地下水循环井修复系统评估方法研究

Research on Assessment Methods for Groundwater Circulation Well Remediation Systems

地下水循环井修复技术逐渐成为地下水污染治理的新方向。通过识别影响循环井修复效果的关键指标,基于高度概化的单一含水层条件结合数值模拟技术建立了两种地下水循环井修复系统评估方法,一种是无量纲分析方法,研究单因素对循环影响半径的影响,给出单因素影响下的循环影响半径公式;另一种是粒子跟踪方法,描述粒子的运动轨迹,研究筛管长度、筛管间距、抽注水量、各向异性、水力梯度对回收率的影响。结果表明:①在无水梯度条件下,循环影响半径与抽取筛管段长度、抽注水量、垂向渗透系数均呈对数关系,与注入筛管段长度、筛管间距均呈二次函数关系;叠加水力梯度后,无量纲化循环影响半径与无量纲化水力梯度呈对数关系,且当Q/B2v(Q为抽注水量,B为含水层厚度,v为地下水流速)为0~5.3时,上游循环影响半径大于下游循环影响半径;当Q/B2v大于5.3时,下游循环影响半径大于上游循环影响半径。②在无水梯度条件下,相同时间内抽注段筛管长度相同时,筛管长度、筛管间距、各向异性均与回收率呈负相关,抽注水量与回收率呈正相关;抽注段筛管长度不同时,筛管长度的变化对回收率的影响不显著。叠加水力梯度后,水力梯度越大,上游的回收率越大,下游的回收率越小。③回收率对参数敏感性分析显示,回收率对抽取、注入筛管长度变化、筛管间距变化、抽注水量变化均较不敏感,对各向异性值的变化最为敏感,即各向异性值越高的含水层对回收率的负面影响越大。研究显示,通过采用无量纲分析方法和粒子跟踪方法识别关键指标参数的变化规律,可有效评估地下水循环井修复系统。

Groundwater circulation wells(GCWs)are emerging as an innovative approach to groundwater remediation.This paper identifies key indices of GCWs in groundwater remediation and establishes two evaluation methods for the GCW system,based on generalized aquifer conditions and numerical simulation.Dimensionless analysis and particle tracking are employed for the evaluation of the GCW system.Dimensionless analysis evaluates the influence of individual factors on the cyclic influence radius and provides a formula for this radius under the single factor conditions.Particle tracking describes the trajectory of particles and investigates the effects of screen length,screen spacing,pumping rate,anisotropy,and hydraulic gradient on the recovery rate.The results show that:(1)Under a non-natural groundwater gradient,the influence radius has a logarithmic relationship with the length of the pumping screen,pumping rate,and vertical conductivity,and a quadratic relationship with the length of the injection screen and the screen spacing.With a natural groundwater gradient,there is a logarithmic relationship between the dimensionless cyclic influence radius and the dimensionless hydraulic gradient.When Q/B2v(Q is the pumping rate,B is the aquifer thickness,and v is the groundwater flow rate)ranges from 0 to 5.3,the influence radius of upstream circulation is larger than that of downstream circulation,and when Q/B2v is greater than 5.3,the downstream influence radius is greater than the upstream influence radius.(2)In a non-natural groundwater gradient scenario,when the pumping and injecting screen lengths are the same,screen spacing and the anisotropy are negatively correlated with the recovery rate,while the pumping rate is positively correlated with the recovery rate.When the pumping and injecting lengths differ,variations in screen length have no significant effect on the recovery rate.With a natural groundwater gradient,a larger gradient leads to a higher recovery rate upstream and a lower recovery rate downstream.(3)Sensitivity analysis of the recovery rate indicates that changes in screen length,screen spacing,and pumping rate have less impact on the recovery rate,whereas the anisotropy ratio is the most sensitive factor,suggesting that aquifers with higher anisotropy ratios negatively affect the recovery rate.Dimensionless analysis and particle tracking methods can effectively identify key parameters and evaluate the performance of a GCW system.