广州某地下水污染场地监控自然衰减修复模拟

Modelling of groundwater remediation using monitored natural attenuation at a contamination site in Guangzhou

监控自然衰减(MNA)作为一种成本低、不产生二次污染物、对污染场地环境影响较小的地下水污染修复方法,具有较高的应用价值和发展前景,值得实践与研究。选取广州某地下水污染场地作为研究区,评价MNA修复方法的适用性。基于水文地质条件及污染现状分析,运用地下水数值模拟程序MODFLOW建立了污染场地地下水流模型,运用污染物迁移数值模拟程序MT3DMS建立了场地污染物迁移模型,分别模拟了场地地下水流、主要污染物总石油烃(TPH)和重金属镍(Ni)的迁移过程。基于模型,对比监控自然衰减和抽出处理与监控自然衰减结合的2种方案修复效果。结果表明,TPH和Ni对于Freundlich常数及Freundlich指数变化均较为敏感;TPH的自然衰减效果较好,采用自然衰减方案,经过850 d可由初始浓度1.52 mg/L衰减到修复目标值(0.3 mg/L);Ni衰减较慢,适宜采用结合抽出处理的监控下自然衰减方案,经过300 d可由初始浓度0.13 mg/L达到修复目标值(0.02 mg/L)。在自然衰减能力较强或地下水流速较缓的条件下,适宜采用监控自然衰减修复方案;在自然衰减能力较弱或地下水有显著流动的情况下,适宜采用结合抽出处理的监控自然衰减修复方案。研究结果对地下水污染修复具有参考价值与借鉴意义。

[Objective]Monitoring natural attenuation(MNA),as a low cost remediation method for groundwater pollution that does not produce secondary pollutants and has little impact on the polluted site environment,has high application value and development prospects,and is worth practicing and studying.[Methods]This paper adopts a groundwater-contaminated site in Baiyun District of Guangzhou to assess the applicability of MNA.Based on the analysis of hydrogeological conditions and pollution status,a groundwater numerical simulation program MODFLOW was used to establish a groundwater flow model for contaminated sites.The pollutant migration numerical simulation program MT3DMS was used to establish a pollutant migration model for the site.The migration processes of groundwater flow,main pollutants total petroleum hydrocarbons(TPH),and heavy metal nickel(Ni)were simulated,respectively.Based on the model,the performances of the MNA alone and the MNA combined with pump and treat methods were compared.[Results]The results show that TPH and Ni are both sensitive to changes in the Freundlich constant and Freundlich exponent.The TPH shows good natural attenuation effect and can be substantially attenuated by the MNA alone.The concentration of TPH decreased from the initial value of 1.52 mg/L to the target(0.3 mg/L)after 850 days.Ni decay is relatively slow and it is suitable to adopt to a natural attenuation scheme under monitoring combined with the pump&treat method.The concentration of Ni decreased from the initial value of 0.13 mg/L to the target(0.02 mg/L)after 300 days.For a contaminated site with large natural attenuation capacities and/or low groundwater flow velocities,MNA alone is an appropriate remediation strategy.In contrast,for a contaminated site with low natural attenuation capacities and/or high groundwater flow velocities,the MNA combined with pump and treat may be a better remediation strategy.[Conclusion]This study provides an appropriate reference for the application of MNA to groundwater pollution remediation.