Study on Solute Migration in Heterogeneous Vadose Zone Under Heavy Rainfall in Coastal Cities of China Using One-Dimensional Soil Column
- Yiru Zheng (Tongji University) | Shuguang Liu (Tongji University, Key Laboratory of Yangtze River Water Environment) | Chaomeng Dai (Tongji University) | Xueji You (Tongji University)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- migration rule, conserved solute, onedimensional soil column, heavy rainfall, heterogeneous vadose zone
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- 16 since 2007
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With the phenomenon of groundwater pollution becoming more and more serious in the coastal city of China, laboratory experiments (continuous rainfall pattern and intermittent rainfall pattern) with different rainfall intensity (3.00 mm/min, 6.92 mm/min, 11.7 mm/min) of heavy rainfall were conducted using a one-dimensional soil column to investigate the influence of heavy rainfall on the process of conserved solute's migration in heterogeneous vadose zone. The results indicated that the rainfall patterns and intensities had significant effect on solute diffusion, transport and re-release in heterogeneous vadose zone, with another finding that the intermittent rainfall pattern increased the range of solute diffusion and the concentration was relatively lower. Not only the results did provide a reliable scientific basis for further study of the influence of heavy rainfall on the migration of heavy metal contaminants in vadose zone, but also provide a reference for the selection of LID measures to control groundwater pollution in the construction of sponge city in China.
With the rapid development of urbanization in the coastal city in China, water problems have become increasingly prominent. Coastal urban storm runoff causes flood and waterlogging, even worsens the quality of surface water. However, the surface runoff carrying contaminants will seep into groundwater through the soil. And then it will exert great influence on the safety of groundwater quality. Among them, heavy metal contaminant has become the top priority of groundwater pollution control in China for the reason that heavy metal toxicity can affect industrial production, product quality, people's lives, destruction of ecology, even human health. Furthermore, heterogeneous vadose zone is the transition band between underlying contaminated soil and the saturated zone. The soil texture, structure and thickness of heterogeneous vadose zone have large effects on heavy metal transport, which will further determine the degree of groundwater contamination. But the migration of heavy metal contaminants in groundwater is very complicated, involving physical, chemical and biological processes, such as adsorption and desorption, convection, molecular diffusion, mechanical dispersion and so on. Many domestic and foreign experts have done a lot of researches on the migration of heavy metal contaminants in groundwater. But at present, it is mainly focused on the study of the transfer and transformation of contaminants in the saturated zone, lacking of the researches on the migration in unsaturated zone, especially in the consideration of complex boundary conditions, such as the numerical simulation and experimental study of contaminant migration in vadose zone under heavy rainfall. Grifoll and Cohen (1996) established the one-dimensional transport equation of contaminants in vadose zone by using the deterministic dynamic modelling, considering the two-phase flow of water and gas in vadose zone, to study the migration rule of contaminants in vadose zone under rainfall and evaporation conditions. The results showed that the concentration of contaminants in vadose zone during the initial pollution period was significantly affected by rainfall. It was discovered (Foussereau and Graham, 2001) that uncertain rainfall patterns dominate transport prediction uncertainty in the shallow unsaturated zone, while uncertain solute breakthrough to the saturated zone and uncertain hydraulic conductivity dominate prediction uncertainty in the saturated zone, by Monte Carlo simulation. It was also noted (Marshall, 2000; Zuo, 2011) that variability of rainfall intensity had great influence on pollutant transport by establishing migration model of contaminant in unsaturated zone. Except for the study on numerical simulation, some researchers have carried out experimental study on the contaminant migration in vadose zone under rainfall. The transfer and transformation of nitrogen in heterogeneous vadose zone structure under rainfall were discovered (Liu, 2011) by sand box simulation test. Wang (2012) studied the migration of Cr(VI) in vadose zone and the influence of water infiltration on contaminant transport by using a onedimensional soil column experiment. Besides, the infiltration mechanism of unsaturated zone under rainfall condition was also researched (Qin, 2017).
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