某危险废物填埋场地下水污染预测及控制模拟

Simulation on Contamination Forecast and Control of Groundwater in a Certain Hazardous Waste Landfill

以某危险废物填埋场为研究对象,在收集其水文地质资料基础上,运用Visual Modflow建立填埋场地下水水流和溶质运移耦合模型,对填埋场防渗层发生渗漏后,渗滤液中Cr6+在地下水中的运移过程以及地面硬化、防渗墙和排水沟3种污染控制措施对污染羽阻隔效果进行模拟预测.结果表明,Cr6+随地下水流方向运移形成污染羽,10 a后污染羽到达水塘边界,运移距离约为1 450 m,但随后10～20 a之间污染羽扩散范围没有明显扩大;地表硬化后,20 a内污染羽未扩散至水塘边界;防渗墙设置到上层含水层底部时,监测井Cr6+浓度高于未设置防渗墙时浓度,设置到下层含水层底部时,Cr6+浓度与设置于上层含水层时监测结果相反;排水沟日排水量达到2 642 m3时能有效控制污染羽扩散,20 a后污染羽尚未污染监测井;地表硬化与排水沟组合控制污染物扩散,效果最佳,同时排水沟日排水量可减少为1 878 m3.因此,当填埋场发生渗漏时,建议采用设置排水沟与周边地表硬化组合的地下水污染控制措施.

On the basis of site investigation and data collection of a certain hazardous waste landfill, the groundwater flow and solute transport coupled models were established by applying Visual Modflow software, which was used to conduct a numerical simulation that forecast the transport process of Cr6＋ in groundwater and the effects of three control measures（ground-harden, leakage-proof barriers and drainage ditches） of contaminants transport after leachate leakage happened in impermeable layer of the landfill. The results show that the contamination plume of Cr6＋ transports with groundwater flow direction, the contamination rang would reach the pool＇s boundary in 10 years, and the distance of contamination transport is 1450 m. But the diffusion range of contamination plume would not be obviously expanded between 10 and 20 years. While the ground is hardened, the contamination plume would not reach the pool＇s boundary in 20 years. When the leakage-proof barrier is set in the bottom of water table aquifer, the concentration of Cr6＋ is higher than that the leakage-proof barrier is unset, but the result is just opposite when setting the leakage-proof barrier in the bottom of underlying aquifer. The range of contamination plume is effectively controlled by setting drainage ditches that water discharge is 2642 m3·d-1, which makes the monitoring wells would not be contaminated in 20 years. Moreover, combining the ground-harden with drainage ditches can get the best effect in controlling contaminants diffusion, and meanwhile, the drainage ditches＇ daily discharge is reduced to 1878 m3·d-1. Therefore, it is suggested that the control measure combining the ground-harden with drainage ditches should apply to prevent contamination diffusion in groundwater when leachate leakage have happened in impermeable layer of the landfill.