简易垃圾填埋场渗滤液地下水溶质运移数值模拟

Numerical Simulation of Mass Transport of Simple Landfill Leachate in Groundwater

简易垃圾填埋场防渗措施薄弱,渗滤液易发生渗漏污染土壤,随着时间的累积通过包气带进入含水层对地下水水质安全构成威胁。以西南山区凉山州某简易垃圾填埋场为研究对象,利用Visual MODFLOW软件建立了该简易垃圾填埋场及其周围地下水渗流场和溶质运移数值模型,通过MT3DMS模块模拟垃圾渗滤液在不同渗漏工况下地下含水层中高锰酸盐指数(COD_(Mn))和氨氮(NH^+_4-N)的运移规律,并预测垃圾填埋场封场5年和10年后地下水中COD_(Mn)和NH^+_4-N浓度的变化情况。结果表明:该简易垃圾填埋场在HDPE土工膜上漏洞率为0.5、GCL黏土出现轻微开裂现象时,填埋场区下方地下水中COD_(Mn)在5年后的超标范围为972 m^2,中心污染物浓度为4.0 mg/L,地下水中NH^+_4-N在10年后的超标范围为12 500 m^2,中心污染物浓度为1.0 mg/L;在HDPE土工膜上漏洞率为1.0、GCL黏土出现严重开裂现象时,填埋场区下方地下水中COD_(Mn)在5年后的超标范围为36 261 m^2,中心污染物浓度为20 mg/L,地下水中NH^+_4-N在10年后的超标范围为19 083 m^2,中心污染物浓度为3.5 mg/L。该研究可为渗滤液污染的有效防治以及地下水监测方案的制定提供理论依据。

The anti-leakage measures of simple landfills are usually weak,and thus the leachate is prone to leakage and pollutes soil.The contaminants in leachate could reach the groundwater table through vadose zone,posing a threat to groundwater quality. Taking a simple landfill in Liangshan Prefecture in China southwestern mountainous area as an example, this paper establishes the groundwater seepage field and mass transport model in the landfill by Visual MODFLOW, then simulates the fates of CODMn and NH4^+-N in the aquifer by MT3DMS, and finally predicts CODMn and NH4^+-N concentrations in groundwater after 10 years of landfill closure.The results show that given 50 percent damage of HDPE and slight cracking of GCL clay,the area of CODMn contamination plume in the aquifer expands to 972 m^2 after 5 years,and CODMn concentration in the centre plume is 4.0 mg/L;the area of NH4^+-N contamination plume in the aquifer expands to 12 500 m^2 after 10 years,and NH4^+-N concentration in the center plume is 1.0 mg/L.Given 100 percent damage of HDPE and serious cracking of GCL clay,the area of CODMn contamination plume in the aquifer expands to 36 261 m^2 after 5 years,and CODMn concentration in the centre plume is 20.0 mg/l;the area of NH4^+-N contamination plume in the aquifer expands to 19 083 m^2 after 10 years,and NH4^+-N concentration in the centre plume is 3.5 mg/L.Simulating the effects of leachate leakage on groundwater can provide the theoretical support for the design of landfill leakage controlling and groundwater monitoring system.