Assessing risk to groundwater quality using an integrated risk framework

Source-water protection strategies are ideally focused where the greatest amount of harm reduction can occur. This process of risk management requires an assessment of the spatial variability of risk to water. The assessment methodology presented herein combines aquifer susceptibility with a hazard threat inventory and an analysis of the consequence of contamination to assess the risk to water quality. Aquifer susceptibility combines the intrinsic susceptibility of the physical system with anthropogenic features that locally increase susceptibility. Hazard threats are assessed based on the properties of the chemicals (toxicity and environmental fate), the potential magnitude (extent and quantity of release) and the likelihood of release. The consequence is herein considered as the financial costs of the loss of the resource, including the replacement of a water source and the economic loss where water intensive businesses are lost. A second scenario is included that analyses health issues related to pathogen sources as well as the financial impact to the community where people fall ill and present a financial burden to the public health care system. The risk assessment methodology is applied to the Township of Langley, in southwestern British Columbia, Canada. The results outline the most vulnerable areas as those where susceptible aquifers coexist with potential chemical and biological threats. The risk is greatest where these vulnerable areas coincide with those with the greatest potential for financial loss: within the capture zones of major municipal production wells and where private wells serve agricultural operations with high annual farm sales.     

Application of MODFLOW for simulating groundwater flow in the Trifilia karst aquifer, Greece

Karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features. As a result, a three-dimensional finite-difference groundwater flow model (equivalent porous media) may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated. Statistical analysis of karst hydrographs of the Trifilia aquifer in Greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow. An equivalent porous media model was developed to simulate the Trifilia karst aquifer using MODFLOW. Steady state and transient state calibration gave encouraging results for the equivalent porous media approach, which does not consider pipe flow or turbulence. Detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent; and flux to/from the aquifer. Only hydraulic conductivity and specific yield were adjusted during calibration, as the flux to/from the system was considered known and applied as boundary conditions. Small mean absolute and RMS piezometric head error of the model under both steady and transient state conditions were achieved.     

Impact of land-surface elevation and riparian evapotranspiration seasonality on groundwater budget in MODFLOW models

Riparian groundwater evapotranspiration (ETg) constitutes a major component of the water balance especially in many arid and semi-arid environments. Although spatial and temporal variability of riparian ETg are controlled by climate, vegetation and subsurface characteristics, depth to water table (DTWT) is often considered the major controlling factor. Relationships between ETg rates and DTWT, referred to as ETg curves, are implemented in MODFLOW ETg packages (EVT, ETS1 and RIP-ET) with different functional forms. Here, the sensitivity of the groundwater budget in MODFLOW groundwater models to ETg parameters (including ETg curves, land-surface elevation and ETg seasonality) are investigated. A MODFLOW model of the hypothetical Dry Alkaline Valley in the Southwestern USA is used to show how spatial representation of riparian vegetation and digital elevation model (DEM) processing methods impact the water budget when RIPGIS-NET (a GIS-based ETg program) is used with MODFLOW’s RIP-ET package, and results are compared with the EVT and ETS1 packages. Results show considerable impact on ETg and other groundwater budget components caused by spatial representation of riparian vegetation, vegetation type, fractional coverage areas and land-surface elevation. RIPGIS-NET enhances ETg estimation in MODFLOW by incorporating vegetation and land-surface parameters, providing a tool for ecohydrology studies, riparian ecosystem management and stream restoration.     

地下水化学动力学方法运用过程中的若干问题探讨

对用地下水化学动力学方法计算出的5种水文地质参数定量评价研究区水文地质条件的整个过程中存在的问题，进行了较全面的分析，认为用地下水化学动力学方法计算出的5种水文地质参数，通常只能粗略地评价研究区的水文地质条件，对于无钻孔或钻孔很少的区域，此方法便难以应用。     

人工回灌对地下水年龄分布规律的影响

地下水可更新能力是评价地下水开发可持续性的关键指标,可更新能力可以用地下水年龄来定量表达。在人类活动影响下,地下水的实际更新状况已与自然条件下截然不同。基于台兰河流域地下水库建设和人工回灌工作现状,通过物理试验和数值模拟相结合的方法分别研究了入渗池位置,回灌强度和包气带厚度对地下水年龄分布规律的影响。结果表明:人工回灌使地下水年龄整体变年轻;入渗池位置和回灌强度的改变对地下水年龄分布的影响显著;包气带厚度的增大使回灌水滞留时间延长,导致地下水年龄增大,该研究可为合理评价区域地下水可更新能力提供技术指导。     

Application of MODFLOW and geographic information system to groundwater flow simulation in North China Plain, China

MODFLOW is a groundwater modeling program. It can be compiled and remedied according to the practical applications. Because of its structure and fixed data format, MODFLOW can be integrated with Geographic Information Systems (GIS) technology for water resource management. The North China Plain (NCP), which is the politic, economic and cultural center of China, is facing with water resources shortage and water pollution. Groundwater is the main water resource for industrial, agricultural and domestic usage. It is necessary to evaluate the groundwater resources of the NCP as an entire aquifer system. With the development of computer and internet information technology it is also necessary to integrate the groundwater model with the GIS technology. Because the geological and hydrogeological data in the NCP was mainly in MAPGIS format, the powerful function of GIS of disposing of and analyzing spatial data and computer languages such as Visual C and Visual Basic were used to define the relationship between the original data and model data. After analyzing the geological and hydrogeological conditions of the NCP, the groundwater flow numerical simulation modeling was constructed with MODFLOW. On the basis of GIS, a dynamic evaluation system for groundwater resources under the internet circumstance was completed. During the process of constructing the groundwater model, a water budget was analyzed, which showed a negative budget in the NCP. The simulation period was from 1 January 2002 to 31 December 2003. During this period, the total recharge of the groundwater system was 49,374 × 10⁶ m³ and the total discharge was 56,530 × 10⁶ m³ the budget deficit was −7,156 × 10⁶ m³. In this integrated system, the original data including graphs and attribution data could be stored in the database. When the process of evaluating and predicting groundwater flow was started, these data were transformed into files that the core program of MODFLOW could read. The calculated water level and drawdown could be displayed and reviewed online.     

地下水人工补给研究现状与前瞻

关于地下水人工补给的研究现状,本文从理论研究、方法技术及工程应用等方面进行了全面的归纳和总结;比较了国内外研究工作的新进展。通过分析表明,地下水人工补给在理论及其定量计算方法上的缺陷制约了其工程应用。结合当前研究的新进展,指出了地下水人工补给研究和工程应用领域存在的其他重要问题,从理论和实践两方面提出了地下水人工补给今后需要进一步加强研究的方向和任务。     

Quantitative and qualitative simulation of groundwater by mathematical models in Rafsanjan aquifer using MODFLOW and MT3DMS

Agriculture sector by using 80% of freshwater is the greatest water consumer in Iran. Excessive use of agricultural fertilizers in last decade, caused accumulation of enormous amounts of salts and subsequence declined the physical properties of soil. In desert and dry regions such as Rafsanjan plain, use of the groundwater resources is more than the surface water resources. Therefore, information about the quality of these resources remains a necessary task for optimum management, protection of water resources, and stopping the future damages. In this study, the groundwater quantity and quality of Rafsanjan plain was investigated by MODFLOW and MT3DMS. The presented quantitative model for this aquifer was compared by observed data and calibrated. This model was used to predict a 10-year period. Results show that water elevation decreases approximately 15 m for 10 years to come in this plain. Qualitative model results show that most quality parameters will increase. Electrical conductivity will increase more than other parameters. As values of this parameter will reach 16,000 µs/l for next 5 years. Therefore, we suggest that exploitation of water from these resources should be reduced and discharge from some of agricultural wells stop; also we suggested that recharge to groundwater resources should be increased and agricultural activities should be limited or improved using of modern irrigation systems in this plain.     

Relation of streams, lakes, and wetlands to groundwater flow systems

 Surface-water bodies are integral parts of groundwater flow systems. Groundwater interacts with surface water in nearly all landscapes, ranging from small streams, lakes, and wetlands in headwater areas to major river valleys and seacoasts. Although it generally is assumed that topographically high areas are groundwater recharge areas and topographically low areas are groundwater discharge areas, this is true primarily for regional flow systems. The superposition of local flow systems associated with surface-water bodies on this regional framework results in complex interactions between groundwater and surface water in all landscapes, regardless of regional topographic position. Hydrologic processes associated with the surface-water bodies themselves, such as seasonally high surface-water levels and evaporation and transpiration of groundwater from around the perimeter of surface-water bodies, are a major cause of the complex and seasonally dynamic groundwater flow fields associated with surface water. These processes have been documented at research sites in glacial, dune, coastal, mantled karst, and riverine terrains. Received, April 1998 · Revised, July 1998, August 1998 · Accepted, September 1998     

Quantification of groundwater discharge into lakes using radon-222 as naturally occurring tracer

A case study was carried out with the aim to practically test whether estimates of groundwater discharge rates into dredging lakes can be made via an uncomplicated and straightforward technique using radon-222 as naturally-occurring groundwater tracer. Lake Ammelshainer See, a dredging, seepage lake, approximately 25 km east of Leipzig, Germany, was chosen as the investigation site. In order to evaluate changes in the spatial and temporal radon-222 patterns in the lake during different stages of stratification, sampling campaigns were conducted in April 2007 (well mixed stage) and in May 2007 (thermal stratification stage). Groundwater flow estimates were made using a radon mass balance approach accounting for all radon fluxes into and out of the lake and assuming steady-state conditions with respect to these radon fluxes. Once all positive and negative radon fluxes related to the lake water volume were determined, groundwater discharge was estimated by using the advective radon input and the radon activity concentration of the pore water as key parameters. The results showed that in case of a lake with a size and shape of Lake Ammelshainer See (530,000 m²) reasonable groundwater discharge estimates can be made by collection and analyzing just a few water samples and a few samples from the sediment layer.     

The use of infiltration field tests for groundwater artificial recharge

 When using surface infiltration as a method of recharge, infiltration testing is considered an important additional data input along with other hydrogeologic data into the recharge decision. As part of an investigation into the potential for groundwater recharge, two desert basins in Jordan (Wadi Madoneh and Wadi Butum) were investigated to determine the possibility of recharge using floodwater retention structures. For each area, short-duration (up to 7-h) infiltration tests were conducted to estimate surface infiltration capacity of the upper soil layers in order to present to the authorities preliminary information which could be used along with other factors to aid in the selection of the best site for a pilot recharge project. Given the highly fractured rock formations that constitute the underlying aquifers in the two areas, it was assumed that the upper alluvium layers are the limiting factors in transmitting water to target aquifers. The infiltration tests conducted to estimate the recharge characteristics of the recharge sites yielded test results that indicated a representative infiltration rate of 0.44 m/day for the Wadi Madoneh site and 0.197 m/day for the Wadi Butum site. The data input was used subsequently with other decision factors to select the most promising site for the pilot project. Received: 9 January 1998 · Accepted: 27 April 1998     

改进的DRASTIC模型在地下水易污染性模糊评价中的应用

为了有效避免地下水系统遭受污染,保护地下水资源,采用改进的DRASTIC模型对地下水易污染性进行了评价.鉴于DRASTIC模型的诸多缺陷,将模糊综合评价方法运用到模型中,构建了各评价指标于各个级别的最优相对隶属度矩阵;引用语气算子确定指标权重,计算出了研究区样本集的级别特征值向量.将样本的易污染性进行排序,用研究区样段的水质评价结果进行了验证,结果证明,易污染性程度越高的地区综合评价水质越差;为进一步验证评价方法的真实性,将易污染性排序结果与传统DRASTIC法评价排序结果进行对比,两种方法排序一致.可见,本次改进的模型在克服了DRASTIC的诸多缺陷的同时,使得计算结果真实、可靠,且更加体现了计算过程的科学性与合理性.     

Use of deuterated water as a conservative artificial groundwater tracer

Conservative tracers are necessary to obtain groundwater transport velocities at the field scale. Deuterated water is an effective tracer for this purpose due to its similarity to water, chemical stability, non-reactivity, ease of handling and sampling, relatively neutral buoyancy, and reasonable price. Reliable detection limits of 0.1 mg deuterium/L may be obtained in field tests. A field example is presented in which deuterated water, bromide, and pentafluorobenzoic acid are used as groundwater tracers. Deuterated water appeared to be transported conservatively, producing almost identical breakthrough curves as that of other soluble tracers. Electronic Publication     

Integrating an artificial intelligence approach with k-means clustering to model groundwater salinity: the case of Gaza coastal aquifer (Palestine)

Artificial intelligence (AI) techniques have increasingly become efficient alternative modeling tools in the water resources field, particularly when the modeled process is influenced by complex and interrelated variables. In this study, two AI techniques—artificial neural networks (ANNs) and support vector machine (SVM)—were employed to achieve deeper understanding of the salinization process (represented by chloride concentration) in complex coastal aquifers influenced by various salinity sources. Both models were trained using 11 years of groundwater quality data from 22 municipal wells in Khan Younis Governorate, Gaza, Palestine. Both techniques showed satisfactory prediction performance, where the mean absolute percentage error (MAPE) and correlation coefficient (R) for the test data set were, respectively, about 4.5 and 99.8% for the ANNs model, and 4.6 and 99.7% for SVM model. The performances of the developed models were further noticeably improved through preprocessing the wells data set using a k-means clustering method, then conducting AI techniques separately for each cluster. The developed models with clustered data were associated with higher performance, easiness and simplicity. They can be employed as an analytical tool to investigate the influence of input variables on coastal aquifer salinity, which is of great importance for understanding salinization processes, leading to more effective water-resources-related planning and decision making.     

Late Quaternary volcanism in New Zealand: Towards an integrated record using distal airfall tephras in lakes and bogs

Studies on distal airfall tephra layers preserved in lake sediments and peats in northern New Zealand have documented the stratigraphic, chronologic, and compositional relationships of 46 eruptives, aged c. 17000–700yr BP, which originated from six North Island volcanic centres: Taupo (9 tephras), Okataina (8), Maroa (1) (rhyolitic); Mayor Island (2) (peralkaline); Tongariro (11), Egmont (15) (andesitic). Sources were distinguished by mineralogy and composition, field relations, and ¹⁴C chronology. All known rhyolitic tephra-producing eruptions from Taupo, Okataina, and Maroa volcanoes since c. 17000yr BP are represented, but only a small proportion of the known tephras erupted from Tongariro, Egmont, or Mayor Island volcanoes is recorded. The distal tephras from these latter volcanic centres may thus reflect atypically powerful (or oblique) eruptions, or dispersal by strong winds. An improved record of volcanism for the Tongariro, Egmont, and Mayor Island centres might be obtainable from suitable lakes or bogs more proximal to them.     

Simulating the influence of two shallow, flow-through lakes on a groundwater system: implications for groundwater mounds and hinge lines

Groundwater mounds and hinge lines are important features related to the interaction of groundwater and lakes. In contrast to the transient formation of groundwater mounds, numerical simulations indicate that permanent groundwater mounds form between closely spaced lakes as the natural consequence of adding two net sinks to a groundwater flow system. The location of the groundwater mound and the position of the hinge lines between the two lakes are intimately related. As the position of the mound changes there is a corresponding shift in the position of the hinge line. This results in a change in the ratio of groundwater inflow to outflow (Q_i/Q_o) for the lake. The response of the lake is an increase or decrease in the lake level. Our simulations indicate that the movement of the hinge line in a natural system is a consequence of the dynamic interrelationships between recharge, the slope of the water table upgradient and downgradient of the lake, and the loss of water from the lake by evaporation. The extent of the seasonal movement of the hinge line will vary from one year to the next depending on local changes in the magnitude of the hydrologic variables. Electronic Publication     

Interactions between groundwater and surface water: the state of the science

The interactions between groundwater and surface water are complex. To understand these interactions in relation to climate, landform, geology, and biotic factors, a sound hydrogeoecological framework is needed. All these aspects are synthesized and exemplified in this overview. In addition, the mechanisms of interactions between groundwater and surface water (GW–SW) as they affect recharge–discharge processes are comprehensively outlined, and the ecological significance and the human impacts of such interactions are emphasized. Surface-water and groundwater ecosystems are viewed as linked components of a hydrologic continuum leading to related sustainability issues. This overview concludes with a discussion of research needs and challenges facing this evolving field. The biogeochemical processes within the upper few centimeters of sediments beneath nearly all surface-water bodies (hyporheic zone) have a profound effect on the chemistry of the water interchange, and here is where most of the recent research has been focusing. However, to advance conceptual and other modeling of GW–SW systems, a broader perspective of such interactions across and between surface-water bodies is needed, including multidimensional analyses, interface hydraulic characterization and spatial variability, site-to-region regionalization approaches, as well as cross-disciplinary collaborations. Electronic Publication