«EPA
United States
Environmental Protection
Agency
Solid Waste And
Emergency Response
5403G
EPA 510-9-97-001
March 1997
Expedited Site Assessment
Tools For Underground
Storage Tank Sites
A Guide For Regulators
Printed on Recycled Paper
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Expedited Site
Assessment Tools For
Underground Storage Tank
Sites
A Guide For Regulators
United States Environmental Protection Agency
Office of Underground Storage Tanks, OSWER
March 1997
-------
Comments And Additional Information
Do you have comments?
We welcome your comments on this Guide. You can e-mail
them to Robert Hitzig, Office Of Underground Storage
Tanks at:
hitzig.robert@epamail.epa. gov
Or you can mail them to us at:
U.S. EPA
Office Of Underground Storage
Tanks (5401G)
401 M Street, SW.
Washington, DC 20460-0001
Attention: SAM
Do you want to order additional copies of this Guide?
You can write, fax, or phone your request to:
U.S. Government Printing Office
Super-intendant of Documents
P.O. Box 371954
Pittsburgh, PA 15250-7954
Stock Number 055-000-00564-8
$26.00
Phone 202 512-1800
Fax 202 521-2250
Do you want more information on the UST Program?
You can contact us via our world wide web site at:
http: //www. epa. gov/OUS T
Or you can call EPA's RCRA/Superfund Hotline, Monday
through Friday, 8:30 a.m. to 7:30 p.m. EST. The toll-free
number is 800-424-9346.
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Acknowledgments
The U.S. Environmental Protection Agency's (EPA's) Office of
Underground Storage Tanks (OUST) would like to thank the numerous
individuals who contributed to this document. Because of the broad range of
subjects covered, the authors required the input of experts from many different
disciplines and perspectives. The principal authors are Robert Hitzig (U.S. EPA),
Roy Chaudet (Logistics Management Institute), and Murray Einarson (Einarson,
Fowler, and Watson, Inc.). In addition, Susan Kraemer (ICF Kaiser) is a
contributor to the initial developement of the document. Internal technical review
was provided by Dana Tulis and Hal White (both of OUST).
A group of experts drawn from U.S. EPA headquarters, regional offices
and laboratories, as well as other federal departments, state regulatory agencies,
universities, and private industry reviewed this document extensively. The most
significant contributors to the technical review process included Gilberto Alvarez
(U.S. EPA), David Anail (U.S. EPA), Jay Auxt (Hogentogler and Company,
Inc.), Kent Cordry (Geolnsight), Jeff Farrar (Department of Interior), Blayne
Hartman (Transglobal Environmental Geochemistry), Dana LeTourneau
(Spectrum Geophysics), Barry Lesnik (U.S. EPA), Aldo Mazzella (U.S. EPA),
Duncan McNeil 1 (Geonics Limited), David and Gillian Nielsen (The Nielsen
Environmental Field School, Inc.), H. James Reisinger II (Integrated Science and
Technology, Inc.), Willie Staudt (Land Tech Remedial, Inc.), and Tom Zdeb
(Woodward Clyde Consulting).
Other individuals who provided valuable comments for improvement of
the manual include Al Bevolo (Ames Laboratory), Michael Billa (Rizzo
Associates, Inc.), Ken Blom (NORCAL, Inc.), David Borne (Sandia National
Laboratories), Russell Boulding (Boulding Soil-Water Consulting), Jim Butler
(Geotech, Inc.), Kevin Carter (Ensys Environmental Products, Inc.), Thomas
Christy (Geoprobe Systems), Gerald Church (Transglobal Environmental
Geochemistry), Jeff Daniels (Ohio State University), Dominick DeAngelis
(Mobil Oil Corporation), Brendon Deyo (Home Engineering and Environmental
Services), Gary Dotzlaw (FCI), Jeff Erikson (Mobil Oil Corporation), Chi-Yuan
"Evan" Fan (U.S. EPA), John Gregg (Gregg In Situ, Inc.), Doug Groom
(Geometries, Inc.), Peter Haeni (U.S. Geological Survey), John Hanby (Hanby
Environmental Laboratory Procedures, Inc.), Mark Hathaway (Northeast Research
Institute LLC), Sam Heald (Geophysical Survey Systems, Inc.), Paul Henning
(Quadrel Services, Inc.), Ross Johnson (Geometries, Inc.), Steve Kane (Photovac
Monitoring Instruments), Bruce Kjartanson (Iowa State University), Eric Koglan
(U.S. EPA), Bill Kramer (Handex Corporation), Donald Lavery (General Analysis
Corporation), Al Liguori (Exxon Research and Engineering Company), Ted B.
Lynn (Dexsil Corp.), Sriram Madabhushi (South Carolina Department of Health
March 1997 iii
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and Environmental Control), Don Marrin (Independant Consultant), Ray
Maytejczyk (Viking Instruments), Finn Michelson (OYO Geosciences), Chris
O'Neill (New York Department of Environmental Conservation), Emil Onuschak,
Jr. (Delaware Department of Natural Resources and Environmental Control), Gary
Placzek (U.S. Geological Survey), Gary Robbins (University of Conneticut), Dan
Rooney (Vertek), Charlita Rosal (U.S. EPA), Greg Reuter (Handex Corporation),
Mark Shaver (ORS Environmental Systems), Tom Starke (Department of
Energy), Sandy Stavnes (U.S. EPA), Mike Taylor (Land Tech Remedial, Inc.),
Glenn Thompson (Tracer Research Corporation), James Ursic (U.S. EPA), Mark
Wrigley (W.L. Gore & Associates, Inc.), Katrina Varner (U.S. EPA), and Mark
Vendl (U.S. EPA).
Special thanks are also due to Kate Becker (OUST) for her editorial
review of the document and to Denise Mason (Einarson, Fowler, and Watson,
Inc.) for developing many of the graphics.
Robert Hitzig
Office of Underground Storage Tanks
March 1997
iv March 1997
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Contents
Chapter
Number Title Page
I. Introduction 1-1
II. Expedited Site Assessment Process 11-1
III. Surface Geophysical Methods 111-1
IV. Soil-Gas Surveys IV-1
V. Direct Push Technologies V-1
VI. Field Methods For The Analysis Of Petroleum Hydrocarbons . VI-1
Appendix A: Data Requirements For Corrective Action
Evaluations A-1
Appendix B: Table Of U.S. EPA Test Methods For Petroleum
Hydrocarbons B-1
Abbreviations Abbreviations-1
Glossary Glossary-1
March 1997
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Chapter I
Introduction
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Introduction
The U.S. Environmental Protection Agency's Office of Underground
Storage Tanks (OUST) encourages the use of expedited site assessments (ESAs)
as a way to streamline the corrective action process, improve data collection, and
reduce the overall cost of remediation. The implementation of ESAs is especially
important as many owners and operators of underground storage tanks (UST)
facilities comply with the December 22, 1998 regulatory deadline for upgrading,
replacing, or closing their USTs. As of March 1997, OUST has estimated that of
the 1.1 million federally regulated USTs, between 400,000 and 500,000 meet the
1998 regulatory standards. The process of complying with these standards may
result in the closure of about 300,000 USTs and the identification of 100,000
additional releases. Each of these sites will require an assessment. Furthermore,
of the 317,000 releases confirmed since December 1988, about 64,000 still need
to initiate cleanup activities. As a result, at least 360,000 sites are likely to require
site assessments in the next few years.
As the first step in the overall corrective action process, the site
assessment process is critical to making appropriate corrective action decisions.
When site assessments are complete, they provide accurate information about the
presence and distribution of contaminants, thereby facilitating cost-effective and
efficient remediation. When they are incomplete, they can provide inaccurate or
misleading information which can delay effective remediation, increase overall
corrective action costs, and, result in an increased risk to human health and the
environment. By nature, there are always gaps in the information provided in site
assessments. It is, therefore, not always obvious when a site assessment is
complete and when the information has been accurately interpreted. As a result, a
tremendous amount of data is needed to determine where contaminants are
located and how best to remediate them.
Site assessments can also contribute directly to a large percentage of the
overall corrective action costs. Sampling equipment, sample analysis, and labor
hours may cost between 10 and 50 percent of the total remediation costs at
petroleum-contaminated sites. When investigators and regulators have
determined that remediation by natural attenuation is appropriate, the site
assessment may encompass an even higher percentage of remediation costs.
In many cases, regulators do not directly oversee site assessments and do
not select specific site assessment equipment. Regulators do, however, have
tremendous influence over the site assessment process in their jurisdictions
through their issuance of regulations and guidance and by their acceptance of
certain kinds of data for regulatory decisions.
March 1997 1-1
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With the emergence of an enormous number of new site assessment tools
recently, regulators are often hard pressed to keep current with the latest
technologies and maintain their other duties of reviewing site assessments,
evaluating corrective action plans, and/or issuing regulations. There is, therefore,
a need for a document that evaluates site assessment methods and tools for
regulators. This guide addresses the overall ESA process as well as specific site
assessment tools and methods. Topics include:
The ESA process;
Surface geophysical methods;
Soil-gas surveys;
Direct push technologies; and
Field methods for the analysis of petroleum hydrocarbons.
Purpose
The purpose of this guide is to provide federal, state, and local regulators
with information that will help them to evaluate new as well as conventional site
assessment technologies, develop their own guidance documents, and promote the
use of ESAs. The guide does not advocate the use of one technology over
another; rather it focuses on appropriate technology use, taking into consideration
site-specific conditions.
The guide is designed to enable the reader to answer the following basic
questions about expedited site assessments at UST facilities:
What is an ESA?
How is an ESA conducted?
What equipment can be used in an ESA?
Under what site conditions are specific site assessment tools appropriate?
Scope And Limitation
This guide does not represent the issuance of formal policy or in any way
affect the interpretation of federal regulations. The text focuses on scientific and
practical considerations for evaluating various types of technologies used to assess
UST sites. It does not provide instructions on the use of any specific tool and
does not supersede or replace equipment manufacturer instructions. Although,
this guide may be used by state and local agencies in the development of guidance
documents, it should not be interpreted as providing guidance on securing
permits, health and safety regulations, or state-specific requirements.
1-2 March 1997
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The material presented is based on available technical data and
information as well as the knowledge and experience of the authors and peer
reviewers.
How To Use This Guide
EPA's OUST encourages you to use this guide at your desk or in the field
as you review, oversee, or manage site assessments. We have designed the guide
so that you can tailor it to meet your own needs. The three-hole punch format
allows you to place the guide in a binder with additional material (e.g., state-
specific information, guidance documents, journal articles, equipment literature)
and remove certain tools (e.g., summary tables) for photocopying. The wide
margins were provided to enable you to add your own notes to the text.
In addition to this chapter, the guide contains five chapters—each addresses
a major consideration necessary for promoting and conducting expedited site
assessments.
Chapter II The Expedited Site Assessment Process. This chapter presents an
overview of the steps involved in an expedited site assessment,
explains how site assessment equipment can be used to expedite
the process, and makes comparisons with conventional site
assessments.
Chapter III Surface Geophysical Methods. This chapter describes the six
surface geophysical methods that are most often appropriate at
UST facilities and discusses their effectiveness as compared with
other methods.
Chapter IV Soil-Gas Surveys. This chapter provides a comparison of active and
passive soil-gas surveying methods and discusses their applicability
Chapter V Direct Push Technologies. This chapter discusses direct push rod
systems, sampling equipment, specialized probes, methods for
advancing rods, and methods for sealing direct push holes. Each
section explains the applications of all the discribed equipment.
Chapter VI Field Methods For The Analysis Of Petroleum Hydrocarbons.
This chapter discusses the eight most appropriate field analytical
methods, including the applicability and limitations of each
method.
March 1997 1-3
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The discussion in each chapter contains illustrations, comparative tables,
and references. For the readers convenience, a list of manufactures are presented
at the end of relevant chapters. At the end of each chapter are lists of references
and peer reviews. At the end of the guide are two appendices. Appendix A
covers data requirements for corrective action evaluations, and Appendix B is a
table of U.S. EPA test methods for petroleum hydrocarbons. The appendices are
followed by a list of abbreviations, and a glossary of relevant terms. Throughout
this guide, discussions of specific equipment are presented in generic terms so as
to not advocate any product of any specific manufacturer.
1-4 March 1997
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Chapter II
Expedited Site Assessment Process
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Contents
Exhibits ll-v
Expedited Site Assessment Process 11-1
Expedited Site Assessment Process Steps II-4
Step 1: Establish Site Assessment Objectives II-4
Step 2: Review Existing Site Information II-4
Step 3: Develop Initial Conceptual Model Of Site Conditions . . II-6
Step 4: Design Data Collection And Analysis Program II-6
Step 5: Implement On-Site Iterative Process II-9
Substep 1: Collect And Analyze Data II-9
Substep 2: Evaluate Data And Refine Conceptual
Model 11-10
Modify The Data Collection And Analysis
Program 11-10
Complete Expedited Site Assessment 11-10
Step 6: Consider Interim Remedial Actions 11-11
Step 7: Report The Findings 11-11
Conventional And Expedited Site Assessment Examples 11-12
Release Scenario 11-12
Step 1: Establish Site Assessment Objectives
(ESAAndCSA) 11-12
Step 2: Review Existing Site Information (ESA And CSA) ... 11-12
Site Interviews 11-13
Site Geology 11-13
Inventory Records Search 11-13
Receptor Survey 11-13
Other Environmental Investigations 11-13
Geologic Reports 11-14
Step 3: Develop Initial Conceptual Model Of Site
Conditions (ESA And CSA) 11-14
Geology 11-14
Hydrogeology 11-14
Source Area And Extent Of Contamination 11-16
Step 4: Design Data Collection And Analysis
Program (CSA) 11-16
Conventional Site Assessment Work Plan 11-16
Step 5: Field Work (CSA) 11-18
Step 6: Consider Interim Remedial Actions (CSA) 11-18
Step 7: Report The Findings (CSA) 11-18
March 1997 ll-iii
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Step 4: Design Data Collection and Analysis
Program (ESA) 11-19
Direct Push Sampling 11-19
Field Analysis 11-19
Soil Screening 11-19
Groundwater Sampling 11-19
Physical Properties II-20
Communicating Project Status II-20
Permits II-20
Utility Clearance II-20
Step 5: Implement On-Site Iterative Process (ESA) 11-21
Day 1: Conduct Initial Investigation 11-21
Days 2 And 3: Refine Conceptual Model II-23
Finalize Conceptual Model II-25
Decommission Site II-25
Step 6: Consider Interim Remedial Actions (ESA) II-25
Step 7: Report The Findings (ESA) II-26
Analysis Of Conventional And Expedited Site Assessments . . II-26
References II-28
Peer Reviewers , , , II-29
l-iv March 1997
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Exhibits
Number Title Page
11-1 Comparison Of Conventional And Expedited Site
Assessments II-2
II-2 Expedited Site Assessment Process II-5
II-3 Sources And Types Of Site History Information II-7
II-4 Initial Conceptual Model (Both CSA And ESA) 11-15
II-5 Final CSA Conceptual Model (First Phase) 11-17
II-6 ESA Conceptual Model After Day 1 II-22
II-7 Final ESA Conceptual Model After Day 3 II-24
March 1997 n-v
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Chapter II
Expedited Site Assessment Process
The expedited site assessment (ESA) process is a framework for rapidly
characterizing underground storage tank (UST) site conditions for input into
corrective action decisions. This framework has been described with other names
including accelerated site characterization, rapid site characterization, and
expedited site investigation. An ESA is conducted in a single mobilization that
typically covers several days and is made up of the following features:
Field-generated data and on-site interpretation;
A flexible sampling and analytical program; and
Senior staff in the field who are authorized to make sampling and
analytical decisions.
The ESA process contrasts with conventional site assessments (CSAs) in
which a significant amount of analysis and data interpretation is completed off-
site at a later date. As a result, CSAs can:
Take weeks or months to generate a preliminary report;
Require several phases of investigation; and
Delay corrective action decisions for months and sometimes years.
ESAs have been made possible in recent years by the development of
improved, cost-effective methods for rapid collection and field analysis of soil,
soil-gas, and groundwater samples. When appropriate, conventional sampling and
analytical methods can also be used in the ESA process. For example, an air
rotary drilling rig may be used in consolidated material, or off-site certified
laboratory analysis may be used on a limited basis to verify field analytical
methods. The ESA process emphasizes the appropriate use of technologies in a
way that minimizes the time required for complete characterization and
maximizes the data available for making corrective action decisions.
Exhibit II-1 presents a comparison of CSAs and ESAs. The focus for a
CSA is usually on installing groundwater monitoring wells that are sited with
limited subsurface information. The sampling and analysis plan is typically rigid
and defines the number of wells and their location. Most data analysis and
synthesis are performed off-site and may take weeks or months to complete. The
results of the assessment are usually focused on mapping the boundaries of the
groundwater plume rather than the source areas or locating the most significant
contaminant mass. In addition, the approach to mapping generally ignores the
3-dimensional nature of contaminant migration. Consequently, the CSA process
March 1997 11-1
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Exhibit 11-1
Comparison Of Conventional And Expedited Site Assessments
Process
Component
Number of phases of
investigation
Field management
Technical strategy
Work plan
Data analysis
Innovative
technologies (i.e.,
direct push and field
analytical methods)
Conventional Site
Assessments
Multiple
Manager typically in
office; junior staff in field.
Focus on plan view map;
sampling location based
on limited information.
Sampling locations are
pre-determined.
Rigid plan
Interpretation of data is
weeks or months later.
May or may not be used;
not integrated into
process.
Expedited Site
Assessments
Single
Manager in field with
experienced staff.
Use of multiple,
complementary
technologies; sampling
locations depend on existing
data; minimal well
installation; locating most
significant contaminant
mass in 3-dimensions.
Flexible plan
Regular (hourly/daily)
interpretation of data.
Standard practice, allows
on-site iterative process.
Source: Modified from Burton, 1995
tends to be time consuming, the total costs tend to be relatively high, and the site
conditions reported are often incomplete or incorrect.
In contrast, the ESA process uses senior scientists as field managers to
conduct the entire assessment. Both types of assessments evaluate existing data to
develop an initial conceptual model of site conditions, however, with ESAs the
sampling and analysis plan is dynamic. As new site information is generated, it is
used to direct the assessment. The field-generated data are used to update and
refine the conceptual model as the assessment proceeds. In this way, data gaps are
filled, and anomalies are resolved, prior to demobilization. The ESA is complete
when the data being obtained and the 3-dimensional characterization of the site
are in agreement.
II-2
March 1997
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In recent years, Risk-Based Corrective Action (RBCA) has been
recognized by regulators and industry as a valid approach to dealing with the
enormous number of petroleum-contaminated sites, RBCA is a process that
utilizes risk and exposure assessment methodology to help UST implementing
agencies make determinations about the extent and urgency of corrective action
and about the scope and intensity of their oversight of corrective action by UST
owners and operators (EPA, 1995). The American Society for Testing and
Materials (ASTM) RBCA standard (ASTM, 1995b) describes a three-tiered
approach to site evaluations in which each tier requires more extensive site-
specific data.
ESAs can be integrated with RBCA evaluations because the ESA process
is a method of obtaining accurate site information that is necessary for making an
appropriate corrective action decision, The first two RBCA tiers can be evaluated
in a single mobilization as part of a standard ESA, provided the investigator has
the cooperation of the appropriate regulatory agency. The data needs for a Tier 3
evaluation can also be acquired in the same mobilization; however, because of the
complexity and cost of the data needed for this level of evaluation, investigators
must be prepared for this tier level prior to mobilization and there should be a
method for rapidly acquiring authorization from the implementating agency. A
list of the data requirements for corrective action evaluations is provided in
Appendix A which is located at the end of the manual. This information can be
collected during an ESA and used in the RBCA process.
This chapter is divided into two major sections. The first section walks
the reader through the steps in the ESA process and discusses how this process
compares with conventional site assessments. The second section presents an
example of an actual ESA and compares it with a CSA that occurred at the same
site. This section illustrates how innovative data collection techniques and field
analysis methods can be used with the ESA process to complete a site assessment
quickly, while providing enough information to make remediation decisions. The
ESA process described in this chapter and referenced throughout the manual is
based on the provisional Accelerated Site Characterization standard by ASTM
(ASTM, 1995c) and State of Texas guidance (TNRCC, 1995).
March 1997 II-3
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Expedited Site Assessment Process Steps
The flowchart in Exhibit II-2 depicts the ESA process in seven steps.
While many of the steps are similar to those in a CSA, the activities within the
highlighted box labeled "Implement On-Site Iterative Process" are unique to an
ESA. These activities include:
Collect and analyze field data;
Refine the conceptual model as new data are produced; and
Modify the sampling and analysis program when necessary.
In an ESA, a field manager is responsible for this entire process.
Information about regional and site-specific geology/hydrogeology as well as
knowledge of petroleum fate and transport are necessary for making and revising
sampling and analysis decisions on-site. An ESA field manager must, therefore,
have extensive site assessment experience and knowledge about all aspects of the
ESA.
Step 1: Establish Site Assessment Objectives
The general objectives for any site assessment are to understand the:
Geology/hydrogeology of the site;
Nature and extent of contamination; and
Migration pathways and points of exposure.
The site-specific objectives may be to determine the existence of contamination,
investigate suspected contamination, or evaluate known contamination. The
objectives selected will dictate the priority of the type of samples to be collected
and analyzed. For example, an ESA for an initial response action will focus on
defining immediate hazards, while an assessment for a specific corrective action
technology will focus on the parameters that affect the system design and
performance.
Step 2: Review Existing Site Information
Both CSAs and ESAs require a review of existing site information before
mobilization. However, existing site information is especially important in an
I-4 March 1997
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Exhibit 11-2
Expedited Site Assessment Process
Stepl
Step 2
StepS
Step 4
Establish Site Assessment Objectives
Review Existing Site Information
Develop Initial Conceptual Model Of Site Conditions
Design Data Collection And Analysis Program
StepS
Implement On-Site Iterative Process
Collect And Analyze Data
Soil • Physical
Groundwater properties of
Soil Gas fluids and
porous media
Modify Data
Collection And
Analysis Program
Evaluate Data and Refine
Conceptual Model
Are
Appropriate
Methods Used to Collect
And Analyze
Data?
Is
Assessment
Complete?
Yes
StepG
Step?
r
Consider Interim Remedial Actions
Report Findings
Source: Modified from ASTM, 199%.
March 1997
II-5
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ESA because this information is required for the selection of sampling equipment,
analytical methods, and strategies for the initial round of sampling. A list of
potential sources of historical site information is provided in Exhibit II-3. The
review of existing information should include past and current land use, potential
sources of contamination, potential migration pathways and receptors, and likely
geologic and hydrogeologic conditions. If the investigation includes a RBCA
evaluation, potential future land uses would generally also be investigated.
Step 3: Develop Initial Conceptual Model Of Site Conditions
Based on existing site information, a field manager develops an initial
conceptual model before any field work is begun. This model is a basic
compilation of the field manager's understanding of existing conditions. A site
map is used for developing the initial sampling and analysis program. An
example of an initial conceptual model represented on plan view maps and a
cross-section are provided in Exhibit II-4 on page 11-15. The graphics can be
drawn by hand or generated on a computer to be revised as the assessment
progresses. On these maps, the field manager should include suspected geologic
and hydrogeologic conditions; suspected contaminant source areas; and potential
migration pathways, receptors, and sampling constraints (e.g., utilities, depth to
bedrock).
Step 4: Design Data Collection And Analysis Program
Prior to mobilization, the field manager makes use of the conceptual
model to design a data collection and analysis program. This program, which is
also referred to as the work plan, should be flexible so that the field manager can
adjust the location, quantity, depth, and type of samples based on the developing
conceptual model.
The data collection and analysis program is a general work plan which
may be informally written or simply discussed by the field manager with the
appropriate individuals, such as regulators or the responsible party. For example,
the plan may seek to identify appropriate sampling tools and analytical methods,
define the contaminant source area, and assess the property boundaries for
potential off-site or on-site migration. The field manager may need to make
minor adjustments in the program and the scope of work, within a specified
funding level. The need for changes in the program is clarified as the
understanding of the site conditions evolves.
11-6 March 1997
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Exhibit 11-3
Sources And Types Of Site History Information
Sources
Owner/
operator records
Records/Documents
Inventory records, deeds, detailed
site maps, spill and release incident
reports, historic photographs, and
environmental consulting reports
Types Of Available Information
Details regarding the storage, use,
accidental release, and disposal
of petroleum products in USTs,
site features
Municipal and/or
county offices
Records at the following
departments: Tax assessor, fire,
public works, building, utility, sewer,
sanitation, and public health
Information on current and past
owners, site history, UST permits,
maps of drainage features, and
investigation and incident reports
State government
State environmental agency;
regional water quality board; health
department; and fire marshal
Information on active and inactive
UST sites, enforcement
documents, and reports on LUSTs
Federal
government
U.S. EPA
Site investigation and incident
reports, UST and RCRA records
U.S. Geological Survey
Topographic and geologic maps,
geologic/hydrogeologic reports,
aerial photographs
Natural Resources Conservation
Service (NRCS) and Agricultural
Stabilization and Conservation
Service (ASCS)
Aerial photographs and detailed
information about soil properties
available locally
Universities,
libraries
Theses, archives, and historical
information
Information on-site development,
land use, site activities, geology,
and hydrogeology
Key personnel
(e.g., owner,
employees)
Interviews
Information regarding all aspects
of site history, especially spills,
overfills, and leaks
Miscellaneous
Aerial photographs: Listings of
available public and private aerial
photographs for given locations and
periods are available from the
National Cartographic Information
Center in Reston, Virginia
Information regarding site
development, land use,
manufacturing activities, pipeline
and UST locations
Fire insurance maps dating back to
the 1800s which depict the location
of manufacturing facilities and
potential fire hazards (e.g., USTs)
locations are available for all regions
of the U.S. from the Sanborn Map
Company in Pelham, New York
Information regarding site
development, land use, waste
disposal locations, manufacturing
activities, UST locations
Source: Modified from Cohen and Mercer, 1993
March 1997
I-7
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In some instances, the first data are collected with surface geophysical
measurements. Depending on the site conditions, surface geophysical methods
may be able to provide initial information about the location of buried objects, the
geologic and hydrogeologic conditions, and the location of floating and residual
product. This information will influence the selection of sampling tools, sampling
locations, and the analytical program. The applicability of surface geophysical
methods, such as ground penetrating radar, electromagnetics, and magnetometry,
is discussed in Chapter III of this manual.
Soil-gas surveys are also a useful method for obtaining a large amount of
site data quickly. They can play a role in ESAs by providing information on the
presence, type, and general location of contamination which can help focus more
precise sampling activities. Moreover, at some sites the health risk posed by the
upward migration of hydrocarbon vapors through the vadose zone is greater than
the risk posed by groundwater contamination. Vapor-phase pathways of
contaminant migration are especially important where there are thick unsaturated
zones and subsurface structures (e.g., basements, parking garages). Information
obtained in these surveys can also help in the design of remediation technologies
such as soil vapor extraction. A complete discussion of the types of soil-gas
surveys and their applicability to UST sites is presented in Chapter IV.
For all site assessments, at least one type of media—soil, soil gas, or
groundwater—must be sampled. Selection of the appropriate sampling tools
depends primarily on site conditions, sample depth, local geology, availability,
and cost. Direct push (DP) tools (steel rods that are pushed or driven into the
ground) can be used in unconsolidated materials to collect these samples or to
take in situ measurements using specialized DP probes. At other locations, an air
rotary or hollow stem auger (HSA) drilling rig may be required. A complete
discussion of DP applicability and associated sampling equipment appears in
Chapter V.
As mentioned earlier, an ESA requires the use of field analysis. Selection
of the appropriate method(s) for a particular site will depend on a variety of
factors including the analyte to be measured, the quality of the data, the ease of its
use, as well as cost, availability, and the speed with which it provides the data.
Typically, an ESA utilizes several analytical methods of varying quality on a large
number of samples in order to increase resolution of the contaminant plume.
Examples of commonly used methods include immunoassay test kits, calorimetric
test kits, and portable gas chromatographs (GC). These methods and selection
criteria are discussed in Chapter VI.
Acquiring access to properties neighboring a leaking underground storage
tank (LUST) site is an issue of concern in many site assessments, whether
11-8 March 1997
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expedited or conventional. Often, property owners will deny access to site
investigators, and legal methods must be pursued in order to collect soil, soil-gas,
and/or groundwater samples. When conducting an ESA, it is best to acquire
permission to sample neighboring properties, and any necessary permits, prior to
mobilization. Although, acquiring access prior to mobilization may not always be
possible, ESAs will continue to have at least two advantages over CSAs. First, it
is often easier to convince a property owner to allow investigators to collect
samples over a short period of time (i.e., hours or days) as opposed to allowing
access for several mobilizations over a period of weeks or months. Second, by
conducting an ESA, investigators will know within days whether they will require
off-site access. When conducting a CSA, this information may not be known
until much later.
Step 5: Implement On-Site Iterative Process
The on-site iterative process depicted as Step 5 in Exhibit II-2 is unique to
ESAs. As more data are obtained, the field manager refines the conceptual model.
Although CSAs contain iterative processes, it is the ESA process that requires this
work to be completed on-site during a single mobilization. The on-site iterative
process is made up of two substeps: Collecting and analyzing the data, and
evaluating the data to refine the conceptual model. If, during the course of the
investigation, the field manager discovers that the sampling tools and/or analytical
methods are inappropriate for the site conditions, he/she can amend the data
collection and analysis program. Several iterations of this process can be
completed in a day and, when this method is applied with the appropriate tools, a
typical gasoline station site can usually be completely assessed in two to four
days.
Substep 1: Collect And Analyze Data
The data collection and analysis program is an intensive, short-term, field
investigation. The program and conceptual model are refined based on on-site
measurements and observations. In order to ensure that these measurements are
accurate, the field manager checks the field-generated data, usually by developing
a quality control (QC) plan for the methods used. Examples of QC include
instrument calibration, blank results, and control samples. In addition, field
managers should check data by comparing results from different analytical
methods (e.g., field GC with immunoassay test kit) or by comparing results from
other media. The validation process is important for the development of the
conceptual model because it helps to resolve anomalous data.
March 1997 II-9
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Substep 2: Evaluate Data And Refine Conceptual Model
A key aspect of an ESA is the regular evaluation and refinement of the
conceptual model. As the initial sample collection and analysis is conducted,
certain conditions are anticipated based on the initial conceptual model. These
conditions may include the concentrations and locations of contaminants, soil
type, or depth to groundwater. As measurements are taken, variances become
apparent between anticipated conditions and actual measurements. The
conceptual model is then refined to include the current measurements and
minimize the variances.
Modify The Data Collection And Analysis Program
If, after relining the conceptual model, the field manager determines that
the methods used to collect and analyze data are not appropriate, then he/she must
modify the collection and analysis program. Modification may involve selecting
different sample collection technologies or different analytical methods. For
example, a DP rig may be unable to penetrate semi-consolidated material located
on the site and a HSA rig may be needed, or a contaminant that was not expected
(e.g., a solvent) may be discovered, necessitating the use of new field analytical
methods. Because all the analysis is completed on site in an ESA, timely
modification of procedures is possible. Various analytical methods should,
therefore, be readily available so that procedures can be quickly changed if
necessary.
Complete Expedited Site Assessment
An ESA is complete when the conceptual model:
Fits the regional geological/hydrogeological setting;
Is consistent with data collected; and
Can be used to predict subsurface conditions.
Sometimes a technical reviewer who has not been part of the field team can
provide an objective evaluation of how well the conceptual model correlates with
the site data.
11-10 March 1997
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Step 6: Consider Interim Remedial Actions
One of the major advantages of an ESA is that it makes rapid and accurate
interim remedial actions possible. These actions should follow state guidance
(e.g., preapproval may be required), however, many times remedial measures can
take place immediately after the field work of an ESA is completed and before a
formal report is submitted. For instance, an ESA may define the location of a
significant quantity of free product or it may indicate that a contaminant plume is
approaching a public drinking well. Because a formal report may take two weeks
to write and review of the report may take longer, an interim remedial action can
prevent a significant quantity of contaminants from spreading. If appropriate
actions are undertaken in a timely manner, potential adverse affects to human
health and the environment can be avoided, and the long-term cost of remediation
can be minimized.
Step 7: Report The Findings
As with any site assessment, a report is written when the field work is
completed. Because a greater quantity of data will be collected with a ESA than is
possible with a CSA, an ESA should provide a more comprehensive
representation of the site conditions. An ESA report will demonstrate an
understanding of the 3-dimensional distribution of contamination, define the
geological/hydrogeological site conditions, and identify migration pathways and
points of exposure. As a result, ESAs provide a better basis for selection of
appropriate corrective action options in significantly less time than is required
with CSAs.
March 1997 11-11
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Conventional And Expedited Site
Assessment Examples
The following is an example of how a well planned CSA and an ESA
would proceed at the same site. The scenario is based on two actual assessments
at one site, however, the details have been modified in order to provide the reader
with a comparison. The CSA focused on installing a limited number of
groundwater monitoring wells as part of a multiple-phase assessment. The ESA
focused on a 3-dimensional definition of site conditions to develop and refine the
conceptual model.
Release Scenario
In 1995 an UST system was being replaced at a service station in order to
meet the 1998 tank upgrade requirements. The system consisted of two 10,000-
gallon steel tanks and piping that had been installed in 1965. When they were
removed, both tanks and their associated piping showed signs of significant
corrosion, and the soils were stained with gasoline. The pit and the piping trench
were over-excavated to remove some contamination, but stained soils remained.
The release was reported to the state environmental department (SED), which then
ordered that a site assessment be conducted.
Step 1: Establish Site Assessment Objectives (ESA And CSA)
The objectives for this assessment are the same for both an ESA and a
CSA: Define the source area, characterize the site geology/hydrogeology, and
delineate the extent of contamination in soil and groundwater. In addition, the
major migration pathways and points of exposure also need to be determined in
order for the state and the owner to make corrective action decisions.
Step 2: Review Existing Site Information (ESA And CSA)
In both the ESA and the CSA for this site, a review of background
information was completed, however, the focus differed. In the CSA, information
was reviewed in order to select the best location of three monitoring wells. In the
ESA, the background information was reviewed in order to develop a
3-dimensional conceptual model of site conditions which were then plotted on
maps and used to guide the investigation.
11-12 March 1997
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Site Interviews
The current owner stated that he bought the facility in 1984 and did not
have any information about the use of the site prior to 1965. He knew that the
tanks and piping were in need of upgrading but had no indication that they were
leaking. Five tank and line tightness tests had been performed between 1988 and
1994, and none indicated a problem. The owner was not aware of any noticeable
inventory losses. He was also not able to locate any site plans that would indicate
migration pathways.
Employees stated that they did not notice any obvious inventory losses.
However, after the tank and piping were removed, the employees did notice
significant corrosion on the north side of the tank and on some of the pipes. The
employees also stated that all product lines were removed.
Site Geology
Since two 10,000-gallon tanks had just been excavated, the geologist had a
clear view of the site stratigraphy. The excavation was 20 feet deep, 30 feet long,
and 25 feet wide. The soil was composed of silt and clay, and it appeared to have
a low hydraulic conductivity. The pit did not intercept groundwater.
Inventory Records Search
Inventory records were analyzed but did not prove helpful because of
incomplete and inconsistent information.
Receptor Survey
A survey of potential downgradient receptors indicated no wells within 0.5
mile, but several industrial buildings with basements were located nearby.
Other Environmental Investigations
The site assessment personnel reviewed state corrective action reports for
possible upgradient sources and for regional geological information. They found a
report from a LUST site 0.5 mile upgradient. In reviewing the report, the site
assessment personnel noted that buried stream channels existed in the region.
March 1997 11-13
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Geologic Reports
Site assessment personnel reviewed USGS maps and reports, State
Geologic Survey, Soil Conservation Service, and the local Water Service and
found:
Regional depth to groundwater is 20 to 30 feet below ground surface (bgs);
Regional groundwater flow is to the north;
Silts and clays are the predominant regional soil type; and
Buried stream channels occur within the silts and clays and have a
northwest regional orientation.
Step 3: Develop Initial Conceptual Model Of Site Conditions (ESA
And CSA)
Based on the review of existing regional and site data, investigators
developed an initial conceptual model of the site geology, hydrogeology, nature
and extent of contamination, contaminant migration pathways, and points of
exposure. This initial conceptual model is presented in Exhibit B-4. For the
CSA, site assessment personnel used this information to locate monitoring wells,
to determine the approximate depth to be drilled, and to analyze data when
available. For the ESA, the field manager incorporated the information onto site
maps in the field as the assessment proceeded. These maps served as a basis for
the working hypothesis of the site geology, hydrogeology, and extent of
contamination. Sample locations were selected to test these hypotheses and
resolve anomalies while on site.
Geology
Regional fluvial deposits are oriented NW. Sands in these units are
typically 2 to 15 feet thick and are surrounded by silt and clay. Granitic bedrock
occurs at a depth of approximately 500 feet bgs.
Hydrogeology
Unconfined groundwater occurs regionally within the unconsolidated
sediments at depths ranging from 20 to 30 feet bgs. Regional groundwater flows
11-14 March 1997
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to the north, however, localized groundwater flow patterns occur through more
permeable buried stream channels.
Source Area And Extent Of Contamination
Locations of the tanks, subsurface piping, on-site utility lines, and areas of
artificial fill were compiled onto the site map. The relative magnitude of the
petroleum release was estimated to be small (perhaps 300 gallons) because no
significant loss of product was noticed, and field observations indicated a slow
leak. The extent of contamination was believed to be contained on-site if the
plume had not reached a buried stream channel. If a preferential pathway had
been intercepted by the plume, contamination may have migrated off-site.
Step 4: Design Data Collection And Analysis Program (CSA)
Before beginning the field investigation, the site assessment managers
must develop a data collection and analysis program for the field work. This
program is also referred to as the initial work plan. From this point, the two site
assessments begin to differ. The remainder of the CSA is presented first. The
results are compared with the summary of the ESA that follows.
Conventional Site Assessment Work Plan
A hollow stem auger (HSA) drill rig was selected to collect soil samples
and install 4-inch monitoring wells. Two wells would be installed downgradient
from the USTs and pump islands, and a third would be installed upgradient from
the tank excavation. Because the direction of regional groundwater flow is to the
north, the wells would be placed in the locations designated on the map in Exhibit
II-5a. A split-spoon sampler would be used to collect soil every 5 feet and, if
screening analysis with a portable flame ionization detector (FID) indicated
contamination, samples would be sent off-site for laboratory analysis. If no
contamination was indicated through FID screening, a soil sample close to the
water table would be sent to a laboratory. All soil samples would be logged with
information about the vadose zone (e.g., thickness, soil type, porosity, structure,
stratigraphy, heterogeneities, moisture content, and location of contaminants).
Groundwater samples from the three wells would also be analyzed off-site. Soil
samples would be analyzed for both BTEX and TPH, while groundwater samples
would be analyzed for BTEX.
11-16 March 1997
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Step 5: Field Work (CSA)
During days one and two, the three monitoring wells (MW) were installed.
Soil profiles from the two downgradient monitoring wells indicated only silt and
clay sediments. The soil profile from the upgradient monitoring well (MW-3)
indicated 10 feet of sand starting at 20 feet bgs. No soil contamination was
detected at any of the locations; therefore, only three soil samples (one from each
boring) were collected and sent off-site for further analysis.
On the third day, the geologist returned with an assistant to develop the
wells. On the fourth day the groundwater level in MW-3 had fully recovered
(because it was screened in sand) and was sampled. The two downgradient wells
screened in silt and clay took a week to recover. All wells were then sampled,
including MW-3 for a second time. The geologist received the laboratory
analytical results four weeks after samples were collected (standard turnaround
time) and then spent another week preparing a report for the SED and facility
owner.
Step 6: Consider Interim Remedial Actions (CSA)
Prior to the assessment, the SED requested that the tank pit and piping
trenches be over-excavated in order to remove contaminants from the source area.
Because so little information was obtained from the CSA, the site assessment
manager could not recommend additional interim remedial actions.
Step 7: Report The Findings (CSA)
The geologist submitted the report eight weeks after the assessment was
requested. The maps in Exhibit 11-5 show the findings. The major conclusions of
the report are as follows:
Groundwater depth is 26 feet bgs, and the flow appears to be north.
The extent and quantity of contamination at this site is unknown.
Additional investigation is needed in neighboring properties to better
delineate the contaminant plume.
The extent of the sand lens penetrated by MW-3 should be further
investigated.
11-18 March 1997
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Step 4: Design Data Collection and Analysis Program (ESA)
The ESA used a very different process from the CSA; as a result, the
findings of the ESA were more complete. The scope of work of the ESA included
the following equipment and activities.
Direct Push Sampling
The field manager selected a DP rig for sampling of soil and groundwater
because the subsurface materials were unconsolidated and the depth of
investigation was relatively shallow. A cased system (Chapter V, Direct Push
Technologies) was selected because of its capability to quickly collect continuous
core samples. In unconsolidated material, this equipment can generate up to
200 feet of continuous cores per day.
Field Analysis
After obtaining permission from the state environmental department, the
field manager contracted the services of a certified mobile laboratory to perform
the analytical testing using state approved methods. Soil samples would be
analyzed for both BTEX (by the mobile laboratory using EPA Method 8021
(GC/PID)) and total petroleum hydrocarbons as gasoline (TPH-g) (using Modified
EPA Method 8015 (GC/FID)), while groundwater samples would be analyzed for
BTEX only. The mobile laboratory selected could process up to 25 samples/day.
Soil Screening
All soil samples would be screened in the field for total organic volatiles
(TOVs) via ambient air measurements using an FID. An FID was used because of
its high sensitivity to gasoline vapors (0.1 ppmv). Soil samples would be analyzed
by the mobile laboratory either whenever soil screening indicated contamination
or just above the water table if soil screening did not indicate contamination.
Groundwater Sampling
Groundwater samples would be collected and analyzed by the mobile
laboratory at every probe location. Between six and eight temporary monitoring
points would also be installed with DP equipment in order to determine hydraulic
gradient and obtain groundwater samples over time.
March 1997 11-19
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Physical Properties
Continuous cores would be collected at each probe location. Every core
would be logged and recorded by a geologist. Logs would include the vadose
zone thickness; soil type and estimate of porosity; structure; stratigraphy;
heterogeneities; moisture content; and location of constituents of concern. In
addition, soil samples would be collected for off-site analysis of total organic
carbon (TOC), bulk density, and moisture content to make more accurate
estimates of contaminant migration potential. The aquifer flow direction and
gradient would be determined from water level measurements, and hydraulic
conductivity would be determined from slug tests conducted with 1.5 inch
temporary monitoring points. Groundwater quality indicators (e.g., pH, total
dissolved solids, electrical conductivity) would be measured using portable
meters. Dissolved oxygen would also be measured, using a flow-through cell, to
provide information about biodegradation of petroleum compounds. Groundwater
samples would also be sent to an off-site laboratory for analysis of biodegradation
indicators (NO,, SO,, Fe, Mn +, CH4, and CO,). These parameters would help
evaluate the potential for contaminant migration and biodegradation.
Communicating Project Status
The field manager agreed to update the owner and SED with the status of
the ESA at the end of each field day. The field manager had a pager and portable
telephone to communicate with all project participants whenever necessary.
Permits
The field manager obtained the necessary permits for drilling borings with
DP probes and installing monitoring points. The field manager also obtained an
encroachment permit from the city and filed a traffic plan with the county public
works department in order to collect samples off-site under 3rd Street and
B Street, if necessary.
Utility Clearance
Delineating the location of on-site utilities had already been completed for
the tank excavation, however, the field manager suspected that a few off-site
samples would be needed. A utility service was contacted and returned to the site
to delineate the surrounding off-site utilities. This activity was supervised by the
field manager so that the areas to be sampled would be well marked.
11-20 March 1997
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Step 5: Implement On-Site Iterative Process (ESA)
The field investigation was completed in 3 days by using the iterative
process depicted in Exhibit 11-2. Soil and groundwater samples were collected
and analyzed; the conceptual model was refined on-site; and subsequent sampling
and analysis helped to finalize the assessment.
Day 1: Conduct Initial Investigation
On the first day of the field investigation, the following activities were
conducted:
• Continuous soil cores were collected and logged at seven locations to a
depth of 20 to 40 feet.
• Six 1.5-inch-diameter temporary monitoring points were installed to
measure the groundwater elevation and to define groundwater flow
direction.
• Twenty soil samples were analyzed for BTEX and TPH by the mobile
laboratory.
• Seven groundwater samples were collected and analyzed for BTEX by the
mobile laboratory.
• Three soil samples were collected and preserved for off-site analysis of
total organic carbon (TOC), bulk density, and moisture content to evaluate
the potential for contaminant migration.
• Two groundwater samples were collected and preserved for off-site
analysis of water quality to evaluate in situ biodegradation of
contaminants. Dissolved oxygen was measured in the field.
Information obtained on Day 1 was compiled on field drawings shown in
Exhibit II-6. The key findings included the following:
The UST area was the major source of contamination. Soil below the
tanks was contaminated with gasoline, and an inch of free product was
discovered above the water table.
March 1997 11-21
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Although there was significant contamination around the dispensers and
piping, petroleum had not migrated to the water table in this area because
of the low hydraulic conductivity of the surrounding soils.
A buried stream channel was defined at depths between 20 and 33 feet bgs
in four locations.
Isoconcentration contours of benzene in the groundwater samples clearly
indicated a northwest orientation and probable migration of dissolved
contaminants within the sand unit.
Indications of a possible off-site source were also discovered. Benzene
concentrations in groundwater upgradient from the former UST area were
anomalously high, and the chromatograms indicated a higher ratio of toluene to
benzene than from the sample downgradient from the UST area.
Days 2 And 3: Refine Conceptual Model
Characterization of the site continued on Days 2 and 3 to refine the
conceptual model. The information was compiled on-site maps presented in
Exhibit II-7. By the end of Day 3:
Seventeen additional continuous core samples were collected.
Two additional temporary monitoring points were installed.
Fourteen groundwater samples were analyzed by the mobile laboratory.
Twenty-five soil samples were analyzed by the mobile laboratory.
By the end of Day 3, the following information was determined:
The eastern and western limits of the buried stream channel were defined.
The eastern and northern portions of the site were shown to be underlain
entirely by silt and clay. Groundwater was not contaminated in these
locations.
Contours of BTEX in soil showed that the highest levels of contamination
were directly beneath the former UST excavation. Analysis of
groundwater samples showed that the dissolved plume of benzene
extended off-site toward the north-northwest, beneath 3rd Street.
March 1997 II-23
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The tank backfill material was found to be in direct contact with a buried
stream channel.
Two more soil and groundwater samples were collected upgradient from
the site to investigate the anomalous analytical data collected during
Day 1. Although the soil samples were clean, the groundwater samples
confirmed the initial suspicion of an off-site source.
Water elevations measured in the temporary monitoring points indicated
that groundwater within the silt and clay flows toward the north, consistent
with the regional groundwater flow direction. As expected, groundwater in
the buried stream channel flowed toward the northwest.
Low dissolved oxygen levels were found in the core of the plume. There
was also a significant reduction in dissolved BTEX concentrations in
groundwater downgradient from the USTs.
Finalize Conceptual Model
By the end of the third day, the conceptual model had been developed in
sufficient detail to meet the objectives of the project. No anomalies remained, and
new DP probes yielded expected geologic information and analytical results.
Moreover, the site data, including the geologic units, groundwater depth and flow
direction, and upgradient impacts, were consistent with the regional setting.
Decommission Site
Before de-mobilizing, two of the eight temporary monitoring points were
removed, and the resulting holes were filled with bentonite grout. The remaining
six temporary monitoring points were left in place for one year (to provide
additional groundwater elevation and analytical data) before they were removed.
Step 6: Consider Interim Remedial Actions (ESA)
After evaluating the data obtained in the three-day ESA, the field manager
consulted with the SED to determine if any interim remedial actions should be
taken. Since the contaminant plume did not pose an immediate threat to human
health or the environment, and free product was not likely to spread significantly
before a permanent corrective action technology was selected and implemented,
they decided that there was no need to take additional interim remedial actions
March 1997 11-25
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beyond the over-excavation of the contaminated soil in the tank pit and piping
trenches that had occurred prior to the assessment. Because of the limited volume
of gasoline discovered at the site, the SED determined that free product recovery
was not appropriate to implement.
Step 7: Report The Findings (ESA)
Two weeks after the field work was complete, the field manager submitted
a report to the SED and the site owner. The main findings for this investigation
were:
The USTs were the primary source of contamination. Contamination
around associated piping was not continuous to groundwater.
Approximately 600 gallons of petroleum had been released. An inch of
free product was on the water table, and a dissolved plume had migrated
off-site. The areal and vertical extent of BTEX concentrations in soil and
groundwater was defined.
A buried stream channel was the primary migration pathway for the
petroleum release.
A potential upgradient source of dissolved hydrocarbons was identified.
In situ biodegradation of petroleum hydrocarbons is occurring beneath the
site.
Analysis Of Conventional And Expedited Site Assessments
The ESA presented in this example cost significantly more than the CSA;
however, the CSA is only an initial investigation and would require at least one
more mobilization (probably two or three) for the site to be adequately
characterized. In contrast, the ESA is complete. The one report would be enough
for a regulator and facility owner to make effective corrective action decisions. A
direct comparison of the costs is, therefore, not possible with the data provided.
However, if the CSA was completed to provide enough information to make an
accurate corrective action decision, the number of wells and the analyses would
have probably cost significantly more than the ESA.
The primary advantage of an ESA is that it provides the user with rapid,
accurate information about the extent of contamination and migration pathway so
11-26 March 1997
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that effective remedial decisions can be made after only one mobilization.
Although the initial cost of an ESA is often higher than the first phase of a CSA,
the final cost is often much less. These savings are the result of:
Characterization of a site in a single mobilization;
Optimal placement of permanent monitoring wells;
Effective corrective action measures being undertaken and optimized (e.g.,
improved location of air sparging points and soil vapor extraction wells);
Reduction in the administrative costs of writing and reviewing reports; and
Reduced sampling and analysis of unnecessary and poorly placed
monitoring wells.
March 1997 II-27
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References
ASTM. 1995a. Standard guide to site characterization for environmental
purposes with emphasis on soil, rock, the vadose zone, and ground water, D5730-
95. Annual Book of ASTM Standards, Philadelphia.
ASTM. 1995b. Standard guide for risk-based corrective action applied at
petroleum release sites, El739-95. Annual Book of ASTM Standards,
Philadelphia.
ASTM. 1995c. Provisional standard guide for accelerated site characterization
for confirmed or suspected petroleum releases, PS3-95. Annual Book of ASTM
Standards, Philadelphia.
Burton, J.C., J.L.Walker, P.K. Aggarwal, and W.T. Meyer. 1995. Expedited site
characterization: An integrated approach for cost- and time-effective remedial
investigation. Argonne National Laboratory.
Cohen, R.M. and J.W. Mercer. 1993. DNAPL Site evaluation. C.K. Smoley,.
Boca Raton: CRC Press.
New Jersey Department of Environmental Protection and Energy. 1994. Field
analysis manual.
Texas Natural Resource Conservation Commission. 1995. Accelerated site
assessment process procedure: A guidance manual for assessing LPST sites in
Texas. Austin.
U.S. EPA. 1997. Test methods for evaluating solid waste, third update of third
edition, SW-846. Office of Solid Waste, Washington, DC.
U.S. EPA. 1993. Draft field methods compendium. Office of Emergency and
Remedial Response 9285.2-11. Washington, DC.
U.S. EPA. 1995. Use of risk-based decision-making in UST corrective action
programs, Directive 9610.17, Office of Solid Waste and Emergency Response,
Washington, DC.
11-28 March 1997
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Peer Reviewers
Name
Gilberto Alvarez
David Ariail
J. Russell Boulding
Jeff Erikson
Chi-Yuan Fan
Blayne Hartman
Bill Kramer
Al Liguori
Chris O'Neill
Emil Onuschak, Jr.
Greg Reuter
Charlita Rosal
Sandra Stavnes
Michael Taylor
Katrina Varner
Company/Organization
U.S. EPA, Region 5
U.S. EPA, Region 4
Boulding Soil-Water Consulting
Mobil Oil Corporation
U.S. EPA, National Risk Management
Research Laboratory
Transglobal Environmental Geochemistry
Handex Corporation
Exxon Research and Engineering Company
New York State Department of
Environmental Conservation
Delaware Department of Natural Resources
Handex Corporation
U.S. EPA, National Exposure Research
Laboratory
U.S. EPA, Region 8
Land Tech Remedial, Inc.
U.S. EPA, National Exposure Research
Laboratory
March 1997
II-29
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Chapter III
Surface Geophysical Methods
-------
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Contents
Exhibits Ill-iv
Surface Geophysical Methods Ill-l
Geophysical Methods 111-4
Ground Penetrating Radar 111-4
Electromagnetic Methods 111-6
Electrical Resistivity 111-8
Metal Detection 111-1 0
Seismic Methods 111-11
Magnetic Methods 111-14
Geophysical Applications III-I6
Locating Buried Objects 111-16
Ground Penetrating Radar 111-17
Metal Detection III-I7
Magnetometry III-20
Electromagnetic Methods III-22
Assessing Geological And Hydrogeological Conditions Nl-24
Seismic Refraction III-26
Electromagnetic Methods III-28
Ground Penetrating Radar III-28
Electrical Resistivity 111-31
Delineating Residual Or Floating Product 111-31
Ground Penetrating Radar III-32
Electrical Resistivity III-33
Geophysical Equipment Manufacturers III-35
References IH-37
Peer Reviewers III-39
March 1997
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Exhibits
Number Title Page
111-1 Summary Of Surface Geophysical Method Applicability III-3
III-2 Schematic Drawing Of Ground Penetrating Radar
Operating Principles , III-5
III-3 Schematic Drawing Of Electromagnetic Operating
Principles III-7
III-4 Schematic Drawing Of Electrical Resistivity
Operating Principles III-9
III-5 Schematic Drawing Of Metal Detection Operating
Principles 111-11
III-6 Schematic Drawing Of Seismic Refraction
Operating Principles . . . . , 111-13
III-7 Schematic Drawing Of Magnetometry Operating Principles . 111-15
III-8 Summary Of Geophysical Methods For Locating
Buried Objects 111-18
III-9 Ground Penetrating Radar Survey And Interpretation
Of Buried USTs 111-19
111-10 Metal Detection Survey And Interpretation At LIST Site 111-21
111-11 Magnetometry Survey At Stanford University Test Site III-22
111-12 Electromagnetic Survey And Interpretation At LIST Site .... III-23
111-13 Summary Of Geophysical Methods For Assessing Geologic
And Hydrogeologic Conditions III-25
111-14 Seismic Refraction Survey And Interpretation III-27
111-15 Time-Domain Electromagnetic Survey Of Stratigraphy III-29
l-iv March 1997
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11-16 Ground Penetrating Radar Survey And Interpretation
Of Karst , III-30
11-17 Summary Of Geophysical Methods For Delineating Residual
And Floating Product III-32
1-18 Petroleum Contamination Detected With Ground
Penetrating Radar III-34
11-19 Geophysical Equipment Manufacturers III-35
II-20 Matrix Of Manufacturers And Equipment IH-36
March 1997 m-v
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Chapter III
Surface Geophysical Methods
Geophysical methods provide information about the physical properties of
the earth's subsurface. There are two general types of methods: Active, which
measure the subsurface response to electromagnetic, electrical, and seismic
energy; and passive, which measure the earth's ambient magnetic, electrical, and
gravitational fields. Information provided by these tools can be applied to UST
sites by helping to locate buried objects, to determine geologic and hydrogeologic
conditions, and, occasionally, to locate residual or floating product.
Geophysical methods can also be subdivided into either surface or
borehole methods. Surface geophysical methods are generally non-intrusive and
can be employed quickly to collect subsurface data. Borehole geophysical
methods require that wells or borings be drilled in order for geophysical tools to
be lowered through them into the subsurface. This process allows for the
measurement of in situ conditions of the subsurface. In the past, using borehole
geophysical methods had not been cost-effective for most UST site investigations;
however, in recent years, direct push (DP) technology probe rods have been fitted
with geophysical sensors that can provide geophysical information rapidly.
Although many geophysical methods are not available with DP technologies, the
methods that are available can often provide information more cost effectively
than traditional borehole geophysical methods. As a result, borehole geophysics
will be mentioned only briefly in this chapter. Geophysical sensors available
with DP equipment are discussed in Chapter V, Direct Push Technologies.
Data collected with geophysical tools are often difficult to interprete
because a given data set may not indicate specific subsurface conditions (i.e.,
solutions are not unique). Instead, data provided by these tools indicate anomalies
which can often be caused by numerous features. As a result, geophysical
methods are most effectively used in combination with other site information
(e.g., data from different geophysical methods, sampling and analytical tools,
geological and historic records, anecdotal information). A combination of these
sources is often necessary to resolve ambiguities in geophysical plots (i.e., the
graphical representation of data produced by a specific method).
Geophysical methods can be important tools both in the implementation of
cost-effective expedited site assessments (ESAs) and in the remediation design
and monitoring phases. When they are used as part of an ESA, geophysical
methods are, typically, best used in the initial phase of an investigation to help
focus resources for the remainder of the assessment.
March 1997 111-1
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Exhibit III-l provides a general guide to the applicability of the most
appropriate geophysical methods for UST site investigations. The six
technologies are ground penetrating radar, electromagnetic methods, electrical
resistivity, metal detection, seismic methods, and magnetometry. All geophysical
methods have limitations that will affect their applicability at specific sites. This
chapter is designed to provide the reader with a basic understanding of when to
consider using geophysical methods and which methods are applicable for specific
conditions. It is beyond the scope of this chapter to discuss all geophysical
methods that are potentially useful for the applications discussed below. There
are numerous geophysical methods that are only marginally applicable for UST
site investigations because of the interferences from cultural objects (e.g.,
buildings, pipes) or because of the cost. In addition, there are numerous
configurations for applying geophysical methods that can be used to minimize
interferences and improve resolution. These specific configurations are also
beyond the scope of this chapter and are best resolved by discussing specific site
assessment objectives with an expert geophysicist. The reader may also refer to
Dobecki (1985) and Daily ( 1995) for more information on these configurations.
In addition to this chapter, there are several documents developed by the
U.S. EPA that provide useful information for the lay reader. A complete
overview of available geophysical methods is provided in Use of Airborne,
Surface, and Borehole Geophysical Techniques at Contaminated Sites (EPA,
1993b). The Geophysical Advisor Expert System (Olhoeft, 1992) is a software
program that can help the user determine the most applicable geophysical methods
for specific site conditions. Information about a specific site is entered in
response to questions asked by the program. Geophysical Techniques for Sensing
Buried Wastes and Waste Migration (Benson, et al, 1984) is also a useful
resource that provides a more complete discussion of the most applicable
geophysical methods for environmental site assessment purposes.
The remainder of this chapter is divided into two sections. First, a
methodology section provides general information about the applicability,
operating principles, advantages and limitations of the geophysical methods listed
in Exhibit III-l. Because many of these methods have multiple applications at
UST sites, application sections have been developed to make comparisons
between methods for specific tasks. The applications fall into three categories
also presented in Exhibit III- 1: Locating buried objects, assessing geologic and
hydrogeologic conditions, and delineating residual and floating product. For the
convenience of the reader a list of equipment manufacturers and a matrix of their
products are included at the end of the chapter.
1-2 March 1997
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III-3
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Geophysical Methods
The following section provides overviews of the geophysical methods that
are most likely to be useful at UST sites. The discussions summarize the uses of
the method, its operating principles, and its advantages and limitations.
Schematic drawings of the operating principles of these methods are also
provided.
Ground Penetrating Radar
Ground penetrating radar (GPR) can be a very useful geophysical method
for UST sites because it is appropriate for a broad range of investigations and is
only rarely affected by cultural interferences (e.g., buildings, fences, power lines).
GPR can be helpful in:
Locating USTs, utilities, and backfilled areas;
Determining geologic and hydrogeologic conditions; and
Occasionally, delineating floating product.
GPR uses high frequency electromagnetic waves (i.e., radar) to acquire
subsurface information. The waves are radiated into the subsurface by an emitting
antenna. When a wave strikes a suitable object, a portion of the wave is reflected
back to a receiving antenna. Measurements are continuously recorded with a
resolution that is significantly higher than most other surface geophysical
methods, providing a profile (i.e., cross-section) of subsurface conditions.
Exhibit III-2 provides a schematic drawing of the GPR operating principles.
The GPR method utilizes antennas that emit a single frequency between
10 and 3000 MHz. Higher frequencies within this range provide better subsurface
resolution at the expense of depth of penetration. Lower frequencies in this range
allow for greater penetration depths but sacrifice subsurface target resolution. In
UST investigations, the working frequency range is generally 100 to 900 MHz.
Frequencies above 900 MHz are typically used for investigations less than 2 feet
below ground surface (bgs).
In addition to the antenna frequency, the depth of wave penetration is
controlled by the electrical properties of the media being investigated. In general,
the higher the conductivity of the media, the more the induced radar wave is
attenuated (absorbed), lessening the return wave. Electrically conductive
materials (e.g., many mineral clays and soil moisture rich in salts and other free
ions) rapidly attenuate the radar signal and can significantly limit the usefulness
111-4 March 1997
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Exhibit 111-2
Schematic Drawing Of Ground Penetrating Radar
Operating Principles
Graphic Recorder
Antenna
Source: Benson et al., 1984
of GPR. For example, in shallow, wet clays with high conductivity values
(30 millimhos per meter or greater), the depth of penetration may be less than
2 feet. In contrast, in dry materials that have electrical conductivity values of only
a few millimhos per meter, such as clay-free sand and gravel, penetration depths
can be as great as 90 feet. Penetration depths typically range between 3 and 15
feet bgs. As a result, it is important to research the likely subsurface materials in
an area before deciding to use this method. Test surveys are also commonly used
to help predict the success of GPR.
The depths to reflecting interfaces can be calculated from the two-way
travel times of the reflected waves. Travel times are measured in nanoseconds
(i.e., 1 billionth of a second). Because the velocity of electromagnetic radiation
through various materials is well established, one can calculate the depth of
penetration with various techniques. Estimations can also be made if the nature of
the subsurface materials is only generally known.
March 1997
I-5
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GPR measurements are usually made along parallel lines that traverse the
area of interest. The spacing of the lines depends on the level of detail sought and
the size of the target(s) of interest. Traverse rates can vary greatly depending on
the objective of the survey. Typically, an average walking pace of 2 to 3 miles per
hour is used. Some very detailed investigations can be as slow as 0.1 mile per
hour, and newer systems can be mounted on vehicles and used at speeds up to 65
miles per hour for reconnaissance of the shallow subsurface. The data can be
recorded for processing off-site, or they can be produced in real-time for analysis
in the field.
GPR is relatively unaffected by above surface cultural interferences if the
GPR antennas are shielded. For antennas that are not shielded, an experienced
operator can often distinguish and ignore reflections from overhead objects.
Subsurface cultural interferences include densely packed rebar used in reinforced
concrete (the density at which rebar is a problem is site specific), wire mesh (often
used for concrete floors in buildings), and pipes and utilities (if geology is the
target).
Electromagnetic Methods
Electromagnetic (EM) methods, also referred to as electromagnetic
induction methods, are some of the most diverse and useful geophysical
techniques. Although they are commonly subject to cultural interferences, they
can:
Locate buried objects (metal and non-metal);
Obtain geologic and hydrogeologic information; and
On rare occasions, delineate residual and floating product,
Although both GPR and metal detectors utilize electromagnetic radiation,
EM methods in this chapter refer to the measurement of subsurface conductivities
by low frequency electromagnetic induction. A transmitter coil radiates an
electromagnetic field which induces eddy currents in the subsurface. The eddy
currents, in turn, induce a secondary electromagnetic field. The secondary field is
then intercepted by a receiver coil. The voltage measured in the receiver coil is
related to the subsurface conductivity. These conductivity readings can then be
related to subsurface conditions. Exhibit III-3 presents a schematic drawing of
EM operating principles.
The conductivity of geologic materials is highly dependent upon the water
content and the concentration of dissolved electrolytes. Clays and silts typically
exhibit higher conductivity values because they contain a relatively large number
111-6 March 1997
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Exhibit 111-3
Schematic Drawing Of Electromagnetic Operating Principles
Second&y Fields
From Current Loops
^ Sensed by
Receiver Coil
Source: U.S. EPA, 1993a
of ions. Sands and gravels typically have fewer free ions in a saturated
environment and, therefore, have lower conductivities. Metal objects, such as
steel USTs, display very high conductivity measurements which provide an
indication of their presence.
There are two basic types of EM methods—frequency domain (FD) and
time domain (TD). FDEM measures the electrical response of the subsurface at
several frequencies (different separation distances between the transmitter and
receiver can also be used) to obtain information about variations of conductivity
(or its reciprocal, resistivity) with depth. TDEM achieves the same results by
measuring the electrical response of the subsurface to a pulsed wave at several
time intervals after transmission, longer time intervals measure greater depths.
Both methods have overlapping applicabilities.
March 1997
I-7
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The EM receiver and transmitter coils can be configured in many different
ways, depending on the objectives of the survey. One common configuration for
shallow environmental investigations utilizes transmitter and receiver coils that
are attached to the ends of a rigid fiberglass rod at a fixed distance (i.e., fixed-coil
separation). The equipment is then moved across the area of investigation. This
configuration is particularly suitable for detection of USTs and metal pipes.
The limitations of EM methods are primarily a result of the interferences,
typically caused when this method is applied within 5 to 20 feet of power lines,
buried metal objects (including rebar), radio transmitters, fences, vehicles, or
buildings. In addition, its success depends upon subsurface conductivity
contrasts. For example, the difference in conductivity between an UST and
surrounding natural or fill material is typically adequate for detection. However,
mapping more subtle targets, such as fine versus coarse material or contamination,
is less predictable. Consequently, pilot studies can be conducted to determine if
an adequate conductivity contrast exists for the objective of the study.
Electrical Resistivity
Electrical resistivity, also referred to as galvanic electrical methods, is
occasionally useful at UST sites for determining shallow and deep geologic and
hydrogeologic conditions. By measuring the electrical resistance to a direct
current applied at the surface, this geophysical method can be used to:
Locate fracture zones, faults, karst, and other preferred
groundwater/contaminant pathways;
Locate clay lenses and sand channels;
Locate perched water zones and depth to groundwater; and
Occasionally, locate large quantities of residual and floating product.
A variety of electrode configurations or arrays (e.g., Wenner,
Schlumberger, dipole-dipole) can be used depending on the application and the
resolution desired. Typically, an electrical current is applied to the ground
through a pair of electrodes. A second pair of electrodes is then used to measure
the resulting voltage. The greater the distance between electrodes, the deeper the
investigation. Because various subsurface materials have different, and generally
understood, resistivity values, measurements at the surface can be used to
determine the vertical and lateral variation of underlying materials. As with EM,
success depends upon subsurface resistivity contrasts. Exhibit III-4 presents a
schematic drawing of electrical resistivity operating principles using the Wenner
array.
1-8 March 1997
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Exhibit 111-4
Schematic Drawing Of Electrical Resistivity Operating Principles
Current
Source
Current Meter
Surface
Current Flow
Through Earth
Source: Benson et al., 1984
Although resistivity is subject to interferences from the same objects as
EM, it is less affected by them. In addition, if the location of metal pipes and
utilities is known, electrode arrays can often be arranged to minimize
interferences. Furthermore, resistivity resolution is comparable to, and sometimes
better than, EM.
Electrical resistivity, however, has a number of limitations. The following
is a list of the most significant issues that should be considered when selecting
this method:
Electrodes must be in direct contact with soil; if concrete or asphalt are
present, holes must be drilled for inserting the electrodes and then refilled
when the survey is complete.
For deep investigations, electrode arrays can be quite long. The distance
between outside electrodes must be 4 to 5 times the depth of investigation.
March 1997
I-9
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Measurements may be limited by both highly conductive or highly
resistive surface soils. If shallow clays and extremely shallow
groundwater are present, most of the current may concentrate at the
surface. Although the condition is very rare, the presence of thick, dry,
gravelly material (or massive dry material) at the surface may prevent the
current from entering the ground.
Metal Detection
Metal detectors, also referred to as pipeline and cable detectors, are widely
used at UST sites for the specific application of locating buried metal objects,
both ferrous and non-ferrous in a process called metal detection (MD). MD can
be used at UST sites to locate:
Steel and composite (i.e., fiberglass-coated steel) tanks;
Metal piping; and
Utilities.
There are two types of MD~frequency domain and time domain.
Frequency-domain metal detectors are typically used for locating shallow metals
(less than 2 feet) and for tracing piping and cables at UST sites. Time-domain
metal detection is useful for investigations from 0 to 15 feet and for locating USTs
or buried drums. Both types provide good response to all metal objects.
Metal detectors operate by the same principles as EM methods, but they
are adapted to the specific purpose of locating metal objects. When the
subsurface current is measured at a specific level, the presence of metal is
indicated with a meter reading, with a sound, or with both. Commercial metal
detectors used for locating USTs also have data recording capabilities although
stakes or paint marks are typically placed over targets as the survey proceeds.
Exhibit III-5 presents a schematic drawing of MD operating principles.
The depth of investigation with MD surveys is dependent primarily on the
surface area and the depth of the object. The response of MD decreases
dramatically with depth. As a target depth is doubled, the response decreases by a
factor of as much as 64 (the response to small objects decreases more rapidly than
the response to large objects). However, metal detectors are very appropriate for
UST sites because they are capable of detecting metal utilities up to 3 feet bgs,
a 55-gallon metal drum up to 10 feet bgs, or a 10,000-gallon steel tank up to
20 feet bgs.
1-10 March 1997
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Exhibit 111-5
Schematic Drawing Of Metal Detection Operating Principles
Source: Benson et al., 1984
MD is less sensitive to surface and subsurface interferences than EM
methods, but care must be taken to minimize noise from metal fences, vehicles,
buildings, and buried pipes. Rebar in concrete is perhaps the most common
problem for this method at UST sites. The electrical conductivity of the soil does
not cause significant interferences for MD methods; however, mineralized soils
and iron-bearing minerals can provide significant natural interference with
surveys.
Seismic Methods
Seismic methods provide stratigraphic information by measuring how
acoustic waves travel through the subsurface. They can be used at UST sites to:
Determine depth and thickness of geologic strata;
March 1997
1-11
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Determine depth to groundwater;
Estimate soil and rock composition; and
Help resolve fracture location and orientation.
There are primarily two types of seismic method applications—refraction
and reflection. Seismic refraction measures the travel times of multiple sound
(i.e., acoustic) waves as they travels along the interface of two layers having
different acoustic velocities. Seismic reflection, on the other hand, measures the
travel time of acoustic waves in the subsurface as they reflect off of these
interfaces. Traditionally, seismic reflection has been used for deep geological
investigations (up to 3000 feet), and seismic refraction has been used for shallow
investigations (up to 100 feet). Although recent developments have blurred the
applications of the two methods, seismic refraction remains more commonly used
for shallow investigations because it is less expensive and easier to use for
resolving stratigraphy less than 50 feet bgs. This chapter will focus on seismic
refraction.
Seismic refraction utilizes an energy source, such as a sledge hammer or
small explosives, to create acoustic waves in the subsurface. When there is a
change in the seismic velocity of the waves traveling from one layer to the next,
refracted waves are created. These waves are recorded by geophone sensors (i.e.,
seismic wave receivers) arranged in a direct line from the energy source. The time
it takes the waves to refract is dependent on the composition, cementation,
density, and degree of weathering and fracturing of the subsurface materials.
Exhibit III-6 presents a schematic drawing of seismic refraction operating
principles.
The advantage of seismic refraction is that it can resolve three to five
layers of stratigraphy and provide good depth estimates. Furthermore, it is fairly
easy to implement, and the energy source can be as simple as a lO-pound sledge
hammer. Seismic refraction, however, has a number of limitations that should be
considered:
Geophone spreads may be as much as five times as long as the desired
depth of investigation, therefore limiting its use in congested locations.
If velocity contrasts do not exist between sediment layers they will not be
resolved.
Thin layers cannot be resolved.
If numerous buried utilities are in the vicinity of the seismic profiles, they
may interfere with the collection of usable data by creating a false layer
near the surface.
For surveys in paved areas, holes need to be drilled in order to provide a
firm contact between the geophones and the soil.
111-12 March 1997
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Exhibit 111-6
Schematic Drawing Of Seismic Refraction Operating Principles
Hammer
Source
Source: Benson et al., 1984
Seismic velocities of geologic layers must increase with depth. Although
this situation is typical, conditions such as frozen soil or buried pavement
will prevent detection of underlying formations.
Seismic methods are sensitive to acoustic noise and vibrations; however,
there are a number of ways to minimize this noise, including using data
filtering software or taking profiles (i.e., geophysical subsurface cross-
sections) when there is no traffic (e.g., taking measurements during red
lights or at night).
Although seismic refraction can be used for depths below 300 feet, it is
usually used for depths less than 100 feet because of the very long geophone
spreads required and the energy sources (e.g., a 500 Ib. drop weight, explosives)
necessary to reach these depths.
March 1997
1-13
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Magnetic Methods
Magnetometers are useful at UST sites for locating tanks and piping made
of ferrous materials. Although highly sensitive magnetometers have been
developed that can detect the void space within large buried objects of any
material (e.g., fiberglass tanks), this technology is not often used in UST
investigations because many cultural interferences present at UST sites will mask
the affect.
Magnetometers that are commonly used at UST sites work by measuring
the earth's total magnetic field at a particular location. Buried ferrous materials
distort the magnetic field, creating a magnetic anomaly. There are two methods
for measuring these anomalies—the total field method and the gradient method.
The total field method utilizes one magnetic sensing device to record the value of
the magnetic field at a specific location. The gradient method uses two sensors,
one above the other. The difference in readings between the two sensors provides
gradient information which helps to minimize lateral interferences. Total field
magnetic methods are often used at sites with few cultural features. Gradiometer
methods can be used in culturally complex areas. As a result, gradiometers are
more applicable for UST sites. Exhibit III-7 presents a schematic drawing of
magnetometry operating principles.
Magnetometers may be useful for reconnaissance surveys of UST sites
because they are very fast and relatively inexpensive. Potential cultural
interferences include steel fences, vehicles, buildings, iron debris, natural soil
minerals, and underground utilities. Gradiometer methods are useful for
minimizing these interferences. Power lines are an additional source of
interference that can be neutralized with the use of very sophisticated equipment
that synchronizes readings with the oscillating electrical current.
Some magnetometers are very simple and do not have a data recording or
processing ability. They indicate the presence of iron with a sound or meter and
can be used as a rapid screening tool. Magnetometers that record data can, with
the aid of data processing software, be used to estimate the size and depth of
ferrous targets.
1-14 March 1997
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Exhibit 111-7
Schematic Drawing Of Magnetometry Operating Principles
Natural Orientation Of The
\~ Earth's Magnetic Field
Magnetometer
///////// /Ground Surface / / '
Buried Ferrous Mass
General Distortion Area Of The Earth's
Magnetic Field Due To Buried Mass
Source: Modified from U.S. EPA, 1993a
March 1997
1-15
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Geophysical Applications
There are three general applications for geophysical tools in the
assessment of UST sites: Locating buried objects; assessing geological and
hydrogeological conditions; and, to a lesser extent, delineating residual or floating
product. The following text contains discussions of the geophysical methods that
are most applicable for these activities. Specific information about each method
and a comparison chart of all methods are provided to help the reader decide
which method to use under various conditions.
Each of the following discussions includes a summary table highlighting
the parameters that affect the applicability of the described methods. Only
information that is relevant to the specific application is presented for each of the
methods. Some of the parameters discussed in the previous section that affect the
applicability of a method are presented in the tables but not repeated in the text.
The summary tables include cost estimates which are presented as low,
moderate, or high. More accurate estimates are not possible because there are an
enormous number of site-specific factors that affect cost (e.g., survey objectives,
survey size, spacing between traverse lines, mobilization costs). Furthermore, the
expense of a survey will be greatly affected by who conducts the investigation
(e.g., a consultant or an individual renting equipment directly from the
manufacturer), how much data processing will be required, and whether a written
report is necessary.
Similar to cost estimates, time requirements for a geophysical survey are
presented as fast, moderate, and slow. Geophysical methods can be ranked by
how quickly they can be used, but the specific time that a survey will take varies
considerably depending on the level of detail required and the size of the area to
be investigated. In general, all of the methods presented in this chapter can be
completed within one day at a typical UST site (i.e., less than 2 acres); in some
cases, a survey can be completed within half a day. Sometimes, no data
processing will be necessary beyond what is immediately presented; or, additional
data processing may be completed in the field; in other situations, extensive off-
site data processing will be necessary.
Locating Buried Objects
Many times the initial step to a site assessment is to determine the location
of USTs, associated piping, and/or utilities. This type of activity is ideally suited
1-16 March 1997
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to geophysical tools. If the location of these structures has not been recorded, the
use of geophysical methods can save an enormous amount of time and money.
There are four primary methods used for locating buried objects: Ground
penetrating radar (GPR), time-domain metal detection (MD), magnetometry
(MAG), and electromagnetic methods (EM). Exhibit III-8 provides a summary of
the information presented in this discussion.
Ground Penetrating Radar
Ground penetrating radar is effective for locating buried objects, whether
metal or non-metal. Targets of investigation include:
Steel, fiberglass, composite, and steel-reinforced concrete USTs;
Utilities;
Rebar; and
Backfill.
When site conditions are favorable, GPR provides the best resolution of
any geophysical method for locating buried objects. Although the exact resolution
depends on the frequency of the antenna used and the depth of penetration
required, GPR can generally locate a tank to within a foot, both vertically and
horizontally. However, because GPR is typically used at much slower rates and
with more dense traverse lines than MAG, MD, and EM, it is often more cost-
effective to use GPR for focused investigations. When the location of an object is
only suspected or estimated, other (i.e., reconnaissance) methods may be more
appropriate. Exhibit III-9 is an example of a plot and interpretation of GPR being
used to locate buried USTs. The hyperbolic shape of the radar wave reflections is
a typical profile of a buried object.
Metal Detection
Metal detection (MD) surveys are useful for locating only metal objects,
both ferrous and non-ferrous. Investigations at UST sites include:
Steel, composite, and steel-reinforced concrete USTs;
Reinforced concrete covering fiberglass USTs; and
Utilities composed of any metal.
March 1997 111-17
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Ground Penetrating Radar Survey And Interpretation Of Buried USTs
Q.
-------
MD provides excellent horizontal resolution. Utilities can be traced better
than with magnetometry, however, resolution of depth can only be defined to
within 20 percent of the actual depth. If better resolution is required, a follow-up
survey with GPR may be appropriate. Exhibit III-10 presents an example of a
survey plot and interpretation using a very sophisticated MD that was able to
locate the UST and associated piping.
Magnetometry
Magnetometry (MAG) methods are well suited for reconnaissance surveys
because they collect data rapidly, they give large responses for buried ferrous
objects, and they are cost-effective. As described in the method overviews, MAG
surveys can be useful at UST sites for detecting:
Steel, composite, and steel-reinforced concrete USTs;
Utilities composed of ferrous materials; and
Trenches.
In addition to being able to detect ferrous materials, very sensitive MAG
equipment can also detect the void space in a large container of any material.
However, because fiberglass tanks are typically covered with reinforced concrete,
the magnetic response will be dominated by the presence of the reinforcing steel.
Highly sensitive magnetometers can be more useful in detecting backfilled
trenches because their iron content often contrasts with the surrounding soils.
Depth of penetration is as deep as necessary for most UST sites. For example, a
55-gallon drum can be detected at 10 to 15 feet (depending on the sensitivity of
the magnetometer), and a 10,000-gallon tank can be detected much deeper. The
resolution of the data is also good when processed with the appropriate software,
the vertical and horizontal location of an object can be determined to within 10 to
15 percent.
Exhibit III-l 1 provides an example of a MAG survey at a Stanford
University test site. This section of the test site contained metal and non-metal
objects, all of which were detected with the highly sensitive magnetometer. The
large mounds indicate the location of metal drums buried at various depths and
positions. Also of interest is the negative anomaly that is caused by six plastic
drums buried 9 feet bgs.
1-20 March 1997
-------
Exhibit 111-10
Metal Detection Survey And Interpretation At LIST Site
Survey
12w I0w 8W 6W 4W 2W 0 2E 4E
1 l ) I I
I I
12W 10W 8W 6W 4W 2W 0 2E 4E
Interpretation
12W 10W 8W 6W 4W 2W 0 2E 4E
I l
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\7
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- 0
- 2S
- 4S
- 6S
- 8S
-10S
12W 10W 8W 6W 4W 2W 6 2E 4E
Legend
I - Underground
I Storage Tank
• - Possible Pipes
- Shallow Metallic Object
- Small Manhole
Scale In Meters
Source: Geonics Limited
March 1997
1-21
-------
Exhibit 111-11
Magnetometry Survey At Stanford University Test Site
Three 55-Gallon
Metal Drums, Horizontal
3 Feet to Bottom
One 55-Gallon
Metal Drum, Horizontal
6 Feet to Bottom
One 55-Gallon
Metal Drum, Vertical
6 Feet to Bottom
One 55-Gallon
Metal Drum, Horizontal
9 Feet to Bottom
Source: Geometries, Inc.
Electromagnetic Methods
The most widely used EM method for UST investigations is frequency-
domain fixed-coil EM (the distance between transmitter and receiver coils is
fixed). It is useful for locating buried objects, whether metal or non-metal. This
method can be used at UST sites to locate:
Steel, composite, and steel-reinforced concrete USTs;
Utilities; and
Backfill soils.
EM methods are well suited for reconnaissance of large open areas
because data collection is rapid, and a large variety of subsurface anomalies can
I-22
March 1997
-------
be located, whether metal or non-metal, including the backfill of former USTs.
Because EM methods can indicate the location of many types of buried objects,
follow-up investigations with GPR are often applicable.
For EM instruments commonly used at UST sites for assessment of buried
objects, the depth of investigation is limited to 12 feet or less, regardless of the
size of the object detected. Horizonal resolution with EM is approximately 4 feet,
and vertical resolution is between 4 and 12 feet. Exhibit III-12 is an example of
contoured EM data and an interpretation map at an UST site. The survey was able
to locate several USTs and associated piping as well as to delineate the area of
backfill.
Exhibit 111-12
Electromagnetic Survey And Interpretation At UST Site
120-
100-
80-
20 40 60 80 100 120 140 160
i I i i i i I i i i i I i i i , I i i , , I , i , i I . , , , I , , , , i ,
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0 20 40 60 80 100 120 140 160
Feet
Source: NORCAL Geophysical Consultants, Inc.
March 1997
I-23
-------
Assessing Geological And Hydrogeological Conditions
All geophysical methods are capable of providing information about
geologic and/or hydrogeologic conditions. By assessing the subsurface,
investigators can make judgements about where contamination is likely to be
located and the direction it is likely to migrate. This information is also critical in
the design of appropriate remediation technologies. Geophysical methods are, of
course, not always necessary for determining the geologic and hydrogeological
conditions of UST sites; however, when adequate background information does
not exist and site geology is complicated, geophysical methods may be a cost-
effective means of supplementing intrusive methods of characterization (e.g., soil
logging).
Geophysical methods can be helpful in resolving depth to groundwater;
determining depth, thickness, and composition of soil and rock layers; and
mapping local features such as permeable zones, joints, faults, karst, and buried
stream channels. The following text summarizes the most useful methods for
these tasks and explains their applicability. The geophysical methods most likely
to be useful at UST sites include ground penetrating radar (GPR), seismic
refraction (SR), electrical resistivity (ER), and electromagnetics (EM). Although
all of these methods may on occasion be useful in determining the depth to the
saturated zone, they all require sharp boundaries to be successful. As a result,
when there is a large capillary fringe, they may not distinguish the saturated zone
from the vadose zone.
Magnetometry, very low frequency electromagnetics (VLF-EM), self-
potential (SP), and seismic reflection are other surface geophysical methods that
may provide additional information; however, they are not discussed in detail
because they are rarely useful at UST sites for assessing geologic and
hydrogeologic conditions because of sensitivities to cultural interferences, cost, or
applicability for rare conditions. Magnetometry and VLF-EM methods can be
useful for delineating faults and large fracture zones. SP surveys, although
sensitive to interferences, can be used to assess karst, fractures, and groundwater
recharge. Borehole methods may also be useful for logging soil types and fracture
characterization. Borehole methods that have been adapted to direct push
technologies are discussed in the Chapter V. Exhibit III-13 summarizes the
application of each of the major surface geophysical methods used for subsurface
characterization of geologic and hydrogeologic conditions.
1-24 March 1997
-------
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III-25
-------
Seismic Refraction
Seismic refraction is typically the most applicable seismic method for
assessing subsurface conditions at UST sites. It can be used to resolve:
Sediment depth and thickness;
Karst, fractures, and faults;
Depth to bedrock; and
Occasionally, depth to groundwater.
Seismic refraction supplies semi-continuous data which, in combination
with borings and other sampling techniques, can be extrapolated to resolve
localized geologic features over the entire area of investigation. It is possible to
resolve three to five distinct soil or rock layers and penetrate depths over 100 feet.
Occasionally, this method can be helpful in determining the depth to
groundwater. In order to be successful, the velocity of the saturated zone must be
significantly greater than the overlying formation. Because consolidated
formations typically have very fast seismic velocities that are not significantly
affected by groundwater, if the water table is located in a consolidated formation,
it will not likely be discernable. Seismic velocities will typically increase
significantly in unconsolidated formation; however, if the boundary is sharp (e.g.,
as in course sands), a refraction survey will not be capable of determining if the
layer is groundwater or another formation. Additional seismic tests, which are
beyond the scope of this document, can be used to determine if the refraction is
water or soil/rock.
Exhibit III-14 provides an example of a seismic refraction survey and
interpretation used to resolve the depth to bedrock at a hazardous waste site. Each
dot and circle represents the measured response of a geophone. Its placement on
the graph is determined by the geophone location in the array and the time
between energy release and the seismic wave arrival to the geophone.
Measurements are taken in two directions (e.g., forward and reverse) in order to
resolve dipping (i.e., inclined) stratigraphy. Because distance divided by time
equals velocity, the inverse of the slope of the lines equals the seismic velocity of
the subsurface material. Therefore, a change in the slope represents a change in
the material. This survey was able to resolve three separate velocity layers (V,,
V2, and V3). The depth to bedrock throughout the area of investigation was
resolved with V,. The buried trench depicted in the interpretation was based on
historical site information and was not resolved with seismic refraction.
111-26 March 1997
-------
Exhibit 111-14
Seismic Refraction Survey And Interpretation
Survey
40-e
o
10 20 30 40 50 60 70 80 90 100
100 90 80 70 60 50 40 30 20 10 0
Distance (In Feet)
,East
West
Interpretation
Q.
0)
10-
20-
30.
Loess Layer
.Vi =6ao F/S
Probable Outline of Burial Trench /
\ ^ __ _ o i .
I — —— __ _~ ^^ I m^ ^^ «••
Clayey Soil
With Chert Blocks
V2 = 2493 F/S
V3 = 4131 F/S
Karst
Limestone
0 Surface
-10
-20
•30
Source: Benson et al., 1984
March 1997
I-27
-------
Electromagnetic Methods
EM methods can be useful for assessing both the shallow subsurface and
deep geological features. At some UST sites, it can provide information about:
Stratigraphy;
Preferred groundwater pathways;
Fracture zones and faults; and
Occasionally, depth to groundwater.
There are various EM methods that are useful for both shallow and deep
geological and hydrogeological investigations. The frequency-domain fixed-coil
separation EM method is the most practical EM approach for the shallow
subsurface (less than 12 feet) at UST sites because its lateral resolution and speed
of operation is superior to other EM methods. For collecting data from deeper
than 12 feet, there are time-domain (TDEM) and other frequency-domain
equipment available that can reach depths below 100 feet.
Exhibit III-15 is a schematic drawing of a TDEM survey. The black
vertical lines are soundings (i.e., vertical measurements) of subsurface electrical
conductivity. The information between the lines is interpolated. By comparing
information from the TDEM soundings with boring logs, it is possible to
extrapolate the geology over a wide area. In this example, the approximate
location of sediments is measured to a depth of 200 feet bgs.
The resolution provided by EM methods is often not as good as other
geophysical methods. Horizontal resolution may indicate the location of features
to within 4 feet; vertical resolution can only be approximated. However, general
indication of stratigraphy can be presented. The direction and general location of
fractures and faults can also be presented.
Ground Penetrating Radar
When soil conditions are favorable, GPR can be very effective for
assessing shallow, localized subsurface conditions. The geologic and
hydrogeologic features that can be detected with GPR include:
Karst, fractures, and faults;
Depth and thickness of shallow sediments and bedrock; and
Occasionally, depth to groundwater.
1-28 March 1997
-------
Exhibit 111-15
Time-Domain Electromagnetic Survey Of Stratigraphy
Resistivity
IW1 Very Low
I I Low
I I Medium
Very High
Lithology
Clay
Sandy Clay
Sand
Sandy Gravel
Gravel
10
Source: NORCAL Geophysical Consultants, Inc.
GPR provides excellent resolution; however, interpretation of plots can be
very difficult and require an experienced practitioner. Because it is not generally
used as a reconnaissance tool, it is best used to clarify the existence and location
of suspected features within a specific area. In addition, GPR is typically only
useful for delineating shallow geological features because its depth of penetration
can be significantly limited by site conditions. However, when soil conductivities
are very low (e.g., in sand, gravel), geologic features can be resolved up to 90 feet
bgs.
March 1997
III-29
-------
GPR can be used to estimate the depth and thickness of soil and rock
layers to within one foot. Occasionally, depth to groundwater can be determined,
but the site must be above shallow, well-sorted sands that produce a water table
with a small (less than 1 foot) capillary fringe.
Exhibit III- 16 presents an example of a GPR survey and interpretation of
karst. Although GPR did not provide good resolution in zones of solid limestone,
the karst could be mapped because the radar signal is not attenuated as much in
the sand that fills the karst.
Exhibit 111-16
Ground Penetrating Radar Survey And Interpretation Of Karst
Survey
30 60 90 120
Horizontal Distance In Meters
150
180
Interpretation
]Ct'! I T" r
i T r
Source: Benson et al., 1984
I-30
March 1997
-------
Electrical Resistivity
Electrical resistivity can occasionally be used at UST sites to provide
information about subsurface conditions. When used for this purpose, resistivity
measurements can help resolve:
Sediment depth and thickness;
Karst, fractures, and faults;
Depth to bedrock; and
Depth to groundwater.
ER can easily collect data beyond 100 feet bgs, however, geologic features less
than approximately 5 feet may not be resolved. Depths of these features can be
estimated to within 5 feet if additional subsurface data (e.g., boring logs) are
available. The accuracy of depth estimates decreases with depth.
Delineating Residual Or Floating Product
One of the most difficult aspects of a site assessment is delineating the
extent of contamination. Although geophysical tools are not helpful in mapping
the extent of dissolved product at a site, in some situations they can play an
important role in mapping the location of residual product in the vadose zone and
floating product above groundwater. This is an area of active research and many
issues involved with the uses of appropriate methods remain unresolved
In general, hydrocarbons are difficult to detect because they are resistive
compounds that often cannot be distinguished from the surrounding soils and rock
layers. However, among the hydrocarbons, light non-aqueous phase liquids
(LNAPLs) (e.g., gasoline, jet fuel, diesel fuel) are the most likely hydrocarbons to
be detected because they float and form a distinct layer above the groundwater.
For some geophysical methods, the LNAPL layer must be several feet thick for
detection. Some detection methods may detect older spills more easily than newer
spills because the natural rise and fall of a water table will "smear" the product
over a greater area. In addition, the natural lateral geologic variations will
interfere with the interpretation of geophysical plots for all methods because
distinguishing between changes due to geology or LNAPLs may be difficult.
There are several surface geophysical methods that have the potential to
detect LNAPLs in the subsurface. Ground penetrating radar (GPR) and electrical
resistivity (ER) are currently the best documented methods and are discussed in
the following text. A summary of the effectiveness of these two methods for
delineating residual or floating product is presented in Exhibit 111-17.
March 1997 111-31
-------
Exhibit 111-17
Summary Of Geophysical Methods For Delineating
Residual And Floating Product
Depth Of Detection
Cultural
Interferences
Natural
Interferences
Produces Usable
Field Data
Detection Limit
(Quantity Of
Product)
cost
Ground
Penetrating Radar
3 to 15ft
Densely packed rebar
Conductive soils (e.g.,
clays), lateral geologic
variations
Yes
Unknown
Low to Moderate
Electrical
Resistivity
10 to 15ft
Concrete, metal surface
structures
Highly conductive soils (e.g.,
wet dense clays), lateral
geologic variations
No
Unknown
Moderate to High
Other methods that are undergoing research but that are not yet appropriate
for inclusion, include electromagnetic methods (EM), induced polarization
(Olhoeft, 1986; also known as complex resistivity), and ultrasonic imaging
(Geller, 1995; a type of seismic method). Borehole methods are extremely useful
for the purpose of determining the thickness of floating product because they
provide exact, in situ measurements that cannot be accomplished with any other
means. These methods are discussed in detail in Direct Push Technologies,
Chapter V.
Ground Penetrating Radar
Occasionally, GPR can provide an indication of the presence of
hydrocarbons although success may be difficult to predict, and the reasons for its
occurrence are not yet completely understood. There are several observations
reported in scientific literature. In most cases, interpretation requires a boring log
to compare reflection depths with actual soil types.
One study (Daniels, 1995) reports that in areas of petroleum hydrocarbon
contamination, radar waves will not necessarily reflect back to the GPR receiver.
1-32
March 1997
-------
This effect causes a "halo" (i.e., decrease in reflection) over the area of
contamination which contrasts with neighboring areas of reflection. A similar
result was observed in a controlled kerosene spill in Canada (DeRyck, 1993).
However, in another controlled spill experiment (Campbell, 1996), a bright spot
(i.e., an increase in the reflected GPR signal) was observed. The reason for these
contradictory results has not yet been adequately explained.
In addition (Benson, 1995) observed that, on occasion, a small amount of
petroleum can cause the groundwater capillary fringe to collapse. If the water
table is located in a zone of low permeability soils that create a large capillary
fringe (e.g., clays), then a drop in the location of the groundwater reflection
compared with the surrounding area may be observed. Exhibit III-18 provides an
example of this phenomenon.
The amount of floating product required for these observations, and the
conditions that cause them requires further research. As a result, the use of GPR
to detect contamination is still experimental.
Electrical Resistivity
Electrical resistivity surveys are primarily used for determining site
stratigraphy. On occasion, as a secondary aspect of the survey, this method may
present evidence of LNAPL contamination (DeRyck, 1993). In order for this
method to be successful, a number of conditions must exist at a site. Groundwater
must be no more than 15 feet deep, conductive soils must be present in the
contaminated zone, and floating product must exist (although the minimum
quantity is unknown). Because this method is relatively expensive and success in
locating hydrocarbon contamination is not predictable, it is not typically used for
the sole purpose of locating petroleum plumes.
March 1997 III-33
-------
Exhibit 111-18
Petroleum Contamination Detected With Ground Penetrating Radar
Source: U.S. EPA, 1995
\-U
March 1997
-------
Geophysical Equipment Manufacturers
A list of geophysical equipment manufactures is included below in Exhibit
III-19 and a matrix of their products is presented in Exhibit 111-20. The equipment
has not been evaluated by the EPA and inclusion in this manual in no way
constitutes an endorsement. These vendors are listed solely for the convenience
of the reader.
Exhibit 111-19
Geophysical Equipment Manufacturers
Bison Instruments, Inc.
5708 West 36th Street
Minneapolis, MN 55416-2595
Tel: (612) 931-0051
Fax:(612)931-0997
Geometries
395 Java Dr.
Sunnyvale, CA 94089
Tel: (408) 734-4616
Fax: (408) 745-6131
Geonics Limited
8-I745 Meyerside Dr.
Mississauga, Ontario
Canada L5T IC6
Tel: (905) 670-9580
Fax: (905) 670-9204
Geophysical Survey Systems, Inc.
13 Klein Dr.
North Salem, NH 03073-0097
Tel: (603) 893-1109
Fax: (603) 889-3984
GeoRadar, Inc.
19623 Vis Escuela Dr.
Saratoga, CA 95070
Tel: (408) 867-3792
Fax: (408) 867-4900
GeoStuff, Inc.
19623 Vis Escuela Dr.
Saratoga, CA 95070
Tel: (408) 867-3792
Fax: (408) 867-4900
CISCO
900 Broadway
Denver, CO 80203
Tel: (303) 863-8881
Fax: (303) 832-1461
Oyo-Geosciences, Inc.
7334 North Gessner
Houston, TX 77040
Tel: (800) 824-2319
Fax:(713)849-2595
Phoenix Geophysics, Ltd.
3871 Victoria Park Ave.
Unit No. 3
Scarborough, Ontario
Canada MIW 3K5
Tel: (416) 491-7340
Scintrex, Ltd.
222 Snidecroft Rd.
Concord, Ontario
Canada L4K 1B5
Tel: (905) 669-2280
Fax: (905) 669-6403
Sensors and Software, Inc.
5566 Tomken Rd.
Mississauga, Ontario
Canada L4W 1P4
Tel: (905) 624-8909
Fax: (905) 624-9365
Zonge Engineering and Research
Organization, Inc.
3322 East Fort Lowell Rd.
Tucson, AZ 85716
Tel: (602) 327-5501
Fax:(602)325-1588
March 1997
I-35
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References
ASTM. 1996. Standard guide for using the seismic refraction method for
subsurface investigation, D5777-95. Annual Book of ASTM Standards.
Philadelphia.
Benson, R.C., R. Glaccum, and M. Noel. 1984. Geophysical techniquesfor
sensing buried wastes and waste migration (NTIS PB84- 198449). Prepared for
U.S. EPA Environmental Monitoring Systems Laboratory, Las Vegas, 236 p.
Benson, R.C. and L. Yuhr. 1995. Geophysical methods for environmental
assessment. In The Geoenvironmental 2000, 1995 ASCE Conference and
Exhibition, New Orleans.
Beres, M., Jr. and F.P. Haeni. 1991. Application of ground-penetrating-radar
methods in hydrogeologic studies. Gr. Water, vol. 29, no. 3: 375-86.
Campbell, D.L., I.E. Lucius, KJ. Ellefsen, and M. Deszez-Pan. 1996.
Monitoring of a controlled LNAPL spill using ground-penetrating radar. In
Proceedings of the symposium on the application of geophysics to engineering
and environmental problems, Denver.
Daily, W., A. Ramirez, D. LaBrecque, W. Barber. 1995. Electrical resistance
tomography experiments at Oregon Graduate Institute. J. ofApp. Geophys., vol.
33: 227-37.
Daniels, J.J., R. Roberts, M. Vendl. 1995. Ground penetrating radar for the
detection of liquid contaminants. J. ofApp. Geophys., vol. 33, no. 33: 195-207.
DeRyck, S.M., J.D. Redman, and A.P. Annan. 1993. Geophysical monitoring of
a controlled kerosene spill. In Proceedings of the symposium on the application
of geophysics to engineering and environmental problems, San Diego.
Dobecki, T.L. and P.R. Romig. 1985. Geotechnical and groundwater geophysics.
In Geophys., vol. 50, no. 12: 2621-36.
Geller, J.T. and L.R. Myer. 1995. Ultrasonic imaging of organic liquid
contaminants in unconsolidated porous media. J. ofContam. Hydrology, vol. 19.
Goldstein, N.E. 1994. Expedited site characterization geophysics: Geophysical
methods and tools for site characterization. Prepared for the U.S. Department of
Energy by Lawrence Berkeley Laboratory, Univ. of California. 124 p.
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Morey, R.M. 1974. Continuous subsurface profiling by impulse radar. In
Proceedings: Engineering foundation conference on subsurface exploration for
underground excavations and heavy construction. Henniker, NH, American
Society Civil Engineers.
NORCAL Geophysical Consultants, Inc. 1996. Product literature. 1350 Industrial
Avenue, Suite A. Petaluma, CA.
Olhoeft, G.R. 1986. Direct detection of hydrocarbon and organic chemicals with
ground penetrating radar and complex resistivity. In Proceedings of the National
Water Well Association/American Petroleum Institute conference on petroleum
hydrocarbons and organic chemicals entitled Ground Water - Prevention,
Detection and Restoration. Houston.
Olhoeft, G.R. 1992. Geophysical advisor expert system, version 2.0, EPA/600/R-
92/200. U.S. EPA Environmental Monitoring Systems Laboratory, Las Vegas: 21
pages and a floppy disk.
Pitchford, A.M., A.T. Mazzella, and K.R Scarbrough. 1988. Soil-gas and
geophysical techniques for detection of subsurface organic contamination,
EPA/600/4-88/019. (NTIS PB88-208194). 81 p.
U.S. EPA. 1993a. Subsurface characterization and monitoring techniques: A
desk reference guide. Volume 1: Solids and groundwater, EPA/625/R-93/003a.
Office of Research and Development, Washington, DC.
U.S. EPA. 1993b. Use of airborne, surface, and borehole geophysical
techniques at contaminated sites: A reference guide, EPA/625/R-92/007. Office
of Research and Development, Washington, DC.
U.S. EPA. 1995. Accelerated leaking underground storage tank site
characterization methods. Presented at LUST Site Characterization Methods
Seminar sponsored by U.S. EPA Region 5, Chicago. 108 p.
Ward, S.H. 1990. Resistivity and induced polarization methods. Geotech. And
Environ. Geophys. vol. 1, no. 1.
1-38 March 1997
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Peer Reviewers
Name
David Ariail
Al Bevolo
J. Russell Boulding
Ken Blom
David Borne
Jeff Daniels
Douglas Groom
Peter Haeni
Sam Heald
Ross Johnson
Dana LeTourneau
Al Liguori
Sriram Madabhushi
Aldo Mazzella
Duncan McNeil
Finn Michelsen
Chris O'Neil
Emil Onuschak, Jr.
Charlita Rosal
Thomas Starke
Sandra Stavnes
James Ursic
Katrina Varner
Mark Vendl
Company/Organization
U.S. EPA, Region 4
Ames Laboratory
Boulding Soil-Water Consulting
NORCAL Geophysics Consultants, Inc.
Sandia National Laboratories
Ohio State University
Geometries, Inc.
U.S. Geological Survey
Geophysical Survey Systems, Inc.
Geometries, Inc.
Spectrum ESI
Exxon Research and Engineering Company
South Carolina Department of Health and
Environmental Control
U.S. EPA, National Exposure Research
Laboratory
Geonics Limited
OYO Geosciences Corporation
New York Department of Environmental
Conservation
Delaware Department of Natural Resources
and Environmental Control
U.S. EPA, National Exposure Research
Laboratory
Department of Energy, Los Alamos
National Laboratory
U.S. EPA, Regions
U.S. EPA, Regions
U.S. EPA, National Exposure Research
Laboratory
U.S. EPA, Regions
March 1997
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Chapter IV
Soil-Gas Surveys
-------
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Contents
Exhibits IV-v
Soil-Gas Surveys IV-1
Applicability Of Soil-Gas Sampling IV-2
Physical And Chemical Properties Of Hydrocarbons IV-2
Vapor Pressure IV-2
Henry's Law Constant (Water To Vapor Partitioning) . . IV-3
Geologic Factors IV-4
Biodegradation IV-5
Summary IV-6
Active Soil-Gas Sampling Methods IV-7
Applications For Active Soil-Gas Sampling IV-8
Active Soil-Gas Survey Design IV-8
Review Existing Site Information IV-8
Preliminary Measurements For Soil-Gas Sampling .... IV-9
Relative Soil-Air Permeability Testing IV-9
Purge Volume And Rates IV-9
Subsurface Short Circuiting IV-9
Initial Sampling IV-IO
Sampling Depth IV-IO
Sample Spacing IV-IO
Sample Containers IV-11
Quality Assurance/Quality Control Procedures IV-11
Interpretation Of Active Soil-Gas Data IV-12
Costs Of Active Soil-Gas Surveys IV-13
Active Soil-Gas Survey Case Study IV-13
Site History IV-13
Soil-Gas Survey Objective IV-15
Sampling And Analytical Methods IV-15
Results And Discussion IV-15
Passive Soil-Gas Sampling Methods IV-19
Applications For Passive Soil-Gas Sampling IV-20
Passive Soil-Gas Survey Design IV-20
Interpretation Of Passive Soil-Gas Data IV-21
Cost Of Passive Soil-Gas Surveys IV-21
Passive Soil-Gas Survey Case Study IV-21
Site History IV-21
Soil-Gas Survey Objectives IV-25
March 1997 IV-iii
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Sampling And Analytical Methods IV-25
Results And Discussion IV-25
Comparison Of Soil-Gas Sampling Applications IV-27
Passive Soil-Gas Sampling Equipment Manufacturers IV-28
References IV-29
Peer Reviewers IV-31
IV-iv March 1997
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Exhibits
Number Title Page
IV-I Vapor Pressure And Henry's Law Constant Of Various
Organic Compounds At 20°C IV-3
IV-2 Summary Of General Active Soil-Gas
Sampling Criteria IV-6
IV-3 Active Soil-Gas Survey Site Map With Vapor Point
And Monitoring Well Locations IV-14
IV-4 Active Soil-Gas Survey Plot Of Total Volatiles (ppm,)
Isoconcentrations At 9 Feet IV-16
IV-5 Active Soil-Gas Survey Plot Of Total Volatiles (ppm,)
Isoconcentrations At 12 Feet IV-17
IV-6 Advantages And Limitations Of Active Soil-Gas
Sampling IV-18
IV-7 Example Of Passive Soil-Gas Sampler IV-19
IV-8 BTEX Distribution In Groundwater Based On
Monitoring Well Data (ug/l) IV-22
IV-9 Passive Soil-Gas Survey Results For Diesel Fuel
Constituents (ion counts of naphthalene
and alicylic hydrocarbons) IV-23
IV-10 Passive Soil-Gas Survey Results For BTEX
(ion counts) IV-24
IV-11 Advantages And Limitations Of Passive Soil-Gas
Sampling IV-26
IV-12 Applications For Active And Passive Soil-Gas Data IV-27
IV-13 Passive Soil-Gas Sampling Equipment Manufacturers IV-28
March 1997 IV-V
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Chapter IV
Soil-Gas Surveys
Soil-gas surveys are defined as the collection, analysis, and interpretation
of soil-gas data. As such, soil-gas surveys provide information on the soil
atmosphere in the vadose zone that can aid in assessing the presence, composition,
source, and distribution of contaminants. Soil-gas surveys can provide relatively
rapid and cost-effective site data that can help direct more costly and invasive
techniques. Although, they are typically performed early in the expedited site
assessment (ESA) process, soil-gas surveys can also be used to monitor
underground storage tanks (USTs) for releases, to evaluate remediation
effectiveness, and to assess upward migration of vapors into buildings for risk
assessments.
There are two basic types of soil-gas surveys commonly performed during
UST site assessments. The first type is the active soil-gas survey in which a
volume of soil gas is pumped out of the vadose zone into a sample collection
device for analysis. The second type is the passive soil-gas survey in which a
sorbent material is left in the ground so that contaminant vapors can be selectively
adsorbed over time using the ambient flow of soil gas. Active soil-gas surveys
can be completed in as little as one day and are most commonly used for sites
with volatile organic compounds (VOCs). Passive soil-gas surveys take several
days or weeks to complete and are most useful where semivolatile organic
compounds (SVOCs) are suspected or when soils prevent sufficient air flow for
active sampling.
This chapter provides a discussion of soil-gas principles affecting soil-gas
surveys, the applicability and the essential elements of both active and passive
soil-gas surveys, and case studies illustrating the effective use of both soil-gas
surveying methods. Details on soil-gas sampling equipment are provided in
Chapter V, Direct Push Technologies, and a discussion of soil-gas analytical
methods is presented in Chapter VI, Field Methods For The Analysis Of
Petroleum Hydrocarbons.
March 1997 IV-1
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Applicability Of Soil-Gas Sampling
In order to understand the applicability and design of soil-gas surveys, it is
important to first understand the parameters that control the migration of
contaminants through the vadose zone. The primary controlling parameters are
the physical and chemical properties of the contaminant, the site geology, and
biological processes. This section contains brief descriptions of these parameters,
how they affect various contaminants, and how they relate to the applicability of
active and passive soil-gas sampling.
Physical And Chemical Properties Of Hydrocarbons
To assess whether soil-gas sampling is applicable to characterize
subsurface contamination at an UST site, the potential for the contaminant to be
present in the vapor phase first needs to be evaluated. Petroleum products stored
in USTs, such as gasoline, diesel fuel, and kerosene, are complex mixtures with
more than 100 different compounds, each with a different degree of volatility.
Therefore, individual constituents must be assessed independently. The degree to
which a chemical will partition into the vapor phase is primarily controlled by the
compound's vapor pressure and its Henry's law constant.
Vapor Pressure
Vapor pressure is one of the most important constituent characteristics for
determining if a particular hydrocarbon can be detected as a gas in the source area.
The vapor pressure of a constituent is a measure of its tendency to evaporate.
More precisely, it is the pressure that a vapor exerts when it is in equilibrium with
its pure liquid or solid form. As a result, the higher the vapor pressure of a
constituent, the more readily it evaporates into the vapor phase. As a general rule,
vapor pressures higher than 0.5 mm Hg are considered to be detectable with active
methods. Occasionally, constituents with lower vapor pressures can be detected,
but the soil concentrations must be high and the geological formation should be
permeable. If the contaminant is dissolved in groundwater or soil moisture,
Henry's law constant must be considered along with the vapor pressure to
determine the potential for detection (see below). Exhibit IV-1 lists the vapor
pressures of selected petroleum constituents.
Gasoline contains a number of hydrocarbons that have sufficient vapor
pressures to be easily sampled with active soil-gas surveying methods. Jet fuel,
IV-2 March 1997
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Exhibit IV-1
Vapor Pressure And Henry's Law Constant
Of Various Organic Compounds At 20° C
Compound
n-Butane
Methyl t-butyl ether
n-Hexane
Benzene
Toluene
Ethylbenzene
Xyleoes
Naphthalene
Vapor Pressure
(mm Hg)
1560
245
121
76
22
7
6
0.5
Compound
n-Hexane
n-Butane
Ethylbenzene
Xylenes
Toluene
Benzene
Methyl t-butyl ether
Naphthalene
Henry's Law
Constant
(dimensionless)
36.61
25.22
0.322
0.304
0.262
0,215
0.018
0.018
^Values above dotted line indicate active active soil-gas sampling methods are
appropriate.
diesel fuel, and kerosene contain SVOCs that can be actively sampled only under
optimal conditions. Lubricating and waste oils contain mainly low volatility
compounds and cannot be directly sampled through active methods. Passive
sampling methods, which are more successful in detecting SVOCs, may be
successful in detecting some low volatility compounds.
Henry's Law Constant (Water To Vapor Partitioning)
Henry's law constant is a measure of a compound's tendency to partition
between water and vapor. This constant can be used to estimate the likelihood of
detecting a constituent in the vapor phase that had dissolved in soil moisture or
groundwater. There are several ways to express this constant, but the most useful
way is in the dimensionless form. Henry's law constant can be obtained by
dividing the equilibrium concentration of a compound in air with the equilibrium
concentration of the compound in water (at a given temperature and pressure).
Because the units on both values are the same, the resulting constant is
dimensionless.
March 1997
IV-3
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Compounds with a greater tendency to exist in the vapor phase have a
Henry's law constant greater than 1, compounds with a greater tendency to exist
in water have a Henry's law constant less than 1. Henry's law constants for
several common constituents found in petroleum products are shown in Exhibit
IV-1.
Notice that alkanes (chained hydrocarbons [e.g., butane, hexane]
commonly found in gasoline) have Henry's law constant values two orders of
magnitude greater than aromatics (ringed hydrocarbons [e.g., benzene, toluene]).
In a state of equilibrium, 36 molecules of hexane will exist in the vapor phase for
every molecule of hexane dissolved in water. Whereas, for every five molecules
of benzene dissolved in water, only one will be found in the vapor phase.
Consequently, if equal volumes of alkanes and aromatics have been spilled on a
site, in the source area alkanes will be found in much higher concentrations in the
soil gas. However, because alkanes partition out of the dissolved phase to a
greater extent, aromatics are more likely to provide an indication of dissolved
contaminant plumes. In addition, vapor phase concentrations of compounds such
as methyl t-butyl ether (MTBE) or naphthalene will not be useful indicators of
contamination in soil gas outside the source area because they tend to remain
dissolved in water.
In general, compounds with Henry's law constants greater than 0.1 are
considered to be detectable with active soil-gas sampling if the vapor pressure is
also sufficient and geologic conditions are favorable. Constituents with slightly
lower values may also be detectable if initial concentrations are high. Passive soil
gas techniques are able to detect compounds with lower Henry's law constants,
however, a precise limit of detection cannot be estimated because site conditions,
exposure times, and product sensitivities will vary.
Geologic Factors
The most important geologic factor in the movement of soil gas through
the vadose zone is soil permeability, a measure of the relative ease with which
rock, soil, or sediment will transmit a gas or liquid. Soil permeability is primarily
related to grain size and soil moisture. Soils with smaller grain sizes, and hence
smaller pore spaces, are less permeable. Clays, having the smallest grain size,
significantly restrict soil vapor migration.
Soil moisture decreases permeability because moisture trapped in the pore
space of sediments can inhibit or block vapor flow. Since soil moisture content
varies seasonally and geographically, effective air permeabilities are often
unknown prior to sampling. For active soil-gas surveys, soil-air permeability
IV-4 March 1997
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testing should be conducted in vertical profiles at select locations in order to
optimize sampling depth. For passive soil-gas surveys, soil-air permeability is
important but usually not determined because additional equipment is required.
In addition, there are several other soil factors that can create misleading
information about the location of contamination. Preferential pathways (e.g., tree
roots, soil cracks, utilities, backfill) and vapor impervious layers (e.g., clay layers,
foundations, buried pavement, perched groundwater) are features that should be
evaluated. Moreover, adsorption of hydrocarbons on soils with high percentages
of clay or organic matter can limit partitioning of contaminants into the vapor
phase.
Although active soil-gas sampling is applicable for all soil types except
tight clays, it is generally ineffective when the soil moisture is above SO- to 90-
percent saturation (Corey, 1986) because of the absence of connected air-filled
pores. High soil moisture conditions can be overcome with sampling procedures
(e.g., minimizing sample volume, increasing the air volume around the tip,
waiting for equilibrium to take place), but these procedures can often be very time
consuming.
Passive soil-gas sampling is generally useful in all soil types and
conditions, however, sediments with low intrinsic permeabilities and high degrees
of saturation can affect both the quantity of contaminants coming into contact
with the sampler and the quantity of contaminant that is adsorbed. For example,
the presence of a dense moist clay lense will reduce the amount of vapor that
contacts a sampler directly above it. In addition, Werner (1985) demonstrated that
activated carbon, a common soil-gas adsorbent, will adsorb significantly less TCE
with increasing relative humidity levels. Other contaminants may, therefore, also
be adsorbed to a lesser degree under humid conditions. Although passive soil-gas
sampling remains more sensitive to contaminant detection than active soil-gas
sampling under low permeability and high humidity, geologic heterogeneities in
the subsurface can also affect passive soil-gas results.
Biodegradation
Biodegradation of VOCs in the vadose zone can reduce the ability to
detect the contaminants in soil gas. Petroleum hydrocarbons are readily degraded
by microorganisms to produce increased levels of numerous gases (e.g., carbon
dioxide, hydrogen sulfide, methane) while decreasing the concentration of
oxygen. The rate of biodegradation is controlled by several factors, including soil
moisture content, concentration of electron acceptors (e.g., oxygen) available
nutrients in the soils, contaminant type, and soil temperatures.
March 1997 IV-5
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Sampling for soil gases affected by biodegradation (e.g., oxygen, carbon
dioxide, methane, hydrogen sulfide) can provide useful information about the
contaminant source area and plume, provided background samples are collected in
a neighboring uncontaminated area. Measurement of these parameters is most
useful when active soil-gas sampling is being employed and the contaminant is a
semivolatile or non-volatile compound, or if a volatile contaminant is known to
exist but has not been directly detected.
Summary
Detection of individual constituents by both active and passive soil-gas
sampling methods is limited by the physical and chemical properties of
hydrocarbons. General parameters for selecting active soil-gas sampling are
presented in Exhibit IV-2. Passive soil-gas sampling methods are more sensitive
than active soil-gas sampling, but individual manufacturers should be contacted
for specific compounds that can be detected.
Vapor pressure and Henry's law constant are indicators of the potential of
a method to detect a specific constituent. For active sampling, the vapor pressure
should be above 0.5 mm Hg. If contamination is dissolved in soil moisture or
groundwater, the Henry's law constant should also be above 0.1. Geologic factors
(e.g., clay layers, high soil moisture content) will affect both active and passive
sampling capabilities, but passive sampling will generally provide more sensitive
results under these conditions. In addition, the byproducts of biodegradation can
provide valuable information in active soil-gas sampling for indirect detection of
contaminants.
Exhibit IV-2
Summary Of General Active Soil-Gas
Sampling Criteria*
Vapor Pressure > 0.5 mm Hg
Henry's Law Constant > 0.1
Degree Of Saturation < 80%
Sampling Zone Is Free Of Clay
^Active sampling may still be useful for the indirect detection of contaminants
below these vapor pressure and Henry's law constant values.
IV-6 March 1997
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Active Soil-Gas Sampling Methods
Of the two soil-gas sampling methods—active and passive—active soil-gas
sampling is the method typically used for site investigations where VOCs are the
primary constituents of concern. This method allows for rapid soil-gas collection
from specific depths by analyzing soil gas that has been pumped from the ground
through probe holes. The samples are typically analyzed on-site so that real-time
data can be used to direct further sampling. VOCs can be detected directly with
soil-gas sampling methods, while SVOCs and low volatility organic compounds
may be detected indirectly through the measurement of gases (0,, CO,, H2S, CH4)
influenced by biogenic processes.
Active soil-gas surveying was initially utilized by the oil industry in the
1960s to monitor gas control systems, track gas migration off-site, and evaluate
resources. It was first applied to VOC site assessments in the early 1980s and
rapidly gained popularity as a screening tool to detect and delineate subsurface
contamination.
Samples are collected by inserting a sampling device into a borehole,
usually with a slam bar, a direct push system, or a hollow stem auger. Most
sampling devices consist of screens or ports that are pushed directly into the
ground or inserted through the insides of drill rod or pipe. Soil gas is drawn
through the port or screen through plastic (primarily polyethylene or Teflon ) or
metal tubing and into a collection vessel using a vacuum device. The port or
screen, tubing, sample vessel, and vacuum source are collectively referred to as
the "sample train." For a more detailed discussion of soil-gas sampling
equipment refer to Chapter V, Direct Push Technologies.
As active soil-gas sampling has evolved and become more cost effective
through the application of direct push technology, on-site analysis of soil-gas
samples by mobile laboratories utilizing transportable gas chromatographs has
become more common. Mobile laboratories provide quantitative chemical data
with rapid turnaround time and do not necessitate the packaging and shipping of
samples. Other useful pieces of analytical equipment include total organic vapor
detection instruments, such as photoionization detectors (PID) and flame
ionization detectors (FID), field portable gas chromatographs, and detector tubes.
Assessment objectives must be considered in the selection of analytical methods
because capabilities and limitations are extremely variable. A detailed discussion
of analytical methods for soil-gas analysis is provided in Chapter VI, Field
Methods For The Analysis Of Petroleum Hydrocarbons.
March 1997 IV-7
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Applications For Active Soil-Gas Sampling
Active soil-gas sampling can be an important aspect of an ESA because it
provides the ability to assess many different aspects of a site in a short period of
time, typically in 1 to 3 days. Active soil-gas sampling can help the investigator:
• Identify releases;
• Identify sources of contaminants;
• Identify the types of VOCs present in the vadose zone;
• Provide an indication of the magnitude of VOC and S VOC contamination;
• Infer contaminant distribution of SVOCs and low volatility organic
hydrocarbons by measuring indicators of biodegradation;
• Optimize the placement of soil borings and monitoring wells;
• Monitor potential off-site sources;
• Collect data that could be useful in the design of soil vapor extraction
(SVE) or bioventing systems;
Assess the potential for upward migration of vapors in buildings; and
Monitor the effectiveness of remedial systems.
One major advantage of active soil-gas sampling is that data can be
collected from discrete depths for vertical profiling of contaminant concentrations
and relative air permeabilities in the vadose zone. This information helps to
provide a 3-dimensional conceptualization of the contaminant distribution and
allows for calculation of upward and downward contaminant fluxes.
Active Soil-Gas Survey Design
Although active soil-gas surveys are a rapid and effective way to focus
subsequent assessment methods, several procedures are needed to ensure that the
data provided are valid. The following section describes some of the essential
elements required for a successful active soil-gas survey.
Review Existing Site Information
Investigators should review and evaluate existing site information in order
to make an initial determination of the applicability of active soil-gas sampling
(refer to previous section). If active sampling is appropriate, this information will
also help the investigator select sampling locations. Information to be reviewed
may include:
Type of contaminant and suspected release mechanism (e.g., spills, leaks);
IV-8 March 1997
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Estimates of volume of contaminant discharged;
Length of time contaminant has been present;
Stratigraphy of the site;
Depth of groundwater, direction and rate of flow;
Map of site facility with subsurface structures (e.g., tanks, sewers, piping,
wells); and
Reports of site inspections.
Preliminary Measurements For Soil-Gas Sampling
There are three conditions that should be assessed prior to sampling, to
determine how soil-gas samples should be extracted and to ensure that the
samples are representative of subsurface conditions: Relative soil-air
permeability, purge volume and rates, and subsurface short circuiting.
Relative Soil-Air Permeability Testing
Relative soil-air permeability can help to assess the influence of geologic
materials and the moisture content at the locations tested. An estimate can be
calculated by comparing air flow data with the corresponding vacuum pressure or
more accurately by using a pressure transducer. Low permeability zones should
be identified to help interpret the data.
Purge Volume And Rates
Prior to initiating sampling at a site, tests should be conducted to optimize
the purge volume and rates. Generally, these tests should be conducted in various
soil types encountered at the site and in the areas of suspected elevated VOC
concentrations. The tests are performed by varying the purge volume and rates at
a single location while samples are being taken. Optimal sampling conditions
occur when contaminant concentrations stabilize.
Subsurface Short Circuiting
Purge volume and rate tests should also be used to check for subsurface
short circuiting with the above-ground atmosphere. This condition is indicated
when contaminant levels decrease rapidly or when atmospheric gases (e.g.,
atmospheric oxygen levels) are detected. Sometimes indicator VOCs (e.g.,
pentane) are placed on a rag near the probe hole. In order to prevent short
March 1997 IV-9
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circuiting, it is important to seal the probe hole, typically with wet bentonite. In
addition, the drive-point should not be larger than the diameter of the probe
because the open space created by the drive-point would provide a conduit for
atmospheric gases to travel.
Initial Sampling
Initial sampling points are usually located in potential source areas. The
proposed sampling locations should be located on a facility map with subsurface
structures noted. Additional sampling points need to be considered along possible
conduits (e.g., sewer lines, trenches, utility vaults, pipelines) where contaminants
may preferentially migrate. Sampling may also be organized along a standard
orthogonal grid.
Sampling Depth
The depth of sampling will vary depending on the depth to groundwater
and the stratigraphy of the site. Active soil-gas sampling in a vertical profile is
necessary to determine the permeable horizons and vertical contaminant
distributions. Initial profiles should be completed in known or suspected source
areas and in areas where elevated VOCs are detected. If liquid phase hydrocarbon
delineation is the objective, soil-gas surveys should be collected just above the
water table.
Sample Spacing
Sample spacing depends primarily on the objectives of the investigation,
the size of the site, and the size of potential contaminant sources. At 1- or 2-acre
USTs sites, initial spacing is generally between 10 and 50 feet. When trying to
track down the source at a major industrial site, spacing may be as great as 400 or
500 feet. Sufficient soil-gas data from shallow and deeper vadose zone horizons
should also be collected to provide a 3-dimensional distribution of the
contaminants. The spacing between vertical samples depends primarily on the
depth to groundwater and the objectives of the investigation. Data should be
integrated into maps and contoured in the field to determine if additional sampling
locations are necessary. As a general rule, if two sampling points have a 2 to
3 orders of magnitude change, samples should be collected in the area between the
two points.
IV-10 March 1997
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Sample Containers
There are four commonly used sample containers, each with different
advantages and limitations. Stainless steel canisters are durable, but they can be
difficult to decontaminate. Glass bulbs are easy to decontaminate, but they are
(R)
breakable and may have leakage through the septa. Tedlar bags are easy to
handle and leakage is readily apparent, but some contaminants may sorb onto the
bag (for the primary gasoline constituents, however, this is not a problem).
Syringes are inexpensive and allow for easy collection of samples, but they have
short holding times and are difficult to decontaminate. Although no sampling
container is perfect, problems are minimized by analyzing samples as soon as
possible after collection.
Quality Assurance/Quality Control Procedures
There are numerous QA/QC procedures that must be undertaken during an
active soil-gas survey to ensure that the samples are representative of subsurface
conditions. The following list is not comprehensive for all site conditions or
equipment; rather, it contains the primary issues that regulators should check
when they evaluate active soil-gas survey reports. QA/QC procedures include:
All soil-gas surveys should be collected following the same procedures.
Sampling should be completed in a relatively short period of time (e.g.,
hours, days) because temporal variations such as temperature, humidity,
barometric pressure, and rain can affect contaminant concentrations.
Decontamination procedures should be practiced to prevent contaminant
gain or loss that results from adsorption onto sampling equipment.
The insides of the sample train components should be as dry as possible
because water can raise or lower contamination values.
Ambient air present in the sample train must be purged prior to sample
collection.
When sampling directly through probe rods, the sample train connections
should be checked prior to collecting each sample to ensure they are air-
tight.
Annular space between the side of the borehole and the installation device
(e.g., probe rod) should be sealed at the ground surface with a bentonite
paste or similar material.
Blank samples should be tested regularly to ensure that decontamination
procedures are adequate and to determine background VOC levels.
Duplicate soil-gas samples should be collected each day (generally 1 for
every 10 samples) to assess the reproducibility of the data.
Sample containers should be monitored for leakage.
March 1997 IV-11
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Interpretation Of Active Soil-Gas Data
A thorough understanding of the capabilities of the active soil-gas
sampling methods and the site conditions is necessary for avoiding over-
interpretation of the soil-gas survey results. Soil-gas concentrations must be
compared with stratigraphic and cultural features in order to determine how soil-
gas migrates and how contaminants are distributed. Subsurface barriers (e.g., clay
lenses, perched groundwater, infrastructure, buildings) and secondary pathways
(e.g., utility trenches, animal burrows) can cause soil-gas distribution to be
significantly different than soil and groundwater contamination. As a result,
stratigraphic cross-sectional maps should be used to evaluate vertical
concentrations. Trends noted should be evaluated to assess whether they are
associated with soil types, chemical migration, influence of diffusion from
groundwater, potential preferential pathways, or obstructions.
Interpretation of the soil-gas data should begin in the field. Posting the
data on a site map as the results are reported will help to direct and refine the
sampling program. The final results of the soil-gas survey are usually presented in
maps showing contours of gas concentrations at various subsurface depths.
Sample depths should be corrected for site elevation changes so that the contour
represents a horizontal layer. By creating several horizontal contours, data can be
analyzed in 3-dimensions. Plotting total VOCs is often the easiest method, but it
is important to evaluate if differing sources exist by examining the distribution of
individual constituents.
An example of this type of analysis is the use of the ratio between pre-
benzene hydrocarbons (i.e., constituents that pass through a gas chromatograph
column prior to benzene) to total VOCs to determine the relative length of time a
contaminant has been present. Since the pre-benzene constituents of gasoline
migrate more rapidly than other hydrocarbons, a relatively high ratio will indicate
a more recent release while a low ratio will indicate an older release. Because
there are many factors that affect the absolute ratio, the ratios can only be used to
compare multiple releases at a single site.
An additional issue that is important for interpretation of results is analysis
of the units of measurement. Commonly, two types of units are used for reporting
soil-gas data: Volume per volume (e.g., ppmv or ppbv) or mass per volume (e.g.,
(ig/1 or mg/m ). Although for water, (ig/1 is equivalent to ppb, this is not true for
gases. If concentrations are reported in (ig/1, a conversion may be required. For
samples analyzed at 20 C and 1 atm pressure:
ppbv = M9/1 2.447 x IP4
molecular weight of the gas.
IV-12 March 1997
-------
Costs Of Active Soil-Gas Surveys
Because the sampling and analytical equipment used in active soil-gas
surveys varies considerably according to the site conditions, the survey objectives,
and the investigator preferences, the cost will also vary considerably. Most soil-
gas surveys are performed using direct push (DP) technology. The cost of
collecting active soil-gas surveys with truck mounted DP ranges from $1,000 to
$2,000 per day. In some cases, DP can be deployed manually, which may be less
expensive. Typically, 10 to 30 samples can be collected per day depending
primarily on soil type, sampling depths, and sampling method. Numerous field
analytical methods are applicable for soil-gas surveys (listed in Chapter VI, Field
Methods For The Analysis Of Petroleum Hydrocarbons), however, portable and
transportable gas chromatographs are most common because of their high data
quality level capabilities. Samples are rarely sent off-site to a fixed laboratory
because on-site information is often used for determining subsequent sample
locations and delays in analysis can affect data quality. Active soil-gas survey
sampling can be completed in as little as 1 day at a 1-acre site and should rarely
require more than 3 days. As a result, the cost of a complete soil-gas survey with
a report will typically range from $3,000 to $15,000.
Active Soil-Gas Survey Case Study
The following case study provides an example of the type of data that can
be collected with an actual active soil-gas survey at an UST site and how it may
be interpreted. A map of the site described in this case study, including the vapor
point and monitoring well locations, is presented in Exhibit IV-3.
Site History
In 1966, a retail gasoline marketing company purchased an UST facility
from an independent dealer. The facility had been operated as a gasoline station
for an undetermined period of time; there were an unknown number of USTs on
the property. The company reconstructed the facility shortly after the purchase
date and remodeled in 1981. In 1991, the site was closed, and the tanks were
removed. In order to remove petroleum-stained soil, the tank pit and piping
trenches were over-excavated. Five monitoring wells were installed to determine
if groundwater had been contaminated. The results indicated that groundwater
remained uncontaminated; however, a high degree of soil contamination was
discovered in MW-4, and significantly less contamination was discovered in
MW-1. In addition, monitoring well data indicated that the water table was
located at approximately 21 feet and the gradient flowed to the south.
March 1997 IV-13
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Soil-Gas Survey Objective
The main objective of the survey was to determine the risk of contaminant
migration. Emphasis was placed on source identification and delineation because
of the multiple ownership history of the facility and the potential for multiple
responsibilities for the contamination.
Sampling And Analytical Methods
The site was divided into a grid with spacing of 30 feet by 30 feet.
Twenty-four sampling locations were established, providing comprehensive areal
site coverage. A small-diameter steel probe sampler with a slotted terminal end
was driven into the subsurface with a mechanical hand-held hammer. An electric
vacuum pump was used to purge the system for 5 minutes prior to sampling.
Samples were collected with a gas-tight glass syringe and immediately analyzed
with a field portable GUPID.
In order to assess the soil heterogeneities, vertical profiling was performed
at all 24 locations. Sampling depths were at 3, 6, 9, 12, 15, and 18 feet. When no
significant contamination was indicated, samples were only taken at the first two
or three levels. A total of 87 samples was collected and analyzed over 3 days.
Results and Discussion
An evaluation of the vertical profiles indicated that the site geology was
relatively homogenous, permeable, and appropriate for active soil-gas sampling.
Short circuiting of the above-ground atmosphere was determined to not have
affected the data. In total, all QA/QC procedures supported the validity of the
data collected.
Exhibits IV-4 and IV-5 present the isoconcentration contours for total
volatiles at 9 and 12 feet, respectively. The data indicated three separate areas of
contamination. Most of the hydrocarbons were located at the north end of the
station, directly under the former operation area (pre-1966). A smaller zone of
contamination was located just north of the existing building and at the northwest
side of the site, next to existing product line trenches. Multi-level sampling
proved very useful at this site because if samples had been collected from only
one level, only one release would likely have been identified.
The absolute hydrocarbon vapor concentrations indicated the presence of
moderately high levels of soil residual hydrocarbons, especially in the north
March 1997 IV-15
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corner of the facility. The measurements at the 15 and 18 feet depth were lower
than would be expected if floating product existed on the water table. In addition,
the pre-benzene to total VOC ratio was examined for each sample to determine
the relative age of the source areas. The data indicated that the source area in the
north corner was significantly older than the other two areas. This evidence
suggested that there were at least two—and possibly three—separate source areas.
Because the oldest and largest source area had been present for at least
25 years without contamination reaching the groundwater, and because there were
no sensitive receptors in the vicinity, the state regulator determined that further
remediation of this site was not necessary.
A summary of the advantages and limitations of active soil-gas surveys is
presented in Exhibit IV-6.
Exhibit IV-6
Advantages And Limitations Of Active Soil-Gas Sampling
Advantages
Limitations
Samples can be analyzed on site
for "real time" data reporting.
From 10 to 30 samples can
typically be collected and analyzed
per day.
Can delineate contaminant source
area and plume of VOCs.
SVOCs and heavy petroleum
product contamination can be
inferred indirectly by measuring
products of biodegradation.
Not effective for identifying SVOCs
or low volatility compounds.
Extensive QA/QC must be
followed.
Cannot be easily conducted in
very low permeability or saturated
soils.
Analytical equipment selected may
not be capable of identifying all
constituents present.
IV-18
March 1997
-------
Passive Soil-Gas Sampling Methods
Of the two soil-gas sampling methods—active and passive—passive soil-
gas sampling techniques are typically used when SVOCs or low volatility
compounds are the primary constituents of concern. Passive soil-gas surveys
utilize probes that are placed in the ground for days or weeks to adsorb soil-gas
constituents on sorbent material using the ambient flow of vapors in the
subsurface. After the probe is removed from the ground, it is sent to a laboratory
where contaminants are desorbed and analyzed. An example of a passive soil-gas
sampler is presented in Exhibit IV-7.
Exhibit IV-7
Example Of Passive Soil-Gas Sampler
Ground Surface
i$&&
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g;$ Adsorbent
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Applications For Passive Soil-Gas Sampling
Passive soil-gas surveys are not considered an expedited site assessment
method because of the extended time required to collect and analyze the data.
However, in certain applications, the passive devices may be used as a screening
tool to help determine the soil and groundwater sampling location needed to
complete a site assessment. Generally, passive sampling is most applicable when
SVOCs are a primary concern, when numerous unknown compounds are
suspected (e.g., a Superfund site), or when subsurface conditions do not permit
adequate penetration with DP methods for active soil-gas sampling. Capabilities
of passive soil-gas surveys include:
Providing an initial screening at very large sites;
Screening the site for potential leakage from a UST or product line;
Providing data on the types of contaminants present in the vadose zone,
including a wide range of VOCs, SVOCs, and complex mixtures;
Providing information on the lateral distribution of contaminants in the
vadose zone;
Identifying sources of contaminants; and
Tracking a groundwater plume.
Passive Soil-Gas Survey Design
The specific survey design will vary between sites for a number of reasons
including the size of the site, the survey objectives, and the capabilities of the
sampler; however, some generalities can be presented. Sampling devices are
placed just below the surface (between 3 inches and 4 feet) and can be quickly
installed (between 2 and 15 minutes per device). A grid design is used because all
sampling devices are analyzed at the same time (i.e., analytical results do not
affect sampling locations). The number of samples and their spacing vary but, in
general, 15 to 30 samples are sufficient for a 1- to 2-acre gasoline station survey.
Sampling devices are left in the ground for 3 to 21 days and then removed and
typically shipped to the manufacturer's laboratory for analysis. Individuals
installing the sampling devices must ensure that contamination does not occur
prior to installation or after removal. Field blanks are, therefore, a necessary
check on field procedures.
IV-20 March 1997
-------
Interpretation Of Passive Soil-Gas Data
A report can usually be developed 2 to 3 weeks after removal of the
sampling devices. The results are reported in the amount of contaminant detected
per sorbent device. It is not possible to quantify the concentration of
contaminants present in the soil gas using passive sorbent devices because the
volume of gas contacting the sorbent material is unknown. The relative
concentrations of analytes on the sorbent may be related more to differences in the
affinity of individual VOCs for the sorbent (as well as sorbent capacity for that
VOC) and vapor flow rates than to the relative VOC concentrations in soil gas. In
addition, passive soil-gas surveys typically collect samples from a single depth
which will provide only a 2-dimensional view of contaminant distribution.
Usually there is not sufficient site-specific geologic information to make a
judgement about the actual distribution of contaminants. For example, perched
water tables may appear as clean zones, and changes in the data may be related to
changes in the thickness of clay layers rather than changes in subsurface
contaminant concentrations. As a result, although passive soil-gas surveys are an
effective screening method, interpretation of the data is more limited than active
soil-gas surveys.
Cost Of Passive Soil-Gas Surveys
The cost of passive soil-gas surveys varies among manufacturers of
sampling devices, ranging from $75 to $225 per sample (including analysis).
Because analytical costs for UST sites tend to be on the low end of this range and
because sampling 15 to 30 locations is typical for a 1-acre site, most gasoline
stations can be screened for between $1,200 and $3,000.
Passive Soil-Gas Survey Case Study
The following case study provides an example of the type of data that can
be collected with an actual passive soil-gas survey at an UST site and how it may
be interpreted. A site map is presented in Exhibit IV-8 with isoconcentration lines
for BTEX in groundwater. Exhibits IV-9 and IV-10 present isoconcentration lines
for diesel fuel and gasoline constituents in soil gas.
Site History
In 1990, a public highway agency began a systematic assessment of
environmental site conditions at public refueling stations under its jurisdiction.
March 1997 IV-21
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Records at one site indicated a significant degree of contamination and warranted
further investigation. Diesel fuel and gasoline USTs were replaced in 1982 and
1990. Evidence of contamination was found at both tank removals. Records
suggested the potential for substantial releases throughout the site history
including a potential major release of about 8,000 gallons in 1983. Sixteen
monitoring wells were initially installed, and free product was discovered in four
of them (Exhibit IV-8). Because the site overlaid shallow bedrock at depths
between 2 and 20 feet and because of the need to delineate the SVOCs found in
diesel fuel, a passive soil-gas survey was conducted.
Soil-Gas Survey Objectives
The main objective of the survey was to determine the location of the
contaminant source area to facilitate remediation. The direction of plume
migration was also a concern, particularly in the underlying fractured bedrock,
because several drinking water wells were located within 0.5 mile.
Sampling And Analytical Methods
Eighty canisters containing ferromagnetic wires coated with active carbon
adsorbent were place in a grid pattern throughout the 3 acres of the site. The
canisters were left in the ground for 11 days. After the canisters were retrieved,
the samples were analyzed with a gas chromatograph/mass spectrometer. Data
were reported as relative flux (ion counts) for both gasoline character (BTEX) and
diesel fuel character (naphthalene and alicyclic hydrocarbons).
Results And Discussion
The passive soil-gas data provided useful information about the diesel fuel
source area. Exhibit IV-9 indicates that the "hot spots" are between the pump
islands and the diesel fuel UST. In addition, the passive soil-gas survey correlated
well with monitoring well data. Exhibit IV-10 shows that the highest BTEX
concentrations were located near wells that contained floating product. Both
passive soil-gas maps indicated areas that warranted additional investigation. In
particular, the gasoline source area at the south end of the site appears to be
centered in two locations, suggesting that the undulating bedrock might partially
control the migration pattern of the petroleum compounds. Subsequent
investigations with seismic refraction and boring log data supported these
findings.
March 1997 IV-25
-------
A summary of the advantages and limitations of passive soil-gas surveys is
presented in Exhibit IV-11.
Exhibit IV-11
Advantages And Limitations Of Passive Soil-Gas Sampling
Advantages
Limitations
A wide range of VOCs, SVOCs, and
low volatile mixtures can be detected.
More effective than active sampling in
low permeability and high moisture
soils.
From 40 to 100 devices can be
installed in a day.
There is minimal disturbance to
subsurface and site operations.
Easy to install.
The data cannot be used to estimate
contaminant mass.
The vertical distribution of
contaminants is typically not
assessed.
The time required to collect and
analyze samples is typically 3 to 6
weeks.
Sorbent desorption may destroy some
compounds.
Measurements are time weighted and
are not directly comparable to soil and
groundwater laboratory methods.
Impervious layers and changes in the
thickness of clay layers can create
misleading information.
IV-26
March 1997
-------
Comparison Of Soil-Gas Sampling Applications
Active soil-gas surveys are more appropriate than passive soil-gas surveys
for most petroleum UST expedited site assessments because active soil-gas
surveys provide more information, more rapidly, and often at a cost that is
comparable to that of passive soil-gas surveys. Data collected with active soil-gas
surveys can be used immediately to direct additional sampling and analysis so that
the site assessment can be completed in a single mobilization. Active soil-gas
surveys also provide 3-dimensional information about the distribution of
contaminants and subsurface stratigraphy which allows for better interpretation of
data than is possible with passive soil-gas surveys.
Passive soil-gas surveys are most useful as a screening tool when SVOCs
and low volatility compounds are known or suspected to be present at a site. In
addition, passive soil-gas surveys may also be useful in real estate transactions
because passive soil-gas surveys provide valuable screening information which
can be obtained during time-consuming negotiations without more expensive,
intrusive techniques. Because of their high sensitivity to contaminant vapors,
passive soil-gas surveys can provide accurate information about the specific
compounds present and their relative concentration in 2-dimensions. A summary
and comparison of the applications of these two soil-gas sampling methods are
listed in Exhibit IV-12.
Exhibit IV-12
Applications For Active And Passive Soil-Gas Data
'•;,•• Application
Detect presence of VOCs
Detect presence of SVOCs
Active
^
Infer assessment of hydrocarbon presence through the S
measurement of indicators of biodearadation
Identify specific compounds
Evaluate (indirectly) contaminant concentrations in soil
Evaluate 2-dimensional contaminant distribution
Evaluate 3-dimensional contaminant distribution
Evaluate remedial options
Monitor remedial system effectiveness
v
s
-------
Passive Soil-Gas Sampling Equipment Manufacturers
A list of passive soil-gas sampling equipment manufactures is included
below as Exhibit IV-13. The equipment has not been evaluated by the EPA and
inclusion in this manual in no way constitutes an endorsement. These vendors are
listed solely for the convenience of the reader.
Because active soil-gas surveys are performed by numerous contractors
throughout the country, they have not been listed here. Because these surveys are
typically performed with direct push technologies, a list of active soil-gas
sampling equipment manufactures is presented in Chapter V, Direct Push
Technologies.
Exhibit IV-13
Passive Soil-Gas Sampling Equipment Manufacturers
PCR Laboratories
1318 East Mission Road, Suite 133
San Marcos, CA 92069
(619) 630-5106
Quadrel Services, Inc.
1896 Urbana Pike, Suite 20
Clarksburg, MD 20871
(301) 874-5510
Transglobal Environmental
Geochemistry (TEG)
13 locations across the country
(800) 834-9888
W.L. Gore & Associates, Inc.
101 Lewisville Road
P.O. Box 1100
Elkton, MD 21922-1100
(410) 392-3300
IV-28
March 1997
-------
References
ASTM. 1993. Standard guide for soil gas monitoring in the vadose zone,
D5314-93, Annual Book of ASTM Standards, Philadelphia.
Corey, A.T. 1986. Air permeability. In Methods of soil analysis, Part 1, 2nd
edition, A. Klute, ed.,Am. Soc. ofAgron. Monograph No. 9: 1121-36. Madison:
Univ. of Wisconsin Press.
Devitt, D.A., R.B. Evans, W.A. Jury, T.H. Starks, B. Eklund, and A. Gholson.
1987. Soil gas sensing for detection and mapping of volatile organics,
EPA/600/8-87/036. (NTIS PB87-228516).
Deyo, E.G., G.A. Robbins, and GB. Binkhorst. 1993. Use of portable oxygen
and carbon dioxide detectors to screen soil gas for subsurface gasoline
contamination. Gr. Water, vol. 31, no. 4.
Integrated Science and Technology, Inc. 1996. Example report of soil vapor
contaminant assessment. 1349 Old Highway 41, Suite 225. Marrietta, GA.
Kerfoot, H.B. and LJ. Barrows. 1987. Soil gas measurements for detection of
subsurface organic contaminants, EPA/600/2-87/027 (NTIS PB87-174884).
Kerfoot, H.B. and P.B. Durgin. 1987. Soil-gas surveying for subsurface organic
contamination: Active and passive techniques. In Superfund '87: Proceedings of
the 8th national conference. Washington, D.C: The Hazardous Materials Control
Research Institute.
Marrin, D.L. 1991. Subsurface biogenic gas ratios associated with hydrocarbon
contamination, eds. RE. Hinchee and RF. Ofenbuttle. In In-Situ Bioreclamation,
Stoneham: Butterworth-Heinemann.
Marrin, D.L. and H.B. Kerfoot. 1988. Soil gas surveying techniques. Environ.
Sci. Tech. vol. 22, no.7: 740-45.
Marrin, D.L. and GM. Thompson. 1987. Gaseous behavior of TCE overlying a
contaminated aquifer. Groundwater, vol. 25, no. 1: 740-45.
Pitchford, A.M., A.T. Mazzella, and K.R Scarbrough. 1988. Soil-gas and
geophysical techniques for detection of subsurface organic contamination,
EPA/600/4-88/019 (NTIS PB88-208194). 81 p.
March 1997 iv-29
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Robbins, G.A., E.G. Deyo, M.R. Temple, J.D. Stuart, and MJ. Lacy. 1990a.
Soil-gas surveying for subsurface gasoline contamination using total organic
vapor detection instruments: Part I. Theory and laboratory experimentation. Gr.
Water Mon. Rev. vol. 10, no. 3: 122-31.
Robbins, G.A., E.G. Deyo, M.R Temple, J.D. Stuart, and MJ. Lacy. 1990b.
Soil-gas surveying for subsurface gasoline contamination using total organic
vapor detection instruments: Part II. Field experimentation. Gr. Water Mon. Rev.,
vol. 10, no. 4: 110-17.
Robbins, G.A. 1995. Acceleratedfield site characterization employing 'push'
technologies (II) (With supplement gas chromatography section by B. Hartman).
Short Course Notes, 4M Center, Univ. of Tennessee/Chattanooga.
Robbins, G.A., B. E. McAninch, P.M. Gavas, and P.M. Ellis. 1995. An
evaluation of soil-gas surveying for H,S for locating subsurface hydrocarbon
contamination. Gr. Water Mon. Rev., vol. 15, no. 1: 124-32.
Roberts, N., M.E. Billa, and GE. Furst. 1992. A phased approach to remediation
of a complex site. In Proceedings of the National Ground Water Association
focus conference on eastern regional ground-water issues, Columbus, OH.
Thompson, GM. and D.L. Marrin. 1987. Soil gas contaminant investigations: A
dynamic approach. Gr. Water Mon. Rev., vol. 7, no. 2: 88-93.
Ullom, W.L. 1995. Soil gas sampling. In Handbook of vadose zone
characterization and monitoring, eds.L.G Wilson, L.G. Everett, S.J. Cullen,
pp. 555-67. Lewis Publishers.
U.S. EPA. 1993. Subsurface characterization and monitoring techniques: A desk
reference guide. Volume 2: The vadose zone, field screening and analytical
methods, EPA/625/R-93/003b. Office of Research and Development,
Washington, DC.
U.S. EPA. 1995. How to evaluate alternative cleanup technologies for
underground storage tank sites: A guide for corrective action plan reviewers,
EPA 510-B-95-007. Office of Underground Storage Tanks, Washington, DC.
Werner, M.D. 1985. The effects of relative humidity on the vapor phase
adsorption of trichloroethylene by activated carbon. Amer. Indus. Hygien. Ass. ].,
vol. 46, no. 10: 585-90.
IV-30 March 1997
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Peer Reviewers
Name
Gilberto Alvarez
David Ariail
Michael Billa
Steve Billets
J. Russell Boulding
Gerald Church
Brendon Deyo
Chi-Yuan Fan
Blayne Hartman
Mark Hatheway
Paul Henning
Bruce Kjartanson
Bill Kramer
Al Liguori
Donn Marrin
Chris O'Neill
Emil Onuschak, Jr.
H. James Reisinger, II
Gary Robbins
Charlita Rosal
Sandra Stavnes
Glenn Thompson
Katrina Varner
Mark Wrigley
Tom Zdeb
Company/Organization
U.S. EPA, Region 5
U.S. EPA, Region 4
Rizzo Associates, Inc.
U.S. EPA, National Exposure Research
Laboratory
Boulding Soil-Water Consulting
Transglobal Environmental Geochemistry
Home Engineering and Environmental
Services
U.S. EPA, National Risk Management
Research Laboratory
Transglobal Environmental Geochemistry
Northeast Research Institute LLC
Quadrel Services Inc.
Iowa State University
Handex Corporation
Exxon Research and Engineering Company
Consulting and Research Scientist
New York State Department of
Environmental Conservation
Delaware Department of Natural Resources
Integrated Science and Technology, Inc.
University of Connecticut
U.S. EPA, National Exposure Research
Laboratory
U.S. EPA, Region 8
Tracer Research Corporation
U.S. EPA, National Exposure Research
Laboratory
W.L. Gore and Associates, Inc.
Woodward-Clyde Consultants
March 1997
IV-31
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Chapter V
Direct Push Technologies
-------
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Contents
Exhibits V-v
Direct Push Technologies V-1
Direct Push Rod Systems V-4
Single-Rod Systems V-4
Cased Systems V-4
Discussion And Recommendations V-4
Direct Push Sampling Tools V-8
Soil Sampling Tools V-8
Nonsealed Soil Samplers V-8
Barrel Samplers V-8
Split-Barrel Samplers V-10
Thin-Wall Tube Samplers V-10
Sealed Soil (Piston) Samplers V-10
Discussion And Recommendations V-11
Lithologic Description/Geotechnical
Characterization V-11
Chemical Analysis V-11
Sample Contamination V-13
Active Soil-Gas Sampling Tools V-13
Expendable Tip Samplers V-14
Retractable Tip Samplers V-16
Exposed-Screen Samplers V-16
Sampling With Cased Systems V-16
Methods For Retrieving Active Soil-Gas Samples .... V-17
Sampling Through Probe Rods V-17
Sampling Through Tubing V-17
Discussion And Recommendations V-17
Groundwater Sampling Tools V-18
Exposed-Screen Samplers V-20
Sealed-Screen Samplers V-26
Discussion And Recommendations V-27
General Issues Concerning Groundwater Sampling ... V-27
Loss Of VOCs V-28
Stratification Of Contaminants V-29
Conclusion V-29
In Situ Measurements Using Specialized Direct Push Probes V-30
Cone Penetrometer Testing V-30
March 1997 V-iii
-------
Three-Channel Cone V-31
Piezocone ..V-34
Geophysical And Geochemical Logging Probes V-34
Conductivity Probes V-34
Nuclear Logging Tools V-36
Chemical Sensors V-36
Discussion And Recommendations V-37
Equipment For Advancing Direct Push Rods V-39
Manual Hammers V-39
Hand-Held Mechanical Hammers V-39
Percussion Hammers And/Or Vibratory Heads Mounted
On Small Vehicles V-41
Small Hydraulic Presses Anchored To The Ground V-41
Conventional Drilling Rigs V-41
Trucks Equipped With Hydraulic Presses V-42
Discussion And Recommendations V-42
Methods For Sealing Direct Push Holes V-44
Surface Pouring ..V-45
Re-entry Grouting V-45
Retraction Grouting V-47
Grouting During Advancement. V-48
Discussion And Recommendations V-48
Direct Push Equipment Manufacturers V-52
References V-57
Peer Reviewers V-62
V-iv March 1997
-------
Exhibits
Number Title Page
V-1 Overview Of Direct Push Technologies V-3
V-2 Schematic Drawing Of Single And Cased Direct Push
Rod Systems V-5
V-3 Comparison Of Single-Rod And Cased Systems V-7
V-4 Types Of Nonsealed Direct Push Soil Sampling Tools V-9
V-5 Using The Sealed Direct Push Soil Sampler
(Piston Sampler) V-12
V-6 Summary Of Sealed And Nonsealed Soil Sampler
Applications V-14
V-7 Types Of Direct Push Soil-Gas Sampling Tools V-15
V-8 Summary Of Soil-Gas Sampling Tool Applications V-19
V-9 Permanent Monitoring Well Installed With Pre-Packed
Well Screens V-21
V-10 Types Of Direct Push Groundwater Sampling Tools V-22
V-11 Using The Check Valve Tubing Pump V-24
V-12 Using A Drive-Point Profiler V-25
V-13 Summary Of Groundwater Sampling Tool Applications V-28
V-14 Components Of A CPT Piezocone V-32
V-15 Example CPT Data V-33
V-16 CPT Soil Behavior Types V-33
V-17 Small-Diameter Direct Push Conductivity Probe V-35
March 1997 V-V
-------
V-18 Summary Of In Situ Logging Equipment Used With
Direct Push Technologies V-38
V-19 Typical Equipment Used To Advance Direct Push Rods V-40
V-20 Summary Of Equipment For Advancing Direct Push Rods . . . V-43
V-21 Methods For Sealing Direct Push Holes V-46
V-22 Sealing Direct Push Holes With Cased Systems V-49
V-23 Sealing Direct Push Holes By Grouting During
Advancement V-50
V-24 Summary Of Direct Push Hole Sealing Applications V-51
V-25 Direct Push Equipment Manufacturers V-52
V-26 Matrix Of Manufacturers And Equipment V-54
V-vi March 1997
-------
Chapter V
Direct Push Technologies
Direct push (DP) technology (also known as "direct drive," "drive point,"
or "push" technology) refers to a growing family of tools used for performing
subsurface investigations by driving, pushing, and/or vibrating small-diameter
hollow steel rods into the ground. By attaching sampling tools to the end of the
steel rods they can be used to collect soil, soil-gas, and groundwater samples. DP
rods can also be equipped with probes that provide continuous in situ
measurements of subsurface properties (e.g., stratigraphy, contaminant
distribution). DP equipment can be advanced with various methods ranging from
30 pound manual hammers to trucks weighing 60 tons.
DP technology has developed in response to a growing need to assess
contaminated sites more completely and more quickly than is possible with
conventional methods. As explained in Chapter II, The Expedited Site
Assessment Process, conventional assessments have relied heavily on traditional
drilling methods, primarily hollow stem augers (HSA), to collect soil and
groundwater samples and install permanent monitoring wells. Because installing
permanent monitoring wells with HSA is a relatively slow process that provides a
limited number of samples for analysis, the most economical use for the
equipment is to perform site assessments in phases with rigid work plans and off-
site analysis of samples.
With the development of DP technologies, large, permanent monitoring
wells are no longer the only method for collecting groundwater samples or
characterizing a site. Multiple soil, soil-gas, and groundwater samples can now be
collected rapidly, allowing high data quality analytical methods to be used on-site,
economically. As a result, DP technologies have played a major role in the
development of expedited site assessments (ESAs).
DP technologies are most applicable in unconsolidated sediments,
typically to depths less than 100 feet. In addition to being used to collect samples
from various media, they can also be used to install small-diameter (i.e., less than
2 inches) temporary or permanent monitoring wells and small-diameter
piezometers (used for measuring groundwater gradients). They have also been
used in the installation of remediation equipment such as soil vapor extraction
wells and air sparging injection points. Penetration is limited in semiconsolidated
sediments and is generally not possible in consolidated formations, although
highly weathered bedrock (i.e., saprolite) is an exception for some equipment. DP
equipment may also be limited in unconsolidated sediments with high percentages
of gravels and cobbles. As a result, other drilling methods are necessary in site
assessment and remediation activities where geological conditions are unfavorable
March 1997 V-1
-------
for DP technologies or where larger diameter (i.e., greater than 2 inches) wells are
needed.
An additional benefit of DP technologies is that they produce a minimal
amount of waste material because very little soil is removed as the probe rods
advance and retract. Although this feature may result in some soil compaction
that could reduce the hydraulic conductivity of silts and clays, methods exist for
minimizing resulting problems.
In contrast, although most other drilling methods remove soil from the
hole, resulting in less compaction, conventional drilling methods create a
significant amount of contaminated cuttings and they also smear clay and silt
across more permeable formations which can obscure their true nature. Moreover,
these other drilling methods have the potential of causing a redistribution of
contamination as residual and free product are brought to the surface.
Choosing a DP method (or combination of DP methods) appropriate for a
specific site requires a clear understanding of data collection goals because many
tools are designed for only one specific purpose (e.g., collection of groundwater
samples). This chapter contains descriptions of the operation of specific DP
systems and tools, highlighting their main advantages and limitations; its purpose
is to assist regulators in evaluating the appropriateness of these systems and tools.
This chapter does not contain discussions of specific tools manufactured
by specific companies because equipment is evolving rapidly. Not only are
unique tools being invented, but existing equipment is being used in creative ways
to meet the needs of specific site conditions. As a result, the distinctions between
types of DP equipment is becoming blurred and it is necessary to focus on
component groups rather than entire DP systems. The four component groups
discussed in this chapter include:
Rod systems;
Sampling tools;
In situ measurements using specialized probes; and
Equipment for advancing DP rods.
The chapter also includes a discussion of methods for sealing DP holes
because of their importance in preventing the spread of contaminants and,
therefore, in the selection of DP equipment. The cost of various DP equipment is
not discussed in this chapter because cost estimates become quickly outdated due
to rapid changes in the industry. An overview of the advantages and limitations
of DP equipment and systems discussed in this chapter are presented in Exhibit
V-l.
V-2 March 1997
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Exhibit V-1
Overview Of Direct Push Technologies
Direct Push
Component
Probing
systems
Soil, soil-gas,
and
groundwater
sampling
In situ
measurement
of subsurface
conditions
Methods for
advancing
probe rods
Sealing
methods
Example
Single-rod or
cased
Piston
samplers,
expendable
tip samplers
Conductivity
probes, laser
induced
fluorescence
Percussion
hammers,
hydraulic
presses
Re-entry
grouting,
retraction
grouting
Advantages
Minimizes the
need for waste
disposal or
treatment
Relatively rapid
Can be used to
rapidly log site
Some methods
are extremely
portable
Holes can be
sealed so that
contaminants
cannot
preferentially
migrate through
them
Limitations
Compaction of
sediments may
decrease hydraulic
conductivity
Permanent
monitoring wells are
limited to 2 inch
diameter or less
Correlation with
boring logs is
necessary
Very dense,
consolidated
formations are
generally
impenetrable
Appropriate sealing
methods may limit
sampling
equipment options
March 1997
V-3
-------
Direct Push Rod Systems
DP systems use hollow steel rods to advance a probe or sampling tool.
The rods are typically 3-feet long and have male threads on one end and female
threads on the other. As the DP rods are pushed, hammered, and/or vibrated into
the ground, new sections are added until the target depth has been reached, or
until the equipment is unable to advance (i.e., refusal). There are two types of rod
systems, single-rod and cased. Both systems allow for the collection of soil, soil-
gas, and groundwater samples. Exhibit V-2 presents a schematic drawing of
single-rod and cased DP rod systems.
Single-Rod Systems
Single-rod systems are the most common types of rods used in DP
equipment. They use only a single string (i.e., sequence) of rods to connect the
probe or sampling tool to the rig. Once a sample has been collected, the entire
string of rods must usually be removed from the probe hole. Collection of
samples at greater depths may require re-entering the probe hole with an empty
sampler and repeating the process. The diameter of the rods is typically around 1
inch, but it can range from 0.5 to 2.125 inches.
Cased Systems
Cased systems, which are also called dual-tube systems, advance two
sections—an outer tube, or casing, and a separate inner sampling rod. The outer
casing can be advanced simultaneously with, or immediately after, the inner rods.
Samples can, therefore, be collected without removing the entire string of rods
from the ground. Because two tubes are advanced, outer tube diameters are
relatively large, typically 2.4 inches, but they can range between 1.25 and 4.2
inches.
Discussion And Recommendations
Single-rod and cased systems have overlapping applications; they can be
used in many of the same environments. However, when compared with cased
systems, single-rod systems are easier to use and are capable of collecting soil,
soil-gas, or groundwater samples more rapidly when only one sample is retrieved.
They are particularly useful at sites where the stratigraphy is either relatively
homogeneous or well delineated.
V-4 March 1997
-------
Exhibit V-2
Schematic Drawing Of Single
And Cased Direct Push Rod Systems
Single-Rod Direct Push System
'• ii t •: •
:!>!"•
ij:
,',>,«•" •• . .•!i'ili'|iil .,...
• V, •. «!,". ' ' L! "'
1) DP sampling tool is advanced on the
end of a single sequence of rods.
2) Once the sampling tool is full, tool and
rods are withdrawn from the ground. To
collect another sample, the tool must be re-
inserted and pushed to the next sampling
depth.
Cased Direct Push System
1) DP sampling tool is attached to inner
rods. Sampling tool, inner rods, and outer
drive casing are advanced simultaneously.
2) To collect the sample, only the sampling
tool and inner rods are removed. The outer
drive casing remains in the ground to
prevent sloughing or hole collapse. To
collect a deeper sample, the tool and inner
rods are re-inserted to the bottom of probe
hole and advanced along with the outer drive
casing. The outer casing is removed only
after the last sample has been collected.
March 1997
V-5
-------
The primary advantage of cased DP systems is that the outer casing
prevents the probe hole from collapsing and sloughing during sampling. This
feature allows for the collection of continuous soil samples that do not contain any
slough, thereby preventing sample contamination. Because only the inner sample
barrel is removed, and not the entire rod string, cased systems are faster than
single-rod systems for continuous sampling at depths below 10 feet. The
collection of continuous samples is especially important at geologically
heterogeneous sites where direct visual observation of lithology is necessary to
ensure that small-scale features such as sand stringers in aquitards or thin zones of
non-aqueous-phase liquids (NAPLs) are not missed.
Another advantage of cased systems is that they allow sampling of
groundwater after the zone of saturation has been identified. This feature allows
investigators to identify soils with relatively high hydraulic conductivities from
which to take groundwater samples. If only soils with low hydraulic conductivity
are present, investigators may choose to take a soil sample and/or install a
monitoring well. With most single-rod systems, groundwater samples must be
taken without prior knowledge of the type of soil present. (Some exposed-screen
samplers used with single-rod systems as described in the Groundwater Sampling
Tools section are an exception.)
A major drawback of single-rod systems is that they can be slow when
multiple entries into the probe hole are necessary, such as when collecting
continuous soil samples. In addition, in non-cohesive formations (i.e., loose
sands), sections of the probe hole may collapse, particularly in the zone of
saturation, enabling contaminated soil present to reach depths that may be
otherwise uncontaminated. Sloughing soils may, therefore, contaminate the
sample. This contamination can be minimized through the use of sealed soil
sampling tools (i.e., piston samplers, which are discussed in more detail in the
Soil Sampling Tools section that follows).
Multiple entries made with single-rod systems into the same hole should
be avoided when NAPLs are present because contaminants could flow through the
open hole after the probe rods have been removed; particularly if dense-non-
aqueous phase liquids (DNAPLs) are present. In addition, multiple entries into
the probe hole may result in the ineffective sealing of holes. (These issues are
discussed in more detail in Methods For Sealing Direct Push Holes at the end of
the chapter.) If samples need to be taken at different depths in zones of significant
NAPL contamination, single-rod systems can be used, but new entries into soil
should be made next to previous holes.
The major drawback of cased systems is that they are more complex and
difficult to use than single-rod systems. In addition, because they require larger-
diameter probe rods, cased systems require heavier DP rigs, larger percussion
hammers, and/or vibratory systems for advancing the probe rod. Furthermore,
V-6 March 1997
-------
even with the additional equipment, penetration depths are often not as great as
are possible with single-rod systems and sampling rates are slower when single,
discrete samples are collected. Exhibit V-3 summarizes the comparison of single
and cased systems.
Exhibit V-3
Comparison Of Single-Rod And Cased Systems
Allows collection of a
single soil, soil-gas, or
groundwater sample
Allows collection of
continuous soil
samples
Allows collection of
groundwater sampling
after determining ideal
sampling zone3
Lighter carrier vehicles
can be used to
advance rods
Greater penetration
depths
Multiple soil samples
can be collected when
NAPLs are present
Single-Rod
/
(faster)
/1
/
/
Cased
/
/2
(faster)
S
,/
Sloughed soil may also be collected.
2 Faster at depths below approximately 10 feet.
3 Some exposed-screen samplers, discussed in the groundwater sampling
section, also have this ability.
March 1997
V-7
-------
Direct Push Sampling Tools
A large number of DP tools have been developed for sampling soil, soil-
gas, and groundwater. Each of these tools was designed to meet a specific
purpose; however, many of these tools also have overlapping capabilities. This
section describes the commonly used tools currently available and clarifies their
applications. All of the tools described in this section can be advanced by rigs
designed specifically for DP. In addition, many of these tools can also be used
with conventional drilling rigs.
Soil Sampling Tools
There are two types of soil samplers: Nonsealed and sealed. Nonsealed
soil sampling tools remain open as they are pushed to the target depth; sealed soil
samplers remain closed until they reach the sampling depth.
Nonsealed Soil Samplers
The three most commonly used nonsealed soil samplers are barrel, split-
barrel, and thin-walled tube samplers. All three are modified from soil samplers
used with conventional drilling rigs (e.g., HSA). The primary difference is that
DP soil samplers have smaller diameters. Nonsealed soil samplers should only be
used in combination with single-rod systems when sampling in uncontaminated
fine-grained, cohesive formations because multiple entries into the probe hole are
required. When sloughing soils and cross-contamination are a significant
concern, nonsealed soil samplers may be used with cased DP systems or more
conventional sampling methods (e.g., HSA). In addition, nonsealed samplers
necessitate continuous soil coring because there is no other way to remove soil
from the hole. All three types of nonsealed soil sampling tools are presented in
Exhibit V-4.
Barrel Samplers
Barrel samplers, also referred to as solid-barrel or open-barrel samplers,
consist of a head assembly, a barrel, and a drive shoe (Exhibit V-4a). The sampler
is attached to the DP rods at the head assembly. A check valve, which allows air
or water to escape as the barrel fills with soil, is located within the head assembly.
The check valve improves the amount of soil recovered in each sample by
allowing air to escape. With the use of liners, samples can be easily removed for
volatile organic compound (VOC) analysis or for observation of soil structure.
V-8 March 1997
-------
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Without the use of liners, soil cores must be physically extruded using a hydraulic
ram which may damage fragile structures (e.g., root holes, desiccation cracks).
Split-Barrel Samplers
Split-barrel samplers, also referred to as "split-spoon" samplers, are
similar to barrel samplers except that the barrels are split longitudinally (Exhibit
V-4b) so that the sampler can be easily opened. The primary advantage of split-
barrel samplers is that they allow direct observation of soil cores without the use
of liners and without physically extruding the soil core. As a result, split-barrel
samplers are often used for geologic logging. Split-barrel samplers, however,
may cause more soil compaction than barrel samplers because the tool wall
thickness is often greater. In addition, although liners are not compatible with all
split-barrel samplers, liners are necessary if samples are used for analysis of
Vocs.
Thin-Wall Tube Samplers
Thin-wall tube samplers (larger diameter samplers are known as Shelby
Tubes) are DP sampling tools used primarily for collecting undisturbed soil
samples (Exhibit V-4c). The sampling tube is typically attached to the sampler
head using recessed cap screws or rubber expanding bushings. The walls of the
samplers are made of thin steel (e.g., 1/16-inch thick). The thin walls of the
sampler cause the least compaction of the soil, making it the DP tool of choice for
geotechnical sample analysis (e.g., laboratory measurement of hydraulic
conductivity, moisture content, density, bearing strength).
Samples are typically preserved, inside the tube, for off-site geotechnical
analysis. If the samples are intended for on-site chemical analysis, they can be
extruded from the sampler using a hydraulic ram, or the tubes can be cut with a
hacksaw or tubing cutter. Because of their fragile construction, thin-wall tube
samplers can be used only in soft, fine-grained sediments. In addition, the
sampler is usually pushed at a constant rate rather than driven with impact
hammers. If samples are needed for off-site VOC analysis, the tube is used as the
sample container which can be capped and preserved.
Sealed Soil (Piston) Samplers
Piston samplers are the only type of sealed soil sampler currently
available. They are similar to barrel samplers, except that the opening of the
sampler is sealed with a piston. Thus, while the sampler is re-inserted into an
open probe hole, contaminated soil and water can be prevented from entering the
V-10 March 1997
-------
sampler. The probe displaces the soil as it is advanced. When the sampler has
been pushed to the desired sampling depth, the piston is unlocked by releasing a
retaining device, and subsequent pushing or driving forces soil into the sampler
(Exhibit V-5).
Several types of piston samplers are currently available. Most use a rigid,
pointed piston that displaces soil as it is advanced. Piston samplers are typically
air- and water-tight; however, if o-ring seals are not maintained, leakage may
occur. Piston samplers also have the advantage of increasing the recovery of
unconsolidated sediments as a result of the relative vacuum that is created by the
movement of the piston.
Discussion And Recommendations
Issues affecting the selection of soil samplers include the ability of the
sampler to provide samples for lithological description, geotechnical
characterization, or chemical analysis. In addition, the potential of a sample
contamination with a specific sampler must be considered.
Lithologic Description/Geotechnical Characterization
All soil samplers can be used to some extent for lithologic description and
geotechnical characterization but because the disturbance to the sample varies
between tools, the preferred tool will vary depending on the application. Split-
barrel samplers or barrel samplers used with split-liners are the best DP sampling
methods for lithological description because they allow the investigator to directly
inspect the soil without further disturbing the sample. Thin-walled tube samplers
are best for collecting undisturbed samples needed for geotechnical analysis;
barrel and piston samplers are the next best option. With single-rod systems,
piston samplers are the only tools that can reliably be used for these same
objectives because they produce discrete soil samples.
Chemical Analysis
All sealed or nonsealed soil samplers can be used for the collection of
samples for VOC analysis. If samples are analyzed on-site, liners of various
materials (e.g., brass, stainless steel, clear acrylic, polyvinylchloride [PVC]) can
be used as long as the soil is immediately subsampled and preserved. Soil
samples intended for off-site analysis should be collected directly into brass or
stainless steel liners within the DP soil sampling tool. Once the tool has been
retrieved, the liners can be immediately capped, minimizing the loss of VOCs.
Unfortunately, without extruding the soil core from the metal liners, detailed
March 1997 V-11
-------
Exhibit V-5
Using The Sealed Direct Push Soil Sampler (Piston Sampler)
.r!.
. i .••
•[•'-..
-I/- . :'
''
• ix-'-J-.
• •' ' '••)
-.-Pin
-Sample
..'.barrel
• Piston
1) Previously
cored hole.
Lower portion of
hole collapsed.
'V.:V • ' -••'
2) Sealed
piston sampler
is driven to
beginning of
next sampling
interval. Piston
is locked in
place to
prevent soil
and water from
entering
sample barrel.
-v
3) Unlocking
(releasing)
internal piston by
removing
retaining pin.
—-Sample
'-.'barrel
^ Drive
shoe
Source: Geoprobe® Systems
4) Sampler driven to
collect next soil core.
Piston remains
stationary while
sample barrel is
advanced. Soil core
is retrieved by
removing entire
assembly from hole.
V-12
March 1997
-------
logging of the soil core is not possible. Short liners (4 to 6 inches long) may be
useful for providing a minimal amount of lithological information. The soil
lithology can be roughly discerned by inspecting the ends of the soil-filled liners;
specific liners can then be sealed and submitted for chemical analysis. Extruding
soil cores directly into glass jars for chemical analysis should be avoided since up
to 90 percent of the VOCs may be lost from the sample (Siegrist, 1990).
Sample Contamination
The potential for sample contamination will depend on both the type of
soil sampler and the type of DP rod system. The major concern with nonsealed
samplers is that the open bottom may, when used with single-rod systems, allow
them to collect soil that has sloughed from an upper section of the probe hole;
they, therefore, may collect samples that are not representative of the sampling
zone. If the sloughed soil contains contaminants, an incorrect conclusion could be
made regarding the presence of contaminants at the target interval. Alternatively,
if the overlying soil is less contaminated than the soil in the targeted interval,
erroneously low concentrations could be indicated. As a result, nonsealed
samplers should not be used with single-rod DP systems where contaminated soils
are present. In such cases, piston samplers are the only appropriate soil samplers.
Nonsealed samplers can be safely used with cased DP systems above the
water table. When sampling below the water table, particularly through
geological formations with a high hydraulic conductivity, nonsealed samplers
should not be used because contaminated water can enter the drive casing. In this
situation, water-tight piston samplers must be used in combination with cased DP
systems. In many low permeability formations, water does not immediately enter
the outer drive casing of cased DP systems, even when the casing is driven to
depths well below the water table. In these settings the potential for sample
contamination is greatly reduced, and nonsealed soil samplers can be lowered
through the outer casing. A summary of sealed and nonsealed soil samplers is
presented in Exhibit V-6.
Active Soil-Gas Sampling Tools
Chapter IV, Soil-Gas Surveys, discusses the methods, capabilities, and
applicabilities of both active and passive soil-gas surveys. Because active soil-gas
sampling is performed with DP equipment, the various DP tools used in the
collection of active soil-gas samples are covered in this section.
March 1997 V-13
-------
Exhibit V-6
Summary Of Sealed And Nonsealed Soil Sampler Applications
Sampling
Above
Water-table
Sampling
Below
Water-table
NAPLs Not
Present
NAPLs Present
NAPLs Not
Present
NAPLs Present
Single-Rod System
Nonsealed
/1
/1
Sealed
/
/
/
/
Cased System
Nonsealed
/
/
/
/2
Sealed
/
/
/
/
1 Fine-grained (cohesive) formations where probe hole does not collapse.
2 In low permeability soil where groundwater does not enter drive casing.
In active soil-gas sampling, a probe rod is pushed (either manually or
mechanically) to a specified depth below the ground surface (bgs) into the vadose
zone. A vacuum is applied to the rods (or tubing within the rods), and the sample
is collected. The use of probe tips with larger diameters than the probe rods is a
practice that should be discouraged when soil-gas sampling. Some DP
practitioners use these large tips in order to reduce friction on advancing probe
rods and therefore increase depth of penetration. This practice, however, will
increase the likelihood of sampling atmospheric gases and diluting constituent
concentrations.
There are four variations of soil-gas sampling tools and procedures:
expendable tip samplers, retractable tip samplers, exposed samplers, and cased
system sampling. Exhibit V-7 presents several soil-gas sampling tools.
Expendable Tip Samplers
Expendable cone-shaped tips, made of either steel or aluminum, are held
in a tip holder as the DP rod advances (Exhibit V-71;). Once the desired depth
has been reached, the DP rods are pulled back a few inches (Exhibit V-7a2) and
the tip can be separated from the tip holder, exposing the soil. Deeper samples
can be collected in the same hole by withdrawing the probe and attaching another
expendable tip. The previous tip can usually be pushed out of the way in most
soils; however, some soils (e.g., dense clays) may prevent the tip from moving
and, therefore, prevent re-entry into the same hole.
V-14
March 1997
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V-15
-------
The advantage of this method is that it allows retraction grouting
(discussed in detail on page V-47). The major disadvantage of this method is that
collection of deeper soil-gas samples in the same probe hole can be very time
consuming because of the need to retract and re-insert the entire probe rod.
Retractable Tip Samplers
Retractable tips are similar to the expendable tips described above, except
that the tip is physically attached to the tip holder by a small steel connecting tube
(Exhibit V-7b). The connecting tube contains small holes, slots, or screens, and is
held within the probe rod until the sampling depth is reached. As with the
expendable tip sampler, the probe rod is withdrawn a few inches so that the tip
can be dislodged, exposing the connecting tube.
Retractable tip samplers can be used to sample a single probe hole at
multiple levels if the formation will not allow an expendable tip to be moved out
of the way of the advancing probe rod. Generally, the probe rod should be
withdrawn entirely from the probe hole in order to properly secure the tip. The
probe rod should not be pushed back over the tip while in the hole because if the
tip does not seat properly the assembly will be damaged. A disadvantage of this
method is that it does not allow retraction grouting.
Exposed-Screen Samplers
Exposed screen samplers are probe rods that are fitted with slotted or
screened terminal ends. They are similar to the exposed-screen samplers
described in the groundwater sampling section which follows and which is
depicted in Exhibit V-lOa (page V-22). They may be made of steel or PVC and
are exposed to the subsurface as they are driven to the sampling depth.
The major advantage of this tool is that it allows rapid sampling of
multiple intervals within the same probe hole because the probe rod does not need
to be retrieved before advancing to the next depth. The primary drawback is that
if the slots are exposed to contaminants as the probe is pushed into the subsurface,
sample contamination can result. In addition, the slots or screen may become
clogged as the probe is pushed through fine grained soils, and retraction grouting
can not be used with this method.
Sampling With Cased Systems
Soil-gas sampling can also be accomplished with cased DP systems. Once
the sampling depth is reached, samples can be collected either directly through the
V-16 March 1997
-------
outer casing or through disposable tubing (Exhibit V-7c). The major advantages
of this method are that it creates less compaction of soils and it enables multiple
level sampling. The major disadvantage is that it can be slower than single-rod
methods.
Methods For Retrieving Active Soil-Gas Samples
Active soil-gas samples can be retrieved by two methods: soil gas can be
drawn directly through the probe rods, or soil gas can be drawn through tubing
inside the probe rods. Both methods are available with all the above-mentioned
sampling tools.
Sampling Through Probe Rods
Soil gas can be pumped to the surface directly through probe rods, whether
single-rod or cased systems. The advantage of this method is that it is relatively
simple and less equipment is needed than for sampling through tubing. The
drawbacks, however, are significant. First, because the volume of air within the
probe rods is large (compared with sampling through tubing), the amount of time
needed to purge the rods and collect a representative sample of soil-gas is
relatively long. The increased volume of soil gas also increases the chances that
short circuiting will occur, resulting in the sampling of atmospheric gases. This
issue is particularly a problem with cased systems because the inside diameter of
the casing can be much larger than single-rod systems. Second, the joints of most
DP rods are not air-tight, so when the rod string is placed under vacuum, soil gas
may be drawn from intervals other than the targeted zone.
Sampling Through Tubing
Sampling through tubing (Exhibit V-7d) is a method used to overcome
many of the problems associated with sampling directly through the probe rods.
The tubing is commonly made of polyethylene (PE) or Teflon
(polytetrafluoroethylene [PTFE]). The advantages of this method are that air is
not withdrawn from the joints between rod sections, and purge volumes and
sampling times are reduced. The disadvantage is that the tubing makes the
sampling equipment more complicated and adds an additional expense.
Discussion And Recommendations
In general, sampling soil-gas through PE or PTFE tubing is the preferred
method. Sampling directly through the probe rods can be successfully
March 1997 V-17
-------
accomplished, but it requires longer sampling times and investigators must ensure
that probe rod joints are completely sealed.
If a soil-gas survey requires multi-level sampling, retraction tip samplers
are applicable; however, these samplers require multiple entries into the same
probe hole. Exposed screen samplers and cased systems allow for rapid sampling
without the problems associated with multiple entry (discussed previously in the
Direct Push Rod System section). However, exposed samplers may also result in
sample contamination if NAPLs are dragged down in the slots or screen.
If soil gas is to be sampled in fine-grained sediments, sampling through
tubing should be used to minimize sample volumes and the rod string should be
withdrawn a greater distance than normal in order to expose a larger sampling
interval. Alternatively, expendable tip samplers and cased systems may be useful
if macropores (e.g., root holes, desiccation cracks) exist. These features may be
sealed by the advancing probe rod. Expendable tip and cased systems may allow
brushes to be inserted into the sampling zone to scour away compacted soil, thus
restoring the original permeability. Exhibit V-S provides a summary of the
applicability of the soil-gas sampling tools discussed in this section.
Groundwater Sampling Tools
DP technologies can be used in various ways to collect groundwater
samples. Groundwater can be collected during a one-time sampling event in
which the sampling tool is withdrawn and the probe hole grouted after a single
sample is collected; groundwater sampling tools can be left in the ground for
extended periods of time (e.g., days, weeks) to collect multiple samples; or, DP
technologies can be used to construct monitoring wells that can be used to collect
samples over months or even years.
In general, when the hydraulic conductivity of a formation reaches
10" cm/second (typical for silts), collection of groundwater samples through one-
time sampling events is rarely economical. Instead, collection of groundwater
samples requires the installation of monitoring devices that can be left in the
ground for days, weeks, or months. In general, however, it is difficult to get an
accurate groundwater sample in low permeability formations with any method
(whether DP or rotary drilling) because the slow infiltration of groundwater into
the sampling zone may cause a significant loss of VOCs. As a result, DP
groundwater sampling is most appropriate for sampling in tine sands or coarser
sediments.
As with soil-gas sampling, probe tips for one-time groundwater sampling
events should not be larger than DP rods because they can create an open annulus
V-18 March 1997
-------
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V-19
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that could allow for contaminant migration. When installing long-term
monitoring points, large tips can be used in conjunction with sealing methods that
do not allow contaminant migration (e.g., grouting to the surface).
Although most DP groundwater sampling equipment can also be used for
determining groundwater gradients, using piezometers (i.e., non-pumping,
narrow, short-screened wells used to measure potentiometric pressures, such as
the water table elevation) early in a site assessment is typically the best method.
Piezometers are quick to install; they are inexpensive to purchase, and, because of
their narrow diameter, they are quick to reach equilibrium. DP-installed
monitoring wells may also be used for this purpose; however, they are more
appropriate for determining groundwater contaminant concentrations once
groundwater gradients and site geology have been characterized. Undertaking
these activities first greatly simplifies the task of determining contaminant
location, depth, and flow direction.
Methods now exist for installing permanent monitoring wells with both
single-rod and cased DP systems (Exhibit V-9). These methods allow for the
installation of annular seals that isolate the sampling zone. In addition, some
methods allow for the installation of fine-grained sand filter packs that can
provide samples with low turbidity (although the need for filter packs is an issue
of debate among researchers). When samples are turbid, they should not be
filtered prior to the constituent extraction process because organic constituents can
sorb onto sediment particles. As a result, filtering samples prior to extraction may
result in an analytical negative bias. For further information on the need for
sediment filtration, refer to Nielsen, 1991.
The following text focuses on the tools used for single-event sampling.
These tools can be divided into two groups—exposed-screen samplers and sealed-
screen samplers. Exhibit V-10 presents examples of these two groups of
groundwater samplers. Exhibit V-lOa is a simple exposed-screen sampler;
Exhibit V-lOb is a common sealed-screen sampler; and Exhibit V-lOc is a sealed-
screen sampling method used with cased systems. Because new tools are
continually being invented, and because of the great variety of equipment
currently available, this Guide can not provide a detailed description and analysis
of all available groundwater sampling tools. Instead, the advantages and
limitations of general categories of samplers is discussed.
Exposed-Screen Samplers
Exposed-screen samplers are water sampling tools that have a short
(e.g., 6 inches to 3 feet) interval of exposed fine mesh screens, narrow slots, or
small holes at the terminal end of the tool. The advantage of the exposed screen is
V-20 March 1997
-------
Exhibit V-9
Permanent Monitoring Well Installed
With Pre-packed Well Screens
Protective cover
Water-tight cap
Probe hole (1.25 in. to 3.5in.
diameter)
Cement or bentonite grout seal
PVC pipe or flexible tubing
(OS-in. to 1.5-in. diameter)
Pre-packed PVC well screens.
Sand pack contained between
small-diameter slotted pipe
and larger-diameter slotted pipe.
March 1997
V-21
-------
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March 1997
-------
that it allows multi-level sampling in a single DP hole, without withdrawing the
DP rods. The exposed screen, however, also causes some problems that should be
recognized and resolved when sampling contaminants. These problems may
include:
Dragging down of NAPLs, contaminated soil, and/or contaminated
groundwater in the screen;
Clogging of exposed screen (by silts and clays) as it passes through
sediments;
The need for significant purging of sampler and/or the sampling zone
because of drag down and clogging concerns; and
Frigility of sampler because of the perforated open area.
There are several varieties of exposed-screen samplers. The simplest
exposed-screen sampler is often referred to as a well point (Exhibit V-lOa). As
groundwater seeps into the well point, samples can be collected with bailers,
check-valve pumps (Exhibit V-ll), or peristaltic pumps. (Narrow-diameter
bladder pumps may also soon be available for use with DP equipment.) Because
well points are the simplest exposed-screen sampler, they are affected by all of the
above mentioned limitations. As a result, they are more commonly used for water
supply systems than groundwater sampling. They should not be used below
NAPL or significant soil contamination.
The drive-point profiler is an innovative type of exposed-screen sampler
that resolves many of the limitations of well points by pumping deionized water
through exposed ports as the probe advances. This feature minimizes clogging of
the sampling ports and drag down of contaminants and allows for collection of
multiple level, depth-discrete groundwater samples. Once the desired sampling
depth is reached, the flow of the pump is reversed, and groundwater samples are
extracted. Purging of the system prior to sample collection is important because a
small quantity of water is added to the formation. Purging is complete when the
electrical conductivity of the extracted groundwater has stabilized. The data
provided by these samples can then be used to form a vertical profile of
contaminant distributions. Exhibit V-12 provides a schematic drawing of a drive-
point profiler. Additional information about a drive-point profiling system is
presented in Pitkin, 1994.
Another innovative exposed-screen sampler can be use in conjunction with
cone penetrometer testing (CPT). This sampler allows for multi-level sampling
by providing a mechanism for in situ clearing of clogged screens through the use
of a pressurized gas and in situ decontamination of the sampling equipment with
an inert gas and/or deionized water. Various CPT cones, which allow
investigators to determine the soil conditions of the sampling zone, can be used
simultaneously with this tool.
March 1997 V-23
-------
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March 1997
-------
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V-25
-------
Sealed-Screen Samplers
Sealed-screened samplers are groundwater samplers that contain a well
screen nested inside a water-tight sealed body. The screen is exposed by
retracting the probe rods once the desired sampling depth has been reached. They
can be used for collecting accurate, depth-discrete samples. A very common type
of sealed-screen sampler is presented in Exhibit V-lOb.
The design of sealed-screen samplers is extremely variable. Many are
similar to expendable or retractable tip samplers used for soil gas sampling. Some
samplers are designed only for a single sampling event; others are designed to be
left in the ground for an extended period of time (many weeks or even beyond one
year) so that changes in concentrations can be monitored.
The main advantage of this type of sampler is that the well screen is not
exposed to soil while the tool is being pushed to the target depth. Thus, the screen
cannot become plugged or damaged, and the potential for sample contamination is
greatly reduced. O-rings are used to make the sampler water-tight while it is
being pushed to the sampling depth. (In order to ensure a water-tight seal, o-rings
should be replaced frequently; water tightness can be checked by placing the
sealed sampler in a bucket of water.) Sealed-screen samplers are appropriate for
the collection of depth-discrete groundwater samples beneath areas with soil
contamination in the vadose zone. Because there is no drag-down of
contaminants or clogging of the sampling screens, sealed-screen samplers do not
require purging.
Some sealed-screen samplers allow sample collection with bailers, check-
valve pumps, or peristaltic pumps. (Bladder pumps can also be used with wide
diameter cased DP systems.) The quantity of groundwater provided by these
samplers is limited only by the hydraulic conductivity of the formation. Other
samplers collect groundwater in sealed chambers, in situ, which are then are
raised to the surface. Depending on their design, these samplers may be
extremely limited in the quantity of groundwater that they can collect (e.g., 250
ml per sampling event), and they may not collect free product above the water
table. If the storage chamber is located above the screen intake, groundwater
samples must be collected sufficiently below the water table to create enough
hydrostatic pressure to fill the chamber. Only sampling chambers located below
the screen intake are, therefore, useful for collecting groundwater or LNAPL
samples at or above the water table.
Cased DP systems can also be used as sealed-screen groundwater
samplers. After the target zone has been penetrated and the inner rods have been
removed, well screen can be lowered through the outer casing to the bottom of the
probe hole. The drive casing is then retracted (a few inches to a few feet)
exposing the well screen (Exhibit V-lOc). This method allows for the collection
V-26 March 1997
-------
of deeper samples by attaching a sealed-screen sampling tool that is pushed into
the formation ahead of the tip of the drive casing.
Discussion And Recommendations
Exposed-screen samplers are most appropriate for multi-level sampling in
coarse-grained formations (i.e., sediments of fine-grained sands and coarser
material). They are typically used in a single sampling event. The major concern
with using exposed-screen samplers is that they can cause cross contamination if
precautions are not taken (e.g., pumping deionized water through sample
collection ports). As a result of these concerns, significant purging of the
sampling zone is required.
Sealed-screen samplers are most appropriate for single-depth samples.
When they are used in a single sampling event, they are appropriate in formations
of fine-grained sands or coarser material because these soils typically allow rapid
collection of groundwater. When they are used as either temporary or long-term
monitoring wells, they can also be used in formations composed of silts. In
addition, because sealed-screen groundwater samplers do not require purging of
groundwater, they allow more rapid sampling from a single depth than exposed-
screen samplers. Multi-level sampling with sealed-screened samplers is possible
with cased and single-rod systems; however, with single-rod systems, the entire
rod string must be withdrawn after samples are collected from a given depth. This
practice with single-rod systems may create some cross contamination concerns in
permeable, contaminated aquifers because the hole remains open between
sampling events, allowing migration.
In addition, DP groundwater sampling tools have several advantages over
traditional monitoring wells. DP tools allow groundwater samples to be collected
more rapidly, at a lower cost, and at depth-discrete intervals. As a result, many
more samples can be collected in a short period of time, providing a detailed 3-
dimensional characterization of a site. Exhibit V-13 provides a summary of DP
sampling tool applications.
General Issues Concerning Groundwater Sampling
There are several issues concerning the collection, analysis and
interpretation of groundwater samples that affect both DP equipment and more
conventional monitoring wells. Two major issues are the loss of VOCs and the
stratification of contaminants.
March 1997 V-27
-------
Exhibit V-13
Summary Of Groundwater Sampling Tool Applications
Multi-level sampling
Samples can be collected
immediately, little or no purging
required
Used to install long-term
monitoring point
Can be used in formations
composed of silts
Appropriate below
contaminated soil
Exposed-Screen
/1
/4
Sealed-Screen
/2
/3
/
S'
S
Cross contamination may be an issue of concern, and purging is required.
2 Multi-level sampling without withdrawing all DP rods is only possible with cased
DP systems.
3 Collection of a single sample is more rapid with this method.
4 One type of exposed-screen sampler (i.e., well points) has been used to install
monitoring points, but this method is generally not recommended in zones of
NAPL contamination. It may be appropriate at the leading edge of a contaminant
groundwater plume.
Sampling in silts is generally only appropriate when temporary monitoring wells
are installed. Significant VOC loss may occur if water flows into sampling point
over days, weeks, or months.
Loss Of VOCs
The ability of DP groundwater sampling methods to collect samples
equivalent to traditional monitoring wells is a topic of continued debate and
research. Loss of VOCs is the most significant groundwater sampling issue. All
groundwater sampling methods—including methods used with traditional
monitoring wells—can affect VOC concentrations to some degree. The key to
preventing the loss of VOCs is to minimize the disturbance of samples and
exposure to the atmosphere. Several studies that have compared VOC
concentrations of samples collected with DP methods with samples collected by
traditional monitoring wells have shown that DP methods compare favorably
(Smolley et al., 1991; Zemo, et al., 1994).
V-28
March 1997
-------
Stratification Of Contaminants
Being able to take multiple, depth-discrete groundwater samples with DP
equipment is both an advantage and a necessity. At least one recent study has
shown that the concentration of organic compounds dissolved in groundwater can
vary by several orders of magnitude over vertical distances of just a few
centimeters (Cherry, 1994). Because DP sampling tools collect samples from
very small intervals (e.g., 6 inches to 3 feet), they may sometimes fail to detect
dissolved contamination if the tool is advanced to the wrong depth. Therefore,
multiple depths should be sampled to minimize the chances of missing
contaminants. At sites with heterogeneous geology, contamination may be
particularly stratified. Because the distribution of the contaminants is controlled
by the site geology and groundwater flow system, the hydrogeology of the site
must be adequately defined before collecting groundwater samples for chemical
analysis.
The stratification of contaminants may also result in artificially low
analytical results from traditional monitoring wells. These wells are typically
screened over many feet (e.g., 5 to 15 feet), while high concentrations of
contaminants may be limited to only a few inches (in the case of LNAPLs,
typically the top of the aquifer). The process of sampling groundwater, however,
may cause the water in the well to be mixed, resulting in a sample that represents
an average for the entire screen length (i.e., very high concentrations from a
specific zone may be diluted). DP methods avoid this problem by collecting
depth-discrete samples.
Conclusion
The practice of collecting groundwater samples both with DP systems and
with traditional monitoring wells is a subject of continued research and debate.
Both methods can provide high quality groundwater samples for regulatory
decisions. Both methods may also provide misleading information if appropriate
procedures are not followed and/or if the hydrogeology of a site is not well
characterized. Investigators and regulators must be aware of the issues that affect
groundwater sample quality and interpretation in order to make appropriate site
assessment and corrective action decisions.
March 1997 V-29
-------
In Situ Measurements Using Specialized
Direct Push Probes
In addition to collecting samples of soil, soil-gas, and groundwater/NAPL
samples, specialized DP probes are also available for collecting in situ
geophysical, geochemical, and geotechnical measurements of subsurface
conditions. Because these methods record vertical profiles, they are often called
logging instruments. They provide objective information, but the interpretation of
measurements may still be subjective, requiring correlation with actual samples.
Information that can be collected with these tools includes stratigraphy, depth to
groundwater, approximate hydraulic conductivity, and residual and free product
location.
Cone penetrometer testing (CPT) is the most common method for
collecting in situ measurements. In addition, several recent innovations have
adapted some logging methods to other DP rigs. The following section discusses
CPT and other logging tools currently available with DP rigs. The growth of this
technology is very rapid; there are likely to be many new tools in the near future.
Cone Penetrometer Testing
CPT is a method for characterizing subsurface stratigraphy by testing the
response of soil to the force of a penetrating cone. It was developed in the 1920s
in Holland by the geotechnical industry and became commercially available in the
United States in the early 1970s.
CPT is most commonly performed to depths ranging from 50 to 100 feet;
however, depths as great as 300 feet are attainable under ideal conditions (e.g.,
soft, unconsolidated sediments). Typically, 100 to 300 feet of CPT can be
performed per day if the decontamination of probe rods (also referred to as cone
rods when used with CPT) and the sealing of holes are necessary; productivity can
be doubled when this is not necessary. Production rates can be significantly less
if site access is limited or if significant soil, soil-gas, or groundwater sampling is
performed.
Traditionally, CPT methods have been used less frequently at sites where
investigation depths are less than 40 feet because CPT cones have been pushed
with heavy, poorly-maneuverable rigs. Recently, lighter, more maneuverable DP
rigs have become available to advance CPT cones. This innovation should make
CPT more cost-effective for investigating sites that may have contamination
located closer to the surface.
V-30 March 1997
-------
CPT uses sensors mounted in the tip or "cone" of the DP rods to measure
the soil's resistance to penetration. The cone, presented in Exhibit V-14, is
pushed through the soil at a constant rate by a hydraulic press mounted in a heavy
truck or other heavy weight.
Several types of sensors are commonly available with CPT cones. These
include piezometric head transducers (piezocones), resistivity sleeves, nuclear
logging tools, and pH indicators. Most recently, CPT cones have incorporated
sensors to measure the type and location of petroleum hydrocarbons in the
subsurface (e.g., laser induced fluorescence, fuel fluorescence detector). The
electronic signals from the sensors are transmitted through electrical cables which
run inside the cone rods and to an on-board computer at the ground surface, where
they are processed. CPT cones can often measure several parameters
simultaneously. An example of a CPT log with multiple parameters is presented
in Exhibit V-l5.
DP rigs that perform CPT can also be used to collect soil, soil-gas, and
groundwater samples. In fact, some CPT cones allow the collection of soil-gas or
groundwater samples without removing the cone from the hole. Collection of soil
samples (and in many cases groundwater samples as well) with CPT, however,
currently requires the attachment of DP sampling tools in place of the CPT cone.
Because removing cone rods and inserting DP sampling tools is time consuming,
most CPT contractors will first advance a CPT hole to define the stratigraphy,
then advance another DP hole a few feet away to collect soil or groundwater
samples.
The following text describes the cones that are available only with CPT
and is followed by a section which describes in situ logging tools available for
both CPT and other DP systems.
Three-Channel Cone
The most common type of CPT cone is referred to as a three-channel cone
because it simultaneously measures the tip resistance, sleeve resistance, and
inclination of the cone. The ratio of sleeve resistance to tip resistance, which is
referred to as the friction ratio, is used to interpret the soil types encountered
(Chiang et al, 1992). In general, sandy soils have high tip resistance and low
friction ratios, whereas clayey soils have low tip resistance and higher friction
ratios. As a result, this information can also be used to estimate the hydraulic
conductivity of sediments. With the use of the other CPT channels, stratigraphic
layers as thin as 4 inches can be identified.
March 1997 V-31
-------
Exhibit V-14
Components Of CRT Piezocone
Inclinometer
Pressure
Transducer
Friction Sleeve
1.40 in.
35.7 mm
""Cone Tip
V-32
March 1997
-------
Exhibit V-15
Example CPT Data
Pore
Sleeve Cone Tip Friction Cone Pore Pressure Soil Behavior Type
Friction Resistance Ratio Pressure Ratio Increasing Grain Size Geologic
(tsf) (tsf) (tsf) (tsf) (u/qc) » Log
. ...1 "i0. ,400 ...«...? *..«..9 o o.s 1.0 CM? s«
s
Source: Berzins, 19931
gravel
c/a
clay
clay
clay & silt
sand
day & silt
clay
sano
gravel
sand
Exhibit V-16
CPT Soil Behavior Types
1000
FRICTION RATION (%), Rf
Source: Berzins, 1993'
Zone Soil Behavior Types
1 Sensitive fine grained
2 Organic material
3 Clay
4 Silty clay to clay
5 Clayey silt to silty clay
6 Sandy silt to clayey silt
7 Silty sand to sandy silt
8 Sand to silty sand
9 Sand
10 Gravelly sand to sand
11 Very stiff to fine grained
12 Sand to clayey sand
' Reprinted by permission of the National Ground Water Association, Westerville, Ohio. Copyright 1993. All rights reserved.
March 1997
V-33
-------
Three-channel cones record soil behavior rather than actual soil type
because in addition to grain size, the soil's degree of sorting, roundness, and
mineralogy can also influence tip resistance. As a result, a boring log may help in
the interpretation of CPT data for site-specific conditions. In general, soil
behavior type correlates well with soil type. An empirically produced plot of
friction ratios and soil behavior types is presented in Exhibit V-16.
The inclinometer mounted in the three-channel cone provides a
measurement of the inclination of the cone from vertical. Rapid increases in
inclination indicate that the rods are bending, allowing the CPT operator to
terminate the sounding (i.e., cone penetrometer test) before the cone and/or rods
are damaged.
Piezocone
The piezocone is similar to the three-channel cone, described above,
except that a pressure transducer is also mounted in the cone (previously
presented in Exhibit V-14) in order to measure water pressure under dynamic and
static conditions. Pore-pressure dissipation tests can be performed by temporarily
halting advancement of the tool and letting the pore pressure reach equilibrium.
The slope of a plot of pore pressure versus time is proportional to the permeability
of the soil and can be used to estimate hydraulic conductivity and define the water
table.
Geophysical And Geochemical Logging Probes
Logging probes are continually being developed for both CPT rigs and
other DP probing equipment. The following section describes probes that are
available for use with DP technologies in general. Information provided by these
probes can be used to interpret site stratigraphy, moisture conditions, and in some
cases, contaminant type and distribution.
Conductivity Probes
Conductivity probes measure the electrical conductivity of the subsurface
sediments. Conductivity probes are available with CPT probes and, more
recently, with small 1-inch diameter DP systems (Christy, 1994). Components of
a small-diameter conductivity probe system are depicted in Exhibit V-17.
Because clay units commonly have a greater number of positively charged
ions than sand units, clay layers can typically be defined by high conductivity and
V-34 March 1997
-------
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V-35
-------
sand by low conductivity. These measurements, however, must be correlated with
other logging information because conductivity may be the result of other
conditions (e.g., moisture content, soil density, mineral content, contaminants).
Groundwater tends to increase the electrical conductivity of sediments.
Consequently, the zone of saturation may be discernible in logging data if the
water table is located in a known resistive layer (e.g., sand) and the contrast is
sharp. In a similar way, conductivity measurements may occasionally indicate
hydrocarbon contamination if a significant quantity of residual or free product is
located in a conductive layer (e.g., clay) because hydrocarbons are resistive (i.e.,
poorly conductive).
Nuclear Logging Tools
Nuclear logging tools are geophysical instruments that either detect natural
radiation of a formation or emit radiation and measure the response of the
formation. They have an advantage over other geophysical methods in being able
to record usable data through metal casings. Nuclear logging tools can be
advanced with DP probes to define the site stratigraphy, groundwater conditions,
and, occasionally, subsurface contaminant distribution. They can be used with
CPT cones, some small diameter probe rods, and inside of the outer drive casing
of cased DP systems. There are primarily three nuclear methods—natural gamma,
gamma-gamma, and neutron.
Natural gamma tools log the amount of natural gamma particles emitted
by sediments. Because clays typically have a greater number of ions than sands,
clays tend to have more radioactive isotopes that emit gamma radiation. By
logging the change in gamma radiation, it is often possible to characterize the site
stratigraphy. Gamma-gamma tools emit gamma radiation and measure the
response of the formation. Because the response is related to the density of the
soil, this method can also provide information about the stratigraphy as well as the
porosity of soil. Neutron methods emit neutrons into a sediment and measure a
response which is dependent on the moisture content. These methods can,
therefore, be used to define the water table. In addition, if the stratigraphy and
moisture conditions are defined with other methods, neutron logs can indicate the
presence and thickness of free-phase petroleum hydrocarbons. A complete
discussion of geophysical logging is presented in Keys (1989).
Chemical Sensors
Chemical sensors provide screening level analysis of petroleum
hydrocarbons at a specific depth, without removing a soil or groundwater sample.
When used over an extended area, they can rapidly provide a 3-dimensional
characterization of the contaminant source area. There are several in situ chemical
V-36 March 1997
-------
sensors that have recently been developed for use with DP technologies, and more
may be available in the near future. Currently available methods are laser-induced
fluorescence (LIF), fuel fluorescence detectors (FFD), and semipermeable
membrane sensors. These three methods are discussed in more detail in Chapter
VI, Field Methods For The Analysis Of Petroleum Hydrocarbon.
Discussion And Recommendations
In situ logging methods are ideal for heterogeneous sites with complex
geology because they can rapidly provide continuous profiles of the subsurface
stratigraphy. In addition, unlike boring logs, these logging methods provide an
independent, objective measurement of the site stratigraphy. When in situ logging
methods are used in combination with boring logs, data can be used to
extrapolate/interpolate geologic units across a site. If boring log information is
not available, several in situ logging parameters collected simultaneously will
often provide similar information.
Investigators should be aware that in situ logging methods should
generally be calibrated by pushing a probe next to at least one boring that has
been continuously cored. In addition, while geophysical logging methods for
defining stratigraphy produce reliable information about the primary lithology of
the strata, they provide very little data regarding secondary soil features like
desiccation cracks, fractures, and root holes. In silts and clays, these secondary
soil features (i.e., macropores) may control the movement of contaminants into
the subsurface and may greatly influence the options for active remediation. At
interbedded sites where defining macropores is important, continuous soil coring
may be a better alternative. Exhibit V-18 presents a summary of in situ logging
equipment used with DP technologies.
March 1997 V-37
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Exhibit V-18
Summary Of In Situ Logging Equipment
Used With Direct Push Technologies
DP
Method
Application
Three-Channel
Cone
CRT
Only
Measures tip resistance, sleeve resistance,
and inclination. It is used to determine soil
behavior types which can be correlated with
boring logs.
Piezocone
CRT
Only
Measures the rate at which the water pressure
returns to static conditions and can be used to
estimate hydraulic conductivity and define the
water table.
Conductivity
Probe
DP
Measures the conductivity of stratigraphic
layers and can be used in conjunction with
other methods to determine soil type and,
sometimes, contaminant location.
Natural Gamrr
a DP
Measures the natural gamma radiation emitted
by a formation and can be used to determine
stratigraphy
Gamma-
Gamma
DP
Measures the response of a formation to
gamma radiation and can be used to
determine soil density/porosity.
Neutron Prob(
s DP
Measures the response of a formation to
neutron bombardment and can be used to
determine moisture content of soils.
Chemical
Sensors
DP
Measures the presence of free or residual
product and can be used to delineate source
areas.
CPT = Available with cone penetrometer testing equipment only
DP = Available with CPT and other direct push equipment
V-38
March 1997
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Equipment For Advancing Direct Push Rods
A few years ago, small-diameter probes were advanced exclusively with
manual hammers or rotohammers mounted in light-weight vans, and CPT rods
were advanced using heavy (e.g., 20-ton) trucks. Now, contractors mix and match
DP rod systems and sampling tools depending on the objectives and scope of the
investigation. It is not unusual to see DP rods, sampling tools, and CPT cones
being advanced with a wide range of equipment, ranging from small portable rigs
to heavy trucks. The following text describes some of the more common methods
used to advance DP rods and sampling tools. Drawings of several types of
equipment used for advancing DP rods are presented in Exhibit V-19.
Manual Hammers
Manual hammers allow a single operator to advance small-diameter DP
rods to shallow depths (Exhibit V-19a). Other names for this type of hammer are
"fence post driver" or "slam bar," since it was adapted from hammers used to drive
steel fence posts. Manual hammers are used mostly for driving 0.5- to 1 -inch
diameter soil-gas sampling tools and are best suited to advancing single DP rods
to depths of 5 to 10 feet. The maximum attainable depth with this method is
approximately 25 feet. These hammers are the smallest and lightest DP rod
advancing equipment weighing between 30 to 60 pounds. As a result, manual
hammers are the most portable method available, but they are capable of the least
depth of penetration.
Hand-Held Mechanical Hammers
There are two types of hand-held mechanical hammers—jack hammers and
rotohammers. Although rotohammers also rotate, they both apply high-frequency
percussion to the DP rods, resulting in more rapid penetration and greater
sampling depths than manual hammers can attain. Hand-held mechanical
hammers are best suited to collecting soil, soil-gas, and groundwater samples
using 0.5- to 1-inch diameter equipment. They may also be used to advance
small-diameter cased DP rod systems. Typical attainable depth with this method
is between 8 and 15 feet, while the maximum depth is approximately 40 feet. This
equipment weighs between 30 and 90 pounds and is, therefore, extremely
portable.
March 1997 V-39
-------
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March 1997
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Percussion Hammers And/Or Vibratory Heads Mounted On
Small Vehicles
The most common methods for advancing DP rods are percussion
hammers and vibratory heads mounted on small vehicles (Exhibit V-19b and
19Q. Hydraulic cylinders press the rods into the ground with or without pounding
or driving. The pounding/driving action is typically provided by hydraulic post-
hole drivers or percussion hammers mounted on the vehicle. The hammers pound
on a drive head attached to the uppermost DP rod. On some rigs, vibratory heads
clamp onto the outside of the DP rods, applying high-frequency vibrations. The
vibratory action reduces the side-wall friction, resulting in an increased rate of
penetration and greater sampling depths. Some rigs are mounted on trucks, some
(S)
on vans, yet others on the front of Bobcat -like construction vehicles. These
types of rigs can be used to advance single DP rods or cased DP systems. The
reactive weight is typically between 5,000 and 17,000 pounds. Depths of 20 to 50
feet are generally attainable, and maximum depths of around 150 feet have been
recorded. This equipment is as mobile as the vehicle on which it is mounted.
Small Hydraulic Presses Anchored To The Ground
Small hydraulic presses that are anchored to the ground are fairly light-
weight units (200 to 300 pounds) and portable so they can be quickly
disassembled and reassembled at new sampling locations. The reactive weight for
these rigs is created by the weight of the rig and the pull-down pressure applied
against the anchor. On concrete floors, the base plates of the rigs are anchored
with concrete bolts or anchoring posts (referred to as "deadmen") that can be set
in pre-drilled holes. On asphalt or open ground, earth augers are spun into the
ground to anchor the rigs. Reactive forces as great as 40,000 pounds can be
applied with these rigs. Hydraulic cylinders press the DP rods into the ground,
usually without percussion hammers. These types of rigs are most commonly
used for advancing CPT cones in areas that are difficult to access, but they can
also be used to advance other types of DP rods and sampling tools. They can
generally attain depths between 20 and 100 feet with a maximum attainable depth
of approximately 200 feet.
Conventional Drilling Rigs
Conventional drilling rigs are commonly used to advance soil, soil-gas,
and groundwater sampling DP tools inside of hollow-stem augers. In fact, open-
barrel and split-barrel samplers have been advanced inside of hollow stem augers
to collect soil samples for geotechnical investigations for decades. In
geotechnical investigations, the force for advancing these samplers is applied by
March 1997 V-41
-------
striking the DP rods with a 140-pound hammer dropped a distance of 30 inches as
described in ASTM D1586 (American Society of Testing and Materials, 1984).
In addition, many conventional drill rigs are now equipped with hydraulic
percussion hammers to advance the DP sampling tools more rapidly. The reactive
weight of conventional drill rigs is between 5,000 and 20,000 pounds. When they
are used for DP sampling, they can generally attain depths of 20 to 80 feet with a
maximum depth of approximately 200 feet. Because of their size, conventional
drill rigs are less maneuverable than construction vehicles.
Trucks Equipped With Hydraulic Presses
Trucks equipped with hydraulic presses are commonly used to advance
CPT cones (Exhibit V-19d). Because the force for advancing the rods comes from
the weight of the truck, the maximum depth attainable with the DP rods depends
on the weight of the truck. Generally, depths of 30 to 100 feet can be obtained;
maximum penetration is about 300 feet. Most rigs weigh from 30,000 to 40,000
pounds. Although trucks weighing more than approximately 46,000 pounds are
not allowed on public roads, CPT rigs as heavy as 120,000 pounds can be used if
weight is added on site. Unlike other DP tools, the force applied to CPT cones is
a static push; no pounding or vibration is applied to the rods which could damage
the sensitive electrical components and circuitry in the cones.
Hydraulic cylinders mounted inside the trucks apply the static weight of
the truck to the DP rods, pushing them into the ground. While designed for CPT
applications, these large trucks are equally capable of advancing all other types of
DP sampling tools using single-rod or cased DP systems. However, because the
rigs were designed primarily for pushing CPT cones, few of them are equipped
with hydraulic hammers or vibratory heads.
Discussion And Recommendations
The major differences among the kinds of equipment used to advance DP
rods are their depth of penetration and their ability to access areas that are difficult
to reach (e.g., off-road, inside buildings). The depth of penetration is controlled
primarily by the reactive weight of the equipment although other factors such as
the type of hammer used (e.g., vibratory, manual, percussion) can affect the
attainable depth. Soil conditions generally affect all DP methods in a similar way.
Ideal conditions for all equipment are unconsolidated sediments of clays, silts, and
sands. Depending on their quantities and size, coarser sediments (e.g., gravels,
cobbles) may pose problems for DP methods. Semi-consolidated and
consolidated sediments generally restrict or prevent penetration; however,
saprolite (i.e., weathered bedrock) is an exception.
V-42 March 1997
-------
The portability of equipment is controlled by its size and weight. For
instance, 20-ton trucks with hydraulic presses would not be appropriate for rough
terrain, and conventional drill rigs are often not capable of sampling below fuel
dispenser canopies or below electrical power lines. On the other hand, manual
hammers or hand-held mechanical hammers are capable of sampling in almost
any location, including within buildings. Exhibit V-20 presents a summary of
equipment for advancing DP rods.
Exhibit V-20
Summary Of Equipment For Advancing Direct Push Rods
Manual
Hammers
Hand-Held
Mechanical
Hammers
Hammers
Mounted On
Vehicles
Anchored
Hydraulic
Presses
Conventional
Drill Rig
Truck With
Hydraulic
Presses
Reactive
Weight (Ibs)
30 to 60
30 to 90
5,000 to
17,000
200 to 40,000
5,000 to
20,000
30,000 to
120,000
Average
Attainable
Depth (ft)
5 to10
8 to 15
20 to 50
20 to 100
20 to 80
30 to 100
Maximum
Attainable
Depth (ft)
25
40
150
200
200
300
Portability
Excellent
Excellent
Good
Good
Poor
Poor
March 1997
V-43
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Methods For Sealing Direct Push Holes
One of the most important issues to consider when selecting DP
equipment is the method for sealing holes. Because any hole can act as a conduit
for contaminant migration, proper sealing of holes is essential for ensuring that a
site assessment does not contribute to the spread of contaminants. The issue of
sealing holes and preventing cross-contamination is not an issue unique to DP
technologies. Conventionally drilled holes must also be sealed; in fact, they may
pose an even greater risk of cross-contamination because the larger diameter holes
provide an even better conduit for contaminants. Many of the recommendations
presented here apply to both DP and conventional drilling methods; however,
because of the small diameter of DP holes, DP technologies provide some
additional challenges.
The selection of appropriate sealing methods depends on site-specific
conditions. For example, at sites underlain by homogeneous soil and shallow
groundwater, light non-aqueous phase liquids (LNAPLs) released from an UST
quickly penetrate the unsaturated soil and come to rest above the water table.
Because the LNAPLs are lighter than water, the water table becomes a barrier to
continued downward migration. In these settings, DP probe holes pose little risk
to the spread of contaminants.
However, at other sites, improperly sealed DP holes can cause significant
contaminant migration. For example, at UST sites where there are LNAPLs
perched on clay layers in the unsaturated zone, intrusive sampling can facilitate
deeper migration of contaminants. In addition, where interbedded formations
create multiple aquifers, unsealed holes may allow for the vertical migration of
dissolved contaminants into otherwise protected lower aquifers.
The presence of dense non-aqueous phase liquids (DNAPLs) poses an
additional risk of cross-contamination. Because DNAPLs are denser than water
and typically have low viscosities, they can quickly penetrate soil and migrate
below the water table. Although DNAPLs are usually not the primary
contaminant at UST sites, they may be present as a result of the use of chlorinated
cleaning solvents (e.g., trichloroethylene, methylene chloride). DNAPLs may
also be present at refineries and other industrial sites where LUST investigations
are performed.
The objective of hole sealing is to prevent preferential migration of
contaminants through the probe hole. At a minimum, the vertical permeability of
the sealed DP hole should not be any higher than the natural vertical permeability
of the geologic formation. In some formations, preferential migration may be
prevented without the use of sealants. For example, in heaving, homogeneous
V-44 March 1997
-------
sands, the hole will cave immediately as the probe is withdrawn, thus re-
establishing the original permeability of the formation. Or, in some expansive
clays, the hole may quickly seal itself. Unfortunately, it is usually impossible to
verify that holes have sealed completely with these "natural" methods. As a
result, more proactive methods of probe hole sealing are generally necessary.
DP holes are typically sealed with a grout made of a cement and/or
bentonite slurry. Dry products (e.g., bentonite granules, chips, pellets) may also
be used, but they may pose problems because small granules are typically needed
for the small DP holes. These granules absorb moisture quickly and expand, often
before reaching the bottom of the hole, resulting in bridging and an incomplete
seal. Recent technological innovations are aimed at keeping these granules dry
until they reach the bottom of the hole and may help to make the use of dry
sealing materials more common with DP holes.
There are four methods for sealing DP holes—surface pouring, re-entry
grouting, retraction grouting, and grouting during advancement. The following
text summarizes the advantages, limitations, and applicability of these methods.
Additional information can be found in Lutenegger and DeGroot (1995).
Surface Pouring
The simplest method for sealing holes is to pour grout or dry products
through a funnel into the boring from the surface after DP rods have been
withdrawn (Exhibit V-21 a). This method is generally only effective if the hole is
shallow (<10 feet), stays open, and does not intersect the water table. Usually,
surface pouring should be avoided because the small DP holes commonly cause
bridging of grout and dry bentonite products, leaving large open gaps in the hole.
Re-entry Grouting
Re-entry grouting is also a method in which the DP hole is sealed after the
DP rods have been withdrawn from the ground. It is used to prevent the bridging
of grout and to re-open sections of the hole that may have collapsed. One method
is to place a flexible or rigid tube, called a tremie pipe, into the DP hole (Exhibit
V-21 a), and pump the grout (or pour the dry material) through the tremie pipe,
directly into the bottom of the open hole. To ensure a complete seal by
preventing bridging, the tremie pipe is kept below the surface of the slurry as the
grout tills the hole. However, flexible or rigid tremie pipes may be difficult or
impossible to use if the probe hole collapses. The flexible tremie pipe may not be
able to penetrate the bridged soil and a rigid tremie may become plugged.
March 1997 V-45
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Exhibit V-21
Methods For Sealing Direct Push Holes
a) Re-entry Methods Of
Sealing DP Holes
Grouk
b)
\7
llL-Flexible^/:
V/.
tube
V
% Rigid-^
J"l
rp-|
«
Reentry Grouting With DP Rods
And Expendable Tip
Grout-
from
pump
1) Surface
pouring
2) Flexible
tremie tube
3) Rigid tremie
pipe
1) Installation
of rods
2) Grouting while
retracting rods
c) Retraction Grouting Through
Expendable Tip In CPT Cone
Grout tube
Grout port
CPT rod
Electrical
cable
Friction
sleeve
Load cell
d) Retraction Grouting Through
Ports In Friction Reducer
Grout-\
Electrical from
cable pump
Grout
ports
Grout
Expendable tip
1) Installation
2) Grouting through
grout ports
Source: Lutenegger & DeGroot, 1995
V-46
March 1997
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If tremie pipes are not appropriate for sealing DP holes, re-entry with
probe rods and an expendable tip may be used (Exhibit V-21b). This method
allows the rods to be pushed through soil bridges to the bottom of the probe hole.
The probe rods are then withdrawn slightly, and the expendable tip is knocked out
(by lowering a small diameter steel rod inside the DP rods) or blown off (by
applying pressure with the grout pump). Grout is then pumped through the DP
rods as they are withdrawn from the hole.
Re-entry grouting with DP rods and expendable tips usually results in
adequate seals; however, this method is not always reliable because, on occasion,
DP rods may not follow the original probe hole, but instead create a new hole
adjacent to the original one. If this happens, sealing the original hole may be
impossible. This situation is rare but may be a problem when sampling:
Soft silts or clays that overlie a dense layer. In this situation, the clays
provide little support and may not guide the rods back to the original hole.
In cobbly or boulder-rich sediments overlying a clayey confining
formation. Here the probe may be deflected, and the underlying clays may
not guide the rods into the original hole.
Loose homogenous sands that overlie a clayey formation. Here the sands
may collapse as the rods are withdrawn. Without a hole to guide the rods,
the underlying clay may be penetrated in a slightly different location. In
these environments, the likelihood of new holes being created with re-
entry grouting increases with smaller diameter probe rods and with deeper
investigations.
Retraction Grouting
Retraction grouting is a method in which the DP hole is sealed as the DP
rods are being withdrawn. The DP rods act as a tremie pipe for grout that is either
poured or pumped down the hole, ensuring a complete seal of the probe hole.
Retraction grouting can be used with single-rod systems; however, its application
is limited by the sampling method. With cased systems, retraction grouting can
be used in any situation.
There are two methods for using retraction grouting with single-rod
systems. One method can be used when expendable tips or well screens are
attached to the probe rod for soil-gas or groundwater sampling. Grouting with
these sampling tools occurs as described in re-entry grouting with expendable tips
except there is only a single entry, and the sampling tool is also used for grouting.
With well screens, the screen must be expendable. With both tools, grout may be
poured or pumped into the ground as the rods are retrieved. Other sampling tools
March 1997 V-47
-------
attached to single-rod systems do not allow retraction grouting because the end of
the DP rods is sealed by the sampling tools.
Cone penetrometer testing (CPT) allows a second method of retraction
grouting with single-rod systems through the use of a small-diameter grout tube
that extends from the cone to the ground surface inside the CPT rods. One
variation utilizes an expendable tip that is detached from the cone by the pressure
of the grout being pumped through the tube (Exhibit V-21c). Another variation of
this method consists of pumping the grout through ports in the friction reducer
instead of the cone (Exhibit V-21d). Most CPT contractors perform re-entry
grouting instead of retraction grouting because the grout tube is very small and
subject to frequent plugging.
With cased systems, retraction grouting can be used regardless of the type
of sampling tools employed because the outer casing can maintain the integrity of
the hole after samples have been collected. As a result, proper use of cased
systems can ensure complete sealing of DP holes. This feature is presented in
Exhibit V-22.
Grouting During Advancement
Grouting during advancement is a method that utilizes expendable friction
reducers (i.e., detachable rings that are fitted onto the DP probe or cone). The
space between the probe rod and the hole, created by the friction reducer, is tilled
with grout that is pumped from the ground surface as the probe rod advances
(Exhibit V-23). When the probe rods are withdrawn, the weight of the overlying
grout forces the expendable friction reducer to detach. Additional grout is added,
while the rods are being withdrawn, to till the space that was occupied by the
rods.
Discussion And Recommendations
Surface pouring can be used in shallow holes (less than 10 feet bgs) that
do not penetrate the water table and in which the formation is cohesive. This
method is the least favorable and should only rarely be used because the small
size of the DP holes increases the probability of grout or dry products bridging
and not completely sealing.
Re-entry grouting is the next best alternative and is often adequate for
providing a completely sealed hole. Re-entry grouting can be used if deflection of
probe rods is not likely, if NAPLs are not present, or if NAPLs are present but do
not pose a risk of immediately flowing down the open hole. Because DNAPLs
V-48 March 1997
-------
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V-49
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Exhibit V-23
Sealing Direct Push Holes By Grouting During Advancement
Temporary
Surface >
Casing
Grout •
CRT-
Rod
Sacrificial
Friction
Ring
CRT
1) Advancing cone.
2) Withdrawing cone.
Source: Lutenegger & DeGroot, 1995
V-50
March 1997
-------
are denser than water and tend to have low viscosities, they easily overcome the
soil pore pressure and, therefore, require retraction grouting or grouting during
advancement. If LNAPLs are present the risk of cross-contamination will depend
on many other factors (e.g., soil grain size, quantity of LNAPLs). Hence, while
re-entry grouting may at times effectively prevent cross-contamination in source
areas, it should be used judiciously.
Retraction grouting and grouting during advancement are the most
effective sealing methods for preventing cross-contamination. They are required
if:
DNAPLs are present,
Sufficient LNAPLs are present to rapidly flow down an open hole,
A perched, contaminated water table is encountered, or
Deflection of probe rods may occur.
A summary of DP hole sealing methods is presented in Exhibit V-24.
Exhibit V-24
Summary Of Direct Push Hole Sealing Applications
NAPLs
Not
Present
NAPLs
Present
Cohesive
Formation
Formation
Collapses
Cohesive
Formation
Formation
Collapses
Deflection Of Probe
Rod May Occur3
Surface
Pouring1
/
/2
Re-entry
Grouting
/
/
/2
/2
Retraction
Grouting
/
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/
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1
This method should not be used if the DP hole intersects the water table.
These methods may be used if there is not an immediate danger of NAPLs flowing down
the open hole (ie., DNAPLs are not present or large quantities of LNAPLs are not
perched on clay layers).
There are three conditions when this might occur: Sampling in soft silts or clays that
overlie a denser layer; sampling in cobbly or boulder-rich sediments overlying a clayey
confining formation; sampling in loose homogenous sands that overlie a confining
formation. Note that these situations are not typical. The likelihood of probe deflection
increases with depth and decreases with the increase in probe rod diameters.
March 1997
V-51
-------
Direct Push Equipment Manufacturers
A list of DP equipment manufactures is included in Exhibit V-25 and a
matrix of equipment is presented in Exhibit V-26. The equipment has not been
evaluated by the U.S. EPA and inclusion in this manual in no way constitutes an
endorsement. Because of the rapidly changing nature of the DP industry, these
tables may quickly become outdated; therefore, readers should not use the tables
as their only source of available manufacturers. These vendors are listed solely
for the convenience of the reader.
Exhibit V-25
Direct Push Equipment Manufacturers
Art's Manufacturing & Supply
105 Harrison
American Falls, ID 83211
(800) 6357330
Boart/Longyear Company
2340 W. 1700S.
Salt Lake City, UT84127
(801)972-1395
Checkwell, Inc.
12 Linden Street
Hudson, MA 01749-2045
(508) 562-4300
Christensen Mining Products/Acker
P.O. Box 30777
Salt Lake City, UT84127
(800)453-8418
Clements Associates Inc.
R. R.#1 Box 186
Newton, IA 50208
(515) 792-8285
Concord Environmental Equipment
R. R. 1 Box 78
Hawley, MN 56549
(218)937-5100
Conetec Investigations, Limited
9113 Shaughnessy
Vancouver, British Columbia V6P 6R9
Canada
(604)327-4311
Diamond Drilling
Contracting Company
P.O. Box11307
Spokane, WA99211
(800)325-1563
Diedrich Drill, Inc.
P. 0. Box 1670
La Porte, IN 46352
(800) 348-8809
Direct Push Technologies, Inc.
605 Alamitos Blvd.
Seal Beach, CA
(310)430-3326
Foremost Drills/Mobile
1225 64th Ave, N.E.
Calgary, Alberta
T2E 8K6 Canada
(403) 295-5800
Geolnsight
6200 Center St., Ste. 290
Clayton, CA 94517
(510)672-0919
V-52
March 1997
-------
Geoprobe Systems
601 N. Broadway
Salina, KS 67401
(800) 436-7762
Hogentogler & Co., Inc.
P. 0. Box2219
Columbia, MD 21045
(800) 638-8582
KVA Analytical Systems
P. 0. Box 574
Falmouth, MA 02541
(508) 540-0561
Mavrik Environmental & Exploration
Products
104 S. Freya Street
Suite 218, Lilac Bldg.
Spokane, WA 99202
(800)376-4135
MPI Drilling
P. B. Box 2069
Picton, Ontario
KOK 2TO Canada
(613) 476-5741
Precision Sampling, Inc.
47 Louise Street
San Rafael, CA 94901
(800)671-4744
ProTerra
367 Boston Road
Groton, MA 01450
(508) 448-9355
QED Environmental
Systems, Inc.
6095 Jackson Road
P. 0. Box 3726
Ann Arbor, Ml 48106
(800) 624-2026
SIMCO
Drilling Products Division
Box 448
Osceola, IA50213
(800) 338-9925
SimulProbe Technologies, Inc.
150 Shoreline Highway
Bldg. E.
Mill Valley, CA 94941
(800)553-1755
Solinst Canada, Ltd.
35 Todd Road
Georgetown, Ontario
L7G 4R8 Canada
(800)661-2023
Universal Environmental
Engineering, Inc.
740 North 9th Ave., Suite E
Brighton, CO 80601
(303) 654-0288
Vertek
120A Waterman Road
South Royalton, VT 05068
(800) 639-6315
Xitech Instruments, Inc.
300-C Industrial Park Loop
Rio Ranch, NM 87124
(505) 867-0008
March 1997
V-53
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References
Aller, L., T.W. Bennett, G. Hackett, R. Petty, J. Lehr, H. Sedoris, and D.M.
Nielsen. 1991. Handbook of suggested practices for the design and installation
of ground-water monitoring wells. National Water Well Association, Columbus,
OH.
American Petroleum Institute. 1983. Groundwater monitoring and sample bias
API Publication 4367. Washington, DC.
Archabal, S.R., J.R. Hicks, and M.C. Reimann. 1995. Application of cone
penetrometer technology to subsurface investigation at a solvent-contaminated
site. In Proceedings of the 9th national outdoor action conference. National
Ground Water Association, Columbus, OH.
ASTM. 1984. Standard test method for penetration test and split-barrel
sampling of soil, D-1586. Annual Book of Standards, Philadelphia.
ASTM. 1994. Standard test method for deep, quasi-static, cone and friction-
cone penetration tests of soil, D-3441. Annual Book of Standards, Philadelphia.
ASTM. 1995. Standard test method for performing electronicfriction cone and
piezoconepenetration testing of soils, D-5778. Annual Book of Standards,
Philadelphia.
ASTM (in press). Draft standard for direct push water sampling for
geoenvironmental purposes. D-6002 ASTM Task Group D-18.21.01,
Philadelphia.
ASTM (in press). Draft standard for direct push sampling in the vadose zone.
ASTM Task Group D-18.21.02, Philadelphia.
ASTM (in press). Draft standard on cone penetrometer testing for environmental
site characterization. ASTM Task Group D- 18.21.01, Philadelphia.
ASTM (in press). Draft standard on direct push soil sampling. ASTM Task
Group D-18.21, Philadelphia.
Berzins, N.A. 1993. Use of the cone penetration test and BAT groundwater
monitoring system to assess deficiencies in monitoring well data. In Proceedings
of the 6th national outdoor action conference. National Ground Water
Association, Columbus, OH.
March 1997 V-57
-------
Cherry, J.A. 1994. Ground water monitoring: some current deficiencies and
alternative approaches. Hazardous waste site investigations: Toward better
decisions. Lewis Publishers.
Chiang, C.Y., K.R. Loos, and. R.A. Klopp. 1992. Field determination of
geological/chemical properties of an aquifer by cone penetrometry and headspace
analysis. Gr. Water, vol. 30, no.3: 428-36.
Christy, T.M. 1992. The use of small diameter probing equipment for
contaminated site investigation. Proceedings of the 6th national outdoor action
conference. National Ground Water Association, Columbus, OH.
Christy, C.D., T.M. Christy, and V. Wittig. 1994. A percussion probing tool for
the direct sensing of soil conductivity. In Proceedings of the 8th national outdoor
action conference. National Ground Water Association, Columbus, OH.
Cordry, K.E. 1986. Ground water sampling without wells. In Proceedings of the
sixth national symposium and exposition on aquifer restoration and ground water
monitoring. National Water Well Association, Columbus, OH,
Cordry, K.E., 1995. The powerpunch. In Proceedings of the 9th national outdoor
action conference. National Ground Water Association, Columbus, OH.
Cronk, G.D., M.A. Vovk. 1993. Conjunctive use of cone penetrometer testing
(R)
and hydropunch sampling to evaluate migration of VOCs in groundwater. In
Proceedings of the 7th national outdoor action conference. National Ground
Water Association, Columbus, OH.
Edelman, S. and A. Holguin. 1995. Cone penetrometer testing for
characterization and sampling of soil and groundwater. In Proceedings of the
symposium on sampling environmental media, ASTM Committee D-34. Denver.
(R)
Edge, R.W. and K.E. Cordry. 1989. The hydropunch : An in situ sampling tool
for collecting ground water from unconsolidated sediments. Gr. Mon. and
Remed.
(R)
Einarson, M.D. 1995. Enviro-Core — A new vibratory direct-push technology
for collecting continuous soil cores. In Proceedings of the 9th national outdoor
action conference. National Ground Water Association, Columbus, OH.
Fierro, P. and I.E. Mizerany. 1993. Utilization of cone penetrometer technology
as a rapid, cost-effective investigative technique. In Proceedings of the 7th
national outdoor action conference. National Ground Water Association,
Columbus, OH.
V-58 March 1997
-------
Keys, W.S. 1989. Borehole geophysics applied to ground-water investigations.
In Proceedings of the 3rd National Outdoor Action Conference, National Water
Well Association, Columbus, OH.
Kimball, C.E. and P. Tardona. 1993. A case history of the use of a cone
penetrometer to assess a UST release that occurred on a property that is adjacent
to a DNAPL release site. In Proceedings of the 7th national outdoor action
conference. National Ground Water Association, Columbus, Ohio.
Lutenegger, AJ. and D.J. DeGroot. 1995. Techniques for sealing cone
penetrometer holes. Canadian Geotech. J. October.
Michalak, P. 1995. A statistical comparison of mobile and fixed laboratory
(S)
analysis of groundwater samples collected using Geoprobe direct push sampling
technology. In Proceedings of the 9th national outdoor action conference.
National Ground Water Association, Columbus, OH.
Mines, B.S., J.L. Davidson, D. Bloomquist, and T.B. Stauffer. 1993. Sampling
of VOCs with the BAT® ground water sampling system. Gr. Water Mon. &
Remed., vol. 13, number 1:115-120.
Morley, D.P. 1995. Direct push: Proceed with caution. In Proceeding of the 9th
national outdoor action conference. National Ground Water Association,
Columbus, OH.
New Jersey Department of Environmental Protection. 1994. Alternative ground
water sampling techniques guide. Trenton, 56 p.
Nielsen, D.M. 1991. Practical handbook of ground water monitoring. Lewis
Publishers.
Pitkin, S., R.A. Ingleton, and J. A. Cherry. 1994. Use of a drive point sampling
device for detailed characterization of a PCE plume in a sand aquifer at a dry
cleaning facility. In Proceedings of the 8th national outdoor action conference.
National Ground Water Association, Columnbus, OH.
Robertson, P.K. and R.G. Campanella. 1989. Guidelines for geotechnical design
using the cone penetrometer test and CPT with pore pressure measurement.
Hogentogler & Company, Inc., Columbia, MD.
Siegrist, R.L. and P.O. Jenssen. 1990. Evaluation of sampling method effects on
volatile organic compound measurements in contaminated soils, Environ. Sci. and
Tech. vol. 24: 1387-92.
March 1997 V-59
-------
Smolley, M. and J.C. Kappmeyer. 1991. Cone penetrometer tests and
hydropunch sampling: A screening technique for plume definition. Gr. Water
Mon. Rev., vol. 11, no. 3: 101-6.
Starr, R.C. and R.A. Ingleton. 1992. A new method for collecting core samples
without a drill rig. Gr. Water Mon. Rev., vol. 12, no. 1:91-5.
Torstensson, B. 1984. A new system for ground water monitoring. Gr. Water
Mon. Rev., vol. 4, no. 4: 131-38.
U.S. EPA. 1993a. Subsurface characterization and monitoring techniques: A
desk reference guide. Volume 1: Solids and groundwater, EPA/625/R-93/003a.
Office of Research and Development, Washington, DC.
U.S. EPA. 1993b. Subsurface characterization and monitoring techniques: A
desk reference guide. Volume 2: The vadose zone, field screening and analytical
methods, EPA/625/R-93/003b. Office of Research and Development, Washington,
DC.
U.S. EPA. 1995a. Rapid optical screen tool (ROST™): Innovative technology
evaluation report. Superfund innovative technology evaluation, EPA/540/R-
95/1519. Office of Research and Development, Washington, DC.
U.S. EPA. 1995b. Site characterization analysis penetrometer system (SCAPS):
Innovative technology evaluation report. Superfund innovative technology
evaluation, EPA/540/R-95/520. Office of Research and Development,
Washington, DC.
U.S. EPA., 1995c. Ground Water Sampling —A Workshop Summary,
EPA/600/R-94/205. Office of Research and Development, Washington, DC.
Varljen, M.D. 1993. Combined soil gas and groundwater field screening using
the hydropunch and portable gas chromatography. In Proceedings of the 7th
national outdoor action conference. National Ground Water Association,
Columbus, OH.
Zapico, M.M., S.E. Vales, and J.A. Cherry. 1987. A wireline piston core barrel
for sampling cohesionless sand and gravel below the water table. Gr. Water Mon.
Rev., vol. 7, no. 3: 74-82.
Zemo, D.A., Y.G. Pierce, and J.D. Galinatti. 1994. Cone penetrometer testing
and discrete-depth ground water sampling techniques: A cost effective method of
site characterization in a multiple-aquifer setting. Gr. Water Mon. and Remed.
vol. 14, no. 4: 176-82.
V-60 March 1997
-------
Zemo, D.A., T.A. Delfino, J.D. Galinatti, V.A. Baker, and L.R. Hilpert. 1995.
Field comparison of analytical results from discrete depth groundwater sampling.
Gr. WaterMon. andRemed. vol. 15, no. 1: 133-41.
March 1997 V-61
-------
Peer Reviewers
Gilberto Alvarez
David Ariail
Jay Auxt
James Butler
Kent Cordry
Thomas Christy
Jeffrey Farrar
John Gregg
Blayne Hartman
Bruce Kjartanson
Eric Koglin
Patricia Komor
William Kramer
Al Liguori
David Nielsen
Emil Onuschak, Jr.
Dan Rooney
Charlita Rosal
Katrina Varner
U.S. EPA, Regions
U.S. EPA, Region 4
Hogentogler & Company, Inc.
Geotech Environmental Equipment, Inc.
Geolnsight
Geoprobe Systems
U.S. Department of Interior, Bureau of
Reclamation
Gregg In Situ, Inc.
Transglobal Environmental Geochemistry
Iowa State University
U.S. EPA, National Exposure Research
Laboratory
Underground Tank Technology Update
Handex Corporation
Exxon Research and Engineering Company
The Nielsen Environmental Field School
Delaware Department of Natural Resources
and Environment Control
Applied Research Associates, Inc. (Vertek)
U.S. EPA, National Exposure Research
Laboratory
U.S. EPA, National Exposure Research
Laboratory
V-62
March 1997
-------
Chapter VI
Field Methods For The Analysis Of
Petroleum Hydrocarbons
-------
-------
Contents
Exhibits Vl-vi
Field Methods For The Analysis Of Petroleum Hydrocarbons VI-1
Data Quality Levels VI-4
Data Quality Level 1: Screening VI-4
Data Quality Level 1A: Qualitative Screening VI-5
Data Quality Level 1B: Semiquantitative
Screening VI-5
Data Quality Level 2: Quantitative-Delineation VI-5
Data Quality Level 3: Quantitative-Clean Zone VI-5
Field Analytical Method Descriptions VI-7
Detector Tubes VI-7
Operating Principles VI-7
Method Descriptions VI-8
Ambient Air Measurements VI-8
Soil-Gas Test Kits VI-8
Liquid Test Kits VI-8
Method Capabilities And Practical Considerations . . . VI-10
Fiber Optic Chemical Sensors VI-10
Operating Principles VI-10
Method Descriptions VI-11
Water Wells VI-11
Vapor Wells VI-12
Method Capabilities And Practical Considerations ... VI-13
Calorimetric Test Kits VI-13
Operating Principles VI-14
Method Descriptions VI-15
Water Test Kit VI-15
Soil Test Kit VI-16
Method Capabilities And Practical Considerations ... VI-16
Analysis With Reflectance Spectrophotometer VI-17
Total Organic Vapor Analytical Methods With Flame
lonization And Photoionization Detectors VI-17
Operating Principles VI-17
Flame lonization Detectors VI-19
Photoionization Detectors VI-19
Comparison Of Flame lonization Detectors
And Photoionization Detectors VI-19
March 1997 Vl-iii
-------
Method Descriptions VI-21
Ambient Air Measurements VI-21
Headspace Screening VI-21
Headspace Analysis VI-22
Method Capabilities And Practical Considerations ... VI-22
Turbidimetric Test Kits VI-22
Operating Principles VI-23
Method Description VI-24
Method Capabilities And Practical Considerations ... VI-24
Immunoassay Test Kits VI-25
Operating Principles VI-26
Method Descriptions VI-27
Water Test Kits VI-27
Soil Test Kits VI-28
Method Capabilities And Practical Considerations ... VI-28
Portable Infrared Detectors VI-29
Operating Principles VI-29
Method Description VI-32
Method Capabilities And Practical Considerations ... VI-32
Field Gas Chromatographs VI-33
Operating Principles VI-33
Portable GCs VI-36
Transportable GCs VI-36
Comparison Of Portable And
Transportable GCs VI-36
Method Descriptions VI-37
Soil-Gas Analysis VI-37
Soil And Water Analysis VI-37
Static Headspace VI-37
Solvent Extraction VI-38
Purge And Trap VI-38
Method Capabilities And Practical Considerations ... VI-38
Emerging Methods VI-41
Gas Chromatography/Mass Spectrometry VI-41
Portable GC/MS VI-41
Transportable GC/MS VI-42
In Situ Analysis Using Direct Push Technologies VI-42
Laser-Induced Fluorescence VI-42
Fuel Fluorescence Detector VI-43
Semipermeable Membrane Sensor VI-44
Petroleum Hydrocarbon Analytical Equipment Manufacturers VI-45
Vl-iv March 1997
-------
References Vl~50
Peer Reviewers VI-52
March 1997 vuv
-------
Exhibits
Number Title Page
VI-1 Summary Table Of Field Methods For Petroleum
Hydrocarbon Analysis VI-3
VI-2 Summary Of Data Quality Levels . . . , VI-4
VI-3 Detector Tube Liquid Extraction Apparatus VI-9
VI-4 Summary Of Detector Tube Method Capabilities And
Practical Considerations VI-11
VI-5 Schematic Drawing Of FOCS Operating Principles VI-12
VI-6 Summary Of FOCS Method Capabilities And Practical
Considerations VI-14
VI-7 Example Of Friedel-Crafts Alkylation Reaction Utilized In
Calorimetric Test Kits VI-15
VI-8 Summary Of Calorimetric Test Kit Method Capabilities And
Practical Considerations VI-18
VI-9 Comparison Of FIDs And PIDs , VI-20
VI-10 Summary Of Total Organic Vapor Method Capabilities
And Practical Considerations VI-23
VI-11 Summary Of Turbidimetric Method Capabilities
And Practical Considerations VI-25
VI-12 Schematic Drawings Of Antibody And Enzyme Conjugate . . VI-26
VI-13 Summary Of Immunoassay Test Kit Method Capabilities
And Practical Considerations VI-30
VI-14 Infrared Spectra For Selected Aliphatic And
Aromatic Hydrocarbons VI-31
Vl-vi March 1997
-------
VI-15 Summary Of Infrared Spectroscopy Method Capabilities
And Practical Considerations VI-34
VI-16 Example Of A Portable GC Chromatogram VI-35
VI-17 Summary Of Field GC Method Capabilities And
Practical Considerations VI-40
VI-18 Petroleum Hydrocarbon Analytical Equipment
Manufacturers VI-45
March 1997 Vl-vii
-------
-------
Chapter VI
Field Methods For The Analysis Of
Petroleum Hydrocarbons
Analysis of soil, soil-gas, and groundwater samples in the field is an
essential element of expedited site assessments (ESAs). Field managers require
field-generated data in order to complete a site assessment in a single
mobilization. In recent years many field methods for petroleum hydrocarbon
analysis have been developed and improved. These technological improvements
can change the way site assessments are conducted by providing reliable data in
the field that can then be used to select subsequent sampling locations.
Historically, the analysis of contaminated media during UST site
assessments has been completed off-site in fixed laboratories that use certified
analytical methods. While these methods provide a very high data quality level
(DQL), their results may take days or weeks and their cost is relatively high. In
addition, many studies have shown that samples can undergo significant
degradation during the shipping and holding times before analysis.
The development and improvement of many field methods have allowed
site assessments to be performed more rapidly and completely than is feasible
with off-site analysis. By combining field methods of different DQLs, ESAs can
improve the resolution of contaminant distribution and minimize analytical costs.
Low DQL (i.e., screening) methods can be used to provide a high density of data
to determine source areas (i.e., zones of non-aqueous-phase liquid [NAPL]
contamination). Higher DQL methods can be used to identify low concentrations
or specific chemicals of concern at select locations (e.g., leading edge of
contaminant plume). Data from higher DQL methods can also be used as part of a
quality control check for the field analytical program.
Exhibit VI-1 is a summary table of the primary selection criteria for eight
commonly available field methods applicable for the analysis of petroleum
hydrocarbons. It is followed by a brief discussion of the DQL system used in this
chapter. The majority of the chapter is dedicated to discussions of the eight field
methods listed in Exhibit VI-1. Each method is summarized with a capabilities
and limitations table. A brief description and discussion of emerging technologies
(i.e., new technologies that are subject to significant innovation in the immediate
future) appears at the end of the chapter. In addition, Appendix B, at the end of the
manual, provides the reader with a table of relevant U.S. EPA test methods for
petroleum hydrocarbons.
March 1997 VI-1
-------
The chapter is organized so that readers can use the summary table
(Exhibit VI- 1) for initial selection of the most appropriate methods for a specific
situation. They can then make a final selection by referring to the discussions of
the individual methods that follow. The simpler, lower DQL methods are
presented first.
VI-2 March 1997
-------
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Data Quality Levels
Data quality levels (DQLs) represent a classification system of analytical
methods by the quality of data they provide. DQLs are one of several criteria that
can be used for selecting an appropriate analytical method. Exhibit VI-2 presents
the summary table of the DQL classification system used in this manual, which
was adapted from the classification system developed by the New Jersey
Department of Environmental Protection (1994). The levels are organized in a
data quality hierarchy in which DQL 1 provides screening information, DQL 2
provides quantitative data, and DQL 3 provides the most rigorous quantitative
data. Every state will have its own definition and requirements for various field
analytical methods and its own DQLs, so a complete list of QA/QC procedures for
each level is not provided.
Data Quality Level 1: Screening
DQL 1 screening methods are divided into two subgroups: 1A and IB.
Both are used for an initial screening of samples or for health and safety
evaluations. DQL 1A provides a general indication of the presence of
contaminants, DQL IB provides relative numerical values. All DQL 1 methods:
May require confirmation with higher DQL methods; and
Detect the presence of classes or groups of constituents.
Exhibit VI-2
Summary Of Data Quality Levels
Data Quality Level S
1A: Qualitative Screening
1B: Semiquantitative Screening
2: Quantitative Delineation
3: Quantitative Clean Zone
^^^fMi^M&iiiiM
General presence of contamination
(e.g., "Yes/no," low/medium/high);
health and safety
Approximation of contaminated zone;
provides order of magnitude
estimations (e.g., IDs, lOOs, 1000s)
Delineation of specific contaminants
Regulatory monitoring, determining
clean samples
VI-4 March 1997
-------
Data Quality Level IA: Qualitative Screening
DQL 1A is designated for initial screening of soil, soil gas, and
groundwater by providing a "yes/no" indication of contamination. Measurements
made with these methods may not always be consistent because of the lack of
sample control and inherent method variability. As a result, clean samples cannot
be determined from this level. Examples of DQL 1A methods include ambient air
analysis or jar headspace using flame-ionization detectors (FIDs) and
photoionization detectors (PIDs).
Data Quality Level 1B: Semiquantitative Screening
DQL IB provides a rough, order of magnitude (e.g., 10s 100s, 1000s)
estimate of contamination. It can be used for defining the location of known types
of contamination. QA/QC procedures include a calibration curve generated using
matrix spiked standards, regular calibration checks, and field blank/background
samples. An example of DQL IB is the data from some immunoassay test kit
methods.
Data Quality Level 2: Quantitative-Delineation
DQL 2 methods provide reliable data for the delineation of contaminants
during a site assessment. Typically, they are laboratory methods adapted for the
field (e.g., portable GC methods). DQL 2 methods:
Measure individual constituents (e.g., benzene) or groups of constituents
(e.g., BTEX, gasoline/diesel range organics),
Produce data that are highly reproducible and accurate when appropriate
QA/QC procedures are used, and
Accomplish contaminant delineation, which may be correlated with a
higher DQL method.
Data Quality Level 3: Quantitative-Clean Zone
DQL 3 methods are approved laboratory methods (e.g., U.S. EPA SW-846
Laboratory Methods) and are intended to provide the most reliable data
practicable. These methods can be used for confirming "clean" samples and for
March 1997 VI-5
-------
regulatory monitoring. DQL 3 can be performed both off-site in a fixed
laboratory or on-site in a mobile laboratory.
VI-6 March 1997
-------
Field Analytical Method Descriptions
There are eight commonly available field analytical methods that can be
used to detect petroleum hydrocarbons. Whenever any of these methods are used
to determine the constituent concentrations, the use of appropriate standards is
essential. There are two aspects to creating appropriate standards—using
constituents that match as closely as possible the constituents (or type of
contamination) found at the site and using the media (e.g., soil, groundwater) that
will be analyzed at the site. For example, if a silty soil contaminated with
weathered gasoline is to be analyzed, free product found at the site may be used to
spike a background sample of silty soil. If free product is not available, gasoline
(from the local USTs) may be artificially weathered (e.g., allow to sit in the sun
for a period of time) and used to spike the silty soil.
The following text contains discussions of each method, including its
operating principles, method descriptions, and method capabilities. At the end of
each method discussion is a table of important selection criteria.
Detector Tubes
Detector tubes measure volatile gases and can be used for analyzing
individual constituents or compound groups (e.g., petroleum hydrocarbons). In
addition to their frequent use for health and safety measurements, detector tubes
can also be used as screening tools for volatile hydrocarbon contamination.
Operating Principles
Detector tubes are glass tubes that change color when exposed to specific
gases. The glass tubes are sealed and filled with a porous solid carrier material
which is coated with color reagents. The breakaway ends of the tube are snapped
off and a known volume of air is drawn through the tube at a fixed flow rate using
a hand or electric pump. As air passes through the tube, a stain is produced by the
reaction of target constituents with the reagents inside the tube. The investigator
reads the concentration from a scale on the tube. For most of the detector tubes
that are used for hydrocarbon assessments, the length of the stain in the tube is
proportional to the concentration of the constituent. In addition to visual
observations, gas-specific measurements can be made using an optical analyzer.
March 1997 VI-7
-------
Method Descriptions
Detector tubes provide a direct measurement of volatile hydrocarbon
vapors in ambient air. They can also provide an indirect indication of soil and
groundwater contaminant concentrations when used in field test kits for analysis
of soil gas and headspace for liquids.
Ambient Air Measurements
Simple ambient air measurements can be made by inserting a detector tube
into a hand pump or mounting it in an optical analyzer, drawing air through the
tube, and reading the results. For hand-held pumps, readings can be taken in the
ambient air directly above the soil or groundwater samples. Test kits are available
for on-site identification and classification of ambient air above unknown liquids
during an emergency response. Attachments are also available that allow for the
testing of ambient air in monitoring wells or sumps.
Soil-Gas Test Kits
Soil-gas test kits allow for active soil-gas sampling and analysis with
detector tubes. This method utilizes a probe that is driven into the soil to a
desired depth. A detector tube is inserted into a sampling chamber near the tip of
the probe and connected to the ground surface with an extension tube. After air is
drawn through the detector tube, the probe is removed for reading. For a more
complete discussion of active soil-gas sampling, refer to Chapter IV, Soil-Gas
Surveys.
Liquid Test Kits
The liquid test kits consist of two types of headspace analyses: A bottle
system where the liquid sample is aerated, partitioning volatiles from the liquid
into the headspace; or a sealed sample bottle is agitated and the headspace is
subsequently analyzed. The aerating test kit system utilizes a fretted bubbler tube
fitted in a wash bottle containing the water sample that the investigator has
measured to a specific volume. A known quantity of air is drawn through the
bubbler to aerate the sample, volatilizing the constituents according to their
Henry's law constant. The headspace then passes through detector tubes for
analysis of the headspace in the bottle. The headspace concentration is correlated
to a water concentration using calibration and temperature corrections. Exhibit
VI-3 depicts a liquid extraction apparatus that can be used with detector tubes.
VI-8 March 1997
-------
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VI-9
-------
Method Capabilities And Practical Considerations
Detector tubes are available for hundreds of compounds including many
specific petroleum hydrocarbons and various general classes of petroleum
hydrocarbons (e.g., aliphatics). Detector tubes used in hydrocarbon analyses
generally provide readings in the parts per million (ppm) range, although some
can detect as low as 100 parts per billion (ppb). In addition, because detector
tubes and pumps are precalibrated, the procedures are relatively easy to learn.
Detector tubes provide DQL 1A information with ambient air and soil-gas test kit
analysis. Because liquid test kit analysis is performed under more controlled
conditions, detector tubes are able to provide DQL IB information when used
with this method.
A major limitation of this method is that the reagents in the detector tubes
are generally cross-reactive with compounds of similar chemical behavior.
Consequently, false positive and inaccurately high readings are possible. In
addition, detector tubes can only be used in specific ambient temperature ranges
as specified by the manufacturer. The minimum temperature is typically 32 F
(0 C) and the maximum temperature typically ranges from 86 to 104 F (30" to
40 C). A summary of the capabilities and practical considerations for analysis
using detector tubes is shown in Exhibit VT-4.
Fiber Optic Chemical Sensors
Fiber optic chemical sensors (FOCS) are used for in situ qualitative and
semiquantitative measurements of volatile and semi-volatile hydrocarbons in
groundwater and soil vapor. Some FOCS are used for detecting leaks of liquid
and vapor-phase petroleum products. They can also be used for continuous
monitoring of groundwater wells, soil vapor wells, and vapor extraction wells.
Operating Principles
FOCS use an optical fiber coated with a hydrophobic/organophyllic
chemical to detect hydrocarbons. FOCS operate on the principle that the index of
refraction of the optical fiber coating changes in direct proportion to the
concentration of hydrocarbons in air or water. As hydrocarbons partition into the
organophyllic coating, the change in the effective index of refraction can be
determined by measuring the amount of light transmitted through the optical fiber.
The response depends on the total number and type of hydrocarbons present.
Exhibit VT-5 is a schematic drawing of FOCS operating principles.
VI-10 March 1997
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Exhibit VI-4
Summary Of Detector Tube Method Capabilities
And Practical Considerations
Compounds
Detected
Measuring Range
Limitations
Time For Analysis
Difficulty of
Procedure
Data Quality Level
Cost Per Sample'
Ambient Air
Soil Vapor
Test Kit
Liquid
Test Kit
100s of specific compounds and compound groups
including benzene, toluene, xylenes, gasoline, aliphatic
hydrocarbons, MTBE, 0, CO,, and H,S.
Varies with analyte. Most compounds can be detected
in the ppm range, some as low as 100 ppb.
Cross reactivity may result in false positives or
inaccurately high readings because many tubes are
sensitive to chemically similar compounds (e.g.,
benzene tubes also measure toluene to some degree).
Minimum ambient air temperature is typically 32° F,
maximum is typically between 86° and 104° F.
2 to 5 minutes
10 to 15 minutes
(includes probe
placement)
5 to 10 minutes
Low
1A
$8
1A
$27
1B
$14
1 Based on 100 analyses, includes cost of tube, pump, and test kit.
Method Descriptions
FOCS are typically used for the in situ measurement of groundwater
monitoring wells and soil vapor wells. They can also be used to analyze the
ambient air immediately above soil or for soil headspace analysis.
Water Wells
Before an analysis is performed, the probe sensor is cleaned and calibrated
to zero in a solution of distilled water that is within 9 F (5 C) of the temperature
of the well water. Calibrations are checked daily or periodically between samples
March 1997
VI-11
-------
Exhibit VI-5
Schematic Drawing Of FOCS Operating Principles
Hydrocarbon
Photodiode Detector
Organophyllic Coating
Optical Fiber
Light Source
Source: Modified from ORS Environmental Systems product literature
using field standards or standards provided by the manufacturer (e.g., p-xylenes,
isopropanol).
To measure hydrocarbon concentrations in groundwater wells, the meter is
set to measure continuously, and the probe is removed from the zero solution and
lowered down the well to the desired depth. Readings are also affected by
changes in temperature during analysis. If the well water temperature changes by
more than 0.18 F (0. 1° C) every 4 seconds, a 5-minute analysis is required to
compensate for the temperature variations. Because results are site-specific,
response factors are used to obtain specific constituent concentrations for specific
wells with known contaminants (using a ratio of laboratory results to probe sensor
results for a specific well being tested).
Vapor Wells
Before an analysis is performed, the probe sensor is cleaned, zeroed in a
Tedlar bag with 5 liters of zero air (i.e., air that contains less than 0.1 ppm total
hydrocarbons), and calibrated using field standards or standards provided by the
VI-12
March 1997
-------
manufacturer (e.g., p-xylenes, isopropanol). Calibrations must be checked daily
or periodically between samples.
To measure hydrocarbon concentrations in vapor wells, a humidity tube is
used to zero the probe to the humidity in which the measurement will be made.
The probe sensor is then lowered to the desired depth. When the readings have
stabilized, the measurement can be recorded. The time required to reach a stable
reading is related to the temperature difference between the temperature at which
the probe sensor was zeroed and the temperature of the well. Well-specific
response factors may be used to obtain a specific concentration for that well.
After the measurement is completed, the probe must remain above ground for
5 minutes to allow any vapors in it to dissipate.
Method Capabilities And Practical Considerations
FOCS are capable of detecting VOCs and SVOCs with six or more carbon
atoms. Thus, benzene (C,) can be detected while methane (C,) cannot. The
response of the sensor probe is directly related to the quantity of hydrocarbons
present in a sample, calibrated to a p-xylene response. However, highly soluble
constituents yield a lower response than less soluble constituents. For example,
benzene, which is approximately 10 times more soluble in water than p-xylene,
responds with one-tenth the sensitivity of p-xylene. In addition, the response is
affected by temperature. FOCS, therefore, almost always require temperature
compensation, which is usually built into the sensor. The optimal temperature
range of FOCS is generally between 50° and 86° F (10° and 30° C).
Because the readings provide a relative value, a response factor
(empirically determined by the manufacturer) must be used to estimate
contaminant levels once the constituents and their relative ratios have been
determined. The strongest correlation of results with GC analysis comes either
from a single well monitored over time or from wells contaminated by the same
source. Exhibit VT-6 presents a summary of FOCS method capabilities and
limitations.
Calorimetric Test Kits
Calorimetric test kits provide qualitative or semiquantitative screening of
aromatic hydrocarbons in soil and water. They can generally provide information
about compound groups (e.g., BTEX, PAHs) but can also help determine
concentrations of specific compounds. A portable spectrophotometer has recently
been developed to aid in the evaluation of concentrations in samples, however, the
March 1997 VI-13
-------
Exhibit VI-6
Summary Of FOCS Method Capabilities
And Practical Considerations
Compounds Detected
Lower Detection Limits
Limitations
rime For Analysis
Difficulty of Procedure
Data Quality Level
Cost Per Sample'
Water Vapor
VOCs and SVOCs > C6 (Benzene)
0.1 to 5 ppm 3 to 65 ppm
Does not measure specific constituents
Concentrations at specific locations must be
calculated by comparing historical DQL 3 results
with FOCS results
Free product saturates coating and exceeds meter
scale
Optimal temperature range is between 50° and
86° F.
3 to 5 minutes
Low
1A/1B
<$1 to $10
1 Reflects the averaged cost over an extended period of time including
consumables (e.g., calibration standards) and the capital cost of equipment,
ranging from $5000 to $6900.
primary method of evaluation is by visual comparison of sample results with
calibrated photographs of specific substances (e.g., gasoline, diesel fuel).
Operating Principles
Calorimetric test kits that are designed for hydrocarbon analysis create
intensely colored aromatic compounds through the Friedel-Crafts alkylation
reaction. This reaction utilizes a catalyst (e.g., A1C13) to attach an alkyl group to
an aromatic hydrocarbon (e.g., benzene). In these test kits, an alkylhalide (e.g.,
carbon tetrachloride [Ccl,]) is typically used as both an extracting agent for the
hydrocarbons and as a reagent. Once the catalyst is added, the reaction proceeds.
The resulting color (e.g., orange, violet) provides information about the type of
VI-14
March 1997
-------
constituent; the intensity of the color is directly proportional (within a specific
range) to the concentration. Exhibit VI-7 presents a common Friedel-Crafts
alkylation reaction utilized in calorimetric test kits.
Method Descriptions
Calorimetric test kits are available for soil and water analysis. The kits
provide the reagents and equipment needed for the extraction and calorimetric
analysis of aromatic hydrocarbons. Color charts, created from known
concentrations of various constituents, are used for comparison with field results
to determine the constituents and their approximate concentrations.
Water Test Kit
The water test kit requires the following steps:
Pour the water sample into a separator/ funnel;
Add the solvent/extract (an alkylhalide) to the sample, agitate it, and wait
until solvent/extract has settled to the bottom of the separatory funnel;
Drain the extract into a test tube;
Add the catalyst and agitate it while the reaction proceeds between the
aromatics and the alkylhalide; and
Compare the color of the sample in the test tube (precipitate) with the
color chart standard.
Exhibit VI-7
Example Of Friedel-Crafts Alkylation Reaction Utilized
In Calorimetric Test Kits
AICI3
or
March 1997 VI-15
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Soil Test Kit
The soil test kit requires the following steps:
Measure a soil sample;
Add the solvent/extract to the soil, agitate it vigorously, and wait for the
solvent/extract to separate;
Pour the extract into a test tube;
Add the catalyst and agitate; and
Compare the color of the sample in the test tube (precipitate) with the
color chart standard.
Method Capabilities And Practical Considerations
Calorimetric test kits can be used to analyze aromatic hydrocarbons (with
particular sensitivity to PAHs) in soil and water. In soil, the detection limit is
generally in the 1 to 10 ppm range; in water it is less than 1 ppm. Calorimetric
test kits are effective for analysis of gasoline, diesel fuel, and other fuel oil
contamination. A particular advantage of this method is that it is not dependent
on analyte volatility, making it especially useful for older spills and for heavier
fuel oils.
One of the major limitations of the method is that when comparing
samples with the color chart photos, constituent concentrations and colors (i.e.,
type of constituent) can be difficult to determine when constituent concentrations
are low. In addition, if the contamination is a mixture of constituents, lighter
aromatics (e.g., BTEX) which turn to shades of orange will be hidden by heavier
constituents (e.g., PAHs) which turn to shades of violet. As a result, constituents
present in the sample should be known before analysis.
There are a number of potential interferences for this type of analysis.
First, the presence of chlorinated solvents may result in false positive analysis
with water or soil. Second, color interferences for organic-rich or clayey soils
may make color interpretation difficult. Clay soils may also pose additional
problems because the sample tends to clump, making contaminant extraction
difficult. Finally, the reaction products are sensitive to UV radiation, becoming
darker with time and causing the potential for overestimation of constituent levels.
Constituents and concentrations should, therefore, be determined within
30 minutes of color formation.
VI-16 March 1997
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A health and safety issue involved with the use of this method is that
analysis of all water samples and soil samples with hydrocarbon concentrations
less than 1000 ppm requires a heptane-carbon tetrachloride solution to be used for
sample extraction. Therefore, reagents and waste products must be properly
handled and disposed of after use, typically, they are shipped back to the
manufacturer. For analysis of soil samples with greater than 1000 ppm
hydrocarbons, a much more environmentally safe heptane solution (without
tetrachloride) can be used for extraction.
Both soil and water test kits provide data for screening level analysis.
Because the soil test provides variable response to a wide range of aromatic
hydrocarbons, has several interferences, and can be difficult to use, it is classified
as a DQL 1A analysis. The water analysis is more accurate and allows for an
order of magnitude determination of contamination. As a result, it is capable of
providing DQL IB analysis. A summary of the capabilities and practical
considerations for analysis using calorimetric methods is shown in Exhibit VT-8
Analysis With Reflectance Spectrophotometer
A portable reflectance spectrophotometer and associated software have
been developed that allow objective measurement of color intensity. Future
innovations may allow quantification of specific constituents and increase the
upper level of measurement. It is available for approximately $4,500.
Total Organic Vapor Analytical Methods With Flame
lonization And Photoionization Detectors
Total organic vapor (TOV) analytical methods detect the total volatile
organic compounds in a sample. Although, they provide information about the
relative magnitude of contamination, TOV methods are unable to distinguish
specific compounds.
Operating Principles
There are two types of instruments commonly used in TOV analysis--
flame ionization detectors (FIDs) and photoionization detectors (PIDs).
March 1997 VI-17
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Exhibit VI-8
Summary Of Calorimetric Test Kit Method Capabilities
And Practical Considerations
Compounds
Detected
Measuring Range
Limitations
Time For Analysis
Difficulty Of
Procedure
Data Quality Level
Cost Per Sample'
Soil Test Kit
Water Test Kit
Monoaromatic and polyaromatic hydrocarbons
Benzene 1 to 200 ppm
Toluene 0.5 to 250 ppm
Gasoline 1 to 1,000 ppm
Diesel 1 to 1,000 ppm
JP-5 1 to 2,000 ppm
Benzene 0.2 to 10 ppm
Toluene 0.2 to 10 ppm
Gasoline 0.5 to 20 ppm
Diesel 0.5 to 20 ppm
Naphthalene 0.1 to 2.5 ppm
Mixtures of constituents may make colors difficult to
distinguish without spectrophotometer.
Investigators should know constituents present before
analyzing samples
UV light degrades the color of samples (i.e., they become
darker) approximately 30 minutes after color formation.
Extraction of constituents may be difficult in clays.
Organic and clay-rich soils may interfere with color.
Carbon tetrachloride must be used, and properly
disposed of, for analysis < 1000 ppm.
10 to 20 minutes
medium
IA
10 to 15 minutes
low-medium
1B
$17 to $42
11nitial 30 analyses cost $42; subsequent analyses may cost as little as $17.
VI-18
March 1997
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Flame lonization Detectors
FIDs use a hydrogen flame to ionize organic vapors. The measured
electrical current that is generated by the free ions, called the instrument response,
is related to the concentration of volatile compounds present in the sample. While
FIDs provide significant response to most organic vapors, they are more sensitive
to aliphatic (or chained) hydrocarbons because these compounds burn more
efficiently than aromatic (or ringed) hydrocarbons. FIDs are typically calibrated
with methane.
Photoionization Detectors
PIDs use an ultraviolet lamp to ionize organic vapors. As with FIDs, the
instrument response is related to the electrical current generated by the ionized
compounds. Compounds with higher ionization potentials (e.g., aliphatics)
require more energy for ionization; therefore, the strength of the UV lamp
determines the compounds that are ionized. UV lamps range in energy from 8.4
to 11.7 eV. Isobutylene is typically used as the calibration gas for PIDs. These
instruments are most sensitive to aromatic hydrocarbons (e.g., BTEX
compounds), but some aliphatics can also be detected with the higher energy
lamps.
Comparison Of Flame lonization Detectors And
Photoionization Detectors
In addition to the response differences to aliphatic and aromatic
hydrocarbons, other factors to consider when selecting an FID or PID include the
following.
Response factors for specific constituents, which differ between types of
instruments and among manufacturers, are important to know when
calculating actual concentrations. For example, an FID calibrated with
methane may respond 150 percent greater when exposed to the same
concentration of benzene but the response may be only 25 percent for
ethanol.
FIDs remain linear from 1 to 1,000 ppm, (parts per million by volume),
and some can even reach 10,000 ppmv; PIDs remain linear from 1 to
300 ppmv, with some reaching 750 ppmv under ideal conditions.
Most PIDs are affected by high electrical currents (e.g., power lines).
PIDs can operate in conditions of high relative humidity and low O2, but
they require the calibration gas to approximate the test conditions. FIDs
March 1997 VI-19
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can operate in humid condition, but low O , high CO,, or windy
environments will extinguish the FID flame.
FIDs require more training than PIDs.
FIDs require a source of ultra-pure hydrogen that may not always be
available and requires special handling and shipping.
PIDs are subject to false low values when methane (CH4) concentrations
are greater than 1 percent; FIDs have the opposite problem of being
sensitive to methane and providing to false positive.
Both instruments are adversely affected by low air flow and, although FIDs
are more sensitive to slightly weathered gasoline (because of the presence
of several aliphatics), neither is effective for detecting highly weathered
gasoline, nor is either instrument accurate when ambient air temperatures
are below 32° F (O°C).
Exhibit VI-9 provides a summary of the comparison between FIDs and PIDs.
Exhibit VI-9
Comparison Of FIDs And PIDs
FIDs
PIDs
Compounds
Detected
Aliphatic hydrocarbons
(e.g., butane, hexane), less
sensitive (although
significant response) to
aromatics (e.g., BTEX
compounds)
Aromatic hydrocarbons and
some aliphatics
Linear Range of
Detection
1 to > 1,000 ppmv
1 to <300 ppmv
Unfavorable
Environmental
Conditions
High CO,, low 02 (<15%),
high winds, temperature
below 32° F
High humidity (e.g., 90%),
>l% CH4, low 02 (<5%),
temperature below 32° F
Miscellaneous
Issues
Requires a hydrogen
source
Requires more training than
PIDs
High methane levels may
be interpreted as
contamination
Adversely affected by
electrical power sources
(e.g., power lines and
transformers)
Methane can depress
readings
VI-20
March 1997
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Method Descriptions
TOV analytical methods provide an indirect indication of soil or
groundwater contaminant concentrations by measuring the organic constituents
that partition into the headspace. There are three general types of methods used
with FIDs and PIDs—ambient air measurements, headspace screening, and
headspace analysis. Each provides a varying degree of data quality.
Ambient Air Measurements
Ambient air measurements are performed by taking direct readings with
either an FID or a PID in the air immediately above soil or groundwater samples.
It is commonly used as a screening method to determine which soil or water
samples should be analyzed with a higher data quality method. It is also used to
help determine future sampling locations.
Headspace Screening
In order to perform a headspace screening, a soil or groundwater sample is
placed in an airtight container, typically a glass jar or polyethylene bag, leaving
one-half to one-third empty. The container is then either shaken, heated, or left to
sit for a period of time in order to allow the hydrocarbons to partition into the
headspace (i.e., the air space above the sample). The headspace is then measured
with an FID or PID. The use of a polyethylene bag allows for a steady sample
flow rate to the instrument, however, hydrocarbons partitioning from the bag may
affect the analysis so a blank sample should be tested and the results factored into
the analyses.
This method involves a more controlled sample analysis than ambient air
measurements. As a result, headspace screening provides more consistent
readings that can be used for estimating relative concentrations. However,
readings remain relatively inconsistent, because volatilization of contaminants is
affected by:
Soil type;
Moisture content;
Ambient air dilution into jar;
Temperature variations; and
Time to prepare and analyze sample.
March 1997 VI-21
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Headspace Analysis
Headspace analysis is similar to headspace screening but the procedures
are more controlled and the results more accurate. A measured quantity of a soil
or groundwater sample is placed in a polyethylene bag. For soil samples, a
specified volume of deionized water is also placed in the bag in order to facilitate
a more consistent partitioning of organic vapors. The bag is then inflated and the
sample is agitated. After a specified time, an FID or PID is used to measure the
headspace. QC procedures include the development of a calibration curve using
field standards. These standards help in the interpretation of instrument responses
and provide a comparison with samples of known concentrations.
Method Capabilities And Practical Considerations
Ambient air measurements are classified as DQL 1A analysis because
these readings are highly variable and little or no QA/QC is used with sample
analysis. The lower detection limit is generally around 100 ppm, but may be
significantly lower under ideal conditions (e.g., no wind, no humidity, high 02
levels). Headspace screening measurements are also only qualitative and fall
within the DQL 1A range, however, their detection limits are generally between
10 and 100 ppm. Headspace analysis is classified as DQL IB, semiquantitative,
method because it provides an order of magnitude indication of contamination,
but it does not provide information about the concentration of specific
constituents. The lower detection limit with this method may be as low as
0.1 ppm for gasoline in water, but it is generally above 1 ppm. For all three
methods, soil samples that are clay rich or contain high organic content may
provide inconsistent results. In addition, gasoline should be relatively fresh or
only slightly weathered for useful results.
TOV analysis is one of the least expensive analytical methods available. A
summary of the capabilities and practical considerations of these three analytical
methods using an FID or PID is summarized in Exhibit VI-10.
Turbidimetric Test Kits
Turbidimetric test kits are used for measuring the total petroleum
hydrocarbon (TPH) content in soil. These test kits provide quantitative screening
of soils for the presence of mid-range petroleum hydrocarbons (e.g., diesel fuel,
fuel oils, grease). Turbidimetric test kits can be used to identify source areas of
contamination in the vadose zone. This method is also being adapted for analysis
of TPH in water and may soon be commercially available.
VI-22 March 1997
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Exhibit VI-10
Summary Of Total Organic Vapor Method Capabilities
And Practical Considerations
Compounds
Detected
Lower Detection
Limits
Gasoline in water
Gasoline in soil
Diesel in soil
Limitations
Time For Analysis
Difficulty Of
Procedure
Data Quality Level
Cost Per Sample2
Ambient Air
Headspace
Screening
Headspace
Analysis
FIDs: Aliphatics (e.g., butane), less sensitive to
aromatics (e.g., BTEX)
PIDs: Aromatics, some aliphatics
>IOO ppm
>IOO ppm
>IOO ppm
10s to 100s ppm
10s to 100s ppm
100s ppm
0.1 to 1 ppm
1 to 10ppm
10s to 100s ppm
Clay-rich or high organic content may provide inconsistent
results.
Best used with relatively fresh or only slightly weathered
gasoline.
2 minutes
low
1A
<$1
10 to 30 minutes
low
1A
$1 to $5
10 to 30 minutes
medium
1B1
$10
1 Only if constituents are predetermined.
2 Equipment costs are typically between $4,000 and $8,000.
Operating Principles
Turbidimetric soil test kits indirectly measure the TPH in soil by
suspending extracted hydrocarbons in solution and then measuring the resulting
turbidity (i.e., the relative cloudiness of a solution) with a turbidity meter. The
suspending solution causes extracted TPH to separate out of solution (i.e.,
precipitate) while remaining suspended. Because the concentration of petroleum
hydrocarbons in the soil is directly proportional to the turbidity measurement, a
standard calibration curve can be developed to estimate TPH.
March 1997
VI-23
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Method Description
Turbidimetric soil test kits utilize extraction solvents, analytical reagents,
and a portable turbidity meter to determine contamination levels. The three steps
in the test are as follows.
Extraction: A methanol-based (chloroflorocarbon-free) solvent is used to
extract hydrocarbons from the soil sample. The sample is then agitated,
and the soil is allowed to settle.
Filtration: The extract is then separated from the soil with a filter and
placed in a vial with a developing solution.
Analysis: When the developing solution equilibrates, a reading is taken
with the turbidity meter. The turbidity value is proportional to the amount
of petroleum hydrocarbons present.
The constituents should be identified before using this method so that a
response factor can be selected from a reference table provided by the
manufacturer. The meter can be calibrated using an extraction solvent vial as a
blank and the calibration standard provided with the kit. Samples can be run
individually or batched. Optimum performance and throughput are accomplished
by running groups of 10 samples along with a blank and a standard.
Method Capabilities And Practical Considerations
Turbidimetric test kits are primarily used to screen petroleum
hydrocarbons in soil. The method, which is sensitive to heavier molecular weight
hydrocarbons (e.g., diesel fuel), is capable of detecting C12 to C30 hydrocarbons
with greatest sensitivity at the high end of the range. Turbidimetric soil test kits
provide results in the part per million (ppm) range. Organic-rich soils may limit
the effectiveness of the extraction or cause a positive interference. Background
levels outside the zone of contamination can be used for a correction of results.
The effective temperature range of this method is between 40 and 113 F (4 to
40 C). In addition, high moisture content in the soil sample may dilute the
concentration of hydrocarbons in the extract resulting in negative interference. A
summary of turbidimetric method capabilities and practical considerations is
presented in Exhibit VI-11.
VI-24 March 1997
-------
Exhibit VI-11
Summary Of Turbidimetric Method Capabilities
And Practical Considerations
Compounds Detected
Measuring Range
Limitations
Time For Analysis
Difficulty Of Procedure
Data Quality Level
Cost Per Sample'
Soil Test Kit
It is most sensitive to "middle" chain hydrocarbons
(e.g., C12 to C,), including diesel fuel and kerosene
Diesel 13to2000ppm
Used Motor Oil 19to2000ppm
Light-weight petroleum hydrocarbons (e.g.,
gasoline) are not detected.
Organic-rich soil may limit the effectiveness of the
extraction or cause positive interferences.
High soil moisture content may cause negative
interferences.
Filtration may be difficult with clay soils.
Effective temperature range is 40° to 113° F.
15 to 20 minutes
25 samples per hour when batched
Low-Medium
1B
$10 to $28
1 Initial 30 analyses cost $28; subsequent analyses may cost as little as $10.
Immunoassay Test Kits
Immunoassay test kits can be used to measure petroleum hydrocarbons in
soil and water. Test kits may measure groups of compounds (e.g., short chain
hydrocarbons, TEX) or a general assay range (e.g., PAHs, TPH). Although they
provide quantitative screening information, immunoassay test kits can determine
if samples are above or below an action level (i.e., whether a sample is "clean").
March 1997
VI-25
-------
Operating Principles
Immunoassay test kits use antibodies (i.e., proteins developed by living
organisms to identify foreign objects as part of their immune systems) to identify
and measure target constituents (i.e., antigens) through the use of an antibody-
antigen reaction. Antibodies are very useful for identifying specific compounds
because they have binding sites that are designed to preferentially bond to specific
antigens, as depicted in Exhibit VI-12. This technology has been used for decades
by the medical industry.
In order to facilitate analysis, immunoassay test kits utilize special
reagents, called enzyme conjugates, to allow for color development. Enzyme
conjugates, as depicted in Exhibit VT-12, are a combination of molecules of the
constituent of interest attached to specialized enzyme molecules. During analysis,
the enzyme conjugate and the sample are mixed with the antibodies at
Exhibit VI-12
Schematic Drawings Of Antibody And Enzyme Conjugate
Antibody
Enzyme Conjugate
Analyte
Binding Site
Analyte
Source: ENSYS Environmental Products, inc.
VI-26
March 1997
-------
approximately the same time causing them to compete for binding sites on the
available antibodies. When the constituents of interest have had time to bind to
the antibodies, the system is washed and a substrate solution is added. This
solution reacts with any enzyme conjugate that remains bound to the antibodies,
producing a color. As a result, for most immunoassay test kits, the color is
inversely proportional to the contaminant concentration (i.e., the darker the color,
the lower the concentration). The final concentration can be determined by
comparing the color developed in the sample with that of a reference standard,
either visually; with a portable photometer; or with an optical reflectance meter.
Method Descriptions
Although the procedures developed by the manufacturers of immunoassay
test kits may vary, a number of steps can be outlined. Methods are available for
both water and soil analysis. Water samples are analyzed directly, but soil
samples require an extraction process that results in an indirect analysis.
Test kits are used for semiquantitative screening. This procedure involves
setting an action level and observing whether the contaminant concentration is
above or below that level. Multiple action levels can be set to place the sample
within a discrete range (e.g., above 100 ppm but below 500 ppm). Multipoint
calibration curves can be used to further define concentrations (e.g., above
200 ppm but below 250 ppm). These calibration curves are generated using
standards that are provided by the manufacturer. Multiple analyses can be run in
batch assays for both types of test kits. Standards and blanks are run with each
batch.
Water Test Kits
To perform a water analysis:
The water sample is placed in a reaction cell or test tube that contains the
analyte-specific antibodies;
An enzyme conjugate is added;
After a specific period of time has passed, the sample is then washed,
leaving behind analyte and/or enzyme conjugate bound to antibodies;
The color development reagents (i.e., substrate solution) are added and
allowed to incubate;
A stop solution is added; and
The contaminant concentration is evaluated.
March 1997 VI-27
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Soil Test Kits
Soil test kits utilize the same steps as water test kits except they have
additional steps involved in extraction of analytes. The soil test kit analysis steps
are as follows:
An alcohol-based solvent (typically methanol) is added to the soil sample
to extract the contaminant;
The mixture is agitated to disaggregate the soil and extract the
contaminants;
The soil extract is placed in a reaction cell or test tube containing
antibodies;
The enzyme conjugate is added; and
The remaining part of the test is conducted like the water test described
above.
Method Capabilities And Practical Considerations
Immunoassay test kits are available for both water and soil analysis of
short chain hydrocarbons (TEX), PAHs, and petroleum fuels (TPH). Tests can be
performed for DQL IB screening, however, constituent concentrations can be
determined to be lower than a set action level with a high degree of certainty
within a test kit's detection limit. As a result, they can be used for determining
"clean" samples. In general, immunoassay test kits are best suited for analyzing
short and middle chain hydrocarbons (<7 ring aromatic compounds and
-------
data for many hydrocarbon constituents and mixtures are available from
the manufacturer; this information is important in interpreting test results.
"BTEX" test kits actually measure a broad range of short-chain
hydrocarbons because benzene is difficult to detect. These test kits give
results that correspond with TEX concentrations for gasoline constituents
and are designed for selectivity to xylenes with varying sensitivity for
other aromatics.
Immunoassay test kits must be used within each manufacturer's specified
temperature range, which is generally between 40 and 90 F (4 and 32 C)
and must be stored under conditions specified by the manufacturer
(ranging from refrigeration at 40 F to room temperature). In addition,
these kits must be used before the expiration date to provide valid data.
There are two problems that are specific to soil analysis. First, organic and
clay-rich soils may limit the effectiveness of soil extraction and require longer
extraction times than other soil types. Second, field extraction of PAHs may be
less effective than the extraction methods used in the laboratory, and excessive
amounts of oil in soil samples will interfere with the analysis of PAHs. Exhibit
VI-13 presents a summary of immunoassay test kit method capabilities and
practical considerations.
Portable Infrared Detectors
Portable infrared (IR) detectors measure the total petroleum hydrocarbons
(TPH) in soil and water samples. Field methods involve a modification of
U.S. EPA Method 418.1 or U.S. EPA SW-846 Method 8440 (U.S. EPA, 1997).
IR detectors are most effective for mid- to heavy-range hydrocarbons.
Operating Principles
Portable IR detectors are spectrophotometers that measure the absorbance
of IR radiation as it passes through sample extracts. The method operates under
the principle that the hydrogen-carbon bond of petroleum hydrocarbons will
absorb IR radiation at specific wave lengths, typically between 3.3 and
3.5 microns. Once contaminants are extracted from water or soil samples,
absorption measurements can be directly related to TPH concentrations through
the use of appropriate calibration standards.
Several petroleum hydrocarbons are shown in Exhibit VI-14. The top
graph presents the IR spectra for two aliphatics—hexane and hexadecane; the
March 1997 VI-29
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Exhibit VI-13
Summary Of Immunoassay Test Kit Method Capabilities
And Practical Considerations
Compounds
Detected
Lower Detection
Limit
Limitations
Time For Analysis
Difficulty of
Procedure
Data Quality Level
Cost Per Sample'
Water Test Kit Soil Test Kit
Short chain hydrocarbons (TEX)
PAHs
TPH
TEX 100 ppb TEX 2 ppm
PAHs 10 ppb PAHs 1 ppm
TPH 100 ppb TPH 5 ppm
Antibodies may cross react with petroleum contaminants
not targeted.
Kits must be used between 40° and 90° F.
Kits may be damaged if frozen or exposed to prolonged
heat.
Organic and clay-rich soil may limit effectiveness of
extraction (soil kits only).
Field extraction of PAHs with methanol is not as rigorous
as laboratory extraction (soil kits only).
30 to 45 minutes
8 tests per hour when 5 tests per hour when
running batches running batches
Medium
1B
$20 to $60
1 Cost decreases with greater number of samples
bottom graph presents the IR spectra for several aromatics—benzene, toluene,
xylene, and chlorobenzene. The concentration for all these constituents is
approximately 500 ppm, except for hexane which is about 250 ppm. Note that
peak response for the aliphatics is at wave lengths of approximately between
3.4 (im and 3.5 (im. The peak response for the aromatics is approximately
between
VI-30
March 1997
-------
Exhibit VI-14
Infrared Spectra For Selected Aliphatic And Aromatic Hydrocarbons
3.1
3.2
3.2
3.3 3.4
Wavelength (mm)
3.3 3.4
Wavelength (mm)
3.5
3.6
Source: General Analysis Corporation
March 1997
VI-31
-------
wavelengths of 3.3 pm and 3.4 (im. Also note that the absorbance scale is
different for aliphatics and aromatics, the aliphatics absorbance is much greater
and, as a result, measurements may be biased toward them.
Method Description
Analysis of petroleum hydrocarbons with portable IR detectors requires
that calibration standards be developed so that sample measurements can be
correlated to actual concentrations. Calibration standards are preferably made
with the constituents that are present at the site. If necessary, reference standard
specified in U.S. EPA Method 418.1 may also be used, but this standard is best
suited for the measurement of aliphatic hydrocarbons and it will give only
approximate values.
For analysis of soil, samples must first be chemically dried by adding
anhydrous sodium sulfate. For both soil and water samples a solvent that will not
interfere with the analysis is added for extraction of hydrocarbons and manually
shaken for a period of time. Method 418.1 uses Freon- 113TM( 1,1,2-trichloro-
1,2,2-trifluroethane). The SW-846 method utilizes supercritical CO, for
extraction into perchloroethane (PCE). Analysis can then be completed with
Method 8440. Field extraction procedures generally consist of a single extraction
while laboratory procedures typically consists of at least three extractions. A
silica gel should then be added to remove polar nonpetroleum hydrocarbons (e.g.,
esters and fatty acids) that can cause false positives. The extract is then poured
into a quartz curvette for measurement with the infrared spectrophotometer.
Method Capabilities And Practical Considerations
Infrared spectroscopy is useful for measuring the TPH of hydrocarbons in
the C6 to C26 range, however, results are biased toward hydrocarbons greater than
C12 because of their greater response to IR, and because larger hydrocarbons
volatilize less during extraction. As a result, it is not effective for measuring
VOCs. In addition, responses are typically biased toward aliphatic hydrocarbons
because of their larger response to IR when wave lengths between 3.4 (im and
3.5 (im are used. If wave lengths around 3.3 (im are used, aromatic hydrocarbons
can also be measured with minimal interference from aliphatics as long as
compounds are known and appropriate standards are used. Detection limits are
approximately 2 ppm for soil analysis and 0.08 ppm for water analysis.
Another limitation of this method is that results can not be correlated with
health or environmental risks because all hydrocarbons are grouped together and
presented as one number. Positive results may be related to compounds found
VI-32 March 1997
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naturally in organic and clay-rich soils, or in petroleum products, which are not
carcinogenic. As a result, although they give results at DQL 2, IR data require
correlation with constituent specific methods as well (e.g., GC analysis).
In addition, there are also a number of natural interferences with this
method. Soil type is an important consideration because the extraction efficiency
is much higher in sands than in clays. Furthermore, although most non-petroleum
hydrocarbons can be removed by silica gel treatment, terpenes, which are found in
conifers, citrus oils, and eucalyptus are not removed and can cause false positives.
The operational temperature range of IR spectroscopy is generally between
40 and 104 F (4" and 40 C) but may vary between manufacturers. The difficulty
of this procedure is medium compared with other field methods. The cost and the
time of analysis depend primarily on the number of extractions used per sample
and the soil type (because clays require a longer extraction time). Each extraction
takes about 5 minutes; analysis time is less than one minute. Exhibit VI-15
presents a summary of IR spectroscopy method capabilities and limitations.
Field Gas Chromatographs
Field gas chromatographs (GCs) are used for constituent-specific analysis
of soil, soil-gas, and water samples for volatile and semi-volatile hydrocarbons.
They have the capability to provide the highest data quality of all commonly used
field analytical methods.
Operating Principles
Gas chromatographs are comprised of two major components: A column
that separates individual constituents and a detector that measures the signal
response of constituents. The column is a long, thin, coiled tube. An inert carrier
gas (e.g., hydrogen, helium, nitrogen, or zero air) is used to transport constituents
through the column. Because compounds with low molecular weights and high
volatility travel through the column faster than heavier compounds with low
volatility, the constituents of a sample separate through the distance of the
column. Discrimination of constituents is often difficult if two or more
compounds exit the column at the same time (i.e., coelute). The likelihood of
compounds coeluting decreases with increasing column length.
A detector is located at the end of the column. For hydrocarbon
investigations, the most applicable detectors are PIDs and FIDs. The design of
PIDs and FIDs is modified slightly for GC analysis, allowing for greater detection
March 1997 VI-33
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Exhibit VI-15
Summary Of Infrared Spectroscopy Method Capabilities
And Practical Considerations
Compounds Detected
Detection Limit
Limitations
rime For Analysis
Difficulty Of Procedure
Data Quality Level
Cost Per Sample
Soil Analysis Water Analysis
C6 to C26 range hydrocarbons
2 ppm 0.08 ppm
Lighter petroleum hydrocarbons (e.g., BTEX) are
not accurately detected because of their volatility.
Results are biased toward medium and heavy
hydrocarbons compounds (i.e., >C121 unless
appropriate standards are used.
Extraction efficiency in clays may be lower than in
other soil types.
Organic and clay-rich soils may result in false
positives unless appropriate standards and IR
wavelengths are used because many non-
petroleum hydrocarbons (e.g., terpenes) are also
extracted and analyzed.
Health and environmental risks are difficult to
determine from TPH levels.
Operating temperature range is generally between
40° and 104° F.
5 to 20 minutes
Medium
2
$5 to $30
limits. The detector responses are displayed on either a chart recorder or a
computer screen to form a chromatogram (i.e., the detector reponses plotted
against retention time for a sample). The integrated area under each response
peak is proportional to the concentration of that constituent. Constituents are
identifed through a comparison of retention times with standards. Exhibit VI-16
is an example of a chromatogram created by a portable GC.
VI-34
March 1997
-------
2
G)
O
+->
(0
O
<
5
Q.
(0
X
HI
m
CL
LU
CO
zi
0
O
CO
March 1997
VI-35
-------
There are two types of field GCs currently used for assessing petroleum
releases—portable and transportable. Both types utilize the same basic operating
principles, however, their capabilities differ and, as a result, so do their
applications.
Portable GCs
Portable GCs are durable, compact, and light weight. Portability is
possible because these GCs are equipped with internal batteries and carrier gas
supplies. These features, however, limit the available energy supply that is
needed for rapid temperature ramping (i.e., heating) of the column. Instead,
portable GC columns are heated isothermally.
Transportable GCs
Transportable GCs are typically mounted in a mobile laboratory, but
because they require external power and gas supplies, they are not portable. Most
transportable GCs are capable of rapid temperature ramping of the column, and
many transportable GCs can be certified to perform U.S. EPA, SW-846 methods.
As a result, they can provide data in the field that are equivalent to the data
generated by certified fixed laboratory GCs.
Comparison Of Portable And Transportable GCs
The primary advantages of portable GCs are that they are easily carried
into the field and that the time they require for analysis is generally shorter than
for transportable GCs. Analysis with portable GCs is generally less than
10 minutes while transportable GCs commonly require 10 to 40 minutes (although
60 minutes may be required for some methods). Portable GCs tend to use PID
detectors because hydrogen gas is not required. As a result, many aliphatic
compounds cannot be detected with this equipment.
The primary advantage that transportable GCs have over portable GCs is
that transportable GCs are capable of providing better constituent separation and,
therefore, more accurate identification and quantitation of constituents. Greater
separation of constituents is possible because transportable GCs generally use
longer capillary columns than portable GCs (10 to 15 meters versus 30 to
60 meters). In addition, rapid temperature ramping of transportable GC columns
and consistent temperature control of the entire GC system provides better
separation and reproducibility than the isothermal heating of portable GCs.
VI-36 March 1997
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Transportable GCs are available with a variety of detectors, including PIDs and
FIDs.
Method Descriptions
Field GCs are capable of performing soil, soil-gas, and water analyses.
Soil-gas samples are the simplest to analyze because they do not require sample
preparation. Soil and water samples, however, require preparation of which a
couple of options are available.
Soil-Gas Analysis
Soil-gas samples are collected as described in Chapter IV, Soil-Gas
Surveys. Analysis can be performed with GCs through direct injection of the
sample by two methods. A microliter syringe or a loop injector (i.e., a sample
container that has been adapted for automatic injection via a pump internal to the
GC) can be used.
Soil And Water Analysis
There are generally three methods used for analyzing soil and water
samples for petroleum hydrocarbons with GCs. The simplest method is static
headspace which is used for analysis of VOCs with both portable and
transportable GCs. Solvent extraction is also used with both portable and
transportable GCs. It is commonly used for SVOCs. The more complicated,
time-consuming method called "purge and trap," is most effective for VOCs and
is typically not performed with portable GCs because the energy requirements are
excessive.
Static Headspace
The static headspace method is described in SW-846 Method 5021 (EPA,
1997). A version of this method has been modified for use by portable GCs.
Static GC headspace analysis of water involves placing an aqueous sample in a
sealed septum vial (analysis of a soil sample involves placing soil in a septum vial
with analyte-free water), agitating, and then placing the sample in a water bath at
constant temperature. Volatile hydrocarbons from the sample partition into the
headspace, eventually reaching equilibrium. The concentration of volatile
hydrocarbons in the headspace is representative of the concentration of dissolved
March 1997 VI-37
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volatiles in the water. An aliquot of the headspace is then withdrawn from the
vial with a gas-tight microliter syringe and injected directly into the GC column.
Solvent Extraction
The solvent extraction method provides higher hydrocarbon recovery than
the static headspace method for SVOCs. A specified mass of soil is dispersed in
an organic solvent which partitions the hydrocarbons into the solvent (e.g.,
pentane). The solvent can then be introduced into the GC by using direct
injection.
Purge And Trap
The purge-and-trap method provides higher hydrocarbon recovery and
lower detection limits than the static headspace method. It is conducted with
transportable GCs because of the high energy requirements. Prepared samples are
sparged with an inert gas (usually helium) in a purge chamber at ambient
temperature causing volatile hydrocarbons to be transferred from the aqueous to
the vapor phase. The vapor passes through an adsorbent trap that strongly retains
selective hydrocarbon constituents. The sorbent is then heated to release
hydrocarbon constituents and an effluent sample is directly transferred into the
GC column for analysis.
Method Capabilities And Practical Considerations
Field GCs provide quantitative, constituent-specific analysis of volatile
and semi-volatile hydrocarbons. In particular, field GCs can resolve key
constituents for evaluating risk and determining corrective action criteria. Field
GCs can measure constituent concentration in the part per billion (ppb) range for
soil, soil-gas, and water with a lower detection limit of between 1 to 10 ppb,
depending on the method and equipment. Samples with concentrations of less
than one thousand ppb can be analyzed without dilution. GC analyses are the
primary method for determining "clean zones" when delineating contamination.
They also be used to identify the type of hydrocarbon/fuel contamination (e.g.,
gasoline, diesel fuel). In addition, they are the only available field method for
determining MTBE concentrations.
VI-38 March 1997
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Limitations of field GCs include the following:
• Variations in temperature must be minimized and ambient air must not be
contaminated.
• Analytical schemes for field GCs are usually not set up to measure low
volatility and nonvolatile hydrocarbons (e.g., crude oil).
• A wide range of hydrocarbons (e.g., gasoline to fuel oil) are typically not
measured in a single analysis.
• Highly contaminated samples may require dilution to prevent them from
exceeding the maximum calibration range of the detector.
• Nontarget constituents may interfere with peak resolution if they have
similar retention times or coelute with the target compounds. If many
interfering peaks are present, the separation may not be adequate to
determine constituent concentrations. In this case, total chromatogram
integration can be used to determine the total VOCs.
• A greater level of operator training is required for field GCs than with
other field analytical methods. Although portable GCs may require less
training than transportable GCs, both methods typically require a chemist
or someone with significant chemistry training.
DQLs are dependent on the analytical method, the QA/QC procedures, and
the equipment capabilities. In addition, differences in the construction of portable
and transportable GCs (e.g., column heating, column length, temperature control)
control the attainable DQL. Portable GCs are capable of providing DQL 2
information, and transportable GCs may provide DQL 3 data. Exhibit VI-17
presents a summary of field GC method capabilities and limitations.
March 1997 VI-39
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Exhibit VI-17
Summary Of Field GC Method Capabilities
And Practical Considerations
Compounds
Detected
Lower Detection
Limits
Limitations
Time For
Analysis
Difficulty Of
Procedure
Data Quality
Level
Cost Per Sample
Water
Constituent-specific
Soil
volatile/semivolatile
Soil-Gas
hydrocarbons
1 to 10 ppb
Does not measure wide range of hydrocarbons in a single
analysis (e.g., gasoline to fuel oil).
Samples >IOOO ppb
may require dilution
to prevent
exceeding maximum range of detector.
Non-target compounds that coelute with
target compounds
will cause a positive bias in the interpretation of results.
Operation affected by extreme temperature and
contaminated working environments.
Requires high degree of training.
Portable:
Transportable:
<10 minutes
10 to 60 minutes depending on
constituents and method
Medium-High
Portable
Transportable
Portable
Transportable
High
2
213
$20 to $50
$50 to $70
Medium
VI-40
March 1997
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Emerging Methods
Several new field analytical methods are currently available for use in
expedited site assessments. They are classified as emerging because they are
recent developments and/or they are undergoing rapid change. Accordingly,
information in this text is not presented in as much detail as in the previous
section because details may soon become outdated. These methods include two
types of GC/mass spectrometry (MS) and three types of in situ sensing methods
that are used in conjunction with direct push technologies described in
Chapter V.
Gas Chromatography/Mass Spectrometry
Gas chromatography/mass spectrometry (GCNS) systems operate under
the same principles as the field GCs, but instead of using a PID or FID as the
detector, they use a mass spectrometer. Because MS records constituent specific
mass spectra (i.e., a spectrum of molecular fragments produced from the ionized
parent compound, that is resolved according to the mass-to-charge ratio), it allows
for identification of specific compounds.
GC/MS systems have been available in fixed laboratories for many years.
Recently, portable and transportable GC/MS has been developed. These systems
are typically not needed at UST sites because the types of contaminants are
generally known. In addition, it is inappropriate for TPH analysis. If, however,
chlorinated hydrocarbons migrate onto the site, or confirmation of specific
constituents is necessary, GC/MS may be appropriate. GC/MS detectors are no
more sensitive than GC/PID or GC/FID detectors, and they can be less sensitive
for certain analytes.
Portable GC/MS
Portable GC/MS systems have been designed primarily for air monitoring,
but they can also be used for headspace analyses. They are equipped with internal
batteries and carrier gas supplies. Because of these features, portable GC/MS
systems (as with portable GC/PIDs) have a limited energy supply and,
consequently, operate isothermally. In addition, these features also limit the types
of constituents that can be analyzed.
March 1997 VI-41
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Transportable GC/MS
Compared with laboratory-grade systems, transportable GUMS systems
are smaller, more rugged, lighter in weight, and use less power. Typically,
GUMS systems have been used to analyze chlorinated contaminants. GUMS
methods can be used to confirm and delineate the leading edges of contaminant
plumes and to verify contaminants suspected with GC/PID/F1D (e.g., MTBE).
EPA Methods 624 and 8260 (VOCs) and 8270 (SVOCs) can be performed using
transportable GUMS systems. In general, GUMS systems are well-suited for
analyzing a broad range of constituents, especially heavier molecular weight
constituents (e.g., PAHs) which are not as easily resolved by GC methods alone.
In Situ Analysis Using Direct Push Technologies
Several methods have recently been developed for the in situ analysis of
petroleum hydrocarbon contamination using direct push (DP) probes. They are
typically used in conjunction with several other sensors (e.g., soil conductivity,
temperature, friction/resistance) to provide detailed, objective logging
information. These measurements provide screening level information about the
presence of contamination while at the same time logging soil for various
parameters including soil type and depth to groundwater.
There are three emerging methods currently available for in situ analysis
with DP systems—laser-induced fluorescence (LIF), fuel fluorescence detectors
(FFD), and semi-permeable membranes. All three systems can be used with
sensors that simultaneously measure other parameters (e.g., soil conductivity,
temperature). The results from these methods can be used in an ESA to develop
and refine the conceptual model by identifying the contaminant location, tracing
lithologic units across the site and revising geologic cross sections, tracing
specific conductivity zones which may serve as preferential migration pathways,
and defining the thickness and lateral continuity of aquifers, aquitards, or other
definable units (e.g., clay, sand lenses). The results from these in situ
measurements can be used to effectively select sample locations and to verify the
results by direct sampling and analysis with a higher DQL method.
Laser-Induced Fluorescence
Two laser-induced fluorescence (LIF) systems have been developed for
use as part of a cone penetrometer test (CPT): The Rapid Optical Screening Tool
(ROST ) System developed by the Air Force, and the Site Characterization and
Analysis Penetrometer System (SCAPS) developed by the Navy as part of
VI-42 March 1997
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collaborative effort with the Army and Air Force under the auspices of the Tri-
Service SCAPS Program. The ROST system is currently available from a
single CPT firm, and the SCAPS technology is available only for use by federal
and state agencies.
The method uses a fiber-optic based LIF sensor deployed with a standard
20-ton cone penetrometer which simultaneously provides a continuous log of
subsurface materials. Two fiber-optic cables run from the sensor up through the
penetrometer rods. A pulsed nitrogen laser transmits ultraviolet (UV) light down
one of the fibers to the sensor probe and through a sapphire window built into the
side of the cone penetrometer tip. The UV light that exits the window causes
fluorescence of the polynuclear aromatics present in the soil adjacent to the probe.
The induced fluorescence signal is returned over a second fiber to the above
ground analytical equipment where it is dispersed with a spectrograph and
measured with a photodiode array.
The LIP system can provide qualitative information on polynuclear
aromatic hydrocarbons (PAHs). The ROST system uses wavelength-time plots
to identify the general type of petroleum hydrocarbon present. The SCAPS
system is intended to provide initial information on the distribution of
hydrocarbons in the soil and water prior to collecting soil cores and samples, and
selecting locations for groundwater monitoring wells. It provides information on
contaminant distribution with a continuous log of soil conditions.
Fuel Fluorescence Detector
A fuel fluorescence detector (FFD) has been developed for in situ
measurement of TPH as part of a cone penetrometer test. The FFD system uses a
254-nm ultraviolet light source that is focused on soil or groundwater through a
sapphire window. If aromatic hydrocarbons are present, the resulting fluorescence
will return through a fiber-optic cable for analysis at the ground surface. The FFD
system provides a detection limit of 100 ppm TPH (in sand), and it can detect a
broad range of petroleum hydrocarbons including gasoline, diesel fuel, and jet
fuel. In general, most aromatic hydrocarbons with less than four rings can be
detected. Creosote cannot currently be detected with this method. Potential
future developments may include the use of a spectrometer for determination of
specific types of fuels.
March 1997 VI-43
-------
Semipermeable Membrane Sensor
A semipermeable membrane sensor probe is an emerging technology that
can be used to detect the presence of volatile hydrocarbons above and below the
water table using DP rigs with percussion hammers. The sensor operates by
allowing volatile constituents in the subsurface to diffuse across a thin permeable
polymer membrane on the side of the probe. The inside surface of the membrane
is swept with a constant flow of an inert carrier gas. Volatile hydrocarbons in the
soil adjacent to the probe cross the membrane and are carried to the surface where
they can be analyzed (e.g., PID, FID, GC). Hydrocarbons in various phases (e.g.,
gas, sorbed, dissolved, free product) can be detected. The lighter, more volatile
constituents cross the membrane faster than heavier molecular weight
hydrocarbon constituents. The membrane can operate in an ambient temperature
mode or at an increased temperature of up to 250 F (121 C) to increase the
movement of volatile constituents through the membrane. Heating the membrane
can also significantly increase the sensitivity of the systems and decrease the time
required to remove residual contaminants from the membrane.
VI-44 March 1997
-------
Petroleum Hydrocarbon Analytical Equipment
Manufacturers
A list of petroleum hydrocarbon analytical equipment manufacturers is
included below in Exhibit VI-18. The equipment has not been evaluated by the
U.S. EPA and inclusion in this manual in no way constitutes an endorsement.
These vendors are listed solely for the convenience of the reader.
Exhibit VI-18
Petroleum Hydrocarbon Analytical Equipment Manufacturers
Detector Tubes
Mine Safety Appliances Company
P.O. Box 426
Pittsburgh, PA 15230
(412)273-3000
(800) 672-2222
Sensidyne, Inc.
16333 Bay Vista Drive
Cleatwater, FL 34620
(813)530-3602
(800)451-9444
National Draeger, Inc.
P.O. Box 120
Pittsburgh, PA 15230
(412) 788-5605
(800)922-5518
Fiber Optic Sensors
FCI Environmental, Inc.
1181 Grier Drive
Building B
Las Vegas, NV 89119
(702) 361-7921
(800)510-3627
ORS Environmental Systems
32 Mill Street
Greenville, NH 03048
(603) 878-2500
(800)228-2310
Colorimetric Test Kits
Hanby Environmental Laboratory
Procedures, Inc.
501 Sandy Point Road
Wimberly, TX 78676
(512)847-1212
(800) 304-2629
March 1997
VI-45
-------
Total Organic Vapor (TOV) Detectors (PIDs and FIDs)
Control Instruments Corp. (FIDs)
25 Law Drive
Fairfield, NJ 07004-3295
(201) 575-9114
Foxboro Analytical (FIDs and Dual
FID/PID)
600 North Bedford
East Bridgewater, MA 02333
(800) 321-0322
Gas Analysis Systems Company
3825 26th Street, West
Bradenton, FL 34205
(914) 755-8806
HNU Systems, Inc. (PIDs)
160 Charlemont Street
Newton, MA 02161
(617)964-6690
(800) 724-5600
MSA Baseline Industries (FID/PIDs)
P.O. Box 649
Lyons, CO 80450
(800) 321-4665
Photovac Monitoring Instruments
(FID/PIDs)
25-B Jefryn Boulevard, West
Deer Park, NY 11729
(516)254-4199
Thermo-Environmental Instruments,
Inc. (PID/FID)
8 West Forge Parkway
Franklin, MA 02038
(508) 520-0430
Turbidimetric Test Kit
Dexsil Corporation (PetroFLAG)
One Hamden Park Drive
Hamden, CT 06517
(203) 288-3509
Immunoassay Test Kits
Strategic Diagnostics, Inc. (Includes
products by D Tech, EM Science,
ENSYS, Omnicon, and Millipore)
375 Pheasant Run
Newtown, PA 18940
(800) 544-8881
VI-46
March 1997
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Portable: Infrared Spectraphotometers
Foxboro Analytical
600 North Bedford
East Bridgewater, MA 02333
(800) 321-0322
Horiba Instruments, Inc.
17671 Armstrong Avenue
Irvine, CA 92714
(800) 446-7422
General Analysis Corporation
140 Water Street, Box 528
South Norwalk, CT 06856
(203) 852-8999
Portable Gas Chromatographs
Foxboro Analytical
600 North Bedford
East Bridgewater, MA 02333
(800) 321-0322
HNU Systems, Inc.
160 Charlemont Street
Newton, MA 02161
(617) 964-6690
(800) 724-5600
Microsensor Technology, Inc.
41762 Christy Street
Fremont, CA 94358
(510)490-0900
Photovac Monitoring instruments
25-B Jefryn Blvd., West
Deer Park, NY 11729
(516)254-4199
Gas Analysis Systems Company
3825 26th Street, West
Bradenton, FL 34205
(914) 755-8806
Microsensor Systems, Inc.
62 Corporate Court
Bowling Green, KY 42103
(410) 939-1089
Ol Analytical
P.O. Box 9010
College Station, TX 77842
(409) 690-1711
Sentex Sensing Technology, inc.
553 Broad Avenue
Ridgefield, NJ 07657
(201) 945-3694
(800) 736-8394
Transportable Gas Chromatographs
Gas Analysis Systems Company
3825 26th Street, West
Bradenton, FL 34205
(914) 755-8806
Hewlett Packard
2850 Centerville Road
Wimington, DE 19808
(302) 633-8000
GOW-MAC instrument Company
P.O. Box 25444
Lehigh Valley, PA 18002
(610) 954-9000
HNU Systems, Inc.
160 Charlemont Street
Newton, MA 02161
(617) 964-6690
(800) 724-5600
March 1997
VI-47
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Microsensor Technology, Inc.
41 762 Christy Street
Fremont, CA 94358
(510)490-0900
Perkin Elmer Corporation
761 Main Avenue
Norwalk, CT 06859
(203) 763-1000
(888) 732-4766
SRI Instruments
3882 Del Amo Boulevard
Suite 601
Torrance, CA 90503
(310)214-5092
MSA Baseline Industries
P.O. Box 649
Lyons, CO 80450
(800) 321-4665
Shimadzu Scientific Instruments, Inc.
7102 Rivet-wood Drive
Columbia, MD 21046
(410) 381-1227
(800)477-1227
Varian Analytical Instruments
505 Julie River Road
Suite 150
Sugarland, TX 77478
(800) 926-3000
Gas Chromatographl Mass Spectrometer
Bruker instruments, Inc.
19 Fortune Drive
Manning Park
Bollerica, MA 01821
(508) 667-9580
Teladyne Electronic Technologies
1274 Terrabella
Mountain View, CA 94043
(415) 968-2211
INFICON
Two Technology Place
East Syracuse, NY 13057
(315) 434-1264
Viking Instruments
3800 Concorde Parkway
Suite 1500
Chantilly, VA 22021
(703) 968-0101
Laser Induced Fluorescence
Fugro Geosciences, Inc.
6105 Rookin
Houston, TX 77074
(713)778-5580
Fuel Fluorescence Detector
Applied Research Associates, Inc.
Vertek Division
120A Waterman Road
South Royalton, VT 05068
(800)639-6315
VI-48
March 1997
-------
Geoprobe Systems, Inc.
601 North Broadway
Salina, KS 67401
(913)825-1842
March 1997
VI-49
-------
References
American Petroleum Institute. 1996. Compilation of field analytical methods for
assessing petroleum product releases, API Publication 4635. Washington, DC.
Amick, E.N. and I.E. Pollard. 1994. An evaluation of four field screening
techniques for measurement ofBTEX, EPA 600/R-94/181. Washington, DC.
55 p.
Klopp, C. and D. Turrif 1994. Comparison of field screening techniques with
fuel-contaminated soil. In Proceedings NWWA/API conference on petroleum
hydrocarbons and organic chemical in groundwater; prevention, detection, and
restoration. National Well Water Association. Houston.
New Jersey Department of Environmental Protection. 1994. Field analysis
manual. Trenton, 121 p.
Robbins, G.A., R.D. Bristol, and V.D. Roe. 1989. A field screening method for
gasoline contamination using a polyethylene bag sampling system. Gr. Water
Mon. Rev., vol. 9, no. 4.
Roe, V.D., MJ. Lacy, J.D. Stuart, and G.A. Robbins. 1989. Manual headspace
method to analyze for the volatile aromatics of gasoline in groundwater and soil
samples. Analyt. Chem., vol. 61.
Stuart, J.D., S. Wang, G.A. Robbins. and C. Wood. 1991. Field screening of
BTEX in gasoline-contaminated groundwater and soil samples by a manual, static
headspace GC method. In U.S. EPA, Second international symposium, field
screening methods for hazardous wastes and toxic chemicals, EPA/600/9-91/028
(NTIS PB92-125764). L.R Williams and E.N. Koglm (eds.),.
U.S. EPA. 1990. Field measurements: Dependable data when you need it,
EPA/530/UST-90-003. Office of Underground Storage Tanks. 92 p.
U.S. EPA. 1993a. Subsurface characterization and monitoring techniques: A
desk reference guide. Volume 1: Solids and groundwater, EPA/625/R-93/003a.
Office of Research and Development, Washington, DC.
U.S. EPA. 1993b. Subsurface characterization and monitoring techniques: A
desk reference guide. Volume 2: The vadose zone, field screening and analytical
methods, EPA/625/R-93/003b. Office of Research and Development, Washington,
DC.
VI-50 March 1997
-------
U.S. EPA. 1994. Superfund innovative technology evaluation (SITE) program:
Technology profiles seventh edition, EPA/540/R-941526. Office of Research and
Development, Washington, DC.
U.S. EPA. 1995. Accelerated leaking underground storage tank site
characterization methods. Presented at LUST site characterization methods
seminar sponsored by U.S. EPA Region 5, Chicago: 108 p,
U.S. EPA. 1995. Rapid optical screen tool (ROST™): Innovative technology
evaluation report. Superfund innovative technology evaluation, EPA/540/R-
95/1519. Office of Research and Development, Washington, DC.
U.S. EPA. 1995. Site characterization analysis penetrometer system (SCAPS).
Innovative technology evaluation report. Superfund innovative technology
evaluation, EPA/540/R-951520. Office of Research and Development,
Washington, DC.
U.S. EPA. 1997. Test methods for evaluating solid waste, third update of third
edition, SW-846. Office of Solid Waste, Washington, DC.
March 1997 VI-51
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Peer Reviewers
David Ariail
J. Russell Boulding
James Butler
Kevin Carter
Dominick De Angelis
Gary Dotzlaw
John Hanby
Blayne Hartman
Stephan Kane
Bruce Kjartanson
Eric Koglin
William Kramer
Donald Lavery
Barry Lesnik
Al Liguori
Theodore B. Lynn
Ray Maytejczyk
Gillian Nielsen
Emil Onuschak, Jr.
Dan Rooney
Charlita Rosal
Mark Shaver
Wilfned Staudt
Sandra Stavnes
Katrina Varner
U.S. EPA, Region 4
Boulding Soil-Water Consulting
Geotech Environmental Equipment, Inc.
ENSYS Environmental Products, Inc.
Mobil Oil Corporation
FCI Environmental, Inc.
Hanby Environmental Laboratory
Procedures, Inc.
Transglobal Environmental Geochemistry
Photovac Monitoring Instruments
Iowa State University
U.S. EPA, National Exposure Research
Laboratory
Handex Corporation
General Analysis Corporation
U.S. EPA, Office of Solid Waste
Exxon Research and Engineering Company
Dexsil Corporation
Viking Instruments
The Nielsen Environmental Field School
Delaware Department of Natural Resources
and Environment Control
Applied Research Associates, Inc. (Vertek)
U.S. EPA, National Exposure Research
Laboratory
ORS Environmental Systems
Land Tech Remedial, Inc.
U.S. EPA, Region 8
U.S. EPA, National Exposure Research
Laboratory
VI-52
March 1997
-------
Appendix A
Data Requirements For Corrective
Action Evaluations
-------
Appendix A
Data Requirements For Corrective Action Evaluations
Key Parameters
Methodology/Source
Regional And Site-Specific Hydrogeologic Conditions
Regional Geology/Hydrogeology
Site-Specific Soil Characteristics
Site-Specific Aquifer Properties
Site-Specific Attenuation Factors
Soil, bedrock, and aquifer properties from
published maps/reports.
Observations/analysis of samples from
impacted and non-impacted areas.
Observations/measurements from impacted and
non-impacted areas.
Observations/analysis of samples for natural
attenuation factors/biodegradation parameters
(DO, NO:,, So4, Fe, Mn+2, CH4, CO,)
Evaluating Constituents Of Concern (COC)
Source, Nature Of Release, And
COC
Affected Media
Maximum COC Concentrations
Evaluate historical data, release reports, site
specific information
Soil/groundwater/vapor sampling and analysis
for concentration/distribution of COC
Analysis of soil, groundwater, and/or vapor
samples, identify presence or absence of
NAPLs
Potential Receptors And Land Use
Receptor Survey
Land Use Survey
State and local health department water supply
maps/records. Site-specific receptor survey to
locate unrecorded private wells/nearby
structures.
Site-specific survey to identify land use
(residential, commercial, industrial), review local
zoning ordinances/land use plans.
Exposure Assessment
Transport Media
Transport Mechanism
Exposure Pathways
Points Of Exposure
Site-specific transport media through which
COC may migrate (e.g., soil gas, groundwater).
Primary transport mechanism (e.g., leaching,
vapor/groundwater migration)
Primary exposure pathways (e.g., ingestion of
soil or groundwater, vapor inhalation, dermal
contact)
Review receptor survey and site-specific
information to identify points of exposure
March 1997
A-l
-------
Appendix B
Table Of U.S. EPA Test Methods For
Petroleum Hydrocarbons
-------
Appendix B
Table Of U.S. EPA Test Methods For Petroleum Hydrocarbons
fi)
to
to
SW-646 Method
40302
40352
80153
80213,5
8100
82606
8270
8310
84407
Water/ Waste
Water Method
502.2/602
524.2/624
525/625
610
418.18
Analytes
TPHs
PAHs
Aliphatic and Aromatic
Hydrocarbons;
Nonhalogenated
VOCs
Aromatic VOCs
PAHs
VOCs
SVOCs
PAHs
TPH
Primary Equipment
Immunoassay
Immunoassay
GC/FID
GC/PID
GC/FID
GC/MS
GC/MS
High Performance Liquid
Chromatography
IR Spectrophotometer
Sample Preparation'
Included in kit
Included in kit
Extraction (SVOCS)4; Purge-
and-Trap and Headspace
(VOCs)4; Azeotropic
Distillation (Nonhalogenated
VOCs)3, 4
Purge-and-Trap4
Extraction4
Purge-and-Trap, Headspace,
Azeotropic Distillation4
Extraction4
Extraction4
Supercritical Fluid Extraction
from soils4
1 These are the standard methods of preparation for the corresponding method. They may vary depending on specific analytical needs.
2 Sceening method for soils
3 MTBE can be analyzed with U.S. EPA SW-846 Method 8015 or 8021, however, 8021 has lower detection limits, is subject to less
interference in highly contaminated samples, and tends to be more economical by providing BTEX data in the same analysis. Concerns
about coelution with some alkanes requires at least one confirmitory analysis with SW-846 Method 8260 per site.
— 4 See Chap. 4 of SW-846 for specific appropriate methods.
^ 5 8021 replaces 8010 and 8020.
6 The old method, 8240, is replaced by 8260.
7 This method is similar to 418.1, however, perchlorethane (PCE) is used as an IR solvent instead of Freon-113.
8 418.1 is used extensively although it is not on the list of promulgated methods.
-------
Abbreviations
-------
Abbreviations
atm atmosphere(s)
bgs below ground surface
BTEX benzene, toluene, ethylbenzene, and xylene(s)
C Celsius/Centigrade
COC constituent(s) of concern
CRT cone penetrometer test
CSA conventional site assessment
DO dissolved oxygen
DP direct push
DQL data quality level
EM electromagnetic method
ER electrical resistivity
ESA expedited site assessment
eV electron volts
F Fahrenheit
FFD fuel fluorescence detector
FID flame ionization detector
FOCS fiber optic chemical sensor
ft foot/feet
gal. gallon(s)
GC gas chromatograph
GPR ground penetrating radar
HSA hollow stem auger
ID inside diameter
IR infrared
LIF laser induced florescence
LNAPL light non-aqueous-phase liquid
LUST leaking underground storage tank
MAG magnetometry
MD metal detection
MTBE methyl tertiary-butyl ether
Ug microgram(s)
um micrometer(s)
MW monitoring well
MS mass spectrometry
NAPL non-aqueous-phase liquid
nanometer(s)
OD outside diameter
PAH polyaromatic hydrocarbons
PCE perchlorethane
PE polyethylene
March 1997 Abbreviations-!
-------
TM
PID
ppb
ppm
PTFE
PVC
QA
QC
ROST
SCAPS
SED
SR
SVOCs
TEX
TOV
TPH
UST
uV
VOCs
photoionization detector
parts per billion
parts per million
polytetrafluoroethylene (Teflon@)
polyvinylchloride
quality assurance
quality control
Rapid Optical Screening Tool
Site Characterization and Analysis Penetrometer System
state environmental department
seismic refraction
semivolatile organic compounds
toluene, ethylbenzene, and xylene(s)
total organic vapor
total petroleum hydrocarbons
underground storage tank
ultraviolet
volatile organic compounds
Abbreviations-2
March 1997
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Glossary
-------
-------
Glossary
absorption: The penetration of atoms, ions, or molecules into the bulk mass of a
substance.
adsorption: The retention of atoms, ions, or molecules on the surface of another
substance.
air permeability: Permeability of soil with respect to air. Measured in darcys or
units of centimeters per second. An important parameter in the design of soil-gas
surveys.
aliphatic: Of or pertaining to a broad category of carbon compounds
distinguished by a straight, or branched, open chain arrangement of the
constituent carbon atoms. The carbon-carbon bonds may be either saturated or
unsaturated. Alkanes, alkenes, and alkynes are aliphatic hydrocarbons.
aliquot: A measured portion of a sample taken for analysis. One or more
aliquots make up a sample.
alkanes: Aliphatic hydrocarbons having the general formula CnH2n+2. Alkanes
can be straight chains, branched chains, or ring structures. Also referred to as
paraffins.
alkenes: The group of unsaturated hydrocarbons having the general formula
CnH2n and characterized by being highly chemically reactive. Also referred to as
olefms.
alkynes: The group of unsaturated hydrocarbons with a triple carbon-carbon
bond having the general formula CnH2n_2.
alkylated aromatics: The class of ringed aromatic compounds containing one or
more aliphatic side chains.
anaerobic: In the absence of oxygen.
analyte: The element, ion, or compound that an analysis seeks to identify; the
element of interest.
annular space, annulus: The space between two concentric tubes or casings, or
between the casing and the borehole wall.
March 1997 Glossary-l
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aquifer: A geologic formation capable of transmitting significant quantities of
groundwater under normal hydraulic gradients.
aquitard: A geologic formation that may contain groundwater but is not capable
of transmitting significant quantities of groundwater under normal hydraulic
gradients. In some situations aquitards may function as confining beds.
aromatic: Organic compounds that are unsaturated and contain at least one 6-
carbon benzene ring.
auger: A tool for drilling/boring into unconsolidated earth materials (soil)
consisting of a spiral blade wound around a central stem or shaft that is commonly
hollow (hollow-stem auger). Augers commonly are available in flights (sections)
that are connected together to advance the depth of the borehole.
azeotrope: A mixture with a fixed boiling point that cannot be further separated
by fractional distillation.
azeotropic distillation: A technique which uses the ability of selected organic
compounds to form binary azeotropes with water to facilitate the separation of the
compounds from complex mixtures.
barrel sampler: Open-ended steel tube used to collect soil samples. The sampler
has a sharpened end, or "shoe," that is pushed or driven into the ground. A soil
core is collected inside of sampler.
batch: A group of samples prepared at the same time in the same location using
the same method.
bentonite: A colloidal clay, largely made up of the mineral sodium
montmorillonite, a hydrated aluminum silicate. Because of its ability to expand
when moist, bentonite is commonly used to provide a tight seal around a well
casing.
biodegradation: A process by which microbial organisms transform or alter
(through metabolic or enzymatic action) the structure of chemicals introduced into
the environment.
bladder pumps: Also known as squeeze pumps, bladder pumps operate by the
compression of a flexible bladder housed inside the pump. Water enters the
bladder through a check valve. Once the bladder is filled, it is squeezed by
compressed air that has been injected into the housing surrounding the bladder.
Water cycles through the bladder in evenly spaced pulses.
blank: See "method blank."
Glossary-2 March 1997
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borehole: Hole made with boring (drilling) equipment. Also used in reference to
hole made by DP equipment, but "DP hole" and "probe hole" are preferred terms
in the latter case.
boring logs: The record of formations penetrated, drilling progress, record of
depth of water, location of contaminants, and other recorded information having
to do with the drilling well.
calibration: The establishment of an analytical curve based on the absorbance,
emission intensity, or other measured characteristic of known standards. Used to
define the linearity and dynamic range of the response of the analytical equipment
to the target compounds.
calibration standards: A series of known standard solutions used by the analyst
for calibration of the instrument (i.e., preparation of the analytical curve).
capillary fringe: The zone of a porous medium above the water table within
which the porous medium is saturated by water under pressure that is less than
atmospheric pressure.
cased DP system: A rod system consisting of inner rods and outer drive casing.
Also referred to as "dual-tube" DP systems. The soil sampling barrel is attached
to inner rods. The inner rods and outer casing are typically driven simultaneously.
The sampling tool is then withdrawn, emptied, and re-inserted, while the outer
drive casing is left in the ground to keep the hole open. Minimizes sloughing and
contamination of soil samples.
check-valve tubing pump: A water sampling tool consisting of plastic tubing
(S3
with a check valve attached to the bottom. Also referred to as a Waterra pump.
Oscillation of the tubing moves water up through it. The check valve prevents
water from draining out of the tubing when it is withdrawn from the well. In this
way, the tubing acts like a long, skinny bailer.
composite underground storage tank: A fiberglass coated steel tank.
conceptual model: A written description or illustrated picture of the geologic,
hydrogeologic, or environmental conditions of a particular area.
conductivity: A coefficient of proportionality describing the rate at which a fluid
(e.g., water or gas) can move through a permeable medium. Conductivity is a
function of both the intrinsic permeability of the porous medium and the
kinematic viscosity of the fluid which flows through it.
conductivity probe: A DP tool that measures the electrical conductivity of the
soil to define lithology.
March 1997 Glossary-3
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cone: Down-hole sensor used with CPT. At a minimum, consists of load cells to
measure tip resistance and side-wall friction.
cone penetrometer testing (CPT): A DP system used to measure lithology
based on the penetration resistance of the soil. Sensors are mounted in the tip
(cone) of the DP rods to measure tip resistance and side-wall friction. Electrical
signals are carried to digital processing equipment at the ground surface, where
plots of soil type versus depth are recorded. It defines the type of soil based on
calibration curves, not site-specific conditions. Therefore, CPT data requires on-
site calibration/correlation with actual soil cores.
confining layer: A geologic formation characterized by low permeability that
inhibits the flow of water (see also aquitard).
constituent: An essential part or component of a system or group (e.g., an
ingredient of a chemical mixture). For instance, benzene is one constituent of
gasoline.
constituent(s) of concern: Specific chemicals that are identified for evaluation in
the site assessment process.
conventional site assessment: A site assessment in which the majority of sample
analysis and interpretation of data is completed off-site. The process typically
requires multiple mobilizations in order to fully determine the extent of
contamination.
cross contamination: The movement of contaminants from one depth to another
due to invasive subsurface activities.
cross reactivity: The potential for constituents that are not the target compound
to be detected as the target compound by an analytical method.
cuttings: The spoils created from conventional drilling with hollow stem auger or
rotary drilling equipment. Cuttings are not generated with DP equipment.
deadmen: Anchors drilled or cemented into the ground to provide additional
reactive mass to DP sampling rigs. The rigs are able to pull against the anchors,
thus increasing the force that can be applied to the DP rods.
dense non-aqueous phase liquid (DNAPL): A non-aqueous phase liquid
(NAPL) with a specific gravity greater than 1.0. Because the specific gravity of
water is equal to 1.0, DNAPLs sink through the water column until they encounter
a confining layer. DNAPLs flow along the surface of the confining layer and can
migrate in directions contrary to the hydraulic gradient. Because DNAPLs are
found at the bottom of aquifers (rather than floating on the water table) typical
Glossary-4 March 1997
-------
monitoring wells will not indicate whether DNAPLs are present. DNAPLs are
typically chlorinated hydrocarbon solvents or very heavy petroleum fractions and
are, therefore, not usually of concern at petroleum UST sites.
direct push: A growing family of tools used for performing subsurface
investigations by driving, pushing, and/or vibrating small-diameter hollow steel
rods into the ground. Also known as "direct drive," "drive point," or "push"
technology.
downgradient: It the direction of decreasing static (potentiometric) head..
DP hole: A hole in the ground made with direct push equipment.
DP rod: Small diameter hollow steel rod that is pushed, driven, or vibrated into
the ground in order to investigate and sample the subsurface. DP rods used with
CPT rigs may be referred to as "cone rods"; DP rods used with other DP systems
may be referred to as "probe rods."
drilling fluids: Fluid used to lubricate the bit and convey drill cuttings to the
surface with rotary drilling equipment. Usually composed of a bentonite slurry,
muddy water, or air. Can become contaminated, leading to cross contamination,
and may require special disposal. Not used with DP methods.
drive cap: A steel cap that is attached to the top of the sequence of DP rods.
Percussion hammers pound on the drive head, rather than the DP rods, to prevent
damaging the threads on the rod connections.
drive casing: Heavy duty steel casing that is driven along with the sampling tool
with cased DP systems. The drive casing keeps the hole open between sampling
runs, and is not removed until the last sample has been collected.
drive head: See "drive cap."
drive shoe: The sharp, beveled end of a DP soil sampling tool. The shoe is
beveled out, so that the soil core is cut cleanly. The beveled surface of the shoe
forces soil to the outside of the sampler, where it is pushed into the formation.
drive-point profiler: An exposed groundwater DP system used to collect
multiple depth-discrete groundwater samples. Ports in the tip of the probe
connect to an internal stainless steel or Teflon tube that extends to the ground
surface. Samples are collected via suction or air-lift methods. Deionized water is
pumped down through the ports to prevent plugging while driving the tool to the
next sampling depth.
dual tube DP system: See "cased DP system."
March 1997 Glossary-5
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duplicate: A second aliquot of a sample that is treated the same as the original
sample in order to determine the precision of the analytical method.
electrical conductivity: A measure of a substance ability to transmit an electrical
current. Units are typically expressed in millimhos/meter when geophysical
measurements are made.
electrical resistivity: A measure of a substance ability to inhibit the transmission
of an electrical current. Units are typically expressed in ohms/meter when
geophysical measurements are made. Electrical resistivity is the reciprocal of
electrical conductivity.
electrical resistivity geophysical methods: Methods of measuring subsurface
conditions through the use of an electrical current that is applied to the ground
through a set of electrodes. Another set of electrodes is then used to measure the
resulting voltage. The greater the distance between electrodes, the deeper the
investigation.
electromagnetic geophysical methods: Methods of measuring subsurface
conductivities by low frequency electromagnetic induction. A transmitter coil
radiates an electromagnetic field which induces eddy currents in the subsurface.
The eddy currents, in turn, induce a secondary electromagnetic field. The
secondary field is then intercepted by a receiver coil. The voltage measured in the
receiver coil is related to the subsurface conductivity.
enzyme: Any of numerous proteins or conjugated proteins produced by living
organisms and functioning as biochemical catalysts.
evaporation: The process by which a liquid enters the vapor (gas) phase.
expedited site assessment: A process for collecting and evaluating site
information in a single mobilization. Parameters assessed include site
geology/hydrogeology, nature, and distribution of the chemicals of concern,
source areas, potential exposure pathways, and points of exposure. An ESA
employs rapid sampling techniques, field analysis and hydrogeological
evaluation, and field decision making to provide a comprehensive "snap-shot" of
subsurface conditions.
expendable tip: A disposable steel or aluminum tip that attaches to the end of
DP rods. The tip seals the DP rods or sampling tool while it is driven through the
soil. Once the desired sampling depth has been reached, the rods are pulled back,
exposing the target interval.
field analytical methods: Methods or techniques that measure physical
properties or chemical presences in soils, soil-gas, and groundwater immediately
Glossary-6 March 1997
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or within a relatively short period of time to be used during a site assessment.
Measurement capabilities range from qualitative (positive/negative) response to
below parts per billion quantitation. Accuracy and precision of data from these
methods depends on the method detection limits and QA/QC procedures.
field manager: An individual who is on site and is responsible for directing field
activities and decision-making during the site assessment. The field manager
should be familiar with the purpose of the site assessment, pertinent existing data,
and the data collection and analysis program. The field manager is the principle
investigator, developing and refining the conceptual model of site conditions.
This individual should have the necessary experience and background to perform
the required site characterization activities, to accurately interpret the results, and
to direct the investigation.
false negative: A negative result when the concentration of the target constituent
is above the detection limit of the analytical method.
false positive: A positive result when the concentration of the target constituent
is below the detection limit of the analytical method.
field blank: Any sample submitted from the field identified as a blank.
fill: Man-made deposits of natural soils or rock products and waste materials,
fluorescence: The emission of electromagnetic radiation (e.g., visible light) by a
substance during exposure to external electromagnetic radiation (e.g., x-rays).
fracture: A break in a rock formation due to structural stresses. Faults, shears,
joints, and planes of fracture cleavage are all types of fractures.
free product: A petroleum hydrocarbon in the liquid ("free" or non-aqueous)
phase (see also non-aqueous phase liquid, NAPL).
friction reducer: A wide section of the DP cone or probe designed to enlarge a
boring so that the DP rods above the friction reducer do not inhibit the
advancement of the probe. Expendable friction reducers can be used for grouting
on advance.
ground penetrating radar: A geophysical method that uses high frequency
electromagnetic waves to obtain subsurface information. The waves are radiated
into the subsurface by an emitting antenna. When a wave strikes a suitable object,
a portion of the wave is reflected back to the receiving antenna.
groundwater: The water contained in the pore spaces of saturated geologic
media.
March 1997 Glossary-7
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grout: Cement and/or bentonite slurry used to seal DP holes and other
exploratory borings. It is also used to seal the annular space around well casings
to prevent infiltration of water or short-circuiting of vapor flow.
headspace: The vapor/air mixture trapped above a solid or liquid in a sealed
vessel.
Henry's Law: The relationship between the partial pressure of a compound and
the equilibrium concentration in the liquid through a proportionality constant
known as the Henry's Law Constant.
Henry's Law Constant: The ratio of the concentration of a compound in air (or
vapor) to the concentration of the compound in water under equilibrium
conditions. Henry's Law Constants are temperature dependent.
heterogeneous: Varying in structure or composition at different locations in
space.
holding time: The maximum amount of time a sample may be stored before
analysis.
hollow stem auger drilling: A conventional drilling method that uses rotating
augers to penetrate the soil. As the augers are rotated, soil cuttings are conveyed
to the ground surface via spiral flights. Hollow stem augers allow the rig operator
to advance DP tools inside of the augers.
homogeneous: Uniform in structure or composition at all locations in space.
hydraulic conductivity: A coefficient of proportionality describing the rate at
which water can move through a permeable medium. Hydraulic conductivity is a
function of both the intrinsic permeability of the porous medium and the
kinematic viscosity of the water which flows through it. In older documents,
hydraulic conductivity is referred to as the coefficient of permeability.
hydraulic gradient: The change in total potentiometric (or piezometric) head
between two points divided by the horizontal distance separating the two points.
hydrocarbon: Chemical compounds composed only of carbon and hydrogen.
hydrophilic: Having an affinity for water ("water-loving"), or capable of
dissolving in water; soluble or miscible in water.
hydrophobic: Tending not to combine with water, or incapable of dissolving in
water; insoluble or immiscible in water ("water-fearing"). A property exhibited
by non-polar organic compounds, including the petroleum hydrocarbons.
Glossary-8 March 1997
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immunoassay: A test for a constituent or class of constituents based on the
antibody/antigen reaction.
infrared radiation: Electromagnetic radiation with wave lengths greater than
visible light but less than microwave radiation.
inner barrel: Internal sample barrel seated inside of a cased DP systems.
in situ: In its original place; unmoved; unexcavated; remaining in the subsurface.
injection: Introduction of the analytical sample into the instrument excitation
system for the purpose of measuring absorbance, emission, or concentration of an
analyte.
ionization potential: The energy required to ionize a particular molecule.
isoconcentration: More than one sample point exhibiting the same analyte
concentration.
isopleth: The line or area represented by an isoconcentration.
intrinsic permeability: A measure of the relative ease with which a permeable
medium can transmit a fluid (liquid or gas). Intrinsic permeability is a property
only of the medium and is independent of the nature of the fluid.
kinematic viscosity: The ratio of dynamic viscosity to mass density. Kinematic
viscosity is a measure of a fluid's resistance to gravity flow—the lower the
kinematic viscosity, the easier and faster the fluid will flow.
laser induced fluorescence: A method for measuring the relative amount of soil
and/or groundwater contamination with an in situ sensor. Laser light is
transmitted to the sensor, where it fluoresces in proportion to the concentration of
petroleum hydrocarbons adjacent to the sensor.
light non-aqueous phase liquid (LNAPL): A non-aqueous phase liquid (NAPL)
with a specific gravity less than 1.0. Because the specific gravity of water is equal
to 1.0, LNAPLs float on top of the water table. Most of the common petroleum
hydrocarbon fuels and lubricating oils are LNAPLs.
linear range: The concentration range over which the analytical curve remains
linear.
liners: Tubes lining DP soil sampling tools. Used to collect soil cores for
chemical and/or lithologic analysis. Commonly made of stainless steel, brass, or
March 1997 Glossary-9
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plastic. Liners can be covered with caps to prevent loss of volatile constituents.
Also known as sample sleeves.
lithology: Mineralogy, grain size, texture, and other physical properties of
granular soil, sediment, or rock.
lower detection limit: The smallest signal above background noise that an
instrument can reliably detect.
lower explosive limit (LEL): The concentration of a gas below which the
concentration of vapors is insufficient to support an explosion. LELs for most
organics are generally 1 to 5 percent by volume.
macropores: Soil pores that are secondary soil features such as root holes or
desiccation cracks. They can create significant conduits for vertical migration of
NAPL, dissolved contaminants, or vapor-phase contaminants.
magnetic geophysical methods: Methods of determining subsurface conditions
by measuring the earth's total magnetic field at a particular location. Because
buried ferrous materials distort the magnetic field, a magnetic anomaly is created
and their location can be approximated.
matrix spike: Aliquot of a matrix (water or soil) fortified (spiked) with known
quantities of specific compounds and subjected to the entire analytical procedure
in order to indicate the appropriateness of the method for the matrix by measuring
recovery.
matrix spike duplicate: A second aliquot of the same matrix as the matrix spike
(above) that is spiked in order to determine the precision of the method.
metal detection geophysical methods: Methods designed to specifically locate
metal in the subsurface through electromagnetic induction (see electromagnetic
geophysical methods). When the subsurface current is measured at a specific
level, the presence of metal is indicated with a meter reading, with a sound, or
with both.
method blank: An analytical control consisting of all reagents, internal
standards, and surrogate standards, that is carried through the entire analytical
procedure. The method blank is used to define the level of laboratory background
and reagent contamination.
microorganisms: Microscopic organisms including bacteria, protozoans, yeast,
fungi, mold, viruses, and algae.
Glossary-10 March 1997
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mobilization: The movement of equipment and personnel to the site, conducted
during a continuous time frame to prepare for, collect, and evaluate site
assessment data.
moisture content: The amount of water lost from a soil upon drying to a constant
weight, expressed as the weight per unit weight of dry soil or as the volume of
water per unit bulk volume of the soil. For a fully saturated medium, moisture
content equals the porosity.
molecular weight: The amount of mass in one mole of molecules of a substance
as determined by summing the masses of the individual atoms which make up the
molecule.
monoaromatic: Aromatic hydrocarbons containing a single benzene ring.
non-aqueous phase liquid (NAPL): Contaminants that remain as the original
bulk liquid in the subsurface (see also free product).
nonsealed DP tools: Sampling tools that are not sealed as they are advanced
through the soil. Examples of these tools are barrel samplers and split-barrel
samplers. Can yield erroneous chemical results because samples collected with
these devices can be a composite of samples from different horizons. Can result
in cross-contamination of samples.
nuclear logging: A down-hole geophysical logging method that uses naturally
occurring or induced radiation to define lithology, groundwater conditions, or
contaminant distributions.
olefins: See "alkenes."
organophyllic: A substance that combines with organic compounds.
outer drive casing: Same as drive casing.
oxidation-reduction (redox): A chemical reaction consisting of two half-
reactions; an oxidation reaction in which a substance loses or donates electrons,
and a reduction reaction in which a substance gains or accepts electrons. Redox
reactions are always coupled because free electrons cannot exist in solution and
electrons must be conserved.
packer: An inflatable gland, or balloon, that is used to create a temporary seal in
borehole, probe hole, well, or drive casing. Made of rubber or non-reactive
(S3
materials like Viton .
paraffins: See alkanes.
March 1997 Glossary-11
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perched aquifer: A lens of saturated soil above the main water table that forms
on top of an isolated geologic layer of low permeability.
percussion hammer: A hydraulic or pneumatic hammer, much like a
jackhammer, that is used to pound DP rods into the ground. Commonly used in
the construction industry to break concrete.
peristaltic pump: A type of suction-lift pump that creates a vacuum by turning a
rotating head against flexible tubing. Generally limited to approximately 25 feet
of lift.
permeability: Also referred to as intrinsic permeability. It is a qualitative
description of the relative ease with which rock, soil, or sediment will transmit a
fluid (i.e., liquid or gas). Often used as a synonym for hydraulic conductivity or
coefficient of permeability, however, unlike hydraulic conductivity, permeability
is not a function of the kinematic viscosity of the fluid that flows through it.
petroleum: Crude oil or any fraction thereof that is liquid at standard conditions
of temperature and pressure (60 F at 14.7 psia). The term includes petroleum-
based substances comprised of a complex blend of hydrocarbons derived from
crude oil through the process of separation, conversion, upgrading, and finishing,
such as motor fuels, jet oils, lubricants, petroleum solvents, and used oils.
pH: A measure of the acidity of a solution. pH is equal to the negative logarithm
of the concentration of hydrogen ions in a solution. A pH of 7 is neutral. Values
less than 7 are acidic, and values greater than 7 are basic.
piezocone: A type of CPT cone that incorporates a pressure transducer to
measure hydrostatic pressure.
piezometer: A nonpumping well, generally of small diameter, which is used to
measure the elevation of the water table or potentiometric surface. A piezometer
generally has a short well screen; the water level within the casing is considered to
be representative of the potentiometric surface at that particular depth in the
aquifer.
piezometric head: Hydrostatic pressure in an aquifer, relative to a common
datum, such as mean sea level. The piezometric head in an unconfined aquifer is
the water table. The piezometric head in a confined aquifer occurs above the top
of the aquifer.
piezometer nest: A set of two or more piezometers set in close proximity to one
another but screened at different depths. This allows for determination of vertical
flow gradients or differences in water chemistry with depth.
Glossary-12 March 1997
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piezometric surface: An outdated term for "potentiometric surface."
piston sampler: Sealed soil sampling tool that uses an internal piston to seal the
tool while it is pushed or driven to the target zone. Once the sampling zone has
been reached, the internal piston is unlocked, and the tool is driven to fill the
sample barrel. The tool is removed from the ground to retrieve the sample.
poly aromatic hydrocarbon: Aromatic hydrocarbons containing more than one
fused benzene ring. Polyaromatic hydrocarbons are commonly designated PAH.
polynuclear aromatic hydrocarbon: Synonymous with polyaromatic
hydrocarbon. Designated PNA.
porosity: The volume fraction of a rock or unconsolidated sediment not occupied
by solid material but usually occupied by liquids, vapor, and/or air.
potentiometric surface: The surface to which water in an aquifer will rise by
hydrostatic pressure.
pressure gradient: A pressure differential in a given medium (e.g., water, air)
which tends to induce movement from areas of higher pressure to areas of lower
pressure.
probe hole: Synonym for DP hole (the hole resulting from advancement of DP
tools).
protocol: Describes the exact procedures to be followed with respect to sample
receipt and handling, analytical methods, data reporting and deliverables, and
document control.
purge and trap (device): Analytical technique (device) used to isolate volatile
(purgeable) organics by stripping the compounds from water or soil with a stream
of inert gas, trapping the compounds on an adsorbent such as a porous polymer
trap, and thermally desorbing the trapped compounds into the gas
chromatographic column.
purging: Removing stagnant air or water from sampling zone or sampling
equipment prior to collecting the sample.
quality assurance: Documentation designed to assure that proper sampling
and/or analysis protocol are being followed.
quality control: The implementation of protocols designed to assure that the
final sampling or analytical results are reliable.
March 1997 Glossary-13
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re-entry grouting: A grouting method that requires re-entering the probe hole
with special DP rods or tremie pipe for grouting. In some circumstances, the DP
rods used for grouting may not go down the same hole as the hole created by the
DP sampling tool. Generally inferior to retraction grouting.
retainers: Plastic or steel retaining caps that prevent soil cores from falling out of
sample barrel when they are withdrawn from the ground. Also referred to as "soil
catchers."
retention time: In chromatography, the time between when a sample is injected
and the time the chromatographic peak is recorded.
retractable tip: A steel tip that is connected to the DP rods so that it can be
detached at a designated depth while still being removed when the DP rods are
withdrawn. The tip is connected to the tip holder with a small-diameter steel rod.
rotary drilling: A conventional drilling method that uses water- or air-based
fluids to cool the drill bit and remove drill cuttings from the borehole.
rotohammers: A hand-held, high-frequency impact hammer used to advance
small-diameter DP rods.
sample: A portion of material to be analyzed that is contained in single or
multiple containers.
saprolite: A soft, earthy, clay-rich, thoroughly decomposed rock formed in place
by chemical weathering of igneous or metamorphic rocks. Forms in humid,
tropical, or subtropical climates.
saturated zone: The zone in which all the voids in the rock or soil are filled with
water at a pressure that is greater than atmospheric. The water table is the top of
the saturated zone in an unconfined aquifer.
sealed DP tools: Soil, groundwater, and soil-gas sampling tools that are sealed
while they are pushed to the target depth.
seismic reflection: A method of determining subsurface conditions by creating
acoustic waves and measuring the travel time as they reflect off of materials of
different composition.
seismic refraction: A method of determining subsurface conditions by creating
acoustic waves and measuring their travel times to the surface as they interface
with two materials having different acoustic velocities.
Glossary-14 March 1997
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semiquantitative: Numeric values which only approximate the true
concentration of the analytes. Provides an order of magnitude of concentrations
(e.g., 10s, 100s, 1000s).
semivolatile organic compounds: A general term for organic compounds that
volatilize relatively slowly at standard temperature (20" C) and pressure (1 atm).
shoe: See "drive shoe."
short circuiting: As it applies to soil gas surveys, the entry of ambient air into
the extraction well without first passing through the contaminated zone. Short
circuiting may occur through utility trenches, incoherent well or surface seals, or
layers of high permeability geologic materials.
single-rod DP system: A DP rod system that uses a single sequence of rods to
advance the sampling tool or sensor.
Site Characterization and Analysis Penetrometer System: Also referred to as
"SCAPS," it is an in situ sensor that uses laser-induced fluorescence to determine
the relative amounts of polyaromatic hydrocarbons in the subsurface. The sensor
is mounted in the cone of CPT equipment. Developed by the U.S. military.
slam bar: A hand-held weight used to pound DP rods into the ground.
Originally designed for steel fence posts.
slough: Soil that falls into a probe hole after a sampling tool or in situ sensor has
been withdrawn.
soil catchers: Flexible attachments on the bottom of soil sampling tools that
allow soil to enter the sampler but inhibit soil from falling out while the sampler
is being retrieved. Also referred to as "soil retainers."
soil moisture: The water contained in the pore spaces in the unsaturated zone.
solubility: The amount of mass of a compound that will dissolve in a unit volume
of solution.
sorption: A general term used to encompass the processes of absorption,
adsorption, ion exchange, and chemisorption.
sounding: A general term indicating the recording of vertical measurements.
Commonly used to describe vertical measurements collected with geophysical
methods and cone penetrometer testing.
March 1997 Glossary-15
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source area(s): The location(s) of liquid hydrocarbons or the zone(s) of highest
soil or groundwater concentrations, or both, of the chemical(s) of concern.
sparge or sparging: Injection of air below the water table to strip dissolved
volatile organic compounds and/or oxygenate the groundwater to facilitate aerobic
biodegradation of organic compounds.
specific gravity: The dimensionless ratio of the density of a substance with
respect to the density of water. The specific gravity of water is equal to 1.0 by
definition. Most petroleum products have a specific gravity less than 1.0,
generally between 0.6 and 0.9. As such, they will float on water—these are also
referred to as LNAPLs, or light non-aqueous phase liquids. Substances with a
specific gravity greater than 1.0 will sink through water—these are referred to as
DNAPLs, or dense non-aqueous phase liquids.
split-barrel sampler: A nonsealed soil sampling tool that is split longitudinally.
The split barrel allows easy removal of soil cores. Some split-barrel samplers can
hold stainless steel liners, which facilitate preservation of samples for chemical
analysis (the steel liners minimize the loss of volatile organic compounds). Also
known as a split-spoon sampler.
standard analysis: An analytical determination made with known quantities of
target compounds; used to determine response factors.
stratification: Layering or bedding of geologic materials (e.g., rock, sediments).
stratigraphy: The formation, composition, and sequence of sediments, whether
consolidated or unconsolidated.
(K)
Tedlar bags: Gas-tight bags constructed of non-reactive material (Tedlar) for
the collection and transport of gas/vapor samples.
thin-walled tube samplers: A thin-walled non-sealed soil sampling tool used to
collect undisturbed soil samples. Used in unconsolidated fine sands, silt, and
clay. Larger diameter thin-walled tube samplers are referred to as Shelby tubes.
total petroleum hydrocarbons (TPH): A measure of the concentration or mass
of petroleum hydrocarbon constituents present in a given amount of soil or water.
The term "total" is a misnomer—few, if any, of the procedures for quantifying
hydrocarbons are capable of measuring all fractions of petroleum hydrocarbons
present in the sample. Volatile hydrocarbons are usually lost in the process and
not quantified, and some non-petroleum hydrocarbons are sometimes included in
the analysis.
Glossary-16 March 1997
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total recoverable petroleum hydrocarbons (TRPH): A U.S. EPA method
(418.1) for measuring petroleum hydrocarbons in samples of soil or water.
Hydrocarbons are extracted from the sample using a chlorofluorocarbon solvent
(typically Freon- 113) and quantified by infrared spectrophotometry. The method
specifies that the extract be passed through silica gel to remove the non-petroleum
fraction of the hydrocarbons. The comparable SW-846 method is 8440 which
uses perchlorethane (PCE) as an IR solvent instead of Freon-113.
tremie pipe: A flexible or rigid pipe used to convey grout to the bottom of a
boring or probe hole.
ultraviolet radiation: Electromagnetic radiation with wave lengths less than
visible light but greater than x-rays.
unconfined aquifer: An aquifer in which there are no confining beds between
the capillary fringe and land surface, and where the top of the saturated zone (the
water table) is at atmospheric pressure.
unsaturated zone: The zone between land surface and the capillary fringe within
which the moisture content is less than saturation and pressure is less than
atmospheric. Soil pore spaces also typically contain air or other gases. The
capillary fringe is not included in the unsaturated zone.
upgradient: It the direction of increasing static (potentiometric) head.
upper detection limit: The largest concentration that an instrument can reliably
detect.
vadose zone: The zone between land surface and the water table within which the
moisture content is less than saturation (except in the capillary fringe) and
pressure is less than atmospheric. Soil pore spaces also typically contain air or
other gases. The capillary fringe is included in the vadose zone.
vapor pressure: The force per unit area exerted by a vapor in an equilibrium
state with its pure solid, liquid, or solution at a given temperature. Vapor pressure
is a measure of a substance's propensity to evaporate. Vapor pressure increases
exponentially with an increase in temperature.
vibratory head: An assembly made of hydraulically operated vibrators that
clamp onto DP rods. High-frequency vibration helps advance DP rods in fine-
grained soil. Usually accompanied by simultaneously applying pressure to the DP
rods.
March 1997 Glossary-17
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volatile organic compounds: A general term for organic compounds capable of
a high degree of vaporization at standard temperature (20" C) and pressure
(1 atm).
volatilization: The process of transfer of a chemical from the aqueous or liquid
phase to the gas phase. Solubility, molecular weight, and vapor pressure of the
liquid and the nature of the gas-liquid interface affect the rate of volatilization.
water table: The water surface in an unconfined aquifer at which the fluid
pressure in the pore spaces is at atmospheric pressure (the phreatic surface).
weathering: The process during which a complex compound is reduced to its
simpler component parts, transported via physical processes, or biodegraded over
time.
zero air: Atmospheric air that has been purified to contains less than 0.1 ppm
total hydrocarbons.
GIOSS3rV-18 'U.S. Government Printing Office: 1997-517-912/83631 M^fph 1 QQ7
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