&EPA
United States Office of Research and Office of Solid Waste and EPA/540/R-97/Q05
Environmental Protection Development Emergency Response May 1997
Agency Washington, DC 20460 Washington, DC 20460
Bioremediation Field
Evaluation
Hill Air Force Base, Utah
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EPA/540/R-97/505
May 1997
Bioremediation Field Evaluation
Hill Air Force Base, Utah
U.S. Air Force Center for Environmental Excellence
Technology Transfer Division
Brooks AFB, Texas
U.S. Environmental Protection Agency
Office of Solid Waste and Emergency Response
Washington, D.C. 20460
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Cincinnati, Ohio 45268
Printed on Recycled Paper
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Notice
This project has been funded wholly or in part by the U.S. Environmental Protection Agency
(EPA). It has been subjected to the Agency's peer and administrative review and approved
for publication as an EPA document. Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
11
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Contents
The Bioremediation Field Initiative 1
Acknowledgments 2
Hill Air Force Base Abstract 3
Field Evaluation 4
Purpose of the Evaluation 4
Site History 5
Conducting the Evaluation 6
Site Assessment 7
Soil and Ground-Water Samples 7
Air Injection Flow Rate Evaluation .8
Soil-Gas Permeability and Radius of Influence 8
Results 9
Summary and Conclusions 12
References 13
in
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Figures
1 Schematic diagrams of injection bioventing (A) and extraction
bioventing (B) technology 4
2 Hill AFB site map illustrating the 280 fuel storage lot site 5
3 Hill AFB 280 site map showing the locations of the four
removed underground storage tanks (USTs), two new USTs,
existing utilities, and existing fuel system pipelines 6
4 Plan view of Hill AFB site with soil gas cluster wells (CW),
surface monitoring points (SMP), and injection well (IW) 8
5 Comparison of extractable TPH concentrations within the
IW 25-ft zone before (1990) and after (1994) air injection 10
6 Comparison of extractable TPH concentrations within the
IW 25- to 75-ft zone before (1990)71991) and after (1994)
air injection 10
7 Comparison of BTEX concentrations within the 25-ft zone
before (1990) and after (1994) air injection 11
8 Comparison of BTEX concentrations within the IW 25- to
75-ft zone before (1990/1991) and after (1994) air injection 11
Tables
1 Chronology of Soil and Ground-Water Testing Events at the
280 Site 7
2 In Situ Respiration and Biodegradation Rates for Hill AFB
280 Site Data Collected April 1991 Through November 1994 9
3 Summary of Mean Extractable TPH Levels in Soil Samples 10
4 Summary of Mean BTEX Concentraions in Soil Samples 11
IV
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The Bioremediation Field Initiative
In 1990, the U.S. Environmental Protection Agency (EPA) established the Bioremediation
Field Initiative as part of its overall strategy to increase the use of bioremediation to treat
hazardous wastes at Comprehensive Environmental Response, Compensation, and Liabil-
ity Act (CERCLA, or Superfund) and other contaminated sites. The primary purpose of the
Initiative is to collect and disseminate information on the capabilities of bioremediation
technologies so that EPA and state project managers, consulting engineers, and industry
representatives can make better-informed decisions about applying bioremediation in the
field. Participants in the Initiative include EPA's Office of Research and Development, Office
of Solid Waste and Emergency Response, and regional offices, as well as other federal
agencies, state agencies, industry, and universities.
The Initiative conducts a variety of activities to facilitate the exchange of information about
bioremediation, including sponsoring technology-transfer conferences on topics related to
bioremediation, maintaining an electronic database of information on bioremediation sites
nationwide, and publishing a bulletin of recent developments in field applications of biore-
mediation. In addition, the Initiative provides support;to states and regions for intensive
evaluation of bioremediation at selected sites across the country. The extent of the Initia-
tive's involvement at these sites varies from providing support for laboratory feasibility stud-
ies, to assisting with field treatability studies, to overseeing and assessing full-scale site
remediation.
Sites are nominated for field evaluations through the EPA regional offices or through the
states with concurrence from the regional offices. To date, nine sites have been selected
for performance evaluation of bioremediation: West KL Avenue Landfill Superfund site,
Kalamazoo, Michigan; Libby Ground Water Superfund site, Libby, Montana; Park City
Pipeline, Park City, Kansas; Bendix Corporation/Allied Automotive Superfund site, St.
Joseph, Michigan; Eielson Air Force Base Superfund site, Fairbanks, Alaska; Hill Air Force
Base Superfund site, Salt Lake City, Utah; Escambia Wood Preservation site—Brookhaven,
Brookhaven, Mississippi; Public Service Company site, Denver, Colorado; and Reilly Tar
and Chemical Corporation Superfund site, St. Louis Park, Minnesota.
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Acknowledgments
This document was prepared for the U.S. Environmental Protection Agency's (EPA's) Office
of Research and Development (ORD) and Office of Solid Waste and Emergency Response.
Dr. Fran Kremer, ORD, served as Program Director, and Dr. Gregory Sayles, EPA National
Risk Management Research Laboratory, provided technical direction from EPA for the re-
search conducted at Hill Air Force Base. Technical direction from the U.S. Air 'Force was
provided by Mr. Robert Elliott. The work was carried out by Battelle Memorial Institute, with
Dr. Robert Hinchee serving as Project Manager.
EPA also gratefully acknowledges the technical and financial contributions of those who
collaborated with EPA to conduct this field evaluation. In particular, EPA wishes to acknow-
ledge the additional funding provided by Hill Air Force Base.
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mil
Force Base
ABSTRACT
This publication, one of a series presenting the findings of the Bioremediation Field Initia-
tive's bioremediation field evaluations, provides a detailed summary of the evaluation con-
ducted at the Hill Air Force Base (AFB) Superfund site in Salt Lake City, Utah. At this site,
the Initiative provided support for an evaluation of bioventing at several airflow rates to
stimulate in situ bioremediation of soil contamination resulting from a JP-4 jet fuel spill at
the 280 Fuel Storage Yard Site. The main objective of the evaluation was to determine the
effect of airflow injection rate on the effectiveness of bioventing in stimulating biodegrada-
tion while minimizing volatilization. The evaluation was conducted as a joint effort of the
U.S. Air Force and the U.S. Environmental Protection Agency's (EPA's) National Risk Man-
agement Research Laboratory (NRMRL). The effort was initiated in November 1990 with the
installation of an injection well and three soil-gas monitoring wells as well as collection and
analysis of soil samples for JP-4 constituents. Air injection began in December 1990 at a
flow rate of 67 cubic feet per minute (cfm). Over the next 4 years, seven additional soil-gas
monitoring wells were installed and soil samples from these wells were analyzed. In situ
respiration tests were conducted to evaluate four different injection rates (28, 40, 67, and
117 cfm). In addition, a soil-gas permeability test was conducted in June 1993, and final site
characterization was completed in November 1994.
Bioventing was successful in the remediation of vadose zone soils at the site. Total petro-
leum hydrocarbons (TPH) and benzene, toluene, ethylbenzene, and xylenes (BTEX) con-
centrations were significantly reduced in the more contaminated soils within 25 ft of the
injection well. In situ respiration tests indicated an average biodegradation rate of 0.53
mg/kg/day, compared to 0.75 mg/kg/day based on soil samples. Hydrocarbon concentra-
tions did not increase in surrounding cleaner soils as the result of air injection, and surface
emission testing found no measurable emission of hydrocarbons to the atmosphere as a
result of air injection. The radius of influence ranged from 73 ft at an injection rate of 20 cfm
to 278 ft at 117 cfm.
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FIELD EVALUATION
Purpose of the
Evaluation
Petroleum distillate fuel hydrocar-
bons such as JP-4 jet fuel are gen-
erally biodegradable if indigenous
microorganisms receive an ade-
quate supply of oxygen and nutri-
ents. Typically, much of the
hydrocarbon residue at fuel-con-
tamination sites lies in unsaturated
(vadose) zone soils immediately
above the water table. To success-
fully bioremediate such sites, an
adequate supply of oxygen must
be provided to the unsaturated
zone soils. To date, most efforts to
bioremediate fuel spills have fo-
cused on soluble fuel components
in ground water rather than hydro-
carbon residues in unsaturated
zone soils.
Conventional bioremediation sys-
tems use water to carry oxygen to
the contamination. Water, how-
ever, does not deliver enough oxy-
gen to the contaminated soil. This
problem has led researchers to in-
vestigate the use of air as an alter-
native source of oxygen. Air has
two major advantages over water.
First, on a mass basis, less air than
water is needed to deliver a suffi-
cient amount of oxygen. Second,
air is more diffusible than water, fa-
cilitating delivery of oxygen to soils
such as clay that are relatively im-
permeable to water.
Researchers had reason to believe
that moving air through soil could
indeed supply enough oxygen to
promote biodegradation of petro-
leum contaminants. As early as
1981, researchers had begun evalu-
ating the use of soil vapor extrac-
tion (SVE) technology—the pulling
of air through the ground—to reme-
diate petroleum-contaminated
soils. The technology involved mov-
ing air through contaminated soils
at high rates to promote volatiliza-
tion of the contaminants. Although
SVE technology was designed to
promote volatilization, researchers
found that it stimulated aerobic
biodegradation as well. This find-
ing generated interest in develop-
ing a different soil aeration
technology—called "bioventing"—
that would maximize biodegrada-
tion rather than volatilization.
Researchers found that by using
airflow rates lower than those used
during the SVE process (and by al-
tering other design parameters)
they could in fact maximize biode-
gradation rather than volatilization.
Thus, bioventing is the process of
moving air through subsurface
soils to provide oxygen to microor-
ganisms and stimulate aerobic
biodegradation. As Figure 1
shows, the air movement required
for bioventing can be achieved by
blowing air into the soil (injection
bioventing) or by creating a vac-
uum to pull air out of the soil (ex-
traction bioventing).
In 1988, the Air Force initiated a
study at Hill AFB to examine the
potential of bioventing to remedi-
ate JP-4 jet fuel-contaminated
soils. Promising results prompted
the Air Force and NRMRL to con-
Low Rate
Air Injection
(A)
[
i
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r i
Biodegradation
of Vapors
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Figure 1. Schematic diagrams of injection bioventing (A) and extraction bioventing
(B) technology.
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duct a field evaluation at the site,
consisting of two separate but inte-
grated projects. The Air Force ef-
fort involved air injection at one
flow rate along with surface-emis-
sion monitoring and in situ respira- .
tion testing to estimate .
biodegradation rates. A total of
seven'soil-gas monitoring wells
(cluster wells), seven ground-water
monitoring wells, and an injection
well were installed for the Air
Force effort. The NRMRL project in-
volved injecting air at several differ-
ent flow rates, along with follow-up
in situ respiration tests, installation
of three additional soil-gas wells,
and additional soil sampling.
The objectives of the field evalu-
ation were to:
• Determine site-specific condi-
tions, including the extent of
soil contamination.
• Estimate the effectiveness of
injecting air to stimulate biode-
gradation, and to determine
the kinetics of the biodegrada-
tion process.
• Determine if hydrocarbon re-
leases occurred at the ground
surface due to injection of air
into the soil.
• Estimate the radius of influ-
ence that is caused by air in-
jection into the specific soils
at the site.
• Develop recommendations for
routine bioventing applications.
Site History
The Hill AFB is an active base lo-
cated 10 miles south of Ogden,
Utah, and near the Great Salt Lake
(see Figure 2). Approximately
15,000 people work on the base
and approximately 4,000 live on
the base. The area of the base
studied is known as the 280 Fuel
Storage Lot Site. It is located in the
southeast corner of the base, next
to the runway.
The 280 Site has been used since
1941 as a fuel storage area, first
containing aviation-grade fuel and
later JP-4 jet fuel. Four original
25,000-gallon underground stor-
age tanks (Hill AFB designation
Hill
Air Force
Base
North
To Salt
\yjjkeCHy
Figure 2. Hill AFB site mop illustrating the 280 fuel storage lot site.
Mite
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280.1, 280.2. 280.3. and 280.4)
were removed in 1989 and re-
placed with two new 25.000 gal-
lon tanks (Hill AFB designation
10268.1 and 10268.2). The 280
Site also contains tool mainte-
nance and storage areas, jet en-
gine storage and testing areas,
pumping facilities, above- and be-
low-ground piping, and other bur-
ied utilities. The land around the
280 Site is used for industrial pur-
poses and contains warehouses,
aircraft hangers, and aircraft serv-
ice facilities.
There is no evidence that the fuel
leaked from the storage tanks. Pe-
troleum releases via surface spills
during fuel transfer operations,
maintenance of the system, and
overfill into the pump and piping
vaults appear to have occurred dur-
ing the life of the system. The
most recent recorded surface-spill
event occurred around 1982,
when the tanks were overfilled.
Prior to bioventing, the Hill AFB
site was contaminated with JP-4
jet fuel from a depth of about 35 ft
down to the ground water at 95 ft
below the surface. Soil samples
taken in September 1991 revealed
an average TPH level of 890
mg/kg, with TPH levels at some
depths reaching 5,000 mg/kg. At
most depths, BTEX levels ranged
from about 300 mg/kg to about
800 mg/kg. The area of contami-
nation extended beneath the tool
maintenance building, engine stor-
age yard, and fuel storage yard
(see Figure 3).
Because of the location of the pota-
ble ground water, the contami-
nated soil—consisting of sand and
various clayey, silty, and gravelly
sand zones—is not likely to pose a
risk to human health. A shallow
aquifer and two deeper aquifers
(the Sunset Aquifer and the Delta
Aquifer) lie below the 280 Site.
The shallow aquifer is 95 ft below
Underground Pipeline
FOB Atom Cibte
Sanitary Sewer
GosMiki
Steam Main (Bevated)
Abow Ground PtpclM
Storm Swmr and Manbota
Catch Bash*
Industrial Wnte
BteWcPowtrin Duets WManhote
Abandoned Piping
Figure 3. Hill AFB 280 site map showing the locations of the four removed
underground storage tanks (USTs), two newUSTs, existing utilities, and existing fuel
system pipelines.
the surface water. The deeper aqui-
fers are approximately 300 to 800
ft below the site. The ground water
flows from east to west.
Conducting the
Evaluation
From November 1990 through No-
vember 1994, the Air Force and
NRMRL conducted their study of
the effectiveness of air injection as
a method of remediating the JP-4
jet fuel-contaminated 280 Site at
Hill AFB. The study involved sev-
eral steps:
• Initial site assessment.
• Installation of soil gas and
ground-water monitoring wells
to monitor soil gas and
ground-water constituents
over time.
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• Testing to determine the loca-
tions of several of the ground-
water monitoring wells.
• Varying the air injection flow
rates in conjunction with in situ
respiration and surface emis-
. sions testing to provide informa-
tion for system optimization.
• Soil-gas permeability testing
to quantify migration rates
and dispersion/diffusion of
vadose zone gases.
• Final site assessment to deter-
mine site-specific conditions
after approximately 4 years of
low-intensity bioreclamation ef-
forts.
Site Assessment
A preliminary assessment of the
280 Site conducted in 1990 indi-
cated that air injection technology
appeared to be suitable for applica-
tion but needed to be refined. The
initial assessment, which utilized
three multilevel soil-gas sampling
wells and an air injection well, es-
tablished a baseline of contamina-
tion levels.
To refine the study and determine
the optimal parameters of an air in-
jection bioremediation process, an-
other injection well, 23 soil
borings, 10 soil-gas monitoring
wells, 7 ground-water monitoring
wells, and 5 final soil borings were
made over the course of the study.
Cone Penetrometer Testing (CPT)
was also conducted to determine
the feasibility of this method for
deep (approximately 125 ft) sam-
pling and evaluation at the site,
and to help locate several of the
groundwater monitoring wells.
Soil and Ground-Water
Samples
Soil samples were collected during
drilling, and ground-water samples
.were collected after the ground-
water monitoring wells were in-
stalled and completed. Soil and
ground-water samples were submit-
ted to the Utah State University
Water Research Laboratory (USU-
WRL) for testing for JP-4 constitu-
ents using modified EPA methods
(EPA method 5030, a modified
8020 Method for volatile organic
compounds, and a modified gas
chromatographic method for non-
volatile organic compounds).
A total of 82 separate soil, soil-gas,
and ground-water sample collec-
tion events were conducted at Hill
AFB 280 Site from November
1990 to November 1994. (An
"event" is a discrete date on which
individual tests, samples, or read-
ings were performed.) A total of
Table 1.
558 individual tests, samples, or
readings were performed at semi-
regular intervals during that time.
The busiest testing year was 1993.
Table 1 summarizes the individual
tests, samples, or readings per-
formed in each year.
Over the course of these collection
events, soil samples were drawn
from bore holes and cluster wells;
ground-water samples were taken
from injection wells and ground-
water monitoring wells; soil gases
were collected from cluster wells
and surface monitoring points; and
ground-water depth gauging was
conducted at injection wells and
ground-water monitoring wells
Chronology of Soil and Gji
YEAR (Number of events:
Discrete dates on which
individuals tests, samples
or readings were per-
formed)
1990(3)
1991 (9)
1992 (17)
1993 (36)
1994 (17)
1990-1994 (82)
INDIVIDUAL TESTS, SAMPLES, OR
READINGS TAKEN DURING THE YEAR (#)
Initial soil samples (5)
Initial soil-gas 02, C02, TPH (4)
Initial ground-water sample (1)
YEAR TOTAL: 10
In situ respiration test for 02, C02, TPH (3)
Ground-water samples (5)
Surface emission tests (2)
Soil samples (6)
SoiIgas.02,C02,TPH(12)
ORS interface probe testing (4)
YEAR TOTAL: 32
CPTs(6)
Soilgas02,C02,TPH(66)
Ground-water depth gauging (28)
In situ respiration test for 02, C02, TPH (1)
Soil samples (4)
Surface emission tests (2)
YEAR TOTAL: 107
Soil samples (1)
Soil gas 02,C02, TPH (245)
Ground-water depth gauging (95)
Pressure reading (6)
In situ respiration test for 02, C02, TPH (2)
Surface emission tests (3)
YEAR TOTAL: 352
Surface emission; soil gas 02, C02, TPH (1)
Ground-water depth gauging (50)
In situ respiration test for 02, C02, TPH (1)
Soil samples (5)
YEAR TOTAL: 57
1990-1994(558)
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(see Figure 4). An ORS interface
probe was used to determine
whether hydrocarbon product was
present at the ground-water table
for selected ground-water monitor-
ing well locations. No hydrocarbon
interface was detected at the
ground-water table.
Air Injection Flow Rote
Evaluation
A key objective of the Hill AFB
study was to test different airflow
rates to determine the maximum
biodegradation rate while eliminat-
ing volatilization. A total of five
flow rate evaluations were con-
ducted at rates of 67, 40, 117, and
28 cfm. (The 67 cfm evaluation
was repeated to include additional
soil-gas monitoring wells com-
pleted at the site.) As the flow rate
increased, so did the area of aera-
tion.
Each evaluation was followed by in
situ respiration testing (U.S. EPA
and U.S. Air Force, 1995). Monthly
soil-gas monitoring was initiated
on August 13, 1992, to measure
the oxygen, carbon dioxide, and
TPH parts per million by volume
(ppm) levels during each of the dif-
ferent airflow rates.
Each test consisted of injecting air
into the injection well and perform-
ing:
• An in situ respiration test-
measurement of the rate of
oxygen uptake by microorgan-
isms in the soil to estimate
the rate of biodegradation oc-
curring there.
• Surface emissions tests—both
during air injection and while
the air injection system was
shut off so that emissions
rates could be compared.
• Soil gas sampling—to monitor
oxygen, carbon dioxide, TPH,
and BTEX levels.
• SMP = Surface Monitoring Point
O CW = Soil Vapor Cluster Well
A-A'- Cross-Section Trace
<- Projection of Cluster Well Onto Cross-Section Trace
Figure 4. Plan view of Hill AFB site with soil gas cluster wells (CW), surface
monitoring points (SMP), and injection well (IW).
Table 2 shows the in situ and
biodegradation rates, by cfm, col-
lected between April 1991 and No-
vember 1994 from a cluster well
(280-CW1) situated 13.5 ft from
the injection well and from a clus-
ter well (280-CW3) situated 63 ft
from the injection well. The great-
est influence on changes in the res-
piration rate with time is the drop
in contaminant concentrations
with time. It is difficult to see any
influence of airflow rate on respira-
tion rate. However, the surface
emission rate was negligible at all
flow rates. Thus, the maximum
flow rate that produces minimal
surface emissions was not deter-
mined. Adequate oxygen levels
were obtained at the lowest flow
rate (28 cfm).
Soil-Gas Permeability and
Radius of Influence
Estimates of the soil's permeability
to gas flow and the radius of influ-
ence of venting wells are impor-
tant elements of a full-scale
bioventing design. Onsite testing
also can be used to determine the
radius of influence, flow rate, and
air pressure that can be achieved
for a given well configuration (U.S.
EPA and U.S. Air Force, 1995).
When full-scale systems are being
designed, these data are used to
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Table 2.
i|»;fflti;fSn7lBitT»)»w?Irt«i!l^ffB^^ffi^tmS;ffHS*^B?mK ip«.>wn . . »«». ^J-.Y.*^-;
Well
280-CW1:
(13.5 ft from
IW)
280-CW1:
(13.5 ft from
IW)
r—
Depth
(ft)
20
30
40
50
60
70
80
90
10
20
30
40
50
60
70
80
90
4/91
(67 cf m)
0.119
0.126
0.080
0.048
0.014
0.009
0
0.012
0.010
0.032
0.035
0.026
0.096
0.014
0.004
0.009
0.038
In Situ Respiration Rate
(% oxygen/hr)
9/92
(67cfm)
0.016
0.020
0.079
0.077
0.010
0.008
0.001
0.062
0.006
0.008
0.007
0.013
0
0.021
0.030
0.025
0.002
6/93
(40 cf m)
0.008
0.011
0.022
• 0.086
0.023
0.011
0.012
0.018
0.004
0.006
0.014
0.006
0.004
0.004
0.009
0.051
0.043
10/93
(117cfm)
0.009
0.011
0.017
0.038
0.011
0.011
0.013
0.077
0.002
0.003
0.004
0.003
0
0.007
0.007
0.022
0.016
10/94
(28 cf m)
0.007
0.008
0.009
0.026
0.011
0.011
0.019
0.004
0.002
0.004
0.004
0.003
<0.001
0.004
0.004
0.014
0.008
1
Biodegradation Rate
(mg/kg/day)
4/91
(67cfm)
2.27
2.41
1.52
0.921
0.270
0.168
0
0.236
0.189
0.607
0.663
0.494
1.83
0.262
0.069
0.169
0.727
9/92
(67 cfm)
0.313
0.379
1.51
1.47
0.182
0.140
0.126
1.20
0.118
0.154
0.134
0.258
0
0.394
0.565
0.482
0.042
6/93
(40 cf m)
0.164
0.219
0.448
1.79
0.482
0.238
0.248
0.359
0.088
0.121
0.299.
0.132
0.079
0.076
0.193
1.07
0.979
10/93
(117cfm)
0.193
0.219
0.359
0.794
0.229
0.225
0.260
1.59
0.036
0.069
0.075
0.058
0
0.146
0.155
0.456
0.324
10/94
(28 cfm)
0.151
0.157
0.189
0.535
0.227
0.231
0.386
0.089
0.052
0.082
0.081
0.064
0.002
0.083
0.082
0.283
0.163
space venting wells, size blower
equipment and ensure that the en-
tire site receives a supply of oxygen-
rich air to sustain in situ
respiration. Assuming steady-state
conditions, the soil-gas permeabil-
ity value calculated for only the air
injection at 280-IW was 0.057
darcy. The radius of influence at
the 280 Site was estimated to be
approximately 200 ft (from 73 ft at
an injection rate of 20 cfm to 278
ft at 117 cfm).
Results
The biodegradation rate for TPH
and BTEX at the 280 Site was de-
termined by testing samples taken
from 10 equal depths down to
100 ft. The samples were taken
from within two separate zones: a
radius of 25 ft from the injection
well and a radius of between 25
and 75 ft from the injection well.
Samples taken from the 25-ft zone
indicate that at every level (0 to 10
ft, 10.1 to 20 ft, etc.) except the
90.1 to 100 ft level, a significant re-
duction in the TPH level occurred
over the course of the study. The
mean reduction was about 1000
mg/kg: from 1,384 mg/kg in
1990 to 330 mg/kg in 1994,
which represents a hydrocarbon re-
moval rate of 0.5 to 0.75
mg/kg/day. These rates are lower
than those recorded at most
bioventing sites, but are significant.
The most likely reason for the low
rates is moisture limitation, as
there was considerable variation in
the moisture levels at the site. Mois-
ture addition was not used be-
cause of the extensive
development on the site made
moisture addition infeasible, and re-
searchers desired to test the feasi-
bility of bioventing at the site
without water addition.
Samples taken from the 25-ft to 75-
ft zone indicated that while an over-
all reduction of TPH levels
occurred, reduction occurred at
only 5 of the 10 levels. The mean
reduction was about 100 mg/kg;
179 mg/kg in 1990 to 80 mg/kg
in 1994, which represents a hydro-
carbon removal rate of .07 to .28
mg/kg/day (see Table 3 and Fig-
ures 5 and 6).
Like TPH levels within the 25-ft
zone, BTEX levels decreased ex-
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Table 3.
Summary of Mean Extractable TPH Levels in Soil Samples
Injection
Well Zone
<25ft
25-75 ft
TPH Concentration (mg/kg)
1990/1991
Mean
1.384
179
SD
1264
434
1994
Mean
330
80
SD
606
272
Significantly
Different
Yes, p = 0.001
No,p>0.1
cept at the 90.1 ft to 100 ft level.
Over the course of the study, the
levels fell from 312 mg/kg to 50
mg/kg. The final average BTEX
concentration was 52 mg/kg. Like
the TPH levels within the 25- to 75-
ft zone, BTEX levels did not drop at
all levels. In fact the mean level
was virtually unchanged from
1990 to 1994: from 55 mg/kg to
64 mg/kg (see Table 4 and Fig-
ures 7 and 8).
"J4200
D Before
•Ana-
1 10 100
TPH Concentration (mg/kg)
' AmlyuaconducMbyimthyhnacMoritelodtlntraUon. Detection (mil 0.5 mo/kg
pO.WO It 50.1-60 ft; 70.1«J fl): after coootrtiitkxl U DM vrtM for 290401
Flgur* 5. Comparison of extractable TPH concentrations within the IW 25-ft zone before (1990) and after (1994) air injection.
, 10 100 1000
TPH Concentration (mg/kg)
• Anton conducted by meUiytae cWoftJo «oxMet extraction. DetKttonHmlt 0.5 tngftg
- Brfora OTiceiKnlloiM in I itmn o( v»lu« from 2NXW3.2WXCW4,2KMNS. «nd 2«W»V$; after conoonlraBonj are a moan of
ISO-BM. 28OB05. and 290-B06
Fignr* 6. Comparison of extractable TPH concentrations within the IW 25- to 75-ft zone before (1990/1991)
and after (1994) air injection.
10
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Table 4.
Summary of Mean BTEX Concentrations in Soil Samples *
Injection '
Well Zone
<25ft
25-75 ft
TPH Concentration (mg/kg)
1990/1991
Mean
312
. 55
SD
276
110
1994
Mean
52
64
SD
183
255
Significantly
Different
Yes, p< 0.001
No, p = 0.608
One pattern observed for the 280
Site TPH and BTEX results was
that the mid-range (40.1-to 50-ft)
and deepest (90.1-to 100-ft)
depth intervals generally showed
an increase in TPH and BTEX levels
after the air injection effort. One
possible explanation for this may
be the inability of the limited soil
sampling conducted to accurately
represent the heterogenous nature
30.1-40
80.1-90
10 100
BTEX Concentration (mg/Kg)
Aiulys««conduei*dbypur0eantf trap
B»fa»ianc»iiUrtloiih«ni«inofu»ic
(30.1-40 Ifc 50.140 It 70.1-80 ID; liter conwnmtlon H the vak» tor 280*01
Figure 7. Comparison of BTEX concentrations within the 25-ft zone before (1990) and after (1994) air injection.
0-10
10.1-20
20.1-30
40.1-50
50.1-00
•11.4
'" j 5.7
.*'
171
~_^_ _"1^"fi' | 1»
**
J 110
M1.3
<1
~" " 1 31
a Before
•After
10 100
BTEX Concentration (mg/kg)
Analytts conducted by purge and frap
Beftxi core»*«tkm»ir
-------
represent the heterogenous nature
of the hydrocarbon soil contamina-
tion. Thus, the high TPH and BTEX
levels recorded for specific soil sam-
ples may represent a small pocket
of contamination, and not the con-
tamination for the entire 10-ft
depth interval.
Surface emissions rates remained
about the same with increasing air-
flow rates. More importantly, sur-
face emissions rates during air
injection were not significantly dif-
ferent from those during bioventing
shutdowns (no injection). This was
an important finding because it in-
dicates that bioventing at the air-
flow rates evaluated does not
increase emissions of volatilized
contaminants.
Summary and
Conclusions
Bioventing was successful in the re-
mediation of vadose zone soils at
the Hill AFB 280 Site, Final soil
sampling conducted in December
1994 revealed that TPH and BTEX
levels had declined at all but one
soil depth within a 25-ft radius of
the injection well. Only at a depth
of 90 to 100 ft (at the capillary
fringe) did TPH and BTEX levels fail
to decline, suggesting that the cap-
illary fringe was not adequately aer-
ated. These results help
demonstrate the feasibility and ef-
fectiveness of bioventing at the air-
flow rates evaluated.
Key findings of the study include
the following:
• In the more contaminated
soils (within 25 ft of the injec-
tion well) hydrocarbon concen-
trations were significantly
reduced from initial average
TPH concentrations of 1,384
mg/kg to final average concen-
trations of 330 mg/kg, and
from initial average BTEX con-
centrations of 312 mg/kg to fi-
nal average BTEX concentra-
tions of 52 mg/kg.
• The in situ respiration test pro-
vided a reasonably good indi-
cation of the biodegradation
rate in the most contaminated
zone (within 25 ft of the injec-
tion well). In situ respiration
testing estimated an average
rate of 0.53 mg/kg/day, while
soil sampling indicated an av-
erage rate of 0.75 mg/kg/day.
• Hydrocarbon concentrations
did not increase in surround-
ing cleaner soils as the result
of air injection
• Surface emission testing
found no measurable emis-
sion of hydrocarbons to the at-
mosphere as a result of air
injection.
• The radius of influence was
measured to range from 73 ft
at 20 cfm to 278 ft at 117 cfm.
12
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References
Soyles, G.D. R.C. Brenner, R.E. Hinchee, A. Leeson, C.M. Vogel, R.N. Miller, and R. Elliott.
1994. Bioventing of Jet Fuel: Demonstrations at Hill and Eielson Air Force Bases.
Symposium on Bioremediation of Hazardous Wastes: Research, Development, and Field
Evaluations. San Francisco, CA Qune). EPA/600/R-94/075.
Sayles, G.D., R.E. Hinchee, R.C. Brenner, and R. Elliott. 1993. Documenting Bioventing of
Jet Fuel to Great Depths: A Field Study at Hill Air Force Base. Symposium on
Bioremediation of Hazardous Wastes: Research, Development and Field Evaluations,
Dallas, TX (May). EPA/600/R-93/054.
U.S. Environmental Protection Agency. 1995. Bioremediation Field Initiative Site Profile:
Hill Air Force Base Superfund Site. Office of Research-and Development and Office of
Solid Waste and Emergency Response. Washington, DC. EPA/540/F-95/506C.
U.S. Environmental Protection Agency. 1995. Bioremediation Field Evaluation: Eielson Air
Force Base, Alaska. Office of Research and Development and Office of Solid Waste and
Emergency Response. Washington, DC. EPA/540/R-95/533.
U.S. Environmental Protection Agency and U.S. Air Force. 1995. Bioventing Principles and
Practices. Office of Research and Development. Washington, DC. EPA/540/R-95/534.
•&U.S. GOVERNMENT PRINTING OFFICE: 1997 - 549-001/60170
13
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