Page 190 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 173

Step 5: Calculate the mass removal rate by multiplying the flow rate
(from Step 1) with the adjusted concentration (from Step 4).

Information needed for this calculation

• Extracted vapor flow rate, Q
• Extracted vapor concentration, G
• Overall efficiency factor relative to the theoretical removal rate, η

Example 5.14: Estimate the COC Removal Rate (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 COC removal rate at the beginning of the project 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

Solution:
(a) The flow rate has been determined in Example 5.10 to be 0.216
m /min, or 7.6 ft /min.
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(b) Assuming the free-product phase is present, the saturated vapor
concentration corresponding to the fresh gasoline is 1,340,000
ppmV, or 1,343 g/m (see Example 5.1). On the other hand, the
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saturated vapor concentration corresponding to the weathered
gasoline is 49,000 ppmV, or 226 g/m .
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(c) Assuming the overall efficiency factor is equal to unity, the
removal rate can be found from Equation (5.9) as:

R removal = [(η)(G)](Q)
= [(1.0)(1,343 g/m )](0.216 m /min)
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= 290 g/min = 0.64 lb/min = 920 lb/day (for the
fresh gasoline)
= [(1.0)(226 g/m )](0.216 m /min)
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= 48.8 g/min = 0.107 lb/min = 155 lb/day (for the
weathered gasoline)