Chemical oxidation of volatile organic compounds

Volatile organic compounds are removed from contaminated soil by introducing one or both a water soluble peroxygen compound, such as a persulfate, and a permanganate into the soil, either in situ or ex situ, in amounts and under conditions wherein both the soil oxidant demand is satisfied and volatile organic compounds in the soil are oxidized. In a preferred embodiment, when both are used the peroxygen satisfies the soil oxidant demand and the permanganate oxidizes the volatile organic compounds. Sodium persulfate is the preferred persulfate and potassium permanganate is the preferred permanganate. The persulfate and the permanganate may be added to the soil sequentially, or may be mixed together and added as an aqueous solution.

TECHNICAL FIELD 
The present invention relates to the in situ and ex situ oxidation of 
organic compounds in soils, groundwater and process water and wastewater 
and especially relates to the in situ oxidation of volatile organic 
compounds in soil and groundwater. 
BACKGROUND OF THE INVENTION 
The presence of volatile organic compounds (VOCs) in subsurface soils and 
groundwater is a well-documented and extensive problem in industrialized 
and industrializing countries. As used in this specification and its 
appended claims, volatile organic compounds or VOCs means any at least 
slightly water soluble chemical compound of carbon, with a Henry's Law 
Constant greater than 10.sup.-7 atm m.sup.3 /mole, which is toxic or 
carcinogenic, is capable of moving through the soil under the influence of 
gravity and serving as a source of water contamination by dissolution into 
water passing through the contaminated soil due to its solubility, 
including, but not limited to, chlorinated solvents such as 
trichloroethylene (TCE), vinyl chloride, tetrachloroethylene (PCE), 
methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane (TCA), 
carbon tetrachloride, benzene, chloroform, chlorobenzenes, and other 
compounds such as ethylene dibromide, and methyl tertiary butyl ether. 
In many cases discharge of volatile organic compounds into the soil have 
lead to contamination of aquifers resulting in potential public health 
impacts and degradation of groundwater resources for future use. Treatment 
and remediation of soils contaminated with volatile organic compounds have 
been expensive and in many cases incomplete or unsuccessful. Treatment and 
remediation of volatile organic compounds that are either partially or 
completely immiscible with water (i.e., Non Aqueous Phase Liquids or 
NAPLs) have been particularly difficult. This is particularly true if 
these compounds are not significantly naturally degraded, either 
chemically or biologically, in soil environments. NAPLs present in the 
subsurface can be toxic to humans and other organisms and can slowly 
release dissolved aqueous or gas phase volatile organic compounds to the 
groundwater resulting in long-term (i.e., decades or longer) sources of 
chemical contamination of the subsurface. In many cases subsurface 
groundwater contaminant plumes may extend hundreds to thousands of feet 
from the source of the chemicals resulting in extensive contamination of 
the subsurface. These chemicals may then be transported into drinking 
water sources, lakes, rivers, and even basements of homes. 
The U.S. Environmental Protection Agency (USEPA) has established maximum 
concentration limits for various hazardous compounds. Very low and 
stringent drinking water limits have been placed on many halogenated 
organic compounds. For example, the maximum concentration limits for 
solvents such as trichloroethylene, tetrachloroethylene, and carbon 
tetrachloride have been established at 5 .mu.g/L, while the maximum 
concentration limits for chlorobenzenes, polychlorinated biphenyls (PCBs), 
and ethylene dibromide have been established by the USEPA at 100 .mu.g/L, 
0.5 .mu./L, and 0.05 .mu.g/L, respectively. Meeting these cleanup criteria 
is difficult, time consuming, costly, and often virtually impossible using 
existing technologies. 
One technology, which has been attempted at pilot-scale test applications, 
is the use of potassium permanganate (KMnO.sub.4) alone as an oxidant for 
in situ soil remediation. (Treatment performed in situ does not involve 
physical removal of the contaminated phase itself, whereas, ex situ 
treatment methods involve physical removal of the contaminated phase and 
treatment elsewhere. This has been attempted in view of KMnO.sub.4 's 
known capacity to oxidize target VOCs present at typical sites (e.g. 
trichloroethylene, dichloroethylene, and vinyl chloride). An example of 
such a reaction is: 2MnO.sub.4.sup.- +C.sub.2 HCl.sub.3 .fwdarw.2CO.sub.2 
+2MnO.sub.2 +3Cl.sup.- +H.sup.+. 
It is also well known that KMnO.sub.4 has versatile chemistry and high 
aqueous solubility. Once dissolved into aqueous phase, permanganate salts 
(such as potassium permanganate, sodium permanganate, calcium permanganate 
and the like) dissociate to form permanganate ions (MnO.sub.4.sup.-) that 
may transform to a variety of species with oxidation states of manganese 
in +1, +2, +3, +4, +5, +6, and +7. The most common species of manganese 
are manganese ions (Mn.sup.++), manganese dioxide (MnO.sub.2), and 
permanganate (MnO.sub.4.sup.-). The oxidation strength of 
(MnO.sub.4.sup.-) depends on the electron accepting capability of 
(MnO.sub.4.sup.-) which is pH dependent. The lower the pH, the greater the 
tendency of (MnO.sub.4.sup.-) to accept the electrons as indicated by the 
redox potential (E.sub.o) values in Eqs. 1 through 4: 
##EQU1## 
The reactivity of KMnO.sub.4 depends on the reaction conditions and the 
types of organic compounds being oxidized. 
While, chemically, potassium permanganate is effective at oxidizing 
unsaturated volatile organic compounds, currently known methods to use 
that ability to actually clean up a site require exceedingly large 
quantities of KMnO.sub.4 to overcome the natural oxidant demand exerted by 
the soil, thereby limiting, for a given amount of KMnO.sub.4, the 
percentage of KMnO.sub.4 available for oxidizing the volatile organic 
compounds. Large amounts of KMnO.sub.4 are thus required per unit of soil 
volume limiting the application of this technology due to high cost. 
Another disadvantage of potassium permanganate, which has not been overcome 
by prior art clean-up methods, is the formation of solid manganese dioxide 
(MnO.sub.2) precipitates. This precipitate may result in clogging of the 
soil, resulting in a reduced permeability of the soil to water, reducing 
the hydraulic conductivity thereof, and thereby inhibiting oxidant access 
to the entire contaminated site rendering treatment of the soil and 
volatile organic compounds incomplete. 
A further disadvantage of adding potassium permanganate alone and in large 
quantities for subsurface remediation is that it can result in the 
formation of soluble manganese compounds in groundwater that may exceed 
drinking water standards. For this and the foregoing reasons, attempts to 
date to use potassium permanganate for in situ applications have not been 
fully successful. 
Early use of peroxydisulfate is reported for the purpose of organic 
compound synthesis. Additionally, thermally catalyzed decomposition of 
ammonium persulfate as a method of organic carbon digestion has been 
reported being accomplished at very low pH (i.e. in the vicinity of pH 
2.0), but has not been thought to be useful for that purpose at higher pH. 
More recent publications have indicated that, under ambient temperature 
and uncatalyzed conditions, atrazine and PCBs may be oxidized by ammonium 
persulfate in aqueous solutions and in contaminant spiked soils under 
batch conditions. There has been no suggestion that this oxidation 
reaction has any application to the treatment of volatile organic 
compounds in contaminated soil or groundwater. 
Divalent and heavy metal cation adsorption onto manganese oxide surfaces is 
a known phenomenon. The order of preference for selected cations to adsorb 
onto MnO.sub.2 surfaces is reported as follows: 
EQU Pb.sup.++ &gt;Cu.sup.++ &gt;Mn.sup.++ &gt;Co.sup.++ &gt;Zn.sup.++ &gt;Ni.sup.++ &gt;Ba.sup.++ 
&gt;Sr.sup.++ &gt;Ca.sup.++ &gt;Mg.sup.++. 
Stoichiometry and rates of redox interactions with manganese dioxide and 
various organic compounds in aqueous solutions has been studied for some 
organic compounds, such as aniline and primary aromatic amines; 
hydroquinone; various organic acids, substituted phenols, and 
chlorophenols. In all of the above systems reduction of the manganese 
dioxide to Mn.sup.++ results in the redox couple with the organic 
compound being oxidized, the reaction being identified in the literature 
as interfacial. There has been no recognition, however, that this 
knowledge has application to the removal of contaminants from soil. 
DISCLOSURE OF THE INVENTION 
The present invention relates to a method for the treatment of contaminated 
soil, sediment, clay, rock, and the like (hereinafter inclusively referred 
to as "soil") containing volatile organic compounds, as well as for 
treatment of contaminated groundwater or wastewater containing volatile 
organic compounds. 
The method of the present invention uses one or more water soluble oxidants 
under conditions which enable oxidation of most, and preferably 
substantially all, the volatile organic compounds in the soil, 
groundwater, and/or wastewater, rendering them harmless. 
The oxidant may be solid phase water soluble peroxygen compound and/or a 
permanganate compound, introduced into the soil in amounts, under 
conditions and in a manner which assures that the oxidizing compound(s) 
are able to both 1) satisfy most and preferably substantially all the soil 
oxidant demand, and 2) contact and oxidize most, and preferably 
substantially all, the target VOCs, rendering the target VOCs harmless. 
The soil oxidant demand referred to above can be created by various 
species including natural organic matter, reduced inorganic species such 
as ferrous ion, ferrous carbonate, and other allochthonous (anthropogenic) 
organic and reduced inorganic species. 
In a preferred embodiment of the invention a peroxygen compound is 
introduced into the soil in sufficient quantities to satisfy the soil 
oxidant demand, and a permanganate compound is introduced into the soil in 
sufficient quantities to oxidize the VOCs and render them harmless. These 
compounds may be introduced or injected into the soil simultaneously, such 
as in a mixture, or sequentially. Since the permanganate compound will not 
have to satisfy the soil oxidant demand to any significant extent, the 
formation of undesirable amounts of soil clogging MnO.sub.2 precipitate, 
as occurred with prior art methods, is avoided, and the permanganate 
compound is readily able to reach and react with the target VOCs. This 
methodology may also be used ex situ to treat quantities of contaminated 
soil which have been removed from the ground. As used herein and in the 
appended claims, "sequential" introduction of the peroxygen compound and 
the permanganate compound is intended to mean introduction or injection of 
the compounds "one after the other" (i.e. "alternately"), and includes 
repeating the sequence as many times as necessary to achieve a desired 
result. 
In another embodiment of the present invention, wherein only relatively low 
levels of VOCs and other organic compounds need to be treated, such as at 
a distant end of a groundwater plume extending downstream from a 
contaminated site which has been treated to remove a high percentage of 
the VOCs and other organic compounds, a permanganate compound alone is 
introduced into the ground in the path of the contaminated groundwater 
plume. The permanganate compound creates a zone of material through which 
the groundwater passes and within which the VOCs and other organic 
compounds in the groundwater are oxidized. The permanganate compound, when 
introduced into the soil, will initially react with constituents in the 
soil to form a "barrier" zone of MnO.sub.2 precipitate. The VOCs and other 
organic compounds in the groundwater readily attach themselves to the 
MnO.sub.2 by adsorption. Reduction of the manganese and oxidation of the 
VOC then takes place within the zone, resulting in the elimination of the 
VOCs. 
According to another aspect of the present invention, under conditions 
where metal cations are present in the contaminated soil, persulfate may 
be introduced into the contaminated soil to remove VOCs. The metal cations 
catalytically decompose the persulfate to form sulfate free radicals, 
which oxidize the target VOCs. If the metal cations are not naturally 
present in sufficient quantities, they may be added from an external 
source. 
The foregoing and other features and advantages of the present invention 
will become clear from the following description. 
BEST MODE FOR CARRYING OUT THE INVENTION 
In accordance with an exemplary embodiment of the present invention, the 
oxidation of volatile organic compounds at a contaminated site is 
accomplished by the sequential injection of persulfate and then 
permanganate into the soil. 
Alternating injection of the persulfate and permanganate entails 
introducing sufficient persulfate into the soil to satisfy a sufficient 
amount of the soil oxidant demand such that, upon the introduction of the 
permanganate, the permanganate does not excessively react with the normal 
soil constituents, as it would if used alone. By "excessively" it is meant 
enough to form MnO.sub.2 precipitate in quantities that reduce the soil 
permeability and diffusivity to the point where the permanganate cannot 
readily move through the soil to reach and oxidize the VOCs. Due to the 
lessening of the soil oxidant demand as a result of the persulfate, a 
faster and more uniform distribution of the permanganate through the soil 
to the target contaminant is enabled and much less permanganate is 
required to oxidize the VOCs. However, as the amount of volatile organic 
compounds decrease, to react with the remaining volatile organic compound 
the permanganate will need to migrate through additional soil that has an 
additional soil oxidant demand. This may require an additional injection 
of persulfate at that location. This sequential injection of persulfate 
and permanganate would be repeated, as and if required, to oxidize VOCs 
within the soil volume being treated until the VOC concentration is 
reduced to the desired level. 
In a preferred form of the invention, sodium persulfate (Na.sub.2 S.sub.2 
O.sub.8) is introduced into the soil, followed by potassium permanganate 
(KMnO.sub.4). The persulfate satisfies the oxidant demand of the soil by 
oxidizing the soil constituents, resulting in less of those constituents 
being available to react with the permanganate. (The persulfate reaction 
is relatively slow; and it may be desirable, although it is not required, 
to wait long enough for the persulfate reaction to go to completion before 
starting the permanganate.) Because less permanganate reacts with the 
soil, more is available to oxidize the VOCs in the soil. Further, the 
reduction of (MnO.sub.4.sup.-) to the solid precipitate MnO.sub.2 is 
lessened. Thus, there is less precipitate to reduce permeability of the 
soil and restrict the potassium permanganate from reaching, reacting with 
and destroying VOCs. In other words, the introduction of both the sodium 
persulfate and the potassium permanganate into the soil, allows the 
potassium permanganate to more quickly and more uniformly move through the 
soil to the target VOCs, rather than forming an unacceptable amount of 
cementatious-like solid precipitate. (This process may be initiated by the 
use of injection means, such as wells for in situ application, or by 
nozzles, pipes or other conduits to inject the oxidants into soil which 
has been removed from the ground for ex situ treatment.) 
For in situ soil treatment, injection rates must be chosen based upon the 
hydrogeologic conditions, that is, the ability of the oxidizing solution 
to displace, mix and disperse with existing groundwater and move through 
the soil. Additionally, injection rates must be sufficient to satisfy the 
soil oxidant demand and chemical oxidant demand in a realistic time frame. 
It is advantageous to clear up sites in both a cost effective and timely 
manner. Careful evaluation of site parameters is crucial. It is well known 
that soil permeability may change rapidly both as a function of depth and 
lateral dimension. Therefore, injection well locations are also site 
specific. Proper application of any remediation technology depends upon 
knowledge of the subsurface conditions, both chemical and physical, and 
this process is not different in that respect. 
While potassium permanganate is preferred, in view of its lower cost, any 
compound that dissociates into the desired permanganate ion 
(MnO.sub.4.sup.-) will work. Examples of other possible permanganates 
useful in the method of the present invention are sodium permanganate and 
calcium permanganate, in order of increasing cost. At an ambient 
temperature, the aqueous solubility of KMnO.sub.4 is about 60 g/L, while 
that of NaMnO.sub.4 is about 600 g/L. Upon dissolution in water, both 
dissociate to generate (MnO.sub.4).sup.- ions that undergo various 
reactions. Although a primary issue is often cost, NaMnO.sub.4, due to its 
order of magnitude greater solubility relative to KMnO.sub.4, could be 
useful whenever the soil permeability is very low and only a small amount 
of liquid can travel from the injection point toward the contaminant. 
Additionally, potassium ions have been shown to cause the swelling of 
certain clays that could lead to permeability reductions. The use of 
sodium ions, in selected instances, could eliminate such difficulties. 
Similarly, while sodium persulfate is the preferred compound for oxidizing 
the soil constituents, other solid phase water soluble peroxygen compounds 
could be used. By "solid phase water soluble peroxygen compound" it is 
meant a compound that is solid and water soluble at room temperature and 
contains a bivalent oxygen group, O--O. Such compounds include all the 
persulfates, peroxides, and the like, with the persulfates being preferred 
because they are inexpensive and survive for long periods in the 
groundwater saturated soil under typical site conditions. The persulfate 
anion is the most powerful oxidant of the peroxygen family of compounds. 
Although the persulfate ion is a strong two-electron oxidizing agent with 
a standard reduction potential of 2.12v, in the majority of its reactions 
persulfate undergoes either a one-electron reduction with formation of one 
sulfate radical ion (and hence has effectively lower reduction potential 
than 2.12v) or a breakage of the weak oxygen-oxygen bond with formation of 
two sulfate radical-ions. The former reaction is represented by the 
following equation: 
EQU S.sub.2 O.sub.8.sup.-- +2H.sup.+ +2e.sup.- .fwdarw.2HSO.sub.4 E.sub.o =2.12 
v 
The second reaction generally occurs when solutions of persulfates are 
sufficiently heated, and is represented by the following equation: 
EQU S.sub.2 O.sub.8.sup.-- +Heat.fwdarw.2.SO.sub.4.sup.- 
Similarly, free radicals can also be generated in the presence of 
transition metal ions, such as Fe.sup.++, as follows: 
EQU S.sub.2 O.sub.8.sup.-- +Fe.sup.++ .fwdarw.Fe.sup.+++ +SO.sub.4.sup.-- 
+.SO.sub.4.sup.- 
The highly reactive sulfate radical-ion may undergo reactions with a 
variety of substrates present in the solution. In addition, the 
one-electron oxidation intermediate of the substrate may be a reactive 
intermediate, which may further react with other substrates present in the 
solution or the peroxide ion. Thus, depending on the reaction conditions 
and type of substrate present, persulfate may follow a direct oxidation 
pathway, radical formation, or both. 
The most preferred persulfate is sodium persulfate as it has the greatest 
solubility in water and is least expensive. Moreover, it generates sodium 
and sulfate upon reduction, both of which are relatively benign from 
environmental and health perspectives. Potassium persulfate and ammonium 
persulfate are examples of other persulfates which might be used. 
Potassium persulfate, however, is an order of magnitude less soluble in 
water than sodium persulfate; and ammonium persulfate is even less 
desirable as it may decompose into constituents which are potential health 
concerns.

The following are other examples of reactions of KMnO.sub.4, 
MnO.sub.4.sup.-, and S.sub.2 O.sub.8.sup.31 - with selected organic and 
inorganic species: 
EQU S.sub.2 O.sub.8.sup.-- +2Fe.sup.++ .fwdarw.2Fe.sup.+++ +2SO.sub.4.sup.-- 
EQU S.sub.2 O.sub.8.sup.-- +NO.sub.2.sup.- +H.sub.2 O.fwdarw.NO.sub.3.sup.- 
+2SO.sub.4.sup.-- +2H.sup.+ 
EQU S.sub.2 O.sub.8.sup.-- +HCO.sub.2.sup.- .fwdarw.CO.sub.2 +HSO.sub.4.sup.- 
+SO.sub.4.sup.-- 
EQU S.sub.2 O.sub.8.sup.-- +2Cr(III).fwdarw.2Cr(VI)+2SO.sub.4.sup.-- 
EQU 3C.sub.6 H.sub.5 OH+28KMnO.sub.4 +5H.sub.2 O.fwdarw.18CO.sub.2 
+28KOH+28MnO.sub.2 
EQU 2MnO.sub.4.sup.- +3Mn.sup.++ +2H.sub.2 O.fwdarw.5MnO.sub.2 +4H.sup.+ 
EQU 8MnO.sub.4.sup.- +3S.sup.-- +4H.sub.2 O.fwdarw.5MnO.sub.2 +3SO.sub.4.sup.-- 
+8OH.sup.- 
An experiment which demonstrated the successful aqueous phase oxidation of 
VOCs using potassium permanganate is described in the following example: 
EXAMPLE 1 
Groundwater contaminated with 21.8 mg/L TCE and 18.1 mg/L cis-1,2-DCE was 
treated with 500 mg/L KMnO.sub.4 solution at an initial pH of 6.95 in a 
zero head space batch reactor. The concentration of TCE decreased from 
21.8 mg/L to 0.01 mg/L in 132 minutes and the concentration of cis-1,2-DCE 
decreased from 18.1 mg/L to 0.032 mg/L in 26 minutes. The amount of 
chloride generated as a result of oxidation of TCE and cis-1,2-DCE was 39 
mg/L indicating a complete oxidation of these volatile organic compounds. 
An experiment which successfully demonstrated in situ oxidation of VOCs in 
contaminated soil using potassium permanganate is described in the 
following example: 
EXAMPLE 2 
A soil core taken from a site contaminated with 103.7 mg TCE/kg of soil and 
29.7 mg cis-1,2-DCE/kg of soil was subjected to oxidation using a 
continuous flow, at 0.3 mL/min, of a 510 mg/L KMnO.sub.4 solution. The 
column was run for 55 h, representing 32.46 pore volumes. After 1.77 pore 
volumes had passed through the column, cis-1,2-DCE was no longer 
detectable in the column effluent; after 11.80 pore volumes, TCE was no 
longer detectable. Elevated Cl.sup.- concentrations were observed in the 
effluent of the column confirming oxidation of the cis-1,2-DCE and TCE. 
An experiment which successfully demonstrated that the soil oxidant demand 
for KMnO.sub.4 is considerably lower with soil sequentially treated with 
Na.sub.2 S.sub.2 O.sub.8 and KMnO.sub.4 than soil treated with KMnO.sub.4 
alone is described in the following example: 
EXAMPLE 3 
An experiment was conducted in which an oxidant solution was passed through 
two different stainless steel columns (43 mm dia.times.76 mm long) 
containing uncontaminated, undisturbed soil from a site. In both the 
cases, the flow rate of oxidant solution was maintained at 0.3 mL/min. In 
the column A, a solution of 503 mg/L KMnO.sub.4 was passed upward through 
the column for a sufficient length of time so that no further change in 
concentration of KMnO.sub.4 was observed in the effluent. The amount of 
KMnO.sub.4 consumed (or, soil oxidant demand for KMnO.sub.4) was 2.71 g 
KMnO.sub.4 /kg soil. In the column B, a solution of 961 mg/L Na.sub.2 
S.sub.2 O.sub.8 was passed upward through the column for a sufficient 
length of time so that no further change in concentration of Na.sub.2 
S.sub.2 O.sub.8 was observed in the effluent. The amount of Na.sub.2 
S.sub.2 O.sub.8 consumed (or, soil oxidant demand for Na.sub.2 S.sub.2 
O.sub.8) was 0.26 g Na.sub.2 S.sub.2 O.sub.8 /kg soil. After the passage 
of Na.sub.2 S.sub.2 O.sub.8 solution in Column B, a solution containing 
503 mg/L KMnO.sub.4 was passed for a sufficient length of time so that no 
further change in concentration of KMnO.sub.4 was observed in the 
effluent. This time, the amount of KMnO.sub.4 consumed (or, soil oxidant 
demand for KMnO.sub.4) was 0.72 g KMnO.sub.4 /kg soil. Moreover, a much 
faster breakthrough of KMnO.sub.4 was observed in column B (treated with 
the sequenced oxidation by Na.sub.2 S.sub.2 O.sub.8, and then with 
KMnO.sub.4) than in Column A where the soil was treated with KMnO.sub.4 
alone. 
The present invention may also be practiced by simultaneously injecting the 
permanganate and the persulfate into the soil or even by first injecting 
the permanganate and thereafter injecting the persulfate, in view of the 
fact that the permanganate reaction front is much more retarded than is 
the persulfate. If injected together, the permanganate will be used up 
rather quickly near the point of introduction or injection; and the 
persulfate front will expand more rapidly than the permanganate due to its 
slower reaction rate. After injection of the persulfate, the permanganate 
reaction front will then travel through the soil. 
Typically, the oxidation of VOCs is a solubility-limited reaction. The 
destruction of VOCs occurs in aqueous phase solution. If the oxidant is 
present in sufficient quantity, it will oxidize the VOCs leading to the 
depletion of its concentration in the aqueous phase. This will, in turn, 
lead to dissolution of the pure phase VOCs into the water (since the VOCs 
are at least partially soluble). Dissolution is driven by solubility and 
the concentration gradient. Once the VOCs in the aqueous phase is 
oxidized, its concentration drops leading to an increased concentration 
gradient that promotes dissolution of pure phase VOCs into aqueous phase 
and the process continues until all the VOCs are destroyed. 
For simultaneous injection the chemicals, being compatible with each other, 
may be mixed together in the same vessel prior to injection. The amounts 
mixed together are not critical, except it is preferred that enough 
persulfate is present to satisfy substantially all the soil oxidant demand 
and enough permanganate is present to destroy the VOCs to acceptable 
levels, or as close thereto as possible. More specifically, if potassium 
permanganate is used, the amount of persulfate used should be sufficient 
to oxidize most of and preferably substantially all the organic and 
inorganic soil constituents that are reactive with potassium permanganate 
in order to minimize the amount of potassium permanganate needed, thereby 
keeping both the generation of MnO.sub.2 and cost to a minimum. 
Depending upon the type of soil, target VOCs, and other oxidant demand by 
the site, the concentrations of persulfates likely to be used in the 
present invention may vary from 250 mg/L to 200,000 mg/L, and, that of 
permanganate may vary from 250 mg/L to 100,000 mg/L. The preferred 
concentrations are a function of the soil characteristics, including the 
site-specific oxidant demands. Hydrogeologic conditions govern the rate of 
movement of the chemicals through the soil, and those conditions must be 
considered together with the soil chemistry to understand how best to 
perform the injection. The techniques for making these determinations and 
performing the injections are well known in the art. For example, wells 
could be drilled at various locations in and around the suspected 
contaminated site to determine, as closely as possible, where the 
contamination is located. Core samples would be withdrawn, being careful 
to protect the samples from atmospheric oxidation. The samples would be 
used to determine soil oxidant demand and chemical (i.e. VOC) oxidant 
demand existing in the subsurface. The precise chemical compounds in the 
soil and their concentration would also be determined. Contaminated 
groundwater would be collected. Oxidants would be added to the collected 
groundwater during laboratory treatability experiments to determine which 
compounds are destroyed in the groundwater. It would then be determined 
whether the same oxidants are able to destroy those chemicals in the soil 
environment. 
One method for calculating the preferred amounts of persulfate and 
permanganate to be used per unit soil mass (for an identified volume of 
soil at the site) is to first determine the minimum amount of persulfate 
needed to fully satisfy soil oxidant demand per unit mass of 
uncontaminated soil. A contaminated soil sample from the identified volume 
of soil is then treated with that predetermined (per unit mass) amount of 
persulfate; and the minimum amount of permanganate required to eliminate 
the VOCs in that treated sample is then determined. The amount of the 
permanganate required is a function of the mass of target chemical and its 
distribution in the subsurface, as well as any unreacted soil oxidant 
demand. More specifically, it is desired to have sufficient permanganate 
to fully oxidize all the target compound(s). Permanganate is consumed 
during the oxidation process. Chemical reaction stoichiometry governs the 
mass/mass ratios and thus the total amount required to achieve the desired 
result. It is assumed that the persulfate will react and destroy most of 
the soil oxidant demand, but there will likely be some low permeability 
regions in the soil which will have unsatisfied oxidant demand, so excess 
permanganate would normally be applied to account for this "unreacted" 
soil oxidant demand. In actuality the amounts of persulfate and 
permanganate injected into various locations at a single contaminated site 
will vary depending upon what is learned from the core samples and other 
techniques for mapping what is believed to be the subsurface conditions. 
The goal is for the concentration of persulfate in the injected persulfate 
solution to be just enough to result in the persulfate reaction front 
traveling at the same velocity as the groundwater in the saturated zone, 
or as close as possible thereto. (The saturated soil zone is the zone of 
soil which lies below the water table and is fully saturated. This is the 
region in which groundwater exists and flows.) In certain saturated zones 
where the natural velocity of the groundwater is too slow for the purposes 
treatment within a certain timeframe, the velocity of groundwater can be 
increased by increasing the flow rate of the injected persulfate solution 
or installation of groundwater extraction wells to direct the flow of the 
injected persulfate solution. Certain soils to be treated may be in 
unsaturated zones and the method of persulfate injection may be based on 
infiltration or trickling of the persulfate solution into the subsurface 
to provide sufficient contact of the soils with the injected chemicals. 
Certain soils and conditions will require large amounts of persulfate to 
destroy soil oxidant demand, while other soils and conditions might not. 
For example, sandy soils having large grain size might have very little 
surface area, very little oxidizable compounds and therefore very little 
soil oxidant demand. On the other hand, silty or clayey soils, which are 
very fine grained, would have large surface area per unit volume. They are 
likely to also contain larger amounts of oxidizable compounds and thus 
have a high soil oxidant demand. 
Another exemplary form of the invention is useful for destroying relatively 
low level, but unacceptable, concentrations of VOCs in groundwater. This 
involves the use of permanganate alone to be reduced, either naturally by 
the soil or by other means, to form manganese dioxide that can 
subsequently form a barrier type interception zone in the soil (e.g., a 
reactive permeable wall) for the destruction of VOCs present in the 
groundwater passing through the zone. MnO.sub.2 is formed in situ by 
injecting permanganate into the soil. Permanganate is reduced to MnO.sub.2 
by reduced inorganic and organic species (both naturally occurring and 
those as a result of human activities) present in the soil. The VOCs 
readily attach themselves to the MnO.sub.2 by adsorption. Simultaneous 
reduction of the manganese and oxidation of the VOC (redox) then takes 
place, thereby destroying the VOC. More specifically, the MnO.sub.2 
precipitates, under certain conditions, oxidize certain organic compounds 
such as aniline and primary aromatic amines; hydroquinone; various organic 
acids; and, substituted phenols and chlorophenols. Oxidation reactions 
with MnO.sub.2 and chlorinated solvents are possible as well. 
These reactions of MnO.sub.2 and organic compounds can be engineered into 
oxidation-based in situ remediation systems. Reactive, permeable 
subsurface trenches, treated with permanganate, may be "built" at 
appropriate locations; or a series of injection wells where MnO.sub.2 is 
formed by permanganate injections could provide protection from off-site 
migration of aqueous phase pollutants. In both systems, a reactive barrier 
zone is created of sufficient length to remove, by oxidation, relatively 
low but unacceptable concentrations of VOCs in groundwater passing 
therethrough. Barrier zones of this nature are expected to be particularly 
effective at the downstream end of a plume of groundwater extending from a 
treated contaminated soil site, wherein the concentrations of VOCs in the 
plume are low. By "low concentration" it is meant a concentration low 
enough such that an injection of oxidant into the plume of VOC 
contaminated soil and groundwater will not be immediately consumed, and 
the amount of MnO.sub.2 precipitate created does not prevent water flow 
through the zone. (It is believed such low concentrations will need to be 
on the order of from five parts per billion to ten parts per million.) 
This will permit the oxidant to continuously (or at least for a long 
period of time) intercept and destroy VOCs in the contaminated water as it 
moves through the zones. More specifically, after the MnO.sub.2 zone is 
established resulting from the injection of KMnO.sub.4, the formed 
MnO.sub.2 will react with the VOCs passing through this zone. As the VOCs 
are oxidized the MnO.sub.2 will be reduced. Once the MnO.sub.2 is 
sufficiently depleted from the soil, KMnO.sub.4 can be reinjected into the 
soil to replenish the MnO.sub.2 treatment zone. This process can be 
repeated on a periodic or event driven basis. During the KMnO.sub.4 
injection, the KMnO.sub.4 acts as the oxidizing agent; and when the 
MnO.sub.2 zone is established the MnO.sub.2 acts as the oxidizing agent. 
High concentrations of VOCs cannot be treated in this manner because the 
oxidant would be consumed too quickly in the process of destroying the 
target chemical, requiring continual frequent replacement. On the other 
hand, occasional replacement after reasonable periods of time may be 
acceptable. 
In another embodiment of the present invention a persulfate alone (i.e., 
without the permanganate), such as, but not limited to, sodium persulfate, 
may be used to oxidize VOCs where the contaminated soil contains divalent 
metal cations and has reducing conditions. The reducing conditions must 
result in the divalent metal cations in the soil remaining in solution in 
the ground water passing through the soil for a sufficient length of time 
to catalyze persulfate decomposition. If the temperature of the soil is 
sufficiently high (from about 40.degree. C. to 99.degree. C.), or if the 
soil is heated to within that range, the persulfate will catalytically 
decompose to form sulfate free radicals; the free radicals will then 
oxidize the target VOCs. If there are insufficient divalent metal cations 
occurring naturally in the soil, they may be introduced into the soil. For 
example, ferrous sulfate may be injected into the soil to add iron cations 
(Fe.sup.++). During this process the persulfate may also be used to 
destroy (i.e. satisfy) some of the soil oxidant demand, as well as oxidize 
VOCs. Permanganate may also be added, along with or sequentially with the 
persulfate. The permanganate and the sulfate radicals would both act to 
oxidize volatile organic compounds in the soil. The amount of each 
ingredient would be selected based upon conditions, with the goal that 
between the permanganate and the sulfate radicals, substantially all the 
volatile organic compounds would be oxidized. This procedure is suitable 
for either in situ or ex situ soil treatment. 
Although the invention has been shown and described with respect to 
detailed embodiments thereof, it will be understood by those skilled in 
the art that various changes in form and detail thereof may be made 
without departing form the spirit and scope of the claimed invention.