A natural-gradient field tracer test for evaluation of pollutant-transport parameters in a porous-medium aquifer

This paper describes a natural-gradient field tracer test to characterise solute-transport properties in a sand and gravel aquifer in the Hebei Province, northern China. Some laboratory-scale column tests on aquifer material and a local-scale field borehole-dilution test have been conducted previously, but the field test reported herein represents the only large-scale tracer test in the aquifer, which is the sole water supply to the city of Shi Jiazhuang and which is threatened by urban pollution. The aim of the study was to quantify the transport behaviour of nonreactive pollutants in this aquifer. Little quantitative data are available concerning its solute-transport properties; thus, the results of the tracer test are significant and critical for understanding pollutant transport and fate. The in-situ tracer test was carried out in the aquifer using a slug injection of the geochemically conservative, radioactive iodine tracer ¹³¹I. The longitudinal (α _L ) and transverse (α _T ) hydrodynamic dispersivities for solute transport in the field are 1.72 and 0.0013 m, respectively. The ratio of longitudinal dispersivity α _L and the flow length at the field scale is 1:10. The ratio between α _L and α _T from the in-situ test (~1,300:1) demonstrates a dominant longitudinal dispersion in this fluvial sand and gravel aquifer. The tracer test further indicates a relatively short transit time for the aquifer (linear velocities ~13 m/d) under natural-gradient conditions. Electronic Publication     

半无限含水层中带衬砌隧洞渗流解析研究

现有关于半无限含水层中隧洞渗流的解析解不能考虑衬砌部分排水的特性。假定土体和衬砌均为饱和均匀连续介质,采用土体与衬砌分算;利用复变函数解决孔口问题基本方法,对土体采用共形映射坐标变换,将土体中的渗流方程转换为与衬砌部分类似的二维Laplace方程圆环域的Dirichlet问题;通过Fourier解法,根据边界条件并利用流量连续条件,求得半无限空间中带衬砌隧洞渗流量和衬砌周边水头解析解答。分析了径深比、土体与衬砌渗透系数相对值、内壁水压力等因素对渗流量和衬砌周边水头的影响,并与数值算例进行了比较。结果表明,对浅埋隧洞该解析解仍具有较好的精度,是简便、实用的计算方法。     

屋面雨水回灌裂隙岩溶水工程风险评价

济南城市雨洪水回灌岩溶含水层是维护自然水循环,增加地下水补给量,维持济南泉群喷涌以及城市防洪的有效途径。但由于裂隙岩溶含水层具有渗透系数大、水流速度快,地下水一旦污染很难短时间恢复等特点,需要对回灌工程开展风险评价。本文以济南大学西校区的屋面雨水深井回灌裂隙岩溶水工程为例,利用澳大利亚MAR指南对工程进行风险评价。主要由初级风险评估、试运行调查、试运行风险评价及风险控制与管理4部分组成。初级风险评估结果显示屋面雨水回灌裂隙岩溶含水层工程的总体难度水平较低,项目可行。试运行调查期间监测的屋面雨水和回灌前后地下水水质可知屋面雨水经初期弃流、沉淀和过滤后,除浊度外基本达到地下水Ⅲ类标准,且处理后达标的雨水可迅速补充地下水。试运行风险评价结果显示屋面雨水中浊度经预处理后仍较高,使其成为该系统的最大风险项和关键控制点,故本项目的风险控制措施为改进预处理设施,降低雨水中的浊度。为保证工程能够高效持续运行,加强后期管理也尤为重要。      

沉积物和悬浮颗粒物在岩溶水系统污染物衰减与运移中的作用

本文讨论了沉积物和悬浮颗粒物/胶体在岩溶水系统污染物衰减与运移中的作用,介绍了关于瑞士某岩溶水系统内颗粒物与微生物污染间关系的实验结果。该实验场包括一个接纳农田排水的落水洞及与其相连的两个泉,其中一个泉是供水水源地。利用便携式粒子计实时监测泉水中颗粒分布的变化情况,同时对浊度、总有机碳和其它参数进行连续监测;并对水中E型大肠菌群进行了分析。在暴雨过后,观测到了浊度的两种不同表现:即泉排泄量增加时,浊度最初表现为脉状水动力条件下岩溶系统内沉积物的二次运移;几天后观测到的浊度则表明水已从落水洞到了泉口,常常具有高的总有机碳、硝酸盐及E型大肠菌群。颗粒分布分析结果差异更大:早期的浊度是不同粒径颗粒物的混合,而后期的浊度更多是由较细颗粒构成,因为大颗粒物已沉积在落水洞到泉口之间的岩溶系统内。E型大肠菌群与0.9～1.5 μm颗粒物之间具有很好的相关性。因而较细颗粒的相对增加可应用于微生物污染 “早期预报系统”。除了水污染,颗粒分还可以帮助我们研究岩溶环境的其它问题,如土壤侵蚀。      

利用观测孔中地下水位潮汐效应计算天津滨海新区含水层参数

在沿海地区,尤其是围海造陆工程形成的陆域地区地下水水位受潮汐影响较大,使传统水文地质试验求取含水层参数存在较大误差。因此通过合理概化地下水在潮汐作用下运动规律,建立数学模型,推导解析公式求取沿海含水层参数具有重要意义。分析天津滨海新区两处观测孔地下水位及潮汐波动特征,在滞后时间不明显的情况下,利用观测孔水位变幅数据计算了含水层水头扩散系数,并根据承压含水层储水系数经验值进一步获得含水层渗透系数。通过两个观测孔分别计算,对比计算结果互相验证发现,该方法取得了令人满意的结果。利用地下水潮汐效应计算含水层参数可以广泛应用于沿海地区水文地质工作中。     

Interpreting the borehole water chemistry of the Permo-Triassic sandstone aquifer of the Liverpool area,UK

Using hydrogeological data, historical chemical data and the results of studies in adjacent aquifers, an interpretation of the water chemistry from a sparse network of boreholes is presented for the Liverpool area. The chemistry of the fresh groundwater samples is influenced by geology, pollution and pumping history. The oldest waters, present where the sandstone is covered by Quaternary deposits, are calcite-saturated, contain little NO⁻₃ and have low SO²⁻₄ and Cl⁻ concentrations. However, water from the Collyhurst Sandstone are depleted in HCO⁻₃ whatever the concentrations of the other anions. Samples from boreholes in areas where the sandstones are not covered by Quaternary deposits are characterized by very low alkalinity and pH, and by high NO⁻₃, SO²⁻₄, and Cl⁻. In the regions of the aquifer close to sandstone outcrop, or where the Quaternary deposits are thin, the water samples have higher alkalinity and pH, and lower anion concentrations. Scattered throughout the region are boreholes yielding waters with very high SO²⁻₄ concentrations: where associated with industrial sites, these waters also have high NO⁻₃ concentrations and industrial pollution is suspected. In rural areas the high SO²⁻₄ concentrations are derived from leakage through the sulphur-bearing tills in response to pumping-induced lowering of the piezometric surface. The distribution of borehole water types can be described with the help of a set of rules relating water type to hydrogeological features; these rules allow a map of hydrochemical distributions to be constructed. Saline groundwaters occur in the aquifer adjacent to the Mersey Estuary and have chemistry compositions equivalent to slightly modified, diluted Estuary water. With the exception of a single deep borehole sample, there is no indication of the widespread presence of ancient saline groundwaters in the base of the sandstone sequences as is found in the sandstones to the east of the study area. However, slightly saline, reduced waters occur below the Mercia Mudstone Group in the north of the area. Historical records give some indication of the changes in water chemistry distributions through time.     

Identification of hydrogeochemical zones in postglacial buried valley aquifer (Wielkopolska Buried Valley aquifer,Poland)

This article presents the difficulty in identifying the hydrochemical zoning of a semi-confined aquifer, characterised by a relative small spatial differentiation of groundwater chemistry. It is shown that multivariate statistical methods can be used for the recognition and interpretation of the groundwater chemistry distribution in an aquifer. The hydrochemical zonation caused by both natural and anthropogenic processes was identified using factor analyses in combination with a classical interpretation of the hydrogeological material. The interpretation of the groundwater chemistry allows both identification of the aquifer recharge mechanism and verification of the groundwater-flow system.     

Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA

Geochemical reaction models were evaluated to improve radiocarbon dating of dissolved inorganic carbon (DIC) in groundwater from confined parts of the Upper Floridan aquifer in central and northeastern Florida, USA. The predominant geochemical reactions affecting the ¹⁴C activity of DIC include (1) dissolution of dolomite and anhydrite with calcite precipitation (dedolomitization), (2) sulfate reduction accompanying microbial degradation of organic carbon, (3) recrystallization of calcite (isotopic exchange), and (4) mixing of fresh water with as much as 7% saline water in some coastal areas. The calculated cumulative net mineral transfers are negligibly small in upgradient parts of the aquifer and increase significantly in downgradient parts of the aquifer, reflecting, at least in part, upward leakage from the Lower Floridan aquifer and circulation that contacted middle confining units in the Floridan aquifer system. The adjusted radiocarbon ages are independent of flow path and represent travel times of water from the recharge area to the sample point in the aquifer. Downgradient from Polk City (adjusted age 1.7 ka) and Keystone Heights (adjusted age 0.4 ka), 14 of the 22 waters have adjusted ¹⁴C ages of 20–30 ka, indicating that most of the fresh-water resource in the Upper Floridan aquifer today was recharged during the last glacial period. All of the paleowaters are enriched in ¹⁸O and ²H relative to modern infiltration, with maximum enrichment in δ¹⁸O of approximately 2.0‰. Electronic Publication     

Temporal variations in the depth-specific hydrochemistry and sewage-related microbiology of an urban sandstone aquifer,Nottingham, United Kingdom

The temporal and spatial characteristics of groundwater recharge in urban environments remain poorly understood. Depth-specific monitoring of groundwater quality in the Triassic Sandstone underlying the city of Nottingham, UK, indicates that contamination results primarily from sewage and atmospheric sources. The temporal and depth-specific characteristics of microbial and inorganic (e.g. nitrate, chloride, sulphate) contamination over the investigation period differ significantly and reflect the contrasting transport characteristics of surface-loaded solutes and particulate microbial species (bacteria and viruses) in the Triassic Sandstone. Differences result from a variety of factors, which include microbial die-off, dilution, and the contaminant-source characteristics. Observations in this study show that low levels of microbial contamination should be expected at depth in fissured sandstone due to aquifer heterogeneities such as fissuring and the occurrence of mudstone bands, though the magnitude of this contamination will vary over time. Furthermore, urban groundwater-protection measures based on solute-transport estimates may not be applicable to microbial contamination. Electronic Publication     

上海地区浅层地下水有机污染基本特征

上海地区浅层地下水中含有不同种类的有机物,大多数检出浓度相对较低,并呈散点状空间分布特征。局部地段存在有机物聚集与含量偏高,与以往的工业污染源关系密切。环境治理成效的显现将使地下水中有机物的检出与含量进一步降低。     

小尺度含水层热量运移试验研究及热弥散效应评估

将小尺度含水层热机械弥散系数模型应用于对流弥散传热过程中,推导了该条件下对流弥散热量运移的解析解,结合试验进行验证,对含水层热弥散效应进行评估,结果表明,热机械弥散系数等于1×10-2 W/(m?°C)可以作为热弥散对温度场影响的临界点,从而将热机械弥散系数的分布划分为不可忽略的三角区域和可以忽略的多边形区域;明确了自然含水层结构条件下纵向热弥散度范围,从小尺度的热弥散研究结果来看,纵向热弥散度最大值为厘米数量级,它与野外大尺度条件下热弥散度的研究成果有着显著差异,表明热弥散尺度效应的存在,这将是进一步开展研究工作的方向。     

定水头补给半无限带状含水层矿坑涌水量评价

通过对广西某石灰岩矿区水文地质条件的分析,对该水文地质单元的水文地质模型进行概化,推导出了定水头补给半无限带状含水层中完整井流公式,并运用该公式对开采条件下矿坑涌水量作了评价。最后,运用传统的逐个干扰井叠加法对该公式的评价结果进行验证,结果表明,当映射叠加次数足够多时,其计算结果极为相近。但就其计算方法而言,映射叠加方法较为繁琐,而运用该公式计算则显得较为方便。     

A computer method based on simulated annealing to identify aquifer parameters using pumping‐test data

Conventional graphical or computer methods for identifying aquifer parameters have their own inevitable limitations. This paper proposes a computer method based on a drawdown model and a heuristic approach of simulated annealing (SA) to determine the best‐fit aquifer parameters of the confined and unconfined aquifer systems. The drawdown model for the confined aquifer is the Theis solution and the unconfined aquifer is the Neuman solution. The estimated results of proposed method have better accuracy than those of the graphical methods and agree well with those of the computer methods based on the extended Kalman filter and Newton's method. Finally, the sensitivity analyses for the control parameters of SA indicate that the proposed method is very robust and stable in parameter identification procedures. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydrogeology and hydrochemistry of the Parmelia aquifer,northern Perth Basin,Western Australia

This study aims to characterise the hydrogeology and hydrochemistry of the Parmelia aquifer and to understand controls on recent water-level changes as these are needed to underpin a quantitative analysis of recharge. The Parmelia aquifer, a layered sequence of sand, silt and discontinuous lenses of clay, receives diffuse rainfall recharge on its outcrop and groundwater recharge occurs across the Dandaragan Plateau at different rates. Water levels have risen steadily over the last three decades between 10 and 55 cm/y in response to the replacement of native vegetation with pasture and annual crops. The mean aquifer properties from sediment analyses indicate a very wide range of porosity (8.9 – 49.5 %) with an arithmetic mean of 26% and consequently a very broad range of specific yield (0.0004 – 0.4) with an arithmetic mean of 0.14. Groundwater in the Parmelia aquifer has an underlying meteoric origin with compositional changes due to reactions with silicate minerals and leaching of chloride that has concentrated in the soil by evapotranspiration. The hydrochemistry sampled at different depths and locations in the aquifer indicates that the groundwater is not well mixed, and variations arise due to relatively recent recharge that has undergone evaporation in some areas.     

Great tritium ages explain the occurrence of good-quality groundwater in a phreatic aquifer of an urban area, Lublin, Poland

The phreatic aquifer of the Lublin chalk in the watershed of the Bystrzyca River, eastern Poland, is characterized by waters of good quality. Its hydraulic conductivity is related to a fissure network of low porosity, as much as 0.006 at the outcrops. The good quality of water in this urban setting is surprising because, according to estimates based on Darcy's law, a high seepage velocity would be expected, resulting in rapid transport of pollutants in the aquifer. However, tritium sampling reveals that the mean ages range from about 55 to 92 years in four cases, and about 250 to 350 years in 11 cases. One sampling site is free of tritium, which indicates an even greater age. Such great ages can be explained only by a retardation of solute transport due to matrix diffusion, that is, an exchange between mobile water in the fissures of low porosity and stagnant water in the matrix of high porosity. The delay factor is given as the ratio of total porosity to fissure porosity. In consequence, all types of dissolved constituents and, to some degree, fine suspended matter are delayed in their transport to springs and wells. In addition, non-conservative constituents have longer times to sorb, react, and decay than in the case of transport without a dominant influence of matrix diffusion. Though pollutants are greatly delayed, their accumulation in the matrix and slow diffusion into the fissures contribute to their persistence in groundwater. Regional values of hydraulic conductivity, estimated from tritium ages and known matrix porosity, agree reasonably well with the values known from pumping tests, which supports the interpretation of a dominant influence of matrix diffusion on solute transport. Electronic Publication     

Effects of water extraction in a vulnerable phreatic aquifer: Consequences for groundwater contamination by pesticides, Sint-Jansteen area, The Netherlands

Pesticides are a potential threat to the quality of extracted groundwater when the water-supply area is used for agricultural activities. This problem is discussed for the water-supply area of Sint-Jansteen, The Netherlands, where measured pesticide concentrations in the extracted water regularly exceed EU limits (0.1 μg/L). Groundwater samples taken from the aquifer within the water-supply area show low contamination, but samples taken from the extracted water occasionally contain pesticides, making the water inadequate for drinking-water purposes. The more intense contamination of the extracted water is caused by the change in the natural groundwater flow pattern near the extraction wells. In this area, pesticide use cannot be avoided easily, and an approach is given to differentiate pesticide use in the area according to expected travel time toward the wells and the chemical characteristics of the pesticides. A groundwater flow model for the area is developed and the effects of groundwater extraction on the natural flow pattern are evaluated. Using particle tracking, the travel-time zones are determined. Combining these results and the degradation behavior of certain pesticides led to an optimal scheme to integrate agricultural activities and groundwater extraction in the area. This is illustrated for five different types of pesticides (atrazine, simazine, bentazone, MCPA, and mecoprop). Received, October 1998/Revised, July 1999, September 1999/Accepted, November 1999     

岩溶区地下水微生物污染特征及来源——以重庆南山老龙洞流域为例

文章选取老龙洞地下河流域10个地下水点采集样品,分析水样中的水化学指标和三种重要微生物指标,以了解城市化进程对老龙洞地下河流域水质的影响,探究该地区微生物污染的主要来源。结合岩溶区独特的水文地质条件,利用粪大肠杆菌（FC）与粪链球菌（FS）比值法,初步分析得到该地区微生物污染程度和污染来源。研究结果表明:（1）老龙洞流域地下水存在严重的微生物污染,地下水总细菌数、大肠菌群远超过国家地下水标准规定,分别是国家地下水标准规定的2.3×102～5.5×104倍、0.8×104～0.9×106倍,粪大肠菌群数量为100～4.38×106 CFU?L-1;（2）4#、6#采样点微生物污染主要来源于温血动物,1#、7#、8#采样点地下水受城市化进程的影响大;（3）微生物污染主要来源于人类粪便,同时SO42-、PO43-、NO3-含量高且与微生物污染相关性密切,说明生活污水引起的次生微生物污染较严重,2#、3#、5#、10#采样点受生活污水和禽畜粪便影响较小,属于单纯的NO3-农业污染型地下水,微生物污染较轻。      

Characterizing vertical contaminant distribution in a thick unconfined aquifer,Hanford site,Washington, USA

Drilling-intensive aquifer characterization techniques have been used to obtain depth-discrete water samples from a thick, hydrogeologically continuous unconfined aquifer system; groundwater results indicate that carbon tetrachloride contamination is widespread and extends deeper and at concentrations much higher than detected in monitoring networks at the water table. Carbon tetrachloride, a legacy waste, was used in the plutonium extraction process at the Hanford site in south-central Washington State. Vertical, depth-discrete groundwater samples were collected during well drilling throughout a 28-km² region to determine the concentration of carbon tetrachloride present as a dissolved phase in the aquifer. Results indicate that high concentrations of carbon tetrachloride, three orders of magnitude above the allowable regulatory limit, are present at depths greater than 25 m beneath the water table. In support of future efforts to remediate the carbon tetrachloride contamination, it is imperative to locate the remaining chemical inventory, determine the vertical as well as the lateral distribution of this contaminant and its physical form. Depth-discrete aquifer characterization throughout the uppermost-unconfined aquifer system is providing this information and improving the understanding of the contaminant distribution and the hydrogeologic framework through which it moves.

鹏山水源地开采条件下的含水层固结模型

以鹏山水源地地下水系统作为研究对象,针对研究区地下水开采引发的地面沉降问题,应用土力学和地下水动力学原理,建立了该水源地开采条件下的含水层固结模型。为保证模型的准确性,从渗流空间场和地下水运动过程两个方面,对模型误差积累、误差分布和模型稳定性进行了较全面的评估,使模型具有较高的可信度。     

含水层层状非均质对地下水流系统的影响

区域尺度上含水层非均质具有复杂的结构性和随机性,难以准确刻画,造成非均质对区域地下水流系统的影响机制研究不够深入。本文以鄂尔多斯盆地白垩系地下水流系统为研究实例,选择典型剖面,采用剖面二维随机数值模拟方法,通过对比不同非均质刻画方法下地下水流场的变化,探讨含水层层状非均质对地下水流系统的影响机制。结果显示,均质条件下模型各向异性（含水层水平和垂向渗透系数比值Kh/Kv）取值为1000时,地下水流场与实际条件较为接近;非均质条件下,渗透系数方差取值0.91,水平相关长度取值5000 m,Kh/Kv取值150时,接近实际条件。研究表明,在大尺度地下水流模拟研究中,采用水平相关长度、渗透系数方差和各向异性值三个变量生成的随机场能很好地刻画含水层的层状非均质特征及其对水流系统的影响控制作用。由于含水层不同尺度层状非均质的叠加效应,采用均质各向异性介质等效概化含水层层状非均质性会造成等效各向异性值偏大失真的效应。