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Guidance for Wood Preservation Facilities Reporting to the NPRI

IV-F Creosote Wood Preservation Facilities



Creosote contains a large number of compounds, many of which are polycyclic aromatic hydrocarbons (PAHs). Creosote solutions contain a number of NPRI reportable substances including naphthalene, anthracene, biphenyl, and certain individual PAHs.

Process Description

(Figure 4.7)

Where high creosote retentions are required the full-cell or Bethel process is used. Creosote is heated to 70 to 90°C to reduce its viscosity and promote better penetration. Wood is loaded on trams and sealed in the pressure retort, and a vacuum is applied to remove air from the retort and accessible wood cells. The heated solution is drawn or pumped in and pressure is applied until the target retentions are achieved. After the impregnation stage, treated wood is subjected to an expansion bath before the preservative is drained and a final vacuum is applied in order to remove excess preservative from the surface. In some cases, the treated wood is subjected to a post-steaming treatment to improve the wood's surface cleanliness.

Where lower retentions are required, empty-cell processes can be performed, either by the Rueping or the Lowry process. These processes result in preservative coating the inner cell walls rather than saturating the cell voids. Empty-cell processes differ from the full-cell process in the initial impregnation stage. In the Rueping process, treating commences by applying air pressure of 200 to 500 kPa for a short time, so that the air inside the wood is compressed. Creosote is pumped under pressure into the treating retort and pressure is increased to about 1,040 kPa and held for sufficient time for the predetermined amount of solution to enter the wood. After pressure release, the compressed air in the wood expands pushing the excess preservative out, which is facilitated by a final vacuum.

In the Lowry process no air pressures are applied at the initial impregnation stage. The preservative is pumped into the retort at atmospheric pressure (no initial vacuum). When pressure is applied, the air in the wood is compressed as the preservative penetrates. When the pressure is released, the air inside the wood expands resulting in the "kick out" of treating solution, although to a lesser extent than the Reuping process. The application of an expansion bath, final vacuum and post-treatment steaming are also common with empty-cell treatments.

It is also possible to season and condition wood in the retort prior to pressure treatment. These processes result in contaminated water condensates. For example, unseasoned pilings can be seasoned in the retort by the Boultonizing or boiling under a vacuum process. Piles are sealed in the retort and hot creosote is then added. A vacuum is applied, resulting in rapid evaporation of water from the wood under the reduced pressure and high-temperature conditions. It is possible to dry large timbers to a low enough moisture content to permit treatment in 24 hours or less. The evaporated water containing the low-boiling-point components of the creosote is condensed out for treatment and disposal.

It is also common practice to condition poles and other timbers by steam/vacuum cycles in the retort. This results in condensate in the retort, which is contaminated by creosote components from the retort walls. This condensate must also be collected and treated.

The thermal treatment process is rarely used for the treatment of cedar, lodge poles or pine poles. The poles are placed in rectangular treatment tanks and hot creosote (88 to 113°C) is pumped in until the poles are immersed. This causes the air in the wood to expand out of the wood. After a minimum of six hours the hot preservative is quickly replaced by preservative at ambient temperature. This causes contraction of the air remaining in the wood cells drawing the preservative oil into the wood. After a few hours, the cold oil is pumped out. Full sapwood penetration may be achieved by this process. It is possible to impregnate only the butt portion of cedar poles by the thermal process.

In this practice, instead of the rectangular and horizontal tanks, cylindrical and vertical tanks are used. Poles are loaded so that preservative reaches only to a certain height of their lengths. Method, temperature, and time are otherwise the same as in the regular thermal treatment.

Chemical Discharges

(Figure 4.8)

Creosote components have measurable vapour pressures at ambient temperatures and, since solutions are heated for treatment and storage, there may be significant airborne emissions at all stages of the process, but especially at the retort door, vacuum pump vents, storage tank vents, and from freshly treated wood. Contaminated process-water results from conditioning treatments such as Boultonizing or steaming pretreatments. Contaminated storm water run-off can result from leached preservative or uncontained drips, leaks and spills. Oil-based preservatives are not chemically fixed in the wood and they may be prone to liquid bleeding of preservative from stored treated wood. Sludges can result from creosote/water emulsions produced by treating inadequately seasoned wood. Other solid wastes result from contaminated dirt and sawdust as well as used filters.

Table 4.5: Probable Reportable Compounds with CAS Numbers-Creosote Wood Preservation Facilities

CompoundCAS* Registry NumberVFT Typical Analysis**Typical Analysis AWPA P1 creosote~
Criteria air contaminants (including oxides of nitrogen (expressed as NOx), sulphur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOCs), total particulate matter (TPM), particulate matter with a diameter = 2.5 microns (PM2.5), and particulate matter with a diameter = 10 microns (PM10))Refer to the Canada Gazette Part I Notice for the year being reported.NA***NA***
* CAS denotes Chemical Abstracts Service.
** Environment Canada 2000a
*** Not applicable
~ Betts (1990)


Figure 4.7: Creosote Treating Plant Layout
Creosote treating plant layout

Figure 4.8: Sources of Releases from Creosote Wood Preservation Plants
Sources of releases from creosote wood preservation plants

Estimation Methodologies to Determine Releases and Transfers for Creosote Wood Preservation Plants

For a creosote treating facility, information requirements can be grouped into the following categories:

  • Process
  • Storm water
  • Remedial action
  • Catastrophic events
  • Non-hazardous solid waste
  • Hazardous wastes

Facilities that meet the NPRI reporting criteria for CACs should refer to the Supplementary Guide for Reporting Criteria Air Contaminants (CACs) to the National Pollutant Release Inventory (NPRI) and other reference documents to estimate emissions of CACs to air.

Potential types of releases and other waste management activities from the sources described above include fugitive and stack air emissions, direct and indirect wastewater discharges, and on-site and off-site management of solid wastes.

Process Air Emissions

Air emissions from the retort door opening, from valves, flanges, and pumps, and from the treated wood while on the drip pad and in storage are typically considered fugitive emissions because they are often released into the ambient air and not from a specific point or stack. Air releases from storage and working tanks are considered stack emissions released through a controlled exhaust or channeled through a pollution control device. Air emissions from the vacuum system may be fugitive emissions if they are emitted direct to the ambient air, or stack emissions if they are channeled through an air-pollution control.

Direct Measurement

PAH emissions can be estimated directly, based on air-monitoring results. Stack emissions are the most easily and reliably estimated since representative concentrations can be determined as well as stack flow rates.

Example 1:
Calculating Air Releases of PAHs Using Stack Monitoring Data

Stack testing has determined that PAHs are detected in the stack gases at a facility at concentrations (g per dry standard cubic metre of gas) as tabulated below. The moisture content in the stack is typically 10%. The stack gas velocity is typically 1.8 m/sec. The diameter of the stack is 0.3 metres. The annual air release of the PAHs from the stack of the facility may be estimated as follows.

1. Calculate the volumetric flow of stack gas stream:

Volumetric flow = (gas velocity) x [Pi x (internal stack diameter)2 / 4]
= (1.8 m/s) x [3.142 x (0.3m)2 / 4]
= 0.13 m3/s

2. Correct the volumetric flow for moisture content in stack gas stream:

Stack gases may contain large amounts of water vapour. The concentration of the chemical in the exhaust is often presented on a 'dry gas' basis. For an accurate release rate, correct the stack or vent gas flow rate in step 1 for the moisture content of the facility's stack gas. This is done as follows:

Corrected dry gas volumetric flow = (volumetric flow) x (1 - fraction of water vapour)
= (0.13 m3/s) x (1 - 0.10)
= 0.11 m3/s

3. Estimate annual stack emissions to air:

Multiply the dry gas volumetric flow rate by the concentration of PAHs measured in the stack gases:

R air = C x V x CF x H


R air = Annual release of PAHs to air (g/year)
C = Stack gas concentration of PAHs (g/dry standard m3)
V = Hourly volumetric flow rate of combustion stack gas (m3/hour)
CF = Capacity factor, fraction of time that the facility operates on an annual basis (e.g. 0.85)
H = Total hours in a year (8,760 hours/year)

SubstanceConcentration (g/m3), CAir flow (m3/h), VHours / year active (CF x H)Emissions (grams/year), R
 6 x 10-44123,842950
Anthracene2 x 10-44123,842317
Benzo(a)anthracene3 x 10-64123,8424.75
Benzo(b)fluoranthene6 x 10-64123,8429.50
Benzo(k)fluoranthene4 x 10-74123,8420.63
Benzo(a)pyrene2 x 10-74123,8420.32

Example 2:
Emission Factors

The U.S. EPA has developed emission factors for several PAHs for different creosote treating scenarios and for losses from freshly treated wood (Table 4.6).

A creosote treating plant that treats 130,000 cubic feet of Boultonized and full-cell treated marine pilings per year and 900,000 cubic metres of empty-cell treated railway ties per year. The estimated emissions are:

  • Relevant volume x emission factor
Benzo(a)pyrene:Pilings:130,000 x 6.5 x 10-8 = 0.00845 lb. or 3.8 g
 Ties:900,000 x 8.2 x 10-9 = 0.00738 lb. or 3.3 g
 Total process 7.1 g or 0.0071 kg
Naphthalene:Pilings:130,000 x 7.9 x 10-5 = 10.27 lb. or 4.67 kg
 Ties:900,000 x 4.6 x 10-6 = 4.14 lb. or 1.88 kg
 Total process 6.55 kg

The same methodology may be used to calculate estimated emissions of other substances for which emission factors are available.

Table 4.6: Emission Factors for Wood Treated with Creosote

Emission factors in kg emitted per cubic metre (pounds per cubic foot in brackets) of wood treated with creosote with and without Boultonizing conditioning and surface emissions to air during storage (g/m2) (MRI 1999)

 Emission Factors
SubstanceTotal treatment with Boultonizing kg/m3(lb./ft.3)Total treatment without Boultonizing kg/m3(lb./ft.3)Emissions from freshly treated wood g/m,sup>2(lb./1000 ft.2)
Anthracene2.1 x 10-6
(1.3 x 10-7)
2.6 x 10-7
(1.6 x 10-8)
Naphthalene1.3 x 10-3
(7.9 x 10-5)
7.3 x 10-5
(4.6 x 10-6)
Total VOC**0.093
(5.8 x 10-3)
(7.4 x 10-4)
Benzo(a)anthracene2.1 x 10-6
(1.3 x 10-7)
2.6 x 10-7
(1.6 x 10-8)
Benzo(b)fluoranthene2.1 x 10-6
(1.3 x 10-7)
2.6 x 10-7
(1.6 x 10-8)
Benzo(k)fluoranthene7.7 x 10-7
(4.8 x 10-8)
9.6 x 10-8
(6.0 x 10-9)
Benzo(a)pyrene1.0 x 10-7
(6.5 x 10-8)
1.3 x 10-7
(8.2 x 10-9)
Fluoranthene1.1 x 10-5
(6.8 x 10-7)
1.4 x 10-6
(8.6 x 10-8)
Fluorene6.2 x 10-5
(3.9 x 10-6)
1.2 x 10-6
(7.8 x 10-8)
Phenanthrene3.0 x 10-5
(1.9 x 10-6)
4.5 x 10-6 (2.8 x 10-7)10.74
Pyrene9.3 x 10-6
(5.8 x 10-7)
1.2 x 10-6
(7.3 x 10-8)
Chrysene1.1 x 10-6
(6.7 x 10-8)
1.3 x 10-7
(8.4 x 10-9)
All PAHs; fugitive leaching losses in storage: No emission factors available.
* Not Determined
** Refer to the Supplementary Guide for Reporting Criteria Air Contaminants (CACs) to the National Pollutant Release Inventory (NPRI) and other reference documents to estimates emissions of the other CACs to air.

Example 3

Estimate the PAH emissions from stored railway ties in 90 stacks, 8.5-feet wide, 30-feet long and 20-feet high. Assume emissions are from the outer stack surface area only (MRI 2000).

The total exposed area is from the top (8.5 ft. x 30 ft. or 255 ft.2), two ends: (2 x 8.5 ft. x 20 ft. or 340 ft.2) and two sides: (2 x 20 ft. x 30 ft. or 1,200 ft.2) for a total surface area per stack of 1,795 ft.2 or a total surface area of 90 x 1,795 or 161,550 ft.2.

The estimated emissions to air are as follows:

Naphthalene:161,550 ft.2 x 6.3/1000 psf = 1,018 lb. or 463 kg
Anthracene:161,550 ft.2 x 0.488/1000 psf = 78.8 lb. or 35.8 kg
Fluoranthene:161,550 ft.2 x 0.10/1000 psf = 16.15 lb. or 7.34 kg
Phenanthrene:161,550 ft.2 x 2.2/1000 psf = 355 lb. or 161.5 kg

The same methodology may be used to calculate estimated emissions of other substances where emission factors for freshly treated wood are available.

Wastewater Discharges

Example 1

A facility discharges its wastewater via storm sewers to a local sewage-treatment plant. The reportable PAHs are sampled and analyzed. The total flow for the year was 5,520 m3 and the naphthalene concentration averaged 0.5 mg/L, the anthracene concentration 0.14 mg/L, and the benzo(a)pyrene concentration 0.02 mg/L.

The amount of naphthalene discharged is:

= (5,520 m3/year, total flow) x (103 L/m3) x (0.5 mg/L concentration) x (10-6 kg/mg)
= 2.76 kg

The amount of anthracene discharged is:

= (5,520 m3/year, total flow) x (103 L/m3) x (0.14 mg/L concentration) x (10-6 kg/mg)
= 0.77 kg

The amount of benzo(a)pyrene discharged is:

= (5,520 m3/year, total flow) x (103 L/m3) x (0.02 mg/L concentration) x (10-6 kg/mg)
= 0.110 kg or 110 g

Releases Caused by Remedial Action

Remedial action can include a number of activities including disposal of contaminated soils, recovery and treatment of contaminated groundwater, or other one-time, non-routine clean-ups.

If groundwater near the plant has been contaminated, it is usually pumped out of the ground, treated and released where the amount released is a function of the concentration and volume of water discharge meeting provincial and federal limits. Remediation of contaminated soil may result in the off-site transfer of contaminated soil. Releases are determined by applying the results from soil sample analysis of the relevant PAHs in the samples to the total amount of soil involved.

Example 1

Groundwater in the amount of 250,000 imperial gallons was recovered, treated, and discharged with concentrations of naphthalene, pyrene and benzo(a)pyrene of 0.15 mg/L, 0.10 mg/L and 0.03 mg/L, respectively. The amount released is calculated as:

250,000 gallons x 4.54 L/gal. x concentration mg/L x 10-6 kg/mg

This results in releases of 0.170, 0.113 and 0.034 kg (170, 113 and 34 g) per year of naphthalene, pyrene and benzo(a)pyrene, respectively.

Example 2

Twenty thousand pounds (9,090 kg) of contaminated soil were removed as a result of remedial activities on soil containing PAH concentrations above current CCME guidelines for industrial sites. The actual concentrations of PAHs in the soil are as shown in the table below.

The releases in kilograms can be calculated as follows:

Weight of soil (kg) x concentration (mg/kg) x 10-6 (kg/mg)

SubstanceSoil Concentration mg/kgReleases kg (g)
Naphthalene50.00.45 (450)
Benzo(a)anthracene1.50.014 (14)
Benzo(b)fluoranthene0.850.0077 (7.7)
Benzo(k)fluoranthene0.400.0036 (3.6)
Benzo(a)pyrene0.550.0050 (5.0)
Fluoranthene2.50.023 (23)
Phenanthrene4.50.041 (41)

Release Due to Catastrophic Events

These involve spills or accidental releases outside the containment areas and in all cases require reporting to the environmental authorities. The amount of the release is the amount released minus that recovered.

Example 1

Creosote in the amount of 200 imperial gallons (1.08 kg/L) is spilled outside the containment area due to a ruptured hose during the unloading process. The release is promptly cleaned up and stored in drums as waste for shipment to a secure landfill. The appropriate regulatory authorities are notified promptly. The total release of NPRI-listed substances depends on the concentration found in the solution.

  1. Calculate the total mass of the spill (kg) as follows:
    200 gal. X 4.54 L/gal. x 1.08 kg/L = 980.6 kg
  2. Determine concentration (C) of components in the creosote (from manufacturer).
  3. Multiply the percentage concentration of substance by the determined total mass of the spill, as shown in the table below.
SubstanceContent in Creosote (%)Release
Anthracene2.019.6 kg
Naphthalene3.029.4 kg
Biphenyl0.87.84 kg
Benzo(a)anthracene0.98.82 kg
Benzo(g,h,i)perylene0.040.392 kg
Benzo(a)pyrene0.171.67 kg
Fluoranthene1098.1 kg
Phenanthrene21205.9 kg
Pyrene8.583.4 kg
Chrysene3.029.4 kg

Transfers in Solid Hazardous Waste

For solid hazardous waste, a determination of the total quantity of waste and the concentration of the PAH components must be made. Hazardous waste manifests are used to determine the amount of hazardous waste that was shipped off site. In addition, a waste analysis should be performed to determine the concentration of PAHs in the waste. This analysis should then be used to determine the actual transfer to landfill.


A facility sent 10 45-gallon drums of waste to a secure landfill. The total quantity of waste disposed was 3,520 kg, containing naphthalene (300 mg/kg), anthracene (130 mg/kg), biphenyl (98 mg/kg), phenanthrene (450 mg/kg), benzo(a)fluoranthene (2 mg/kg), pyrene (34 mg/kg), and benzo(a)pyrene (3.5 mg/kg). Therefore, the actual quantities in the waste are as follows:

3,520 kg x 300 mg/kg x 10-6 kg/mg = 1.06 kg naphthalene
3,520 kg x 130 mg/kg x 10-6 kg/mg = 0.46 kg anthracene
3,520 kg x 98 mg/kg x 10-6 kg/mg = 0.344 kg biphenyl
3,520 kg x 450 mg/kg x 10-6 kg/mg = 1.58 kg phenanthrene
3,520 kg x 2 mg/kg x 10-6 kg/mg = 0.007 kg benzo(a)fluorene
3,520 kg x 34 mg/kg x 10-6 kg/mg = 0.120 kg pyrene
3,520 kg x 3.5 mg/kg x 10-6 kg/mg = 0.012 kg benzo(a)pyrene

The facility had additional manifests for the soils disposed of during remedial action. However, these releases have already been accounted for in that section.

Summary of NPRI Reporting Steps - Creosote Wood Preservation Facilities

  1. Gather information on sources of releases to air, soil, groundwater, storm water, and off-site releases.
  2. Determine reporting thresholds for NPRI reportable substances from Canada Gazette Part I Notice for the year being reported..
  3. Estimate quantities released on site or transferred off-site, based on monitoring data, engineering calculations or emission factors.

Sample Release Summary Form

SubstanceType of ReleaseReleaseKg Released
NaphthaleneProcessFugitive aerosol and vapour 
 ProcessFugitive losses to groundwater 
 ProcessFugitive losses to soil 
 StorageFugitive vapour and leachate 
 Storm waterRelease to sewer 
 Catastrophic releasesRelease to soil/groundwater 
 Hazardous wasteSolid waste transferred to hazardous waste site 
Benzo(a)pyreneProcessStack emissions to air 
 ProcessFugitive aerosol and vapour 
 ProcessFugitive losses to soil 
 StorageFugitive vapour and leachate 
 Storm waterRelease to sewer 
 Catastrophic releasesRelease to soil/groundwater 
 Hazardous wasteSolid waste transferred to hazardous waste site
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