地下水环境影响评价中污染物运移模拟软件的适宜性评估

Evaluation of Contaminant Transport Modeling Software for Groundwater Environmental Impact Assessment

目前国内外已发展了一系列成熟的地下水污染物运移模拟软件,但是软件功能各异,易造成使用者的选择困扰.为满足HJ 610—2016《环境影响评价技术导则地下水环境》(简称"《导则》")中关于环境影响预测工作精细化的要求,对国内外常用饱和带和包气带污染物运移模拟软件的适宜性进行了评估.首先,针对三款常用饱和带污染物运移模拟软件BIOSCREEN、AT123D和MT3D,基于理想算例对比4组水动力条件设置下的计算结果,分析软件的适宜性;其次,针对《导则》中暂未给出的包气带污染物运移模拟软件,以FEMWATER为例探讨了包气带阻滞作用对于地下水环境影响评价的重要性.结果表明:(1)BIOSCREEN由于忽略了分子扩散作用,当Pe(Peclet数)为0. 25×10^(-3)时,其预测的污染源下游10 m处污染物浓度为AT123D和MT3D计算值的1. 8倍,存在高估污染风险的可能.(2)相比污染源直接设置于潜水面的情景,污染物从距潜水面11 m的地表泄露,经过包气带后污染源强降低了24%,下游85 m处污染物浓度达到0. 1 mg/L的时间延迟了390 d.(3)当地下水流速较慢,分子扩散作用相比对流作用占优势时,适用MT3D开展数值模拟或者采用AT123D进行解析预测;当对流作用占优势且水文地质条件接近解析解假设时,可利用BIOSCREEN粗估污染风险.研究显示,包气带污染物运移模拟软件有助于合理地预测污染物在地下水环境中的运移转化行为,从而更准确地估计污染源强和判定地下水环境污染风险.

Currently,a series of groundwater contaminant transport modeling software have been developed both at home and abroad,but the functions of different programs are different,which makes them difficult for the users to select.In order to meet the meticulous requirements for environmental impact prediction in the ‘Technical Guidelines of Environmental Impact Assessment,Groundwater Environment’(HJ 610-2016),we evaluate the applicability of commonly used contaminant transport modeling software to saturated zones and vadose zones respectively.Firstly,for commonly used saturated zone contaminant transport modeling software BIOSCREEN,AT123D and MT3D,we evaluate their applicability by comparing their outputs of 4 sets of hydrodynamic conditions based on a synthetic saturated example.Secondly,For the vadose zone contaminant transport modeling software,which is not documented in the guidelines,we use FEMWATER as an example to discuss the importance of the retardation effect of vadose zones on the environmental impact assessment of groundwater.The results show that:(1)Because BIOSCREEN ignores the molecular diffusion of solute,the predicted concentration of pollutants at 10 m downstream of the pollution source is 1.8 times higher than that predicted by AT123D and MT3D with Pe of 0.25×10^-3 ,which may lead to overestimating the risk of contamination.(2)Compared with the scenario where the pollution source is directly placed above the phreatic surface,the pollution source intensity is reduced by 24% when the pollutant passes through the 11 m thick vadose zone and then reaches the phreatic surface,and the time is delayed 390 d when the concentration of the pollutant reaches 0.1 mg L at 85 m downstream of the pollution source.(3)When the groundwater flow rate is slow and the molecular diffusion is superior to the convection effect,it is recommended to carry out numerical simulation with MT3D or to use AT123D for analytical prediction;when convection is dominant and hydrogeological conditions are close to the analytical solution hypothesis,it is recommended to use BIOSCREEN to roughly estimate the risk of pollution.The use of the vadose zone transport modeling software helps to reasonably predict the transport and transformation behavior of pollutants in the groundwater,thereby more accurately estimating the pollution source intensity and determining the risk of groundwater contamination.