Why In Situ Thermal Remediation Should be Considered for Treatment of MGP Sites

Are you remediating a former Manufacturing Gas Plant (MGP) site and considering excavation, in situ soil mixing/stabilization, or in situ chemical oxidation (ISCO)?  Then you might also want to throw In Situ Thermal Remediation (ISTR) into the evaluation mix for the following reasons:

• ISTR does not require extensive heavy truck traffic on urban or local roads, thereby reducing the carbon footprint and improving the safety and noise impacts of the project.
• ISTR does not require digging up and handling of MGP impacted soils, which can result in generation of significant odors and exposures to COCs.
• Groundwater extraction and treatment is significantly reduced or eliminated with ISTR.
• The treatment volume is defined, and costs are known upfront, ensuring project budget expectations are met.
• ISTR is a well-known, safe, and proven technology capable of delivering predictable results; meaning that treatment will be completed on time, often in less than 12 months, thereby ensuring cost and schedule certainty which is often a primary consideration of redevelopment projects.
• Long term liability is eliminated as the impacted soil is treated on site and not placed in a landfill, which could present future legacy risks and liability.

So, if any of this sounds interesting to you, please read on.

Thermal Treatment Options

There are three ISTR technologies that can be used to treat MGP sites: electrical resistance heating (ERH), thermal conductive heating (TCH), and steam enhanced extraction (SEE). Choosing the right one depends on site geologic and hydrogeologic conditions, the nature of the MGP wastes being targeted, and the remedial goals. All three technologies can be used to heat the target treatment volume to ~100°C, which enhances and facilitates four key mass removal mechanisms:

• Reduces the viscosity of the NAPL and makes it more pumpable
• Increases the volatilization of volatile contaminants
• Stream strips higher boiling point compounds
• Causes the desorption of contaminants

Treating MGP sites to 100°C using these technologies, combined with aggressive multi-phase extraction of vapors and liquids (water and NAPLs), can be an effective solution for removing mobile LNAPL and DNAPL. It can also remove the volatile fraction from the remaining mass (e.g., BTEX and naphthalenes) and lock up the remaining mass in an immobile fraction that does not result in a risk to groundwater or indoor air.

Complicated Sites

Not all projects are that straightforward, though, and some may require a more tailored solution. For example, if the complete removal of TPH and achievement of stringent soil standards for contaminants like PAHs are required, TCH may be the best solution—as it can be used to heat the treatment zone to 300 to 350°C, effectively addressing the contaminants with a higher boiling point.

There are potential challenges with this approach, however, as it requires that the targeted treatment interval is above the water table or, if it is below the water table, that groundwater flux into the treatment zone can be controlled (e.g., pumping, sheet pile, or slurry wall). This is because achieving temperatures >>100°C requires boiling off all the water present in the target treatment zone first and to do this there cannot be ongoing groundwater flux into the treatment zone. This is certainly achievable but must be factored into the project planning and design.

Reduced Risks & Costs

Using ISTR solutions for MGP sites reduces risks for safety and exposure involved with excavation and transportation of soils, eliminates long-term liability, and has the potential to reduce costs. ISTR also shortens the treatment timeline, reducing costs associated with personnel or lost opportunity for site usage and is a good fit for redevelopment projects where schedule certainty and remedy performance is important.

A well-planned and successful remedy is reliant on an accurate conceptual site model (CSM) to thoroughly understand subsurface conditions and contaminant extent, identify the best technology for each treatment zone, and target each with the most appropriate and cost-effective remediation option. Contact us today to find out more about how ISTR can meet your MGP site remediation objectives. We would be happy to provide a free preliminary evaluation and design, including budgetary costs, for your site.

Also, if you would like to learn more or have questions about working on MGP sites, register for the webinar, What You Need to Know About Thermal Remediation for MGP Sites.