Injection of silicate grouting materials is widely used to create temporary horizontal layers for reducing inflow of groundwater at construction sites, in regions with shallow water tables. The erosion of a grouting layer was investigated by means of analytical solutions for groundwater flow and transport within a pit after construction finished. Erosion is assumed to occur by dissolution of the temporary injection layer and subsequent advective transport. Thereby, the hydraulic conductivity changes with time. This paper presents novel analytical solutions and approximate solutions for the major fluxes in the construction pit as a function of the domain settings, aquifer gradient and hydraulic conductivity. In addition, the mass flux and the dilution ratio of erosion-related components leaving the construction pit and entering the aquifer are quantified. Derived solutions are verified against numerical simulations. A sensitivity study shows the impact of domain settings on fluxes and dilution ratio. The results confirm that mass flux of grout components increases with ongoing erosion. Thus, its effect on groundwater quality increases with time after construction ceased.

The dynamics related to evolution of nitrate-contaminated groundwater are analyzed with focus on the impact of intrinsic aquifer properties, agricultural activities and restoration measures at Campina de Faro aquifer (M12), southern Portugal. Agricultural practices in the region developed in the 1970s and resulted in high abstraction rates, nitrate contamination and salinization. Despite the implementation of the European Union (EU) Nitrates Directive since 1997, nitrate levels still show increasing trends at some locations, constituting a threat to the chemical status of M12 and consequent nitrate discharge to Ria Formosa coastal lagoon. Simultaneously, groundwater levels are not dropping consistently, despite apparent overexploitation. A groundwater flow and mass transport model is developed for M12 to assess the evolution of nitrate under different scenarios. Model results reveal that M12 has a hydraulic connection with northernmost aquifers, a process not properly assessed so far. Results further show that nitrate contamination in the upper Plio-Quaternary layer of M12 is extremely persistent and mostly linked to unbalanced fertilizer application practices and irrigation return flows. The response of M12 to implementation of good agricultural practices in compliance with EU policies is slow, indicating that good qualitative status would be impossible to reach by the required EU deadlines. Integration of climate change scenarios into the transport model reveals that despite the implementation of restoration measures, there could be a retardation of the nitrate levels’ decrease in the upper aquifer as a result of enhanced evapoconcentration caused by lower recharge, higher water demands and incomplete mixing within the aquifer.

The aquifer beneath Chengdu Plain is a main water resource for drinking and industry, which has severe groundwater nitrate contamination due to the shallow water table and intensive agricultural activities. The aim of this study is to estimate nitrogen loading to the aquifer and to predict nitrate concentration in groundwater in response to changes in land-use and agricultural practices, i.e. nitrogen fertilizer application, in ‘Jingyang region’ of the Chengdu Plain, one of the most developed agriculture areas in southwestern China. The framework utilized a geographic information system to account for the spatial and temporal distribution of on-ground nitrogen sources and corresponding loadings, and employed an export coefficient model to estimate the corresponding nitrogen loss. The simulation of nitrate fate and transport in the aquifer was conducted by developing a groundwater mass transport model using MODFLOW and MT3DMS. A number of predictive simulations for year 2026 were carried out to evaluate the impact of land-use and proposed future management options on controlling groundwater nitrate contamination. The results show that a nitrate plume would extend over most of the study area with some local areas having concentrations exceeding 20 mg L⁻¹ under the current setting and the scenario of increasing agricultural land use. Reduction in fertilizer application rates did mitigate nitrate contamination; however, this effect diminished with the expansion of agricultural land use. Land-use planning should consider the significant effects of agriculture to improve the quality of groundwater in the Chengdu Plain.

The Caohai Wetland serves as an important ecosystem on the Yunnan–Guizhou Plateau and as a nationally important nature reserve for migratory birds in China. In this study, surface water, groundwater and wetland water were collected for the measurement of environmental isotopes to reveal the seasonal variability of oxygen and hydrogen isotopes (δ¹⁸O, δD), sources of water, and groundwater inflow fluxes. Results showed that surface water and groundwater are of meteoric origin. The isotopes in samples of wetland water were well mixed vertically in seasons of both high-flow (September) and low-flow (April); however, marked seasonal and spatial variations were observed. During the high-flow season, the isotopic composition in surface wetland water varied from −97.13 to −41.73‰ for δD and from −13.17 to −4.70‰ for δ¹⁸O. The composition of stable isotopes in the eastern region of this wetland was lower than in the western region. These may have been influenced by uneven evaporation caused by the distribution of aquatic vegetation. During the low-flow season, δD and δ¹⁸O in the more open water with dead aquatic vegetation ranged from −37.11 to −11.77‰, and from −4.25 to −0.08‰, respectively. This may result from high evaporation rates in this season with the lowest atmospheric humidity. Groundwater fluxes were calculated by mass transfer and isotope mass balance approaches, suggesting that the water sources of the Caohai Wetland were mainly from groundwater in the high-flow season, while the groundwater has a smaller contribution to wetland water during the low-flow season.

Nitrate contamination of groundwater is an important public health issue worldwide. For environmental and public health reasons, water should not contain more than 50 mg/L NO₃. An aquifer for which this limit is exceeded can be designated as a nitrate vulnerable zone (NVZ) and subject to action programs to minimize the NO₃ input. The study aims to assess future trends of groundwater quality and to predict the time required for groundwater to achieve the environmental goals in the Esposende–Vila do Conde NVZ (Portugal). Flow and transient nitrate transport modelling were performed using the FEFLOW software. The numerical model represents the saturated zone of phreatic aquifers, designed in a three-dimensional three-layer model. The calibration process was completed through the tool FEPEST. Sensitivity analysis was performed to investigate the model response to changes in hydraulic parameters and aquifer recharge. Two major simulations of mass transport were performed considering different options on nitrogen loads: (1) agricultural nitrogenous loads of diffuse origin; (2) nitrogen loads from agricultural and livestock sectors together. The results show that the minimization measures imposed in the NVZ are effective, shown by the groundwater nitrate concentration decreasing over time; however, concentrations above 50 mg/L will persist for the next two decades in both simulated scenarios. Combining the conceptual hydrogeological model, geovisualization techniques, and numerical flow and mass transport modelling has been shown as a comprehensive approach to understanding the measures needed for sustainable water resources management and particularly to predicting hydraulic heads and NO₃ dispersion in aquifers.