SOLUTION: GEOS 5120 Ground Water Quality and Contamination Paper

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1

Principles of Hydrology
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Principles of Hydrology
Answers
1. Average velocity of ground water is defined as the ratio of darcy velocity and porosity.
Velocity =Q/A
Where Q= volume flux and A=Surface area
For Sandstone, velocity = (5×10-4)/1000
= 5×10-7m/s
For carbonate, velocity= (1 x10-5)/1000
= 10-8m/s
Variation based on porosity= V/M where V=Velocity and M=Matrix porous
For sandstone, variation = (5×10-7)/0.25
=2×10-6m/s
For carbonate, variation = (10-8)/0.02
=5×10-7m/s
The distance covered=0.5km=500m
Time =d/velocity
One year= (365 x24 x3600) seconds =31 536 000 seconds
One second= 1/31 536 600 years
=3.17×10-8 years
For sandstone =500/ (2.0 x10-6)
=2.5 x108 x 3.17×10-8
=7.925 years
For carbonate=500/ (5×10-7)
= 1.0×109 x 3.17x 10-8
=31.7 years
2. The ground water velocity in carbonate aquifer is faster than sandstone due to the less
porosity of carbonate rock hence high darcy velocity than sandstone.
3. Conservation of mass for a chemical that is transported yields the advection-reactiondispersion (ARD) equation:

, (107)
Where C is concentration in water (mol/kgw),
t is time (s),
v is pore water flow velocity (m/s),
x is distance (m),
D L is the hydrodynamic dispersion coefficient [m 2 /s,

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, with D e the effective diffusion coefficient
and aL the dispersivity (m)

Represents adjective transport,

represents dispersive transport

Is the change in concentration in the solid phase due to reactions (q in the same units as C )
The usual assumption is that v and D L are equal for all solute species, so that C can be the total
dissolved concentration for an element, including all redox species
DL = αLv
Clay
=1.0*1.0E-15
= 1e-15
Crystalline Rock
=1.0*1.0E-08
=1e-8
Then,
0.2= De+ 1e-15
De= (0.2) -(1e-15)
=0.2……clay
0.2 = De + 1e-8
De= (0.2) -(1e-8)
De= 0.19999999
Therefore, diffusion dominates dispersion.
4. Bentonite is considered as a buffer due to its good swelling capacity and low hydraulic
conductivity. Bentonite is chosen as a buffer material in deep geological respiratory as it helps in
dealing with high level of nuclear waste.
5.K= 20m/d,

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b= 30m
dh/dx= 0.005
Determine the minimum pumping rate.
To calculate the pump rate, divide th…