Simulation and Prediction of the Groundwater Pollution Caused by the Leakage from a Sewage Plant in an Aluminum Factory Under the Action of Ocean Tide Support

In order to predict the impact of wastewater from an aluminum plant treatment station on the groundwater environment under abnormal conditions (i.e., sewage leakage accident). Through the investigation of hydrogeological conditions, and then the permeability coefficient of the aquifer was measured through borehole injection tests. Finally, the groundwater pollution transport halo was obtained by numerical simulation based GMS software. The simulation results showed that the groundwater aquifer will be seriously polluted by COD and fluoride (F-) after the sudden sewage seepage accident. What’s more, the simulation results showed that the pollution concentration is getting higher and higher with time, which is analyzed to be caused by the small permeability of the water-bearing medium in the aquifer and the groundwater flow field was supported by seawater tide.

Hydrochemical Characteristics and Evolution Laws of Shallow Groundwater in Shuangliao City

Shuangliao City is an important part of the Xiliaohe Plain, and one of the most important bases of grain production in the north of China. Therefore, it is important to ascertain the hydrochemical characteristics of groundwater and their causes and evolution laws in the Xiliaohe Plain to provide guidance to agriculture development and ecological improvement. After collection of detailed data and identification of the groundwater flow field, we studied the causes and evolution of the identified hydrochemical types by zone with mathematical statistics, correlation analysis, ion proportional coefficient and other methods. The results show that the concentrations of HCO3-, Cl-, and Na+ are relatively high, and these of Ca2+, Mg2+, SO42-, and NO3- are relatively low. The concentration of TDS increases gradually along the flow direction of groundwater, and TDS is positively correlated to the variation in concentration of Cl-, Na+, Mg2+, and SO42-. Along the flow direction of groundwater, the hydrochemistry of shallow groundwater show the evolution law from HCO3-Ca·Mg to HCO3·Cl-Na·Ca and HCO3·Cl-Na·Mg, and then to Cl·HCO3-Na·Mg. The hydrochemical types are formed mainly due to the mineral dissolution and deposition, and reaction of cation exchange and adsorption in the aquifer, and the hydrogeochemical processes include leaching, evaporation and concentration, and mixing.

Hydrogeological Behaviour and Geochemical Features of Waters in Evaporite-Bearing Low-Permeability Successions: A Case Study in Southern Sicily, Italy

Knowledge about the hydrogeological behaviour of heterogeneous low-permeability media is an important tool when designing anthropogenic works (e.g., landfills) that could potentially have negative impacts on the environment and on people’s health. The knowledge about the biogeochemical processes in these media could prevent “false positives” when studying groundwater quality and possible contamination caused by anthropogenic activities. In this research, we firstly refined knowledge about the groundwater flow field at a representative site where the groundwater flows within an evaporite-bearing low-permeability succession. Hydraulic measurements and tritium analyses demonstrated the coexistence of relatively brief to very prolonged groundwater pathways. The groundwater is recharged by local precipitation, as demonstrated by stable isotopes investigations. However, relatively deep groundwater is clearly linked to very high tritium content rainwater precipitated during the 1950s and 1960s. The deuterium content of some groundwater samples showed unusual values, explained by the interactions between the groundwater and certain gases (H2S and CH4), the presences of which are linked to sulfate-reducing bacteria and methanogenic archaea detected within the saturated medium through biomolecular investigations in the shallow organic reach clayey deposits. In a wider, methodological context, the present study demonstrates that interdisciplinary approaches provide better knowledge about the behaviour of heterogeneous low-permeability media and the meaning of each data type.

Numerical simulation of steady state groundwater flow field in discretely fractured rocks using the Green element method with the concept of multiple interacting normal flux

<p>Numerical simulation is an effective tool for estimating the groundwater flow field in discretely fractured rocks (DFR). Unlike most numerical simulation methods that require the discretization of the model domain, boundary element method (BEM) is renowned of waiving the spatial discretization task but focusing on solving the integral form of the governing groundwater flow equation. However, for groundwater flow simulation in DFR, the solution obtained by BEM tends to have large error in the vicinity of fracture intersection. Therefore, a new numerical scheme, the green element method (GEM) is adopted in this study. GEM is built on the same mathematical background as BEM but turns the domain discretization back on as a necessary task. Using the second Green’s identity, GEM produces a general equation that applies to each grid block by integrating the governing equation. By making use of the singular characteristic of the Green’s function, GEM transforms the integral equation into a discretized system of equations with nodal head or nodal head gradient as unknowns. The cost of discretizing the model domain is compensated by the convenience of handling the heterogeneity of the medium. Conventional GEM manages the normal flux across a boundary segment by differentiating head values from 2 nodes in an individual grid block. This approximation overlooks the mechanism of normal flux as the exchange of fluid mass between grid blocks. To take this mechanism into consideration, a modified model of normal flux is proposed if the fracture plane is discretized into triangular elements. This model expresses the normal flux across a grid boundary segment in terms of the difference of head values in two grid blocks that are connected to this segment. For convenience, the head value at the centroid of a triangular element is used to calculate the normal flux. In other words, the unknowns of a triangular element are three nodal heads plus one centroidal head. Thus, the modified normal flux will be able to consider the interaction of all grid blocks that are connected to a target grid block. More importantly, the resulting global coefficient matrix is a square one and the system of equations is closed. The solution obtained from the closed system of equations will be exact but not a least-square approximated one. This modified GEM will be applied to simulate the steady state groundwater flow field in discretely fractured rocks.</p>

The role of hyporheic fluxes in regional groundwater modelling

<p>The effect of hyporheic fluxes on deep groundwater flow field was investigated in a numerical modelling framework over a spectrum of spatial scales ranging from local bed forms to landscape structures in a Swedish boreal catchment. The groundwater modelling was conducted for the whole catchment in which the site-specific landscape morphology and geological heterogeneity were accounted for. Deep groundwater discharge was quantified through conducting particle tracing analysis for 10,000 inert particles (grid of 100 × 100) released from a flat horizontal surface located 500 meter below the minimum topographical elevation. Further, the streambed scale modelling was performed independently by applying an exact spectral solution to the hyporheic fluxes in streambeds based on fluctuations of the streambed topography. Monte Carlo simulations were used in the streambed scale modelling to cover uncertainties in hydrostatic and dynamic head contributions, as well as topographic fluctuations. Through superpositioning of the two model results, we found that the magnitude of deep groundwater vertical velocity at the stream-water interface was generally lower than the hyporheic exchange velocity at the streambed interface. Finally, the deep groundwater particles’ travel time and the fragmentation of groundwater upwelling zones used as the main metrics to evaluate the impact of hyporheic fluxes on deep groundwater flow field. The results showed that the regional groundwater travel time distribution near the streambed surface was influenced by hyporheic fluxes, an impact that was  substantial for the particles with longer travel times. The size of coherent groundwater upwelling zone at the streambed interface was also affected by hyporheic fluxes. Almost half the superimposed cases were found to be more fragmented due to the presence of hyporheic flow field, which shifted the cumulative distribution function for upwelling regions towards smaller areas. This study, highlights the role of hyporheic fluxes in groundwater modelling, which controls the streambed sediment ecosystem as well as fate and transport of contaminations between aquifer and streams.</p>

Harnessing Paleohydrologic Modeling to Solve a Prehistoric Mystery

A riddle arises at the Epipaleolithic and Neolithic sites that dot the lower Jordan Valley. The area has no water resources yet it has long been a focus of inquiry into the transition from mobile hunter-gatherer to sedentary agriculture-based cultures. How then is there such clear evidence of life here, and particularly at such a critical moment in human evolution? Keen to unravel this conundrum, a numerical hydrological model was devised to simulate the groundwater flow field within the Eastern Aquifer of the Judea and Samaria Mountains during the transition from the last glacial to the current interglacial. The model exhibits a range of groundwater flow regimes that prevailed in the past, demonstrating that there was once much larger groundwater discharge at these sites.

Case Study of Heat Transfer during Artificial Ground Freezing with Groundwater Flow

For the artificial ground freezing (AGF) projects in highly permeable formations, the effect of groundwater flow cannot be neglected. Based on the heat transfer and seepage theory in porous media with the finite element method, a fully coupled numerical model was established to simulate the changes of temperature field and groundwater flow field. Firstly, based on the classic analytical solution for the frozen temperature field, the model’s ability to solve phase change problems has been validated. In order to analyze the influences of different parameters on the closure time of the freezing wall, we performed the sensitivity analysis for three parameters of this numerical model. The analysis showed that, besides the head difference, the thermal conductivity of soil grain and pipe spacing are also the key factors that control the closure time of the frozen wall. Finally, a strengthening project of a metro tunnel with AGF method in South China was chosen as a field example. With the finite element software COMSOL Multiphysics® (Stockholm, Sweden), a three-dimensional (3D) numerical model was set up to simulate the change of frozen temperature field and groundwater flow field in the project area as well as the freezing process within 50 days. The simulation results show that the freezing wall appears in an asymmetrical shape with horizontal groundwater flow normal to the axial of the tunnel. Along the groundwater flow direction, freezing wall forms slowly and on the upstream side the thickness of the frozen wall is thinner than that on the downstream side. The actual pipe spacing has an important influence on the temperature field and closure time of the frozen wall. The larger the actual pipe spacing is, the slower the closing process will be. Besides this, the calculation for the average temperature of freezing body (not yet in the form of a wall) shows that the average temperature change of the freezing body coincides with that of the main frozen pipes with the same trend.