Page 183 - Materials Chemistry, Second Edition

166 Practical Design Calculations for Groundwater and Soil Remediation

Example 5.9: Estimate the Pressure Drawdown in a
Soil-Venting Monitoring Well
Using the pressure drawdown data given in Example 5.8, estimate the pres-
sure drawdown (vacuum) in a monitoring well that is 20 ft away from the
extraction well.

Strategy:
Example 5.8 gives the pressure drawdown data at (1) the monitoring
well (P = 0.88 atm), (2) 40 ft away from the monitoring well (P = 0.98
atm), and (3) the R (P = 1 atm). We can use any two of these three to
I
estimate the pressure drawdown in a well that is 20 ft away from the
extraction well.

Solution:
(a) First, use the data of the extraction well and the monitoring well
(r = 40 ft). The pressure at the monitoring well (r = 20 ft) can be
found by using Equation (5.3) as:

ln[20/(2/12)]
P r − (0.88) = (0.98 − 0.88 )
2
2
2
2
ln[40/(2/12)]
P = 0.968 atm = 13.0 in. of water (vacuum)
r
(b) We can also use the data of the extraction well and the R . The
I
pressure at the monitoring well (r = 20 ft) can be found by using
Equation (5.3) as:
ln[20/(2/12)]
2
2
2
2
P r − (0.88) = (1.0 − 0.88 )
ln[128/(2/12)]
P = 0.968 atm = 13.0 in. of water (vacuum)
r
(c) We can also use the data of the monitoring well (r = 40 ft) and the
R . The pressure at the monitoring well (r = 20 ft) can be found by
I
using Equation (5.3) as:

ln[20/40]
2
P r − (0.98) = (1.0 − 0.98 )
2
2
2
ln[128/40]
P = 0.968 atm = 13.0 in. of water (vacuum)
r