EPA/600/A-95/141
Intrinsic Bioremediation of Fuel Contamination in Ground Water at a
Field Site
Don H. Kampbell', T.H. Wiedemeier51, and J.E. Hansenc
°R.S. Kerr Environmental Research Laboratory, Ada, OK 74820,
bParsotts Engineering Science, Inc., Denver, CO 80290
"U.S. Air Force Center for Environmental Excellence, Brooks Air Force Base, TX 78235
Abstract
A spill of gasoline occurred at an automobile service station in 1986. Oily phase
residue in the subsurface has continued for the past eight years to release water soluble
fuel hydrocarbons into the aquifer. The site was characterized for implementation of
intrinsic remediation. The subsurface was a beach sand with sea shell fragments. Hie
water table was near 1.3 meters below ground surface. Surface dimensions over the
plume were about 200 meters downgradient and 60 meters in width. Three points to
coincide with direction of ground-water flow were selected in the plume for water quality
assessments. Both methane and trimethylbenzene were used as surrogate tracers to
normalize loss of contaminants. Aerobic respiration and methanogenesis.accounted for
most biodegradation obtained. Assimilation capacities of dissolved oxygen, ferrous iron,
and methane distributions when compared to BTEX concentrations showed that the
ground water has sufficient capacity to degrade all dissolved BTEX before the plume
moves beyond 250 meters downgradient. Evidence obtained from loss of contaminants,
geochemistry, and microbial breakdown chemicals showed that intrinsic bioremediation
technology would be a viable option to restore the site.
Kev Words: intrinsic remediation. BTEX plume, aerobic respiration,
methanogenesis.
Introduction
A detailed characterization study was conducted during March 1994 at a fuel spill
location on Patrick Air Force Base in Cocoa Beach, Florida. Core material and ground-
water samples were collected and analyzed to predict the influence of natural attenuation
on dissolved contaminant migration and attenuation. Technical protocol followed was
reported by Wiedemeier et al. (1994).The remediation of contaminants in ground water is
called intrinsic remediation which incorporates mechanisms of biodegradation, sorption,
dilution, volatilization, dispersion, and advection. All of these processes can operate
concurrently during field scale implementation of bioremediation technology. The
respiration processes microorganisms used to bring about a reduction in total contaminant
mass in ground water are aerobic respiration, denitrification, iron or manganese

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reduction, sulfate reduction, and methanogenesis. These processes called intrinsic
bioremediation are important contributors to benzene, toluene, ethylbenzene, xylenes
(BTEX) removal from ground water.
If oily phase residue is present in the subsurface, it can act as a continuing source
of contamination. To demonstrate intrinsic bioremediation at field spill sites, the
quantification of biodegradation of BTEX which arc major fuel constituents is very
important Patterns and rates can vary from site to site. The loss of contaminants
downgradient to our site characterized was used as evidence for the occurrence of
intrinsic bioremediation.
Spill Site
About 700 gallons of unleaded gasoline was released into the subsurface in 1986
at an on-base service station location. The subsurface matrix consisted of beach sand
containing sea shell fragments to a depth of about 7.5 meters below ground surface (bgs)
where a confining marl formation was located. The water table was near 1.3 meters bgs
and the downward gradient measured in monitoring point wells was 0.002 m/m. Slug
testing indicated that average hydraulic conductivity was near 0.026 cm/sec. The average
advective ground-water velocity was about 48 m/year assuming a sand porosity of 0.35.
Using TOC fneasurements, a retardation factor of 2.6 was calculated'for benzene. The
effective solute transport velocity was 18.3 m/year.
Results
The extent of the plume was measured by the BTEX dissolved in the ground
water as shown in Figure 1. Surface area over the plume was about 200 meter long and
60 meter wide. Free-floating gasoline was not detected in any well sampled.
Loss of Contaminants
Point A as shown in Figure 1 was selected for the highest dissolved BTEX with
points B and C at 38 and 98 meters, respectively, downgradient in the plume. BTEX lost
to biodegradation is listed in Table 2. Methane produced from BTEX and TMB =
(measured BTEX + TMP) x (0.78). Ground water isopleth maps for BTEX, dissolved
oxygen, ferrous iron, and methane are shown in Figures 1,2,3, and 4 respectively. Both
methane and trimethylbenzene (TMB) were selected as surrogate tracers. It was assumed
that all methane was both stable and produced from BTEX components (Table 3). Our
usual approach has been to use trimethylbenzene (TMB) as a recalcitrant compound to
correct BTEX concentrations for dispersion, dilution, sorption, and volatilization. For
some reason benzene was higher at point B than at point A which indicated that TMB
was under this site conditions not entirely recalcitrant However, the TMB corrected
toluene, ethylbenzene, and xylenes decreased 30 to 60 percent between point A and B
which confirmed that biodegradation occurred (Table 4). Even though some
biodegradation of TMB may have occurred the corrected values would underestimate the

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percent BTEX biodegraded. Between points B and C the relative decrease in TMB had a
reduction rate similar to BTEX. Therefore, we choose not to use TMB as a surrogate
tracer and concluded that BTEX/TMB radios did not substantiate that intrinsic
bioremediation occurred.
Ground Water Geochemistry
««
The redox potential at the site ranged from 54 to -293 mV. Low redox potential
coincided with sampling points of high BTEX contamination, low dissolved oxygen,
some ferrous iron, and elevated methane concentrations. Water temperature was a warm
26°C which suggested that bacterial growth, rates could be high. Total alkalinity ranged
from 148 to 520 mg/L which would suffice to buffer pH changes caused by BTEX
biooxidation reactions. pH's near 7 were in the optimal range of BTEX-degrading
microbes. Nitrate was very low so denitrifvcation for BTEX removal was not viable.
Sulfate at levels up to 86 mg/L was fairly high, but a relationship between sulfate and
BTEX changes was not apparent. Hie water chemistry suggested that dissolved BTEX
would be subjected primarily to aerobic respiration, iron reduction and methanogenesis.
The distribution of dissolved oxygen is shown in Figure 2. Site areas with
depleted dissolved oxygen coincided with areas of elevated BTEX which indicated that
aerobic biodegradation was occurring. Background dissolved oxygen was 3.7 mg/L so
based on the Table 1 stoichiometry the shallow ground water had an assimilation capacity
of 1200 ug/L total BTEX (Table 5)..
Ferrous iron distribution (Figure 3) in the site ground water showed a direct
relationship with elevated total BTEX. Background of ferrous iron was near 0.1 mg/L
while levels up to 1.9 mg/L were present in the plume. Based on the Table 1
stoichiometry, the iron reduction would have the capacity to assimilate at least 90 ug/L of
the total BTEX. Replenishment of the ferrous iron from soil iron oxides could occur to
increase iron reduction capacity.
Methane distribution is shown in Figure 4. A direct relationship occurred
between elevated methane and total BTEX concentrations which indicated that
methanogenesis was occurring. Background methane was near 1 mg/L while the highest
plume methane concentration was 14.6 mg/L. Assimilation capacity during
methanogenesis based on stoichiometry would be at least 17,400 ug/L of total BTEX
(Table 5). Actual methanogenic assimilative capacity could be much higher because the
amount of carbon dioxide available was not included. Methane corrected BTEX
concentrations at points A,B, and C also provided evidence that intrinsic bioremediation
was occurring (Table 3 ).
Assimilative Capacity
The expressed BTEX assimilative capacity of the site ground water was 18,690
(ig/L (Table 5) based on stoichiometry and site geochemical data. Since the highest

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dissolved BTEX concentration at the site was 7300 ug/L the ground water has sufficient
capacity to degrade dissolved BTEX that partitions from the soil oily residual into ground
water before the plume moves beyond 250 meters downgradient from the source. The
remainder assimilative capacity could be consumed by other gasoline components such as
aliphatic hydrocarbons.
Microbial Breakdown Components
A ground-water sample was collected at Point A (Figure 1) for analysis of phenols
and aliphatic/aromatic acids. The technique involved liquid-liquid extraction,
derivatization, and gas chromatography/mass spectrometry analysis. Major components
detected were branched heptanoic and octanoic acids, trimethylbenzonic acids,
dimethylbenzonic acids, and some lower molecular weight acids such as propinoic and
butyric. The presence of these fatty acid components in the BTEX plume is further
evidence that viable microbial biodegradation processes are functional at the site.
Rate Constant
A first order biological decay rate was calculated using methane as a surrogate
tracer. We assumed that once methane is produced from the fuel biodegradation was
stable and therefore can be used as a tracer. Table 2 lists methane corrected BTEX and
the amount lost between the A,B, and C. points. The biodegradation line slope between
points A and C approximates a first order process. The average decay rate using retarded
solute transport velocity for total BTEX was 0.014 week"1. This was within the range
reported by Wilson et al. (1994).
Conclusion
Three lines of evidence to identify intrinsic bioremediation at the site were loss of
contaminants at field scale, geochemical data, and the presence of intermediate microbial
BTEX breakdown products. Contaminant loss showed that natural attenuation was
occurring. Ground water chemistry determined the relative importance of each operating
natural attenuation mechanism. The presence of volatile organic acids showed that
microbial biodegradation processes were viable. Aerobic respiration and methanogenesis
accounted for the greatest mass of BTEX mineralized.
Disclaimer
The research described has not been subjected to the U.S. Environmental..
Protection Agency's review process. Therefore, an official endorsement should not be
inferred.

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References
1.	Wiedemeier, T.H., D.C. Downey, J.T. Wilson, D.H. Kampbell, R.N, Miller, and
J.E, Hansen. 1994. Technical Protocol for Implementing Intrinsic Remediation with
Long-Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in
Groundwater (draft). Air Force Center for Environmental Excellence, Brooks Air Force
Base, Texas.
2.	Wilson, B.H., J.T. Wilson, D.H. Kampbell, and B.E. Bledsoe. 1994. "Traverse
City: Geochemistry and Intrinsic Bioremediation of BTX Compounds." In Proceedings
of the Symposium on Intrinsic Bioremediation of Ground Water, August 30 - September
1,1994. U.S. Environmental Protection Agency, pp 94-102.

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Table 1. Benzene Biodeeradation Reactions
Aerobic respiration
7.502 + QH* = 6C02 + 3H20
Denitrification
6NO"3 + 6H+ + C6H6 = 6C02 + 6H20 + 3N2
Iron reduction
60H+ + 30Fe(0H)3 + C6H< = 6C02 + 30Fe2+ + 78H20
Sulfate reduction
7.5H+ + 3.75SO,2- + QH* = 6C02 + 3.75H2S + 3HzO
Methanogenesis
4.5H20 + CA = 2.25C02 + 3.75CH4
Table 2. BTEX Mass Lost to Biodeeradation, mg/L
Compound
Point A
Point B
Point C
Benzene
724
960
1
Toluene
737
17
2
Ethylbenzene
823
12
1
Xylenes
*5020
120
15
Trimethylbenzene
750
28
3
Total BTEX + TMB
8054
1137
23
Measured methane
14000
8800
2140
Methane produced
from BTEX & TMB
6282
887
18

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Table 3. Percent Loss Using Methane-Corrected Levels
Compound
Point B
Corrected
mg/L
Biodegradation
A to B
%
Point C
Corrected
mg/L
Biodegradation
B to C
%
Benzene
2008
0
4
100
Toluene
35
95
9
46
Ethylbenzene
24
97;
9
22
Xylenes
251
95
67
43
Total BTEX
&TMB
2400
70
103
91
Table 4. Percent Loss Using TMB - Corrected Concentrations
Compound
" "Point B
Corrected
mg/L
Biodegradation
A to B
%
Point C
Corrected
mg/L
Biodegradation
B to C
%
Benzene
25710
0
9
99
Toluene
455
38 '
19
0
"Ethylbenzene
321
61
19
0
Xylenes
3214
36
139
0
Trimethylbenzene
750
0
28
0
Table 5. Assimilative Capacity of Site Ground Water
Aerobic Respiration
1200 ug/1
Ferric Hydioxide Reduction
90
Methanogenesis
17400
Total
18690
Highest total BTEX
7300

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Figure 1: Total BTEX in Groundwater
Patrick AFB, Florida
Groundwater
Flow Direction
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Figure 2: Dissolved Oxygen in Groundwater
Patrick AFB, Florida
Groundwater
Flow Direction
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03
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Figure 3: Ferrous Iron in Groundwater
Patrick AFB, Florida
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4jQ_
Groundwater
Flow Direction
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Figure 4: Methane in Groundwater
Patrick AFB, Florida
Groundwater
Flow Direction
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2.14
14.95
J4
3.49
• 7M
416
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before compietinf
1. REPORT NO. 2.
EP A/600/A-95/141
3. RE
4. title and subtitle
INTRINSIC BIOREMEDIATION OF FUEL CONTAMINATION
IN GROUND WATER AT A FIELD SITE
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHORISI
1DON H. KAMPBELL, "T.H. WIEDEMEIER, & 3J.E. HANSEN
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME ANO ADDRESS
1U.S, EPA, RSKERL, P.O. Box 1198, Ada, OK 74820
2Parsons Engineering Science, Inc., Denver, CO 80290
3U.S.A.F. Center for Environ Excellence, Brooks AFB, TX 78235
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
In-House RPDK2
12. SPONSORING AGENCY NAME AND ADDRESS
Robert S. Kerr Environmental Research Lab. - Ada, OK
U.S. EPA
P.O. Box 1198
r\v TAann
13. TYPE OF REPORT ANO PERIOD COVERED
14, SPONSORING AGENCY CODE
EPA/600/15
is." £uPpleme'nta"ry notes
Poster presentation at the symposium on Bioremediation of Hazardous Wastes: Research, Development, and Field
Fvaluatinn?;* Annus! R-10 IQQ1! R\/a Prnn|< fslY Pfnroorjjpqc pi |f-i|ichorl
A spill of gasoline occurred at an automobile service station in 1986. Oily phase
residue in the subsurface has continued for the past eight years to release water soluble
fuel hydrocarbons into the aquifer. The site was characterized for implementation of
intrinsic remediation. The subsurface was a beach sand with sea shell fragments. The
water table was near 1.3 meters below ground surface. Surface dimensions over the
plume were about 200 meters downgradient and 60 meters in width. Three points to
coincide with direction of ground-water flow were selected in the plume for water quality
assessments. Both methane and trimetbylbenzene were used as surrogate tracers to
normalize loss of .contaminants. Aerobic respiration and methanogenesis .accounted for
most biodegradation obtained. Assimilation capacities of dissolved oxygen, ferrous iron,
and methane distributions when compared to BTEX concentrations showed that the
ground water has sufficient capacity to degrade all dissolved BTEX before the plume
moves beyond 250 meters downgradient. Evidence obtained from loss of contaminants,
geochemistry, and microbial breakdown chemicals showed that intrinsic bioremediation
technology would be a viable option to restore the site.
17' key WORDS ANO DOCUMENT ANALYSIS
2' DESCRIPTORS b,IO£NTif IERS/OPEN ENOED TEAMS
COSATI field,Group



18. DISTRIBUTION STATEMENT
RELEASE TO THE PUBLIC
19 stcuR,Tufe»r';
?i NO Of "AGES
9
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UNCLASSIFIED
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^ * Form 2220-1 (R*v. 4-77} p«Evious fdition is ossoietc

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