The Environmental
Consequences of a
Release of Ethanol to
Ground Water
John T. Wilson and Cherri Adair
National Tanks Conference
March 7, 2007
San Antonio, Texas
How much ethanol should we expect from
a gasohol spill?
It should be directly related to the amount
of gasoline that was spilled, and the
ethanol content of the gasoline.
Assume aquifer solids are quartz, with a density
of 2.64 kg/cubic decimeter (a cubic decimeter is
the volume of a substance contained in a liter).
Assume aquifer porosity of 25%; then each cubic
decimeter has 2.0 kg of sediment in contact with
0.25 liter of water.
Assume gasoline is measured at a
residual saturation of 4,000 mg/kg TPH;
this is equivalent to 8,000 mg/cubic
decimeter of aquifer sediment.
Density of gasoline is near 740,000
mg/cubic decimeter; 8,000 mg/cubic
decimeter is equivalent to 0.011 of the
total volume or 4.3% of the total porosity.
There is 0.239 liters of water and 0.011
liters of gasoline in each cubic decimeter
of aquifer material.
Assume gasoline measured at a residual
saturation of 4,000 mg/kg TPH; equivalent to
8,000 mg/cubic decimeter of aquifer sediment.
Assume the gasoline is 15% ethanol (mass basis);
there is 1200 mg of ethanol in contact with 0.239
liters of ground water. The “expected” ethanol
content would be approximately 5,000 mg/liter.
However, mass transfer limitations will make the
actual concentrations in the aquifer lower.
How long will it take for 5,000 mg/liter
ethanol to biologically degrade?
Sources of Data on Rates of Degradation
of Ethanol
Pilot or Field Scale Estimates
Results of a Natural Attenuation Field Experiment for an
Ethanol-Blended Gasoline Spill. Corseuil, H.X., M. Fernandes,
M. do Rosario, and P.N. Seabra. (2000) Proceedings of
NGWA/API Conference and Exposition on Petroleum and
Organic Chemicals in Ground Water: Prevention, Detection and
Remediation. Anaheim, California, November 15-17, 2000,
pages 24-31.
Field Evaluation of the Solvent Extraction Residual Treatment
(SERB) Technology. S.C. Mravik, G.W. Sewell, R.K. Sillan, and
A.L. Wood. 2003. Environmental Science & Technology 37(21):
5040-5049.
Impact of Ethanol on the Natural Attenuation of Benzene,
Toluene, and o-Xylene in a Normally Sulfate-Reducing Aquifer.
2006. D.M. Mackay, N.R. de Sieyes, M.D. Einarson, K.P. Feris,
A.A. Pappas, I.A. Wood, L. Jacobson, L.G. Justice, M.N. Noske,
K.M. Scow, and J.T. Wilson. 2006. Environmental Science &
Technology in press.
Pilot or Field Scale Estimates
Transport and Degradation of Ethanol in Groundwater. Zhang,
Yi, I. A. Khan, X-H Chen, and R. F. Spalding. Journal of
Contaminant Hydrology 82(2006), 183-194.
Behavior of Gasoline Pools Following a Denatured Ethanol
Spill. McDowell, C. J., T. Buscheck, and S. E. Powers. Ground
Water 41(6), 746-757 (2003).
The Fate of Oxygenates and BTEX from Gasolines containing
MTBE, TBA, and Ethanol: Is Ethanol more Persistent than
MTBE? Mocanu, M., J. L. Zoby, J. Barker, and J. Molson.
Keynote Presentation: NGWA Petroleum Hydrocarbons and
Organic Chemicals in Ground Water: Prevention, Assessment,
and Remediation Conference. November 6-7, 2006. Houston,
Texas.
Rates in long term field studies
Corseuil et al. (2000)
0.42 per year starting with a release of gasohol,
producing 2,500 mg/L,
or 2.9 mg/L/day
Mravik et al. (2003)
0.33 per year starting at 12,000 mg/L,
or 10.8 mg/L/day
Mackay et al. (2006)
500 mg/L never detected at first down gradient well
>500 mg/L/day
Rates in long term field studies
McDowell et al. (2003)
18,000 mg/L to not detected in no more than 26 months,
or 22 mg/L/day
Zhang et al. (2006)
0.32 per day starting at 220 mg/L,
or 70 mg/L/day
Mocanu et al. (2006)
15,700 mg/L to 5,030 mg/L in 230 days
1,390 mg/L to 560 mg/L in 230 days
or 46 and 3.6 mg/L/day
Laboratory Studies
The Influence of the Gasoline Oxygenate Ethanol on Aerobic
and Anaerobic BTX Biodegradation. 1998. Corseuil, H. X, C.
S. Hunt, R.C. F. Dos Santos, and P. J. J. Alvarez. Water
Research, 32(7): 2065-2072.
Anaerobic biodegradation of known and potential gasoline
oxygenates in the terrestrial subsurface. Suflita, J. and
Mormile, M. 1993. Environmental Science & Technology
27(5):976-78.
Rates of Ethanol Degradation in Aquifer Sediment
Reference
Type of Study
Geochemistry
Rate
(mg/L/day)
Suflita & Mormile
1993
Laboratory
Methanogenic
34
Conseuil et al.
1998
Laboratory
Nitrate Reducing
50
Conseuil et al.
1998
Laboratory
Iron Reducing
12.5
Conseuil et al.
1998
Laboratory
Sulfate Reducing
10
EPA Kerr Center Project
Use microcosms to determine the rate and
extent of biodegradation of ethanol and BTEX
compounds in sediment samples from six sites
where gasoline spills have resulted in
methanogenic conditions in ground water.
Source Locations
• BP Amoco Service Stations
4243 Boca Raton, FL
4320 Parsippany, NJ
5106 Deer Park, NY
2150 Petaluma, CA
• Port Hueneme, CA, Naval Construction
Battalion Center
• Vandenburg AFB Lompoc, CA
Ethanol Data
• Compare ethanol concentrations for
living vs. autoclaved control
microcosms from six sample locations.
• Initial concentrations of ethanol
approximately 2,000 mg/liter.
Rates of Ethanol Degradation in Aquifer Sediment at
Gasoline Spill Sites
Cherri Adair, Unpublished
Location
Geochemistry
Rate (mg/L/day)
Boca Raton, FL
Methanogenic
2.6
Parsippany, NJ
Methanogenic
36
Petaluma, CA
Methanogenic
70
Port Hueneme, CA
Methanogenic
22
Vandenberg AFB, CA
Methanogenic
90
Time required to degrade 5000 mg/L ethanol
(days)
10000
Laboatory data
Field Rates
1000
100
10
1
1
10
100
Rate of Ethanol Degradation (mg/L/day)
1000
For most plumes, the ethanol is gone in a
year or two.
What do we know about the impact of
ethanol in gasoline on the length of
benzene plumes at UST sites?
Geochemistry of Ethanol Biodegradation
Ethanol Degradation by Sulfate Reduction
CH3CH2OH + 1.5 SO4-2 → 2 CO2 + 3 H2O + 1.5 S-2
144 mg/liter sulfate consumes 46 mg/liter ethanol
Handex
NY
PA
IN
NJ
OH
FL
MD
DC
FL
BP Amoco Retail Site Locations in
the MTBE NA Study
Sulfate supply in gasoline spills
800
Sulfate (mg/liter)
700
600
Sulfate in Background
Sulfate in Plume
500
400
300
200
100
0
Rank by sulfate supply
100
90
Percent of Sites
80
Ethanol Assimilative Capacity
based on Ambient
Concentrations of Sulfate
70
60
50
40
30
20
10
0
0
100
200
300
Ethanol Assimilative Capacity (mg/l)
400
Ethanol Fermentation to
Methane
CH3CH2OH + H2O → CH3COOH + 2 H2
CH3COOH → CO2 +
CH4
46 mg/L ethanol produces 16 mg/L methane
What Should We Expect?
Most sites will be depleted of sulfate.
Methane will be the dominant degradation
product for ethanol at many sites.
Transect in
next slide
No Ethanol
Lane
Ethanol
Lane
?
200
Methane
180
Methane expected from Ethanol
160
Sulfate
140
Acetate
mg/L
120
100
80
60
40
20
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21
Ethanol Added
Monitoring well in EA transect
What Should We Expect?
•Ethanol degradation will be rapid in the
context of ground water flow.
Sulfate, Nitrate, and Oxygen will be
exhausted.
•Methane will be the dominant degradation
product for ethanol at many sites.
What Should We Expect?
•Methane concentrations will exceed their
solubility in water, methane will escape to
the vadose zone and may present an
explosion hazard.
•Benzene plumes may be longer when
ethanol is in the ground water. At many
spills, the increased plume length may be
acceptable from the point of view of risk
management.