Page 218 - Materials Chemistry, Second Edition

Vadose Zone Soil Remediation 201

(e) The rate of TPH emission = (Q)(G)
= (1.0 m /min)(3,534 mg/m )
3
3
= 3,534 mg/min = 3.534 g/min
= 5,090 g/day = 5.09 kg/day
= 11.2 lb/day

Discussion:
1. To calculate the rate of biodegradation, we should consider the
entire 7-day cycle.
2. To determine the air-emission rate of TPH, we may need to con-
sider the instantaneous emission rate.

5.6 In Situ Chemical Oxidation

5.6.1 Description of the In Situ Chemical Oxidation Process
In situ chemical oxidation (ISCO) involves the introduction of a chemical oxi-
dant into a subsurface to transform COCs in soil or groundwater into less
harmful compounds. ISCO is predominantly used to address COCs in the
source area so that the mass flux to the groundwater plume can be reduced.
Consequently, it can shorten anticipated cleanup times for natural attenua-
tion and other remedial options [7].

5.6.2 Commonly Used Oxidants

There are various oxidants that have been used for ISCO; however, the most
commonly used oxidants include:

• Permanganate (MnO )
−
4
• Hydrogen peroxide (H O )
2
2
• Fenton’s reagent (hydrogen peroxide + ferrous iron)
• Ozone (O )
3
• Persulfate (S O )
2−
2
8
The persistence of the oxidant in the subsurface is critical because it affects
the extent to which the oxidant can be delivered to the target zone in subsur-
face. Permanganate can persist for months, persulfate for hours to weeks, and
hydrogen peroxide, ozone, and Fenton’s reagent can only persist for minutes
to hours. Free radicals formed from H O , S O , and O are generally con-
2−
8
3
2
2
2
sidered to be responsible for transformation of COCs. These intermediates