E AP Project Summary

United States

Environmental Protection

Agency

Risk Reduction

Engineering Laboratory

Cincinnati, OH 45268

Research and Development

In situ air sparging (IAS) has been

used at an increasing number of sites

to address groundwater contamination.

Because of the lack of substantive performance data, however, the actual effectiveness of this system is not known.

The EPA Office of Research and Development Risk Reduction Engineering

Laboratory (ORD RREL) with the EPA

Region 5 Office of Underground Storage Tanks, the Ohio State Fire Marshal, and BP Exploration & Oil, Inc.

(BP) participated in a field evaluation

of an IAS system at a petroleum leaking UST site in Cleveland, OH. The purpose of this study was to provide

performance data that will be independently evaluated by EPA to better understand 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 concentrations in groundwater to

nondetectable levels shortly after

startup of the IAS system. Some of the

IAS system chemical data were collected before the Quality Assurance

Project Plan (QAPP) was developed,

however, and did not meet Quality Control (QC) criteria. Variability in the

chemical and process data also precludes making any definitive link between the decrease in contaminant

concentrations and IAS performance at

this site. Although these data did not

allow a definitive evaluation of IAS system performance, they provided valuable information used to develop

lessons learned that should be considered 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 number of underground storage tank (UST)

sites across the nation as an alternative

groundwater treatment technology; however, 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 substantive peer-reviewed performance data to

support the claims of practitioners who

propose using these systems. Consequently, independently reviewed performance data are needed to evaluate the

effectiveness and limitations of IAS systems at leaking UST 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. Environmental Protection Agency (EPA) Office of Research and Development (ORD)

Risk Reduction Engineering Laboratory

(RREL) UST Research Program has proEPA/600/SR-95/040 March 1995

Assessing UST 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
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vided technical support to EPA regions for

evaluating selected technologies while they

are being used to remediate actual UST

sites. Under this program, RREL worked

with the EPA Region 5 Office of Underground 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-Science, in developing a site-specific quality

assurance project plan (QAPP) to define

the quality of data required and to describe the sampling and analytical methodologies to be used in evaluating the

performance of the system installed at

this site at West 65th and Denison Avenue 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 generated 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 contaminant 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 systems. Therefore, the purpose of this report 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 volatilization and oxygenation to enhance

aerobic biodegradation processes. Hydrocarbon 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. Contaminant vapors are removed via soil vapor extraction wells manifolded to a blower.

Water present in the extracted vapor

stream is removed in an air/water separator. 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 design and operation are presented as well

as the monitoring program for examining

this IAS system.

Site Characteristics

The BP Oil Site (No. 04216) is an active gasoline retail service station located

on the southwest corner at the intersection 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 eastern lake and till plains of the Central Lowland 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 horizontal direction and even more significantly in

the vertical direction. In general, discontinuous and interfingered silt and silty clay

lenses are shown from the ground surface to a depth of approximately 15 ft.

Interbedded and discontinuous low permeability 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 groundwater 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 predominately 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 southeastern 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 generated at the Denison Avenue site. Two

general types of parameters are discussed.

The first are soil and groundwater quality

parameters including dissolved hydrocarbon concentrations, dissolved oxygen, dissolved metals, and hydrocarbon

concentrations in soils. The second are

vadose zone parameters including soil gas

pressure, hydrocarbon and oxygen concentrations in the soil gas, and hydrocarbon 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 performance parameters, it is important to

understand the critical role of the placement of the monitoring points within the

context of the stratigraphy of a site. The

placement of monitoring points for representative 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 following lessons were learned: (1) A significant 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 stratigraphy 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
3

system performance. Based on the data

from this site, however, BTEX cannot be

solely used to indicate system performance. (Low and variable concentrations

may reflect “naturally-occurring” changes

in concentration over time.) (3) Other system parameters measured, such as dissolved oxygen and pressure, can be used

along with contaminant indicators to provide additional insight as to the impact of

IAS on the site. (At this site, however,

these parameters are influenced by processes 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 natural 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 “control.” (2) Defining the vertical and horizontal 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 sampling 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 extraction system and if the vapor monitoring

points reflect the influence of the IAS system. (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 inferring the contribution of biodegradation to

changes in contaminant concentration. (6)

The parameters that will be used to monitor 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 technology 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 performance of IAS, the final sampling and

analysis should be conducted after a period 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. Environmental Protection Agency.
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T.R. Clark and R.E. Chaudet are 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," (Order No. 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

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/SR-95/040