摘要
垃圾填理后,由于自含水、生化反应及大气降水淋滤等来源,会产生具有污染性的垃圾渗滤液。填埋场在运行和维护监管期,渗滤液可穿透防渗系统而进入地下水含水层。渗滤液从形成、下渗至地下水环境中的运移为三维运移过程。本文利用数值模拟法对填埋场防渗系统不同运行状态下,渗滤液下渗对地下水污染的程度及范围进行模拟计算。揭示填埋渗滤液溶质迁移过程及其对地下水环境污染的特点,从而为垃圾填埋场污染控制和地下水环境保护提供科学依据。
通过对某垃圾填埋场野外调查及地质、水文地质资料收集,分析研究区含水层特征及水文地质条件,阐明四川“红层”地区浅层风化裂隙水边界与地表分水岭密切相关的规律。根据填埋场防渗系统所处的三种不同工况,计算渗滤液下渗量：在防渗系统的理想状态下,渗滤液下渗量仅154.81L/d；在常规状态(膜部分破损)下,渗滤液下渗量增加至1623.1L/d；而在防渗系统失效的状态下,渗滤液下渗量极大,约为8404.8L/d。
应用Visual MODFLOW软件中的MODFLOW及MT3DMS模块,对研究区地下水渗流场及地下水中溶质运移过程进行模拟。结果显示,至填埋场运行结束,在理想状态下,超标溶质仅是5种(COD、NH4、Cl、Cr及Hg)模拟计算溶质中的2种(COD、 NH4),而最大超标范围为115m,在距离垃圾坝100m处COD、NH4浓度分别为3mg/L0.4mg/L；在常规状态下,超标溶质类别及数量与理想状态一致,仅超标范围增至240m,在距离垃圾坝100m处COD、 NH4浓度分别为263mg/L、30mg/L；防渗层失效的条件下,5种模拟计算溶质均超标,超标范围100-300m,在距离垃圾坝100m处COD、 NH4、 Cl、Cr及Hg浓度分别为1800mg/L、220mg/L、250mg/L、0.2mg/L及0.03mg/L。由以上模拟计算结果显示,防渗系统对渗滤液的下渗起到极好的阻隔作用,能有效缓解地下水环境的污染。在设置防渗系统并保证其完整性的前提下,进入地下水系统中污水量明显减少,不仅污染影响范围明显收缩,且地下水系统中污染组分的富集量亦减少,更有利于填埋场地下水环境的保护与恢复。
Landfill leachate generated from self-aqueous biochemical reactions and precipitation leaching that has pollution characteristics after landfill. The landfill is a long-running project, the leachate can penetrate impervious system into the groundwater aquifer. The migration process that leachate infiltration into the groundwater environment is three-dimensional. In this paper, the extent and scope of the groundwater pollution is calculated by numerical simulation method under different operating conditions of impervious system. The leachate solute transport process and the groundwater environmental pollution characteristics is revealed.And thus provide scientific basis for the the landfill pollution control and groundwater environmental protection control measures.
In this paper, it is expound the law that the shallow weathered fissure water boundary is equivalent to the surface watershed in red-stratum area through surveys and data collection of geological, hydrogeological. A landfill as an example which is located in red stratum area, the amount of leachate infiltration is154.81L/d under ideal condition of impervious system, the amount is1623.08L/d under normal condition,and the amount is8404.81L/d under invalid condition.
And then,leachate pollution factor is determined based on the research data. The MODFLOW and MT3DMS module of Visual MODFLOW is applied to simulation calculate the groundwater seepage field and solute transport.The results showed that5kinds of ion (COD、NH4、Cl、Cr and Hg)there are2kinds(COD、NH4) of excessive in the ideal conditions until the end of the operation of the landfill. The maximum range exceeded115m. The concentration of COD-. NH4is3mg/L and0.4mg/L in where distance garbage dam form100m.The excessive ion in the normal conditions as same as the ideal it's. The maximum range exceeded240m. The concentration of COD、 NH4is263mg/L and30mg/L in the same position.The5kinds of ion are excessive in the invalid conditions. The maximum range exceeded100～300m. The concentration of COD,NH4,Cl,Cr and Hg is180mg/L,220mg/L、250mg/L、0.2mg/L and0.03mg/L in the same position.
By the simulation calculation results show that impermeable system has an important role to obstruct leachate infiltration that effective mitigation of environmental pollution of groundwater.Though the barrier effect is obvious in low-permeability red-stratum area.In the settings of the impervious system, leachate infiltration was significantly reduced. Therefore, the scope of influence and ion enrichment of contamination in the groundwater system is significant contraction.Under this conditions, it is conducive to the recovery of the groundwater environment after landfill closure.
引文
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