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<< Click to Display Table of Contents >> Description |
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The results of a laboratory diffusion test are analyzed in this example [see Rowe, Caers & Barone, 1988; Barone, Yanful, Quigley & Rowe, 1989]. In this example the diffusion of Potassium in a clay is examined. The clay has an initial background concentration of Potassium of 10 mg/L.
The leachate source has an initial concentration (co) of 400 mg/L, and the physical height of the leachate in the reservoir above the soil was 6 cm. At the base of the specimen there was an impermeable barrier (i.e., zero flux).
Following are the parameters used in this example:
Property |
Symbol |
Value |
Units |
Darcy Velocity |
va |
0 |
m/a |
Diffusion Coefficient |
D |
0.648 |
cm2/d |
Distribution Coefficient |
Kd |
2.68 |
cm3/g |
Soil Porosity |
nm |
0.39 |
- |
Dry Density |
|
1.68 |
g/cm3 |
Soil Layer Thickness |
H |
4.5 |
cm |
Number of Sub-layers |
|
10 |
- |
Source Concentration |
co |
400 |
mg/L |
Ref. Height of Leachate |
Hr |
6 |
cm |
Background Concentration |
|
10 |
mg/L |
When using an initial concentration profile (eg. background 10 mg/L in this example) the user should have at least three layers, with the top and bottom layer being very thin. In this example layers 1 and 3 are taken to be 0.1 cm thick and layer 2 (the main layer) is taken to be 4.5 - 0.2 = 4.3 cm thick.