EPA/600/A-93/178
COMPARISON OF BIOVENTING AND AIR SPARGING
FOR IN SITU BIOREMEDIATION OF FUELS
Don H. Kampbell
U.S. Environmental Protection Agency
Ada, OK
and
Christopher J. Griffin
Solar Universal Technology, Inc.
Traverse City, MI
and
Frank A. Blaha
U.S. Coast Guard
Cleveland, OH
Bioremediation pilot-scale subsurface venting and sparging systems were operated at a low
aeration rate at an aviation gasoline spill site. Bioventing removed 99 percent of vadose zone
contamination in 8 months with minimal surface emissions. The biosparging process is presently
operating and has removed one-third of oily phase residue below the water table in 1 year. The
ground water plume has been cleansed of benzene, toluene, ethylbenzene, and xylene (BTEX)
components by sparging. . ,
INTRODUCTION
The failure in 1969 of a buried transfer pipe flange within an underground storage area of
a U.S. Coast Guard Air Station resulted in an aviation gasoline (Avgas) spill of about 35,000 gallons.
The Avgas migrated downward and laterally to form a plume below a surface area of 260 ft wide
and 1,200 ft long. The subsurface to 45 ft was a fairly uniform beach sand with the present water
table near 15 ft. Water table fluctuations over the years, as much as 5 ft, formed an oily phase smear
of Avgas contamination with about 30 percent in the vadose zone, just above the present water table.
Venting and sparging can be in situ bioremediation processes that provide air flow to
vaporize and transport volatile organic pollutants upward to more amenable media for
mineralization. Microbial degradation processes also utilize the oxygen provided by the air. Injection
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before comp
1. REPORT NO.
EPA/600/A-93/178
2,
4. TITLE AND SUBTITLE
COMPARISON OF BIOVENTING AND AIR SPARGING
FOR IN SITU BIOREMEDIATION OF FUELS_
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7, AUTHOR
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wells can be installed at spill sites to emit air just above the water table for venting and below the
water table for sparging. Laboratory soil microcosm studies using surface soil from the site showed
that once acclimation occurred the degradation of Avgas vapor was rapid and complete (1).
The objective of the study was to demonstrate by pilot-scale process units that venting and
sparging can effectively bioremediate an aviation gasoline contaminated subsurface. Since this report
has not been subjected to EPA review, however, official endorsement should not be inferred.
EXPERIMENTAL DESIGN
Turf was established on a 75 by 45 ft rectangular area overlying the plume of contamination.
An initial nutrient solution of 64 Ib nitrogen, 5 Ib potassium, and 13 Ib phosphorus was applied for
dispersion throughout the unsaturated subsurface. Aeration injection wells screened across the water
table were placed 10 ft apart in a 3 by 5 grid. A blower rate of 5 cfm was used, which was estimated
to be equivalent to a subsurface air retention time of 24 hours.
Vadose zone soil gas samples were obtained with 1/2-inch diameter stainless steel tubing
clusters set at depths of 3.2, 6.5, 9.7, and 13.0 ft. A portable Bacharach TLV combustible gas meter
was used to measure subsurface Avgas vapors. An inverted stainless bowl with a nipple outlet at the
top was used as a collection device for surface emissions. Vented air was removed from the bowl
canopy at the same rate of entrance as determined by a propane dilution test and passed through
a cartridge trap. The trapped hydrocarbons were analyzed by gas chromatography.
Vertical profile core samples were obtained using a drilling rig with hollow stem augers and
a piston barrel sampler. Core samples were placed in glass jars and capped immediately. Within 15
minutes, jars were uncapped one at a time, and a plug aliquot was removed and preserved for later
analysis of total petroleum hydrocarbons. Avgas vapors in the plug-evacuated space were quickly
measured using a real-time core assay method (2). Ground water samples were collected from
installed monitoring wells and analyzed by EPA standard methods.
One year after installation of the venting process, the apparatus was revised into a sparging
process. Eight 2-in. diameter polyvinyl chloride (PVC) sparge wells were installed to a depth of 10
ft below the water table in a 2 by 4 grid 10 ft apart. A minimum radius of influence of 15 ft was
determined by pressure changes at distances away from a sparge well (3). A blower rate of 10 cfm
was used.
RESULTS
Venting operations started during October 1990. Gasoline hydrocarbon vapor in the vadose
zone initially increased to near 5,000 mg/L, then within 3 weeks decreased 80 percent (Figure 1). A
gradual decline continued until the operation was shut down in January 1991 because the turf root
zone was frozen. Venting was restored, 3 months later, after the soil had thawed. Vapor
concentrations increased to near 1,000 mg/L then decreased rapidly. After 8 months of operation,
soil gas concentrations were 50 mg/L or less. Surface emissions during mid-term operation of the
venting system were less than 10 ^tg/L, compared to 3.2 ft depth soil gas levels of 163 mg/L. Biomass
degradation activity from the turf rhizosphere was greater by a factor of 10 than at the same depth
of a barren soil control that was not acclimated to gasoline vapor.
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Vertical profile fuel carbons for October 1990 and October 1991 are shown in Figure 2. The
water table was at the same level of 15.3 ft for both time periods. A reduction of oily phase residue
in the vadose zone occurred in excess of 99 percent, while reduction below the water table was only
about 22 percent.
Sparge wells were installed and operation started in November 1991. Initial gasoline vapor
concentrations exceeded 6,000 mg/L in the vadose zone (Figure 1), then after 5 months sparging
were near 1,000 mg/L. After 1 year, the levels were 50 mg/L or less. Ground water monitoring well
samples were collected and analyzed after 7 months of sparge operation (Table 1), Sparging
effectively reduced contaminants dissolved in the ground water. Vertical profile core samples were
collected and analyzed October 1991 and September 1992. Heterogeneity obtained from vertical
profile sampling was partially compensated by averaging replicates to obtain a trend shift in Avgas
contamination. Real-time core assays are shown in Table 2. Assay levels of control profiles had a
4 percent reduction during the 12-month period, while sparging reduction was 80 percent. Oily phase
residue as total fuel carbon was reduced 39 percent by sparging during the 12-month period (Table
3). The data suggested that inaccessibility of gasoline globule contact with air flow had restricted
vaporization and transport upward.
CONCLUSION
The vadose zone contaminated with aviation gasoline was satisfactorily bioremediated by
venting in 8 months. Surface emissions of gasoline vapor during process operation were minimal.
Sparging of the ground water plume at a low aeration rate has reduced oily phase residue by at least
one-third in a 12-month period. The sparging system has been operational for 17 months and will
continue.
REFERENCES
1. Kampbell, D.H., and J.T. Wilson. 1991. Bioventing to treat fuel spills from underground
storage tanks. J. Haz. Materials 28:75-80.
2. Kampbell, D.H., and M.L. Cook. 1992. Core assay method for fuel contamination during
drilling operations. Proceedings of Subsurface Restoration Conference, Dallas, TX, pp. 139.
3. Griffin, C J., J,M. Armstrong, and R.H. Douglass. 1991. Engineering design aspects of an in-
situ soil vapor remediation sparging system. Proceedings of 1991 International Conference
on On-Site and In-Situ Bioremediation, San Diego, CA, pp. 517.
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Startup R*ct*rt«p
Start wp
Tms 0yfania sh» 10/1/90)
Raptleata
Location
CL-2N
CL-3N
Figure 1. Soil gas hydrocarbons at 4-m depth for injection-only plot.
600
598-
o
GW Table
1000 2000 3000
Fuel Ctrboo, cog/Kg Core Material
4000
Figure 2. Vertical profile oily phase residue in bioventing of north plot.
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Table 1. Ground Water Quality after Seven Months of Biosparging
Monitoring
Well
Control
Sparge Plot
Well Depth
-ft-
16
17.5
20.5
22
15
18
19.5
21
Benzene
Xylenes
Total Fuel
Carbon
• HS/L
9.9
228
70
57
1.9
>1
>1
>1
19
992
38
7.7
5.3
5.0
>1
>1
2880
4490
956
783
559
>6
>6
>6
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Table 2, Core Assay of Avgas Vapor during Drilling Operations
Control
Sparge plot
Initial
One Year Later
Replicate Average over 40 in. profile,
rag Avgas/ft
4070 (3 reps)
5980 (3 reps)
3920 (2 reps)
1220 (4 reps)
Reduction
%
80
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Table 3. Total Fuel Carbon in Vertical Profile
Sparge plot
Initial
One Year Later
Replicate average, rag/ft2 surface area
139,540 (4 reps)
85,230 (5 reps)
Reduction
%
39
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