Environmental Impact Assessment On Groundwater Throughout The Life-cycle Of Secure Landfill

Secure landfill sites, as tombs of hazardous waste, are established in means of geotechnical engineering, with the purpose of controlling environmental pollution brought about by industrial hazardous waste, and forcing the surrounding areas to undertake environmental risks of administrative regions or industrial parks. Taking qualitative identification and quantitative simulation as research methods, it was developed in a logical order as definition of secure landfill life-cycle, process identification in life-cycle, uncertainty analysis of typical process. To provide theoretical foundation and practical case in support of groundwater environmental impact assessment of similar secure landfill, the technology of life-cycle of secure landfill impaction on groundwater was established with a case study.The research results and findings in the paper mainly are as follows:(1)The life-cycle of secure landfill includes not only the construction, operation and closure period, meanwhile, argumentation, engineering design and planning phase also shall be incorporated in the life-cycle of the project. The life-cycle of secure landfill site creatively proposed including5stages such as planning, engineer designing, engineering, project operation and post-closure management. Engineering, Project operation and post-closure management stages are classified as the occurrence periods of environmental pollution and risks, while the others belong to incubation periods, which lay a basis for establishing the framework of groundwater environmental impact assessment of secure landfill.(2) Leachate leaking, which seriously affects the groundwater quality, is the focus of the content of groundwater environmental impact assessment. Taking the process of groundwater quality affected by secure landfill leachate leakage as a starting point, theoretically analysis the uncertainty, with which groundwater environment impact assessment is faced, of the content of the groundwater flow and solute transport. The main sources of the uncertainty include boundary conditions, initial conditions, the control equations and their parameters.(3) Taking a secure landfill located in the southern bank of Hangzhou Bay as an empirical research, the uncertainties of groundwater flow field, pollution load boundary and system parameter were quantitatively analyzed with MODFLOW and MT3DMS. The difference of flow field between pre-and post construction is small, which shows that the impact of secure landfill on the groundwater flow field is limited. For type of evaporation discharge-infiltration area, the groundwater flow field scenarios plays a limited role in the secure landfill impact on groundwater quality. It is different that the decisive factors of the organic matter from the leachate of secure landfill impact on groundwater quality from the heavy metals one, the former one is controlled by the leachate load scope and concentration, and influenced by adsorption reaction items, while the latter one is affected by hydraulic dispersion parameters significantly.(4)When taking pore water as assessment object, groundwater flow field and water quality impact by secure landfill is localized in landfill areas and the surrounding region. The simulated area using in the numerical simulation could be defined to an independent hydrogeological unit including landfill zone firstly, in order to improve the spatial resolution of the simulating. And then it needs to extend the simulated area when the impact is to reach the boundary of hydrogeological unit.