United States
Environmental Protection
Agency
Research and Development
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
EPA/600/S2 85/104 Feb. 1986
SER& Project Summary
Practical Guide for
Ground-Water Sampling
Michael J. Barcelona, James P. Gibb, John A. Helfrich, and Edward E. Garske
This work was initiated as the second
phase of an investigation of the reliabil-
ity of monitoring well construction and
ground-water sampling techniques. The
project also included both laboratory
and field testing of sampling materials
and sampling mechanisms with an
emphasis on minimizing error, particu-
larly for volatile organic compound
sampling and analysis. The Guide is a
companion volume to the Phase 1
report, "A Guide to the Selection of
Materials for Monitoring Well Construc-
tion and Ground-Water Sampling,"
(EPA/600/2-83/024).
The full report explains the need to
address the quality control and quality
assurance considerations of a ground-
water monitoring program at the outset
of planning. The sampling and analytical
protocols for specific monitoring instal-
lations should be integrated into a well
conceived design for the collection of
high quality hydrologic and chemical
data. Though accuracy and precision
data provide measures of data quality, it
is equally important to collect samples
that are representative of in situ condi-
tions. These goals can be achieved if the
essential elements of a ground-water
sampling program are addressed in the
preliminary and implementation phases
of monitoring program development.
The essential elements of effective
ground-water sampling include:
• Evaluation of the hydrogeologic set-
ting and program information needs,
• Proper placement and construction
of the well,
• Evaluation of performance of the
well and purging strategies, and
• The design and execution of sampling
and analytical protocols which entail
appropriate selection of sampling
mechanisms and materials as well as
sample collection, handling and
analysis procedures.
Detailed discussions of the advan-
tages and disadvantages of various
approaches to selecting appropriate
methods and materials for specific
monitoring purposes are provided in the
Guide. The emphasis is on straightfor-
ward techniques which minimize both
the disturbance of the subsurface envi-
ronment and the potential sources of
error for routine sampling applications.
Further, specific recommendations are
made for step-by-step sampling proto-
cols which should be applied in sampling
for volatile organic compounds which
are among the most difficult chemical
constituents to sample effectively. The
recommendations are supported by
extensive references, where the litera-
ture permits, and it should prove useful
to the planning and execution of regula-
tory and research activities which
demand high quality ground-water
quality data.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, and the
Environmental Monitoring Systems
Laboratory, Las Vegas, NV, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
Ground-water monitoring is conducted
for a variety of purposes, though detective
and assessment compliance monitoring
efforts are most common. The absence of
proven recommendations for effective
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monitoring network designs and reliable
sampling protocols has resulted in the
collection of ground-water quality data
with questionable value. When this type
of data is used as a basis for assessment
or remedial action activities, the success
of these actions may be very limited.
Recent research has demonstrated that
the details of well construction, choice of
sampling mechanisms and materials and
sampling protocols can introduce errors
into analytical results which exceed those
involved in the analytical procedures.
Analytical operations have been the major
focus of quality assurance and quality
control (QA/AC) recommendations for
monitoring programs. Sampling QA/AC
is equally important to the development
of high quality data which is representa-
tive of the site under investigation. Re-
quiring that water samples be represen-
tative of the in situ condition is insufficient
to ensure a high level of confidence in the
monitoring results. The hydraulic per-
formance of the well (i.e., sampling point)
and the integrity of the sampling protocol
must be established before samples are
collected, if representative data are to be
generated. Then the characteristics of a
representative sample can be established
for the specific goals of the program.
The Guide provides a thorough discus-
sion of the essential elements of well
construction and sampling protocols for
the collection of high quality ground-
water quality data. Representative water
samples are generally defined by being
minimally disturbed samples which satis-
fy charge balance considerations and
permit the determination of trace organic
compounds at their limits of quantitation
within acceptable accuracy and precision
limits. Each element of the sampling
protocol for a particular investigation can
be evaluated for its contribution to error
in the final results.
The available literature supports the
approach that a representative sampling
protocol for volatile or reactive chemical
constituents can satisfy the most demand-
ing data quality requirements applied to
routine monitoring efforts. Sampling and
analytical protocol development must be
tailored to the actual hydrogeologic con-
ditions of the site under investigation.
Careful attention to the elements of the
sampling protocol will permit the refine-
ment of routine procedures as the moni-
toring activity develops. The emphasis of
the recommendations is on the simplest
sampling procedures possible which
provide data of known quality over the
duration of the monitoring effort.
Hydrogeologic Setting and
Information Requirements
The hydrogeologic conditions at each
site (e.g., background and regulated unit)
must be evaluated for the potential im-
pacts the setting may have on the devel-
opment of the monitoring program and
the quality of the resulting data. The types
and distribution of geologic materials, the
occurrence and movement of ground
water through those materials, the loca-
tion of the site in the regional ground-
water flow system, the relative perme-
ability of the materials and the potential
interactions between the mineral and
biological constituents of the formations
of interest, and the chemical constituents
of interest must all be considered. Both
the direction and the rate of ground-
water movement are important. Piezo-
metric surface data or water level infor-
mation on each geologic formation at
properly selected locations will provide
the basis for determining horizontal and
vertical ground-water flow paths at the
site. There are significant differences
between the hydrogeology of arid and
humid climatic regions, as well as sea-
sonal variations which should be taken
into account. The rate of ground-water
travel can be used to calculate optimum
sampling frequencies, should additional
detail beyond that provided in quarterly
sampling become necessary.
Additional site and waste information
needs arise when tailoring the sampling
and analytical protocols to the specific
needs of the program. A minimum data
set for ground-water monitoring should
include general water quality parameters,
hydrologic parameters and pollutant indi-
cator parameters. A suggested list of
basic measurements is provided below:
Chemical Parameters
pH, CT\ TOC, TOX
Alkalinity, CL , NO3 , SO/, PO« , silicate
Na*, K+, Ca++, Mg++, Fe and Mn
Hydrologic Parameters
Water Level, hydraulic conductivity
The pollutant indicator parameters
noted above [i.e., pH, Q~1, (specific con-
ductance), TOC andTOX] provide minimal
capability to ensure the detection of target
chemical constituents in ground water.
The pH and conductance parameters
should be measured with care in the field.
TOC and TOX determinations should be
made after collection in headspace-free
glass vials with Teflon®* septa to preserve
the volatile organic fraction of the dis-
solved organic matter The pollutant
indicator parameters should also be sup-
plemented with determinations of specific
chemical constituents which are likely to
be mobile and persistent in the subsur-
face.
Well Placement and
Construction Procedures
The placement and construction of
monitoring wells are among the most
difficult tasks involved in developing an
effective monitoring program. The prelim-
inary locations and depths of monitoring
wells should be selected on the basis of
the best available pre-drilling information.
Then, as the installation of these wells
progresses, new geologic and hydroiogic
data should be incorporated into the
overall monitoring plan to ensure that the
wells will perform the tasks for which
they are designed. It is advisableto select
initially a minimum array of monitoring
wells for the collection of geologic and
hydrologic data. Additional wells can be
positioned later at monitoring points likely
to intercept contaminant flow paths.
Well construction should be accom-
plished with minimal disturbance of the
subsurface. The selection and cleaning of
both drilling equipment and well con-
struction materials should be performed
with the aim of minimizing the intro-
duction of foreign materials into the
subsurface environment. Given the rela-
tively shallow depths of interest in many
ground-water monitoring efforts, hollow-
stem auger drilling techniques are pre-
ferred because they are mobile, fast, and
inexpensive. Also, disturbance of the
subsurface can be effectively minimized.
To properly define the movement of
pollutants, in both vertical and horizontal
directions, it is essential to collect depth
discrete water level data. Well completion
depth will depend on the location of the
uppermost permeable, saturated zone
(i.e., "water-table") in unconfined forma-
tions or the piezometric surface of the
most shallow permeable zone in confined
formations. Vertically nested wells pro-
vide information on the vertical direction
of ground-water movement and their
placement will be a function of the hydro-
geologic setting, particularly the relative
horizontal and vertical permeabilities of
the formations beneath the site. Screen
size, grouts, seals and sampling point
•Mention of trade names or commercral products
does not constitute endorsement or recommenda-
tion for use
-------
documentation are also important aspects
of monitoring well construction which
should be addressed in the monitoring
program.
Evaluation of Well Performance
The effectiveness of a ground-water
monitoring program may be judged on the
attention which has been paid to the
evaluation of the hydraulic performance
of the monitoring well network. Each well
should be properly developed after con-
struction and periodically redeveloped to
ensure that it provides useful hydraulic
data. Development also reduces the time
and effort necessary to collect representa-
tive ground-water quality information. A
variety of proven well development tech-
niques are amenable to the development
of shallow 2" o.d. monitoring wells.
Accurate water level measurements pro-
vide the primary data for the evaluation of
well performance. Steel tapes(graduated
to the nearest hundredth of a foot with
raised lettering and divisions), electrical
drop lines and sensitive pressure trans-
ducers are useful tools in this regard.
Field hydraulic conductivity testing of
the monitoring wells will avoid the un-
resolved issues which attend the inter-
pretation of laboratory conductivity test
results. Slug or bail tests, repeated at
least threetimes, should provide accurate
hydraulic conductivity determinations
with a precision of ±20%. In general,
multiple pump tests are too expensive to
consider for evaluating the hydraulic
performance of all monitoring wells with-
in a site network. The results of conduc-
tivity tests provide a basic measure of
well hydraulic well performance which is
useful for judging the significance of
water level excursions and long-term well
performance. The testing procedures
should be repeated at least every five
years and after each redevelopment effort
is performed. Well performance evalua-
tion also provides a basis for determining
an appropriate well purging strategy prior
to sampling. No single number of purge
volumes to be pumped prior to sampling
can be expected to suit all situations. A
well conceived purging strategy that
includes pumping rates and volumes
calculated on the basis of well perform-
ance and the transmissivity of the forma-
tion of interest is essential to effective
ground-water sampling efforts.
Sampling Protocol
The hydraulic performance of the
sampling points permits the design and
execution of effective water sampling and
analytical protocols. These protocols
should be planned for collecting verif iably
high quality water chemistry results in
order to distinguish natural variability in
the geochemistry of the subsurface from
those caused by site operations. The
sampling protocol should incorporate
sampling mechanismsand materialsthat
are appropriate for the information needs
of the program. Since contaminant
migration may be detected at trace (e.g.,
ppb) levels of individual constituents,
sampling mechanisms and materials
must be very carefully chosen to avoid
biases caused by contamination or sorp-
tion. The materials of well construction,
samplers and sample transfer tubing are
as important as sample storage vessels
and analytical performance in this re-
spect. Recommended materials for well
construction and sampling devices are
shown in Tables 1 and 2. Materials'
selections should be made with the long-
term use of the sampling points in mind.
Sampling mechanisms are devices for
the collection of water samples. They are
not, of themselves, sampling methods.
This should be clear from inspection of
Figure 1. The steps in the sampling
protocol in the first column of the figure
are common to all ground-water monitor-
ing efforts. Though the details of indi-
vidual monitoring efforts may vary, the
steps in Figure 1 provide a guide for
effective planning. The performance of
the sampling point, materials selected
and the chemical constituents of interest
will dictate the choice of appropriate
sampling devices. Figure 2 contains
recommendations for sampling mecha-
nisms according to the specific demands
of the monitoring effort.
Conclusions
The development of reliable sampling
protocols for ground-water quality moni-
toring is a complex, programmatic process
that must be designed to meet the specific
Table 1.
Recommendations for Rigid Materials in Sampling Applications (In Decreasing
Order of Preference)
Material
Recommendations
Teflon®
(flush threaded)
Stainless Steel 316
(flush threaded)
Stainless Steel 304
(flush threaded)
PVC
(flush threaded)
other noncemented
connections, only NSF*
approved materials for
well casing or potable
water applications
Low-Carbon Steet
Galvanized Steel
Carbon Steel
Recommended for most monitoring situations with detailed
organic analytical needs, particularly for aggressive, organic
leachate impacted hydrogeologic conditions. Virtually an ideal
material for corrosive situations where inorganic contaminants
are of interest.
Recommended for most monitoring situations with detailed
organic analytical needs, particularly for aggressive, organic
leachate impacted hydrogeologic conditions.
May be prone to slow pitting corrosion in contact with acidic high
total dissolved solids aqueous solutions. Corrosion products
limited mainly to Fe and possibly Cr and Ni.
Recommended for limited monitoring situations where inorganic
contaminants are of interest and it is known that aggressive
organic leachate mixtures will not be contacted. Cemented
installations have caused documented interferences.
The potential for interaction and interferences from PVC well
casing in contact with aggressive aqueous organic mixtures is
difficult to predict. PVC is not recommended for detailed organic
analytical schemes.
Recommended for monitoring inorganic contaminants in
corrosive, acidic inorganic situations. May release Sn or Sb
compounds from the original heat stabilizers in the formulation
after long exposures.
May be superior to PVC for exposures to aggressive aqueous
organic mixtures. These materials must be very carefully cleaned
to remove oily manufacturing residues. Corrosion is likely in high
dissolved solids, acidic environments, and particularly when
sulfides are present. Products of corrosion are mainly Fe andMn,
except for galvanized steel which may release Zn and Cd.
Weathered steel surfaces present very active adsorption sites for
trace organic and inorganic chemical species.
®Trademark of DuPont, Inc.
* National Sanitation Foundation approved materials carry the NSF logo indicative of the product's
certification of meeting industry standards for performance and formulation purity.
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Table 2. Recommendations for Flexible Materials in Sampling Applications fin Decreasing
Order of Preference)
Materials
Recommendations
Teflon®
Polypropylene
Polyethylene (linear)
PVC (flexible)
Viton®
Silicone
(medical grade only)
Neoprene
Recommended for most monitoring work, particularly for detailed
organic analytical schemes. The material least likely to introduce
significant sampling bias or imprecision. The easiest material to
clean in order to prevent cross-contamination.
Strongly recommended for corrosive high dissolved solids
solutions. Less likely to introduce significant bias into analytical
results than polymer formulations (PVC) or other flexible
materials with the exception of Teflon®.
Not recommended for detailed organic analytical schemes.
Plasticizers and stabilizers make up a sizable percentage of the
material by weight as long as it remains flexible. Documented
interferences are likely with several priority pollutant classes.
Flexible elastomeric materials for gaskets, O-rings, bladder and
tubing applications. Performance expected to be a function of
exposure type and the order of chemical resistance as shown.
Recommended only when a more suitable material is not
available for the specific use. Actual controlled exposure trials
may be useful in assessing the potential for analytical bias.
®Trademark of DuPont, Inc.
goals of the monitoring effort in question.
The long-term goals and information
needs of the monitoring program must
first be thoroughly understood. Once
these considerations have been identified,
the many factors that can affect the
results can be addressed.
In formulating the sampling protocol,
the emphasis should be to collect hydro-
logic and chemical data that accurately
represent in situ hydrologic and chemical
conditions. With good quality assurance
guidelines and quality control measures,
the protocol should provide the needed
data for successful management of the
monitoring program at a high level of
confidence. Straightforward techniques
that minimize the disturbance of the
subsurface and the samples at each step
in the sampling effort should be given
priority.
The planning of a monitoring program
should be a staged effort designed to
collect information during the exploratory
or initial stages of the program. Informa-
tion gained throughout the development
of the program should be used for refining
the preliminary program design. During
all phases of protocol development, the
long-term costs of collecting the required
hydrologic and chemical data should be
kept in mind. These long-term costs may
be several orders of magnitude larger
than the combined costs of planning, well
construction, purchase of sampling and
support equipment, and data collection
start-up. It also should be remembered
that high quality data cannot be obtained
from a poorly conceived and implemented
monitoring program, regardless of the
added care and costs of sophisticated
sampling and analytical procedures.
Finally, the ultimate costs of defending
poor quality data in court or in compliance
to regulatory requirements should not be
overlooked. Due to the lack of documented
standard techniques for developing moni-
toring programs, constructing monitoring
wells, and collecting samples, quality
control measures must be tailored for
each individual site to be monitored. They
should be designed to ensure that dis-
turbances to both the hydrogeologic
system and the sample are minimized.
The care exercised in the well placement
and construction, and sample collection
and analysis can pay real dividends in the
control of systematic errors. Repeated
sampling and field measurements will
further define the magnitude of random
errors induced by field conditions and
human error. The burden of assuring the
success of a program relies on careful
documentation and the performance of
quality assurance audit procedures.
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Step
Procedure
Essential Elements
Well Inspection
Well Purging
Sample Collection
Filtration*
Field
Determinations**
Preservation
Field Blanks
Standards
Hydrologic Measurements
\
Removal or Isolation of
Stagnant Water
\
Determination of Well-Purging
Parameters (pH, Eh. T, fT1)**
Unfiltered
Volatile Organics, TOX
Dissolved Gases. TOO
Large Volume Samples for
Organic Compound
Determinations
Assorted Sensitive
Inorganic Species
NOi, NH<\ Fe (II)
(as needed for good
QA/QCI
Field Filtered*
Alkalinity/A cidity*
Trace Metal Samples
S°, Sensitive
Inorganics
Major Cation and
Anions
Storage
Transport
Water-level Measurements
Representative Water Access
Verification of Representa-
tive Water Sample Access
Sample Collection by
Appropriate Mechanism
Minimal Sample Handling
Head-Space Free Samples
Head-Space Free Samples
Minimal Aeration or
Depressurization
Minimal Air Contact,
Field Determination
Adequate Rinsing Against
Contamination
Minimal Air Contact,
Preservation
Minimal Loss of Sample
Integrity Prior to Analysis
'Denotes samples that should be filtered in order to determine dissolved constituents. Filtration should be accomplished preferably with in-line filters
and pump pressure or by /Vz pressure methods. Samples for dissolved gases or volatile organics should not be filtered. In instances where well
development procedures do not allow for turbidity-free samples and may bias analytical results, split samples should be spiked with standards before
filtration. Both spiked samples and regular samples should be analyzed to determine recoveries from both types of handling.
**Denotes analytical determinations which should be made in the field.
Figure 1. Generalized flow diagram of ground- water sampling steps.
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Type of
Constituent
Volatile
Organic
Compounds
Organometallics
Dissolved Gases
Well-Purging
Parameters
Trace Inorganic
Metal Species
Reduced Species
Major Cations
& Anions
Example of
Constituent
Chloroform
TOX
CHaHg
Oa. C02
PH. rr1
Eh
Fe, Cu
NOi. S"
Na\ 1C. Ca"
Mg"
cr, so**
Positive
Displacement
Bladder Pumps
Sample Sensitivit
Increasing ,'
Superior
Performance for
Most Applications
Superior
Performance for
Most Applications
Superior
Performance for
Most Applications
Superior
Performance for
Most Applications
Thief, in situ or
Dual Check Valve
Bailers
May be adequate if
well purging is
assured
May be adequate if
we II purging is
assured
May be adequate if
well purging is
assured
Adequate
May be adequate if
we/I purging is
aec//r^/V
Mechanical Positive
Displacement Pumps
Gas-Drive
Devices
Suction
Mechanisms
'eliability of Sampling Mechanisms
May be adequate if
design and operation
are controlled
May be adequate if
design and operation
are controlled
Adequate
Adequate
Not
recommended
Not
recommended
May be
adequate
Adequate
Not
recommended
Not
recommended
May be ade-
quate if
materials
are approp-
riate
Adequate
Figure 2. Matrix of sensitive chemical constituents and various sampling mechanisms.
. S. GOVERNMENT PRINTING OFFICE:] 986/646-116/20770
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Michael J. Barcelona, James P. Gibb, John A. Helfrich. and Edward E. Garskeare
with the Illinois State Water Survey. Champaign, IL 61820.
Marion R. Scalf is the EPA Project Officer (see below).
The complete report, entitled "Practical Guide for Ground-Water Sampling,"
(Order No. PB 86-137 304/AS; Cost: $16.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P.O.Box 1198
Ada, OK 74820
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
All
Official Business
Penalty for Private Use S300
EPA/600/S2.-85/104
0000329 PS
4GENCT
230 S DEARBORN STREET
CHICAGO it 60604
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