Remediation

Remediation Approaches: In-Situ Chemical Oxidation (ISCO)

In‑situ chemical oxidation (ISCO) is an environmental remediation technique used to treat contaminated soil and groundwater directly in place, without the need for excavation. ISCO has become a widely used alternative to conventional soil and groundwater remediation methods such as soil vapor extraction, air sparging, bioremediation, dig-and-dump, and pump-and-treat.

Beyond technical feasibility, however, ISCO is typically evaluated in the context of a client’s broader objectives, including cleanup timelines, redevelopment plans, regulatory closure milestones, and budget constraints.

While highly effective for many contaminants, ISCO is not suitable for every site. In this article we examine how to determine when ISCO is a good fit, how to select an appropriate oxidant, and how ISCO is typically evaluated and implemented to align remedial performance with project goals.

When Is ISCO a Good Choice for a Site?

Determining whether in‑situ chemical oxidation is the right solution begins with a comprehensive screening process that evaluates site conditions, contaminants, and feasibility in achieving the client’s overall goals.

Key Screening Considerations Include:

Contaminants of concern
Geologic setting and deliverability
Site constraints (access, utilities, receptors, land use)
Regulatory requirements

These factors determine whether ISCO can be safely applied, whether oxidants can reach the target zone, and which oxidant is most appropriate.

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The ISCO Evaluation Process

ISCO implementation follows a step-wise approach to confirm technical feasibility and effective delivery.

1. Screening for ISCO Compatibility

This first stage determines whether chemical oxidation matches:

Site Specifics

The site setting and context affect the decision to use in-situ chemical oxidation. Significant factors include current and future receptors, land use, adjacent properties, water bodies, accessibility, liability, value, utility and site constraints, and site construction.

Geology

Site geology determines how easily and by what mechanism in-situ chemical oxidation can be applied. The key geological parameters considered are:

Lithology
Hydrogeology
Location of contaminant
Depth to water
Heterogeneity
Depth to contamination

Applicable Regulations

Regulatory context often determines the required level of cleanup. It also specifies permit requirements for the application of in situ oxidants. In many instances, remediation such as ISCO should be paired with a Risk Assessment to achieve cleanup levels in the most cost-efficient manner.

Contaminant Compatibility

Various contaminant characteristics contribute to the selection of the most appropriate oxidant system.
These characteristics include:

Contaminant type(s)
Mass
Phase distribution (i.e., dissolved, adsorbed, Nonaqueous Phase Liquids (NAPLs))
The contaminant’s physical, chemical, and toxicological properties

The interaction between a contaminant and potential oxidant can be evaluated using a treatability table which rates the potential applicability of each of the four oxidants to a range of compounds. In many cases, the contaminant will respond to several different oxidants. Therefore, the choice of a particular oxidation system must consider a number of factors including reaction time, achievable cleanup levels, cost, ease of application, and regulatory acceptance.

Selecting the Right Oxidant

Any of these four common oxidants commonly used for ISCO can be integrated with other remedies and used for pretreatment, primary treatment, or polishing.

Oxidant	Suitability
Permanganate (MnO₄⁻)	Well-suited for chlorinated ethenes (PCE, TCE, DCE and vinyl chloride) Offers residual oxidation potential because it decomposes slowly Can also oxidize some smaller PAHs, PHCs, and phenolic compounds Less effective for BTEX compounds, which are often comingled with PHC contamination
Fenton’s Reagent (Hydrogen Peroxide and Ferrous Iron mixture)	Effective for most hydrocarbons, including PHCs, PAHs, BTEX and chlorinated ethenes Highly reactive but decomposes rapidly, reducing persistence Safety concerns typically relegate Fenton’s Reagent to niche applications
Persulfate (Na₂S₂O₈)	Best for recalcitrant organics and mixed contaminant sources, including chlorinated ethanes (e.g., DCA, TCA), PAHs, PHCs, BTEX, PAHs, and oxygenates More persistent form of oxidant, which can last for several years Residual sulfate formed by reactions can trigger secondary remediation by stimulating bacterial growth
Ozone (O₃)	Regulatory info Effective for recalcitrant compounds such as PAHs, pesticides, phenolics, plasticizers, and PCBs Also applicable for VOCs Typically requires injection in the gaseous form

2. Bench Scale (Laboratory) Testing

Design of a chemical oxidation program is dependent on many properties unique to each site’s soil and groundwater characteristics. To help select the best chemical oxidation system, it is important to first test the reactivity of the different oxidants with the soil and groundwater from the site. This can be done by testing small batches of site soil and groundwater directly with the oxidants or by sampling for soil and groundwater properties, such as natural oxidant demand.

Bench testing is used to verify that the oxidant will:

React effectively with site contaminants
Consume oxidant at manageable rates
Achieve reductions within a reasonable timeframe

Bench testing also helps:

Estimate oxidant dosage
Identify potential hazards
Support design and permitting

3. Pilot Testing

When it is known or demonstrated through bench testing that a particular contaminant can be effectively oxidized, the focus of the design becomes the delivery of the oxidant into the contaminated soil or groundwater, which is a key factor in field success. AEL typically recommends carrying out a pilot test, where ISCO is applied to a small portion of the contaminated area using the delivery method most anticipated to be successful, based on understanding of the site geology. Distribution and remedial effectiveness are monitored during and after the pilot test. Following the pilot test, information learned can be applied to full-scale ISCO remediation to minimize any unexpected surprises once full-scale operations begin.

Pilot tests determine:

Whether oxidants can be distributed effectively
Required injection or soil mixing approaches
Appropriate oxidant volumes and dosage concentrations
Injection delivery rates

Summary

ISCO is a powerful remediation tool when chemistry, geology, site conditions and client objectives align. Selecting the correct oxidant and confirming both reactivity (bench‑scale testing) and deliverability (pilot testing) are essential for meeting regulatory, budgetary, and schedule goals. When properly applied, ISCO can significantly enhance cleanup efficiency, whether used as a standalone technology, as part of a treatment train, or integrated into a Risk Assessment.

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Our team specializes in developing clear, cost-effective solutions tailored to your property and overall goals. We can assess your site, design an appropriate Remedial Action Plan (RAP), and help you move forward with confidence.

Find out whether ISCO is a suitable or even ideal solution for your site and discuss your options with an expert.

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