OSWER Directive 9360.4-16
EPA xxx/x-xx/xxx
PBxx-xxxxxx
December 1995
SUPERFUND PROGRAM
REPRESENTATIVE SAMPLING GUIDANCE
VOLUME 5: WATER AND SEDIMENT
PART II-- Ground Water
Interim Final
Environmental Response Team
Office of Emergency and Remedial Response
Office of Solid Waste and Emergency Response
U.S. Environmental Protection Agency
Washington, DC 20460
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Notice
This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved
for publication.
The policies and procedures established in this document are intended solely for the guidance of government
personnel for use in the Superfund Program. They are not intended, and cannot be relied upon, to create any rights,
substantive or procedural, enforceable by any party in litigation with the United States. The Agency reserves the right
to act at variance with these policies and procedures and to change them at any time without public notice.
For more information on Ground-Water Sampling procedures, refer to the U.S. EPA Compendium ofERT Ground-
Water Sampling Procedures, OSWER Directive 9360.4-06. Topics covered in this compendium include: sampling
equipment decontamination; ground-water monitoring well installation, development, and sampling; soil gas
sampling; water level measurement; controlled pump testing; slug testing.
Please note that the procedures in this document should be used only by individuals properly trained and certified
under a 40-hour hazardous waste site training course that meets the requirements set forth in 29 CFR 1910.120(e)(3).
This document should not be used to replace or supersede any information obtained in a 40-hour hazardous waste site
training course.
Questions, comments, and recommendations are welcomed regarding the Superfund Program Representative
Sampling Guidance, Volume 5 Water and Sediment, Part II Ground Water. Send remarks to:
Mr. William A. Coakley
Chairman, Representative Sampling Committee
U.S. EPA-ERT
Rantan Depot - Building 18, MS-101
2890 Woodbridge Avenue
Edison, NJ 08837-3679
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Disclaimer
This document has been reviewed under U.S. Environmental Protection Agency policy and approved for publication.
Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
The following trade names are mentioned in this document:
Teflonฎ is a registered trademark of E.I. DuPont de Nemours and Company of Wilmington, Delaware
Geoprobeฎ is a registered trademark of Geoprobe, Inc. of Salina, Kansas
Gilianฎ is a registered trademark of Gilian Instrument Corporation of Wayne, New Jersey
in
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Contents
Notice ii
Disclaimer iii
List of Figures vii
List of Tables vii
1.0 INTRODUCTION 1
1.1 OBJECTIVE AND SCOPE 1
1.2 UNIQUE CHARACTERISTICS OF GROUND WATER 1
1.3 REPRESENTATIVE SAMPLING 2
1.4 REPRESENTATIVE SAMPLING OBJECTIVES 2
1.4.1 Identify Contamination and Determine Hazard 2
1.4.2 Establish Imminent or Substantial Threat 2
1.4.3 Determine Long-Term Threat 3
1.4.4 Develop Containment and Control Strategies 3
1.4.5 Evaluate Treatment Options 3
1.5 CONCEPTUAL SITE MODEL 3
1.6 OVERVIEW OF GROUND-WATER MONITORING WELL INSTALLATION AND
GROUND-WATER MODELING 5
1.6.1 Ground-Water Monitoring Well Installation 5
1.6.2 Ground-Water Modeling 6
1.7 EXAMPLE SITE 6
2.0 GROUND-WATER SAMPLING DESIGN 7
2.1 INTRODUCTION 7
2.1.1 Pre-Sampling Plan Investigation 7
2.1.2 Types of Information Provided by Ground-Water Sampling Assessment 8
2.1.3 Site Reconnaissance 9
2.2 PARAMETERS OF CONCERN, DATA QUALITY OBJECTIVES, AND QUALITY
ASSURANCE MEASURES 10
2.2.1 Parameters of Concern 10
2.2.2 Data Quality Objectives 10
2.2.3 Quality Assurance Measures 11
2.3 REPRESENTATIVE GROUND-WATER SAMPLING APPROACHES
AND SAMPLE TYPES 11
2.3.1 Judgmental Sampling 11
2.3.2 Random, Systematic Grid, and Systematic Random Sampling 12
2.3.3 Grab versus Composite Sample Types 12
2.4 SAMPLING PLAN 12
2.5 EXAMPLE SITE 13
2.5.1 Background 13
2.5.2 Site History and Reconnaissance 15
2.5.3 Identification of Parameters of Concern 15
2.5.4 Sampling Objectives 16
2.5.5 Selection of Sampling Approaches 16
2.5.6 Sampling Plan 16
IV
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3.0 FIELD ANALYTICAL SCREENING, SAMPLING EQUIPMENT, AND GEOPHYSICAL
TECHNIQUES 18
3.1 FIELD ANALYTICAL SCREENING 18
3.1.1 Flame lonization Detector 18
3.1.2 Photoionization Detector 18
3.1.3 Gas Chromatograph 19
3.1.4 Geoprobe 19
3.1.5 Soil Gas Technique 19
3.1.6 Field Parameter Instruments 19
3.1.7 X-Ray Fluorescence 19
3.2 GROUND-WATER SAMPLING EQUIPMENT 20
3.2.1 Bailer 20
3.2.2 Hydraulic Probe 20
3.2.3 Air-Lift Pump 20
3.2.4 Bladder Pump 20
3.2.5 Rotary Pump 21
3.2.6 Peristaltic Pump 21
3.2.7 Packer Pump 21
3.2.8 Syringe Sampler 21
3.2.9 Ground-Water Sampling Equipment Selection Factors 21
3.3 GEOPHYSICAL METHODS 22
3.3.1 Surface Geophysics 22
..
Borehole Geophysics ................................................ 23
3.3.3 Geophysical Techniques for Ground- Water Investigations .................... 25
3.4 EXAMPLE SITE [[[ 26
3.4.1 Selection of Field Analytical Screening Techniques ......................... 26
3.4.2 Selection of Sampling Equipment ...................................... 26
3.4.3 Selection of Geophysical Methods ...................................... 26
4.0 GROUND-WATER SAMPLE COLLECTION AND PREPARATION ....................... 31
4.1 INTRODUCTION [[[ 31
4.2 STATIC WATER LEVEL [[[ 31
4.3 WELL PURGING [[[ 31
4.3.1 Stabilization Purging Techniques ....................................... 32
4.3.2 Wells that Purge Dry ................................................ 32
4.4 GROUND-WATER SAMPLE COLLECTION ................................... 32
4.5 GROUND-WATER SAMPLE PREPARATION .................................. 33
4.5.1 Filtering [[[ 34
4.5.2 Homogenizing/Aliquotting ............................................ 34
4.5.3 Splitting [[[ 34
4.5.4 Final Preparation [[[ 34
4.6 EXAMPLE SITE [[[ 34
4.6. 1 Sample Collection .................................................. 34
4.6.2 Sample Preparation ................................................. 37
5.0 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC) ............................... 38
5. 1 INTRODUCTION [[[ 38
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5.4 QA/QC SAMPLES 39
5.4.1 Field Replicate Samples 39
5.4.2 Background Samples 39
5.4.3 Rinsate Blank Samples 40
5.4.4 Field Blank Samples 40
5.4.5 Trip Blank Samples 40
5.4.6 Performance Evaluation/Laboratory Control Samples 40
5.4.7 Matrix Spike/Matrix Spike Duplicate Samples 40
5.4.8 Laboratory Duplicate Samples 41
5.5 EVALUATION OF ANALYTICAL ERROR 41
5.6 CORRELATION BETWEEN FIELD SCREENING RESULTS AND DEFINITIVE
LABORATORY RESULTS 41
5.7 EXAMPLE SITE 42
5.7.1 Data Categories 42
5.7.2 Sources of Error 42
5.7.3 Field QA/QC Samples 42
5.7.4 Laboratory QA/QC 42
6.0 DATA PRESENTATION AND ANALYSIS 43
6.1 INTRODUCTION 43
6.2 DATA POSTING 43
6.3 CROSS-SECTION/FENCE DIAGRAMS 43
6.4 CONTOUR MAPPING 43
6.5 WELL LOCATION MAP 43
6.6 STATISTICAL GRAPHICS 43
6.7 RECOMMENDED DATA INTERPRETATION METHODS 44
6.8 EXAMPLE SITE 44
Appendix A EXAMPLE OF FLOW DIAGRAM FOR CONCEPTUAL SITE MODEL 45
References 48
VI
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List of Figures
1 Conceptual Site Model 4
2 Site Sketch: ABC Plating Site 14
3 Soil Boring/Monitoring Well Completion Log 36
A-l Migration Routes of a Gas Contaminant 45
A-2 Migration Routes of a Liquid Contaminant 46
A-3 Migration Routes of a Solid Contaminant 47
List of Tables
1 Applicability of Surface Geophysical Techniques to Ground-Water Investigations 27
2 Advantages and Disadvantages of Surface Geophysical Techniques to Ground-Water Investigations . 28
3 Applicability of Borehole Geophysical Techniques to Ground-Water Investigations 29
4 Advantages and Disadvantages of Borehole Geophysical Techniques to Ground-Water Investigations 30
vn
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1.0 INTRODUCTION
1.1 OBJECTIVE AND SCOPE
This is Part II of the fifth volume in a series of
guidance documents that assist Superfund Program
Site Managers, On-Scene Coordinators (OSCs),
Remedial Project Managers (RPMs), and other field
staff in obtaining representative samples at Superfund
sites. The objective of representative sampling is to
ensure that a sample or a group of samples accurately
characterizes site conditions.
Most hazardous waste site investigations utilize some
form of a ground-water sampling or monitoring
program to fully characterize the nature and extent of
contamination. Because site conditions may differ,
experienced hydrogeologists and geochemists should
be consulted to establish the most suitable types of
sampling and monitoring for each site.
The purpose of this document is to address
representative ground-water sampling. Ground-water
modeling and monitoring well installation are briefly
introduced but are not addressed in detail in this
document. References on these topics are provided in
Section 1.6
The representative ground-water sampling principles
discussed in this document are applicable throughout
the Superfund Program. The following chapters will
help field personnel to assess available information,
select an appropriate sampling approach and design,
select and utilize field analytical/geophysical
screening methods and sampling equipment,
incorporate suitable types and numbers of quality
assurance/quality control (QA/QC) samples, and
interpret and present the site analytical data.
As the Superfund Program has developed, the
emphasis of the response action has expanded beyond
addressing emergency response and short-term
cleanups. Each planned response action must
consider a variety of sampling objectives, including
identifying threat, delineating sources of
contamination, and confirming the achievement of
clean-up standards. Because many important and
potentially costly decisions are based on the sampling
data, Site Managers and other field personnel must
characterize site conditions accurately. To that end,
this document emphasizes the use of cost-effective
field analytical and geophysical screening techniques
to characterize the site and aid in the selection of
sampling locations.
1.2 UNIQUE CHARACTERISTICS
OF GROUND WATER
The following are media-specific variables of ground
water that should be considered when performing
representative ground-water sampling:
Homogeneity - Ground water, as a medium, is
usually homogeneous, especially when compared
to other media such as soil, air, or waste.
Seasonal and Localized Variation in Flow -
Seasonal and localized variations in ground-water
flow should be considered when developing a
ground-water assessment program. Seasonal
variations are generally controlled by weather.
Surface streams gain or lose water to the
subsurface when flood or drought conditions are
present. Localized variations in flow are caused
by nearby, outside influences, as when a
production well creates a cone of depression in
the water table.
Inaccessibility for Investigation - Ground water
is often inaccessible to standard grab sampling
techniques. Because ground water is subsurface,
wells must often be drilled and completed for
sampling if no existing wells are available.
Sampling ground water is generally more
complicated, labor-intensive, time-consuming,
and expensive than sampling other media.
Natural Background Composition - Knowledge of
the natural background composition is necessary
in order to determine the effects of a site on the
ground water. Background or control monitoring
wells are necessary to determine ambient
composition.
Water Treatment - Ground-water samples are
often extracted from existing residential or
commercial wells that have been treated with
softeners or have been filtered or altered in other
ways. Sampling (times, parameters, methods,
preservatives, etc.) may have to be altered in
order to compensate for or avoid treatment
variables.
Reproducibility of Sampling Results - Ground
water is a flowing water body below the earth's
surface. Physical and chemical characteristics
may vary over time and space because of the
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factors listed above (e.g., seasonal variation).
Contaminants tend to flow through ground water
in a plume or plug of varying concentration;
contamination sources may discharge in pulses or
as a continuous flow; and contaminants may react
with ground water to chemically transform over
time. Because of this flowing nature,
contaminant or natural constituent concentrations
can vary. This variation could affect duplicating
sample results over an extended time period.
Contaminants will most often continue to be
detected in ground water, but sample
concentration ranges may be altered, either by an
increase or a decrease, or contaminant by-
products may be detected.
1.3 REPRESENTATIVE SAMPLING
Representative ground-water sampling ensures that a
sample or group of samples accurately reflects the
concentration of the contaminant(s) of concern at a
given time and location. Analytical results from
representative samples reflect the variation in
pollutant presence and concentration throughout a site.
In addition to the variables introduced due to the
characteristics of the sample media (as discussed in
Section 1.2), this document concentrates on those that
are introduced in the field. These latter variables
relate to site-specific conditions, the sampling design
approach, and the techniques for collection and
preparation of samples. The following variables
affect the representativeness of samples and
subsequent measurements:
Media variability - The physical and chemical
characteristics of ground water.
Contaminant concentration variability
Variations in the contaminant concentrations
throughout the site and/or variables affecting the
release of site contaminants into ground water on
or away from the site.
Collection and preparation variability
Deviations in analytical results attributable to bias
introduced during sample collection, preparation,
and transportation (for analysis).
Analytical variability - Deviations in analytical
results attributable to the manner in which the
sample was stored, prepared, and analyzed by the
on-site or off-site laboratory. Although analytical
variability cannot be corrected through
representative sampling, it can lead to the false
conclusion that error is due to sample collection
and handling procedures.
1.4 REPRESENTATIVE SAMPLING
OBJECTIVES
Representative sampling objectives for ground water
include the following:
Identify the presence of contamination, including
source, composition, and characteristics.
Determine if it is hazardous.
Establish the existence of an imminent or
substantial threat to public health or welfare or to
the environment.
Establish the existence of potential threat
requiring long-term actions.
Develop containment and control strategies.
Evaluate treatment options.
Note: Clean-up goals are generally established for
ground water and are not considered a sampling
objective.
1.4.1 Identify Contamination and
Determine Hazard
One of the first objectives during a response action at
a site is to determine the presence, identity, and
potential threat of any hazardous materials. Field
screening techniques can be used for rapid detection
of contaminants. Upon confirming the presence of
hazardous materials, sample and/or continue screening
to identify their compositions and determine their
concentrations.
1.4.2 Establish Imminent or
Substantial Threat
Establishing threat to the public or environment is a
primary objective during any response action. The
data obtained from characterizing the contaminants
will help the Site Manager to determine whether an
imminent or substantial threat exists and whether a
response action is necessary. The type and degree of
threat determines the rate at which a response action
is taken.
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1.4.3 Determine Long-Term Threat
Site conditions may support a long-term threat that is
not imminent or substantial. Characterization of the
contaminants can assist the Site Manager to determine
the need for long-term remediation and response.
Samples should be collected in a manner that enables
their use for evaluating the site under the Hazard
Ranking System.
1.4.4 Develop Containment and
Control Strategies
Once the chemical constituents and threat have been
determined, many strategies for ground-water
containment and control are available. Analytical data
indicating the presence of chemical hazards are not in
themselves sufficient to select a containment or
control strategy. Site reconnaissance and historical
site research provide information on site conditions
and the physical state of the contaminant sources;
containment and control strategies are largely
determined by this information. For example,
trenching and pump and treat systems can prevent
spread of contamination in an aquifer.
1.4.5 Evaluate Treatment Options
The contaminants should be identified, quantified, and
compared to action levels (e.g., maximum
contaminant levels (MCLs) for drinking water).
Where regulatory action levels do not exist, site-
specific clean-up levels are determined by the Region
(often in consultation with the Agency for Toxic
Substances and Disease Registry (ATSDR)) or by
State identification of Applicable or Relevant and
Appropriate Requirements (ARARs). If action levels
are exceeded, a series of chemical and physical tests
may be required to evaluate possible treatment
options.
1.5 CONCEPTUAL SITE MODEL
A conceptual site model is a useful tool for selecting
sampling locations. It helps ensure that sources,
migration pathways, and receptors throughout the site
have been considered before sampling locations are
chosen. The conceptual model assists the Site
Manager in evaluating the interaction of different site
features. Risk assessors use conceptual models to
help plan for risk assessment activities. Frequently, a
conceptual model is created as a site map (see Figure
1) or it may be developed as a flow diagram which
describes potential migration of contaminants to site
receptors (See Appendix A).
A conceptual site model follows contaminants from
their sources, through migration pathways (e.g., air,
ground water), and eventually to the assessment
endpoints. Consider the following when creating a
conceptual site model:
The state(s) of each contaminant and its potential
mobility
Site topographic features
Meteorological conditions (e.g., wind
direction/speed, average precipitation,
temperature, humidity)
Human/wildlife activities on or near the site
The conceptual site model in Figure 1 is an example
created for this document. The model assists in
identifying the following site characteristics:
Potential Sources: Site (waste pile, lagoon);
drum dump; agricultural activities.
Potential Migration Pathway (Ground Water):
Leachate from the waste pile, lagoon, drum
dump, or agricultural activities.
Potential Migration Routes: Ingestion or direct
contact with water from the aquifer (e.g.,
ingestion of drinking water, direct contact when
showering).
Potential Receptors of Concern:
Human Population (Residents/Workers):
Ingestion or direct contact with contaminated
water from the aquifer.
Preliminary site information may provide the
identification of the contaminant(s) of concern and the
level(s) of the contamination. Develop a sampling
plan based upon the receptors of concern and the
suspected sources and pathways. The model may
assist in the selection of on-site and off-site sampling
locations.
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FIGURE 1:
CONCEPTUAL
SITE MODEL
PRECIPITATION
DUST &
PARTICULATES
STATE GAME
LANDS
> iv/vsre
PRECIPITATION
GRAZING
LAND
DUST&
PARTICULATES
^
^jr/
DUST&
PARTICULATES
WATER PLANT
INTAKE
PESTICIDE
r^r;-ri
DRUM DUMP
SEWAGE PLANT
OUTFALL
RESIDENTIAL
WELLS
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1.6 OVERVIEW OF GROUND-
WATER MONITORING WELL
INSTALLATION AND
GROUND-WATER MODELING
Ground-water monitoring well installation and
ground-water modeling are complex issues which fall
outside the scope of this document. Many standard
operating procedures (SOPs) covering ground-water
monitoring well installation techniques have been
published. Monitoring well installation and ground-
water modeling are briefly introduced here with
several specific items for consideration. Refer to
existing SOPs and other reference documents for more
in-depth study.
1.6.1 Ground-Water Monitoring Well
Installation
For most Superfund response actions where ground-
water sampling is performed, existing ground-water
production wells (commercial or residential) are used,
if available, to obtain samples. Chemical data
obtained from this type of well depict the general
quality of water that is being delivered to the user
community. Ground water is usually a composite of
multiple aquifer strata which may mask the presence
of narrow or small contaminant plumes from a single
stratum. For this reason, production wells are not
suitable for detailed source, case-preparation, or
research types of monitoring. Such detailed
monitoring efforts require wells designed to determine
the geologic and hydrologic quality at specific
locations and depths. The following items must be
considered for ground-water sampling from
monitoring wells:
Drilling method
Monitoring well components
Monitoring well location
Well diameter
Well depth
Well screen location
Refer to the U.S. EPA A Compendium of Superfund
Field Operations Methods, OSWER
Directive 9355.0-14; Compendium of ERT
Ground-water Sampling Procedures, OSWER
Directive 9360.4-06; RCRA Ground-Water
Monitoring Technical Enforcement Guidance
Document, OSWER Directive 9950.1; and RCRA
Ground-Water Monitoring: Draft Technical
Guidance, EPA/530-R-93-001, for specific details on
monitoring well installation. The latter two
documents should be referenced for information on
locating, installing, and developing monitoring wells.
Locating Monitoring Wells
Often, one well is sited near the center of the
contaminant plume just downgradient from the
contamination source. Another well is installed
downgradient of the contaminant source, outside the
limits of the plume. For background data, one well
may be placed outside of the contaminant plume,
upgradient of the contaminant source. Additional
wells may be installed to track the amount of
contaminant dispersion taking place.
Determining the depth to sample is critical for
successful ground-water monitoring. Sampling depth
depends on the contaminant density, the aquifer
characteristics, and the slope of the water table or
potentiometric surface. The number of wells
necessary to monitor ground water varies depending
on many factors. For example, if an impoundment
contamination source is higher than the surrounding
landscape, leachate may flow locally in all four
downgradient directions. In this case, at least four
wells are needed to monitor plume movement, plus a
background well may be desired in an unaffected area.
In addition, some wells may be installed at more than
one depth in a contaminant plume to verify vertical
flow or spread of contamination at different depths.
See Driscoll, 1986, pp. 715-16 for more information
on locating monitoring wells.
Well Casing and Well Screen
Select a well casing material based on water quality,
well depth, cost, borehole diameter, drilling
procedure, and Federal, state, and local regulations.
Types of casing materials include: steel, poly vinyl
chloride (PVC), fiberglass, and Teflonฎ. Common
well casing diameters range from 2 inches to 12
inches or greater, and depend on well type, well size,
well depth, and subsurface geology. Often a series of
progressively smaller-diameter well casings are used
from the ground surface to the well depth.
A well screen is a filtering device which permits
water to enter the well from the saturated aquifer
while preventing sediment from entering the well. A
well screen has slots or perforations and attaches to
the well casing. It can be constructed of metal,
plastic, or other material. Important criteria for
selecting a well screen include: a large percentage of
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open area, nonclogging slots, resistance to corrosion,
and a sufficient column and collapse strength.
SeeDriscoll, 1986, pp. 413-431, and Fetter, 1993, pp.
339-344 for more information regarding well casing.
See Driscoll, 1986, pp. 395-405, and Fetter, 1993, pp.
345-346 for more information regarding well screens.
See U.S. EPA, November 1992, pp. 6-16 - 6-38 for
advantages and disadvantages of selecting well casing
and screen materials.
1.6.2 Ground-Water Modeling
Ground-water models, like conceptual site models,
can be useful when selecting sampling approaches,
objectives, and locations. Ground-water models
developed for Superfund sites attempt to provide an
estimation of how the actual ground-water system
functions.
There are many types of ground-water models
available (e.g., physical, analog, mathematical). The
International Ground-Water Modeling Center
(IGWMC) has developed a ground-water model
definition which emphasizes the importance of
describing a ground-water system mathematically.
The IGWMC defines a ground-water model as " a non-
unique, simplified, mathematical description of an
existing ground-water system, coded in a
programming language, together with a quantification
of the ground-water system the code simulates in the
form of boundary conditions, system parameters, and
system stresses."
A ground-water model may be useful throughout site
investigation activities because it can be adjusted as
conditions in the actual ground-water system become
better defined. The data which are generated by the
model can be used to refine sampling approaches and
locations as necessary. Typically, a ground-water
modeling report will include data (results), along with
a discussion of activities such as model calibration
and conceptual model development. A suggested
format for a ground-water modeling report can be
found in U.S. EPA Ground-Water Issue:
Fundamentals of Ground-Water Modeling
(EPA/540/S-92/005).
1.7 EXAMPLE SITE
An example site, presented at the end of each chapter,
illustrates the development of a representative ground-
water sampling plan that meets Superfund Program
objectives for early actions or emergency responses.
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2.0 GROUND-WATER SAMPLING DESIGN
2.1 INTRODUCTION
The purpose of ground-water sampling is to provide
technical information relative to the nature and
condition of subsurface water resources at a specific
time and place. Designs to monitor the status of
ground water range from the studies of naturally
occurring geochemical constituents to the detection or
assessment of contamination within a ground-water
system.
Ground-water sampling objectives include identifying
threats, delineating sources and extent of
contamination, determining treatment and disposal
options, and confirming the attainment of targeted
clean-up levels. Representative sampling designs are
developed to most accurately characterize the
hydrogeologic system and its interaction with the
environment. Sampling protocols must integrate
detailed sampling methodology, techniques and
practices to ensure valid assessment. Sampling
methodology and practice may be the most common
source of assessment error. Consequently, sampling
methodology and practice collectively demand careful
preparation, execution, and evaluation to accurately
characterize the hydrogeologic system or its
subsystems. (For additional information see: U.S.
EPA Ground Water, Volume II: Methodology,
EPA/625/6-90/016b; and Palmer, Christopher M,
Principles of Contaminant Hydrogeology.)
There are many methods and types of equipment
useful for site characterization and sample collection.
Selection of these factors is a critical component of a
site-specific sampling design.
A properly developed ground-water sampling design
defines the sampling purpose, protects site worker
health and safety, effectively utilizes resources, and
minimizes errors. The sampling design will vary
according to the characteristics of the site. When
developing a sampling design, consider:
Prior actions at the site (e.g., sampling events,
compliance inspections)
Regional ground-water properties and
characteristics
Potential on-site waste sources (e.g.,
impoundments, waste piles, drums)
Topographic, geologic, hydrologic, and
meteorologic conditions of the site
Flora, fauna, and human populations in the area
2.1.1 Pre-Sampling Plan
Investigation
The pre-sampling plan investigation provides the
planner with information critical to the development
of a sound ground-water sampling design. Integration
of all pertinent facts regarding the site history, the
population(s) affected, and concentrations of
substances on a site must be reviewed. After all of the
pertinent information has been processed and
incorporated into a thorough site pre-evaluation, the
sampling plan can be developed. Considerations for
sampling plan modification should be reviewed as
necessary in light of the complex nature of ground-
water resource dynamics.
Site History
Review of the site's history helps assess the natural
and man-made impacts on a site. Geographic,
geologic, tax, and fire insurance maps can indicate the
status of the site. These maps can usually be found at
local and collegiate libraries or municipal and county
tax offices. Aerial photographs are helpful in
reviewing operational use of the site. Archival aerial
photographs may show changes in operation and site
condition over time. This information can be
correlated with information from potentially
responsible parties.
Hydrogeologic information is critical to developing a
sampling plan. A ground-water system is site
specific, depending upon local geology, land and
subsurface use, precipitation and water use, proximity
to water bodies, and hydrogeologic parameters
affecting contaminant transport. Hydrologic and
hydrogeologic information can be found in libraries or
requested from the U.S. Geological Survey (USGS),
Water Resources Division, or state geological
agencies and their water branches. Inspection
histories can be used to determine prior health status
of the site in view of possible trends. Local, state, and
federal agencies dealing with health or environmental
inspection can provide such historical information
about a site.
Affected Populations
Human population statistics for the selected area can
establish the number of people threatened by the
contaminant exposure. Include populations affected
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by projected migration of contaminants within the
ground-water system. Knowing the interaction of the
contaminant within a ground-water system and the
potential regional populations exposed to the
contaminant will focus the sampling plan to the source
and possible pathways of the contaminant. Wildlife
populations in the area must be studied as well.
Wildlife in ponds, lakes, streams, rivers, and bays is
often affected by contaminants transported by ground
water discharging into surface water. Information
regarding regional wildlife populations and
susceptibility to hazardous substances can be obtained
from federal and state wildlife and conservation
agencies.
Detection Levels versus Maximum
Contaminant Levels
Sampling plan development must also address the
concentration level of the contaminant within the
ground-water system in relation to the maximum
contaminant levels (MCLs) allowed within a public
water system. Refer to the Federal Register for the
levels requiring enforceable action. Knowledge of the
chemical contaminant interaction within the ground-
water system can add insight into the fate of the
contaminant (soluble or insoluble in water; less or
more dense than water; the nature of reactivity with
sediment or geology of the subsurface). Correlate the
concentration level versus the location of these
concentrations. A sequence of order can then be
applied to the locations. Ideally, a pattern may
develop that can be related to the ground-water system
and its dynamics. In the case of a single location,
investigate potential sources in the surrounding area
either by working backwards from an identified
contaminant spot to a potential source, or from a
potential source to an identified contaminant spot.
Also consider source-to-current-location pathways and
projected pathways when developing a sampling plan.
2.1.2 Types of Information
Provided by Ground-Water
Sampling Assessment
There are several types of information that a ground-
water sampling assessment provides. These include
but are not limited to: measure of ground-water
quality, contaminant concentrations compared to
action levels, selection of the appropriate response
action, and determination of ground-water flow and
contaminant plume movement.
Measure of Ground-Water Quality
Ground-water sampling assessments provide
information concerning measure of ground-water
quality of a site or region. Water quality is classified
according to many categories and its intended use.
Drinking water is especially subject to guidelines. A
sampling assessment of ground water can determine
whether the quality of the water has been maintained,
upgraded, or allowed to degrade. The natural and
artificially induced characteristics of ground water
from a specific site or region can be established by
ground-water sampling assessments specifically, the
chemical, biological, and physical characteristics of
the ground water.
Contaminant Concentrations Compared
to Action Levels
Ground-water sampling assessments provide a single
contamination level for a particular sampling location,
or a set of contamination levels for several sampling
locations within a site. Comparison to action levels in
ARARs determines the basis for further action. Thus,
sampling can evaluate potential hazards and represent
a condition of ground-water character requiring
enforceable action procedures.
Selection of Appropriate Response
Action
The level of contaminant concentration as determined
through sampling assessments is a critical factor in
selecting a site response action. Depending upon the
degree or level of contaminant concentration,
contaminant frequency, or number of locations
established as contaminated, and the site's potential
threat to human health or the environment, a rapid or
extensive clean-up program can be formulated, as well
as temporary or short-term responses (e.g., provision
of bottled water).
A sampling assessment may not always indicate
contamination of the site. Careful examination of
sampling protocol must consider the range of
explanations. A miscalculation of suspected source
sites; gross procedure error in sampling, laboratory
analysis, or documentation; or error at many other
points in sampling protocol could be the source of
assessment error. These errors are addressed more
extensively in Chapter 5.
If quality assurance/quality control (QA/QC)
procedures have been followed for ground-water
sampling assessment, then it is possible that sources
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of contamination may originate from above ground
systems (e.g., lead entering tap water in the proximity
of the facility). In any case, a sampling assessment at
the least can characterize the natural ground-water
conditions, which can be used as a control or
comparison.
Determination of Ground- Water Flow and
Contaminant Plume Movement
Knowing the direction of ground-water flow is
important when evaluating a contaminated aquifer.
When contamination enters the ground at a higher
head (gradient) than exists at nearby shallow wells,
these wells may become contaminated. Ground water
flows from higher head to lower head. The direction
of water movement may be determined using water-
elevation data from a minimum of three wells. See
Driscoll, 1986, pp. 79-85 and Freeze and Cherry,
1979, pp. 168-236 for more information regarding
ground-water flow.
Ground-water tracers, such as dye or salt may be used
to track ground-water flow velocities and contaminant
plume movement. A tracer is placed in one well and
the time of its arrival in a second well downgradient
from the first well is noted. The dilution of the tracer
detected in the second well can indicate the
contaminant dilution rate and help determine the
contaminant source concentration as well as the width,
depth, and spreading velocity of the plume. Tracers
also may be used to help determine aquifer porosity,
hydraulic conductivity, and dispersivity.
The tracer selected must be detectable in extremely
low concentrations and must not react chemically or
physically with the ground-water or aquifer
composition. See Driscoll, 1986, pp. 84-85 for more
information regarding ground-water tracers.
2.1.3 Site Reconnaissance
A site reconnaissance can be conducted at an earlier
date or immediately prior to sampling activities. It
allows field personnel to assess actual, current site
conditions, evaluate areas of potential contamination,
evaluate potential hazards associated with sampling,
and finalize a sampling plan. Site reconnaissance
activities for a ground-water assessment include:
observing and photographing the site; noting site
access and potential evacuation routes; noting
potential safety hazards; inventorying and recording
label information from drums, tanks, or other
containers; mapping process and waste disposal areas
such as landfills, impoundments, and effluent pipes;
mapping potential contaminant migration routes such
as drainage, streams, and irrigation ditches; noting the
condition of animals and/or vegetation; noting
topographic and/or structural features; noting and
mapping existing ground-water monitoring or other
types of wells for potential sampling; and siting
potential locations for new monitoring wells if
necessary. Field personnel should use appropriate
personal protective equipment when engaged in any
on-site activities. Consider the following site-specific
factors while performing a site reconnaissance:
Sampling Objectives - Sampling is conducted
typically to comply with regulations for the
detection or assessment of suspected
contamination within the subsurface. The
information gathered aids in the identification of
known and unknown substances present within
the site and the level and extent of contamination
of the environment. The information is used to
document the condition of the ground-water
system as an initial assessment, a record of
development, or as evidence of remediation
efficiency and compliance.
Sample Collection and Toxicity - The samples
collected are intended to document the absence or
measure the presence of contaminants. The
measure of acute or chronic toxicity is evaluated
by assessing the site's extent of contamination,
the time period in relation to the extent, and
health hazards associated with the contaminant
exposure time frame.
Statistical Concerns - A site visit will familiarize
the sampling planner with the environment to be
sampled. Conspicuous indicators of potential
contamination sources or contamination effects
may suggest use of a judgmental or bias sampling
design. A geostatistical sampling method can be
cost-effective and time-efficient when compared
to strictly random or random-stratified
procedures. When using less random methods,
the choice of sampling locations should be
documented and justified. Employ random
sampling in addition to bias sampling and include
background or control samples for a thorough
representation of the ground-water character.
(See Section 2.3 for a discussion of sampling
approaches.) (For additional information see
Keith, Lawrence H., Principles of Environmental
Sampling.)
Timing of the Response - Consider seasonal
variation when evaluating a site. Predictions of
bad weather can influence technique and design.
The urgency of the action weighed against
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seasonal constraints may dictate the options
available within the targeted budget.
Site-Specific Factors Affecting Ground-Water
Flow Many factors of a site control the path or
direction of ground-water flow. A combination of
geologic survey information with the site
reconnaissance can better familiarize the planner
with the dynamics of the hydrogeologic system.
The local geology of a site can determine the
direction and rate of ground-water movement by
means of its orientation and composition (e.g.,
horizontal, tilted or vertical structures, and
confining clay versus unconfining sand and
gravel). The degree of development of a site and
its local topography can affect the ground-water
flow (e.g., parking lot runoff disproportionally
delivers water quantities to the subsurface and
greater slopes afford less infiltration of water to
the subsurface). The extent and type of
vegetation can affect the amount of rainfall that
actually recharges an aquifer system. Dense
vegetation and high evapo-transpiration from
vegetation allows very little water to descend to
the subsurface. Seasonal variations can cause
reversal of ground-water flow direction. This is
usually associated with water bodies such as
streams, rivers, ponds, and lakes. Water may
flow to or from streams depending upon its
surface elevation in relation to adjacent water
table surfaces. During flood conditions, water
usually flows from rivers toward the surrounding
subsurface. During drought, water moves toward
the lower level of the stream surface from higher
ground-water surfaces. (Consult U.S. EPA
Handbook, Ground Water, EPA/625/6-87/016,
Chapter 4: Basic Hydrogeology.)
Analytical Parameters - The site reconnaissance
can help develop the list of analytical parameters.
For example, a reconnaissance may indicate the
presence of battery casings. Lead would then be
a substance of concern. The site may contain
constraints that may or may not allow a variety of
tests to be performed. The cost-effectiveness of
testing within the site's constraints can lead to
limited options available to properly analyze the
ground-water system. Testing methods may vary
within one site (e.g., monitoring well sampling,
hydroprobe extraction, etc.) in order to evaluate
multiple criteria vital to the site assessment.
Degradation for Transformation') Products - Sites
may contain degradation (or transformation)
products, or by-products, of the contaminant that
are detectable and potentially as hazardous as the
contaminant itself. Sampling for the product can
lead to clues of the source substance location and
its reactive status within the subsurface.
Sampling Order - The sampling plan should
address a specific order of sampling locations
(and depths at a single location) to be developed.
In order to use equipment efficiently, the plan
should attempt to sample from "clean" to "dirty"
locations, reducing the potential for contaminants
to affect relatively less contaminated locations.
Typically, the background or "clean" location of
a site is hydrologically upgradient from the
suspected contaminant "hot spot." Depending
upon the nature of the contaminant (e.g., a
"sinker" or "floater"), the sampling at different
depths within a column of water in a monitoring
well should also follow a sequence.
2.2 PARAMETERS OF CONCERN,
DATA QUALITY OBJECTIVES,
AND QUALITY ASSURANCE
MEASURES
2.2.1 Parameters of Concern
Drinking water populations, contaminants, and
migration pathways are additional parameters that
should be considered when developing a sampling
plan. Often, ground-water contamination goes
undetected because it is not directly visible. Drinking
water odor or taste complaints by residents close to
the site are usually the initial indication of ground-
water contamination and potential health hazards.
The sampling data should accurately delineate the
extent of ground-water contamination, determine the
impact on drinking water populations, and indicate
potential migration pathways to such populations. It
is important to design the sampling plan to determine
where contaminants are most highly concentrated, and
to locate areas of decreasing detectable concentrations
and those not yet contaminated.
2.2.2 Data Quality Objectives
Data quality objectives (DQOs) state the level of
uncertainty that is acceptable for data collection
activities and define the certainty of the data necessary
to make decisions. The overall goal of DQOs for a
representative ground-water sampling plan are to
acquire thorough and accurate information about
subsurface water conditions at a site. DQOs are
unique and site specific and should address the
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contaminant's interaction with the immediate site
environment. When establishing DQOs for a
particular project, consider:
Decision(s) to be made or question(s) to be
answered
Why analytical data are needed and how the
results will be used
Time and resource constraints on data collection
Descriptions of the analytical data to be collected
Applicable model or data interpretation method
used to arrive at a conclusion
Detection limits for analytes of concern
Sampling and analytical error
2.2.3 Quality Assurance Measures
To ensure that analytical samples are representative of
site conditions, quality assurance measures must be
associated with each sampling and analysis event.
The sampling plan must specify QA measures, which
include, but are not limited to, sample collection,
laboratory SOPs, sample container preparation,
equipment decontamination, field blanks, replicate
samples, performance evaluation samples, sample
preservation and handling, and chain-of-custody
requirements. Quality assurance components are
defined as follows:
Precision - Measurement of variability in the data
collection process
Accuracy (bias) - Measurement of bias in the
analytical process; the term "bias" throughout this
document refers to (QA/QC) accuracy
measurement
Completeness - Percentage of sampling
measurements which are judged to be valid
Representativeness - Degree to which sample
data accurately and precisely represent the
characteristics and concentrations of the
source/site contaminants
Comparability - Evaluation of the similarity of
conditions (e.g., sample depth, sample
homogeneity) under which separate sets of data
are produced
Refer to Chapter 5, Quality Assurance/Quality Control
(QA/QC), for more detailed ground-water QA/QC
information.
2.3 REPRESENTATIVE GROUND-
WATER SAMPLING
APPROACHES AND SAMPLE
TYPES
Judgmental sampling is the primary representative
sampling approach used for ground water. Other
representative sampling approaches for ground water
such as random, systematic grid, and systematic
random sampling are described below. For
information on the other types of sampling
approaches, refer to U.S. EPA, Superfund Program
Representative Sampling Guidance, Volume 1 Soil,
OSWER Directive 9360.4-10.
2.3.1 Judgmental Sampling
Judgmental sampling is the biased selection of
sampling locations at a site, based on historical
information, visual inspection, sampling objectives,
and professional judgment. A judgmental approach is
best used when knowledge of the suspected
contaminant(s) or its origins is available. Judgmental
sampling includes no randomization in the sampling
strategy, precluding statistical interpretation of the
sampling results. Criteria for selecting sampling
locations are dependent on the particular site and level
of contamination expected.
Once a contaminant has been detected in the ground
water, the source and extent must be identified. To do
this, an understanding of the contaminant
characteristics and the local geologic and
hydrogeologic conditions is needed. Characteristics
of the contaminant and any daughter (degradation)
products must be known in order to understand how
the material may be transported (both vertically and
laterally) from the contamination source. Knowledge
of the local hydrogeology is needed in order to
identify areas or zones that would facilitate
contaminant migration, such as water bodies and
gravelly or sandy soils. The permeability of the
underlying rock type should be analyzed, as well as its
depth, which will help to narrow the potential
sampling area. For example, if the underlying
bedrock strikes northeast to southwest, then sampling
of an aquifer should also be in this direction, unless
cross-contamination between aquifers has already
been identified.
When appropriate (based on sampling objectives,
availability, sampling parameters, and budget), sample
available local residential or commercial wells
following a relatively systematic pattern based on the
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geology of the area. In the example given in the
paragraph above, wells would be sampled along a line
northeast to southwest. If the number of wells
available is not sufficient to adequately identify the
extent of contamination, then additional monitoring
wells could be installed.
During a ground-water assessment, the selection of
locations for monitoring well installation is done with
a judgmental approach. This is generally because
monitoring wells are complex, expensive, and time-
consuming to install. In order to best determine the
nature of a suspected contaminant plume, monitoring
wells need to be placed in areas most likely to
intercept the plume. Using a random, systematic grid
or a systematic random approach would likely result
in too many wells that miss the contaminant plume.
Even placement of background or control monitoring
wells favors a judgmental approach. Locations are
selected based on the site reconnaissance and the
planner's knowledge of the suspected contaminants,
site geology, and hydrology.
2.3.2 Random, Systematic Grid, and
Systematic Random Sampling
Random, systematic grid, and systematic random
sampling are generally not used for ground-water
sampling because sampling points are pre-determined
from either existing wells or monitoring wells which
are placed by judgment. However, these approaches
may be useful for soil gas testing to assist in the siting
of new monitoring wells. They can also be useful for
conducting Geoprobeฎ sampling, if necessary. For
additional information on these sampling approaches,
refer to U.S. EPA, Superfund Program
Representative Sampling Guidance, Volume 1 Soil,
OSWER Directive 9360.4-10.
2.3.3 Grab versus
Sample Types
Composite
Grab samples are essentially the only type of samples
collected for ground water. Unlike surface water,
ground water is not composited. Each ground-water
sample is representative of a discrete location and
horizon in the subsurface.
Site Location - The location of the site will often
influence the size of the sampling area and
whether sampling should be conducted on or off
site or a combination of both.
Local Geology and Hydrology - Local geology
and hydrology can determine whether off-site
sampling is necessary and defines ground-water
sampling boundaries and locations. For example,
if an aquifer is very deep or there is a confining
layer between the ground surface and the aquifer,
then sampling within a small area may be all that
is necessary in order to determine the extent of
contamination within that aquifer.
Topography - Topography will control the
direction of surface runoff and may give clues to
subsurface conditions. For example, wells in
valleys may not be of the same aquifer as wells
on a hill.
Analytical Parameters - If contaminants are
initially unknown, then a broad spectrum of
analytical parameters is usually collected. As
more information about the site becomes
available (through screening or laboratory
analysis), the number of parameters can be
streamlined or altered in order to more effectively
characterize the site. If the contaminant is
known, then concentrate on sampling for it and
its degradation products.
Sampling Budget - Budget constraints inevitably
affect operations. A combination of screening
and analytical techniques minimizes expenses
while still providing an acceptable level of
quality for the sampling data.
Physiochemical Nature of Suspected
Contamination When designing the sampling
plan, take into account the physical and chemical
nature of the suspected contaminants, then design
the sampling plan to facilitate efficient detection
of the contaminants through sampling
methodology, equipment, and analyses. For
example, the water density or solubility of a
contaminant may provide an indication of the
contaminant's physical location within the water
column.
2.4 SAMPLING PLAN
To develop a successful and practical representative
ground-water sampling plan, the following site-
specific information is required:
Water has a specific gravity of one. Some
chemical compounds, such as many complex
petrochemicals, have a specific gravity of greater
than one, and are therefore more dense than
water. These substances tend to sink and include
chlorinated solvents, wood preservatives, other
12
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coal tar wastes, and pesticides. These compounds
are referred to as dense nonaqueous phase
liquids (DNAPLs), or "sinkers". On the other
hand, a specific gravity of less than one will
allow a contaminant to float on or near the water
table, and includes many fuel oil products and
byproducts (e.g., gasoline, benzene, toluene, ethyl
benzene, xylene (BTEX), and other straight chain
hydrocarbons). These compounds are referred to
as light nonaqueous phase liquids (LNAPLs), or
"floaters". Nonaqueous phase liquids (NAPLs)
tend to exist as separate layers in the water
column. A substance with a specific gravity
value near to or equal to one will generally
dissolve in the water column (e.g., acetone,
phenols, and creosote). Because of the potential
stratification in the water column due to NAPL
substances, sampling location with respect to the
suspected contaminant location within the well
should always be considered.
LNAPLs commonly occupy the capillary fringe
zone above the water table. In a confined aquifer,
these compounds are found along the upper
surface of the permeable unit and also within the
overlying confining layer.
DNAPLs cause additional representative
sampling concerns. These compounds move
downward under the influence of gravity until
reaching a less permeable formation where they
may either accumulate, move downslope along
the bedrock, or penetrate fractures. Special
precautions should be taken during drilling at
sites suspected of DNAPL contamination; ensure
that the drilling does not induce the spread of
free-phase DNAPL contaminants. Monitoring
well installation should be suspended when a
DNAPL or low permeability lithogic unit is
encountered. Fine-grained aquitards (e.g., silt or
clay) should be assumed to permit downward
DNAPL migration. For guidance on sites with
potential DNAPL contamination, see U.S. EPA
Estimating the Potential for Occurrence of
DNAPL at Superfund Sites, OSWER Directive
9355.4-07.
Additional elements which should be addressed in a
representative ground-water sampling plan include:
Sample Number - The number of samples
collected depends on the number of sample
locations. Normally one sample is taken at each
location, except for QA/QC requirements (e.g.,
replicates, and matrix spike/matrix spike
duplicates). If there are multiple, discreet
aquifers at the site, then samples of each may be
necessary. Splitting samples also requires an
increase in the number of samples.
Sample Volume - The sample volume is
dependent on the analytical parameters. It is also
dependent on whether the contaminant is known
or unknown. A greater volume is generally
needed when the contaminant is unknown
because a larger suite of parameters is usually
selected.
Sample Location - Sample location is generally
dictated by the availability of existing
monitoring, residential, or commercial wells.
New monitoring wells are located by judgmental
methods.
Sample Depth - Sampling depth is typically the
bottom or screened zone of a well. However,
there may be times when certain stratigraphic
horizons within the water column may need to be
discreetly sampled (e.g., capturing "floaters" or
"sinkers"). (Procedures for addressing stratified
samples are discussed in Section 4.4.)
Sample Order - Sampling order is from the least
contaminated to the most contaminated wells or
areas (if known).
2.5 EXAMPLE SITE
2.5.1 Background
The ABC Plating Site is located in northeastern
Pennsylvania approximately 1.5 miles north of the
town of Jonesville. Figure 2 provides a layout sketch
of the site and surrounding area. The site covers
approximately four acres and operated as a multi-
purpose specialty electroplating facility from 1947 to
1982. During its years of operation, the company
plated automobile and airplane parts with chromium,
nickel, and copper. Cyanide solutions were used in
the plating process. ABC Plating deposited
electroplating wastes into two unlined shallow surface
settling lagoons in the northwest portion of the site.
Pennsylvania Department of Environmental Resources
(PADER) personnel cited the owner/operator for the
operation of an unpermitted treatment system and
ordered the owner to submit a remediation plan for
state approval. Before PADER could follow up on the
order, the lagoons were partially backfilled with the
wastes in place. The process building was later
destroyed by a fire of suspicious origin. The owner
abandoned the facility and could not be located by
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Figure 2: Site Sketch
ABC Plating Site
A
TREELINE
SCALE IN FEET
SUSPECTED
LAGOONS
SUSPECTED
- TRENCH
HOUSE
TRAILER
100 50
100
LEGEND
DAMAGED
BUILDING
AREA
SURFACE FLOW
SITE BOUNDARY
14
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enforcement and legal authorities. Several vats,
drums, and containers were left unsecured and
exposed to the elements. The state contacted EPA for
an assessment of the site for a possible federally
funded response action; an EPA On-Scene
Coordinator (OSC) was assigned to the task.
2.5.2 Site History and
Reconnaissance
The EPA OSC reviewed the PADER site file. In 1974
the owner was cited for violating the Clean Streams
Act and for storing and treating industrial waste
without a permit. The owner was ordered to file a site
closure plan and to remediate the settling lagoons.
The owner, however, continued operations and was
then ordered to begin remediation in 90 days or be
issued a cease and desist order. Soon after, a follow -
The OSC obtained copies of aerial photographs of the
site area from the local district office up inspection
revealed that the lagoons had been backfilled without
removing the waste.
The OSC and a sampling contractor (Team) arrived on
site to interview local and county officials, fire
department officers, neighboring residents (including
a former facility employee), and PADER
representatives regarding site operating practices and
other site details. The former employee sketched
facility process features on a map copied from state
files. The features included two settling lagoons and
a feeder trench which transported plating wastes from
the process building to the lagoons. The OSC
obtained copies of aerial photographs of the site area
from the local district office of the U.S. Soil
Conservation Service. The state provided the OSC
with copies of all historical site and violation reports.
These sources indicated the possible presence and
locations of chromium, copper, and zinc plating
process areas.
The Team mobilized to the site with all the equipment
needed to perform multi-media sampling. The OSC
and Team made a site entry, utilizing appropriate
personal protective equipment and instrumentation, to
survey the general site conditions. They observed 12
vats, likely containing plating solutions, on a concrete
pad where the original facility process building once
stood. Measurements of pH ranged from 1 to 11.
Fifty drums and numerous smaller containers (some
on the concrete pad, others sitting directly on the
ground) were leaking and bulging because of the fire.
Some rooms of the process building could not be
entered due to unsafe structural conditions caused by
the fire. The Team noted many areas of stained soil,
which indicated container leakage, poor waste
handling practices, and possible illegal dumping of
wastes.
2.5.3 Identification of Parameters of
Concern
During the site entry, the OSC and Team noted that
several areas were devoid of vegetation, threatening
wind erosion which could transport heavy metal- and
cyanide-contaminated soil particulates off site. These
particulates could be deposited on residential property
downwind or be inhaled by nearby residents.
Erosion gullies located on site indicated surface soil
erosion and stormwater transport. Surface drainage
gradient was toward the west and northwest. The
Team observed stressed, discolored, and necrotic
vegetation immediately off site along the surface
drainage route. Surface drainage of heavy metals and
cyanide was a direct contact hazard to local residents.
Surface water systems were also potentially affected.
Further downgradient, site runoff entered an
intermittent tributary of Little Creek, which in turn
feeds Barker Reservoir. This reservoir is the primary
water supply for the City of Jonesville and
neighboring communities, which are located 2.5 miles
downgradient of the site.
The site entry team observed that the site was not
secure and there were signs of trespass (confirming a
neighbor's claim that children play at the facility).
These activities could lead to direct contact with
cyanide and heavy metal contaminants, in addition to
the potential for chemical burns from direct contact
with strong acids and bases as might be found in
leaking or unsecured drums or containers.
After interviewing residents, it was established that
the homes located to the south and nearest to the site
rely upon private wells for their primary drinking
water supply. Ground water is also utilized by several
small community production systems which have
wells located within 2 miles of the site. The on-site
settling lagoons were unlined and therefore posed a
threat to ground water, as did precipitation percolating
through contaminated soils. Contamination might
have entered shallow or deeper aquifers and
potentially migrated to off-site drinking water wells.
During Phase 1 sampling activities, full priority
pollutant metals and total cyanide analyses were
conducted on all soil and ground-water samples sent
to the laboratory. These parameters were initially
selected based on a study of plating chemistry:
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plating facilities generally use either an acid or basic
cyanide bath to achieve the desired coating on their
metal products. Since Phase 1 samples were collected
from the areas of highest suspected contaminant
concentration (i.e., sources and drainage pathways),
Phase 2 samples (all media types) were analyzed for
total chromium, hexavalent chromium (in water only),
and cyanide, the only analytes detected consistently
during the Phase 1 analyses. During Phase 3, the
samples sent to the laboratory for definitive analysis
were analyzed for total chromium and cyanide.
2.5.4 Sampling Objectives
The OSC initiated an assessment with a specific
sampling objective, as follows:
Phase 1 Determine whether a threat to public
health, welfare, and the environment exists.
Identify sources of contamination to support an
immediate CERCLA-funded activation for
containment of contaminants and security fencing
(site stabilization strategies) to reduce direct
contact concerns on site. Sample the nearby
drinking water wells for immediate human health
concerns.
Once CERCLA funding was obtained and the site was
stabilized:
Phase 2 Define the extent of contamination at
the site and adjacent residential properties.
Estimate the costs for early action options and
review any potential long-term remediation
objectives. For example, install and sample soil
borings and monitoring wells on site to evaluate
potential impact on subsurface soils and ground
water.
Phase 3 After early actions are completed,
document the attainment of goals. Assess that the
response action was completed to the selected
level and is suitable for long-term goals.
2.5.5 Selection of Sampling
Approaches
The OSC, Team, and PADER reviewed all available
information to formulate a sampling plan. The OSC
selected a judgmental sampling approach for Phase 1.
Judgmental sampling supports the immediate action
process by best defining on-site contaminants in the
worst-case scenario in order to evaluate the threat to
human health, welfare, and the environment. Threat
is typically established using a relatively small
number of samples (fewer than 20) collected from
source areas or suspected contaminated areas based on
the historical data review and site reconnaissance. For
this site, containerized wastes were screened to
categorize the contents and to establish a worst-case
waste volume, while soil samples were collected to
demonstrate whether a release had already occurred,
and nearby residential drinking water wells were
sampled for immediate human health concerns.
For Phase 2, a stratified systematic grid design was
selected to define the extent of contamination in soils.
The grid could accommodate analytical screening and
geophysical surveys. Based on search sampling
conducted at sites similar to ABC Plating, a block grid
with a 50-foot grid spacing was selected. This grid
size ensured a 10 percent or less probability of
missing a "hot spot" of 45 feet by 20 feet. The grid
was extended to adjacent residential properties when
contaminated soil was identified at grid points near
the boundary of the site.
Based on the results of soil sampling and geophysical
surveys, a judgmental approach was used to select
locations for installation of 15 monitoring wells: at
"hot spots"; along the perimeter of the suspected
plume established from analytical results and
geophysical survey plots; and at background ("clean")
locations. Subsurface soil and ground- water samples
were collected from each of the 15 monitoring well
locations for laboratory analysis to establish the
presence and, if applicable, the degree of
contamination at depth.
2.5.6 Sampling Plan
During Phase 1, containerized wastes were evaluated
using field analytical screening techniques. Phase 1
wastes-screening indicated the presence of strong
acids and bases and the absence of volatile organic
compounds. The Team collected a total of 12 surface
soil samples (0-3 inches) and 3 ground-water samples
during this phase and sent them to a laboratory for
analysis. The soil sampling locations included stained
soil areas, erosion channels, and soil adjacent to
leaking containers. Background samples were not
collected during Phase 1 because they were
unnecessary for activating immediate action response
funding. Ground-water samples were collected from
three nearby residential wells. Based on Phase 1
analytical results, chromium was selected as the target
compound for determination of extent of
contamination in soil and ground water.
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During Phase 2 sampling activities, the OSC used a
transportable X-ray fluorescence (XRF) unit installed
in an on-site trailer to screen soil samples for total
chromium in order to limit the number of samples to
be sent for laboratory analysis. Soil sampling was
performed at all grid nodes at the surface (0-4 inches)
and subsurface (36-40 inches). The 36-40 inch depth
was selected based on information obtained from state
reports and local interviews, which indicated that
lagoon wastes were approximately 3 feet below
ground surface. Once grid nodes with a
contamination level greater than a selected target
action level were located, composite samples were
collected from each adjoining grid cell. Based on the
XRF data, each adjoining grid cell was either
identified as "clean" (below action level) or
designated for response consideration (at or above
action level).
Also during Phase 2, the OSC oversaw the
performance of ground penetrating radar (GPR) and
electromagnetic conductivity (EM) geophysical
surveys to help delineate the buried trench and lagoon
areas, any conductive ground-water plume, and any
other waste burial areas. The GPR and
comprehensive EM surveys were conducted over the
original grid. Several structural discontinuities,
defining possible disturbed areas, were detected. One
GPR anomaly corresponded with the suspected
location and orientation of the feeder trench. The EM
survey identified several high conductivity anomalies:
the suspected feeder trench location, part of the lagoon
area, and a small area west of the process building,
which may have been an illegal waste dumping area.
(Field analytical screening and geophysical techniques
are further discussed in Chapter 3.)
Using the data obtained during soil sampling and the
geophysical surveys, a ground-water assessment plan
for Phase 2 was prepared. The Team collected depth
soundings and water level measurements of the nearby
residential wells to assess aquifer usage and location
(depth). With these data and the analytical results
from Phase 1, a work plan for monitoring well
installation and testing on site was developed. The
plan consisted of:
Installation of overburden, bedrock contact and
bedrock (open borehole) monitoring wells in
order to evaluate the shallow water table and
aquifer conditions
Analysis of subsurface soils retrieved during
borehole/well drilling in order to evaluate the
extent of contamination in overlying soils
Collection of depth soundings and water level
measurements of the newly installed monitoring
wells to map aquifer and water table gradients
Collection of ground-water samples from each
monitoring well
Performance of hydraulic tests in order to
evaluate aquifer characteristics
The monitoring wells were located in areas shown,
during soil sampling, to be heavily contaminated;
along the outer perimeter of a contaminant plume
based on soil XRF results and the geophysical
surveys; and an apparent upgradient location for
background conditions comparison. Fifteen wells
were located at grid nodes corresponding to the above
results. (Section 4.6.1 provides details on the
performance of well installation (drilling), testing and
surveying, and ground-water sampling procedures.)
Upon monitoring well installation and sampling, a
hydraulic (pumping) test was completed of the
bedrock monitoring wells to gather information about
aquifer characteristics. These data characterize
contaminant transport through the ground-water
aquifer. The hydraulic test provided transmissibility,
hydraulic conductivity, and storativity values.
Utilizing these values with ground-water level data,
the estimated vertical and horizontal ground-water
gradient and velocity could be calculated. All
monitoring wells installed were surveyed for elevation
above mean sea level, needed to determine accurate
depth to ground water (piezometric surface) and
relative gradients.
Phase 3 activities are discussed in Section 6.8.
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3.0 FIELD ANALYTICAL SCREENING, SAMPLING EQUIPMENT,
AND GEOPHYSICAL TECHNIQUES
3.1 FIELD ANALYTICAL
SCREENING
Field analytical screening techniques can provide
valuable information in ground-water sampling. Field
analytical screening for ground water is used primarily
as a tool for siting monitoring wells and for on-site
health and safety assessment during well drilling
activities. When used correctly, screening techniques
can help to limit the number of "non-detect"
monitoring wells installed. Some of the commonly
used screening methods for ground-water assessment
are presented in this chapter in the general order that
they would initially be used at a site, although site-
specific conditions may mandate a different sequence.
For more information on ground-water field screening
devices, refer to the U.S. EPA Compendium ofERT
Field Analytical Procedures, OSWER Directive
9360.4-04, and Compendium of ERT Ground-Water
Sampling Procedures, OSWER Directive 9360.4-06.
Refer to Standard Operating Safety Guides for each
instrument, and the U.S. Department of Health and
Human Services Occupational Safety and Health
Guidance Manual for Hazardous Waste Site
Activities (NIOSH Pub. 85-115) for site entry
information.
3.1.1 Flame lonization Detector
The flame ionization detector (FID) detects and
measures the level of total organic compounds
(including methane) in the ambient air in proximity to
a well or in a container headspace. The FID uses the
principle of hydrogen flame ionization for detection
and measurement. It is especially effective as an
ethane/methane detector when used with an activated
charcoal filter because most organic vapors are
absorbed as the sample passes through the filter,
leaving only ethane and methane to be measured.
The FID operates in one of two modes: the survey
mode, or the gas chromatography (GC) mode. In the
survey mode, the FID provides an approximate total
concentration of all detectable organic vapors and
gases measured relative to the calibration gas (usually
methane). The GC mode identifies and measures
specific components, some with detection limits as
low as a few parts per million (ppm), using known
standards analyzed concurrently in the field. Since the
GC mode requires standards to identify classes of
compounds, it is necessary to have an idea of which
compounds might be present on site before sampling.
Advantages of the FID are that it is portable,
relatively rugged, and provides real-time results.
During a ground-water assessment, the FID is used in
the survey mode for monitoring the borehole during
drilling and in the survey or GC mode for health and
safety screening.
The FID does not respond to inorganic substances. It
has positive or negative response factors for each
compound depending on the selected calibration gas
standard. Ambient air temperatures of less than 40
degrees Fahrenheit will cause slower responses;
relative humidity of greater than 95 percent can cause
inaccurate and unstable responses. Interpretation of
readings (especially in the GC mode) requires training
and experience with the instrument.
3.1.2 Photoionization Detector
Another portable air monitoring instrument frequently
used for field screening during ground-water
assessments is the photoionization detector (PID).
Like the FID, the PID provides data for real-time total
organic vapor measurements, identifying potential
sample locations and extent of contamination, and
supporting health and safety decisions. The PID is
useful in performing soil gas screening, health and
safety monitoring during well drilling activities, and
headspace screening analysis. The PID works on the
principle of photoionization. Unlike the FID, the PID
can be used to detect gross organic and some
inorganic vapors, depending on the substance's
ionization potential (IP) and the selected probe energy.
It is portable and relatively easy to operate and
maintain in the field.
The PID detects total concentrations and is not
generally used to quantify specific substances. PIDs
cannot detect methane; however, methane is an
ultraviolet (UV) light absorber, and false negative
instrument readings may register in methane-rich
environments. The PID cannot detect substances with
IPs greater than that of the UV light source.
(Interchangeable UV lamps are available.) Readings
can be affected by high wind speeds, humidity,
condensation, dust, power lines, and portable radios.
Dust particles and water droplets (humidity) in the
sample may collect on the light source and absorb or
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deflect UV energy, causing erratic responses in PIDs
not equipped with dust and moisture filters.
3.1.3 Gas Chromatograph
Although many FIDs are equipped with a GC mode,
an independent, portable GC (gas chromatograph) can
also be used on site to provide a chromatographic
profile of the occurrence and intensity of unknown
volatile organic compounds (VOCs) in ground water.
The GC is useful as a soil gas screening tool to
determine "hot spots" or plumes, potential
interferences, and semi-quantitation of VOCs and
semi-volatile organic compounds (semi-VOCs) in
ground-water samples. For example, when installing
a monitoring well, the GC might be used to screen
water samples during drilling in order to indicate
when a target contaminated aquifer zone is
encountered.
Compounds with high response factors, such as
benzene and toluene, produce large response peaks at
low concentrations, and can mask the presence of
compounds with lower response factors. However,
recent improvements in GCs, such as pre-concentrator
devices for lower concentrations, pre-column
detection with back-flush capability for rapid
analytical time, and the multi-detector (PID, FID, and
electron capture detector (BCD)), all enable better
compound detection. The GC is highly temperature-
sensitive. It requires set-up time, many standards, and
operation by trained personnel.
3.1.4 Hydraulic Probe
The hydraulic probe (Geoprobeฎ is one brand) is a
truck-mounted device used to collect screening
ground-water, soil, and soil gas samples at relatively
shallow depths. The probe is mounted on the back of
a small truck or van and is operated hydraulically
using the vehicle's engine. Small diameter hardened
steel probes are driven to depths of up to 40 feet or
more, depending on soil conditions. Soil gas samples
can then be collected using a vacuum pump. Soil or
water samples can also be collected using a small-
diameter shelby tube or slotted well point and foot
valve pump.
The hydraulic probe can be used in ground-water
investigations to assess vertical and horizontal extent
of contamination. Shallow samples can be collected
relatively quickly and easily. It is useful in a ground-
water assessment to assist in siting monitoring wells
and to install shallow wells if necessary. It can also
collect undisturbed ground-water samples without
installing wells. The hydraulic probe is only effective
in unconsolidated geologic materials, however. In
general, probing is possible under conditions
amenable to hollow stem auger drilling.
3.1.5 Soil Gas Technique
Soil gas testing is a quick method of site evaluation.
For ground-water assessments, soil gas testing is used
to track contaminant plumes and determine
appropriate locations for installing monitoring wells.
For this technique, a thin stainless steel probe is
inserted into a hole made in the soil with a special
slam bar. The hole is sealed around the probe and a
sampling pump is attached. Samples are then
collected in Tedlar bags, sorbent cartridges, or
SUMMA canisters. The samples are analyzed using
an FID, PID, or GC. A disadvantage of the soil gas
technique is that its ability to detect contaminants
diminishes the further it is from the source (as
contaminant concentration diminishes).
3.1.6 Field Parameter Instruments
Field parameters measured during ground-water
sampling include pH, specific conductivity,
temperature, salinity, and dissolved oxygen. Specific
conductivity, pH, and temperature are often used as
standard indicators of water quality. Instruments that
measure these three indicators are used during ground-
water assessments to determine if a well has been
purged sufficiently (stabilized) prior to sampling (see
Section 4.3).
3.1.7 X-Ray Fluorescence
Field analytical screening using X-ray fluorescence
(XRF) is a cost-effective and time-saving method to
detect and classify lead and other heavy metals in a
sample. XRF screening provides immediate semi-
quantitative results. The principle behind XRF is the
detection and measurement of the X-rays released
from an atom when it is excited by the absorption of
source X-rays. The energy released (fluorescent X-
rays) are characteristic of the atoms present.
Results of XRF analysis help determine the presence
of metals and are often used to assess the extent of
soil contamination at a site. For ground-water
assessment, XRF may be used on subsurface soil
samples collected during drilling or with surface soils
when selecting locations for monitoring well
installation. XRF use requires a trained operator and
may require numerous site-specific calibration
samples.
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3.2 GROUND-WATER SAMPLING
EQUIPMENT
Conducting representative ground-water sampling
requires an understanding of the capabilities of the
equipment used for sampling, since the use of
inappropriate equipment may result in biased samples.
Select appropriate sampling equipment based on the
sampling objectives, the analytical parameters, the
type of well being sampled (e.g., monitoring well or
drinking water well), and other site-specific
conditions. Follow SOPs for the proper use and
decontamination of sampling equipment. This section
presents various types of ground-water sampling
equipment and information to assist in selecting
appropriate materials.
The ground-water sampling devices discussed below
are covered in greater detail in many SOPs and
references on the various types of available ground-
water sampling devices. Refer to U.S. EPA A
Compendium of Superfund Field Operations
Methods, OSWER Directive 9355.0-14, and
Compendium of ERT Ground-Water Sampling
Procedures, OSWER Directive 9360.4-06, for details
on the equipment listed. Also refer to Driscoll,
Fletcher G., Ground-Water and Wells, 2nd ed., and
the 1985 "Proceedings of the Fifth National
Symposium and Exposition on Aquifer Restoration
and Ground-Water Monitoring," for additional
comparisons of the various types of sampling
equipment.
3.2.1 Bailer
A bailer is a simple purging device for collecting
samples from monitoring wells. It usually consists of
a rigid length of tube with a ball check-valve at the
bottom. A line is used to mechanically lower the
bailer into the well to retrieve a volume of water.
Because bailers are portable and inexpensive, they can
be dedicated to monitoring wells at a site, thus
avoiding the need to use a bailer for sampling more
than one well (and avoiding cross-contamination).
Bailers are available in a variety of sizes and
construction materials (e.g., polyvinyl chloride (PVC),
Teflonฎ, and stainless steel).
Bailers are best suited for purging shallow or narrow
diameter monitoring wells. Deeper, larger diameter,
and water supply wells generally require mechanical
pumps to evacuate a large volume of water.
For VOC analysis, a positive-displacement volatile
sampling bailer is most effective. Bottom-fill bailers,
which are more commonly used, are suitable provided
that care is taken to preserve volatile constituents. Fill
sample containers directly from the bailer, filling
samples for VOC analysis first.
3.2.2 Hydraulic Probe
The hydraulic probe can be used to collect shallow
(generally 40 feet or less) ground-water samples using
a mill-slotted well point or retractable screen drive
point. After the well point is driven to the desired
depth, the probe rod is connected to a vacuum pump
for purging. (Since ground water is sampled in situ
and is not exposed to the atmosphere, extensive
purging is not required.)
Water samples are collected using dedicated
polypropylene tubing fitted with a small diameter
foot-valve pump. Samples are collected in 40-ml vials
or other containers for laboratory analysis. See
Section 3.1.4 for more information on the hydraulic
probe.
3.2.3 Air-Lift Pump
An air-lift pump operates by releasing compressed air
via an air line lowered into the well. The air mixes
with the water in the well to reduce the specific
gravity of the water column and lift the water to the
surface.
Air-lift pumping is used in well development and for
preliminary testing. For sampling, air-lift pumping is
less efficient than other pumping methods which
follow; it may be selected for use when aeration is
needed to remove gas or corrosive water which can be
destructive to a well pump. Because an air-lift pump
aerates the water, it is not applicable for VOC sample
collection.
3.2.4 Bladder Pump
A bladder pump consists of a stainless steel or
Teflonฎ housing that encloses a Teflonฎ bladder.
The bladder pump is operated using a compressed gas
source (bottled gas or an air compressor). Water
enters the bladder through a lower check valve;
compressed gas moves the water through an upper
check valve and into a discharge line. The upper
check valve prevents back flow into the bladder.
The bladder pump can be used to purge and sample to
a depth of approximately 100 feet. It is recommended
for VOC sampling because it causes minimal
alteration of sample integrity as compared with other
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ground-water sample methods. The bladder pump
requires a power supply and a compressed gas supply
or air compressor. The pump is somewhat difficult to
decontaminate and should thus be dedicated to a well
(or dedicated tubing should be used).
3.2.5 Rotary Pump
A rotary pump is a positive displacement pump which
discharges the same volume of water regardless of the
water pressure. The rate of discharge is the same at
both low and high pressure, but the input power varies
in direct proportion to the pressure. The rotary pump
consists of a housing with inlet and outlet ports and
rotating gears or vanes. As water is discharged from
the pump, a replacement supply of equal volume is
taken in.
Rotary pumps are useful for well purging and general
sample collection at shallow to deep sampling depths.
Because of water agitation, they may not be suitable
for sampling VOCs, and they are difficult to
decontaminate between sampling stations.
3.2.6 Peristaltic Pump
A peristaltic pump is a suction lift pump consisting of
a rotor with ball-bearing rollers. Dedicated Teflonฎ
tubing is threaded around the rotor. Additional
lengths of dedicated Teflonฎ tubing are attached to
both ends of the rotor tubing: one end is inserted into
the well; the other end is a discharge tube. The
sample makes contact with the tubing only, not with
the pump. The tubing should be equipped with a foot
valve to avoid having aerated water from the tubing
fall back into the well.
A peristaltic pump is suitable for sampling small
diameter wells (e.g., 2 inches). Cross-contamination
is not of concern because dedicated tubing is used and
the sample does not come into contact with the pump
or other equipment. The peristaltic pump has a depth
limitation of 25 feet and its use can result in a
potential loss of the volatile fraction due to sample
aeration.
3.2.7 Packer Pump
A packer pump is used to isolate portions of a well or
water column for sampling. The pump consists of two
expandable parts that isolate a sampling unit between
them. The parts deflate for vertical movement within
the well and inflate when the desired sampling depth
is reached. The packers are constructed of rubber and
can be used with various types of pumps.
An advantage of the packer pump is it allows the
isolation of a portion of the water column in order to
sample at a discrete depth. Disadvantages relate to
the rubber construction of the packers which may
deteriorate over time allowing cross contamination.
The rubber also poses potential contaminant
compatibility concerns. A packer pump should not be
used if the contaminants are unknown, or where well
casing or contaminant characteristics interfere or
interact with the pump construction materials.
3.2.8 Syringe Sampler
Syringe samplers are a relatively new and less
commonly available sampling device. Syringe
samplers were developed by research groups to obtain
ground water samples over a period of time. The
device consists of a syringe (15 to 1500 ml in volume)
which is lowered into the well to the desired sampling
depth. The syringe plunger is then pulled open by a
remote method, either mechanical or pneumatic,
allowing the syringe to fill.
The remote operation allows the collection of a
sample at a discrete depth. In addition, the interior of
the sampler (i.e., the syringe) is not exposed to the
water column. Disadvantages to this device include
the small volume of sample that can be collected, it
cannot be adapted for evacuation/purging uses, and it
is not readily commercially available.
3.2.9 Ground-Water Sampling
Equipment Selection Factors
The following factors should be considered when
selecting ground-water sampling equipment.
Composition - Select the composition of the
sampling equipment based on the sampling
parameters and objectives. For example, use
samplers made of Teflonฎ, glass, or stainless
steel instead of PVC when sampling for VOCs.
Consider well composition when selecting
sampling equipment. For example, select a
stainless steel bailer when bailing a well with
stainless steel casing to avoid the introduction of
organic constituents. When sampling a PVC-
cased well, PVC, stainless steel, or Teflonฎ
bailers may be used.
Physical Constraints - Physical constraints of the
monitoring well location, power availability, and
topography are factors that affect selection of
ground-water sampling equipment. For example,
a small diameter or particularly deep well may
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require the use of different purging and sampling
equipment than that used for other wells at the
site. Site accessibility may hinder the use of
large or vehicle-mounted equipment.
Sample Analysis - Equipment should be chosen
based on its impact on the samples. For example,
sampling equipment selected for collecting VOCs
should agitate the water as little as possible. This
is not as critical for metals or other non-volatile
analyses.
Ease of Use - Generally, the more complicated
the sampling equipment is, the greater the chance
for some form of failure in the field. Utilize the
simplest effective sampling devices available.
Adequate training in equipment safely and use is
critical to personnel safety as well as to sample
representativeness. Consider ease of
decontamination when using non-dedicated
equipment.
3.3 GEOPHYSICAL METHODS
Geophysical methods can be useful in conjunction
with screening and sampling activities to help
delineate subsurface features and boundaries,
contaminant plumes, and bedrock types. Geophysical
data can be obtained relatively rapidly, often without
disturbing the site. The data are helpful in selecting
well locations and screen depths. The following
sections discuss surface and borehole geophysics and
preferable geophysical techniques for ground-water
investigations.
3.3.1 Surface Geophysics
The following surface geophysical techniques may be
useful in ground-water investigations. As implied by
the name, these techniques are performed above
ground. For more detailed information on each of
these techniques (with the exception of gravimetric
surveys), see ERT SOP #2159 and Driscoll, 1986.
For more information on gravimetric surveys, see
Driscoll, 1986.
Ground Penetrating Radar (GPR) - Uses a high
frequency transmitter that emits radar pulses into
the subsurface. These waves are scattered at
points of change in the dielectric permittivity of
the subsurface material and are reflected back to
an antenna. (Dielectric permittivity is a function
of bulk density, clay content, and water content of
the subsurface.) The returning energy wave is
then plotted as a function of time on an analog
plot. Interpretation of the analog plot identifies
anomalies, clay layers, and water content in the
substrate.
GPR works best in dry, sandy soil above the
water table, and at depths between 1 and 10
meters (although the full instrument depth range
is less than one meter to tens of meters). When
properly interpreted, GPR data can indicate
changes in soil horizons, fractures, and other
geological features, water-insoluble
contaminants, man-made buried objects, and
hydrologic features such as water table depth.
Uneven ground surfaces or cultural noise affect
GPR results.
Electromagnetic Conductivity (END - Relies on
the detection of induced electrical current flow
through geologic strata. This method measures
bulk conductivity (inverse of resistivity) of
subsurface materials below the transmitter and
receiver. EM is commonly used in the detection
of ground-water pollution, as well as to locate
pipes, utility lines, cables, trenches, buried steel
drums, and other buried waste.
EM has limited applications in areas of cultural
noise, including above-ground power lines and
metal fences, and lateral geologic variations
which might be misinterpreted as contaminant
plumes.
Electrical Resistivity - Used to map subsurface
structures through differences in their resistance
to electrical current. Material resistivities are
measured as functions of porosity, permeability,
water solution, and concentrations of dissolved
solids in pore fluids. Bulk resistivity is measured
in the subsurface by measuring electrical currents
injected through electrodes placed in the soil.
Electrical resistivity surveys are limited by
electrical noise, such as occur in industrial areas.
Resistivity surveys should ideally be conducted
in areas removed from pipelines and grounded
metallic structures such as metal fences and
railroad tracks. This requirement precludes use
of electrical resistivity surveys on many sites.
Resistivity can often be used off site to map area
stratigraphy. Resistivity surveys are labor
intensive, requiring ground setup and removal of
electrodes for each station measurement. Use
extreme care during rain or wet ground
conditions.
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Seismic Investigations - Conducted by two
methods: refractive and reflective. In the
refractive method, the travel time of acoustic
waves is measured as they move through and are
refracted along an interface of the subsurface.
The reflective method measures travel time of
acoustic waves as they are reflected off an
interface. Seismic refraction is typically used
when bedrock is within 500 feet of the ground
surface.
Seismic refraction is useful for mapping discrete
stratigraphic layers and therefore can help in
selecting monitoring well locations and depths.
A seismic refraction survey can provide
subsurface stratigraphic and structural data in
areas between existing wells or boreholes.
Seismic reflection is used less often in ground-
water investigations, but is more commonly used
for deeper and larger-scale stratigraphic mapping
(e.g., petroleum exploration).
Magnetic Investigations - Rely on local variations
in the earth's magnetic field to detect ferrous or
magnetic objects. By mapping variations in the
concentrations of the local magnetic fields,
detection of buried objects such as drums or tanks
may be accomplished. Magnetic surveys are
limited by cultural noise such as power lines,
utilities, and metal structures.
Gravimetric Surveys - Measure small localized
differences in the earth's gravity field caused by
subsurface density variations, which may be
produced by changes in rock type (porosity and
grain type), saturation, fault zones, and varying
thickness of unconsolidated sediments overlying
bedrock. This method is useful in identifying
buried valleys, particularly in glaciated areas.
Gravimetric surveys use a portable gravity meter
which can survey a large area relatively quickly.
The accuracy of the readings is dependent upon
the accuracy of the elevation determination of
each station. (Most altimeters are accurate only
to plus or minus 2 ft (0.6 m), so gravity stations
should be surveyed.) A gravimetric survey can
provide a quick preliminary screening of an area.
Other geophysical methods or test drilling can
then be used to help identify stratigraphy and
aquifer characteristics.
Table 1 illustrates the applicability of various surface
geophysical techniques to ground-water
investigations. Table 2 lists some advantages and
disadvantages of surface geophysical techniques to
ground-water investigations.
3.3.2 Borehole Geophysics
The following borehole geophysical techniques may
be useful in ground-water investigations. Borehole
geophysics may be used alone or to supplement
surface geophysical techniques. Site terrain is an
important factor when conducting borehole
geophysical surveys. Much of the equipment is
mounted or housed inside a truck but can be carried to
well locations if necessary. Some borehole logs can
be run in a cased as well as open hole.
Often several of the following tests are run at the
same time for comparative purposes. Borehole
geophysical logs can be interpreted to determine the
lithology, geometry, resistivity, formation factor, bulk
density, porosity, permeability, moisture content, and
specific yield of water-bearing formations as well as
the chemical and physical characteristics of ground
water. The operating principles of the various
borehole geophysical techniques are similar. A sonde
(a cylindrical tool containing one or more sensors) is
lowered to the bottom of the borehole, activated, and
slowly withdrawn. Signals or measurements at
various depths are recorded at the surface.
Instruments vary from hand-held portable gear to
truck-mounted, power-driven equipment. For more
detailed information on each of these techniques, see
Driscoll, 1986.
Resistance Logs - Electric logs measuring the
apparent resistivity of the rock and fluid
surrounding a well. They are good indicators of
subsurface stratigraphy and water quality.
Electric current is measured as it flows from
electrodes in the probe to other electrodes in the
probe or on the ground surface.
Resistance logs have a small radius of
investigation and are very sensitive to
conductivity of borehole fluid and changes in
borehole diameter. Increases in formation
resistivity produce corresponding increases in
resistance measurements on the log. Deflections
on the log are interpreted as changes in lithology.
Because of its excellent response to lithology
changes, the resistance log is very useful for
geological correlation. Formation fluids are
perhaps the most important variable in
interpreting resistance logs. For example, dry
sands and clays have high resistivities, but their
resistivities decrease with water saturation.
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Dissolved minerals also affect resistivity. (Fresh
water is a poor conductor whereas salt water is a
good conductor; water in saturated clays contains
dissolved minerals from the clay, which results in
high conductivities.)
A limitation of resistance logs is that they can be
run only in uncased boreholes that are filled with
drilling fluid and water. Resistance logging is
therefore most appropriately conducted before
monitoring well completion.
Spontaneous Potential CSP) Logs - Used in
conjunction with resistivity logs to show the
naturally occurring electric potentials of the
chemical and physical changes at contacts
between differing types of geologic materials.
The electric current is measured between an
electrode placed in an uncased borehole and one
placed at the surface.
SP response is due to small voltage differences
caused by chemical and physical contacts
between the borehole fluid and the surrounding
formation. Voltage differences appear at
lithology changes or bed boundaries and their
response is used to quantitatively determine bed
thickness or formation fluid resistivity.
Qualitative interpretation of the data can be used
to identify permeable beds.
Buried cables, pipelines, magnetic storms, and the
flow of ground water can all cause anomalous
readings. Caution must be exercised when using
SP data in a quantitative fashion. Mathematical
formulas are structured for oil well logging and
incorporate assumptions which may not apply to
fresh water wells. As with resistance logs, SP
logs can be run only in uncased, liquid-filled
boreholes.
Gamma Logs - Measure the naturally occurring
gamma radiation emitted from the decay of
radioisotopes normally found in the substrate.
Elements that emit natural gamma radiation are
potassium-40 and daughter products of the
uranium and thorium decay series. Changes in
radiation levels are commonly associated with
differences in substrate composition.
Gamma logs can be run in open or cased
boreholes filled with water or air. The sensing
device can be part of the same sonde that
conducts SP and resistance logs. Gamma rays or
photons are measured and plotted as counts per
minute. This method is useful in identifying clay
layers or other naturally radioactive geologic
units.
Gamma logging is used to identify the lithology
of detrital sediments, where the finer-grained
units have higher gamma intensity. (Fine-grained
materials also tend to have lower permeability
and effective porosity, important for evaluating
aquifer zones.) A limitation with gamma and
other nuclear logs is that they are affected by
changes in borehole diameter and borehole media
(e.g., air, water, or mud). Gamma logs record the
sum of the radiation emitted from the formation
and do not distinguish between radioactive
elements. For use in stratigraphic correlation
however, specific element identification is not
critical. Interpretation of gamma logs is difficult
where sandstone and other strata contain volcanic
rock fragments with radioactive minerals (e.g.,
rhyolite). Interpretation is also difficult in
sandstone containing a large proportion of
feldspar (which contains radioactive potassium-
40).
Gamma-Gamma Logs - Similar to gamma logs
except that a radioactive gamma source is
attached to the gamma sonde and the gamma
particles reflected back from the geologic
formation are measured. Gamma-gamma logs
measure the differing bulk densities of geologic
materials. They can be used to identify lithology
and also to calculate porosity when fluid and
grain density are known.
Neutron Logs - Also utilize a radiation source in
the sonde. The neutron source is a europium-
activated, lithium iodide crystal enriched in
lithium-6. The neutron logging tool bombards
the formation with neutrons and measures the
returning radiation. Neutrons, when ejected from
a nucleus, have great penetrating power and may
travel through several feet of subsurface
formation. All free neutrons are eventually
captured by the nuclei of some element. Neutron
logs respond primarily to hydrogen density. The
high energy neutrons from the source are slowed
by collision with hydrogen ions in the formation.
This response to hydrogen ion content is then
cross-calibrated to porosities for water-saturated
rocks. Neutron logs respond to the hydrogen
content in the borehole and surrounding
formation and indicate the porosity of the various
geologic units in the survey. Neutron logs can be
run in cased or open holes which are dry or filled
with fluid.
24
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Neutron logs are typically used to determine
moisture content above the water table and total
porosity below the water table. Neutron logs are
effective for identifying perched water tables.
Neutron log information can also be used to
determine lithology and conduct stratigraphic
correlation of aquifers and associated formations
as well as to help determine the effective porosity
and specific yield of unconfined aquifers.
Acoustic CSonic') Logs - Measure the travel time
and attenuation of an acoustic signal created by
an electromechanical source in the borehole. A
transmitter in the borehole converts the electrical
energy to acoustic (sound) energy which travels
through the formation as an acoustic pulse to one
or more receivers. The acoustic energy is then
converted back to electrical energy, which is
measured at the surface. The acoustic wave
velocity is affected by the type of material
through which it passes (rock or sediment is more
conductive than is pore fluid), hence it is useful in
determining porosity.
Acoustic logs can help determine fracture patterns
within semiconsolidated and consolidated
bedrock such as sandstone, conglomerate, and
igneous rocks. Knowledge of fracture patterns in
an aquifer is helpful in estimating ground-water
flow, and thereby estimating the rate of plume
movement. Acoustic logs can be used to locate
the static water level and to detect perched water
tables.
Temperature Logs - Used to measure the thermal
gradient of the borehole fluid. The sonde
measures changes in temperature of the fluid
surrounding it, and the log records resistivity as a
function of temperature. Borehole fluid
temperature is influenced by fluid movement in
the borehole and adjacent strata. In general, the
temperature gradient is greater in low
permeability rocks than in high permeability
rocks, likely due to ground-water flow.
Temperature logs provide information regarding
ground-water movement and water table
elevation. Temperature logs are useful for
detecting seasonal recharge and subsurface
infiltration of irrigation and industrial wastewater
runoff, and quantitative interpretation of
resistivity logs.
Temperature logs are designed to be operated
from the top to the bottom of the borehole, in
order to channel water past the sensor. Repeat
temperature logs should be delayed until the
borehole fluid has had time to reach thermal
equilibrium.
Table 3 illustrates the applicability of various borehole
geophysical techniques to ground-water
investigations. Table 4 lists some advantages and
disadvantages of borehole geophysical techniques to
ground-water investigations.
3.3.3 Geophysical Techniques for
Ground-Water Investigations
The following situations illustrate uses for
geophysical techniques in ground-water assessment.
To define the location, extent, and the movement
of a contaminant plume, several geophysical
techniques may be utilized, including EM,
electrical resistivity, and possibly GPR.
Resistivity and spontaneous potential (SP) logs
could also be utilized as borehole geophysical
methods.
To locate faults and fracture systems, seismic
refraction and reflection and EM are the preferred
methods, but GPR, electrical resistivity and
acoustic logs could also be used.
The mapping of grain size distribution in
unconsolidated sediments is not possible with
any geophysical technique. It is possible,
however, to identify different soil types of
different grain sizes (e.g., sand, silt, and clay).
Seismic reflection and refraction, GPR, and
gravimetric surveys may be used to identify
differing formations. Several borehole
geophysical techniques could also be utilized in
this type of analysis, including gamma, gamma-
gamma, neutron porosity, resistivity, and SP logs.
Definition of lithologic boundaries may be
accomplished with seismic reflection and
refraction and with GPR techniques. When using
borehole geophysics, resistivity, SP, and acoustic
logs are useful.
For mapping water tables, GPR and electrical
resistivity are preferred but seismic refraction and
reflection and gravimetric surveys may also be
used. If using borehole geophysics, direct
measurement or temperature logs would be the
method of choice. Resistivity and SP logs could
also be used.
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To define the bedrock topography, seismic
refraction and reflection, GPR and gravimetric
surveys may be used.
For delineating stratigraphic layers or subsurface
features, such as buried stream channels and
lenses, seismic refraction and reflection, electrical
resistivity, gravimetric surveys, and possibly GPR
could be used.
collected directly from the residential taps into sample
containers. For Phase 2, soils were collected from the
near surface (0-4 inches) and at depth. Stainless steel
trowels were used to retrieve shallow soil samples.
Subsurface samples were collected by advancing
boreholes using a hand-operated power auger to just
above the sampling zone and then using a stainless
steel split spoon to retrieve the soil. The split spoon
was advanced with a manual hammer attachment.
3.4 EXAMPLE SITE
3.4.1 Selection of Field Analytical
Screening Techniques
Phase 1 sampling identified the sources and types of
on-site contaminants in order to establish a threat.
Hazard categorization techniques, organic vapor
detecting instruments (FID and PID), and radiation
and cyanide monitors were utilized to tentatively
identify containerized liquid wastestreams in order to
select initial judgmental soil sampling locations.
During Phase 2 sampling, a portable XRF unit was
used to determine the extent of soil contamination and
to identify additional "hot spots." A FID and PID
continued to be utilized throughout all field activities
for health and safety monitoring during Phases 1
through 3.
The portable XRF for soil screening was also used
during monitoring well installation. Continuous split
spoon samples were collected during advancement of
the boreholes. Each spoon was sampled and screened
in the field using the XRF unit. Selected samples (one
per borehole location) were submitted to the
laboratory for confirmation analysis. One off-site
sample was selected by the field geologist based on
field observations and professional judgment.
Ground-water samples were screened in the field for
pH, specific conductivity, and temperature using a
three-in-one monitoring instrument. The instrument
probe was placed into a clean glass jar containing an
aliquot of the ground-water sample. The instrument
was decontaminated prior to and after each sample
screening.
3.4.2 Selection of Sampling
Equipment
Dedicated plastic scoops were used for Phase 1 soil
sampling. Phase 1 ground-water samples were
Monitoring wells were installed using a dual-tube, air
percussion drill rig. Borehole soil samples were
retrieved using 2-foot stainless steel split spoon
samplers. Soil from the split spoons was transferred
to sample containers using disposable plastic scoops.
Monitoring well installation is described further in
Section 4.6.1.
Ground water was sampled in Phase 2 from the
monitoring wells installed on site. First, monitoring
wells were purged using a 1.5 gallon per minute (gpm)
submersible rotary pump with flexible PVC outflow
hose and safety cable. The pump and hose were
decontaminated between well locations by pumping
deionized water through the system. A similar pump
and hose system was used to perform the hydraulic
(pumping) test. The pumps are operated by a gas-
powered generator placed near the well location.
The ground-water samples were obtained using
dedicated bottom-fill Teflonฎ bailers. The bailer was
attached to nylon rope, which was selected because
less material would be adsorbed onto the nylon and
brought out of the well. Residential ground-water
samples were collected directly into the sample
containers from the kitchen sink tap. Water level and
depth measurements were obtained from monitoring
wells using decontaminated electronic measuring
equipment.
3.4.3 Selection of Geophysical
Methods
The GPR instrument delineated buried trench and
lagoon boundaries. The EM meter detected
subsurface conductivity changes, thereby identifying
buried metal containers and contaminants. The EM-
3 ID, a shallower-surveying instrument than the EM-
34, was selected because of the instrument's
maneuverability and ease of use, and because the
expected contaminant depth was less than 10 feet.
26
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Table 1: Applicability of Surface Geophysical Techniques to Ground-Water Investigations
Contaminant
Plume Delineation
Faults/Fracture
Detection
Lithologic
Boundary
Delineation
Bedrock
Topography
Delineation
Stratigraphic
Mapping
Water Table
Mapping
Soil Type of
Unconsolidated
Sediments
Metallic Detection
Non-Metallic
Detection
Seepage Detection
Buried Structure
Detection
Seismic
Reflection
P
P
P
P
A
P
Seismic
Refraction
P
P
P
A
P
Electromagnetic
Conductivity
P
P
P
A
Magnetic
Investigations
p
A
Ground
Penetrating
Radar
A
A
A
A
A
P
P
P
P
A
Electrical
Resistivity
P
A
P
P
A
P
A
Gravi-
metric
Surveys
A
A
P
A
P
P - Preferred Method A - Applicable Method (in most cases)
27
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Table 2: Advantages and Disadvantages of Surface Geophysical Techniques to Ground-Water Investigations
Advantages
Disadvantages
Seismic Reflection
1 Ability to discern discrete layers
1 Less offset space is required than for
refraction
Velocities 10-20% of true velocities
Data collection and interpretation are
more labor intensive and complex than
for refraction
Depth data not as precise as refraction
Signal enhancement needed to identify
reflected waves
Seismic Refraction
1 Relatively precise depth can be
determined
1 Provide subsurface data between
boreholes
1 Ability to map water table and top of
bedrock
Data collection can be labor intensive
Large geophone line lengths needed
Electromagnetic
Conductivity
1 Lightweight, portable equipment
1 Continuous or quick scan survey
1 Rapid data collection
Interference from cultural noise and
surface metal objects
Limited use where geology varies
laterally
Magnetic
Investigations
1 Can survey large area quickly and cost
effectively
1 Little site preparation needed
Interference from cultural noise, and
large metal objects
Unable to differentiate between steel
anomalies
Ground Penetrating
Radar
Can survey large area quickly
Continuous real-time data display
Quick data processing
Interference from cultural noise,
uneven terrain, and vegetation
Clay content and shallow water table
inhibit radar penetration
Gravimetric Surveys
1 Can survey large area quickly
1 Little site preparation
Accurate elevations require surveying
Should be used only as preliminary
screening tool
Electrical
Resistivity
Quantitative modeling can estimate
depth, thickness, and resistivity of
subsurface layers
Interference from cultural noise,
surface metal objects, and industry
A minimum of two to three crew
members is required
Surveys are labor intensive
28
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Table 3: Applicability of Borehole Geophysical Techniques to Ground-Water Investigations
Contaminant
Plume Delineation
Faults/Fracture
Detection
Lithologic Boundary
Delineation
Bedrock
Topography
Delineation
Stratigraphic
Mapping
Water Table
Mapping
Soil Type of
Unconsolidated
Sediments
Resistance
Logs
P
P
P
P
A
P
Spontaneous
Potential
Logs
P
P
P
P
A
P
Gamma
Logs
P
P
P
P
P
Gamma-
Gamma
Logs
P
P
P
P
Neutron
Logs
A
A
P
P
P
Temperature
Logs
P
P
Acoustic
Logs
P
A
P
P
A
P - Preferred Method A - Applicable Method (in most cases)
29
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Table 4: Advantages and Disadvantages of Borehole Geophysical Techniques to Ground-Water Investigations
Advantages
Disadvantages
Resistance Logs
Indicates lithologic changes
Indicates amount and type of subsurface
fluid (water quality)
Can only be run in uncased borehole
Difficult to interpret lithology when
using drilling fluid with clay additives
Spontaneous
Potential Logs
Can be run in conjunction with resistance
log
Indicates lithologic changes and
permeable beds
Can only be run in uncased borehole
Interpretation for water well often
more difficult than for oil well
Gamma Logs
1 Easy to operate
1 Can be run in open or cased borehole
1 Qualitative guide for stratigraphic
correlation and permeability
Affected by changes in borehole
diameter and borehole media
Feldspar and volcanic rock fragments
make interpretation difficult
Gamma-Gamma
Logs
Can identify lithology and calculate
porosity when fluid and grain density are
known
Porosity readings of low density
materials can be erroneously high
Neutron Logs
Can determine total porosity in saturated
zone
Can determine moisture content in
unsaturated zones
Can be run in open or cased borehole
Radioactive source requires special
handling by trained personnel
Logging can be somewhat complex
Acoustic Logs
1 Useful for determining relative porosity
1 Indicates fracture patterns in aquifer
1 Can indicate static water level and
perched water tables
Clays may distort readings
Temperature Logs
1 Can indirectly measure permeability
1 Provides information regarding
ground-water movement and water table
elevation
Delay repeat logs until borehole fluid
reaches thermal equilibrium
30
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4.0 GROUND-WATER SAMPLE COLLECTION AND PREPARATION
4.1 INTRODUCTION
During a response action, proper field sample
collection and preparation is as important as proper
sampling equipment selection. Sample collection
refers to the physical removal of an aliquot of ground
water from its source (i.e., aquifer) for the purpose of
either screening or laboratory analysis. Ground-water
sample collection procedures should be selected so
that the resultant sample is representative of the
aquifer or particular water zone being sampled. Field
sample preparation refers to all aspects of sample
handling from collection to the time the sample is
received by the laboratory. This chapter provides
information on sample collection and preparation for
ground water.
The representativeness of a ground-water sample is
greatly influenced by the sampling device used and
the manner in which the sample is collected. Proper
training and use of SOPs will limit variables and
enhance sample representativeness. Selection of
ground-water sampling devices such as bailers and
pumps should be site-specific and dependent on well
diameter, yield, lift capacity, and the analytes being
sampled. Excessive aeration should be minimized to
preserve volatile constituents. Where possible, the
bailer or pump used should be compatible with the
analyte(s) of concern.
4.2 STATIC WATER LEVEL
Prior to sampling, the static water level elevation in
each well should be measured. All measurements
should be completed prior to the sampling event so
that static water levels will not be affected. The water
level measurements are necessary to establish well
purging volumes. These measurements can also be
used to construct water table or potentiometric surface
maps and hence determine local ground-water flow
gradient. Measure the depth to standing water and the
total depth of the well to calculate volume of stagnant
water in the well for purging. See ERT SOP #2151
for detail on collecting static water level
measurements.
4.3 WELL PURGING
There is little or no vertical mixing of water in a
nonpumping well, therefore stratification occurs. The
well water in the screened section mixes with the
ground water due to normal flow patterns, but the well
water above the screened section will remain isolated
and become stagnant. The stagnant water may contain
foreign material inadvertently or deliberately
introduced from the surface, resulting in
unrepresentative data. Adequate well purging prior to
sample withdrawal will safeguard against collecting
nonrepresentative stagnant water samples.
Well purging techniques are specific to the following
well types.
Residential. Commercial, and Public Supply
Wells - Sample residential, commercial, and
public supply wells as near to the wellhead as
possible and at a point before treatment, such as
filtering and water softening units, whenever
possible. Open the tap to a moderate flow and
purge for approximately 15 minutes. If this is not
possible, a 5-minute purge is considered a
minimum. As an alternative to a minimum
volume, purging can be conducted until the field
parameters pH, temperature, and specific
conductivity have stabilized (see Section 4.3.1).
Monitoring Wells - To obtain a representative
sample from a monitoring well, it is necessary to
evacuate the standing water in the well casing
prior to sampling. The minimum recommended
amount that should be purged from a monitoring
well is one casing volume, but three to five
casing volumes of standing water should be
evacuated where possible in order to obtain a
ground-water sample representative of the
aquifer. In a high yield aquifer where there is no
standing water above the screened section of the
well casing, purging three volumes is not as
critical as in lower yield aquifers. (The faster
recharge rate limits the amount of time that the
water has to interact with the atmosphere and
casing materials.) If the well is purged dry, it
should be considered sufficiently purged for
sampling (refer to Section 4.3.2 for additional
information).
31
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The amount of purging a well receives prior to sample
collection depends on the intent of the sampling as
well as the hydrogeologic conditions. When the
sampling objective is to assess overall water resource
quality, long pumping periods may be required to
obtain a sample that is representative of a large
volume of the aquifer. The pumped volume is
determined prior to sampling, or the well is pumped
until the stabilization of parameters such as
temperature, specific conductivity, and pH has
occurred.
Monitoring to define a contaminant plume requires a
representative sample of a small volume of the
aquifer. These circumstances require that the well be
pumped enough to remove the stagnant water but not
enough to induce flow from other areas. Generally,
three well volumes are considered effective.
Otherwise, the appropriate volume to be removed
prior to sampling can be calculated, based on aquifer
parameters and well dimensions.
Well purging devices include bailers, submersible
pumps (rotary-type), non-gas contact bladder pumps,
suction pumps, and hand pumps. See ERT SOP
#2007 for specific guidelines on purging wells prior to
sampling and for more detail on each purging device.
4.3.1 Stabilization Purging
Technique
The stabilization technique is an alternative to volume
purging. This method requires that several field
parameters be continuously monitored during purging.
When these parameters stabilize, begin sampling. The
parameters used for this method are pH, temperature,
and specific conductivity. Stabilization of these
parameters indicates that the standing water in the
monitoring well has been removed and that a
representative sample of the aquifer water may now
be collected. This method of purging is useful in
situations where it is not feasible to evacuate three
casing volumes from the well prior to sampling (e.g.,
large casing diameter, extremely deep, and active
supply wells). See ERT SOP #2007 for specific
volume and stabilization purging techniques.
4.3.2 Wells that Purge Dry
A well that is purged dry should be evacuated and
allowed to recover prior to sample withdrawal. If the
recovery rate is fairly rapid and time allows,
evacuation of more than one volume of water is
desirable. If the recovery rate is slow, the first
recharge can be considered suitable for sample
collection.
4.4 GROUND-WATER SAMPLE
COLLECTION
In order to maintain sample representativeness,
dedicated samplers should be used for each well
whenever possible. When not possible, the sampler
should be decontaminated after each sample collection
and sufficient QA/QC blank samples should be
collected to assess potential cross-contamination.
After well purging is complete, collect and
containerize samples in the order of most volatile to
least volatile, such as:
Volatile organic analytes (VOAs)
Purgeable organic carbon (POC)
Purgeable organic halogens (POX)
Total organic halogens (TOX)
Total organic carbon (TOC)
Extractable organic compounds
Total metals
Dissolved metals
Phenols
Cyanide
Sulfate and chloride
Turbidity
Nitrate and ammonia
Radionucliides
See ERT SOP #2007 for specific detail on filling
sample containers, with special considerations for
VOA sampling.
If the contaminants in the water column are stratified
(e.g., DNAPLs, LNAPLs), be certain to use an
appropriate sampling device. Modify, where possible,
standard sampling procedures to collect the sample
from the suspected depth for the contaminant layer. It
may be necessary to lower the bailer used for sample
collection to a particular depth in the well, or to use a
point-source bailer or other discrete-depth sampling
device.
After a monitoring well is initially constructed, it
should be developed and purged to remove invaded
water. The well should sit idle for at least two weeks
to allow the water level to fully stabilize and the
suspected stratified layers to settle out. Measurement
of the thickness of a floating (LNAPL) layer may be
accomplished in several ways. An indicator gel, chalk
or paste may be applied to an incremented steel tape.
32
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The indicator changes color in the presence of water
or the immiscible layer, depending on the specific use
of the indicator compound. For example, water-level
indicator gel is used to determine the depth to the
water surface. A weighted float is then used to
determine the depth to the top of the LNAPL layer.
The difference between these two readings is the
thickness of the floating layer.
An electronic monitoring device called an interface
probe is also available for the LNAPL layer
measurement. This device, like an electric water-level
sounder, is lowered into the well along an electronic
wire/line. When the probe contacts the surface (the
LNAPL layer) a sound is generated. As the sampler
continues to lower the probe, a different electronic
sound is emitted when the water surface, or water/oil
interface, is reached. The line of the device is
incremented, like a water-level sounder, so the layer
thickness can be determined. Standard electric water-
level sounding devices, however, will not work
properly for these measurements. The interface probe
is a specialized instrument which is commonly
available and used at fuel oil/ground-water
contamination sites.
A sample of a floating layer may be obtained using a
bottom-fill bailer. Care should be taken to lower the
bailer just through the floating layer, but not
significantly down into the underlying ground water.
(A clear bailer is preferable for this activity.)
For sampling sinking layers, a discrete-depth-capable
sampling device, such as a packer pump or syringe
sampler, is best suited. When these specialized
devices are not available, depending on the sampling
parameters, standard devices may be used. For
example, samples at the bottom of the screen or at
some intermediate location may also be obtained with
a standard bailer and a second well casing. In order to
avoid mixing the waters, a separate casing is
temporarily lowered inside the permanent well casing.
The temporary casing is equipped with an easily
removed cap on the bottom so that no fluid enters the
casing until it has reached the desired sampling depth.
The cap is then freed from the bottom of the inner
casing, allowing water to enter to be sampled by a
bailer. At significant depths below the nonaqueous
layer, several bailers full of water may need to be
withdrawn and discarded before the sample is
obtained from a fresh formation sample.
When a temporary casing and all other specialized
equipment is unavailable, a standard bailer alone may
be used. Collect a water sample from the well and
transfer it to the sample container. Allow the sample
to settle in the sample container into the separate
stratified layers. The analytical laboratory may then
decant, as appropriate, to obtain a sample of the
desired layer. More commonly, the parameters of
concern in the stratified layers are simply included in
the laboratory analysis of the sample as a whole
without the need to separate into unique layers. In
this last example, care must be taken to allow the
bailer to reach the desired depth in the water column
to insure collecting any dense layers at the bottom of
the well. (See Section 2.4 for additional discussion on
sampling concerns and the physiochemical nature of
contaminants.)
4.5 GROUND-WATER SAMPLE
PREPARATION
This section addresses appropriate ground-water
sample preparation and handling techniques. Proper
sample preparation and handling maintain sample
integrity. Improper handling can render samples
nonrepresentative and unsuitable for analysis.
The analyses for which a sample is being collected
determines the type of bottles, preservatives, holding
times, and filtering requirements. Samples should be
collected directly into appropriate containers that have
been cleaned to EPA or other required standards.
Check to see that a Teflonฎ liner is present in the
sample bottle cap, if required.
Samples should be labeled, logged, and handled
correctly, including appropriate chain-of-custody
documentation. Place samples in coolers to be
maintained at 4ฐC. Ship samples to arrive at the
designated analytical laboratory well before their
holding times are expired. It is preferable that
samples be shipped or delivered daily to the analytical
laboratory in order to maximize the time available for
the laboratory to do the analysis.
Certain conditions may require special handling
techniques. For example, treatment of a sample for
VOAs with sodium thiosulfate preservative is required
if there is residual chlorine in the water (e.g., a public
water supply) that could cause free radical
chlorination and change the identity of the original
contaminants. (The preservative should not be used if
there is no chlorine in the water.) All such special
requirements must be determined prior to conducting
fieldwork.
Sample preparation for ground water may include, but
is not limited to:
33
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Filtering
Homogenizing/Aliquotting
Splitting
Final Preparation
4.5.1 Filtering
Samples may require filtering, such as for total metals
analysis. Samples collected for organic analyses
should not be filtered. Two types of filters may be
used, which must be decontaminated prior to use. A
barrel filter works with a bicycle pump, which builds
up positive pressure in the chamber containing the
sample and then forces it through the filter into a
container placed underneath. A vacuum filter has two
chambers; the upper chamber contains the sample, and
a filter divides the chambers. Using a hand pump or
a Gilianฎ-type pressure pump, a vacuum is created in
the upper chamber and the sample is filtered into the
lower chamber. Preservation of the sample, if
necessary, should be done after filtering.
See ERT SOP #2007, Section 2.7.5, for more detail on
filtering ground-water samples.
4.5.2 Homogenizing/Aliquotting
Homogenizing, or aliquotting, is the mixing or
blending of a grab sample to distribute contaminants
uniformly. Ideally, proper homogenizing ensures that
all portions of the sample are equal or identical in
composition and are representative of the total sample
collected. Incomplete homogenizing can introduce
sampling error. Homogenizing disturbs the ground-
water sample, so it is not appropriate for VOC
sampling.
Homogenizing is done during only one sampling event
per well location, and only after the VOC sample
portions have first been filled. It may be utilized for
wells with extremely low yield and potentially
insufficient sample volume to fill all sample
containers provided by the laboratory. In some low
yielding wells, the percentage of suspended material
in a bailer-full of sample will increase as sampling
proceeds. Homogenizing ensures that at least a
minimum volume is aliquotted per analytical
parameter, and the percentage of suspended material
is equitably divided among all containers (excluding
VOCs).
4.5.3 Splitting
Split samples are created when the samples have to be
separated into two or more equivalent parts and
analyzed separately. Split samples are most often
collected in enforcement actions to compare sample
results obtained by EPA with those obtained by the
potentially responsible party. Split samples also
provide measures of sample variability and analytical
error. Fill two sample collection jars simultaneously,
alternating the sample stream or bailer full of sample
between them.
4.5.4 Final Preparation
Final preparation includes preserving, packaging, and
shipping samples.
Sample preservation is used to retard chemical
breakdown of the sample. Preservation of ground-
water samples includes controlling pH with chemical
preservatives, refrigerating samples, and protecting
samples from light.
Select sample containers on the basis of compatibility
with the material being sampled, resistance to
breakage, and capacity. Appropriate sample volumes
and containers will vary according to the parameters
being analyzed. Actual sample volumes, appropriate
containers, and holding times are specified in the
U.S. EPA Compendium of ERT Ground-Water
Sampling Procedures, OSWER Directive 9360.4-06.
Package all samples in compliance with current
International Air Transport Association (IATA) or
U.S. Department of Transportation (DOT)
requirements, as applicable. Packaging should be
performed by someone trained in current DOT
shipping procedures.
See ERT SOP #2007, Section 2.3 for more detail on
ground-water sample preparation.
4.6 EXAMPLE SITE
4.6.1 Sample Collection
During Phase 1 and Phase 2, surface soil samples
were collected from shallow locations. The samples
were collected as grab samples. The sample locations
were cleared of surface debris, then samples were
retrieved with disposable plastic scoops and placed
directly into sample containers. During Phase 2,
subsurface soil samples were collected at the soil
boring/well installation locations, using stainless steel
split spoon samplers. The split spoon samples were
collected using a hand-held power auger to advance
the hole. A 2-foot stainless steel split spoon sampler
with hammer attachment was then pushed into the
34
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hole. The soil sample was retrieved from the split
spoon sampler using a disposable plastic scoop to
transfer the soil into a stainless steel bowl. Several
scoopfuls were collected along the length of the split
spoon sampler and composited in the bowl. The
composite sample was then transferred directly into
the sample container using the disposable plastic
scoop.
Phase 1 and Phase 2 residential well ground-water
samples were collected directly from the kitchen taps
of homes using private wells near to the site. The
configuration of the residential system was noted in
the logbook prior to sampling. If present, water
softeners were taken off line. Any screen or filter was
first removed from the tap, which was allowed to run
for a minimum of five minutes prior to sampling. The
samples were collected directly into the sample
containers.
Fifteen monitoring wells were installed at the site at
locations described in Section 2.5.6. The wells were
drilled with a dual-tube, air percussion rig. Each
boring was completed to a 9.5-inch diameter. After
completion of the boring, 4-inch Schedule 40 PVC
casing and 0.010 slot screen were installed in lengths
appropriate to each well. Shallow wells were drilled
to approximately 40 feet below grade surface (BGS)
and bedrock contact wells were drilled to
approximately 55 to 60 feet BGS. Continuous split
spoon sampling was performed at each well location
from 4 feet BGS to well completion depth. The
boreholes were grouted from the bottom to the top of
the lower confining layer, then 10 feet of screen were
set above the grouted portion. PVC casing was set
above the screen to above the ground surface. Casing
was extended to accommodate a 2-foot stick-up above
grade, and then capped. A 6-inch diameter metal
outer casing with locking cover was installed over the
well casing stick-up and secured 2 feet BGS in
concrete. A concrete spill pad was then constructed
around each well outer casing to prevent re-infiltration
at the well point. Upon completion, all monitoring
wells were developed by purging using a
decontaminated rotary pump and flexible PVC
disposable hose.
A Team geologist supervising the monitoring well
installation logged each borehole soil lithology from
the retrieved split spoon samplers collected during
drilling of the boreholes. The geologist scanned each
sampler with a PID immediately upon opening (into
halves) for health and safety monitoring. All logging
was accomplished utilizing the Unified Soils
Classification System standard method. Figure 3
provides an example of a soil boring and monitoring
well completion log.
Soil samples were then collected in wide-mouth clear
glass jars by transferring a portion of each lithologic
unit in the split spoon with a disposable plastic scoop
and compositing the sample in the jar. At the
completion of each borehole, each sample was
screened in the field using the XRF unit. Select
samples (one per borehole location) were forwarded to
the laboratory for confirmation analysis. Split spoon
samplers were decontaminated after each use.
Upon completion and development, the 15 on-site
monitoring wells were sampled for ground-water
analysis. The well caps were brushed and cleaned off
prior to opening. Immediately upon removing the
well cap, a PID was operated over the opening to
determine VOC levels, if any, in the breathing zone.
The VOC monitoring was performed to establish if a
higher level of respiratory protection was required.
Depth to water level measurements were then taken of
each well to the nearest 0.01 ft. The total depth of the
well was obtained with a depth sounder. The volume
of water in the well was then calculated using the
formula below. For a four-inch well, well volume
would equal 0.632 gallon/ft.:
Well volume = it x (radius of well)2 x height
of water column x 7.48 gallon/ft3
(conversion factor for ft3 to gallons)
Each monitoring well was purged prior to obtaining a
representative sample. Wells with sufficient yield
were purged three well volumes. Low-yielding wells
were purged once to dryness. (Most wells on site are
low-yielding.) Purging was completed using a 1.5
gpm decontaminated submersible (rotary-type) pump
with flexible PVC outflow hose and safety cable. The
pump was slowly lowered to a point approximately 3
feet above the bottom of the well. With the known
flow rate, length of pumping required was calculated.
Purge water was pumped into 55-gallon steel drums.
(The drums were staged and later disposed of properly
based on the results of analysis of their contents.)
Low-yielding overburden wells were purged with a
decontaminated stainless steel bottom-fill bailer and
polypropylene rope until dry. All wells were allowed
to recover overnightbefore sample collection, or until
sufficient water was present to complete a sample set.
Each monitoring well was sampled after purging and
recovery. Ground-water samples were collected using
dedicated disposable Teflonฎ bailers. Each bailer
was attached to a clean polypropylene rope and intro-
-------
Figure 3: Soil Boring/Monitoring Well Completion Log
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36
-------
duced into the well. The bailer was lowered slowly to
the approximate mid-point of the well. Once the
sample was collected, care was taken not to agitate the
water while pouring directly into the appropriate
sample containers. An additional ground-water
aliquot was placed into a large wide-mouth glass jar
in order to obtain conductivity, temperature, and pH
measurements. These measurements were recorded in
the field logbook.
After well sampling, a hydraulic (pumping) test was
performed to determine aquifer characteristics for
mathematical modeling of potential contaminant
plume migration. The hydraulic test was conducted
using one well as a pumping well with three
observation wells. The pumping well was purged at
a rate of 22 gpm for 30 hours. All wells (observation
and pumping) were monitored during pumping and for
4 hours after pumping ceased. Drawdown data from
the wells were used to calculate the characteristics of
the aquifer.
To generate accurate gradient and well location maps,
the 15 newly installed monitoring wells were surveyed
for vertical location using feet above mean sea level
(MSL) units. Vertical elevations were taken at a mark
on the top of the inner casing of each monitoring well,
to establish a permanent location for all future water
level measurements and elevations. A permanent
benchmark was located near to the site by the survey
team to determine all the well elevations. Elevations
were then measured against the benchmark and
mapped in MSL units.
All non-disposable equipment, including drill rig and
equipment, stainless steel bailers, pumps, water level
indicators, and depth sounders, were decontaminated
between each location and prior to the first sampling
event each day.
4.6.2 Sample Preparation
All sample containers were supplied by the contracted
analytical laboratory. Chemical preservation was also
provided by the laboratory through pre-preserved
bottleware. Sample containers for ground-water
samples consisted of:
1-liter polyethylene bottles for total chromium,
pre-preserved with reagent-grade nitric acid
lowering the pH to less than 2 after addition of
the sample
1-liter polyethylene bottles for hexavalent
chromium
1-liter polyethylene bottles for cyanide, pre-
preserved with sodium hydroxide
Sample containers for soils consisted of 8-ounce glass
jars with Teflonฎ caps for all parameters.
All samples were preserved to 4ฐ C by placing them
in coolers packed with "blue ice" immediately after
collection and during shipment. (The laboratory was
responsible for cooling and refrigeration of samples
upon arrival.)
The samples were packaged in compliance with IATA
requirements for environmental samples. Chain-of-
custody paperwork was prepared for the samples.
Laboratory paperwork was completed as appropriate
and the samples were shipped to the predesignated
laboratories for analysis. Holding times for total
chromium and cyanide are less than six months, but
hexavalent chromium has a holding time of less than
24 hours. This was coordinated in advance with the
analytical laboratory and required daily ground
delivery of samples to the laboratory.
Because many of the ground-water samples from the
on-site wells were extremely turbid, the non-volatile
portions of samples were filtered in the laboratory
prior to analysis. Filtering was accomplished using a
barrel filtering device with a minimum pore size of
0.45 microns. Samples for chromium analysis were
split and filtered so that dissolved and particulate
chromium could be differentiated. Dissolved
chromium is of concern because of its ability to be
transported in ground water.
37
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5.0 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC)
5.1 INTRODUCTION
The goal of representative sampling is to obtain
analytical results that accurately depict site conditions
during a defined time interval. The goal of quality
assurance/quality control (QA/QC) is to implement
correct methodologies which limit the introduction of
error into the sampling and analytical procedures, and
ultimately into the analytical data.
QA/QC samples evaluate three types of information:
1) the magnitude of site variation; 2) whether samples
were cross-contaminated during sampling and sample
handling procedures; and 3) whether a discrepancy in
sample results is a result of laboratory handling and
analysis procedures.
5.2 DATA CATEGORIES
EPA has established data quality objectives (DQOs)
which ensure that the precision, accuracy,
representativeness, and quality of environmental data
are appropriate for their intended application.
Superfund DQO guidance defines two broad
categories of analytical data: screening and
definitive.
Screening data are generated by rapid, less precise
methods of analysis with less rigorous sample
preparation than definitive data. Sample preparation
steps may be restricted to simple procedures such as
dilution with a solvent, rather than elaborate
extraction/digestion and cleanup. At least 10 percent
of the screening data are confirmed using the
analytical methods and QA/QC procedures and
criteria associated with definitive data. Screening
data without associated confirmation data are not
considered to be data of known quality. To be
acceptable, screening data must include the following:
chain-of-custody, initial and continuing calibration,
analyte identification, and analyte quantification.
Streamlined QC requirements are the defining
characteristic of screening data.
Definitive data are generated using rigorous analytical
methods (e.g., approved EPA reference methods).
These data are analyte-specific, with confirmation of
analyte identity and concentration. Methods produce
tangible raw data (e.g., chromatograms, spectra,
digital values) in the form of paper printouts or
computer-generated electronic files. Data may be
generated at the site or at an off-site location, as long
as the QA/QC requirements are satisfied. For the data
to be definitive, either analytical or total measurement
error must be determined. QC measures for definitive
data contain all of the elements associated with
screening data, but also may include trip, method, and
rinsate blanks; matrix spikes; performance evaluation
samples; and replicate analyses for error
determination.
For further information on these QA/QC objectives,
please refer to U.S. EPA Data Quality Objectives
Process for Superfund, pp. 42-44.
5.3 SOURCES OF ERROR
There are many potential sources of data error in
ground-water sampling. The following is a list of
some of the more common potential sources of error:
Sampling design
Sampling methodology
Analytical procedures
Seasonal variations
See U.S. EPA Data Quality Objectives Process for
Superfund, pp. 29-36, for more information on error.
5.3.1 Sampling Design
The sampling design should utilize approved SOPs
and previously approved sampling designs to ensure
uniformity and comparability between samples. The
actual sample collection process should be determined
prior to sampling. Sampling equipment and
techniques must be standardized for like sampling
situations.
The sampling design should fulfill sampling and data
quality objectives. The quality assurance objectives
selected should be built into the sampling design,
including all necessary QA/QC samples.
Sampling design errors for ground water include: well
selection, well location, well construction and
development, background sample location, and
equipment (material and type).
38
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5.3.2 Sampling Methodology
Sampling methodology and sample handling
procedures have possible sources of error, including:
cross-contamination from inappropriate use of sample
collection equipment; unclean sample containers;
improper sampling equipment decontamination; and
improper shipment procedures. Procedures for
collecting, handling, and shipping samples should be
standardized to allow easier identification of any
source(s) of error, and to minimize the potential for
error. Use approved SOPs to ensure that all given
sampling techniques are performed in the same
manner, regardless of the sampling team, date, or
location of sampling activity. Use field blanks,
replicate samples, trip blanks, and rinsate blanks
(discussed in Section 5.4) to identify errors due to
improper sampling methodology and sample handling
procedures. An example of a sampling methodology
error for ground water is inappropriate purging.
5.3.3 Analytical Procedures
Analytical procedures may introduce errors from
laboratory cross-contamination, inefficient extraction,
and inappropriate methodology. Matrix spike,
laboratory duplicate, performance evaluation, and
laboratory control samples help to distinguish
analytical error from sampling error.
5.3.4 Seasonal Variations
Seasonal variations are not controllable but must be
taken into consideration as a source of error during
ground-water assessments. Changes in flow direction
or volume can redistribute contaminants throughout a
site, making assessment difficult. Plan sampling
events in order to minimize the effects of seasonal
variations, if possible.
5.4 QA/QC SAMPLES
QA/QC samples are collected at the site or prepared
for or by the laboratory. Analysis of the QA/QC
samples provides information on the variability and
usability of sampling data, indicates possible field
sampling or laboratory error, and provides a basis for
future validation and usability of the analytical data.
The most common field QA/QC samples are field
replicate, background, and rinsate, field, and trip blank
samples. The most common laboratory QA/QC
samples are performance evaluation (PE), matrix
spike (MS), matrix spike duplicate (MSD), and
laboratory duplicate samples. QA/QC results may
suggest the need for modifying sample collection,
preparation, handling, or analytical procedures if the
resultant data do not meet site-specific quality
assurance objectives.
Ground water is typically characterized by low or
trace concentrations of contaminants, making
precision and accuracy more important than for
samples with higher concentrations (e.g., waste).
Frequent field blanks are thus appropriate in ground-
water sampling.
The following sections briefly describe the most
common types of QA/QC samples appropriate for
ground-water sampling.
5.4.1 Field Replicate Samples
Field replicates, also referred to as field duplicates and
split samples, are field samples obtained from one
sampling point, homogenized (where appropriate),
divided into separate containers, and treated as
separate samples throughout the remaining sample
handling and analytical processes. Use replicate
samples to assess error associated with sample
methodology and analytical procedures. Field
replicates can also be used when determining total
error for critical samples with contamination
concentrations near the action level. In such a case, a
minimum of eight replicate samples is recommended
for valid statistical analysis. Field replicates may be
sent to two or more laboratories or to the same
laboratory as unique samples. For total error
determination, samples should be analyzed by the
same laboratory. Generally, one field replicate per 20
samples per day is recommended.
5.4.2 Background Samples
Defining background conditions may be difficult
because of natural variability and the physical
characteristics of the site, but it is important in order
to quantify true changes in contaminant concentrations
due to a source or site. Defining background
conditions is critical for avoiding false positives and
for enforcement purposes in naming responsible
parties. Background sampling is often required in
ground-water sampling to verify plume direction,
ambient conditions, and attribution of sources. A
properly collected background sample serves as the
baseline for the measure of contamination throughout
the site. Ground-water background sample locations
should be chosen carefully, usually upgradient from
the suspected source of contamination where there is
little or no chance of migration of contaminants of
39
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concern. Collect at least one background sample for
comparison, although additional samples are often
warranted by site-specific factors such as natural
variability of local geology and multiple sources.
Background samples may be collected to evaluate
potential error associated with sampling design,
sampling methodology, and analytical procedures.
Refer to U.S. EPA "Establishing Background Levels"
fact sheet, OSWER Directive 9285.7-19FS, for
detailed discussion on the proper selection and
considerations of a background sample location.
5.4.3 Rinsate Blank Samples
A rinsate blank, also referred to as an equipment
blank, is used to assess cross-contamination from
improper equipment decontamination procedures.
Rinsate blanks are samples obtained by running
analyte-free water over decontaminated sampling
equipment. Any residual contamination should appear
in the rinsate sample data. Analyze the rinsate blank
for the same analytical parameters as the field samples
collected that day. Handle and ship the rinsate like a
routine field sample. Where dedicated sampling
equipment is not utilized, collect one rinsate blank per
type of sampling device per day.
5.4.4 Field Blank Samples
Field blanks are samples prepared in the field using
certified clean water (FJPLC-grade water (carbon-free)
for organic analyses and deionized or distilled water
for inorganic analyses) which are then submitted to
the laboratory for analysis. A field blank is used to
evaluate contamination or error associated with
sampling methodology, preservation,
handling/shipping, and laboratory procedures.
Handle, ship, and analyze a field blank like a routine
field sample. Submit one field blank per day.
5.4.5 Trip Blank Samples
Trip blanks are samples prepared prior to going into
the field. They consist of certified clean water
(HPLC-grade) and are not opened until they reach the
laboratory. Utilize trip blanks for volatile organic
analyses only. Handle, transport, and analyze trip
blanks in the same manner as the other volatile
organic samples collected that day. Trip blanks are
used to evaluate error associated with shipping and
handling and analytical procedures. A trip blank
should be included with each shipment.
5.4.6 Performance Evaluation/
Laboratory Control Samples
A performance evaluation (PE) sample evaluates the
overall error contributed by the analytical laboratory
and detects any bias in the analytical method being
used. PE samples contain known quantities of target
analytes manufactured under strict quality control.
They are usually prepared by a third party under an
EPA certification program. The samples are usually
submitted "blind" to analytical laboratories (the
sampling team knows the contents of the samples, but
the laboratory does not). Laboratory analytical error
may be evaluated by the percent recoveries and
correct identification of the components in the PE
sample. Note: Even though they are not available for
all analytes, analyses of PE samples are
recommended in order to obtain definitive data.
A blind PE sample may be included in a set of split
samples provided to the potentially responsible party
(PRP). The PE sample will indicate PRP laboratory
accuracy, which may be critical during enforcement
litigation.
A laboratory control sample (LCS) also contains
known quantities of target analytes in certified clean
water. In this case, the laboratory knows the contents
of the sample (the LCS is usually prepared by the
laboratory). PE and LCS samples are not affected by
matrix interference, and thus can provide a clear
measure of laboratory error.
5.4.7 Matrix Spike/Matrix Spike
Duplicate Samples
Matrix spike and matrix spike duplicate samples
(MS/MSDs) are field samples that are spiked in the
laboratory with a known concentration of a target
analyte(s) in order to determine percent recoveries in
sample extraction. The percent recovery from
MS/MSDs indicates the degree to which matrix
interferences will affect the identification of a
substance. MS/MSDs can also be used to monitor
laboratory performance. When four or more pairs of
MS/MSDs are analyzed, the data obtained may be
used to evaluate error due to laboratory bias and
precision. Analyze one MS/MSD pair to assess bias
for every 20 samples, and use the average percent
recovery for the pair. To assess precision, analyze at
least eight matrix spike replicates from the same
sample, and determine the standard deviation and the
coefficient of variation. MS/MSDs are recommended
for screening data and are required as one of several
methods for determining analytical error for definitive
40
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data. Since the MS/MSDs are spiked field samples,
provide sufficient volume for three separate analyses
(triple volume). When selecting a well for spiked
samples, choose a well capable of providing steady
volume.
5.4.8 Laboratory Duplicate Samples
A laboratory duplicate is a sample that undergoes
preparation and analysis twice. The laboratory takes
two aliquots of one sample and analyses them as
separate samples. Comparison of data from the two
analyses provides a measure of analytical
reproducibility within a sample set. Discrepancies in
duplicate analyses may indicate poor homogenization
in the field or other sample preparation error, either in
the field or in the laboratory.
5.5 EVALUATION OF
ANALYTICAL ERROR
The acceptable level of error in sampling data is
determined by the intended use of the data and the
sampling objectives, including the degree of threat to
public health, welfare, or the environment; response
action levels; litigation concerns; and budgetary
constraints.
Error may be determined with replicate samples. To
evaluate the total error of samples with contaminant
concentrations near the response action level, prepare
and analyze a minimum of eight replicates of the same
sample. Analytical data from replicate samples also
serve as a quick check on errors associated with
sample heterogeneity, sampling methodology, and
analytical procedures. Different analytical results
from two or more replicate samples could indicate
improper sample preparation, or improper sample
handling, shipment, or analysis.
Although a quantified confidence level may be
desirable, it may not always be possible. A 95%
confidence level (5 percent acceptable error) should be
adequate for most Superfund activities. Note that the
use of confidence levels is based on the assumption
that a sample is homogeneous.
5.6 CORRELATION BETWEEN
FIELD SCREENING RESULTS
AND DEFINITIVE
LABORATORY RESULTS
One cost-effective approach for delineating the extent
of site contamination is to correlate inexpensive field
screening data and other field measurements with
definitive laboratory results. The relationship between
the two methods can then be described by a regression
analysis. The resulting equation can be used to
predict laboratory results based on field screening
measurements. In this manner, cost-effective field
screening results may be used in conjunction with off-
site laboratory analysis.
Statistical regression involves developing an equation
that relates two or more variables at an acceptable
level of correlation. In this case, the two variables are
field screening results and definitive laboratory
results. The regression equation can be used to
predict a laboratory value based on the results of the
screening device. The model can also be used to
place confidence limits around predictions.
Additional discussion of correlation and regression
can be found in most introductory statistics textbooks.
A simple linear regression equation can be developed
on many calculators or computer databases. Consult
a statistician to check the accuracy of more complex
models.
Evaluation of the accuracy of a model relies in part on
statistical correlation, which involves computing an
index called the correlation coefficient (r) that
indicates the degree and nature of the relationship
between two or more sets of values. The correlation
coefficient ranges from -1.0 (a perfect inverse or
negative relationship), through 0 (no relationship), to
+1.0 (a perfect, or positive, relationship). The square
of the correlation coefficient, called the coefficient of
determination, or simply R2, is an estimate of the
proportion of variance in the dependent variable. The
value of an acceptable coefficient of variation depends
on the sampling objectives and intended data uses. As
a rule of thumb, statistical relationships should have
an R2 value of at least 0.6 to determine a reliable
model. However, for health assessment purposes, the
acceptable R2 value may be more stringent (e.g., 0.8).
Analytical calibration regressions have an R2 value of
0.98 or greater.
41
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Field screening data can be used to predict laboratory
results if there is an acceptable correlation between
them. The predicted values can be located on a base
map and contoured. These maps can be examined to
evaluate the estimated extent of contamination and the
adequacy of the sampling program.
5.7 EXAMPLE SITE
5.7.1 Data Categories
Screening data which generate non-definitive,
unconfirmed results were used to select analytical
parameters and samples to be sent for laboratory
confirmation analysis. Samples were sent to the
analytical laboratory under protocols which provided
definitive data. The rigorous laboratory analyses
provided definitive identification and quantitation of
contaminants.
5.7.2 Sources of Error
All direct reading instruments were maintained and
calibrated in accordance with their instruction
manuals. Many of these instruments are class-specific
(e.g., volatile organic vapors) with relative response
rates that are dependent on the calibration gas
selected. Instrument response to ambient vapor
concentrations may differ by an order of magnitude
from response to calibration standards. If compounds
of interest are known, site-specific standards may be
prepared.
The number and location of initial field samples were
based on observation and professional judgment (as
outlined in Section 2.5.5). Field standard operating
procedures, documented in the site sampling plan,
established consistent screening and sampling
procedures among all sampling personnel, reducing
the chances for variability and error during sampling.
Site briefings were conducted prior to all sampling
and screening events to review the use of proper
screening and sampling techniques.
Other steps taken to limit error included proper
sample preparation, adherence to sample holding
times, and the use of proper IATA shipment
procedures. All off-site laboratory sample analyses
were performed using approved EPA standard
methods and protocols.
5.7.3 Field QA/QC Samples
Field QA/QC samples were collected during soil and
ground-water sampling at the ABC Plating site. Two
field replicate samples were collected for subsurface
soils; two wells (one overburden and one bedrock)
were selected for replicate collection and analysis of
ground water. Rinsate blanks were collected from
split spoon samplers, a bailer, and the submersible
rotary pump after decontamination by pouring
deionized water through the respective piece of
equipment and then into a sample container. The field
replicates and blanks were preserved and prepared as
"regular" field samples. A trip blank for VOC
analysis and a performance evaluation (PE) sample for
metals were sent to the laboratory. (The PE sample is
not affected by matrix interferences.) The trip blank
was provided by the laboratory (pre-filled and
preserved) and sent with the sample containers prior
to sample collection. One trip blank per day was
submitted to the laboratory. Additional volume was
collected and provided to the laboratory for matrix
spike/matrix spike duplicate analyses for one per 20
sample locations for each medium.
5.7.4 Laboratory QA/QC
Instructions on matrices, target compounds, and
QA/QC criteria of particular interest were provided to
the laboratory to help ensure that analytical results
met the required quality assurance objectives. The
laboratory analyzed for metals using the methods of
inductively coupled plasma (ICP) spectrometry and
atomic absorption (AA). Two SW-846 methods were
employed for hexavalent chromium analysis: Method
7196, a colorimetric method, and Method 2185, a
chelation method. These two methods were utilized
in an attempt to better quantify hexavalent results.
The presence of cyanide was confirmed in the
laboratory using total and amenable cyanide analyses
(colorimetric manual Method 9010).
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6.0 DA TA PRESENTA TION AND ANAL YSIS
6.1 INTRODUCTION
Data presentation and analysis techniques are
performed with analytical, field screening, or
geophysical results. The techniques discussed below
can be used to compare analytical values, to evaluate
numerical distribution of data, and to reveal the
location of "hot spots," contaminant plumes, and the
extent of contamination at a site. The appropriate
methods to present and analyze sample data depend on
the sampling objectives, the number of samples
collected, the sampling approaches used, and other
considerations.
6.2 DATA POSTING
Data posting involves placement of sample values on
a site base map or cross-section. Data posting is
useful for displaying the distribution of sample values,
visually depicting the location of contamination with
associated assessment data. Data posting requires
each sample to have a specific location (e.g., x, y, and
sometimes z coordinates). Ideally, the sample
coordinates are surveyed values facilitating placement
on a scaled map. Data posting is useful for depicting
concentration values of ground-water and plume
migration.
6.3 CROSS-SECTION/FENCE
DIAGRAMS
Cross-section diagrams (two-dimensional) and fence
diagrams (three-dimensional) depict subsurface
features such as stratigraphic boundaries, aquifers,
plumes, impermeable layers, etc. Two-dimensional
cross-sections may be used to illustrate vertical
profiles of ground-water concentrations on a site.
Both cross-sections and fence diagrams can provide
useful visual interpretations of contaminant
concentrations and migration.
6.4 CONTOUR MAPPING
Contour maps are useful for depicting ground-water
contaminant concentration values throughout a site.
Contour mapping requires an accurate, to-scale
basemap of the site. After data posting sample values
on the basemap, insert contour lines (or isopleths) at
a specified contour interval, interpolating values
between sample points. Contour lines can be drawn
manually or can be generated by computer using
contouring software. Although the software makes
the contouring process easier, computer programs
have a limitation: as they interpolate between data
points, they attempt to " smooth" the values by fitting
contour intervals to the full range of data values. This
can result in a contour map that does not accurately
represent general site contaminant trends. If there is
a big difference in concentration between a "hot spot"
and the surrounding area, the computer contouring
program, using a contour interval that attempts to
smooth the "hot spots," may eliminate most of the
subtle site features and general trends.
6.5 WELL LOCATION MAP
A well location map should be prepared using
surveyed data for all features at the site. This map
serves as a basemap onto which other data may be
plotted (e.g., data posting, contaminant plume
contours, water elevation contours). The map is
drawn to scale and incorporates all wells located,
installed, and sampled, including residential and
monitoring wells. The surveyed coordinates for each
monitoring well location could also be posted onto the
map (in feet above mean sea level (msl)) to illustrate
topography and surface gradient.
6.6 STATISTICAL GRAPHICS
The distribution or spread of the data set is important
in determining which statistical techniques to use.
Common statistical analyses, such as the t-test, rely on
normally distributed data. The histogram is a
statistical bar graph which displays the distribution of
a data set. A normally distributed data set takes the
shape of a bell curve, with the mean and median close
together about halfway between the maximum and
minimum values. A probability plot depicts
cumulative percent against the concentration of the
contaminant of concern. A normally distributed data
set, when plotted as a probability plot, appears as a
straight line. A histogram or probability plot can be
used to see trends and anomalies in the data from a
ground-water site prior to conducting more rigorous
forms of statistical analysis.
43
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6.7 RECOMMENDED DATA
INTERPRETATION METHODS
The data interpretation methods chosen depend on
project-specific considerations, such as the number of
sampling locations and their associated range in
values. Data which are dissimilar in composition
should not be compared using statistical interpretation
methods. Data posting, screening, and sampling data
sheets, and cross-section/fence diagrams may be
appropriate. A site feature showing extremely low
data values (e.g., non-detects), with significantly
higher values (e.g., 5,000 ppm) from neighboring "hot
spots" and little or no concentration gradient in
between, does not lend itself to contouring software.
6.8 EXAMPLE SITE
A water table contour map was generated with the
water level data for the shallow overburden
monitoring wells. This indicated a westward flow
direction, which generally coincides with the surface
topography. The deep bedrock wells lie nearly on a
straight line, and therefore a confident determination
of flow direction was not possible. A westward
component of flow direction is evident in the data,
however. The bedrock contact wells provided
inconsistent water level data, most likely due to the
presence of discontinuous perched water zones at the
well locations.
All ground-water samples were analyzed for total
chromium and cyanide. Cyanide was not found in any
of the samples above the 50 (ig/1 detection limit.
Using a detection limit of 50 (ig/1 for chromium, three
filtered samples were found to be contaminated at two
locations (3OB, and 6OB/6AW). Five of the
unfiltered ground-water samples (Wells 2SA, SOB,
4SA, 6OB, and 6AW) exceeded the detection limit.
These data were posted on a site/well location map to
illustrate well proximities, as well as a map indicating
the contours of contamination.
The rate of chromium contaminant migration in
ground water and the potential long-term impact to
nearby residential wells were estimated using a
mathematical model which included worst case
assumptions and evaluated attenuation of
contaminants through soil and ground water. The
OSC concluded that the potential for residential well
contamination was minimal. Removal of soil, the
source of contamination, was recommended. This
decision met the Phase 2 objective of establishing
early action options and consideration of long-term
remediation requirements for ground water.
All containers of wastes were removed from the site.
Soil treatment/disposal was completed using the
existing grid design. Cells were sampled and
designated as clean or excavated. Excavated material
was stockpiled while treatment/disposal options were
evaluated. Excavated cells were filled with stone and
clean soil. Composite sampling in each cell verified
cleanup, using an action level of 100 mg/kg chromium
in the soil composite. (The clean-up level was
established based on the earlier mathematical model
and soil attenuation calculations.) The soil response
served as an early action to meet the Phase 3 objective
originally established for the site.
44
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APPENDIX A -- Example of Flow Diagram For Conceptual Site Model
Figure A-1
Migration Routes of a Gas Contaminant
from Origin to Receptor
Change of
Original state Pathway contaminant
of contaminant from state In
of concern" origin pathway
conch
RpQ > A:r
V-^CIO r Mil
solldl
insatlon
> Liquid
_ **
> Solid
Mcatlon
Final
pathway
to receptor
> SO
^ sw
> so
> AT
> ^V J.
> sw
^ so
^ sw
Receptor
Human
G,D
G,D
I,D
I,D
G,D
G,D
G,D
Ecological Threat
Terrestrial
G,D
G,D
I,D
I,D
I,D
G,D
G,D
Aquatic
N/A
G,D
N/A
N/A
G,D
N/A
G,D
* May be a transformation product
** Includes vapors
Receptor Key
D - Dermal Contact
] - Inhalation
G Ingestlon
N/A - Not Applicable
Pathway Key
Al -Air
SO - Soil
SW = Surface Water
(Including sediments)
GW - Ground Water
45
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Figure A-2
Migration Routes of a Liquid Contaminant
from Origin to Receptor
Original state
of contaminant
of concern*
Liquid
sw
* Liquid
-> Gas**
SO
solidification
leachate,
Infiltration
AI
* May be a transformation product
** Includes vapors
Solid
Liquid
Gas
**
-> so
-> sw
-> GW
-> SO
-> AI
+ sw
Receptor Key
D Dermal Contact
I - Inhalation
G Ingestlon
N/A - Not Applicable
Receptor
Human
G,D
I,D
G,D
G,D
Ecological Threat
Terrestrial
G,D
I,D
G,D
G,D
Aquatic
G,D
N/A
G,A
G,D
G,D
G,D
G,D
G,D
G,D
N/A
N/A
G,D
N/A
G,D
I,D
G,D
G,D
I,D
G,D
N/A
N/A
G,D
Pathway Key
AI - Air
SO - Soil
SW - Surface Water
(Including sediments)
GW - Ground Water
46
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Figure A-3
Migration Routes of a Solid Contaminant
from Origin to Receptor
Original state
of contaminant
of concern*
Solid
AI
partlculates/
dust
Solid
sw
^ Solid
-> Liquid
SO
Gas
**
Solid
Liquid
* May be a transformation product
** Includes vapors
AI
SW
so
sw
sw
Receptor Key
D - Dermal Contact
I - Inhalation
G - Ingestlon
N/A - Not Applicable
Pathway Key
AI . Air
SO - Soil
SW - Surface Water
(Including sediments)
GW - Ground Water
Receptor
Human
I,D
G,D
G,D
Ecological Threat
Terrestrial
I,D
G,D
G,D
Aquatic
N/A
G,D
N/A
G,D
G,D
G,D
G,D
G,D
G,D
so
AI
SW
SO
SO
sw
G3D
I,D
G,D
G,D
G,D
G,D
G,D
G,D
I,D
G,D
G,D
G,D
N/A
G,D
N/A
N/A
G,D
N/A
N/A
N/A
G,D
47
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