United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
*
Research and Development
EPA/600/S2-87/096 Jan. 1 988
v°/EPA Project Summary
A Field Evaluation of In-Situ
Biodegradation for Aquifer
Restoration
Lewis Semprini, Paul V. Roberts, Gary D. Hopkins, and Douglas M. Mackay
The in-situ remediation of aquifers
contaminated with halogenated ali-
phatic compounds, commonly known
in water supply as chlorinated solvents,
is a promising alternative in efforts to
protect ground water.
The full report presents the experi-
mental methodology and the initial
results of a field experiment evaluating
the feasibility of in-situ biotransforma-
tion of trichloroethylene (TCE) and
related compounds. The method being
tested relies on the ability of methane-
oxidizing bacteria to degrade these
contaminants to stable, non-toxic, end
products.
The field site is located at the Moffett
Naval Air Station, Mountain View, CA.
The test zone is a shallow, confined
aquifer composed of coarse grained
alluvial sediments.
This Project Summary was devel-
oped by EPA's Robert S. Kerr Envir-
onmental Research Laboratory, Ada,
OK. to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
The in-situ remediation of aquifers
contaminated with halogenated aliphatic
contaminants, commonly known in
water supply as chlorinated solvents, is
a promising alternative in efforts to
protect ground water quality.
This project aims to assess under field
conditions the capacity of native microor-
ganisms, i.e., bacteria indigenous to the
subsurface environment, to metabolize
halogenated synthetic organic contam-
inants, when proper conditions are
provided to enhance microbial growth.
Specifically, the growth of
methanotrophic bacteria is being stim-
ulated in a field situation by providing
ample supplies of dissolved methane and
oxygen. Under biostimulation conditions,
the transformation of representative
halogenated organic contaminants, such
as trichloroethylene (TCE), is assessed by
means of controlled addition, frequent
sampling, quantitative analysis, and
mass balance comparisons.
The field demonstration study is being
conducted at Moffett Naval Air Station,
Mountain View, CA, with the support of
the Robert S. Kerr Environmental
Research laboratory of the U.S. Environ-
mental Protection Agency (EPA), and
with the cooperation of the U.S. Navy.
To provide guidance for and confirmation
of the field work, laboratory experiments
and analyses are also being conducted,
both at Stanford University's Water
Quality Control Research Laboratory and
at the Kerr Laboratory.
The full report summarizes the exper-
imental approach taken in the field study
and the characterization of the test zone
before the initiation of the evaluation
experiments. The results of the first
phase of the field evaluation are
presented.
Research Objectives
The overall objective of this work is to
assess the efficacy of a proposed method
for enhancing the in-situ degradation of
the halogenated aliphatic compounds.
The specific objectives of the field study
are:
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1. To demonstrate whether the pro-
posed method of promoting the
enzymatic decomposition of TCE
and related compounds is effective
under controlled experiments per-
formed in-situ, in an aquifer
representing conditions typical of
ground water environments;
2. To quantify the rate of decompo-
sition and to identify intermediate
transformation products, if any;
and
3. To bracket the range of conditions
under which the method is effec-
tive, and to establish criteria for
dependable treatment of a real
contamination incident.
Field Experiment Methodology
The basic approach of the evaluation
experiments is to create a test zone in
the subsurface. An array of injection,
extraction, and monitoring wells is
installed within a confined aquifer. An
induced flow field is created by the
injection and extraction of fluid. The
chemicals of interest for a specific
experiment are metered into a stream
comprising 10 to 15 percent of the
extracted ground water and then rein-
jected. The concentrations of the specific
chemicals are monitored at several
locations, including the injected fluid, the
three monitoring wells, and the extracted
fluid. The spatial and temporal response
of the chemicals in the test zone is
determined by frequent monitoring,
using an automated data acquisition and
control system located at the site.
The sequence of field experiments
using this approach is outlined in Table
1. The initial experiments study the
transport of bromide ion as a conserva-
tive tracer. The experiments determine
fluid residence times in the system, the
degree of dispersion, and the recovery
of the injected fluid at the extraction well.
In later experiments, bromide, dissolved
oxygen and the chlorinated aliphatic
compounds of interest are injected
simultaneously. The retardation factors
of the different chemicals with respect
to bromide, owing to sorption, are
determined. The transformation of the
chlorinated aliphatic compounds in these
experiments is evaluated based on
comparisons with the bromide tracer.
Two criteria are used; (1) the degree of
steady-state fractional breakthrough
achieved at the monitoring wells, and (2)
mass balances on the amounts injected
Table 1. Sequence of Experiments and Processes Studied During the First Phase of th
Field Evaluation
Injected Chemicals
Process Studied
(21 Br~+ O2
(3) Br'+TCE + O2
(5)
02+(nutrients)
Oi+( nutrients)* TCE
A dvection/Dispersion
Retardation/Dispersio
fTCA - Elution)
Retardation
(Transformation)
Biostimulation
Biotransformation
and extracted. These tracer experiments
therefore, serve as pseudo-controls,
permitting a comparison of the observed
responses before and after the test zone
is biostimulated.
The biostimulation experiments
involve adding methane, oxygen, and
nutrients (if required), to stimulate the
growth of methane-consuming bacteria
in the test zone. The transient response
of the different chemical components is
monitored, as previously discussed. This
experiment determines: (1) how easily
the methane-oxidizing bacteria are
stimulated and whether nutrients are
required, (2) stoichiometric requirements
of oxygen to methane, (3) information on
the kinetics and the rate of growth, and
(4) the areal extent over which biostim-
ulation is achieved.
The degree of biotransformation of the
chlorinated aliphatic compound (TCE) is
evaluated in the final stage (Stage 5) of
the program. Known quantities of TCE
are introduced into the biostimulated
zone along with methane, oxygen and
bromide. The extent of transformation of
TCE is determined based on both mass
balances and steady-state breakthrough
concentrations at monitoring points,
compared to those of bromide as a
conservative tracer. The results are also
compared with those obtained during the
earlier transport and retardation exper-
iments (Stage 3) before the test zone was
biostimulated.
Field Site Description
After a reconnaissance study of sev-
eral sites, a location at the Moffett Naval
Air Station, Mountain View, CA, was
chosen. The experimental site is located
in a region where the ground water is
contaminated with several organic
solutes for which this biorestoration
method might be applied. Thus, if effec-
tive, the treatment method may have
direct use in the area where it was
evaluated.
Well logs indicate the aquifer i
approximately 1.2 meters thick with a to
4.4 to 4.6 meters below the groum
surface; the bottom ranges from 5.3 t
5.7 meters below the surface. Thi
aquifer is confined between silty cla
layers. The aquifer consists of fine- t
coarse-grained sand and appears wel
bedded in most cores. Gravel lenses witl
pebbles up to 2.5 cm in diameter occu
in some cores within the sand layers.
Pump test results indicate an esti
mated hydraulic conductivity of 100 m/i
(based on an aquifer thickness of 1.'
meters). The hydraulic conductivity is i
the range of values typical for coars
sand(20-100 m/d), gravel (100-1000 m,
d) and sand-gravel mixes (20-100 m/d
and is consistent with the particle siz
distributions measured for cores mate
rials taken from the aquifer. The pum
tests indicated that the site had severe
favorable hydraulic features: (1) hig
transmissivity should permit the require
pumping and injection of fluids into th
test zone; (2) loss of permeability b
clogging due to biological growth c
chemical precipitation, would be limitec
due to the original high permeability; (;.
the aquifer is semi-confined, thus th
test zone is fairly well bounded in verticc
direction; and (4) the aquifer was capabl
of supplying ground water at rate
required for the experiments with les
than one meter of drawdown at th
extraction well.
Chemical Characteristics
Analyses of the ground water provide
information on the quality of the groun
water in the area of the test zone an
determined whether the aquifer wa
contaminated with chlorinated aliphatic
of interest. Four volatile organic corr
pounds were detected. The highe;
concentrations in the native groun
water were found for 1,1,1
trichloroethane (TCA) which is preset
-------
at a concentration on the order of 100
//g/l, varying over a range of 56-131 fjg/
I for analyses conducted over several
months. Trichloroethylene (TCE) was not
detected in these samples.
The results of the initial inorganic and
organic analyses indicated that the
ground water was of a suitable chemical
composition for performing the experi-
ments. The chemical composition would
not inhibit the stimulation of the metha-
notrophic bacteria, and it appears feas-
ible to inject and transport dissolved
oxygen in the test zone without undue
consumptive losses.
Aquifer Solids Characterization
Core samples of the aquifer material
were obtained to characterize the aquifer
material's physical, chemical, and micro-
biological properties. Some of the core
material was to be used for microbiolog-
ical studies in the laboratory. Aseptic
procedures were used for obtaining the
cores samples and transferring the
materials to storage containers.
The acridine orange-epifluorescence
procedure was used to enumerate the
active bacteria attached to solid samples
from the test zone. The analysis indicated
that the microorganisms were typically
attached to particles of organic matter.
The bacterial numbers per gram of dry
solids varied from 2 x 106 to 39 x 106,
within the range obtained in previous
subsurface investigations. No apparent
trend with depth was indicated. The
highest value, however, was observed in
the sand and gravel zone, 17 - 17.5 ft
below the surface, and is believed to be
associated with the high permeability of
this zone and a corresponding greater
flux of nutrients.
The presence of methanotrophic bac-
teria was not established using this
enumeration procedure, since the
method is not type specific. The presence
of methane-consuming bacteria on
aquifer solids was, however, demon-
stratred in column experiments con-
ducted at the Kerr Laboratory. In these
studies, columns were packed with core
solids obtained from well SI. After
exchanging the pore water with water
containing methane and oxygen, oxygen
and methane consumption was
observed. This study and the bacteria
enumeration study indicated that the test
zone had an indigenous microbial pop-
ulation that could be successfully
biostimulated.
The degree of sorption of several
chlorinated aliphatic compounds onto
aquifer solid samples was determined in
batch sorption experiments. It was found
that TCA sorbs less than TCE, while PCE
sorbs more strongly. Linear fits resulted
in Kd values of 0.42, 1.4 and 4.0 cm3/
g for TCA, TCE, and PCE respectively.
The Kd values were also predicted
based on established partitioning rela-
tionships, according to which Kd is
dependent on the organic carbon fraction
of the aquifer solids, measured as 0.001
at the Moffett site. The predicted Kd
values were 0.266,0.318, and 1.06 cm3/
g for TCA, TCE and PCE, respectively.
Estimates of the degree of retardation
of the sorbing solutes relative to a
nonsorbing solutes were made based on
the retardation factor given by R = 1 +
pt>Kd/n, where pb is the bulk density of
the aquifer material (g/cm3); n is the
porosity (cmVcm3); and Kd is the equil-
ibrium distribution coefficient. The
estimated retardation factors are pres-
ented in Table 2. Based on these esti-
mates,the movement of TCE through the
test zone would be expected to be
retarded by a factor of 6.5 to 8.5. This
has important implications for the time
required to establish steady-state con-
centrations during the tests, and the
effect the sorption process may have on
the biotransformation of the TCE.
The Well Field
Figure 1 shows the locations of the
wells installed at the test site. The well
field was designed to permit simultane-
ous experiments by creating two test
zones through the injection of fluids at
both the south (SI) and north (Nl) injection
wells, and extraction at the central
extraction well (P). The operation of the
extraction well is intended to dominate
the regional flow field in the study area
in an approximation of radial flow. The
injection wells are located 6 meters from
the extraction well. The monitoring wells
are located 1.0, 2.2, and 4.0 meters from
the injection wells. This spacing should
result in roughly equivalent fluid resi-
dence times between monitoring wells
if radial flow conditions exist.
An automated data acquisition system
has been devised at the site to implement
the field experiments. The system per-
mits the continuous measurement of the
experiment's principal parameters: the
concentrations of the bromide ion tracer,
methane, halogenated aliphatic com-
pounds of interest, and dissolved oxygen,
as well as pH. A schematic of the system
is shown in Figure 2. The system is driven
by a microcomputer. A data acquisition
and control program (DAC) has been
designed and programmed that can be
operated in either manual or automated
mode. Manual mode permits selection of
samples, creation of a sample sequence
for automated operation, calibration of
13
O
Scale, meters
72
11
Figure 1. Layout of the well field at
the Moffett site.
Table 2. Measured and Predicted Ka Values for PCE, TCE, and 1,1,1-TCA. and Estimated
Retardation Factors
Compound
TCA
TCE
PCE
Measured
Sorption^
Coefficient
Ks
(cm/g)
0.42
1.4
4.0
Predicted
Sorption2
Coefficient
Kd
(cm/g)
0.27
0.32
1.06
Retardation3
Factor
R
2.5-3
65-8.5
17-22
'Based on measured linear sorption isotherm
2Based on the empirical correlation with water solubility of Kanckhoff et a/. (1979) and the
measured foc = 0.001
3Based on Eq 1 .range p*=f1.6-1 9 g/cm3), range n=(0.3-Q 4)
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Automated Data Acquisition
and Control System
Figure 2. Schematic of the automated data acquisition and control system.
various instruments, and graphing the
results as the sampling proceeds.
In order to realize real-time control and
interpretation, measurements are made
continually for several weeks or months
at a frequency of approximately two per
hour. The sampling points are typically
six in number, the mj jcted fluid,
extracted fluid, three intermediate mon-
itoring points, and the effluent from the
air stripper (for monitoring the ground
water discharged to a storm sewer). In
order to obtain precise and reproducible
measurements during an experiment,
the instruments are calibrated daily.
A series of experiments were per-
formed using the DAC system to study
the transport characteristics of the test
zone under a variety of flow conditions.
Natural gradient tests were performed in
order to estimate the ground water
velocity and direction at the site. Induced
flow tests were performed, in which
ground water was injected and extracted,
to study transport under conditions
similar to those used in the biostimula-
tion and biodegradation stages of the
experiment. The DAC system was found
to work reliably and generated sufficient
data to observe the transient responses
at observation locations.
The natural gradient tracer tests
indicated that the ground water flow was
primarily in a northerly direction, with an
average velocity of 2.6 m/d Two induced
flow tracer experiments were performed
under the conditions used in the later
evaluation experiments, quantifying the
transport of bromide ion, dissolved
oxygen, and TCE through the test zone.
Figure 3 shows the response of both
bromide and TCE at the S1 observation
well, during the early stages of the Tracer
5 experiment. The movement of TCE is
shown to be retarded with respect to
bromide, with a more gradual approach
to the injected concentration.
The average fluid reside nee times from
the injection to the observation wells and
correpsonding fluid velocities were
estimated based on the results of the
tracer experiments and the initial bios-
timulation experiment. The average flui
residence times based on the bromid
tracer are 7.3 hrs and 16.0 hrs from th
injection well to the S1 and S2 obser
vation wells, respectively. This corres
ponds to an average fluid velocity of 0.1 •
m/hr in both cases. Methane and D(
analyses were found to yield simila
residence time estimates as obtaine
using the bromide. This result indicate
that these dissolved gases are easil
transported through the test zone and ar
not retarded.
The data for TCA and TCE indicat
retardation factors of 1.4 for TCA an
5.75 for TCE. Estimates based on the S
well data yield retardation values of 1.
and 9.8 for TCA and TCE, respectively
The values are in good agreement wit
those predicted from the batch exper
ments performed in the laboratory (Tabl
2).
The results of the tracer experiment
demonstrate that reproducible transpoi
experiments can be performed in the tes
zone. The fluid residence times in the tes
zone are fairly short, about 8 hrs to th
first observation well to 30 hrs at th
extraction well. Owing to the high groun
water velocity under natural gradier
conditions, longer transport times are nc
possible, since an extraction rate of £
least 8 l/min is required to ensur
Br and TCE Response—Tracer 5
Observation Well S1
Figure 3.
i 1 1 r
120 140 16(
Time Ihrs)
Normalized response of bromide and TCE at theSJ observation well in the Trac
5 experiment.
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effective recovery of the injected fluid at
the extraction well. The tracer experi-
ments indicated recovery of 60 to 75 of
the bromide injected. TCE was recovered
to the same degree as bromide, indicat-
ing negligible loss of TCE. There is some
dilution of the injected ground water by
the native ground water with the degree
of dilution increasing with distance from
the injection well.
Pulsed Injection
To enhance the effectiveness of bios-
timulation, it was decided to introduce
the methane (primary substrate) and
oxygen (electron acceptor) as alternating,
timed pulses. This decision was reached
based upon consideration of two crucial
requirements: (1) the need to avoid
clogging of the injection well and bore-
hole i nterface, and (2) the need to achieve
as uniform a distribution of microbial
growth as possible throughout a sub-
stantial portion of the aquifer. Failure to
fulfill the first requirement would cause
loss of hydraulic capacity and premature
termination of our experiments, as the
drastic chemical measures such as
chlorination or strong acid treatment that
are customarily employed to rejuvenate
clogged wells would interfere with
biostimulation. Failure to satisfy the
second requirement would lead to con-
ditions of extremely high microbial
densities near the injection point and low
bacterial populations elsewhere, which
would not be conducive to secondary
substrate utilization as needed to
degrade halogenated aliphatic com-
pounds by methanotrophs.
It was thought that introducing the two
essential additives, methane and oxygen,
as alternating timed pulses would assure
their separation in the injection well and
borehole, thus discouraging biological
growth in that critical region. The
methane and oxygen would then mix
gradually, owing to the action of hydro-
dynamic dispersion and associated
mixing processes, during transport
through the aquifer, stimulating the
growth of methanotrophic bacteria over
the zone in which mixing occurs. In
designing the pulsed injection system,
two important variables had to be
selected: (1) the ratio of the individual
pulses of methane and oxygen, and (2)
the overall pulse length.
Biostimulation and
Biotransformation Experiments
The biostimulation and biotransforma-
tion experiments in the first (1986) field
season were conducted in two stages.
First, the test zone was biostimulated by
the pulse injection of methane and
oxygen into the test zone. After the zone
had been successfully stimulated, TCE
injection was commenced.
The injection system uses two counter-
current columns to sorb the methane and
oxygen to approximately 80 percent
saturation, resulting in concentrations
that are approximately 20 mg/l for CH4
and 32 mg/l for DO. These solutions are
alternately pulsed, with a pulse time ratio
of about 2:1 (methane:oxygen), based on
the stoichiometric requirements. A pulse
timer permits the ratio and the length
of the pulses to be varied. The other
components of the injection system
permit the accurate and continuous
addition of the bromide tracer and TCE
into the injection stream, the monitoring
of the injection rates, and the sampling
of the injection fluid, while maintaining
a constant rate of injection.
The biostimulation experiment was
performed under same induced flow
conditions as the earlier tracer tests. The
pulse cycle for the injection of either
methane or oxygen containing ground
water was varied during the course of
the experiment, from less than 1 hr
during start-up to ensure the pulsing
would not interfere with growth, to a 12-
hr period during the later stages to
distribute growth in the test zone. No
additional nutrients were added to the
ground water.
The first signs of consumption were
observed in the extraction well and the
S3 observation well after approximately
200 hrs of injection. The concentration
at the extraction well decreased below
the detection limit after 300 hrs of
injection. Owing to the continuous
removal by microorganisms, the
decrease in DO was greater the longer
the travel paths through the aquifer. As
time proceeds, the increase in the growth
of microbial population throughout the
test zone results in an increase in the
DO consumption along the flow path. The
methane response was similar to that
observed for the DO, which is expected,
as methane is the electron donor and
oxygen the electron acceptor for microb-
ial growth. Figure 4 shows the response
of the methane and DO at the S2
observation well. The fairly rapid
decrease in the methane concentration
over the period of 200 to 400 hrs
indicates fairly rapid growth kinetics
typical of aerobic microorganisms. A
significant amount of methane substrate
is also incorporated into cells. Based on
the concentration values during the
period of 350 - 375 hrs, the ratio of
oxygen to methane consumed was 2.25
mg O2/mg CH4, which is significantly
Biostimulation Experiment
Methane and DO Well S2
I
100
200
Time (Hrs)
300
400
Figure 4.
The response of methane and DO at the S2 observation well during the
biostimulation of the test zone.
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lower than the ratio of 4 required for
complete oxidation. The lower value
suggests incorporation of the methane
substrate into the cell mass, with a yield
coefficient of approximately 0.5 mg cells
per mg CH4.
After 450 hrs of injection, the methane
concentration at the S2 observation well
decreased below the detection limit,
indicating that the microbial mass was
increasing near the injection well. The
pulse cycles were therefore lengthened
to 12 hrs in order to prevent biofouling
near the wellbore. Figure 5 shows the
response of the system to the pulsing at
the S2 observation well. Peak methane
values are shown to increase from below
detection to approximately 1 mg/l, as a
result of the longer pulse duration. Peak
methane concentrations are noted to
occur when minimum DO concentrations
are observed, which is anticipated based
on transport theory.
Long pulse cycles were continued
throughout the biostimulation and bio-
degradation experiments, with durations
ranging from 6 hrs to 12 hrs. Based on
continued methane breakthrough at the
observation wells, the pulsing is believed
to have helped to distribute the microbial
population in the test zone and prevented
biofouling of the aquifer.
The biostimulation experiment demon-
strated that methane-oxidizing bacteria
could be successfully established in the
test zone. No additional nutrients were
required to stimulate growth. The tran-
sient methane and DO responses indi-
cated that a population was stimulated
which grew closer to the injection well
with time. The response indicates that
microorganisms have fairly rapid growth
kinetics, typical of aerobic organisms.
Thus, pulsing was required to distribute
the growth in the test zone and to prevent
biofouling of the aquifer.
Biotransformation Experiments
Biotransformation experiments were
performed after the test zone was
biostimulated. TCE was continuously
injected over a three-month period.
During the initial stages, TCE was
injected at an average concentration of
100 ug/\. During the later stages, the
concentration was lowered to 60 (JQ/\
Methane and oxygen (no nutrients) were
continuously pulse-injected during this
period to support the methane-oxidizing
microorganisms that had been
biostimulated.
During the initial phase of the exper-
iment, the TCE concentrations slowly
I
I
c
u
c
o
ID-
S'
7-
6-
5-
4-
3
2-
1-
Pulsed Biostimulation
Methane and DO Well S2
0
DO
400 420 440 460 480 500 520 540 560 580 60>
Time (Hrs)
Figure 5. The effect of long-term pulsing of DO and methane on the response at the S
observation well.
approached steady-state values. The
early breakthrough results indicated that
degradation is on the order of 30 percent.
The degradation of TCE is illustrated in
Figure 6, which shows the time series
observations of TCE concentrations at
monitoring wells S1 and S2 during
steady-state operation under biostimula-
tion conditions. Comparisons of mass
balances of the amount injected and
extracted in the two experiments also
confirms that TCE was degraded durini
the biotransformation experiment.
Figure 7 represents a summary of th<
biostimulation experiments, where th
fractional breakthroughs of TCE relativ
to bromide ion (TCE/Br) at the observa
tion wells are compared. The ratios rang
from 70 percent to 80 percent, indicatin
a maximum degree of degradation of 3<
percent. Degradation is noted to occu
in the area of the test zone in whic
o
O
•o
I
"5
I
1 •
0.9
0.8
0.7
0.6
0.5
04
03
02
0.1
0
Extract,
0
40
80
240 280
Figure 6.
120 160 200
Time (Hrs)
Steady-state TCE concentrations during the biostimulation experiment.
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<§
o
.o
I
1.1
1 -
0.9 -
0.8 -
0.7 -
0.6 -
0.5 -
0.4 -
0.3 -
0.2 -
0.1 -
0
\\X\\X\l
S2
S3
Extract
\S/\ Average
l\.\l Standard Deviation
Figure 7.
Estimated TCE biotransformation based on comparisons with bromide as a
conservative tracer.
methane is present to support the
methane-oxidizing bacteria.
The different methods of assessing the
degree of degradation—including mass
balances, comparison of TCE break-
through concentrations with the pseudo
control experiment, and comparisons
with bromide concentrations at steady-
state within an experiment— yield
similar estimates of the degree of TCE
degradation in the test zone. The degree
of degradation is in the range of 20 to
30%. The results demonstrate that, if
sufficient care is taken in obtaining the
experimental data, quantitative evidence
of degradation can be obtained in a real
aquifer situation.
A mass balance for TCE over the course
of the TCE biostimulation experiment
shows that of the total 10.1 g that wsre
injected during the course of this exper-
iment, 4.5 g were recovered in the water
pumped from the extraction well, repres-
enting a recovery of 45 percent. During
this same overall period, 65 percent of
the bromide tracer was recovered. The
lower recovery of TCE supports the
conclusion that 25 to 30 percent of the
injected TCE was degraded.
This interim report was submitted in
partial fulfillment of Cooperative Agree-
ment No. R-812220 by Stanford Univer-
sity under the sponsorship of the U S.
Environmental Protection Agency.
Lewis Semprini, Pau! V. Roberts, Gary D. Hopkins, and Douglas M. Mackay
are with Stanford University, Stanford, CA 94305.
Jack W. Keeley is the EPA Project Officer (see below).
The complete report, entitled "A Field Evaluation of In-Situ Biodegradation for
Aquifer Restoration," (Order No. PB 88-130 257/AS; Cost: $14.95) 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
P.O. Box 1198
Ada, OK 74820
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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