United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
v-/EPA
Research and Development
EPA-600/S2-81-066 Sept 1981
Project Summary
Wood Preserving Industry
Multimedia Emission
Inventory
Bruce DaRos, Bill Fitch, Carole Franklin, Mike Friedman, Richard Merrill, and
Dean Wolbach
Restriction of wastewater discharge
generated during the preservation of
wood has resulted in the increased use
of evaporation techniques by the
wood preserving industry. The Project
Report that is summarized here dis-
cusses emissions that may occur during
evaporation and projects the pollutant
burden on the environment. The in-
formation presented in the full report
includes a description of the wood
preserving industry, its products, the
regulations impacting its emissions,
and the nature of its emissions. The
application of preservatives is discussed
in detail and includes discussions of
the waste streams generated during
the treatment process. Disposal of the
generated wastewater is the primary
topic of discussion, supported by
laboratory and field sampling data.
The measured emissions are compared
to evaporation models, followed by an
industry wide projection of the emis-
sion of organics if evaporation is used
for the disposal of wastewater. The
impact of regulations on future emis-
sion rates is also projected.
The primary conclusion of this work
is that organic compounds are emitted
to the atmosphere during evaporation.
The rate of release is based on the type
of evaporation system used: solar
ponds, thermal (pan) evaporators,
spray ponds, or cooling towers; the
temperature (thermal) driving force
used; the molecular weight and vola-
tility of the substances; and the con-
centration of each component in solu-
tion following wastewater pretreat-
ment.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory, Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back}.
Introduction
There are approximately 475 wood
preserving plants in the United States
The principal product of these plants is
chemically treated wood for use as
utility poles, railroad ties, and construc-
tion materials. Chemicals used to treat
the wood are toxic, and waste from
these plants can cause environmental
problems.
Wastewaters are generated as a
result of the preservatives used, plant
operations, surface runoff, and excess
process water discharge. Solid residues
include waste sludges from wastewater
treatment, insoluble inorganic materials
from waterborne salts, and contaminated
soils from spills or drippage. Air emis-
sions result when the retort is opened
during charge change or from the vacuum
vents. Other air emissions occur during
wastewater evaporation processes
Industry's technical response to re-
quirements for control of process waste-
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water has included increased recycling
and evaporation of water using thermal
evaporators, spray and solar ponds, and
cooling towers to decrease aqueous
discharges. The primary purpose of this
program is to determine if organic
chemicals are emitted to the atmosphere
during evaporation and to quantitate
these emissions. Table 1 summarizes
this program.
Conclusions
Organic constituents contained in
wastewater from pressurized wood
preserving processes using organic
preservatives can be emitted to the
atmosphere during wastewater evapo-
ration.
Thermal (pan) evaporation tests
showed that fractions of the organic
constituents present, including penta,
naphthalene, chemical phenol, and
other nonvolatile organics were dis-
charged to the atmosphere. Cooling
Table 1. Summary Information
Process of Concern—Pressure treating with organic preservatives.
Pollutants—Polynuclear aromatic hydrocarbons (i.e., naphthalene), chlorinated phenolic compounds (i.e., pentachlorophenol),
waterborne inorganic salts.
Pollutant Media—Air emissions, wastewater, waste solids.
Multimedia Emission Points—Vacuum vent, retort charge changes, charge cooling, open process vessels, wastewater evaporation,
condensed retort discharge during treating cycle, surface runoff, boiler blowdown. wastewater treatment
processes, contaminated soils, housekeeping wastes.
Purpose of Work Conducted—To evaluate organic emissions to the air during wastewater evaporation and quantitate multimedia
environmental impacts.
Predictive Models—Surface vaporation model based on Pick's law of evaporation. Droplet evaporation based on free falling
drop evaporation. Verification with laboratory and field testing programs.
Results—
Thermal (Pan) Evaporation Concentrations (mg/l)
Evaporation
Temperature pH
Pentachlorophenol
Naphthalene
Acenaphthene
Fluorene
Phenanthrene/
Anthracene
70
90
70
80
70
80
70
80
70
80
Pentachlorophenol
Naphthalene
2
12
10
2
10
2
10
2
10
2
Evaporation
Evaporation
Temperature
70
90
70
80
Charge
197
475
27
14
5.5
4
3.6
1.8
1.6
0.6
Filter Water Air
Cake Evaporated Emission
165
1.5
4.6
1.3
0.8
0.48
29
470.8
26.95
9.39
5.5
27
36
1.0
1 6
012
16.8
436
26.2
10.0
1.94
0.34
0.72
0.11
0.62
0.16
Residue
3
2.7
0.05
0.01
0.01
0.002
0.01
0.002
0.07
0.002
Rate (gmoles/hr-m2)
pH
2
12
10
2
Predicted
5.28 x 10'&
5.36 x 10~7
1.15* 10~5
1.07 x 10's
Measured
3.44 x 10~*
8.92 x 10'3
1.11 x 10'3
4.25 x 10~*
—Droplet evaporation models predict 1.9x 10 6 and 1x10 8 gmoles/min versus 7.2 x 1O~5and1.2x
phenol and penta.
measured for
Magnitude of Problem — Potential increase in organic emissions if forced evaporation at elevated temperature is
technology employed.
Value of Results — Confirmed release of organics during processing and has led to method of evaluation of potential organic
emissions from point sources.
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tower tests showed that phenol was the
only organic material emitted in the air
stream. The cooling tower represents a
lower source of emissions than the
thermal (pan) evaporator and may be
lower than spray pond systems (not
tested) because atomization and drift
are expected to be less.
The effect of molecular weight on
evaporation losses was also determined
As the molecular weight increased, the
potential for evaporation decreased. As
thermal driving force increased,
increasingly higher molecular weight
substances were evaporated. Acidifying
the wastewater (to pH 2), coupled with
filtration, significantly reduced the
volume of organic material available for
evaporation.
On an industry-wide basis, it is
projected that approximately 20,000
kg/yr of organic material may be dis-
charged to the atmosphere when waste-
water is evaporated. These emissions
primarily consist of volatile organics. If
thermal evaporation techniques are
used, the emission rate will be increased
as the nonvolatile components are dis-
charged. The projected use of creosote is
expected to decline slightly and penta
and waterborne preservatives to in-
crease slightly, resulting in the continued
emission of organics to the atmosphere
for the near-term future. Other potenti-
ally greater sources of organic emissions
to the atmosphere (from the retort and
vacuum vents) were not tested during
this program.
Recommendations
To better qualify the mass emissions
from wood treating sources, it is
recommended that sampling and anal-
ysis studies be initiated to further
evaluate the fraction of organic emis-
sions from thermal evaporation devices
and spray ponds. The data collected
should be used to further evaluate the
effects of solution pH, molecular weight,
and thermal driving force for each
evaporation device applicable to waste-
water disposal. In addition, tests char-
acterizing fugitive emissions should
also be conducted. This is especially
necessary for gases discharged at ele-
vated temperature and pressure, and
those that have come in contact with the
preservatives. Fugitive emission sources
include vacuum vents, hoods, retort
doors, and storage vessels.
To qualitatively determine each com-
ponent potentially discharged during
the evaporation of wastewater contain-
ing creosote, careful separation of
creosote into basic, acidic, and neutral
extractables should be conducted to
identify the species present in the
coaltar-derived mixture. Other analytical
activities include the disappearance of
OCDD during cold storage. In addition,
analytical work to qualitatively identify
organic components contained in surface
runoff should be conducted.
Solar evaporation ponds, the most
widely used evaporation devices, should
be tested to confirm the release of
volatile components. Other field testing
activities recommended include the
evaluation of oil-water separators. This
work should be directed to yield informa-
tion to maximize the removal of free oils
from the wastewater, ultimately reducing
the emission of organic species.
Industry Profile
Presently, the wood preserving
industry uses three types of preserva-
tives: creosote, waterbprne salts, and
penta. While research concerning new
preservatives or alternate meth'ods is
continuing, new preservatives are not
considered realistic options for the near
term due to long periods of required
testing.
Preservative Usage and
Industrial Growth
Creosote is a distillate of coal tar. It is
a mixture of many compounds, mostly
aromatic hydrocarbons. As a wood
preservative, it is primarily used to
improve the weathering characteristics
of wood, provide protection from insects
and fungi, and promote insolubility in
water. The primary disadvantages of
creosote-treated wood products are
color, odor, oily unpaintable surfaces,
and tendency to bleed.
Penta is a crystalline compound
dissolved in light petroleum oil. Wood
treated with penta is resistant to insects
and fungi and is more paintable than
creosote.
Waterborne preservatives are com-
pounds of arsenic, chromium, copper,
zinc, and fluoride. The principal pre-
servatives include chromated copper
arsenate (CCA), fluor-chrome-arsenate-
phenol (FCAP), chromated zinc chloride,
and acid copper ohromate. They produce
a clean, odorless, paintable product.
One disadvantage is that the wood must
be dried before it is treated rather than
using a simultaneous processing step.
A projection of 0.2 percent/year will
be used to describe the growth of the
wood treating industry. Within that
sector, creosote is projected to decrease
at a rate of 1.5 percent/year and penta
and waterborne salts will increase at a
rate of 6.8 percent/year and 5.8 percent/
year, respectively. These projections are
based on historical consumption data
and do not reflect future regulation of
waste streams or preservation use.
Regulation Review
The Federal Water Pollution Control
Act (FWPCA) of 1972, as amended by
the Clean Water Act of 1977, and the
Resource Conservation and Recovery
Act (RCRA) of 1976 are the two primary
federal laws carried out by EPA that
regulate the effluent and sludge disposal
practices of the wood preserving industry.
Overlapping laws administered by EPA
are the Clean Air Act (1972), The Federal
Insecticide, Fungicide, and Rodentcide
Act (1972), and the Marine Protection,
Research, and Sanctuary Act (1972).
Future Regulations
Considering the current wood pre-
serving waste management methods, it
is reasonable to assume that the primary
area of concern regarding future envi-
ronmental regulations will be the dispos-
al and handling of solid wastes (sludges)
and air emissions that result from the
treatment processes.
State and Local Regulations
RCRA (Section 3006) provides au-
thority for state management of haz-
ardous waste programs. According to
RCRA regulations, states must initiate
programs equivalent and consistent
with federal programs. Therefore, state
legislation will not be less complex than
RCRA regulations. It is conceivable that
some states will promulgate more
stringent regulations than the federal
program.
Health and Environmental
Impacts
Considerable evidence exists associ-
ating wood preservative contact with
adverse health effects, and although the
impacts of continued, long-term expo-
sure to low levels of these toxic com-
pounds are still under investigation,
there is evidence indicating that they
may be mutagenic, teratogenic, and
carcinogenic. It is imperative that the
fate of these toxic chemicals, their
generation, disposal, environmental
transport mechanisms, and emission
rates be thoroughly understood.
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Treatment Process
Descriptions and Wastes
The treatment of wood with preser-
vatives requires impregnation of the
wood with foreign materials designed to
protect it from attack by insects, fungi,
weather, or fire. The processing steps
include wood preparation (debarking,
shaping, drying) and treatment.
Waste Treatment or Disposal
Technology and Emissions
Characterization
This section presents options for
wastewater treatment or disposal. Char-
acterization, through field test programs
and theoretical model analysis, of evap-
orative technology and the emissions
that ultimately escape control, is pre-
sented. In wood preserving plants,
wastSwater generated by wood treating
processes contains the largest amount
of pollutants requiring disposal. To
comply with zero pollutant discharge
regulations, the wastewater is usually
contained within the plant's boundaries.
Reflecting the scope of work performed,
the primary topics of discussion are
devoted to the evaporation of waste-
water and resulting gaseous and solid
emissions.
Wastewater Treatment
In general, the wastewater generated
will vary in volume as well as content,
depending on the treatment process and
degree of dilution from other sources. The
design of a disposal system isdependent
on the characteristics of the wastewater.
Such wastewater typically contains free
and emulsified oils, organic compounds,
toxic materials, and heavy metals. A
decrease in the volume of wastewater
traditionally requiring disposal can be
achieved and is quite cost effective.
There are in-plant changes that can
result in both a volume and pollutant
burden reduction. These changes include:
• Closed steaming—The switch from
open to closed or modified closed
steaming can result in a large
water volume reduction as well as
a decrease in the formation of oil-
water emulsions.
• Separation of effluent streams—
When a plant uses more than one
preservative it is necessary to keep
the different effluent streams from
these preservatives separate. This
improves recovery of preservatives.
• Reuse of cooling water—The recy-
cling of cooling and process water.
as opposed to treating it as waste,
will reduce the volume of effluent.
This is essential for plants using
barometric condensers.
• Plant sanitation—Wastewater vol-
umes can be reduced by eliminating
leaks, spills, and drips from retort
doors, and by segregating storm-
water runoff and improving general
plant maintenance.
Oil-Water Separators
Oil-water separators operate as gravity
separators allowing for the continuous
removal of segregated liquids. To achieve
maximum recovery of free oil, devices
can be staged. Removal efficiencies of
60 to 95 percent can be achieved in a
single stage.
Evaporation
Following free oil removal, a primary
disposal option is to evaporate the
remaining wastewater. Evaporation is a
viable disposal option to reach zero
discharge because of the relatively low
volumes of wastewater generated at a
typical plant. There are four types of
evaporation techniques used: contain-
ment with solar evaporation, thermal
evaporation, spray pond evaporation,
and cooling tower evaporation. In a
survey of 183 plants using pressure
treating technology, 93 plants disposed
of their accumulated wastewater by
evaporation. Of this number, 39 used
containment ponds, 16 used thermal
evaporation, 30 used spray pond evap-
oration, and 8 used cooling towers.
The principle behind the evaporation
of the wastewater is to dispose of the
water fraction while leaving the organic
constituent for subsequent recycling to
the process or disposal. Since volatile
and other low-molecular-weight organic
constituents are present in the waste-
water, the potential exists for the release
of organic compounds to the atmosphere.
The Project Report presents the results
and data analysis of laboratory and field
testing programs designed to character-
ize evaporation technology!
Several conclusions can be drawn
from this discussion and data presen-
tation:
• Organic compounds, including
penta, naphthalene, phenol, and
similar molecular weight substances,
can be volatilized and discharged to
the atmosphere during evaporation
of water, or at lower than expected
temperatures based solely on vapor
pressures.
• Adjustment of the pH and filtering
the wastewater prior to evaporation
can remove significant quantities
of organic material that might
otherwise be emitted into the at-
mosphere.
• Reductions in the liquid tempera-
ture can reduce the volitalization of
the organics by three orders of
magnitude, indicating that solar
evaporation ponds (T < 35°C) may
result in significantly less emissions.
A solar pond was not tested during
this program.
Droplet Evaporation Emissions
A second test program was undertaken
to determine if organic compounds
were emitted from a cooling tower. The
cooling tower operates by exposing the
surface of water to air, thus creating the
necessary conditions for evaporation of
organics. A Boulton drying process was
identified and a testing program initiated.
In this test series, phenol, the most
volatile compound present, was emitted
from the tower. In addition, no phenol
accumulations occurred in the tower
sump, indicating that the material
vaporized at the same rate it entered the
system.
Several conclusions can be drawn
from this effort:
• Low-molecular-weight compounds
can be emitted to the atmosphere
from a cooling tower.
• Phenol is emitted at the same rate
it enters the tower.
• The molecular weight of chlorinated
phenols is sufficiently high so that
they were not volatilized at atmos-
pheric temperature.
Though a field test program to quantify
organic emissions has not been con-
ducted, it is expected that organic
emissions may be higher than those for
cooling towers. This is based on the
following considerations:
• Forced ejection of the liquid, result-
ing in the generation of larger
surface areas for evaporation.
• High potential for drift (carryover of
droplets from the pond by the
wind).
Summary of Wastewater
Treatment Technologies
Laboratory and field data have been
presented showing that organic con-
stituents in the wastewater are emitted
to the atmosphere. In addition, treatment
of the wastewater, by flocculation (pH
adjustment) and filtration prior to evap-
-------
oration can lead to reductions in the
-mission rates of the toxic substances.
iodegradation, chemical flocculation,
carbon adsorption, and soil irrigation
have also been reported to reduce the
COD and organic content in the waste-
water.
Solid Waste Disposal
The amount of solid waste material
generated by the wood preserving
industry depends on the preservative
used and the treatment technologies
employed. The water effluent from
waterborne salt processes is recycled to
the process. Insoluble materials con-
tained in the process water are filtered
out and disposed. However, since the
preservative category does not generate
waste containing organic compounds,
the treatment category will not be
discussed further.
Each of the treatment processes
discussed for wastewater result in the
formation of a sludge material. The
volume of material generated is pre-
sented. This material is typically disposed
in landfills; onsite, if land is available; or
offsite. Incineration of solid waste is not
currently practiced. Additional testing of
the combustion of these preservatives is
to be conducted.
4/r Emissions
Emissions from the wood preserving
industry include boiler exhaust and a
variety of fugitive source emissions.
Boiler stack emissions will be regulated
under the Office of Air Quality Per-
formance Standard's (OAQPS's) new
source performance standards for non-
fossil or industrial boilers. Reports of
work quantifying the organic constit-
uents in fugitive air emissions from the
wood preserving industry were not
identified These sources include the
dense vapor plumes emitted as the
pressure vessel is opened and wood
charge removed, the treated wood as it
cools, and the vacuum exhaust. Testing
programs to quantify these emissions
are to be conducted.
A control technique for emissions
from the retort and treated wood consists
of a water blanket around the opening.
The blanket is formed using spray
headers mounted a few centimeters
from the open end of the retort. The
sprays cover the end of the retort and
the emerging wood. The wood is cooled
to approximately 45°C thereby reducing
the driving force for emission of high-
molecular-weight compounds. The or-
ganics are transferred to the water
phase which then must be treated prior
to ultimate disposal.
The evaporation devices used to
reduce wastewater volumes are not
equipped with devices to remove organic
compounds from air emissions. This is
due to the low concentrations of organics
present per volume of gas. Control of
these organics, as described previously,
would most likely be by flocculation and
filtration or other treatment techniques
for the wastewater prior to possible air
emission.
Information was not identified or
collected in the field that would allow
quantification or estimation of the drift
from either the cooling tower or a spray
pond. The cooling tower tested was
designed and operated such that no drift
was detected during the test sequence.
Drift is expected to contain organic
constituents similar to the recirculating
liquid. Therefore, the impact on air
emissions could be estimated from the
charge material composition and an
assumed amount of drift.
Impact of Evaporation on
Multimedia Emissions
Inventory
The primary emphasis of the work
conducted during this program has
been the evaporation of wastewaters
generated during wood preserving
operations. The impact of evaporation
technology on the inventory of industry
emissions is developed from data on
established industry practices and
research results. To establish the mass
emissions of organic material from a
typical wood treating plant, the projected
wastewater generation rate and con-
stituent concentrations identified are
coupled with the fractional emission
rates. Major operational factors affecting
these projections are also presented.
These factors include the organic emis-
sions due to operation of spray ponds
and the projected probability of plant
closure under the burden of promulgated
wastewater discharge regulations.
Fractional Emission Rates
of Evaporation Devices and
Emission Projections
For solution temperatures near atmo-
spheric temperature, such as in the
case of spray ponds, cooling towers, and
solar ponds, it has been shown that the
low-molecular-weight organics, such
as benzene, toluene, and phenol, may
be emitted. As the molecular weight of
an organic constituent increases, the
probability that the constituent will
remain in the sludge fraction also
increases. Likewise, as the solution
temperature increases, such as in pan
evaporation, the probability of additional
organic emissions exists. For penta
solutions, it has also been shown that
reductions in the organics in solution
can be obtained by pH adjustment and
filtration.
Review of the data shows several
impacts of treatment and/or evapora-
tion. Primarily, it is expected that all
volatile organics, including phenol, will
be emitted from the wastewater. Though
quantitative data are not available at the
time of this report, other sources,
primarily vacuum vents from the retorts,
may represent more significant emis-
sion sources for volatiles than does the
evaporation of the wastewater.
The second impact is the increased
emissions of heavier organics at elevated
temperatures. Without pretreatment of
the wastewater, significant organics
could be emitted to the atmosphere. The
use of wastewater treatment, whether
acidification and filtration or floccula-
tion and gravity settling, is expected to
reduce the emissions of nonvolatile
organics during evaporation. Clearly,
evaporation of wastewaters with min-
imal use of thermal enhancementdunng
poor weather operation represent the
lowest source of air emissions. Since
creosote components are not readily
removed by pH adjustment and filtration,
and penta components are, the decreased
use of creosote and increased use of
penta (coupled with pretreatment) may
result in an overall decrease in air
emissions.
Regulatory Impact on
Emissions Burden and Control
Costs
EPA's Effluent Limitations will require
further industry wastewater discharge
control that will impact industry emis-
sions. Capital and operating cost data
was examined for three evaporation
systems: pan evaporators, cooling
towers, and spray ponds. Pretreatment
of process wastewater is usually re-
quired before disposal into these sys-
tems. Often gravity oil and water re-
moval, flocculation, filtration, aerated
lagoons, spray cooling ponds, and hold-
ing ponds may also be connected in
series or parallel with each other.
Cooling towers have the highest
capital expenditure and also the highest
total annual costs. The latter is due to
-------
the high amortization rate of the initial
capital investment. Forced evaporation
systems are the second most costly.
These systems will become more ex-
pensive to operate as energy costs
increase. It should be noted that pan
evaporation may represent the least
economic impact of any of the three
technologies, but also is the greatest
emitter of organic pollutants to the
atmosphere.
Regulatory Impact on Existing
Sources
An interagency analysis of EPA's
proposed effluent limitations shows
that the projected costs of compliance to
best available technology regulations
falls disproportionately on the smaller
plants (i.e., those with a lower sales
volume are impacted more heavily).
Twelve plants with sales under $3.5
million would not be able to afford the
control equipment required for the
wastewater disposal options considered.
This evaluation is based on a plant likely
to incur operating losses as a result of
compliance costs or being unable to
finance the investment for the necessary
control equipment.
Eleven plants are likely to shut down
and 10 others face potential shutdown if
zero discharge regulations are imple-
mented. Though the closure of any plant
would be significant to individuals
directly impacted, it is expected that the
lost treating capacity could be replaced
by excess capacity at other facilities. In
addition, potential plant closures are not
expected to initiate additional research
efforts to identify new treatment
processes or preservatives.
Review of Ongoing Wood
Treating Preserving and
Waste Disposal Studies
EPA, the Department of Agriculture
(USDA), and the National Institute for
Occupational Safety and Health (NIOSH)
are presently studying the effects of the
disposal of wood treating wastes on the
environment, the impact of using treated
products, and other questions relating
to the use of creosote, penta, and other
preservatives.
To determine if additional study is
required to characterize the multimedia
emissions from the wood treating indus-
try , Table 2 has been prepared. This
table presents a summary of work that
has been or is being performed. Infor-
mation was obtained from the literature
and project officers conducting the
work. In addition, if work is being
conducted, it should be qualitative or
quantitative for the organic constituents
in the waste stream to be included.
Table 2. Study Areas Defining the Multimedia Emissions from the Wood Treating and Wood Treating Products Industry
Agency
EPA
EGD
OWQPS
OSW
OPTS
IERL-FWPB
MERL
IERL-IRB
WRS
NIOSH
/. Hygn
COD
USDA
Process wastewater
<*
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ill it i
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X XX
X
X
X
X XX
Wastewater treatment
1 3
ell
13 ! .S c c 5
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X X X X X X X
Evaporative
air emissions
Still ponds
Pan evaporators
Spray ponds
Cooling towers
XX X
Fugitive air
emissions
$
0
Chemical storage
Chemical transport
Open treatment vessels
Opening pressurized ret
Gas purging of retorts
Vacuum exhaust gas
Hoods and vents
X
X X X X
Sludge
disposal
-------
Bruce DaRos, Bill Fitch, Carole Franklin. Mike Friedman, Richard Merrill, and
Dean Wolbach are with Acurex Corporation, Mountain View, CA 94042
Donald L. Wilson is the EPA Project Officer (see below).
The complete report, entitled "Wood Preserving Industry Multimedia Emission
Inventory," (Order No. PB 81 -205 999; Cost. $20.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
> US GOVERNMENT PRINTING OFFICE 1981 -757-012/7299
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