The remediation of certain organic substances such as chlorinated solvents (trichloroethene and tetrachloroethene), and gasoline-related compounds (benzene, toluene, ethylbenzene, MTBE, and xylenes) by ISCO is effective.
[2] A wide range of ground water contaminants respond well to ISCO, so it is a popular method to use.
[3] Fenton's reagent (hydrogen peroxide catalyzed with iron) and potassium permanganate are the oxidants that have been used the longest and remain used widely.
Hydrogen peroxide was first used in 1985 to treat a formaldehyde spill at Monsanto's Indian Orchard Plant in Springfield, Massachusetts.
The specificity of permanganate (chlorinated solvents require double bonds) and consumption by non-target organic material in soil are examples of these limitations.
Persulfate is more stable, treats a wider range of contaminants, and is not consumed by soil organics as easily.
[5] Potassium permanganate is a crystalline solid that is typically dissolved in water before application to the contaminated site.
[5] Unfortunately, several studies have shown that this byproduct seems to cement sand particles together forming rock-like material that has very low permeability.
When the peroxide is catalyzed by soluble iron it forms hydroxyl radicals(·OH) that oxidize contaminants such as chlorinated solvents, fuel oils, and BTEX.
When applied to In Situ Chemical Oxidation, the collective reaction results in the degradation of contaminants in the presence of Fe2+ as a catalyst.
The overall end result of the process can be described by the following reaction: Advantages of this method include that the hydroxyl radicals are very strong oxidants and react very rapidly with contaminants and impurities in the ground water.
[5] Traditional Fenton's reagent applications can be very exothermic when significant iron, manganese or contaminant (i.e. NAPL concentrations) are present in an injection zone.
However, NAPL contaminant concentrations can still result in rapid oxidation reactions with an associated temperature increase and more potential for surfacing even with reagent stabilization.
The hydroxyl radicals can be scavenged by carbonate, bicarbonate, and naturally occurring organic matter in addition to the targeted contaminant, so it important to evaluate a site's soil matrix and apply additional reagent when these soil components are present in significant abundance.
More specifically, sodium persulfate is used because it has the highest water solubility and its reaction with contaminants leaves least harmful side products.
Various agents, such as heat, ultraviolet light, high pH, hydrogen peroxide, and transition metals, are used to activate persulfate ions and generate sulfate radicals.
Conversely, the sulfate radical does not react as much in compounds that contain electron attracting groups like nitro (-NO2) and carbonyl (C=O) and also in the presence of substances containing chlorine atoms.
Because the bubbles travel more vertically than horizontally, close placement of ozone injection wells is needed for uniform distribution.
Again, it is not very soluble and stays in gas form in the water, which makes ozone prone to nonuniform distribution and rising up to the top of contamination site by the shortest routes rather than traveling through the entire material.
Injection wells for ozone are typically constructed of a 1–2" stainless-steel screen set in sand pack, grouted to the surface using a combination of cement and bentonite clay.
In order to optimize the amount of contaminant that is oxidized, the probes are set into the ground relatively close together, about .6-1.2 meters apart.
[6] Horizontal well networks are basically the use of long pipes that lead in and out of the contaminated aquifer or plume used to inject oxidants and extract the treated ground water.
Another version of this delivery system is the use of a disconnected series of vertical wells to inject the oxidant into the ground water.
In January 2007, the groundwater around the Naval Air Station North Island in San Diego County, California was treated.
Activities in the Complex included parts cleaning and engine flushing, which left two chlorinated volatile organic compound (CVOCs) source areas.
In order to stop the spread of the contaminated groundwater, an elaborate system of 11 extraction wells has been placed to contain the plumes.
The results of the oxidation was a temporary contaminant decrease in the wells by 70–80%, but permanganate was not evenly distributed through the curtain.
Fenton's reagent in particular is highly exothermic and can cause unwanted effects on microbial life in the aquifer if it is not used carefully or stabilized.
Recent evidence suggests that the oxidation of benzene results in the formation of phenol (a relatively benign compound) and a novel aldehyde side-product, the toxicology of which is unknown.
To overcome this limitation at sites which have substantial soil contamination, and/or non-aqueous phase liquid (NAPL), surfactants can be injected simultaneously with oxidants.