Page 194 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 177

• Dry bulk density of soil, ρ b
• Total bulk density of soil, ρ t

Example 5.16: Estimate the Cleanup Time (in the
Presence of Free-Product Phase)

Recently, a gasoline spill occurred at a gasoline station and caused subsur-
face contamination. A soil-venting well (4-in. diameter) was installed at a
site. The pressure in the extraction well is 0.9 atm, and the radius of influence
of this soil-venting well has been determined to be 50 ft.
Estimate the required cleanup time for total petroleum hydrocarbon (TPH)
using the following information:

• Permeability of the formation = 1 darcy
• Well screen length = 20 ft
• Viscosity of air = 0.018 centipoise
• Temperature of the formation = 20°C
• Porosity = 0.35
• Organic content in soil = 0.01
• Degree of water saturation = 40%
• Dry bulk density of soil = 1.6 g/cm 3
• Total bulk density of soil = 1.8 g/cm 3
• Size of the plume = 6,500 ft 3
• Initial average TPH concentration in soil = 6,000 mg/L
• Required cleanup level = 100 mg/L
• Overall efficiency factor relative to theoretical removal rate = 0.11

Solution:
(a) The flow rate has been determined in Example 5.10 to be 0.216
m /min, or 7.6 ft /min.
3
3
Presence of the Free-Product Phase
(b) Determine the maximum possible TPH concentration in soil
absent of free product, X (use the procedure illustrated in
sat
Example 5.3):
Since no Henry’s constant and K data are available for gasoline,
ow
we use those of toluene, one of the common gasoline compo-
nents, as an approximation: