Understanding the pattern of regional groundwater circulation is essential for sustainable management of groundwater resources and ecosystems protection. A large-scale basin may develop nested groundwater flow systems including local, intermediate and regional flow systems. Hydrogeochemical tracing may be an effective methodology to identify different groundwater flow systems, considering its routine application in field investigation. This study uses wavy-topography-driven regional groundwater flow in the groundwater-fed lakes area of the northern Ordos Plateau, China, as an example to test the effectiveness of a hydrogeochemical method for groundwater-flow-system characterization. Samples of groundwater from wells with different depths and lake water were collected and analyzed. Hierarchical cluster analysis was conducted using the pH, electrical conductivity, and major ions as the input, which leads to three clusters with distinct geochemical compositions. Considering the hydrochemical characteristics, wells depths, and sampling locations, different groundwater flow systems were identified. Geochemical evolution was affected by processes such as leaching, cation exchange, evaporation and human activities. The relationship between δD and δ¹⁸O indicates that the shallow and deep groundwater were recharged by atmospheric precipitation during the modern time and a past colder period, respectively. The groundwater geochemistry is closely related to groundwater circulation depth within different flow systems, indicated by comparison of geochemical processes among the three clusters. This work highlights a hydrochemical method that can identify nested groundwater flow systems in the lakes discharge area of this large-scale basin and provides a better understanding of the hydrogeochemical evolution from the processes involved in relation to groundwater flow systems.

Co-management through local collective action appeals as a way of effectively responding to critical groundwater management issues, including groundwater quality degradation and pumping that lowers water tables. Co-management may also build sufficient trust for stakeholders to agree to investigate, and potentially implement, new opportunities for the use and management of groundwater resources. This paper examines the potential of collective action to underpin co-management and lead to improved groundwater management. The case study is the Angas Bremer (AB) irrigation district in South Australia, which provides a rare example of community-lead groundwater management since the late 1970s. The key questions were: (1) Was the AB an example of collective action, and did that spark successful co-management? and, (2) What were the key outcomes of collective action throughout the years? Data were gathered through semi-structured interviews with key stakeholders. By working together, and with government departments, AB irrigators successfully recovered an aquifer that was at risk of depletion and salinization. Drawing on this evidence, it is suggested that co-management through local collective action may be a useful option for those setting out to improve the social acceptability of new groundwater initiatives in farming landscapes, including managed aquifer recharge (MAR) and conjunctive use of surface water and groundwater.

This study evaluates the applicability of the chloride mass balance (CMB) method for groundwater recharge estimation in a semi-arid region in Canada, where recharge largely occurs under topographic depressions. The CMB applicability was tested at three scales: point-scale recharge rates at different topographical positions; average recharge rates incorporating multiple topographical positions on a local scale; and an identification of spatial trends of recharge on a regional scale. Agricultural chloride inputs were shown to be a major factor affecting chloride concentrations at all three scales, where elevated chloride concentrations in the shallow subsurface affected by agricultural inputs surpassed background concentrations by an order of magnitude. The propagation depth of elevated concentrations varied among study sites from being largely confined to the unsaturated zone to extending well into the saturated zone. Lateral chloride redistribution further affected the CMB applicability for point-scale recharge rates. Specific solutions enabling the CMB application in these conditions are presented, including runoff concentration measurements for point-scale estimates, using groundwater age tracers on a local scale, and using the harmonic mean concentration of a large number of samples on a regional scale.

The edge of regional aquifers can be complex hydrodynamic systems with unique flow dynamics, water quality, and continuity relationships with the main aquifer system. A site near the southwestern margin of the High Plains Aquifer (USA) was investigated to characterize the local hydrogeology and its relationship with the regional aquifer system. Measurements of tritium, ion concentrations, oxygen and hydrogen isotopes, and hydraulic heads documented (1) a discontinuous saturated zone, (2) no inflow to the study area from the regional aquifer, (3) focused recharge beneath playas with limited local mixing between pockets of saturation, (4) outflow orthogonal to the regional aquifer flow direction, (5) localized multi-year reversals in flow direction following high precipitation events, and (6) a magnified influence of the paleo-erosional surface of the basement rock (Dockum Group) on groundwater isolation and flow direction. In isolated areas, groundwater can be trapped on decadal time scales by depressions in the Dockum, or by recharge events that periodically reverse groundwater gradients.

Sustainable yield is defined as the amount of groundwater abstraction that can be maintained for an indefinite time without causing unacceptable environmental, economic and social consequences. It is usually determined by monitoring the water-table depth, without the need for costly pumping exercises and subsequent deterioration of the groundwater and ecological environment. Groundwater numerical modelling provides an effective way to determine the yield by analysing the responding water levels to various pumping scenarios. In this study, the natural flow system and flow with pumping scenarios were simulated using FEFLOW for the fractured-rock aquifer in Table Mountain Group, South Africa. Results for different pumping rates show the distinct impact of groundwater abstraction on hydraulic head, which indicates that long-term abstraction slowly increases the well drawdown, but it would stabilize at a level that is dependent on pumping rate and induced recharge. To estimate the aquifer sustainable yield, a relationship between simulated drawdown and pumping rate was established, namely an exponential function with parameters that may change value between sites. This empirical relation, derived from this site-specific study, provides an option for informed decision-making. The issue of how to sustainably abstract groundwater might rely on a compromise between the groundwater user and the governmental authority.

Groundwater movement through the slope area of Mt. Fuji to the coastal area of Suruga Bay (central Japan) was investigated using spatially dense geochemical data, as a case study for elucidating the groundwater flow system in a stratovolcano adjacent to the coast. Spatial distributions of the hydrogen stable isotope ratio, vanadium concentration, and water temperature in the groundwater showed anomalies at the coastal area of Suruga Bay. The anomalies were characterized as depleted isotope ratio, high vanadium concentration, and low water temperature relative to surroundings. This can be explained as a regional deep groundwater flow from the slope of Mr. Fuji to the coastal area of Suruga Bay because groundwater recharged at higher elevation has a depleted isotope ratio caused by the altitude effect and high vanadium concentration as a result of dissolution from the basaltic aquifer. These characteristics also imply a hierarchical flow system, which is incorporated into a hydrogeological model of the coastal aquifer.

Hydrogeochemistry and environmental isotopes were used to gain insight into the recharge processes, water–rock interactions, and groundwater residence time, and to identify groundwater flow systems (GFSs) in an interfluve between the Han River and Yangtze River in the eastern Jianghan Plain (China), an alluvial-lacustrine plain in the middle reaches of the Yangtze River. Because of carbonate mineral weathering, groundwater in the plain is predominantly HCO₃-Ca or HCO₃-Ca-Mg type. The decrease in typical ions and isotopic depletion with increasing depth indicates that the GFSs were divided into local and regional GFSs with an approximate depth limitation of 20 m. The consistent variations are attributable to complex anthropogenic activities, water–rock interactions and groundwater flow patterns. The multiple independent local GFSs exhibited a pattern in which groundwater was discharged into surface waters during the non-flood season. Groundwater age of local GFSs is modern according to the ³H concentrations, so the hydrodynamic circulation is active. Furthermore, the regional GFS pattern is controlled by slow lateral flow from west or northwest to east, eventually discharging into the Yangtze and Han rivers. The distribution of δ¹⁸O indicated three zones in regional GFSs that are likely dominated by the altitude effect of recharge areas. The groundwater age of regional GFSs varied from hundreds of years to 5000 years, estimated by ¹⁴C isotope data, revealing that the hydrodynamic circulation of regional GFSs is slow to relatively stagnant. The hydrodynamic characteristics and hydrochemical distributions corroborated the mixing zones of differently hierarchical GFSs in the discharge area of the Jianghan Plain.

A case study is presented that implements two numerical models for simulating a 30-year pump-and-treat (PAT) operation conducted at a large contaminated site for which high-resolution data sets are available. A Markov chain based stochastic method is used to conditionally generate the realizations with random distribution of heterogeneity for the Tucson International Airport Area (TIAA) federal Superfund site in the USA. The fields were conditioned to data collected for 245 boreholes drilled at the site. Both MT3DMS and the advanced random-walk particle method (RWhet) were used to simulate the PAT-based mass removal process. The results show that both MT3DMS and RWhet represent the measured data reasonably, with root mean square error (RMSE) less than 0.03. The use of fine grids and the total-variation-diminishing method (TVD) limited the effects of numerical dispersion for MT3DMS. However, the effects of numerical dispersion were observed when compared to the simulations produced with RWhet using a larger number of particles, which provided more accurate results with RMSE diminishing from 0.027 to 0.024 to 0.020 for simulations with 1, 20, and 50 particles, respectively. The computational time increased with more particles used in the model, but was still much less than the time required for MT3DMS, which is an advantage of RWhet. By showing the results using both methods, this study provides guidance for simulating long-term PAT systems. This work will improve understanding of contaminant transport and plume persistence, and in turn will enhance site characterization and site management for contaminated sites with large plumes.

A new semi-analytical solution to study groundwater flow fields associated with pumping or injection wells in confined isotropic aquifers with uniform regional flow is proposed and tested against steady-state and transient-state numerical simulations on MODFLOW-MODPATH. The solution is based on the complex potential theory and can be used for large numbers of arbitrarily positioned wells operated with different rates. The solution can be used to follow the movement of water particles in space (within pores or within the equivalent continuous media) and in time with two tracking modes: forward (from origin to target) and backward (from target to origin). The proposed solution is a useful tool that can be used for establishing groundwater resources management practices like designing groundwater remediation solutions, delineating capture zones, defining safeguard perimeters and mapping groundwater vulnerability. Moreover, the paper gives a comparative numerical study of flow fields near pumping wells, showing that, in terms of their shape and position, delineating capture zones using either steady-state or transient-state simulations would lead to practically similar results for long pumping periods. It is also shown that in such cases, the main differences between steady-state and transient-state simulation are present in the computed water particles’ transport time.

The Gravity Recovery and Climate Experiment (GRACE) twin satellites introduced a new opportunity to monitor changes in groundwater level. However, the performance of the GRACE-derived Liquid Water Equivalent Thickness (GRACE-LWET) in estimating groundwater-level changes at a local scale requires evaluation. Thus, the main aim of this study is to evaluate the performance of the GRACE-derived estimation in monitoring groundwater-level changes in Iran, which is experiencing decreasing trends and subsequent impacts. Another aim is to investigate the time lag between the water levels derived from the GRACE estimation and direct measurements. Four regions in Iran were studied between the years 2002 and 2016. To evaluate the results of GRACE-LWET, groundwater levels in 144 piezometric wells were measured monthly. The changes of the earth’s mass due to surface-water changes were assessed using four datasets of the Global Land Data Assimilation System. Furthermore, the statistical trend of the groundwater-level changes acquired from the GRACE estimations and observational data was investigated using the Mann-Kendall test and Sen’s slope estimator at a significance level of 0.05. The results showed that the best performance of the GRACE estimations was acquired when considering a 2-month time lag. In this case, the average correlation coefficient of the GRACE estimations against the observational data for the entire study region was 0.57. Moreover, the GRACE-LWET showed a significant decreasing trend for the whole study area using both considered tests. Hence, GRACE-derived estimation of groundwater-level changes can be used in regions with insufficient observational well data with an acceptable accuracy.