {r}_e $$ . The first published design featured L / r e $$ L/{r}_e $$ ratio values ranging from 13 to 9, which corresponded to maximum discrepancies between intended and actual slug movement of 7% to 10%, respectively. The second design featured L / r e $$ L/{r}_e $$ ratio values ranging from 12 to 2, which corresponded to maximum discrepancies of 8% to 29%, respectively. These analyses suggest that methods featuring a rotating drive coupled to an effective transfer link are suboptimal. Instead, designs featuring either modified flywheel apparatus or winches driven by digitally controlled stepper motors can minimize the potential for discrepancies between intended and actual slug movement. The accurate generation of sinusoidal slug movement will minimize uncertainties associated with hydraulic properties inversely estimated from observations acquired during sinusoidal slug testing.
Although groundwater flow directions are influenced by hydraulic gradients and density gradients, density gradients are often assumed negligible outside coastal zones and saline lake environments. Density gradients are rarely considered in mining studies, but can alter groundwater flow patterns, and cause outflow of water from pit lakes despite inward hydraulic gradients. Open mine pits often intersect regional water tables, requiring dewatering during mining operations. At the end of mine life, groundwater abstraction ceases, frequently leading to the development of pit lakes. Due to prolonged water residence time, and evaporation, pit lake water quality may deteriorate with salinization being a common problem. While salinity differences between pit lake water and groundwater are small initially, they increase with time, inducing density contrasts. Consequently, dense pit lake water may move along density gradient towards less dense groundwater. This changes the flow patterns around the pit lake and impact on surrounding aquifer water quality. In this study, we advance process understanding of how density effects alter flow and salinity patterns in pit lake environments post-mining using numerical modeling. We show the impact of ambient groundwater salinity, regional hydraulic gradients, evaporation rates, and hydraulic conductivities on the interaction between a pit lake and the surrounding aquifer. We demonstrate how density effects can substantially increase lake water outflow and decrease pit lake water salinities. Pit lakes can turn from terminal sinks into throughflow systems purely due to variable-density flow. Understanding the hydraulic and salinity evolution of pit lakes is crucial for planning post mining rehabilitation.
