50

CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

Groundwater is an important source of water supply for

municipalities, agriculture and industry. Therefore the capability to predict the

behavior of chemical contaminates in flowing groundwater is of vital

importance for a). the reliable assessment of hazardous or risks arising from

groundwater contamination problems, and b) the design of efficient and

effective techniques to mitigate them. There are several studies reported in this

filed. Reliable and quantitative prediction of contaminant movement can be

made only if we understand the processes controlling the transport of

contaminants. These include a) advection, b) hydrodynamic dispersion and c)

physical, chemical and biological reactions that affect their soluble

concentrations in groundwater.

The most challenging problems associated with groundwater

contamination are: a). to prevent the introduction of contaminants in an

aquifer; b). to predict their movement if they are introduced; and c). to remove

them, to some extent in order to protect the biosphere effectively.

Groundwater contamination studies generally include.

i. the scientific understanding of physical, chemical, and biological

processes controlling the fate and movement of contaminants in the

subsurface environment;

ii. the mathematical representation in the transport models to predict the

contaminant movement;

51

iii. the determination of different model parameters in the field and the

laboratory using different methods;

iv. the development of transport models to predict contaminant movement

if they are introduced;

v. the development of management models to control and/or prevent the

introduction of contaminants in the aquifer and to determine the

methodology for the safe disposal of hazardous wastes, and

vi. the development of methodology for the removal of contaminates to the

extent necessary to effectively protect the biosphere.

2.2 GROUNDWATER QUALITY MODELING STUDY

The earliest observation of the dispersion phenomena was reported

by Slichter (1905) who used an electrolyte as a tracer to study the movement

of groundwater. Remarkable studies on related processes in groundwater flow

and contamination transport in 1950 and gradually received the increasing

attention of researchers. Bachmat et al. (1980) conducted a survey of

numerical models mainly related to groundwater management. His report

contained a list of 138 flow models and 39 mass transport models in 14

countries. Naymik (1987) presented a systematic review of 44 technically

advanced articles on mathematical modeling of solute transport in the

subsurface system. His review covers the period 1980-1985 only. Another

comprehensive review paper on modeling of solute transport in groundwater

was presented by Abriola (1987). She reviewed models reported upto 1986.

Many models have been developed to assess traditional surface

water loading impacts of NPS pollution. Some include groundwater recharge

for baseflow generation purposes, but exclude the detailed vadose zone

modeling necessary for assessing potential leaching of agricultural chemicals.

Typical models include CREAMS (Krisel etal 1980). HSPF (Donigian et al

52

1983), ANSWERS (Beasley et al 1977), and WLF (Haith and Shoemaker

1987). However, these models will not be adequately address in areas where

groundwater may locally or regionally be impacted. Hazardous waste

management research has greatly advanced modeling capability to predict

hazardous waste plumes and plan or assess remedial action efforts. These

models often emphasize transport in the saturated zone and deal with localized

(point) sources. Several models have been developed to specifically address

the NPS pollution problem that include unsaturated zone modeling with

varying degrees of complexity and emphasis eg. Chemical movement in soil

(CMIS) is a simple continuous simulation model that locates the leading edge

of non-polor organic chemicals in the unsaturated zone (Nofziger et al 1983,

Nofziger and Hornsby 1985). Groundwater Loading Effects of Agricultural

Management Systems (GLEAMS) is a continuous daily simulation model

developed to predict movement of agricultural chemicals in and from root

zone (Leonard et al 1986). Leaching Estimation and Chemistry Model-

Pesticides (LEACHMP) - Simulates non-volatile pesticides in the unsaturated

zone (Wagenet and Hutson, 1986). Method of Underground Solute Evaluation

(MOUSE) is a simplified model developed for tracking soluble chemical

movement in both the saturated and unsaturated zone (Pacenka and Steenhuis

1984). Pesticide Analytical Model (PESTAN) - It is used for estimating

organic chemical movement in unsaturated zone - USEPA. Seasonal Soil

Compartment Model (SESOIL) - Long term simulations of pesticide transport

by advection, diffusion and volatilization (Foster et al 1980).

Angelakis et al (1987) described simultaneous transformation and

transport of two solutes with different dispersion coefficients by two one-

dimensional partial differential equations. They used the linear equilibrium

adsorption-desorption relationship for both solutes and irreversible microbial

first-order kinetics as an overall transformational mechanism. Analytical

53

solutions were obtained using Laplace transformation for zero initial

conditions, pulse input conditions, and semi-infinite media.

Hassanizadeh and Leijinse (1988) worked on modeling of brine

transport in porous media. They discussed certain important physical and

mathematical differences between low and high concentrations situations.

They solved a set of two nonlinear coupled partial differential equations

obtained from a modified formulation of Darcy’s and Fick’s laws by means of

iterative methods. Lassey (1988) derived an analytical solution to the

advection-dispersion equation for one-dimensional solute or tracer transport

including sorption and first-order loss. Miller and Weber (1988) described

laboratory investigations and mathematical modeling of the sorption of

hydrophobic solutes by aquifer materials. They obtained accurate

representations of the sorpotion process with either a dual resistance diffusion

model or an equilibrium/first-order sorption rate model.

A three dimensional mixing cell solute transport model on the

principles of conservation of mass for water and solute was developed by

Bhasker Rao and Hathaway. As a first approximation to solute transport

phenomenon, dispersion introduced as an artifact of the solution procedure

represents physical dispersion in the results obtained from the model. The

numerical dispersion can be controlled to some extent. The simplicity of

principles on which the model is based makes it easy to understand and use.

The formulation is used in conjunction with the McDonald and Harbaugh

ground-water flow model. The model has been applied to an aquifer located in

Southern New Mexico and Texas to predict chlorine concentration changes

resulting from proposed future pumping to supply municipal water for the city

of EI Paso, Texas. The calculated historical trend of changes in chloride

concentration lies within the range of estimates of the observed trend. A

54

relationship between future drawdown and chloride concentration has been

developed.

Pesticide movement in groundwater by way modeling was

described by Shoemaker et al (1990). The assessment of agricultural impacts

on water quality is now being redirected to include both groundwater and

surface water. Agricultural Non Point Source (NPS) pollution has several

unique characteristics. Agricultural production generally takes place in an

uncontrolled environment involving vast land areas with pollutant losses

affected by the complex interrelationships of meteorology, management and

cropping practices, geology, topography, and soils. NPS pollution is a diffuse

source phenomena affecting water on filed, watershed, or regional scale.

Because NPS pollution is derived from unpredictable climatic events, it must

be treated as stochastic problem with consideration for long-term risks.

Possible groundwater pollutants from agricultural production activities include

nitrogen, pesticides and their inherent compounds. Surface water pollutants

include phosphorous and sediment. If agricultural waste management is

considered- involving the application of animal manures to cropland-

additional pollutant include bacteria, other microorganisms, and

biodegradable, oxygen-demanding organic substances (eg. fecal matter).

Pollution control requires a diverse collection of chemical, managerial, and

structural (eg. terraces, diversions, and other soil conservation structure)

practices. The economic implications (cost benefit ratio) of each management

practice, or combinations thereof should be considered in assessing any NPS

pollution alternative. Because of the complexity of NPS pollution, the

development of abatement techniques is not a simple process. Only two

methods for assessing the effectiveness of NPS management techniques

currently exist: (1) actual field testing of alternatives, or (2) computer

modeling of various management scenarios. Field testing is limited to the

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number of locations and scenarios that can be feasibly examined and requires

several years of observations to collect valid data that reflect climate

variability. Thus, computer models are the preferred alternative in examining a

greater diversity of management scenarios and locals (Baker 1985, Donigian

and Carsel 1986). Computer models can also address the problem of

meteorological variability (Leonard et al. 1986, Pacenka and Steenhuis 1984).

Long-term rainfall records and rainfall generation techniques can be used to

examine the interactions between meteorology and management alternatives.

Process models also can be linked to economic models to determine the

economically optimal management solutions (Crowder et al 1985, Roka 1988,

Roka et al. 1989).

GIS based urban groundwater recharge pollutant flux model was

given by Abraham Thomas et al (1991). They presented the use of GIS in

assessing the spatial distribution of pollutant fluxes reaching an urban

unconfined aquifer system in Birmingham, UK. Urban groundwater recharge

and pollution is a complex and poorly understood process. No suitable method

is available for assessing the amount of recharge and pollutant fluxes reaching

in urban aquifer sustainability, a desktop GIS (Arc View GIS and Arc View

Spatial Analyst extension)-based runoff-recharge–pollutant flux model has

been developed to estimate the potential recharge and pollutant fluxes to an

urban unconfined aquifer system. The authors explained how an integrated

approach (involving analysis of various thematic maps and other attribute

information of a UK urban area using the above desktop GIS-based recharge

pollutant flux model could help in assessing the amount of groundwater

recharge and pollutant fluxes (currently a few chosen pollutant species such as

nitrate, chloride, and BTEX compounds) reaching to the groundwater of the

Birmingham area.

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A ground-water flow modeling study was performed by Haitjema

(1992) for the Four County Landfill (FCL) in Fulton County, Indiana. The

modeling was performed with the relatively new analytic element method. The

new method employs superposition of closed form analytic solutions, rather

than a grid or element network, and proved an effective tool in answering

some unresolved hydrogeological questions. The study results demonstrate

substantially higher regional and local hydraulic conductivities than suggested

by the landfill consultants, well-connected upper and lower aquifer zones at

the site, and potential ground-water travel times from the landfill to the nearby

Tippecanoe River of less than 15 years.

Tedaldi and Loehr (1992) made a comprehensive assessment of the

environmental impact of a full-scale, operating overland flow (OLF) land

treatment system at the Campbell Soup (Texas), Inc. facility in Paris, Texas.

The system treats over 16,000 m3/d of waste water and has been in operation

for over 25 years. Field samples of soil, waste water, OLF runoff, and ground

water collected during the study and detailed long-term process records

maintained by Campbell Soup were used as part of the evaluation.

Geochemical data indicated that sulfate-chloride facies were dominant for the

ground water collected at the OLF site. Field data and calculations indicated

that the evapotranspirative concentration of salts in the applied waste water

would be insufficient to produce the measured concentrations in the ground

water. A pattern of increasing ionic concentration over time (1968 to 1989)

with small changes in ionic ratios suggested a trend toward the dissolution and

concentration of naturally present minerals (such as gypsum and sodium

chloride) in the slow moving ground water. Predictions made with the aid of

MINTEQA2, a thermodynamic equilibrium model, indicated that precipitation

of carbonates and simultaneous ion exchange on clays could represent a

significant mechanism for the removal of calcium and magnesium from

57

solution and the addition of sodium. The development of a slightly saline,

semiconfined aquifer was strongly suggested by the ground-water geochemical

data, soil data, the estimated rate of infiltration, field hydraulic conductivity,

MINTEQA2 model predictions and the magnitude of the volume of waste

water applied.

It was reported by Goode (1992) that during unsteady or transient

ground-water flow, the fluid mass per unit volume of aquifer changes as the

potentiometric head changes, and solute transport is affected by this change in

fluid storage. Three widely applied numerical models of two-dimensional

transport partially account for the effects of transient flow by removing terms

corresponding to the fluid continuity equation from the transport equation,

resulting in a simpler governing equation. However, fluid-storage terms

remaining in the transport equation that change during transient flow are, in

certain cases, held constant in time in these models. For the case of increasing

heads, this approximation, which is unacknowledged in these models'

documentation, leads to transport velocities that are too high and increased

concentration at fluid and solute sources. If heads are dropping in time,

computed transport velocities are too low. Using parameters that somewhat

exaggerate the effects of this approximation, an example numerical simulation

indicates solute travel time error of about 14 percent but only minor errors due

to incorrect dilution volume. For horizontal flow and transport models that

assume fluid density is constant, the product of porosity and aquifer thickness

changes in time: initial porosity times initial thickness plus the change in head

times the storage coefficient. This formula reduces to the saturated thickness in

unconfined aquifers if porosity is assumed to be constant and equal to specific

yield. The computational cost of this more accurate representation is

insignificant and is easily incorporated in numerical models of solute

transport.

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Wilson et al (1996) applied GIS based solute transport modeling to

study the scale effects of soil and climate data input. The weather generator

(WGEN) and chemical movement through layered soils (CMLS) computer

models were modified and combined with two sets of soil and climate inputs

to evaluate the impact of input data map resolution on model predictions. The

basic soil and climate inputs required by WGEN and CMLS were acquired

from either; (i) the USDA-NRCS State soil geographic (STATSGO) database;

(ii) the USDA-NRCS (County) soil survey geographic (SSURGO) database;

(iii) the Montana agricultural potential system (MAPS) database which divides

Montana into approximately 18,000 twenty square kilometer cells and stores

more than 200 different land and climate characteristics for each of these cells;

and (iv) a series of fine-scale monthly climate surfaces developed by the

authors (0.55km2 cell size) using thin-plate splices, published climate station

records, and USGS digital elevation models (DEMs). Fifteen years of daily

precipitation and evapotranspiration (ET) values were generated and combined

with soil and pesticide inputs in CMLS to estimate the depth of picloram (4-

amino-3,5,6-trichloro-2-pyridinecarboxylic acid) movement at the end of the

growing season for every unique combination (polygon) of soil and climate in

a 320 km2 area in Teton County, Montana. Results indicate that: (i) the mean

depths of picloram movement predicted for the study area with the SSUGO

(county) soils and MAPS (coarse-scale) climate information and the two

model runs using the fine-scale climate data were significantly different from

the values predicted with the STATSGO (state) soils and MAPS climate data

based on a new variable containing the differences between the depths of

leaching predicted with the different input data by soil / climate map unit and

testing whether the mean difference was significantly different from zero at

the 0.01 significance level; and (ii) CMLS identified numerous (small) areas

where the mean center of the picloram solute front was likely to leach beyond

the root zone when the county soils information was used. This last measure

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may help to identify areas where potential chemical applications are likely to

contaminate groundwater.

Effects of land use on ground water quality in the Anoka sand plain

aquifer of Mimmesota was studied by Trojan et al (1996) to compare ground

water quality under irrigated and non irrigated agriculture, sewered and non

sewered residential developments, industrial, and non developed land uses.

Twenty-three monitoring wells were selected in the unconfined sand aquifer.

Sampling were carried out and analyzed for major ions, trace inorganic

chemicals, volatile organic compounds (VOC), herbicides and herbicide

degrades. They also collected samples for polynuclear aromatic hydrocarbons,

perchlorate and coliform bacteria. They observed significant differences in

water chemistry beneath different land uses. Concentrations of several trace

inorganic chemicals were greatest under sewered urban areas. VOC detections

were 100% in commercial areas, 52% in sewered residential area, and < 10%

for other land uses. Median nitrate concentrations were greatest under irrigated

agriculture (15,350µg/L) and non sewered residential area

(6080µg/L).Herbicides and degrades of acetanilide and triazine herbicides

were detected in 86 % of samples from irrigated agriculture areas, 68 % of

samples from nonirrigated areas and < 10% of samples from other land uses.

Degrades accounted for 96% of the reported herbicide mass. They did not

observe seasonal difference in water chemistry, but observed trends in water

chemistry when land use changes occurred. Their result shows land use is the

dominate factor affecting shallow ground water quality.

Gregorauskas et al (1999) carried out a model on groundwater flow

and contaminant transport at Klaipeda oil terminal, Lithuania and found that

water table aquifer in the area of Klaipeda oil terminal is polluted with

hydrocarbons (oil products) dissolved in water. Above this aquifer, there is a

layer containing oil and reaching 0.5 m in thickness. These pollutants do not

60

threaten drinking water sources, but oil can enter the lagoon of Kursiu Marios

and the Baltic Sea. Groundwater monitoring has been organized, shallow

groundwater investigations have been done, filtration and migration models of

the terminal and adjacent areas have been consulted. Modeling results showed

that the flow of hydrocarbons to the lagoon could be efficiently barred by a

horizontal drain.

Moreno and Sinton explained about groundwater model flow

calibration-comparison of a decision tree approach and automated parameter

estimation for a practical application with limited data. Groundwater modeling

calibration can often result in multiple plausible results, especially in a case

with limited data. Sensitivity analysis varying single parameters may be

unsuccessful in testing the envelope of possible calibrated solutions. The

authors considers alternate approaches to simulating the effects of developing

a new groundwater supply on water levels and river flow rates in a river valley

in the desert Southwest. A 400 square mile model of three aquifers was

prepared. For this application, a range in model predictions from ‘worst

reasonable’ to ‘best reasonable’ predictions was required in order to assess

potential long-term environmental impacts. Two alternate approaches were

tested: a decision tree approach in which parameters were applied in worst or

best combinations based on the combined experience of a modeling

committee, and an automated parameter estimation approach. Several

measures of model calibration and behavior were used in assessing the model

simulations of current conditions, and the accumulation of ‘hidden errors’ in

long-term transient simulations was also evaluated. Most likely predictions

and estimated uncertainty were compared for each approach.

Solute transport model in structured soils and the movement of

chemicals through the soil was reported by Stagnitti et al (2001). He reported

that current models and methods do not adequately describe the leaching of

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nutrients through soil, often underestimating the risk of groundwater

contamination by surface-applied chemicals, and overestimating the

concentration of resident solutes. This inaccuracy results primarily from

ignoring soil structure and non-equilibrium between soil constitutes, water,

and solutes. A multiple sample percolation system (MSPS), consisting of 25

individual collection wells, was constructed to study the effects of localized

soil heterogeneities on the transport of nutrients (NO3-, Cl

-, PO4

3-) in the

vadose zone of an agricultural soil predominantly dominated by clay. Very

significant variations in drainage patterns across a small spatial scale were

observed (one-way ANOVA, p < 0.001) including considerable heterogeneity

in water flow patterns and nutrient leaching. The authors have used data

collected from the multiple sample percolation experiments and compared the

performance of two mathematical models for predicting solute transport, the

advective-dispersion model with a reaction term (ADR), and a two-region

preferential flow model (TRM) suitable for modeling non-equilibrium

transport. These results have implications for modeling solute transport and

predicting nutrient loading on a larger scale.

Numerical simulations of ground water flow and physical transport

associated with a natural gradient tracer experiment within a heterogeneous

alluvial aquifer of the Natural Attenuation Study (NATS) site near Columbus

Mississippi was carried out by Julian et al (2001). The principal goal of NATS

is to evaluate biogeochemical models that predict the rate and extent of natural

biodegradation under field conditions. They describe the initial phase in the

model evaluation process, i.e calibration of flow and physical transport models

that simulate conservative bromide tracer plume evolution during NATS. An

initial large scale flow model (LSM) is developed encompassing the

experimental site and surrounding region. This model is subsequently scaled

down in telescopic fashion to an intermediate-scale ground water flow model

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(ISM) covering the tracer-monitoring network, followed by a small-scale

transport model (SSM) focused on the small region of hydrocarbon plume

migration observed during NATS. The LSM uses inferred depositional

features of the site in conjunction with hydraulic conductivity (K) data from

aquifer tests and borehole flowmeter tests to establish large-scale K and flow

field trends in and around the experimental site. The subsequent ISM

incorporates specified flux boundary conditions and large-scale K trends

obtained from the calibrated LSM, while preserving small-scale K structure

based on some 4000 flowmeter data for solute transport modeling. The

configuration of the ISM predicted potentiometric surface approximates that of

the observed surface within a root mean squared error of 0.15 m. The SSM is

based on the dual-domain mass transfer approach. Despite the well-

recognized difficulties in modeling solute transport in extremely

heterogeneous media as found at the NATS site, the dual-domain model

adequately reproduced the observed bromide concentration distributions.

Differences in observed and predicted bromide concentration distributions are

attributed to aquifer hetrogenetity at the decimeter (dm) and smaller scales.

The calibrated transport parameters for the SSM (i.e 1:7 for the ratio of

mobile-to-total porosity; 2.5 x 10-3

day-1

for the mass–transfer coefficient ; 1 m

for longitudinal dispersivity; and 0.1 m for transverse dispersivity are

consistent with separate numerical simulations of two earlier tracer

experiments at the site. The multiscale modeling approach adopted in the study

permits the incorporation of both large-scale geologic features important for

flow simulation and small scale heterogeneities critical for transport

simulation. In addition, the dual-domain transport model provides a foundation

for multi species reactive transport modeling studies of natural attenuation

hydrocarbons during NATS.

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One-dimensional reactive multi-component landfill leachate

transport model coupled to three modules (geochemical equilibrium, kinetic

biodegradation, and kinetic precipitation-dissolution) was developed by Islam

and Singhal (2001) to simulate the migration of contaminants in soils under

landfills. A two-step sequential operator splitting method is applied to solve

the coupled transport equations and the biogeochemical reaction equations.

The geochemical module is based on the equilibrium speciation model

(MINTEQA2), which uses ion-association equilibrium-constant approach to

represent the various geochemical reactions. The biodegradation module

describes the sequential biological degradation of organic compounds by

multiple functional bacterial populations. Analytical equations based on

macroscopic approach are used to model changes in porosity and permeability

caused by biomass accumulation and mineral precipitation in soils. The model

has been evaluated by comparing the model results with widely used one-

dimensional mixing is applied to a hypothetical landfill to simulate the effect

of biological degradation of organic matter on the local inorganic

geochemistry and also to demonstrate the effect of microbial activity on the

evolution of porosity reduction of soils under the landfill.

Three-dimensional solute transport model with biological reactions

was developed by Braunerand Mark and Widdowson (2001) for simulating the

natural attenuation study (NATS) at the Columbus Air Force Base in eastern

Mississippi. NATS consisted of the release of a petroleum-based non-aqueous

phase liquid (NAPL) and subsequent monitoring of BTEX (benzene, toluene,

ethyl benzene, p-xylene), naphthalene, decane, and bromide in a shallow,

unconfined aquifer. Conceptual and mathematical models were developed for

NAPL source release, sequential aerobic/anaerobic bio-degradation, and

sorption during NATS. A multiple species, solute transport code (SEAM3D)

was used to simulate fully three-dimensional transport and aerobic, nitrate-

64

reducing, ferrogenic, and methanogenic hydrocarbon biodegradation.

Simulation results matched individual BTEX concentration distributions

collected five-and nine months following NAPL release. SEAM3D mass-

balance calculations at t = nine months indicated that 49% of the hydrocarbon

mass that dissolved into the aqueous phase was consumed by biodegradation,

13% of this mass was sorbed, and the remaining 38% was present in the

aqueous phase. Mass calculations at t = nine months further indicated that

aerobic biodegradation accounted for the majority of hydrocarbon

biodegradation (46% of the biodegraded mass), followed by ferrogenesis

(28%), nitrate-reduction (Fe [III]) concentration, hydrocarbon utilization rates,

initial condition for the anaerobic microbial populations, and dispersivity.

Anne Coudrain et al (2001) carried out a study on subsurface

transfer of chloride after a lake retreat in Central Andes. The area under study

covers 3500 km2 in the upstream part of the closed catchment basin of the salt

crust of Uyuni. This crust is a remnant of the saline lake Tauca, which covered

the area about 15,000 years ago. In the downstream part of the aquifer, the

Chloride concentration of ground water and Cl content in the unsaturated zone

exceed 20 meq/L and 18 kg/m2, respectively. With the present hydrological

conditions under semiarid conditions, the groundwater residence time in the

study are exceeds 3000 years. Transient simulations over 11,000 years were

made using initial conditions as the retreat of Lake Tauca and taking into

account a low recharge during the arid mid-Holocene period. The modeling

simulates groundwater flow, Cl transport, and groundwater residence time. It

includes the evaporation from the aquifer that leads to the accumulation of

chloride in the unsaturated zone. Results of the modeling are consistent with

the observations if it is assumed that the Cl previously accumulated in

unsaturated zone was flushed back into the aquifer around 2000 years B.P.,

contemporaneously with the end of the arid period.

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Langevin (2002) presented a method for incorporating the hydraulic

effects of vertical fracture zones into two-dimensional cell based continuum

models of ground water flow and particle tracking. High hydraulic

conductivity features are used in the model to represent fracture zones. For

fracture zones that are not coincident with model rows or columns, an

adjustment is required for the hydraulic conductivity value entered into the

model cells to compensate for the longer flow path through the model grid. A

similar adjustment is also required for simulated travel times through model

cells. A travel time error of less than 8% can occur for particles moving

through fractures with certain orientations. The fracture zone continuum model

uses stochastically generated fracture zone networks and Monte Carlo analysis

to quantify uncertainties with simulated advective travel times. An approach is

also presented for converting an equivalent continuum model into a fracture

zone continuum model by establishing the contribution of matrix block

transmissivity to the bulk transmissvity of the aquifer. The methods are used

for a case study in west-central Florida to quantify advective travel times are

assumed to result from the presence of vertical fracture zones, commonly

observed on aerial photographs as photolineaments.

A laboratory experiment on chalk samples from Denmark and Israel

to determine diffusion and distribution coefficients was performed by

Witthuser et al (2003). They used batch tests to define sorption isotherms for

naphthalene and o-xylene. Linear sorption isotherms were observed and

described with Henry-isotherms. Because of the high purity and low content of

clay minerals and organic carbon, Danish and white Israeli chalk generally

have low retardation capacities. Contrarily, gray Israeli chalk, with organic

carbon fractions as high as 1.092%, remarkably retards organic contaminants.

The Koc concept is not applicable to predicting distribution coefficients based

on the organic carbon content in the chalk samples. Effective diffusivities of o-

66

xylene, naphthalene and several artificial tracers were determined using

through-diffusion experiments. Based on measured diffusion coefficients and

available literature values, a chalk specific exponent of 2.36 for Archoe’s law

was derived, allowing a satisfactory estimate of relative diffusivities in chalk.

A field-scale tracer test with uranine and lithium was performed in the Negev

desert (Israel) to examine the transferability of diffusivities determined on

small rock samples in the laboratory. Due to low recovery rates of the tracer, a

modified single fissure dispersion model was used for inverse modeling of the

breakthrough curves. Resulting diffusivities deviate insignificantly from the

laboratory values, which are considered to be representative for the

investigated part of the aquifer and applicable in transport models.

A large and diverse body of subsurface characterization data was

generated by Scheibe and Chien (2003) at a field research site near Oyster,

Virginia, which provides a unique opportunity to test the impact of

conditioning data of various types on predictions of flow and transport.

Bromide breakthrough curves (BTCs) were measured during a forced-gradient

local-scale injection experiment conducted in 1999. Observed BTCs are

available at 140 sampling points in a three-dimensional array within the

transport domain. A detailed three-dimensional numerical model is used to

simulate breakthrough curves at the same locations as the observed BTCs

under varying assumptions regarding the character of hydraulic conductivity

spatial distributions, and variable amounts and types of conditioning data. We

present comparative results of six cases ranging from simple (deterministic

homogeneous models) to complex (stochastic indicator simulation conditioned

to cross-borehole geophysical observations). Quantitative measures of model

goodness-of-fit are presented. The results show that conditioning to a large

number of small-scale measurements does not significantly improve model

predictions, and may lead to biased or overly confident predictions. However,

67

conditioning to geophysical interpretations with larger spatial support

significantly improves the accuracy and precision of model predictions. In all

cases, the effects of model error appear to be significant in relation to

parameter uncertainty.

Use of nonlinear parameter estimation techniques is now

commonplace in groundwater model calibration. However, there is still ample

room for further development of these techniques in order to extract more

information from calibration datasets, to more thoroughly explore the

uncertainty associated with model predictions, and to make easier to

implement in various modeling contexts. John Doherty (2003) described the

use of "pilot points" as a methodology for spatial hydraulic property

characterization. When used in conjunction with nonlinear parameter

estimation software that incorporates advanced regularization functionality

(such as PEST), use of pilot points can add a great deal of flexibility to the

calibration process at the same time as it makes this process easier to

implement. Pilot points can be used either as a substitute for zones of

piecewise parameter uniformity, or in conjunction with such zones. In either

case, they allow the disposition of areas of high and low hydraulic property

value to be inferred through the calibration process, without the need for the

modeler to guess the geometry of such areas prior to estimating the parameters

that pertain to them. Pilot points and regularization can also be used as an

adjunct to geostatistically based stochastic parameterization methods. Using

the techniques described herein, a series of hydraulic property fields can be

generated, all of which recognize the stochastic characterization of an area at

the same time that they satisfy the constraints imposed on hydraulic property

values by the need to ensure that model outputs match field measurements.

Model predictions can then be made using all of these fields as a mechanism

for exploring predictive uncertainty.

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Zheng and Gorelick (2003) carried out macrodispersion experiment

(MADE) at a site in Columbus, Mississippi. The experiment indicated that the

relative preferential flowpaths and flow barriers resulting from decimeter-scale

aquifer heterogeneities appear to have a dominant effect on plume-scale solute

transport. Numerical experiments are thus conducted in this study to explore

the key characteristics of solute transport in two-dimensional flow fields

influenced by decimeter-scale preferential flowpaths. A hypothetical but

geologically plausible network of 10 cm wide channels of high hydraulic

conductivity is used to represent the relative preferential flowpaths embedded

in an otherwise homogeneous aquifer. When the hydraulic conductivity in the

channels is 100 times greater than that in the remaining portion of the aquifer,

the calculated concentration distributions under three source configurations all

exhibit highly asymmetrical, non-Gaussian patterns. These patterns, with peak

concentrations close to the source and extensive spreading down gradient,

resemble that observed at the MADE site tracer tests. When the contrast

between the channel and non channel hydraulic conductivities is reduced to

30:1 from 100:1, the calculated mass distribution curve starts to approach a

Gaussian one with the peak concentration near the central portion of the

plume. Additional analysis based on a field scale model demonstrates that the

existence of decimeter-scale preferential flowpaths can have potentially far-

reaching implications for groundwater remediation. Failure to account for

them in numerical simulation could lead to over-estimation of the

effectiveness of the remedial measure under consideration.

Groundwater quality modeling study of Kancheepuram district,

Tamilnadu was done by Kumar and Venugopal (2003). They studied the

vulnerability of migration of pollutants. Groundwater resources underlying the

ground surface in the district of Kancheepuram is vulnerable to contamination.

Contamination of these ground water resources could be prevented by

69

development of accurate vulnerability models, which could be used to predict

the ground water vulnerability and there by give appropriate recommendations

for decreasing the potential impact of ground water contaminants being

used/applied on the land surface. The authors have carried out a study to test a

vulnerability index equation, using cell based GIS analysis. The vulnerability

index equation incorporates soil characteristics, hydro geologic factors, depth

to ground water and extant of irrigation. The vulnerability index equation is

calibrated to a subset of groundwater analytical results. Spatial representations

of these results are produced which would assist land use planners,

agriculturists in planning and regulating land use in the district with out

harming the quality of ground water resources. The authors have concluded

that the water quality is generally good in this district except in areas where

there is acute pollution due to the discharge of effluents from zari factories and

distilleries into the alluvial belt. These effects spoil not only the water but also

the soil characters. In areas in and around Kancheepuram, and Chengalpattu

require special attention for pollution study. Recommendation for optimum

utilization could be made only at the rate of natural replenishment. The authors

have used DRASTIC model to study the groundwater vulnerability of the

study area.

Solute transport modeling and inverse modeling for parameter

estimation of Mahi right bank canal command area was presented by Rastogi

and Mishra (2003). Sea water intrusion model is also considered for a

synthetic multilayer coastal aquifer. The study finds that a proper formation of

models augmented with adequate data can yield reasonably accurate results.

Together these numerical models are essential for effective groundwater

systems planning and management of regional aquifers. They finds that the

net annual recharge to be 685.93 MCM (GA approach) and 688.45 MCM

(GNM method) by inverse modeling, which are in close agreement with the

70

estimated net annual recharge (614.32 MCM) derived from the mass balance

approach considering the various inflow and outflow data collected from the

field. Stochastic models, fractured rocks modeling, heavy element adsorption

models and aqueous-non aqueous phase (NAPL, DNAPL) models were not

considered which, however, also form a part of the complete GSPM strategies.

GSPM being a multi-disciplinary approach may further be used to work out

the groundwater flow quantities, contamination predictions, and remediation

strategies for real groundwater systems.

Mao et al (2004) applied three-dimensional model for multi-

component reactive transport with variable density groundwater flow and

reported as follows: PHWAT is a new model that couples a geochemical

reaction model (PHREEQC-2) with a density-dependent groundwater flow and

solute transport model (SEAWAT) using the split-operator approach. PHWAT

was developed to simulate multi-component reactive transport in variable

density groundwater flow. Fluid density in PHWAT depends not only the

concentration of a single species as in SEAWAT, but also the concentrations

of other dissolved chemicals that can be subject to reactive process. Simulation

results of PHWAT and PHREEQC-2 were compared in their predictions of

effluent concentrations from a column experiment. Both models produced

identical results, showing that PHWAT has correctly coupled the sub-

packages. PHWAT was then applied to the simulation of tank experiment in

which seawater intrusion was accompanied by cation exchange. The density

dependence of the intrusion and snow plough effect in the breakthrough curves

were reflected in the model simulations, which were in good agreement with

the measured breakthrough data. Comparison simulations that, in turn,

excluded density effects and reactions allowed to quantify the marked effect of

ignoring these processes. Next, they explored numerical issues involved in the

practical could model physically unstable flow and that numerical instabilities

71

were suppressed. Physical instability developed in the model in accordance

with the increase of the modified Rayleigh number for density-dependent

flow, in agreement with previous research.

Groundwater pollution and its chemical quality in some parts of

Unnao district of Uttar Pradesh State was studied by Mamta Goyal et al

(2006). The study reveals that in the most of the villages the quality of

groundwater is good and suitable for drinking and domestic uses. In few

villages, the quality of groundwater is found to be contaminated as the cations,

anions and fluoride concentrations are found higher than the maximum

permissible limit of drinking water specially in the open wells (shallow

aquifers) where as the groundwater quality of hand pumps (deep aquifers) is

better than of open wells. The higher concentration of cations and anions are

found during pre-monsoon due to evaporation process, and due to dilution

effect through rain fall recharge, the values are found comparatively low in

post-monsoon period. The higher concentration, use of fertilizers, pesticides

and industrial effluents contamination, which leads the pollution of

groundwater.

A water quality index of groundwater in and around Khandaleru

catchments in Nellore district, Andhra Pradesh State was developed by Asadi

et al (2006). The groundwater samples collected at the predetermined locations

are analyzed for physico-chemical parameters for the generation of attribute

database. Based on the results of the analysis maps showing spatial

distribution of selected water quality parameters namely; pH, alkalinity,

chlorides, sulphates, nitrates, hardness, TDS, fluorides and sodium are

prepared using curve-fitting method in GIS software. The analysis of the

physico-chemical properties and computation of WQI are helpful in the

grouping of groundwater samples into excellent, good, poor, very poor and

unfit.

72

Asadi et al (2007) applied remote sensing and GIS techniques for

evaluation of groundwater quality in Municipal Corporation of Hyderabad

(Zone-V). Groundwater quality in Hyderabad has special significance and

needs great attention of all concerned since it is the major alternative source of

domestic, industrial and drinking water supply. The study monitors the

groundwater quality, relates it to the land use / land cover and maps such

quality using remote sensing and GIS techniques for a part of Hyderabad

metropolis. Thematic maps for the study are prepared by visual interpretation

of SOI toposheets and linearly enhanced fused data of IRS-ID PAN and LISS-

III imagery on 1:50,000 scale using AutoCAD and ARC/INFO software.

Water Quality Index (WQI) was then calculated to find the suitability of water

for drinking purpose. The overall view of the water quality index of the

present study area revealed that most of the study area with > 50 standard

rating of water quality index exhibited poor, very poor and unfit water quality

except in places like Banjara Hills, Erragadda and Tolichowki. Appropriate

methods for improving the water quality in affected areas have been

suggested.

Emmanuel et al (2007) explored the physico-chemical

characteristics of all drinking water sources of Nalgonda sub-division, Andhra

Pradesh State. About 35 water samples were collected from the various

locations of the study area including bore well, hand pump and analysed pH,

EC, TDS, turbidity, total hardness, fluoride, nitrate and nitrite, sulphates,

phosphates, calcium, magnesium, sodium, potassium, iron and dissolved

oxygen. On an average, in almost all the samples, one or the other chemical

constituent was beyond the permissible limits. It was concludes water sources

in the study are not fit for drinking as well as agricultural purpose also. The

study indicates the need for periodic monitoring of groundwater in the study

area.

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Sources and fate of nitrate (NO3-) transport in the Illinois River

from the Chicago area to the river’s confluence with the Mississippi river was

conducted by Panno et al (2008). After two years of study they concluded that

samples from waterways in the Chicago area (Des Plaines River and the

Sanitary and Ship Canal) had relatively high concentrations of nitrogen (N)

species and NO3 isotopic compositions indicative of treated wastewater

(TWW). Downstream of the Brandon Road Lock and Dam, NO3, in tributaries

discharging to the Illinois River primarily as well as drain tiles were indicative

of synthetic fertilizer and/or soil organic matter (SOM) at various stages of

denitrification. Nitrate-N concentrations generally decreased in the Illinois

River with distance from Chicago area primarily due to dilution. The decrease

in NO3-N concentrations was especially conspicuous during the summer, when

there is minimal discharge from drain tiles and NO3-N concentrations in the

tributaries were low. In August 2005, when conditions were very dry, NO3-N

concentrations decreased from 7.4 mg/L in the Chicago area to less than

1mg/L near where the Illinois River discharges to the Mississippi River. The

isotropic composition of NO3 in water samples from the Illinois River were a

mixture of three end members: (1) fertilizer and/or SOM in drain tile water,

typically showing the least amount of denitrification, (2) fertilizer and/or SOM

in deeper ground water, showing the height degree of denitrification, and (3)

TWW. There was seasonal variability depending on the volume of water

flowing in the Illinois River. During high flow periods a greater influence of

TWW was observed in the isotopic composition. A subset of summer samples

from the Chicago waterways had isotopic values plotting near and within the

domain that characterizes manure and sewage. Nitrate in the Chicago area is

primarily derived from TWW, with its isotopic signature evident downstream

at least as far as Pekin during most of the year and all the way to the

Mississippi River during periods of low flow. Denitrification occurs

predominantly in groundwater between and away from drain tiles, although

74

there is evidence that in stream denitification and/or biological uptake of NO3-

occurs in the Peoria Lake reach of the Illinois River, at least during periods of

low flow in the summer. They calculated that the river was losing about half of

its NO3-N load in Peoria Lake in August 2005 (a period of very low flow), at a

rate of about 7500 kg/day.

A study on a hyperbolic asymptotic function in dispersivity was

carried out by Jui-Sheng Chen et al (2008). The study indicates that the

dispersivity initially increases with travel distance and eventually reaches an

asymptotic value at long travel distance. It is adopted and incorporated into the

general advection-dispersion equation for describing scale-dependent solute

transport in porous media. An analytical technique for solving advection-

dispersion equation with hyperbolic asymptotic distance-dependent

dispersivity is presented. The analytical solution is derived by applying the

extended power series method coupling with the Laplace transform. The

developed analytical solution is compared with the corresponding numerical

solution to evaluate its accuracy. Results demonstrate that the breakthrough

curves at different locations obtained from the derived power series solution

agree closely with these from the numerical solution.

Hassan et al (2008) evaluated the use of the generalized likelihood

uncertainty estimation (GLUE) methodology in analyzing the results of

stochastic groundwater models. They investigated the ability of the GLUE

methodology to mitigate the effect of the selection of the input parameter prior

distributions on the modeling results. This is important when no prior

information is available or when significantly different priors come from

different sources or experts. The different approaches that can be used to

implement the GLUE methodology in analyzing the stochastic results of such

models and quantifying the uncertainty in model prediction are evaluated.

Recent debates about the GULF methodology and the problem of using ‘less

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formal likelihood’ functions are discussed in terms of the applicability of such

issues to groundwater studies in general and a given filed site specifically.

These issues are investigated using a density-driven groundwater flow model

of a nuclear testing site (Milrow) on Amchitka Islan, Alaska. Results of the

analysis highlight the subjectivity of the choice of the shape factor associated

with the GULF likelihood measures. However, the arbitrary choice of this

factor can be tied to the level of confidence one can place on the available

observations. While traditional GULF applications focus on displaying

prediction quantities, GLUE can be used to develop uncertainty bounds that

are qualitatively similar to predictive uncertainty. Interestingly, for the case

study shown the traditional GLUE quantities and the uncertainty bounds are

almost identical. Results also show that the GLUE- based ensemble averaging

yields results that are controlled by the data more than by the prior

distributions. The GLUE developed uncertainty bounds provide conditional

predictions that are free from the artificial smoothing associated with ensemble

averaging.

Groundwater quality management relies more and more on models

in recent years. These models are used to predict the risk of groundwater

contamination for various land uses. Cors van den Brink et al (2008) presented

an assessment of uncertainties and sensitivities to input parameters for a

regional model. The model had been set up to improve and facilitate the

decision-making process between stakeholders and in a groundwater quality

conflict. The stochastic uncertainty and sensitivity analysis comprised a Monte

Carlo simulation technique in combination with a Latin hypercube sampling

procedure. The uncertainty of the calculated concentrations of nitrate leached

into groundwater was assessed for the various combinations of land use, soil

type, and depth of the groundwater table in a vulnerable, sandy region in The

Netherlands. The uncertainties in the shallow groundwater were used to assess

76

the uncertainty of the nitrate concentration in the abstracted groundwater. The

confidence intervals of the calculated nitrate concentration in shallow

groundwater for agricultural land use functions did not overlap with those of

non-agricultural land use such as nature, indicating significantly different

nitrate leaching in these areas. The model results were sensitive for almost all

input parameters analyzed. However, the NSS is considered pretty robust

because no shifts in uncertainty between factors occurred between factors

towards systematic changes in fertilizer and manure inputs of the scenarios. In

view of these results, there is no need to collect more data to allow science

based decision making in this planning process.

Rapid expansion of major cities throughout the world is resulting in

the degradation of water quality in local aquifers. Increased use of road deicers

since the middle of the 20th

century in cities in the northern United States,

Canada, and Europe has been linked to degraded ground water quality.

Chicago, Illinois, and its outlying suburban area are used as an example of the

effects of urbanization in a historical context. A statistical study of historical

water quality data was undertaken by Kelly (2008) to determine how

urbanization activities have affected shallow (<60m) ground water quality.

Chloride (Cl-) concentrations have been increasing, particularly in counties

west and south of Chicago. In the majority of shallow public supply wells in

the western and southern counties. Cl- concentrations have been increasing

since the 1960s. About 43% of the wells in these counties have rate increases

greater than 1 mg/L/year, and 15 % have increases greater than 4mg/L/year.

Approximately 24% of the samples collected from public supply wells in the

Chicago area in the 1990s had Cl- concentrations greater than 100 mg/L (35%

in the western and southern counties); medium values were less than 10 mg/L

before 1960. The greater increase in Cl- concentrations in the outer counties is

most likely due to both natural and anthropogenic factors, including the

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presence of more significant and shallower sand and gravel deposits, less

curbing of major highways and streets, and less development in some parts of

these counties.

Kraft et al (2008) identified that the leakage of pollutants from

agricultural lands to aquifers has increased greatly, driven by increasing

fertilizer and pesticide use. Because this increase is recent, ground water

pollutant concentrations, loads, and exports may also be increasing as

pollutants penetrate more deeply into aquifers. They established in an aquifer

profile a ground water recharge and pollutant leakage chronology in an

agricultural landscape where 30 m of till blankets a 57 m thick sandstone

aquifer. Pollutant concentration increased from older ground water (1963) at

the aquifer base to younger ground water (1985) at its top, a signal of

increasing pollutant leakage. Nitrate load and export could increase from

130% to 230% before reaching a steady state in 20 to 40 years. Chloride

increase and then a leveling corresponding to the timing of product adoption

and leveling of demand. Unlike NO3, projecting pesticide residue steady states

is complicated by the phasing in and out of pesticide products over time; for

example, neither alachlor nor atrazine is currently used in the area, and newer

products, which have not had time to transit to the aquifer, have been adopted.

The circumstances that resulted in the lack of a pollutant steady state are not

rare; thus, the lack of steady states in agricultural region aquifers may not be

uncommon.

Shaoyuan Feng et al (2008) reported that in arid regions, human

activities like agriculture and industry often require large ground water

extractions. Under these circumstances, appropriate ground water management

polices are essential for preventing aquifer overdraft, and thereby protecting

critical ecologic and economic objectives. Identification of such polices

requires accurate simulation capability of the ground water system in response

78

to hydrological, meteorological, and human factors. In their research, artificial

neural networks (ANNs) were developed and applied to investigate the effects

of these factors on ground water levels in the Minqin oasis, located in the

lower reach of Shiyang River Basin, in Northwest China. Using data spanning

1980 through 1997, two ANNs were developed to model and simulate

dynamic ground water levels for the two sub regions of Xinhe and Xiqu. The

ANN models achieved high predictive accuracy, validating to 0.37 m or less

mean absolute error. Sensitivity analysis were conducted with the models

demonstrating that agricultural ground water extraction for irrigation is the

predominant factor responsible for declining ground water levels exacerbated

by a reduction in regional surface water inflows. ANN simulations indicate

that it is necessary to reduce the size of the irrigation is the predominant factor

responsible for indicate that it is necessary to reduce the size of the irrigation

area to mitigate ground water level declines in the oasis. Unlike previous

research, this study demonstrates that ANN modeling can capture important

temporally and spatially distributed human factors like agricultural practices

and water extraction patterns on a regional basin (or sub basin) scale,

providing both high-accuracy prediction capability and enhanced

understanding of the critical factors influencing regional ground water

conditions.

According to Frippiat et al (2008) classical Fickian model for solute

transport in porous media cannot correctly predict the spreading (the

dispersion) of contaminant plumes in a heterogeneous subsurface unless its

structure is completely characterized. Although the required precision is

outside the reach of current filed characterization methods, the advection-

dispersion model remains the most widely used model among practitioners.

Two approaches can be adopted to solve the effect of physical heterogeneity

on transport. First, based on a given characterization of the spatial structure of

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the subsurface, up scaling methods allow the computation of apparent scale-

dependent parameters (especially longitudinal dispersivity) to be used in the

classical Fickian model. In the second approach, upscaled (non-Fickian)

transport equations with scale-independent parameters are used. Efforts are

made to classify and review up scaling methods for Fickian transport

parameters and non-Fickian upscaled transport equations for solute transport,

with an emphasis on their mathematical properties and their (one-dimensional)

analytical formulations. In particular, their capacity to model scale effects in

apparent longitudinal dispersion is investigated. Upscaling methods and up

scaled models are illustrated in the case of two three-dimensional synthetic

aquifers, with lognormal hydraulic conductivity distributions characterized by

variance values of 2 and 8.

Reduction / oxidation (redox) conditions in 15 principal aquifer

(PA) systems of the United States, and their impact on several water quality

issues was studied by McMahon and Chapelle (2008) from a large data base

collected by the National Water Quality Assessment Program of the USGS.

The logic of these assessments was based on the observed ecological

succession of electron acceptors such as dissolved oxygen, nitrate, and sulfate

and threshold concentrations of these substrates needed to support active

microbial metabolism. Similarly, the utilization of solid-phase electron

acceptors such as Mn (IV) and Fe (III) is indicated by the production of

dissolved manganese and iron. An internally consistent set of threshold

concentration criteria was developed and applied to a large data set of 1692

water samples from the Pas to assess ambient redox conditions. The indicated

redox conditions then were related to the occurrence of selected natural

(arsenic) and anthropogenic (nitrate and volatile organic compounds)

contaminants in ground water. For the natural and anthropogenic contaminants

assessed in this study, considering redox conditions as defined by this

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framework of redox indicator species and threshold concentrations explained

many water quality trends observed at a regional scale. An important finding

of this study was that samples indicating mixed redox processes provide

information on redox heterogeneity that is useful for assessing common water

quality issues. Given the interpretive power of the redox framework and given

that it is relatively inexpensive and easy to measure the chemical parameters

included in the framework, those parameters should be included in routine

water quality monitoring programs whenever possible.

Influence of spatial variations in aquifer properties on contaminant

transport was studied by Murray Close et al (2008) by constructing two large

scale (9.5 m long, 4.7 m wide, 2.6 m deep), three-dimensional artificial

aquifers. One aquifer was uniformly filled with coarse sand media (0.6 to 2.0

mm) and the other was constructed as a heterogeneous aquifer using blocks of

fine, medium, and coarse sands. The key features of these artificial aquifers are

described. An innovative deaeration tower was constructed to overcome a

problem of the aquifers becoming blocked with excess air from the ground

water source. A series of tracer injection experiments were conducted to test

the homogeneity of the first aquifer that was purposely built as a homogeneous

aquifer and to calculate values of aquifer parameters. Experimental data show

that the aquifer is slightly heterogeneous, and hydraulic conductivity values

are significantly higher down one side of the aquifer compared to the mean

value. There was very good agreement in estimated dispersivity values

between the plume area ratio methods and the curve fitting of tracer

breakthrough curves. Dispersivity estimates from a full aerial sources injection

(12.2 m2) experiment using a 1D analytical model were higher than estimates

from limited source injection (0.2 m2) experiment using a 3D model, possibly

because the 1D model does not take account of the heterogeneity of hydraulic

conductivity in the aquifer, thus overestimating dispersivity. Transverse and

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vertical dispersivity values were about five times less than the longitudinal

dispersivity. There was slight sorption of Rhodamine WT onto the aquifer

media.

A lumped model known as Tank model for regional groundwater

flows to estimate the groundwater flow system of the Osaka plain aquifer of

Japan was proposed by Shija Kazumba et al (2008). The aquifer is divided into

Tanks within which the average values of the groundwater levels is assumed to

be representative in the Tanks. For each Tank the mass-balance equations

expressing the conservation of water are written. The Quasi-Newton

optimization technique together with Akaike’s Information Criterion, AIC, are

employed in order to response and reliability of the parameter estimation. A

stable model is estimated which is believed to be reliable to simulate the

groundwater flow pattern of the Osaka plain seawater to the deeper layers in

the studied period.

Esling et al (2008) reported that the U.S. Environmental Protection

Agency has established several methods to delineate wellhead protection area

(WHPAs) around community wells in order to protect them from surface

contamination sources. Delineating a WHPA often requires defining the

capture zone for a well. Generally, analytical models or arbitrary setback zones

have been used to define the capture zone in areas where little is known about

the distribution of hydraulic head, hydraulic conductivity, or recharge.

Numerical modeling, however, even in areas of sparse data, offers distinct

advantages over the more simplified analytical models or arbitrary setback

zones. The systematic approach discussed here calibrates a numerical flow

model to regional topography and then applies a matrix of plausible recharge

to hydraulic conductivity ratios (R/K) to investigate the impact on the size and

shape of the capture zone. This approach does not attempt to determine the

uncertainty of the model but instead yields several possible capture zones, the

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composite of which is likely to contain the actual capture zone. A WHPA

based on this composite capture zone will protect ground water resources

better than one based on any individual capture zone. An application of the

method to three communities illustrates development of the R/K matrix and

demonstrations that the method is particularly well suited for determining

capture zones in alluvial aquifers.

Model based contaminant source identification plays an important

role in effective site remediation. Alexander Sun (2008) introduced a frame

work called contaminant source identification toolbox (CONSID) for solving

contaminant source identification problems. It is known that the presence of

various types of model uncertainties can severely undermine the performance

of many existing source estimators. The current version of CONSID consists

of two robust estimators for recovering source release histories under model

uncertainty; one was developed in the deterministic framework and the other

in the stochastic framework. To use the robust estimators provided in

CONSID, the user is required to have only modest prior knowledge about the

model uncertainty and be able to estimate the bound of model deviations

resulting from the uncertainty. The toolbox is designed so that other source

estimators can be added easily. A step-by-step guidance for using CONSID

with an example is provided by the author.

A new method for simulating large scale sub-surface contaminant

transport that combines an Analytic Element Method (AEM) groundwater

flow solution with a split-operator Streamline Method for modeling reactive

transport was introduced by Bandilla et al (2009). The key feature of the

method is the manner in which the vertically integrated AEM flow solution is

used to construct three-dimensional particle tracks that define the geometry of

the streamline method. The inherently parallel nature of the algorithm supports

the development of reactive transport models for spatial domains much larger

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than current grid–based methods. The applicability of the new approach is

verified for cases with negligible transverse dispersion through comparisons to

analytic solutions and existing numerical solutions, and parallel performance is

demonstrated through a realistic test problem based on the regional-scale

transport of agricultural contaminates from spatially distribute sources.

According to Shadab Anwar and Michael Sukop (2009) the flow

transport simulation in karst aquifers remains a significant challenge for the

groundwater modeling community. Darcy’s law based models cannot simulate

the inertial flow characteristic of many karst aquifers. Eddies in these flows

can strongly affect solute transport. The simple two-region conduit/matrix

paradigm is inadequate for many purposes because it considers only a

capacitance rather than a physical domain. Relatively new Lattice Boltzmann

Methods (LBMs) are capable of solving inertial flows and associated solute

transport in geometrically complex domains involving karst conduits and

heterogeneous matrix rock. LBMs for flow and transport in heterogeneous

porous media, which are needed to make the models applicable to large-scale

problems, are still under development. The authors explore aspects of theses

future LBMs, present simple examples illustrating some of the processes that

can be simulated, and compare the results with available analytical solutions.

Simulations are contrived to mimic simple capacitance-based two-region

models involving conduit (mobile) and matrix (immobile) regions and are

compared against the analytical solution. There is a high correlation between

LBM simulations and the analytical solution for two different mobile region

fractions. In more realistic conduit/matrix simulation, the break through curve

showed classic features and two-region model fit slightly better than the

advection-dispersion equation (ADE). An LBM based anisotropic dispersion

solver is applied to simulate break through curves from a heterogeneous

porous medium, which fit the ADE solution. Finally, breakthrough from a

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karst-like consisting of a conduit with inertial regime flow in a heterogeneous

aquifer is compared with the advection – dispersion and two-region analytical

solutions.

A field study on soil chloride and deep drainage responses to land

clearing for cropping was carried out by Radford et al (2009) at seven sites in

Central Queensland, northern Australia. They summarized as follows: Soil

cones were taken at seven paired sites (native vegetation and adjacent dry land

cropping on cracking clay soils) which had been cropped for 10-65 years in

the Fitzroy Basin in central Queensland, northern Australia. Levels of soil

chloride (Cl-) and nitrate nitrogen (NO

3-N) were determined in 0.3 m

increments to a depth of 5m where possible. The amounts of Cl- in the soil (0-

1.5 m depth) under native vegetation were generally high (10-23tha-1

at six of

seven sites). The amounts of Cl- that had leached below 1.5 m depth during

dry land cropping varied from 2.2 to 16.8 tha-1

or 19-91% of the original totals

at 0-1.5 m. Leaching of salt from the crop rooting zone in combination with

higher rates of deep drainage can lead to out breaks of soil salinisation but can

also increase the soil plant available water capacity (PAWC). NO3-N had also

been leached below crop rooting depth at three sites. Such leaching not only

contaminates the groundwater but also wastes crop nutrients. The transient

chloride mass balance approach was used to determine mean annual rates of

deep drainage below crop rooting depth (1.5m). At all seven sites annual deep

drainage was low under native vegetation (0.2-1.7 mm yr-1

) but increased

under dry land cropping (1.6-27.5mm yr-1

). Drainage losses showed an inverse

relationship with plant available water content (PAWC). Drainage losses waste

the limited supply of water available for dry land cropping but can be reduced

by practicing opportunity cropping or by growing ley (temporary) pastures in

rotation with annual crops.

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In many hydrological investigations accurate representation of the

spatial distribution of water table depth remains one of the greatest

deficiencies. Buchanan and Triantafilis (2009) used both inverse distance

weighting (IDW) and ordinary Kriging (OK) to interpolate depths. These

methods, however, have major limitations: namely they require large number

of measurements to represent the variation between measurements points.

They address this issue by assessing the benefits of using stepwise multiple

linear regression (MLR) with three different ancillary data sets used are

electromagnetic (EM 34 and EM 38), gamma radio metric: potassium (K),

uranium (eU), thorium (e Th), total count (TC), and morphometric data.

Results show that MLR offers significant precision and accuracy benefits over

OK and IDW. Inclusion of the morphometric data set yielded the greatest

(16%) improvement in prediction accuracy compared with IDW, followed by

the electromagnetic data set (5%). Use of the gamma radiometric data set

showed no improvement. The greatest improvement, however, resulted when

all data sets were combined (37%) increase in prediction accuracy over (IDW).

Significantly, however, the use of MLR also allows for prediction in variations

in water table depth between measurements points, which is crucial for land

management.

2.3 GROUNDWATER QUALITY MODELING STUDY USING

MODFLOW

John Doherty (2001) reported that use of USGS ground water flow

model MODFLOW is often hampered by the occurrence of ‘dry cells’. While

MODFLOW allows such cells to ‘rewet’ in the course of a simulation,

stability of the heads solution process is often problematical with rewetting

functionality operative. In many case of practical interest (particularly in

mining applications), MODFLOW simply fails to converge. However by

making a number of adjustments to the MODFLOW block-centered flow

package, it is possible to overcome this problem in many instances of

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MODFLOW development. These adjustments are such as to allow a layer to

transmit water, albeit with vastly reduced transmissivity, even if the water

level in that layer is below its base. With these alterations MODFLOW cells

can remain active even if they lie within the unsaturated zone.

Contaminant transport models often use a velocity field derived

from a MODFLOW flow field. Consequently, the accuracy of MODFLOW in

representing a ground water flow filed determines in part the accuracy of the

transport predictions, particularly when advective transport is dominant. Henk

Haitjema et al (2001) compared MODFLOW ground water flow rates and

MODPATH particle traces (advective transport) for a variety of conceptual

models and different grid spacing to exact or approximate analytic solutions.

All of the numerical experiments concerned flow in a single confined or semi

confined aquifer. While MODFLOW appeared robust in terms of both local

and global water balance, they found that ground water flow rates, particle

traces, and associated ground water travel times are accurate only when

sufficiently small cells are used. For instance, a minimum of four or five cells

are required to accurately model total ground water inflow in tributaries or

other narrow surface water bodies that end inside the model domain. Also,

about 50 cells are needed to represent zones of differing transmisivities or an

incorrect flow filed and (locally) inaccurate ground water travel times may

result. Finally, to adequate represent leakage through aquitards or through the

bottom of surface water bodies it was found that the maximum allowable cell

dimensions should not exceed a characteristic leakage length , which is

defined as the square root of the aquifer transmissvity times the resistance of

the aquitard or stream bottom. In some cases a cell size of one-tenth of is

necessary to obtain accurate results.

Thiyagarajan and Ranghaswami (2003) validated Visual

MODFLOW model using the monthly ground water levels (heads) of 65

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observation wells of the Gundar river basin recorded over a period of 3 years

from July 1999 to June 2002. These wells were distributed in the regions of

hard rock, sedimentary and alluvial formations of Gundar river basin. The

calculated wellheads by the model in 57 wells showed a deviation of ± 10 -

20% from the observed or actual heads. The remaining 8 wells showed a

deviation of ± 25 to 35%. The error in the computed values of the model

secures to stem from the difference in the direction of groundwater flow,

irrigation practices, variation in recharge rate of aquifer and difference

between the calculation date and actual date of recording data. In all, the

permissible error of ± 10-20% was observed in 87.3% of computed values by

the model. This value of 87.3% is more than acceptable (80%), particularly for

models dealing with groundwater. Thus the model was validated successfully

and consequently all other outputs generated by the model are also validated.

The groundwater potential is more near the river and it occurs at a depth of

around 23.0 m. It occurs at a depth of 29.0 m, the deepest in the highest

elevated areas of the basin. The water table gradually goes down from the river

to the boundaries within the basin, the contours are wider spaced indicating a

lower hydraulic gradient for the groundwater flow. The groundwater potential

in the basin is poor due to excessive pumping along with poor recharge. To

have an idea about the areas contributing for groundwater recharge, a

groundwater recharge contour map was generated using the model. The

recharge source is surface water from precipitation and to a lesser degree, from

irrigation or artificially constructed recharge ponds or losing streams. In

Gundar river basin, the recharge rate varies from 0.1m/month to 0 m/month.

The recharge structures should be built on the lower boundary of the basin in

order to arrest the water flowing into the adjacent basin and also some

recharge structures in the lower reach of the basin to collect the water flowing

to the sea as surface runoff. The model was used to generate groundwater

scenarios when the northeast monsoon was reduced by 25%, 50%, 75% and

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100% from the reference rainfall of the year 2001-2002. The water table near

the river reduced by 3m, 6m, 7m and 8m when the northeast monsoon reduced

by 25%, 50%, 75% and 100% respectively. The corresponding water table

depths in the entire basin were 26-32m, 29-34m, 30-36m and 30-40m

respectively. The authors had concluded that groundwater status in the basin is

very poor and hence, suitable recharge methods (natural and artificial) should

be adopted. This can be done by arresting the water flowing towards the sea as

surface runoff by constructing suitable structures at appropriate places.

Groundwater simulation studies in the Hirakud command area was

carried out by Anandha Kumar and Sinha (2003). In the study a mathematical

model had been developed using MODFLOW package of USGS to simulate

hydrogeological condition of the groundwater flow systems in the command

area and to generate alternative management scenario to evolve optimal

conjunctive use strategy. The main objective of the study was to arrest the ever

rising ground water levels as well as to control further extension of water

logged areas, at the same time care had been taken to optimally utilize both the

resources so that more area can be brought under irrigation. The model was

calibrated using filed hydrographs and using the observed and computed water

table contours. The calibrated model had been used to develop different water

use scenarios and their effect on the groundwater regime. The groundwater

simulation studies have shown that the water logging condition prevailing in

part of the Hirakud command area can be controlled by the development of

groundwater in conjunction with surface water without any deterioration to the

groundwater regime. The groundwater simulation studies have shown that the

water logging condition prevailing in part of the Hirakud command area can

be controlled by development of groundwater in conjunction with surface

water without any deterioration to the groundwater regime.

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Variable density ground water flow models are rarely used to

estimate submarine ground water discharge because of limitations in computer

speed, data availability, and availability of a simulation tool that can minimize

numerical dispersion. Langevin (2003) presented an application of the

SEAWAT code, which is a combined version of MODFLOW and MT3D, to

estimate rates of submarine ground water discharge to a coastal marine

estuary. Discharge rates were estimated for Biscayne Bay, Florida, for the

period from January 1989 to September 1998 using a three-dimensional

variable density ground water flow and transport model. Hydrologic stress in

the 10 layer model include recharge, evapotranspiration, ground water

withdrawal from municipal wellfields, interactions with surface water (canals

in urban areas and wetlands in the Everglades), boundary fluxes, and

submarine ground water discharge to Biscayne Bay. The model was calibrated

by matching groundwater levels in morning wells, base flow to canals, and the

position of the 1995 salt water intrusion line. Results suggest that fresh

submarine ground water discharge to Biscayne Bay may have exceeded

surface water discharge during the 1989, 1990 and 1991 dry seasons, but the

average discharge for the tidal canals intercept fresh ground water that might

otherwise have discharged directly to Biscayne Bay. This application

demonstrates that regional scale variable models are potentially useful tool for

estimating rates of submarine ground water discharge.

Groundwater quality modeling of Chennai Nandanam area was

carried out by Barathi (2004). She simulated groundwater flow using Visual

MODFLOW. The aquifer characteristics, water level data for the observation

wells and rainfall data were used to run the model. The model was run to

simulate water level in 2001 and validated with field data by comparing with

the hydraulic head of observation wells. Other outputs such as ground water

flow and movement were obtained for the period of 2001. The volumetric

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budget for the model was checked and the changes in storage of groundwater

system were assessed. The computed groundwater storage was compared with

the conventional Theisson polygon method. The model was run to simulate

water level in 2004. The calibrated model was used in determining the

quantity of recharge and the optional location for recharge to improve the

groundwater storage. The author concluded that there is a good agreement

between the computed values and filed data. The variation of predicted water

level with time is almost identical with that of variation of water level in the

filed. This could be possible only if the computed flow components are in

close agreement with the actual flows. The water level is high in central

western part and declining towards the Adyar river. Adyar river acts as a

drainage during November 2001 and March 2004 (monsoon and post monsoon

season), and the only source for recharge is the rainfall. The velocity increases

as the flow moves towards the river. The velocity of flow is high in the central

part and also in the north-east and south-west part indicating recharging in

these areas may drain more quickly into the river and canals. The total inflow

into and outflow from the system are nearly equal with a percentage

discrepancy of 0.03 which indicates proper execution of the model simulation.

The author also recommended that modeling of salt water intrusion into the

coastal aquifer using Visual MODFLOW.

An assessment of groundwater flow and pollutant transport through

modeling for Sulur watershed situated in the Coimbatore District was done by

Ljungberg and Qvist (2004). Most inhabitants in the Sulur water shed are

dependent on agriculture, and as the surface water is limited, groundwater is

the main source of water. Continuous increase in population has lead to

increased demand for water and overexploitation of the water resources. The

Sulur watershed is situated on a plateau surrounded by mountains forming a

rain shadow area that results in a dry climate, which affects the availability. As

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a measure to reduce the impacts of water scarcity, the Indian Government has

initiated a project of so called percolation ponds that collect rainwater and let

it percolate to the groundwater. To meet the demand for irrigation, water is

also diverted from the river Noyal to the Sulur Big and Small tank. Due to the

discharge of untreated sewage water into the small tank the water has become

unsuitable for irrigation. The contaminated water will also infiltrate to the

groundwater and affect the water quality in the surrounding wells. The Sulur

watershed hence faces a problem of both quantity and quality of water.

Groundwater flow and pollutant transport can be assessed through modeling.

The groundwater flow pattern of Sulur watershed has been established using

the flow model MODFLOW. The spatial distribution of the contaminants from

the Small tank has been assessed with the transport simulation programme

MODPATH. The effects of the constructed percolation ponds have also been

examined during the modeling session. Water samples were taken in the two

tanks and in the surrounding wells in order to assess the general water quality

in the watershed and the potential influence of the Small tank. The results from

the modeling show that the flow pattern in the Sulur watershed is generally

from south to north. The modeling results clearly show the influence of

pumping wells on the flow pattern. In the northeastern part of the watershed, a

large density of wells creates an unnatural discharge area. This is mainly the

result of the poor availability of water in combination with the un

sustainability high withdrawal rates. The results show that under the prevailing

conditions, the water level will continue to decline unless measures are taken.

However, the results show that the water level can be increased by the

introduction of percolation ponds, which gives verification to the Government

project of construction of ponds and consequently gives great importance to

this study. As a result of the small amount of available water, the influence of

the Small tank is restricted to its direct vicinity, which means that only a

relatively small number of wells situated very close to the tank will be

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affected. The quality of both surface and groundwater in Sulur watershed is

generally poor. The water cannot be used for drinking, and in some cases it is

not even suitable for irrigation. The main problems are high values of salinity,

alkalinity and sodium.

A method to estimate the uncertainty of the location of pathlines in

two-dimensional, steady-state confined or unconfined flow in aquifers due to

the uncertainty of the spatially variable unconditional hydraulic conductivity

or transmissivity filed was proposed by Fritz Stauffer (2005). The method is

based on concepts of the semi analytical first-order theory, which allows

estimates of the lateral second moment (variance) of the location of a moving

particle. However, this method is reformulated in order to account for

nonuniform recharge and nonuniform aquifer thickness. One prominent

application is the uncertainty estimation of the catchment of a pumping well

by considering the boundary pathlines starting at a stagnation point. In this

method, the advective transport of particles is considered, based on the

velocity filed. In the case of a well catchments, backtracking is applied by

using the reversed velocity field. Spatial variability of hydraulic conductivity

or transmissivity is considered by taking into account an isotropic exponential

covariance function of log-transformed values with parameters describing the

variance and correlation length. The method allows post processing of results

from ground water models with respect to uncertainty estimation. The code

PPPath, which was developed for this purpose, provides a post processing of

pathline computations under PMWIN, which is based on MODFLOW. In

order to test the methodology, it was applied to results from Monte Carlo

simulations for catchments of pumping wells. The results correspond well.

Practical applications illustrate the use of the method in aquifers.

Potter et al (2008) mentioned that the primary goals for most

ground water capture systems (i.e. pump-and-treat systems) are that (1) all

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contaminants within zones of interest will eventually be captured and (2) the

extraction and reinjection wells are best located and operated at optimal flow

rates, creating hydraulically efficient flow systems. A new tool, MODular

ALLocation (MODALL), is presented to aid in the design and assessment of

capture systems. MODALL uses the MODFLOW calculated cell by cell flow

terms to evaluate internodal flow balances to determine the percentage of flow

in each cell which has either originated from a given source(s) or flows to a

specified sinks(s). Output from MODALL can be easily displayed in isopleths

of ‘capture fraction’ (CF) to indicate the certainty or strength of capture in

various area. MODALL results are compared to the results from an analytical

solution, a pathline analysis using MODPATH, and solute transport simulation

with MT3DMS.

In large mountainous catchments, shallow unconfined alluvial

aquifers play an important role in conveying subsurface runoff to the foreland.

According to Jens Wolf et al (2008) river basin scale models describing the

entire water cycle are necessary in integrated water resources management and

to study the impact of global climate change on ground water resources.

Integrated regional-scale models must use a coarse, fixed discretization and

the geometrical properties of natural systems. Here, an approach to overcome

this discrepancy is discussed using the example of the German-Austrian Upper

Danube catchments, where a coarse ground water flow model was developed

using MODFLOW. The method developed uses a modified concept from a

hydrological catchments drainage analysis in order to adapt the aquifer

geometry such that it respects the numerical requirements of the chosen

discretization, that is, the width and the thickness of cells as well as gradients

and connectivity of the catchment. In order to show the efficiency of the

developed method, it was tested and compared to a finely discretized ground

water model of the Ammer subcatchment . The results of the analysis prove

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the applicability of the new approach and contribute to the idea of using

physically based ground water models in large catchments.

Concurrent existence of confined and unconfined zones of an

aquifer can arise owing to ground water withdrawal by pumping. Using

Girinskii’s potential function, Li-Tang Hu and Chong-Xi Chen (2008)

developed an approximate analytical solution to analyze transient ground

water flow to a pumping well in an aquifer that changes from an initially

confined system to a system with both unconfined and confined regimes. They

presents the details of the Chen model and then compares it with the analytical

model developed by Moench and Prickett (1972) for the same problem.

Hypothetical pumping test examples in which the aquifer undergoes

conversion from confined to water table conditions are solved by the two

analytical models and also a numerical model based on MODFLOW.

Comparison of the results suggests that the solutions of the Chen model give

better results than the Moench and Prickett model except when the radial

distance is very large or aquifer thickness is large compared with drawdown.

Accurate estimation of aquifer parameters such as transmissivity

and specific storage is often an important objective during a ground water

modeling investigation or aquifer resource evaluation. Yan and Burbey (2008)

mentioned that parameter estimation is often accomplished with changes in

hydraulic head data as the key and most abundant type of observation. The

availability and accessibility of global positioning system and interferometric

synthetic aperture radar data in heavily pumped alluvial basins can provide

important subsidence observations that can greatly aid parameter estimation.

The aim of this investigation is to evaluate the value of spatial and temporal

subsidence data for automatically estimating parameters with and without

observation error using UCODE – 2005 and MODFLOW – 2000. A synthetic

conceptual model (24 separate cases) containing seven transmissivity zones

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and three zones each for elastic and inelastic skeletal specific storage was used

to simulate subsidence and drawdown in an aquifer with variably thick

interbeds with delayed drainage. Five pumping wells of variable rates were

used to stress the system for up to 15 years. Calibration results indicate that (1)

the inverse of the square of the observation values is a reasonable way to

weight the observations, (2) spatially abundant subsidence data typically

produce superior parameter estimates under constant pumping even with

observation error, (3) only a small number of subsidence observations are

required to achieve accurate parameter estimates, and (4) for seasonal

pumping, accurate parameter estimates for elastic skeletal specific storage

values are largely dependent on the quantity of temporal observational data

and less on the quantity of available spatial data.

Junqi Huang et al (2008) stated that when managing large-scale

ground water contamination problems, it is often necessary to model flow and

transport using finely discretized domains-for instance (1) to simulate flow and

transport near a contamination source area or in the area where a remediation

technology is being implemented; (2) to account for small-scale

heterogeneities; (3) to represent ground water-surface water interactions; or (4)

some combination of these scenarios. A model with a large domain and fine-

grid resolution will need extensive computing resources. In this work, a

domain decomposition-based assembly model implemented in a parallel

computing environment is developed, which will allow efficient simulation of

large-scale ground water flow and transport problems using domain-wide grid

refinement. The method employs common ground water flow (MODFLOW)

and transport (RT3D) simulators, enabling the solution of almost all

commonly encountered ground water flow and transport problems. The basic

approach partitions a large model domain into any number of subdomains.

Parallel processors are used to solve the boundaries. For the transport model,

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an extended numerical array is implemented to permit the exchange of

dispersive and advective flux information across sub domain boundaries. The

model is verified using a conventional single-domain model. Model

simulations demonstrate that the proposed model operated in a parallel

computing environment can result in considerable savings in computer run

times (between 50% and 80%) compared with conventional modeling

approaches and may be used to simulate grid discretizations that were

formerly intractable.

Scott Painter et al (2008) stated that dewatered or dry cells in the

USGS groundwater modeling software MODFLOW may cause non physical

artifacts, trigger convergence failures, or interfere with parameter estimation.

These difficulties can be avoided in two dimensions by modifying the spatial

differencing scheme and the iterative procedure used to resolve nonlinearities.

Specifically, the spatial differencing scheme is modified to use the water level

on the upstream side of a pair of adjacent cells to calculate the saturated

thickness and hence intercell conductance for the pair. This makes it possible

to explicitly constrain the water level in a cell to be at or above the cell bottom

elevation without introducing nonphysical artifacts. Thus constrained, all

initially active cells will remain active throughout the simulation. It was

necessary to replace MODFLOW’s Picard iteration method with the Newton-

Raphson method to achieve convergence in demanding applications involving

many dry cells. Tests using a MODFLOW variant based on the method

produced results nearly identical to conventional MODFLOW in situations

where conventional MODFLOW converges. The new method is extremely

robust and converged in scenarios where conventional MODFLOW failed to

converge, such as when almost all cells dewatered.

In environments with shallow groundwater elevations, small

changes in the water table can cause significant variations in recharge and

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evapotranspiration fluxes. Rebecca Doble et al (2009) designed the most

commonly used ground water flow model MODFLOW with a modular

structure with independent packages representing recharge and evaporation

processes. Systems with shallow groundwater, however, may be better

represented using either a recharge function that varies with groundwater

depth or a continuous recharge and evapotranspiration function that is

dependent on depth to water table. In situations where the boundaries between

recharging and non recharging cells change with time, such as near a seepage

zone, a continuous ground water flux relationship allows recharge rates to

change with depth rather than having to calculate them at each stress period.

They described the modification of the MODFLOW 2000 recharge and

segmented evapotransparation packages into a continuous recharge- discharge

function that allows ground water flux to be represented as a continuous

process, dependent on head. The modifications were then used to model long

term recharge and evapotranspiration processes on a saline, semiarid

floodplain in order to understand spatial patterns of salinization and an

overview of this process is given.

Reimann and Hill (2009) mentioned that the USGS recently

developed the MODFLOW-2005 conduit flow process (CFP) (Shoemaker et

al. 2008), which implements the non-Darcian, dual-permeability flow regimes

that are not considered in traditional ground water flow codes based solely on

Darcy’s Law. MODFLOW-2005 CFP can operate in one of three modes. In

Mode 1, the ground water flow equation is coupled to discrete network of

cylindrical pipes, representing a conduit system. Flow within the pipes is

calculated by the Darcy-Weisbach equation for turbulent flow conditions and

the Hagen-Poiseuille equation for laminar flow. Volume concentration in the

pipe network is implemented according to Kirchhoff’s law. Fully and partly

water-filled tubes are considered (Shoemaker et al.2008). CFP Mode 1 is

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mainly based on the Carbonate Aquifer Void Evolution (CAVE) code (Liedl et

al.2003). In Mode 2, a turbulent form of hydraulic conductivity is computed as

power function of the Reynolds number to simulate horizontal flow that

transitions between laminar and turbulent conditions in preferential flow layers

representing laterally extensive, well-irrigated, conduit networks consisting of

vuggy porosity (Shoemaker et al.2008). In Mode 3, the first two modes are

combined to simultaneously simulate a discrete pipe network and a

preferential flow layer (Shoemaker et al.2008).

2.4 GROUNDWATER QUALITY STUDY OF TANNERY

CLUSTER

Sundarajan (2000) carried out modeling of groundwater in

Pernampet block, Vellore district using MODFLOW. The model was

calibrated and used for simulation. The aquifer parameters, lithology

particulars, bed rock details, land use map, twenty eight years water level data

of observed wells and rainfall data were used for model calibration. Using the

calibrated model, volumetric budget for the Pernampet block (ie) change in

groundwater storage was obtained and the head vs time, draw down vs time

curves for the wells were plotted by the model. At any stress period difference

between storage in and out was equal to the difference in recharge and

abstraction. Temporal variation of groundwater level indicates the magnitude

of recharge and discharge and aquifer storage co. efficient. The occurrence and

its movement were directly proportional to the rainfall and general geology of

the area. The water requirement due to cropping practices and other

groundwater withdrawal has a link to water flow and fluctuation. Water

balance study reveals that the irrigation abstraction is the main parameter for

groundwater depletion. The total outflow from the volumetric budget was in

higher side than the dynamic groundwater potential obtained from the

Theisson polygon map method. MODFLOW can be effectively used to study

the groundwater flow and fluctuations.

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Groundwater quality degradation of upper Palar river basin of

Vellore district, due to tanneries and improvement due to CETPs was studied

by Srisathya (2001) using MODFLOW. He collected data on location of

tanneries, their points of discharge into Palar river, the characteristics of

tanneries, CETPs location, aquifer characters, lithology, soil, water level and

water quality data for the period 1997 and 2000 from PCB and CGWA. The

author concluded that groundwater quality has improved after the

commissioning of CETPs and closure of number of tanneries. Velocity vectors

in 1997 and 2000 show considerable change in the flow direction and

magnitude on the western side of the study area. In 2000, the flow from

CETPs is towards the boundaries except from the two CETPs located in the

north eastern side where the particles move towards the river. There is a

drastic change in the water level showing a severe depletion of groundwater in

the year 2000 when compared to 1997. The author also recommended that the

same study area could be used for future predictions of TDS concentration.

The disposal of effluent by the tanneries in Vellore district caused

severe damage to the groundwater quality in the Palar river basin. The

movement of total dissolved solids (TDS) in the groundwater was studied by

Molykutty et al (2003). The model was developed using VISUAL

MODFLOW package. At first, the flow modeling of the basin is developed to

find out the hydraulic heads and velocity of flow of groundwater in the basin.

The calculated values are retrieved in the mass transport package MT3D to

find the concentration of TDS in the groundwater for various scenarios. The

total area of Palar basin is 18270 km2 (IWS report). Palar river basin consists

of crystalline rock masses. Pumping tests conducted in this region by PWD

indicates transmissibility as 2.2 to 145 m2/day for hard rock and 200 to 300

m2/day for alluvium. A number of tanneries are located on both sides of Palar

river and tanneries adopt chrome tanning and vegetable tanning methods. The

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TDS of the untreated effluents vary from 35,000 – 25,000 mg/l and that the

treated effluent vary from 20,000 – 6000 mg/l. The effluent from the industries

find their way to Palar river through small nallas and the pollutants move

through the alluvium below the river bed to the ground water. Water samples

collected from the area show that water is contaminated with high TDS.

Common effluent treatment plants were installed and treated effluent is being

sent since January 1996. The authors used VISUAL MODFLOW for the

prediction of TDS values for the following scenarios. i). when untreated

effluent is discharged till December 1995 and then treated is discharged, ii).

when effluent is discharged without treatment, iii). when no effluent is

discharged since January 1996. They concluded that the first half of the model

area, which include Vaniyambadi, Pernampet, and Ambur are more polluted

than the other areas. It is found that Pernampet block is highly polluted and by

sending the treated effluents from 1996, there is a reduction in the TDS

concentration of ground water in the study area. Since there is a wide variation

of TDS concentration in Pernampet block and the nearby Gudiyatham block,

the spread of pollutants is more in this area. It is also observed that the TDS

concentration is migrating from Pernampet to Gudiyatham block and due to

this, in future there is a chance of increase of TDS concentration in the

Gudiyatham area. In the study area, since the velocity is less, the spread of

pollutants is due to molecular diffusion. In Vaniyambadi and Ambur area,

almost all the places are having more or less same TDS concentration.

Therefore spread of pollutants due to molecular diffusion is also less here.

Hydraulic conductivity is also very less here. The river water depth in this

portion and rainfall recharge are less in this region compared to the down

stream portion. All these factors give rise to a uniform concentration in the

Vaniyambadi-Ambur area.

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Mohan and Muthukumaran (2004) carried out a modeling of

pollutant transport in groundwater in Palar river basin. Mathematical model

for prediction of pollutant transport in subsurface flow in Palar river basin has

been studied. Palar river flows across North Arcot district which is important

district in the State where there are various types of industries among them

tannery stands dominant. The river Palar is the major drainage system in the

district. The flow in this river is seasonal with water flowing mainly in the

monsoon seasons. There are 600 tanneries in this district. The tanneries in the

district are mainly located at Vaniyambadi, Ambur, Pernambet and Ranipet in

clusters and about 95% of these tanneries are small sector. Excepting a few

industries most of the industries do not have proper effluent treatment measure

and reasons cited for this are inadequate space, finance, non availability of

appropriate treatment technology, and personnel, lack of motivation on the

tanneries part in setting up effluent treatment measures. The impact of

continued discharge of partially treated and mostly untreated effluents from

the tanneries, not only affected the land due to the presence of high amounts of

dissolved oxygen, chromium etc, and leave the water quality much to be

desired. The model was calibrated and validated for its performance with the

actual observed concentrations in the selected reach of Palar basin. The

authors have used the validated model to predict the fate of TDS concentration

over a longer period for the following six different scenarios. i). the same level

of pollution is continued, ii). the tannery effluent is treated to the extant so that

the TDS level is limited to 10000 mg/l from the year 1997, ii). the tannery

effluent is treated to the extant that it adheres to inland surface water standards

prescribed by the TNPCB, i.e, 2100 mg/l from the year 1997, iii). no effluent

discharge into the river Palar basin from the year 1997, iv). the quantum of

effluent is doubled with the TDS concentration value of 2100 mg/l from the

year 1997, v). ground water recharge is increase by 1.5 times from the year

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1997 with the same conditions as that of scenario ii). The authors have

summarized as below:

i. Mass transport modeling simulation can effectively be used for

studying the pollutant migration in a river basin. Thus the role of water

quality models in the filed of groundwater quality and pollutant

transport in subsurface studies is fully affirmed.

ii. The model parameters can be effectively estimated by solving the

inverse problem.

iii. The study area which is one of the most critically polluted area needs

immediate attention and measures so that the contamination of the

entire alluvial aquifer can be avoided. The effect of recharge of

groundwater is significant as the contamination development in the

aquifer getting very much reduced if the recharge rate is increased.

iv. The model results show that the effect of contamination will be there

for a quite long time even if there is no effluent discharge into the

aquifer which infers that remediation measures are to be employed to

remove the pollutants from contaminated aquifers.

v. The tanneries that are the major pollutants have to be thoroughly

monitored for quality and quantity of effluent discharge. Stringent

measures are to be adopted to ensure that the discharged effluent is

treated properly and it adheres to the discharge standards prescribed by

the TNPCB in order to avoid further deterioration of the existing

condition.

Groundwater in and around Dindigul town of Tamilnadu State is

polluted due to discharge of untreated effluents from 80 functional tanneries.

Total dissolved solids (TDS) in about 100 km2 area are observed ranging from

2000 to 30,573 mg/l in open dug wells. A mass transport model was

constructed by Mondal, and Singh (2005) to study pollutant migration. The

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study area covering 240 km2 was chosen to construct the groundwater flow

model in the weathered part of unconfined aquifer system. The shallow

groundwater potential field computed through the flow model was then used

as input to the mass transport model. MT3D computer code was used to

simulate mass transport in groundwater. The mass transport model was

calibrated with filed observations. The available database was, however, quite

sparse. Not with standing, efforts were made to arrive at reasonable

guesstimates of the characteristic parameters. Sensitivity analysis, an integral

part of calibration was carried out whereby model parameters, viz.

transmissivity, dispersivity etc., were altered slightly and the effect on

calibration statistics was observed. This study strive role than dispersivity,

indicating that the migration phenomenon is mainly through advection rather

than dispersion. The study also indicated that even if the pollutant sources

were reduced to 50% of the present level, TDS concentration level in the

groundwater, even after 20 years, would not be reduced below 50% of present

level.

Thangarajan (2008) reported that Palar river basin, a crystalline

rock region in Vellore district (Tamil Nadu), India, possesses vast groundwater

potential along and near the river course and its lands are fertile. Serious

contamination of both surface water and groundwater has been reported in this

basin as a result of uncontrolled discharge of untreated effluents by the tanning

industries for the last three decades. The health of the rural farming

community and people working in the tanning industries has been seriously

affected and they are suffering from occupational diseases such as asthma,

chromium ulcers and skin diseases. About 11000 hectares area of fertile land

has lost its fertility. Total dissolved solids (TDS) concentration in groundwater

at some pockets varies from 3000 to 10000 mg/l. As the discharge of effluents

is continuing, a prognosis of further pollutant migration is carried out using a

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mathematical model. A numerical model of the Upper Palar river basin was

developed using the finite difference technique coupled with method of

characteristics and used to predict TDS migration for the next 20 years.

Sensitivity analysis was carried out to identify the parameters which are

influencing the contaminant migration. Sensitivity analysis shows that

advection and not dispersion is the predominant mode of solute migration in

Palar basin. Prognosis using the model confirms that the polluted area zone as

well as the concentration of pollutants in the groundwater will continue to

increase in future. The study also indicated that even if the pollutant sources

are reduced to 25% of the present level, the TDS concentration level in the

groundwater, even after 20 years, will not be reduced below 50% of its 1992

level.

2.5 GROUNDWATER QUALITY STUDY OF DYEING UNITS

CLUSTER

The development of bleaching and dyeing industries in and around

Tiruppur block of Tamil Nadu State has led to groundwater pollution. A

simulation study on groundwater pollution in Tiruppur block using VISUAL

MODFLOW was carried by Viswanathan (2002). He reported that samples

were collected from 20 wells and analyzed for TDS concentration. The

location of industries, their effluent characteristics and lithology were

collected. The model was run with these inputs. The velocity vectors, pathlines

and contaminant transport were obtained for selected locations for a specified

time period. From the waterlevel and velocity vectors it is inferred that there is

depletion of groundwater in some areas where there is pumping of

groundwater for agricultural purpose and from groundwater flow pattern it is

clear that Noyyal river act as source of recharge for groundwater and

Chinnakarai river and Nallar river act as drainage. In present condition, the

industries discharge their effluents with high TDS concentration. An attempt is

made to simulate for 2003 considering if there is a decrease in TDS

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concentration. The simulated concentration indicated considerable

improvement in the groundwater quality. The above result encourages the

utilization of models in decision making in groundwater management.

2.6 GROUNDWATER QUALITY STUDY IN PULP & PAPER

INDUSTRY AREA

Selvakumar and Ranghaswami (2003) assessed the characteristics

of recharge water and its impacts on aquifers in ground water recharge project.

They carried out a study to assess the groundwater quality changes due to

recharge by treated effluent irrigation from Viscose pulp plant of M/s SIV

Industries in Coimbatore (The factory is not in operation since 2000). The

study area falls with in the Bhavani river basin, located on the south bank of

Bhavani on the foreshore of Lower Bhavani Project reservoir. The effluent

(10,000 m3/day) from SIV Industries pulp mill is treated in the factory located

at Sirumugai village and pumped to the farms located 6 km away for irrigation

in an extant of 565 acres. The major crop cultivated is sugar cane. The

VISUAL MODFLOW (VMF) was used to simulate the three-dimensional

ground water flow and contaminant transport in the effluent irrigated area with

two years filed observations. The application of sustainable option was

demonstrated through the simulated values of future concentration levels for

TDS, chlorides and sulphate. It is observed that the concentration values are on

the increasing trend at all the observation points irrespective of options.

However, the effect is minimized if diluted effluent irrigation was carried out.

At 25 % and 50 % dilution, the reduction in the rate of accumulation was

observed as 2-3 times and 7 times respectively. The application of this

developed model with VMF has created a new platform for the design of eco-

friendly management of effluent irrigation schemes. The authors used the

aquifer parameters as follows: hydraulic conductivity-0.000026 m/sec, storage

co. efficient-0.0000136 m-1

, specific yield-0.005. 12 observation well were

used to observe monthly water table depth, pumping rate, and TDS, chlorides

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& sulphate levels in the water. The chemical constituent of treated effluent is

TDS 2080 mg/l, sulpahe 219 mg/l, chlorides 377 mg/l. The authors used

simulation model to predict the groundwater quality under different

management options namely i). same level of irrigation (without dilution), ii).

25 % dilution of effluent irrigation iii). 50 % dilution of effluent irrigation. To

achieve the different management options on filed, only concentration of the

effluent was changed by keeping all other parameters as constant including the

quantity of effluent (10,000 m3/ day in 565 aces). The permissible

concentration of effluent TDS, chlorides and sulphate for sustainable irrigation

should be minimum so that the TDS, chlorides and sulpahte concentration of

ground water can be kept within its limited value. In the present case, it was

found that 50% dilution of effluent irrigation is safe for ground water. Hence,

the effluent from the factory should be treated to reduce the TDS, chloride and

sulpahte concentration of effluent to 50% before irrigation. The above study

indicates that the groundwater contamination can be a controlling factor. The

practical use of this study can be enhanced by a systemic research i.e improved

or new techniques are needed to determine filed value of certain aquifer

properties such as effective porosity and dispersion, which cannot readily be

evaluated. In some areas, the spatial and temporal variation of these

parameters may be important and that should be incorporated in the simulation

model.

Mukherjee (2006) stated that industrial disposal of effluents on land

and subsequent pollution of groundwater and soil of surrounding farmlands-is

relatively new area of research. Environmental and socio-economic aspects of

industrial effluent irrigation have not been studied as extensively as domestic

sewage based irrigation practices, at least for developing countries like India.

Disposal of treated and untreated industrial effluents on land has become a

regular practice for some industries. Industries located in Mettupalayam taluk,

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Tamilnadu dispose their effluents on land, and the farmers of the adjacent

farmlands have complained that their shallow open wells get polluted and also

the salt content of soil has started building up slowly. This study attempts to

capture the environmental and socio-economic impacts of industrial effluent

irrigation in different industrial locations at Mettupalayam taluk through

primary surveys and secondary information. This study found that continuous

disposal of industrial effluents on land, which has limited capacity to

assimilate the pollution load, has led to groundwater pollution. Groundwater

quality of shallow open wells surrounding the industrial locations has

deteriorated, and the application of polluted groundwater for irrigation has

resulted in increased salt content of soils. In some locations drinking water

wells (deep bore wells) also have high concentration of slats. Since the farmers

had already shifted their cropping pattern to salt tolerant crops (like jasmine,

curry leaf, tobacco etc.) and substituted their irrigation source from shallow

open wells to deep bore wells and / or river water, the impact of pollution on

livelihood was minimized. It is observed that with the rise in concentration of

electrical conductivity of groundwater samples, revenue from banana

cultivation has gone down. However blending open well water with the river

water and / or water from deep bore wells has arrested the fall in revenue. For

salt tolerant crop like jasmine, the rise in EC did not seem to have significant

impact on productivity. Since the local administration is supplying drinking

water to households the impact in the domestic sector has been minimized. It

has also been noticed that in some locations industries are supplying drinking

water to the affected households. However, if the pollution continues unabated

it could pose serious problems in the future.

2.7 GROUNDWATER QUALITY STUDY OF MUNICIPAL

SOLID WASTE DUMP AREA

Centre for Environmental Studies, Anna University (2003) carried

out a modeling of groundwater pollution due to solid waste dumping at

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Perungudi, Chennai. Perungudi is a dumpsite, receiving urban solid waste

from Chennai city. In the study, the groundwater pollution due to the dumpsite

was analyzed. With dumpsite at center, around 5km was considered as the

study area. The whole of the area is low-lying, close to sea level and is poorly

drained. The area is occupied by marshland and mud flats, which are

permanently wet and seasonally inundated. The exact dumpsite boundary was

mapped with GPS. The solid waste samples were collected within the

dumpsite and characterized. The TCLP test was conducted to find out the

leachate and characteristics. Water samples were collected from around 36

wells for different seasons and analyzed for pH, TDS, fluoride, COD,

hardness, nitrate and heavy metals such as Fe, Zn, Cd, Cr and Cu. The

influence of dumpsite on various water quality parameters was studied. Water

level fluctuations during the different seasons were also examined. Visual

MODFLOW, a groundwater modeling package was used to model the

groundwater contamination from the dumpsite. With aquifer characteristics as

input to the model, the groundwater flow and the path of contaminant

migration were understood. The model results were calibrated with the filed

observations. Using Iron as a key parameter, the existing dispersion pattern

was found out. Also future scenarios for various pollutant loads were

simulated. The study concluded that the current dumping area is 44.75

hectares, which is doubled in a period of 8 years (20 hectare in 1995), soil

predominates in the solid waste, water level in the study area ranges from 0.05

m and 9.3 m, pH ranges from 6.2 – 9.2, dumpsite does not have any influence

on fluoride, COD values are always exceeding the drinking standard, majority

of study area has hardness more than 600ppm, nitrate concentration is well

within the standards except few patches, leachate has high concentration of Fe,

Cd and Cr, groundwater flows vertically upto the top layer in all the seasons

(except December) and then horizontally in the second layer, irrespective of

the season the flow is towards dumpsite from north, leachate plume from

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dumpsite is expected to pollute the aquifer system. The study recommends for

waste management options including waste minimization/reduction at source,

material recycling, and waste processing with recovery of resources.

Mohan and Gandhimathi (2009) carried out a study on the

characterization of the solid waste and the effect of the leachate from the major

dumping site in Perungudi, Chennai city, on groundwater. From the study the

authors have come to a conclusion as follows: Various physical and chemical

parameters were estimated, this includes pH, total hardness, electrical

conductivity, and total dissolved solids, major cations such as Ca2+

, Mg2+

, Na+,

and K+, major anions such as NO3

-, Cl

- and SO4

2- and heavy metals such as Pb,

Cu, Mn, Cd, Cr and Zn. Perungudi dumping site receives 1650 tonnes of

municipal solid waste (MSW) daily from Chennai Corporation. The leachate is

a result of anaerobic decomposition of MSW. The chemical analysis shows

that all leachate samples and water samples have high concentration of heavy

metals, especially lead. This would adversely affect aquatic life and ultimately

enter the food chain, the consumption of which can cause adverse health

effects. From the results of the water quality study, it was found that the

groundwater is non-potable because most of the physical and chemical

parameters examined exceed the permissible limits. Therefore dumping site

leachates constitute a serious threat to the local aquifers.

2.8 GROUNDWATER QUALITY STUDY OF CHROMIUM

SLUDGE DUMP SITE

National Geophysical Research Institute (NGRI), Hyderabad (2008)

carried out geo-environmental investigations for developing comprehensive

remediation plan in and around Tamilnadu Chromate and Chemicals Ltd,

Ranipet, Vellore district, where approximately 1,60,000 tonnes of chromium

waste was dumped on 2 acres of open land and lying for more than 20 years.

They studied chromium heavy metal transport in groundwater using visual

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MODFLOW. The 17.4 sq.km study area was divided into 71 rows and 46

columns with grid size of 105mX117m and simulated the plume migration for

30 years.

2.9 GROUNDWATER QUALITY STUDY OF SOLID WASTE

DUMP SITE IN COPPER SMELTER PLANT

Ernst & Young (2003) carried out a study on fluoride and heavy

metals transport in groundwater from gypsum pond and effluent treatment

plant’s sludge secured land fill facility of M/s. Sterlite Industries India

Limited, Thoothukudi. They performed the study using 3D finite difference

groundwater model MODFLOW, the advective transport model PMPATH and

solute transport model MT3D. They developed the model consisting of a

single layer with a depth of 15m. The model covers an area of 6km in north-

south direction (Y co-ordinate) and 12km in east-west direction (X co-

ordinate), with grids size being 100mx100m. However, in the Sterlite Copper

Smelter Plant area, the mesh has been refined for better simulation. The terrain

is considered to be sloping from the west to the east at a gradient of 2m/km.

They simulated the results for different scenarios on rupture of HDPE liners

provided at the bottom of gypsum pond and ETP sludge SLF facility.

2.10 SUMMARY

There are lots of studies conducted on groundwater contaminant

transport by using mathematical model. Mathematical models provide a

framework for understanding the physical, chemical, and biological processes

that determine the cycling of elements and compounds through the

environment. They provide a basis for relating human activities and

environmental impacts and thus for predicting the changes that might occur in

response to alterations in the activities. It is to be noted that so far no

groundwater quality simulations study has been conducted for Amaravtahi

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river basin of Karur area using mathematical models. The Amaravathi river

and the groundwater in Karur area are severely polluted due to discharge of

effluent by the textile bleaching and dyeing units. Hence mathematical

modeling study is very essential to the under the system behavior and to take a

decision on corrective and remediation measures. Visual MODFLOW is a well

established tool to study the groundwater flow and contaminant transport. It is

used in the research.