Answer:
(a) For benzene, t = 909.33 days or 2.49 years
(b) For toluene, t = 1612.67 days or 4.42 years
Explanation:
Kd value of benzene = 1.8L/kg
Kd value of toluene = 3.3 L/kg
Density of soil (p) = 2.6 kg/L = 2600 kg/m3
Hydraulic conductivity K = 2.9 x 10-5 m/s
Porosity (n) = 0.37
Well depth(x) = 12m
To calculate the time for benzene and toluene to reach the well, we use the formula;
x = t u /R -----------------------------1
But velocity (u) = Ki/n
u= 2.9 x 10-5 x (0.4/15) / 0.37
= 2.09 x 10-6 m/s or 0.18 m/day
For benzene:
R = 1 + (p*Kd)/n
R= 1 + 2.6(1.8)/0.37
= 1 + 12.64
= 13.64
Substituting the values for R and u into equation 1, we have
x = t u /R
12 = t x 0.18 / 13.64
12 = 0.013t
t = 12/0.013
t = 909.33 days
or t = 909.33/365 days = 2.49 years
(b) For Toluene:
R = 1 + (p*Kd)/n
R= 1 + 2.6(3.3)/0.37
= 1 + 23.19
= 24.19
Substituting into equation 1, we have
x = t u/R
12 = t x 0.18 /24.19
12 = 0.00744 t
t = 12/0.00744
t = 1612.67 days
or 1612.67/365 = 4.42 years