Page 182 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 165

Example 5.8: Determine the Radius of Influence of a Soil-Venting
Well by Using the Pressure Drawdown Data
(Pressure Data Are Given in Inches of Water)
Determine the radius of influence of a soil-venting well using the following
information:

• Pressure at the extraction well = 48-in. water vacuum
• Pressure at a monitoring well 40 ft away from the extraction well =
8-in. water vacuum
• Diameter of the vapor extraction well = 4 in.

Strategy:
The pressure data are expressed in inches of water. We need to convert
them to the atmospheric unit or convert the atmospheric pressure to
inches of water. A pressure of 1 atmosphere is equivalent to 33.9 ft
of water column.

Solution:
(a) Pressure at the extraction well = 48-in. water vacuum
= 33.9 − (48/12) = 29.9 ft of water = (29.9/33.9) = 0.88 atm
Pressure at the monitoring well = 8-in. water vacuum
= 33.9 − (8/12) = 33.23 ft of water = (33.23/33.9) = 0.98 atm

(b) Let us define the R as the location where P is equal to the atmo-
I
spheric pressure. The R can be found by using Equation (5.3) as:
I
ln[40/(2/12)]
2
2
(0.98) − (0.88) = (1.0 − 0.88 )
2
2
R I
ln[/(2/12)]
R = 128 ft
I
(c) For comparison, let us now define the R as the location where the
I
drawdown is equal to 1% of the vacuum in the extraction well:
Thus, P = 1 – (1 – 0.88)(1%) = 0.9988 atm
RI
ln[40/(2/12)]
2
2
(0.98) − (0.88) = (0.9988 − 0.88 )
2
2
ln[/(2/12)]
R I
R = 120 ft
I
Discussion:
The R value from part (c), 120 ft, is about 7% smaller than that from
I
part (b).