United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/040
March 1995
^ EPA Project Summary
Assessing LIST Corrective Action
Technologies: Lessons
Learned about In Situ Air
Sparging at the Denison
Avenue Site, Cleveland, Ohio
T. R. Clark, R. E. Chaudet, and R.L. Johnson
In situ air sparging (IAS) has been
used at an increasing number of sites
to address groundwater contamination.
Because of the lack of substantive per-
formance data, however, the actual ef-
fectiveness of this system is not known.
The EPA Office of Research and Devel-
opment Risk Reduction Engineering
Laboratory (ORD RREL) with the EPA
Region 5 Office of Underground Stor-
age Tanks, the Ohio State Fire Mar-
shal, and BP Exploration & Oil, Inc.
(BP) participated in a field evaluation
of an IAS system at a petroleum leak-
ing LIST site in Cleveland, OH. The pur-
pose of this study was to provide
performance data that will be indepen-
dently evaluated by EPA to better un-
derstand IAS effectiveness.
This report presents the site and
monitoring data provided by BP over a
2-yr period. The chemical data indicated
an overall decrease of BTEX concen-
trations in groundwater to
nondetectable levels shortly after
startup of the I AS system. Some of the
IAS system chemical data were col-
lected before the Quality Assurance
Project Plan (QAPP) was developed,
however, and did not meet Quality Con-
trol (QC) criteria. Variability in the
chemical and process data also pre-
cludes making any definitive link be-
tween the decrease in contaminant
concentrations and IAS performance at
this site. Although these data did not
allow a definitive evaluation of IAS sys-
tem performance, they provided valu-
able information used to develop
lessons learned that should be consid-
ered when system parameters are
evaluated.
This Project Summary was deveoped
by EPA's Risk Reduction Engineering
laboratory, Cincinnati, OH, to announce
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).
Introduction
In situ air sparging (IAS) in combination
with soil vapor extraction (SVE) is being
proposed and used at an increasing num-
ber of underground storage tank (LIST)
sites across the nation as an alternative
groundwater treatment technology; how-
ever, the applicability and effectiveness of
IAS is not known. Claims have been made
that IAS can be used to successfully
remediate hydrocarbon contamination in
both the saturated and unsaturated zones.
Unfortunately, there is a lack of substan-
tive peer-reviewed performance data to
support the claims of practitioners who
propose using these systems. Conse-
quently, independently reviewed per-
formance data are needed to evaluate the
effectiveness and limitations of IAS sys-
tems at leaking LIST sites. These data are
also needed to provide a comparision with
conceptual and laboratory models that are
used to better understand the processes
that determine the performance of IAS
systems.
In response to this need, the U.S. Envi-
ronmental Protection Agency (EPA) Of-
fice of Research and Development (ORD)
Risk Reduction Engineering Laboratory
(RREL) UST Research Program has pro-
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vided technical support to EPA regions for
evaluating selected technologies while they
are being used to remediate actual LIST
sites. Under this program, RREL worked
with the EPA Region 5 Office of Under-
ground Storage Tanks, the Ohio State Fire
Marshal, Bureau of Underground Storage
Tank Regulations (BUSTR), and BP to
identify a site at which an IAS system was
being operated. RREL provided assistance
to BP and its contractor, Engineering-Sci-
ence, in developing a site-specific quality
assurance project plan (QAPP) to define
the quality of data required and to de-
scribe the sampling and analytical meth-
odologies to be used in evaluating the
performance of the system installed at
this site at West 65th and Denison Av-
enue in Cleveland, OH. Interim site and
operational data generated at this site were
provided by BP. The EPA RREL then
examined and evaluated the data gener-
ated during operation of the IAS system
at this site. These data provided the basis
for developing the lessons learned about
evaluating IAS at this site.
Purpose
The original purpose of this report was
to evaluate the impact and performance
of the IAS system installed at the site in
Cleveland, OH. A tremendous amount of
data were collected at this site. However,
the comparability and quality of some of
the chemical data (BTEX, TPH) did not
meet the QC criteria established in the
QAPP. In addition, the low initial contami-
nant concentrations in groundwater and
the large variability in the chemical and
process data that were noted over the
course of this study (approximately 2 yr)
prevented a definitive evaluation of the
performance of the IAS system at this
site. Although these data could not be
used to evaluate the performance of the
IAS system, they can be used to develop
lessons learned for evaluating IAS sys-
tems. Therefore, the purpose of this re-
port is to present the lessons that were
learned from the data collected at this
site.
Technology Description
The in situ air sparging system at this
site involves injection of clean air directly
into the porous medium below the water
table in an attempt to remove organic
contaminants by a combination of volatil-
ization and oxygenation to enhance
aerobic biodegradation processes. Hydro-
carbon vapors are then recovered by use
of soil vapor extraction (SVE).
At this site, an oil-free air compressor is
used to inject atmospheric air into vertical
sparging wells in the subsurface. Con-
taminant vapors are removed via soil va-
por extraction wells manifolded to a blower.
Water present in the extracted vapor
stream is removed in an air/water separa-
tor. The off-gas from the SVE wells did
not require treatment at this site. The well
configuration used for the IAS system
examined in this study consists of two
"remediation cells," each consisting of three
vertical air sparging or injection wells with
a central SVE well. The IAS system de-
sign and operation are presented as well
as the monitoring program for examining
this I AS system.
Site Characteristics
The BP Oil Site (No. 04216) is an ac-
tive gasoline retail service station located
on the southwest corner at the intersec-
tion of West 65th and Denison Avenue in
Cleveland, OH. Petroleum products had
been released at this site, but the source
of this release is not known. Surrounding
properties are largely residential, with light
commercial development along Denison
Avenue and private residences on the side
streets. Potable water for the immediate
area surrounding the site is provided by
the City of Cleveland.
This site, which is located on the east-
ern lake and till plains of the Central Low-
land Province, is characteristic of a
remnant beach ridge on the lake plain
bordering the southern shore of Lake Erie.
The soil texture of subsurface soils varies
widely throughout the site in the horizon-
tal direction and even more significantly in
the vertical direction. In general, discon-
tinuous and interfingered silt and silty clay
lenses are shown from the ground sur-
face to a depth of approximately 15 ft.
Interbedded and discontinuous low per-
meability silts and silty clays overlie and
in certain locations partially confine the
more permeable sands and silty sands
that constitute the main water-bearing
zone. A continuous clay layer underlies
the entire site at a depth of over 22 to 25
ft from the surface.
Based on the regional topography, the
predominant direction of groundwater
movement on a regional scale is to the
north toward Lake Erie. Reported ground-
water elevations taken at the site, prior to
start-up of the IAS system, indicate that
groundwater movement is to the north,
which is consistent with regional trends.
Groundwater can be found at an average
depth of 19 ft. The water-bearing zone is
a semiconfined aquifer comprising pre-
dominately sands or sandy silt that ranges
from approximately 4 to 7 ft thick across
the site. As mentioned, silts and silty clays
overlie these sandy soils and, at certain
locations on the eastern part of the site,
semiconfine portions of the aquifer. Over
much of the site, these sandy soils extend
above the groundwater table. In the south-
eastern part of the site, the silty clay above
the aquifer is breached by silt. A clay
aquitard underlies the aquifer across the
entire site.
An Evaluation of Parameters for
Monitoring Performance of In
Situ Air Sparging
An evaluation of parameters that are
used as indicators of IAS performance is
first presented before the discussion of
the lessons learned from the data gener-
ated at the Denison Avenue site. Two
general types of parameters are discussed.
The first are soil and groundwater quality
parameters including dissolved hydrocar-
bon concentrations, dissolved oxygen, dis-
solved metals, and hydrocarbon
concentrations in soils. The second are
vadose zone parameters including soil gas
pressure, hydrocarbon and oxygen con-
centrations in the soil gas, and hydrocar-
bon concentrations in the soil vapor
extraction off-gas. The significance and
limitations are discussed for each of these
parameters.
In reviewing the importance of the per-
formance parameters, it is important to
understand the critical role of the place-
ment of the monitoring points within the
context of the stratigraphy of a site. The
placement of monitoring points for repre-
sentative data collection are at least as
important as the actual parameters used
in the analysis of system performance.
Lessons Learned About In Situ
Air Sparging at the Denison
Avenue Site
The primary lesson learned from the
monitoring data at the Denison Avenue
site is that it is very difficult to evaluate
the performance of in situ air sparging. A
tremendous amount of data was collected
during the study. Even so, the data do not
provide a clear picture of how well the IAS
process was working.
Based on these data, however, the fol-
lowing lessons were learned: (1) A signifi-
cant contribution to the difficult
interpretation of the data is the fact that
relatively minor changes in horizontal, and
especially vertical, placement of wells and
monitoring points in the complex stratigra-
phy at this site can have a major impact
on the performance data collected. (2)
Contaminant indicators such as BTEX are
often used as the primary indicators of
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system performance. Based on the data
from this site, however, BTEX cannot be
solely used to indicate system perfor-
mance. (Low and variable concentrations
may reflect "naturally-occurring" changes
in concentration over time.) (3) Other sys-
tem parameters measured, such as dis-
solved oxygen and pressure, can be used
along with contaminant indicators to pro-
vide additional insight as to the impact of
IAS on the site. (At this site, however,
these parameters are influenced by pro-
cesses that are not well understood at
this time.)
Recommendations
Based on the lessons learned in an
attempt to evaluate the performance of
the IAS system at the Denison Avenue
site, the following recommendations should
be considered in the experimental design
for future technology applications of IAS
systems: (1) Whenever possible, a full
year of background data (e.g., BTEX in
groundwater, dissolved oxygen) should be
reviewed before the IAS system is started
up to better understand any trends or natu-
ral variations in concentrations. This is
often difficult because either the data do
not exist or the data quality is inconsistent
over time. Alternatively, in the absence of
historical data, wells within the zone of
contamination, but outside the zone of
active remediation, can be used as a "con-
trol." (2) Defining the vertical and horizon-
tal zone of contamination in soil and
groundwater as well as the hydrogeologic
characteristics of the site is necessary to
determine proper well and monitoring point
placement. (3) To ensure that samples
collected from the monitoring wells reflect
the general water quality, the IAS system
should be shut down prior to each sam-
pling event. The period of IAS system
shutdown will usually be site-specific based
on the parameter being measured and
the hydrogeologic characteristics of the
site. (4) System design diagnosis can be
performed using tracer tests to determine
if the injected air from the IAS system is
being captured by the soil vapor extrac-
tion system and if the vapor monitoring
points reflect the influence of the IAS sys-
tem. (5) An additional test that can be
used to assess system performance is
routine shutdown/in situ respiration tests.
These in situ respiration tests can be used
to assess bioactivity and microbial oxygen
uptake rate changes over time for infer-
ring the contribution of biodegradation to
changes in contaminant concentration. (6)
The parameters that will be used to moni-
tor performance, the appropriate methods
for obtaining these parameters, and
method performance criteria need to be
established prior to the start-up of the
system and used throughout the technol-
ogy application since the field evaluation
may be several years in duration.
In general, the best indicator of system
performance or the effectiveness of an
IAS system is the long-term improvement
in soil/groundwater quality after the air
sparging system has been shut down. As
part of evaluating the application and per-
formance of IAS, the final sampling and
analysis should be conducted after a pe-
riod of system shutdown.
The full report was submitted in partial
fulfillment of Contract No. 68-C2-0108,
Work Assignment No. 2 by IT Corporation
under sponsorhiop of the U.S. Environ-
mental Protection Agency.
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T.R. Clark and R.E. Chaudetare with IT Corporation, Cincinnati, OH 45246.
R. L Johnson is with the Oregon Graduate Institute of Science and
Technology, Beaverton, OR 97006.
Chi-Yuan Fan is the EPA Project Officer (see below).
The complete report, entitled "Assessing UST Corrective Action Technologies:
Lessons Learned About In Situ Air Sparging at the Denison Avenue Site,
Cleveland, OH," (OrderNo. PB95-188082; Cost: $27.00, 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:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Edison, NJ 08837
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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