Wellhead Protection Research Articles

Biofilms Controlling in Industrial Cooling Water Systems: A Mini-Review of Strategies and Best Practices.

Biofilm formation and growth is a significant concern for water treatment professionals, as it can lead to the contamination of water systems and pose a threat to public health. Biofilms are complex communities of microorganisms that adhere to surfaces and are embedded in an extracellular matrix of polysaccharides and proteins. They are notoriously difficult to control, as they provide a protective environment for bacteria, viruses, and other harmful organisms to grow and proliferate. This review article highlights some of the factors that favor biofilm growth, as well as various strategies for controlling biofilm in water systems. Adopting the best available technologies, such as wellhead protection programs, proper industrial cooling water system maintenance, and filtration and disinfection, can prevent the formation and growth of biofilms in water systems. A comprehensive and multifaceted approach to biofilm control can reduce the occurrence of biofilms and ensure the delivery of high-quality water to the industrial process.

Interplay of legacy irrigation and nitrogen fertilizer inputs to spatial variability of arsenic and uranium within the deep vadose zone

The vadose zone is a reservoir for geogenic and anthropogenic contaminants. Nitrogen and water infiltration can affect biogeochemical processes in this zone, ultimately affecting groundwater quality. In this large-scale field study, we evaluated the input and occurrence of water and nitrogen species in the vadose zone of a public water supply wellhead protection (WHP) area (defined by a 50-year travel time to groundwater for public supply wells) and potential transport of nitrate, ammonium, arsenic, and uranium. Thirty-two deep cores were collected and grouped by irrigation practices: pivot (n = 20), gravity (n = 4) irrigated using groundwater, and non-irrigated (n = 8) sites. Beneath pivot-irrigated sites, sediment nitrate concentrations were significantly (p < 0.05) lower, while ammonium concentrations were significantly (p < 0.05) higher than under gravity sites. The spatial distribution of sediment arsenic and uranium was evaluated against estimated nitrogen and water loading beneath cropland. Irrigation practices were randomly distributed throughout the WHP area and presented a contrasting pattern of sediment arsenic and uranium occurrence. Sediment arsenic correlated with iron (r = 0.32, p < 0.05), uranium negatively correlated to sediment nitrate (r = −0.23, p < 0.05), and ammonium (r = −0.19 p < 0.05). This study reveals that irrigation water and nitrogen influx influence vadose zone geochemistry and mobilization of geogenic contaminants affecting groundwater quality beneath intensive agricultural systems.

Analysis and comparison of wellhead protection areas delimitation methods applying a stochastic MODFLOW model as a reference.

Sustainable use of groundwater while maintaining economic and social development is a major challenge, and the implementation of wellhead protection areas (WHPA) for public supply wells has been applied as an instrument to overcome it. This study analyzes the WHPA delineation methods: calculated fixed radius (CFR) and two solutions of the WhAEM software (USEPA, 2018), one analytical and one semi-analytical. We compare their results with WHPAs generated by a stochastic three-dimensional MODFLOW-MODPATH model in two scenarios: eight pumping wells operating simultaneously and a single well pumping, both at the same public drinking water supply wellfield located on a coastal plain in Jaguaruna County, south Brazil. For the specific hydrogeological settings, all methods produced satisfactory results when delineating a 50-day time-of-travel (TOT) WHPA for a single well. However, as TOT increases, uncertainties are introduced, and the precision of the results is reduced. Multiple well pumping simultaneously presented similar issues regarding uncertainties caused by three-dimensional flow complexities resulting from well interferences. Despite being the simplest method applied in terms of hydrogeological data needs, the CFR method demonstrated reliability in its results. Additionally, we present an analysis comparing the dimensions of the capture zone with the 10- and 20-year TOT WHPAs, indicating that managing the entire capture zone is the best way to protect groundwater against conservative contaminants. Finally, we compare WHPA generated by a stochastic and a deterministic model to understand how uncertainties can affect model results.

The effects of influence radius and drawdown cone on the areas related to the protection of water wells

Determining a suitable protection zone around the pumping well is necessary to protect the quantity and quality of water. Multiple researchers have facilitated the determination of protective zones around the pumping wells by introducing specific definitions (concepts such as influence zone, capture zone, transport zone, and wellhead protection zone) and developing analytical and numerical methods. However, determining the quantitative and qualitative protection zones is still challenging. The influence zone is a region where the water level decreases due to well discharge. Since most concepts of “protective zones” depend on the influence zone, the current study focused on investigation of the drawdown cone and influence radius as two characteristics of the influence zone. Investigations were performed using the numerical MODFLOW model and the results were compared with some analytical models including Moench, Neuman, Theis, etc. The entire drawdown cone was considered to determine the protection zones of the pumping well. The influence radius solely represented one of the drawdown cone curves, and when calculated by the uncertain assumptions methods, significant amounts of volume and flow in the drawdown cone are ignored. The influence radius could not be considered as a definitive parameter, as this radial distance strongly depends on the definition.

Long Term Effectiveness of Wellhead Protection Areas

A preventive instrument to ensure the protection of groundwater is the establishment of wellhead protect areas (WPA) for public supply wells. The shape of the WPA depends on the rate of pumping and aquifer characteristics, such as the transmissivity, porosity, hydraulic gradient, and aquifer thickness. If any parameter changes after the design of the WPA, it will no longer be effective in protecting the aquifer and its catchment. With population growth in urban areas, the pressure on groundwater abstraction increases. Changes in flow, drawdowns and hydraulic gradients often occur. The purpose of this work is to evaluate the effectiveness of the WPA after a long period of establishment, in public wells with continuous pumping, located in densely populated urban area of the municipality of Montijo (Portugal). Considering the aquifer scenario in 2019, new extended WPAs were calculated using the combined results of three analytical methods and numerical modelling. In 2009 the aquifer presented hydraulic gradients varying between 0.0005 and 0.002, giving rise to a protection area with essentially circular shape. Although there was no increase in extraction flow, in 2019 the hydraulic gradients vary from 0.0008 to 0.008, and the flow directions have changed because of the water level decline. The shape of the WPA in this case is essentially elliptical and longer upstream and it can pose difficulties in the protection of public water catchments, in an urban area with already defined and consolidated land use. The best protection of the public supply wells in disturbed aquifers is obtained through numerical modeling.

Optimization-based clustering of random fields for computationally efficient and goal-oriented uncertainty quantification: Concept and demonstration for delineation of wellhead protection areas in transient aquifers

A general approach to deal with parameter uncertainty in natural systems is to use ensembles of many parameter realizations. However, this might result in extremely expensive computational time, especially when additional loops for transient simulation and for optimization are involved. One possibility to mitigate computing time is to use few but well-selected realizations that best represent the involved geological uncertainties, e.g., by clustering techniques.The goal of this paper is to address the search for representative realizations that best approximate the distribution and its tails of a model ensemble. In our test application, this ensemble is used to delineate wellhead protection areas (WHPAs) under transient flow conditions and subject to random heterogeneity of the aquifer. Our approach is based on clustering and proposes that the cluster medoids (representatives) should be optimized not for “statistical representation in the space of some selected proxy metrics”, but for “a minimum of decision-relevant errors”. And, if the underlying decision problem is multi-objective, then the clustering optimization can be made multi-objective, too. In this way, many subsequent analyses can be performed on the condensed set of representative scenarios that would be computationally too expensive otherwise, even if distribution tails and extreme realizations are relevant. We demonstrate the advantage of our clustering optimization methodology on a dynamic probabilistic WHPA delineation, and we compare its performance with a standard clustering analysis.Our results show that: (1) in probabilistic transient WHPA analysis, clustering is a suitable technique to account for geological uncertainty. (2) However, clustering analysis should be based on optimization concepts rather than on simple medoid concepts, and (3) of course, it should use problem-specific and decision-relevant metrics for cluster optimization. In our WHPA application, this leads to a more accurate representation of decision-relevant statistical extremes. (4) The additional extension to multi-objective cluster selection probes to be a valid approach in multi-objective WHPA delineation. (5) Using our framework, we reduce the computational cost of addressing highly expensive simulations.

Delineation of wellhead protection area based on the analytical elements method (AEM) – a case study with comparative research

The delineation of protection zones for groundwater intakes is a difficult task resulting from the significant variability of regional and local environmental conditions. Different methods are used, both simple (analytical or graphic), giving estimated results, and the most reliable, but also the most time-consuming ones, based on numerical groundwater flow models. An alternative method for the delineation of protection zones is the analytical elements method (AEM), which gives solutions like those obtained using FDM/FEM modelling methods with a relatively low degree of complexity. The estimated ranges of protection zones obtained with the use of four methods are presented for the selected test area (groundwater intake around Olesno). Results obtained with the use of the FDM model were taken as reference and CFR and SimpleWHPA were used as simplified methods. Comparative studies indicate that the results obtained by the CFR method differ significantly from the results of other methods, and their reliability is low. The results of the SimpleWHPA method are satisfactory, given the relative simplicity of the method. On the other hand, the results obtained with the AEM are close to the results obtained with the FDM treated as a reference. Considering that AEM is less time-consuming than FDM (which requires the most effort for proper model preparation), the use of AEM in the practice of protection zone delineation seems to be an interesting alternative.

Risk-Based Wellhead Protection Decision Support: A Repeatable Workflow Approach.

Environmental water management often benefits from a risk-based approach where information on the area of interest is characterized, assembled, and incorporated into a decision model considering uncertainty. This includes prior information from literature, field measurements, professional interpretation, and data assimilation resulting in a decision tool with a posterior uncertainty assessment accounting for prior understanding and what is learned through model development and data assimilation. Model construction and data assimilation are time consuming and prone to errors, which motivates a repeatable workflow where revisions resulting from new interpretations or discovery of errors can be addressed and the analyses repeated efficiently and rigorously. In this work, motivated by the real world application of delineating risk-based (probabilistic) sources of water to supply wells in a humid temperate climate, a scripted workflow was generated for groundwater model construction, data assimilation, particle-tracking and post-processing. The workflow leverages existing datasets describing hydrogeology, hydrography, water use, recharge, and lateral boundaries. These specific data are available in the United States but the tools can be applied to similar datasets worldwide. The workflow builds the model, performs ensemble-based history matching, and uses a posterior Monte Carlo approach to provide probabilistic capture zones describing source water to wells in a risk-based framework. The water managers can then select areas of varying levels of protection based on their tolerance for risk of potential wrongness of the underlying models. All the tools in this workflow are open-source and free, which facilitates testing of this repeatable and transparent approach to other environmental problems.

A new framework for experimental design using Bayesian Evidential Learning: The case of wellhead protection area

Groundwater management practices, such as sustainable drinking water extraction or contamination protection, can have significant socioeconomic impacts. A complete uncertainty analysis should ideally be performed to anticipate all possible outcomes and assess any risk. Uncertainties arise as a result of our limited understanding of the physical processes involved, as well as a scarcity of measurement data, whether directly or indirectly related to the physical parameters of interest. In this paper, we use a small number of tracing experiments (predictor) to predict the wellhead protection area (WHPA, target), the shape and extent of which are influenced by the distribution of hydraulic conductivity (K). Our first goal is to make stochastic predictions of the WHPA within the Bayesian Evidential Learning (BEL) framework, which uses machine learning to find a direct relationship between predictor and target. This relationship is learned using a small number of training models (400) drawn from the prior distribution of K. Forward modelling is used to obtain the 400 pairs of simulated predictors and targets. Newly collected field data can then be used directly to predict the approximate posterior distribution of the corresponding WHPA, obviating the need for the traditional step of data inversion. The number and location of data sources (injection wells) influence the posterior WHPA distribution's uncertainty range. Our second goal is to extend BEL to determine the optimal design of data source locations that minimises the WHPA's posterior uncertainty. Because the BEL model, once trained, allows the computation of the posterior uncertainty corresponding to any new input data, experimental design can be done explicitly, without averaging or approximating. We estimate the WHPA's posterior uncertainty range using the Modified Hausdorff Distance (MHD) and Structural Similarity (SSIM) index metrics. Because the breakthrough curves store information on a large area of the K field surrounding the pumping well, increasing the number of injection wells reduces the derived posterior WHPA uncertainty. Our method can also estimate which injection wells are more informative than others, as demonstrated by a k-fold cross-validation procedure. Overall, the application of BEL to experimental design allows for identifying data sources that maximise the information content of any measurement data while keeping budget constraints and computational costs to a minimum.

Delineation of wellhead protection zones: the analysis of main geological factors

Introduction. Analysis of the projects concerning wellhead protection (WHP) zones delineation shows the majority of the reports to use a simplified calculation. The applied analytical solutions do not refer to the actual geological conditions of the operating water intakes. The lack of distinct guidelines for geological data to be used in the research and the cost increase force the researchers to represent a simplified assessment. Materials and methods. The control of different WHP zone size geological parameters was studied by applying a series of theoretical calculations. Thus, software for analytical modelling of groundwater wells ANSDIMAT developed by the Institute of environmental geoscience, RAS, was used. Delineation of WHP zones is performed by the Particle-Tracking method. Results. Both size and geometry of WHP zones are controlled by several geological and hydrogeological parameters, which entail a synergetic effect. Within the parameters mentioned above, there are such as 1) pumping discharge; 2) aquifer thickness; 3) accessible porosity; 4) flow direction and the hydraulic gradient; 5) hydraulic conductivity; 6) the hydraulic connectivity of an aquitard. Our research shows all six factors perceptibly influence the results. To avoid significant errors each of the factors should be taken into account. Conclusion. Regulations actualization and the Guideline for delineation of wellhead protection zones, in particular, remain to be an area for improvement. Clear requirements for geological and hydrogeological parameter contamination, parameters uncertainty.

Delineation of Wellhead Protection Areas: Methodology and Application

About 97% of global fresh water is sourced from Groundwater, positioning it as an important, and sometimes the sole, source of drinking-water in many parts of the world. Sustainable Development Goals, Goal No. 6, calls to foster all efforts to ensure access to water and sanitation for all. Nevertheless, with groundwater providing nearly half the world population with drinking water, the responsibly of sustaining this resource is a priority to all. Pumping wells can sometimes, if not carefully protected, be an instant source of pollution to the groundwater. Wellhead protection areas (WHPAs) serve the purpose of protecting the quality of groundwater by means of restrictions imposed on land use activities within the WHPA. Many approaches are being used to delineate WHPAs all over the world. The study used the numerical groundwater flow modeling with particle tracking codes approach, as it allows full interaction of hydrogeological, land-use, PCS, and different extraction rates in delineating the WHPA. The study area is a drinking water plant, located in Menofia Governorate and belongs to the Nile Delta aquifer. The study used 50-day isochron horizontal travel distance for the three pumping wells, located in the drinking water plant. The WHPA radius was determined for wells and the resulted radii range from 37m to 54.5m. Keywords: Wellhead protection area, groundwater protection, contaminant transport, MT3D, groundwater modelling DOI: 10.7176/CER/13-4-04 Publication date: June 30 th 2021

Outcomes of the first combined national survey of pesticides and emerging organic contaminants (EOCs) in groundwater in New Zealand 2018

The first national survey of Emerging Organic Contaminants (EOCs) involved sampling 121 wells located throughout New Zealand and analysis for a suite of 29 EOCs. This survey was carried out in conjunction with the 2018 national survey of pesticides in groundwater, a survey that is conducted on a four-yearly basis which included the analysis of glyphosate for first time. A total of 227 EOCs were detected in the 85 wells (70%). There were 29 different EOCs in the analytical suite and 25 different EOCs were detected in at least one well. The highest concentration measured was 655 ng/L for sucralose, an artificial sweetener. These results indicate that EOCs, sourced from either animal or human effluents/activities, are making their way into shallow groundwater systems and can be detected at low concentrations. A total of 135 wells were analysed for glyphosate, glufosinate and their principal metabolites. There was only one detection of glyphosate at a concentration of 2.1 μg/L. This well showed evidence of poor wellhead protection and the contamination likely came from containers that were stored near the well. A total of 279 wells were sampled and analysed for pesticides and 68 wells (24.4%) contained detectable residues of pesticides, with 28 of these wells having two or more pesticides detected. The maximum number of pesticides detected in one well was six. None of the sampled wells exceeded the Maximum Acceptable Value (MAV) for drinking water in New Zealand and the concentrations of most of the detected pesticides were equivalent to less than 0.5% of the MAV. Comparisons with earlier National Surveys of pesticides in groundwater in New Zealand indicate the frequencies of pesticide detections have remained similar over the last 16 years, with higher detection frequencies occurring before that time.

Managed Aquifer Recharge at a Farm Level: Evaluating the Performance of Direct Well Recharge Structures

A field study evaluated the performance of direct well recharge structures (DWRS) in order to harvest and filter farm runoff and its discharge into open dug wells to augment groundwater recharge. This was undertaken between 2016 and 2018 using a total of 11 wells in the Dharta watershed, situated in a semi-arid hardrock region of Udaipur district, Rajasthan, India. The depth to water level in each DWRS well was monitored weekly for 1 to 3 years before and after the DWRS was established, and water samples were taken for water quality analysis (pH, electrical conductivity (EC), total dissolved solids (TDS), turbidity, fluoride, and Escherichia coli) before and during the monsoon period. For each DWRS well, two control wells in close proximity were also monitored and sampled. Five of the DWRS established in 2018 also had flow meters installed in order to measure discharge from the filter to the well. The volume of water recharged through DWRS into individual wells during the 2018 monsoon ranged from 2 to 176 m3 per well. Although the mean rise in water levels over the monsoon was higher in DWRS wells than in nearby control wells, the difference was not significant. Values of pH, EC, TDS, and F decreased in DWRS and control wells as each monsoon progressed, whereas the turbidity of wells with DWRS increased slightly. There was no significant difference between DWRS and control wells for pH, EC/TDS, turbidity, or fluoride. The presence of E. coli in DWRS wells was higher than in control wells, however, E. coli exceeded drinking water guidelines in all sampled wells. On the basis of this study, it is recommended that rural runoff should not be admitted to wells that are used for, or close to, wells used for drinking water supplies, even though salinity and fluoride concentrations may be reduced. For this study, none of the 11 DWRS wells produced sufficient additional recharge to potentially increase dry season irrigation supplies to justify expenditure on DWRS. This even applies to the DWRS well adjacent to a small ephemeral stream that had a significantly larger catchment area than those drawing on farmers’ fields alone. An important and unexpected finding of this study was that no sampled open dug well met drinking water standards. This has led to a shift in local priorities to implement well-head water quality protection measures for wells used for drinking water supplies. It is recommended that parapet walls be built around the perimeter of such dug wells, as well as having covers be installed.

A Dual Delineation Approach to Untangle Interferences in Well Doublets Systems.

Traditional numerical methods for the delineation of wellhead protection areas span deterministic and probabilistic approaches. They provide time-related capture zones. However, none of the existing approaches identifies the groundwater contribution areas related to each source or sink. In this work, the worthiness of the so-called double delineation approach was extended. This task was achieved by simple postprocessing of its dual outputs leading to a highly efficient screening tool. In the particular context of geothermal resources management through the well doublets of the Dogger aquifer in the Paris Basin (France), the approach was extended to forecast the compositional heat breakthrough at production wells. Hence, cold-water breakthrough and temperature decline in production wells are timely assessed in low-enthalpy geothermal reservoirs. The method quantifies how groundwater volumes are moving through space and time between any couple of source and sink. It provides unprecedented tools advancing the enhanced understanding of water resources systems functioning. It is highly recommended to implement the presented concepts in the current and future generations of community groundwater models.

Determination of the travel time and path of pollution in Iranshahr aquifer by particle-tracking model

Recognitions and predictions of the contamination origin are essential steps in the protective measures to avoid well-water contamination and the first step in managing groundwater resources. In this regard, finite-difference model software (GMS 10.0.6) was used to model the transport path, the origin of contaminants and to determine the wellhead protection area in Iranshahr aquifer. Since contamination transport models require a calibrated groundwater flow model, we first prepared this model. Accordingly, after collecting all geological, meteorological, hydrological and hydrogeological data (based on the maps, geophysical tests and exploratory borehole drilling, rainfall statistics and groundwater level in exploitation wells), a database was constructed in ArcGis10.1 software and a conceptual model was developed by transporting this information to GMS software. Based on the developed model, the aquifer’s groundwater level was simulated, calibrated and validated using MODFLOW2000 code in GMS software. The particle transport model in the aquifer was provided to examine and model the transport path and the origin of contaminants through MODPATH module. In the end, the aquifer wells’ protection area against contaminants was illustrated. According to the results, contaminant transport path in the wells of central plains is directed from the river to the wells, in forward particle-tracking model; the maximum time taken by particles is 508,952.5 days, the minimum time is 144 days, and the average radius of 50-day wellhead protection area based on the protection against contaminations such as pathogenic bacteria in Iranshahr aquifer was determined to be about 100 m.

Mapping fecal pollution in rural groundwater supplies by means of artificial intelligence classifiers

Fecal contamination poses a threat to groundwater supplies in low income regions. This is often due to the coexistence of pit latrines with domestic wells in densely populated areas. In this context, developing alternative methodologies to map fecal pollution in shallow wells is needed. A thorough survey of over 240 domestic wells and 570 pit latrines was conducted in a rural town of southern Mali. Water samples were collected from all wells and tested for temperature, pH, electric conductivity, total dissolved solids, turbidity and thermotolerant coliforms. The outcomes of the field survey were incorporated into a GIS database. Thirteen machine leaning classifiers, including different statistical algorithms, instance-based learners and tree-based models, were used to determine the spatial distribution of fecal pollution as per five explanatory variables (latrine density, distance to the closest latrine, borehole yield, water table depth and population density). The best performing classifiers, selected on test scores, were then used to develop predictive maps. Random forest and logistic regression rendered prediction scores for fecal pollution in excess of 0.90. Multilayer perceptrons, support vector machines and quadratic discriminant analyses also proved adept at forecasting fecal pollution. Ensemble mapping shows that 30–50 m buffers around domestic wells may be sufficient to prevent contamination of domestic supplies in most instances. This demonstrates that machine learning may provide a versatile methodological alternative to traditional Darcian approaches. On the other hand, the practical difficulties involved in maintaining wellhead protection areas suggests the need to implement piped water supplies.

Addressing Italy’s urban flooding problems through the holistic watershed approach by using blue/green infrastructure

Water resources have been neglected and stressed for many years, as anthropogenic changes in watersheds have increased runoff, decreased infiltration and aquifer recharge, caused stream incision and streambank erosion and degraded water quality and water resources. The watershed is the management unit to begin to solve stormwater problems and flooding issues. Reversing the mismanagement from the past is a complicated process and must consider a holistic approach factoring in all the processes that cause the aforementioned problems. There are many technological tools such as GIS and hydrologic, hydraulic and water quality models that help pinpoint the sources of problems in the watershed and help derive at a comprehensive solution. The objective of this paper is to provide researchers and practitioners a systematic, methodical and proven approach to documenting and solving water management issues cause by unmanaged anthropogenic changes that have occurred in rural and urban watersheds. There are many regulations and literature about flooding and watershed plans with very detailed guidelines composed by state authorities, however, there are few that completely address the comprehensive, inclusive approach to watershed management to solve a variety of problems. For example, the State of Pennsylvania, USA has separate flood plain management, stormwater management, erosion and sediment pollution control and nonpoint discharge and elimination system (NPDES), and water supply / wellhead protection programs and regulations as opposed to one single “water resources management” regulatory program. This paper defines an innovative approach to overcome some of the restrictions placed on engineers and planners by regulatory programs.

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Viruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead protection areas. To show this, we use the dolostones of the Permian Magnesian Limestone aquifer in NE England, where we incorporated such information in a groundwater flow and particle tracking model. Within this aquifer, flow in relatively narrow (mechanical aperture of ~ 10−1–1 mm) fractures is coupled with that in pipe cavities (~ 0.20-m diameter) following normal faults. Karstic cavities and narrow fractures are hydraulically very different. Thus, the solutional features are represented within the model by a pipe network (which accounts for turbulence) embedded within an equivalent porous medium representing Darcian flowing fractures. Incorporation of fault conduits in a groundwater model shows that they strongly influence particle tracking results. Despite this, away from faulted areas, the effective flow porosity of the equivalent porous medium remains a crucial parameter. Here, we recommend as most appropriate a relatively low value of effective porosity (of 2.8 × 10−4) based on borehole hydrogeophysical testing. This contrasts with earlier studies using particle tracking analyses on analogous carbonate aquifers, which used much higher values of effective porosity, typically ~ 102 times higher than our value, resulting in highly non-conservative estimates of aquifer vulnerability. Low values of effective flow porosities yield modelled flow velocities ranging from ~ 100 up to ~ 500 m/day in un-faulted areas. However, the high fracturing density and presence of karstic cavities yield modelled flow velocities up to ~ 9000 m/day in fault zones. The combination of such flow velocities along particle traces results in 400-day particle traces up to 8-km length, implying the need for large well protection areas and high aquifer vulnerability to slowly degrading contaminants.

Comparative Study of Methods for Delineating the Wellhead Protection Area in an Unconfined Coastal Aquifer

Various delineation methods, ranging from simple analytical solutions to complex numerical models, have been applied for wellhead protection area (WHPA) delineation. Numerical modeling is usually regarded as the most reliable method, but the uncertainty of input parameters has always been an obstacle. This study aims at examining the results from different WHPA delineation methods and addressing the delineation uncertainty of numerical modeling due to the uncertainty from input parameters. A comparison and uncertainty analysis were performed at two pumping sites—a single well and a wellfield consisting of eight wells in an unconfined coastal aquifer in Israel. By appointing numerical modeling as the reference method, a comparison between different methods showed that a semi-analytical method best fits the reference WHPA, and that analytical solutions produced overestimated WHPAs in unconfined aquifers as regional groundwater flow characteristics were neglected. The results from single well and wellfield indicated that interferences between wells are important for WHPA delineation, and thus, that only semi-analytical and numerical modelling are recommended for WHPA delineation at wellfields. Stochastic modeling was employed to analyze the uncertainty of numerical method, and the probabilistic distribution of WHPAs, rather a deterministic protection area, was generated with considering the uncertain input hydrogeological parameters.

Dynamic re-distribution of pumping rates in well fields to counter transient problems in groundwater production

Groundwater modelers usually delineate Wellhead protection areas (WHPAs) assuming steady-state flow conditions. However, time-varying groundwater flow conditions dynamically change the area from which the water is actually pumped. For instance, seasonal changes in the ambient flow direction might bring locations with hazardous land use activities (e.g., gas stations or agricultural lands) into the actual abstraction zone for parts of the year. Thus, steady-state WHPA solutions can become inadequate for reliable drinking water well protection. Of course, one might simply enlarge the delineated WHPA to account for all seasonal conditions, but this could lead to a massive enlargement of required WHPAs.The goal of this paper is to present a management scheme that reduces the influence of transient flow on the actual abstraction zone by optimally re-distributing pumping rates within well fields. We solve our management problem utilizing time-dependent multiobjective optimization (MOO) concepts to search for compromise solutions that consider three objectives: 1) to minimize the risk of pumping water from outside a given WHPA, 2) to minimize the gap between groundwater supply and demand and 3) to minimize the involved costs of pumping. Additionally, we address aquifer heterogeneity through scenarios representative of the uncertainty in hydraulic conductivity. Our results from a synthetic application case show that: 1) The competitiveness among the objectives shows that the MOO formulation is a valid approach 2) An optimal dynamic pumping scheme can indeed reduce the transient influence on the actual abstraction zone while still covering the groundwater demand. 3) Implementing optimal pumping rates leads to a more densely utilized and more static capture area. 4) Geological uncertainty has an important influence on the obtained optimal set of solutions and should be included via Monte Carlo simulation.