Groundwater flow pattern and age distribution under transient conditions

<p>The distribution of groundwater ages under transient conditions are investigated by a numerical model coupled groundwater flow and age, and the nested pattern of groundwater flow are determined by the probability density function of residence time. The variation of local groundwater flow system to the fluctuation of upper boundary head evolves rapidly. During the process from the initial steady to the unsteady state, the groundwater age field evolves with simulation time and gradually reaches a new dynamic equilibrium after about 50 years. The age abrupt interface between the local and intermediate flow systems gradually shifts upward, and the scale of the local flow system gradually decreases. The groundwater ages of the regional and intermediate flow systems are mainly controlled by the long-term dynamic component of the upper boundary head, while the local flow systems are mainly influenced by the transient periodic fluctuation. The location of the stagnation points are mainly controlled by the upper boundary head. The larger head difference between recharge and discharge area is, the greater penetrated depth of the stagnation point is. The location of the stagnation point indicates the penetrated depth of the local flow system. The larger head fluctuates, the deeper stagnation point is, leading to a greater penetration depth of the local flow system. Molecular dispersion causes the scatters of residence time probability density function to aggregate near the inflection point, and the aggregation area mainly locates at the junction of basin-scale flow systems. The transition of groundwater flow field will intensify the mixing of old and new water, leading to the blurring or even disappearance of the residence time abrupt interface. The dispersion of groundwater mixing is poor in steady state, and the convective-dispersive effect gradually increases with time in unsteady state. Traditional hydraulics methods based on flow nets and stagnation points can effectively identify the groundwater flow system, but the differences in groundwater chemical characteristics and ages at long-term scales cannot be clearly described by these methods, as well as the evolution of groundwater flow system at long time scale. The groundwater residence time distribution expressed by the probability density function, which comprehensively involves the spatial and temporal information of groundwater interaction, can help accurately distinguish different groundwater flow systems at long time scales. The methods proposed in this study will act as a meaningful guidance for the delineation of groundwater flow system in the real world.</p>

Establishment of groundwater baseline using end-member mixing analysis in the groundwater flow system approach

<p>The aim of this research is to establish the groundwater baseline in a sub-basin located in the southwest of Mexico City, an area affected by anthropogenic activities.</p><p>The methodology consists of groundwater sampling in 40 sites to measure major ions and physicochemical parameters as temperature, pH, Eh, and total dissolved solids. The end-member mixing analysis was applied using the groundwater flow system approach. The groundwater baseline was established using flow components that were defined.</p><p>The main results are: to found four groundwater flow components: 1) local, 2) intermediate, 3) cold regional, and 4) hot regional; to established a groundwater baselines; to relate the anomalous concentrations of nitrate and sulfate due to anthropogenic activities in the area; to associate the fertilizer use, wastewater, and the canal leaching black waters as the principal sources of these concentrations.</p><p>The conclusions show the importance to use the groundwater flow system approach to differentiate natural processes as hydrochemical evolution due to water-rock interaction of the anthropogenic influence. In the context where groundwater is extracted without knowing its baseline and the anthropological implications, the groundwater flow system approach to permit generated best management and administration strategies.</p>

Investigation of Groundwater Flow Using Δ18O and ΔD in a Sulfur Mine in Japan

The A sulfur mine is located in the Iwate Prefecture of Japan. This mine has both surface and underground parts and was operatedfrom the late 1800s to the late 1900s. Since the early 1900s, acid mine drainage (AMD) has been reported in this mine, and the wastewater has been neutralized in a treatment plant since the mine was closed. Recently, reducing the AMD volume by decreasing waterinflow to the underground mine has been considered as a way to reduce the AMD treatment cost. The first step in such an approachis to understand in detail the groundwater flow around the mine. However, part of the study area is covered by lava and comprisescrystalline rocks with complicated structures, making it difficult to understand the groundwater flow. Therefore, the present studyinvestigated the groundwater flow around this mine by focusing on water quality, such as pH and electrical conductivity (EC), stableisotopes (i.e. δ18O and δD) and 3H in the surface and ground water. The spatial distributions of pH, Stiff diagrams, and δ18O and δDvalues in the surface and ground water indicated that the groundwater flow system was divided into three basins in the study area,as predicted from geomorphological information. Moreover, the spatial distribution of δ18O and δD in the surface and ground watersuggested that the groundwater recharged at the highest altitudes in the B mountain in the northwest of the mine might flow in theunderground mine. Furthermore, the 3H values in the waste water discharged from the underground part of mine implied that thegroundwater age was no more than approximately 60 years old.