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Soft subgrades are not strong enough to provide the required degree of compaction for a pavement embankment's foundation. Therefore, it is required to treat the subgrade soil or construct a working platform on top of the soft subgrade to ensure proper compaction of the subsequent layers. The constriction sizes of the granular materials used for a working platform are comparatively higher to restrict the erosion of overlying embankment materials. This condition would lead to severe material loss in the embankment layer in cases where the embankment is constructed with dispersive soil, which becomes structurally unstable in wet conditions and appears to disperse in water. This paper investigates the contact erosion failure at the foundation of a pavement embankment constructed with dispersive soil as a result of groundwater fluctuation. Experimental studies were conducted on a laboratory model test apparatus designed to simulate the conditions in the pavement embankment's foundation. The experimental studies revealed that the magnesium dominant clayey soils also susceptible to contact erosion failure due to soil dispersion. Also, the experimental results show that even a small percentage of dispersive clay particles present in the embankment soil would influence the contact erosion failure. [ABSTRACT FROM AUTHOR]

A review is given of some currently available solutions for the calculation of stream depletion from pumped aquifers. A brief history is given of the development of analytical and semianalytical models. A solution published in 2003, which is also capable of duplicating many previously published solutions, is described in detail. In this solution, the stream partially penetrates a Boulton delayed-yield aquifer and is shown herein to apply when different segments of a stream may be either gaining or losing water to the pumped aquifer. Excel computational tools freely available to practitioners are referenced and used in an illustration for the calculation of the 2003 solution, and the general behavior of the solution is discussed. Generalizations and additional solutions are discussed for streams and aquifers with finite width, for systems containing several aquifers and for abstraction wells that are either horizontal or slanted. The review concludes with a very brief discussion of the advantages and disadvantages of using numerical solutions for modeling stream-depletion behavior. [ABSTRACT FROM AUTHOR]

An optimization method is proposed for estimating transmissivity, storage coefficient, and effective well radius from drawdowns in large-diameter wells. Unsteady pumping is considered; any variation in pumping discharge can be accounted for. Pumping and residual drawdowns can be analyzed simultaneously using the new method. The application of the method is illustrated through the examples of prior studies. The new method reliably estimates the parameters. For the examples considered, the estimates of transmissivity and effective radius of well are more accurate than the estimate of storage coefficient. The proposed method is superior to the prior method because it is objective, more quantitative, and more general. [ABSTRACT FROM AUTHOR]

The SIMGRO hydrologic simulation model was extended to include irrigation practice. It could then be used to evaluate the effect of hydrologic changes in an irrigated area in the province of Mendoza, Argentina where, given an average annual rainfall of approximately 200 mm, irrigation is crucial for agriculture. A storage dam was recently constructed in the Mendoza River to control the fluctuating river flow and to guarantee that the demand for water is met throughout the year. The dam will impact on parts of the irrigation system where groundwater levels are already high and salinization occurs. To evaluate these changes and possible mitigation measures, two performance indicators that consider groundwater and surface water were used: Relative evapotranspiration and the depleted fraction. Scenario runs revealed that the irrigation water losses from the canals affect the groundwater levels in the downstream part of the irrigated area; an increase in salinity was also revealed. [ABSTRACT FROM AUTHOR]

If two independent sets of data are available—the piezometric heads and the related source terms for two stationary flow situations, such that the hydraulic gradients are not parallel to each other—the aquifer transmissivity can be identified with the differential system method (DSM), provided that an initial value of transmissivity is given at least at one point. In field applications, it is difficult to collect two data sets that are independent throughout the aquifer, and the results depend on the location of the point where the initial value is assigned. These difficulties are reduced if several data sets are available and the differential system is obtained either by applying a least square technique to the whole ensemble of data sets, or by choosing the “best” couple of data at each point. Numerical tests on a synthetic aquifer show that both techniques yield good results and make the DSM more robust to noise on the piezometric heads than the standard DSM applied with two data sets only. [ABSTRACT FROM AUTHOR]

Differentiation of upper and lower regions of the unsaturated (vadose) zone is important for modeling evapotranspiration, infiltration, and water table recharge. This study developed a methodology to describe relative moisture conditions in both zones for modeling soil hydrologic response. A comprehensive distributed parameter model was developed based on deterministic and physically based soil and vegetative properties. The Integrated Hydrologic Model (IHM) uses a unique relative soil moisture approach for land segment integration and is intended to simulate the complex interaction between surface-water and groundwater systems. No prior rigorous investigation or validation of the upper and lower soil response has been made. In this study, field soil moisture observations and soil characterization data were used to formulate a new basis for the upper and lower zones in the IHM. Several tests were performed to illustrate how the model reduces field-scale variability in soil moisture behavior and enhances representation of antecedent conditions. Results show that the two zones commonly exhibit different relative moisture conditions. Evidence is presented to document the existence of prolonged (many days) air entrapment and excess pore pressure, which affect soil water storage and observed water table levels. [ABSTRACT FROM AUTHOR]

A simple approximation of the well function for a constant drawdown is developed. This approximation is used to estimate the storage coefficient and transmissivity of the aquifer from observed unsteady discharge under a constant drawdown condition, using an optimization method. Another simple approximation for calculating the total production volume during a time span is also developed. The developed approximations for the well function and production function are accurate within a maximum error of 0.7% for the practical range of the argument. [ABSTRACT FROM AUTHOR]

Numerical and experimental solutions to steady infiltration from a strip basin to a groundwater table of infinite horizontal extent are presented. Because of the unknown location of the phreatic surface, the flow domain is transformed into the complex potential plane using the inverse formulation method where the phreatic surfaces with and without recharge become straight lines. The method of finite differences was used to solve the boundary value problem in the transformed plane. The problem was also investigated experimentally using a sand tank model. For comparison purposes, a one-dimensional analytical solution is also presented. The results were compared with each other. The parameters affecting the seepage rate are investigated and the resulting relationships were presented in dimensionless graphs. It is believed that these graphs may be of use in design problems. The conditions for which the simplified one-dimensional analytical solution agrees well with the results of the sophisticated two-dimensional numerical solution are identified. The shape of the water table in response to recharge depends on the size of the recharging area, the hydraulic and geometric properties of the aquifer, and the recharge rate. [ABSTRACT FROM AUTHOR]

Water-rights driven surface-water allocations for irrigated agriculture can be simulated using the farm process for MODFLOW-2000. This paper describes and develops a model, which simulates routed surface-water deliveries to farms limited by streamflow, equal-appropriation allotments, or a ranked prior-appropriation system. Simulated diversions account for deliveries to all farms along a canal according to their water-rights ranking and for conveyance losses and gains. Simulated minimum streamflow requirements on diversions help guarantee supplies to senior farms located on downstream diverting canals. Prior appropriation can be applied to individual farms or to groups of farms modeled as “virtual farms” representing irrigation districts, irrigated regions in transboundary settings, or natural vegetation habitats. The integrated approach of jointly simulating canal diversions, surface-water deliveries subject to water-rights constraints, and groundwater allocations is verified on numerical experiments based on a realistic, but hypothetical, system of ranked virtual farms. Results are discussed in light of transboundary water appropriation and demonstrate the approach’s suitability for simulating effects of water-rights hierarchies represented by international treaties, interstate stream compacts, intrastate water rights, or ecological requirements. [ABSTRACT FROM AUTHOR]

A conventional simulation-optimization model with constraint on drawdown at an area of interest is used to optimize additional groundwater withdrawal at multiple demand locations in a coastal aquifer. After obtaining the optimal solution, a decision-making analysis is conducted using fuzzy logic concepts. The goal is to evaluate multiple objectives and select the best management strategy. This methodology is applied to a hypothetical case consisting of six groundwater demand locations in Savannah, Ga. The objective function of the optimization model includes a penalty term which can be adjusted by the user to control the degree of “fairness” with respect to the distribution of limited groundwater resources in the region. The decision-making framework incorporates hydrologically, politically, and economically motivated multiple conflicting objectives into the evaluation process. Results of the coupled simulation-optimization model are used to determine individual satisfaction degrees of each management strategy with respect to multiple objectives. Based on this outcome, an overall performance value is calculated by using the ordered weighted averaging (OWA) operator and the management strategy with the highest overall performance is identified as the best strategy. The OWA operator is an averaging operator that avoids ruling out some alternatives in favor of others which is observed in the logical operators such as “and” and “or.” When combined with expert knowledge to identify the appropriate membership functions for the fuzzy objectives, the procedure developed in this study may yield transparent and robust groundwater management solutions in coastal aquifers. [ABSTRACT FROM AUTHOR]

A head loss concept, new to the stream-aquifer interaction, is introduced for modeling laboratory observations. Using this concept, the equation applicable to fully penetrating streams is modified to account for the head loss at the entrance. The modified model is able to explain and fit the observed laboratory data correctly. Equations are proposed to calculate the hydraulic diffusivity of aquifer and head loss at the entrance from the estimate of diffusivity obtained without considering the head loss. An optimization approach is also proposed to estimate the hydraulic diffusivity of the aquifer and head loss from the observed groundwater heads at different sections. [ABSTRACT FROM AUTHOR]

Parts of New England have naturally high arsenic concentrations in groundwater. High arsenic correlates broadly with bedrock type, but levels are patchy, so other conditions must affect arsenic mobilization. Microorganisms capable of arsenate (As(V)) respiration, if present, could affect arsenic speciation and mobility in groundwater. An arsenate-reducing bacterium, designated NP4, was isolated from groundwater obtained from a well in Northport, Me., with extremely high (>1,400 μg L-1) arsenic. Sequencing of the 16S rDNA showed that NP4 groups with the Sulfurospirillum genus. It can grow using arsenate, nitrate, iron(III), selenate, manganese(IV), sulfite, sulfur or thiosulfate as terminal electron acceptors and lactate, formate and pyruvate as electron donors. It can also grow on fumarate or lactate alone. This Sulfurospirillum isolate is distinct from other members of the genus in its carbon and electron acceptor usage. The activity of this type of microorganism could negatively affect groundwater quality by converting As(V) to the more toxic and difficult to remove As(III) form. [ABSTRACT FROM AUTHOR]

The sorptive capabilities of soils for organic contaminants can be greatly enhanced by treatment with cationic surfactants, and this has been suggested as a potential in situ approach for contaminant plume management. The hydraulic properties of soils modified by injection of hexadecyltrimethylammonium (HDTMA) were investigated using soil columns and a fixed-ring consolidometer. Oshtemo soil (87% sand, 10.5% clay, 2.5% silt) under two different effective stresses, was equilibrated with 1 mMNaCl and treated by recirculation of two different HDTMA soil concentrations, one above and one below the cation exchange capacity. No statistically significant changes in hydraulic conductivity occurred as a result of HDTMA treatment at any of the experimental conditions studied. These results suggest that sorptive zones created in situ with HDTMA may be hydraulically feasible. [ABSTRACT FROM AUTHOR]

Genetic algorithms allow solution of more complex, nonlinear civil, and environmental engineering problems than traditional gradient-based approaches, but they are more computationally intensive. One way to improve algorithm performance is through inclusion of local search, creating a hybrid genetic algorithm (HGA). The inclusion of local search helps to speed up the solution process and to make the solution technique more robust. This paper focuses on the effects of different local search algorithms on the performance of two different HGAs developed in previous phases of this research, the self-adaptive hybrid genetic algorithm (SAHGA) and the enhanced SAHGA. The algorithms are tested on eight test functions from the genetic and evolutionary computation literature and a groundwater remediation design case study. The results show that the selection of the local search algorithm to be combined with the simple genetic algorithm is critical to algorithm performance. The best local search algorithm varies for different problems, but can be selected prior to solving the problem by examining the reduction in fitness standard deviation associated with each local search algorithm, and the time distribution associated to the local search algorithm. [ABSTRACT FROM AUTHOR]

Adequate knowledge of the hydraulic characteristics of production wells is indispensable for the proper development and management of wells and for the selection of suitable pumps. In this study, the characteristic hydraulic parameters of production wells were determined by the widely used graphical analysis of step-drawdown pumping test data as well as the two traditional gradient-based nonlinear optimization techniques (viz., Levenberg–Marquardt and Gauss–Newton) and the nontraditional optimization technique, genetic algorithm. Three stand-alone and interactive computer programs were developed to optimize the hydraulic parameters of production wells by these numerical techniques. The efficacy and robustness of the developed computer codes were examined using eleven sets of step-drawdown data from diverse hydrogeologic conditions. The results of this study revealed that all the three numerical techniques yielded superior well parameters with lower values of root-mean-square errors (RMSE) for all the eleven data sets compared to the parameters obtained by the graphical method. The values of the exponent (P) ranged from 1.2 to 6.0, which gave minimum RMSE values. Furthermore, it was found that both the Gauss–Newton and Levenberg–Marquardt techniques are sensitive to the initial guess values of well parameters. It is concluded that both the traditional and nontraditional numerical techniques offer an efficient and reliable tool for the determination of well parameters with a greater accuracy and better insight. [ABSTRACT FROM AUTHOR]

Water resources optimization models often use spatial numerical models to approximate the physics of natural systems. The discretization of the numerical grids can affect their search for optimal solutions, in terms of both solution reliability and computational costs. Computational costs are particularly significant for population-based optimization techniques such as genetic algorithms (GAs), which are being applied to water resources optimization. To overcome these bottlenecks, this paper proposes multiscale strategies for GAs that evaluate designs on different spatial grids at different stages of the algorithm. The strategies are initially tested on a hypothetical groundwater remediation problem, and then the best approach is used to solve a field-scale groundwater application at the Umatilla Chemical Depot in Oregon. For the Umatilla case, the multiscale GA was able to save as much as 80% of the computational costs (relative to the GA that used only the fine grid) with no loss of accuracy, thus exhibiting significant promise for improving performance of GA-based optimization methodologies for water resources applications. [ABSTRACT FROM AUTHOR]

A field problem involving pumping of groundwater from a series of existing skimming wells to meet drinking water needs from a river flood plain is examined within a conceptual framework. A simplified hypothetical aquifer system that is representative of a study area, skimming wells, input variables, and aquifer parameters is solved using a simulation-optimization (S/O) approach. The S/O model proposed in this study is solved as a nonlinear, nonconvex problem using a simulated annealing algorithm and a variable density flow simulator. An artificial neural network is used to replace the simulator to reduce the computational burden. An optimal pumping schedule in terms of location and pumpages is presented that controls up coning from underlying saline water. The study suggests that an increased number of skimming wells do not necessarily yield more water, and that the pumping schedule must be staggered in space and time. [ABSTRACT FROM AUTHOR]

Analytical expressions for rate and volume of flow depletion of semipervious streams due to sinusoidal variation in pumping rate are obtained. An analytical but approximate method is developed for obtaining the rate and volume of stream flow depletion due to arbitrary unsteady pumping discharge. The method uses the ramp kernel and convolution. The use of ramp kernels permits linear interpolation between two consecutive discretized discharge values. The analytical equations for the ramp kernels for the rate and volume of stream flow depletion are derived. The proposed method is applicable for homogeneous and isotropic aquifers that are hydraulically connected to streams. [ABSTRACT FROM AUTHOR]

The determination of aquifer diffusivity from water level observations in various wells close to a stream, in response to an arbitrary variation in the stream stage, is discussed. The stream stage has been approximated by the sum of a series of basis functions, which are products of a linear and an exponential term. The aquifer response to individual basis function is investigated in detail. Approximate but very accurate expressions are proposed for explicit determination of diffusivity from data on peak attenuation and lag for cases where the stream stage may be represented by a single basis function. For other cases, a linear combination of 3–7 basis functions was found to represent a typical stage variation quite well. Application to a field data set demonstrates the suitability of the proposed methodology and the predicted aquifer diffusivity agrees with that reported in the literature. [ABSTRACT FROM AUTHOR]

Slope stabilization procedures for seven landslides in the Niigata Prefecture of Japan had provided an excellent and rare opportunity to examine the composition of ground water, and residual shear strength of the sliding surface soil, as well as unsheared mudstone. Ring shear tests were conducted on the soil samples collected from sliding surface soil, revealed during the installation of 3 m diameter drainage galleries. Shear strength and index properties of the soil were measured by mixing the soil with distilled water and sea water, and after leaching the NaCl from the pore water. The residual shear strength of the soil sample with distilled water was 3–5° lower than that with the sea water. The residual shear strength of the intact rock powder after leaching the dissolved salt was close to that of the soil from sliding surface, and the residual shear strength of the soil from sliding surface after mixing with sea water was close to that of the intact rock powder. The increase in residual shear strength had a parabolic increment with the specific surface area. This research finding has very important practical implications on the postfailure stability analysis of the landslides having saline pore water. [ABSTRACT FROM AUTHOR]

Analytical but approximate methods are developed for obtaining pumping induced rate and volume of stream flow depletion, which can account for unsteady (any variation) pumping discharge and are also applicable for intermittent pumping and recovery. Exact analytical solutions for a sinusoidal variation in the pumping discharge are proposed; the proposed methods are verified using these solutions. The proposed methods use ramp kernels that give results superior to the conventional convolution. These ramp kernels assume the linear variation in pumping discharge between the two consecutive discretized points as opposed to the uniform variation assumed in the conventional convolution. The proposed solutions are applicable for homogeneous and isotropic aquifers hydraulically connected to streams. [ABSTRACT FROM AUTHOR]

Verification and application results are presented for a new saturated-unsaturated 3D groundwater flow model (SU3D) developing in Dogan and Motz, which can be used to calculate the pressure distribution over the entire groundwater flow domain in response to rainfall and evapotranspiration. SU3D solves the nonlinear 3D, modified mixed form of the Richards equation continuously throughout the groundwater flow domain, including both the unsaturated and saturated zones. The block-centered finite-difference method, a modified Picard iteration scheme, and the preconditioned conjugate gradient method are used to solve the governing partial differential equations in the new model. SU3D can simulate evaporation from land surface and transpiration from the root zone. Potential evapotranspiration is partitioned into potential evaporation and potential transpiration as a function of the leaf area index; actual evaporation and actual transpiration are then calculated individually. As shown in this paper, SU3D has been verified by reproducing the results of five analytical and numerical studies and a 3D unconfined-aquifer pumping test from the published literature. [ABSTRACT FROM AUTHOR]

A new saturated-unsaturated three-dimensional (3D) groundwater flow model (SU3D) has been developed that calculates the pressure distribution over the entire groundwater flow domain in response to rainfall and evapotranspiration. Recent advances in solving the saturated-unsaturated groundwater flow equation are incorporated into SU3D, which solves the nonlinear, 3D, modified mixed form of the Richards equation continuously throughout the groundwater flow domain. The block-centered, finite-difference method with a variably sized grid is employed to solve the governing partial differential equation. The non-linear terms of the governing equation are linearized using a modified Picard iteration scheme, and the preconditioned conjugate gradient method is used to solve the linearized system of equations. SU3D can simulate the effects of pumping from an aquifer, and it has an option to calculate potential evapotranspiration (PET) from meteorological data. The PET is partitioned into potential evaporation and potential transpiration as a function of the leaf area index, and then the actual evaporation and transpiration are calculated. Overland flow and seepage face calculations are not included in SU3D. [ABSTRACT FROM AUTHOR]

In this study, fuzzy sets are utilized to interpret uncertainty in aquifer parameters in the solution of groundwater optimization problems. For this purpose, an optimization model is developed for the design of groundwater remediation systems with multiple uncertain parameters and multiple candidate pumping wells. The uncertain parameters selected include hydraulic conductivity and longitudinal and transverse dispersion coefficients. A genetic algorithm embedded with fuzzy vertex algebra is used to solve the optimization model. This approach is an extension of an earlier method proposed by the writers that is more suitable for large scale applications with multiple uncertain parameters. The numerical experiments are conducted to demonstrate the effectiveness of the procedures discussed in this study. The approach presented in this study provides guidance for the interpretation of uncertain parameters in groundwater optimization problems using fuzzy sets. The computational results show that the combined use of genetic algorithms and fuzzy vertex analysis yields an efficient method for the solution of optimization problems with multiple uncertain aquifer parameters. [ABSTRACT FROM AUTHOR]

This paper presents the basis for using groundwater circulation wells (GCWs) for removal actions focused on contaminated domestic water supplies. A properly placed GCW could be used to pretreat water before it enters a domestic well. Commercial software was used to develop a model for GCWs installed at a Nebraska Superfund site to perform a feasibility study of a GCW-based removal action. Deterministic capture zone analysis provided guidance for locating vertically installed GCW up-gradient of an existing domestic well at the site. A deviation of up to 7.6 m off-center of the hydraulic gradient may be permissible. A GCW flow rate range to provide a sufficiently large recharge zone to protect a typical domestic well was identified for the site. Stochastic analysis indicated that the system was sensitive to horizontally variable hydraulic conductivity. Modeling results indicate that a GCW may both reduce contaminant mass in the aquifer, and act as a water supply replacement alternative to point of use treatment systems. [ABSTRACT FROM AUTHOR]

Conjunctive management of surface and ground water requires an understanding of the degree to which surface water resources will be impacted by aquifer stresses at different locations. Response functions quantify the rate of depletion or accretion of a surface-water body relative to a unit stress on an aquifer under simplified, but often realistic, conditions. Response functions for four reaches of the Snake River have been determined for each cell of the eastern Snake River Plain aquifer model grid in southern Idaho. Mapping the response functions for each reach creates a visual image of how effects of aquifer stresses at different locations are distributed among the four hydraulically connected river reaches. The mapped distribution of response functions reflects aquifer properties such as the distribution of aquifer transmissivity. Cluster analysis of the response functions for each cell and each river reach has proven useful for subdividing the aquifer into zones for the conjunctive management of ground water and surface water. The response function variance within each zone is minimized in this procedure. In most situations, zone boundaries defined through cluster analysis will likely be modified to better conform to existing political and administrative units. The selection of the number of zones, and the degree to which boundaries based on response functions are modified, reflect a balance between the exactness provided by the science and administrative convenience and efficiency. The approach of managing an aquifer through response function based zones has gained initial acceptance in Idaho, as evidenced by the citation of these zones in Idaho’s draft Water Management Rules. How management zones based on response functions will ultimately be used in Idaho water policy and procedures has not yet been determined. [ABSTRACT FROM AUTHOR]

In order to rigorously examine near surface, field to field interactions between irrigation management regimes and a shallow fluctuating water table, an enhanced deforming finite element (DFE) model was recently developed. The enhanced DFE model, through a process of iteration within each time step, avoids making common assumptions regarding the changing geometry of an aquifer free surface. This paper demonstrates the usefulness and effectiveness of the model by employing it to an irrigated region in the western San Joaquin Valley, Calif., where shallow subsurface tile drains have been installed to control shallow water tables. By virtue of the problems created by the need to dispose off the drainage water, this region has been the focus of several important regional scale modeling exercises, which have evaluated the utility of management strategies, such as source control, groundwater pumping, and land retirement. By refining the focus of the analysis, the enhanced DFE model is found to be able to show that both sources control and managed pumping could be more effective drainage control strategies than predicted based on the results of regional models. [ABSTRACT FROM AUTHOR]

An expert system for the evaluation of groundwater pollution potential due to leaching of nutrients from land application of manure is developed in this study. The expert system consists of five modules: surface loading, sorption, vadose zone transport, saturated zone transport, and final module. The expert system evaluates the pollution potential in two steps. In the first step, rating values are evaluated for the selected modules. A set of expert system rules is assigned by the writers to evaluate the rating value of each selected module. In the second step, the pollution potential is evaluated from calculating the weighted average rating of the selected modules. Finally, the expert system is validated against a site assessment done by a group of experts for a concentrated animal feeding operation (CAFO) facility in Oklahoma. The advantages of the expert system are its user-friendliness, requirement of easily available input data, and faster evaluation time. The expert system is recommended to the farmers for improving their management practices and for selecting sites suitable for building new CAFOs. It is also recommended to the regulatory agencies as a screening level tool to identify the most vulnerable sites. [ABSTRACT FROM AUTHOR]

The quantification of the natural oxidant demand (NOD) of aquifer materials is required to estimate the fate of reagents injected into contaminated aquifers during in situ chemical oxidation applications. Three push-pull tests were conducted at a horizontal spacing of 12–20 m within an uncontaminated region of the saturated zone in the Canadian Forces Base Borden aquifer located near Alliston, Ont., Canada to estimate the NOD for permanganate. Each test contacted a minimum of 270 kg of aquifer material. Upper estimates of NOD values from the three tests were 0.51–0.75 g/kg based on the initial mass of aquifer material contacted, and lower estimates were 0.29–0.42 g/kg based on additional aquifer material mass contacted during the drift or reaction phase. These results compared favorably to NOD values determined from bench-scale tests with high solids mass to solution volume ratios. If design and operational concerns can be overcome, the push-pull test offers significant advantages over the variety of bench-scale testing methods currently used to determine the NOD of aquifer materials. [ABSTRACT FROM AUTHOR]

The problem of steady-state seepage from a lined canal toward asymmetrical drainages has been solved using the finite-element method, analyzing the effect of canal lining on canal seepage discharge. Studies show that the effectiveness of canal lining in reducing seepage is less when drainage distance is large. With a decrease in the permeability of the canal lining, the canal seepage also decreases; however, the decrease in canal seepage is relatively more when the ratio of lining permeability and subsoil permeability ranges in the region from 2. The decrease in canal seepage is very steep with initial increase in the lining thickness. However, with further increase in the lining thickness, the decrease in canal seepage is not very significant. Therefore, an effective lining permeability must range between 1 and 1 of the subsoil permeability and its thickness must be kept less than 0.2, where h1 is the difference between right drainage water level and canal water level. [ABSTRACT FROM AUTHOR]

Permeable reactive walls have proven to be successful in laboratory and pilot-scale field applications. However, the long-term efficacy of reactive permeable walls has not been established due to the novelty of the technology. Also, the impact of common groundwater ions such as calcium and magnesium (i.e., hardness) on permeable reactive walls is unknown. In theory, the ions may react competitively with chromium in solution and/or other materials on the surface of the zero-valent iron. The ions may also form precipitates that could clog the reactive zone over time, resulting in decreased contaminant removal and a shorter wall lifetime. The purpose of this research was to determine the effects of common groundwater ions on permeable reactive walls. A range of calcium and magnesium concentrations was tested in laboratory columns to determine the effect of these ions on removal of a constant chromium concentration (100 mg/L). Results from the laboratory tests indicated that calcium and magnesium had a significant impact on chromium removal. The most dramatic effects were witnessed at hardness levels up to 140 mg/L as CaCO3 where zero-valent iron capacity was reduced by 45%. [ABSTRACT FROM AUTHOR]

In November 1997 an outflow of up to 0.4 m3/s of groundwater from deep seated aquifers occurred in the open-cast lignite mine of Hambach, Germany. Although this incident was technically under control and did not affect the mining activities, it was studied in a joint research project to exclude recurrences at other locations. In this paper we summarize the results from a hydromechanical point of view. One key issue of this paper is to present a continuous and consistent explanation of the progression of the incident based on an analysis of the available geological, hydraulic, and chemical data. The probability of similar incidents is highly unlikely due to the rare combination of a thin sealing clay smear in the fault, high pressure gradient, and fractured coal seams in direct contact with the sealing clay. As a perspective, strategies for a responsible mining policy are derived based on the outcome of this study to prevent a recurrence of this type of incident and to ensure optimal safety for the mining operations with minimum effects on water resources. [ABSTRACT FROM AUTHOR]

Declining fall flows are limiting the ability of the Cosumnes River to support large fall runs of Chinook salmon. Management scenarios linking surface water and groundwater alternatives to provide sufficient fall flows are examined using groundwater flow and channel routing models. Results show that groundwater overdraft in the basin has converted the river to a predominantly losing stream, practically eliminating base flows. Management alternatives to increase net recharge (for example, pumping reductions) were examined along with surface water augmentation options. Using a minimum depth standard for fish passage, average surface water flow deficits were computed for the migration period of Chinook salmon. Groundwater deficits were evaluated by comparing simulated current groundwater conditions with conditions under various scenarios. Increases in net recharge on the order of 200 to 300 million m3/year would be required to reconnect the regional aquifer with the channel and in turn reestablish perennial base flows. Options that combine surface water augmentation with groundwater management are most likely to ensure sufficient river flows in the short term and to support long-term restoration of regional groundwater levels. [ABSTRACT FROM AUTHOR]

This paper offers solutions for drawdowns due to intermittent pumping cycles or cyclic pumping, which are high accuracy approximations of the series of Theis functions superimposed in time. The proposed approximation formulas are an improvement over the earlier works. The earlier approximations are valid only if the number of pumping cycles is greater than 10 and involve gamma functions that are less convenient to evaluate than the rational approximation formulas offered in this paper. The proposed approximations are valid for any number of pumping cycles and involve simple functions that can be computed even using a calculator. The drawdown functions are defined for the drawdowns at the end of pumping or shutoff periods. The proposed expressions for these functions are also suitable for the estimation of aquifer parameters by plotting the observed drawdowns on semilogarithmic paper. Procedures for estimation of storage coefficient and head loss at the well from cyclic pumping drawdowns are not available. This paper also offers procedures for the estimation of transmissivity, storage coefficient, and head loss at the pumped well from the observed intermittent (cyclic) pumping drawdowns. [ABSTRACT FROM AUTHOR]

The Hula Decision Support System (HDSS) is designed to aid Hula site operators in managing groundwater levels in the Hula Lake region of Israel. Groundwater levels are managed by controlling water levels by using adjustable dams in a grid of drainage canals and by the timing and intensity of irrigation. Water levels in the canals are controlled by a set of hydraulic structures. Groundwater levels are to be maintained within a specified range to minimize decomposition and subsidence of the peat soils, ensure year-round green cover of the area, and avoid saturation conditions in the crop root zone, thereby allowing farmers to continue cultivation of their fields. The management module for the HDSS performs optimization with the following two objectives: (1) minimize deviation from the specified groundwater target level, and (2) minimize supply of water from the Jordan River to the Hula drainage canals (water quantity is limited). The second objective is achieved indirectly in the HDSS by determining the dam settings and irrigation quantity and timing over a period of eight weeks and then solving again whenever conditions change. The results are checked by simulation using MODFLOW within the GMS modeling package. The procedure is demonstrated and analyzed. [ABSTRACT FROM AUTHOR]

A regional conjunctive use model is developed for a near-real deltaic aquifer system, irrigated from a diversion system, with some reference to hydrogeoclimatic conditions prevalent in the east coastal deltas of India. Water resources are sufficiently available in these regions under average monsoon rainfall conditions, but their distribution in space and time has been ever challenging to water managers. Surface-water availability shows temporal fluctuations in terms of floods and droughts, and groundwater availability shows mainly spatial variability in terms of quality and quantity due to the hydrogeologic setting, boundary conditions, and aquifer properties. The combined simulation-optimization model proposed in this study is solved as a nonlinear, nonconvex combinatorial problem using a simulated annealing algorithm and an existing sharp interface model. The computational burden is managed within practical time frames by replacing the flow simulator with artificial neural networks and using efficient algorithmic guidance. [ABSTRACT FROM AUTHOR]

The feasibility of training an artificial neural network (ANN) for accurately predicting transient water levels in a complex multilayered ground-water system under variable state, pumping, and climate conditions is demonstrated. Using real-world data, an ANN was developed for a public supply wellfield and ground-water monitoring network located near Tampa Bay, Florida. The ANN was trained to predict transient water levels at 12 monitoring well locations screened in different aquifers in response to changing pumping and climate conditions. The trained ANN was then validated with ten sequential seven-day periods, and the results were compared against both measured and numerically simulated ground-water levels. The absolute mean error between the ANN predicted and the measured water levels is 0.16 m, compared to the 0.85 m absolute mean error achieved with the calibrated numerical model at the same locations over the same time period. The ANN also more closely reproduced the dynamic water level responses to pumping and climate conditions. The practical implication is that if ANN technology can achieve superior ground-water level predictions, it can be used to improve management strategies for a wide range of ground-water problems, from water quantity to water quality issues. It can also serve as a powerful sensitivity analysis tool for quantifying interrelationships between different variables, fostering a better understanding of the hydrogeologic system, and improving future modeling endeavors. And while physical-based numerical modeling retains some advantages over the ANN technology, both approaches may be used in a complementary fashion to achieve sound decision-making for complicated ground-water management problems. [ABSTRACT FROM AUTHOR]

Bench-scale reactor experiments were performed to study the dissolution of a binary naphthalene-in-nonane mixture nonaqueous phase liquid (NAPL) pool over a wide range of average pore water velocities, v[sub x] (≈0.1–60 m/day). Experimental NAPL pool dissolution flux values were determined using a steady-state mass balance approach. The experimental flux data were compared to model predictions made assuming either local equilibrium or mass-transfer limited conditions. The local equilibrium model could describe the trends in the average effluent concentration and dissolution flux with 0.110 m/day. Data determined to be under mass-transfer limited conditions were fit to the nonequilibrium model to estimate values for an overall mass-transfer coefficient. The calculated overall mass-transfer coefficients had an average value of 0.407 m/day and showed no correlation with v[sub x], probably due to mass-transfer resistance becoming dominated by the diffusional resistance in the NAPL. These results suggest that the nonequilibrium approach is better suited for describing high velocity (v[sub x]>10 m/day) dissolution of multicomponent NAPL pools, and that flushing of groundwater at very high velocities may not be an effective approach for enhancing NAPL-pool dissolution flux. [ABSTRACT FROM AUTHOR]

An optimization method is proposed for estimating the storage coefficient and transmissivity of an aquifer from drawdowns in large diameter wells consequent to an unsteady pumping. The concept of an optimal time step size is propagated in the proposed method. The estimate of the aquifer parameters corresponding to the optimal time step size is termed final estimate. The estimates for any other time step size are not reliable. The proposed method can also take into account the residual drawdowns. The application of the method is illustrated using an example. [ABSTRACT FROM AUTHOR]

A computationally simple and accurate algebraic approximation of the well function for large diameter wells is proposed. This approximation can be used to calculate drawdown in a large diameter well due to steady pumping. Using this approximation, a method is proposed for calculating drawdowns in large diameter wells due to unsteady pumping discharge. The proposed method is also applicable for calculating residual drawdowns in large diameter wells. In principle, the proposed method that uses the approximation of the well function should yield more accurate results than the previously proposed kernel methods. [ABSTRACT FROM AUTHOR]

Simple equations are proposed for estimating storage coefficient and transmissivity of an aquifer from drawdowns in large- diameter wells. The proposed method requires determination of the peak and time to peak of a unimodal curve. Using these values and utilizing the provided set of equations, the aquifer parameters are estimated through an iterative procedure. The proposed method is void of subjectivity involved in the previously proposed curve matching methods. Also, the new method can be used when the conventional curve matching methods cannot be applied to estimate the aquifer parameters. The new method can be used to estimate the aquifer parameters from the drawdown data observed only up to a time so that the peak could be determined. [ABSTRACT FROM AUTHOR]