Wellhead Protection Zones Research Articles

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.

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.

Wellhead protection zones for sustainable groundwater supply

Wellhead protection zones (WPZs) and groundwater supply protection areas are strategies to minimize contamination hazards and ensure a safe groundwater supply. Their implementation may require land use restrictions, industrial process changes and/or waste and effluent treatment changes, service adaptations, systematic controls of groundwater levels and groundwater quality and detailed well inspections. The aim of this paper is to present a scheme to ensure the protection of drinking water sources comprising the new pumping field supplying Esperanza and Rafaela cities in Santa Fe Province, Argentina. A 5–10-m radius was adopted for delineating the wellhead operational zones. To define the microbiological and surveillance zones, the fixed radius and Wyssling methods were applied, taking into account the groundwater travel time of 50 and 100 days, respectively. The land activities were inventoried and categorized according to their potential for generating a subsurface contaminant load. A sanitary survey and assessment of pumping wells was made using a checklist. The results have shown that appropriate radii might be 70 m for the microbiological protection zone and 100 m for the surveillance zone. These values were obtained taking into account a pumping rate of approximately 60–70 m3/h. This abstraction rate should be regulated and maintained because it not only affects the validity of the defined zones but also, when it is exceeded, induces an influx of water of different quality to the semi-confined aquifer.

Study on the Comprehensive Mechanism of Hangzhou Water Landscape Governance

The article is to analyze the spatial structure, type structure and the existent main problems of water landscape in Hangzhou. Aiming at “clear water, liquidity, green bank, beautiful scenery, livability, prosperity”, the tasks and construction targets of the mechanism of Hangzhou water landscape are studied form the perspectives of wellhead protection zone, transport water landscape and urban water landscape. In order to solve the problems like dirty, black and odorous urban water, the guiding ideology and comprehensive governance measures are proposed.

A GIS policy approach for assessing the effect of fertilizers on the quality of drinking and irrigation water and wellhead protection zones (Crete, Greece)

Fertilizers have undoubtedly contributed to the significant increase in yields worldwide and therefore to the considerable improvement of quality of life of man and animals. Today, attention is focussed on the risks imposed by agricultural fertilizers. These effects include the dissolution and transport of excess quantities of fertilizer major- and trace-elements to the groundwater that deteriorate the quality of drinking and irrigation water. In this study, a map for the Fertilizer Water Pollution Index (FWPI) was generated for assessing the impact of agricultural fertilizers on drinking and irrigation water quality. The proposed methodology was applied to one of the most intensively cultivated with tree crops area in Crete (Greece) where potential pollutant loads are derived exclusively from agricultural activities and groundwater is the main water source. In this region of 215 km2, groundwater sampling data from 235 wells were collected over a 15-year time period and analyzed for the presence of anionic (ΝΟ−3, PO−34) and cationic (K+1, Fe+2, Mn+2, Zn+2, Cu+2, B+3) fertilizer trace elements. These chemicals are the components of the primary fertilizers used in local tree crop production. Eight factors/maps were considered in order to estimate the spatial distribution of groundwater contamination for each fertilizer element. The eight factors combined were used to generate the Fertilizer Water Pollution Index (FWPI) map indicating the areas with drinking/irrigation water pollution due to the high groundwater contamination caused by excessive fertilizer use. Moreover, by taking into consideration the groundwater flow direction and seepage velocity, the pathway through which groundwater supply become polluted can be predicted. The groundwater quality results show that a small part of the study area, about 8 km2 (3.72%), is polluted or moderately polluted by the excessive use of fertilizers. Considering that in this area drinking water sources (wells) are located, this study highlights an analytic method for delineation wellhead protection zones. All these approaches were incorporated in a useful GIS decision support system that aids decision makers in the difficult task of protection groundwater resources.

A Multi-objective Optimization Concept for Risk-based Early-warning Monitoring Networks in Well Catchments

Groundwater wells are often protected by restricted land use within wellhead protection zones. Unfortunately, one cannot restrict land use in the entire catchment (especially in urban areas), and there is uncertainty in wellhead delineation. Thus, nearly all well catchments have an entire inventory of risk sources. Each of these risk sources may fail at any time, release contamination and affect the well earlier or later. In fact, most catchments are equipped with some form of monitoring network. Such networks, however, often grow historically, follow various purposes that changed over time, and thus are often suboptimal (if not even inadequate) for rigorous risk control. In this work, we propose a concept to plan monitoring networks through multi-objective optimization. The different objectives are minimal costs, maximal probability to detect all possible contaminants once they entered the aquifer, and earliest possible detection. Also, risk sources that are classified as severe versus medium or tolerable should be treated with different priorities. Therefore, we propose to treat detection probability and early-warning time as separate objectives for each risk class. The concept will allow catchment managers to obtain optimal monitoring networks for risk control, and to gain insight into the costs of certainty, the costs of early warning, and the costs of covering top risks versus the luxury situation of controlling even minor risks.

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.

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.

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.

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.

On using simple time‐of‐travel capture zone delineation methods

As part of its Wellhead Protection Program, the U.S. EPA mandates the delineation of "time-of-travel capture zones" as the basis for the definition of wellhead protection zones surrounding drinking water production wells. Depending on circumstances the capture zones may be determined using methods that range from simply drawing a circle around the well to sophisticated ground water flow and transport modeling. The simpler methods are attractive when faced with the delineation of hundreds or thousands of capture zones for small public drinking water supply wells. On the other hand, a circular capture zone may not be adequate in the presence of an ambient ground water flow regime. A dimensionless time-of-travel parameter T is used to determine when calculated fixed-radius capture zones can be used for drinking water production wells. The parameter incorporates aquifer properties, the magnitude of the ambient ground water flow field, and the travel time criterion for the time-of-travel capture zone. In the absence of interfering flow features, three different simple capture zones can be used depending on the value of T . A modified calculated fixed-radius capture zone proves protective when T < 0.1, while a more elongated capture zone must be used when T > 1. For values of T between 0.1 and 1, a circular capture zone can be used that is eccentric with respect to the well. Finally, calculating T allows for a quick assessment of the validity of circular capture zones without redoing the delineation with a computer model.

Computation of stochastic wellhead protection zones by combining the first-order second-moment method and Kolmogorov backward equation analysis

Input parameters of groundwater models are usually poorly known and model results suffer from uncertainty. When conservative decisions have to be drawn, the quantification of uncertainties is necessary. Monte Carlo techniques are suited for this analysis but usually require a huge computational effort. An alternative and computationally efficient approach is the first-order second-moment (FOSM) analysis which directly propagates the uncertainty originating from input parameters into the result. We apply the FOSM method to both the groundwater flow and solute transport equations. It is shown how calibration on the basis of measured heads yields the “Principle of Interdependent Uncertainty” that correlates the uncertainties of feasible transmissivities and recharge rates. The method is used to compute the uncertainty of steady state heads and of steady state solute concentrations. The second-moment analysis of solute concentrations is combined with the Kolmogorov backward equations and applied to the stochastic computation of wellhead protection zones for a pumping well group in Gambach (Germany). Unconditional and conditional simulation results are compared to corresponding Monte Carlo simulations. The unconditioned FOSM method reveals a computational advantage of a factor of 5–10 against the Monte Carlo method in terms of CPU time requirements. Conditioned FOSM shows an even larger advantage with a factor of 50–100 against the usual inverse stochastic modeling method based on Monte Carlo techniques.

Stochastic Approach to Delineating Wellhead Protection Areas

Delineating the wellhead protection area (WPA) is a vital component in the development of a comprehensive wellhead protection program. WHPA is a series of computer programs developed for the U.S. Environmental Protection Agency to delineate WPAs. In the state of Tennessee, the WPA is delineated using a two-dimensional particle tracking code (GPTRAC) in a leaky-confined aquifer, or a modified containment front tracking code (RESSQC) in an unconfined aquifer. Both WHPA delineation methods require constant values for all model parameters. To overcome the difficulty of estimating values for each input parameter and to provide some measure of the uncertainty in the size and shape of wellhead protection zones, the Environmental Protection Agency WHPA models are integrated into a parallelized Monte Carlo (MC) simulation. The MC-WHPA model is used to compute a discrete two-dimensional cumulative distribution function for a WPA. MC-WHPA uses a parallel virtual machine computing environment developed over a network of computers. The MC-WHPA model is used to delineate the wellhead protection and management zones for two wellfields in western Tennessee.

How Uncertain Is Our Estimate of a Wellhead Protection Zone?

AbstractProtection zones for wells are defined through the use of pathline tracing in ground water flow models. Traditional approaches to ground water flow modeling focus on obtaining a single best model, occasionally supplemented by the use of sensitivity analyses. In most situations this approach is inappropriate because the ground water flow model is so poorly determined that a variety of different boundary conditions and parameter values would give similar predictions of heads. However, the range of feasible models may well give radically different predictions of the variable for which the model has been built. For example, the area, orientation, or many other descriptive variables of a catchment may be much more sensitive to the parameters used in a ground water flow model than are the values of head commonly used to calibrate the model.This paper outlines a procedure to determine the range of predictions of catchments which would arise from alternative calibrations of a model. The range of catchments is used to identify zones of certainty and uncertainty, leading to alternative definitions of the protection zone for differing purposes. An example is presented, based on Bestwood Pumping Station, Nottinghamshire, which is located in the Triassic Sandstone Aquifer of the northern East Midlands of the United Kingdom. A trial and error calibration of a ground water flow model is used to determine an acceptable level for automatic calibration in the subsequent step. Only 12 measurements of ground water head were available, and these were used to determine the fit of a variety of model structures. A search routine revealed a range of feasible models and superposition of their catchments delineated the zones of certainty and uncertainty, which had areas of 7.4 and 15.2 km2, respectively.

THE DEVELOPMENT AND IMPLEMENTATION OF A GIS‐BASED CONTAMINANT SOURCE INVENTORY OVER THE SPOKANE AQUIFER, SPOKANE COUNTY WASHINGTON1

ABSTRACT: U.S. Environmental Protection Agency (EPA) statutes require identification of all potential sources of contamination within a wellhead protection area. All wells over Spokane County's aquifer are included in one wellhead protection zone called the Aquifer Sensitive Area (ASA).A GIS‐based Contaminant Source Inventory (CSI) was developed for the ASA. Datasets listing businesses and agencies within the ASA were imported into the GIS from state, county, city, and local agencies. These datasets were selected, joined, and sorted using GIS relational database capabilities into one ASA “business master file.” Map files were projected and transformed into common coordinates. Next, business sites within the master file were spatially related by address to the digital map files. Likely Critical Materials Users (CMU) were identified by sorting on selected standard Industrial Codes (SIC). Additional files of CMUs were imported into the Contaminant Source Inventory. GIS queries were performed to locate specific materials, quantities, and storage facilities, and to analyze CMU activity within selected buffer zones.This project demonstrated the usefulness of GIS technology in the development, management, maintenance, and analysis of vast quantities of data associated with a local wellhead protection pro. gram.

Protecting Water Resources: Legal and Operational Aspects

AbstractIn France, from a legal standpoint, the protection of aquifers and wellheads supplying drinking water is achieved through wellhead protection zones. Within these zones, which are defined by a certified geologist, the appropriate restrictions which are needed to minimize the risk of pollution are specified.Unfortunately, despite these precautions, accidents are still possible, and it is for this reason that Lyonnaise des Eaux‐Dumez has developed, for the Paris region, a true pollution risk management strategy, based on procedures, alert systems, computer models and crisis drills.

Wellhead Protection Zones in Germany: Delineation, Research and Management

ABSTRACTIn Germany there is much legislation to guarantee adequate protection of groundwater quality and quantity. The main objective of the legislation is to maintain the natural high quality of groundwater. The most important Act in this context is the Water Resources Policy Act.One aspect of German groundwater protection is the possibility to delineate up to four wellhead protection zones in the recharge area of a drinking‐water well. The time‐distance integrated protection zone concept, with bans and limitations on use increasing towards the well, was developed in the 1930s. It has guaranteed for decades a safe drinking water supply from the point of view of quality. However, recent scientific investigations have shown gaps especially with regard to (a) the importance of the 50‐days line, (b) the behaviour of micro‐organisms and (c) the mobility and persistence of man‐made pollutants.

Computer‐Controlled Groundwater Management in Zurich

Computer control of the Hardhof groundwater plant is necessary to adhere to operational criteria stipulated by the canton of Zurich. Drawdown cannot exceed the licensed levels of the wells, and to maintain water quality, recharge of the wells from the Limmat River must be balanced against streamflow and the direction of runoff within the wellhead protection zones. The computer installation at Hardhof also assists with managing energy costs for the city's water supply and security systems for the physical plants.