Numerical Simulation Study On Groundwater Environment Caused By Leakage Of Upper Reservoir Of Seawater Pumped Storage Power Station

Seawater pumped storage is a new technology that uses seawater instead of fresh water as the working medium and uses the ocean as the lower reservoir.It has the advantages of rich resources,low cost and saving fresh water resources.It has broad prospects in coastal and island areas with rich marine resources.However,as a special power generation medium,seawater will cause corrosion of power generation components,pollution of vegetation and soil by seawater splash,and groundwater pollution by seawater leakage.Among them,seawater leakage from the upper reservoir is one of the most significant problems to the environment.However,there are few studies on the migration law of seawater leakage in groundwater,and there is a lack of corresponding guidance for the site selection and construction of offshore pumping projects.Based on the national key research and development project "Research on Key Technologies of environmental impact assessment and ecological restoration of seawater pumped storage power station",this paper takes dawanshan island in Zhuhai City as the research object.On the basis of on-site hydrogeological exploration,through the groundwater seepage solute transport model,this paper compares three different lithology,fault geological structures,such as sandstone,granite and island reef,which are 90 m,120m The following conclusions can be drawn from the law of leakage seawater movement in the upper reservoir under three effective heads of150m:（1）Under the same effective water head and geological structure,when the stratum with strong permeability leaks,the solute migrates faster and the migration direction is less affected by the terrain and flow field.On the contrary,when the stratum with weak permeability leaks,the solute migrates slower and the migration direction is greatly affected by the terrain and flow field.（2）Under the same lithology and geological structure conditions,the model with higher average water head has faster leakage speed and larger leakage range.The formation with stronger permeability is more affected by water head,and the higher the water head,the higher the sensitivity of solute transport to water head change.On the whole,the change of water head has no significant effect on solute transport in the three lithologic islands;（3）Under the condition of the same lithology and effective head,the existence of fault will greatly increase the permeability coefficient of rock stratum,accelerate the transport speed of leakage solute in the groundwater environment,and solute tends to diffuse along the fault with high permeability.The fault has a significant impact on solute transport.（4）Under the same hydrogeological conditions,since the center of the reservoir basin is located at the upstream of the dam bottom,and the hydraulic gradient is large,the leakage amount and leakage area of seawater under the leakage condition of the center of the reservoir basin are larger.On the basis of the simulation of leakage seawater migration in dawanshan Island,this paper puts forward a monitoring and remediation scheme through the numerical simulation of groundwater remediation by pumping,that is,in the granite island with an average effective head of 120 m,monitoring points are set at the center of the reservoir basin and the bottom of the Quaternary aquifer at the dam bottom,which can timely monitor the leakage seawater pollution of groundwater.At the same time,setting a complete well at the leakage point can effectively reduce the seawater concentration in groundwater,Repair the groundwater environment.The research results of this paper show that the site selection of seawater pumped storage power station should focus on the problems of lithology and fault structure,which have a great impact on seawater migration.In order to prevent Island groundwater pollution,islands with low rock permeability,low reservoir effective head and no fault structure should be selected,whose seawater diffusion speed is slow and the pollution range is small.In addition,during the operation of the seawater pumped storage power station,the groundwater pollution monitoring points shall be set at the groundwater level,which can respond in time when leakage occurs,and the groundwater environment can be repaired by pumping when the groundwater level is shallow.