Page 200 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 183

Example 5.18: Determine the Number of Venting Wells Required
For the soil-venting project described in Example 5.16, it is desired to clean
up the site in 9 months. Determine the number of venting wells needed. The
maximum cross-sectional area of the plume is equal to 9,000 ft .
2
Solution:
(a) The flow rate from one venting well has been determined to be
0.216 m /min, or 7.6 ft /min. At this flow rate, the cleanup will
3
3
take 498 days (from Example 5.16). To meet the 9-month cleanup
schedule, the removal rate should be 1.8 (= 498 ÷ 270) times faster.
Therefore, we need to increase the flow rate by 1.8 times or to
have two venting wells.
(b) The radius of influence of one venting well has been determined
to be 50 ft. The number of wells needed to cover the plume can
be determined by using Equation (5.16) as:
1.2( A plume ) 1.2(9,000)
N wells = 2 = 2 = 1.38
π R I π(50)

Therefore, two wells should be enough to cover the entire plume,
unless the plume has a very long stripe shape.
(c) Based on these results, two venting wells would be required.

5.2.9 Sizing the Vacuum Pump (Blower)
The theoretical horsepower requirements (hp theoretical ) of vacuum pumps,
blowers, or compressors for an ideal gas undergoing an isothermal compres-
sion (PV = constant) can be expressed as [5]:

hp theoretical = 3.03 10× − 5 PQ ln P 2 (5.19)
1
1
P 1
where
P = intake pressure, lb /ft 2
f
1
P = final delivery pressure, lb /ft 2
2
f
Q = air flow rate at the intake condition, ft /min
3
1
For an ideal gas undergoing an isentropic compression (PV = constant),
k
the following equation is applicable for single-stage compressors [5]:
3.03 10× − 5 k   P 2  k ( − 1)/ k 
hp theoretical = PQ 1    − 1 (5.20)

1
k 1−   P 1   