胶态微泡沫在非饱和多孔介质中的迁移规律及影响因素

传统原位土壤淋洗修复存在淋洗效率低、淋洗液迁移难控制、污染范围易扩大的弊端。胶态微泡沫（CGAs）密度轻、粒径小、流动性好,可以有效解决传统液相淋洗修复中的问题。在修复过程中,压力作为一项重要的指标,可以有效地反映CGAs在介质中的迁移分布;因而本研究通过一维和二维动态模拟实验探讨了介质粒径、介质含水量、聚合物（黄原胶）添加等对土壤修复体系压力的影响以及CGAs在土壤中的运移规律。研究表明：随着介质粒径、介质含水量、黄原胶质量浓度的增大,体系中压力总体呈现降低趋势;CGAs从模拟槽一侧单点注入介质时,其在介质中的迁移轨迹呈现近似半圆形,在覆盖区域分布均匀,能够有效克服重力对其迁移分布的影响;随着介质粒径的增大,CGAs在介质中的波及效率先增大后减小,介质粒径为0.8~1.0 mm时波及效率最大,为34.77%;随着含水量的增加,CGAs的波及效率随之增加;黄原胶的添加有效增加了CGAs在介质中的波及效率,黄原胶质量浓度为500 mg/L时CGAs波及效率最大,为40.28%,是未添加黄原胶时的1.48倍。     

六价铬污染模拟含水层的注入型黄原胶凝胶阻截屏障试验研究

由于工业废物的不合理排放,大量的重金属污染物Cr(Ⅵ)进入地下环境,严重威胁着人类健康和生态环境。Cr(Ⅵ)在地下水环境中高度易迁移的特性,造成其污染修复上的困难,亟待一种绿色、经济、有效的阻截方式提高地下水对Cr(Ⅵ)的阻控能力。研究利用焦亚硫酸钠原位还原地下水中的Cr(Ⅵ),产生Cr³⁺作为黄原胶交联剂,形成凝胶阻截屏障,探究了各类成分对凝胶时间、黏度变化的影响及凝胶屏障对含水层的阻截效果,得到如下结论：(1)在Cr(Ⅵ)质量浓度达到200 mg/L的体系中,质量分数0.4%的黄原胶溶液在1.5 h内即可形成具有一定机械强度的凝胶;(2)凝胶具有耐盐性,适用于常见含水层,2.5～5 g/L的Na⁺和K⁺对凝胶起促进作用;(3)注入型凝胶阻截屏障能够大幅降低中砂介质的渗透系数至1×10^-7 cm/s,满足地下水阻截需求。注入型凝胶屏障的形成无需引入有害物质,阻截结束后注入型屏障可经生物作用自然降解,不会长期改变含水层水力条件。研究成果可为Cr(Ⅵ)污染地下水中凝胶阻截屏障的构筑提供理论基础。     

颗粒迁移作用下宽级配土渗透性研究

宽级配土作为堆积层滑坡的主要物源,其渗透性研究是开展降雨型堆积层滑坡机制研究的前提和基础。宽级配土的渗透是一个包括水分运移和土体细颗粒迁移的复杂过程,但在研究其渗透性时通常只考虑了水分的运移而忽略了细颗粒的迁移。为此,采用自制大型渗透仪对3组不同D15/d85值(D15为粗粒组中小于该粒径的颗粒质量分数为15%的粒径;d85为细粒组中小于该粒径的颗粒质量分数为85%的粒径)的土样进行了饱和渗流试验,研究了宽级配土的水分运移特征和细颗粒迁移规律。研究结果表明:D15/d85值对宽级配土的渗透系数和细颗粒迁移有重要影响,D15/d85值越小,则土体渗透系数越小,细颗粒不易发生迁移;D15/d85值越大,渗透系数越大,试验过程中渗透系数变化越剧烈,迁出细颗粒的量也更大。根据渗透系数的变化也可判定土体内部细颗粒的运动情况,据此提出了3种宽级配土颗粒迁移模式。该研究成果加深了对宽级配土渗透特性的认识,为完善降雨型堆积层滑坡机制研究提供了新思路。     

人工回灌条件下滨海砂质含水层渗透性的时空演变特征

人工回灌补给滨海含水层是海水入侵修复经常采用的工程措施,然而人工回灌条件下滨海砂质含水层经常出现渗透性显著降低的现象,其含水介质渗透性的时空演变规律仍不清楚。本文以青岛市大沽河下游咸水入侵区含水层砂样为研究对象,通过利用不同尺度的室内砂柱淡咸水驱替试验,对定水头和定流速条件下人工回灌咸淡水驱替过程中砂质含水层渗透性的时空演变特征进行了研究。结果表明：当淡水驱替咸水时含水介质的渗透性会发生显著变化,整个砂柱的渗透性先降低后回升,原因是回灌过程中砂柱中的黏土矿物发生释放、迁移、沉积;定水头条件下,在砂柱的前半段存在一个淘空区,渗透系数是初始渗透系数的1.6~2.0倍,砂柱其它部分渗透性是先降低再轻微回弹;定流速条件下,砂柱的渗透系数随时间的变化均呈现先降低后升高趋势,且砂柱各段离入水口的距离越远其渗透系数的值越小;砂柱黏粒含量的变化规律与渗透性的演化特征相吻合。研究成果可为人工回灌治理滨海含水层海水入侵提供一定的科学依据。     

污染场地六价铬迁移转化机制与数值模拟研究

随着全球工业化迅猛发展,土壤和地下水六价铬污染日益严重。基于某铁合金厂铬渣场地现场调查与采样分析,开展铬渣场地土样吸附、渗透和弥散试验,研究六价铬在粉质黏土土样中的吸附特性和迁移规律,建立考虑对流-弥散-吸附的六价铬迁移三维动力学模型,结合数值软件获取污染源位于场地上、下游时地下水中六价铬迁移分布特征,并揭示弥散度?和分配系数 对六价铬时空分布的影响。试验结果表明,粉质黏土对六价铬吸附符合Langmuir等温吸附模型,最大吸附量为466.6 mg/kg;蒸馏水和160 mg/L 六价铬溶液入渗下粉质黏土渗透系数约为6.5×10–7～6.7×10–7 cm/s,1 000 mg/L六价铬溶液的渗透系数增大至4.4×10–6 cm/s;粉质黏土水动力弥散系数D为1.4×10–4 m2/d,计算得到阻滞因子 为4.2～10。数值模拟结果表明,场地下游受到六价铬污染时,即使不考虑分子扩散作用,上游仍有被污染的风险,污染程度取决于含水层的弥散度;考虑含水层对六价铬吸附时,土体分配系数越大,六价铬污染羽分布范围越小,在预测地下水中六价铬浓度分布时应重点考虑六价铬吸附等转化过程。     

不同应力状态下地层渗透系数的变化及其对流体运移影响的数值模拟研究

本文选择地层渗透系数受应力影响而变化作为研究流体运移的基础。压实固结和构造作用所产生应力对渗透系数影响的有限元数学模拟研究表明,平均有效应力与介质渗透性能呈负相关的变化趋势,应力驱动流体由应力高值区向应力低值区运移。     

非均质孔隙介质中两相流的光透法应用研究

地下水中非水相液体(Non-aqueous Phase Liquid,NAPL)的流动及其曝气修复技术是典型的两相流问题。基于实际地下水含水介质的普遍非均质性,本文应用光透法对非均质孔隙介质中两相流进行了定量试验研究,设计了两组砂箱实验,研究气体和重非水相液体(DNAPL)在非均质孔隙介质中的迁移规律,应用了水/气两相和水/NAPL两相饱和度计算模型。实验结果表明:气体主要由不规则通道向上运动,遇到低渗透性透镜体时在其下方堆积,并开始横向运动,绕过透镜体后继续向上运动,最终在砂箱顶部形成连续气体分布,注气速度越大,气体运移范围越宽;DNAPL在自身重力作用下克服毛管压力向下迁移至低渗透性透镜体,DNAPL无法克服该介质的毛管压力,停止垂向入渗,并在其表面堆积,开始横向运移,绕过透镜体后继续向下运动,最终在砂箱底部形成连续DNAPL污染池。均质介质中建立的计算流体饱和度的水/气模型及水/NAPL模型与实验结果较吻合,可用于非均质多孔介质中水/气相和水/NAPL相饱和度的计算。     

含水层非均质性不同刻画方法对地下水流和溶质运移预测的影响

为探讨含水层非均质性不同刻画方法对地下水流和溶质运移预测的影响,基于非均质含水层砂箱实验,分别用传统等效均质模型、克立金插值和水力层析刻画含水层渗透系数场,并探讨了先验信息对水力层析结果的影响.将不同方法估算的渗透系数场用以预测地下水流和溶质运移过程,以此判断不同方法估算结果的优劣,分析含水层非均质性对地下水流和溶质运移的影响.结果表明:与克立金插值法相比,水力层析法可以更好地刻画含水层非均质性,较准确地预测地下水流和溶质运移过程;钻孔岩心渗透系数样本值作为先验信息可以提高水力层析法估算结果的精度;传统等效均质模型无法准确预测地下水流和溶质运移过程.含水层非均质性的增强将导致溶质污染羽分布形态和运移路径的空间变异性增强,并且优势通道直接决定溶质的分布及运移路径.      

层状非均质性影响下河流对地下水的补给过程研究

河流对地下水的补给过程研究是科学认识水循环规律及地下水资源可持续管理的基础。河床沉积层与其下伏潜水含水层岩性差异是河流下伏含水层的主要结构特征,也是控制河流对地下水补给过程的主要因素。为揭示含水介质分层结构特征影响下河流对地下水的补给过程,基于黄河干流河南段野外试验结果,建立了地表水地下水相互作用概念模型,并以地下水流路径为对象,精细刻画了地表水地下水的相互作用过程。结果表明：(1)河流对地下水的补给量主要受河床沉积层渗透性影响,河床沉积层厚度变化对河流向地下水的补给量影响不大。即：河床低渗透性沉积物的存在是河流向地下水补给量降低的主要原因,当河床沉积层与其下伏含水层厚度比(HS/H)由0增大为0.125时,河流向地下水补给量的减小幅度达72%。(2)与均质条件相比,河床沉积层渗透性及其厚度变化均明显改变了河水向地下水补给的水流路径及径流时间。随着河床沉积物与下伏含水层渗透系数比K_U/K_L的增大,河水向地下水补给的水流路径穿透深度增大,径流时间延长。(3)河流对地下水的补给量及地下水径流时间对低渗透性河床沉积层渗透系数的敏感性随渗透系数的减小...     

多孔介质中非水相流体运移的数值模拟

针对多孔介质中水、气和非水相流体(NAPLs)的多相流动特点,建立了非水相流体(NAPLs)污染物迁移模型,分析了非水相流体在土壤非饱和区和地下水系统中的运移规律。通过有限元数值解对轻非水相流体和重非水相流体在土壤系统中的迁移过程进行模拟,得到了污染物的时空分布特征和污染范围。计算结果表明,数值模拟方法能够合理地描述非水相流体的运移过程和污染特征。土体渗透性和污染物残余饱和度是其重要影响因素。     

空气扰动技术修复氯苯污染地下水的影响因素研究

通过实验室一维砂柱模拟研究了不同影响因素下空气扰动技术(air sparging,AS)修复氯苯污染地下水的效果,包括介质渗透性、曝气方式、共存污染物、残余饱和态氯苯。结果表明:介质渗透性极大地影响着AS的效果,渗透系数越大,去除效果越好。对渗透系数为10-5m/s数量级及其以下的介质应用AS较为困难;在曝气时间相同的情况下,对于渗透系数为5.1×10-4m/s的中砂,脉冲曝气较连续曝气效果好,对于渗透系数为6.2×10-3m/s的粗砂,2种曝气方式效果相仿;苯和氯苯共存时各污染物的去除存在协同作用;AS对残余饱和态氯苯的去除存在着明显的拖尾效应。     

含水介质对地下水污染曝气修复的影响

为进一步研究地下水曝气原位修复技术的影响因素,采用室内实验的方法系统地研究了含水介质对原位曝气技术修复地下水污染的影响。研究结果表明:大量水相中的柴油在曝气的开始阶段被去除,随着时间的延长,污染物去除率不断增加,但增加的幅度逐渐减小。污染物去除率与时间关系曲线符合对数曲线规律,相关方程为y=alnx+b,R2=0.802 4～0.907 1,相关性较好。含水介质的渗透系数对地下水污染修复的影响较大,渗透系数与污染物的去除率基本呈正相关关系,渗透系数越大,污染物的去除率越大;含水介质密度与污染物去除率基本呈负相关关系,含水介质密度越大,污染物的去除率越小。     

Effect of sand lenses on groundwater flow and contaminant migration

The effect of homogeneous sand lenses on the groundwater flow in an otherwise homogeneous clayey deposit is examined by performing Monte Carlo simulations using a finite element flow model. In the simulations, the locations of the sand lenses are assumed to be mutually independent. The paper examines the effect on the flow field in a clayey deposit of (a) different percentages of sand lenses, (b) different hydraulic conductivities of the sand lenses, (c) different average sand lens sizes, (d) non-uniformity of the sizes of the sand lenses, and (e) localization of the sand lenses. The effect of these non-uniform flow fields on contaminant migration is then examined using a finite element contaminant transport model. For the range of cases considered it is shown that: the volume of sand lenses present has a greater influence than the shape, size, location and hydraulic conductivity of the sand lenses; simplified calculations performed using the geometric and harmonic means of hydraulic conductivity bracket the behaviour evident from more complex analyses; and the maximum impact on an aquifer separated from a waste disposal facility by a deposit containing sand lenses can be modelled to sufficient accuracy, using quite simple flow and contaminant transport models.     

咸淡水驱替过程中含水介质渗透性变化的试验研究

在野外水文地质调查的基础上,采集青岛市大沽河下游咸水入侵区砂样,首先对含水介质的粒度和矿物组成进行了分析,然后通过室内砂槽模拟试验,对咸淡水驱替过程中含水介质的渗透性变化规律进行了研究。结果表明,当咸淡水相互驱替时,含水介质的渗透性会发生显著变化,这种变化主要是由于驱替液盐浓度的变化,使得伊利石、高岭石和绿泥石等非膨胀性粘土矿物经释放、迁移、絮凝和沉积,从而重新分布所引起的。含水介质渗透性的变化具有明显的非均质性,即位于距入水处不同水平距离以及不同高度处的含水介质,其渗透性变化规律有所不同。     

Hydrogeological behaviour of some fault zones in a carbonate aquifer of Southern Italy: an experimentally based model

Complex flow circulation patterns are likely to be present in fault‐controlled groundwater flow systems, such as carbonate aquifers. Nevertheless, not much information is available for faults in carbonates, and their hydrogeological behaviour is often neglected in conceptual and numerical models. The understanding of this aspect of subsurface fluid flow has been improved in a carbonate aquifer, where hydrogeological investigations at site scale demonstrated the existence of fault zones that act as barriers. The hydraulic conductivity of the fault core is as low as that of siliciclastic rocks that represent the regional aquitard of the carbonate aquifer. Despite the lower permeability, the fault zones allow a significant groundwater flowthrough and a good interdependence of piezometric heads upgradient and downgradient of the faults. Because of this discontinuous heterogeneity, the aquifer looks like a basins‐in‐series system, where seasonal springs can be detected along some fault zones, as a function of groundwater level fluctuations.     

Groundwater flow and capture zone analysis of the Central Passaic River Basin, New Jersey

Delineating capture zones of pumping wells is an important part of safe drinking water and well protection programs. Capture zones or contributing areas of a groundwater extraction well are the parts of the aquifer recharge areas from which the wells draw their water. Their extent and location depend on the hydrogeologic conditions such as groundwater recharge, pumping scenario and the aquifer properties such as hydraulic conductivity, porosity, heterogeneity of the medium and hydraulic gradient. Different methods of delineation can be used depending on the complexity of the hydrogeologic conditions. In this study, a 3-dimensional transient numerical MODFLOW model was developed for the Central Passaic River Basin (CPRB), and used with a MODPATH particle tracking code to determine 3-dimensional transient capture zones. Analytically calculated capture zones from previous studies at the site were compared with the new numerically simulated capture zones. The study results revealed that the analytical solution was more conservative, estimating larger capture zones than the numerical models. Of all the parameters that can impact the size, shape and location of a capture zone, the hydraulic conductivity is one of the most critical. Capture zones tend to be smaller in lower hydraulic conductivity areas.     

准饱和多孔介质中圈闭气体对渗透系数的影响

含圈闭气体的地下水流称为准饱和流,准饱和流中的圈闭气体对含水层渗透系数有重大影响。通过柱试验开展了粉砂、细砂、中砂和粗砂4种介质圈闭气体饱和度与准饱和渗透系数关系的研究。结果表明:圈闭气体饱和度明显受介质的粒径影响,在细粒介质中圈闭气体饱和度明显较大;4种介质圈闭气体饱和度在0~15%范围内,准饱和渗透系数与完全饱和相比减少了32.82%~56.38%,且准饱和渗透系数与圈闭气体饱和度之间可表达为一个负线性相关的经验公式;该公式与Faybishenko公式等效,但形式简单,参数较少,使用方便;准饱和渗透系数的变化规律可概化为圈闭气体占据了原有的有效孔隙,造成原有效孔隙度减少,从而使渗透系数减小。利用该理论,Kozeny-Carman方程能较准确地描述准饱和渗透系数的变化规律,而基于哈根-泊肃叶方程的渗透系数公式则存在较大误差,不适用于描述准饱和渗透系数;试验结果证明了室内测定饱和渗透系数时排除圈闭气体的必要性。     

Evaluation of remedial alternatives for a petroleum contaminated unconfined aquifer with fluctuating groundwater level

This study evaluated remedial alternatives for a petroleum-contaminated site where an unconfined aquifer composed of a sandy layer of about 3–3.5 m thickness is covered by alluvial deposits and reclaimed soil of about 1.5 m thickness. Precambrian gneiss, of low permeability, lies below the sandy layer. The shallow water table is about 3 m below the surface, but shows high fluctuations of up to 1.5 m in response to precipitation events. The unsaturated soil near the water table and the groundwater are highly contaminated with petroleum hydrocarbons, especially toluene, which have apparently leaked from storage tanks. Selection of the remedial alternatives required consideration of the relevant laws on soil and groundwater conservation in Korea, the results of risk analysis and the hydrogeological conditions. The contaminated area has been divided into zones in which different remediation goals are set based on risk analysis and the degree of natural attenuation. It is estimated that the clean-up goal can be achieved in two years by the combined use of a trench drain and well point pumping to collect the contaminated groundwater for treatment, and a dual air injection system for the contaminated soil.     

Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA

Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m³/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms.     

A study of the contaminated banks of the Mahoning River, Northeastern Ohio, USA: characterization of the contaminated bank sediments and river water–groundwater interactions

The Mahoning River is one of the five most contaminated rivers in the U.S. This study characterized the contaminated sediments in the river banks and investigated the hydraulic interconnection between shallow aquifer in the banks with the river water. The study was conducted along the most polluted section of the river, which is 50-km long, using over 50 monitoring wells. The characterization part of the study investigated the sedimentology, hydraulic conductivity, and spatial distribution of the contaminated sediments. Results of the characterization revealed that the contaminated sediments consist of fine-grained sand, silt, mud, and clay. The spatial distribution of the contaminated sediment is heterogeneous and positively correlates with the hydraulic conductivity values, i.e., the greatest contamination occurs in high conductivity areas. Hydraulic conductivity was determined by the Hazen formula using 82 sediment samples. Bioremediation, which is one of the remedial options considered for the banks, is found to be hydraulically feasible because of sufficient hydraulic conductivity values (≥10^?4 cm/s) that ensure reasonable rates of nutrient delivery. Monitoring of water levels in the river and groundwater for a 10-month period shows that flow occurs from the river to groundwater and vice versa. The exchange of flow is influenced by rainfall. Flow of groundwater to the river will continually transport the dissolved contaminants in groundwater to the river. Therefore, findings of this study show that one of the remedial options that proposes dredging of channel sediments and permits no action for bank sediments cannot be chosen due to river water–groundwater interactions.