Page 187 - Materials Chemistry, Second Edition

170 Practical Design Calculations for Groundwater and Soil Remediation

Discussion:
1. The answers from parts (a) and (b) should be the same. The
apparent difference is from truncation errors.
2. The Darcy velocity at 20 feet away from the well is relatively
slow, at 1.4 m/day.

Example 5.12: Estimate the Radius of Influence of a Soil-Venting
Well by Using the Extracted Vapor Flow Rate
Determine the radius of influence of a soil-venting well using the following
information:

• Pressure at the venting well = 0.85 atm
• Flow rate measured at the extraction pump discharge = 0.21 m /min
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• Well screen length = 4 m
• Diameter of the venting well = 0.1 m
• Permeability of the formation = 1.0 darcy
• Viscosity of air = 1.8 ×10 poise
−4
• Temperature of the formation = 20°C

Strategy:
This problem can be viewed as the reverse of Example 5.10, in which
the radius of influence was given for estimation of the vapor extrac-
tion flow rate. In this problem, the flow rate was given to estimate
the radius of influence. As in the previous example, a few unit con-
versions need to be performed first:

• 1 atm = 1.013 × 10 N/m 2
5
• 1 darcy = 10 cm = 10 m 2
2
−8
−12
• 1 poise = 100 centipoise = 0.1 N/s/m 2
• (So, 0.018 centipoise = 1.8 × 10 poise = 1.8 ×10 N/s/m )
−5
−4
2
Solution:
(a) The vapor flow rate entering the extraction well can be found by
using Equation (5.7):

 P well   0.85 
Q atm =   P atm   Q well = 0.21 =   1   Q well

Q well = 0.24 m/min= 0.004 m/s
3
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