Wellhead Protection Research Articles

Insights from four decades of model development on the Waterloo Moraine: A review

Modelling has played a key role in the evolution of insights on the Waterloo Moraine groundwater system as a water source for Waterloo Region. As models evolved over the last four decades, so did new insights. Starting from a simple layer-cake concept, models eventually became three-dimensional, while the focus changed from well interference to multi-layer analysis, capture zone delineation, wellhead protection areas, groundwater age and the prediction of impact due to various land uses and threats. An important insight gained was that the reliability of predictive methods depends heavily on the travel paths from source to receptor, which in turn depend on the connectivity between the various hydrogeologic units – i.e. the conceptual model. The elusive issue of predictive uncertainty in the delineation of well capture zones is approached at two scales: the local scale representing uncertainty due to heterogeneities within the individual aquifer units, and the global scale representing different conceptualizations and scenarios, where the latter is found to be the dominant uncertainty. In the case of a multi-scenario analysis involving scenarios of equal plausibility, the precautionary approach can be used to arrive at a conservative prediction. Practical applications provide insights on the dynamics of groundwater systems, the impact of changes and threats being imposed and the effectiveness of mitigation measures, as well as the time scale at which threats and mitigation measures act. These insights should help hydrogeologists to use models more effectively, and to better understand and manage predictive uncertainties that inevitably arise in dealing with complex groundwater systems such as the Waterloo Moraine.

Groundwater source contamination mechanisms: Physicochemical profile clustering, risk factor analysis and multivariate modelling

An integrated domestic well sampling and "susceptibility assessment" programme was undertaken in the Republic of Ireland from April 2008 to November 2010. Overall, 211 domestic wells were sampled, assessed and collated with local climate data. Based upon groundwater physicochemical profile, three clusters have been identified and characterised by source type (borehole or hand-dug well) and local geological setting. Statistical analysis indicates that cluster membership is significantly associated with the prevalence of bacteria (p=0.001), with mean Escherichia coli presence within clusters ranging from 15.4% (Cluster-1) to 47.6% (Cluster-3). Bivariate risk factor analysis shows that on-site septic tank presence was the only risk factor significantly associated (p<0.05) with bacterial presence within all clusters. Point agriculture adjacency was significantly associated with both borehole-related clusters. Well design criteria were associated with hand-dug wells and boreholes in areas characterised by high permeability subsoils, while local geological setting was significant for hand-dug wells and boreholes in areas dominated by low/moderate permeability subsoils. Multivariate susceptibility models were developed for all clusters, with predictive accuracies of 84% (Cluster-1) to 91% (Cluster-2) achieved. Septic tank setback was a common variable within all multivariate models, while agricultural sources were also significant, albeit to a lesser degree. Furthermore, well liner clearance was a significant factor in all models, indicating that direct surface ingress is a significant well contamination mechanism. Identification and elucidation of cluster-specific contamination mechanisms may be used to develop improved overall risk management and wellhead protection strategies, while also informing future remediation and maintenance efforts.

Nine Steps to Risk‐Informed Wellhead Protection and Management: A Case Study

Wellhead-protection zones are commonly delineated on the basis of advective travel-time analysis without considering any aspects of model uncertainty. In the past decade, research efforts have produced quantifiable risk-based safety margins for protection zones. These margins are based on well-vulnerability criteria (e.g., travel times, exposure times, peak concentrations) and take model and parameter uncertainty into account. There are three main reasons why practitioners still refrain from applying these new techniques. (1) They fear the additional areal demand of probabilistic safety margins; (2) probabilistic approaches are allegedly complex, not readily available and require huge computing resources, and (3) uncertainty bounds are fuzzy, whereas final decisions are binary. The primary goal of this paper is to show that these reservations are unjustified. We present a straightforward, computationally affordable framework that offers risk-informed decision support for robust and transparent wellhead delineation under uncertainty. We show that reliability levels can be increased by exchanging delineated low-risk areas for previously nondelineated high-risk areas. We also show that further improvements may often be available with only little additional delineated area. As proof of our concept, we illustrate our key points with the example of a pumped karstic well catchment, located in Germany.

Controlling scaling metrics for improved characterization of well-head protection regions

Summary We addressed the value of hydrogeological information on the assessment of the risk that an operating pumping well is polluted. The work considered a heterogeneous aquifer and focused on the statistical characterization of the contaminant mass fraction from a diffused source recovered at the well and the solute arrival times. We explored the role of the key length scales that characterize and control the well capture region and its probabilistic delineation with respect to the contaminant source location and size. The impact of augmenting the data-base of hydraulic information on the reduction of uncertainty associated with the environmental scenario analyzed was then investigated. It was found that obtaining a robust characterization of the target Environmental Performance Metrics (EPMs) depends on the length scale considered. For the sampling scheme considered, the importance of conditioning on the probability distributions of solute mass fraction and travel times is strongly affected by the location of the contaminant source within the probabilistic well catchment. With reference to the characterization of the travel time distribution associated with the recovery of a given mass fraction, the worth of augmenting the hydraulic parameter data-sets tends to decrease with decreasing solute residence time within the well catchment.

Wellhead protection area delineation using multiple methods: a case study in Beijing

Determining a wellhead protection area (WHPA) is a basic and important step in protecting groundwater from contamination. Based on availability of data and complexity of hydrogeological conditions, different delineation methods can be adopted. This study’s objective was to examine the relation and difference of the results calculated using six WHPA delineation methods, which ranged from simplified shapes to stochastic models with superior sampling means. All the methods were applied to a well field in Beijing, China. The WHPA probability distribution from a stochastic simulation was used as reference for comparison with other methods. WHPAs calculated using simplified and analytical approaches turned out to be smaller than reference WHPA. Those calculated using the numerical model provided better results but still cannot include a considerable area of reference WHPA. The stochastic approach based on efficient orthogonal Latin hypercube sampling provided an estimation of the probability distribution of WHPA delineation with different degrees of uncertainty, which played an important role in the WHPA delineation of the well field in Beijing. To attain a realistic WHPA delineation in a complex aquifer system, various delineation approaches can be adopted and all results that validate each other must be considered.

Water Sources and Their Protection from the Impact of Microbial Contamination in Rural Areas of Beijing, China

Bacterial contamination of drinking water is a major public health problem in rural China. To explore bacterial contamination in rural areas of Beijing and identify possible causes of bacteria in drinking water samples, water samples were collected from wells in ten rural districts of Beijing, China. Total bacterial count, total coliforms and Escherichia coli in drinking water were then determined and water source and wellhead protection were investigated. The bacterial contamination in drinking water was serious in areas north of Beijing, with the total bacterial count, total coliforms and Escherichia coli in some water samples reaching 88,000 CFU/mL, 1,600 MPN/100 mL and 1,600 MPN/100 mL, respectively. Water source types, well depth, whether the well was adequately sealed and housed, and whether wellhead is above or below ground were the main factors influencing bacterial contamination levels in drinking water. The bacterial contamination was serious in the water of shallow wells and wells that were not closed, had no well housing or had a wellhead below ground level. The contamination sources around wells, including village dry toilets and livestock farms, were well correlated with bacterial contamination. Total bacterial counts were affected by proximity to sewage ditches and polluting industries, however, proximity to landfills did not influence the microbial indicators.

An integrated approach for addressing uncertainty in the delineation of groundwater management areas

Uncertainty is a pervasive but often poorly understood factor in the delineation of wellhead protection areas (WHPAs), which can discourage water managers and practitioners from relying on model results. To make uncertainty more understandable and thereby remove a barrier to the acceptance of models in the WHPA context, we present a simple approach for dealing with uncertainty. The approach considers two spatial scales for representing uncertainty: local and global. At the local scale, uncertainties are assumed to be due to heterogeneities, and a capture zone is expressed in terms of a capture probability plume. At the global scale, uncertainties are expressed through scenario analysis, using a limited number of physically realistic scenarios. The two scales are integrated by using the precautionary principle to merge the individual capture probability plumes corresponding to the different scenarios. The approach applies to both wellhead protection and the mitigation of contaminated aquifers, or in general, to groundwater management areas. An example relates to the WHPA for a supply well located in a complex glacial aquifer system in southwestern Ontario, where we focus on uncertainty due to the spatial distributions of recharge. While different recharge scenarios calibrate equally well to the same data, they result in different capture probability plumes. Using the precautionary approach, the different plumes are merged into two types of maps delineating groundwater management areas for either wellhead protection or aquifer mitigation. The study shows that calibrations may be non-unique, and that finding a "best" model on the basis of the calibration fit may not be possible.

Delineating cost‐effective wellhead protection zones in a rural area in Greece

AbstractThe aim of this study is the protection of groundwater resources from nitrate pollution by regulating land use and by establishing guidelines for agricultural activities within specific wellhead protection areas. Wellhead protection zones are specifically designed in four wells in the municipality of Nea Moudania, an area of intensive agricultural activities in northern Greece. Recent water samples from these wells indicate high levels of nitrates concentrations. Wellhead protection areas are delineated through a geographic information systems (GIS) analysis in order to determine the boundaries of protection zones, as well as to identify the land use patterns and the specific crop types around the contaminated wells. Different land use management techniques for groundwater protection zoning are also examined with respect to their implementation cost. The purpose of this analysis is to identify the least expensive management strategy for wellhead protection. The results show that land use changes are always more expensive than implementing agro‐environmental measures.

Avaliação de métodos para a proteção dos poços de abastecimento público do Estado de São Paulo

Os perímetros de proteção de poços têm importante papel na proteção da qualidade da água subterrânea explotada para fins de abastecimento público. Existem vários métodos que permitem definir as dimensões e os formatos das zonas de contribuição, ou seja, a área em superfície onde toda recarga do aquífero é captada pelo poço, além de zonas baseadas em tempos de trânsito, definidas no tempo em que um determinado contaminante pode alcançar o poço. Ambas as zonas permitem o controle do uso do solo com o objetivo de proteger a captação. Este artigo apresentou um estudo comparativo entre três diferentes métodos aplicados nos diferentes aquíferos do Estado de São Paulo. Os métodos estudados foram: raio fixo calculado, baseado na técnica do cilindro, que usa equação de fluxo volumétrico; modelo analítico, com uso da equação de fluxo uniforme; e modelo numérico, por meio de modelos matemáticos de simulação de fluxo. Os resultados mostraram que cada método gerou áreas diferentes, tanto em formato como em dimensões. Os dois primeiros métodos definiram tamanhos de zonas de contribuição semelhantes, porém com formatos diferentes, e aproximadamente 200% maiores do que aqueles definidos com o numérico para as mesmas condições hidrogeológicas. Pelos resultados, depreende-se que a utilização do método analítico é viável numa primeira avaliação, pois os dados para tal já se encontram disponíveis para quase todos os poços de abastecimento público do Estado e sua acurácia é superior ao método raio fixo calculado. Já numa fase posterior, na qual a definição das zonas de contribuição seja mais sensível, o modelo numérico seria a alternativa natural.

Capture zone of a multi-well system in confined and unconfined wedge-shaped aquifers

In this paper we present the equation of capture zone of a multi-well system in wedge-shaped confined and unconfined aquifers. Three wedge boundary configurations: barrier–barrier wedge, barrier–constant head wedge and constant head–constant head wedge are considered. The well system may be consisted of any number of production or injection wells or a combination of both with various flow rates. Method of image wells is used in the wedge-shaped domain and an appropriate complex function is formulated to find the capture zone. The stream function and velocity potential are derived from the imaginary part and real part of the complex function, respectively. Solutions are provided for the wedge domains with and without a uniform regional flow and can also be used for aquifers of infinite extent. The presented equations are of general character and have removed the limitations of the previous equations in regards to well numbers, positions and types, extraction/injection rate, and regional flow rate and direction. Capture envelopes are presented in dimensionless form which can be used as tools in real engineering practices to plan pump-and-treat operations, groundwater remediation projects or well-head protection plans. It is also demonstrated that the equations may also be used for the verification of numerical models. The developed equations are constrained by the image well theory limitations.

Aquifer Vulnerability Assessment and Wellhead Protection Areas to Prevent Groundwater Contamination in Agricultural Areas: An Integrated Approach

To implement successful policies for the protection of groundwater and curtail the possibility of water supply contamination, an early evaluation of aquifer vulnerability is needed. Rather than implementing broad restrictions to land use and effluent discharge, it is more cost-effective and economically favourable to approach protection in a stepwise manner by first assessing the intrinsic vulnerability of the aquifer when defining the level of land use control that is needed to protect groundwater quality. Following aquifer vulnerability evaluation, specific land uses and restrictions should be defined locally for each water supply within the wellhead protection areas (WHPAs), which are identified by means of the groundwater time of travel (TOT). The WHPA should be established for each individual situation, considering the level of vulnerability of the exploited aquifer. We applied our findings to a specific test site in the Piemonte region of NW Italy, following the current local procedure for individuating the WHPAs. Using data gathered from this site-specific exercise, we identified that the procedure allows methods that consider only aquifer parameters to evaluate vulnerability and discourages the use of techniques that already compartmentalize soil parameters in the vulnerability assessment.

Protection of groundwater intended for human consumption: a proposed methodology for defining safeguard zones

Carbonate aquifers constitute a water reserve of essential importance for human supply. For this, it is necessary to establish suitable protection measures in order to achieve the good status of groundwater bodies intended for human supply according to the requirements of the Water Framework Directive. The objective of this paper is to present a methodology to define safeguard zones for the protection of carbonate groundwater bodies intended for human consumption. To do this, firstly the risk of groundwater contamination is evaluated through a combination of characterising pressures and the evaluation of the intrinsic vulnerability to contamination. Secondly, the existing water abstraction points are identified and their zones of contribution are delineated in order to establish priorities when defining protective measures in the region. Finally, the existing wellhead protection areas and those defined according to the proposed methodology must be integrated into the delineated safeguard zones. The results obtained in a carbonate groundwater body in southern Spain are consistent with the existing quality data and they show the percentage of land that must be protected to preserve the quality of water intended for human consumption, thus facilitating their future integration into adequate land use planning tools.

Approximate Solutions for Radial Travel Time and Capture Zone in Unconfined Aquifers

Radial time-of-travel (TOT) capture zones have been evaluated for unconfined aquifers with and without recharge. The solutions of travel time for unconfined aquifers are rather complex and have been replaced with much simpler approximate solutions without significant loss of accuracy in most practical cases. The current "volumetric method" for calculating the radius of a TOT capture zone assumes no recharge and a constant aquifer thickness. It was found that for unconfined aquifers without recharge, the volumetric method leads to a smaller and less protective wellhead protection zone when ignoring drawdowns. However, if the saturated thickness near the well is used in the volumetric method a larger more protective TOT capture zone is obtained. The same is true when the volumetric method is used in the presence of recharge. However, for that case it leads to unreasonableness over the prediction of a TOT capture zone of 5 years or more.

Capture Zone of a Partially Penetrating Well with Skin Effects in Confined Aquifers

The analysis of the capture zone of wells is useful to design pumping systems and wellhead protection programs. In this study, an analytical solution for the head distribution of a partially penetrating well, and semi-analytical methods to determine the geometry of the capture surface are presented. The analytical solution is derived based on an infinitesimal radius under a constant pumping rate in a two-zone confined aquifer. Using the developed solution, a sensitivity analysis is performed to study the influence of skin on the drawdown, location of the stagnation point, maximum horizontal and vertical extent of the capture surface. The results show the efficiency of a partially penetrating well in the plume removal process is different for positive and negative skins. Also it can be concluded, the skin effect will decrease as the degree of penetration and pumping discharge of the well increase. Generally, the thickness of the skin zone is an influential factor in well hydraulics and hydraulic head distribution. However, it can be seen where the skin zone is less than some specific values, the skin effect is not a significant factor, thus, the geometry of the capture surface can be obtained by assuming a single-zone aquifer. Moreover, the effects of different parameters (pumping rates, degree of penetration of the well, thickness of the skin zone, etc.) on the capture zone are studied.

Probabilistic exposure risk assessment with advective–dispersive well vulnerability criteria

Time-related advection-based well-head protection zones are commonly used to manage the contamination risk of drinking water wells. According to current water safety plans advanced risk management schemes are needed to better control and monitor all possible hazards within catchments. The goal of this work is to cast the four advective–dispersive intrinsic well vulnerability criteria by Frind et al. [1] into a framework of probabilistic risk assessment framework. These criteria are: (i) arrival time, (ii) level of peak concentration, (iii) time until first arrival of critical concentrations and (iv) exposure time. Our probabilistic framework yields catchment-wide maps of probabilities to not comply with these criteria. This provides indispensable information for catchment managers to perform probabilistic exposure risk assessment and thus improves the basis for risk-informed well-head management. We resolve heterogeneity with high-resolution Monte Carlo simulations and use a new reverse formulation of temporal moment transport equations to keep computational costs low. Our method is independent of dimensionality and boundary conditions, and can account for arbitrary sources of uncertainty. It can be coupled with any method for conditioning on available data. For simplicity, we demonstrate the concept on a 2D example that includes conditioning on synthetic data.

Probabilistic risk analysis and fault trees: Initial discussion of application to identification of risk at a wellhead

Wellhead protection is of critical importance for managing groundwater resources. While a number of previous authors have addressed questions related to uncertainties in advective capture zones, methods for addressing wellhead protection in the presence of uncertainty in the chemistry of groundwater contaminants, the relationship between land-use and contaminant sources, and the impact on health of the receiving population are limited. It is herein suggested that probabilistic risk analysis (PRA) combined with fault trees (FT) provides a structure whereby chemical transport can be combined with uncertainties in source, chemistry, and health impact to assess the probability of negative health outcomes in the population. As such, PRA-FT provides a new strategy for the identification of areas of probabilistically high human health risk. Application of this approach is demonstrated through a simplified case study involving flow to a well in an unconfined aquifer with heterogeneity in aquifer properties and contaminant sources.

Conceptual Framework for Protecting Groundwater Quality

A conceptual framework is defined to establish safeguard zones in groundwater bodies intended for drinking water according to the requirements of the Water Framework Directive. For this, the foundations of a three-phase methodology within a dynamic process are proposed. The results of the first two phases are presented, which contemplate the distribution of groundwater body abstraction points as well as hydrogeological criteria, evaluation of pressures and aquifer vulnerability, in addition to the defined wellhead protection areas of abstraction points. As a final proposal, it will be necessary for competent authorities to create a recommendations and restrictions guideline, which should be integrated into the rest of the policies related to land-use planning in order to protect groundwater adequately.

Groundwater Protection Using Vulnerability Maps and Wellhead Protection Area (WHPA): A Case Study in Mexico

The need to protect groundwater resources against quality deterioration due to anthropogenic activities is unquestionable. The concept of aquifer pollution vulnerability maps and of wellhead protection areas (WHPA) as protection tools is not new; however, in spite of the elapsed time, their use has been increased as a result of the increase in economic development—and everything that this entails—and the increase in prohibitive costs of treating contaminated water or of the decontamination of aquifers. The study’s objective was to establish an integrated method that defines, first of all, the areas of highest vulnerability in the aquifer, and second, within these areas, the wells that most urgently need protection. To identify these wells, additional criteria were taken, such as well constructive data, pumped volume, and the region’s socioeconomic characteristics (social exclusion index). Once the wells were ranked, several of them were chosen as a pilot study to compare different methods for the delineation of WHPA based on calculated fixed radius and analytical methods and, this way, identify which method or methods best adapt to the characteristics of the study area. The Minkin analytical method proved to offer the best results since it protects well on both sides and achieves a balance in the well’s upgradient distances. It is also worth mentioning that the delimitation of the WHPAs in the study area was limited in respect to hydrogeologic and technical data.

Vulnerability of drinking water supply wells to VOCs

As part of a US Geological Survey study of national water quality, untreated water samples from ~ 1,100 public supply and 2,400 domestic wells were analyzed for 55 volatile organic compounds (VOCs). Findings indicated that drinking water from public supply wells is more vulnerable than domestic well water to VOC contamination. Analyses showed that the solvents perchloroethene and trichloroethene in public well samples were associated with point sources and pumping rates, potentially resulting from contaminant plumes that are drawn into wells with large capture zones. In contrast, detections of the trihalomethanes chloroform and bromodichloromethane and detections of methyl tertiary butyl ether were not associated with pumping rates. Chloroform detections were inversely correlated with the percentage of undeveloped land, indicating a nonpoint source signal. Widespread VOC detections in public well samples confirmed that wellhead protection efforts are warranted and that prudent managerial decisions regarding well planning, construction, and operation can result in reduced risks of VOC contamination to drinking water supplies.

Comparative Identification of Wellhead Protection Areas for Municipal Supply Wells in Gaza

Groundwater is the only source of fresh water in Gaza Strip while its inhabitants and its water consumption increased rapidly. This study aims at preserving and protecting the groundwater from any pollutants caused by 141 industrial installations through the work of delineation of Wellhead Protection Areas (WHPA) for 47 Municipal Supply Wells in Gaza Governorate boundaries. WHPA has been determined in three different methods: Calculated Fixed-Radius Method (CFR), Analytical Method (AM), and Wellhead Analytic Ele-ment Model (WhAEM2000) which is currently used by the United States Environmental Protection Agency (EPA). These methods mainly depend on the time it takes groundwater to travel a specified horizontal dis-tance. Three well zones were delineated for each municipal production well, the first zone is 50 days time of travel (TOT), the second zone is 2 years TOT and the third zone is 5 years TOT. Different values of the ra-dius of WHPA of each well were obtained using the three methods. Consequently, several industrial installa-tions were laid inside the WHPA according to the radius values. The results show that CFR method is the weakest method because it does not take into account regional groundwater flow, causing a hydraulic gradi-ent. WHPAs identified by these methods may be either too large or too small, resulting in wellhead overpro-tection or under protection. Analytical Method incorporates hydrogeologic characteristics of the aquifer, groundwater flow, and hydrogeologic boundaries into the model. Often produces a WHPA that is smaller than the one produced using CRF. WhAEM2000 method is the best method because it uses a hydrogeologi-cal computer model of groundwater flow and it provides a more accurate delineation of the WHPA. It often produces a smaller area to manage than other methods. The study concluded that all industrial installations located in the WHPA should be carefully checked and investigated by governmental authorities. Mitigation measures for pollutants and licenses for the establishment of any new industrial installations could be based on the delineation of WHPAs using the previously mentioned methods.