Creosote & Coal Tar Remediation
What Are Creosote and Coal Tar, and Why Are They a Problem?
Coal tar is a dense, viscous byproduct of coal gasification at manufactured gas plant (MGP) sites and coke production at steel plants. It includes lighter oils, coal tar creosote fractions, and heavier residues such as coal tar pitch. Coal tar has historically been used in roofing, pavement sealants, and as feedstock for chemicals.
Creosote or coal tar creosote is a complex distillate of coal tar. It is primarily used as a wood preservative (e.g., railroad ties, utility poles, marine pilings). Chemically, it is not a single compound but a mixture of hundreds to thousands of volatile and semi-volatile organic constituents, dominated by polycyclic aromatic hydrocarbons (PAHs). Their hydrophobic nature, multicomponent composition, persistence, and tendency to form dense non-aqueous phase liquids (DNAPLs) make them particularly challenging to remediate.
Once released into the environment, creosote and coal tar bind tightly to soil and organic matter, migrate downward in complex non-uniform distributions following small-scale heterogeneities, and pool on top of low-permeability zones or in bedrock fractures. In addition, the releases are often very large resulting in significant contaminant volumes and masses present in the subsurface. As such, they present long-term sources of contaminants and risks to groundwater, vapor intrusion pathways, and human health.
Common Sites with Creosote and Coal Tar Contamination
- Former MGP sites
- Wood-treating and timber preservation operations such as railroad tie and utility pole treatment yards
- Steel manufacturing and coking operations
Why Thermal Remediation Works for Creosote and Coal Tar
Typical in situ remedial methods such as injection based amendments or multi-phase extraction at ambient temperatures cannot overcome the limitations of delivering enough chemicals to sufficiently oxidize the large mass present or recover sufficient mass to achieve typical site remedial goals for the protection of groundwater and surface water resources or elimination of VI risks.
TerraTherm’s thermal technologies apply intense, controlled heat to mobilize, extract, and partially degrade creosote and coal tar at the source, dramatically reducing remediation timelines and residual risk. Our thermal remediation approaches for creosote and coal tar sites offer three levels of treatment (sometimes performed sequentially) to address the mass required to meet specific remedial goals:
- Controlled gentle heating to 80 to 90°C to reduce viscosity for enhanced product recovery,
- Heating to 100°C and boil-off of 30 to 50% of the pore volume for removal of the volatile fraction (e.g., BTEX), and lighter semi-volatile components such as naphthalenes, and
- Heating to 300 to 350°C to remove PAHs and petroleum hydrocarbon mass (e.g.,TPH).
For example, if the remedial goal for a site is focused on product removal, then gentle heating up to 80 to 90°C is often the selected approach. While the site is heating from ambient temperature up to 80 to 90°C, multi-phase extraction is employed to recover as much creosote/ coal tar non-aqueous phase liquid (NAPL) as possible. Heating to these temperatures can significantly reduce the viscosity of the NAPL, making it more pumpable. However, if the site is heated too quickly, and the volatile fraction is boiled off, the NAPL may transition to a high-viscosity DNAPL that cannot be pumped and recovered effectively, thereby prematurely ending product recovery.
Once product recovery has diminished at 80 to 90°C, the system can be shut down if product recovery is the remedial goal or the site can be heated to 100°C and held there for a period of time necessary to remove the volatile and lighter semi-volatile contaminants. The period a site is held at 100°C depends on the contaminants targeted and the remedial goals. For example, if removal of the volatile contaminants (BTEX) is the goal, then heating a site to 100°C and holding it there until 25 to 30% of the pore water volume is boiled off is usually sufficient to achieve diminishing returns.
However, if the remedial goals also include achieving low concentrations of naphthalenes in soil and groundwater, then a site may need to be heated and held at 100°C until 50% or more of the pore water volume is removed (more steam is formed and removed from the soil pores resulting in effective removal of the targeted lighter semi-volatile contaminants).
One other benefit of heating to 100°C is that the removal of the volatile and lighter semi-volatile contaminants typically results in the thermal-chemical weathering of the NAPL to an inert asphaltic material that does not leach PAHs to groundwater or result in VI issues for BTEX. This can be an effective way to target removal of the potentially mobile contaminants (BTEX and naphthalene), while eliminating the ongoing mass flux of PAHs to groundwater.
If the remedial goals are to substantially reduce PAH and TPH concentrations, then the site will continue to be heated until all the pore water is boiled off and soil temperatures of 300 to 350°C are achieved. These temperatures are sufficient to desorb and volatize PAHs and petroleum hydrocarbons making them recoverable in the vapor phase. Some subsurface destruction is also possible at these temperatures through oxidation and pyrolysis.
If a site is heated to 300 to 350°C, then all three approaches and goals can be achieved: NAPL recovery, removal of VOCs and lighter semi-volatile contaminants (e.g., BTEX and naphthalenes), and removal of PAHs and TPH, resulting in the highest and most complete contaminant mass removal.
For all of these approaches, a vapor extraction system, typically together with a vapor cap, is used to capture and remove steam and contaminant vapors produced during heating to ensure pneumatic control is maintained.
For the high temperature 300 to 350°C approach, surface water and groundwater influx must be controlled and eliminated if performed in situ. If this is not practical, then impacted soil or sediment can be placed in an ex situ engineered treatment pile and treated using our In Pile Thermal Desorption (IPTD®) technology.
Our Thermal Solutions
Electrical Resistance Heating (ERH)
Ideal for moist, heterogeneous soils (e.g., silty, clayey sands and clays), ERH can be used to heat subsurface areas to approximately 100°C, reducing the viscosity of NAPLs and volatilizing VOCs like BTEX and lighter molecular weight naphthalenes. As ERH relies on the flow of current between electrodes placed in and around the target treatment zone to heat the soil and groundwater, ERH requires sufficient soil moisture and electrical conductivity. For example, performance may be reduced in dry formations unless moisture can be practically and effectively maintained through water addition at the electrodes. In some resistive formations (e.g., fractured granite and dry sand), adding water to the formation to maintain power input is not effective. Soil resistivity should also be incorporated into the design to ensure uniform heating, as the electrical resistivity encountered in common geologies can vary by a factor of 200.
For Level 1 and Level 2 treatment of creosote and coal tar sites (NAPL recovery and thermal-chemical stabilization, respectively), a combination of multiphase and vapor extraction wells, are required to remove the creosote and coal tar and maintain pneumatic and hydraulic control during treatment.
ERH can be used to heat the target zone to specific temperatures between ambient and 100°C, for various treatment options ranging from enhanced bio (35 to 40°C), enhanced NAPL recovery (70 to 100°C), and volatilization and recovery of VOCs and lighter molecular weight SVOCs.
Thermal Conduction Heating (TCH)
Effective in all soil types, regardless of moisture content (wet and dry, above and below the water table) and especially effective in fractured rock. TCH relies on thermal conduction of energy from a heater into the surrounding soil or rock. TCH provides highly uniform and predictable heating because the thermal conductivity of most sites only varies by a factor of 2 to 3.
TCH can be used to uniformly heat soil and rock to the full range of treatment temperatures required for the various creosote and coal tar treatment approaches: 70 to 100°C for Level 1 – NAPL removal, 100°C for Level 2 – Volatilization of BTEX and naphthalenes, and 300°C or greater for Level 3 – removal and destruction of PAHs and TPH. TCH can also be used to heat to 35 to 40°C for thermally enhanced biodegradation, Importantly, at some sites with low permeability soils (e.g., silts and clays), the soil immediately surrounding the heaters (e.g., 6 inches) will dry out, which can provide beneficial pathways for volatilized COCs to migrate from deeper soils to the vadose zone where they can be effectively captured and removed for treatment.
For all treatment approaches, vapor and/or multiphase extraction wells are required to maintain pneumatic control and recover mobile NAPL during treatment.
Steam Enhanced Extraction (SEE)
SEE injects steam into the subsurface to heat treatment zones to 100°C. Generally, SEE is best suited for lithologies with an effective hydraulic conductivity of 1 x 10-3 cm/s or higher (e.g., sand and/or gravel formations). It is used for creosote and coal tar sites where Level 1 and Level 2 treatment are the objectives (NAPL recovery and volatilization and removal of BTEX and naphthalenes).
When properly designed, SEE can inject high rates of energy and quickly and uniformly heat and treat creosote and coal tar sites. If site conditions are amenable and subsurface permeabilities high enough, SEE is often the most cost-effective way of heating and treating creosote and coal tar source zones due to the wide spacings that can be used between the steam injection wells, the high energy input rates, and typically low cost of the fuel for producing the steam paired with local availability of boilers.
Because the steam is injected under pressure and can condense as water, an aggressive network of multiphase extraction wells is required to extract both vapors and liquids (water and NAPL) to maintain pneumatic and hydraulic control during treatment.
SEE can be combined with ERH or TCH to treat sites with both low and high permeability zones that have low and high groundwater flux. SEE is often paired with ERH or TCH when groundwater flux within a portion of the target treatment zone exceeds 1 ft/day.
In-Pile Thermal Desorption (IPTD®)
IPTD uses TCH to provide ex-situ thermal remediation of soil and sediment that can treat any organic contaminant, streamline material handling, and eliminate the need for off-site disposal of contaminated soils and sediment.
IPTD is highly flexible and easily customizable to optimize treatment of any soil volume, large or small. It involves placing contaminated soil and/or sediment within an engineered above-ground, fully covered and insulated treatment pile structure, and then heating the soil to the required temperature to destroy and/or remove the contaminants over periods of several weeks to several months. The design temperature and treatment period depend on the contaminants and remedial goals. For treatment of soil contaminated with creosote and coal tar associated with former MGP sites and wood treating sites, containing SVOCs such as PAHs and heavy molecular weight TPHs, treatment temperatures between 300°C and 350°C are typically required.
IPTD is a good fit for shallow soil contamination, excavated soil, or IDW when off-site disposal is not an option. On-site IPTD can be a cost-effective option for the total treatment of contaminants like PFAS, PCBs, dioxins, and PAHs, which eliminates the long-term liability of disposal of the soil in a landfill. Importantly, stringent soil standards can be achieved even for recalcitrant contaminants like PFAS, PCBs, dioxins, and PAHs.
IPTD has been used to treat soil volumes as low as 50 cy and up to 70,000 cy. The size of the pile depends on the volume of material to be treated, space available, electrical power available, and desired schedule.
How Does Thermal Compare to Other Methods?
Choosing the Right Solution
Every site requires a tailored approach. TerraTherm evaluates:
- COCs and co-contaminants
- Presence and distribution of DNAPL/LNAPL
- Soil type and permeability
- Source zone depth and distribution
- Redevelopment goals and cleanup criteria
TCH is ideal for deep, tight, or fractured bedrock zones and can heat treatment zones to temperatures required to treat the full range of organic contaminants (VOCs, CVOCs, SVOCs, PCBs, PAHs, PFAS, TPH, etc.)
ERH is ideal for moist, electrically conductive soil and for thin shallower contamination involving volatile contaminants such as VOCs, CVOCs, and lighter SVOCs.
SEE is ideal for permeable formations and for treating volatile contaminants such as BTEX, CVOCs, and lighter SVOCs, and/or mobilization and removal of NAPL.
IPTD is optimal where high temperature treatment of high-boiling point, recalcitrant contaminants such as SVOCs, PCBs, PAHs, PFAS, TPH is required.
Regulatory Trends and Standards
- USEPA SW846 Method 8270E is commonly used to quantify SVOCs and PAHs in environmental media.
- Cleanup standards are set by state and federal regulatory bodies and vary based on risk-based thresholds.
- State programs like NYSDEC and MassDEP continue to enforce stringent cleanup requirements for MGP-related contamination.
- Brownfield and redevelopment programs increasingly prioritize permanent, in-place treatment methods.
Thermal technologies help site owners meet aggressive cleanup goals while minimizing long-term operations and maintenance requirements.
Ready to Address Creosote or Coal Tar at Your Site?
TerraTherm has successfully remediated some of the most challenging creosote and coal tar source zones in North America. Our thermal solutions are engineered for precision, performance, and permanent results.
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