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
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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
                                                 18

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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
                                                 21

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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.
                                                   22

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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.
                                                   23

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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

-------
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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Symbol
Stratigraphy
SP/
SM


SM


SP



SC


SP

SM


SM/
SC




SC

Sample Description

Tan. vf. Sd. w. 10% Sit.

As above w. 30% Sit.

Tan. vf. Sd. coarsening
to med. Sd. at 25'



Tan. vf. Sd. w. 10% Gry.
lumpy Cly.
Iron oxide staining
Tan. F-med. Sd.
As above w. 2% Sit. & Cly.

Tan. vf. Sd. & Sit. w. lumps of
Gry. Cly. w. Iron oxide staining



Brn. vf. Sd. & Sit. w. lumps of
Gry. Cly. w. Iron oxide staining
Cly. 30%
Completion Data
Protective steel casing
with locking cap





Portland
Cement
+ 5%
Bentonite
Grout

41 Diam.
PVP
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Casing


# 2/16
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0.010
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TD56ft
                       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.
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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).
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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.
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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.
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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.
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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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                                       50

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