Page 171 - Materials Chemistry, Second Edition

154 Practical Design Calculations for Groundwater and Soil Remediation

Example 5.1: Estimate the Saturated Gasoline Vapor Concentration
Use the information in Table 5.1 to estimate the maximum gasoline vapor
concentration for two soil-venting projects. Both sites are impacted by acci-
dental gasoline spills. The spill at the first site happened recently, while the
spill at the other site occurred three years ago.

Solution:
The site with fresh gasoline:

(a) Vapor pressure of fresh gasoline is 0.34 atm at 20°C, as shown in
Table 5.1. The partial pressure of this gasoline in the void can be
found by using Equation (5.1) as:

P A = P ( vap x ) (0.34 atm)(1.0) 0.34 atm= =
)( A

Thus, the partial pressure of gasoline in the air is 0.34 atm
(= 340,000 × 10 atm), which is equivalent to 340,000 ppmV.
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Use Equation (2.1) to convert the ppmV concentration into a mass
concentration (at 20°C), as
1 ppmV fresh gasoline = [(MW of fresh gasoline)/24.05] mg/m 3
= (95)/24.05 = 3.95 mg/m 3
So, 340,000 ppmV = (340,000)(3.95)
= 1,343,000 mg/m = 1,343 mg/L
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The site with weathered gasoline:

(b) Vapor pressure of the weathered gasoline is 0.049 atm, which is
equivalent to 49,000 ppmV.

Use Equation (2.1) to convert the ppmV concentration into a mass
concentration (at 20°C), as

1 ppmV weathered gasoline = [(MW of weathered
gasoline)/24.05] mg/m 3
= (111)/24.05 = 4.62 mg/m 3
So, 49,000 ppmV = (49,000)(4.62)
= 226,000 mg/m = 226 mg/L
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