北京通州区地下水污染评价及监测网布设

为准确刻画通州区地下水污染的分布特征,基于2008年6月采集的151个浅、中、深层地下水样进行了分层污染评价。采用数理统计学方法,计算了各层不同级别的污染面积。初步探讨了污染机理和原因。结果表明研究区内浅层地下水均已经遭受污染且污染程度较为严重,中层地下水绝大部分显示为轻度污染,而深层地下水只在西部小范围地区遭受轻度污染。提出了“重点突出、区域控制、分层监测、有机无机并重”监测网布设原则,整合并新施工监测井,形成了立体分层的地下水监测网络：其中污染源专项监孔共计71眼,区域浅层监测孔共计48眼,区域中层共计36眼,区域中深层共计26眼,区域深层共计22眼。最后对监测网的运行情况进行了简要介绍。     

A statistical and geographical information system analysis for groundwater intrinsic vulnerability: a validated case study from Sfax–Agareb,Tunisia

The groundwater vulnerability to the pollution assessment was considered as an efficient tool to limit and to control its quantitative and qualitative degradation risks. The DRASTIC high, moderate and low groundwater vulnerability zones of the Sfax–Agareb basin (Tunisia) cover about 10, 29 and 61% of the study area, respectively. The validation of the DRASTIC vulnerability map was undertaken through comparison of areas of high nitrate concentration and their relative vulnerability index. The DRASTIC vulnerability map illustrates a good rate of coincidence between the nitrate concentration ranges and the various vulnerability classes as recognized by statistical analysis. The reliability of the final vulnerability map has been tested, showing a general positive trend relating the mean nitrate concentration in the wells to their relative vulnerability classes (R²=0.88). When correlating the 214 available groundwater nitrate concentrations to the DRASTIC index in these wells location, a significant positive correlation with Cor=0.55 was found.     

缺少观测地区地下水位统测方案优化设计

地下水位统测数据属于基础性资料,可为区域水文地质编图提供重要依据,也是地下水数值模拟建立初始流场的必要数据.部分地区由于缺少观测资料,布置地下水位统测点比较困难.针对这一难题,本文提出了一种设计、优化地下水位统测网的方法:首先通过密网格数值模拟获得参考地下水位等值线图,再根据初步设计的若干水位统测方案,进行水位采样作为...     

Analytical solution for steady-state groundwater inflow into a drained circular tunnel in a semi-infinite aquifer: A revisit

This study deals with the comparison of existing analytical solutions for the steady-state groundwater inflow into a drained circular tunnel in a semi-infinite aquifer. Two different boundary conditions (one for zero water pressure and the other for a constant total head) along the tunnel circumference, used in the existing solutions, are mentioned. Simple closed-form analytical solutions are re-derived within a common theoretical framework for two different boundary conditions by using the conformal mapping technique. The water inflow predictions are compared to investigate the difference among the solutions. The correct use of the boundary condition along the tunnel circumference in a shallow drained circular tunnel is emphasized.     

A geostatistical methodology to estimate the base of the Trifa aquifer (Morocco) with limited drilling and geo-electrical sounding data

The paper presents the methodology used to estimate the base and thickness of the Trifa aquifer, north-east Morocco, from very limited drilling and geoelectrical sounding data. The methodology is applicable where the aquifer is a single horizon with considerable lateral variation. The procedure is based on geostatistical techniques: kriging of apparent resistivities, calibration of the resistivities with information from drilling, co-kriging of resistivities and estimation of the thickness of the aquifer by inverting the apparent resistivity formula. Calculated and measured substratum levels are obtained by subtracting the estimated and measured thickness from the topography at the drilling and geo-electrical sounding locations. By co-kriging the estimated substratum levels with the measured values in the drilling locations, a map of the substratum over the plain was prepared.     

3D finite element method (FEM) simulation of groundwater flow during backward erosion piping

Backward erosion piping is an important failure mechanism for cohesive water retaining structures which are founded on a sandy aquifer. At present, the prediction models for safety assessment are often based on 2D assumptions. In this work, a 3D numerical approach of the groundwater flow leading to the erosion mechanism of backward erosion piping is presented and discussed. Comparison of the 2D and 3D numerical results explicitly demonstrates the inherent 3D nature of the piping phenomenon. In addition, the influence of the seepage length is investigated and discussed for both piping initiation and piping progression. The results clearly indicate the superiority of the presented 3D numerical model compared to the established 2D approach. Moreover, the 3D numerical results enable a better understanding of the complex physical mechanism involved in backward erosion piping and thus can lead to a significant improvement in the safety assessment of water retaining structures.     

A case study of urban water balancing in the partly sewered city of Nablus-East (Palestine) to study wastewater pollution loads and groundwater pollution

Untreated sewage can contribute a significant proportion of urban groundwater recharge, via on-site sanitation facilities and sewer exfiltration. In the West Bank of the Palestinian Territories 94% of sewage is discharged untreated to the ground or surface waters. This has contributed to increasing nitrate concentrations in groundwater, which is the critical water source. In this case study of a drainage catchment from the city of Nablus, a water balance indicates that sewage as a source of groundwater recharge is as much as 50% of total recharge from precipitation, and nitrogen pollutant loads by area are up to 60% as much as those from agriculture. Results suggest that 22% of total wastewater flow directly infiltrates the ground via cesspits and sewer exfiltration.     

Learning from project monitoring feedback: A case of optimizing behavior of contractors

Monitoring is an essential part of construction project management and has typically been devised to guard against non-compliance. When contractors are subjected to regular performance feedback, instead of just taking remedial action, they may take the opportunities to enhance their operations in the light of the feedback. Thus, it has been advocated that responding to performance feedback has a learning element. This study takes on this notion and examined the performance change pattern of contractors that have been subjected to regular performance feedback. Longitudinal performance scores were fitted against five well established learning curve models using the Least Square Curve Fitting Analysis (LSCFA). It was found that the 3-parameter hyperbolic model is the ‘best-fit’ model in terms of effectiveness and stability. The LSCFA results also suggested that the contractors in the sample can be arranged in four clusters: Competent Learners, Incidental Learners, Indifferent Learners and Optimizers. The majority of them fall into the optimizing cluster. This suggests that these contractors may adjust their resources to maintain their performance at an acceptable level which do not deprive their future opportunities. With due caveat to the constraints and limitations of working sample, this finding is thought provoking for project managers in exercising project monitoring.     

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.     

Assessment quality of a nonuniform suspended sediment transport model under unsteady flow condition (case study: Aras River)

This study presents a one‐dimensional, fully coupled numerical model for nonequilibrium suspended sediment transport that can be applied to channels and alluvial rivers. The accuracy of calculations was enhanced using a nonuniform size distribution, and evaluating probability of hiding and exposure effect of particles. This model is also capable of calculating the flocculation and temperature effect on sediment transport. In addition, the BOD and its influence on suspended sediment transport have been discussed. The study was conducted on the Aras River, Iran's third major river with a relatively high sediment concentration. To verify the model, water depth and sediment concentration of measured field data are compared with simulated data. Comparisons show a regression coefficient of more than 95% and mean computational error is less than 5%. The agreement of the data shows that the model is capable of predicting flow and suspended sediment transport with a correlation coefficient higher than 98%.     

Microbial degradation of nitrilotriacetate (NTA) during river water/groundwater infiltration: Laboratory column studies

In laboratory column experiments with aquifer material collected from a natural river water/groundwater infiltration site, the effects of changes in NTA concentration (0.06–3.40 μM), temperature (5–20°C), and redox conditions on the microbial degradation of NTA during infiltration have been investigated. Under both aerobic and denitrifying conditions, NTA was rapidly mineralized and supported microbial growth as a sole carbon and energy source. The presence of other degradable organic compounds and of trace metals had no significant effect on the total rate of NTA elimination after a 21.8 cm flow distance. At concentrations between 0.02 and 0.05 μM, NTA degradation was still rapid (apparent pseudo first-order rate constants of up to 15 d⁻¹). From the results of the column experiments it may be concluded that under environmental conditions typical for Switzerland, very low residual NTA concentrations (< 0.01 μM) should be present at all times of the year in the groundwater after only a few meters of infiltration, even when concentrations of NTA in river water reach 3–4 μM. This conclusion is corroborated by results of field measurements.     

A multi-layer sampler for the study of detailed hydrochemical profiles in groundwater

A modular multi-layer sampler was developed and utilized for sampling undisturbed groundwater chemical profiles. Sampling at 3 cm depth intervals is based on the dialysis-cell method and has no depth limitations. The sampler may be used for water quality monitoring and research, both in existing or specially drilled screened wells     

Causes of the changes in groundwater levels at Daegu,Korea: the effect of subway excavations

The paper presents the investigations into the decline in groundwater level recorded at national groundwater monitoring stations in Daegu Metropolitan City, Korea. The effect of precipitation and the pumping of wells in nearby areas was considered, but it was concluded that the main influence was the construction of a 1,110 m subway line some 250 m from the monitoring station. This was checked using a simplified conceptual model, which gave results consistent with field observations and suggested that groundwater levels may be depressed for a period of 10 years or more.      

Thermal performance of borehole heat exchanger under groundwater flow: A case study from Baoding

The performance of ground source heat pumps (GSHPs) depends strongly on the heat transfer between the soil and borehole heat exchangers (BHEs). In the present work, a thermal performance experiment of a BHE under groundwater flow was conducted in Baoding, China. Based on the measurement of the natural ground temperature profile, a simplified theoretical model was presented to estimate the characteristics of groundwater flow. The results showed that the presence of groundwater had an obvious influence on the temperature profile in the aquifer. Due to the strong groundwater advection, the thermal performance of the BHE was enhanced. The enhanced effect depends to a great extent on the distribution and thickness percentage of the ground layer with the greatest groundwater flow. In the present case, the heat injection and heat extraction of the BHE were enhanced on average by 9.8% and 12.9%, respectively, compared with the case without groundwater flow, when the total thickness of coarse sand and gravel layer as a percentage of the borehole depth was 10.6%. This enhanced effect is favorable for reducing the possible imbalance between heat injection and extraction from and to the ground, which is helpful for the long-term operation of GSHP systems.     

Long-term continuous monitoring of the dissolved CO2 performed by using a new device in groundwater of the Mt. Etna (southern Italy)

We present a new device for continuous monitoring of the concentration of CO₂ dissolved in water. The device consists of a tube made of a polymeric semi-permeable membrane connected to an infrared gas analyser (IRGA) and a pump. Several laboratory experiments were performed to set the best operating condition and test the accuracy of measurements. We used the device for performing 20 months of continuous monitoring of dissolved CO₂ concentration (DCC) in groundwater within a drainage gallery at Mt. Etna. The monitored groundwater intercepts the Pernicana Fault, along which degassing is observed related to volcano-tectonic activity. The acquired data were compared with continuous and discrete data obtained using existing methods. The measurements of DCC resulted in some period of the year well correlated with air temperature. We also found that long-term trends, as well as short-term variations, are probably linked to the dynamics of volcanic activity and/or perturbations in the local or regional stress fields.     

斜拉桥结构健康监测系统的设计与实现(I):系统设计

结构智能健康监测愈来愈成为重大工程结构健康与安全的重要保障技术,也愈来愈成为重大工程结构损伤积累乃至灾害演变规律的重要研究手段。斜拉桥健康监测系统是由传感器子系统、数据采集与传输子系统、结构分析子系统和数据管理子系统组成的,不同系统的谐调运行需要通过系统集成技术来实现。首先从监测内容、等级和功能等方面研究健康监测系统的总体设计原则;然后,分局部监测变量和整体监测变量研究传感器的最优测点确定方法和原则,提出传感器的选型原则;提出数据采集系统的总线设计方法和方案,研究数据采集系统硬件和软件设计方法;提出数据传输系统的设计原则和方法;给出斜拉桥基于构件和基于结构体系的安全评定设计方法;提出斜拉桥施工监控、成桥试验、运营健康监测和养护管理四位一体系统的共享设计原则;提出系统集成技术的软件设计方法。     

油气矿山遥感监测方法初探——以鄂尔多斯盆地为例

随着对地质规律认识的不断提高,非常规油气勘查开采技术的不断创新,我国页岩气、煤层气等非常规油气资源新增地质储量取得突破性进展。但由于种种原因,对油气矿山(石油、天然气、煤层气、页岩气)关注力度不够,还没有开展区域性遥感监测研究。文章采用2018年高辨率遥感数据,运用人机交互解译的技术方法,建立了油气矿山遥感解译标志,开展了油气矿山遥感监测方法探索,并在鄂尔多斯盆地完成了油气矿山开发状况遥感监测,证明了遥感监测方法切实可行。     

VLDA模型及其在潜水脆弱性评价中的应用——以新疆焉耆县平原区为例

在地下水脆弱性评价的GOD法和DRASTIC模型的基础上,提出了VLDA模型,其中V为包气带岩性(1ithology of vadose zone)、L为土地利用方式(pattern of land use)、D为地下水埋深(groundwater depth)、A为含水层特征(aquifer characterist...     

典型地质环境下的高氟地下水形成影响因素分析——以山东省高密市为例

高密市是山东省地氟病防治的重点地区,该区地下水中氟含量之高、地氟病分布之广,危害程度之严重均居山东省之最。高密市典型的地形地貌、气候条件、地质条件以及水文地质条件是造成该区地氟病高发的主要原因。本文分析了高密市与高氟地下水相关的地质环境,通过大量水样岩土样品的分析测试,半定量阐述了地下水中F元素的富集与地形地貌、地质岩性、气候条件、水动力条件的相关关系,总结出高密市典型地质环境下高氟地下水形成的影响因素。以期对高氟地下水形成机制的研究工作提供借鉴,以及对高氟区寻找低氟地下水提供参考。