Regional-scale Groundwater Flow Research Articles

Accelerating regional-scale groundwater flow simulations with a hybrid deep neural network model incorporating mixed input types: A case study of the northeast Qatar aquifer

ABSTRACT This study presents the ‘Dual Path CNN-MLP’, a novel hybrid deep neural network (DNN) architecture that merges the strengths of convolutional neural networks (CNNs) and multilayer perceptrons (MLPs) for regional groundwater flow simulations. This model stands out from previous DNN approaches by managing mixed input types, including both imagery and numerical vectors. Such flexibility allows the diverse nature of groundwater data to be efficiently utilized without the need to convert it into a uniform format, which often leads to oversimplification or unnecessary expansion of the dataset. When applied to the northeast Qatar aquifer, the model demonstrates high accuracy in simulating transient groundwater flow fields, benchmarked against the well-established MODFLOW model. The model's efficacy is confirmed through k-fold cross-validation, showing an error margin of less than 12% across all examined locations. The study also examines the model's ability to perform uncertainty analysis using Monte Carlo simulations, finding that it achieves around 1% average absolute percentage error in estimating the mean hydraulic head. Errors are mostly found in areas with significant variations in the hydraulic head. Switching to this ML model from the conventional MODFLOW simulator boosts computational efficiency by about 99%, showcasing its advantage for tasks like uncertainty analysis in repetitive groundwater simulations.

Assessment of installation suitability of a vertical closed loop ground source heat pump system in regional scale

Installation suitability of a vertical closed loop GSHP system in the Echigo Plain of Japan was assessed considering the regional scale groundwater flow and heat transport analysis. For evaluating and understand the variation of development potential of the system, the necessary length of ground heat exchanger (GHE) was analyzed at different points, where groundwater, geology and subsurface temperature distribution varies. The computation was done for the model case of the Japanese single-family dwelling with reference to standard for energy saving in Japan. The necessary length of GHE ranged from 67 m to 101 m within the plain and found comparatively longer at the central coastal area around the Niigata City. These results showing the variation of the necessary length of GHE in the plain scale is significant and essential for the proper design and site selection of the system in the Echigo Plain, and can also be beneficial for the development of GSHP system in Japan. Influence of the existing groundwater pumping system was also evaluated to determine if the pumping system can enhance heat exchange performance for space-heating. The effect of groundwater pumping was not so significant to improve heat exchange rates due to the natural existence of groundwater flow.

Subsurface microbial communities as a tool for characterizing regional-scale groundwater flow

Subsurface microbial community distribution patterns are influenced by biogeochemical and groundwater fluxes and may inform hydraulic connections along groundwater-flow paths. This study examined the regional-scale microbial community of the Death Valley Regional Flow System and evaluated whether subsurface communities can be used to identify groundwater-flow paths between recharge and discharge areas. Samples were collected from 36 sites in three groundwater basins: Pahute Mesa–Oasis Valley (PMOV), Ash Meadows (AM), and Alkali Flat–Furnace Creek Ranch (AFFCR). Microbial diversity within and between communities varied by location, and communities were separated into two overall groups that affiliated with the AM and PMOV/AFFCR basins. Network analysis revealed patterns between clusters of common microbes that represented groundwaters with similar geochemical conditions and largely corroborated hydraulic connections between recharge and discharge areas. Null model analyses identified deterministic and stochastic ecological processes contributing to microbial community assemblages. Most communities were more different than expected and governed by dispersal limitation, geochemical differences, or undominating processes. However, certain communities from sites located within or near the Nevada National Security Site were more similar than expected and dominated by homogeneous dispersal or selection. Overall, the (dis)similarities between the microbial communities of DVRFS recharge and discharge areas supported previously documented hydraulic connections between: (1) Spring Mountains and Ash Meadows; (2) Frenchman and Yucca Flat and Amargosa Desert; and (3) Amargosa Desert and Death Valley. However, only a portion of the flow path between Pahute Mesa and Oasis Valley could be supported by microbial community analyses, likely due to well-associated artifacts in samples from the two Oasis Valley sites. This study demonstrates the utility of combining microbial data with hydrologic, geologic, and water-chemistry information to comprehensively characterize groundwater systems, highlighting both strengths and limitations of this approach.

Investigation of groundwater recharge mechanism for sustainable urban water system planning and management in Hanoi city

Seasonal variation of water levels and water quality of groundwaters and ponds was investigated to illustrate the recharge mechanism and seasonal effects of groundwater in Hanoi suburbs. Water level monitoring data showed that the upper aquifer had a fluctuating water level (variation: 2.0 m) corresponding to heavy rains, representing a substantial impact by infiltration of rainwater from the surface and perhaps pond water. In the area with less permeable surface, there was small response to rainy events, suggesting that the ground water levels were governed by a regional scale groundwater flow. The stable isotope ratios in pond waters had a clear seasonal change, in which isotopes were enriched throughout the dry season. In groundwater, isotope signatures indicated that the dominant sources had evaporation process. In studied areas, the isotope ratios in groundwaters and pore waters in the shallow soil (<25 m depth) were clearly heavier than that in the deep soil. Isotope results suggested that groundwaters close to the Red River are largely recharged by the river itself. In areas far from the river, surface waters having evaporation process (e.g., ponds and paddy fields) and the rainwater directly infiltrating from the surface mainly recharges the upper aquifer. The lower aquifer in inland locations would be recharged by lateral inflow, either from the Red River or surrounding mountains. The results revealed the recharge mechanism for groundwater budget which could contribute for the planning and sustainable development of urban water system in Hanoi City.

Editorial of Special Issue “Advances in Groundwater Flow and Solute Transport: Pushing the Hidden Boundary”

The theme of this special issue is to explore the new territories beyond conventional subsurface flow and transport theories. We have selected 12 articles in this special issue and these articles cover a wide range of problems including (1) Non-Fickian chemical transport in various environments; (2) Non-Darcian flow; (3) Flow and transport in low-permeability media; (4) Vadose zone process; (5) Regional scale groundwater flow and groundwater-surface interaction; (6) Innovative numerical methods. The major contributions of these papers are summarized in this editorial.

Hydrogeochemical Evolution Along Groundwater Flow Paths in the Manas River Basin, Northwest China.

The impacts of long-term pumping on groundwater chemistry remain unclear in the Manas River Basin, Northwest China. In this study, major ions within five surface water and 105 groundwater samples were analyzed to identify hydrogeochemical processes affecting groundwater composition and evolution along the regional-scale groundwater flow paths using the multivariate techniques of hierarchical cluster analysis (HCA) and principal components analysis (PCA) and traditional graphical methods for analyzing groundwater geochemistry. HCA classified the groundwater samples into four clusters (C1 to C4). PCA reduced the dimensionality of geochemical data into three PCs, which explained 86% of the total variance. The results of HCA and PCA were used to identify three zones: "recharge," "transition," and "discharge." In the recharge zone the groundwater type is Ca-HCO3 -SO4 and is primarily impacted by the dissolution of calcite and silicate weathering. In the transition zone the groundwater type is Ca-HCO3 -SO4 -Cl and is impacted by rock dissolution and reverse ion exchange. In the discharge zone the groundwater type is Na-Cl and is impacted by evaporation and reverse ion exchange. In addition, anthropogenic activities impact the groundwater chemistry in the study area. The groundwater type generally changes from Ca-HCO3 -SO4 in the recharge area to Na-Cl in the discharge area along the regional-scale groundwater flow paths. This study provides a process-based knowledge for understanding the interaction of groundwater flow patterns and geochemical evolution within the Manas River Basin.

Estimating the thickness of unconsolidated coastal aquifers along the global coastline

Abstract. Knowledge of aquifer thickness is crucial for setting up numerical groundwater flow models to support groundwater resource management and control. Fresh groundwater reserves in coastal aquifers are particularly under threat of salinization and depletion as a result of climate change, sea-level rise, and excessive groundwater withdrawal under urbanization. To correctly assess the possible impacts of these pressures we need better information about subsurface conditions in coastal zones. Here, we propose a method that combines available global datasets to estimate, along the global coastline, the aquifer thickness in areas formed by unconsolidated sediments. To validate our final estimation results, we collected both borehole and literature data. Additionally, we performed a numerical modelling study to evaluate the effects of varying aquifer thickness and geological complexity on simulated saltwater intrusion. The results show that our aquifer thickness estimates can indeed be used for regional-scale groundwater flow modelling but that for local assessments additional geological information should be included. The final dataset has been made publicly available (https://doi.pangaea.de/10.1594/PANGAEA.880771).

Benefits and limitations of using isotope-derived groundwater travel times and major ion chemistry to validate a regional groundwater flow model: example from the Centre-du-Québec region, Canada

Understanding groundwater dynamics at the regional scale (> 100 km) is essential to the development of sustainable water management regulations. Groundwater flow models are increasingly used to support these strategies. However, in order to be reliable, these models need to be calibrated and validated. The objective of this work is to evaluate the benefits and the limitations of using isotope-derived groundwater travel times and major ion chemistry to validate a regional-scale groundwater flow model in the humid continental climate of southern Québec (Canada). A three-dimensional regional-scale steady-state groundwater model was created using MODFLOW for the fractured bedrock aquifer of the Centre-du-Québec region (Québec, Canada), using data acquired during recent aquifer characterization projects. The model covers an area of 7452 km2, from the unconfined Appalachian Mountains to the confined St. Lawrence Platform. Groundwater travel times were simulated for 211 wells using particle tracking. The groundwater flow model was calibrated using 11,775 regionally distributed heads and 15 baseflow values. The model was validated using 23 3H/3He residence time (3 to 60 years), 17 14C residence time (226 to 22,600 years), and the major ion compositions from 211 wells. Results indicate that the model is able to satisfactorily simulate ³H/³He isotopic residence time, while 14C isotopic residence times are generally underestimated. These results suggest substantial mixing between groundwater recharged during the last deglaciation and recently recharged water. Regional groundwater flow is limited or absent, and most of the recharge discharges to the river network as baseflow. The analysis of travel times indicates a statistically distinct mean travel time for the different groundwater types. Median travel time is 68 years for recently recharged groundwater (Ca-HCO3), 274 years for semi-confined groundwater (Na-HCO3), and 738 years for confined groundwater (Na-Cl). This confirms that groundwater chemistry is a broad indicator of groundwater travel time.

Hydrogeochemistry and geothermometry of deep thermal water in the carbonate formation in the main urban area of Chongqing, China

Many geothermal reservoirs in Chongqing in southwestern China are located in carbonate rock aquifers and exploited through drilling. Water samples from 36 geothermal wells have been collected in the main urban area of Chongqing. Chemical types of the thermal water samples are Ca·Mg-SO4 and Ca-SO4. High contents of Ca2+ and SO42− in the thermal water samples are derived from the dissolution of evaporates. Furthermore, the HCO3− concentration is constrained by the common ion effect. Drilling depth has no effect on the physical and chemical characteristics according to the results of a t-test. The geothermal reservoir’s temperature can be estimated to be 64.8–93.4°C (average 82°C) using quartz and improved SiO2 geothermometers. Values of δD and δ18O for the thermal water samples indicate that the thermal water resources originate from local precipitation with a recharge elevation between 838 and 1130m and an annual air temperature between 10.4 and 13.9°C. A conceptual model of regional scale groundwater flow for the thermal water is proposed. The thermal water mainly originates from the meteoric water recharged in the elevated areas of northeastern Tongluoshan and Huayingshan by means of percolation through exposed carbonate before becoming groundwater. The groundwater is heated at depth and moves southwest along the fault and the anticlinal core in a gravity-driven regime. The thermal water is exposed in the form of artesian hot springs in river cutting and low-elevation areas or in wells.

Numerical modelling of groundwater flow to understand the impacts of pumping on arsenic migration in the aquifer of North Bengal Plain

In this paper, numerical simulations of regional-scale groundwater flow of North Bengal Plain have been carried out with special emphasis on the arsenic (As)-rich alluvium filled gap between the Rajmahal hills on the west and the Garo hills on the east. The proposed concern of this modelling arose from development that has led to large water table declines in the urban area of English Bazar block, Malda district, West Bengal and possible transport of As in the near future from the adjacent As-polluted aquifer. Groundwater occurs under unconfined condition in a thick zone of saturation within the Quaternary alluvial sediments. Modelling indicates that current pumping has significantly changed the groundwater flowpaths from pre-development condition. At the present pumping rate, the pumping wells of the urban area may remain uncontaminated till the next 25 yrs, considering only pure advection of water but some water from the As-polluted zone may enter wells by 50 yrs. But geochemical and other processes such as adsorption, precipitation, redox reaction and microbial activity may significantly retard the predicted rate by advective transport. In the rural areas, majority of the water pumped from the aquifer is for irrigation, which is continuously re-applied on the surface. The near-vertical nature of the flowpaths indicates that, where As is present or released at shallow depths, it will continue to occur in pumping wells. Modelling also indicates that placing all the pumping wells at depths below 100 m may not provide As-free water permanently.

Spatial and temporal constraints on regional-scale groundwater flow in the Pampa del Tamarugal Basin, Atacama Desert, Chile

Aquifers within the Pampa del Tamarugal Basin (Atacama Desert, northern Chile) are the sole source of water for the coastal city of Iquique and the economically important mining industry. Despite this, the regional groundwater system remains poorly understood. Although it is widely accepted that aquifer recharge originates as precipitation in the Altiplano and Andean Cordillera to the east, there remains debate on whether recharge is driven primarily by near-surface groundwater flow in response to periodic flood events or by basal groundwater flux through deep-seated basin fractures. In addressing this debate, the present study quantifies spatial and temporal variability in regional-scale groundwater flow paths at 20.5°S latitude by combining a two-dimensional model of groundwater and heat flow with field observations and δ18O isotope values in surface water and groundwater. Results suggest that both previously proposed aquifer recharge mechanisms are likely influencing aquifers within the Pampa del Tamarugal Basin; however, each mechanism is operating on different spatial and temporal scales. Storm-driven flood events in the Altiplano readily transmit groundwater to the eastern Pampa del Tamarugal Basin through near-surface groundwater flow on short time scales, e.g., 100–101 years, but these effects are likely isolated to aquifers in the eastern third of the basin. In addition, this study illustrates a physical mechanism for groundwater originating in the eastern highlands to recharge aquifers and salars in the western Pampa del Tamarugal Basin over timescales of 104–105 years.

Development of a groundwater flow model for the highly parameterized Qatar aquifers

Groundwater models are powerful tools for water resources management, assessment and protection. The main challenge facing model development is the calibration process, especially in large models with a high number of calibrated parameters. Qatar aquifers comprise karst limestone with lots of cavities, sinkholes and underground channels. Therefore, the aquifer is highly heterogeneous. This study presents the development of a regional scale groundwater flow model for the entire country of Qatar, with emphasis on calibration process. Pilot points approach with regularization has been utilized to calibrate the model to re-produce historical water levels representing steady state conditions. Hydraulic conductivity and natural rainfall recharge were calibrated, using historical groundwater levels from 1958. Results of the model included pre-development water budget for the country, and estimation of natural groundwater recharge, which was found to be 65.6 million m3 per year. Calibration process also reveals that the top layer of the aquifer, and the northern part have the highest hydraulic conductivity, compared to other areas. The calibrated hydraulic conductivity values are quite variable, as it ranges from 0.1 m/days to more than 200 m/days. Results of this model can help understanding the flow regime, aquifer parameterization and design of artificial recharge scheme in Qatar.

A high-resolution global-scale groundwater model

Abstract. Groundwater is the world's largest accessible source of fresh water. It plays a vital role in satisfying basic needs for drinking water, agriculture and industrial activities. During times of drought groundwater sustains baseflow to rivers and wetlands, thereby supporting ecosystems. Most global-scale hydrological models (GHMs) do not include a groundwater flow component, mainly due to lack of geohydrological data at the global scale. For the simulation of lateral flow and groundwater head dynamics, a realistic physical representation of the groundwater system is needed, especially for GHMs that run at finer resolutions. In this study we present a global-scale groundwater model (run at 6' resolution) using MODFLOW to construct an equilibrium water table at its natural state as the result of long-term climatic forcing. The used aquifer schematization and properties are based on available global data sets of lithology and transmissivities combined with the estimated thickness of an upper, unconfined aquifer. This model is forced with outputs from the land-surface PCRaster Global Water Balance (PCR-GLOBWB) model, specifically net recharge and surface water levels. A sensitivity analysis, in which the model was run with various parameter settings, showed that variation in saturated conductivity has the largest impact on the groundwater levels simulated. Validation with observed groundwater heads showed that groundwater heads are reasonably well simulated for many regions of the world, especially for sediment basins (R2 = 0.95). The simulated regional-scale groundwater patterns and flow paths demonstrate the relevance of lateral groundwater flow in GHMs. Inter-basin groundwater flows can be a significant part of a basin's water budget and help to sustain river baseflows, especially during droughts. Also, water availability of larger aquifer systems can be positively affected by additional recharge from inter-basin groundwater flows.

Multi-scale groundwater flow modeling during temperate climate conditions for the safety assessment of the proposed high-level nuclear waste repository site at Forsmark, Sweden

Forsmark in Sweden has been proposed as the site of a geological repository for spent high-level nuclear fuel, to be located at a depth of approximately 470 m in fractured crystalline rock. The safety assessment for the repository has required a multi-disciplinary approach to evaluate the impact of hydrogeological and hydrogeochemical conditions close to the repository and in a wider regional context. Assessing the consequences of potential radionuclide releases requires quantitative site-specific information concerning the details of groundwater flow on the scale of individual waste canister locations (1–10 m) as well as details of groundwater flow and composition on the scale of groundwater pathways between the facility and the surface (500 m to 5 km). The purpose of this article is to provide an illustration of multi-scale modeling techniques and the results obtained when combining aspects of local-scale flows in fractures around a potential contaminant source with regional-scale groundwater flow and transport subject to natural evolution of the system. The approach set out is novel, as it incorporates both different scales of model and different levels of detail, combining discrete fracture network and equivalent continuous porous medium representations of fractured bedrock.

Differential-Evolution algorithm based optimization for the site selection of groundwater production wells with the consideration of the vulnerability concept

• New groundwater well sites are sought by considering intrinsic aquifer vulnerability. • Pumping rates of existing wells are optimized to prevent seawater intrusion to them. • Optimization is based on Differential-Evolution algorithm. • Pumping is maximized or total pumping costs is minimized. • Method finds best sites for new wells in terms of groundwater quantity and quality. The objective of this study is to present an optimization approach to determine locations of new groundwater production wells, where groundwater is relatively less susceptible to groundwater contamination (i.e. more likely to obtain clean groundwater), the pumping rate is maximum or the cost of well installation and operation is minimum for a prescribed set of constraints. The approach also finds locations that are in suitable areas for new groundwater exploration with respect to land use. A regional-scale groundwater flow model is coupled with a hybrid optimization model that uses the Differential Evolution (DE) algorithm and the Broyden–Fletcher–Goldfarb–Shanno (BFGS) method as the global and local optimizers, respectively. Several constraints such as the depth to the water table, total well length and the restriction of seawater intrusion are considered in the optimization process. The optimization problem can be formulated either as the maximization of the pumping rate or as the minimization of total costs of well installation and pumping operation from existing and new wells. Pumping rates of existing wells that are prone to seawater intrusion are optimized to prevent groundwater flux from the shoreline towards these wells. The proposed simulation–optimization model is demonstrated on an existing groundwater flow model for the Tahtalı watershed in Izmir–Turkey. The model identifies for the demonstration study locations and pumping rates for up to four new wells and one new well in the cost minimization and maximization problem, respectively. All new well locations in the optimized solution coincide with areas of relatively low groundwater vulnerability. Considering all solutions of the demonstration study, groundwater vulnerability indices for new well locations range from 29.64 to 40.48 (on a scale of 0–100, where 100 indicates high vulnerability). All identified wells are located relatively close to each other. This implies that the method pinpoints the best area for new wells both in terms of groundwater quantity and quality. Furthermore, sensitivity analysis results indicate that identification results are insensitive to the selection of DE parameters.

Conceptual and numerical modeling approach of the Guarani Aquifer System

Abstract. In large aquifers, relevant for their considerable size, regional groundwater modeling remains challenging given geologic complexity and data scarcity in space and time. Yet, it may be conjectured that regional scale groundwater flow models can help in understanding the flow system functioning and the relative magnitude of water budget components, which are important for aquifer management. The Guaraní Aquifer System is the largest transboundary aquifer in South America. It contains an enormous volume of water; however, it is not well known, being difficult to assess the impact of exploitation currently used to supply over 25 million inhabitants. This is a sensitive issue because the aquifer is shared by four countries. Moreover, an integrated groundwater model, and therefore a global water balance, were not available. In this work, a transient regional scale model for the entire aquifer based upon five simplified, equally plausible conceptual models represented by different hydraulic conductivity parametrizations is used to analyze the flow system and water balance components. Combining an increasing number of hydraulic conductivity zones and an appropriate set of boundary conditions, the hypothesis of a continuous sedimentary unit yielded errors within the calibration target in a regional sense. The magnitude of the water budget terms resulted very similar for all parametrizations. Recharge and stream/aquifer fluxes were the dominant components representing, on average, 84.2% of total inflows and 61.4% of total outflows, respectively. However, leakage was small compared to stream discharges of main rivers. For instance, the simulated average leakage for the Uruguay River was 8 m3 s−1 while the observed absolute minimum discharge was 382 m3 s−1. Streams located in heavily pumped regions switched from a gaining condition in early years to a losing condition over time. Water is discharged through the aquifer boundaries, except at the eastern boundary. On average, pumping represented 16.2% of inflows while aquifer storage experienced a small overall increment. The model water balance indicates that the current rate of groundwater withdrawals does not exceed the rate of recharge in a regional sense.

Groundwater-surface water interaction in Lake Nasser, Southern Egypt

A cross-sectional model, based on the two dimensional groundwater flow equation of Edelman, was applied at seven transects distributed over four geological cross sections to estimate groundwater heads and recharge from/or groundwater discharge to Lake Nasser. The lake with a length of 500 km and an average width of 12 km was created over the period 1964–1970, the time for constructing the Aswan High Dam (AHD). The model, constrained by regional-scale groundwater flow and groundwater head data in the vicinity of the lake, was successfully calibrated to timeseries of piezometeric heads collected at the cross sections in the period 1965–2004. Inverse modeling yielded high values for the horizontal hydraulic conductivity in the range of 6.0 to 31.1 m day−1 and storage coefficient between 0.01 and 0.40. The results showed the existence of a strong vertical anisotropy of the aquifer. The calibrated horizontal permeability is systematically higher than the vertical permeability (≈1000:1). The calibrated model was used to explore the recharge from/or groundwater discharge to Lake Nasser at the seven transects for a 40-year period, i.e. from 1965 to 2004. The analysis for the last 20-year period, 1985–2004, revealed that recharge from Lake Nasser reduced by 37% compared to the estimates for the first 20-year period, 1965–1984. In the period 1965–2004, seepage of Lake Nasser to the surrounding was estimated at 1.15 × 109 m3 year−1. This led to a significant rise of the groundwater table. Variance-based sensitivity and uncertainty analysis on the Edelman results were conducted applying quasi-Monte Carlo sequences (Latin Hypercube sampling). The maximum standard deviation of the total uncertainty on the groundwater table was 0.88 m at Toshka (west of the lake). The distance from the lake, followed by the storage coefficient and hydraulic conductivity, were identified as the most sensitive parameters. Copyright © 2012 John Wiley & Sons, Ltd.

Consideration of boreholes in modeling of the regional-scale groundwater flow in a fractured rock

To evaluate the necessity of considering borehole structures in modeling regional groundwater flow in a fractured rock, the groundwater flow in natural and long-term pumping conditions at the Olkiluoto island, which is the selected site for a radioactive waste repository in Finland, was simulated. The structures of boreholes installed in the site were considered in modeling using 1-D finite elements. The recharge rate and the hydraulic conductivity of the overburden were calibrated using observed hydraulic heads at the boreholes, and the results were regarded as the basic case. To examine the influences of boreholes, two cases were simulated: one where the sizes of the fractured zones were expanded to infinity and the other where the borehole structures were ignored. The results of each simulation showed that the effect of borehole structures, which could be influential conduits of groundwater in fractured rocks, were definitely demonstrated in all cases, especially in the simulation of pumping test, and it was necessary to consider the borehole structures when the groundwater flow system in a fractured rock was modeled although it is a regional-scale one.

Identifying the contribution of regional groundwater to the baseflow of a tropical river (Daly River, Australia)

Summary A mixture of older regional-scale groundwater flow and relatively modern local-scale groundwater was identified as the source of baseflow to a perennial river in a tropical savanna. Multiple environmental tracers, including 222Rn, CFCs, SF6, and 4He were measured in the river, groundwater, and springs along a 60 km segment of the Daly River in the Northern Territory of Australia. At the location where a group of springs intersected the river, groundwater discharge contained elevated 4He and very low concentrations of CFCs and SF6. This influx of regional-scale groundwater could be detected at downstream locations in the river and was used to parameterize a one-dimensional model for estimating the groundwater discharge flux. Upstream and downstream of the springs, the source of baseflow is composed of waters containing SF6 and CFCs from local-scale groundwater sources adjacent to the river. Within 1 km of the river, a redox fence was detected, with reducing conditions leading to degradation of CFCs that could have masked detecting the contribution of local-scale sources. This study confirmed the applicability of a new technique using 4He to identify regional-scale groundwater flow contributions to rivers, and demonstrated that multi-tracer studies are needed to identify the locations, rates, and sources of baseflow.

Assessing connections between aquifers in the CSG industry

Development of conventional and unconventional gas resources, including CSG, has many similarities; however, there are some key differences that may lead to potential impacts on groundwater supply. Conventional reservoirs are usually located at greater depths than commonly exploited groundwater resources and develop when gas becomes trapped by impermeable bounding layers. In the CSG industry, reservoirs are often lower in permeability than aquifers that commonly provide groundwater supply for agricultural, industrial, urban and other uses; the CSG plays may be located above and below these aquifers. The management of reservoir/aquifer interconnections necessitates a program of focused-data acquisition. For example, groundwater transfer from shallow aquifers to underlying CSG reservoirs may occur where CSG-containing units subcrop beneath shallow aquifers, possibly at significant distances from operating wells. Arrow Energy is undertaking investigations of connectivity between aquifers, including the connection between the Condamine Alluvium and the CSG-containing Walloon Subgroup. This extended abstract explores the use of analytical and numerical modelling to represent the aforementioned situation as follows: The behaviour of numerical models at the point of contact between CSG-containing units and overlying alluvial aquifers is being examined in detail—there is specific focus on how horizontal and vertical hydraulic conductivities are assigned at the interface between aquifers. This localised sub-region within a regional scale groundwater flow model has the potential to control the estimations of flows that are most interesting to stakeholders. The relationship between modelling approaches used by reservoir engineers and hydrogeologists is also explored.