EPA/600/R-95/040
December 1994
ASSESSING UST CORRECTIVE ACTION TECHNOLOGIES:
Lessons Learned About In Situ Air Sparging
at the Denison Avenue Site
Cleveland, Ohio
by
Thomas R. Clark
and
Roy E. Chaiudet
IT Corporation
Cincinnati, Ohio 45268
Richard L. Johnson
Oregon Graduate Institute
of Science and Technology
Beaverton, Oregon 97006
Contract No. 68-C2-0108
Project Officer
Chi-Yuan Fan
Superfund Technology Demonstration Division
Risk Reduction Engineering Laboratory
Edison, New Jersey 08837
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
Printed on Recycled Paper
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NOTICE
The information in this document has been funded by the U.S. Environmental
Protection Agency under Contract 68-C2-0108 to IT Corporation. It has been subjected to
the Agency's peer and administrative review, and has been approved for publication.
Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
11
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if improperly
dealt with, may threaten both human health and the environment. The U.S. Environmental
Protection Agency (EPA) is charged by Congress with protecting the Nation's land, air, and
water resources. Under a mandate of national environmental laws, the Agency strives to
formulate and implement actions leading to a compatible balance between human activities
and the ability of natural resources to support and nurture life. These laws direct the EPA to
perform research to define our environmental problems, measure the impacts, and search for
solutions.
The Risk Reduction Engineering Laboratory (RREL) is responsible for planning,
implementing, and managing research, development, and demonstration programs to provide
an authoritative, reasonable engineering basis in support of the policies, programs, and
regulations of the EPA with respect to drinking water, toxic substances, solid and hazardous
wastes, and other environmental programs. This report presents information obtained from a
joint effort of EPA-RREL, EPA Office of Underground Storage Tanks (OUST) Region 5,
and BP Exploration & Oil, Inc., to better understand how to monitor and evaluate an
innovative corrective action technology~in situ air sparging (IAS). The information from
this project provides a vital communication link between the researcher and the user
community.
An area of major concern to the Risk Reduction Engineering Laboratory is the
selection and use of appropriate corrective action technologies for cleanup of petroleum
hydrocarbon releases from leaking underground storage tanks (UST). This report presents
the lessons learned about an IAS system that was proposed to reduce subsurface contaminant
concentrations.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
m
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ABSTRACT
In situ air sparging (IAS) has been proposed and installed at an increasing number of
sites to address contamination in both the saturated and unsaturated zones. Because of the
lack of experimental and substantive performance data, however, the actual performance and
effectiveness of this system is not known. Therefore, an objective evaluation of performance
data is needed to better determine the effectiveness of this technology.
In response to this need, the EPA Office of Research and Development (ORD) Risk
Reduction Engineering Laboratory in conjunction with the EPA Region 5 Office of
Underground Storage Tanks, the Ohio State Fire Marshal, Bureau of Underground Storage
Tank Regulations (BUSTR), and BP Exploration & Oil, Inc. (BP) are participating in a field
evaluation of an IAS system at a petroleum leaking UST site in Cleveland, OH. The purpose
of this field evaluation is to provide performance data that will be independently evaluated by
EPA so that the effectiveness of the IAS system installed at this site can be better understood
and thereby assist state regulatory agencies in,formulating guidance on IAS systems.
This report presents the results of this study based on site and operational monitoring
data provided by BP Exploration & Oil, Inc., over a 2-year period. In general, the chemical
data collected indicated an overall decrease of concentrations of benzene, toluene,
ethylbenzene, and xylenes (BTEX) in groundwater to nondetectable levels shortly after
startup of the IAS system. Some of the historical chemical data were collected before the
Quality Assurance Project Plan (QAPP) was developed and therefore did not meet Quality
Control (QC) criteria. The low initial contaminant concentrations in groundwater and the
large variability in both the chemical and process data collected during the study precludes
making any definitive link between the decrease in contaminant concentrations and the
performance of the IAS system at this site. Although these data did not allow a definitive
evaluation of IAS system performance, they provided valuable information that was used to
develop lessons learned that should be considered during an evaluation of different system
parameters. The parameters discussed include dissolved oxygen in groundwater, BTEX
concentrations in groundwater, hydrocarbon off-gas concentrations, pressure and flow rates,
hydrocarbon and oxygen concentrations in soil gas, and monitoring point placement. In
addition, an evaluation of these parameters was presented with considerations for sampling
methodologies and data interpretation.
IV
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CONTENTS
Section
Page
Foreword . . iii
Abstract -..'.. iv
Figures vii
Tables . ix
List of Abbreviations and Symbols x
Acknowledgements xi
1. Introduction 1
Background .1
Purpose 2
Site Selection and Project History 3
2. Executive Summary , 5
3. Process Description 8
Technology Description 8
Site Characteristics 10
An Evaluation of Parameters for Monitoring Performance of In Situ
Air Sparging 15
4. System Design and Operation 24
System Design . . ; ., 24
System Operation 33
5. Sampling and Analysis Program .; . . . 36
Sample Collection and Analysis Methodology 36
System Monitoring Methodology 38
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CONTENTS (continued)
Section
6. Lessons Learned About In Situ Air Sparging at the Denison Avenue Site 40
Overview 40
Brief Discussion of Significant System Parameters 43
Summary 65
References 68
Appendix A Quality Assurance .69
Appendix B Technical Site Evaluation Report 83
Appendix C Soil and Groundwater Data 94
VI
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FIGURES
Number
Page
1 A Schematic of the IAS System 9
2 Site Map and Cross Section Locations , . 11
3 Cross Section A - A' 12
4 Cross Section B - B' - 13
5 Cross Section C - C' . 14
6 Groundwater Elevation Map, July 10, 1991 . 16
7 Site Plan and System Configuration 25
8 Schematic Diagrams of Air Sparging and Vapor Extraction Wells 27
9 Schematic Diagrams of Air Sparging and Groundwater Monitoring Wells 29
10 Schematic Diagram of Vapor Monitoring Points 32
11 Process Flow and Instrumentation Diagram of the Remediation
System 34
12 Times-Series Data Showing Dissolved Oxygen Concentrations in
Monitoring Wells 1, 5, 6, and 7 .. • 44
13 Time-Series Data Showing Dissolved Oxygen Concentrations in
Monitoring Wells 2, 3, 4, and 8 45
14 Time-Series Data Showing Dissolved Oxygen Concentrations in
Air Sparging Monitoring Wells 46
VII
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FIGURES (Continued)
Number Page
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Time-Series BTEX Concentrations in the Vapor Extraction System
Off-Gas
Time-Series Pressure Data From Monitoring Wells 1, 5, 6, and 7
Time-Series Pressure Data From Monitoring Wells 2, 3, 4, and 8
Time-Series Pressure Data at Vapor Monitoring Points 2, 22, 21
and 13
Time-series Pressure Data at Vapor Monitoring Points 8-11
Time-Series Pressure Data at Vapor Monitoring Points 1, 3, 4, and 5
Time-Series Pressure Data at Vapor Monitoring Points 17-20
Site Plan View Showing Pressure Data for the Monitoring Wells
and Vapor Monitoring Points on October 4, 1991
Site Plan View Showing Pressure Data for the Monitoring Wells
and Vapor Monitoring Points on October 14, 1991
Site Plan View Showing Pressure Data for the Monitoring Wells
and Vapor Monitoring Points on October 25, 1991
Time Series Oxygen Concentrations in the Soil Gas in Vapor
Monitoring Points 2, 22, 21, and 13
Time Series Oxygen Concentrations in the Soil Gas in Vapor
Monitoring Points 8 Through 11
Time-Series Hydrocarbon Concentration Data for Vapor Monitoring
Points 2, 22, 21, and 13
Time-Series Hydrocarbon Concentration Data for Vapor Monitoring
Points 8 Through 11
48
50
51
52
53
, , , 54
55
57
58
59
60
61
63
. ... 64
Vlll
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TABLES
Number
1 IAS System Operation Chronology . 35
2 Parameters Measured at the Denison Avenue Site 41
IX
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LIST OF ABBREVIATIONS AND SYMBOLS
AS air sparging
ASM air sparging monitoring well
ASW air sparging well
BP BP Exploration & Oil, Inc.
BTEX benzene, toluene, ethylbenzene,
xylenes
BUSTR Bureau of Underground Storage
and Tank Regulations
DO dissolved oxygen
EPA Environmental Protection Agency
ES Engineering Science, Inc.
FID flame ionization detector
FRP fiberglass reinforced plastic
hp horsepower
IAS In situ air sparging
i.d. inside diameter
MDL method detection limit
rag/kg milligrams per kilogram
MW monitoring well
NAPL nonaqueous phase liquids
ORD Office of Research and Development
OUST Office of Underground Storage
Tanks
PID
pptV
PSI
PVC
QA
QAPP
QC
RREL
RSD
SB
scfh
scfm
SVE
TDS
TPH
TRPH
TSE
UST
VEW
VMP
VOC
photoionization detector
parts per thousand by volume
pounds per square inch
polyvinyl chloride
Quality Assurance
Quality Assurance Project Plan
Quality Control
Risk Reduction Engineering
Laboratory
relative standard deviation
soil boring
standard cubic feet per hour
standard cubic feet per minute
soil vapor extraction
total dissolved solids
total petroleum hydrocarbons
total recoverable petroleum
hydrocarbons
Technical Site Evaluation
underground storage tank
vapor extraction well
vapor monitoring point
volatile organic compound
micrograms per liter
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ACKNOWLEDGEMENTS
This document was prepared for the U.S. Environmental Protection Agency (EPA),
Office of Research and Development, Risk Reduction Engineering Laboratory (RREL) under
Contract No. 68-C2-0108 by IT Corporation.
The design and field installation and operation of the in situ air sparging and soil vapor
extraction system was conducted by BP Exploration & Oil, Inc., and its contractor
Engineering Science. All data presented in this report were provided by Engineering
Science.
IT acknowledges the guidance and assistance provided by Anthony Tafuri, UST Research
Program Manager, Michael Grunfeld, RREL's Project Officer, Chi-Yuan Fan, RREL's
Work Assignment Manager for this Work Assignment, and Gerald Phillips and Gilberto
Alvarez of the EPA Region 5 Office of Underground Storage Tanks (OUST).
The cooperation and assistance provided by James Rocco and Peg Chandler of BP
Exploration & Oil, Inc., and Ray Banary, John Masterson, Greg Jones, and Lorri Beabes of
Engineering-Science are appreciated. Review comments were provided by Gilberto Alvarez,
OUST EPA Region 5; George Mickelson of the Wisconsin Department of Natural Resources;
and Raymond Roe, Ohio State Fire Marshal, Bureau of Underground Storage Tank
Regulations. Technical review and input were provided by Dr. Paul Johnson of Arizona
State University and Dr. Ryan Dupont of Utah State University.
This document was produced under the direction of Robert Amick, IT's Program
Director. Roy Chaudet served as the Work Assignment Leader. Tom Clark and Roy
Chaudet of IT Corporation, and Dr. Rick Johnson of the Oregon Graduate Institute of
Science and Technology are the principal authors. Jerry Day provided the editorial support.
Jim Molloy prepared the graphics, and Sherri O'Regan, Mildred Mills, and Connie Roth
prepared the manuscript.
XI
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SECTION 1
INTRODUCTION
BACKGROUND
Over the past 30 years, extraction and treatment was the most common technique used
to remediate hydrocarbon-contaminated groundwater. Although such "pump-and-treat" ap-
proaches are relatively simple, in many instances they do not effectively treat the dissolved
hydrocarbons and typically require significant expenditures for long-term operation and main-
tenance.
Several emerging corrective action technologies are being proposed and used at an
increasing number of underground storage tank (UST) sites across the nation; however, the
applicability and effectiveness of these technologies are not widely known. In situ air
sparging (IAS) in combination with soil vapor extraction (SVE) is one of these technologies.
Claims have been made that IAS can be used to successfully remediate hydrocarbon contami-
nation in the saturated zone. Many consulting engineers are also proposing the use of this
system to State regulators to address hydrocarbon contamination in both the saturated and
unsaturated zones. Unfortunately, there is a lack of substantive performance data to support
the claims of practitioners who propose using these systems. Consequently, performance
data are needed to determine the effectiveness and limitations of IAS systems at UST sites.
In addition, researchers (Ahlfeld, et al., 1994; Ji, et ah, 1993; Johnson, et ah, 1993; and
Johnson, 1993) have described conceptual and laboratory models that are used to better
understand the processes that determine the performance of IAS systems. Performance data
for IAS systems at actual sites are needed to compare with these models.
In response to this need, the U.S. Environmental Protection Agency (EPA) Office of
Research and Development (ORD) Risk Reduction Engineering Laboratory (RREL) UST
1
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Research Program has provided 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
Exploration & Oil, Inc. (BP) to identify a site at which an IAS system was being operated.
RREL provided assistance to BP and their contractor, Engineering-Science, in developing a
site-specific quality assurance project plan (QAPP) to define the quality of data and to detail
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.
This 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 (U.S. EPA, 1993). In
addition, the large variability in the chemical and process data that were noted over the
course of this study (approximately 2 years) prevented a definitive evaluation of the
performance of the IAS system at this site. A discussion of the data collected is presented in
the following sections. Although these data could not be used to evaluate the performance of
the IAS system at this site, 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. As part of these lessons, the potential strengths and
weaknesses of different subsurface monitoring parameters as indicators of IAS performance
will also be discussed. Because this purpose continued to evolve throughout the project, a
brief discussion of the site selection and project history will be provided for general context
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and to allow an understanding of what was known about IAS systems when the project
started.
SITE SELECTION AND PROJECT HISTORY
The West 65th and Denison Avenue site was selected in 1991 as a continuation of a
project designed to improve the leaking UST corrective action and permitting process in Ohio
that was initiated in 1989 by EPA Region 5, BUSTR, and BP. At the time BP selected the
site and the project was initiated, very little information was available on system design
features or appropriate monitoring parameters for IAS systems. In addition, the magnitude
of reported effects such as artificial mounding of groundwater during system operation and
the potential for off-site migration of dissolved hydrocarbons were not well documented but
were considered a major health and safety concern. Because of this concern, the relatively
low concentrations of dissolved hydrocarbons at this site were believed to pose a minimal
potential health risk if off-site contaminant migration were to occur.
BP's initial objectives in this evaluation were to test the effectiveness of the
technology to remediate this site and to collect data for a wide range of parameters to
determine which were most appropriate for evaluating IAS systems. EPA Region 5 was also
interested in observing how the technology performed in heterogeneous soils. It was
anticipated that the information collected, when summarized, would assist State Regulatory
Agencies in formulating guidance on IAS systems. BP decided not to conduct a pilot test
before installing this system because the start-up time for the project was short and a protocol
or procedure for conducting an effective pilot test had not been developed.
When the IAS system was installed, "best engineering practices" were used to design
the system. Based on preliminary soil and contaminant data, and past experience, an
oversized oil-free compressor and blower were used., The extraction and injection wells were
placed based on experience at other sites. The system was installed on only the eastern part
of the site mainly because of the higher contaminant concentrations observed; the western
part of the site served as a control because relatively lower levels of hydrocarbons in soil and
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groundwater were observed. BUSTR approved the installation of this IAS system on only
half of the site for the purposes of the evaluation.
Operational and monitoring data were collected to evaluate the impact of the IAS
system at this site. After the initial site and operational data had been collected, RREL
provided assistance to BP and their contractor Engineering-Science in developing a QAPP for
this site that would define the quality of the data required to conduct an RREL technology
evaluation at this site. RREL then reviewed the data provided by BP. That data formed the
basis for this report. The lessons learned from this site may be used to better understand the
difficulties of evaluating IAS systems and to provide input that can be used to design an
adequate technology evaluation program for these types of systems.
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SECTION 2
EXECUTIVE SUMMARY
An in situ air sparging (IAS) system installed and operated at the BP Exploration &
Oil, Inc. (BP) site in Cleveland, Ohio, was examined to determine IAS system performance.
The U.S. Environmental Protection Agency (EPA), Office of Research and Development,
Risk Reduction Engineering Laboratory (RREL) worked with the EPA Region 5 Office of
Underground Storage Tanks (OUST), and the Ohio State Fire Marshal, Bureau of
Underground Storage Tank Regulations (BUSTR) to evaluate the data provided by BP and
their contractor Engineering Science (ES). The data examined in this study were from the
IAS system that was being used to remediate the site.,
An immense amount of data were collected at this site; however, some of the
chemical data (e.g., BTEX, TPH) collected prior to the development of the QAPP did not
meet QC criteria. Also, the large variability in the chemical and process data during the
approximately 2-year study prevented a definitive evaluation of IAS performance at this site.
Even though these data did not allow an evaluation of the IAS system performance, they
provided valuable information that was used to develop lessons learned in designing
performance evaluations and interpreting performance data for IAS systems. Based on these
data, the following lessons were learned:
• It is difficult to monitor and evaluate the performance of in situ air sparging. The
data collected did not clearly define how well the IAS system was working due to
a number of factors discussed below.
• 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. Appropriate placement of monitoring
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points for collecting data representative of the IAS system being operated is as
important as the parameters measured.
• Contaminant indicators such as BTEX are often used as the primary indicators of
system performance. Based on the data from this site, BTEX cannot be solely
used to indicate system performance. Low and variable concentrations may
reflect "naturally-occurring" changes in concentration over time.
• 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.
Based on the lessons learned while trying to evaluate the performance of the IAS system at
the Denison Avenue site, the following should be considered in the experimental design for
future technology applications of IAS systems:
• 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."
• 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.
• 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.
• 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 extraction system
and if the vapor monitoring points reflect the influence of the IAS system.
• 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.
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• The parameters that will be used to monitor performance, the appropriate methods
for obtaining these parameters, and the method performance criteria need to be
established prior to the start-up of the system and used throughout the technology
application since the demonstration 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 improvements in soil/groundwater quality after the air sparging
system has been shut down. As part of the evaluation of the application and performance of
IAS, the final sampling and analysis should be conducted after a period of system shutdown.
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SECTION 3
PROCESS DESCRIPTION
TECHNOLOGY DESCRIPTION
The in situ air sparging (IAS) system at this site involves injection of clean air direct-
ly into the porous medium below the water table in an attempt to remove organic contami-
nants by a combination of volatilization and oxygenation to enhance aerobic biodegradation
processes. Hydrocarbon vapors are then recovered by use of soil vapor extraction (SVE).
Figure 1 presents a schematic diagram of the IAS configuration examined in this
study. 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.
Depending on the hydrogeology of the site, the contaminant distribution, and the
remediation goals, the IAS system design, the types of wells, well construction and place-
ment, and monitoring locations will be unique for each application. The types of well
construction and configuration include separate vertical injection and extraction wells as well
as dual or nested wells. 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 is described in Section 4.
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SITE CHARACTERISTICS
Site Description
The BP Site is an active gasoline retail service station located on the southwest corner
at the intersection of West 65th and Denison Avenue in Cleveland, OH. The site includes a
station building with two service bays and an office area as shown on the site map in Figure
2. North of the station building are three 10,000-gallon fiberglass reinforced plastic (FRP)
underground storage tanks holding different grades of gasoline and one 6,000-gallon UST
holding diesel fuel. The FRP USTs are connected to three dispenser islands by buried FRP
product lines. A 550-gallon used oil UST is located near the southwest corner of the station
building. The entire site is paved with asphalt.
Surrounding properties are largely residential, with light commercial development
along Denison Avenue and private residences on the side streets. According to the Ohio
Department of Natural Resources, two wells are located within 0.5 mile of the site.
However, these wells are not part of the city water supply system. Potable water for the
immediate area surrounding the site is provided by the City of Cleveland.
Physiographic Setting and Local Geology
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 site is located on the northeast crest of the ridge striking northwest-
southeast and sloping downward to the northeast and southwest. The soil texture of
subsurface soils varies widely throughout the site in the horizontal direction and even more
significantly in the vertical direction. Subsurface soils include sand, silt, and clay as well as
intermediate soils of these three end members. Figures 3 through 5 illustrate north-south and
east-west cross sections of the eastern portion of the site where the IAS system is located.
The cross sections illustrate the heterogeneous nature of the soils beneath the site. In
general, discontinuous and interfingered silt and silty clay lenses are shown from the ground
surface to a depth of approximately 15 feet. Interbedded and discontinuous low permeability
silts and silty clays overlie and in certain locations partially confine the more permeable
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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 feet from the surface.
Local Hydrology
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 feet. A hydraulic gradient of approximately 0.02 foot per
foot was interpreted from the groundwater contours based on Water-level data collected on
July 10, 1991. The reported groundwater elevations [Figure 6 (Engineering-Science, 1993)]
show the contours used to determine the hydraulic gradient. Over the duration of the
project, groundwater elevations varied initially by as much as +4 feet when the air sparging
system was started up and, with the exception of one well (MW-4) on November 13, 1991,
otherwise varied ±2 feet during system operation.
The water-bearing zone is a semi confined aquifer comprising predominately sands or
sandy silt that ranges from approximately 4 to 7 feet 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, semiconfme 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
It is difficult to monitor the remediation performance of IAS systems. Relatively few
studies to date have identified the limitations of conventional monitoring parameters for
evaluating IAS performance. The following discussion outlines the potential strengths and
weaknesses of a number of conventional subsurface monitoring parameters as indicators of
IAS performance. The parameters fall into two general categories. The first are soil and
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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.
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 is at least as important as the actual parameters that are used in the analysis of
system performance. If monitoring points are isolated from the remediation system in low
permeability soils* or connected to it by short-circuiting, then erroneous and non-
representative performance data will be generated. Monitoring points should be placed so as
to allow a better understanding of the structure and physical properties of the subsurface. In
that context, it is often desirable to use nests of monitoring points as well as conventional
monitoring wells. The performance data generated by those points will only be useful if it
can be interpreted in the context of the stratigraphy of the site.
Dissolved Hydrocarbon (BTEX1 Concentrations
Dissolved BTEX concentrations are an important indicator of remediation
performance. This is in part because groundwater BTEX concentrations are often the
parameter that drives the remediation activities. In addition, it is often the reduction of
BTEX concentrations that signals the end of remediation. At the same time, BTEX
concentrations at many sites are low and variable. This means that it is often difficult to
establish with certainty that statistically significant changes have occurred. As a consequence
of naturally occurring variations in concentrations, as well as the possibility of temporal
variations occurring during the sparging process, it is often difficult to assess IAS
performance using BTEX concentrations in groundwater during the active IAS process.
Nevertheless, as discussed below, in many cases BTEX concentrations can provide useful
information about sparging performance when examined with other process-related data.
If BTEX data are to be useful in monitoring improvements in groundwater quality, it
is important to understand any trends in concentrations as well as the natural variation in
17
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concentrations observed at the site. The primary way to establish this is to use historical
water quality data from the site. This is often difficult to do either because the data simply
do not exist, or because data quality is inconsistent over time. In general, one or two
samples (e.g., collected quarterly) prior to IAS start-up is not adequate to establish trends in
BTEX concentrations. To understand natural variations in concentrations, it will generally
be necessary to review data from at least a full year (e.g., collected monthly, quarterly, etc.)
prior to starting up the IAS system. Once again, in many cases those data will not be
available. In the absence of historical data, it may be possible to use data from a well
outside the treatment zone as a "control." For example, if it can be determined that a
groundwater well is located within the zone of contamination, but outside the zone of active
remediation, then changes in water quality in that well may make it possible to conclude that
changes in BTEX concentrations were due to natural variations. (This approach may also be
useful for monitoring changes in other parameters, e.g., dissolved oxygen and metals, which
are discussed below.)
Monitoring BTEX concentrations in groundwater within the treatment zone during
active IAS operation can be problematic because direct interactions between the sparge air
and the water in the monitoring well may produce unrepresentative concentrations in the
well. The significance of this can often be assessed by monitoring water quality in real time
in the well during IAS start-up. For example, dissolved oxygen concentrations in monitoring
wells often show dramatic increases within one day of system start-up. In addition, BTEX
concentrations may decrease sharply within a few days following IAS start-up. These
observations can be taken as indications that there is some level of interaction between the
sparge air and the water in the monitoring well."Therefore, it is generally preferred that IAS
be halted for some period prior to groundwater sampling. The period of IAS shutdown prior
to sampling is probably site specific. In general, if significant purging takes place prior to
sampling (e.g., > 10 well volumes), then a 24-hour shutdown prior to sampling is probably
adequate. (However, it is important to recognize that there is currently very little basis for
making these kinds of monitoring decisions.)
18
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If BTEX concentrations drop during active IAS, but show a rapid rebound in samples
collected after system shutdown, then it must be concluded that the water quality observed
during active I AS was not indicative of the system as a whole. On the other hand, if
concentrations continue to remain low for a period of weeks following cessation of sparging,
then it is likely that groundwater quality is substantially improved.
Dissolved Oxygen
Dissolved oxygen (DO) has become a widely used indicator of IAS performance.
Increases in DO shortly after system start-up (e.g., within 1 to 2 days) are interpreted to
indicate the extent to which air has moved laterally in the saturated zone (i.e., the radius of
influence). At the same time, it is important to recognize that those rapid changes probably
indicate direct interaction between the sparge air and the water in the well. As discussed
above, the implication of this is that water quality measured in that well during active IAS
will probably not be indicative of general water quality in the formation in the vicinity of the
well.
Increases in DO over the course of weeks or months following start-up are commonly
interpreted to indicate general oxygenation of the groundwater in the vicinity of the sparging
system. Data from numerous field sites indicate that there can be significant temporal
fluctuations in DO in wells during IAS. The reasons for these fluctuations are not well
known, but probably relate to either changes in background DO concentrations or to changes
in air distribution patterns within the subsurface during IAS. As with BTEX concentrations,
it is useful to have historical data from the site and/or "control" wells to monitor trends and
variability in DO concentrations. It is also important to insure that samples collected from
the monitoring wells reflect general water quality. In this context it may be necessary to shut
down the IAS system prior to sampling in order to collect a representative water sample.
When trends in dissolved oxygen data are interpreted, it is important to remember
that there are multiple methods of dissolved oxygen measurement. The most common
include the use of electronic meters (e.g., YSI and Leeds and Northrup) and field titration
kits (e.g., Hach kits). Not all electronic meters operate in the same way. For example,
dissolved oxygen is actually consumed by most sensors (e.g., YSI) during the measurement
19
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process. It is a characteristic of these meters that when the sensor is placed in a container of
water, a decreasing trend in DO levels is observed within a few minutes. Other electronic
meters, (e.g., Leeds and Northrup) do not consume oxygen and therefore will give a stable
reading over a long period of time. Field titration kits are probably the most accurate
measurement of DO in the low (< 1 mg/L) range. In any case, it is important to check that
the measuring device has been properly calibrated.
In addition to the measuring device, the sample collection protocol also can influence
the results. Some practitioners will perform in-well measurements where the sensor is
dropped down the well. Experience indicates that this approach produces highly variable
results (1-2 mg/L) because many practitioners like to continuously raise and lower the sensor
to avoid errors caused by oxygen consumption. The preferred approach is to set up an
aboveground flow-through cell in which the sensor is placed. Water is slowly pumped from
the aquifer (e.g., at 100-mL/min) and passed through the cell. When a continuous source of
water is provided, concerns about the influence of oxygen consumption by the sensor are
minimized.
Dissolved Metals in Groundwater
High concentrations of dissolved metals (e.g., iron and manganese) in ground water
are often associated with dissolved hydrocarbon plumes. As such, they often indicate high
oxygen demand and anaerobic conditions associated with an ongoing contaminant source. In
the context of IAS, dissolved metals can be used to assess the extent to which groundwater
is oxygenated by the sparging process. In general, it is anticipated that chemical oxidation of
dissolved metals is more rapid than biological oxidation; thus, it is expected that oxygen
introduced by sparging will be consumed by the metals prior to its use for the biodegradation
of the hydrocarbons. In that context, persistent high dissolved metals concentrations may
indicate that little oxygen is currently available for biodegradation. In addition, the
simultaneous presence of elevated metals concentrations and dissolved oxygen in groundwater
samples may indicate that the monitoring point is being influenced by the sparge air, and that
conditions in the well groundwater do not reflect those in the bulk groundwater.
20
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Two other potentially important implications of high dissolved metals concentrations
and oxygen introduced by sparging are precipitation of the dissolved metals and biofouling.
However, the significance of these in the context of long-term IAS performance is not
currently known.
Post-Remediation Soil Cores
As with BTEX concentrations in groundwater, hydrocarbon analysis of soil samples
after remediation is often used as an indicator of the effectiveness of remediation. It is
widely recognized, however, that a major difficulty with soils analyses is the large
uncertainties caused by spatial variability (e.g., samples collected adjacent to one another can
have dramatically different concentrations.) As a consequence, it is often difficult to
determine quantitatively the extent to which soils have been improved by the remediation
activities. This is particularly the case for soil samples collected below the water table,
where initial hydrocarbon concentrations may be low.
Vadose Zone Pressure
Unlike the soil and groundwater parameters discussed above, vadose zone pressure
measurements are relatively simple to make and are generally reliable. The primary purpose
for making them is to assess the effectiveness of the SVE system at capturing the sparge air.
In general, capture is assumed to take place if the SVE system is able to maintain a negative
pressure throughout the subsurface. In contrast, pressures above ambient values are an
indication that not all of the sparge air is being captured. Of course, positive pressures also
indicate the potential for off-site vapor migration. Practical experience indicates that at most
sites if soil vapor extraction system flow exceeds IAS airflow by a factor of 5 times, then the
SVE system can maintain measured soil pressures at subambient values. At the same time, it
is important to recognize that this does not completely eliminate the possibility that sparge air
will escape the SVE system. For example, if the soil at the site is layered (e.g., sands with
more-or-less continuous silt layers), then lateral spreading of the air in the groundwater zone
may carry the sparge air outside of the radius of influence of the SVE system before the
sparge air can reach the unsaturated zone.
21
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A more rigorous means of determining IAS air capture is the use of tracer tests. In
these tests, a tracer is added to the sparge air at a constant known rate. The percent of the
tracer recovered at the SVE system is calculated based on the concentration of the tracer and
the flow rate of the SVE air. Protocols are currently being developed for tracer tests to
evaluate recovery of injected air during I AS.
Off-Gas Hydrocarbon Concentrations
Hydrocarbon (BTEX) off-gas concentrations from the soil vapor extraction system
may or may not be useful indicators of IAS performance. If groundwater concentrations are
low (e.g., /xg/L), then the concentrations in the IAS air will be very low and it is likely that
it will not be possible to differentiate the contribution of the lAS-derived hydrocarbons from
the hydrocarbon concentrations coming from the vadose zone. (Simple calculations can show
that/zg/L hydrocarbon concentrations in groundwater would lead to sub-ppmV hydrocarbon
concentrations in the off-gas. In general, this will be below the detection limit of most off-
gas monitoring systems.) Nevertheless, IAS may still be improving groundwater quality in
those cases where off-gas concentrations do not increase.
If the IAS air directly contacts residual or free product, either above or below the
groundwater table, then it is possible that SVE off-gas concentrations will be significantly
increased. Remediation of the zone near the water table is an important aspect of IAS; thus,
increases in off-gas concentration as the result of sparging can indicate the success of IAS in
that zone.
Soil Gas BTEX Concentrations
As discussed in the previous section, sparging may increase vapor concentration in the
off-gas from SVE of the unsaturated zone. This could also result in increased BTEX
concentrations observed at soil gas monitoring points. It is also possible that sparging could
decrease concentrations in the soil gas. This could result from either increased flushing of
zones poorly flushed by SVE alone or increased biodegradation due to increased oxygen
delivery. As a consequence, it may be difficult to use soil gas BTEX concentrations to
assess IAS performance. In general, it will be necessary to consider the overall behavior of
22
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hydrocarbon vapor concentrations at numerous vapor monitoring points and in the SVE off-
gas as well as to consider in situ biodegradation if conclusions are to be drawn about IAS
performance based on hydrocarbon vapor concentration:s.
Soil Gas Oxygen Concentrations
Increased oxygen concentrations in soil gas samples resulting from IAS can be viewed
as evidence of increased airflow in the vicinity of the sampling location. This is particularly
the case in the vicinity of the water table where airflow is often poor because soil water
contents are higher. As discussed in the previous sections, the vicinity of the water table is
an important target for IAS remediation; thus, increased oxygen in that area can be
interpreted as a positive indication of sparging performance. However, it is difficult to
translate those data into quantitative measures of sparging performance without some measure
of in situ biodegradation rates.
Conclusions on Determination of IAS Performance
From these discussions it is clear that no single indicator will be sufficient to assess
IAS performance. In fact, the combination of all of the monitoring parameters may still not
be adequate to quantitatively determine the effectiveness of IAS. In general, the best
indicator of the effectiveness of remediation using IAS will be long-term improvements in
soil and/or groundwater quality after the sparging system has been shut down.
Unfortunately, these data do not provide much insight to sparging performance during the
period of active IAS. There are, however, several monitoring trends which should improve
future IAS performance monitoring. These include continuous monitoring of system
parameters using data loggers, practical performance assessment tools such as in situ
respiration tests and tracer tests, and potentially geophysical tools. Research and protocol
development in all of these areas is currently under way.
23
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SECTION 4
SYSTEM DESIGN AND OPERATION
As mentioned in the Introduction, when the IAS system at the Denison Avenue site
was designed and installed, IAS was just beginning to be applied at a limited number of sites.
At the time, little was known about how to design, operate, and monitor IAS systems. This
system was designed based on previous experience at a limited number of sites. As dis-
cussed later in Section 6, an important lesson learned is that relatively minor changes in
vertical and horizontal placement of wells and monitoring points can have a major impact on
the performance data collected.
SYSTEM DESIGN
The discussion in this section will include the well configuration, placement, con-
struction, the major system components, and operation of the IAS at this site.
Well Configuration. Placement, and Construction
The IAS system was installed only on the eastern half of the site and was designed in
two "remediation cells" consisting of one centrally located vapor extraction well with three
air sparging wells located in proximity to the vapor extraction well (Figure 7).
The air sparging well system includes 6 air sparging wells, 3 air sparging monitoring
wells, and 3 groundwater monitoring wells in the portion of the site being treated. The soil
vapor extraction well system includes 2 soil vapor extraction wells (VEW) and 25 vapor
monitoring points. As previously stated, no SVE or air sparging pilot tests were conducted
at this site prior to installation of the full system.
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Air Sparging Wells--
Six air sparging wells (ASW-1 through 6) were installed in the two remediation cells:
ASW-1, 2, and 3 in proximity of VEW-1; and ASW-4, 5, and 6 in proximity of VEW-2.
For discussion purposes, these two groups of wells will be referred to as "Cell 1" and "Cell
2." The saturated thickness of the water table aquifer (above the underlying clay) varies
from 4 to 7 feet. Because of this relatively thin aquifer, the screened interval of the air
sparging wells had to be installed at shallow depths below the groundwater table. Therefore,
the zone of influence of the sparging wells is likely to be limited.
As reported in soil borings (Engineering-Science, 1993), the tops of the air sparging
well screens in Cell 1 are approximately 1 to 2 feet below the groundwater table. The lower
portions of all of the well screens for ASW-1, 2, and 3 are placed in the underlying clay.
The upper portions of the well screens of ASW-1 and ASW-2 are placed in silt and silty
clay, and sandy clay (indicated as a silty sand in Figure 5). Because these sparging wells
were placed in soils with lower permeability, it is unlikely that they impacted much of the
surrounding soil. As indicated in soil borings and Figure 4, however, ASW-3 is placed in
the sandy soil and therefore was more likely to impact the more permeable soils.
For the air sparging wells in Cell 2, the tops of the air sparging well screens are
placed approximately 1 to 2 feet below the groundwater table. As with the other sparging
wells, the lower portions of all of these well screens are placed in clay. The upper portion
of the ASW-4 well screen is placed in silt, the upper portion of ASW-6 is screened in sand,
and the middle portion of the well is screened in silt. The upper portion of ASW-5 is
screened in sand (as shown in Figure 3) and was more likely to impact the more permeable
soils than ASW-4.
A schematic of the air sparging well is shown in Figure 8. The wells were con-
structed of 5-foot sections of 4-in. inside-diameter (i.d.) Schedule 40 PVC continuous-wound
well screen. The well screen gap is a 0.010-inch opening typically 5 feet in length. The
bottom of the screened interval was attached to a 1-foot section of Schedule 40 PVC riser
with a bottom cap. The 1-foot sump at the bottom of the well screen collects any
precipitated matter or fine-grained soil that may accumulate and plug the well screen. The
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top of the well screen was flush threaded to a Schedule 40 PVC riser that extends to within 8
inches of surface grade. The annular space of each well was filled with a sand filter pack to
1 foot above the screened interval. Twelve to 18 inches of bentonite pellets were provided to
seal the top of the sand pack, and the remaining annular space was grouted to within 12
inches of surface grade.
Air Sparging Monitoring Wells--
Three air sparging monitoring wells (ASM-1, 2, and 3) were used in conjunction with
existing groundwater monitoring wells (MW-4, 5, and 6) to monitor the groundwater in
proximity to the air sparging wells (see Figure 2). Wells ASM-1 and 2 are close to ASW-2,
and the top of the well is screened approximately 4 feet above the groundwater table. As
shown in Figure 4, ASM-2 is screened in lower permeability silty sand. Well ASM-3 is
located close to ASW-5 and ASW-6, and the top of the screened interval is approximately 4
feet above the groundwater table in the more permeable sand (see Figures 2 and 3).
The air sparging monitoring wells were constructed of 10-foot sections of 2-in.-i.d.
Schedule 40 PVC well screen with 0.010-inch slots (Figure 9). The screened interval was
flush threaded to a Schedule 40 PVC riser that extends to within 8 inches of the ground
surface. All three ASM wells encountered water at 19 feet below surface grade, and the
bottom of the screened interval extends to 25 feet below surface grade. The annular space
was filled with a sand filter pack to 1 foot above the screened interval, and was then sealed
with 2 feet of bentonite pellets on top of the sand pack. The remaining annular space was
filled with grout, and each well was protected with a locking well cap.
Groundwater Monitoring Wells--
Three groundwater monitoring wells are located in proximity to the treatment zone:
MW-4, MW-5, and MW-6 (Figure 7). The most upgradient groundwater monitoring well is
MW-4, and the downgradient well is MW-6. Well MW-5 is approximately in the middle of
the treatment zone on the northern edge of cell 1 in proximity to ASW-3. As reported by
Engineering-Science (1993), MW-4 is screened at approximately 3 feet above the
groundwater table and extends to a depth of 12 feet below the groundwater table. MW-5 is
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screened at approximately 6.5 feet above the groundwater table and extends to a depth of 8.5
feet below the groundwater table near ASW-3. MW-6 is screened 5 feet above and below
the groundwater table primarily in sand.
The groundwater monitoring wells were constructed of 10- to 15-foot sections of 4-
in.-i.d. Schedule 40 PVC well screen with 0.010-inch slots (Figure 9). The screened interval
of the wells straddles the groundwater surface. The well screen was capped at the bottom
and flush threaded to a Schedule 40 PVC riser that extends to within 8 inches of surface
grade. Each monitoring well is secured with an expandable locking well cap. The annular
space between the PVC and the borehole walls was filled with a sand filter pack to 1 to 2
feet above the top of the screened interval. The annular space above the sand pack was then
sealed with 1 to 2 feet of bentonite pellets and grouted to within 12 inches of surface grade.
Soil Vapor Extraction Wells-
The vapor extraction wells are used to remove hydrocarbons from the vadose zone
when negative pressure is applied to the well. The vapor extraction wells are also used to
monitor vacuum/pressure, hydrocarbon concentrations in soil vapor, airflow, and tem-
perature.
„ Two vertical wells (VEW-1 and VEW-2) were installed on the eastern part of the site
in July and August 1991 as part of the IAS system being demonstrated at this site. As
reported, these wells were intended to capture air injected from the three sparging wells on
each cell. To address the residual contamination in the vadose zone, additional wells were
installed in November 1992: well VEW-3 in the far southeastern corner of the site and a
horizontal vent (VEW-4) in the northern part of the site. These additional wells (VEW-3 and
4) were not part of the IAS system being evaluated at this site and will not be included in
this discussion. A schematic of the vertical soil vapor extraction wells (VEW-1 and VEW-2)
is shown in Figure 8.
The vapor extraction wells were constructed of 10-foot sections of 4-in.-i.d. Schedule
40 PVC well screen. The well screen consists of continuous-wound PVC gapped to 0.010
inch. The screen was flush-threaded to a Schedule 40 PVC riser that extends to within 8
inches of surface grade. The annular space of each well was filled with a sand filter pack to
30
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2 feet above the screened interval. Eighteen inches of bentonite pellets were provided to seal
the top of the sand pack, and the remaining annular space was grouted to within 12 inches of
surface grade. A 2-in.-i.d. pipe connects each vapor extraction well to a common vacuum
header made of 2-in.-i.d. Schedule 40 PVC. The vapor extraction wells extend one foot into
the groundwater to allow for seasonal fluctuations of the groundwater table. The vapor
extraction wells were reported to be screened across silty clays, silts, clayey silts, and clay
into the very upper portion of the more permeable underlying sand unit. The influence of
seasonal groundwater elevation and possible upwelling as a result of initial start-up of the air
sparging system are not known.
Vapor Monitoring Points—
Twenty-five vapor monitoring points (VMP-1 through VMP-25) were installed on site
to monitor vacuum/pressure and vapor chemistry across the site. Each VMP is constructed
of 15 feet of 1-inch Schedule 40 galvanized pipe. The pipe was driven into the ground with
an air-driven jack hammer until the top of the pipe was approximately 6 inches below surface
grade (Figure 10). The bottom of most VMPs was set at approximately 15.5 feet below
surface grade (approximately 4 feet above the surface of the water table). VMP-23, 24, and
25 were set approximately 6 feet below the surface. A bolt placed in the bottom of the pipe
was then driven out to allow air to be removed from the space at the head of the pipe. Each
VMP is capped with a brass valve and surrounded with a 9-inch-diameter flush mount
manhole. The VMPs were all placed at a given depth in soils with different permeability.
Because of this placement, the VMPs may or may not have been in pneumatic contact with
the IAS or SVE system (see Section 6).
System Components
The process flow, instrumentation, and system components for the IAS system are
shown in Figure 11. The air sparging portion of the system consists of six air sparging wells
connected by a rubber-walled air hose to a 15-horsepower (hp), 100 percent oil-free air
31
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f GROUND SURFACE
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Figure 10. Schematic Diagram of Vapor Monitoring Points
(Engineering-Science, 1993).
32
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compressor (Quincy QRDS-15). The vapor extraction portion of the system consists of four
vapor extraction systems manifolded to a 5-horsepower regenerative blower (Rotron Model
707). The selection and sizing of the compressor and blower were based on the soil and
contaminant data from the initial assessment and the previous experience at other sites.
As shown in Figure 11, each of the air sparging wells has flow control valves, pres-
sure regulators, and pressure gauges. Each SVE well has a flow control valve, sampling
port, and air velocity and temperature ports designed for use with a thermal anemometer. A
knockout tank was installed to remove moisture from the soil vapor recovered by the vapor
extraction wells. No water was reported to have been collected in the knockout tank during
system operation.
SYSTEM OPERATION
Table 1 presents a chronology of the operation of the IAS system from 1991 to 1993.
The SVE part of the remediation system began operation without sparging on
September 3, 1991, and operated continuously for the duration of the evaluation. Negative
pressure (typically in the range of 30 to 50 inches of water below atmospheric pressure) with
a reported air extraction rate of approximately 50 to 80 standard cubic feet per minute (scfm)
was applied to the soil vapor extraction wells (VEW-1 and VEW-2), and the subsurface
response was monitored.
The air sparging part of the remediation system was first activated on October 7,
1991. The full IAS system operated continuously from October 7, 1991, to February 26,
1992. Positive pressure (60 to 110 psi at the supply header and 3 psi at each wellhead) with
very low reported air injection flow rates in standard cubic feet per hour (scfh) was applied
to the air sparging wells (ASW-1 through 6). By January 1992, the BTEX concentrations in
the ground water monitoring wells in the treatment zone (MW-4,MW-5, and MW-6) had
decreased to below laboratory method detection limits. After February 26, 1992, the air
sparging system was operated intermittently for the remainder of the evaluation in an attempt
to enhance SVE operation by pulsed injection of air into the srabsurface. Section 6 presents a
discussion of the operating pressures.
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35
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SECTION 5
SAMPLING AND ANALYSIS PROGRAM
Representative samples of soil, groundwater, and soil vapor are collected and
analyzed over the course of the technology application/field evaluation to assess the
performance of the IAS system at the Denison Avenue site. The IAS system operating
parameters are also monitored to ensure that the system is operated in accordance with
design specifications and to evaluate system performance. Sections 3 and 4 of the Quality
Assurance Project Plan (QAPP) present detailed sample collection and analytical procedures
for these matrices and the process system monitoring methodology. A summary of the
sampling, analytical, and system monitoring methodology used during the technology
application is presented in this Section.
SAMPLE COLLECTION AND ANALYSIS METHODOLOGY
Soil Sampling and Analysis
Soil samples are collected and analyzed to determine concentrations of BTEX, TPH,
and/or TRPH. A split-spoon sampler is used to collect samples from a soil boring located
within 3 feet of the initial and previous soil borings. The actual collection procedure
consisted of lowering the split-spoon device to the bottom of the boring and driving the split
spoon 2 feet into the formation. Once the sample is collected, the device is raised and the
barrel is opened and placed on a sheet of plastic. Initial observations are noted and the
sample is then split in half laterally with a knife. The sample is collected at a depth that, is
based on the results of the field headspace screening for volatile organic compounds (VOCs).
36
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A clean stainless-steel spoon and a pair of clean, dedicated surgical gloves are used to
transfer the soil sample from the sheet of plastic to the sample container. The soil samples
are maintained at 4°C during storage and shipment to the laboratory.
Soil samples are analyzed for BTEX by using SW-846, Methods 5030/8020 (purge
and trap/GC-PID); for TRPH using SW-846 Method 9071 followed by analysis using EPA
Method 418; and for TPH using SW-846, Methods 5030/8015 modified (California DHS) for
gas and diesel fractions.
Groundwater Sampling and Analysis
Groundwater samples are collected from the monitoring wells with a dedicated
disposable bailer. Sample bottles are filled from the bailer. Samples are preserved with HC1
and maintained at 4°C during storage and shipment to the laboratory. Groundwater samples
are analyzed for BTEX using SW-846, Methods 5030/8020, and for TPH using SW-846,
Methods 5030/8015 modified (California DHS) for gas and diesel fractions.
Soil Vapor Sampling and Analysis
Soil vapor samples are collected from the vapor extraction wells to monitor vapor-
contaminant concentrations and to calculate contaminant removal rates, and from the vapor
extraction system effluent stack to monitor organic emissions from the system. Vapor
samples are collected in new Tedlar air sample bags that have been properly purged with soil
vapor. The Tedlar bag samples are stored in a cool area out of direct sunlight until
transported to the laboratory.
Soil vapor samples are analyzed for BTEX and TPH (as toluene) by using modified in
series SW-846 Methods 5030/8020-8015 (purge and trap/GC-PID/FID). These methods are
modified to include the injection of gas phase samples into the purge and trap accessory for
analysis and the initial calibration acceptance criteria of <20% relative standard deviation
(RSD).
37
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SYSTEM MONITORING METHODOLOGY
Soil Vapor Flow and Temperature
Soil vapor flow rate and temperature measurements are collected to determine the
volumetric flow rate of air injected and extracted from the subsurface. These measurements
are reported in standard cubic feet per minute (scfm) at the monitoring points (vapor
extraction wells and vapor extraction stack effluent) by use of a Dwyer® Thermal
Anemometer. Airflow and temperature are measured by inserting the probe of the
anemometer to the midpoint of the system piping at the monitoring point.
System Vacuum/Pressure Measurement
To determine the radial extent influence of the IAS system, vacuum/pressure
measurements are conducted at the SVE wells, VMPs, MWs, and ASWs. The measurement
methodology consists of attaching Magnehelic® gauges to the wells and recording the
vacuum/pressure. A tube placed on the appropriate gauge is taken to each monitoring
location, where the gauge is connected to a brass nipple and valve configuration. The valve
is opened and the system is allowed to equilibrate. The vacuum/pressure reading is then
recorded from the Magnehelic® gauge.
Oxygen/Carbon Dioxide Measurement
Oxygen/carbon dioxide (O2/COJ readings are conducted at VMPs and VEWs. Before
the O2/CO2 data are obtained, the monitoring point is purged of approximately three- to five-
pore volumes of air with a ',4-horsepower vacuum pump. After the monitoring point has
been purged, the valve is closed and the pump turned off. Tygon® tubing is used to connect
a Gas Tech Tor® O2/CO2 indicator, Model 32520X, to the monitoring point brass nipple.
After the instrument is connected, the valve is opened and the CO2 reading is recorded. The
instrument is then switched to the O2 mode, and the O2 reading is recorded.
38
-------
Dissolved Oxygen Measurement
A YSI® Dissolved Oxygen Meter, Model 5 IB, is used to collect dissolved oxygen
data. Dissolved oxygen readings are taken by lowering the DO probe into the well. The
probe is raised and lowered about 1 foot per second to manually stir the water for several
minutes. The probe is then allowed to stabilize, and the dissolved oxygen reading is
recorded.
Soil Gas Volatile Organic Compound Measurement
Volatile Organic Compound (VOC) data are collected from the monitoring points
(VMPs and VEWs) and the SVE stack to provide raw data on system performance and
concentrations in the vadose zone. To collect VOC readings, the tip of the Photovac
Microtip™ photoionization detector is inserted into the effluent of the vacuum pump during
purging of the monitoring point in preparation for O2/CO2 readings. The Microtip™ is
allowed to stabilize, and the reading is recorded.
39
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SECTION 6
LESSONS LEARNED ABOUT IN SITU AIR SPARGING
AT THE DENISON AVENUE SITE
OVERVIEW
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 (IAS). A
tremendous amount of data were collected during the study. Even so, the data do not
provide a clear picture of how well the IAS process was working. The parameters measured
at the site are listed in Table 2. Those parameters which provide useful insight will be
discussed below. The discussion will also include comments on why some parameters are
not useful. These discussions will focus on what was learned at the site and how it can be
used to improve monitoring at other sites.
As is the case at most sites, BTEX concentrations in groundwater are the indicator of
primary interest. However, at this site as at many sites, groundwater concentrations are low
and highly variable (i.e., temporal variations as large or larger than the average value). This
makes BTEX concentrations a difficult parameter to use in assessing performance. Indeed,
other water quality parameters, such as dissolved oxygen, indicate that water quality from the
monitoring wells was quite variable during the sparging process. These data suggest that
changes in any water quality parameter measured during the IAS process may not reflect
system performance.
Another indicator commonly used for assessing sparging performance is BTEX
concentration in the SVE off-gas. At this site the SVE system was started up approximately
one month prior to IAS. When IAS was initiated, there was no significant increase in off-
gas concentrations from either of the SVE wells. This suggests that the IAS system did not
access any large zones of contamination (e.g., a zone of gasoline smeared below the water
40
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TABLE 2. PARAMETERS MEASURED AT THE
DENISON AVENUE SITE
Groundwater Parameters
BTEX in groundwater
TPH in groundwater
Dissolved oxygen in groundwater
BTEX concentrations in SVE off-gas
Total metals in groundwater
Temperature of the groundwater
pH of the groundwater
Groundwater levels
Soil Gas Parameters
Respiratory gases in SVE off-gas
Hydrocarbon concentrations in soil gas
Respiratory gases in soil gas
Pressure of the soil gas '
System Parameters
SVE airflow
IAS airflow
41
-------
table, or product trapped near the water table.) In fact, the data may indicate that off-gas
concentrations actually dropped slightly when the IAS system was turned on. The observed
changes in off-gas concentrations may be due to a number of factors such as changes in
airflow patterns and contact with sparged air contaminant.
The subsurface pressure data once again present a complicated picture. Pressure data
were collected from two types of wells at the site: conventional monitoring wells (MWs) and
soil vapor monitoring points (VMPs). They each tell a somewhat different story of what was
happening at the site, which can be largely attributed to the placement of vapor monitoring
points in soils of different permeability. In general, the monitoring wells show the soil gas
to be at greater than atmospheric pressure whenever the IAS system is in operation. The
vapor monitoring points, on the other hand, show a portion of the site to be under negative
pressure and part of the site to be under positive pressure. With continued sparging, the
portion of the site under positive pressure appears to increase.
Other operational parameters measured at the site were less useful than might have
been expected. These included O2 and CO2 (respiratory gases) in both the off-gas and the
vapor monitoring points. This was probably the case both because of unexplainable
variations in the parameters from measurement to measurement and differences between the
field and laboratory measurements. The same problems were encountered with much of the
hydrocarbon data. In general, these data were taken more frequently at this site than at most
sites. However, it is likely that to explain the observed changes it would have been
necessary to make "continuous" measurements to better assess the time frames of the
changes. This is likely to be true for nearly all of the parameters from the site.
Groundwater temperature and pH did not show much change over the course of the
project, and as a consequence did not provide much insight at this site. However, they are
relatively easy to collect and could have provided useful information under other
circumstances. Other water quality parameters, especially rnetals concentrations, are
potentially quite useful. In this regard, measurement of dissolved species such as Fe2"1" and
Fe3+ would be more useful than total metal values (e.g., total iron).
42
-------
As is often the case with sites such as this one, the historical data collected from the
site are often incompatible with more recent data, do not meet current quality assurance
guidelines, or simply do not exist. As a consequence, It is difficult to assess trends and
variability of the parameters at the site. In general it is important to collect enough
background data as part of the current project to allow Changes in system parameters to be
identified clearly. This is often not possible due to time constraints. However, it should be
recognized that this can seriously limit any assessment of remediation performance.
As a final introductory note, it is important to reiterate the critical role played by the
placement of monitoring points within the stratigraphy of the site. The Denison Avenue site,
like many sites, has a complex stratigraphy with soils of different permeability. That fact
makes interpretation of the data difficult. In that context, the types and placements of the
monitoring points have played a critical role in the interpretation of the data.
BRIEF DISCUSSION OF SIGNIFICANT SYSTEM PARAMETERS
Dissolved Oxygen in Groundwater
The dissolved oxygen (DO) data (Figures 12 through 14) from the site provide an
interesting insight into the complexity of the air sparging process. (In these and all
subsequent figures, the dashed lines are not intended to imply continuity between points, but
were added to aid in visualization.) The remediation system was designed such that
monitoring wells 1 through 3 and 7 through 8 would fall outside the treatment zone. The
DO data generally indicate that those wells are at background levels of DO. (The values
generally fluctuate around 1 mg/L, which is the practical limit of the measurement.) In
contrast, data from MW-5 and MW-6 and ASM-1 and ASM-3, all of which were anticipated
to be within the remediation zone, show DO values which fluctuate from essentially zero to
nearly 8 mg/L. The pattern of these changes is erratic and the reasons for the changes
cannot be inferred from other system parameters. However, there is no basis to conclude
that these data are not valid. Similar fluctuations have been observed at other sites. As
discussed above, the observed variations in DO make it difficult to draw reliable conclusions
about changes in water quality during the sparging process. Furthermore, it is not clear how
43
-------
i
I
1
10
8
6
4
2
0
8
6
4
2
0
8
6
4
2
0
8
6
4
2
MW-1
:
***** *•••-*
*' »
"
t\
/ \
i ^
MW-5
/", '\
/ '.,' "*i MW-6
/ »' »
• i i n
'it IM
f i rut •
n i/ i /»
. .
0
SPARGING ON
MW-7
50
100 150 200
TIME (DAYS)
250
300
Figure 12. Times-series data showing dissolved oxygen concentrations
in monitoring wells 1, 5, 6, and 7.
44
-------
10
9
8
7
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
9
8
7
6
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7
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SPARGING ON
MW-2
v_*
^. V•
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l»
MW-4
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l\
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It
I I
I I
1 I
I I
I I
I ' •
•>*
MW-8
0
50
100 150
TIME (DAYS)
200
250
300
Figure 13. Times-series data showing dissolved oxygen concentrations
in monitoring wells 2, 3, 4, and 8.
45
-------
3"
S
§
p
X
O
D
>J
O
VI
g
10
9
^
8
7
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Ji? v-"\ >'*.-'*' ~~*«-""»*' ;
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A
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1 ? 1 1 \ ' b »
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!' >'
' !»
1) •
_ *
' t
' •
/
100 150
TIME (DAYS)
200
250
300
Figure 14. Times-series data showing dissolved oxygen concentrations in
air sparging monitoring wells.
46
-------
well water quality can be assessed even after IAS has stopped. In this context, these data
suggest that continuous monitoring of DO at one or more locations would be extremely
useful in helping to understand the observed changes. A standard method, however, has not
been developed that provides stable and accurate DO measurements over a long period of
time (see Section 3).
MW-4 was originally designed to lie near the southwestern edge of the treatment
zone. However, based on the DO data, it is likely that MW-4 is outside the IAS treatment
zone. This is not surprising considering the very thin aquifer zone in which the sparging is
being carried out.
Hydrocarbon (BTEX1 Concentrations in Groundwater
BTEX data from the site generally show concentrations which are low (/tg/L range)
and quite variable (see Appendix C). In addition, there is limited data available prior to
system start-up. This is further compounded because the historical data from this site do not
meet the QC criteria for comparability. These low and variable contaminant concentrations
in groundwater and lack of data comparability make it impractical to evaluate IAS
performance based just on the dissolved BTEX concentration data. Nevertheless, the BTEX
data, taken together with other system data, do provide some insights into the sparging
process at the site. In particular, for those wells which fall outside of the IAS treatment zone
(e.g., MW-2), temporal changes in BTEX concentrations probably reflect "natural"
variability in the groundwater. In that context it is significant to note that relative changes in
concentration in those wells is on the same order as the wells within the treatment zone (e.g,
MW-5). In addition, the observed temporal variations in DO concentrations in the wells
suggest that water quality within the wells was being affected by processes which are
currently not well understood. These factors further complicate the interpretation of the
groundwater BTEX data.
Hydrocarbon Off-gas Concentrations
The laboratory-measured BTEX concentrations in the SVE off-gas from the site
(Figure 15) are useful in that they suggest that no significant sources of mass were accessed
47
-------
z
I
2000
1500
1000
500
SPARGING OFF
*
'"' \
t I '.
8 o
PQ
50
SPARGING ON
VEW1
V '""\
\ /
*.'. '•
• *•
ft I »
/' ' *
• I / \
I /
M
\l
A
VEW2
\ /
• x
10 20 30 40 50
TIME (DAYS)
60
70 80
90 100
Figure 15. Time-Series BTEX Concentrations in the Vapor Extraction System Off-Gas.
Concentrations are in parts per million by volume.
48
-------
by the addition of IAS. As mentioned above, if significant zones of pure product had been
contacted by the sparge air, these zones may contribute to changes in off-gas concentration.
Given the very low flow of the IAS system (0.2 to 5 scfh for the sparge wells and 50 to 80
scfm for the vapor extraction wells), however, it is also possible that any changes in off-gas
concentrations due to IAS could have been masked by mass coming from the unsaturated
zone. It is important to reiterate that, given the very low concentrations of BTEX in the
groundwater, it would in general not be possible to observe increases in off-gas
concentrations due to sparging of a dissolved BTEX plume. Thus, the off-gas data are not
likely to provide any indication of improvements in dissolved-phase plumes at this site.
Time Series Pressure Data
The time series pressure data from the monitoring wells (Figures 16 and 17) show
that most of the wells on site (MW-1 through 6, and MW-8) were at a positive pressure
relative to the atmosphere during most of the IAS process. These data can be contrasted to
MW-7, which appears to be isolated from both the SVE and IAS systems. The conditions
which led to these changes are currently not understood.
The time series pressure data from the vapor monitoring points (Figures 18 through
21) are more difficult to interpret than the monitoring well data. Many of the monitoring
points show the influences of both the SVE system and the IAS system, although the
magnitudes of the positive pressures are generally less than for the monitoring wells. This
may be the result of the VMP placement in low permeability soils.
Pressure data from vapor monitoring points at increasing distance from VEW-1 are
shown in Figure 18. VMP-13, the farthest of those points from VEW-1, shows little effect
of either SVE or IAS. The other three points all appear to show the influence of both the
SVE and the IAS. Pressure data around VEW-2 are shown in Figures 19 and 20. Vapor
monitoring points 1, 3, 4, 5, 8, 10, and 11 all appear to show the influence of both SVE and
IAS. VMP-5, because of its proximity to ASW-3, shows a dramatic influence of the air
sparging well. VMP-9 is interesting in that it appears to be strongly influenced by the
49
-------
100 150 200
TIME (DAYS)
250
300
Figure 16. Time-Series Pressure Data From Monitoring
Wells 1, 5, 6, and 7.
50
-------
50
40
30
20
10
0
50
40
30
20
10
o? 0
I50
£ 4°
i 30
0 20
g
g 10
B o
I-IQ
cu
40
30
20
10
0
-10
SPARGING ON
MW-2
/V*..
k *. » «*
MW-3
MW-4
MW-8
A/ - -—
< i
v- \
0
50
100 150 200
TIME (DAYS)
250
300
Figure 17. Time-Series Pressure Data From Monitoring Wells
2, 3, 4, and 8.
51
-------
s
1
§
n
u
CO
3
p«
10
5
0
-5
-10
-15
10
5
0
-5
-10
-15
1 A
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-5
-10
-15
10
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-5
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-20,
n\ J
r+\i\ f\ ... .
*,fl \'t 1 ^. , ( \ ^ •* \ B' l ~ •
- ^ / ^ ' V---»"^^^-Jl»-»
-,'L..V
VMP-2
-
j- //' t" —
-^j^—"
L
VMP-22
*•»/•» '»
/* \Pl --^ . ----m^-* 7
j-..^: • ' ^ iw/ "-—
^ ' »
_
VMP-21
SPARGING ON
^-.."** — - *" ^.'-^.
ii
VMP-13
100 150
TIME (DAYS)
200
250
300
Figure 18. Time-Series Pressure Data at Vapor Monitoring Points
2, 22, 21, and 13.
52
-------
I
^
8
I
1
10
5
-5
-10
-15
1 A
10
5
-5
-10
-15
1 A
10
5
-5
-10
-15
1 A
10
5
-5
-10
-15
on
»* \i • V 1___*'VV ,*-* j-
i • • » -•
\ F '
SPARGING ON , VMP-8
'' v>/ \ i* \ T
TX i r i •' r
. T 7 k»- -*J-
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-f » , '
L" <• J,;\ '"• *-v VMP'9
%j ' 7'''''V*m\
» ^" ^ k' *-•:-..••-.-
• *
VMP-10
^ ••**•»
..•• • ^ • f~ **• jp1^ «. * ^
^ ... Vl- - -
VMP-11
TIME (DAYS)
Figure 19. Time-Series Pressure Data at Vapor Monitoring
Points 8-11.
53
-------
10
0
-10
10
0
-10
< 10
^
0
-10
-20
30
20
10
0
-10
11
11
11
u
n
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-2
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SPARGING ON
" •» '»
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•' *»•»
M Ji ii
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fc»
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• II
III
III
ilt
1 / »
VMP-1
VMP-3
fc. - - -» • ir* h- • •»•
VMP-4
VMP-5
^---^-••••Ir ••
.
0
50
100 150
TIME (DAYS)
200
250
300
Figure 20. Time-Series Pressure Data at Vapor Monitoring
Points 1, 3, 4, and 5.
54
-------
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<
£ '
o
r^
1
w
^5
ft
1U
5
n
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-10
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- - • '''•-.••...'•• •• '
VMPr18
- :
Tl^J- *t^ u-m „, — "i.- --V% -• J
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VMP-19
- : ' '
'
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^^fc.."' •• -•- • . * • » * -•
-
VMP-20
-
0
50
100 150
TIME (DAYS)
200
250
Figure 21. Time-Series Pressure Data at Vapor Monitoring
Points 17-20.
55
300
-------
vapor extraction well, but over time the pressure builds (presumably due to IAS) until it is
actually at a positive pressure. Cessation of sparging causes the pressure to drop (~day
180-190). These data reflect the complex interactions between spatial heterogeneity and
airflow at the site.
Data from the western portion of the site (Figure 21) show that the vapor monitoring
points are relatively isolated from both the SVE and IAS systems.
Area] Pressure Data
The area! pressure data provide two important insights into IAS performance at the
site. First, the two different types of wells used to collect the data give different pictures of
SVE/IAS performance. Second, the airflow patterns in the unsaturated zone appear to
change over the course of several weeks of sparging at the site. Prior to IAS start-up, both
the monitoring wells (MW) and the vapor monitoring points (VMP) show that virtually the
whole site is under the influence of the SVE system (Figure 22). Approximately one week
after start-up (Figure 23), all of the monitoring wells are at greater than ambient pressure, as
are many of the VMPs. Eleven days later (Figure 24), the monitoring wells are still all at
positive pressure, and most of the VMPs are now also at a positive pressure. These data
suggest that locally within the subsurface the SVE system may not be able to capture all of
the IAS air. These data point to the need to better characterize airflow both at the outset of
IAS and during the process. Probably the best way to accomplish this is to conduct tracer
tests during the course of SVE and IAS operation. Protocols for tracer tests to evaluate
airflow during SVE and IAS are currently being developed by EPA.
Oxygen Concentrations in the Soil Gas
Figures 25 and 26 show time-series oxygen concentrations in several vapor
monitoring points around soil vapor extraction wells VEW-1 and VEW-2, respectively. A
number of the points show temporal variations which are difficult to explain (e.g., VMP-9);
however, several of the points show interesting trends. VMP-13 does not show any
increases in oxygen concentration with time. This is consistent with the pressure data at that
point which suggest that the point is relatively isolated from both IAS and SVE. At the same
56
-------
O
mw2
+0.3
mwl
-0.4
o
mw6
-3.0
mw5
-6.7
O
mw7
-0.5
mw4
-0.5
,-3.0
vmp!2
,-5.4
vmpll
vmp9
-2.3
.-1.2
vmp?
-5.1
vmplO
vmp8
1-3.3
,-0.3
vmp20
.-0.6
vmp!9
.-0.4
vmplS
vmp5
'-7.5
-8.6
»-4.9
vmpi
-0.6
«vmnl7
-1.0
|Vmpl6
1.4 -
, vmplS vmp!4
-6.5
vmp3
,-4.l'
vmp22
-3.7.
vpm21
-1.5
vmc!3l
Figure 22. Site Plan view showing pressure data for the monitoring wells and
vapor monitoring points on October 4, 1991. Pressure is in inches of water.
57
-------
o
mw2
+5.8
mwl
+6.9
o
mw6
+12
mw3
+9.5
O
raw?
+0.2
mw4
+0.4
,-0.5
vmp!2
,-1.4
vmpll
-0.3
vmplO
vmp8
h-1.2
,+0.6
vmp20
.+0.3
vmpl 9
+0.3
vmpl 8
.-3.1
vmp?
,
vmp6
+8.6
vmpS
'+22
-0.9
vmp2f
-1,0
vmpl
-0.2
,vpml7
-0.6
iVmplo
-1.2 l-
« vmplS vmpl4
+0.71
vmp3
, «
.-1.0
vmp22
+ 1.1,
vpm21
-0.9
vmol3«
vrap4
Figure 23. Site plan view showing pressure data for the monitoring wells and
vapor monitoring points on October 14, 1991. Pressure is in inches of water.
58
-------
o
mw2
+16
mwl
+18
°mw3 +24
o
mw7
+0.3
NA
vmp20
,+0.3
vmp!9
,+0.1
vmplS
O
mw6
+32
mw5
+36
mw4
+1.6
,+0.8
vmp!2
,+.6
vmpll
vmp9
-16
.+4.0
vmp?
vmpfi
+20
vmpS
'+40
+3.s
vmplO
vmp8
N.9
+4.8
H-1.8
vmpl
+2.5|
vmp3
, ,
,+0.3
-0.2
»vpml7
+0.4
, vmpl6
-0.9 '-1.2-
, vroplS vmp!4 .
+4.6,
vpm21
-0.4
vmpl3j
itb
Figure 24. Site plan view showing pressure data for the monitoring wells and
vapor monitoring points on October 25, 1991. Pressure is in inches of water.
59
-------
t—
@
&
^
rn
1
O
i
*
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^.j
20
15
10
5
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10
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n
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•* 1 _ i\ ^-' •-•
I mm. , 1 \ ^~^
- " \ ' I'"''
fc"*
VMP-2
•M
-* * • -• ** * -•
r •: :\ ^-,
- I > \ -'
1 • • X
V ' •'
-.',' " VMP-22
- *
-
r*""" """ N>/
r ...
/ VMP-21
•
-'L' . . . . .
-T SPARGING ON
J!
,' VMP-13
^
•/ "ir'k v' --,H,»,_
0
50
100 150
TIME(DAYS)
200
250
300
Figure 25. Time series oxygen concentrations in the soil gas in
vapor monitoring points 2, 22, 21, and 13.
60
-------
^_
Z«
O
1
*
1
>-
g
#
JS
W
g
5
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Figure 26. Time series oxygen concentrations in the soil gas in vapor
monitoring points 8-11.
61
300
-------
time, the low oxygen concentrations at VMP-13 suggest that there is an ongoing oxygen
demand at that point.
Data from both VMP-2 and VMP-22 indicate that oxygen concentrations were high
prior to the onset of SVE. Oxygen concentrations at VMP-21 show a gradual increase over
a 2- to 3-month period following the onset of SVE/IAS. This suggests that the region around
the point was flushed very slowly (i.e., it was relatively isolated from the bulk of airflow).
Oxygen data from around VEW-2 are less easy to interpret. VMP-8 and VMP-9
show significantly more scatter than other points. The reason for this is not clear. VMP-11
shows oxygen concentrations which are high throughout the duration of the sparging period.
Oxygen concentration data from VMP-10 show a clear decrease over time. The reason for
this is not clear. Respiration rate measurements that include background measurements can
be used to isolate background respiration from that associated with contaminant degradation.
In addition, it would have been useful to conduct in situ shutdown respiration tests to assess
biodegradation rates within the treatment zone (Hinchee et al., 1992).
Hydrocarbon Concentrations in the Soil Gas
Hydrocarbon data (VOCs in pptV) from the vapor monitoring probes are shown in
time series in Figures 27 and 28. The expected inverse relationship between oxygen and
hydrocarbons can be seen in several of the locations; however, in general the correlation
between oxygen and hydrocarbons prior to SVE is poor. VMP-13, which has consistently
low oxygen concentrations, has consistently high hydrocarbon concentrations. VMP-10 and
VMP-11 had high initial oxygen concentrations and low hydrocarbon concentrations.
However, the other monitoring points do not show consistent trends. This once again
underscores that complicated and poorly understood processes appear to be affecting the
monitoring parameters.
Monitoring Point Placement
The impact of soil stratigraphic conditions at the site cannot be overstated. A good
example of this comes from cross section data in the Engineering Science report (Figures 3,
4, and 5 in this report). Transect A-A' (Figure 3) shows a monitoring well that is connected
62
-------
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Figure 27. Time-Series Hydrocarbon Concentration Data for
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Per Thousand by Volume.
63
-------
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Figure 28. Time-Series Hydrocarbon Concentration Data for Vapor Monitoring
Points 8 Through 11. Concentrations Are in Parts Per Thousand by Volume.
64
-------
to the SVE and IAS wells by a sand unit. At the same time, monitoring points placed in the
lower-permeability units both above and below the sand would behave much differently with
respect to the remediation wells. In contrast to A-A', points along transect B-B' (Figure 4)
would be less impacted by the sparge well because silts and clays are the main soil units
connecting the points along this transect. As a consequence, relatively minor changes in
vertical and area! placement can have a major impact on the performance data collected from
the monitoring points.
SUMMARY
An immense amount of data were collected at this site; however, some of the
chemical data (e.g., BTEX, TPH) collected prior to the development of the QAPP did not
meet the QC criteria. Also, the large temporal variability in some of the chemical and
process data during the approximately 2-year study prevented a definitive evaluation of IAS
performance at this site. Even though this data did not allow a quantitative evaluation of the
IAS system performance, it provided valuable information that was used to develop lessons
learned in designing performance evaluations and interpreting performance data for IAS
systems. Based on this data, the following lessons were learned:
• It is difficult to monitor and evaluate the performance of in situ air sparging. The
data collected did not clearly define how well the IAS system was working due to
a number of factors discussed below.
• 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. Appropriate placement of monitoring
points for collecting data representative of the IAS system being operated is as
important as the parameters measured.
• Contaminant indicators such as BTEX in groundwater are often used as the
primary indicators of system performance. Based on the data from this site,
BTEX cannot be solely used to indicate system performance. The comparison
between MW-2 and MW-5 discussed earlier in this section is an example of that
difficulty. The DO data, as well as the physical location of MW-2, indicate that
it is outside the treatment zone. Nevertheless ^ it showed a decrease in BTEX
concentrations which was of the same order of magnitude as MW-5, which was
65
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near the center of the treatment zone. The low and variable concentrations
observed at those wells may reflect "naturally-occurring" changes in concentration
over time.
• 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.
Based on the lessons learned while trying to evaluate the performance of the IAS system at
the Denison Avenue site, the following should be considered in the experimental design for
future technology applications of IAS systems:
• Where available, 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. In this
context, it is essential to collect that data in a manner which is compatible with
data collected during and after active remediation. 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."
• Defining the general 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.
• If monitoring wells are to be used as the primary indicator of IAS system
performance, then care must be taken to ensure that samples collected from the
wells reflect general water quality. To accomplish this, the IAS system should be
shut down prior to each sampling event and the well should be aggressively
purged prior to sampling. The period of IAS system shutdown will usually be
site-specific based on the parameter being measured and the hydrogeologic
characteristics of the site.
• 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 extraction system
and if the vapor monitoring points reflect the influence of the I AS system.
• 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.
66
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• Continuous monitoring of some system parameters (e.g., pressures, off-gas
concentrations, soil gas concentrations, water levels) can provide valuable input
into the reasons for observed variability of field data. It is recommended that,
whenever practical, data loggers be used to collect such data.
• 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 field
evaluation since it 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 improvements in soil/groundwater quality after the air sparging
system has been shut down. As part of the evaluation of the application and performance of
IAS, the final sampling and analysis should be conducted after a period of system shutdown.
67
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REFERENCES
Ahlfeld, D. P., A. Dahmani, and W. Ji. 1994. A Conceptual Model of Field Behavior of
Air Sparging and Its Implications for Application. Groundwater Monitoring and
Remediation. Vol. 14 No. 4, pp. 132-139.
Engineering-Science. 1993. Air Sparging/Soil Vapor Extraction Remediation Demonstration
Project - Data Evaluation Report. BP Oil Site No. 04216, West 65th Street and Denison
Avenue, Cleveland, Ohio. Draft internal report submitted to BP Exploration & Oil, Inc.
Hinchee, R. E., S. K. Ong, R. N. Miller, D. C. Downey, and R. Frondt. 1992. Test Plan
and Technical Protocol for. a Field Treatability Test for Bioventing, Revision 2. Report to
the U.S. Air Force Center for Environmental Excellence, Brooks AFB, TX.
Ji, W., A. Dahmani, D. Ahfeld, J. D. Lin, and E. Hill. 1993. Laboratory Study of Air
Sparging. Air Flow Visualization. Groundwater Monitoring and Remediation. Vol. 13,
No. 4, pp. 115-126.
Johnson, R. L. 1993. Enhancing Biodegradation With In Situ Air Sparging: A Conceptual
Model. In: Proceedings of the Conference on In Situ and On-Site Bioreclamation, April 6-
8, by Battelle Memorial Institute, San Diego, California.
Johnson, R. L., P. C. Johnson, D. B. McWhorter, R. E. Hinchee, and I. Goodman. 1993.
An Overview of In Situ Air Sparging. Groundwater Monitoring and Remediation, Vol. 13,
No. 4, pp. 127-135.
U.S. Environmental Protection Agency. 1993. Internal Working Document: Quality
Assurance Project Plan for Conducting Field Evaluation for a Soil Vapor Extraction - Air
Sparging System.
68
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APPENDIX A
QUALITY ASSURANCE
INTRODUCTION
This section summarizes the results of the internal QC checks and other QA activities
conducted during the sampling and analytical programs to define and document the quality of
the data reported.
QA OBJECTIVES
QA objectives for the critical parameters to be measured in each sample matrix were
presented in Table 2-1 of the approved Quality Assurance Project Plan (QAPP), dated
September 29, 1992, and the subsequent revision dated October 4, 1993 (U.S. EPA, 1993).
All parties involved in the IAS field evaluation at the BP Oil Company Denison Avenue site
agreed that these objectives (Table A-l) for measuring precision, accuracy, completeness,
and method detection limit (MDL) were consistent with the quality of data for evaluating
technology performance.
INTERNAL QC CHECKS
The internal QC check program designed to monitor the performance of the analytical
methods was presented in Section 6 of the approved QA Project Plan. Table A-2 summariz-
es the internal QC checks for critical analytical parameters.
Soil Sample Analysis
Soil samples were analyzed by Wadsworth/Alert Laboratories during 1991 and by the
Engineering-Science Laboratory in Atlanta, Georgia, during 1992 and 1993. The samples
were analyzed for BTEX, TPH, and/or TRPH by U.S. EPA SW-846 Methods 5030/8020,
69
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5030/8015, modified California DHS, and 9071/418.11, respectively. The data quality
indicators for the soil samples are summarized in Table A-3. During 1991, the TRPH
analysis for samples collected during sampling events 1 and 3 and the toluene in the BTEX
analysis during sampling event 1 did not meet the QA objectives specified in the QAPP.
During the sampling event conducted in 1992, benzene and toluene did not meet the
QA objectives specified in the QAPP for BTEX analysis.
Water Sample Analysis
Water samples were analyzed by Wadsworth/Alert Laboratories during 1991 and by
the Engineering-Science Laboratory in Atlanta, Georgia, during 1992 and 1993. The
samples were analyzed for BTEX and TPH gas and diesel fractions by U.S. EPA SW-846
Methods 5030/8020 and 8015 modified (California DHS). The data quality indicators for the
water samples are summarized in Table A-4.
QC data were not reported for the TPH analyses conducted during the July, October,
and November 1991 sampling events. In the first round of sampling during the October
1991 sampling event, the laboratory report indicated that a modified 5030/8020 analytical
method was used to analyze samples for the TPH gasoline fraction. Method 8020 is
validated for aromatic volatile organic compounds (BTEX) and not TPH. The data report
did not include a discussion of the scope of this analysis or describe the modifications that
were made to the method.
Vapor Sample Analysis
Soil vapor samples were analyzed by Wadsworth/Alert Laboratories during 1991 and
for the first 6 months of 1992. Business Health Management Environmental Laboratory
analyzed the soil vapor samples during the remainder of 1992. The laboratory data reports
do not include QC data other than for laboratory blanks; therefore, the data quality indicators
for the soil vapor samples as well as the quality of this data are not known.
76
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QA SUMMARY
This section was structured to summarize the actual quality of the data generated at
this site to date and used as a basis for the conclusions and recommendations presented in the
report. The basis for the data quality determination was the approved QAPP for this site
(September 1992 and subsequently revised October 1993). As shown by the initial approval
and revision dates, the QAPP was written after a large portion of data had been generated.
In the case of the August 1991 sampling event for soil samples, four sample groups were
collected and analyzed. Toluene did not meet the QAPP acceptance criteria for precision and
accuracy in one of the four sample groups and TRPH did not meet the QAPP precision and
accuracy criteria in two of the four groups. The remainder of the data for this sampling
event did meet the QAPP acceptance criteria. It should be pointed out as footnoted in Table
A-3, however, that the toluene and TRPH analysis did meet the analytical laboratory's QC
acceptance criteria and these data were generated prior to the QAPP.
The TPH as diesel data (8015 Modified, CA. DHS) were reported with a flag
indicating "no recognizable pattern" and in one case a flag indicating that the reported results
were gasoline components. The diesel data were not confirmed and should not be relied on
as representative of diesel contamination at the site.
Several analytes were slightly outside the initially-approved QAPP acceptance criteria
during the sampling events conducted between July 1991 and March 1993. Consultation with
the current analytical laboratory revealed that matrix interference affected the performance of
the soil sample analysis and the TPH determination in groundwater. Therefore, the QAPP
was revised to include QA objectives and acceptance criteria that are more reflective of the
analytical methods performance for these samples (Tables A-l and A-2).
Although analytical method performance for several analytes were not within the
QAPP acceptance criteria, the soil and groundwater data can be used as indicators of the
contaminant levels during specified sampling events. When used in conjunction with data
collected during the same sampling event that meet the QA objectives, these data can be used
as an indicator of the system performance trend over time.
81
-------
TECHNICAL SITE EVALUATION
A Technical Site Evaluation (TSE) was conducted of the field and laboratory
operations being conducted to generate data on the AS-SVE system on August 17 and August
27, 1993, respectively. The field part of the TSE consisted of a qualitative appraisal of the
sample collection methodology, sample preservation and storage procedures, and record-
keeping activities during a soil sampling episode. The laboratory portion of the TSE
consisted of a qualitative appraisal of the laboratory operations including analytical methodol-
ogy, QC check program, sample custody, and report generation. A copy of the TSE is
presented herein. In general, the sample collection and analytical procedures were conducted
in conformance with the procedures specified in the QAPP.
82
-------
APPENDIX B
TECHNICAL SITE EVALUATION REPORT
TECHNICAL SITE EVALUATION OF FIELD SAMPLING AND
LABORATORY OPERATIONS FOR THE BP OIL COMPANY SITE,
WEST 65 AND DENISON AVE., CLEVELAND, OHIO
1. INTRODUCTION
On August 17, 1993 a Technical Site Evaluation (TSE) was conducted of the field
activities being carried out in support of the IAS system operations being conducted to remove
motor fuel from the BP Oil Company site located at West 65th and Denison Ave., Cleveland,
Ohio. A subsequent TSE was conducted on August 27, 1993, at the Engineering Science
Laboratory in Atlanta, Georgia, that is providing analytical support for soil and water sampling
conducted at this site.
The TSEs described herein were performed to assess the field sampling methodology
being used to collect soil samples and the analytical protocol being used by the laboratory to
analyze the samples. The objective of the sampling program is to collect representative samples
from the section of the site being treated by the IAS system in order to assess the removal
progress. This TSE was based on the review of the sampling and analytical activities in
retrospect to the approved revised QA Project Plan dated September 29, 1992.
The TSEs were conducted by Thomas Clark of IT Corporation. The following indi-
viduals were present during the TSEs:
Field
Gilberto Alvarez, U.S. EPA Region V
Ray Barnary, Engineering-Science, Inc.
Ken Yokoyama, Engineering-Science, Inc.
83
-------
Laboratory
Gene Coker, U.S. EPA Region IV
Greg Jones, Engineering-Science, Inc.
n.
FIELD TSE
The TSE began with a review of the scope of the sampling activities to be conducted to
obtain representative soil samples from the portion of the site being treated by the IAS system.
Three soil borings were advanced to approximately 15 feet at locations within a 3-foot radius
of soil boring sites used for an earlier sampling episode. Split spoon samples were collected at
2-foot intervals beginning at a depth of 3 feet.
Headspace screenings of the split spoon samples were conducted by use of a portable
photoionization detector (PID). The samples for headspace screening were collected in 9-ounce
glass containers and sealed with aluminum foil under the lid. The headspace test was conducted
'by removing the lid and piercing the aluminum foil with the PID probe. Soil samples for the
laboratory analysis were collected in 9-ounce glass sample bottles. The laboratory will then
collect aliquots of soil from the 9-ounce sample bottles for BTEX and TPH analysis. This
procedure differs from the protocol and type of sample containers specified in the Quality
Assurance Project Plan (QAPP). Table 3-2 of the QAPP specifies that 40 mL VGA vials be
used to collect soil samples for BTEX analysis and 250-mL glass bottles be used for samples for
TRPH analysis. The use of one 9-ounce sample bottle and the laboratory collecting aliquots for
the individual analyses, however, is not expected to create a bias in the data. Therefore, this
procedure is considered to be an acceptable deviation from the QAPP.
The soil sampling procedures used by the onsite geologist were in compliance with the
procedures discussed in Section 3 of the QAPP. During the collection of the first sample,
however, it was noted that the 9-ounce sample bottle to be shipped to the laboratory was not
filled completely to eliminate headspace. The geologist responded to this observation
immediately, and all remaining sample containers were filled completely to eliminate the
headspace. After collection, samples were stored at the appropriate temperature in an ice chest.
The soil borings for this sampling event were designated SB9, SB10, and SB11. The
approximate locations of these borings are illustrated on Figure B-l. The results of the head
84
-------
Q ^- s •- o>
^ TR !2 -i -i
2 I"
^^ ~i - - - ** - 4jaMainfromoB'F\ ________
- ........ ............. " ............................ "2\" ........ Vin.'aas Main
GO
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CQ
85
-------
space screening indicated relatively high organic concentrations in the intervals between 9 and
15 feet at the SB9 and SB11 locations. These results are summarized in Table B-l. Headspace
screening results for SB10 indicated organic concentrations between 0.4 and 47 ppm.
Table B-l. Headspace Screening Results
Boring
SB9
SB11
Depth (ft)
9-11
11-13
13-15
9-11
11-13
13-15
Organic concentration
2330
3982
1570
402
4226
1390
(ppm)
The sampling activity observed during the soil sample collection was conducted in an
acceptable manner, and the samples should accurately represent the organic concentrations in
the areas of the site that were sampled.
in. LABORATORY TSE
The laboratory TSE began with a tour of the ES laboratory followed by a general
discussion of the laboratory operating practices. Prior to the laboratory visit, laboratory
management raised several concerns regarding analytical methodology, QA objectives, and the
internal QC checks specified for several analytes for the soil and water matrices specified in the
Denison Avenue QAPP. These concerns were discussed with Greg Jones of the ES laboratory.
The concerns generally involved slightly more stringent QA objectives and tighter QC check
acceptance criteria than the laboratory typically achieves for the type of samples and matrices
involved in this project. One concern involved the use of a different extraction solvent than the
one specified in the California DHS method for extracting diesel fuels. The California DHS
method allows the use of an alternative solvent, provided the solvent does not interfere with the
analysis and the laboratory can demonstrate acceptable recovery performance. The ES
laboratory has sufficient data to satisfy these requirements, and the alternative solvent is
86
-------
acceptable. It was recommended that the QAPP be revised to reflect the QA objectives and QG
check acceptance criteria that reflect the performance of the laboratory and accurately define the
methods and the quality of data that will be generated during the analysis. These revisions
should not affect the comparability of the data and are considered acceptable. A summary of
the proposed revisions is presented in Attachment A. Soil samples from Denison Ave. are also
being analyzed for TPH by using the California DHS method to satisfy State of Ohio
requirements. It was recommended that this method be added to the QAPP so that this data can
also be used during the technology evaluation.
Samples are received at the laboratory and logged in on log sheets. Samples are stored
in an appropriate manner and at the proper temperature in refrigerators. Sample custody and
tracking activities are performed by two project managers who also control the schedule and
flow of analysis through the laboratory. Logbooks, which are used to document all phases of
analysis, include data on blanks, spikes, calibrations, etc. The logbooks reviewed were noted
to be complete and legible.
Standards are maintained in a separate refrigerator and are appropriately labeled. The
standards used for the Denison Ave. samples are as follows:
Gasoline
Colonial Pipe Line - Regular unleaded, Grade 44
Diesel
Colonial Pipe Line - 10,000-ppm diesel, Grade 76
Analytical results for this project are reported-in a Level 2 data package. This data package
includes a summary of results plus the required QC data (blanks, matrix spikes, etc.).
The laboratory operations observed during the TSE were found to be in conformance with
good laboratory practices, and the samples from the Denison Ave. site are being analyzed in
accordance with acceptable protocols. The data generated from the sample analysis is belived
to accurately reflect the level of contaminants in the samples and the data is believed to be
comparable with data generated by other laboratories using the same methodology.
87
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ATTACHMENT A
PROPOSED REVISIONS TO THE ANALYTICAL METHODS IN
THE DENISON AVE. QAPP
The following revisions to the soil and groundwater analytical methods presented in the QAPP
will be proposed by the Engineering Science Laboratory. These revisions reflect the analytical
method performance and quality of data produced by the laboratory.
1.
Table 2-1 of the QAPP presents the following QA objectives for the analysis of soil and
groundwater samples.
Parameter/
Measure-
ment
BTEX
TPH
BTEX
TRPH
=====
Classi-
fication
Critical
Critical
Critical
Critical
=====
Matrix
Ground
water
Ground
water
Soil
Soil
================
Method
5030/8020
3510/8015°
mod.
DHSC
5030/8020
9071/418.1
=====
Meas.
Units
/tg/1
mg/L
mg/L
mg/kg
mg/kg
=======
MDL
2b
5d
0.5e
,b
15
=
Preci-
sion
20%
20%
20%
20%
20%
===============
Accuracy
80-120%
80-120%
80-120%
80-120%
80-120%
=======
Complete-
ness (%)
90
90
90
90
For each of the individual components.
DHS Method, Appendix C (requires both gasoline and diesel determination).
Gasoline fraction.
Diesel fraction.
The proposed revisions include the following QA objectives for the soil and ground water
analysis plus the addition of QA objectives for the TPH analysis of soil samples using
the California DHS method.
-------
Parameter/
Measure-
ment
BTEX
TPH
BTEX
TRPH
TPH
Classi-
fication
Critical
Critical
Critical
Critical
Critical
Matrix
Ground
water
Ground
water
Soil
Soil
Soils
Method
5030/8020
5030/8015°
DHS°
5030/8020
9071/418.1
5030/8015° mod.
DHS
Meas.
Units
Mg/1
mg/L
mg/L
mg/kg
mg/kg
mg/kg
mg/kg
MDL
2b
.50d
0.56
lb
15
2d
ioe
Preci-
sion
20%
30%
30%
30%
30%
30%
30%
Accuracy
80-120%
65-135%
65-135%
70-130%
70-130%
70-130%
50-120%
Complete-
ness (%)
90
90
90
90
90
90
For each of the individual components.
° DHS Method, Appendix C (requires both gasoline and diesel determination).
Gasoline fraction.
Diesel fraction.
2. It was proposed to revise Table 3-2 by adding HC1 for the preservation of groundwater
samples for BTEX. This revisions would allow the QAPP to consistently reflect the
preservation techniques being used for these samples.
3. The proposed revisions to Table 6-1 consist of the following:
• Clarify the frequency of the initial calibration and the initial calibration accep-
tance criteria for the BTEX analysis for the soil and water samples.
• Modify the acceptance criteria for spike recoveries to be consistent with labo-
ratory performance for the TRPH analysis of soil samples and the BTEX and
TPH analysis of groundwater samples.
• Add "qualify data" as a corrective action for the blanks, spikes and surrogates
(where applicable), for all of the soil and water analytical methods.
• Add the internal QC checks, frequency, acceptance criteria and corrective actions
for the TPH analysis of soil samples using the California DHS method.
The proposed changes are highlighted in the attached Table 6-1 by a vertical line in the
righthand margin of the table adjacent to the change.
4. Several minor changes to the text in Sections 2, 4, and 6 are required to be consistent
with the changes proposed in Tables 2-1, 3-2, and 6-1.
89
-------
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-------
APPENDIX C
SOIL AND GROUNDWATER DATA
TABLE C-l. SUMMARY OF GROUNDWATER ANALYSIS IN THE TREATMENT ZONE
(ENGINEERING-SCIENCE, 1993)
Well ID
MW-4
MW-5
MW-6
Date
ll-Jul-91
16-Oct-91
30-Oct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
ll-Jul-91
16-0ct-91
30-0ct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
26-Aug-91
16-0ct-91
30-0ct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
Ethyl- Xy-
Benzene Toluene benzene lene
(HS/L) (jug/L) 0»g/L) 0*g/L)
15 <2 <2 <2
98 <3 <3 <3
140 <1 <1 <1
3 <1 <1 <1
<1 <1 <1 <1
<1 <1 <1 <3
<1 <1 <1 <3
13 <1
-------
TABLE C-l (continued)
Well ID
ASM-1
ASM-2
ASM-3
Date
26-Aug-91
I6-Oct-91
30-Oct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
30-0ct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
26-Aug-91
16-Oct-91
30-Oct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
Ethyl- Xy-
Benzene Toluene benzene lene
Otg/L) (^g/L) Otg/L) 0*g/L)
<1 170 <1 <1
4 <1 <1 <1
2 <1 <1 <1
2 <1 <1 <1
2 <1 <1 <1
<1 <1 <1 <3
<1 <1 <1 <3
<1 <1 <1 <3
<1 <1 <1 <3
<1 <1 <1 <3
_<1 <1 <1 <3
-------
TABLE C-2. SUMMARY OF GROUNDWATER ANALYSIS OUTSIDE THE TREATMENT ZONE
(ENGINEERING-SCIENCE, 1993)
Well
ID
MW-1
MW-2
MW-3
MW-7
Date
ll-Jul-91
16-Oct-91
30-0ct-91
13-Nov-9i
ll-Dec-91
15-Jan-92
12-Mar-92
25-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
ll-Jul-91
16-Oct-91
30-Oct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
lS-Nov-92
24-Mar-93
19-Aug-93
ll-Jul-91
16-Oct-91
30-Oct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
lS-Nov-92
24-Mar-93
19-Aug-93
26-Aug-91
16-Oct-91
30-Oct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
Tol- Ethyl- Xylene
Benzene uene benzene G*g/L)
(MR/L) 0*g/L) 0*g/L)
<2 <2 <2 <2
<1 <1 <1 <1
<1 <1 <1 <1
<1 <1 <1 <1
<1 <1 <1 2
<1 <1 <1 <3
3.9 23 4.1 61
-------
TABLE C-2 (continued)
Well
ID
MW-8°
MW-8
Date
26-Aug-91
30-0ct-91
13-Nov-91
ll-Dec-91
15-Jan-92
12-Mar-92
14-Jul-92
18-Nov-92
24-Mar-93
19-Aug-93
Tol- Ethyl- Xylene
Benzene uene benzene (*»g/L)
(fig/L) G*g/L) 0*g/L)
<0.5
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