Simulation Study On The Effects Of Stormwater Recharge Over Deep Groundwater Quality

In Tianjin area, the poor condition of recharge groundwater and the large quantity of artificial exploitation lead to a series of questions, such as regional groundwater depression cone continues to expand, land subsidence, sea water encroachment, and so on. In order to recharge groundwater, stormwater, which has been reached the water quality standard for recharge, is considered to recharge to groundwater through deep wells in the paper. Because the stormwater would directly reach aquifer through the recharge wells, and the processes of intercepting and absorbing pollutants by surface soil are ignored, the groundwater may be contaminated by the stormwater. In order to reduce the risk, before the implementation of artificial recharge techniques, the scheme should be evaluated and guided with cautious attitude. This paper conducts an exploratory research of groundwater quality with the tool of numerical simulation in Tianjin's downtown area.In this paper, the core technology is to build a mathematical model of the groundwater system for the study of Tianjin's downtown area. By analyzing natural geography and hydrogeological condition of the study area, hydrogeological two-dimensional steady flow model of the fourth confined aquifer is established. The groundwater flow modeling and Cl- transport simulation have been researched by the MODFLOW and MT3 DMS, which are two modules of Groundwater Modeling System(GMS). By changing the conditions, such as the amount of recharge water, solute concentration, the quantity and arranged way of recharge wells, the impact of various factors on solute transport in groundwater is simulated. Meanwhile, the regular pattern of solute migration are analyzed and summarized.By comparing the predicted results with the measured pollutants data, the model has competed the simulation scientifically and reasonably for the migration and pervasion of nitrate pollutant in the fourth confined aquifer of Tianjin urban. The simulation results show that both the amount of recharge water and the mass concentration influence the transportation of Cl- obviously, and the influence of the former tends to be greater than the latter; meanwhile, either increasing the amounts of recharge water or reducing the solute concentrations are conducive to transferring and diffusing of Cl-. In the paper, the morphology and basic features of solute migration of the recharge water in the target aquifer are revealed. In addition, the various factors, such as the amount of recharge water, solute concentration, the quantity and arranged way of recharge wells, in recharge simulate are elaborated, which have a significant impact on Cl- migration in underground aquifers. Meanwhile, it provides reasonable proposal and reference for the working of stormwater recharge groundwater in research area.