Page 199 - Materials Chemistry, Second Edition

182 Practical Design Calculations for Groundwater and Soil Remediation

Solution:
The new air flow rate can be found by using Equation (5.15) as

Q@30 o C = 273 20+

Q@20 o C 273 30+

Q @ 30°C = (7.6)(0.967) = 7.3 ft /min
3
Discussion:
The temperature affects the air flow rate insignificantly. For a 10°C
increase in temperature, the flow rate decreases by less than 4%.

5.2.8 Number of Vapor Extraction Wells
There are three main considerations in determining the number of vapor
extraction wells necessary for a soil-venting project. First, a successful soil-
venting project should have a sufficient number of extraction wells to cover
the entire plume. In other words, the entire impacted zone should be within
the influence of the wells, thus

1.2( A plume )
N wells = 2 (5.16)
π R I

The factor of 1.2 is arbitrarily chosen to account for the overlapping of
the influence areas among the wells as well as the fact that the periph-
eral wells may reach outside the impacted zone. Second, the number of
wells should be sufficient to complete the site cleanup within an accept-
able time frame.

R acceptable = M spill (5.17)
T cleanup,acceptable

N wells = R acceptable (5.18)
R removal

The minimum number of the vapor extraction wells should be the larger of
the two that are determined from Equations (5.16) and (5.18).
The last, and probably the most important, consideration is the economical
one. There is a trade-off between the number of wells and treatment cost. One
can install more wells to shorten the cleanup time, but it may be more costly.