Guidance for wood preservation facilities reporting to the National Pollutant Release Inventory

Disclaimer

The Guidance for Wood Preservation Facilities Reporting to the National Pollutant Release Inventory (referred to as the Guide) is intended only to assist owners and operators of wood preservative treatment facilities in reporting releases and transfers to the NPRI. This Guide does not replace or substitute in any manner the official guidance documents listed below that are published and provided by the NPRI for reporters. All wood preservation manufacturing and treatment facilities should refer specifically to the Guide for reporting to the National Pollutant Release Inventory for the applicable reporting year.

Furthermore, should any inconsistencies be found between this Guide, the official NPRI guidance document identified above, and the official Canada Gazette, Part I Notice, the Canada Gazette, Part I Notice for the year being reported will prevail.

It is important to note the following: 

This guide addresses wood preservatives and additives currently in use in Canada, based on information available at the time of writing. Facilities should review all wood preservatives, their components and additives annually, and consult the guidance material and the Canada Gazette, Part I Notice for the year being reported to determine the reporting requirements for substances used.

This guide does not address Pentachlorophenol (PCP), which was prohibited for use in Canada as of October 2023. If any facilities meet the reporting requirements for PCP for 2023, refer to the previous version of this guide (available on request: inrp-npri@ec.gc.ca). 

The Chemical Abstracts Service (CAS) Registry Number (CAS RN) is the property of the American Chemical Society, and any use or redistribution, except as required in supporting regulatory requirements and/or for reports to the government when the information and the reports are required by law or administrative policy, is not permitted without the prior, written permission of the American Chemical Society.

Unless otherwise specified, you may not reproduce materials in this publication, in whole or in part, for the purposes of commercial redistribution without prior written permission from Environment and Climate Change Canada’s copyright administrator. 

For information regarding reproduction rights, please contact Environment and Climate Change Canada’s Public Inquiries Centre at 1-800-668-6767 (in Canada only) or email to enviroinfo@ec.gc.ca.

Introduction

Environment and Climate Change Canada and Health Canada developed a process for managing environmental contaminants under the Canadian Environmental Protection Act, 1999 (CEPA) that consisted of the following stages:

• identification of potentially toxic chemicals
• assessment of the risk to the Canadian environment and population
• identification and review of the options available to reduce environmental and/or public health risk posed by toxic chemicals

This process involved establishing a Priority Substances List, performing an assessment of toxicity, and developing a risk-management strategy through a Strategic Options Process (SOP). In the SOP, recommendations for the most effective options for reducing exposure to toxic substances were developed by stakeholders.

In 1988, Technical Recommendation Documents (TRDs) were published to reduce environmental and public/worker health posed by wood preservative chemicals. One document was prepared for each of the five preservatives in use at the time. The documents had substantial areas and recommendations common to all preservatives and in 1999, the documents were merged into what is known as the TRD (Recommendations for the Design and Operation of Wood Preservation Facilities (March 1999)).

An Issue Table was established in December 1994 to address issues of concern from the wood preservation sector. Representation from the federal government, provincial governments, wood preservative manufacturers, wood preservative treatment facilities, industrial users of treated wood products, and environmental non-government organizations (ENGOs), met as a whole and in various working groups over a four-year period to determine:

• chemical release data
• criteria to determine priority areas for investigation prior to making recommendations for the most effective options for reducing exposure to toxic substances

The wood preservation sector covers a wide range of areas related to the manufacture and use of preservatives: 

• water-based: 
  • ammoniacal copper quaternary (ACQ)
  • chromated copper arsenate (CCA)
  • copper azole type B (CA-B)
  • micronized copper azole (MCA) 
• oil-based: 
  • creosote 
  • DCOI (4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one)

Activities included under the sector definition are: 

• wood preservative manufacture
• application of preservative to the wood
• the use of treated wood products
• the management of used treated wood
• the transportation of both preservative chemicals and treated products
• the contamination of sites

It was determined that both CEPA Schedule 1 and non-CEPA Schedule 1 substances may be released to the environment from the above areas of activity, as shown in the following table. 

The SOP included a baseline assessment (audits) of all Canadian wood treating facilities in 2000 to determine the level of conformance with the TRD. All facilities were given five years to upgrade their operations before a second round of audits was conducted. Many facilities spent substantial funds on the upgrades while some other facilities ceased treating. Based on the information from the industry and the subsequent questions generated, the TRD was once again updated in 2004. All facilities had their second audit in 2005-2006. 

The 2005-2006 audits were the conclusion of the SOP. But they were also the baseline point for the voluntary TRD audit program. In the spirit of environmental responsibility and sustainable development, the members of Wood Preservation Canada (WPC) and certain non-members have endorsed a set of principles to govern their attitude and action in environmental matters, including a commitment to “assess, plan, construct and operate facilities in compliance with all applicable regulations,” including the TRD. They have developed a self-regulation program under which facilities are certified by the Canadian Wood Preservation Certification Authority (CWPCA). 

The CWPCA is administered by WPC with an independent auditing firm conducting external audits of all treating plants once in every 3-year cycle. In the cycle's other years, each facility conducts its own internal audit which is then reviewed by the independent auditors. Minimum scores and mandatory requirements must be met to maintain certification with the program. The TRD document was updated in 2013 to reflect current best management practices, especially since new preservatives were being introduced. The 2013 version is a modernised document meant to provide clarity, uniformity between similar preservatives and detailed recommendations to ensure better comprehension and clarity. Process and operational descriptions included in this guide have been heavily derived from the TRD.

The NPRI 

The National Pollutant Release Inventory (NPRI) is Canada’s legislated, publicly accessible inventory of pollutant releases, disposals and recycling. Since its inception in 1992, the role of the NPRI has expanded over years. It tracks over 320 pollutants from over 7,000 facilities across Canada.

Reporting to the NPRI is mandatory under the Canadian Environmental Protection Act, 1999. Owners or operators of facilities that meet the NPRI reporting requirements published in the Canada Gazette, Part I have to report to the NPRI. The Guide for reporting to the NPRI is designed to assist facility owners and operators in understanding the NPRI reporting requirements, and in determining if they are required to report to the NPRI.

How the NPRI has been modified to accommodate the requirements of the Wood Preservation Sector SOP

As identified in the SOP recommendations, reporting requirements specific to the wood preservation sector were incorporated into the Canada Gazette, Part I Notice for NPRI, and published on December 25, 1999. As such, most wood treatment facilities should meet the reporting requirements for the substances covered by this guide. Reporting requirements for all NPRI-listed substances are subject to change and so the Canada Gazette, Part I notice for the year being reported should be consulted for the relevant reporting criteria. 

This Guide, together with the guidance documents published by NPRI for the year being reported, should be consulted by owners and operators of wood preservative manufacturing and wood preservation treating facilities when reporting to the NPRI.

More information on the NPRI is available on the NPRI website. 

Reporting to the NPRI

Overview of this guide

This Guide provides information on the following:

• reporting requirements for NPRI-listed substances used in pressure treated wood preservation
• methodologies to estimate on-site releases and off-site transfers of NPRI-listed substances applicable for wood preservation treatment facilities
• examples of how to estimate on-site releases and off-site transfers of substances for the purposes of reporting to the NPRI

For a full listing of NPRI substances, please refer to the Canada Gazette, Part I Notice or the Guide for reporting to the NPRI for the year being reported. The NPRI substance list is also available in spreadsheet format.

Please note: this guide does not address the use of Pentachlorophenol (PCP), which was phased out on October 4, 2023. If any facilities meet the reporting requirements for PCP, refer to the previous version of this guide (available upon request: inrp-npri@ec.gc.ca). 

In addition, DCOI has been included into this guide as it is currently under regulatory review for use as a wood preservative in Canada; however, other preservatives that are currently under consideration for use in Canada (i.e. copper naphthenate) are not discussed in this guide.

NPRI reporting requirements

Report due dates

Reporting deadlines for the NPRI are typically June 1 (or the first business day after, should June 1 fall on a weekend), but are subject to change and should be verified in the Canada Gazette, Part I Notice for the year being reported. Current reporting deadlines can be accessed on the deadlines and most recent changes page. 

Information required by wood preservation facilities reporting to the NPRI

In order to make an accurate determination of the quantity of releases each year, a wood preservation facility must gather as much information as possible about its processes, waste shipments, and releases to the environment. This requires a detailed investigation of the sources of releases to each medium (air, water, and land), identification of the components that contribute to those releases or transfers, and the establishment of the proper engineering approaches needed to quantify those releases or transfers. The facility must use all relevant monitoring data and emissions measurements collected to meet other regulatory requirements, or as part of routine plant operations, or to the extent a facility has such data. 

The Notice specifies that if emissions are already monitored or measured under provincial or federal legislation or a municipal bylaw, those measurements must be used to report to the NPRI. An NPRI report is mandatory for any substances that meet the reporting thresholds, regardless of whether the substance is being measured or monitored for other jurisdictions. If emissions are not monitored or measured under provincial or federal legislation or a municipal bylaw, reasonable efforts must still be undertaken to gather information on releases, disposals, and transfers of a substance. In the absence of data, reasonable estimates must be made using published emission factors, mass balance calculations, or engineering calculations. 

Completing reporting to the NPRI 

Information required by the Canada Gazette, Part I Notice is collected via ECCC’s Single Window reporting system. For those who meet the requirements of the Notice, reporting is mandatory and must be submitted no later than the date specified in the Canada Gazette, Part I Notice for that reporting year.

Record keeping

Pursuant to subsection 46(8) of CEPA, the owner/operator of a facility is required to retain copies of all information on which their report is based, including any calculations, measurements and other related data, for three years from the applicable reporting deadline. This information must be kept at the facility or at the principal place of business in Canada of the owner/operator of the facility to which the information relates, for three years.

NPRI definitions

All definitions are subject to modification. The most relevant definitions have been included below. Please consult the Canada Gazette, Part I Notice and the Guide for reporting to the NPRI for the year being reported for the most current definitions and a complete list of NPRI definitions.

Wood preservation treatment activities

Detailed operations of wood preservation treatment activities can be found in the TRD document. This document is periodically updated and reference to it is recommended if further details are required. The four major components of a wood treatment facility are:  

• yards for storage of untreated and treated wood
• wood processing facilities including:
  • peelers
  • framing lines
  • kilns etc. 
• pressure treating facilities 
• offices and laboratory spaces 

The size of storage yards can vary significantly depending on the facilities’ treatment capacity and the manner of drying the wood. 

Before wood can be successfully pressure treated with preservatives, the bark must be removed, and the moisture content reduced by a process involving drying or conditioning. This may be achieved by air seasoning, kiln drying or by a process conducted in the treatment cylinder, for example, a steam/vacuum process.  Air seasoning requires a large storage space. However, facilities that process wood, particularly for the residential market, may employ kiln drying, which requires less white (untreated) wood inventory space.

Preservation processes are aimed at injecting requisite amounts of preservative liquids deep into the wood to provide long-term protection against wood destroyers. In North America, most preserved wood is treated by pressure processes. Thermal treatments (>180°C) are no longer used in Canada since they were only used with PCP. 

The applied treatment parameters for all processes are limited by the directions for use on the registered pesticide labels. The specific treatment times and pressures are dictated by the wood's species, product, and moisture content. A predetermined range of process parameters is defined by the applicable treatment standards of the Canadian Standards Association CSA-O80 Series of Standards to ensure effective treatments for specific uses without damage to the wood. 

Treated wood, removed from the cylinder, is stored on a drip pad until preservative drippage has stopped. The duration of this storage may vary from hours to days. Alternatively, most CC treatment plants now conduct an accelerated fixation process to ensure that the preservative chemicals are highly leach resistant. Such a process entails a heating cycle, usually in the presence of high humidity. Fixation chambers are employed and when fixation has been verified, the treated wood is moved to a segregated (treated wood separated from white wood) outdoor storage area.

Water-based preservatives (ACQ, CA-B, CCA, MCA)

Overview

Water-based wood preservation facilities use aqueous formulations of arsenic, copper, chromium, and organic pesticides depending on the intended application of the treated lumber (residential - patios and fencing or commercial – fence posts, utility poles, construction lumber).

Water-based preservatives include:

• alkaline copper quaternary (ACQ) – residential
• copper azole (CA-B) – residential
• chromated copper arsenate (CCA) – commercial & industrial
• micronized copper azole (MCA) – residential

Process description

Waterborne preservation plants are housed within a heated building. (To see illustrations of a typical CCA treatment facility, refer to the TRD document). The major difference from other water-borne preservation plants is the presence of a fixation chamber. The pressure vessel, also called a retort or cylinder, is commonly 1.8 m in diameter and 24.4 m long. The wood is normally charged and discharged through a single door by means of trams that run on tracks. Other designs use conveyors to move wood in and out of the cylinder and may involve doors at either end to load and remove the wood. Pumps are used to apply process conditions (i.e. vacuum or pressure) and transfer liquids from and to the cylinder and between tanks. A tank farm typically includes a concentrate tank, one or more tanks for working solutions, and an effluent recovery tank or makeup water tank. The process controls and instrumentation vary in sophistication, depending on the degree of automation. Most waterborne preservation plants have systems that are fully automated to control the pressure treating process parameters. Many plants have heated storage areas for recently treated wood and facilities for accelerating the fixation or stabilization of the preservative components in the treated wood.  

The full-cell treatment process, used to apply the preservative in waterborne treatment plants, consists of the following steps: 

1. application of an initial vacuum to remove air from the wood cells  
2. flooding with working solution and pressurization (up to 1040 kPa) until the target retention level is achieved  
3. draining of the excess working solution (to the working tank for reuse with subsequent charges)
4. application of a final vacuum

The specific treatment times and pressures are dictated by the species of wood, the type of wood product (e.g. plywood or poles) and the moisture content of the wood. A predetermined range of process parameters is defined by the applicable treatment standards, and quality control tests are conducted to ensure that the product meets the minimum quality standard. Once the treated wood is withdrawn from the treating cylinder it is either subjected to a fixation process or stored on-site for periods that generally range from days to months for stabilization. The fixation and stabilization process requires a sealed drip pad and a roofed area. This is essential, since the preservatives are water soluble and would leach at various concentrations when exposed to precipitation, except for CCA that is leach resistant due to the fixation process. Paved or concrete flooring often have roofs over all or portions of the treated wood storage area to reduce or eliminate exposure to the elements. 

CCA

CCA is normally purchased as a premixed concentrate solution (50% or 60%) shipped by bulk truck. The concentrate is stored in tanks and diluted with water to a 1.5–5.0% strength working solution. This dilution is accomplished by pumping transfers and by recirculation between bulk tanks. The working solution is then applied to the wood in a pressure cylinder, which may be up to 45m long and 2m in diameter. 

CA-B

Copper as CuO and azole as tebuconazole, the two active components of CA-B, are used because of their fungicidal and termiticidal properties and their ability to offer long-term protection in the wood. CA-B preservative can be shipped via tanker to wood preservation facilities as a premixed concentrated solution or in separate totes of CuO and tebuconazole, that is diluted to working strength by adding a known quantity of water in a mix tank; typically, in the 0.3 to 3.4 % range.

The working-solution strength is determined by the desired treatment level to be retained in the wood. Vacuum and pressure cycles vary depending on the wood species and size of the wood product being treated, such that they meet the desired standard or specification. 

ACQ

There are four formulations of alkaline copper quaternary (ACQ) preservative: 

• Type A 
• Type B 
• Type C  
• Type D

Type A, Type C and Type D are currently registered for use in Canada. The different formulations allow flexibility in achieving compatibility with different wood species and end use applications. All ACQ types contain two active ingredients, which may vary within the following limits: copper oxide which is the primary fungicide and insecticide; and a quaternary ammonium compound (quat), which provides additional fungicide and insect resistance properties. All ACQ types contain copper and quat at either 2:1 or 1:1 ratio copper oxide to quat.  

As of 2023, no treating facilities in Canada were using ACQ. ACQ-C is the formulation previously used, containing 66.7% copper oxide and 33.3% quat alkyldimethylbenzyl-ammonium chloride (ADBAC). Ammonia and/or ethanolamine can be used as the carrying solution in this formulation. 

The ACQ-C preservative was shipped in tanker trucks to wood preservation facilities as a premixed concentrated solution of 14.14% active ingredients (as copper oxide) that is then made into a ready-to-use working-strength solution (0.5–3.4% actives (copper plus quat)) by adding a known quantity of water in a mix tank. It was also delivered in totes as a premix or separately with totes of copper oxide and quat. Boric acid may also be present at various concentrations in ACQ solution; it is added as a corrosion inhibitor and not as an active ingredient which is why it is generally present in low concentration. 

MCA

Micronized copper wood treatment is very similar to alkaline copper quaternary (ACQ) and copper azole (CA-B) wood treatments. However, they use very small particles of solid copper, usually in the form of copper carbonate, rather than soluble copper. The reduced size of the copper solids means less leaching of the metal than ACQ or CA-B.

As with ACQ and CA-B, MCA can be delivered to treating facilities in tanker trucks or totes. The advantage of totes is that the copper oxide or the azole (tebuconazole) can be added separately, and small amounts added if the solution strength requires adjustment.

Substance releases, disposals, and transfers

Generally, the preservation system is closed, meaning preservative losses from leaks, spills and drips are contained and recovered as much as possible and returned to the process. 

Potential substance discharges could occur to water, air or soil, and possible transfers to material or equipment depending on the plant design and operational procedures. The discharge can vary in quantity and in state (e.g. liquid, solid or air). 

Air emissions 

Potential sources of air emissions include the following: 

• exhausts, mists, and vapours from kilns 
• exhausts, mists, and vapours from tank vents 
• mists and vapours from vacuum pump exhausts 
• mists and vapours from opening of retort cylinder doors and tank hatches 
• vapours from freshly treated charges 
• exhausts, mists and vapours from stabilization kiln or accelerated fixation process
• dust, sawdust, debris (Part 4 – criteria air contaminants (CACs))
• dust from vehicles travelling on unpaved roads (Part 4 - CACs)
• releases from stationary combustion (e.g. building heaters etc.) (Part 4 - CACs)

Liquid discharges 

Preservatives and their process chemicals require water or other liquid as a solvent. Due to the toxicity and cost of the preservatives or process chemicals, ideally the facility should use closed loop treatment systems that contain, collect, and reuse the chemical mixture to the greatest possible extent.  

Closed systems may include the following types of equipment: 

• paved or concrete containment surfaces  
• dyking of major process components including the cylinder and tanks  
• containment surfaces for chemical drips from treated wood in storage, stabilization/fixation, or drying areas (drip pads) 
• collection sumps to receive residual preservative cartridge filters to remove dust and wood debris from contaminated liquids entering the system 
• holding tanks for filtered solutions 

Some liquid streams that may not be possible for re-use include the following:

• condensates removed from the wood during conditioning or vacuum application 
• condenser cooling water 
• water released by the wood during the treatment cycle 
• spills, overflows and leaks 
• stormwater runoff from unpaved or unroofed areas or yard soil contamination 
• spills from hose ruptures during the unloading of trucks 
• spills from piping failure 
• spills from damage of waste drum 
• drippage from lumber that was removed from the drip pad too soon 

Solid wastes 

Solid waste generation at wood preservation facilities may include the following: 

• cartridge filters and traps 
• broken treated wood  
• sludge from:
  • tanks
  • sumps
  • fixation/stabilization chambers/kilns 
  • pressure cylinders
• sludge from wastewater treatment processes 
• contaminated soils 
• containers, wrappings, wood lath, stickers and pallets 
• dust, sawdust, debris 

Summary of wastes produced during wood preservation using water-based preservatives 

NPRI-listed substances may be discharged during various steps of the process, including: 

• chemicals delivery:
  • liquid wastes from spills and drips
  • air emissions from vapours
• chemicals concentrate storage / mixing:
  • liquid wastes from spills and drips
  • air emissions from vapours
  • solid waste such as sludge
• working solution tanks:
  • liquid wastes from spills and drips
  • air emissions from vapours
  • solid waste such as sludge
• pressure treatment:
  • liquid wastes from spills and drips
  • air emissions from vapours
  • solid waste such as sludge
  • chemicals are passed through filters
• drip pads:
  • liquid wastes from drips and leachate
  • air emissions from vapours
  • solid waste such as sludge
• fixation:
  • liquid wastes from spills and drips
  • air emissions such as VOCs and dust
• treated wood storage:
  • liquid waste from leachate
  • air emissions such as VOCs

In addition:

• chemicals from the pressure treatment step are passed through filters and recycled back to the working solution tanks 
• spent filters are disposed of in landfill
• contaminated solution in the form of spills, drips and leachate is collected and recycled back into the working solution tanks 

Facilities that meet the NPRI reporting criteria for Part 4 CACs should refer to the current version of the Guide for reporting to the NPRI and other reference documents to estimate emissions of CACs to air including the ECCC wood products operations calculator.

NPRI reportable substances

The following list comprises examples of substances that should be considered for reporting at water-based wood preservation facilities. Refer to the Canada Gazette, Part I Notice for the year being reported for the specific reporting criteria for these substances in determining if reporting is necessary.

It is important to note that if facilities meet the reporting criteria for other NPRI-listed substances not shown above, they are legally obligated to file an NPRI report on those substances to ECCC by the date specified in the Canada Gazette, Part I Notice for the year being reported.

Estimation methodologies to determine releases and transfers

For a water-based treating facility, substance releases disposal and transfers generally can be grouped into the following categories:

• air emissions
• wastewater
• remedial action 
• catastrophic events
• non-hazardous solid waste
• hazardous wastes

Potential types of releases and other waste-management activities from the sources described above include: 

• air emissions: 
  • fugitive
  • stack 
  • storage tank
• wastewater discharges: 
  • direct
  • indirect 
• management of solid wastes: 
  • on-site
  • off-site 

The following sample calculations use measurement units that are industry standards; reportable quantities must be converted to metric units specific to the reportable substance (e.g. Part 1A substances must be reported in tonnes). Refer to the NPRI reportable substance list for applicable reportable units.

Air emissions

Air emissions from water-based preservation facilities may include releases of volatile organic compounds from chemical use and products of combustion from stationary combustion units.

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 emissions from the vacuum system may be fugitive or stack emissions if channeled through a pollution-control device and should be reported appropriately.

Air emissions from waterborne wood preserving plants are considered to be very low. The vapour pressure (measure of tendency to evaporate) of inorganic metals is very low under the low ambient temperature treating conditions (15 to 30°C) and fixing and drying of treated wood (up to 90°C) used in CCA preservative. For example, the concentration of arsenic oxide in a saturated environment is approximately 1.1 mg/m³ at 100°C and the extrapolated value at 20°C is about 0.08 µg/m³. 

Release of the preservation solution as an aerosol, however, can occur at vacuum pump exhausts, work tank vents, retort door openings, and fixation chamber vents (although studies performed in 1984 showed no significant releases), as well as from fixation kiln vents. (Studies cited in: Bridges J.F., Williams D.R. 1984.  Characterization of Airborne Emissions and Waterborne Drainings Associated with Kiln Drying of CCA-Treated Wood, Proceedings - Annual Meeting of the American Wood-Preservers' Association).

Facilities that meet the NPRI reporting criteria for Criteria Air Contaminants (CACs) should refer to the current version of the Guide for reporting to the NPRI and other reference documents to estimate emissions of CACs to air.

Direct measurement

If emissions of volatile organic compounds are collected in a vented hood, the amounts released can be estimated from the time-weighted concentrations measured in the exhaust and from the flow rate through the exhaust. This will allow the determination of positive effects of introducing emission-control technologies such as wet scrubbers to the exhaust. It is important that measurements reflect the effects of different process steps since there will be higher releases at certain points, such as when the retort is opened, or the vacuum pumps are operating.

In addition, ammonia and metal releases can be estimated by direct measurements from occupational exposure monitoring for those process steps where information on flow rates or air-exchange rates are known.

Example 1

Aerosols from the retort door opening, vacuum pumps and storage tanks are all vented through one exhaust vent. The exhaust vent is determined to have a flow rate (F) of 100 m³ per hour. Air concentrations of Cu, Cr and As are measured (Ci in mg/m³) at the vent outlet on several occasions:

• when the retort door is opened and the charge removed 
• when the initial and final vacuum pumps are operating 
• during the rest of the impregnation process (fill retort, pressure treat, empty solution)
• when the treating system is not in operation

The number of days that wood was treated per year (Dt) and the number of days it was inactive (Dnt) are known, as well as the number of hours each day that the different process steps are active (ti). 

The estimated emission during a given process step (such as retort opening and unloading) is derived using the following formula:

Where:

• F = Flow rate (m³/h)
• Ti = Time the different process steps are active (h/day)
• Dt = Number of days that wood was treated per year
• Ci = Air concentrations of substances (mg/m³)

Total annual emissions = 360mg (0.36g)

Use of emission factors

Emission factors for copper and chromium (U.S. Environmental Protection Agency (EPA) AP-42 Section 10.8 Wood Preserving) and for arsenic (Australian Timber Preservers Association - Emission Estimation Technique Manual for Timber and Wood Product Manufacturing) have been developed based on measurements made at representative CCA treating plants. They are, however, based on volumes of wood treated and represent uncontrolled emissions as per the EPA, (Table 4). If the facilities have air pollution control devices installed, they should use the applicable emission control efficiencies with these uncontrolled emission factors.

* ND = Not determined.

Sources: 

• Emission factor documentation for AP-42, Section 10.8 Wood Preserving - Final Report (PDF) (Midwest Research Institute (MRI) for the US EPA)
• Emission estimation technique manual for timber and wood product manufacturing (National Pollutant Inventory (NPI) – Australia) 

Emission factors have not been developed for ACQ airborne emissions.

Example 2

A CCA treating plant treats 600,000 cubic feet of product annually. The estimated airborne emissions of arsenic and chromium, using the above emission factors is 600,000 x 1.4 x 10^-9 or about 0.0008 lbs (0.38 g) and the emissions of copper are 600,000 x 1.9 x 10^-9 or 0.0011 lbs or 0.52 g.

Mass balance

If emissions of volatile organic compounds are collected in a vented hood, the amounts released can be calculated based on a mass balance approach.

Example 3

It is known that much of the ammonia used in the ACQ process will be released to the environment as a result of process losses and evaporation of ammonia from the treated wood to fix the preservative chemicals. However, it is also known that some ammonia is retained in the final treated product as a reaction product between the wood components and the other preservative components, and process ammonia is recovered by vacuum and other post-treatment processes in the retort. It is assumed that 50% of the ammonia is retained in the treated wood and the remainder is released, mainly as vapour.

A treater uses 120,000 kg dry mass basis of ACQ containing 39.9% copper (47,880 kg). They formulate the solution with ammonia at 1.8 x the weight of copper (1.8 x 47,880 = 86,184 kg ammonia).

Assuming 50% is released during and after treatment, the total release is 86,184/2 or 43,092 kg (43.1 tonnes).

Note that this example ignores ammonia recovered by post-treatment conditioning and through scrubbers in vents and will be an overestimate.

Wastewater discharges

Wastewater discharges may result from the wash down of process equipment, and from storm water run-off. They can also be generated from the drip pad and wastewater from the vacuum discharge condensate.

Note: most wood preserving facilities using waterborne preservative solutions recycle 100% of the solution. The following calculation is included to assist any facility that may not conduct 100% recycling of the solution.

Direct measurement - to sewer

Example 1

A facility discharges its wastewater to municipal sewers. Provincial regulations require the facility to record the total flow and monitor for chromium, copper, and arsenic. The average monthly flow was 525,000 US gallons. The chromium concentration averaged 0.5 mg/L. The copper concentration averaged 2.0 mg/L. The arsenic concentration averaged 0.05 mg/L.

The amount of chromium discharged is:

The amount of copper discharged is:

The amount of arsenic discharged is:

Example 2: storm water release estimates (if flow rates are not known)

Quantification of storm water releases is required if a facility has data on the concentration of NPRI-listed substances in its discharges. Determination of the amount of CCA components released in storm water run-off involves calculating the total amount of volumetric run-off from the site and applying the measured or estimated concentration of CCA to that volume.

To determine the total volume of run-off, the facility must determine the total area drained by each outfall and the weighted average run-off coefficient for that area that is dependent on that area's soil structure, topography, usage and development. The run-off coefficient represents the amount of rainfall that does not soak into the ground but runs off as storm water. Once the volumetric flows are determined, the facility must apply the correct concentration (found through sampling during the event) at each outfall to each outfall’s flow.

Source: Environmental Protection Agency (EPA). 2023. Toxic Chemical Release Inventory Reporting Forms and Instructions, Revised 2022 Version

Step 1: calculate total drainage area (length x width) of each outfall using L x W = sq. ft.

• Outfall #1 = 575,200 sq. ft.
• Outfall #2 = 568,100 sq. ft.

Step 2: calculate square footage of each land area in each outfall drainage and determine applicable run-off coefficient for type of land use.

Step 3:  determine amount of storm water traveling into each outfall and off-site.

Calculate average rainfall for area:

Calculate run-off from all areas using the below formula:

Where:

• R = average yearly rainfall in ft/year
• A = Area in ft²
• C = run-off coefficient
• 7.48 gal/ft³ = conversion factor to gallons

Convert gallons to litres:

Step 4: determine kg of copper (Cu), chromium (Cr), and arsenic (As) released for each outfall.

Use composite results from your storm water sample data for your calculations (note: mg/L = ppm):

• Outfall #1: 
  • Cr = 0.03 mg/L 
• Outfall #2: 
  • Cr = 0.20 mg/L 
  • As = 0.02 mg/L

Where:

• Q_i = the quantity of substance "i" released (kg/year)
• L = litres of rainwater traveling off-site as calculated in Step 3
• C_i = concentration of substance "i" (mg/L)
• 10^-6 kg/mg = conversion factor from mg to kg

Step 5: determine total release volumes.

Add kilograms of copper, chromium, and arsenic separately from each outfall to calculate the total kilograms of copper, chromium and arsenic released:

• chromium = 1.62 kg (Outfall #1) + 3.63 kg (Outfall #2) = 5.24 kg Cr/year
• arsenic = 0.36 kg As/year

Direct measurement – releases to soil

One source of emissions to soil is leaching from treated wood during rain events while it is being stored. Leaching rates from freshly treated wood are highly variable, depending on the time of year, type of treated product (species, shape, retention), whether the bundles are wrapped, weather conditions during storage, configuration of stored material (e.g., height of stacks), season and length of storage.

Water drippage from representative stored treated product can be collected and measured for volume and average concentration of components during rain events over the average storage time for the product. Using the amount of wood represented by the tested material and the average amount of similar material in the yard at any time, the leaching emissions to soil can be estimated:

Where:

• V = volume of water drippage from representative stored treated product (L)
• C = average concentration of components during rain events (mg/L)
• t = average storage time (weeks)
• A_t = Amount of wood represented by the tested material (any units)
• A = average amount of similar material in the yard at any time (same units as A_t)
• 10^-6 kg/mg = conversion factor from mg to kg

Example 1

Drip water was collected from a stack of treated lumber containing 800 cubic feet (A_t). At any given time, the amount of wood in the yard (A) is 50,000 cubic feet. Over the average storage time of six weeks (t), there were seven rain events, and a total volume of 1,350 litres (V) of drip water was collected with an average arsenic content of 1.4 mg/L (C). 

Please note that this is only an example; no general emission factors have been developed for wood leaching.

The estimated arsenic emissions for the year are:

Emission factors

Emission factors have been published for freshly treated wood (PDF), but these are variable and depend on estimating the surface area of exposed wood in the yard. Examples of measured emission factors are:

• Cr: 13 mg/m²/rain event
• Cu: 44 mg/m²/rain event
• As: 33 mg/m²/rain event

Example 2

Lumber is piled in rectangular stacks 6.5 m high, 1.4 m wide and 5.1 m long. It is assumed that the area exposed to rain at any time is that of the top and four sides with a total area of 91.6 m². At any given time there are an average of 36 such stacks in the yard and it is determined from meteorological records that there were 47 rain events during the year.

The estimated emissions of the CCA components are:

Releases and transfers caused by remedial action

Remedial action can include several activities: 

• disposal of contaminated soils
• recovery and treatment of contaminated groundwater
• other one-time, non-routine clean-ups 

If groundwater near the plant has been contaminated, it is usually pumped out of the ground and into the treating plant for use as make-up water for the process. In situations where groundwater is treated and released, the amount of release is a function of concentration and volume of water discharge.

Example 1 - release

Groundwater in the amount of 250,000 US gallons was recovered, treated, and discharged with concentrations of copper, chromium, and arsenic to septic drains at 0.15 ppm, 0.10 ppm and 0.2 ppm, respectively. This results in releases of 0.31 lbs, 0.21 lbs, and 0.42 lbs per year of Cu, Cr and As, respectively.

Note that reporting releases to septic drains would be done under “other releases to land”.

Example 2 - transfer

Releases to soil were determined by applying the results from soil sample analysis of the chromium, copper, and arsenic in the soil samples to the total amount of soil involved. In this example, 20,000 pounds of soil were removed as a result of remedial activities containing calculated Cu, Cr, and As concentrations slightly above current Canadian Council of Ministers of the Environment (CCME) guidelines for industrial sites. The actual concentrations of copper, chromium and arsenic by weight were multiplied by 20,000 pounds as follows:

• 20,000 lb x 200 ppm (Cu) x 10^-6 = 4.0 lb

• 20,000 lb x 100 ppm (Cr) x 10^-6 = 2.0 lb

• 20,000 lb x 100 ppm (As) x 10^-6 = 2.0 lb

Release due to catastrophic events

These involve spills or accidental releases outside the containment areas. The amount of the release is a function of concentration and volume released.

Note that the portion of the spill not cleaned up must be reported as a release the year it occurred. Further migration between media does not need to be reported.

For example, if 100 L of an NPRI substance is spilled and 80 L is recovered, a release of 20 L must be reported. If the 80 L is returned to the process, no further action is required. However, if it is sent off-site for treatment or disposal, it must be reported accordingly.

Example

CCA concentrate in an amount of 200 US gallons is spilled outside the containment area due to a ruptured hose during the unloading process. The release is promptly cleaned up and neutralized with spill neutralizer and subsequently stored in drums as hazardous waste for shipment to a secure landfill. The total amount of the spill can be calculated as follows:

Step 1: calculate the total mass of the spill.

Note: percentages of CuO, CrO₃ and As₂O₅ in the CCA concentrate vary, the values used above are examples only.

Step 2:  determine actual elemental Cu, hexavalent Cr, and As.

Step 3: multiply the elemental ratio in Step 2 by the determined total oxide mass from Step 1.

Since the spill was fully cleaned up, these quantities would be reported as off-site transfers to landfill.

Transfers in solid hazardous waste

For solid hazardous waste, a determination of the total quantity of waste as well as the concentration of the copper, chromium and arsenic 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 Cu, Cr and As in the waste. This analysis should then be used to determine the actual disposal to landfill.

Example

The facility sent six 45-gallon drums of hazardous waste to a secure landfill. The total quantity of waste disposed was 2,104 kg containing copper, chromium, and arsenic in the following proportions 1.966%, 2.262% and 4.219%, respectively. None of the results contained hexavalent chromium.

Therefore, actual quantity in the waste is:

The facility had additional manifests for the soils disposed of during remedial action. However, these quantities have already been accounted for in the transfers for disposal as a result of remedial action.

Summary of NPRI reporting steps - water-based wood preservation facilities

First, gather information on NPRI substances manufactured processed or otherwise used and on sources of releases, disposals, and transfers.

Then, determine reporting thresholds for NPRI reportable substances from the Canada Gazette, Part I Notice for the year being reported. For more information about NPRI reporting requirements, refer to the Guide for reporting to the NPRI .

Estimates of the quantity of a substance that is manufactured, processed or otherwise used, and of the quantity that is released, disposed of or transferred for recycling, may be based on one of the following methods:

• continuous emission monitoring (reporting system code M1)
• predictive emission monitoring (M2) 
• source testing (M3)
• remote quantification (RQ)
• mass balance (C)
• site-specific emission factors (E1)
• published emission factors (E2)
• speciation profile (SP)
• engineering estimates (O)

Oil-based preservatives (creosote, DCOI)

Overview

Oil-based preservative solutions contain NPRI listed substances including naphthalene and certain individual polycyclic aromatic hydrocarbons (PAHs). The types of oil-based preservation facilities in Canada include the following:

• creosote
  • commercial uses: 
    • railway ties
    • utility poles
    • piling for marine applications
• dichloro-octyl-isothiazolinone (DCOI) 
  • currently under review for approval in Canada

As DCOI is currently not used in Canada, the information contained herein has been provided by industry representatives and information currently available. The main assumption is that DCOI treatment will follow the same process as Pentachlorophenol (PCP) treatment. Any changes in the treating process that may occur are not expected to substantially change the NPRI listed substances or the potential releases of those substances.

Process description

Plants using oil-based preservatives have a similar layout to those used in water-based preservation. (To see illustrations of a typical oil-based treatment facility, refer to Figure 4 of the TRD document). The pressure cylinders are usually somewhat larger than those used in waterborne preservation plants (2.1 m in diameter and 36.5 m in length). Tank farms are generally placed outdoors, and tanks are equipped with internal heating devices. The production equipment, including the cylinder, pumps, condensers, controls, and effluent treatment systems, is housed within a treating building. Facilities treating with DCOI, or creosote solutions require a heat source for warming the preservative and to conduct specific processes, such as steam conditioning. When treating with DCOI, either an autoclave or a designated mix tank is used to dissolve the solid preservative in a suitable oil solvent. Effluent treatment facilities may consist of an oil/water separator, a flocculation system and carbon filtration. An air filtration system to collect exhausts from treatment vessels, vacuum systems and tank vents may also be part of the installations. The vacuum systems are equipped with condensers and condensate collection tanks.

Creosote

Creosote is used either in a mixture of 50:50 creosote/petroleum oil or alone at full strength. Creosote and petroleum oil are delivered to wood preservation facilities by bulk truck or rail tanker and are stored in bulk storage tanks.  

In Canada, creosote/petroleum oil mixtures are blended by pumping transfers and by recirculation between bulk tanks. The benefits of blending creosote with oil are lower cost and improved penetration (lower viscosity) in applications such as railway ties, where conditions of use allow for less protection than that usually provided by 100% creosote. The physical properties of wood treated with a mix are quite similar to those of material treated with 100% creosote; better dimensional stability (compared with untreated or waterborne treated wood), improved mechanical wear, corrosion inhibition, resistance to chemicals, water repellency and improved resistance to electrical conductivity. Full strength creosote is used where maximum biocidal protection is desired, such as for timbers exposed to marine borers. 

If Boultonizing or steam/vacuum processes have been used for conditioning, creosote is applied in the following steps, either by the full-cell treatment process or the empty-cell treatment process. It should be noted that in contrast to treatments with waterborne preservatives, creosote solutions are applied at an elevated temperature (70–90°C). Depending on the species of wood, the wood product and the moisture content of the wood, the operator of the facility determines the appropriate treatment process (full cell or empty cell), and the pressure, temperature, and times for various process sequences. 

An expansion bath and final vacuum are usually added after the pressure cycle to render product surfaces relatively dry and to minimize long-term “bleeding” of preservative and to improve the surface cleanliness of the material. The expansion bath can be applied before removal of the preservative from the cylinder by quickly re-heating the oil surrounding the material to the maximum temperature permitted by the CSA Standard for a specific species, either at atmospheric pressure or under vacuum. The steam is turned off as soon as the maximum temperature is reached, and the cylinder is then quickly emptied of preservative. A vacuum equal to or stronger than –75 kPa (562.5 mmHg) is created promptly and maintained until the material can be removed free of dripping preservative.

DCOI

DCOI concentrate and treating solutions contain DCOI, resin/wax, emulsifier/surfactant, and solvent(s). Typical treating solution strengths employed are up to 3% DCOI active ingredient, depending on products treated. DCOI is used in the preservation of utility poles with retentions in the range of 1.6 to 3.2 kg/m³. 

DCOI is generally purchased as solid blocks, usually weighing 907 kg (2,000 lbs). Petroleum oils used as carriers for DCOI are delivered by bulk truck or rail tanker and are stored in exterior tanks. The blocks are dissolved by placing them in the treatment cylinder or into a mix tank and recirculating heated oil between the cylinder or mix tank and the bulk storage tanks. A concentrated solution may first be prepared. The concentrate is then diluted to working concentration by recirculation between the cylinder or mix tank and the bulk storage tank. 

The preservative is applied in a pressure cylinder, which may be up to 45 m long and 2 m in diameter. Specific treatment parameters (e.g., temperature, pressure, and duration) are dictated by the species of wood, the wood product, and the initial moisture content of the wood. Many of the operating parameters, preservative standards, and product quality characteristics (e.g. penetration and preservative retention) are defined by the CSA (once DCOI is approved for use as a wood preservative). 

After conditioning, an empty-cell treatment process is generally used to apply the oil-borne DCOI preservative. Following the drain cycle at the end of the pressure cycle, a vacuum is applied to encourage the removal of excess preservative and pressurized air from the wood cells. This process minimizes preservative “bleeding” from the treated product.  

Alternatively, an expansion bath or final steam cycle, followed by a vacuum, may be used to minimize surface exudations and long-term bleeding and to improve the surface cleanliness of the material. This expansion bath can be applied before removal of the preservative from the cylinder, by quickly reheating the oil surrounding the material to the maximum temperature permitted by the CSA Standard for a specific species, either at atmospheric pressure or under vacuum. The steam is turned off as soon as the maximum temperature is reached. The cylinder is then quickly emptied of preservative. A vacuum equal to, or stronger than -75 kPa (-22 in. Hg) is created promptly and maintained until the material can be removed free of dripping preservative.  

Substance releases, disposals, and transfers

Depending on the plant design and operational procedures, potential chemical discharges of NPRI reportable substances may occur to water, air and/or soil. The releases can vary in quantity and in state (e.g. liquid, solid or gas). Waste containing NPRI substances may also be generated and may be sent for disposal or recycling. 

Air emissions 

Creosote and DCOI components have measurable vapour pressures at ambient temperatures and, since solutions are heated for treatment and storage, there may be significant airborne emissions emitted to the environment at all stages of the process. 

Potential sources of air emissions include the following: 

• exhausts, mists, and vapours from kilns 
• exhausts, mists and vapours from tank vents and other oil delivery/storage operations
• mists and vapours from vacuum pump exhausts 
• mists and vapours from opening of retort cylinder doors and tank hatches 
• vapours from freshly treated charges 
• exhausts, mists and vapours from stabilization kiln or accelerated fixation process
• dust, sawdust, debris (Part 4 - CACs)
• dust from unpaved roads (Part 4 - CACs)
• releases from stationary combustion (Part 4 - CACs)

Liquid discharges 

Due to the toxicity and cost of the preservatives or process chemicals, ideally the facility should use closed loop treatment systems that contain, collect, and reuse the chemical mixture to the greatest possible extent. Oil-based preservatives are not chemically fixed in the wood, and they may be prone to liquid bleeding of preservative from stored treated wood.

Closed systems may include the following types of equipment: 

• paved or concrete containment surfaces  
• dyking of major process components including the cylinder and tanks  
• containment surfaces for chemical drips from treated wood in storage, stabilization/fixation, or drying areas (drip pads) 
• collection sumps to receive residual preservative cartridge filters to remove dust and wood debris from contaminated liquids entering the system 
• holding tanks for filtered solutions

Some liquid streams that may not be possible for re-use include the following:  

• condensates removed from the wood during conditioning or vacuum application 
• condenser cooling water 
• water released by the wood during the treatment cycle 
• wash waters  
• conditioning treatments such as Boultonizing or steaming pretreatments
• spills, overflows and leaks  
• stormwater runoff from unpaved or unroofed areas or yard soil contamination 
• spills from hose ruptures during the unloading of trucks 
• spills from piping failure 
• spills from damage of waste drum 
• drippage from lumber that was removed from the drip pad too soon

Solid wastes 

Solid waste generation at wood preservation facilities may include the following: 

• cartridge filters and traps 
• broken treated wood  
• sludge from:
  • tanks
  • sumps
  • fixation/stabilization chambers/kilns 
• pressure cylinders
• sludge from wastewater treatment processes (emulsions)
• contaminated soils 
• containers, wrappings, wood lath, stickers, and pallets 
• dust, sawdust, debris

Summary of wastes produced during wood preservation using oil-borne preservatives 

NPRI-listed substances may be discharged during various steps of the process, including: 

• oil delivery/storage:
  • liquid wastes from spills and drips
  • air emissions from vapours
• working solution tanks:
  • liquid wastes from spills and drips
  • air emissions from vapours
  • solid waste such as sludge
• pressure treatment:
  • liquid wastes from spills and drips
  • air emissions from vapours
  • solid waste such as sludge
  • chemicals are passed to a condenser
• drip pads:
  • liquid wastes from spills and leachate
  • air emissions from vapours
  • solid waste such as sludge
• treated wood storage:
  • liquid waste from leachate
  • air emissions from vapours

In addition: 

• chemicals from the pressure treatment step are passed through a condenser before being sent either to oil water separation
• spills, drips and leachate are collected and are also processed in an oil-water separator
• a portion of the output of oil-water separation is recycled back into the working solution tanks while the remainer is sent to wastewater treatment
• solid wastes (sludges) are disposed of in landfill

Facilities that meet the NPRI reporting criteria for Part 4 CACs should refer to the current version of the Guide for reporting to the NPRI and other reference documents to estimate emissions of CACs to air including the ECCC wood products operations calculator.

NPRI reportable substances

The following list comprises examples of substances that should be considered for reporting at oil-based (e.g., creosote, DCOI) wood preservation facilities. Refer to the Canada Gazette, Part I Notice for the year being reported for the specific reporting criteria for these substances in determining if reporting is necessary.

This Guide, together with the guidance documents published by NPRI for the year being reported, should be consulted by owners and operators of wood preservation treating facilities in reporting to the NPRI.

It is important to note the following:

If facilities meet the reporting criteria for other NPRI-listed substances not shown above, they are legally obligated to file an NPRI report on those substances to ECCC by the date specified in the Canada Gazette, Part I Notice for the year being reported.

Estimation methodologies to determine releases and transfers

For an oil-based treating facility, information requirements can be grouped into the following categories:

• air emissions
• wastewater
• remedial action 
• catastrophic events
• non-hazardous solid waste
• hazardous wastes

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. 

The following sample calculations use measurement units that are industry standards; reportable quantities must be converted to metric units specific to the reportable substance (e.g. Part 1A substances must be reported in tonnes). Refer to the NPRI reportable substance list for applicable reportable units.

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 as storage tanks and related handling releases. 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 device.

Facilities that meet the NPRI reporting criteria for Criteria Air Contaminants (CACs) should refer to the current version of the Guide for reporting to the NPRI and other reference documents to estimate emissions of CACs to air.

Please note the PAHs listed in Part 2 of the NPRI substance list have different NPRI reporting requirements when they result from facilities where wood preservation using creosote takes place compared to any other facility. Where wood preservation using creosote takes place, all releases, disposals, and transfers for recycling from all sources must be reported, regardless of the quantities or concentrations; the 50-kilogram reporting threshold that applies to other facilities does not apply to creosote wood preservation facilities.

Substance 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 (refer to the Guide for reporting to the NPRI for details on calculating stack parameters). When air monitoring results are not available, emissions may be estimated using emission factors or mass balance approaches.

Direct measurement

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 exit velocity is typically 1.8 m/s. 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:

Step 1: calculate the volumetric flow rate of the stack gas stream.

Step 2: correct the volumetric flow for moisture content in the 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:

Step 3: estimate annual stack emissions to air.

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

Where:

• 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)

Use of emission factors

The U.S. EPA has developed emission factors (PDF) for several PAHs for different creosote treating scenarios and for losses from freshly treated wood. Emission factors in kg/m³ and lb/ft³ of creosote wood preservation, with and without Boultonizing conditioning and surface emissions to air during storage (g/m²), are presented in the following tables. Note that no emission factors are available for PAHs in fugitive leaching losses in storage.

Standardized emission factors have not been developed for DCOI airborne emissions; however, a search of U.S. Air Permits does provide several emission factors for VOCs and naphthalene at specific facilities. Once DCOI has been approved and is in use, it is recommended that the most-current industry information be applied at the time of air release calculations.

Example 2 - calculating air releases of PAHs using emission factors

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

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

Example 3 - calculating air releases of PAHs from stored materials

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. These air emissions would be reported as fugitive releases if the railway ties are stored in open area and/or are not directly vented.

The total exposed area is from the top (8.5 ft x 30 ft or 255 ft²), two ends: (2 x 8.5 ft x 20 ft or 340 ft²) and two sides: (2 x 20 ft x 30 ft or 1,200 ft²) for a total surface area per stack of 1,795 ft² or a total surface area of 90 x 1,795 or 161,550 ft². 

The estimated emissions to air are as follows:

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

Storage tanks

There are two types of activities that cause emissions from tanks and vessels at wood preserving facilities. The first activity is the receipt, storage, and mixing of oils and chemicals in tanks to be used for wood preserving. The second activity is the transfer of oils, air, steam, and wood to and from the wood preserving tanks and vessels during the wood preserving process. Additional guidance for estimating atmospheric emissions from storage tanks can be found in the NPRI guidance on estimating atmospheric emissions from storage tanks.

Emissions of NPRI substances from the tanks used to store or mix the solutions used in wood treating operations may be broken into working losses and breathing losses. As tanks are filled or refilled, a volume of air equal to the volume of the incoming liquid is expelled to the atmosphere. This is referred to as a working loss. Breathing losses occur in an unheated tank as a result of diurnal temperature changes that cause the volume of the air in the void space of the tank to change, thereby causing a release. Breathing losses are generally independent of the volume of the liquid throughput. Releases from both types of losses are to be reported under “storage tanks and related handling releases”. 

Working losses

The working losses of one component of a mixture or solution from a fixed roof tank or vessel may be calculated by the following equation (U.S. EPA 2020 equation 1-37 (PDF)):

Where: 

• L_w = working loss of compound A (kg/year)
• V_Q = net working loss throughput (L/year)
• K_N = working loss turnover (saturation) factor, dimensionless, assumed to = 1 
• K_P = working loss product factor 
  • K_p = 1 for organic liquids other than crude oils
• K_B = vent setting correction factor, dimensionless 
  • K_B = 1 for all organic liquids other than crude oil 
• W_V = vapor density (kg/L)

Where: 

• MW_V = molecular weight of compound A (g/mol)
• P_VA = vapour pressure at average daily liquid surface temperature (psia)
  • calculated via the Antoine equation – see example below
• R = ideal gas constant (8.314472 L×kPa/K×mol)
• T_V = temperature (K)

Breathing losses

The breathing (standing) losses from a fixed roof tank or vessel may be calculated by the following equation (U.S. EPA 2020 equation 1-2 (PDF)):

Where: 

• L_S = breathing (standing) loss (kg/year)
• V_V = vapour space volume (m³)
• W_V = vapour density (kg/m³)
• K_E = vapour space expansion factor (day-1)
• K_S = vented vapor saturation factor (dimensionless) 
• 365 = constant, the number of daily events in a year (days/year)

To calculate V_V = vapour space volume (m³), use: 

Where: 

• D = diameter (m)
• H_VO = vapour space outage (m)

To calculate H_VO = vapour space outage (m), use: 

Where: 

• H_S = tank shell height (m)
• H_L = liquid height (m), typically assumed to be at the half-full level, unless known to be maintained at some other level
• H_RO = roof outage (m)

Find K_s= vented vapor saturation factor using: 

Example 4 - storage tank air emissions

A solution of DCOI is stored in a 10,000 L (10 m³) fixed roof tank at 80°C (353.15 K). The tank has a diameter of 2.25 m and a height of 2.5 m. The working solution used to dissolve the DCOI is a diesel fuel containing 2% by weight of naphthalene. The tank was filled and emptied a total of 200 times a year.

The working losses from filling and emptying the tank are calculated as follows:

Naphthalene working loss air emission is 1.05 kg/year. 

The vapour pressure of Naphthalene can be calculated using the Antoine equation ((log P = A – B(T+C)):

The breathing losses from the flat roofed tank are calculated as follows:

Where: 

• V_V = vapour space volume (m³)
• W_V = vapour density (kg/m³)
• K_E = vapour space expansion factor (day-1)
  • assumed to be 0.04 for this example
  • refer to U.S. EPA 2020 (PDF) on how to calculate this value
• K_S = vented vapor saturation factor (dimensionless)
  • assumed to be 0 for this example
  • refer to U.S. EPA 2020 (PDF) on how to calculate this value
• 365 = constant, the number of daily events in a year (days/year)

Naphthalene breathing loss air emission is 1.25 kg/year. 

Wastewater discharges

Direct measurement 

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:

The amount of anthracene discharged is:

The amount of benzo(a)pyrene discharged is:

Note that wastewater discharged directly to surface waters must be reported under the release to water category: direct discharge. If the wastewater is discharged via a local sewer that ends in a municipal treatment plant, then the quantities of substances in the wastewater must be reported under off-site transfers for treatment prior to final disposal and the municipal treatment plant receiving this discharge must be specified. 

Releases and transfers caused by remedial action

Remedial action can include a number of activities including: 

• disposal of contaminated soils
• recovery and treatment of contaminated groundwater
• 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 of contaminants released is a function of the concentration and volume of water discharge. Remediation of contaminated soil may result in the off-site transfer of contaminated soil. Transfer quantities are determined by applying the results from soil sample analysis of the relevant substances in the samples to the total amount of soil involved.

Example 1

Groundwater in the amount of 250,000 US 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:

This results in releases of 0.142 kg, 0.094 kg, and 0.028 kg (142 g, 94 g, and 28 g) per year of naphthalene, pyrene, and benzo(a)pyrene, respectively.

Note that wastewater discharged directly to surface waters must be reported under the “release to water: direct discharge” category. If the wastewater is discharged via a local sewer that ends in a municipal treatment plant, then the quantities of substances in the wastewater must be reported under “off-site transfers for treatment prior to final disposal” and the municipal treatment plant receiving this discharge must be specified. 

Example 2

Twenty thousand pounds (9,090 kg) of contaminated soil were removed and transferred off-site for disposal 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 transfers off-site for disposal in kilograms can be calculated as follows:

The destination(s) of the off-site transfers for disposal must be reported along with the quantities. 

Release due to catastrophic events

These involve spills or accidental releases outside the containment. The amount of the release is a function of concentration and volume released minus the quantities that are recovered.

Note that the portion of the spill not cleaned up must be reported as a release the year it occurred. Further migration between media does not need to be reported.

For example, if 100 L of an NPRI substance is spilled and 80 L is recovered, a release of 20 L must be reported. If the 80 L is returned to the process, no further action is required. However, if it is sent off-site for treatment or disposal, it must be reported accordingly. 

Example 1

Creosote in the amount of 200 US gallons (density of 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 total release of NPRI-listed substances depends on the concentration found in the solution.

Step 1: calculate the total mass of the spill (kg).

Step 2: determine the concentration (C) of components in the creosote (from manufacturer).

Step 3: multiply the percentage concentration of substance by the determined total mass of the spill, as shown in Table 13 below.

Since the spill was fully cleaned up, these quantities would be reported as off-site transfers to landfill.

Transfers in solid hazardous waste

For solid hazardous waste, a determination of the total quantity of waste and the concentration of the NPRI substances 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 NPRI substances in the waste. This analysis should then be used to determine the actual transfer to landfill.

Example

A facility sent ten 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[b]fluoranthene (2 mg/kg)
• pyrene (34 mg/kg)
• benzo[a]pyrene (3.5 mg/kg)

Therefore, the actual quantities in the waste are as follows:

The facility had additional manifests for the soils disposed of during remedial action. However, these quantities have already been accounted for in the transfers for disposal as a result of remedial action.

Summary of NPRI reporting steps - oil-based wood preservation facilities

First, gather information on NPRI substances manufactured processed or otherwise used and on sources of releases, disposals, and transfers.

Then, determine reporting thresholds for NPRI reportable substances from the Canada Gazette, Part I Notice for the year being reported. For more information about NPRI reporting requirements, refer to the Guide for reporting to the NPRI.

Estimates of the quantity of a substance that is manufactured, processed, or otherwise used, and of the quantity that is released, disposed of or transferred for recycling, may be based on one of the following methods:

• continuous emission monitoring (reporting system code M1) 
• predictive emission monitoring (M2) 
• source testing (M3)
• remote quantification (RQ)
• mass balance (C)
• site-specific emission factors (E1)
• published emission factors (E2)
• speciation profile (SP)
• engineering estimates (O)

Additional resources

• Canadian Council of Ministers of the Environment (CCME). 2024. Canadian Environmental Quality Guidelines 
• Environment and Climate Change Canada (ECCC). 2017. Guidance for Wood Preservation Facilities to the National Pollutant Release Inventory. (Available upon request: inrp-npri@ec.gc.ca) 
• Environment and Climate Change Canada (ECCC). 2004. Industrial Treated Wood Users Guidance Document, Version 1 – September 2004. Prepared by Wood Preservation Strategic Options Process’ Guideline Development Working Group.

Acknowledgements

Prepared by: BluMetric Environmental Inc.

In collaboration with: Wood Preservation Canada