Remediation Technologies - Environmental Investigation and Remediation - page 356

Methanes
Ethenes

Ethanes

BTEX
CI-Benzene

Oxygenates

90,000

80,000

70,000

60,000

50,000

40,000

30,000

20,000

10,000

0

0 1 2 3 4 5 6 7

Mole ratio KOH : persulfate

FIGURE 7.13 Effect of KOH ratio on persulfate reactivity. (From Block, P.A., Brown, R.A., and Robinson,
D., 2004, In: A.R. Gavaskar and A.S.C. Chen [Eds], Proceedings of the Fourth International Conference on
Remediation of Chlorinated and Recalcitrant Compounds , Paper 2A-05. Columbus, OH: Battelle Press.)

evaluated at pH values of 3, 5, 7, 9, and 11, for a 25 mM persulfate solution at 25°C containing
1.13 mM 1,4-dioxane. The reaction rate was found to decrease with increasing pH values. Apparently,
sulfate and hydroxyl radicals decay rapidly because of reactions with hydroxyl ions in high-pH
solutions. Additionally, carbon dioxide from oxidation leads to the formation of bicarbonate and
carbonate ions, which may hinder the oxidation of organic compounds.
FMC (2007) discussed an industrial site with a methyl chloroform rail car loading/unloading
operation where contaminant concentrations were elevated as follows: methyl chloroform,
203,000 g/L. Initial testing

at the site using injected calcium hydroxide (hydrated lime) and steam encountered difi culties
with steam daylighting—that is, steam escape through to the ground surface—resulting in an
inability to provide the required heat to the treatment area. Sodium hydroxide was then used to
catalyze the persulfate with high alkalinity. Postinjection concentrations of 1,4-dioxane were
below the local cleanup standard and detection limit of 5

μ g/L; 1,1-dichloroethylene, 82,000 μ g/L; and 1,4-dioxane, 50,000 μ

g/L. Chlorinated VOCs were reduced
dramatically within the i rst year and continued to decline during the following nine-month mon-
itoring period.
Removal of 1,4-dioxane with persulfate has been successfully demonstrated in numerous i eld
applications with a variety of activation methods. Following a successful bench-scale study in which
100% of 1,4-dioxane and 85-99% of chlorinated VOCs were removed, Cronk (2006) executed a
source-area removal at a site in Huntington Beach, California, with 1,4-dioxane levels as high as
260,000

μ

g/L, as well as TCE and dichloromethane as contaminants of concern. Approximately
5000 pounds of persulfate activated with catalyzed hydrogen peroxide was applied to the tight
clayey soil through eight application wells with a radius of inl uence of 10-12 ft each. 1,4-Dioxane
levels were reduced by 88-95% in the source zone, down to 21,000

μ

g/L, during the source-removal
project. In La Mirada, California, another i eld pilot study used chelated iron (EDTA) activation of
sodium persulfate. 1,4-Dioxane concentrations in three wells located down gradient of the injection
area declined from between 100 and 225

μ

g/L to nondetectable levels over the nine-month test
period. Levels have remained below detection limits for several months, and the groundwater will
be monitored periodically to ensure that rebound does not occur (Cronk, 2008).

μ