hydro section 1 - advection

Question 1

Theory of Advection

Answer 1

Some chemical waste can be found buried below the water table, groundwater flowing through the waste will dissolve the chemicals and the resulting solute will be transported by the groundwater; this process is called advection

Question 2

Theory of Dispersion

Answer 2

As the solute mixes with the groundwater, some mixing occurs between the solute-containing groundwater and the surrounding unpolluted groundwater: this process is called dispersion

Question 3

Which form of Darcys Law to estimate advective transport of an unreactive solute

Answer 3

Q = -AKi

Q is flow rate (volume per unit time)
A is cross sectional area at right angles to flow direction
i = change in head / distance

Question 4

to convert flow rate Q to velocity v, we must…

Answer 4

divide though by area A

however, this velocity is best thought of as flow rate per unit cross sectional area - volume per unit time per unit area

the real groundwater flow velocity is greater than this as the water can only flow through pore space in the rock

Question 5

v = ? / ?
v(bar) = ? / (? x ?)

Answer 5

v = Q / A

v(bar) = Q / A(phi) or...
v(bar) = -(K/phi)x i

Q = flow rate 
A = cross sectional area 
phi = porosity

Question 6

What is the average linear velocity (vbar)

i = -0.005
K ~ 1m/day
phi = 0.25

Answer 6

v bar = -(1m/day)/0.25) x -0.005

= 2 x 10^-2 m/day

= 7.3 m/year

Question 7

What is the average linear velocity (vbar)

i = -0.005
K ~ 20m/day
phi = 0.3

Answer 7

v bar = -(20m/day)/0.3) x -0.005

= 0.33 m/day

= 7.3 m/year

Question 8

Main uncertainty in calculating leachate leakage for landfills?

Answer 8

uncertainty in K values
- almost all liners have flaws in them where K is much higher (due to holes in clay liners or rips or cuts in HDPE liners)

Question 9

how to calculate effect of dilution as leachate enters the groundwater

Answer 9

compare the leachate supply rate with the groundwater flow rate, assuming perfect mixing over the whole depth of the aquifer

(flow rate through liner + flow rate through rock) / flow rate through rock = X times dilution of leachate