LNAPL在含裂隙层状非均质地层中运移模拟研究

为研究轻非水相流体（LNAPL）泄露后在土壤中扩散情况,基于室内试验,使用TOUGH2软件进行数值模拟,分析探讨含裂隙层状非均质地层中LNAPL的运移及分布情况。并对LNAPL入渗过程及停止入渗并静置一定时间后,不同粒径砂层及裂隙中LNAPL的分布特征及残留含量进行对比研究。在LNAPL泄露入土壤后,优先进入土壤中的裂隙,形成快速通道,使LNAPL的扩散方式不局限于自上而下逐层渗入,同时也从裂隙中向两侧水平扩散,加快了LNAPL扩散入地层中的速度;停止入渗并静置一定时间后,包气带细砂中的LNAPL饱和度大于粗砂中的饱和度,而饱水带中两种砂土中的LNAPL饱和度相差较小。     

LNAPL在二维含水介质中运移规律的研究

为研究LNAPL(轻质非水相液体)污染物在均匀含水介质中的运移规律,本文建立微元模型推导出LNAPL在均匀含水介质中的对流--弥散方程。针对不同的介质模型,对二维对流--弥散方程运用差分法进行数值模拟,求其数值解。分析LNAPL污染物的运移特征,得出在均匀介质和非均匀层状介质中运移规律:LNAPL污染物在含水介质中的运移规律遵循对流--弥散方程,介质的弥散系数是影响LNAPL污染物运移的主要因素。     

贵阳市某岩溶地区地下汽油污染物运移特征分析

岩溶地区地质环境脆弱,防污能力差,特别是浅埋藏岩溶发育地区,地下水具有易污染性。本文以贵阳市某加油站10年前发生的油灌泄漏污染为例,分析了汽油污染物在岩溶水中的运移特征。调查结果表明(1)汽油污染物运移受包气带的岩性、结构、厚度以及地形坡度、地下水流速等的影响,主要沿岩溶管道、基岩面、裂隙运移;(2)汽油污染物优先在断裂、裂隙、溶缝、溶洞等通道中迁移扩散,以侧向运移为主,垂向次之;(3)有机污染物除了随地下水流动而迁移外,还会发生弥散作用,在基岩隆起部位或地形较高部位,这种现象更为明显;(4)受限于红粘土本身对污染物的拦截吸附作用,污染物向上浸染扩散程度并不高,只有最靠近基岩面的那一部分才会遭受油类污染物的浸染;(5)汽油污染物长期着在岩溶管道壁、岩溶裂隙、土岩接触面上,具有难迁移、难消除的特点。      

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。     

单裂隙中LNAPL残留特点及残留体对水流运动的影响

轻非水相液体(LNAPL)在变隙宽裂隙中的迁移和残留机理复杂,在"裂隙-水-LNAPL"三相系统中,LNAPL和水流运动之间相互作用和影响,同时两者又共同受到裂隙表面和隙宽的影响和控制。采用27.4 cm×20.0 cm(长×宽)的透明仿真裂隙开展甲苯(地下水中常见的LNAPL污染物之一)迁移试验,监测并获取变隙宽裂隙中LNAPL的迁移过程与残留分布的图像,通过数学统计和数值模拟的方法,分别揭示LNAPL 残留分布规律以及"裂隙-水-LNAPL"系统内的相互影响机制。研究结果表明:自由相的LNAPL主要沿着裂隙中的狭长通道迁移到内部,在隙宽较小的区域有少量孤立的LNAPL液滴残留。LNAPL在变隙宽裂隙中的迁移、残留与裂隙隙宽的分布密切相关,LNAPL残留的隙宽符合正态分布规律。甲苯残留的隙宽分布范围为0.01~1.40 mm,残留最多的隙宽分布在0.20~0.30 mm。LNAPL的残留增大了裂隙内水流运动的阻力,使得裂隙两端的压力差增加。LNAPL残留使裂隙内水流流速重新分布,同时也改变了裂隙原有的沟槽流分布和数量。     

山东淄博市大武水源地裂隙岩溶水中污染物运移的数值研究

在分析研究淄博市大武水源地裂隙岩溶含水层的水力性质和污染物运移特征的基础上 ,对裂隙岩溶水的水头和污染物运移进行数值研究。目前国内外对裂隙岩溶水进行数值计算时 ,通常用等价多孔介质模型 ,但裂隙岩溶介质和多孔介质有很大不同。裂隙岩溶介质的储水和导水空间为裂隙网络 ,导水系数大 ,地下水的实际平均流速比孔隙水大得多 ,但给水度和贮水系数小。当用等价多孔介质模型进行模拟时应考虑这些特点。对于污染物运移的模拟 ,要同时求解水头方程和对流弥散方程 ,可采用MODFLOW和MT3D软件进行模拟。研究区裂隙岩溶水水头的数值计算表明 ,等效多孔介质模型水头的拟合误差能满足国标GB/T144 97- 93的要求。各时段地下水水量均衡计算的精度也满足要求。对流弥散方程的数值计算 ,由于Peclet数高达 95 .6 7,对流占绝对优势 ,可能存在数值弥散和数值振荡 ,因而采用多种方法进行了比较。对于同一问题 ,同时采用上游有限差分法 (UFDM) ,混合的欧拉拉格朗日方法 (特征线法MOC、改进特征线法MMOC和混合特征线法HMOC) ,总变异消减法(TVD)进行计算 ,并比较其结果。结果表明 ,混合特征线法 (HMOC)和总变异消减法 (TVD)比较适合于对流占优势的运移问题计算。由于渗透系数K和有效孔隙度θ对溶质运移结果的影响很大 ,?     

裂隙岩体中非饱和渗流与运移的概念模型及数值模拟

探讨了裂隙岩体中非饱和地下水渗流与溶质运移的几种概念模型的构造及数值模拟问题 ,如裂隙网络模型、连续体模型、等效连续体模型、双孔隙度 (单渗透率 )模型、双渗透率模型、多组份连续体模型等。在裂隙岩体中 ,非饱和地下水的渗流可能只局限于岩体中的岩石组份、或裂隙网络 ,也可能在裂隙和岩石中同时发生 ;对前一种情形只需考虑单一连续体中的流动 ,而后一种情况则需要包括地下水在岩石和裂隙之间的交换。岩体中的裂隙网络往往是溶质运移的主要通道 ;但当溶质在裂隙与岩石之间的渗透和扩散是重要的运移机制时 ,就需要考虑岩石与裂隙界面处的溶质交换。为了模拟岩石与裂隙之间地下水和溶质的交换 ,就需要了解岩石与裂隙之间相互作用的模式和范围 ,使得这类问题的概念模型较单一连续体模型多了一层不确定性、其数值模拟也变得更为困难。因为在实际问题中不易、甚至根本不能判别非饱和渗流的实际形态 ,具体采用哪种模型主要取决于分析的目的和对现场数据的掌握程度。不论哪种模型都会受到模型及参数不确定性的影响 ,因此必须考虑与其他辅助模型的比较.     

灰坝工程领域岩体裂隙渗流浸润线及出漏点溶质浓度数值模拟

灰坝工程中灰水渗漏易对地下水产生污染,为预防治理地下水污染,应研究灰场污染物的运移机理,在运移工程中由于岩体裂隙的粗糙性和各向异性,渗流及溶质运移模型实际非常复杂。本文着眼于建立将粗糙裂隙岩体非连续渗流、溶质运移数学模型,应用于陡立裂隙网络岩体渗流浸润线及出漏点溶质浓度数值模拟,为定量分析灰场对地下水的影响提供理论依据。     

纳米零价铁地下水修复技术的最新研究进展

纳米零价铁（NZVI）是粒径在1～100nm之间的铁颗粒,它的比表面积和反应活性远远大于普通铁屑和铁粉,可以直接注入到含水层的重污染区,形成一个高效的原位反应带,灵活、高效、低成本地治理地下水污染。NZVI不仅可以降解各种卤代烃,还可以降解部分不含卤族元素的有机污染物,吸附或降解地下水中的重金属离子和多种无机阴离子。NZVI地下水修复技术在发达国家已经得到工程应用并正在迅速推广,原位场地因素对NZVI地下水修复效果的影响是今后该领域重要发展方向。NZVI在含水层中的有效分散和运移是今后NZVI用于地下水修复的主要突破点。     

Visual MODFLOW在水文地质勘查中的应用——以山东新驿煤矿下组煤先期采区水文地质勘查项目为例

Visual MODFLOW是目前国际上最为流行的三维地下水流和溶质运移模拟评价可视化专业软件系统,在我国主要应用于地下水流及溶质运移的数值模拟分析.根据勘查区地质、水文地质条件,使用Visual MODFLOW4.1三维渗流数值模拟软件,建立反映地下水分布规律、储存条件及其时空变化规律的渗流数值模型,并进行矿井突水量及安全水位疏排水量预报.     

Evaluation of a capture zone overlay method for designing groundwater remediation systems

 Simplified approaches are often used to model the removal of groundwater contamination. These approaches can yield poor remediation schemes because they incorrectly portray the effects of multiple pumping wells. In this study, a pumping configuration designed by graphically overlaying capture zones having an identical, quasi-elliptical shape was evaluated with a numerical mass transport model. After a 3-year period (within which the hypothetical aquifer was to be remediated) the contaminant mass had been reduced by 77%. Due to stagnation zones which developed between extraction wells, approximately 15 years of pumping was required to remediate the aquifer with the overlay configuration. An alternative design, consisting of an extraction well between two injection wells along the long axis of the plume, removed the contaminant within the 3-year design period. Received: 23 October 1995 · Accepted: 18 June 1996     

轻非水相液体在地下环境中的运移特征与模拟预测研究

通过自行设计制备的二维砂箱模拟轻非水相液体(LNAPL)在湿润多孔介质中的渗漏,得出LNAPL在地下环境中的入渗、迁移及分布规律,并利用多相流体理论对其污染机理进行分析.在实验基础上建立模型来预测渗漏的基本特征,即渗流带中污染锋面扩展速度和透镜体的最终形状,预测结果与实测结果较为接近.这种预测模型对控制和治理地下水中LNAPL污染是至关重要的.     

Estimation of emission from an LNAPL contaminated zone considering groundwater recharge

The aim of this work was to develop an easy to handle semi-analytical method to estimate the temporal development of emission from a multi-component LNAPL pool considering groundwater recharge. The presented approach allows the estimation of the total mass flux out of an LNAPL pool into the gas and the water phase, the latter including the mass fluxes from groundwater recharge, advection through and diffusion out of the LNAPL zone. Therefore, the known set of constitutive relationships to determine fluid saturation profiles of 2- and 3-phase systems is extended in this work to account for dynamic conditions due to groundwater recharge. The methodology is applied to a kerosene pool at a former military airfield and it is found that the mass flux due to groundwater recharge dominates the aqueous mass flux from the kerosene contaminated zone. A sensitivity study using field parameters shows, that the apparent kerosene thicknesses observed in monitoring wells and the lithology control mass flux into the gas phase, whereas the mass flux into groundwater mainly depends on the groundwater recharge rate. For the kerosene found at the site, source emission into the soil gas is estimated to last longer than the emission into groundwater, the latter varying between less than 100 and 400 years.     

Detection of free vertical convection and double-diffusion in groundwater monitoring wells with geophysical borehole measurements

Two algorithms for in-situ detection and identification of vertical free convective and double-diffusive flows in groundwater monitoring wells or boreholes are proposed. With one algorithm the causes (driving forces) and with the other one the effects (convection or double-diffusion) of vertical transport processes can be detected based on geophysical borehole measurements in the water column. Five density-driven flow processes are identified: thermal, solutal, and thermosolutal convection leading to an equalization, as well as saltfingers and diffusive layering leading to an intensification of a vertical density gradient. The occurrence of density-driven transport processes could be proven in many groundwater monitoring wells and boreholes; especially shallow sections of boreholes or groundwater monitoring wells are affected dramatically by such vertical flows. Deep sections are also impaired as the critical threshold for the onset of a density-driven flow is considerably low. In monitoring wells or boreholes, several sections with different types of density-driven vertical flows may exist at the same time. Results from experimental investigations in a medium-scale testing facility with high aspect ratio (height/radius = 19) and from numerical modeling of a water column agree well with paramters of in-situ detected convection cells.     

北京典型地区灌溉条件下包气带水分运移特征研究

以张家湾包气带水盐运移试验场灌溉试验资料为依据,运用土壤水分能量观点,分析了灌溉条件下包气带水分运移特征。试验结果表明,在一定灌溉量下包气带水分运移具有明显的分带特征以及灌溉水明显运移到达的深度;在一定灌溉量条件下,灌溉后地下水位上升微小,灌溉补给地下水量较小,并通过非饱和水流达西定律计算了向下入渗补给量。     

Research progress on the soil vapor extraction

Soil vapor extraction (SVE), the most common, efficient and economical means of remediation, is an in-situ remediation technique for removing volatile pollutants from unsaturated soil. The paper briefly introduced the technological rationale and cha?racteristics, summarized the theories and application research for SVE at home and abroad, and made the expectations and suggestions for the research on SVE. The international scholars have systematically researched the influence factors, remediation mechanism and numerical simulation of SVE. At present, SVE has been mostly integrated with other techniques to form enhanced SVE techniques, such as thermally enhanced SVE and AS-SVE (Air sparging-SVE), to be used for the field remediation widely. Compared with foreign countries, researches of Chinese scholars mainly focus on the laboratory research, especially on the influence factors, but rarely study the SVE model and the mass transfer mechanism of pollutant in SVE process. The SVE pilot studies are rare in China, and the field application has not been reported. In view of this situation, Chinese scholars in the future research can focus on the following aspects: (1) strengthening the research and systematized summary of SVE technical parameters and related knowledge; (2) strengthening the research on the mechanism and model of gas-phase mass transfer of pollutants in soil during SVE process; (3) strengthening the research on the enhanced SVE techniques and its application to actual site remediation.     

Augmentation of seasonal low stream flows by artificial recharge in the Spokane Valley-Rathdrum Prairie aquifer of Idaho and Washington, USA

Conjunctive management of surface water and groundwater requires sophisticated spatial and temporal analysis. In situations involving multiple jurisdictions such as state boundaries, management problems are magnified due to often conflicting regulations and policies. A transient MODFLOW model of the Spokane Valley-Rathdrum Prairie (SVRP) aquifer/river system mutually accepted by both the states of Idaho and Washington, USA, was used to evaluate regional solutions to potential water shortages through the use of strategically placed infiltration basins or injection wells. Artificial recharge of the SVRP aquifer was simulated using diversions from Lake Pend Oreille during winter periods when flows are high and excess water is available. Alternative locations for potential wells and detention basins were examined. Lag times for the water to impact stream/groundwater interaction areas along the Spokane River were evaluated to assess the potential for augmenting stream flows from July through September. Results indicated that the aquifer could be used to improve low-flow season streamflow values utilizing both infiltration basins and injection wells with winter surface water diversions. Depending on the location, as much as 30% of the winter diversion rate could be lagged to improve summer flows at the Spokane gage. Thus, a regional mitigation strategy is scientifically feasible.     

石油污染场地浅层地下水MNA原位修复潜能及微生物降解效益评估

监测式自然衰减（MNA）能够高效低耗地原位修复石油污染地下水的场地,微生物对污染物的降解对MNA过程起到了重要作用。在分析东北石油污染场地地下水中总石油烃（TPH）、电子受体的质量浓度分布和变化规律基础上,划分了微生物功能区。采用溶质通量计算法,对MNA原位修复的潜能及其微生物降解效果进行了评估。结果显示,场地微生物降解正在发生,利用的电子受体不同,划分为Mn、Fe和SO^2-₄还原区。污染通量模型计算显示：上游地区微生物降解强度不断增强,下游地区微生物降解强度不断降低。监测期内石油烃总量降低了394 kg,微生物降解为自然衰减过程中的主要作用,其贡献率为64%~93%,每个通量断面内微生物降解率为0.18~0.73 kg/d。由此可以证明,MNA可以有效地修复地下水中的石油污染。     

Delineation of capture zones for municipal wells in fractured dolomite, Sturgeon Bay, Wisconsin, USA

A wellhead protection study for the city of Sturgeon Bay, Wisconsin, USA, demonstrates the necessity of combining detailed hydrostratigraphic analysis with groundwater modeling to delineate zones of contribution for municipal wells in a fractured dolomite aquifer. A numerical model (MODFLOW) was combined with a particle tracking code (MODPATH) to simulate the regional groundwater system and to delineate capture zones for municipal wells. The hydrostratigraphic model included vertical and horizontal fractures and high-permeability zones. Correlating stratigraphic interpretations with field data such as geophysical logs, packer tests, and fracture mapping resulted in the construction of a numerical model with five high-permeability zones related to bedding planes or facies changes. These zones serve as major conduits for horizontal groundwater flow. Dipping fracture zones were simulated as thin high-permeability layers. The locations of exposed bedrock and surficial karst features were used to identify areas of enhanced recharge. Model results show the vulnerability of the municipal wells to pollution. Capture zones for the wells extend several kilometers north and south from the city. Travel times from recharge areas to all wells were generally less than one year. The high seasonal variability of recharge in the study area made the use of a transient model necessary. Electronic Publication