CVOC Remediation

In situ thermal remediation applies heat directly to the contaminated area and interval to accelerate the physical, chemical, and biological processes that remove or degrade CVOCs. Unlike conventional pump-and-treat or soil vapor extraction alone, thermal treatment can quickly address high concentration source zones with DNAPL and contaminant mass stored in low-permeability soil or fractured rock. The appropriate temperature and heating method depend on the contaminant, geology, hydrogeology, cleanup objective, and site-use constraints.

100°C Treatment: Volatilization and Co-Boiling

For CVOC DNAPL source zones, TerraTherm can heat the target treatment zone to the boiling point of water. Heating increases contaminant vapor pressure and mass-transfer rates, while generated steam helps strip and transport CVOCs toward extraction wells. Importantly, any DNAPL present will co-boil in the presence of water resulting in rapid phase transfer from an immobile state to a readily recoverable vapor phase that can be captured and removed. Recovered vapor, water, and any mobile NAPL are conveyed to aboveground equipment for separation and treatment. Some in situ transformation may occur, but recovery and aboveground treatment are the primary design basis for this approach.

Thermal treatment is most often applied to the source zone, where contaminant concentrations and mass are highest. Lower-concentration dissolved plumes outside the heated area may be better addressed through a treatment train that combines thermal source-zone treatment with technologies such as injection technologies, bioremediation, monitored natural attenuation, groundwater extraction, or another polishing remedy.

Required energy input and operating duration are site-specific. Key factors include cleanup goals, initial contaminant mass, soil moisture and organic carbon, CVOC properties, co-contaminants, groundwater flow, treatment depth, and heat losses. TerraTherm uses these inputs to select the optimal heating technology or technologies and establish the design temperature, energy density, extraction capacity, and endpoint strategy.

Moderate-Temperature Treatment: Thermally Enhanced Hydrolysis

Some chlorinated compounds can degrade much faster by hydrolysis as temperature increases. Where the contaminant mixture is demonstrably susceptible, controlled heating below the boiling point of water may support in situ destruction without the intensive vapor and liquid handling associated with boiling-based treatment. Potentially amenable compounds include 1,1,1-TCA and selected chlorinated methanes and ethanes, but site-specific kinetics, daughter products, and cleanup goals must be evaluated before selecting this approach.

After the treatment zone reaches its design temperature, substantially less power is generally required to maintain it than to complete the initial heat-up. Below-grade heater completions and a smaller aboveground footprint may also help preserve access in operating facilities, buildings, and transportation corridors. Vapor control, monitoring, and extraction requirements remain site-specific and are established through design and risk evaluation.

Low-Temperature Treatment: Thermally Enhanced Bioremediation

Gentle heating can increase reaction rates and improve amendment distribution and contaminant availability for enhanced bioremediation. TerraTherm can use low-profile, low-power heaters to warm the target interval uniformly while bioremediation amendments are delivered through nearby or shared installation locations. This integrated approach may shorten the treatment period and reduce contaminant mass flux from the source area.

The optimum temperature depends on the microbial community, amendment system, geochemistry, and target compounds. Temperature limits and performance criteria should therefore be established through site-specific biological testing and monitoring. Because the target temperature is well below boiling, the approach has significantly lower energy and infrastructure requirements than 100°C-temperature treatment; however, vapor control and other safeguards are still evaluated for each site.

Our Heating Solutions for CVOCs

Electrical Resistance Heating (ERH)

ERH passes alternating electrical current through moist soil and groundwater between subsurface electrodes. Electrical resistance of the soil and water to the current flow converts energy to heat within the treatment zone, allowing ERH to heat many heterogeneous formations with sufficient moisture to near the boiling point of water. ERH can also be operated at lower temperatures for thermally enhanced hydrolysis or bioremediation.

ERH performance depends on adequate moisture and electrical conductivity. Dry or highly resistive formations may limit power delivery, and although water addition at electrodes can mitigate electrode dry-out, it is not effective in every geology. A robust design therefore evaluates the range and spatial distribution of electrical resistivity, moisture conditions, groundwater flow, electrode layout, and the ability to maintain balanced power input.

For 100°C-based treatment, vapor extraction is used to maintain pneumatic control and recover volatilized contaminants. Depending on groundwater flow and the potential for mobile NAPL, multiphase extraction may also be used for hydraulic control and liquid recovery.

Thermal Conduction Heating (TCH)

TCH transfers heat from subsurface heaters into the surrounding soil or rock by thermal conduction. Because it does not rely on soil moisture or electrical current flowing through the formation, TCH can be applied in wet or dry soil, above or below the water table, and in fractured rock. The relatively narrow range of thermal conductivity encountered in most geologic materials supports uniform and predictable heating.

TCH can cover the full temperature range used for CVOC treatment, from low-temperature bioremediation enhancement to moderate-temperature hydrolysis and 100°C boiling and volatilization. In fine-grained soil, localized drying near heaters can increase vertical vapor permeability and help create pathways for recovered vapor to move up into the vadose zone and toward extraction wells.

For 100°C-based treatment, the system includes vapor extraction to maintain pneumatic control and capture contaminants. Multiphase extraction may be added where groundwater inflow or mobile NAPL requires hydraulic control and liquid recovery.

Steam Enhanced Extraction (SEE)

SEE injects steam into permeable saturated formations to deliver heat rapidly, mobilize NAPL, and strip or volatilize CVOCs. It is generally best suited to sand, gravel, permeable fill, or fractured rock with sufficient connected permeability to distribute steam. Where site conditions are favorable, wider well spacing and high energy-delivery rates can make SEE a cost-effective option for CVOC source zones.

Because steam is injected under pressure at temperatures above 100°C at the injection point, SEE is not typically used for controlled low-temperature hydrolysis or bioremediation enhancement. Condensed steam also adds water to the treatment zone, so a carefully designed extraction network is needed to recover vapor, groundwater, and NAPL and to maintain pneumatic and hydraulic control.

SEE can be combined with ERH or TCH at heterogeneous sites. Steam can efficiently heat higher-permeability intervals, while ERH or TCH addresses lower-permeability zones that steam may not contact effectively.

Conventional groundwater extraction and soil vapor extraction can control migration and remove readily accessible mass, but they may be slow where DNAPL is present or back-diffusing mass remains in fine-grained soil or fractured rock. In situ chemical and biological remedies can be effective for dissolved contamination, yet performance may be limited by non-uniform amendment delivery, contaminant availability, or unfavorable geochemistry in concentrated source zones.

Thermal remediation addresses these limitations by co-boiling DNAPL and increasing vapor pressure, diffusion, desorption, dissolution, and reaction rates within the source zone. This can remove or destroy a large fraction of the contaminant mass on an accelerated schedule and reduce the continuing load on downgradient groundwater and vapor remedies. Thermal is not automatically the best choice for every site. The strongest remedy often uses thermal treatment in high mass source zones where it adds the most value, followed by a lower-intensity technology for residual or downgradient contamination.

TerraTherm tailors each CVOC remedy to the site and the client’s cleanup objectives. Our evaluation considers:

• Geology, soil type, permeability, and fracture characteristics
• Groundwater conditions, including flow direction, velocity, and recharge
• Treatment depth, target-zone geometry, and access constraints
• Contaminant identity, concentration, distribution, mass, and presence of DNAPL
• Co-contaminants and soil organic carbon
• Electrical resistivity and moisture conditions
• Required cleanup levels, endpoint metrics, schedule, and regulatory requirements
• Existing buildings, utilities, ongoing operations, and surrounding land use
• Energy availability, extraction and treatment needs, and sustainability objectives

TCH and ERH are both strong options for many CVOC sites. Selection depends on factors such as electrical resistivity, moisture, treatment depth, site geology and heterogeneity, groundwater flow, and the need to heat competent or fractured bedrock. SEE can be advantageous in sufficiently permeable formations and can be combined with TCH or ERH where a site contains both high- and low-permeability intervals. TerraTherm’s design process matches the heat-delivery method, extraction system, and operating strategy to the conditions that control performance.

Ready to Address CVOCs at Your Site?

TerraTherm applies field-proven thermal technologies and data-driven design to complex chlorinated-solvent source zones. We work with site owners, consultants, and regulators to define a practical treatment boundary, select the right heating approach, manage vapor and groundwater during operations, and verify that cleanup objectives have been achieved.

 Explore Our SVOC & PAH Remediation Technologies:

• Electrical Resistance Heating (ERH)
  
  
• Steam Enhanced Extraction (SEE)
  
  
• Thermal Conduction Heating (TCH)