Materials Characterization Paper

In Support of the

Advanced Notice of Proposed Rulemaking –

Identification of Nonhazardous Materials That Are Solid Waste

Construction and Demolition Materials – Land Clearing Debris

December 16, 2008

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1.	Definition of Land Clearing Debris 

Land clearing debris is defined as growing stock and other timber
sources cut or otherwise destroyed in the process of converting forest
land to non-forest uses. Growing stock that is removed in silvicultural
operations such as pre-commercial thinning is also included in this
definition. Land clearing debris is typically in the form of tree tops
and branches, trees cut or knocked down and left on site, and stumps. 
In non-forested areas, such as grasslands and desert, land clearing
debris may include soil, rocks, and shrubs, although fuel is primarily
derived from previously forested areas.  

 

2.	Annual Quantities of Land Clearing Debris Generated and Used

Sectors that generate Land Clearing Debris: 

NAICS 561730 Landscaping Services - This industry comprises (1)
establishments primarily engaged in providing landscape care and
maintenance services and/or installing trees, shrubs, plants, lawns, or
gardens and (2) establishments primarily engaged in providing these
services along with the design of landscape plans and/or the
construction (i.e., installation) of walkways, retaining walls, decks,
fences, ponds, and similar structures (U.S. Census Bureau 2007). 

NAICS 11310 - This industry comprises establishments primarily engaged
in one or more of the following: (1) cutting timber; (2) cutting and
transporting timber; and (3) producing wood chips in the field (U.S.
Census Bureau 2007)..

NAICS 236 – This subsector comprises establishments primarily
responsible for the construction of buildings. The work performed may
include new work, additions, alterations, or maintenance and repairs.
The on-site assembly of precut, panelized, and prefabricated buildings
and construction of temporary buildings are included in this subsector.
(U.S. Census Bureau 2007).

Quantities and Prices of Land Clearing Debris Generated:  

In 2002, 30 million short tons of land clearing debris were generated in
the U.S. According to a 2002 USDA Forest Service Study, 10 percent was
considered to be unusable because of size, location, or other reasons.
Based on this assumption, 27 million short tons of land clearing debris
were available for recovery in 2002 (McKeever 2002, p. 3-4). 

Paper mills sign one, two or three year contracts with supply companies
for land clearing debris used as fuel. The price per ton depends
significantly on the distance over which the material must be
transported.  One source identified for the development of this document
suggests that ground wood that meets mill specifications commands a
market price ranging from $15 to $20 per ton (Goldstein 2006, p. 29).

A developing market for biomass is exportation to Europe, where biomass
demand has increased due to cap-and-trade policies and other efforts to
reduce fossil fuel use and emissions (Yepsen 2008, p. 51).

Trends in generation of Land Clearing Debris:  

Information was not readily available to gauge the trend in the
generation of land clearing debris.

3.	Uses of Land Clearing Debris

Fuel uses of Land Clearing Debris:  

Land clearing debris is commonly used as a fuel in industrial boilers. 
In general, this material can be combusted for energy recovery if the
processing capacity and markets for the fuel exist.  Oven-dry wood
produces approximately 9,000 Btu/lb when burned, and can also be
converted to liquid or gaseous fuel.  Mixed wood debris with some green
wood has a Btu value typically near 7,300 Btu/lb, and debris with higher
percentages of green wood can have lower Btu values, though land
clearing debris is typically dried as part of its processing.  In
addition, it is possible to produce different forms of solid fuel from
wood debris, such as charcoal (SWANA 2002, p. 2, 24, 30, Goldstein 2006,
p. 29). 

Non-combustion uses of Land Clearing Debris:

Non-combustion beneficial use applications for land clearing debris
include shredding for mulch and other land applications. Land clearing
debris can also be composted.

Quantities of Land Clearing Debris Landfilled: 

Information was not readily available to gauge the amount of land
clearing debris that is disposed in landfills.

Quantities of Land Clearing Debris Stockpiled/Stored:

The data sources consulted in the development of this document did not
suggest that large quantities of land clearing debris are stored or
stockpiled.  

4.	Management and Combustion processes for Land Clearing Debris

Types of units using Land Clearing Debris:

For combustion/fuel applications, land clearing debris is primarily used
by wood-fired industrial boilers and burners.  Mulch is sold to
landscaping companies, suppliers, or retailers for use by residential
and commercial customers.

Sourcing of Land Clearing Debris:

Some companies that process land clearing debris use wood derived from
their own land.  Other processors typically receive land clearing debris
from land clearing companies and municipalities that collect yard
trimmings. Processing companies then provide wood chips to mills with
whom they have contracted (Goldstein 2006, p. 29). 

Processing of Land Clearing Debris:  

At processing facilities, land clearing debris goes through a multi-step
process to produce marketable wood fuel.  After the debris arrives at
the processing facility, it is inspected for contaminants, and an
excavator is used to remove any contaminants identified. A bulldozer
with a rake then shakes the material to remove any soil that is attached
to the debris. Following this step, the woody products are staged in
stockpiles to dry prior to grinding. Processors then grind the debris so
that it can easily be fed into an industrial boiler.  The ground wood
generally needs to be 2-inch minus in size and scope for most mills.
Some processing facilities achieve the 2-inch minus size in one grind,
whereas other processes will do double grinding (Goldstein 2006, p. 29).

After land clearing debris is processed, the mills that purchase wood
fuel derived from this material will often conduct a test burn to
evaluate the moisture content of the fuel.  Mills prefer wood fuel with
a low moisture content because it has a higher Btu value per pound
(Goldstein 2006, p. 29).   

State status of Land Clearing Debris use as fuel:  

According to state responses to a 2006 survey by the Association of
State and Territorial Solid Waste Management Officials (ASTSWMO), two
states—New York and North Carolina—have approved the use of
recovered wood materials as a fuel source on at least one occasion, but
it is unclear whether these approvals apply to wood debris from land
clearing or the beneficial use of finished wood product.   In both
states, the beneficial use of recovered wood materials as a fuel does
not appear to have pre-approved status (ASTSWMO 2007, p.B-42).  

5.	Land Clearing Debris Composition and Impacts

Composition of Land Clearing Debris:

By definition, land-clearing debris is made up of cleared vegetation,
and may include rocks and soil.

Impacts of Land Clearing Debris use:

Cost Impacts: The net cost impacts associated with the beneficial use of
land clearing debris as a fuel depends on the avoided input or fuel
costs for facilities that use these materials and the cost of beneficial
use itself.  Information on the processing costs for land clearing
debris is not readily available, but the fuel savings associated with
using this material as a substitute for conventional fuels could be as
follows, depending on the fuel replaced: 

Natural Gas (Industrial): $7.35 / MMBtu (EIA 2008a, Table 20)

No. 2 Distillate (Industrial): $16.80 / MMBtu (EIA 2008b, Table 36)

Residual Fuel Oil Average:  $9.19 / MMBtu (EIA 2008b, Table 38)

Coal – Average Delivered Price in 2006: $2.23 / MMBtu (EIA 2007, Table
ES1)

Emissions Impacts of Combustion:  Exhibit 1 compares the emission
factors for wood with the corresponding values for conventional fuels
that land clearing debris may displace.  The estimates in the exhibit
suggest that the combustion of wood results in higher PM emissions than
natural gas or distillate oil, but lower PM emissions than coal or
residual oil systems. The data in Exhibit 1 also suggest that wood
results in lower SO2 emissions than most conventional fuels.  The
estimated NOx emissions associated with wood combustion are similar to
those associated with distillate and lower than the NOx emissions for
other conventional fuels.  

Lifecycle Emissions Impacts: Use of land clearing debris as a
replacement for traditional primary fuels may eliminate the
environmental impacts associated with extraction and processing of
traditional fuels.  In addition to the emissions impacts of combustion
described above, Exhibit 1 lists the quantities of the total
cradle-to-gate emissions for these fuels based on typical processes in
the United States in the late 1990s, with wood scrap combustion
presented as a proxy for land clearing debris.  Note that there may be
impacts associated with the processing of land clearing debris into
useable fuel that are not accounted for in the values presented in
Exhibit 1.  In addition, there may be alternative uses (e.g.,
composting) that are environmentally preferable to combustion.  

Exhibit 1:  Comparative Impacts of Wood Combustion versus Alternative
Primary Fuels

Pollutant	Wood	Coal	Distillate Fuel Oil	Residual Fuel Oil	Natural Gas

	Combustion	Combustion	Combustion plus Upstream	Combustion	Combustion
plus Upstream	Combustion	Combustion plus Upstream	Combustion	Combustion
plus Upstream

	----------------------------------------- lb./MMBtu
-------------------------------------

Criteria Pollutants

PM2.5	-	-	-	-	-	-	-	-	-

PM10	0.019	0.054	0.054	0.011	0.011	0.093	0.093	0.009	0.009

PM, unspecified	-	-	0.246	-	0.012	-	0.012	-	0.004

NOx	0.167	0.482	0.504	0.173	0.234	0.367	0.428	0.301	0.417

VOCs	-	0.006	0.014	0.001	0.363	0.002	0.367	0.009	0.524

SOx	0.008	1.446	1.469	0.209	0.394	1.593	1.781	0.073	1.985

CO	1.511	0.068	0.085	0.036	0.082	0.033	0.079	0.058	0.282

Pb	1.33x10-4	8.93x10-6	9.19x10-6	4.60x10-6	5.61x10-6	5.80x10-5	5.90x10-5
-	2.72x10-7

Hg	-	2.05x10-6	2.14x10-6	1.58x10-6	1.77x10-6	8.67x10-6	8.85x10-6	-
7.18x10-8



Source:

Franklin Associates 1998.

Note:

“-” signifies data not available; may equal zero.

The emission information presented in this table is derived from Life
Cycle Inventory (LCI) data, as compiled by Franklin Associates.   LCI
data identifies and quantifies resource inputs, energy requirements, and
releases to the air, water, and land for each step in the manufacture of
a product or process, from the extraction of the raw materials to
ultimate disposal. The LCI can be used to identify those system
components or life cycle steps that are the main contributors to
environmental burdens such as energy use, solid waste, and atmospheric
and waterborne emissions.  Uncertainty in an LCI is due to the
cumulative effects of input uncertainties and data variability.  

There are several life cycle inventory databases available in the U.S.
and Europe.  For this paper, we applied the most readily available LCI
database that was most consistent with the materials and uses examined.
These LCI data rely on system boundaries as defined by Franklin
Associates, as described in the documentation for this database,
available at:   HYPERLINK
"http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf" 
http://www.pre.nl/download/manuals/DatabaseManualFranklinUS98.pdf .  





References

Association of State and Territorial Solid Waste Management Officials
(ASTSWMO).  November 2007, 2006 Beneficial Use Study Report,.

Biomass Energy Resource Center, "Emissions and Air Quality," Available
at:   HYPERLINK
"http://www.biomasscenter.org/information/emissions.html" 
http://www.biomasscenter.org/information/emissions.html 

Franklin Associates.  1998, “Franklin US LCI 98 Library”.

Goldstein, Nora.  October 2006, "Wood Recycler Taps Biomass Energy
Markets." Biocycle Vol. 47.

McKeever, David B.  2002, "Inventories of Woody Residues and Solid Wood
Waste in the United States, 2002." USDA Forest Service.

Solid Waste Association of North America (SWANA).  2002,  "Successful
approaches to recycling urban wood waste,". Madison, WI: U.S. Department
of Agriculture, Forest Service, Forest Products Laboratory.

United States Census Bureau.  Last updated 9 August 2007, "2007 NAICS
Definitions: 561730 Landscaping Services", Available at:   HYPERLINK
"http://www.census.gov/naics/2007/def/ND561730.HTM#N561730" 
http://www.census.gov/naics/2007/def/ND561730.HTM#N561730 .

United States Energy Information Administration (EIA). 2007, Annual Coal
Report 2006.

United States Energy Information Administration (EIA). 2005, Annual
Energy Review 2004.

United States Energy Information Administration (EIA). 2008a, “Natural
Gas Monthly: July 2008”.

United States Energy Information Administration (EIA). 2008b,
“Preliminary Petroleum Marketing Annual 2007”. 

Yepsen, Rhodes. "Generating Biomass Fuel from Disaster Debris,"
Biocycle, 49 (2008): page 51.

  This is distinct from forest derived biomass, which is extracted from
logging operations on areas that will remain forest land.

 To express these values as dollars per MMBtu, the following thermal
conversion factors were used: 1,031 Btu per 1,000 cubic foot of natural
gas, 138,690 Btu per gallon of Number 2 distillate, 149,690 Btu per
gallon of residual fuel oil, and 22,473,000 Btu per short ton of coal
(EIA 2005, Tables A1, A4, and A5).

 We note that the emission factors for wood presented in Exhibit 1
represent averages for wood-burning boilers.  To the extent that these
data reflect the combustion of finished wood product (e.g., C&D wood
debris), they may not be representative emissions from the combustion of
land clearing debris.

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Construction and Demolition Materials – Land Clearing Debris

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