EPA/540/2-89/047
SUPERFUND TREATABILITY
CLEARINGHOUSE
Document Reference:
Webster, David M. "Pilot Study of Enclosed Thermal Soil Aeration for Removal of
Volatile Organic Contamination at the McKin Superfund Site." Journal of the Air
Pollution Control Association. Volume 36, No. 10, pp. 1156-1163. October 1986.
EPA LIBRARY NUMBER:
Superfund Treatabllity Clearinghouse - FCSF
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SUPERFUND TREATABILITY CLEARINGHOUSE ABSTRACT
Treatment Process:
Media:
Document Reference:
Document Type:
Contact:
Site Name:
Location of Test:
Physical/Chemical - Low Temperature Stripping
Soil/Sandy
Webster, David M. "Pilot Study of Enclosed Thermal
Soil Aeration for Removal of Volatile Organic
Contamination at the McKin Superfund Site."
Journal of the Air Pollution Control Association.
Volume 36, No. 10, pp. 1156-1163. October 1986.
Contractor/Vendor Treatability Study
David Webster
U.S. EPA - Region I
John F. Kennedy Federal Bldg.
Room 2203
Boston, MA 02203
617-565-3715
McKin Superfund Site, Gray, ME (NPL)
Gray, ME
BACKGROUND; This paper reports on the results of a pilot study that
treated vadose zone soil contaminated with VOCs in an enclosed thermal
aeration system. The McKin site, an NPL site in Grey, Maine, was the
location of the pilot study. The pilot study was chosen to demonstrate the
viability of excavating the soil, treating the soil in a material dryer to
aerate the soils and drive off the VOCs, and treating the vapors to remove
contaminants. Results of the pilot study revealed that VOCs were reduced
to non-detectable levels.
OPERATIONAL INFORMATION; The on-site sandy soil is contaminated with high
levels of VOCs including up to 3310 ppm of trichloroethene (TCE) and
1,1,1-trichloroethane. Soils were aerated in a materials dryer at 150 F
and 380°F. Three cubic yards of soils could be treated per run and the
soils passed through the system from 3 to 8 times to ensure adequate
volatilization of the contaminants. Exhaust gases from the materials dryer
were treated with a 3-stage process including a baghouse, a scrubber and
vapor phase carbon bed to remove particulates and organic vapors prior to
release. Aerated soils were solidified and returned to the excavated area.
An important objective of the study was to determine whether ambient air
quality could be maintained during soil excavation and aeration. Continu-
ous air quality monitoring for organic vapors was conducted during testing
at the site and on the perimeter of the site. Techniques to minimize
uncontrolled volatilization of organic chemicals from the soil during
excavation and aeration and to control dust emissions were implemented. An
on-site laboratory was utilized to augment off-site analysis of soils for
organic contaminants by gas chromatography. Methods utilized were EPA
Method 8010 and a modified EPA Method 8020. QA/QC is not reported.
3/89-17 Document Number: FCSF
NOTE: Quality assurance of data may not be appropriate for all uses.
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PERFORMANCE; Treatability tests were conducted from February to May 1986.
During the test, parameters such as drying temperature, dust control and
the number of drying cycles were varied to test their effect on the VOC
removal efficiency. Test results indicated that high drying temperatures
and increasing number of drying cycles produced the greatest amount of VOC
reduction. Treated soils were able to achieve the EPA target of 0.1 PPM
TCE. The results of various tests are shown in Table 1.
The results of air monitoring for organic vapors during the pilot study
revealed that on-site activities had a negligible effect on air quality at
the site perimeter. Pilot test results indicated that concentrations of
VOCs can be significantly reduced to non-detectable levels and that thermal
soil aeration can virtually eliminate volatile organic contaminants from
the vadose zone.
CONTAMINANTS;
Analytical data is provided in the treatability study report. The
breakdown of the contaminants by treatability group is:
Treatability Group CAS Number Contaminants
WOl-Halogenated Aromatic 95-50-1 1,2-Dichlorobenzene
Compounds
W04-Halogenated Aliphatic 127-18-4 Tetrachloroethene
Solvents 79-01-6 Trichloroethene
W07-Heterocyclics and Simple 108-88-3 Toluene
Aromatics 1330-20-7 Xylene
3/89-17 Document Number: FCSF
NOTE: Quality assurance of data may not be appropriate for all uses.
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TABLE 1
PRE-AERATION AND POST-AERATION CONCENTRATIONS OF DETECTED
CONTAMINANTS IN SELECTED SOIL AERATION RUNS (ppm)
Pre-aeration Post-aeration
range concentrations
Trichloroethene (TCE) 17-115 ND 0.05a
Tetrachloroethene 11-19 ND 0.05a
1,1,1-Trichloroethane 0.11-0.3 ND 0.05a
1,2-Dichlorobenzene 3.5-50 ND lb
Toluene 1-2 ND lb
Xylenes 5-69 ND lb
Notes: a) Not detected at a laboratory detection limit of 0.05 ppm.
b) Not detected at a laboratory detection limit of 1 ppm.
c) This is a partial listing of data. Refer to the document for
more information.
3/89-17 Document Number: FCSF
NOTE: Quality assurance of data may not be appropriate for all uses.
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Pilot Study of
Enclosed Thermal Soil Aeration for
Removal of Volatile Organic Contamination
at the McKin Superfund Site
by
David M. Webster
U. S. Environmental Protection Agency
Waste Management Division
Boston, Massachusetts
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Pilot Study of
Enclosed Thermal Soil Aeration for
Removal of Volatile Organic Contamination
at the McKIn Superfund Site
David M. Webster
U.S. Environment*! Protection Agency
Waste Management Division
Boston. Massachusetts
During the winter and spring of 1986 sandy soils contaminated with volatile
organic chemicals were successfully tretted during a pilot study of an
enclosed thermal soil aeration process at the McKin Superfund site in Gny,
Maine. Excavated soil containing up to 3310 ppm of trichloroethylene
(TCE) was fed into a large rotating drum and mixed at J00°F. Aerated toil
was then solidified with cement and water and returned to the on-tite
excavation location. Exhausted air from the enclosed aeration process was
treated in a baghouse, a scrubber, and a vapor phase carbon bed prior to
atmospheric release. Continuous air monitoring for organic vapors and
particulates took place at the site perimeter and for organic vapors at on-
site locations. Techniques to minimi** uncontrolled volatilization of organic
chemicals from the soil during excavation and aeration and to control dust
emissions were implemented. Results of this [iHot study indicate that
concentrations of volatile organic contaminants routinely were reduced to
nondctectable levels and achieved site-specific soil performance targets
established by the CH5L £n vironmeata7 Protection Agency. The pilot study
was conducted by Canonic Environmental Service* Corporation and funded
by private companies under order from EPA,
Soil contamination in the vadose cone
is frequently encountered at hazardous
waste sites. For many hazardous sub-
stances this contamination represents
either a direct public health concern or
a source for continuing contamination
of groundwater. Recently, there has
been increased emphasis on addressing
vadose zone contamination through in-
situ treatment, immobilization tech^
niques or destruction and removal
rather than through land disposal ap-
proaches such as off-site landfilling,
capping or the use of barriers.
Copyncht IMS-Aif Pol
One method for removing volatile
contaminants from soils is by providing
sufficient contact between contaminat-
ed soil and air to allow volatile contam-
inants to vaporize. This aeration meth-
od of reducing soil contaminant levels
is employed when soils contaminated
with volatile* an excavated or other-
wise handled in the presence of uncon-
taminated air. Soil aeration has been
described as an on-sita treatment in
conjunction with photodegradation1
and has been applied in subsurface
venting systems2-* and in the thermal
treatment of excavated soil*.4 The fol-
lowing is a description of how soil aera-
tion, within an enclosed, heated atmo-
sphere, was successfully utilized in a
full scale pilot study to remove volatile
organic compounds from contaminated
soils while controlling air emission
from the excavation and aeration pro-
Site History and Description
The McKin site in Gray, Maine is the
location of a former waste collection,
transfer, and disposal facility operated
by the McKin Company from 1965 and
1978. On-aite waste handling proce-
dures included discharge to the
ground, storage in tanks, incineration,
and on-site burial The site is approxi-
mately seven acres with approximately
five acres being cleared and partially
excavated. The site area is located on a
relatively permeable glacial outwasb
plain comprised of stratified sand,
gravel, and boulders overlying heavily
weathered granitic bedrock. The depth
to water table on the site ranges from
12 to 40 ft below ground level Surface
drainage is contained on-site with inci-
dent water either evapotranspirating
or percolating into the soil Neighbor-
ing lands include residential areas,
wooded areas, and rural farmland with
the nearest home within approximate-
ly 200 ft of the site.
Following detection of organic chem-
ical contamination in nearby residen-
tial wells, an alternate water supply
was constructed in 1978. By 1983 all
surface drums and tanks were removed
from the site in a series of removal ac-
tions. Presently, there an two remain-
ing major contamination problems as-
sociated with the site. The first is on-
Journal of the Air Pollution Control Association
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site soil contamination in specific
areas, which serves as a source for off-
site groundwater contamination. In
some locations this soil contamination
extends to the water table. The second
is groundwater contamination of the
surficial and bedrock aquifers affected
by the site. The primary contaminant*
of concern in soils and groundwater are
volatile organic compounds, particu-
larly trichloroethylene, (TCE), and
1,1,1-trichloroethane.
Regulatory Background
In July 1985 the EPA Region 1 Ad-
ministrator documented the selection
of a remedy for the McKin site by sign-
ing a Record of Decision.9 The remedial
action selected centered on on-site aer-
ation of soils to remove volatile con-
taminants from contaminated on-site
soils, extraction and treatment of
groundwater from off-site contaminat-
ed areas, and certain site removal and
closure activities.
In connection with the selection of
the on-site soil aeration alternative,
EPA established site-specific, target
soil performance standards protective
of human health and the environment
which represent soil contamination
levels which could safely remain onsite
following aeration. For volatile organic
contaminants, trichloroethylene
(TCE) was selected as the indicator
compound based on its prevalence, mo-
bility, and toxicity. The TCE perfor-
mance standard established by EPA to
evaluate soil treatment at the McKin
site was a maximum of 0.1 ppm aver-
aged over a treatment volume of soil.
In addition, EPA called for a soil aer-
ation pilot study with continuous air
monitoring to evaluate methods of aer-
ating soils for removal of TCE while
controlling air emissions to maintain
acceptable air quality. Possible meth-
ods of achieving this goal mentioned in
the Record of Decision include cover-
ing exposed soil, aerating within an on-
site enclosure and subsurface aeration
using a soil venting aeration technique.
In August 1985, an agreement was
reached between EPA and two private
companies that had potential liabilities
associated with the site remediation.
These companies agreed to perform a
soil aeration pilot study for the removal
of TCE at the McKin site within an
enclosed environment. The subsequent
soil aeration pilot study, conducted
from February through May 1986, is
the subject of this discussion. As a re-
sult of an administrative order issued
by EPA, the pilot study as well aa the
associated soil sampling and air moni-
toring described below, were funded by
Fairchild Camera and Instrument Cor-
poration and Sanders Associates and
were performed by Canonic En- iron-
mental Services Corporation of Porter,
Indiana, with oversight and procedural
approvals provided by the U.S. EPA.
Pilot Study Objective* and De*Jgn
The objectives of the pilot study
were to determine the effectiveness of a
specific full scale soil aeration process,
the optimum operating conditions as-
sociated with this process at the McKin
site and the impacts of the process on
ambient air quality. The design chosen
for the McKin soil aeration pilot study
involved a series of conventional con-
struction and pollution control tech-
nologies used together in a innovative
approach to aerate soils in an enclosed,
heated environment and to capture the
organic* vaporized from the soil. Sever-
al key pieces of equipment used in this
approach are components of a portable
asphalt batch plant The major compo-
nents of the design used to excavate,
transport, aerate, solidify,' and rede-
posit soils, and to treat contaminated
air are presented in the Figure 1 flow
diagram and described in the following
discussion.
cket Excavation
SOILS
AIR
Excavation
by catuon
digging bucket
within sttcl
caiooni
Exhausted
air
Bagrxxm
firm
Httttd
craw
oonvtytr
Vapor pnatt
carbon
adsorption
bad
Exhaust "
newt 1. McKin pilot study treatment pi
The selected soil excavation equip-
ment allowed excavations down to 40
feet to be conducted in a manner that
reduced the uncontrolled release of
volatile organic compounds by limiting
soil-air interfaces. A kelly bar caisson
rig fitted with a digging bucket and at-
tached to a 100-ft crane was utilized for
this soil excavation and transfer. The
rotating kelly bar was attached to one
of several digging buckets, approxi-
mately 5 ft in height and 4 ft in diame-
ter. Hinged digging flights extending
below the bottom of the digging bucket
cut into the soils as the bucket rotated
beneath the weight of the kelly bar.
Soils wen discharged from the digging
bucket to a front end loader (see cover
photo) which was equipped with a re-
movable plastic cover to minimize vola-
tilization during soil transfer to the ma-
terials dryer. Following discharge, the
hinged bottom of the digging bucket
was closed and the digging bucket rein-
troduced to the excavation hole. The
use of the digging bucket to excavate
contaminated soils is shown in the pho-
tograph in Figure 2.
To prevent excessive vaporization of
organic contaminants from the hole
and to prevent collapse, cylindrical
steel caissons, approximately 17 ft in
length, and 4-5 ft in diameter, were
augered into the deep excavation holes,
October 1986 Volume 36, No. 10
11S7
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HAZARDOUS WASTE MANAGEMENT
with digging bucket excavation occur-
ring within the caisson's confining
walls. In deep excavations, a 4.5-ft di-
ameter caisson was telescoped within a
5-ft diameter caisson to reach the re-
quired depth. The temporary caissons
remained in place until the excavation
was backfilled with treated, solidified
soils. In this manner, circular excava-
tion holes were sited throughout the
temperature sensor at the soil dis-
charge chute. During various aeration
runs the dryer temperature varied
from 150 to 380° F. A second sensor
monitored the temperature of the flue
gas exhausted from the dryer to the
baghouse. The air flow provided by the
burner blower also varied during the
course of the pilot study, with mini-
mum and maximum flows of 7,500 and
Figure 2. 0»ap excavation WM acoompltehrt wing • cylindrical rotating Oggtog bueki
poMtonod within «•« catoon*.
contaminated soil area in an overlap-
ping honeycomb pattern. During the
pilot study soils from an area of ap-
proximately 640 ft2 to a depth of about
32 ft were excavated using this tech-
nique.
Material Dryer and Recirculating Conveyor
The materials dryer used for soil aer-
ation in the pilot study is normally
used in asphalt production to remove
moisture from fine and coarse aggre-
gate. The dryer is a large, rotating cy-
lindrical drum approximately 7 ft in
diameter and 28 ft in length. Rotating
at approximately 6 rpm, longitudinal
flights within the drum provide «"«««"g
and the slow progression of soils from
the slightly elevated influent end to-
wards a discharge chute at the low end
of the dryer. Thus, the dryer provided
conditions to allow prolonged contact
between contaminated soil particles
and fresh air within an enclosed envi-
ronment Pre-aeration, contaminated
soils were introduced to the dryer by*
conveyor belt, fed by a front-end loader
and hopper.
Forced hot air was generated by an
oil burner and introduced to the drum
to enhance the vaporization of volatile
organic compounds from the soil. The
dryer temperature was monitored by a
15,000 cfm, respectively.
The drum's slowest rotating speed
was used during the pilot study, which
moved soils through the inclined drum
in approximately 2 minutes. In order to
vary the dryer retention time during
the pilot study, a system of conveyors
was assembled to recirculate soils for
multiple passes through the dryer. For
the first three phases of the pilot study
from February 17 to April 5, a series of
three belt conveyors were used to recir-
culate soils. In the final phase of the
pilot study beginning May 8, a single
enclosed bucket conveyor and enclosed
chute was substituted for the belt con-
veyors to minimize dust emissions. Af-
ter the final pass through the dryer,
post-aeration soils were discharged
from a belt conveyor to a front-end
loader when the belt conveyor system
was used and from the enclosed chute
directly to a cement mixer truck when
the bucket conveyor system was used.
With either system, the combined ca-
pacity of the dryer and recirculating
conveyors limited each soil treatment
run to approximately 3 yd1, and sous
passed through the dryer three to eight
times depending on the operating pa-
rameters selected for the pilot study
run. The d-'-charge of post-aeration
soils from the bucket conveyor to the
truck is illustrated in Figure 3.
Sofl Solidification and Redeposftlon
Following aeration within the dryer,
treated soils were physically solidified
with a lean cement mixture and then
redeposited into an excavation hole.
The purpose of this solidification step
was to prevent soil collapse in redeposi-
tion areas. During the initial three
phases of the pilot study, from Febru-
ary 17 to April 5, runs of approximately
three cubic yards each were transferred
by front end loader to stock piles to
allow time for laboratory analysis. Fol-
lowing confirmatory analysis, the post-
aeration treated soils were transferred
from the stock piles to a cement mixer
truck via front-end loader and hopper.
In this process, approximately 9 yd3 of
treated soil were mixed with approxi-
mately 1200 pounds of cement and 600
gallons of water to form a lean solidifi-
cation mixture.
Following the May 8 modification to
a bucket conveyor soil transfer system,
aerated soils were discharged directly
from the recirculating conveyor system
to the cement mixer truck along with
cement and water. In either case, the
soil, cement, and water mixture was
discharged from the cement truck to an
open excavation hole. Before the mix-
ture set, the steel caissons were re-
moved from the hole for another exca-
vation and deposition sequence.
Ah-Treatment
The exhausted air from the materials
dryer was treated in a three-stage pro-
cess for the removal of particulates and
organic vapors. The first stage of air
pollution control was the baghouse
normally used with the asphalt batch
plant The baghouse consisted of an en-
closed series of six banks of fine-mesh
synthetic fabric filters to remove par-
ticulates from the air exhausted from
the materials dryer. During the McKin
pilot study, the particulates collected
in the baghouse were transferred by en-
closed screw conveyors to be added to
treated soils.
Exhausted air from the baghouse
was ducted to the packed tower air
scrubber, the second stage of air pollu-
tion control The scrubber consisted of
a 10-ft cylindrical tower, 6 ft in diame-
ter filled with plastic packing media.
Air to be treated entered the bottom of
the tower where it contacted a down-
flow of cascading water through the
media and exited the top of the tower.
The scrubber was utilized to condition
the air prior to vapor phase carbon ad-
sorption and remove water soluble
chemical constituents and remaining
particulates. The scrubbing water.
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Figure S. Treated soil from thermal soil aeration proceM Is discharged from enclosed
bucket conveyor to cement mixer truck for solidification after aeration. White plume Is hot.
moist air released after treatment m carbon adsorption unit
which was pumped through the scrub-
ber at a rate approximately of 200 gal-
lons per minute, was regenerated by in
a liquid phase carbon unit.
In the final stage of air pollution con-
trol, a vapor-phase carbon adsorption
bed was used to remove volatile organic
compounds. The bed consisted of ap-
proximately 15 tons of activated car-
bon, placed to a depth of approximate-
ly 5 ft within an 8 X 40 ft trailer. Air
from the packed tower air scrubber waa
conveyed to the bottom of the carbon
bed via ductwork which connected to
three distribution pipes installed be-
neath the carbon bed. Breakthrough of
organic contaminants was monitored
by analyzing the carbon bed for chlo-
rine content and by monitoring ambi-
ent air near the exhaust from the bed.
Current plans are for thermal regener-
ation of the used carbon.
SoU SantpHfiQ, Monitoring, aoo AnsvyssB
The soil aeration pilot study was ac-
companied by a number of toil sam-
pling and monitoring activities. Prior
to excavating soils for aeration a toil
profiling program was performed to de-
lineate the vertical and lateral extent of
soil contamination. This waa accom-
plished by developing soil borings in
areal grid patterns encompasing areas
of contamination and sampling the
subsurface soils at regular depth inter-
vals. This soil profiling involved the
analysis of over 400 samples for volatile
organic compound*.
Concentrations of volatile organic
compounds also were monitored dur-
' -y the treatment process as soil aera-
on tests were run. During Phases 1
and 2, samples were retrieved for lab-
oratory analysis prior to aeration, be-
tween various steps in the aeration pro-
cess, and as the treated soil was dis-
charged from the materials dryer. After
March 11, soils were sampled following
discharge from the materials dryer
only. Laboratory analyses of pre-aera-
tion and post-aeration soils routinely
were for all volatile organic priority
pollutants. To supplement off-site lab-
oratory capabilities, an on-site analyti-
cal laboratory with the capability of an-
alyzing soil for volatile organic com-
pounds by gas chromatography (EPA
Method 8010 and a modified EPA
Method 8020) was established.
An important objective of the soil
aeration pilot study waa to evaluate
whether ambient air quality protective
of public health could be maintained
during the course of soil excavation and
aeration. For this evaluation a compre-
hensive air monitoring system waa de-
signed for the pilot study including the
following components:
• Continuous local monitoring of ex-
cavation, soil transfer and aeration
for organic vapors with portable
flame ionization detectors.
• Continuous monitoring for organic
vapors at five permanent site pe-
rimeter stations during working
hours using five flame ionization
detectors with real-time data ac-
quisition transfer at 15-second in-
tervals.
• Daily short-term monitoring at ten
local residences for organic vapors
with a portable flame ionization de-
tector.
• Regular collection and analysis of
air pollutants by 8-h charcoal and
Tenax tube adsorption and Labora-
tory extraction at upwind and
downwind site perimeter sampling
locations.
• Daily 24-h sampling for total sus-
pended particulars at three per-
manent site perimeter high volume
particulate samplers.
• Continuous monitoring for partial-
lates at two permanent site perime-
ter stations using real-time partic-
ulate analyzers and data storage in
an on-site computer system.
• Continuous monitoring and date
storage of wind speed, wind direc-
tor, temperature, barometric pres-
sure, humidity and solar radiation
during working hours as measured
on an on-site meteorological tower.
• Implementation of most compo-
nents of the air monitoring system
during a two week period prior to
soil aeration to estimate baseline
air quality conditions.
Coupled with the air monitoring sys-
tem, contingency plans for corrective
measures, volatilization abatement,
and public protective responses were
developed based on site specific guid-
ance from the Centers for Disease Con-
trol Among the guidance elements
were continuous monitoring for organic
vapors near site activities and public
notification if continuous downwind
organic vapors at the site perimeter
were more than 2 ppm above back-
ground. For the purposes of this moni-
toring and contingency planning, the
background level was assumed to be
the reading on the most upwind of the
five perimeter flame ionization detec-
tors.
MM Study
The sequence of the soil aeration
teats performed during the pilot study
was separated in four phases. From
February 17 to February 25, 13 aera-
tion runs of 1-4 yd3 were aerated under
various operating conditions. Among
the variables were soil volume, dryer
temperature, dryer flue gas tempera-
ture, dryer air flow, soil wetting proce-
dures for dust control, and methods for
handling collected baghouse particu-
lates. The ranges of these operating pa-
rameters are presented in Table L
Phase 2 of the pilot study was con-
ducted between March 3 and March 11,
after adjustments wen made to the
method of handling baghouse dust.
Specifically, collected baghouse dust,
identified as a possible source of recon-
October 1986 Volume 36, No. 10
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HAZARDOUS WASTE MANAGEMENT
Table I. Flange of operating parameters during Phase 1 of soil aerations runs
Vjnaole
Range
Soil •.oiume per batch
Drver temperature
Dr\er Hue gas temperature
Dryer air flow
Soil »eUin? procedures for
du-t control
Handling of collected
baghouse paniculate*
Number of passe* through
the dryer
1-4 cubic yards
150-380»F
186-335'F
7500-15,000 cfcn
Various amounts of water sprayed
on conveyor belts. Dust
suppressant additive used in 3 of
first 4 batches, discontinued afUr
batch 4 of first phase due to lack
of significant effectiveness and
interference in gas
chromatography analysis of
treated soils.
Baghouse paniculate reintroduced
to racirculatioi conveyor at
various time*.
4-8
lamination of treated soils, was ther-
mally treated separately using an en-
closed heated screw conveyor with heat
added by propane burner to enhance
further volatilization. The key opera-
tional parameters varied during Phase
2 were dryer temperature (150-325°F)
and dryer air flow (10,000-15,000 cfm).
During Phase 2, soils were recirculated
for four or five passes through the dry-
er, and the soil samples were analyzed
for volatile organic compounds prior to
aeration and after various passes
through the dryer.
In the third phase of the pilot study,
soil aeration was conducted in a semi-
continuous mode to provide informa-
tion regarding repeated soil aeration
trials under 8-h working day condi-
tions. From March 12 to April 4, 107
batches of soils wen Derated during
Phase 3. These batches contained ap-
proximately 9 yd3 each, composed of
three separate aeration runs. Testing
repeated runs in this fashion allowed
for increased control over operating
conditions, such aa dryer temperature
and dryer floe ga* temperature which
were subject to fluctuations due to
start-up conditions, preheated dryer
temperature, and the presence of soils
with varying temperatures and mois-
ture content in the dryer. Dryer airflow
(15,000 cfm) and the volume of each
run (approximately 3 yd3) were not
varied throughout this third phase. Av-
erage dryer temperature varied cram
200*F to 330*F for the first 53 batches
and was controlled between 290*F and
310°F for the last 49 batches. Each
batch was sampled for volatile organic
chemical analysis after aeration and
stockpiled overnight. Post-aeration
soils meeting the TCE performance
standard were then solidified with ce-
ment for on-site deposition in excava-
tion holes. Soils not meeting this stan-
dard were successfully rerun through
the aeration plant
Phase 4 of the soil aeration pilot
study was performed between May 8
and May 29 following system modifica-
tions to control dust generation. Pri-
mary modifications were the use of the
enclosed bucket conveyor recirculation
system rather than a belt conveyor re-
circulation system and the direct dis-
charge of treated soils from the bucket
conveyor to a cement mixer truck,
avoiding the need for stockpile*. Forty
runs of 3 yd3 each were aerated in
Phase 4 to evaluate these modifica-
tions, and post-aeration soil samples)
were taken for laboratory analysis. In
addition, 11 pre-aeration soil samples
were analyzed from runs suspected aa
having elevated concentrations of vola-
tile organics baaed on a flame ionisa-
tion detector screening. On-stte and
perimeter air monitoring continued on
working days throughout all four
phases of the soil aeration pilot study.
In interpreting the results of repre-
sentative pretreatment and poet-treat-
ment soil sampling, limitations associ-
ated with the heterogeneous nature of
sofls must be kept in mind. Factors cre-
ating these limitations include the fact
that no two soil samples represent the
exact same matrix, the precaution*
necessary to minimize volatilization of
contaminants during field and labora-
tory handling, and practical resource
constraints on the number of analyse*.
However, even with consideration for
these conditions, the results of the pilot
study allow for a number of observa-
tions and conclusions regarding the re-
moval of volatile chemicals from soils
under the applied operating condi-
tions. In general, the pilot study dem-
onstrated that the aeration treatment
configuration studied routinely yields
soils with a TCE content below the 0.1
ppm target concentration.
Phase 1 of the pilot study demon-
strated that significant decreases in the
concentrations of volatile organic com-
pounds were obtained by aerating con-
taminated soils at elevated tempera-
tures. In the 11 batches where the pre-
aeration TCE content ranged from 100
.ppm to 2200 ppm, the TCE content
after one pass through the dryer ranged
from 0.1 to 21 ppm. After multiple
passes, the TCE concentrations ranged
from nondetectable at 0.05-7.4 ppm.
Due to the variety of combinations of
operating conditions, the Phase 1 re-
sults do not support a definitive expla-
nation for variations in treatment effi-
ciency within these post-aeration TCE
concentration range*. In addition to
varying soil volumes, temperatures,
and airflows, procedure* for dust con-
trol and handling baghouse particu-
latea also were varied during Phase 1.
Several methods and sprayer configu-
rations for applying water for dust con-
trol were tested. In addition, baghouse
paniculate* were not reintroduced to
the treated soil* with uniform timing
for each batch. During Phase 1, the
concentration of TCE in the baghouse
particulates ranged from 0.23 to 78
ppm in seven samples, identifying the
collected baghouse particulates as a
possible source of residual contamina-
tion in the treated soils. To remove this
possible contamination source, collect-
ed baghouse particulates were heated
within a enclosed conveyor in later
phase*.
Among the soils aerated in Phase 1,
there were six run* with one or more
pre-aeration samples containing at
least 1000 ppm of TCE. These were
among the highest levels of TCE found
on the sit*. Of these six run*, the four
run* treated at high temperature*.
ranging from 250 to 380*F, yielded ini-
tial post-aeration TCE concentration*
of 0.2-1.2 ppm, while the two treated at
lower temperature*, 150-180'F, yield-
ed higher initial poet-aeration TCE
concentration* from 11 to 21 ppm. Al-
though other factors such a* soil vol-
ume and air flow were not constant in
these trials, these Phase 1 results for
highly contaminated soil* suggest that
dryer temperature is a significant fac-
tor in meeting the pilot study's treat-
. .* .***,,
-------
roent objectives, with higher tempera-
tures yielding low post-aeration TCE
concentrations.
In an effort to select optimum oper-
ating parameters, Phase 2 testing cen-
tered on applying various tempera-
tures, with the dryer temperature rang-
ing from 150 to 3258F. In addition to
temperature, air flow and soil volume
varied slightly during Phase 2 aeration
runs. As in Phase 1. the results from
Phase 2 show significant and repeat-
able reductions in TCE concentrations
resulting from thermal aeration. Post-
aeration TCE concentrations in all but
five of the 22 runs were at or below the
0.1-ppm TCE soil performance target
in the first post-aeration sample. In
two of these five runs, the target TCE
concentration of 0.1 ppm was attained
by the final pass through the dryer. In
two other runs TCE concentrations in-
creased to above the target in the final
pass for unknown reasons but possibly
due to the inherent problems of obtain-
ing repeatable, representative sam-
pling results from soil samples.
Results from Phase 3 provide evi-
dence that contamination reductions
to the 0.1 ppm target TCE concentra-
tion are achievable in repeated aera-
tion runs during full days of treatment
Of the 107 batches of 9 yd3 each, 79
percent demonstrated no TCE at a 0.06
ppm detection limit in post-aeration
samples, and all but five batches dem-
onstrated post-aeration TCE concen-
trations at or below 0.1 ppm. The final
49 batches in Phase 3 were treated with
relatively consistent operating condi-
tions, and of these, only two batches
eiceeded the 0.1 ppm target These two
post-aeration TCE concentrations
were 0.11 ppm and 0.15 ppm. The oper-
ating conditions for these final 49
batches of Phase 3 were an average dry-
er temperature between 290 and
310°F, an air flow of 15,000 cfm, soil
•praying for dust control, approxi-
mately six total minutes in the dryer,
and a soil volume of about three cubk
yards. Reasons for the minor variations
in efficiency are not certain, but likely
Table III. Optimal operating conditions for McKin pilot study configuration.
300-F
15,000 cfm
Enclosed bucket conveyor
system, wetting soil only
after final pan through
dryer
Baghouse paniculate*
treated separately in
enclosed, beat«d
conveyor
3 cubic yards
Dryer temperature
Dryer air flow
Dust control
Handling of collected
bag house particle*
Soil volume per run
Number of passe* through
dryer
Total dryer retention time
3, minimum
6-8 minute*
explanations are minor fluctuations in
temperature, possibly due to water
added to soil for dust control
Phase 4 consisted of 40 aeration runs
conducted after new dust control and
soil handling procedures were imple-
mented. In each run, the post-aeration
concentration of TCE was below lab-
oratory detection limits. Based on the
post-aeration laboratory analyses of
the 11 runs suspected of having elevat-
ed volatile organic content, TCE was
present in excess of 1 ppm in four of
these runs. The pre-aeration and post-
aeration results of these four runs is
summarized in Table IL
A practical objective of the pilot
study was to determine optimal opera-
tional parameters for full scale aeration
given this project's particular configu-
ration, soil performance targets, and
capabilities. The optimal operating
conditions determined in the four
phases of aeration testing are present-
ed in Table III, and the practical effects
of varying temperature and air flow
during the pilot study are discussed be-
low.
Dryer temperatures below approxi-
mately 250*F were not consistently ef-
fective in achieving the TCE target
concentration. Upper limits on dryer
temperature wen constrained by the
ability of the operation to handle air
and soils at high temperatures. Bag-
house temperatures above 375*F endan-
gered the synthetic filters in the bag-
Table II. Pre-aeration and post-aeration concentration* of detected
contaminants in selected Phase 4 soil aeration run* (ppm).
Trichloroethyeue
Tetrachloroethyene
1.1.1-Tnchloroethane
1 ,2 • Dichlorobenzene
Toluene
Xylenes
Pre-aeration
rant*
17^115
11-19
0.11-0.3
3.6-50
1-2
5-69
Port-aeration
concentration*
ND0.06*
ND0.06*
ND0.06*
ND1*
ND1»
ND1"
* Not detected at a laboratory detection limit of 0.05 ppm.
• Not detected at a laboratory detection limit of 1 ppm.
house. In addition, soils heated above
~360°F reacted violently with the ad-
dition of water and behaved as a vis-
cous fluid which was difficult to con-
tain on conveyor belts. As a result, the
optimal temperature established dur-
ing the pilot study was approximately
300°F. While temperature appears to
be the key pilot study operating pa-
rameter controlling repeatable treat-
ment efficiency, the data are insuffi-
cient to support a quantifiable rela-
tionship between temperature and
removal efficiency. One reason for this
is that for most runs, particularly in
Phases 3 and 4, final TCE concentra-
tions were not only below the 0.1 ppm
TCE target, but also below the labora-
tory's 0.05 ppm detection limit for
TCE.
Control of the dryer air flow ap-
peared to be an important operating
parameter due to its effect on air tem-
perature. Maintenance of consistent
treatment efficiencies and baghouse
temperatures protective of the syn-
thetic filters waa difficult with low air
flows. When the maximum attainable
air flow of 15,000 cfm was employed,
baghouse temperature was minimized.
The primary compound of concern
in the McKin soil aeration pilot study
was TCE, however, results of the study
suggest that the aeration process also
was effective in significantly removing
other volatile organic chemicals from
soils. Tetrachloroethylene and 1,1,1-
trichloroethane, detected in 1-100 ppm
ranges in pre-aeration samples, were
routinely not detected above 1 ppm in
post-aeration samples. With only sev-
eral minor exceptions, in the 102 suc-
cessful aeration batches processed dur-
ing Phase 3 of the study, these com-
pounds as well as the other volatile,
aliphatic priority pollutants consis-
tently were not detected in post-aera-
tion samples. (The laboratory detec-
tion limit for these volatile, aliphatic
compounds typically was 0.05 ppm for
these analyses.)
The efficiency of removing aromatic
October 1986 Volume 36. No. 10
1161
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HAZARDOUS WASTE MANAGEMENT
volatile compounds such as benzene
also is of interest. Among the excavated
soils aerated in Phase 2, two pre-aera-
tion samples yielded 680 ppm and 2600
ppm of benzene, the highest concentra-
tions of benzene found on the site by
several orders of magnitude. In post-
aeration analyses of these soil batches,
benzene was not detected at a 1.0 ppm
detection limit. Similar significant de-
creases were found for other aromatic
volatiles such as ethylbenzene, toluene,
lylenes, and dichlorobenzenea.
Discussion o< Air Monitoring Reeutta
The results of air monitoring for or-
ganic vapors during the pilot study in-
dicated that the on-site activities had
negligible effects on air quality at the
perimeter of the 7-acre site. At moni-
tored with portable on-site flame ion-
ization detectors, excavation activities
created the most significant source of
airborne volatile organic compounds.
Total organic vapor concentrations
within 2 ft of a full caisson bucket or
front-end loader were as high as ap-
proximately 1000 ppm as measured on
a flame ionization detector calibrated
to methane. However, at a distance of
approximately 20 ft downwind of exca-
vation activities, 5-minute time-
weighted average readings did not ex-
ceed 5 ppm above background during
the pilot study.
Continuous monitoring for organic
vapors at the site perimeter demon-
strated little evidence of on-site emis-
sions of volatile organic soil contami-
nants. Throughout the study, continu-
ous organic vapor levels of 2 ppm above
background did not occur at the sit*
perimeter as monitored on flame ion-
ization detectors calibrated to meth-
ane. Area background levels as mea-
sured upwind of the site and at sur-
rounding residences with flame
ionization detectors varied from about
1 ppm to 5 ppm during the study. Con-
tinuous background levels above 3.5
ppm occurred only during the early
portion of the pilot study aad were pos-
sibly related to winter wood stove emis-
sions or a systematically biased calibra-
tion procedure. During the spring,
background total organic vapor levels
typically were 1 to 2 ppm as measured
on portable flame ionization detectoo]
calibrated to methane.
Air monitoring results from 8-h sor-
bent tube sampling at the site perime-
ter indicated that TCE concentrations
in the ambient air ranged from leas
than 0.002 ppm to 0.01 ppm. Trichloro-
fluoromethane (Freon 110) was mea-
sured at slightly higher concentrations
ranging from less than 0.010 ppm to
0.018 ppm. Other compounds includ-
ing 1,2-dichloroethylene, toluene, eth-
ylbenzene, and xylene were detected at
levels of 0.02 ppm or less on isolated
occasions.
Ambient levels of suspended partic-
ulates during a brief portion of the pilot
study represented the most significant
air quality impact. On several days
during the latter portion of Phase 3 of
the pilot study, total suspended partic-
ulate levels exceeded 110 pg/m3 as mea-
sured during 24-hour sampling periods
at high volume samplers at the site pe-
rimeter. After dust control measures
were implemented in Phase 4, visual
dust emissions and high volume partic-
ulate concentrations noticeably de-
creased, with the maximum 24-hour
high volume concentration less than 50
Mg/m».
Primary sources of dust emissions
during the first three phases of the pi-
lot study were conveyor belt transfer
points, the transfer of dry, aerated soils
into and out of front end loaders, and
the transfer of treated soils and cement
to the hopper of the cement mixer
truck. Spraying water onto treated
soils on the belt conveyors was moder-
ately successful in abating dust genera-
tion from these extremely dry soils.
This approach was limited by the
amount of water that could be added
while maintaining a consistency trans-
ferable by conveyor and by the violent
release of dusty steam when water was
added to the hot soils. An additional
disadvantage of the use of spray noz-
zles for dust control was that the added
water content increased the tempera-
ture and steam content of the dryer
flue gas, imposing limitations on the
TnaTimiim dryer temperature. The use
of the enclosed bucket conveyor sou*
transfer system and other operational
modifications implemented in Phase 4
were successful in reducing dust emis-
sions. During Phase 4 the only signifi-
cant transfer of treated sous which was
not enclosed was the soil discharge to
the cement mixer. This waa the only
point of water addition to the soil A
canvass enclosure and local exhaust to
the baghouse further reduced duet gen-
eration in this transfer. An additional
benefit of the Phase 4 configuration
was leas restriction on elevating the
dryer temperature since corresponding
flue gas temperatures were lower with
dry air.
For the remediation of certain haz-
ardous waste site situations, thermal
soil aeration can be a viable alternative
that essentially eliminates volatile or-
ganic soil contamination from the va-
dose zone. In considering a soil aeration
method, this study's results suggest
that elevated temperatures during soil
aeration can be used to achieve strin-
gent post-treatment soil performance
criteria for volatile organic* during a
relatively brief period of soil-air inter-
action. The full scale pilot study con-
ducted at the McKin Superfund site
demonstrated the effective removal of
volatile organic contaminants from ex-
cavated soils by thermal soil aeration
within an enclosed environment.
In addition, controlled soil handling
techniques and treatment of the pro-
cess air contributed to negligible air
quality impacts due to organic vapors.
Enclosed handling of treated soils
proved necessary to reduce dust emis-
sions from the operation. Optimum op-
erating conditions were determined for
this particular treatment configuration
that produced consistent, post-aera-
tion TCE concentration less than the
0.1-ppm target level set by EPA. These
field-verified conditions included re-
peatedly mixing the soils at approxi-
mately 300* F for a total of 6-8 minutes.
The study also demonstrated the
practical usefulness, if not necessity, of
a full-scale pilot study to assess the ef-
fectiveness of an innovative use of
treatment technologies for a particular
hazardous waste. A number of process
and equipment problems were encoun-
tered and solved in the course of the
study by making adjustments to the
operating procedures or design. It is
doubtful if the magnitude of these
problems or the success of their solu-
tions could have been projected from
bench-scale or theoretical studies. On
the other hand, a disadvantage of the
full scale pilot study approach is that
its empirical and site-specific goals can
limit its usefulness es a pure research
tool and its direct application to other
remedial action projects.
The McKin Pilot Study was con-
ducted by Canonic Environmental Ser-
vices Corporation of Porter, Indiana
and was funded by Fairchild Camera
and Instrument Corporation and
Sanders Associates,
1. Review of In-Plact Trtvtmint Ttek-
niqu«t for Contaminated Surface Soiu,
Volumt 1: Ttchnical Evaluation, EPA-
540/2-S4-003a, U.S. Environmental Pro-
tection At racy, Cincinnati, OH, Septem-
ber 1M4.
-------
2. J. C. Agrelot. J. J. MaJot, M. I. Visser,
"" "Vacuum Defense System for Ground-
wster VOC Contamination," in froceed-
ings of the Fifth National Symposium
on Aquifer Restoration and Groundwa-
ter Monitoring, Columbus, OH, May
1985.
3 Superfund Record of Dtciiion, Verona
Well Field, Michigan, EPA/ROD/R05-
85/020 U S. Environmental Protection
Agency, August 1985.
4. D Hazaga. S. Fields, G. P. demons,
"Thermal Treatment of Solvent Con-
taminated Soils," in Fifth Motional Con-
ference on Management of Uncontrolled
Hazardous Waste Site*, Washington,
DC, November 1984.
5 Suptrfund Record of Decision, McKin
Company. Maine, EPA/ROD/R01-85/
009, U.S. Environmental Protection
Agency, July 1985.
Mr. Webster is the former U.S.
EPA Region I site manager for the
McKin Superfund Site. He is cur-
rently Section Chief for the'Maine
Superfund Section of Region 1 EPA.
This paper is written by Mr. Webster
in his private capacity and reflects
the views of the author and does not,
in any way, reflect the views, opinions
or policy of the U.S. EPA. This paper
was presented at an Engineering
Foundation conference on Alterna-
tive Technologies for Hazardous
Waste Management, Henniker, NH,
June 1986. Submitted for JAPCA
peer review June 27,1986, the revised
manuscript was received August 25,
1986.
Recovery, Recycle and Reuse
of Hazardous Waste
K. E. Nod, C. N. Haas and J. W. Patterson
Industrial Waste Elimination Research Center
Illinois Institute of Technology
Chicago. Illinois
An overview is provided of hazardous waste recovery, recycle and reuse.
The quantities and types-of hazardous waste that are generated in the
United States are identified. Hazardous wastes are classified according to
their economic potential for recovery. Energy and material recovery from
organic liquids and metal recovery from sludges have the highest potential
for economical recovery. Specific examples are provided of recovery from
these types of wastes. A variety of financial and regulatory strategies can be
used to encourage recovery from waste streams that do not have a potential
for economical recovery. These range from restrictions on burial to the
establishment of waste exchanges.
Increased emphasis has been placed on
studies of the chemistry, biological ef-
fects, treatment, fate, and control of
hazardous pollutants. Discovery of the
presence of such materials at high con-
centrations coupled with the recogni-
tion of their environmental impacts
and potential health hazards has led to
major legislative efforts which would
limit their release into the environ-
ment. The environmental regulations
prohibiting the discharge of toxic pol-
lutants from industrial activities, cou-
pled with the need for conservation of
raw materials has led to consideration
of the recovery, recycle, and reuse of
»aste products.1 The recovery, recycle,
and reuse alternative is doubly advan-
l"t»'«ht IS«6-Air Pollution Control A«ocuUoa
tageous since it conserves a materials
supply which is beginning to be recog-
nized as finite, while reducing the
quantity of hazardous pollutants dis-
charged into the environment
The choice between recovery of ma-
terial from waste and disposal of waste
seems to depend mainly on two factors:
economics and technology. Economics
is probably the most important factor
that limits the recovery of hazardous
industrial byproducts. The high cost of
recovering low-value materials and the
consequent relative unprofitability
seem to prevent many industries from
adoption of recovery technqiues for
waste byproducts. However, a number
of regulatory strategies are now avail-
able to encourage recovery.
Hazardous Waste Generation
The quantity of industrial wastes
generated by various industries is diffi-
cult to identify; however, Jennings2 has
provided an initial evaluation by con-
ducting a national industrial residual
flow study. Table I presents the rank
order of industries producing residues.
Table I. Total quantity of industrial
waste ordered by manufacturing industries
that produce hazardous residual.
Industries
Chemicals
Primary metals
Fabricated metals
Machinery
Paper
Transportation
Food
Petroleum
Stone
Electrical
Rubber
Leather
Lumber
Instruments
Misc. manufacturing
Furniture
Teitiles
Printing
Tobacco
Apparel
Percent of
total quantity*
37.6
29.1
7.7
6.5
4.6
4.0
2.7
2.4
2.0
0.7
0.7
0.5
0.4
0.3
0.2
0.2
0.2
0.1
<0.1
<0.1
a Total • 100% of 27.8 million tons of wastes
reported from 21 states.
Industrial residuals were defined as
those residues that are routed either to
unique treatment technologies or to
chemical waste disposal facilities and
considered "hazardous" under the Re-
source Conservation and Recovery Act
(RCRA) and the Toxic Substances
Control Act (TSCA). Current data in-
dicate that these constitute about 50
percent by weight of the total industri-
al discharge. The remaining fraction is
composed of such items as industrial
trash, foundry sand, wood waste and
Table I shows that 75 percent of the
residual volume is from the chemical,
primary metals, and fabricated metals
industries. Jennings was also able to
estimate the percentage of residual ma-
terial as to solids, liquid, or sludges, as
shown in Table it Under each catego-
ry, the residuals were identified by
physical and chemical properties (Ta-
ble III). These tables show that liquids
and sludges are a large percentage of
the total residue. This remains true
even when the unidentified category is
lumped with the solids. The miscella-
October 1986 Volume 36, No. 10
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