United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada, OK 74820
Research and Development
EPA/600/S2-91/009 April 1991
Project Summary
Nitrate for Bioresto ration of an
Aquifer Contaminated with Jet
Fuel
S.R. Hutchins, W.C. Downs, G.B. Smith, J.T. Wilson, D.J. Hendrix, D.D. Fine,
D.A. Kovacs, R.H. Douglass, and F.A. Blaha
There is little information available In
the open literature on the performance
of bioremediation at field scale. This
report documents the rate and extent
of treatment of a spill of JP-4 In a drink-
ing-water aquifer, using nitrate as the
primary electron acceptor for microbial
respiration of the contaminant hydro-
carbons. Nitrate has theoretical advan-
tages over the more traditional elec-
tron acceptors used in the United
States. It is much more soluble than
oxygen, and less costly and less toxic
than hydrogen peroxide. Ground wa-
ter amended with nitrate and mineral
nutrients was recirculated through a 10
m by 10 m study area. After 165 days
the individual concentrations of ben-
zene, toluene, ethylbenzene, and xy-
lenes were below 5 u,m/l in monitoring
wells under the study area. The con-
centration of benzene was below 0.1
jig/l. Some of the removal of
alkylbenzenes may have been due to
low concentrations of oxygen (0.5 mg/
I) in the recirculation water.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, to an-
nounce key findings of the research
project that Is fully documented In a
separate report of the same title (see
Project Report ordering Information at
back).
Background
A field demonstration project on nitrate-
mediated bio restoration of a fuel-contami-
nated aquifer was conducted at a U.S.
Coast Guard facility in Traverse City, Ml.
Several leaks from an underground stor-
age facility containing JP-4 jet fuel have
resulted in contamination of ground water
at the site. The focus of the field demon-
stration project is a 10 m x 10 m infiltra-
tion area located within the larger area
contaminated by the JP-4 spill. An infiltra-
tion gallery was installed above the study
area; it is part of a closed-loop system
designed to perfuse the study area with
ground water supplemented with nitrate
and nutrients. The 10 m x 10 m section
of the site was instrumented with monitor-
ing wells and piezometers. A series of
recirculation wells was installed down gra-
dient to intercept contaminants, nutrients,
and nitrate and provide hydraulic
recirculation back through the infiltration
gallery. In addition, four purge wells are in
place to provide a net discharge from the
site and prevent escape of nitrate or con-
taminants to regional flow in the aquifer.
The design of the system was facili-
tated by hydraulic modeling to evaluate
the infiltration rate necessary to raise the
piezometric surface above the contami-
nated zone, the withdrawal rates neces-
sary to retain the contaminants and nutri-
ents on-site, and the nutrient contact time
important to biological treatment. A tracer
study was conducted to confirm estimated
breakthrough times and give a preliminary
evaluation of the performance of the in-
situ bioreactor.
The effects of recirculation, purging to
waste, and biodegradation on the decrease
in solution concentration of BTEX com-
pounds within the treatment zone were
examined. The aquifer was cored and ana-
lyzed for total petroleum hydrocarbons and
Printed on Recycled Paper
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for the quantity of selected fuel hydrocar-
bons. Water was recirculated through the
system for 41 days to bring the system to
hydraulic and chemical equilibrium. Then
nitrate and mineral nutrients were added
for an additional 160 days. Ecological
processes supported on the ambient con-
centrations of oxygen and nitrate removed
benzene from the fuel spill and the
recirculated water before nitrate was
added. Benzene concentrations were be-
low 0.1 u.g/1. After addition of nitrate,
toluene was rapidly removed in the fuel
spill. Ethylbenzene and m+p-xylene were
also removed during denitrification; how-
ever, there was little evidence for biodeg-
radation of o-xylene until the end of the
demonstration. As expected, minor
amounts of the alkane fraction were re-
moved.
Conclusions
The technology produced excellent re-
sults. Concentrations of BTEX in monitor-
ing wells were below the appropriate State
of Michigan and Federal Drinking Water
Standards within 165 days. Unit costs for
remediation were calculated by dividing
the cost of construction, labor, chemicals
and electrical service by (1) the volume of
JP-4 beneath the infiltration gallery, (2)
the volume of aquifer material contami-
nated with JP-4 under the infiltration gal-
lery, and (3) the volume of aquifer be-
tween the infiltration gallery and the con-
fining unit beneath the aquifer. The unit
costs for the remediation were $22 per
liter JP-4, $200 per m3 of aquifer material
contaminated with JP-4, and $17 per m3
of aquifer material down to the confining
layer.
Computer simulation was very useful in
determining reasonable injection and with-
drawal rates of water before construction
of the gallery. It allowed a prediction of
the areal extent of the hydraulically af-
fected zones and an estimate of the verti-
cal mounding of the water surface at the
injection gallery and drawdown at the with-
drawal wells. This information was also
required to size pumping and piping ap-
paratus, to estimate electrical power re-
quirements, to size mixing tanks, and to
estimate bulk chemical purchases.
Proper hydraulic control of an infiltration
gallery to maintain saturated conditions
throughout the contaminated zone is ab-
solutely necessary.
In this study, the calculated effect of
dilution using partitioning theory on the
equilibrium solution concentration of BTEX
compounds does not explain their contin-
ued disappearance. Including the effect of
steady purging of a certain percentage of
the recirculated water better explains the
trends in the observed data, but does not
explain the sharp drops seen in the solu-
tion concentrations of benzene, toluene,
and m-xylene. After taking these physical
processes into account, biological pro-
cesses provide a reasonable explanation
for benzene, toluene, and m+p-xylene re-
moval. The decrease in solution concen-
trations of o-xylene was observed to fol-
low that predicted by dilution and wasting,
indicating that it may be less sensitive to
degradation processes. Concentrations
decreased significantly in the monitoring
wells only towards the end of the demon-
stration when the other compounds were
depleted.
The laboratory work has shown that
aromatic hydrocarbons, with the possible
exception of benzene, can be degraded
under strictly anaerobic conditions by na-
tive subsurface bacteria using nitrate as
the terminal electron acceptor. Toluene is
most easily degraded with the xylenes
being more recalcitrant. The project has
demonstrated, through extensive core
analyses, that simple hydraulic flooding
will remove a significant amount of the
lower molecular weight aromatic hydro-
carbons in far greater proportion than the
residual fuel hydrocarbons.
Addition of nitrate and nutrients results
in denitrification occurring within the con-
taminated zone, as shown by decreases
in nitrate concentrations through the infil-
tration gallery along with transient nitrite
production. Core analyses revealed that
BTEX was removed to very low concen-
trations after two months of nitrate addi-
tion. There was a general decrease in all
constituents of the jet fuel, although de-
tectable concentrations of the higher mo-
lecular weight alkylbenzenes still re-
main.
It was impossible to determine the ex-
tent to which a particular BTEX compound
was removed through denitrification. Aero-
bic bbdegradation was feasible in the sys-
tem. Over the course of the demonstra-
tion, 7.4 kilomoles of electrons were ac-
cepted by oxygen, and 178 kilomoles of
electrons were accepted by nitrate.
The actual amount of nitrate consumed
was ten times greater than the theoretical
nitrate demand for oxidation of the BTEX
compounds alone.
.S. GOVERNMENT PRINTING OFFICE: l»*l - S4H-028/40093
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S.R. Hutchlns, W.C. Downs, G.B. Smith, andJ.T. Wilson (also the EPA Project
Officer, see below) are with the Robert S. Kerr Environmental Research Labora-
tory, Ada, OK 74820. D.J. Hendrix is with Solar Universal Technologies, Inc.,
Traverse City, Ml 49684; D.D. Fine and D.A. Kovacs are with NSI Technology
Services Corporation, Ada, OK 74820; R.H. Douglass is with The Traverse
Group, Traverse City, Ml 49684 and F. A. Blaha is with the U.S. Coast Guard,
Cleveland, OH 44199.
The complete report, entitled "Nitrate for Biorestoration of an Aquifer Contaminated
with Jet Fuel," (Order No. PB91-164 285/AS; Cost: $ 17.00, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
Ada, OK 74820
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-91/009
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