Das digitale geologische Strukturmodell Bitterfeld als neuer Baustein in der Sanierungsforschung

Identification, assessment and remediation of a large-scale groundwater contamination requires a profound knowledge of the geological structure to predict the fate of contaminants in the subsurface. Within the SAFIRA-project, a model sector of the Bitterfeld/Wolfen area was chosen to transfer the structural geological data of the Tertiary and Quarternary aquifer units into a digital geological model. Using 125 selected drillholes as a base of 28 networked cross-sections, small-scale lithological and structural heterogeneities, in particular of the Quarternary layers, could be assigned to 31 litho-stratigraphic sedimentation units and depicted using a 10 × 10 m GIS grid. An assignment of hydraulic parameters to individual sedimentary bodies allows a combination with flow and transport models. The structural model was generated by combining gridding sections and additional point and lateral information of sediment distribution and allows -beyond visualisation purposes- volumetric calculations of distinct sedimentary units, which are relevant for an assessment of retardation processes in the remaining lignite seam. The present structural model is the base for a “Spatial Model Bitterfeld” and anables further investigations on the environmental impact of different scenarios.     

Hydrological analysis as a technical tool to support strategic and economic development: A case study of Lake Navaisha,Kenya

Effective integrated water resources management requires reliable estimation of an overall basin water budget and of hydrologic fluctuations between groundwater and surface‐water resources. Seasonal variability of groundwater‐surface water exchange fluxes impacts on the water balance. The long term lake water balance was calculated by Modflow using the stage‐volume rating curve of Lake Package LAK3. The long term average storage volume change is 8.4 × 10⁸ m³/month. The lake water balances suggests that the lake is not in equilibrium with the inflow and outflow terms. Using field abstraction data analysis and model simulation, the combined volume of lake‐groundwater used for industrial abstraction since the last three decades was estimated. This requires an average abstraction amount of 7.0 × 10⁶ m³/month with a long term trend of abstraction ratio 30% (groundwater) and 70% (lake water) since 1980. The amount resulted in a lake which might have been 4.8 m higher than was observed in the last stress period (2010). A long term regional groundwater budget is calculated reflecting all water flow in to and out of the regional aquifer. The model water balance suggests that lake Navaisha basin is in equilibrium with a net outflow about 1% greater than the inflow over the calibrated period of time (1932–2010). The regional model is best used for broad‐scale predictions and can be used to provide a general sense of groundwater to surface water and groundwater to groundwater impacts in the basin. A basin wide water resource management strategy can be designed by integrating the lake/wetland within the regional groundwater model to increase the level of sustainable production and good stewardship in Lake Navaisha. Such hydrological analysis is crucial in making the model serve as simulator of the response of lake stage to hydraulic stresses applied to the aquifer and variation in climatic condition.     

三工河流域地下水资源与可持续利用

三工河流域地处新疆天山北坡经济带,流域发源于天山博格达峰,是独立的小流域。而流域的自然景观和地貌单元的完整性,具有大流域的分布规律。目前流域供水水源以河道来水和开采地下水为主,由于长期的超采地下水,已经造成该流域地下水位持续下降。本文在系统地阐述流域地质条件以及含水层组特征的基础上,利用流域多年基础资料,采用水均衡方法,对现状进行水资源平衡分析、地下水平衡分析、耗水量平衡分析,构建出合理地下水数值模型,并进行了地下水水位、水量远景预报,确定出合理的地下水资源量以及合理的地下水可开采量。根据流域的不同地貌单元,制定出不同的地下水开发利用模式与保护区,按照限制开采、调蓄开采、调控开采和禁止开采等四个区域确定地下水利用模式。     

Methodology to assess groundwater pollution conditions (current and pre-disposition) in the São Carlos and Ribeirão Preto regions,Brazil

The goal of the study was to establish a methodology for territorial zoning based on predicted groundwater pollution. The 31 attributes identified were divided into six different environmental components associated with the transport of contaminants to the geological medium. Two indices were obtained: the pre-disposition index (PI), and the potential pollution intensity index (PPII). The paper reports an assessment of the potential pollution of the groundwater in the sandstones of the Botucatu and Pirambóia Formations, Sao Paulo, Brazil. The region was divided into 447 units according to the type of land use, size of watershed and degree of lithological homogeneity. The units were assessed for potential pollution in the pre-disposition condition (based on geological/geotechnical data) and the complete condition (geological/geotechnical and situation specific data) using the analytical hierarchical process method. A high degree of pollution potential was established for 35 of the units in the complete condition and 157 units in the pre-disposition condition. The study has highlighted areas where attention to pollution control should be focused.      

Factors controlling mobility of 127I and 129I species in an acidic groundwater plume at the Savannah River Site

In order to quantify changes in iodine speciation and to assess factors controlling the distribution and mobility of iodine at an iodine-129 (¹²⁹I) contaminated site located at the U.S. Department of Energy's Savannah River Site (SRS), spatial distributions and transformation of ¹²⁹I and stable iodine (¹²⁷I) species in groundwater were investigated along a gradient in redox potential (654 to 360 mV), organic carbon concentration (5 to 60 μmol L^− 1), and pH (pH 3.2 to 6.8). Total ¹²⁹I concentration in groundwater was 8.6 ± 2.8 Bq L^− 1 immediately downstream of a former waste seepage basin (well FSB-95DR), and decreased with distance from the seepage basin. ¹²⁷I concentration decreased similarly to that of ¹²⁹I. Elevated concentrations of ¹²⁷I or ¹²⁹I were not detected in groundwater collected from wells located outside of the mixed waste plume of this area. At FSB-95DR, the majority (55-86%) of iodine existed as iodide for both ¹²⁷I and ¹²⁹I. Then, as the iodide move down gradient, some of it transformed into iodate and organo-iodine. Considering that iodate has a higher K_d value than iodide, we hypothesize that the production of iodate in groundwater resulted in the removal of iodine from the groundwater and consequently decreased concentrations of ¹²⁷I and ¹²⁹I in downstream areas. Significant amounts of organo-iodine species (30-82% of the total iodine) were also observed at upstream wells, including those outside the mixed waste plume. Concentrations of groundwater iodide decreased at a faster rate than organo-iodine along the transect from the seepage basin. We concluded that removal of iodine from the groundwater through the formation of high molecular weight organo-iodine species is complicated by the release of other more mobile organo-iodine species in the groundwater.     

Evolution model of δ³⁴S and δ¹⁸O in dissolved sulfate in volcanic fan aquifers from recharge to coastal zone and through the Jakarta urban area, Indonesia

The sources of sulfate in an aquifer system, and its formation/degradation via biogeochemical reactions, were investigated by determining sulfate isotope ratios (δ³⁴S_SO4 and δ¹⁸O_SO4) in dissolved sulfate in groundwater from the Jakarta Basin. The groundwater flow paths, water ages, and geochemical features are well known from previous studies, providing a framework for the groundwater chemical and isotopic data, which is supplemented with data for spring water, river water, hot spring water, seawater, detergents, and fertilizers within the basin. The sulfate isotope composition of groundwater samples varied widely from − 2.9‰ to + 33.4‰ for δ³⁴S_SO4 and + 4.9‰ to + 17.8‰ for δ¹⁸O_SO4 and changed systematically along its flow direction from the mountains north to the coastal area. The groundwater samples were classified into three groups showing (1) relatively low and narrow δ³⁴S_SO4 (+ 2.3‰ to + 7.6‰) with low and varied δ¹⁸O_SO4 (+ 4.9‰ to + 12.9‰) compositions, (2) high and varied δ³⁴S_SO4 (+ 10.2‰ to + 33.4‰) with high δ¹⁸O_SO4 (+ 12.4‰ to + 17.3‰) compositions, and (3) low δ³⁴S_SO4 (<+6.1‰) with high δ¹⁸O_SO4 (up to + 17.8‰) compositions. These three types of groundwater were observed in the terrestrial unconfined aquifer, the coastal unconfined and confined aquifers, and the terrestrial confined aquifer, respectively. A combination of field measurements, concentrations, and previously determined δ¹⁵N_NO3 data, showed that the observed isotopic heterogeneity was mainly the result of contributions of pollutants from domestic sewage in the rural area, mixing of seawater sulfate that had experienced previous bacterial sulfate reduction in the coastal area, and isotopic fractionation during the formation of sulfate through bacterial disproportionation of elemental sulfur. Our results clearly support the hypothesis that human impacts are important factors in understanding the sulfur cycle in present-day subsurface environments. A general model of sulfate isotopic evolution along with groundwater flow has rarely been proposed, due to the complicated hydrogeological research setting that causes varied isotope ratios, although its understanding has recently received great attention. This pioneer study on a simple volcanic fan aquifer system with a well-understood groundwater flow mechanism provides a useful model for future studies.     

青海那西郭勒地区沉积—变质型铁矿遥感综合找矿模式构建

文章以那西郭勒铁矿床为例,在深入剖析该铁矿床成矿地质背景及成因的基础上,基于World View-2遥感数据解译了赋矿地层及含矿岩性,总结了地层、含矿岩性及铁矿带遥感影像特征,同时分析该矿床遥感蚀变异常特征,结合构造、磁异常等找矿信息,构建了沉积—变质型铁矿遥感综合找矿模式;通过该找矿模式预测了1处找矿有利地段,为该地区的后续基础地质、矿产勘查工作,以及关键地段的含矿性或找矿潜力评价提供参考依据。     

Agriculture and groundwater nitrate contamination in the Seine basin. The STICS-MODCOU modelling chain

A software package is presented here to predict the fate of nitrogen fertilizers and the transport of nitrate from the rooting zone of agricultural areas to surface water and groundwater in the Seine basin, taking into account the long residence times of water and nitrate in the unsaturated and aquifer systems. Information on pedological characteristics, land use and farming practices is used to determine the spatial units to be considered. These data are converted into input data for the crop model STICS which simulates the water and nitrogen balances in the soil-plant system with a daily time-step. A spatial application of STICS has been derived at the catchment scale which computes the water and nitrate fluxes at the bottom of the rooting zone. These fluxes are integrated into a surface and groundwater coupled model MODCOU which calculates the daily water balance in the hydrological system, the flow in the rivers and the piezometric variations in the aquifers, using standard climatic data (rainfall, PET). The transport of nitrate and the evolution of nitrate contamination in groundwater and to rivers is computed by the model NEWSAM. This modelling chain is a valuable tool to predict the evolution of crop productivity and nitrate contamination according to various scenarios modifying farming practices and/or climatic changes. Data for the period 1970-2000 are used to simulate the past evolution of nitrogen contamination. The method has been validated using available data bases of nitrate concentrations in the three main aquifers of the Paris basin (Oligocene, Eocene and chalk). The approach has then been used to predict the future evolution of nitrogen contamination up to 2015. A statistical approach allowed estimating the probability of transgression of different concentration thresholds in various areas in the basin. The model is also used to evaluate the cost of the damage resulting of the treatment of drinking water at the scale of a groundwater management unit in the Seine river basin.     

Monitoring groundwater variation by satellite and implications for in-situ gravity measurements

In order to establish a new technique for monitoring groundwater variations in urban areas, the applicability of precise in-situ gravity measurements and extremely high precision satellite gravity data via GRACE (Gravity Recovery and Climate Experiment) was tested. Using the GRACE data, regional scale water mass variations in four major river basins of the Indochina Peninsula were estimated. The estimated variations were compared with Soil-Vegetation-Atmosphere Transfer Scheme (SVATS) models with a river flow model of 1) globally uniform river velocity, 2) river velocity tuned by each river basin, 3) globally uniform river velocity considering groundwater storage, and 4) river velocity tuned by each river basin considering groundwater storage. Model 3) attained the best fit to the GRACE data, and the model 4) yielded almost the same values. This implies that the groundwater plays an important role in estimating the variation of total terrestrial storage. It also indicates that tuning river velocity, which is based on the in-situ measurements, needs further investigations in combination with the GRACE data. The relationships among GRACE data, SVATS models, and in-situ measurements were also discussed briefly.     

Geochemistry of redox-sensitive elements and sulfur isotopes in the high arsenic groundwater system of Datong Basin, China

High arsenic groundwater in the Quaternary aquifers of Datong Basin, northern China contain As up to 1820 µg/L and the high concentration plume is located in the slow flowing central parts of the basin. In this study we used hydrochemical data and sulfur isotope ratios of sulfate to better understand the conditions that are likely to control arsenic mobilization. Groundwater and spring samples were collected along two flow paths from the west and east margins of the basin and a third set along the basin flow path. Arsenic concentrations range from 68 to 670 µg/L in the basin and from 3.1 to 44 µg/L in the western and eastern margins. The margins have relatively oxidized waters with low contents of arsenic, relatively high proportions of As(V) among As species, and high contents of sulfate and uranium. By contrast, the central parts of the basin are reducing with high contents of arsenic in groundwater, commonly with high proportions of As(III) among As species, and low contents of sulfate and uranium. No statistical correlations were observed between arsenic and Eh, sulfate, Fe, Mn, Mo and U. While the mobility of sulfate, uranium and molybdenum is possibly controlled by the change in redox conditions as the groundwater flows towards central parts of the basin, the reducing conditions alone cannot account for the occurrence of high arsenic groundwater in the basin but it does explain the characteristics of arsenic speciation. With one exception, all the groundwaters with As(III) as the major As species have low Eh and those with As(V) have high Eh. Reductive dissolution of Fe-oxyhydroxides or reduction of As(V) are consistent with the observations, however no increase in dissolved Fe concentration was noted. Furthermore, water from the well with the highest arsenic was relatively oxidizing and contained mostly As(V). From previous work Fe-oxyhydroxides are speculated to exist as coatings rather than primary minerals.The wide range of δ³⁴S_[SO4] values (from − 2.5 to + 36.1‰) in the basin relative to the margins (from + 8‰ to + 15‰) indicate that sulfur is undergoing redox cycling. The highly enriched values point to sulfate reduction that was probably mediated by bacteria. The presence of monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) is also evidence of microbial reactions. The depleted signatures indicate that some oxidation of depleted sulfide occurred in the basin. It must be noted that the samples with depleted sulfur isotope values have very low sulfate concentrations and therefore even a small amount of sulfide oxidation will bias the ratio. No significant correlation was observed between δ³⁴S_[SO4] values and total arsenic contents when all the samples were considered. However, the wells in the central basin do appear to become enriched in δ³⁴S_[SO4] as arsenic concentration increases. Although there is evidence for sulfate reduction, it is clear that sulfate reduction does not co-precipitate or sequester arsenic. The one sample with high arsenic that is oxidizing cannot be explained by oxidation of pyrite and is likely an indication that there are multiple redox zones that control arsenic speciation but not necessarily its mobilization and contradict the possibility that Fe-oxyhydroxides sorb appreciable amounts of arsenic in this study area. It is evident that this basin like other two young sedimentary basins (Huhhot and Hetao in Inner Mongolia) of northern China with high arsenic groundwater is transporting arsenic at a very slow rate. The data are consistent with the possibility that the traditional models of arsenic mobilization, namely reductive dissolution of Fe-oxyhydroxides, reduction of As(V) to more mobile As(III), and bacteria mediated reactions, are active to varying degrees. It is also likely that different processes control arsenic mobilization at different locations of the basin and more detailed studies along major flow paths upgradient of the high arsenic aquifers will shed more light on the mechanisms.     

Hydrogeological characteristics of a groundwater-dependent ecosystem (La Lantejuela, Spain)

By means of a simple water balance model, together with hydrogeochemical and morphological interpretation, the hydrogeological characteristics of a series of playa lakes forming an endorheic complex within the Guadalquivir river basin in Southern Spain (La Lantejuela) have been evaluated. The lakes are demonstrated to be groundwater-dependent ecosystems. The main source of groundwater input to the lakes is from an unconfined detritic aquifer, the playa lakes being the natural discharge points from the aquifer within the endorheic complex. High rates of evaporation from the lakes induce a centripetal groundwater flow pattern. This water body has been disturbed by a combination of extensive drainage works and intensive groundwater abstraction. There is a need for a sustainable water management strategy for the whole catchment area. It is hoped this will be an issue addressed within the Guadalquivir river basin management plan in accordance with the requirements of the European Water Framework Directive (WFD).     

Human impacts on groundwater flow and contamination deduced by multiple isotopes in Seoul City, South Korea

The influence of human activities on the flow system and contamination of groundwater were investigated in Seoul City, South Korea, one of the largest Asian cities, using a combination of isotopes (δD, T, δ¹⁵N, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr). Eighteen representative groundwater and river water samples, which were collected over a wide area of the city, were compared with previously reported data. The distribution of stable isotopes (δD and δ¹⁸O) with groundwater potential data shows that recharged groundwater from either the surrounding mountainous area as well as the Han River and other surface streams discharged towards the northern-central part of the city, where a subway tunnel pumping station is located. It is suggested from T values (3.3 to 5.8 T.U.) that groundwater was recharged in the last 30 to 40 years. The δ³⁴S and δ¹⁵N of SO₄²⁻ and NO₃⁻ data were efficiently used as indicators of contamination by human activities. These isotopes clarified that the contribution of anthropogenic contaminants i.e., industrial and household effluents, waste landfills, and fertilizers, are responsible for the enrichment by SO₄²⁻ (> 30 ppm as SO₄²⁻) and NO₃⁻ (> 20 ppm as NO₃⁻) of groundwater. The ⁸⁷Sr/⁸⁶Sr values of groundwater vary (0.71326 to 0.75058) in accordance with the host rocks of different origins. Mineral elements such as Ca are also suggested to be derived naturally from rocks. The groundwater under Seoul City is greatly affected by transportation of pollutants along the groundwater flow controlled by subway tunnel pumping, contributing to the degradation of water quality in urbanized areas.     

洛阳盆地浅层地下水资源数值模拟评价

水资源的不合理利用、地下水的过渡开采导致了洛阳盆地水环境的恶化。本文结合洛阳盆地水文地质条件运用数学模型对盆地的浅层孔隙地下水资源进行模拟评价。结果表明:建立二层结构的非均质三维非稳定流数学模型,经模型识别和校正,所选参数是基本合理的,可以比较准确地模拟洛阳盆地第四系浅层地下水系统。盆地地下水补给主要为降水及灌溉入渗补给,地下水排泄主要为人工开采,占总排泄量的75.82%,因此调整和优化现状地下水开采方案,合理开采地下水资源显得尤为必要。     

Comparing isotopic groundwater age measurements with simulated groundwater ages: example of the Abbotsford–Sumas Aquifer (USA and Canada) and application

Elevated nitrate concentrations have been documented since the 1970s within the trans‐national Abbotsford–Sumas aquifer, situated in the central Fraser Valley of southern British Columbia, Canada, and northern Washington State, United States. Nitrate concentrations in excess of 10 mg/L NO₃–N are commonly observed in the monitoring wells. A groundwater model is used in this study to conduct a particle tracking analysis to estimate groundwater travel times and compare these with groundwater ages determined from ³H/³He concentrations measured in several monitoring wells. Groundwater ages estimated from particle tracking show excellent agreement with measured ages (slope=1), although there is scatter (R²=0.76), reflecting the complexity of the travel pathways and ambiguities in groundwater ages because of mixing. An assessment of the efficacy of recommended nutrient management practices, which were implemented in 1992 to reduce nitrogen loading, suggests that wells shallower than about 20 m should be monitoring a decrease in nitrate concentration. However, persistent elevated nitrate concentrations even at shallow depths point to the lingering effects of a remnant manure–nitrate signature in combination with continued high loading.     

Health risk assessment of inorganic arsenic intake of Cambodia residents through groundwater drinking pathway

In order to compare the magnitudes and health impacts of arsenic and other toxic trace elements in well water, groundwater and hair samples were collected from three areas with different arsenic exposure scenarios in the Mekong River basin of Cambodia. Ampil commune in Kampong Cham province was selected as an uncontaminated area, Khsarch Andaet commune in Kratie province was selected as a moderately contaminated area, and Kampong Kong commune in Kandal Province was selected as an extremely contaminated area. Results of ICP-MS analyses of the groundwater samples revealed that As, Mn, Fe and Ba concentrations were significantly different among the three study areas (Kruskal-Wallis test, p < 0.0001). Out of 46 observed wells in the Kandal province study area, 100% detected As > 50 μg L⁻¹ and Fe > 300 μg L⁻¹; 52.17% had Mn > 400 μg L⁻¹ and 73.91% found Ba > 700 μg L⁻¹. In the Kratie province study area (n = 12), 25% of wells showed elevated arsenic levels above 10 μg L⁻¹ and 25% had Mn > 400 μg L⁻¹, whereas samples from Kampong Cham province study area (n = 18) were relatively clean, with As < 10 μg L⁻¹. A health risk assessment model derived from the USEPA was applied to calculate individual risks resulting from drinking groundwater. Computational results indicated that residents from Kandal Province study area (n = 297) confronted significantly higher non-carcinogenic and carcinogenic risks than those in Kratie (n = 89) and Kampong Cham (n = 184) province study areas (Kruskal-Wallis test, p < 0.0001). 98.65% of respondents from the Kandal province study area were at risk for the potential non-cancer effect and an average cancer risk index was found to be 5 in 1000 exposure. The calculations also indicated that, in the Kratie province study area, 13.48% of respondents were affected by non-cancer health risks and 33.71% were threatened by cancer, whereas none of respondents in the Kampong Cham province study area appeared to have non-carcinogenic effect. Positively significant correlations of the arsenic content in scalp hair (As_h) with both arsenic levels in groundwater (As_w) (r_s (304) = 0.757, p < 0.0001) and individual average daily doses (ADD) of arsenic (r_s (304) = 0.763, p < 0.0001) undoubtedly indicated that arsenic accumulation in the bodies of Cambodia residents in the Mekong River basin was mainly through a groundwater drinking pathway. To the best of our knowledge, this is the first comprehensive report comparing individual health risk assessments of arsenic exposure through a groundwater drinking pathway to enriched arsenic levels from groundwater in the Mekong River basin, Cambodia. This study indicates that elevated arsenic concentrations in groundwater may lead to thousands of cases of arsenicosis in the near future if mitigating actions are not taken.     

Sources and controls for the mobility of arsenic in oxidizing groundwaters from loess-type sediments in arid/semi-arid dry climates - evidence from the Chaco-Pampean plain (Argentina)

In oxidizing aquifers, arsenic (As) mobilization from sediments into groundwater is controlled by pH-dependent As desorption from and dissolution of mineral phases. If climate is dry, then the process of evaporative concentration contributes further to the total concentration of dissolved As. In this paper the principal As mobility controls under these conditions have been demonstrated for Salí River alluvial basin in NW Argentina (Tucumán Province; 7000 km²), which is representative for other basins or areas of the predominantly semi-arid Chaco-Pampean plain (1,000,000 km²) which is one of the world’s largest regions affected by high As concentrations in groundwater. Detailed hydrogeochemical studies have been performed in the Salí River basin where 85 groundwater samples from shallow aquifers (42 samples), deep samples (26 samples) and artesian aquifers (17 samples) have been collected. Arsenic concentrations range from 11.4 to 1660 μg L⁻¹ leaving 100% of the investigated waters above the provisional WHO guideline value of 10 μg L⁻¹. A strong positive correlation among As, F, and V in shallow groundwaters was found. The correlations among those trace elements and U, B and Mo have less significance. High pH (up to 9.2) and high bicarbonate (HCO₃) concentrations favour leaching from pyroclastic materials, including volcanic glass which is present to 20-25% in the loess-type aquifer sediments and yield higher trace element concentrations in groundwater from shallow aquifers compared to deep and artesian aquifers. The significant increase in minor and trace element concentrations and salinity in shallow aquifers is related to strong evaporation under semi-arid climatic conditions. Sorption of As and associated minor and trace elements (F, U, B, Mo and V) onto the surface of Fe-, Al- and Mn-oxides and oxi-hydroxides, restricts the mobilization of these elements into groundwater. Nevertheless, this does not hold in the case of the shallow unconfined groundwaters with high pH and high concentrations of potential competitors for adsorption sites (HCO₃, V, P, etc.). Under these geochemical conditions, desorption of the above mentioned anions and oxyanions occurs as a key process for As mobilization, resulting in an increase of minor and trace element concentrations. These geochemical processes that control the concentrations of dissolved As and other trace elements and which determine the groundwater quality especially in the shallow aquifers, are comparable to other areas with high As concentrations in groundwater of oxidizing aquifers and semi-arid or arid climate, which are found in many parts of the world, such as the western sectors of the USA, Mexico, northern Chile, Turkey, Mongolia, central and northern China, and central and northwestern Argentina.     

基于GIS的地下水建模

地下水模拟模型能够模拟地下水动态特征 ,GIS具有强大的空间数据处理与分析功能 ,建立地下水模拟模型与GIS的集成系统 ,将有助于对地下水模拟模型的推广应用和决策分析。本文详细论述GIS支持下的地下水模拟模型的建立过程 ,采用交互式剖分方法不仅提高建模效率 ,而且能充分考虑计算域的水文地质条件 ,使生成的网格单元效果更为理想 ,本文将这种方法应用于北京密怀顺地下水模拟中 ,极大地提高了工作效率。     

The Use of Limestone Bed Filtration for the Treatment of Ferruginous Groundwater

A pilot plant, consisting of limestone bed and sand filtration units, has been built 15 km south of Cairo to serve about 400 people. The plant comprises three limestone filter units (operated in series) and two sand filters. Operation of the pilot plant has shown that a packed limestone filter unit is a simple and cheap method of removing iron from ferruginous groundwater. The results demonstrate an iron removal rate of about 60% after passing through one 1.15?m deep limestone filter operating with a surface loading rate up to 1.4 m³/m². h. The overall iron removal after one limestone filter followed by sand filtration was more than 90%.     

FCKW-Datierung nitratbelasteten Grundwassers: ein Fallbeispiel

In order to determine the mean residence time in a groundwater aquifer system polluted by nitrate, the anthropogenic tracer tritium ( ³ H) and chlorofluorocarbons (CFC) were used. The observed 36 TU (tritium units) indicated that the groundwater residence time is either about eight years or fifty years. The measured CFC concentration of about 2,5 pmol per liter, however, definitely excludes the higher age value. These results allow the estimation of the future nitrate development in the groundwater.     

Occurrence of arsenic in core sediments and groundwater in the Chapai-Nawabganj District, northwestern Bangladesh

Groundwater and core sediments of two boreholes (to a depth of 50 m) from the Chapai-Nawabganj area in northwestern Bangladesh were collected for arsenic concentration and geochemical analysis. Groundwater arsenic concentrations in the uppermost aquifer (10-40 m of depth) range from 2.8 μg L⁻¹ to 462.3 μg L⁻¹. Groundwater geochemical conditions change from oxidized to successively more reduced, higher As concentration with depth. Higher sediment arsenic levels (55 mg kg⁻¹) were found within the upper 40 m of the drilled core samples. X-ray absorption near-edge structure spectroscopy was employed to elucidate the arsenic speciation of sediments collected from two boreholes. Environmental scanning electron microscopy and transmission X-ray microscopy were used to investigate the characteristics of FeOOH in sediments which adsorb arsenic. In addition, a pH-Eh diagram was drawn using the Geochemist's Workbench (GWB) software to elucidate the arsenic speciation in groundwater. The dominant groundwater type is Ca-HCO₃ with high concentrations of As, Fe and Mn but low levels of NO₃⁻ and SO₄²⁻. Sequential extraction analysis reveals that Mn and Fe hydroxides and organic matter are the major leachable solids carrying As. High levels of arsenic concentration in aquifers are associated with fine-grained sediments. Fluorescent intensities of humic substances indicate that both groundwater and sediments in this arsenic hotspot area contain less organic matter compared to other parts of Bengal basin. Statistical analysis clearly shows that As is closely associated with Fe and Mn in sediments while As is better correlated with Mn in groundwater. These correlations along with results of sequential leaching experiments suggest that reductive dissolution of MnOOH and FeOOH mediated by anaerobic bacteria represents an important mechanism for releasing arsenic into the groundwater.