Life Cycle Assessment
Procedures and Findings
for
ACQ-Treated Lumber
Prepared for
Prepared by
Primary Authors
Christopher A. Bolin
Stephen T. Smith
November 2009
Revised June 2010
Final Issue March 2011
Copyright 2011
Treated Wood Council
Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
ADMINISTRATIVE INFORMATION
This life cycle assessment (LCA) of Alkaline Copper Quaternary (ACQ)-Treated Lumber has
been prepared for:
Treated Wood Council
1111 19th St., NW, Suite 800
Washington, DC 20036
This LCA of ACQ-Treated Lumber has been prepared by:
AquAeTer, Inc.
7430 East Caley Avenue, Suite 310
Centennial, Colorado 80111Primary authors: Christopher A. Bolin and Stephen T. Smith
This study and report was completed on November 3, 2009. The report was revised on June 28,
2010. The final was issued on March 10, 2011 following Journal of Cleaner Production
acceptance for publication.
ACKNOWLEDGEMENTS
This LCA study would not have been possible without the support of several key individuals and
organizations. Sincere thanks are given to the following individuals and organizations for their
time and contributions to this study:
Jeff Miller, President and Executive Director, Treated Wood Council, Inc., for the promotion of
this project.
Members of the Treated Wood Council for the financial support and promotion of this project.
Participating companies and individual treating facility respondents from the treated wood
industry for their time and effort in providing the data needed for this project.
James H. Clarke, PhD. Professor of Civil and Environmental Engineering. Vanderbilt
University, Department of Earth and Environmental Sciences, for his review and comments.
Paul Cooper, PhD. Professor of Wood Science and Technology.
Department of Forestry Science, for his review and comments.
University of Toronto,
Mary Ann Curran, PhD. Life Cycle Assessment Research Program Manager. USEPA, Office of
Research and Development, for her review and comments.
Mike H. Freeman. Independent Consultant, Wood Scientist, and Chemist to the Wood
Preservation Industry, for his review and comments.
Craig R. McIntyre, PhD. Independent Consultant, Wood Scientist, and Chemist to the Wood
Preservation Industry. McIntyre Associates, Inc.
Yurika Nishioka, PhD. Research Fellow, Harvard School of Public Health & Consultant,
Sylvatica Life Cycle Assessment Consulting, for her review and comments.
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TABLE OF CONTENTS
REPORT ORGANIZATION
ADMINISTRATIVE INFORMATION ...................................................................................... i
TABLE OF CONTENTS ........................................................................................................... ii
INDEX OF TABLES ..................................................................................................................v
INDEX OF FIGURES .................................................................................................................v
LIST OF APPENDICES ........................................................................................................... vi
EXECUTIVE SUMMARY .................................................................................................... ES-1
1. INTRODUCTION................................................................................................................ 1-1
1.1
BACKGROUND ....................................................................................................... 1-1
1.2
PURPOSE .................................................................................................................. 1-1
1.3
STRUCTURE AND ISO CONFORMITY ................................................................ 1-2
1.4
DEFINITION OF THE PRODUCTS ........................................................................ 1-2
2. GOAL AND SCOPE ............................................................................................................ 2-1
3. LIFE CYCLE INVENTORY .............................................................................................. 3-1
3.1
METHODS DISCUSSION........................................................................................ 3-1
3.1.1 Choice of Spreadsheet.......................................................................................... 3-1
3.1.2 Primary and Secondary Data ............................................................................... 3-1
3.1.3 Format of the LCI Spreadsheet ............................................................................ 3-2
3.1.4 Use of NREL LCI Modules ................................................................................. 3-2
3.1.5 Inputs from Nature or from Technosphere .......................................................... 3-3
3.1.6 Electricity and Supporting Processes ................................................................... 3-3
3.1.7 Distributions......................................................................................................... 3-4
4. LIFE CYCLE INVENTORY ANALYSIS......................................................................... 4-1
4.1
INTRODUCTION TO ACQ LIFE CYCLE INVENTORY ANALYSIS ................. 4-1
4.2
ACQ-TREATED LUMBER LIFE CYCLE INVENTORY ...................................... 4-1
4.2.1 ACQ Introduction ................................................................................................ 4-1
4.2.2 Lumber Production Stage Prior to Wood Treatment (LC Stage 1) ..................... 4-2
4.2.3 ACQ Production (LC Stage 2) ............................................................................. 4-3
4.2.4 ACQ Lumber Treatment Stage (LC Stage 2) ...................................................... 4-5
4.2.5 ACQ-Treated Lumber as Decking - Use Life Stage (LC Stage 3) ...................... 4-9
4.2.6 Landfill Stage (LC Stage 4) ............................................................................... 4-11
4.3
ACQ INVENTORY TOTALS ................................................................................ 4-11
4.4
WOOD PLASTIC COMPOSITE INVENTORY .................................................... 4-12
5. IMPACT ASSESSMENT .................................................................................................... 5-1
5.1
GENERAL ................................................................................................................. 5-1
5.2
IMPACT INDICATORS ........................................................................................... 5-1
5.3
IMPACT INDICATOR DEFINITION AND CLASSIFICATION ........................... 5-3
5.3.1 Greenhouse Gas (GHG) Emissions ..................................................................... 5-3
5.3.2 Fossil Fuel Usage ................................................................................................. 5-3
5.3.3 Releases to Air Potentially Resulting in Acid Rain (Acidification) .................... 5-3
5.3.4 Water Use............................................................................................................. 5-3
5.3.5 Ecotoxicity ........................................................................................................... 5-4
5.3.6 Releases to Air Potentially Resulting in Eutrophication...................................... 5-4
5.3.7 Releases to Air Potentially Resulting in Smog Formation .................................. 5-4
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5.3.8 Impact Indicators Considered But Not Presented ................................................ 5-4
5.4
TOTAL ENERGY ..................................................................................................... 5-7
5.5
CHARACTERIZATION ........................................................................................... 5-7
5.6
NORMALIZATION .................................................................................................. 5-8
5.6.1 Product Normalization ......................................................................................... 5-8
5.6.2 National Normalization of Impact Indicators ...................................................... 5-8
5.7
ACQ IMPACT ASSESSMENT ................................................................................ 5-9
5.7.1 Greenhouse Gas Emissions .................................................................................. 5-9
5.7.2 Fossil Fuel Usage ................................................................................................. 5-9
5.7.3 Emissions Potentially Resulting in Acid Rain (Acidification) ............................ 5-9
5.7.4 Water Use........................................................................................................... 5-10
5.7.5 Releases to Air Potentially Resulting in Ecological Toxicity............................ 5-10
5.7.6 Emissions with Potential to Impact Eutrophication ........................................... 5-10
5.7.7 Emissions with Potential to Form Smog............................................................ 5-10
5.8
ACQ-TREATED LUMBER TOTAL ENERGY IMPACT .................................... 5-10
5.9
WOOD PLASTIC COMPOSITE IMPACT ASSESSMENT ................................. 5-10
5.10 DATA QUALITY ANALYSIS ............................................................................... 5-11
5.10.1 Gravity Analysis ................................................................................................ 5-11
5.10.2 Uncertainty Analysis .......................................................................................... 5-12
5.10.3 Sensitivity Analysis ........................................................................................... 5-14
5.11 COMPARISON OF ACQ-TREATED LUMBER AND WOOD PLASTIC
COMPOSITE LUMBER ......................................................................................... 5-16
5.11.1 Discussion .......................................................................................................... 5-16
5.11.2 Greenhouse Gas Emissions ................................................................................ 5-17
5.11.3 Fossil Fuel Usage ............................................................................................... 5-17
5.11.4 Water Usage ....................................................................................................... 5-17
5.11.5 Releases to Air Potentially Resulting in Acid Rain (Acidification) .................. 5-17
5.11.6 Releases to Air Potentially Resulting in Ecological Toxicity............................ 5-17
5.11.7 Releases to Air Potentially Resulting in Eutrophication.................................... 5-18
5.11.8 Releases to Air Potentially Resulting in Smog .................................................. 5-18
5.11.9 Total Energy Input ............................................................................................. 5-18
5.11.10
Comparisons Conclusion ............................................................................. 5-18
6. INTERPRETATIONS ......................................................................................................... 6-1
6.1
IDENTIFICATION OF SIGNIFICANT ISSUES ..................................................... 6-1
6.1.1 Precision and Confidence .................................................................................... 6-1
6.1.2 Cradle-to-Grave Scope......................................................................................... 6-1
6.1.3 Extended Time Frame .......................................................................................... 6-2
6.1.4 Carbon Accounting .............................................................................................. 6-2
6.1.5 Use of TRACI for Impact Indicators ................................................................... 6-4
6.1.6 Human Health and Ecological Toxicity Indicators .............................................. 6-4
6.1.7 U.S. Average Electricity ...................................................................................... 6-4
6.1.8 Recycled Content ................................................................................................. 6-4
6.1.9 Recycle and Disposal Assumptions ..................................................................... 6-5
6.1.10 Water Use............................................................................................................. 6-5
6.1.11 Comparative Analysis .......................................................................................... 6-5
6.2
EVALUATION.......................................................................................................... 6-5
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6.2.1 Completeness Check ............................................................................................ 6-5
6.2.2 Sensitivity Check ................................................................................................. 6-6
6.2.3 Consistency Check ............................................................................................... 6-6
6.3
CONCLUSIONS, LIMITATIONS, AND ENVIRONMENTAL IMPROVEMENT
OPPORTUNITIES ..................................................................................................... 6-6
6.3.1 Conclusions .......................................................................................................... 6-6
6.3.2 Limitations ........................................................................................................... 6-8
6.3.3 Environmental Improvement Opportunities ........................................................ 6-8
7. CRITICAL REVIEW .......................................................................................................... 7-1
7.1
INTERNAL REVIEW ............................................................................................... 7-1
7.2
INDEPENDENT EXTERNAL REVIEW ................................................................. 7-1
7.3
CRITICAL REVIEW REPORTS .............................................................................. 7-2
8. REFERENCES ..................................................................................................................... 8-1
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INDEX OF TABLES
Table ES-1
Table 4-1
Table 4-2
Table 5-1
Table 5-2
Table 5-3
Table 5-4
Table 5-5
Table 5-6
Table 5-7
ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values Normalized to U.S. Average Family ..................................... ES-4
ACQ Treater Survey Results Summary ............................................................. 4-16
ACQ-Treated Lumber and WPC Life Cycle Inventory Summary .................... 4-17
Impact Indicators, Characterization Models, and Impact Categories .................. 5-2
Summary of Total Energy and Impact Indicator Totals at Life Cycle
Stages for ACQ-Treated Lumber (per Mbf) ...................................................... 5-19
Summary of Total Energy and Impact Indicator Totals at Life Cycle
Stages for ACQ-Treated Lumber (per year of use per average deck) ............... 5-19
Summary of Total Energy and Impact Indicator Totals at Life Cycle
Stages for WPC Decking (per year of use and per average deck) ..................... 5-20
Normalized Cradle-to-Grave Total Energy Use and Impacts of an Average
Deck of ACQ-Treated Lumber and WPC Compared to U.S. Average
Values (per year per family) .............................................................................. 5-20
ACQ-Treated Lumber Comparison to Wood Plastic Composite
(Normalized to ACQ-Treated Lumber in a Landfill) ........................................ 5-21
Sources of Energy by Product and Life Stage ................................................... 5-21
INDEX OF FIGURES
Figure ES-1
Figure ES-2
Figure 2-1
Figure 4-1
Figure 5-1
Figure 5-2
Figure 5-3
Figure 5-4
Figure 5-5
Figure 6-1
Relative Percentage of Impact by Stage During Life Cycle of ACQTreated Lumber ................................................................................................. ES-3
ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values (Values Normalized to ACQ-Treated Lumber Cradle-toGrave = 1) ......................................................................................................... ES-3
Life Cycle Diagram of ACQ-Treated Lumber..................................................... 2-3
Map of U.S. Regions ............................................................................................ 4-2
Relative Percentage of Total Energy and Impacts by Stage During the Life
Cycle of ACQ-Treated Lumber ......................................................................... 5-22
ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values (Values Normalized to ACQ-Treated Lumber Cradle-toGrave = 1) .......................................................................................................... 5-23
ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values Normalized to U.S. Average Family ...................................... 5-23
Sensitivity Analysis: 100 Percent Recycled HDPE .......................................... 5-24
Sensitivity Analysis: 100 Percent Virgin HDPE .............................................. 5-24
Life Cycle Carbon Balance of ACQ-Treated Lumber ......................................... 6-3
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LIST OF APPENDICES
APPENDIX 1
Project Goal and Scope
APPENDIX 2
Example of the Treater Survey
APPENDIX 3
U.S. Electric Energy Grid Life Cycle Inventory Calculations
APPENDIX 4
Life Cycle Inventory Calculations
APPENDIX 5
Life Cycle Inventory Spreadsheet
APPENDIX 6
Assumptions
APPENDIX 7
Sensitivity Analysis Results
APPENDIX 8
Critical Review Reports and Responses
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EXECUTIVE SUMMARY
Alkaline copper quaternary (ACQ) preservative is commonly used for wood product applications
requiring decay and insect attack protection. Sawn lumber preserved with ACQ can be used in
locations ranging from interior dry uses to locations with permanent ground contact, exposed to
severe environments, and extreme decay potential. Typical uses include decking, fencing, and
various lumber applications. This life cycle assessment (LCA) addresses ACQ preserved lumber
used for residential deck surface applications. The LCA was commissioned by the Treated
Wood Council (TWC), which represents the national interests of the wood preserving industry.
ACQ is a wood preservative standardized by the American Wood Protection Association
(AWPA) utilizing copper and quaternary ammonium compound (quat) as active ingredients in a
water solution. ACQ preservative was chosen to provide a benchmark for comparison and as a
representative preservative system for treated wood decking material.
This LCA has been completed in a manner as limited by the final Goal and Scope and consistent
with the principles and guidance in ISO 14040 and 14044 and includes the four phases of an
LCA; 1) Goal and scope definition, 2) Inventory analysis, 3) Impact assessment, and 4)
Interpretation.
Goal and Scope Definition
The Goal and Scope was developed in cooperation with the TWC membership and internal and
independent external reviewers and was revised iteratively as the LCA progressed. The goal is
to identify the environmental impacts attributable to ACQ-treated lumber decking, identify
opportunities to lessen impacts, to complete an LCA of wood plastic composite (WPC) decking
(the primary alternative product), and make comparisons of the product impacts. The scope
covers the full cradle-to-grave life cycle of ACQ-Treated Lumber and WPC decking.
General Conclusions
•
If a family of three people installs an average deck using ACQ-treated lumber, their
“footprint” for energy, greenhouse gas (GHG), fossil fuel, acidification, potential smog,
ecological toxicity, and eutrophication forming air releases generally would be
considered insignificant at less than one-tenth of a percent over the life of the deck;
•
If the same deck was constructed of WPC, the family “footprint” for energy, GHG, fossil
fuel use, acidification, ecological toxicity, and smog would be low, but significantly
greater than ACQ-treated lumber and about equal to ACQ for eutrophication; and
•
WPC requires approximately 14 times more fossil fuel and 8.5 times more total energy
and results in emissions with potential to cause approximately three times more GHG,
four times more acid rain, over two times more smog, approximately two times more
ecological toxicity, and equal the eutrophication, when compared to ACQ-treated lumber.
Inventory Analysis
The cradle-to-grave life cycle inventory (LCI) was developed for life cycle stages of ACQtreated lumber including seedling production, planting and growth of trees, harvest of logs,
milling of logs to dimensional lumber and drying of lumber, production of ACQ preservative,
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pressure treatment of lumber with ACQ preservative, use of ACQ-treated lumber in decks
(including maintenance of decking), demolition at the end of the useful life, disposal in landfills,
and final fate in the landfill. A cradle-to-grave LCI also was developed for WPC to support
product comparisons. LCI flows were first calculated on a per 1,000 board feet (Mbf) basis and
then normalized to an average deck size of 320 square feet of deck surface per year of use life
(average deck per year).
The LCI was developed using publicly available data for most life cycle stages and a survey of
wood preserving facilities for the preservative application stage. The primary source of public
data was the National Renewable Energy Laboratory (NREL) LCI Database. The LCI was
assembled in spreadsheet format and did not utilize proprietary software. Inclusion of the
spreadsheet files as a part of the complete LCA report enhances the transparency of this overall
LCA process.
Impact Assessment
Impact indicators are assessed for ACQ-treated lumber and WPC decking based on the input and
output flows determined in the LCI phase. The impact indicators were chosen to be applicable to
the products evaluated and reflect current environmental concerns. The following indicators
were evaluated:
•
•
•
•
•
•
•
GHG emissions;
Fossil fuel usage;
Amount of water used or consumed;
Releases to air potentially resulting in acid rain (acidification);
Releases to air with potential ecological toxicity;
Releases to air potentially resulting in smog, and
Releases to air potentially resulting in eutrophication of water bodies.
Impact indicator values for releases of GHG emissions and releases potentially related to acid
rain, ecological toxicity, smog, and eutrophication use potency factors from the USEPA’s “Tool
for Reduction and Assessment of Chemical and Other Environmental Impacts” (TRACI) model
were used.
While not an impact indicator, total input energy is tracked as a relative measure of the resources
required for the cradle-to-grave life cycle. This includes renewable and biogenic energy sources,
such as solar, wind, or wood fuel, as well as fossil fuel sources.
Values for each impact indicator were calculated for each process and at each life cycle stage.
Values were normalized to units of impact indicator value per average deck per year of estimated
use. Relative to the cradle-to-grave life cycle impacts of ACQ-treated lumber (which are
insignificant in total): (1) the lumber production stage prior to treatment is a sizable contributor
to the fossil fuel use, water use, acidification, smog, ecological toxicity, and eutrophication
impact indicators; (2) the treating stage is a sizable contributor to the fossil fuel use, water use,
acid rain, smog, and eutrophication impact indicators; (3) the use stage is a sizable contributor to
the fossil fuel use, acid rain, and eutrophication impact indicators; and (4) the landfill stage is a
sizable contributor to the GHG, fossil fuel use, acid rain, ecological toxicity, and smog impact
indicators. Additional information regarding ACQ-treated lumber decking impact indicator
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ACQ-Treated Lumber
relative percentages, by life cycle stage (cradle-to-grave life cycle impact equaling 100 percent),
are shown on Figure ES-1.
Figure ES-1 Relative Percentage of Impact by Stage During Life Cycle of ACQ-Treated
Lumber
Untreated, dried lumber, at mill
ACQ Treating Stage
ACQ-Treated Lumber Use Stage
0%
0%
ACQ-Treated Lumber Disposal Stage
3%
16%
20%
29%
30%
31%
39%
8%
13%
16%
77%
15%
53%
6%
3%
61%
26%
61%
22%
31%
26%
23%
20%
17%
Eutrophication
Smog
Acid Rain
Water Use
Fossil Fuel Use
Greenhouse
Gases
Total Energy
Value
8%
6%
8%
18%
Ecological
Impact
61%
52%
The main alternate product to ACQ-treated lumber is WPC decking. The impact indicator
values for ACQ-treated lumber and WPC were normalized so that the cradle-to-grave life cycle
value for ACQ-treated lumber is 1.0 and all other values are a fraction of 1.0 if smaller or a
multiple of 1.0 if greater. The normalized comparative analysis is shown on Figure ES-2.
Figure ES-2 ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values (Values Normalized to ACQ-Treated Lumber Cradle-to-Grave = 1)
16.0
14.0
12.0
Normalized Value
10.0
8.0
6.0
4.0
2.0
0.0
Total Energy
Value
Greenhouse
Gases
Fossil Fuel Use
Water Use
Acid Rain
Smog
Eutrophication
Ecological
Impact
ACQ Lumber
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
WPC Decking
8.5
2.9
14
2.8
4.3
2.6
1.1
1.7
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The normalized values are applicable for product comparison, but do little to indicate if potential
impacts may be significant. To better answer the question, “Do these impact indicator values
matter?” values also were normalized to better indicate magnitude by calculating the fraction of
the annual impact for an average deck compared to the “average” annual impact of a U.S. family.
Table ES-1 shows cradle-to-grave life cycle annual impact indicator values for 320 square feet of
ACQ decking and WPC decking compared to average annual impacts for a U.S. family of three.
Such a deck, measuring 16 by 20-feet, is typical for a U.S. family.
Table ES-1 ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values Normalized to U.S. Average Family
Product
ACQ-treated lumber
WPC
US Family Average
Total
Energy
Value
Greenhouse
Gas
Emissions
Fossil
Fuel
Use
0.040%
0.34%
100%
0.074%
0.21%
100%
0.028%
0.39%
100%
Water Use
Acid Rain
Potential
Smog
Potential
Eutrophication
Potential
Ecological
Impact
0.00091%
0.0025%
100%
0.049%
0.21%
100%
0.024%
0.063%
100%
0.039%
0.044%
100%
0.053%
0.09%
100%
Readers should keep in mind that the LCA process is not exact science. Uncertainty is
introduced by the broad scope, variability among producers and products, on-going changes in
technology, limited data on key processes, and the need to make assumptions. Calculated values
are accurate for the intended use in this LCA.
Interpretation
A person considering what material to use for decking should view the impact indicators, as
presented in this LCA, as some of the many characteristics of the products. Other characteristics
include, for example, appropriateness for the intended use, purchase price, ease of installation,
proven performance, aesthetics, ease of disposal, and worker acceptance. Using the impact
indicators in the impact assessment, comparisons of the results for ACQ-treated lumber and
WPC decking support the following conclusions:
•
Greenhouse gas emissions are approximately three times more for WPC than for ACQtreated lumber. For ACQ, the average deck accounts for 0.074 percent of a family’s
average annual GHG impact and for WPC, the average deck accounts for 0.21 percent of
a family’s average annual GHG impact.
•
WPC decking requires the use of approximately 14 times more fossil fuel than ACQtreated lumber decking. The average ACQ deck accounts for 0.028 percent of a family’s
average annual fossil fuel use and for WPC, the average deck accounts for 0.39 percent
of a family’s annual fossil fuel use.
•
The total energy use value (including fossil fuel use, biogenic, and renewable resources)
of WPC is approximately 8.5 times more than for an ACQ-treated lumber deck. The
family total energy use “footprint” for an average deck is approximately 0.04% for the
ACQ deck and 0.5% for the WPC deck. Of the total energy approximately 40% is from
biomass and 60% is from fossil fuel.
•
The water use impact indicators are of similar magnitude and insignificant to a family’s
water use “footprint.”
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•
The acid rain impact indicator is approximately four times more for WPC than for ACQtreated lumber decking. The average ACQ deck accounts for 0.049 percent of a family’s
average annual acidification impact and for WPC, the average deck accounts for 0.21
percent of a family’s annual acidification impact.
•
The smog impact indicator is over two times more for WPC than for ACQ-treated lumber
decking. The average ACQ deck accounts for 0.024 percent of a family’s average annual
smog impact and for WPC, the average deck accounts for 0.063 percent.
•
Emissions with potential ecological toxicity are 1.7 times greater for WPC than for ACQtreated lumber decking. The average ACQ deck accounts for 0.053 percent of a family’s
average annual smog impact and for WPC, the average deck accounts for 0.089 percent.
•
The eutrophication indicator is approximately the same for ACQ-treated lumber and
WPC decking. The average ACQ deck or WPC deck accounts for 0.04 percent of a
family’s average annual eutrophication impact.
•
WPC is manufactured using HDPE that ranges from 100% virgin plastic to 100% postconsumer recycled plastic. WPC was modeled, in this LCA, as 50 percent wood fiber, 25
percent recycled HDPE, and 25 percent virgin HDPE. Sensitivity analysis was used to
evaluate impact indicators for both 100 percent recycled HDPE content and 100 percent
virgin HDPE content and results in significant variation in impact indicators for fossil
fuel use and total energy, acidification, and water use. However, even with the
significant reduction of impact indicator values for 100 percent recycled HDPE, impact
indicators for WPC remain greater than for ACQ-treated lumber.
The impact indicator values stated in this LCA are intended to provide generalized indications of
potential environmentally-related releases and to support the comparison of ACQ-treated lumber
to WPC decking. The results are for the U.S. average market for these products. Results for
individual producers or specific products may vary from these values, as will wood products
treated with other preservatives.
The carbon embodied in wood products, such as decking, may be stored for decades while the
product is in use. Temporary storage of carbon in the wood product reduces atmospheric levels
of CO2. However, this LCA does not provide credit for temporary storage and accounts for all
carbon removals from and emissions to the atmosphere without regard for time.
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1.
1.1
INTRODUCTION
BACKGROUND
The use of wood products is a defining aspect of humanity. People have used wood to make
tools, weapons, homes, and, of course, fire since before recorded history. Some early discoveries
related to wood preservation include fire-treating stakes to create harder, more durable points on
spears or charring fence posts to retard decay. People also discovered that some wood species,
such as redwood, last longer than others in harsh environments.
Chemical preservation of wood by industrial technology is a relatively recent development.
Treatment of railroad ties with creosote began in the late 1800s and quickly became the standard
because of the significant improvement in wood tie life that the treatment provided. Chromated
copper arsenate (CCA) was introduced in the 1930s and subsequently adopted throughout the
United States for exterior and marine uses.
Over the years, industry has consistently modified its formula for wood preservation in order to
meet consumer preferences. In the early 2000s, copper-based water-borne preservatives such as
alkaline copper quaternary (ACQ) and copper azoles became popular. Other new preservative
formulations also are entering the market, including micronized copper formulations and
formulations utilizing carbon-based biocides.
Pressure treating of wood products is done at approximately 400 facilities in the U.S., with
roughly 350 facilities using some type of waterborne treatment (Miller 2009). Gross sales for the
wood preserving industry were estimated at $4.5 billion in 2007, with employment provided for
14,800 people (Vlosky 2009).
1.2
PURPOSE
In 2008, the Treated Wood Council (TWC) contracted with AquAeTer, Inc. to conduct a Life
Cycle Assessment (LCA) of ACQ-Treated Lumber including an LCA of wood plastic composite
(WPC) decking for comparison. The purpose of the LCA is to quantitatively evaluate
environmental impacts associated with the national production, use, and disposal of ACQ-treated
lumber and to compare the ACQ-treated lumber LCA results to WPC. The intended audiences
for the LCA include: 1) members of the TWC; 2) building officials; 3) government regulators;
4) “green building” advocates; 5) life cycle inventory databases for building products; and 6) end
product consumers, including homeowners.
The LCA is intended to answer the following questions:
•
What are the environmental impacts resulting from the seedling production, growth,
harvest, manufacture, use, and final disposal of ACQ-treated lumber?
•
What are the opportunities to reduce the impacts?
•
How do the environmental impacts of ACQ-treated lumber compare to those of WPC, the
primary alternative decking product in the market?
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1.3
STRUCTURE AND ISO CONFORMITY
This LCA is conducted and presented in a manner as limited by the final Goal and Scope and
consistent with the principles and guidance provided by the International Organization for
Standardization (ISO) in standards ISO 14040:2006, Environmental Management -- Life Cycle
Assessment -- Principles and Framework and ISO 14044:2006, Environmental Management –
Life Cycle Assessment – Requirements and Guidelines.
1.4
DEFINITION OF THE PRODUCTS
The product of primary focus in the LCA is ACQ Type D-treated Southeastern species
dimensional lumber, treated for above-ground, exterior exposure according to the American
Wood Protection Association (AWPA) standards (2010) for use category UC-3B, with retention
of 0.15 pounds per cubic foot (pcf), intended for outdoor residential decks. The lumber provides
structural strength and a suitable surface for decks and rails. The reasons to replace decks
commonly are associated with aesthetics well before safety concerns (deck failure). An average
assumption of 10 years is used in this LCA, acknowledging that safe service life could be much
longer. Deck sealer (water-based) is assumed to be applied one time during the deck life. At the
end of use, decks were assumed to be demolished and 100 percent of ACQ-treated lumber
disposed in a solid waste landfill, meeting current Subtitle D (non-hazardous) landfill
requirements. Landfills for construction and demolition (C&D) waste and municipal waste of
both bioreactor and dry designs were considered.
The product for comparison to ACQ-treated lumber is WPC decking. In order to support
comparison of products through their complete life cycles, an LCA has been completed for
WPC. A “typical” WPC product design has been assumed to be representative of the general
product category. The national manufacture of WPC is assumed to include a mixture of recycled
wood fiber and recycled and virgin high density polyethylene (HDPE). The WPC product has
approximately the same dimensions and is generally used as interchangeable with ACQ-treated
lumber for decking. Published data and reasoned assumptions are made to complete the LCA for
the complete and comparable life cycle.
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2.
GOAL AND SCOPE
As part of the treated lumber LCA, a Goal and Scope Document was carefully developed prior to
beginning the inventory of inflows and outflows. Specifically, the goal and scope for ACQtreated lumber follows the framework specified in Section 5.2 of ISO 14040:2006 and Section
4.2 of ISO 14044. The purpose of the Goal and Scope Document is to clearly define the intent of
the LCA.
•
The goal defines what the client intends to accomplish with the LCA. That is, “why do
the LCA?”
•
The scope clarifies what is to be included within the assessment and what is not included.
The Goal and Scope Document was subjected to two levels of technical review and an
independent external review further intended as a means to assure the quality and accuracy of the
document and the LCA. The Goal and Scope Document has been used to guide the LCA process
and, through iterative modifications, resulted in changes to the LCA scope. The detailed Goal
and Scope document prepared to support completion of this LCA is included as Appendix 1.
The LCA addresses ACQ-treated lumber for use in exterior decks. This product was chosen as a
baseline for the purpose of conducting the LCA. It is not TWC’s intent that this LCA address all
wood preservative types present in the marketplace for this or other product applications, nor is it
the purpose of this LCA to endorse a specific wood preservative. Rather, a baseline preservative
was chosen for the purpose of conducting the assessment, understanding that preservative
formulations and preservative types can and do change over time and with differences in
geographic locations. The baseline product assessment provides the user a tool by which to
evaluate a group of treated wood products that are common in the marketplace.
ACQ-treated lumber is commonly used in residential applications, especially decks. This LCA
provides a basis for understanding the environmental impacts associated with ACQ-treated
lumber used for decking. Thus, the LCA does not address the structural support components
beneath the decking or the components above the decking (typically railings and balusters).
The Life Cycle Process Diagram of ACQ-treated lumber (Figure 2-1) illustrates the cradle-tograve life cycle considered in the LCA.
For this LCA, the “cradle-to-grave” life cycle of ACQ-treated lumber was assessed. Thus, the
LCA addresses inputs and outputs beginning with seedling production, planting and growing of
trees, then the harvest of logs, the milling of logs to lumber, the manufacture of the components
of the ACQ preservative, the treatment of lumber with ACQ, the installation and normal intended
use of ACQ-treated lumber, appropriate maintenance during use, demolition and disposal at the
end of the use life, transportation between points, and finally the ultimate fate of the ACQtreated lumber product following disposal in landfills. Inputs of resources and outputs of
products and wastes for each process in the life cycle were estimated and totaled.
An alternate product to ACQ-treated lumber, available on the marketplace, is WPC. Most WPC
decks have a treated wood under-structure, so only the deck surfaces are considered in this
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comparative analysis. This report provides an LCA of WPC to support comparison of impact
indicators for ACQ-treated lumber used for decking and WPC decking, based on the functional
unit of 320 square feet of deck surface, the size of an average U.S. deck.
Through the iterative LCA process, the TWC decided that the scope should not include impact
indicators for human health and ecological toxicity based on the opinion that the measures for
these indicators would be misleading, incomplete, and possibly inaccurate.
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Figure 2-1
Life Cycle Diagram of ACQ-Treated Lumber
LEGEND
Fuel, copper,
natural gas,
transport,
electric
Fuel, natural
gas, transport,
electricity
Fuel, transport,
water
Inputs
Process
Copper &
MEA
formulating
Copper amine
concentrate
Copper & MEA
Emissions,
waste
Copper amine
Quat
Emissions,
waste
Quaternary
formulating
Product
Outputs
System
Boundary
Emissions,
waste
Fuel, transport,
electric, water
Sun, CO2,
Fuel
Softwood
planting &
growth
O2, emissions
Fuel, transport,
electric
Fuel, transport
Trees
Softwood
harvest
CO2, emissions,
slash, biomass
Logs
Lumber
milling &
drying
CO2, emissions,
biomass
Fuel,
Transport,
land
Transport
Lumber
ACQPreserving
Treated Lumber
Use as
decking
Used Lumber
Landfill
CO2, emissions,
waste
Emissions to air,
ground
CO2, CH4,
energy,
emissions
LC Stage 2
LC Stage 3
LC Stage 4
LC Stage 1
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3.
3.1
LIFE CYCLE INVENTORY
METHODS DISCUSSION
3.1.1
Choice of Spreadsheet
An early choice faced by AquAeTer in completing the inventory phase of the LCA for ACQtreated lumber was whether or not to use proprietary LCI software programs, such as SimaPro®,
or to use linked spreadsheets developed specifically for this LCA. Inventory data are available
from the U.S. Department of Energy, National Renewable Energy Laboratory (NREL) U.S. Life
Cycle Inventory (LCI) Database. The individual LCI modules may be downloaded in
spreadsheet format and our understanding is that all the pertinent NREL data are made available
in proprietary LCI programs, such as SimaPro®.
The proprietary software is quite powerful, but is only transparent to those who have purchased
it. In order to provide the greatest degree of transparency and to allow full functional control by
the authors, AquAeTer decided to complete the LCI using linked Excel® spreadsheets rather than
proprietary software. In this way, each module from the NREL may be used directly. The
inventory data developed for life cycle stages, including preservation of the lumber, use,
maintenance, and disposal, have been developed in a spreadsheet format and are incorporated
with existing data from the NREL databases. Each separate input is then integrated and
proportioned appropriately with the production, use, and disposal phases of the product life.
In this case, use of spreadsheets means that the many members of the TWC may download and
use the results of this LCI at no additional cost and within a spreadsheet format with which they
are already familiar. Final versions of the spreadsheets, distributed to TWC members, will have
protections in place to help prevent accidental formula manipulations.
3.1.2
Primary and Secondary Data
Consortium for Research on Renewable Industrial Materials (CORRIM January 2002) defines
primary and secondary data as follows:
Primary data are those collected using recognized inventory data collection rules from specific
facilities or operations; such data are typically labeled to indicate the date of collection and the
estimated reliability of the data.
Secondary data are those obtained from secondary sources such as simulation studies, or
published articles containing industry or region-wide, or company specific information.
For the inventory, AquAeTer surveyed TWC member wood treating facilities using ACQ during
the 2007 calendar year to determine representative rates of inputs and outputs. An example of
the treater survey is included as Appendix 2. The survey results are included as a tab 1 within the
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Reference here and elsewhere in this document to “tab” or “tabs” is intended to be a reference to one or more
“worksheets” within a single spreadsheet program electronic file or “workbook.” On the computer screen, the
individual “worksheets” usually appear as folder “tabs” that open individual worksheets for viewing.
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spreadsheet file, and calculations required to develop the normalized rates are transparently
made. These primary data then are incorporated into the appropriate inventory functional unit
columns.
All other functional unit data are obtained from secondary sources, such as other life cycle
inventories that were downloaded from the NREL’s U.S. LCI Database or obtained from other
literature sources. Sources of secondary data are referenced in calculations included in
Appendix 3, U.S. Electric Energy Grid LCI Calculations and Appendix 4, Life Cycle Inventory
Calculations.
3.1.3
Format of the LCI Spreadsheet
The format of the LCI spreadsheets reflects the sequential primary life cycle stages of ACQtreated lumber as a progression from left to right. Additionally, the first section of the
spreadsheet defines process components that are used repeatedly in the life cycle stages, such as
energy and fuel production, combustion, and transportation. The LCI spreadsheets are included
as Appendix 5.
Electric energy production is listed first, since it is used in nearly all stages. Then, other inputs
are entered using modules from the U.S. LCI inventory, including fuel production and
combustion, and truck, rail, barge, and ocean vessel (ship) transportation. For ease of reference,
these primary process categories were highlighted (with gray shading
) and grouped under
the heading “Energy and Other Inputs” on the “ACQ LCI” inventory tab. Note that each of these
inputs has associated outputs to the environment, such as CO2 and other releases that are
proportional to the amount used. In the spreadsheet, each column with numeric data represents a
process with specific inputs and outputs, a subtotal of processes, or a summed total of processes.
Additional life cycle stages are identified on the “ACQ LCI” inventory tab and include
distinctive color coding for easy reference. At the end of each life cycle stage, life cycle
inventory totals are computed for inputs, outputs, and assessment indicators.
Other tabs in the spreadsheet workbook are used for supporting calculations that produce values
used in the LCI. For example, in the “Landfill” tab, a series of assumptions and calculations are
shown that allow an estimation of how much methane and CO2 are emitted from disposed treated
wood and how much carbon would be sequestered in the landfill. These values are linked to the
“ACQ LCI” worksheet as inputs and outputs in the “Landfill Stage” section.
3.1.4
Use of NREL LCI Modules
The National Renewable Energy Laboratory, U.S. Life Cycle Inventory Database, web site
www.nrel.gov/lci/, provides extensive LCI data for public use. The Life Cycle Inventory
Database is described on its website as follows:
NREL and its partners created the U.S. Life Cycle Inventory (LCI) Database to help life
cycle assessment (LCA) experts answer their questions about environmental impact. This
database provides a cradle-to-grave accounting of the energy and material flows into
and out of the environment that are associated with producing a material, component, or
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assembly. It's an online storeroom of data collected on commonly used materials,
products, and processes.
The critically reviewed LCI data are consistent with a common research protocol and
with international standards. The LCI data support efforts to develop product LCAs,
support systems, and LCA tools.
Developing the LCI spreadsheet required the use of several modules from NREL’s U.S. LCI
Database. The U.S. Electric LCI, detailing inputs and outputs related to use of electrical energy
from the U.S. grid, alone required use of NREL LCI data modules for coal mining, oil and gas
extraction, crude oil refining, and utilities. Wood Product Manufacturing data modules included
softwood log harvesting, rough milling, drying, and planing in the Southeastern U.S.
Transportation modules also were used to develop inputs and outputs for product transport.
Where the LCI data modules are used, the resulting process inputs and outputs are entered as a
column in the “ACQ LCI” tab of the spreadsheet. For the LCI inventory spreadsheet, and
because of the wide variety of inputs and outputs, especially related to specific chemicals that are
emitted or discharged, the components displayed in the primary “ACQ LCI” tab of the
spreadsheet are limited to those most applicable to this LCI. For example, emissions/discharges
of copper are presented, even where the numbers are minimal because copper is a component of
ACQ, but lead is not presented on the primary LCI spreadsheet because it is not a primary
component of ACQ and not directly related to the products in question. However, lead (and all
other available emissions data) was tracked and included in calculations of impact indicators.
During the inventory process, some data simplification was done. For example, most values that
were manually entered are rounded to two significant figures. Some numbers were combined to
reduce the number of inputs or outputs. For example, the much smaller amount of lignite coal
used for electric production was added to and assumed to be the same as bituminous coal and
inputs of hydro, wind, and geothermal are combined in an “other renewable energy” input.
3.1.5
Inputs from Nature or from Technosphere
“Inputs from nature” are generally considered as those resources that are mined or otherwise
“taken” from the earth, such as coal, iron ore, limestone, or crude oil and are not readily sold to
end users. “Inputs from the technosphere” are resources that have been processed or altered by
application of technology and which are typically “sold” to downstream processes or users. For
example, crude oil is removed from nature and then processed into fuels, such as gasoline and
diesel fuel, then sold to users as resources from the technosphere. Electricity is a product from
the technosphere that results from use of various fuels derived from nature. For consistency in
accounting for fuels, those inputs used to generate electricity are all considered “from nature,”
even if some processing before such use was involved.
3.1.6
Electricity and Supporting Processes
The inputs and outputs related to the electricity use and other supporting energy processes are
included on the “ACQ LCI” tab of the spreadsheet under the gray shaded (
) column
heading “Energy and Other Supporting Processes”. Energy modules on the NREL website
provide information on the fraction of average U.S. grid electricity generated by coal
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combustion, nuclear, and other types of processes. The modules provide data about the resource
inputs and environmental outputs of combusting the fuels for power and the environmental
inputs and outputs of actual fuel production, such as mining, oil and gas well operations,
refining, and other processing. However, its format does not associate or proportion inputs and
outputs from each generation source type or fuel production process. Because of the complexity
of proportioning the several separate processes into the U.S. average electric grid, a separate
spreadsheet file, “Electric Energy LCI.xls”, was constructed to support the needed calculations.
The calculations are explained in detail in Appendix 3, U.S. Electric Energy Grid LCI
Calculations.
The “Electric Energy LCI.xls” file is used to assemble, in a single spreadsheet workbook, the
basic data downloaded from NREL and to link that data appropriately to average U.S. grid
electricity. The completed spreadsheet workbook is used in the “ACQ LCI” tab by cell
references to this file or by copying sections of this file into other files, such as
“ChemicalFactors.xls”.
Data inputs and outputs for selected other fuel production and combustion data have also been
incorporated into the “Electric Energy LCI.xls” workbook for convenience, such as natural gas,
oil, and coal production and combustion in industrial boilers. The data from the supporting
processes are linked to the “ACQ LCI” tab.
In addition, transportation modules from NREL including truck, rail, barge, and ship transport
are included as the “transport” tab and linked within the gray-highlighted columns (
) of
the “ACQ LCI” tab. The transportation calculations are further explained within Appendix 4.
Electricity and other supporting processes are proportioned to life cycle activities in the
following sections.
3.1.7
Distributions
Each column of the Energy and Other Supporting Processes group is repeated in each stage of
the product life under a gray (
) subheading of “Energy and Other Supporting Process
Distributions”. The amount of each input, such as electricity, used in a life stage is listed in the
“Production/Use Amount” line (line 6) and the units of use (kilowatt hour (kWh), for electricity,
are shown in the next line below. The next line calculates the “distribution factor”, which is the
amount used divided by the unit production rate of the input. For example, the unit production
rate for electricity is 1,000 kWh and a process using 800 kWh of electricity would have a
distribution factor of 0.8 (800/1,000). Each specific process input and output is then calculated
by multiplying the distribution factor times the standard input or output values of the reference
process. Following the same example above, the standard output of CO2 is 1,600 lbs per 1,000
kWh, so the life stage process CO2 emission would be 0.8 x 1,600 or 1,280 lb CO2.
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4.
4.1
LIFE CYCLE INVENTORY ANALYSIS
INTRODUCTION TO ACQ LIFE CYCLE INVENTORY ANALYSIS
The inventory analysis phase of the LCA involves the collection and analysis of data needed to
accomplish the goal of the LCA. For each stage of the product life cycle, inputs of energy and
raw materials, outputs of products, co-products, and waste, and environmental releases to air,
water, and soil are determined. The inventory analysis steps include data collection, validation
of data, relating data to unit processes, relating data to functional units, data aggregation, refining
the system boundary, and completing inventory reporting. These steps are consistent with the
requirements of ISO 14044.
The unit processes for ACQ-treated lumber addressed in this LCA cover the “cradle-to-grave”
stages as follows: seedling production, planting and growth of trees, harvest of logs, milling of
logs to dimensional lumber and drying of lumber, production of ACQ preservative, pressure
treatment of lumber with ACQ preservative, use of ACQ-treated lumber in decks, including
maintenance of decking and demolition at the end of the use life, disposal in landfills, and final
fate in the landfill. These are illustrated on Figure 2-1, Life Cycle Diagram of ACQ-Treated
Lumber. Unit processes are combined into four main life cycle stages including:
•
Untreated, planed and dried lumber, at Southeastern U.S. mill;
•
ACQ-treated lumber, at the treating plant;
•
ACQ-treated lumber deck at end of life; and
•
ACQ-treated lumber in a landfill.
Data related to the various processes are collected and entered into spreadsheets that facilitate the
calculations needed to proportion inputs and outputs to each unit process appropriately. The data
from unit processes are summed to determine inventory totals at each of the stages.
The completed inventory then is used in the following sections of the LCA to assess and interpret
impacts and support comparisons to alternate products.
4.2
4.2.1
ACQ-TREATED LUMBER LIFE CYCLE INVENTORY
ACQ Introduction
The first life cycle stage of ACQ lumber includes the seedling production, growth of the tree,
harvest, and production from logs to lumber. The inputs and outputs are based on the
downloaded modules from the NREL’s U.S. LCI Database modules covering Wood Product
Manufacturing.
The second stage of the ACQ lumber life cycle is treating the lumber with ACQ preservative,
requiring development of inputs and outputs for the manufacture of ACQ preservative, and the
wood treatment process. The LCI data necessary for these processes and the subsequent life
cycle stages were developed specifically for this assessment because down-loadable modules for
these processes were not available in the NREL database.
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The third stage of ACQ-treated lumber is use as residential decking lumber (i.e., the flat surface
of a constructed deck). The model includes the construction, maintenance, use, and eventual
demolition of the deck. Following its use, the ACQ-treated lumber decking is modeled in life
cycle stage 4 as disposed lumber in a landfill.
After each of the four life cycle stages, significant inputs and outputs are totaled, so that the
progressive increases of input resources and outputs can be tracked. This method allows the user
easier access to the stages that result in significant changes. The life cycle inventory
spreadsheets are included as Appendix 5.
4.2.2
Lumber Production Stage Prior to Wood Treatment (LC Stage 1)
The inventory of inputs and outputs associated with the production of lumber sold to treaters for
preservative application is included in the “ACQ LCI” tab in the columns under the yellowhighlighted heading (
), “Lumber Production Prior to Wood Treatment Stage”.
AquAeTer utilized existing LCI data for lumber production. A detailed LCI for forest products
(CORRIM, 2002) evaluates the inputs and outputs related to the production of lumber and other
wood products. One module of this study provides data covering the life cycle stages of
replanting a harvested forest area, growing and maintaining the forest plantation until harvest,
and the eventual harvesting of the trees. Other modules provide data for the manufacture of
lumber from the harvested trees, including drying the lumber in kilns and planing of the lumber.
Similar modules of the CORRIM study report on forest and lumber production in the Pacific
Northwest and in the Southeastern U.S. For this LCI of ACQ-treated lumber, the CORRIM data
for lumber produced in the Southeastern U.S. are used. Specifically, values for surface planed,
dried lumber milled in the southern U.S. are used.
Figure 4-1
Map of U.S. Regions
Map Source: Vlosky 2007
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At the time of the treater survey (calendar year 2007), the majority of ACQ use was in the
Southeastern U.S. where Southeastern lumber species are used 2. From the treater survey
responses, approximately 97 percent of the ACQ-treated lumber volume in 2007 was from
treaters in the Southeastern states. Since the time of the survey, additional preservatives have
been added to the U.S. marketplace.
The Southeastern lumber database module was downloaded from the NREL U.S. LCI Database
and appropriate portions copied into the “SELum” tab of the workbook, and then linked to the
“ACQ LCI” tab in the column headed, “Lumber production (planed, dry)”. Processes including
inputs and outputs related to burning wood biomass to dry lumber, use of electricity in mills, and
transportation related input and outputs were separated and proportioned individually. In this
manner, the amounts of electricity, wood fuel, and transport ton-miles required for each 1,000
board-feet (bf), also referred to as 1.0 Mbf of lumber, are reported.
Total inputs and outputs for lumber production prior to treatment are calculated in the life cycle
process, titled, “LCI Total-Lumber Production”. Here, one can see that for each 1.0 Mbf of
lumber, approximately 83 kWh of electricity and 847 pounds of wood biomass are used.
Emission outputs of approximately 220 pounds of CO2 from fossil fuel and 750 pounds of CO2
from non-fossil fuel result.
4.2.3
ACQ Production (LC Stage 2)
The inventory of inputs and outputs related to the production of ACQ preservative that is sold to
treaters for pressure treatment of lumber is included in the “ACQ LCI” tab in the columns under
the green highlighted heading (
), “ACQ Production Stage”.
Alkaline copper quaternary compound type D (ACQ-D) is a well-established wood preservative
standardized by the AWPA in the Standard for Waterborne Preservatives P5-09. ACQ-D is
established under the Goal and Scope for this LCA as the reference treatment for decking
lumber. It is not intended that this LCA make a detailed inventory for the production of ACQ-D
preservative. Rather, the Goal and Scope document expected reasonable assumptions and
surrogate data to be used to develop approximate estimates of inputs and outputs for ACQ-D
production. LCI assumptions are included in Appendix 6. Because there were at least two
primary U.S. formulators of ACQ used by the treating industry, many different suppliers of
ingredients to those formulators (Freeman 2009), and limited LCI data available from the
formulators and component suppliers, significant assumptions have been made to complete the
input and output estimates. A calculation for the production of ACQ has been completed and is
included in Appendix 4.
ACQ is formulated from copper components and quaternary ammonium (quat). The general
composition of ACQ-D, as stated in AWPA P5-09, Section 14 is as follows:
Copper, as CuO
Quat, as DDAC
66.7%
33.3%
2
AquAeTer acknowledges that recent changes in the treating industry make current ACQ use more prevalent in the
Pacific Northwest U.S. where Pacific Northwest lumber species are used.
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The copper component is dissolved in ethanolamine at 2.75 parts ethanolamine, by weight, for
each part copper oxide (AWPA). The quat is shipped separately and mixed during the treating
process.
For this LCA, inputs and outputs for ACQ-D production are assumed to be the weighted totals
for the basic components of the formulation; copper, quaternary, and ethanolamine. These are
described in more detail below. Supporting calculations are made in the appropriate tabs within
the “ACQ LCI” tab. More detailed descriptions of the calculations are included in Appendix 4.
In the “ACQ” tab of the spreadsheet, the relative weights of components are calculated for each
pound of ACQ used in wood treatment. Although defined as one pound of ACQ, the formulation
actually includes 0.667 pounds of copper oxide, 0.333 pounds of quat, and 1.834 pounds of
ethanolamine.
4.2.3.1 Copper
Copper compounds, generally basic 3 copper carbonate or copper sulfate (Freeman 2009), are
purchased and used by formulators. The copper compounds may either be purchased directly
from mined ore that has been refined or from recycled, scrap, or off-specification copper sources,
such as wire, pipe or sheeting manufacturers. Once purchased, the formulators dissolve the
copper in ethanolamine, resulting in a copper amine concentrate. This process does not involve
melting or other high-energy input, so relatively little input energy is required.
In many instances, inputs and outputs required for recycling of post-use materials have not been
considered in the inventory impacts. Although most copper used in the copper amine
concentrate comes from recycled sources (Freeman 2009), it would not be appropriate to account
for it as if no inputs or outputs are associated with recycling and preparation for use.
Confidential sources contacted stated that copper used in the copper amine concentrate is either
recycled off-spec copper products or reclaimed copper, such as used wiring, and not virgin;
however, the amount of off-spec and reclaimed was widely variable and a function of market
demand. It was assumed that a third the inputs and outputs of virgin copper product production
(including mining, refining, transport, and production) provided a reasonable assumption of
environmental burdens associated with copper used in the copper amine concentrate. The
calculations are made within the “Copper” tab and entered into the “ACQ LCI” tab, Copper
Production process.
4.2.3.2 Quat
For ACQ-D, the quat material specifically is didecyl dimethyl ammonium chloride
(DDAChloride) or didecyl dimethyl ammonium carbonate and/or bicarbonate (DDACarbonate).
Viance, a producer of ACQ preservative, provided a copy of the MSDS for Q50C, the quat they
use in their formulation. In addition, the manufacturer of quat, Lonza, provided additional
production information. This LCA assumes that the quat is of the carbonate and bicarbonate
forms and is manufactured using natural gas as the carbon source. A detailed explanation of the
data, assumptions, and calculations is provided within Appendix 4. The calculations are made
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within the “ACQ” tab and entered into the “ACQ LCI” tab, Quaternary (DDAC) Production
process.
4.2.3.3 Monoethanolamine Production
The form of amine normally used is monoethanolamine (MEA). MEA is produced from the
reaction of ethylene oxide and anhydrous ammonia (Akzo Nobel 2004). As explained in the
ACQ Production calculation included within Appendix 4, data from the NREL USLCI database
for ethylene and ethylene oxide are used to develop reasonable estimates of inputs and outputs
related to the production of MEA. The calculations are made within the “ACQ” tab and entered
into the “ACQ LCI” tab, Monoethanolamine Production process.
4.2.3.4 ACQ Preservative Ingredient Proportions
Inputs and outputs for each of the three main ingredients of ACQ are shown in the first three
columns of the ACQ Production Stage section. In the next three columns, quantities of each
ACQ component are determined based on how much of each is used for each pound of ACQ
preservative that is delivered to a treating plant. Note that the fractions total more than one
because MEA is based on the weight fraction of CuO. In the right column of the section titled,
“ACQ Production Stage”, the total inputs and outputs related to the production of each pound of
ACQ preservative are calculated. Electric energy and transport inputs for ACQ production are
totaled for ACQ production and then proportioned by ACQ use rather than proportioning them to
ACQ production.
4.2.4
ACQ Lumber Treatment Stage (LC Stage 2)
The inventory of inputs and outputs related to the treatment of lumber with ACQ preservative at
wood treating plants is included on the “ACQ LCI” tab in the columns under the light bluehighlighted heading (
), “ACQ Lumber Treatment Stage”.
4.2.4.1 Decking Lumber
Lumber used for residential decks typically consists of nominal 5/4 x 6-inch (also called radius
edge) lumber or nominal 2 x 6-inch lumber. The 5/4-inch lumber typically is installed over joists
spaced at 12-inches. The thicker lumber can be installed over wider spans between joists,
typically 16-inches. In recent years, most deck lumber is sold in 5/4-inch dimension (verbal
communication with independent consultant to the treated wood industry, Mr. Mike
Freeman2009). Vlosky (2009) reports 2007 water-borne treatment of approximately 4.7 billion
board-feet of dimension lumber (2-inch and larger) and 0.7 billion board-feet of radius edge
decking. Additionally, focusing on the 5/4-inch decking material better supports the comparison
to alternate decking material in the later part of this LCA.
In the “Deck&Sealer” tab, the nominal and actual dimensions of the lumber types are used to
calculate the wood volume and average deck surface area per 1.0 Mbf of lumber. For this LCI, it
was assumed that 100 percent of decks are manufactured with 5/4-inch decking materials so
comparable analysis could be done with an alternative product, as further discussed in Section 6.
AquAeTer recognizes that the national average for decking probably is closer to 80 percent 5/4
inch and 20 percent 2-inch dimensional lumber (verbal communication with independent
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consultant to the treated wood industry Mr. Mike Freeman 2009). The LCI spreadsheets are
constructed to allow the user to change the percentages of dimensional lumber types.
1.0 Mbf of 5/4 x 6-inch lumber will result in 800 square-feet of deck surface. Additional detail
regarding the properties of lumber decking used as a reference product in the LCI is included
within Appendix 4. Values from the “Deck&Sealer” tab are entered on the “ACQ LCI” tab as
inventory inputs and outputs.
4.2.4.2 Treater Survey
Life cycle inventory data related to lumber treatment with ACQ preservative are based on results
of a questionnaire completed by representative treating plants. An example of the treater survey
is included in Appendix 2. The questionnaire was prepared by AquAeTer and circulated to
member plants by the TWC. Individual plants were identified by a number only, with TWC
keeping the treater’s identity confidential. Results, with plants identified only by number, were
provided to AquAeTer for compilation and use.
Fifteen (15) plants provided responses to the questionnaire. Two were identified as western
treaters and 13 were identified as southern treaters. The southern treaters accounted for 97
percent of the surveyed ACQ-treated lumber volume.
The total volume of ACQ-treated lumber by treater survey reporting plants in 2007 is
approximately 662,000 Mbf. The total estimated amount of dimensional lumber (4.7 million
Mbf), radius edge heavy decking (739,000 Mbf), and boards (211,000 Mbf) produced in the U.S.
in 2007 is 5.7 million Mbf (Vlosky, 2009). Of the 5.7 million Mbf treated with water-bornes,
Vlosky estimates 25 percent or 1.4 million Mbf were treated with ACQ. Thus, the treater survey
covers approximately 47 percent of the ACQ-treating market.
4.2.4.3 Inventory Inputs from Treater Surveys
AquAeTer assembled the treater responses into a spreadsheet and then processed the results to
determine average or representative values for inventory inputs and outputs normalized to
1.0 Mbf of treated lumber. The actual survey results are included on the “ACQSurveyResults”
tab. Added rows, used to normalize data per 1.0 Mbf, are highlighted in green. In some
instances, results from treaters required conversion from reported units to standard units used in
the LCI.
These conversions and the applied assumptions are included on the
“ACQSurveyResults” tab.
Weighted averages are calculated for inputs and outputs used in the inventory. The weighting
basis is total ACQ treatment volume for copper and quat usage and total volume of all treatments
for remaining values. Based on the survey, significant inputs resulting from ACQ treatment of
1.0 Mbf of lumber include:
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Electricity use
12 kWh/Mbf
Natural gas use
19 ft3/Mbf
Diesel fuel
0.53 gal/Mbf
Truck transport
290* ton-miles/Mbf
Rail transport
63 ton-miles/Mbf
Water use
121 gal/Mbf
*Note: Outbound truck transport distance revised from survey data, due to review
comment.
The AWPA Standard retention of 0.15 pcf was used in the LCI instead of information received
as part of the treater survey. Values important to the calculation of inventory inputs and outputs
were then entered into the “ACQ LCI” tab in the first column of the section labeled, “ACQ
Lumber Treatment”.
4.2.4.4 Inventory Outputs from Treater Surveys
For solid waste generation, the sum of each treater’s hazardous 4, process, and other waste
disposal amounts were divided by the total treatment volume for all preservatives at each treating
facility. The waste generation rates for each facility were then used with the total plant
production to determine a weighted average of waste generation. The weighted average waste
generation was entered as an output of solid waste on the “ACQ LCI” tab.
The survey results did not include adequate data related to copper in stormwater runoff to
estimate such releases. Information was included on treater surveys to support reasonable
assumptions regarding copper releases. This information included details such as general
amount of treated lumber stored under roofs or wrapped, stored on paved or unpaved surfaces,
and some other practices that affect copper releases to storm water runoff or to the ground.
These assumptions are detailed and used in the “StYard” tab and further explained in the Storage
Yard calculation included within Appendix 4. For example, it is assumed that all treated lumber
is stored on a drip pad for the first 24 hours following treatment. Then, intermediate storage is
apportioned between covered or wrapped storage (no runoff), open storage on a paved yard, or
open storage on a gravel yard. Typical lumber bundle and stack sizes are assumed. The outer
surface area is assumed exposed to weather and subject to leaching of copper by rain. Factors
are assumed for the portion of storm water that runs off of each surface and the portion of copper
that fixes or binds to the surface soil from the dissolved copper in the runoff. Copper leached
from the treated lumber and the amounts either discharged with runoff (0.00026 lbs Cu/Mbf) or
left in the surface soil (0.00045 lbs Cu/Mbf) were calculated. With an average ACQ treatment
volume of approximately 44,000 Mbf per plant per year, the estimated amount of copper release
per average treating plant is approximately 11 pounds in surface water runoff and 20 pounds
retained in the soil per year per treating facility.
As a real world check, the USEPA TRI Explorer was used to find the amounts of copper and
copper compounds reported for wood product industry facilities as “On-Site Surface Water
Discharges” in the year 2000. AquAeTer notes that in 2000, most water-borne treatment was
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ACQ treatment itself does not generate hazardous waste. Because of past treatment applications, used at some
treating plants, some waste might be generated that must be managed as hazardous.
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with CCA and copper was a reported chemical. This search indicated that 33 of the top 100
reporting facilities reported such a discharge and the average for these was 45 pounds. This
agrees reasonably well to the above-estimated amounts.
The potential for environmental impact of copper mainly results from copper in its ionic form.
While copper leached from stored lumber at the treating facility or deck may be in ionic form,
such copper rapidly reacts with organic matter and soil minerals to non-harmful levels (Michels,
Boulanger, and Nikolaidis, 2009). Estimates of copper releases from storage yards and decking,
their transport via water transport and resulting concentration in water bodies is a function of
speciation and site specific elements such as climate, soil type, and water quality, research that
was beyond the scope of this LCA. Thus, indicating that copper lost from storage yards or
decking is released “to water” would significantly overstate any potential for environmental
impact.
Some of the MEA and DDAC, like copper, will be released from the lumber while at the treating
plant or from decking. No study of MEA releases or fate from ACQ-D-treated lumber was
found, although two published articles address ACQ-B treated wood. Chen and Randall (1994)
estimated air releases of ammonia and amounts due to simulated rainfall on units of ACQ-B
treated lumber. The ACQ-B formulation tested used ammonia as the solvent for the copper
compound whereas the subject ACQ-D formulation uses MEA. MEA is formulated using
approximately 28% ammonia and the rest ethylene oxide. Calculations assume the ammonia
fraction of MEA behaves similarly to the ammonia in ACQ-B. These data are applied in the
“StYard” tab.
Chen and Randall cite another study that estimates approximately 40% of ammonia is evaporated
from the treated wood, based on testing ¾-inch cubes air dried for 14 days. This value is
assumed to represent the fraction of ammonia that would be released to air from ACQ-D treated
lumber over its full life. One-quarter of that is assumed to be released from lumber in storage at
the plant and the rest during the use life.
Releases to the ground in the storage yard are calculated assuming that leaching from rain is
proportional to the exposed stack surface areas. The test results are normalized to pounds of
ammonia and DDAC per inch of rain per square foot of exposed stack surface area per Mbf. The
estimated amounts released to ground are shown in the calculation tab, but are not carried
through the LCA since they would not affect the impact indicators assessed. Since treatment of
lumber with ACQ is a net user of water and facilities generally are zero dischargers, it is
assumed that there is no copper discharge to publicly owned treatment works (POTWs).
4.2.4.5 ACQ-Treating Proportions
ACQ preservative use is proportioned to ACQ lumber treating based on the use of 8.8 lbs of
ACQ for each 1.0 Mbf of lumber treated. The total inputs and outputs directly associated with
treatment activity are totaled in the “ACQ Lumber Treatment” column. Electricity use, fuels
production and combustion, and transport are proportioned to wood treatment based on the
amounts of each used for 1.0 Mbf of lumber in the wood treatment stage. The inputs and outputs
for treatment are summed to produce the total inputs and outputs for the treatment stage in the
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column headed “LCI Total-ACQ Lumber Treatment”. These are then added to the totals for
lumber production prior to treating in the column headed “ACQ Lumber Life thru Treatment”.
4.2.5
ACQ-Treated Lumber as Decking - Use Life Stage (LC Stage 3)
The inventory of inputs and outputs related to the use stage of ACQ-treated lumber for outdoor
decking is included on the “ACQ LCI” tab in the columns under the magenta-highlighted
heading (
), “Deck Life Span Stage”. Factors discussed below for decking are developed
in the spreadsheet tab, “Deck&Sealer”. A detailed explanation of the data, assumptions, and
calculations made in the tab is provided within Appendix 4.
Lumber for decking may be in two different thicknesses, nominal 2-inch (1 ½-inch actual) or
nominal 5/4-inch (1-inch actual). The 5/4-inch thickness boards are also called “radius edge
decking”. For the purposes of this LCA, it was assumed that 100 percent of decking is 5/4-inch
nominal thickness. Decking material with these dimensions use the same substructure support as
WPC, thus allowing direct comparison without the need to consider the substructure. The LCI
spreadsheets have been constructed to allow the user to alter the amount of dimensional lumber
types (e.g., change to 80 percent 5/4-inch lumber and 20 percent 2-inch lumber).
The LCA Scope assumes that ACQ-treated lumber will be used in an exterior residential deck,
then will be disposed in a landfill. Properly maintained ACQ-treated lumber in such use may
provide good service for several decades. However, typical use life is significantly shorter for
two primary reasons: 1) aesthetic reasons due to lack of maintenance, and 2) owners often
choose to replace a deck as part of a remodel to a different design before the useful service life
has expired. Smith (2005) evaluated studies of CCA treated deck life and developed a model for
deck life in which deck life is represented by a lognormal distribution with mean life of 9.45
years and standard deviation of 5 years. For this LCI, it is simply assumed that the average use
of an ACQ-treated lumber deck is 10 years.
Maintenance of treated wood decking is recommended by the wood preservative and treated
wood manufacturers and retailers. Maintenance generally consists of cleaning and application of
sealer to the wood surface. Sealers vary considerably in material types, quality, and cost. Some
owners clean and seal decks annually, some less often, and some not at all. For this LCA, a
middle-ground approach is taken. A typical sealer was chosen and the manufacturer
specifications used to model sealer application. The sealer was modeled as if applied once in
year five.
This topic received much discussion at a meeting of TWC members in June 2009. Sealant
manufacturers recommend application every 2 to 3 years. TWC members believe that some
individuals apply sealant on a frequent basis (every 2 to 3 years), while most others never apply
sealants. However, the statistics of sealant use are unknown. The consensus of the TWC
members was one application of sealant represents the national average.
The TWC group also considered how application of sealant impacted serviceable life. The
group’s opinion was that sealants have a positive impact on the aesthetics of the wood products,
but do not result a longer serviceable life from a structural standpoint. Most decks are replaced
due to remodeling rather than due to excessive weathering or structural failure. Therefore,
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application of the sealer was not modeled as changing the use life of the deck. This assumption
allows for a reasonable scenario that supports life cycle evaluation and conclusions.
Assumptions, data, and resulting inputs and outputs for deck sealer are assembled in the “Deck
& Sealer” tab of the spreadsheet. All of the VOC content of sealer is assumed to be emitted to
the air. Inputs and outputs for production of the carbon-based portion of the sealer are assumed
to be similar to production of Polyethylene Terephthalate (PET). A more detailed explanation of
data, assumptions, and calculations is provided within Appendix 4. The results are entered into
the “Deck Stain Sealer Prod.” column of the LCI spreadsheet. Based on the recommended
application rates, a total of approximately 8 gallons of sealer/Mbf is assumed to be applied in one
application during the use stage of a deck.
In the “Deck Sealer Application” column, the amount of sealer required per 1,000 bf of ACQtreated lumber decking is proportioned to the deck lumber. The associated inputs and outputs for
sealer production are proportioned to the deck in the “Deck Sealer Application” column.
Copper is assumed to leach from the decking wood during its life. Based on research done by
USDA Forest Products Laboratory in a study entitled Environmental Impact of PreservativeTreated Wood in a Wetland Boardwalk, the leach rate of ACQ lumber is 35 µg Cu/cm2/inch of
rain in the first 11.5 months after construction and after 11.5 months dropped to approximately
5 µg Cu/cm2/inch of rain (Lebow 2000). These data are applied to a new deck installation with
adjustments for retention in the “Deck&Sealer” tab. The data, assumptions, and calculations
involved are explained within Appendix 4.
In the LCI, the copper leached from the deck during its life is listed as “to ground” because
copper is most likely to bind to organic material or minerals in the surface soil immediately
below the deck with minimal migration to surface water or groundwater from the deck location
for the same reasons discussed above for leaching of copper at the treating plant.
Some release of ammonia, as a component of MEA, to the air is assumed to occur from the deck
during its use life, as discussed above for releases at the treating plant. Some additional release
of MEA components during use may occur, but study data to support such estimates was not
found.
DDAC is not expected to be released from treated lumber in use. Brooks (2001) documented
that DDAC releases from samples submerged in water ceased within approximately 5 days.
Releases to rain water from decking are assumed to be similar.
The inputs and outputs related to the actual deck construction and its later demolition are
relatively minor, and mostly consist of human labor. The amounts of metal used for nail or
screws and the electricity for saws and other equipment are not evaluated as they would be minor
and similar for any alternative product used. Transportation of deck lumber to the point of use
and from the point of use to the landfill is included.
Release of carbon dioxide occurs during the life of the deck due to the partial oxidation or decay
of preservative and sealer components. This amount is estimated by calculations in the
“Landfill” tab of the spreadsheet and then entered into the LCA spreadsheet in the “Deck Life,
Demo, and Disposal” column.
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Inputs and outputs for the deck life span stage are subtotaled in the “ACQ Lumber in Decking”
column and then the energy and transportation portions are calculated and added to the subtotal
in the “LCI Total-ACQ Lumber Use” column. These are then added to the previous stage in the
“ACQ Lumber Life thru Use” column.
4.2.6
Landfill Stage (LC Stage 4)
The inventory of inputs and outputs related to the landfill stage of ACQ-treated lumber for
outdoor decking are included on the “ACQ LCI” tab in the columns under the red-highlighted
heading (
), “Landfill Stage”. The data, assumptions, and calculations used to develop the
inputs and outputs attributable to the disposal of treated lumber in landfills are presented in detail
within Appendix 4. The data are entered and calculations made in the “Landfill” tab and the
applicable data are entered by reference into the “ACQ LCI” tab.
The LCI assumes that ACQ-treated lumber is placed into a variety of landfill types, including
municipal landfills of wet (bioreactor) or dry types with and without methane collection and
construction and demolition (C&D) waste landfills. Assumptions about the fate in each type are
made based on USEPA reports and professional judgment.
The energy and transport inputs to construct a municipal waste landfill are proportioned on a perton disposed basis to the lumber placed into landfills. Emissions of methane and carbon dioxide
resulting from decay of the carbon contained in the treated lumber are estimated based on
USEPA data. A portion of the methane is assumed to be collected. Methane capture efficiencies
depend on the landfill type and are further explained in the landfill calculations included within
Appendix 4. Of the captured methane, part is assumed to be used to generate electricity and the
rest is assumed destroyed in flares, so that all the recovered methane is converted to carbon
dioxide. The landfill stage considered for this LCA is 100 years of product life in the landfill
after disposal. This time frame was chosen to allow the primary phase of anaerobic degradation
to take place (i.e., primary generation of methane is completed in the 100-year time frame).
Based on USEPA landfill data, this LCA assumes that 77 percent of the carbon in ACQ-treated
lumber placed in landfills is sequestered. Menard (2003) based this estimate on the disposal of
round tree limbs. The treating of wood likely will significantly reduce the degradation of lumber
in landfills and increase the sequestration of carbon in landfills; however, no data from published
sources were found to support such claims. Thus, the USEPA value of 77 percent sequestration
was used.
The copper not leached during product life is shown in the LCI as released to land in the landfill
phase. Given the limited decay of wood and the long-term storage design for landfills, this LCA
assumes that copper will remain in the landfill forever.
The total inputs and outputs associated with ACQ-treated lumber disposal in landfills are shown
in the “LCI Total-ACQ Lumber in Landfill” column.
4.3
ACQ INVENTORY TOTALS
The life cycle stages from cradle-to-grave are summed on the “ACQ LCI” tab in the columns
under the green-highlighted heading (
), “ACQ-Lumber Complete Life”. The sum
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includes the stages: planting and growth of trees, harvest of logs, milling of logs to lumber,
drying, production of ACQ preservative, pressure treatment of lumber with ACQ preservative,
use of ACQ-treated lumber in decks, maintenance of decking, demolition at the end of the use,
disposal in landfills, and final fate in the landfill.
4.4
WOOD PLASTIC COMPOSITE INVENTORY
One of the goal and scope items of this LCA is the comparison of ACQ-treated lumber decking
material to an alternate product available in the marketplace. The alternate product chosen for
comparison to ACQ-treated lumber decking material is wood plastic composite (WPC) decking
material. Most WPC decks have a treated wood under-structure, so only the deck surfaces are
considered in this comparative analysis. For ease of comparison, radius edge ACQ-treated
lumber decking (5/4-inch thickness) was assessed in this LCA and is directly comparable to 5/4inch WPC, without the need to consider the substructure.
WPC is composed of wood from recovered cellulose fiber materials and virgin and/or waste
plastics (USDA 2004). Comparisons with WPC are based on a functional unit developed
through the LCA process of the average U.S. deck size. The functional unit is 320 square
feet (sf) of decking surface (average deck). This provides a mechanism by which to compare
ACQ-treated lumber decking to WPC decking.
Full, comparable “cradle-to-grave” life cycle inventories are not available for WPC decking.
Thus, it was necessary to develop a life cycle inventory for WPC to allow application of similar
assumptions and to support normalization and impact comparisons. A survey of manufacturers
was not made to inventory inputs and outputs for WPC manufacture and therefore, inputs, such
as, fuel use, water use, and solid waste generation, at the WPC manufacturing facility are
estimated. Information related to materials used in representative plastic composites was
obtained from other sources. Data available from the NREL Life Cycle Inventory database were
used extensively. Additional data were obtained and used as needed. Simplifications and
assumptions were required to complete the inventories. The WPC LCI is developed in the same
spreadsheet as ACQ-treated lumber to maintain consistency and support comparisons. Based on
the life cycle inventory information, environmental impact indicators resulting from the
production and use, and disposal of WPC were calculated. The manufacturers of WPC are
encouraged to conduct a detailed LCA (meeting the ISO requirement for comparative analysis)
of their products to improve future comparisons.
The general category of WPC covers a wide and evolving variety of products. The plastic
content may vary from as little as approximately 30 percent by weight to as much as 100 percent,
and may be derived entirely from post-consumer use recycled material to entirely virgin plastic
(Platt 2005). Plastic may be partially or entirely high-density or low-density polyethylene,
polyvinyl chloride, or other types. Fiberglass reinforcement may be included (Platt 2005). Thus,
it was necessary to make assumptions to represent the “typical” product. Some of these
assumptions are listed below.
For the purpose of this LCI, high-density polyethylene (HDPE) was used as a reference material.
For the LCI, an average wood fiber content of 50 percent was applied as the baseline. It was
assumed that 50 percent recycled and 50 percent virgin HDPE are used for remaining portion of
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WPC. AquAeTer recognizes that some WPC manufacturers use 100% post consumer (recycled)
plastic and others use 100% virgin plastic material. Factors that influence those decisions might
include market price of virgin or recycled plastics, structural considerations, and availability.
This LCI of WPC does not infer that virgin and recycled HDPE are mixed in the same
manufacturing process (although some do), but that both virgin and recycled plastics are used in
WPC. The sensitivity analysis of this LCA is used to evaluate WPC with 100 percent virgin and
100 percent recycled plastic. Thus, comparisons can be made between ACQ-treated lumber and
WPC with varying virgin and recycled plastic content.
Wood powder and fiber
Recycled HDPE
Virgin HDPE
Total
50%
25%
25%
100%
For the purposes of the WPC LCA, a reference material was chosen with nominal dimension of
5/4 x 6 inch and actual dimensions of 1.175 x 5.4 inches. The spacing on a typical deck is one
decking plank every 6 inches, the same assumption used for ACQ-treated lumber decking. Some
WPC has void sections in cross-section to reduce the material used in manufacturing and reduce
product weight. These voids are minimal with 5/4 inch WPC, but are considered in a sensitivity
analysis.
While recycled plastic does not carry the inputs and outputs of virgin material, post-consumer
use plastic does involve significant effort to collect and process. Processes required for plastic
recycling include collection, compaction, sorting, reprocessing, and disposal of reject material.
The reprocessing may include prewashing, sorting, grinding, washing, flotation, drying, fine
screening, and storage (Arena, et al., 2003). Electric, diesel, and gas energy inputs were
estimated to be approximately 8 MJ/kg (3,400 BTU/lb) for recycled polyethylene terephthalate
(PET) and 21 MJ/kg (8,900 BTU/lb) for recycled polyethylene (PE). These compare to
approximately 49 MJ/kg (21,000 BTU/lb) for energy input to the manufacture of virgin high
density polyethylene (HDPE). This LCA uses the lower (PET) value for recycled plastic, which
is approximately 16 percent of the energy input to virgin HDPE. This value compares well to the
results of a separate LCA on thermoplastics recycling (Garrain, et al., 2007).
Inputs and outputs related to the production of HDPE were downloaded from the NREL LCI
database for HDPE and proportioned according to mass. Additional electric energy is assumed
necessary to process the mixture and extrude the product. These and other assumptions are used
in the “WPC” tab of the spreadsheet to create the data needed for the LCI.
The assumption above of 50 percent virgin and 50 percent recycled plastic significantly affects
the impact indicators for WPC. This mixture of virgin and recycled plastic is used to provide a
baseline evaluation of WPC. It is recognized that the proportions vary significantly between
manufactures, and that up to 100 percent recycled plastic is used for some products. As explored
in more detail in the Sensitivity Analysis, total energy, fossil fuel use, and acidification impact
indicators are significantly less if 100 percent recycled plastic is assumed. Conversely, such
impacts are greater if 100 percent virgin plastic is used. This assessment of recycled plastic does
not include an allocation of burdens from the original product; thus the only burdens associated
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with the recycled plastic product are those attributable to the recycling activity. AquAeTer
recognizes that some of the environmental burdens associated with the original product might be
attributable to the recycled product but has not attempted to make such estimates.
Transportation related impacts result from the transport of virgin HDPE pellets from
manufacturing location in Houston, Texas to plants manufacturing WPC. Five WPC
manufacturing plants were identified and an average transport distance of 1,513 miles was
calculated, as shown on the WPC tab. Outbound WPC product was estimated to require
transport of 750 miles to the end user. Finally, it was estimated that used WPC required 25 miles
of transport to a disposal site.
Assumptions similar to those for ACQ-treated lumber are used in the “WPC LF” tab to develop
inputs and outputs related to the landfill. It is assumed that the wood fiber fraction of disposed
WPC will degrade slowly in landfills to the same extent as the treated lumber. The HDPE
component of WPC is assumed to degrade, but to a lesser extent than wood. It is assumed that
94 percent of the HDPE carbon is sequestered with four percent converted to carbon dioxide and
two percent to methane. The low, but measurable, decay rate for HDPE is reasonable since the
HDPE will, as the wood component decays, have a very high surface to volume ratio; much like
a sponge. While HDPE is resistant to decay, in this condition it would not be realistic to assume
no decay.
As with treated wood, the WPC deck life span is often shorter than the potential product use life
because owners often replace decks as part of overall renovation projects related to changing
needs or desires or for aesthetic reasons. While the WPC manufactures’ literature often claims
longer use life than obtained from treated lumber, AquAeTer notes that the same factors of
surface weathering, stains, and the desire to upgrade deck designs applies to WPC as to ACQtreated lumber and results in WPC decks being replaced prior to the full useful product life.
Contrary to popular opinion, WPC decking does weather and decay. Water and oxygen
eventually enter the product, allowing decay fungi to enter with swelling and freeze/thaw cycles
that affect the product (Morrell, et al., 2006). WPC composition and designs varies greatly
between products and manufacturers and continue to evolve as problems are found and
addressed. Current or future WPC products may have research supported longer use lives.
However, to date, experience does not support a significantly different average use life than for
ACQ-treated lumber decking. For this LCI, the average life span for WPC decking is assumed to
be 10 years. It is assumed that no maintenance is done during this time, so the inputs and outputs
at the start of the deck life are nearly the same as at the end. Maintenance applications of
cleaners, bleaches, and/or fungicides may be applied and are recommended by many WPC
producers, but are not addressed by this LCA due to the variability in product compositions and
the lack of knowledge on their application frequency.
In a manner similar to the life cycle of ACQ-treated lumber, WPC decking manufacture, use, and
disposal are tracked on the “ACQ LCI” tab of the spreadsheet. LCI totals were summed at the
end of use stage and at the complete life stage. These totals are used for comparison to life cycle
stages of ACQ-treated lumber.
The life cycle inventory values for WPC are shown in Table 4-2. The sum includes the
extraction of raw materials, HDPE production, WPC manufacture, use as decking, demolition at
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the end of the useful life, disposal in landfills, and final fate in the landfill. The inventory totals
are shown per 1.0 Mbf and per 320 sf of deck (average deck size).
Additional information on the calculation of WPC inputs and outputs is included within
Appendix 4.
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Table 4-1
ACQ Treater Survey Results Summary
Questions
Less than 0.25 pcf treated during reporting year
Less than 0.25 pcf treated as decking during reporting year
Total amount of 0.25 pcf treated during year
Total amount of 0.25 pcf treated as decking during year
Total amount of 0.40 pcf treated during year
Total amount of greater than 0.40 pcf treated during the year
Total ACQ lumber treated
Total other water-borne treatments
Total oil-borne treatments
Total all treatments
CuO use
Quaternary use
Water use
Diesel use
Gasoline use
Propane use (for transportation)
Electric use
Natural gas use
Propane use (for heating and process equipment)
Wood chips use
Hazardous waste disposed
Process waste disposed
Other waste disposal
Truck inbound
Rail transport
Total outbound treated lumber truck
Total inbound chemical truck transport
Units
bf
bf
bf
bf
bf
bf
bf
bf
bf
bf
lb/bf
lb/bf
gal/Mbf
gal/Mbf
gal/Mbf
gal/Mbf
kWh/Mbf
cf/Mbf
gal/Mbf
ton/Mbf
pounds
pounds
pounds
tn-miles/Mbf
tn-miles/Mbf
tn-miles/Mbf
tn-miles/Mbf
4-16
Count
10
9
15
11
15
12
15
8
1
15
15
15
14
15
14
14
12
15
15
3
14
14
6
13
15
12
11
Minimum
0
0
0
0
1,054,861
0
1,870,346
1,200,000
16,873,584
7,140,157
0.0067
0.0028
3.3
0.15
0
0
0.043
0
0
0.0054
0
0
0
33
0
141
0.21
Average
9,338,183
0
25,167,490
3,555,835
10,881,222
2,290,505
44,106,570
11,642,652
16,873,584
51,440,890
0.027
0.0074
131
0.78
0.036
0.12
34
40
0.048
18
6,834
18,593
922,337
161
82
270
5.3
Weighted
Average
0
0
0
0
0
0
0
0
0
0
0.020
0.0057
121
0.53
0.013
0.11
12
19
0.038
NA
5,233
15,157
703,267
145
63
141
2.8
Maximum
62,593,447
0
117,643,219
7,500,000
33,980,011
14,800,000
214,377,529
30,514,452
16,873,584
219,881,395
0.092
0.022
299
2.9
0.41
1.6
250
324
0.40
53
41,463
150,000
3,840,000
678
489
494
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
Table 4-2
ACQ-Treated Lumber and WPC Life Cycle Inventory Summary
ACQ-Lumber Life
Normalized to
average deck size
and 10 yrs of use
Per Mbf
WPC Decking Life
Normalized to
average deck size
and 10 yrs of use
Per Mbf
Infrastructure Process
Units
Inputs from technosphere
Electricity, at grid, US
kWH
417
16.7
1,718
69
Natural gas, processed, at plant (feedstock)
ft3
641
25.6
19,087
763
Natural gas, combusted in industrial boiler
ft3
135
5.4
8,348
334
Diesel, combusted in industrial boiler
gal
5.9
0.2
42
1.7
Liquefied petroleum gas, combusted in industrial boiler
gal
0.15
0.0059
0.0049
0.00019
Residual fuel oil, combusted in industrial boiler
gal
0.081
0.0033
1.2
0.049
Diesel, combusted in industrial equipment
1.6
0.065
0
0
Gasoline, combusted in industrial equipment
gal
0.15
0.0058
0.22
0.0086
Hogfuel/biomass (50%MC)
lb
849
34
46
1.8
Coal-bituminous & sub., combusted in industrial boiler
lb
0.097
0.0039
0.46
0.019
Truck transport, diesel powered
ton-miles
476
19
3,785
151
Rail transport, diesel powered
ton-miles
84
3.4
316
13
Barge transport, res. oil powered
ton-miles
2.7
0.11
57
2.3
Ship transport, res. oil powered
ton-miles
32
1.3
51
2.0
Energy (Unspecified)
MJ
2.8
0.11
0
0
Petroleum refining coproduct, unspecified, at refinery
lb
0
0
254
10
Harvested sawlogs
ft3
59
2.4
0
0
Lumber-dry, planed
bf
1,000
40
0
0
ACQ preservative
lb
8.8
0.35
0
0
Copper
lb
4.7
0.19
0
0
Quaternary (DDAC)
lb
2.9
0.12
0
0
Monoethanolamine (MEA)
lb
16
0.65
0
0
Deck sealer
gal
8.0
0.32
0
0
Landfill capacity
ton
1.1
0.044
2.2
0.087
Inputs from nature
Water
gal
308
12
848
34
Bark from harvest
ft3
5.3
0.21
0
0
Unprocessed coal
lb
246
9.8
948
38
Processed uranium
lb
0.00065
0.000026
0.0024
0.000097
Unprocessed crude oil
gal
5.1
0.20
3.6
0.14
Unprocessed natural gas
ft3
1,043
42
39,723
1,589
Biomass/wood energy
Btu
0
0
0
0
Hydropower
Btu
114,688
4,588
445,138
17,806
Other renewable energy
Btu
13,156
526
33,132
1,325
Carbon (from air)
lb
295
12
825
33
Outputs to nature (air, except where noted)
CO2-fossil
lb
1,116
45
4,957
198
CO2-non-fossil
lb
1,362
54
920
37
Carbon monoxide
lb
3.7
0.15
3.5
0.14
Ammonia
lb
1.8
0.073
0.0032
0.00013
Hydrochloric acid
lb
0.22
0.0089
0.57
0.023
Hydrofluoric acid
lb
0.020
0.00080
0.071
0.0028
Nitrogen oxides (NOx)
lb
2.5
0.10
8.5
0.34
Nitrous oxide (N2O)
lb
0.032
0.0013
0.026
0.0010
Nitric oxide (NO)
lb
0.050
0.0020
0
0
Sulfur dioxide
lb
5.7
0.23
44
1.8
Sulfur oxides
lb
0.53
0.021
0.55
0.022
Particulates (PM10)
lb
3.3
0.13
0.41
0.016
Volatile organic compounds
lb
2.1
0.083
1.9
0.075
Methane
lb
82
3.3
157
6.3
Acrolein
lb
0.015
0.00061
0.00014
0.0000055
Arsenic
lb
0.00014
0.0000056
0.00020
0.0000081
Cadmium
lb
0.000025
0.0000010
0.000039
0.0000016
Lead
lb
0.00024
0.0000098
0.00021
0.0000086
Mercury
lb
0.000026
0.0000010
0.000044
0.0000018
Copper (to water)
lb
0.00033
0.000013
0
0
Copper (to ground)
lb
4.7
0.19
0
0
Solid wastes-landfill
lb
90
3.6
4,463
179
Solid wastes-recycled
lb
0.025
0.0010
0
0
Wood wastes-treated-landfill
lb
2,132
85
0
0
Note: The “ACQ” and “HDPE Prod” spreadsheet tabs include a more comprehensive list of inputs and outputs associated with the manufacture of ACQ
and HDPE.
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ACQ-Treated Lumber
5.
5.1
IMPACT ASSESSMENT
GENERAL
The LCA impact assessment (LCIA) phase establishes links between the production, use, and
disposal of ACQ-treated lumber and potential environmental impacts. The impact assessment
calculates impact indicators, such as greenhouse gas emissions and fossil fuel use. These impact
indicators provide general, but quantifiable, indications of potential environmental impacts.
The impact assessment was carefully planned to be consistent with the goal and scope of the
LCA. The quality of the LCI data, system boundaries and data cut-off decisions were sufficient
to calculate the indicators. Also, the LCI functional unit, averaging, aggregation, and allocations
were all reviewed and found to be acceptable for conducting the impact assessment.
Steps of the life cycle impact assessment for ACQ-treated lumber include:
1. Selection of Impact Categories - identifying relevant environmental impact categories;
2. Definition of Impact Categories – defining the characterization model;
3. Classification - assigning life cycle inventory results to the impact categories;
4. Characterization - modeling life cycle inventory impacts within impact categories
using science-based conversion factors;
5. Normalization - expressing potential impacts in ways that can be compared to
alternative products; and
6. Evaluating and Reporting Life Cycle Assessment Results - gaining a better
understanding of the reliability of the assessment results.
The results of this impact assessment are used in comparison to alternative products on the
market in competition with ACQ-treated lumber. Therefore, weighting was not included in this
impact assessment per the requirements of ISO 14044, Section 4.4.5.
5.2
IMPACT INDICATORS
The impact assessment uses the results of the inventory analysis by applying those results to
general impact indicator categories. Impact indicator values were calculated in the LCI
spreadsheet for each process unit in the products’ life cycle stage and summed for each stage of
the life cycle. This facilitates comparison of indicators between stages and helps quantify the
relative contributions to each indicator, for example, particular manufacturing steps, use
practices, or disposal options.
The results of the LCI are used to quantify relative environmental impacts for comparative
purposes using impact indicators. The target impact indicator, the impact category, and means of
characterizing the impacts are summarized in Table 5-1.
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ACQ-Treated Lumber
For each impact category, impacts occur through a complex series of interactions. For example,
contributions to global warming are thought to result from increasing levels of carbon dioxide
and other chemicals that tend to trap energy within the earth’s biosphere. However, the chemical
reactions, positive and negative feed-back loops, normal earth and solar variability, and other
factors make reaching precise conclusions impossible. While emissions of greenhouse gases
associated with the production and use of a product may be calculated, the endpoint impacts,
such as increased sea level or changes in agricultural productivity, remain unknown. Thus, for
this LCA, category impacts will be characterized by accepted midpoint indicators such as tons of
carbon dioxide equivalents emitted per unit of product. Such impact indicators are useful when
comparing the relative potential impacts of one product to those of another.
Table 5-1
Impact Indicators, Characterization Models, and Impact Categories
Impact Indicator
Greenhouse gas (GHG)
emissions
Fossil fuel usage
Releases to air potentially
resulting in acid rain
(acidification)
Releases with potential
ecological toxicity
Releases to air potentially
resulting in smog
Releases to air potentially
resulting in eutrophication
of water bodies
Amount of water used
Characterization Model
Calculate total equivalent human-caused (anthropogenic)
carbon dioxide (CO2) emissions for CO2, methane, and nitrous
oxide per functional unit.
Total amount of fossil fuel, based on BTU value, used in
product life cycle per functional unit.
Calculate total hydrogen ion (H+) equivalent for released
sulfur oxides, nitrogen oxides, hydrochloric acid, and
ammonia using factors from USEPA’s Tool for Reduction and
Assessment of Chemical and Other Environmental Impacts
(TRACI 2002). Acidification value is in units of H+ moleequivalents per functional unit.
Use the impact factors from TRACI (2002) to calculate the
ecotoxicity potential of releases in units of lbs 2,4-D-eq per
functional unit.
Use the impact factors from TRACI (2002) to calculate the
smog forming potential of releases in units of grams of mononitrogen oxides (g NOx) / meter per functional unit.
Use the impact factors from TRACI (2002) to calculate the
eutrophication potential of releases in units of pounds of
nitrogen (N)-equivalents per functional unit.
Calculate total water use per functional unit.
Impact Category
Global warming
Resource depletion
Acidification
Ecotoxicity
Photochemical
smog
Eutrophication
Water use
Each impact indicator is a standard category as separate measures of an aspect of potential
impact. This LCA does not make value judgments about the impact indicators, meaning that no
one indicator is given more or less value than any of the others. All are presented as equals.
Additionally, each impact indicator value is stated in units that are not comparable to others. For
example, millions of BTUs of energy cannot be compared to pounds of carbon dioxide
equivalents or hydrogen ion mole equivalents. For the same reasons, indicators should not be
combined or added.
For a person considering which product to purchase and use, the impact indicators should be
viewed as some of the many attributes of the products that need to be considered. Other
attributes that may also be important include, for example, appropriateness for the intended use,
purchase price, ease of installation, proven performance, aesthetics, ease of disposal, and worker
acceptance.
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ACQ-Treated Lumber
5.3
5.3.1
IMPACT INDICATOR DEFINITION AND CLASSIFICATION
Greenhouse Gas (GHG) Emissions
Emissions of GHGs, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are
calculated for each unit process and multiplied by their respective global warming potential
equivalence factors of 1, 21, and 296, respectively, to calculate pounds CO2-equivalent emissions
per unit of product (i.e., Mbf and 320 sf of deck) per year of use. The authors note that there are
many additional chemicals that have significantly larger factors, such as the hydrofluorocarbon
HFC-123a with a factor of 1,300. However, these chemicals are either not associated with or not
reported in inventories for the processes in the production of preservative treated lumber so are
not included in the inventory and, therefore, are not a part of the impact assessment.
The intent of the GHG impact indicator is to quantify human-caused (anthropogenic) emissions
that reportedly have the potential to affect the global climate. Although carbon dioxide
molecules behave the same, whether from fossil fuels or biomass, they are addressed differently
in calculating the GHG emissions. Carbon dioxide resulting from burning or decay of wood
(biomass or biogenic material) grown on a sustainable basis are considered to mimic the closed
loop of the natural carbon cycle (USEPA 2009) and are not included in the calculation of
greenhouse gases. However, methane that results from the decay of wood or other carbon-based
waste in landfills is counted. This methane is produced because disposal in engineered landfills
results in anaerobic decay that would not be produced by natural combustion or surface (aerobic)
decay.
5.3.2
Fossil Fuel Usage
The chosen impact indicator for resource depletion is fossil fuel use. It is clear that the amount
of fossil fuel used to make, use, maintain, and dispose products is important to the public. It is
currently an issue related to global climate change, national security, and national and personal
finances. The impact indicator unit of measure chosen is total million BTU (MMBTU) of fossil
fuels used per unit per year of decking lumber use.
5.3.3
Releases to Air Potentially Resulting in Acid Rain (Acidification)
The acidification impact indicator assesses the potential of emissions to air to result in acid rain
deposition on the earth’s surface. Factors relating the relative potential of released chemicals to
form acids in the atmosphere (TRACI, 2002) are multiplied by the chemical release amounts to
calculate equivalent acid rain potential as hydrogen ion (H+) mole equivalents.
5.3.4
Water Use
The total amount of water used in each unit process of the product life is calculated in gallons per
unit per year of use. Since water use data are not available for all supporting process units,
importantly for electric production, results for this impact category may be of limited value.
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
5.3.5
Ecotoxicity
The ecotoxicity impact category includes ecologically toxic impact indicators that are
normalized to a common herbicide of accepted ecological toxicity, 2,4-D (2,4Dichlorophenoxyacetic acid). The amounts of constituents released to air during the products’
life cycle stages are multiplied by the factors contained in TRACI to calculate the indicator
values. The releases of constituents to the land or water are not addressed in this indicator nor in
other indicators in this LCA.
5.3.6
Releases to Air Potentially Resulting in Eutrophication
The eutrophication impact indicator is normalized to pounds of nitrogen equivalent. The factors
contained in TRACI are used to calculate the indicator values. Eutrophication characterizes the
potential impairment of water bodies resulting from emission to the air of phosphorus, mononitrogen oxides (NOx), nitrogen oxide, nitric oxide, and ammonia.
5.3.7
Releases to Air Potentially Resulting in Smog Formation
The smog impact indicator assesses the potential of air emissions to result in smog. Emission
impact indicators from TRACI (2002) are used, as with other indicators noted above, to calculate
the smog forming potential related to emissions. In response to questions about the units used in
TRACI, Jane Bare (USEPA) provided the following explanation via email:
“This is the most common question I get within TRACI, so of course I am changing things
in Version 2. The reason for the original units follows, but we could have just as easily
divided everything by any reference chemical to make it into chemical equivalents.
“They are in units of grams of NOx-equivalents per meter per kg emission. The reason
for these units is that when the site specific characterization factors were being
developed on a state wide basis, we first computed the expected change in NOx
concentration by state (g/m3) per kg emission. We then multiplied these concentration
changes by the area of each state to obtain total NOx concentration impacts in units of
g NOx/m, per kg emission. Finally, the relative reactivity’s of NOx and each VOC are
used to derive the final smog factors for each pollutant.
“So I will agree that this is a very strange unit, which has been very confusing to people.
Chances are very high that you will not see this unit in the next version.”
As with the other impact indicators, this is only useful as a basis of comparison between products
for which the same calculations, via LCI data, have been made.
5.3.8
Impact Indicators Considered But Not Presented
The TRACI model, a product of USEPA and the USEtox model, a product of the Life Cycle
Initiative (a joint program of the United Nations Environmental Program (UNEP) and the
Society for Environmental Toxicology and Chemistry (SETAC)), offer several additional impact
indicators that were considered during the development of the LCA. However, for the reasons
discussed below, the impact indicators were not fully evaluated and presented within this report.
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
5.3.8.1 Human Health
Since inception of this LCA, specifically when the impact assessment phase was in development,
the issue of assessing human health impact has received detailed and careful consideration.
AquAeTer and TWC have maintained that human health can only be assessed if including risk.
Human health risk is a function of chemical toxicity (including, for metals, speciation and
bioavailability), pathway, and exposure; mechanisms that this LCA does not provide the tools to
assess. AquAeTer and TWC originally decided not to include human health indicators in the
LCA scope due to concern that any values would be misconstrued by readers as indicating that
the products posed actual risks to the users.
The independent external reviewers, in commenting on the draft Goal and Scope document,
stated that an LCA should include “all attributes and aspects of natural environment, human
health, and resources.” They further pointed out that the TRACI model provided factors to
equate the various emissions and support comparisons between products. AquAeTer and TWC
then agreed to consider human health indicators using the TRACI factors for cancer, non-cancer,
and criteria air pollutant impact indicators in the LCA.
As the LCA progressed, we found the TRACI model uses toxicity values as the basis for
calculating human health impact indicators. Again, AquAeTer and TWC took issue with this
use, as human health assessment must be made from specific epidemiological studies or
dedicated risk assessments.
Despite the disagreement on human health, AquAeTer and TWC continued our evaluation of
human health impact indicators and found unexpectedly high values for the combustion of wood
in boilers used at sawmills to dry lumber. In particular, human health impact indicators for
cancer and non-cancer were driven by heavy metals emissions. Evaluation of the results
revealed that the TRACI potency factors for the metals appear to estimate health impacts based
on factors that assume metals are emitted and remain in their most toxic speciation forms.
Factors based conservatively on the most potent forms of metals will greatly overestimate
potential impact. In reality, such metals are emitted in various speciation forms and react with
the environment to oxidize to more stable forms and/or combine with or bind to other minerals or
organic matter into compounds that are largely not biologically available 5 and therefore, present
much less potential impact. Considering the issues presented above, AquAeTer and TWC
concluded that the TRACI impact indicators, in their current form, do not provide an appropriate
tool for assessing human health impacts and thus, human health impact indicators were not
included in our draft report made available for independent external review.
The independent external review team commented, in their review of the draft report, that an
LCA without human health cannot claim to be “completed in a manner consistent with the
principles and guidance in ISO 14040 and 14044.” The independent external reviewers
suggested that USEtox may offer a better model for evaluation of human health. The USEtox
5
Conclusion of Paper entitled, Declaration of Apledoorn on Non Ferrous Metals available at:
http://www.uneptie.org/pc/sustain/reports/lcini/Declaration%20of%20Apeldoorn_final_2c.pdf).
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ACQ-Treated Lumber
model was developed from a number of existing models and evolved as a result of collaborative
international effort with the goal of creating a LCA tool that would be widely accepted and used.
The current version was published in 2008 and has a comprehensive list of over 3,000 chemicals.
Characterization Factors (CF) are listed for human health for over 1,200 and for freshwater
ecotoxicity for over 2,500 chemicals. For comparison, TRACI 2002 contains 933 chemicals for
which 146 have cancer and 292 have non-cancer human health factors and 161 have ecotoxicity
factors. USEtox differs from TRACI in that combined cancer and non-cancer human health CFs
are provided, rather than requiring that they be addressed separately. However, the current
version of USEtox, like TRACI, includes toxicity values based on risk and has not yet solved the
metals speciation issue. Instead, metals such as lead and mercury are not included. The paper
describing the USEtox model (Rosenbaum et al, 2008) states that USEtox “does not account for
speciation and other important specific processes for metals, metal compounds…” and lists
“Development of USEtox to accommodate the metals” as one of the future improvements for the
next phase. So, switching to USEtox from TRACI would not solve the metals issue, but sidestep
it. Thus, we conclude that there is not currently an acceptable tool to evaluate human health
impact indicators in an LCA.
TWC members have continuing concerns regarding interpretation of human health indicators.
TWC members understand that elimination of human health is a variance from ISO 14040 and
14044 standard, but note that ISO allows for variance if elements of the LCA are determined to
be unsupported. According to ISO 14040, Section 5.2.1.2, “LCA is an iterative technique, and as
data and information are collected, various aspects of the scope may require modification in
order to meet the original goal of the study.” It is TWC’s opinion that public perception of
human health impacts and risk are inseparable and reporting human health impacts, especially in
terms of potential cancer impact, will inevitably be interpreted as measures of risk applicable to
the use of the product.
Fundamentally, human health impact is a measure of “risk” and risk is a function of chemical
speciation, pathway, and exposure, topics that are site and case specific and we believe,
appropriate for a risk assessment. The TWC has changed the scope of this LCA to not include
human health impact evaluation. Thus, this LCA includes the life cycle emissions potentially
related to human health, but does not address human health impact indicators.
5.3.8.2 Releases to Land and Water
Indicators related to releases to water were not evaluated because water release data would not
support meaningful impact conclusions. For example, while copper is known to be released
from ACQ treated wood during its use stage, releases are nearly always to the surface soil at or
under the deck. Copper tends to bind to mineral and organic matter in soil and not migrate to
surface water as further described in Section 4.2.5. Land and water impact indicator values are
based on concentration of constituents in the respective media. With respect to water releases,
ACQ treaters are zero-discharge facilities. Estimates of amount of constituent of concern
leached from treated wood in storage, its concentration in soil or mobilized and discharged into a
water source, and constituent of concern available for impact are poorly supported.
Scientifically supported estimates of soil and water concentrations would require site specific
information such as facility practices, copper speciation, soil pH and organic content, local water
quality (pH and hardness), precipitation, volumetric water flow off site, and soil type, research
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that was well beyond the scope of this LCA. Thus, the amount of leached constituents of
concern was not used to determine impacts due to soil or water related exposure.
Similarly, constituents of concern released in landfills likely will bind and not be released with
leachate, should that occur. While data are available for some of the supporting processes, those
processes are not the primary subject of this LCA.
5.3.8.3 Land Use
The quantity of waste products generated by all life cycle stages of ACQ-treated lumber and land
use modifications was considered as an impact indicator for this LCA. It was determined that
the primary product in ACQ-treated lumber is wood fiber, harvested from sustainable forests.
Sustainable forest use does not result in change in land use. Furthermore, quantification of land
use modification due to procurement of natural resources was considered out of scope for this
project. Therefore, land use was not retained as an impact indicator.
5.4
TOTAL ENERGY
The total amount of energy input to a product over its life cycle is not considered an impact
indicator, but is tracked rather as an indicator of other indicators. Total energy is the energy
derived from all sources, including fossil, biogenic, and grid electricity converted to common
units of millions of BTU (MMBTU) per unit. Energy sources are, to varying degrees, fungible,
meaning they can be transferred from one use to another. Wood fuel (biomass) can, as in the
case of lumber, be used to heat the dry kilns or it could be used for home heating pellets or to
fuel electric power generation. Similarly, kilns could be heated with natural gas. Generally,
products that require less input of energy will have less environmental impact. Tracking total
energy allows users to compare this aspect of each product.
5.5
CHARACTERIZATION
For characterization of certain impact indicators, AquAeTer used USEPA’s TRACI (2002)
model. The TRACI spreadsheet model includes hundreds of specific chemicals and lists impact
values for various environmental impacts, including those listed above.
This LCA uses a separate workbook, “ChemicalFactors”, including the TRACI spreadsheet, to
calculate unit value impacts for each of the “processes” involved in the ACQ-treated lumber and
WPC LCI. Inventory inputs and outputs for most processes, such as electric power generation,
wood combustion, or truck transportation are those downloaded from the NREL’s U.S. LCI
Database, as previously described. Individual spreadsheets within the “ChemicalFactors”
workbook include the complete list of inputs and outputs for each “process”. Pertinent data are
then copied into a column of the process emissions spreadsheet (“ProcEmis” tab). The sum of
products function is used to calculate the sum of the products of impact indicator value times the
emission for each emitted chemical, resulting in emission factors for each process. The TRACI
factors are provided in “per kg” units. In the “ChemicalFactors” spreadsheet, they are converted
to “per pound” units to match the emission units of the LCI. These are then entered into the
“ACQ LCI” tab for each process and proportioned to the products, so that final impact values for
each life cycle stage may be determined.
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5.6
5.6.1
NORMALIZATION
Product Normalization
Each lumber product is normalized to units of measure that support comparisons to other
products. In this LCA, data are normalized to 1,000 board feet (Mbf) and to 320 sf of deck, the
average size of a U.S. deck. Additionally, the ACQ-treated lumber product is normalized to
years of useful life (indicator value/average deck/yr) in recognition that not all products may last
the same amount of time.
5.6.2
National Normalization of Impact Indicators
Impact indicators, as described above for deck products, support comparison between products,
but provide no basis for understanding practical magnitude. National normalization provides a
means to compare the impact indicator values for one deck to one average American family’s
annual impact. Average U.S. per capita impacts have been calculated for the TRACI and
USEtox impact indicators based on total U.S. emissions in 1999 (Bare, Gloria, and Norris, 2006).
The approach and these data were expanded and updated by use of more recent 2007 energy,
fossil energy, and GHG emission data for the U.S. (EIA, 2008) and national 2000 year water use
(USGS web site).
Consider, for example, what is a significant cost for a household with approximately the U.S.
mean income of $50,000 per year. A new car at $25,000 represents 50% of the annual income.
If the car lasts 5 years, $5,000 per year represents 10% of the annual income. This would be the
financial “footprint” of the new car. If the family is comparing cars, one that costs $50,000 and
lasts the same time would clearly be two times more expensive and, going from 10% to 20% of
annual income would be significant. On the smaller side, consider a cup of coffee once a week;
a standard cup at $1/cup versus a fancy cup at $4. The annual costs for each would be $52 and
$204, or 0.1% and 0.4% of annual income, respectively. At this point, the cost of the fancy cup
has four times the impact, but is not significant to the family budget. At the low end, consider
one box of paperclips per year. The cheap box is $0.50 and the expensive one is $2, four times
more expensive. However, at 0.001% and 0.004% of family income, the financial “footprints”
of both are insignificant.
In the “Norm” tab, these national average impact indicator values and U.S. totals have been
converted to the units used in this LCA (pounds) and compared to the calculated impact
indicators for a “typical deck” of 320 sf of ACQ-treated lumber and WPC deck. This size is
representative of a typical deck in the U.S. and provides a reasonable basis of comparison.
Direct comparisons of the ratio of the deck impact to average family impact, based on a family of
three, are provided in percentage format. Thus, for example, if ecological impact of the average
deck is 0.04 percent of the national average, this would mean generally that if a family installed a
deck at their home, the family impact or “footprint” for ecological impact would be 0.04 percent
– relatively insignificant.
Cautionary Note – U.S. average impact indicator values are based mostly on the 1999 Toxic
Release Inventory (TRI). The TRI data are based on reports to EPA of releases from larger,
mostly industrial type facilities whose releases exceed the reporting thresholds. Thus, totals do
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not include small industrial facilities with emissions below reporting thresholds, transportation
fuel use, home and commercial heating, or most agriculture emissions. Real total U.S. and per
capita releases may be significantly larger than stated and, thus, impact indicators for decking
may actually be a smaller portion of the U.S. averages than indicated.
5.7
ACQ IMPACT ASSESSMENT
Impact indicator values were totaled at four stages along the life cycle of the treated wood
product: just prior to treatment, ACQ-treated lumber delivered to the use site, ACQ-treated
lumber at the end of its use, and ACQ-treated lumber after reaching stable conditions
(approximately 100 years) in a landfill. The impact indicator values for ACQ-treated lumber,
calculated at the four stages and reported per Mbf, are shown in Table 5-2.
Impact indicator values were normalized to per year of installed deck use (assuming a deck use
life of 10 years) and per the average U.S. deck size of 320 sf. The impact indicators again were
evaluated at the four life cycle stages. The impact indicator values per year and per average deck
are provided in Table 5-3.
In an attempt to normalize the magnitude of impact indicators, comparisons to U.S. per capita
per year emissions were made. The results of the comparison to U.S. average emissions are
provided in Table 5-5 and summarized in the following findings.
5.7.1
Greenhouse Gas Emissions
For the cradle-to-grave life of ACQ-treated lumber, an average deck results in GHG impacts of
0.074 percent attributable to an average American family. The releases of GHGs are relatively
minor throughout the production and use stages of ACQ-treated lumber and primarily attributed
to transportation related impacts. During the landfill stage, most of the GHG, as CO2equivalence, is methane resulting from the anaerobic decay of wood and other carbon-based
components of the treated wood. Emissions resulting from the energy used to construct and
close the landfill also are significant.
5.7.2
Fossil Fuel Usage
Fossil fuel usage resulting from an average deck constructed of ACQ-treated lumber is 0.028
percent of the average American family’s annual impact. Fossil fuel usage is minor throughout
the production stage of ACQ-treated lumber and primarily attributable to transportation related
impacts. A significant portion of the fossil fuel use for ACQ-treated lumber used for decking is
attributed to application of sealer during the deck’s use life. Also, a significant portion of the
total fossil fuel use by ACQ-treated lumber is attributable to landfill construction and closure.
Although not an impact indicator, total energy use, including fossil fuel use, is minor at 0.040
percent of the average American family’s annual use.
5.7.3
Emissions Potentially Resulting in Acid Rain (Acidification)
Emissions potentially resulting in acid rain are largely the result of electricity production,
transportation, and production of sealer and are also minor (0.049 percent) for the cradle-to5-9
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grave life of an average deck constructed of ACQ-treated lumber compared to the acidification
impact resulting from one average American family’s annual impact.
5.7.4
Water Use
Water use data were only available for lumber production and treatment processes, so these
results will have only limited value. Water use related to fuels and electricity production, ACQ
production, and landfill construction are not known.
5.7.5
Releases to Air Potentially Resulting in Ecological Toxicity
The ecotoxicity impact indicator is mostly driven by combustion emissions during the lumber
production stage and landfill construction emissions in the disposal stage. The potential impact
to ecological toxicity, resulting from the installation of an average ACQ-treated lumber deck, is
0.053 percent of the average American family’s annual impact.
5.7.6
Emissions with Potential to Impact Eutrophication
The eutrophication indicator is mostly driven (79 percent) by emission of ammonia from MEA
immediately after treatment and during use. The potential impact to eutrophication, resulting
from the installation of an average ACQ-treated lumber deck, is 0.039 percent of the average
American family’s annual impact.
5.7.7
Emissions with Potential to Form Smog
The smog impact indicator value increases with each life cycle stage. Significant process inputs
include wood combustion, sealer manufacture and application, and landfill construction. The
potential to form smog, resulting from the average ACQ-treated lumber deck, is 0.024 percent of
the average American family’s annual impact.
5.8
ACQ-TREATED LUMBER TOTAL ENERGY IMPACT
Total energy use resulting from an average deck constructed of ACQ-treated lumber is 0.040
percent of the average American family’s annual impact. A significant portion of the total
energy use for ACQ-treated lumber used for decking is attributed to application of sealer during
the deck’s use life. Also, a significant portion of the total energy use by ACQ-treated lumber is
attributable to landfill construction and closure.
Of the total energy approximately 40% is from biomass and 60% is from fossil fuel. Biomass is
used as boiler fuel during the production phase. Table 5-7 provides a summary of energy
sources used by product life cycle.
5.9
WOOD PLASTIC COMPOSITE IMPACT ASSESSMENT
Impact indicators, defined in Table 5-1, were calculated for wood plastic composite in a manner
similar to that described for ACQ-treated lumber. Primary data for HDPE was available through
the U.S. LCI database. Manufacturing data for wood plastic composites were not made
available; therefore, professional judgment was used.
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Impact indicator values were totaled at two stages along the life cycle of the WPC product
including: 1) at the end of use as a decking material, and 2) after reaching stable conditions
(approximately 100 years) in a landfill. Note that for WPC there is no comparable life stage to
untreated lumber and that indicator values for WPC prior to installation and at the end of use
remain nearly identical since no sealer is applied to WPC. Thus, only the two life stages are
summarized. Impact indicator values were normalized to per year of installed deck use,
assuming a WPC deck use life of 10 years and a functional unit of 320 sf of deck, the average
size of a deck in the U.S. The normalized impact category values per average deck per year of
use are provided in Table 5-4.
The goal and scope of this study did not include an analysis of the contributing factors to each
impact indicator. The purpose of the wood plastic composite assessment is solely to assess
relative impacts when compared to ACQ-treated lumber. Therefore, no discussion of the impact
indicators and their product specific contributions is provided in this section. AquAeTer
performed sensitivity analyses on inventory items of significance, related to WPC. The items
addressed in the sensitivity analysis and their outcomes are included in Section 5.8.3. Additional
discussion regarding the comparison of ACQ-treated lumber and WPC is provided in Section
5.9.
5.10 DATA QUALITY ANALYSIS
ISO 14044, Section 4.4.4, discusses optional additional techniques to help better understand the
significance, uncertainty, and sensitivity of the LCI results. These tools help distinguish if
significant differences are or are not present, identify negligible LCI results, and guide the
iterative LCIA process.
4.4.4.2 The specific techniques and their purposes are described below.
a) Gravity analysis (e.g. Pareto analysis) is a statistical procedure that identifies those
data having the greatest contribution to the indicator result. These items may then be
investigated with increased priority to ensure that sound decisions are made.
b) Uncertainty analysis is a procedure to determine how uncertainties in data and
assumptions progress in the calculations and how they affect the reliability of the results
of the LCIA.
c) Sensitivity analysis is a procedure to determine how changes in data and
methodological choices affect the results of the LCIA.
Each of the additional data quality analysis tools were used to better assess the impact
assessment findings.
5.10.1 Gravity Analysis
A first simple approach to see what processes have the greatest impact can be accomplished by
inspecting the bar graphs for each indicator as shown on Figure 5-1. The more detailed
spreadsheets can then be evaluated while asking; “Are these results reasonable?” For the ACQtreated lumber, inspection indicates the following:
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•
77 percent of GHG emissions result at the end of the life cycle stage because of methane
generation from decay of the treated wood in the landfill. This is consistent with the
landfill model, but is subject to the landfill assumptions, especially related to methane
generation and capture;
•
Fossil fuel inputs to the treated lumber life cycle occur during all stages. Biomass is the
primary fuel source for boilers used to heat kilns, offsetting the need for natural gas or
other fuel source consumption in the drying of lumber products. Sealer is made from
fossil fuel and accounts for fossil fuel in the use stage (22 percent of the total fossil fuel
use);
•
Releases related to acidification occur in each life stage. Most significant are electricity
use, inputs for the production of the ACQ preservative, and landfill requirements;
•
61 percent of the emissions potentially resulting in ecological toxicity result from
combustion emissions during the lumber production stage;
•
79 percent of the emissions potentially resulting in eutrophication impact result from the
ammonia evaporation during the treatment and use stages; and
•
61 percent of the emissions potentially resulting in smog formation result from the
lumber production stage prior to treatment.
This assessment evaluated the primary causal factors for the impact indicators, as discussed
above, and concluded they are reasonable and suitable for use in this LCA.
5.10.2 Uncertainty Analysis
The scope of this LCA, being cradle-to-grave, requires many data inputs that involve uncertainty.
AquAeTer has strived to make realistic assumptions in all cases. However, some assumptions
are based only on professional judgment. Some areas of uncertainty most likely to impact the
results of the LCA are discussed below.
5.10.2.1 ACQ Production
The ACQ preservative producers did not provide detailed LCI input and output data for ACQ
production, so AquAeTer made assumptions and used analogous processes to estimate the inputs
and outputs. Assumptions used in the calculation of inputs and outputs resulting from the
production of ACQ are included in the ACQ Production Calculation (within Appendix 4) and
summarized in Appendix 6. Since AquAeTer did not survey ACQ producers, uncertainty exists.
5.10.2.2 Copper Releases
Copper released during ACQ lumber treatment, storage, use as decking, and finally in landfills
can only be estimated by use of assumptions. Calculations, included within Appendix 4,
estimate copper releases using professional judgment assumptions. The uncertainty of these
assumptions is large because of variations in production facility containment structure integrity,
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production facility housekeeping practices, regional location of the treating facility and use site
(i.e., precipitation amount will directly impact leaching), and disposal site characteristics.
Since copper is not released to air, the impact indicators identified in Section 5.2 will not change
with increases or decreases in copper amounts released. Copper released to soil or into surface
water rapidly complexes with minerals and carbon-based materials into insoluble compounds
(Michels, 2009). Thus, environmental impact is limited because of the absence of a transport
mechanism.
5.10.2.3 Decking Sealer
In this LCA, decking sealers were assumed to be applied in the use stage of the ACQ-treated
lumber’s life cycle. Numerous manufacturers produce sealers. A representative sealer was
chosen and variations in the sealer contents will result in uncertainties. Assumptions in our
calculation of inputs and outputs from the manufacture, use, and disposal of sealers are included
within Appendix 4.
All of the VOCs associated with the sealer are assumed to be emitted to the air when the sealer is
applied. The remaining sealer is assumed to be a combination of carbon-based solids that
partially oxidize during use and partially remain with the wood to disposal.
5.10.2.4 Landfill Fate and Releases
AquAeTer based emission estimates from landfills on data USEPA uses to estimate greenhouse
gas emissions for its inventory. However, assumptions made have significant impact on
indicator values, especially for GHGs. As more landfills in the U.S. install methane collection
systems, methane emissions will decrease. Further, in the LCA, ACQ-treated wood is assumed
to degrade to the same degree as untreated wood. If treatment retards or prevents degradation of
the wood in a landfill, as expected, then releases could be significantly less. The assumptions
used have uncertainty and result in uncertainty in our calculation of GHGs. Because of the
landfill uncertainties, further analysis was conducted as part of the sensitivity analysis.
Additionally, estimation of releases of copper from landfills to soil and groundwater is
problematic. Modern landfills are designed to prevent such releases, so such releases could be
stated as not occurring. Also, we have assumed that carbon-based components of ACQ
preservative and sealer remaining in the treated lumber are decomposed in the landfill in the
same proportions as the wood. However, the possibility that some release of copper and partially
decomposed carbon-based matter does occur, creates a level of uncertainty.
5.10.2.5 WPC Uncertainty Analysis
The comparative analysis phase of this LCA includes the assembly of an LCA for an alternate
product to ACQ-treated lumber. The scope allows for the cradle-to-grave LCA of WPC to
include data inputs that involve uncertainty. AquAeTer has strived to make realistic assumptions
in all cases. However, some assumptions are based only on professional judgment. No survey
of manufacturers of WPC was done. Areas of uncertainty most likely to impact the results, such
as percentage of the WPC product consisting of virgin and/or recycled HDPE, are discussed in
further detail in Section 5.10.3, Sensitivity Analysis.
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5.10.2.6 Uncertainty Conclusion
While uncertainty of specific factors used within the LCI remain significant, AquAeTer has
determined that, even with the uncertainty present in this LCA, the conclusions are reliable for
the intended use.
5.10.3 Sensitivity Analysis
AquAeTer evaluated the many data inputs and assumptions required for the LCA. Certain items
or categories stand out as most important in affecting the sensitivity of LCA impact indicator
outcomes and are discussed in greater detail below. Additional information and model results
are included in Appendix 7.
5.10.3.1 Copper
Although most copper used in ACQ comes from recycled sources as described in Section 4.2.3.1,
it would not be appropriate to account for it as if no inputs or outputs are associated with
collection, recycling and preparation of copper compounds for use. Thus, a ratio was applied to
the inputs and outputs associated with copper used in ACQ to new copper. In this life cycle
assessment, one third of the inputs and outputs associated with new copper are allocated to the
recycled copper used in ACQ.
As a sensitivity analysis, the ratio of recycled copper associated with copper used in ACQ to new
copper was varied. In our sensitivity analysis, the case where recycled copper is treated as if
newly mined and produced is considered. Based on the model, as the fraction of newly mined
copper increases the amount of energy required for its production increases. The ACQ-lumber
indicators show little sensitivity to the inputs and outputs related to copper production. The
acidification factor increases by approximately 3 percent when compared to the baseline model
and other factors by 1 to 2 percent.
5.10.3.2 ACQ Retention
As a sensitivity analysis, ACQ retention in lumber products was adjusted, as under treating and
over treating of lumber can occur. The baseline used in our assessment is 0.15 pcf. Two cases
were modeled for sensitivity, including: 1) under-treating at 0.10 pcf and 2) over-treating at 0.40
pcf.
As expected, changing the amount of preservative changes indicators. Since production of ACQ
is energy and fossil fuel intensive, increasing the ACQ content from 0.15 to 0.40 pcf results in
increases in total energy of 15 percent, GHG of 5 percent, fossil fuel use of 25 percent,
acidification of 56 percent, and smog at 2 percent. Eutrophication is most dramatically impacted
at an increase of 111 percent.
5.10.3.3 Decking Material
As a baseline case, our model assumes 100 percent of all ACQ-treated lumber decks are
constructed with 5/4-inch by 6-inch lumber. We estimate that actually 20 percent are
constructed with 2-inch by 6-inch lumber, but for the purposes of this LCA and for the purposes
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of conducting comparative analysis with an alternative product, 5/4-inch ACQ-treated lumber
was chosen as representing the majority of the market. For the sensitivity test, an extreme case
assuming 20 percent 5/4-inch with 80 percent 2 x 6-inch lumber was modeled.
Changing from 100 percent to 20 percent 5/4-inch board material and to 80 percent 2-inch
material for decking means more wood volume is required for the same surface area. Thus, all
inputs and outputs and resulting impact indicators are increased proportionally by about 30
percent to 40 percent over the baseline model results.
5.10.3.4 Decking Life and Sealer Application Rates
Deck sealer may be applied to deck surfaces to minimize weathering and improve appearance. If
three sealer applications are made in the ten year life (once every three years), then some impact
indicators are increased significantly; GHG (16%), fossil fuel use (42%), acid rain (19%),
eutrophication (8%), and smog ((14%). However, these increases do not change the comparative
ranking when compared to WPC. Furthermore, manufacturers recommend cleansing product use
on WPC. These products have not been considered in the LCA of WPC.
5.10.3.5 Landfill Disposal
Literature sources state that approximately 77 percent of wood fiber disposed in a landfill is
considered sequestered carbon after primary decomposition has occurred. Since the impacts of
methane significantly impact emissions of GHG, sensitivity analysis of this input was assessed.
Furthermore, preservative in the disposed lumber is expected to increase carbon sequestration
when compared to untreated wood. One case was modeled for sensitivity; 90 percent wood fiber
carbon sequestration in the landfill.
Based on the results of this modeling, increasing sequestration to 90 percent reduces the GHG
impact indicator by approximately 30 percent when compared to the baseline model with
minimal changes to other impact indicators. Additionally, it does not change the comparison of
products.
5.10.3.6 WPC Manufacturing Variables
For the purposes of this LCA, all WPC was considered to be without void (i.e., solid in cross
section). The “WPC” tab of the spreadsheet allows the user to add void space. A sensitivity
analysis was done to assess the impact to indicators when incorporating voids in the WPC. As
expected, including voids in WPC decreases all impact indicators by the percent void space
incorporated into the WPC product. Note that addition of voids will require additional electrical
use in the manufacturing stage, the result of increased extrusion friction; however, assessing
these added complexities was beyond the scope of this LCA and the comparative analysis.
It is our understanding that some manufacturers of WPC use zinc borate and talc as additions to
their formulation. Considering such additives was deemed out of scope. Furthermore, since
manufacturers were not surveyed, assumptions made regarding amounts and ancillary processes
would have been without sufficient basis.
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5.10.3.7 Sensitivity of Recycled HDPE vs. Virgin HDPE
The LCA baseline assumes 50 percent recycled and 50 percent virgin HDPE as the plastics
fraction in WPC. HDPE is mixed with wood fiber at the production facility. A sensitivity test
assuming 100 percent recycled content shows that energy inputs are significantly reduced as
virgin plastic is replaced by recycled material. Fossil fuel use is decreased from 14 to 4.4 times
the value of ACQ-treated lumber and total energy decreases from 8.5 to 2.8 times the value of
ACQ-treated lumber. Acidification is reduced from 4.3 times to 2.6 times the value of ACQtreated lumber and GHG emissions are reduced slightly. Interestingly, the ecological toxicity
and eutrophication indicators increase slightly. This mixed result reflects the significant energy
and transport inputs required to collect and process post-consumer plastic to make it suitable as
feedstock. Under this scenario, the impact indicators for WPC are generally about two to four
times more than for ACQ-treated decking.
A second sensitivity test was done assuming 100 percent virgin plastic content and shows that
fossil fuel use is increased from 14 to 24 times the value of ACQ-treated lumber, the total energy
value increases from 8.5 to 14 times the value of ACQ-treated lumber, and acidification
increases from 4.3 to 6.1 times the value of ACQ-treated lumber.
5.10.3.8 Sensitivity to WPC Deck Life
Extending the life of WPC decks would reduce impacts in reverse proportion to the extension.
Doubling the deck life cuts annual impacts in half. Since WPC has been shown to be subject to
weathering and decay (Laks, Richter, & Larkin, 2008 and Morrell, Stark, Pendleton, and
McDonald, 2006), such life extension does not seem plausible with current designs.
5.10.3.9 Sensitivity to WPC in a Landfill
Assumptions used for WPC disposed in landfills are the same for the wood fiber component as
for the ACQ-treated wood, but assume one-quarter as much decay of the plastic components.
This assumption is judged reasonable, since the plastic is mixed with wood and, as the wood
decays, decay of the plastic may occur by co-metabolism (wood decay fungi enzymes may also
decay plastic) and the very thin layers of plastic surrounded by decaying wood may be more
subject to decay than larger pieces.
5.11 COMPARISON OF ACQ-TREATED LUMBER AND WOOD PLASTIC
COMPOSITE LUMBER
5.11.1 Discussion
LCI data developed in Section 4 and assessed in Section 5 of this report conclude with impact
indicator values for the cradle-to-grave life cycle of ACQ-treated decking and WPC decking
normalized to an average deck of 320 sf and average years of service. Since some impact
indicator values may be in the hundreds while other indicators are tenths or hundredths of one,
comparisons are difficult. Thus, for product comparisons, impact indicators have been
normalized to the final value for ACQ-treated decking for each indicator. ACQ-treated decking
in a landfill receives a value of one and the other life cycle stages and values for WPC are then a
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multiple (if larger) or fraction (if smaller) of one. Results of this normalization process are
shown on Figure 5-2.
Additionally, the U.S. Average impact indicator comparison is provided, as described in Section
5.5.2. Table 5-5 shows the percent of U.S. average impact values per year per capita that could
be attributed to a family of three having an average sized deck of either ACQ-treated lumber or
of WPC.
5.11.2 Greenhouse Gas Emissions
Total life cycle emissions of GHG are approximately three times more for WPC than for ACQtreated deck lumber. For ACQ, the average deck accounts for 0.074 percent of a family’s
average annual GHG impact and for WPC, the average deck accounts for 0.21 percent of a
family’s average annual GHG impact.
5.11.3 Fossil Fuel Usage
Fossil fuel use was approximately 14 times greater for WPC than for ACQ-treated lumber. If
100 percent recycled plastic is used in WPC, fossil fuel use is reduced to approximately four
times more than that of ACQ. The average ACQ deck accounts for 0.028 percent of a family’s
average annual fossil fuel use and for WPC, the average deck accounts for 0.39 percent of a
family’s average annual fossil fuel use.
5.11.4 Water Usage
Water use was approximately three times greater for WPC than for ACQ-treated lumber. If 100
percent recycled plastic is used in WPC, water usage increases to over five times more than that
of ACQ. The average ACQ deck accounts for 0.00091 percent of a family’s average annual
water use and for WPC, the average deck accounts for 0.0025 percent of a family’s annual water
use.
5.11.5 Releases to Air Potentially Resulting in Acid Rain (Acidification)
Acid forming emissions are approximately four times more for WPC than for ACQ-treated
lumber life cycles. These emissions are decreased to approximately two and a half times more
than ACQ if 100 percent recycled plastic is used for WPC. The average ACQ deck accounts for
0.049 percent of a family’s average annual acidification impact and for WPC, the average deck
accounts for 0.21 percent of a family’s annual acidification impact.
5.11.6 Releases to Air Potentially Resulting in Ecological Toxicity
Cradle-to-grave air emissions with potential to result in ecological toxicity are 1.7 times greater
for WPC than for ACQ-treated lumber. The average ACQ deck accounts for 0.053 percent of a
family’s average annual acidification impact and for WPC, the average deck accounts for 0.089
percent of a family’s annual acidification impact.
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5.11.7 Releases to Air Potentially Resulting in Eutrophication
Cradle-to-grave air emissions resulting in potential impact to eutrophication are approximately
equal for WPC and ACQ-treated lumber. The average ACQ deck or WPC deck accounts for
0.04 percent of a family’s average annual eutrophication impact.
5.11.8 Releases to Air Potentially Resulting in Smog
Cradle-to-grave air emissions resulting in potential for smog are over two times more for WPC
than for ACQ-treated lumber. The average ACQ deck accounts for 0.024 percent of a family’s
average annual smog impact and for WPC, the average deck accounts for 0.063 percent.
5.11.9 Total Energy Input
Approximately 8.5 times more energy is needed as input to WPC decking than is input to ACQtreated decking over their cradle-to-grave life cycle. Total energy is decreased to approximately
three times more than ACQ if 100 percent recycled plastic is used for WPC. Of the total energy
ACQ-treated lumber uses, approximately 40% is from biomass fuel sources and 60% is from
fossil fuel sources. WPC uses almost all energy from fossil fuel sources.
5.11.10 Comparisons Conclusion
Figure 5-3 shows cradle-to-grave life cycle annual impact indicator values for 320 sf of ACQ
decking and WPC decking compared to average annual impacts for a U.S. family of three. Such
a deck, measuring 16 by 20-feet, is typical for a U.S. family. All of the impact indicator values
for ACQ-treated lumber and some for WPC seem insignificant at less than one-tenth of a
percent.
Impact indicator comparison supports the following conclusions: WPC requires approximately
14 times more fossil fuel and results in emissions with potential to cause approximately three
times more GHG, four times more acid rain, approximately two times more ecological toxicity,
equal eutrophication impact, and over two times more smog, than ACQ-treated lumber. In
addition, 8.5 times more total energy is required during the life of WPC when compared to ACQtreated lumber.
Sensitivity analysis was used to evaluate impact indicators for both 100 percent recycled HDPE
content and 100 percent virgin HDPE content and results in significant variation in impact
indicators for fossil fuel use and total energy, acidification, and water use. However, even with
the significant reduction of impact indicator values for 100 percent recycled HDPE, impact
indicators for WPC remain greater than for ACQ-treated lumber. Figure 5-4 illustrates the
variation in impact indicators if 100 percent recycled plastic is used. Similarly, Figure 5-5
illustrated the variation in impact indicators if 100 percent virgin plastic is used.
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Table 5-2
Summary of Total Energy and Impact Indicator Totals at Life Cycle Stages
for ACQ-Treated Lumber (per Mbf)
Life Cycle Stage
Impact Indicator
Total Energy Value
Greenhouse Gas Emissions
Fossil Fuel Use
Acid Rain Potential
Water Use
Smog Potential
Eutrophication
Ecological Impact
Units
MMBTU
lb-CO2-eq
MMBTU
H+ moles-eq
gal
g NOx-eq
lb-N-eq
lb-2,4-D-eq
Untreated,
dried
lumber, at
mill
per Mbf
5.3
235
1.4
118
187
1.7
0.057
3.9
ACQ
treating
stage
per Mbf
1.6
174
1.6
110
121
0.41
0.086
0.18
ACQ
lumber use stage
per Mbf
1.3
240
1.3
186
0
0.21
0.18
0.39
ACQ
lumber landfill
stage
per Mbf
2.0
2203
1.7
189
0
0.45
0.010
1.9
ACQ
lumber Cradle-toGrave
per Mbf
10
2853
5.9
604
308
2.7
0.33
6.4
Table 5-3
Summary of Total Energy and Impact Indicator Totals at Life Cycle Stages
for ACQ-Treated Lumber (per year of use per average deck)
Life Cycle Stage
Impact Indicator
Total Energy Value
Greenhouse Gas Emissions
Fossil Fuel Use
Acid Rain Potential
Water Use
Smog Potential
Eutrophication
Ecological Impact
Units
Untreated,
dried
lumber, at
mill
ACQ
treating
stage
MMBTU
lb-CO2-eq
MMBTU
H+ moles-eq
gal
g NOx-eq
lb-N-eq
lb-2,4-D-eq
per 320 sf
per year
0.21
9.4
0.055
4.7
7.5
0.066
0.0023
0.16
per 320 sf
per year
0.063
7.0
0.062
4.4
4.8
0.017
0.0034
0.0072
5-19
ACQ lumber
- use stage
ACQ
lumber landfill
stage
ACQ
lumber Cradleto-Grave
per 320 sf
per year
0.052
10
0.051
7.5
0
0.0084
0.0070
0.015
per 320 sf
per year
0.081
88
0.068
7.6
0
0.018
0.00041
0.076
per 320 sf
per year
0.41
114
0.24
24
12
0.11
0.013
0.25
Copyright 2011
Treated Wood Council
Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
Table 5-4
Summary of Total Energy and Impact Indicator Totals at Life Cycle Stages
for WPC Decking (per year of use and per average deck)
Life Cycle Stage
Impact Indicator
Total Energy Value
Greenhouse Gas Emissions
Fossil Fuel Use
Acid Rain Potential
Water Use
Smog Potential
Eutrophication
Ecological Impact
Units
MMBTU
lb-CO2-eq
MMBTU
H+ moles-eq
gal
g NOx-eq
lb-N-eq
lb-2,4-D-eq
WPC
Decking at
end of deck
life
per 320 sf per
year
3.2
163
3.2
90
34
0.25
0.014
0.28
WPC landfill stage
per 320 sf
per year
0.22
167
0.19
15
0
0.036
0.00082
0.15
WPC - Cradle-to-Grave
per 320 sf per year
3.4
330
3.4
105
34
0.28
0.015
0.43
Table 5-5
Normalized Cradle-to-Grave Total Energy Use and Impacts of an Average
Deck of ACQ-Treated Lumber and WPC Compared to U.S. Average Values (per year per
family)
Impact Indicator
Total Energy Value
Greenhouse Gas Emissions
Fossil Fuel Use
Acid Rain Potential
Water Use
Smog Potential
Eutrophication
Ecological Impact
Impact of Average Deck as Percent of U.S. Avg. Per Family Impact Categories
for Family of 3
ACQ-Lumber
WPC Decking
Converted Units
0.040%
0.34%
MMBTU/yr/family
0.074%
0.21%
lb-CO2-eq/yr/family
0.028%
0.39%
MMBTU/yr/family
0.049%
0.21%
lb-mole H+/yr/family
0.00091%
0.0025%
gal/yr/family
0.024%
0.063%
g NOx-eq/m/yr/family
0.039%
0.044%
N-eq/yr/family
0.053%
0.089%
lb-2,4-D-eq/yr
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
Table 5-6
ACQ-Treated Lumber Comparison to Wood Plastic Composite (Normalized
to ACQ-Treated Lumber in a Landfill)
Life Cycle Stage
Impact Indicator
Total Energy Value
Greenhouse Gas Emissions
Fossil Fuel Use
Acid Rain Potential
Water Use
Smog Potential
Eutrophication
Ecological Impact
Table 5-7
ACQ
lumber
deck at
end of life
per
average
deck per
year
0.80
0.23
0.71
0.69
1.0
0.84
0.97
0.70
Units
MMBTU
lb-CO2-eq
MMBTU
H+ moles-eq
gal
g-NOx-eq
lb-N-eq
lb-2,4-D-eq
ACQ
lumber in
landfill
per
average
deck per
year
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
WPC
Decking
at end of
deck life
per
average
deck per
year
7.9
1.4
13
3.7
2.8
2.3
1.1
1.1
WPC
Decking
in landfill
per
average
deck per
year
8.5
2.9
14
4.3
2.8
2.6
1.1
1.7
Sources of Energy by Product and Life Stage
Total Energy
Fossil Fuel
Biomass
Fossil
Biomass
Input
Use
Energy
Intensity
Intensity
Product and Life Cycle Stage
MMBTU
MMBTU
MMBTU
% of total
% of total
ACQ lumber production and use
6.0
5.4
0.58
89.8%
9.7%
ACQ lumber cradle-to-grave
6.0
4.5
1.6
76%
27%
WPC decking production and use
10
10
0.011
98%
0.10%
WPC decking cradle-to-grave
17
16
0.094
94%
0.56%
Note: Intensity percentages do not always add to 100% because of non-fossil, non-biomass and energy recovery
(recycling) contributions.
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
Figure 5-1
Relative Percentage of Total Energy and Impacts by Stage During the Life Cycle of ACQ-Treated Lumber
Untreated, dried lumber, at mill
ACQ Treating Stage
ACQ-Treated Lumber Use Stage
0%
0%
ACQ-Treated Lumber Disposal Stage
3%
16%
20%
29%
30%
31%
39%
8%
13%
16%
77%
15%
53%
61%
26%
22%
6%
3%
31%
26%
23%
20%
5-22
17%
Smog
Acid Rain
Water Use
Fossil Fuel Use
Greenhouse Gases
Total Energy Value
8%
6%
8%
61%
Ecological Impact
18%
Eutrophication
61%
52%
Copyright 2011
Treated Wood Council
Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
Figure 5-2
ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values (Values Normalized to ACQ-Treated Lumber Cradle-to-Grave = 1)
16.0
14.0
12.0
Normalized Value
10.0
8.0
6.0
4.0
2.0
0.0
Total Energy
Value
Greenhouse
Gases
Fossil Fuel Use
Water Use
Acid Rain
Smog
Eutrophication
Ecological
ACQ Lumber
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
WPC Decking
8.5
2.9
14
2.8
4.3
2.6
1.1
1.7
Figure 5-3
ACQ-Treated Lumber and WPC Decking Total Energy and Impact
Indicator Values Normalized to U.S. Average Family
0.5%
Percent of U.S. Family Average
0.4%
0.3%
0.2%
0.1%
0.0%
Total Energy
Value
Greenhouse
Gases
Fossil Fuel Use
Water Use
Acid Rain
Smog
Eutrophication
Ecological
ACQ Lumber
0.040%
0.074%
0.028%
0.00091%
0.049%
0.024%
0.039%
0.053%
WPC Decking
0.34%
0.21%
0.39%
0.0025%
0.21%
0.063%
0.044%
0.089%
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ACQ-Treated Lumber
Figure 5-4
Sensitivity Analysis: 100 Percent Recycled HDPE
ACQ & WPC Full Life Indicators (/Typical Deck/yr)
Baseline vs. Sensitivity Test
Baseline ACQ-treated lumber
Test ACQ-treated lumber
Baseline WPC deck
Test WPC deck
Total Energy
Value
Green House
Gases
Fossil Fuel Use
Water Use
Acid Rain
Smog
Eutrophication
Ecological
Baseline ACQ-treated lumber
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Test ACQ-treated lumber
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Baseline WPC deck
8.5
2.9
14
2.8
4.3
2.6
1.1
1.7
Test WPC deck
2.8
2.7
4.4
5.5
2.6
2.6
1.2
1.8
Figure 5-5
Sensitivity Analysis: 100 Percent Virgin HDPE
ACQ & WPC Full Life Indicators (/Typical Deck/yr)
Baseline vs. Sensitivity Test
Baseline ACQ-treated lumber
Test ACQ-treated lumber
Baseline WPC deck
Test WPC deck
Total Energy
Value
Green House
Gases
Fossil Fuel Use
Water Use
Acid Rain
Smog
Eutrophication
Ecological
Baseline ACQ-treated lumber
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Test ACQ-treated lumber
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Baseline WPC deck
8.5
2.9
14
2.8
4.3
2.6
1.1
1.7
Test WPC deck
14
3.1
24
0.0
6.1
2.6
1.1
1.5
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
6.
INTERPRETATIONS
The objectives of the interpretation, as defined by ISO, are to analyze results, reach conclusions,
explain limitations, and provide recommendations based on the findings of the inventory and
assessment phases of the LCA, and to report the results of the interpretation in a transparent
manner and provide a readily understandable, complete, and consistent presentation of the results
of the LCA study, in accordance with the goal and scope of the study. The key steps to
interpreting the results of the LCA include: 1) identification of the significant issues based on
the results of the LCA phases; 2) an evaluation that considers completeness, sensitivity and
consistency checks; and 3) conclusions, limitations, and recommendations.
This LCA report is intended to be the basis for communicating LCA findings to public policy
decision makers. The intended audiences include:
•
•
•
•
•
•
Members of the TWC;
Building officials;
Government legislators and regulators;
“Green Building” advocates;
Building product Life Cycle Inventory databases; and
End product consumers, including homeowners.
Since the LCA results are intended for public use and for use in making direct comparisons to
alternative products, care has been taken to adhere to the requirement of ISO 14044:2006.
6.1
IDENTIFICATION OF SIGNIFICANT ISSUES
The goal and scope, inventory, and inventory assessment phases of this LCA were reviewed to
identify data elements that contribute most to the outcome of the results and therefore considered
significant issues. Identification of the significant issues required a careful review of the
products and processes included in the inventory and assessment phases.
6.1.1
Precision and Confidence
Readers should keep in mind that the LCA process is not exact science. Because of the broad
scope, variability among producers and products, on-going changes in technology, limited data
on key processes, and the need to make assumptions, these results are reasonable estimates.
6.1.2
Cradle-to-Grave Scope
Creating an LCA for the cradle-to-grave life cycle of ACQ-treated lumber provides meaningful
results, but is a significantly more complicated process than assessing only a portion of the life
cycle. The cradle-to-grave life cycle approach required developing information for various
processes beyond simply treating wood with ACQ, such as seedling production, planting and
growing softwood trees in the Southeastern U.S., sawmills operations, ACQ formulation, and
future disposal of the products. Modeling the processes often required developing simplified life
cycle inventories by use of published LCIs for analogous processes and making assumptions
about the processes in the absence of full process knowledge.
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
These issues are addressed in this LCA with assumptions that are reasonable, and by clearly
identifying assumptions within the text and tables of the LCA.
6.1.3
Extended Time Frame
The life cycle of ACQ-treated lumber may extend for more than one hundred years, assuming 50
to 100 years for softwood growth, 10 years in service, and up to another 100 years in landfills.
However, one can also consider that all stages of the product life are occurring at once. Trees are
now growing, lumber is being manufactured, treated, and used, and old lumber is being disposed
and previously disposed lumber is decaying in landfills.
For the alternative product, WPC, life of the product begins at manufacture and ends in a mature
landfill.
6.1.4
Carbon Accounting
One goal of this LCA is to determine the extent to which the existence and use of treated wood
products impacts the carbon balance in the atmosphere. Renewable biologic materials
(biogenic), such as food grain or wood, are generally viewed as carbon neutral, meaning carbon
dioxide is removed from the atmosphere during growth and then returned as the products are
used or disposed, so that on a net basis, the atmospheric carbon dioxide level is not altered.
When fossil carbon fuel (such as oil, coal, and natural gas) is used, any emissions resulting from
the fossil fuel use results in carbon dioxide in the air that would not have been there without
human (anthropogenic) intervention. In practice, even biogenic materials are not completely
neutral, due to emissions from transportation and processing that use fossil fuels. On the other
hand, a biogenic material can be used or disposed in such a manner that the embodied carbon
may not be recycled to the atmosphere for many decades or even centuries. Books in libraries,
wood in buildings that become historic, or biogenic material placed in “dry” landfills, can store
carbon so that their life cycle is carbon positive, or better than carbon neutral and better than the
biogenic products natural life cycle.
As explained in Section 5.3.1, GHG calculations done in this LCA, only consider CO2 emissions
from fossil fuel sources. Biogenic CO2 sources are considered carbon neutral. However, when
considering the carbon balance, in terms of CO2-equivalents, it is appropriate to combine the two
for an understanding of the system as a whole.
Accounting for the carbon flows throughout a products cradle-to-grave life cycle is complex, but
assessment can be done using accepted practices. However, a method to assign benefit to
reduced CO2 atmospheric levels due to the long-term, but temporary, storage of carbon in
products is not clear. If release of one pound of carbon dioxide equivalents today counts as one
pound, what is the appropriate value in terms of GHG emissions for one pound released in 50,
100, or 500 years from now?
6.1.4.1 Carbon Balance
This LCA addresses the full “cradle-to-grave” life cycle of ACQ-treated lumber. For wood
products, carbon (as carbon dioxide) is removed from the atmosphere by trees as they grow, CO2
is returned to the atmosphere as portions of the wood (or wood products mix) are burned or
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
decay, and, at final disposition, CO2 is returned to the atmosphere as the product is burned or
decays in landfills. If burned, all of the original carbon taken from the atmosphere is returned as
biogenic carbon dioxide. If landfilled, portions of the biogenic material are stored, portions are
released as biogenic CO2 and a portion is converted to methane. Our USEPA-based model
predicts that 77% of the wood carbon is stored long term, and, depending on the mix of landfill
types in use, approximately 17% and 6% of the wood carbon will be released to the atmosphere
as biogenic carbon dioxide and methane, respectively. Considering that methane is estimated to
have 21 times the global warming impact of CO2, the 6% methane is equivalent to 126% of the
original wood carbon. Of the 100% of CO2 removal by the tree growth, 143% (126% + 17%) of
its GHG equivalent is returned to the atmosphere (prior to consideration of the ancillary process
using fossil fuels to get the wood products into the market). Thus, based on the landfill model
and assumptions, throughout the cradle-to-grave wood product life cycle of more than 100 years,
the net GHG emission, as CO2-equivalent, is approximately 1.5 times the GHG removal during
wood growth. Additionally, fossil fuel based carbon dioxide emissions such as for electricity for
milling, fuel for transport and heat, and fuel and raw materials used to manufacture wood
preservatives, result during the wood product life cycle.
Figure 6-1 shows the generalized carbon balance found for ACQ-treated lumber decking. In this
example, the flux, or change of carbon related to the product, begins at zero, rises due to
transport and fertilizer for planting, then drops well below zero as the trees grow over
approximately 30 to 60 years. Then, the flux starts to increase as emissions result from transport,
milling, preservative manufacture, and treatment. Emissions may climb slowly during the use
stage (such as from sealer application) and take a final climb as the wood decays in landfills.
Most of the final landfill associated increase is related to methane emissions from the landfill.
Figure 6-1
Life Cycle Carbon Balance of ACQ-Treated Lumber
1,500
CO2-eq. Flux
1,000
Tree Planting
CO2 Flux (lbs CO2-eq/Mbf)
500
Tree Growth
0
Product Use
-500
Disoposal and
Landfill Decay
-1,000
-1,500
Harvest, Milling,
and Treatment
-2,000
0
20
40
60
80
100
120
140
160
Time (years)
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
6.1.4.2 Time Value Issues
In the LCA, GHG emissions are totaled for the product’s cradle-to-grave life cycle to a final
number (essentially, a life time carbon balance). However, it is important to understand that
many decades are involved before the final value is realized. Lumber installed in a deck today
contains carbon removed from the atmosphere over approximately the previous 30 to 60 years.
That carbon will remain in the deck lumber for the life of the deck, and then some will be
released back as CO2 and methane as anaerobic decay occurs in the landfill.
There is value in storing carbon and thus preventing release. Sequestered carbon is an important
part of the climate profile of the forest products industry (Miner 2006). It is noteworthy that,
especially for a product with a long use life such as home and building framing, disposal may
happen approximately 100 years in the future with decay related releases occurring over the
following 10 to 50 years. By current LCA accounting, such releases are counted as equal to
releases occurring today. Use of the time in use factor would allow some credit for this delayed
release, but significantly adds to the complexity of the LCA. It also increases uncertainty in the
method and results, and makes the LCA more difficult for readers to understand. Therefore, we
note that time factors more accurately assess carbon balance and GHG emissions, but we provide
no quantitative analysis through this LCA.
6.1.5
Use of TRACI for Impact Indicators
Use of the USEPA sponsored TRACI model indicators, as used, is appropriate for this LCA
since it is being prepared primarily for a U.S. based audience and because of the broad scope of
chemicals and impacts addressed.
6.1.6
Human Health and Ecological Toxicity Indicators
As discussed in Section 5.3.8.1, the TWC membership who funded this LCA differs with the
independent external review team about the appropriateness of including impact indicators for
human health and ecological toxicity. These indicators are measures of risk, and risk assessment
is a better method to characterized health and environmental risk than an LCA. Thus, the TWC
has limited the scope of this LCA, in accordance with ISO 14040, Section 5.2.1.2, to not include
calculation and presentation of impact indicators for human health and ecological toxicity.
6.1.7
U.S. Average Electricity
Emissions resulting from the use of electricity from the grid, as well as offsets of the same due to
recycling to energy, are significant contributors to the impact indicators. Selection of location
specific sources of electricity, such as from the Pacific NW, where hydropower comprises a
larger fraction of sources, could lower impacts. However, recognizing that this LCA is intended
to cover average production in the U.S. and that the mix of power sources will continue to
change in the future supports the decision to use the U.S. average.
6.1.8
Recycled Content
In this LCA, recycled copper processed into copper carbonate is assessed one-third the inputs
and outputs that would be associated with virgin copper. This estimate approximates the
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ACQ-Treated Lumber
processes of collecting, cleaning, dissolving, and producing powder form copper for use in
preservative.
Recycled plastic life cycle inputs and outputs reflect recycling of post-consumer waste that is
energy intensive, often requiring separate recyclable collection vehicles and routes, equipment to
separate, sort and clean materials. Additional processing may include melting, pelletizing,
flaking, and packaging material to produce useable feedstock for manufacturing use. Life cycle
assessments were identified and used to estimate these factors.
For the purpose of this LCI, WPC was modeled with an average wood fiber content of 50 percent
and 50 percent HDPE (and the HDPE consisting of 50 percent recycled and 50 percent virgin
material). AquAeTer recognizes that some WPC manufacturers use 100% recycled plastic and
others use 100% virgin plastic material. The sensitivity analysis of this LCA is used to evaluate
WPC with 100 percent virgin and 100 percent recycled plastic. Thus, comparisons can be made
between ACQ-treated lumber and WPC with varying virgin and recycled plastic content.
6.1.9
Recycle and Disposal Assumptions
Final disposition of products following the use stage of life may have a significant impact on the
cradle-to-grave life cycle impact indicators. This LCA has assumed that both ACQ and WPC
lumber would be disposed in landfills. While this generally reflects current practice, if the
materials could be recycled to a new productive use or in a “waste-to-energy” facility, impacts
could be significantly reduced.
6.1.10 Water Use
As noted previously, data on water use are not available for electrical energy production. Thus,
while water use data are presented, its usefulness as a comparative indicator is very limited.
6.1.11 Comparative Analysis
AquAeTer was not able to find published LCA data for the alternative product, WPC, so, an
LCA was done. The methods, used to derive the inventory and assessment, were done in a
similar manner for both ACQ-treated lumber and the alternative product. The comparisons made
with the alternative product are done as a general comparison and to provide a broad
understanding of how ACQ-treated lumber might compare. AquAeTer encourages the
manufacturers of WPC to conduct a detailed LCA (for comparative purposes) of their products.
6.2
6.2.1
EVALUATION
Completeness Check
This LCA covers the cradle-to-grave life cycle of ACQ-treated lumber. A similar scope was
used in the LCA completed for WPC. Significant inputs and outputs were addressed for the life
cycle stages of each product. The evaluation was significantly more detailed for the ACQtreated lumber LCA than for WPC. However, data were included for WPC to create reasonable
approximations for the cradle-to-grave product life cycle. Significant inputs or outputs have
been considered so that the impact indicators presented support fair comparisons.
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
6.2.2
Sensitivity Check
Sensitivity checks were made for various assumptions used in the LCIs for both ACQ-treated
lumber and WPC. The most significant sensitivity check done evaluated the comparability of
ACQ-treated lumber and WPC as a function of recycled and virgin HDPE content in WPC. The
sensitivity analysis looked at 100 percent recycled HDPE and 100 percent virgin plastic and
found that fossil fuel use and acidification impacts associated with WPC, could be significantly
reduced when WPC manufacturers use 100 percent recycled HDPE. However, even with the
significant reduction, impact indicators for WPC remain greater than for ACQ-treated lumber.
6.2.3
Consistency Check
The data, assumptions, and models developed to conduct this LCA have been reviewed to assure
that they are used in a way that is consistent between products and with the goal and scope.
Areas considered include data quality along the product system lives, regional or temporal
differences, allocation rules, system boundaries, and application of impact assessment methods.
This LCA meets the consistency requirements.
6.3 CONCLUSIONS, LIMITATIONS, AND ENVIRONMENTAL IMPROVEMENT
OPPORTUNITIES
6.3.1
Conclusions
This LCA has been done for ACQ Type D-treated southeastern species dimensional lumber,
treated for above-ground, exterior exposure according to AWPA standards for use category UC3B, with retention of 0.15 pcf, intended for outdoor residential decks. The LCA has determined
the cradle-to-grave environmental impacts resulting from seedling production, growth, harvest,
manufacture, use, and final disposal of ACQ-treated lumber, the opportunities to reduce the
environmental burdens associated with ACQ-treated lumber, and has compared the ACQ-treated
lumber product to an alternative product in the market. This LCA has been completed in a
manner as limited by the final Goal and Scope and consistent with the principles and guidance
provided by ISO in standards ISO 14040 and 14044 and includes ISO specified phases such as a
Goal and Scope described in Section 2 (and included in Appendix 1).
Lumber treating is dependent on the production of dimensional lumber by mills. This LCA has
determined that the lumber production stage, including kiln drying and planing of Southeastern
species lumber, prior to treatment, results in a large fraction of certain impact indicator results
including: 52 percent of total energy input; 23 percent of fossil fuel use; 20 percent of the
acidification potential; 61 percent of the ecological impact; 17 percent of the eutrophication
potential; and 61 percent of water use and smog forming emissions. Many of these impacts
result from wood fired boilers used in the wood drying processes at lumber mills. It is important
to note that wood fired boilers operate on wood by-product biogenic fuel produced at the mills.
The lumber treating process includes impacts from the manufacture and delivery of chemical
preservatives and the treating processes. The more significant impacts associated with the ACQtreatment stage include: fossil fuel use (26 percent of total impact value), water use (39 percent),
acidification (18 percent), smog (15 percent), and eutrophication (26 percent). Electricity use
and transportation are the processes that contribute most of the impacts seen in the lumber
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Life Cycle Assessment Procedures and Findings
ACQ-Treated Lumber
treating stage, except that ammonia releases from the ACQ preservative contribute to the
majority of the eutrophication indicator.
The production and application of sealer to the deck surface during the use stage results in
significant impact indicator value increases of fossil fuel use (22 percent), and acidification (31
percent). Ammonia released from the ACQ adds to the eutrophication indicator value (53
percent).
The landfill stage has the largest impact on the emission of GHG (77 percent), but also
significantly impacts fossil fuel use (29 percent), acidification (31 percent), ecological impact
(30 percent), and smog (16 percent) impact indicators. Anaerobic decay of wood fiber in
landfills generates methane, and not all methane is captured at the landfill. Also significant is the
construction, operation, and closure of the landfills and the associated environmental burdens.
Impact values for each indicator are listed in tables in Section 5 for each product at each life
cycle stage. The values alone do not provide intuitive meaning. They have been normalized in
two ways to help make them more useful. The first normalization is to support product to
product comparisons. Impact indicator values are normalized to the cradle-to-grave life of ACQtreated lumber decking so that the decking in landfills has a value of one and other values are
relative. These are depicted on Figure 5-2 for each product at two comparable life stages, old
decking ready for disposal and decking long disposed in landfills. It is clear from Table 5-6 and
Figure 5-2 that the impact indicator values for ACQ-treated lumber decking are significantly less
than for WPC decking for all impact indicators including: GHG, fossil fuel use, acidification,
and smog forming potential.
The second means of normalization supports consideration of the overall significance or
magnitude of the impacts. It helps to answer the question: Do these impacts matter? This
normalization relates total energy value and the impact indicator values for an average size deck
per year of use life to the American family’s average annual impact. Average family impact is
based on estimated per capita impacts times three for the “average” family assumed likely to
have a deck. The per capita impacts were calculated for U.S. annual emissions divided by the
U.S. population (Bare, 2006) and for annual U.S. energy, fossil energy, and GHG emissions
(EIA, 2008).
Product
ACQ-treated lumber
WPC
US Family Average
Total
Energy
Value
Greenhouse
Gas
Emissions
Fossil
Fuel
Use
0.040%
0.34%
100%
0.074%
0.21%
100%
0.028%
0.39%
100%
Water Use
Acid Rain
Potential
Smog
Potential
Eutrophication
Potential
Ecological
Impact
0.00091%
0.0025%
100%
0.049%
0.21%
100%
0.024%
0.063%
100%
0.039%
0.044%
100%
0.053%
0.09%
100%
Annual impacts for an average deck, whether constructed of ACQ-treated lumber or WPC
decking, are mostly small compared to the family averages at less than one percent. These data
may be interpreted in the following generalized context.
•
If a family of three people installs an average deck using ACQ-treated lumber, their
“footprint” for energy, GHG, fossil fuel, acidification, potential smog forming releases,
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ecological toxicity, and potential eutrophication releases generally would be considered
insignificant at less than one-tenth of a percent over the life of the deck.
•
6.3.2
If the same deck was constructed of WPC, then the family “footprint” for energy, GHG,
fossil fuel use, acidification, ecological toxicity, and smog would be low, but significantly
greater than ACQ-treated lumber.
Limitations
This LCA was limited to boundaries established in the Goal and Scope Document, as modified
over the LCA process (Appendix 1). Limitations included reliance on published or publically
available information in many instances. Such information was assumed to be accurate.
As noted elsewhere in this report, the Scope of this LCA was modified through an iterative
process that included the TWC membership, AquAeTer, internal reviewers, and the independent
external review team. The TWC, as sponsor of this report, decided that the impact indicators for
human health would not be calculated and presented in this LCA for reasons detailed in this
report. The decision to eliminate human health impact discussion is noted as a limitation of this
LCA. AquAeTer and TWC understand this omission is a variance from ISO guidance, but have
supported our opinion in a transparent manner and conclude that this variance is allowed under
ISO 14040 Section 5.2.1.2.
Ratings of products by the impact indicator values in this LCA provide comparative values that
are intended as a tool to assist people in making judgments about the products’ properties.
Selection and the decision to purchase products, such as the decking products addressed in this
LCA, also requires various value judgments that are beyond the scope of this LCA.
The life cycle inventory completed for WPC was designed to represent the typical or average
product on the market, so by design, likely will not be accurate for any specific product in this
category. Further, the scope of investigation of WPC required use of publicly available
information and use of significant assumptions.
This LCA focused on ACQ-treated lumber decking. Other preservative formulations are
common and may hold greater market share at some times or in some locations than ACQ.
While portions of this LCA may apply to decking treated with other preservatives, the overall
conclusions only apply to ACQ-treated lumber decking.
6.3.3
Environmental Improvement Opportunities
One of the goals of the LCA is to determine how the industry might incorporate changes in the
various life cycle stages of ACQ-treated lumber to reduce environmental burdens associated with
the product. The following are opportunities for the continued environmental improvement of
ACQ-treated lumber based on the findings of this LCA.
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6.3.3.1 Electricity Efficiencies
Production facilities should continue to strive to reduce energy inputs through conservation and
innovation. Also, the use of biomass as an alternate energy source can reduce some impact
category values compared to the use of energy sources off the grid.
6.3.3.2 Transportation
Production facilities should continue to strive to source materials from locations closer to use,
and to utilize the most efficient modes of transportation. Rail transport of raw materials or
products can reduce environmental burdens when compared to truck transport.
6.3.3.3 Recycle to Energy Better Than Landfill Disposal
The ACQ-treated lumber LCA scope assumes that the deck lumber is disposed in a landfill at the
time the deck is demolished. That currently is the predominant final disposition practice.
However, considering only landfilling is an overly conservative assumption when used in a longterm life cycle assessment since there is a trend toward more recycling and resource or energy
recovery from biomass. Use of treated wood at the end of its life as fuel for power or heat
generation certainly is a viable alternative. Also, the technology of gasification is especially
promising for municipal waste and would likely be suitable for ACQ-treated lumber. Use of
demolished decking material as fuel has distinct advantages over landfill disposal including: 1)
energy produced from the biomass offsets energy production using fossil fuels and their
associated impacts, 2) wood mass is not disposed in a landfill resulting in less landfill
construction and closure related impacts; and 3) methane generation from anaerobic decay in a
landfill would not occur. Some emissions from the energy production process would occur,
however, the emissions from such equipment are typically well controlled.
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7.
7.1
CRITICAL REVIEW
INTERNAL REVIEW
An internal review of the LCA product was provided using a team of three knowledgeable and
experienced reviewers. The purpose of the AquAeTer internal review is to provide a review of
the LCA process prior to draft submittal to TWC’s member review panel. The review team
reviewed and commented on the LCA products. AquAeTer addressed the internal review team
comments, as appropriate, and maintains a record of all comments and responses for future
reference.
Following AquAeTer’s internal review evaluation, documents were submitted to TWC for
review. TWC assembled a member team to review the LCA. AquAeTer provided TWC with
the draft Goal and Scope and draft LCA reports for review. TWC managed the reviews and
provided comments to AquAeTer. AquAeTer addressed comments, as appropriate, and
maintains a record of comments and responses for future reference.
This LCA is a product of work done by AquAeTer in accordance with its agreement with TWC.
The technical and editorial comments of all reviewers were carefully considered and in most
instances incorporated into the final document. In some instances, including instances where
review comments conflicted with AquAeTer opinions or the opinions of other reviewers, an
appropriate effort was made to reach consensus with the members of the TWC review team.
AquAeTer Internal Reviewers:
•
James H. Clarke, PhD. Professor of Civil and Environmental Engineering.
Vanderbilt University, Department of Earth and Environmental Sciences, for his
review and comments;
•
Mike H. Freeman. Independent Consultant, Wood Scientist, and Chemist to the
Wood Preservation Industry; and
•
Craig R. McIntyre, PhD. Independent Consultant, Wood Scientist, and Chemist to
the Wood Preservation Industry. McIntyre Associates, Inc.
TWC Reviewers:
•
7.2
TWC Members
INDEPENDENT EXTERNAL REVIEW
AquAeTer issued the LCAs to TWC following the comment and response period. One of
TWC’s goals in conducting the LCAs is for comparison of treated wood products to alternative
products. A second goal is the distribution of LCAs for public use. In accordance with ISO
guidance, specific requirements are applied to an LCA that is intended to be used in comparative
assertions and those LCAs disclosed to the public. The LCA report was submitted for
independent external review. TWC was responsible for issue of the report to the independent
external review panel.
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The external review process is intended to ensure consistency between the completed LCA and
the principals (ISO 14040:2006, 4.1) and requirements (ISO 14044:2006) of the International
Standards on LCA and enhance the credibility of the LCA. The independent external review
members include parties familiar with the requirements of LCAs and parties having appropriate
scientific and technical expertise. The independent external review team selected a member to
act as chairperson per the requirements of ISO 14040:2006, 7.3.
The independent external review was tasked to verify whether the LCA has met the requirements
for methodology, data, interpretation and reporting and whether the LCA is consistent with the
principles. The independent external review did not verify nor validate the goals that were
chosen for the LCA nor the ways in which the LCA results were to be used. The independent
external review is not an endorsement of the comparative assertions that are done based on the
findings of the LCA.
Independent External Review Team:
7.3
•
Mary Ann Curran, PhD. Life Cycle Assessment Research Program Manager.
USEPA, Office of Research and Development;
•
Paul Cooper, PhD. Professor of Wood Science and Technology. University of
Toronto, Department of Forestry Science; and
•
Yurika Nishioka, PhD. Research Fellow, Harvard School of Public Health &
Consultant, Sylvatica Life Cycle Assessment Consulting.
CRITICAL REVIEW REPORTS
The Goal and Scope Document and LCA Procedures and Finding Report of ACQ-Treated
Lumber have been reviewed by AquAeTer’s internal review team, TWC review team, including
members of TWC, and an independent external review team. Comments and responses from
AquAeTer’s internal review team and the TWC review team are managed in project files and
available for review upon request. The independent external review panel review comments and
associated responses are included in Appendix 8.
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8.
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Standard P5-09.
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Specification for Treated Wood. 2010.
Standard for Waterborne
Use Category System:
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Chen, A.S.C. and Randall, P., 1994. Comparison of Environmental Emissions from ACQ (Type
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Consortium for Research on Renewable Industrial Materials. Life Cycle Environmental
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Forest Products Laboratory. Environmental Impact of preservation-treated wood in the wetland
boardwalk: Res. Pap. FPL-RP-582. Madison, WI: U.S. Department of Agriculture,
Forest Service, Forest Products Laboratory. Page 126. 2000.
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Franklin Associates. Cradle-to-Gate Life Cycle Inventory of Nine Plastic Resins and Two
Polyurethane Precursors, Prairie Village, Kansas, December 2007.
Freeman, M. H. 2009. Personal Conversation. January 8. www.wooddoc.org.
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Commercial WPC Decking (Abstract).
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Lebow, S. T., Lebow, P. K., and Foster, D. O. USDA: Environmental Impact of PreservativeTreated Wood in a Wetland Boardwalk. Madison, WI. Pages 40-45. 2000.
Life Cycle Centre. Life Cycle Data for Copper Products. The Deutsches Kupferinstitut e.V.
Datbase available at http://www.kupfer-institut.de/lifecycle/. Database accessed 2008.
Lippke, Bruce, and Jim Wilson. CORRIM Report on Environmental Performance Measures for
Renewable Building Materials. CORRIM Fact Sheet #2. College of Forest Resources at
the University of Washington. 2004.
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and
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Available
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States. Revised May 22, 2009.
Milota, M. CORRIM: Final Phase I Report, Softwood Lumber-Pacific Northwest Region. Page
24. 2004.
Miner, R. “The 100-Year Method for Forecasting Carbon Sequestration in Forest Products in
Use.” Mitigation and Adaption Strategies for Global Change. 2006.
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Pages 7-10.
Obtained from
www.fpl.fs.fed.us/documents/pdf2006/fpl_2006_morrell001.pdf.
Platt, B., Lent, T., Walsh, B. The Healthy Building Network’s Guide to Plastic Lumber. 2nd ed.
October 2005.
Rosenbaum, R. K. et al, 2008. USEtox—the UNEP-SETAC toxicity model: recommended
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characterization factors for human toxicity and freshwater ecotoxicity in life cycle impact
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Internet References:
Akzo Nobel. 2004. http://www.ethyleneamines.com/Startpage/Ethanolamines/Processes/.
www.wikipedia.com (Wikipedia Searches):
Horsepower
Ethylene Oxide
Ethanolamine
Copper
HDPE
NREL U.S. LCI Database: Chemical Manufacturing. HDPE resin at plant.
NREL U.S. LCI Database: Chemical Manufacturing. Ethylene production, at plant.
NREL U.S. LCI Database: Chemical Manufacturing. Ethylene oxide production, at plant.
NREL U.S. LCI Database: Chemical Manufacturing. Natural gas, processed, at plant.
NREL U.S. LCI Database:
production.
Chemical Manufacturing.
Polyethylene terephthalate resin
NREL U.S. LCI Database: Rail Transportation. Transport, train, diesel powered.
NREL U.S. LCI Database: Truck Transportation. Transport, combination truck, diesel powered.
NREL U.S. LCI Database: Forestry and Logging. Softwood logs with bark, harvested at
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average intensity site, at mill, US SE.
NREL U.S. LCI Database: Utilities. Anthracite coal, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Bituminous coal, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Diesel, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Diesel, combusted in industrial equipment.
NREL U.S. LCI Database: Utilities. Electricity, alumina refining regions.
NREL U.S. LCI Database: Utilities. Electricity, aluminum smelting and ingot casting regions.
NREL U.S. LCI Database: Utilities. Electricity, anthracite coal, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, at grid, Eastern US.
NREL U.S. LCI Database: Utilities. Electricity, at grid, Texas US.
NREL U.S. LCI Database: Utilities. Electricity, at grid, US.
NREL U.S. LCI Database: Utilities. Electricity, at grid, Western US.
NREL U.S. LCI Database: Utilities. Electricity, bauxite mining regions.
NREL U.S. LCI Database: Utilities. Electricity, biomass, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, bituminous coal, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, diesel, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, lignite coal, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, natural gas, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, nuclear, at power plant.
NREL U.S. LCI Database: Utilities. Electricity, residual fuel oil, at power plant.
NREL U.S. LCI Database: Utilities. Gasoline, combusted in equipment.
NREL U.S. LCI Database: Utilities. Lignite coal, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Liquefied petroleum gas, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Natural gas, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Natural gas, combusted in industrial equipment.
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NREL U.S. LCI Database: Utilities. Residual fuel oil, combusted in industrial boiler.
NREL U.S. LCI Database: Utilities. Wood waste, unspecified, combusted in industrial boiler.
NREL U.S. LCI Database: Water Transport. Transport, barge, residual fuel oil powered.
NREL U.S. LCI Database:
powered.
Water Transport.
Transport, ocean freighter, residual fuel oil
NREL U.S. LCI Database: Wood Product Manufacturing. Dry rough lumber, at kiln, US SE.
NREL U.S. LCI Database: Wood Product Manufacturing. Planed dried lumber processing, at
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sawmill, US SE.
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http://ga/water.usgs.gov/edu/qausage.html.
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APPENDIX 1
PROJECT GOAL AND SCOPE
APPENDIX 2
EXAMPLE OF THE TREATER SURVEY
APPENDIX 3
U.S. ELECTRIC ENERGY GRID LIFE CYCLE INVENTORY CALCULATIONS
APPENDIX 4
LIFE CYCLE INVENTORY CALCULATIONS
APPENDIX 5
LIFE CYCLE INVENTORY SPREADSHEET
APPENDIX 6
ASSUMPTIONS
APPENDIX 7
SENSITIVITY ANALYSIS RESULTS
APPENDIX 8
CRITICAL REVIEW REPORTS AND RESPONSES