Question

Write 5+ pages in one of the following topics :- ( MAKE SURE THE HANDWRITING IS READABLE, * I prefer to be made in M.S word )

1- Contaminant transport in groundwater

2- Modeling of contaminant transport in groundwater

Answer 1

Contaminant Transport in Groundwater

Water is vital for all the living beings in the world. Most of them is the salty water (97%) and only 3% of the fresh water is available to us. But mostly freshwater is present in glaciers, ice caps and due to which only surface and subsurface sources of water like rivers, lakes, groundwater, etc is available for drinking.

Groundwater is vital natural resource for us because most of the people living in this are reliable to it. It is either in the form of public water supply or self domestic supply (wells). Not all groundwater has the sufficient quality for drinking purpose.

Groundwater can be contaminated by the natural process as well as by the anthropogenic activities. First due to natural process the contaminant are transported mainly due to the process of runoff from the agricultural or urban watersheds. The runoff water has many chemicals, micro organisms, nutrients, metals,pesticides,etc and because the water is coming from the wide areas it is type of non point source contaminant.

Another natural process is the Leaching of natural chemicals into the ground which may result in the increased concentration of Sulfates, chlorides, nitrates, etc. In semi arid or arid regions there is evapotranspiration of the water table which can bring the concentrated salt up to the ground level, making the water contaminated.

The human activities like Waste disposal, leaks and spills, mining, agriculture,etc are also making the groundwater Contaminant.

There are three basic mechanism by which contaminants in the groundwater can be transported which are

Advection, Diffusion and Mechanical Dispersion.

Advection is defined as the process by which soluble contaminants are being carried along with the flow of subsurface water. The advective mass flux is given by Ja=qc. Advection process is associated with bulk macroscopic groundwater movement.

When there is random movement in the flied with a concentration gradient, then the contaminants movement is towards the lower concentration, this process is called Diffusion. The diffusive mass flux vector is given by

Jd =-nDs Grad(c).

Diffusion is a molecular based transport phenomenon. When mechanisms occur in concentration gradient, the transport relative to the bulk water movement is known as Mechanical Dispersion. The mass flux vector is Jm=-Dm n grad(c).

Modeling of contaminant transport in groundwater

Modeling means to establish a mathematical relationship which will describe the transport of contaminants in the groundwater.

To solve the problem of this the most commonly used methods are random walk, Eulerian–Lagragian and adaptive grid methods. Bear used the basic equations of contaminant transport in groundwater. Models like Finite Difference Method (FDM) or Finite Element Methods (FEM) is used for the modeling of transport of contaminants in the groundwater.

For modeling some assumptions have to made like Soil is homogenous, isotropic and the flow is one directional. Soil existing in the saturated zone (aquifer) is assumed to be homogeneous, isotropic and isothermal.Within the aquifer is the

Contaminant Transport in Groundwater

Water is vital for all the living beings in the world. Most of them is the salty water (97%) and only 3% of the fresh water is available to us. But mostly freshwater is present in glaciers, ice caps and due to which only surface and subsurface sources of water like rivers, lakes, groundwater, etc is available for drinking.

Groundwater is vital natural resource for us because most of the people living in this are reliable to it. It is either in the form of public water supply or self domestic supply (wells). Not all groundwater has the sufficient quality for drinking purpose.

Groundwater can be contaminated by the natural process as well as by the anthropogenic activities. First due to natural process the contaminant are transported mainly due to the process of runoff from the agricultural or urban watersheds. The runoff water has many chemicals, micro organisms, nutrients, metals,pesticides,etc and because the water is coming from the wide areas it is type of non point source contaminant.

Another natural process is the Leaching of natural chemicals into the ground which may result in the increased concentration of Sulfates, chlorides, nitrates, etc. In semi arid or arid regions there is evapotranspiration of the water table which can bring the concentrated salt up to the ground level, making the water contaminated.

The human activities like Waste disposal, leaks and spills, mining, agriculture,etc are also making the groundwater Contaminant.

There are three basic mechanism by which contaminants in the groundwater can be transported which are

Advection, Diffusion and Mechanical Dispersion.

Advection is defined as the process by which soluble contaminants are being carried along with the flow of subsurface water. The advective mass flux is given by Ja=qc. Advection process is associated with bulk macroscopic groundwater movement.

When there is random movement in the flied with a concentration gradient, then the contaminants movement is towards the lower concentration, this process is called Diffusion. The diffusive mass flux vector is given by

Jd =-nDs Grad(c).

Diffusion is a molecular based transport phenomenon. When mechanisms occur in concentration gradient, the transport relative to the bulk water movement is known as Mechanical Dispersion. The mass flux vector is Jm=-Dm n grad(c).

Modeling of contaminant transport in groundwater

Modeling means to establish a mathematical relationship which will describe the transport of contaminants in the groundwater.

To solve the problem of this the most commonly used methods are random walk, Eulerian–Lagragian and adaptive grid methods. Bear used the basic equations of contaminant transport in groundwater. Models like Finite Difference Method (FDM) or Finite Element Methods (FEM) is used for the modeling of transport of contaminants in the groundwater.

For modeling some assumptions have to made like Soil is homogenous, isotropic and the flow is one directional. Soil existing in the saturated zone (aquifer) is assumed to be homogeneous, isotropic and isothermal. Within the aquifer is, the contaminant transport is assumed to be resulting from a finite length strip source located at the top of the groundwater table. Aquifer is assumed to be free of contamination initially.

First we have taken the initial conditions and then the boundary conditions and then have to formulate the methods to form the model.The model is run and the  Analysis of the model takes place and then the results are found out.

Two software’s are also useful in modeling the transport of contaminant in the groundwater are MODFLOW and MT3DMS and these two models are based on the Finite difference method.

assumed to be resulting from a finite length strip source located at the top of the groundwater table. Aquifer is assumed to be free of contamination initially.

First we have taken the initial conditions and then the boundary conditions and then have to formulate the methods to form the model.The model is run and the  Analysis of the model takes place and then the results are found out.

Two software’s are also useful in modeling the transport of contaminant in the groundwater are MODFLOW and MT3DMS and these two models are based on the Finite difference method.