Study On The Interaction Between Surface Water And Groundwater & Pollution Control In Yitong River (Changchun)

The frequent interaction between surface water and groundwater,accompanied by the exchange of water quantity,quality and energy,is a common phenomenon in nature.Clarifying the relationship of conversion between surface water and groundwater is the key to accurately grasp the qualitative and quantitative changes of water resources.Yitong River is an important river passing through the main urban area of Changchun in Jilin Province.At present,the interaction between surface water and groundwater and its influence on water quality in the area have been not fully understood.Along with the process of urbanization,Yitong River had been polluted to different degrees,and the water quality had deteriorated to the poor Class V.In recent years,a comprehensive treatment project of the Yitong River（Changchun section）basin has been carried out,including four major types of projects,such as point source pollution treatment,surface source pollution treatment,internal source pollution treatment and water ecosystem restoration project.The surface water quality has been greatly improved.However,there are new problems such as low operation efficiency of CSOs（Combined Sewer Overflows）storage tank and unsatisfactory combined sewer overflows pollution control.Meanwhile,the treatment project of the Yitong River,which involved the treatment of surface water and bottom mud,has not considered the groundwater influence from the surface water as the interaction.Considering that the overflows pollution prevention control of Yitong River is in urgent need of optimization and improvement,the groundwater pollution from surface water,and the lack of groundwater pollution prevention control,the paper carried out the research on the interaction between surface water and groundwater&pollution prevention control of Yitong River（Changchun）,it has important theoretical and practical significance.In the paper,in the situation of the polluted river recharge groundwater,the migration and transformation rule of pollutants in the stratum were studied,including the adsorption performance of the typical pollutants NH₄⁺-N,Cd（Ⅱ）and Cr（VI）in the the vadose zone.The effects of the frequency of freeze-thaw alternations and the water content of the medium on the vertical migration of pollutants in the vadose zone were studied.The migration characteristics of pollutants in the capillary zone and aquifer were studied,carried out simulation experiments on groundwater pollution caused by surface water in the process of river recharge;The numerical simulation model of surface water and groundwater in Yitong River was established,studied the interaction between river water and groundwater;the research on the prevention control of surface water pollution was carried out.Optimized the combined drainage system of"CSOs storage tank-drainage pipes-wastewater treatment plant"after scheme comparison and effect evaluation,established the simulation model of combined pipe-surface water-groundwater pollution,in the situation of surface and groundwater pollution caused by overflows under typical rainfall events,clarified and quantified the impact of overflows pollution on surface and groundwater before and after prevention control.Finally,put forward the comprehensive prevention control proposal of surface water and groundwater.The main conclusions of this study are as follows:（1）The adsorption properties of typical pollutants in the vadose zone（1）The isothermal adsorption curves of medium sand,silty sand and clay for NH₄⁺-N conformeed to Henry curve.The isothermal adsorption curves of Cd（Ⅱ）conformed to Langmuir curve.The isothermal adsorption curve of Cr（VI）was consistent with Freundlich curve.The adsorption of medium sand and clay for NH₄⁺-N and Cr（VI）were both spontaneous endothermic process.The adsorption capacity increased with the increase of temperature.The adsorption of medium sand and clay for Cd（Ⅱ）were both spontaneous exothermic process.The adsorption capacity decreased with the increase of temperature.（2）The effect of freeze-thaw on the adsorption capacity of different media and pollutants were different.For medium sand and silty sand,the adsorption capacity of NH₄⁺-N and Cd（Ⅱ）were decreased by freeze-thaw action,which was negatively correlated with freeze-thaw frequency.However,the adsorption capacity of Cr（VI）was increased by freeze-thaw action,which was positively correlated with freeze-thaw frequency.For clay:the adsorption capacity of NH₄⁺-N,Cd（Ⅱ）and Cr（VI）were increased by freeze-thaw action,and the adsorption properties of NH₄⁺-N weas more easily affected by freeze-thaw action.After the freezing of sandy media,the volume of ice crystals in pore expanded,which compressed the medium particles and expanded the gap between medium particles.The freeze-thaw action could promote the mineralization of organic matter,released organic acids,increased the concentration of H⁺,and reduced the adsorption capacity of the cationic pollutants.After the subclay frozen,the expansion of ice crystals in the pores broken the connection between the particles,and caused the agglomeration of large particles to break into small particles,leading to an increase in the adsorption capacity of pollutants.（2）Vertical migration characteristics of the pollutants in the vadose zone（1）The freeze-thaw action increased the water migration quantity and migration speed of the vadose zone in the vertical,and it was positively correlated with the frequency of freeze-thaw.The higher water content of the medium,the higher the water migration quantity and migration speed.（2）Freeze-thaw action increased the vertical migration of NH₄⁺-N,Cd（Ⅱ）and Cr（VI）in the vadose zone,and was positively correlated with the frequency of freeze-thaw,which increased the diffusion and pollution of the pollutants in the vertical space of the vadose zone and increased the risk of pollution to the aquifer.（3）The block ability of media with different water content for different pollutants were different by freeze-thaw action.Under the condition of first freeze-thaw action,when the medium water content were 10%and 20%,the higher water content,the easier to the migration of the pollutants.（3）Migration and transformation rule of the pollutants in the stratum during the recharge process from the river to the groundwaterDuring the recharge process from the river to the groundwater,pollutants migrated into the aquifer after passing through the vadose zone and capillary zone.In the capillary zone.As a result of the capillarity"jacking"action,the pollutants mainly migrated horizontally,but the vertical migration was slow,the capillarity played a blocking effect on the aquifer pollution.Further downward migration of pollutants required a certain amount of infiltrated river to overcome the"jacking"force of the capillary zone and entered the aquifer.（4）Numerical simulation analysis of the interaction between surface water and groundwaterThe recharge and discharge relationship between the river and groundwater was defined.The groundwater drained to the river in the upstream of the Ziyou Gate,and the river supplied to the groundwater in the downstream of the Ziyou Gate.Simulated the migration distance and influence range of the pollutants in underground environment.The waterhead between surface water and groundwater was the main driving force of pollutant transfer to groundwater.The Yitong River landscape project had raised the surface water level of the downstream,which had great influence on underground water quality.（5）Combined overflows pollution prevention and controlThe ICM drainage model was used to evaluate the operation status of Yitong River drainage system and CSOs storage tanks.Under different rainfall conditions,identified problems such as overflows of combined drainage system,low operation efficiency and insufficient elastic capacity of CSOs storage tanks.Proposed the prevention control scheme:built a new combined overflows wastewater treatment plant of 350,000 m³/d in the west bank and another treatment plant of 250,000 m³/d in the east bank.Through model simulation,after completion,the total amount of overflows will be reduced by5.069 million m³,and the total reduction rate of overflows will be 48.8%,which improves the prevention control capacity of combined drainage system for overflows pollution.（6）Prevention control effect of surface water and groundwater pollution based on overflows pollution prevention controlCombined with ICM and GMS,simulated the influence of overflows pollution control on Yitong River and its groundwater quality.Under the control of overflows pollution,COD and NH₄⁺-N concentration in Yitong River and its groundwater were both lower than those without control.The influence range of groundwater pollutants had not changed significantly.The prevention control of groundwater pollution in Yitong River should focus on surface water quality and the water level between Yitong River and groundwater.The main innovations of the thesis are as follows:（1）Clarified the influence mechanism on adsorption retardation characteristics,migration and transformation of the typical pollutants NH₄⁺-N,Cd（Ⅱ）and Cr（VI）in the vadose zone by the seasonal freeze-thaw action,which laid a foundation for the accurate description of the migration and transformation of pollutants in the vadose zone during the interaction between river and groundwater.（2）Combined with laboratory simulation experiment and numerical model simulation analysis,mastered the interaction and pollution mechanism beteewn surface water and groundwater in Yitong River（Changchun）.（3）For the first time,a combined ICM and GMS software was proposed to simulate to study on the combined pipe network-surface water-groundwater of pollution prevention control.Established the response relationship of combined pipe network-surface water-groundwater pollution.