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Ground-Water Sampling
Guidelines for Superfund and
RCRA Project Managers
GROUND WATER FORUM ISSUE PAPER
Douglas Yeskis* and Bernard Zavala*
BACKGROUND
The Ground Water, Federal Facilities and Engineering
Forums were established by professionals from the
United States Environmental Protection Agency
(USEPA) in the ten Regional Offices. The Forums are
committed to the identification and resolution of
scientific, technical, and engineering issues impacting
the remediation of Superfund and RCRA sites. The
Forums are supported by and advise OSWER's
Technical Support Project, which has established
Technical Support Centers in laboratories operated by
the Office of Research and Development (ORD),
Office of Radiation Programs, and the Environmental
Response Team. The Centers work closely with the
Forums providing state-of-the-science technical
assistance to USEPA project managers.
This document provides sampling guidelines primarily
for ground-water monitoring wells that have a screen
or open interval with a length of ten feet or less and
which can accept a sampling device. Procedures that
minimize disturbance to the aquifer will yield the most
representative ground-water samples. This document
provides a summary of current and/or recommended
ground-water sampling procedures. This document
was developed by the Superfund/RCRA Ground Water
Forum and incorporates comments from ORD,
Regional Superfund hydrogeologists and others.
These guidelines are applicable to the majority of
sites, but are not intended to replace or supersede
regional and/or project-specific sampling plans. These
guidelines are intended to assist in developing sam-
pling plans using the project-specific goals and objec-
tives. However, unusual and/or site-specific circum-
stances may require approaches other than those
specified in this document. In these instances, the
appropriate Regional hydrologists/geologists should
be contacted to establish alternative protocols.
ACKNOWLEDGMENTS
A document of this scope involved significant partici-
pation from a number of people, such that any omis-
sion in these acknowledgments is purely uninten-
tional. We thank all of the participants involved in the
development of this document! The authors acknowl-
edge the active participation and valuable input from
the committee from the Ground Water Forum of Dick
Willey, Region 1; Ruth Izraeli and Kevin Willis, Region
2; Kathy Davies, Region 3; Robert Puls, ORD-
NRMRL; and Steve Gardner, ORD-NERL. In addition,
valuable input from former members of the committee
are gratefully acknowledged. And finally, the peer
reviews of the document completed by Franceska
Wilde of the Water Division of the U.S. Geological
Survey, Reston, VA; Richard Duwelius and Randy
Bayless of the Indiana District of the U.S. Geological
Survey, Indianapolis, IN; Steve White of the Omaha
District of the U.S. Army Corps of Engineers, Omaha,
NE and Karl Pohlmann of the Desert Research
Institute, Las Vegas, NV are gratefully acknowledged.
Technical Support Project
* U.S. Environmental Protection Agency, Region 5
77 West Jackson Boulevard
Chicago, Illinois 60604
**U.S. Environmental Protection Agency, Region 10
1200 Sixth Avenue
Seattle, Washington 98101
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Office of Solid Waste
and Emergency
Response
EPA 542-S-02-001
May 2002
www.epa.gov/tio
www.clu-in.org/tio/tsp
TABLE OF CONTENTS
INTRODUCTION.
CONCLUSION 11
SAMPLING OBJECTIVES 3 REFERENCES.
.11
INFORMATION NEEDED PRIOR TO SAMPLING 4
BACKGROUND DATA 4
REFERENCE POINT 4
TOTAL WELL DEPTH 5
DEPTH TO WATER 5
GROUND-WATER SAMPLING METHODS 5
PURGING AND SAMPLING DEVICES 6
POSITION OF SAMPLE INTAKE 7
PURGE CRITERIA 8
Low-Stress Approach 8
Well-Volume Approach 8
LOW-PERMEABILITY FORMATIONS .9
DECISION PROCESS FOR DETERMINING
APPLICABLE SAMPLING METHODOLOGY. 10
POTENTIAL PROBLEMS 10
SAMPLE CONTAINERS .10
FIELD FILTRATION OFTURBIDSAMPLES.10
SAMPLER DECONTAMINATION 11
POST-SAMPLING ACTIVITIES 11
TABLES
1. Stabilization Criteria with References
for Water-Quality-lndicator
Parameters 17
2. Applicability of Different Approaches
for Purging and Sampling Monitoring
Wells 18
ATTACHMENTS
1. Example Sampling Checklist 21
2. Example Ground-Water Sampling Field
Sheets 25
3. Example Standard Operating Procedure:
Standard Operating Procedure for
Low-Stress (Low Flow)/Minimal
Drawdown Ground-Water Sample
Collection 29
4. Example Standard Operating Procedure:
Standard Operating Procedure for the
Standard/Well-Volume Method for
Collecting a Ground-Water Sample...41
INTRODUCTION
The goal of ground-water sampling is to collect
samples that are "representative" of in-situ ground-
water conditions and to minimize changes in ground-
water chemistry during sample collection and han-
dling. Experience has shown that ground-water
sample collection and handling procedures can be a
source of variability in water-quality concentrations
due to differences in sampling personnel, sampling
procedures, and equipment (U.S. Environmental
Protection Agency, 1995).
Several different ground-water sampling procedures
can be used, which vary primarily through the criteria
used to determine when a sample is representative of
ground-water conditions. No single method or proce-
dure is universally applicable to all types of ground-
water-sampling programs; therefore, consideration
should be given to a variety of factors when
determining which method is best suited to site-
specific conditions. These site-specific conditions
include sampling objectives, equipment availability,
site location, and physical constraints. This paper will
discuss each of these conditions and how they may
contribute to the decision in choosing the appropriate
sampling methodology and equipment to be used
during ground-water sampling.
This paper focuses on ground-water sampling proce-
dures for monitoring wells only where separate, free-
phase, Non-Aqueous Phase Liquids (NAPLs) are not
present in the monitoring well. Residential and/or
municipal-production wells where special sampling
procedures and considerations need to be imple-
mented are not discussed in this document. The
recommendations made in this paper are based on
findings presented in the current literature, and will be
subject to revision as the understanding of ground-
water-sampling procedures increases.
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SAMPLING OBJECTIVES
The objective of a good sampling program should be
the collection of a "representative" sample of the
current ground-water conditions over a known or
specified volume of aquifer. Ideally to meet this
objective, sampling equipment, sampling method,
monitoring well construction, monitoring well
operation and maintenance, and sample handling
procedures should not alter the chemistry of the
sample. A sample that is obtained from a poorly
constructed well, or using improper sampling equip-
ment, or using poor sampling techniques, or which
has been preserved improperly, can bias the sampling
results. Unrepresentative samples can lead to
misinterpretations of ground-water-quality data.
Generally, the costs of obtaining representative
ground-water samples are insignificant when
compared to potential remedial responses that may
be implemented based on erroneous data or when
considering the overall monitoring program costs over
the life of the program (Nielson, 1991).
The data quality objectives (DQOs) of the sampling
program should be thoroughly developed, presented
and understood by all parties involved. To develop the
DQOs, the purpose of the sampling effort and data
use(s) should be clearly defined. The sampling
guidelines presented here can be used for a variety of
monitoring programs, these include site assessment,
contaminant detection, site characterization,
remediation, corrective action and compliance
monitoring.
For example DQOs for a site characterization
sampling effort might vary from those of a remediation
monitoring sampling effort. This difference could be in
how much of the screen interval should be sampled. A
site characterization objective may be to collect a
sample that represents a composite of the entire (or
as close as is possible) screened interval of the
monitoring well. On the other hand, the monitoring
objective of a remediation monitoring program may be
to obtain a sample that represents a specific portion of
the screened interval.
Additionally, the site characterization may require
analyses for a broad suite of contaminants, whereas,
the remediation monitoring program may require
fewer contaminants to be sampled. These differences
may dictate the type of sampling equipment used, the
type of information collected, and the sampling
protocol.
In order to develop applicable DQOs, a site concep-
tual model should be developed. The site conceptual
model should be a dynamic model which is constantly
revised as new information is collected and pro-
cessed. The conceptual model, as it applies to the
DQOs, should focus on contaminant fate and trans-
port processes, such as contaminant pathways, how
the geologic materials control the contaminant path-
ways (depositional environments, geologic structure,
lithology, etc.), types of contaminants present (i.e.,
hydrophobic versus hydrophilic), and the processes
that influence concentrations of the contaminants
present such as dilution, biodegradation, and disper-
sion. The detail of the conceptual model will depend
greatly on the availability of information, such as the
number of borings and monitoring wells and the
amount of existing analytical data. Clearly, a site that
is being investigated for the first time will have a much
simpler conceptual model compared to a site that has
had a Remedial Investigation, Feasibility Study, and
Remedial Design, (or, within the RCRA Program, a
RCRA Facility Assessment, a RCRA Facility Investiga-
tion, and a Corrective Measures Study), and is cur-
rently in remediation/corrective action monitoring.
Specific parameters that a conceptual model should
describe that may impact the design of a ground-
water-sampling program include:
a) The thickness, lateral extent, vertical and
horizontal flow direction, and hydraulic con-
ductivity contrasts of the geologic materials
controlling contaminant transport from the site
(thick units versus thin beds versus fractures,
etc.)
b) The types of contaminants to be sampled
(volatile organic compounds, semi-volatile
organic compounds, metals, etc.) and factors
that could bias sampling results (turbidity for
metals, co-solvation effects on PCBs, etc.)
c) Lateral and vertical distribution of contami-
nation (contaminants distributed throughout an
entire unit being monitored versus localized
distribution controlled by small scale features,
etc.)
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Vertical aquifer characterization is strongly recom-
mended prior to the completion of a ground-water
monitoring well installation program. A detailed vertical
aquifer characterization program should include field
characterization of hydraulic conductivities, determi-
nation of vertical and horizontal flow directions, as-
sessment of lithologic and geologic variations, and
determination of vertical and horizontal contaminant
distributions. The successful aquifer characterization
program provides detailed information to guide the
technical and cost-effective placement, vertically and
areally, of monitoring wells.
INFORMATION NEEDED PRIOR TO SAMPLING
To ensure appropriate methodology and expedient
collection of water-quality samples, information is
needed before a sample is collected. Some
information should be obtained prior to the start of
field activities such as well condition, construction,
water-level information, contaminant types and con-
centrations, and direction(s) of ground-water flow.
Field measurements, such as depth to water and total
well depth will be needed prior to purging. Before
commencement of all field activities, the field health
and safety plan should be consulted under the
direction of the site health and safety officer.
BACKGROUND DATA
Well construction and maintenance information are
needed to better plan the sampling program, optimize
personnel, and obtain more representative samples.
Prior to field activities, personnel should have specific
information including well casing diameter, borehole
diameter, casing material, lock number and keys,
physical access to wells, and length of and depth to
well screen. The diameter of each well casing is used
to select the correct equipment and technique for
purging and sampling the well. A site map with pos-
sible physical barriers and description of access is
necessary to allow for the selection of proper equip-
ment based on several factors, such as portability,
ease of repair, power sources, containment of purge
water, and well accessibility. The length and depth of
each well screen and depth to water is important
when placing a sampling device's intake at the proper
depth for purging and sampling and for choosing a
sampling device. Well development information is
needed to ensure that purging and sampling rates will
not exceed well development extraction rates. Previ-
ous sampling information should be provided and
evaluated to determine the nature and concentrations
of expected contaminants. This will be useful in
determining the appropriate sampling method and
quality assurance/quality control (QA/QC) samples
(for example, field duplicates, equipment blanks, trip
blanks). Attachment 1 is an example of a sampling
checklist for field personnel. This information should
be kept in the field for easy access during sampling
activities.
When evaluating previous sampling information,
consideration should be given to the amount of time
that has expired between the last sampling effort and
the planned sampling effort. If this time exceeds one
year, the need for redevelopment of the monitoring
wells should be evaluated. The necessity of redevel-
opment can be evaluated by measuring constructed
depth compared to the measured depth. If the depth
measurement indicates siltation of the monitoring well
screen, or evidence exists that the well screen is
clogged, the well should be redeveloped prior to
sampling. The assessment of the condition of the
monitoring wells should be completed several weeks
prior to sampling activities in order to allow the proper
recovery of the developed wells. This is especially
important in wells where prior sampling has indicated
high turbidity. The time for a well to re-stabilize after
development is dependent on site-specific geology
and should be specified in the site sampling plan. The
development method, if necessary, should be consis-
tent with the sampling objectives, best technical
criteria and USEPA guidelines (Aller et al., 1991;
Izraeli etal., 1992; Lapham etal., 1997).
REFERENCE POINT
Each well should be clearly marked with a well identi-
fier on the outside and inside of the well casing.
Additionally, each well should have a permanent,
easily identified reference point from which all depth
measurements are taken. The reference point (the top
of the inner casing, outer casing, or security/protec-
tive casing) should remain constant through all mea-
surements, should be clearly marked on the casing
and its description recorded. Whenever possible, the
inner casing is recommended as a reference point,
because of the general instability of outer casings due
to frost heaving, vehicular damage, and other phe-
nomena which could cause movement of casings.
The elevation of this reference point should be known
and clearly marked at the well site (Nielson, 1991).
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This reference point should also have a known latitude
and longitude that are consistent with the Regional
and National Minimum Data Elements requirements.
The elevation of the reference point should be sur-
veyed relative to Mean Sea Level (MSL) using the
NAVD 88 datum.
TOTAL WELL DEPTH
The depth of the well is required to calculate the
volume of standing water in the well and to document
the amount of siltation that may have occurred.
Moreover, measuring the depth to the bottom of a well
provides checks for casing integrity and for siltation of
the well screen. Corrosion can cause leaking or
collapse of the well casing, which could lead to erro-
neous or misleading water-level measurements.
Corrosion, silting, and biofouling can clog well
screens and result in a sluggish response or no
response to water-level changes, as well as changes
in ground-water chemistry. Well redevelopment or
replacement may be needed to ensure accurate
collection of a representative water-quality sample.
Total well depths should be measured and properly
recorded to the nearest one-tenth of a foot using a
steel tape with a weight attached. The steel tape
should be decontaminated before use in another well
according to the site specific protocols. A concern is
that when the steel tape and weight hit the bottom of
the well, sediment present on the bottom of a well
may be stirred up, thus increasing turbidity which will
affect the sampling results. The frequency of total well
depth measurements varies, with no consensus for all
hydrogeologic conditions. The United States Geologi-
cal Survey (USGS) recommends a minimum of once
a year (Lapham et al., 1997). USEPA also recom-
mended one measurement per year (Barcelona et al.,
1985) but later recommended a total well depth be
taken every time a water-quality is collected or a
water-level reading taken (Alleretal., 1991). There-
fore, when possible, the total depth measurements
should be taken following the completion of sampling
(Puls and Barcelona, 1996). When total-well-depth
measurements are needed prior to sampling, as
much time as possible should be allowed prior to
sampling, such as a minimum of 24 hours. The weight
of electric tapes are generally too light to determine
accurate total well depth. If the total well depth is
greater than 200 feet, stretching of the tape must be
taken into consideration.
DEPTH TO WATER
All water levels should be measured from the refer-
ence point by the use of a weighted steel tape and
chalk or an electric tape (a detailed discussion of the
pros and cons of the different water level devices is
provided in Thornhill, 1989). The steel tape is a more
accurate method to take water levels, and is recom-
mended where shallow flow gradients (less than 0.05
foot/feet or 0.015 meter/meters) or deep wells are
encountered. However, in those cases where large
flow gradients or large fluctuations in water levels are
expected, a calibrated electric tape is acceptable. The
water level is calculated using the well's reference
point minus the measured depth to water. At depths
approximately greater than 200 feet, the water-level-
measuring device should be chosen carefully, as
some devices may have measurable stretching.
The depth-to-water measurement must be made in all
wells to be sampled prior to activities in any single
well which may change the water level, such as
bailing, pumping, and hydraulic testing. All readings
are to be recorded to the nearest one-hundredth of a
foot.
The time and date of the measurement, point of
reference, measurement method, depth-to-water level
measurement, and any calculations should be prop-
erly recorded. In addition, any known, outside influ-
ences (such as tidal cycles, nearby pumping effects,
major barometric changes) that may affect water
levels should be noted.
GROUND-WATER SAMPLING METHODS
The ground-water sampling methods to be employed
should be dependent on site-specific conditions and
requirements, such as data-quality objectives and well
accessibility. Ground-water sampling methods vary
based on the type of device used, the position of the
sampler intake, the purge criteria used, and the
composition of the ground water to be sampled (e.g.,
turbid, containing high volatile organics, etc.). All
sampling methods and equipment should be clearly
documented, including purge criteria, field readings,
etc. Examples of appropriate documentation are
provided in Attachment 2 of this document and Ap-
pendix E of the U.S. Environmental Protection Agency,
1995 document.
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The water in the screen and filter pack is generally in a
constant state of natural flux as ground water passes
in and out of the well. However, water above the
screened section remains relatively isolated and
become stagnant. Stagnant water is subject to physio-
chemical changes and may contain foreign material,
which can be introduced from the surface or during
well construction, resulting in non-representative
sample data. To safeguard against collecting a
sample biased by stagnant water, specific well-
purging guidelines and techniques should be fol-
lowed.
A non-representative sample also can result from
excessive pumping of the monitoring well. Stratifica-
tion of the contaminant concentrations in the aquifer
may occur, or heavier-than-water compounds may
sink to the lower portions of the aquifer. Excessive
pumping can dilute or increase the contaminant
concentrations from what is representative of the
sampling point.
PURGING AND SAMPLING DEVICES
The device used to purge and sample a well depends
on the inner casing diameter, depth to water, volume
of water in the well, accessibility of the well, and types
of contaminants to be sampled. The types of equip-
ment available for ground-water sampling include
hand-operated or motor-driven suction pumps, peri-
staltic pumps, positive displacement pumps, sub-
mersible pumps, various in-situ devices and bailers
made of various materials, such as PVC, stainless
steel and Teflon®. Some of these devices may cause
volatilization and produce high pressure differentials,
which could result in variability in the results of pH,
dissolved oxygen concentrations, oxidation-reduction
potential, specific electrical conductance, and concen-
trations of metals, volatile organics and dissolved
gases. Therefore, the device chosen for well purging
and sampling should be evaluated for the possible
effects it may have on the chemical and physical
analyses. In addition, the types of contaminants,
detection levels, and levels of concern as described
by the site DQOs should be consulted prior to the
selection of a sampling device. The same device used
for purging the monitoring well should be used for
sampling to minimize agitation of the water column
(which can increase turbidity, increase volatilization,
and increase oxygen in the water).
In general, the device used for purging and sampling
should not change geochemical and physical param-
eters and/or should not increase turbidity. For this
reason, low-flow submersible or positive-displacement
pumps that can control flow rates are recommended
for purging wells. Dedicated sampling systems are
greatly preferred since they avoid the need for decon-
tamination of equipment and minimize turbulence in
the well. If a sampling pump is used, the pump should
be lowered into the well as slowly as possible and
allowed to sit as long as possible, before pumping
commences. This will minimize turbidity and volatiliza-
tion within the well.
Sampling devices (bladders, pumps, bailers, and
tubing) should be constructed of stainless steel,
Teflon®, glass, and other inert materials to reduce the
chance of these materials altering the ground water in
areas where concentrations of the site contaminants
are expected to be near detection limits. The sample
tubing thickness should be maximized and the tubing
length should be minimized so that the loss of con-
taminants through the tubing walls may be reduced
and the rate of stabilization of ground-water param-
eters is maximized. The tendency of organics to sorb
into and out of many materials makes the appropriate
selection of sample tubing materials critical for these
trace analyses (Pohlmann and Alduino, 1992; Parker
and Ranney, 1998). Existing Superfund and RCRA
guidance suggest appropriate compatible materials
(U.S. Environmental Protection Agency, 1992). Spe-
cial material considerations are important when
sampling for non-routine analyses, such as age-
dating and biological constituents.
Preferably, wells should be purged and sampled using
a positive-displacement pump or a low-flow submers-
ible pump with variable controlled flow rates and
constructed of chemically inert materials. If a pump
cannot be used because the recovery rate is so slow
(less than 0.03 to 0.05 gallons per minute or 100 to
200 milliliters per minute) and the volume of the water
to be removed is minimal (less than 5 feet (1.6
meters) of water), then a bailer with a double check
valve and bottom-emptying device with a control-flow
check valve may be used to obtain the samples.
Otherwise, a bailer should not be used when sampling
for volatile organics because of the potential bias
introduced during sampling (Pohlmann, etal., 1990;
Yeskis, etal., 1988; Tai, etal., 1991). A peristaltic
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pump also may be used under these conditions,
unless the bias by a negative pressure may impact
the contaminant concentrations of concern (generally
at depths greater than 15 to 20 feet (4.5 to 6 meters)
of lift). Bailers should also be avoided when sampling
for metals due to increased turbidity that occurs during
the deployment of the bailer, which may bias inorganic
and strongly hydrophobic parameters. Dedicated
sampling pumps are recommended for metals sam-
pling because the pumps avoid the generation of
turbidity from frequent sampler deployment (Puls et
al., 1992). A number of alternate sampling devices are
becoming available, including passive diffusion sam-
plers (Vroblesky and Hyde, 1997; Vroblesky, 2001 a
and b) and other in-situ sampling devices. These
devices may be particularly useful to sampling low-
permeability geologic materials, assuming the device
is made of materials compatible with the analytical
parameters, meet DQOs, and have been properly
evaluated. However, the site investigator should
ensure the diffusion membrane materials are selected
for the contaminants of concern (COCs) present at
the site. Comparison tests with an approved sampling
method and diffusion samplers should be completed
to confirm that the method is suitable for the site.
POSITION OF SAMPLE INTAKE
Essentially there are two positions for placement of
the sample pump intake, within the screen and above
the screen. Each of the positions offers advantages
and disadvantages with respect to the portion of the
well screen sampled, data reproducibility and potential
purge volumes.
When the sampling pump intake is set above the well
screen, the pump generally is set just below the water
level in the well. The sampling pump then is pumped
until a purge criterion is reached (commonly either
stabilization of purge parameters or a set number of
well volumes). If the distance between the water level
and the top of the screen is long, there is concern that
the water will be altered geochemically as it flows
along the riser pipe, as water flows between the well
screen and the sampling pump intake. This is espe-
cially a concern if the riser pipe is made of similar
material as the COC (such as a stainless steel riser
with nickel as a COC, or PVC with organics as a
COC). Keely and Boateng (1987) suggested that to
minimize this potential influence, the sample pump be
lowered gradually while purging, so that at the time of
the sampling the pump intake is just above the screen.
This would minimize contact time between the ground
water and the well construction materials while sam-
pling, as well as ensure the evacuation of the stagnant
water above the screen.
With the final location of the sampling pump intake
just above the well screen, the sample results may be
more reproducible than those collected by positioning
the pump intake within the well screen. Results may
be more reproducible because the sampler can
ensure that the ground water is moving into the well
with the same portions of the aquifer being sampled
each time assuming the same pump rate. If the pump
is placed into different portions of the screen each
time, different portions of the aquifer may be sampled.
Of course, this can be avoided by the use of dedi-
cated, permanently installed equipment. Additionally,
the placement of the pump at the same vertical
position within the screen can be ensured by the use
of calibrated sampling pump hose, sounding with a
weighted tape, or using a pre-measured hose.
The placement of the pump above the screen does
not guarantee the water-quality sample represents the
entire well screen length. Any bias in the pump place-
ment will be consistently towards the top of the well
screen and/or to the zone of highest hydraulic conduc-
tivity. Another possible disadvantage, or advantage,
depending on the DQOs, of the placement of the
pump above the well screen is that the sample may
represent a composite of water quality over the well
screen. This may result in dilution of a portion of the
screen that is in a contaminated portion of an aquifer
with another portion that is in an uncontaminated
portion of the aquifer. However, shorter well screens
would minimize this concern.
When the pump intake is positioned within the well
screen, its location is recommended to be opposite
the most contaminated zone in the well screen inter-
val. This method is known as the low-flow, low-stress,
micropurge, millipurge, or minimal drawdown method.
The well is then purged with a minimal drawdown
(usually 0.33 feet (0.1 meters) based on Puls and
Barcelona, 1996) until selected water-quality-indicator
parameters have stabilized. Use of this method may
result in the vertical portion of the sampled aquifer
being smaller than the well screen length. This
method is applicable primarily for short well-screen
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lengths (less than 5 feet (1.6 meters)) to better char-
acterize the vertical distribution of contaminants (Puls
and Barcelona, 1996). This method should not be
used with well-screen lengths greater than 10 feet (3
meters). By using this method, the volume of purge
water can be reduced, sometimes significantly, over
other purging methods.
However, two potential disadvantages of this method
exist. The first potential disadvantage may involve the
lower reproducibility of the sampling results. The
position of the sampling pump intake may vary be-
tween sampling rounds (unless adequate precautions
are taken to lower the pump into the exact position in
previous sampling rounds, or a dedicated system is
used), which can result in potentially different zones
within the aquifer being sampled. This potential
problem can be overcome by using dedicated sam-
pling pumps and the problem may be minimized by
the use of short well screens. The second potential
disadvantage, or advantage, depending on the DQOs,
may be that the sample which is collected may be
taken from a small portion of the aquifer volume.
PURGE CRITERIA
"Low-Stress Approach"
The first method for purging a well, known as the low-
stress approach, requires the use of a variable-speed,
low-flow sampling pump. This method offers the
advantage that the amount of water to be container-
ized, treated, or stored will be minimized. The
low-stress method is based on the assumption that
pumping at a low rate within the screened zone will
not draw stagnant water down, as long as drawdown
is minimized during pumping. Drawdown should not
exceed 0.33 feet (0.1 meters) (Puls and Barcelona,
1996). The pump is turned on at a low flow rate
approximating the estimated recovery rate (based on
the drawdown within the monitoring well during sam-
pling). This method requires the location of the pump
intake to be within the saturated-screened interval
during purging and sampling. The water-quality-
indicator parameters (purge parameters), pH, specific
electrical conductance, dissolved oxygen concentra-
tion, oxidation-reduction potential, temperature and
turbidity, are monitored at specific intervals. The
specific intervals will depend on the volume within the
tubing (include pump and flow-through cell volumes),
pump rate and drawdown; commonly every three to
five minutes. These parameters should be recorded
after a minimum of one tubing volume (include pump
and flow-through-cell volumes) has been purged from
the well. These water-quality-indicator parameters
should be collected by a method or device which
prevents air from contacting the sample prior to the
reading, such as a flow-through cell (Barcelona et al.,
1985; Garske and Schock, 1986; Wilde et al., 1998).
Once three successive readings of the water-quality-
indicator parameters provided in Table 1 have stabi-
lized, the sampling may begin. The water-quality-
indicator parameters that are recommended include
pH and temperature, but these are generally insensi-
tive to indicate completion of purging since they tend
to stabilize rapidly (Puls and Barcelona, 1996).
Oxidation-reduction potential may not always be an
appropriate stabilization parameter, and will depend
on site-specific conditions. However, readings should
be recorded because of its value as a double check
for oxidizing conditions, and for some fate and trans-
port issues. When possible, especially when sampling
for contaminants that may be biased by the presence
of turbidity, the turbidity reading is desired to stabilize
at a value below 10 Nephelometric Turbidity Units
(NTUs). For final dissolved oxygen measurements, if
the readings are less than 1 milligram per liter, they
should be collected with the spectrophotometric
method (Wilde et al., 1998, Wlkin et al., 2001),
colorimetric or Winkler titration (Wlkin et al., 2001).
All of these water-quality-indicator parameters should
be evaluated against the specifications of the
accuracy and resolution of the instruments used.
During purging, water-level measurements must be
taken regularly at 30-second to five-minute intervals
(depending on the hydraulic conductivity of the
aquifer, diameter of the well, and pumping rate) to
document the amount of drawdown during purging.
The water-level measurements will allow the sampler
to control pumping rates to minimize drawdown in
the well.
"Well-Volume Approach"
The second method for purging wells is based on
proper purging of the stagnant water above the
screened interval and the stabilization of water-
quality-indicator parameters prior to sampling. Several
considerations in this method need to be evaluated
before purging. For monitoring wells where the water
level is above the screens, the pump should be set
8
-------
near the top of the water column, and slowly lowered
during the purging process. For water
columns within the well screen, the pump should be
set at a sufficient depth below the water level where
drawdown during pumping does not allow air to enter
the pump. The pump should not be allowed to touch
or draw sediments from the bottom of the well, espe-
cially when sampling for parameters that may be
impacted by turbidity. The well-purging rate should not
be great enough to produce excessive turbulence in
the well, commonly no greater than one gallon per
minute (3.8 liters per minute) in a 2-inch well. The
pump rate during sampling should produce a smooth,
constant (laminar) flow rate, and should not produce
turbulence during the filling of bottles. As a result, the
expected flow rate for most wells will be less than one
gallon per minute (3.8 liter per minute), with expected
flow rates of about one-quarter gallon per minute (500
milliliter per minute).
The stabilization criteria for a "well-volume approach"
may be based on the stabilization of water-quality-
indicator parameters or on a pre-determined well
volume. Various research indicates that purging
criteria based on water-quality-indicator parameter
stabilization may not always correlate to stabilization
of other parameters, such as volatile organic com-
pounds (Gibs and Imbrigiotta, 1990; Puls et al., 1990).
A more technically rigorous sampling approach that
would yield more consistent results over time would
be a time-sequential sampling program at regular well-
volume intervals while measuring water-quality-
indicator parameters. However, the cost would be
prohibitive for most sites. For comparison of water-
quality results, by sampling under the same conditions
(same purge volume and rate, same equipment,
same wells, etc.) temporal evaluations of trends may
be considered.
The stabilization requirements of the water-quality-
indicator parameters are consistent with those
described above for the low-stress approach. The
parameters should be recorded approximately every
well volume; when three successive readings have
reached stabilization, the sample(s) are taken
(Barcelona et al., 1985). If a ground-water monitoring
well has been sufficiently sampled and characterized
(at least several rounds of water-quality samples
obtained, including the field parameters, during several
seasonal variations), and if water-quality-indicator
parameters are no longer needed as a part of site
characterization and/or monitoring, then samples
could be obtained based on a specific number of well
volumes at the previous pumping rates.
LOW-PERMEABILITY FORMATIONS
Different procedures must be followed in the case of
slow-recovery wells installed in low hydraulic conduc-
tivity aquifers. The following procedures are not
optimum, but may be used to obtain a ground-water
sample under less than ideal conditions. One
suggested procedure is to remove the stagnant water
in the casing to just above the top of the screened
interval, in a well screened below the water table, to
prevent the exposure of the gravel pack or formation
to atmospheric conditions (McAlary and Barker,
1987). At no point should the pump be lowered into
the screened interval. The pumping rate should be as
low as possible for purging to minimize the drawdown
in the well. However, if a well has an open interval
across the water table in a low permeability zone,
there may be no way to avoid pumping and/or bailing
a well dry (especially in those cases with four feet of
water or less in the well and at a depth to water
greater than 20 to 25 feet (which is the practical limit
of a peristaltic pump)). In these cases, the well may
be purged dry. The sample should be taken no sooner
than two hours after purging and after a sufficient
volume for a water-quality sample, or sufficient recov-
ery (commonly 90%) is present (Herzog et al., 1988).
In these cases, a bailer with a double check valve with
a flow-control, bottom-emptying device may be used,
since many sampling pumps may have tubing capaci-
ties greater than the volume present within the well. If
the depth of well and water column are shallow
enough, consideration of a very low-flow device, such
as a peristaltic pump, should be considered, espe-
cially if constituents are present that are not sensitive
to negative pressures that may be created with the
use of the peristaltic pump. If such constituents are
present and sampled with a peristaltic pump, a nega-
tive bias may be introduced into the sampling results.
To minimize the bias, thick-walled, non-porous tubing
should be used, except for a small section in the
pump heads, which require a greater degree of
flexibility. As stated earlier in this paper, the DQOs for
the sampling should be consulted to consider the
potential impact of the sampling device on the poten-
tial bias versus the desired detection levels.
-------
Another method to be considered for low-permeability
conditions is the use of alternative sampling methods,
such as passive diffusion samplers and other in-situ
samplers. As more sites are characterized with these
alternative sampling methods and devices, the poten-
tial bias, if any, can be evaluated with regard to the
sampling DQOs. Regional hydrologists/geologists and
Regional quality-assurance specialists should be
consulted on the applicability of these methods for the
site-specific conditions.
DECISION PROCESS FOR DETERMINING
APPLICABLE SAMPLING METHODOLOGY
Once the project team has determined the sampling
objectives and DQOs, reviewed the existing data, and
determined the possible sampling devices that can be
used, the team must decide the appropriate sampling
methodology to be used. Table 2 provides a summary
of considerations and rationale to be used in estab-
lishing the proper ground-water-sampling program
using site-specific conditions and objectives.
POTENTIAL PROBLEMS
The primary objective is to obtain a sample represen-
tative of the ground water moving naturally (including
both dissolved and particulate species) through the
subsurface. A ground-water sample can be compro-
mised by field personnel in two primary ways: taking
an unrepresentative sample and handling the (repre-
sentative) sample incorrectly. There are numerous
ways of introducing foreign contaminants into a
sample. These must be avoided by following strict
sampling protocols and transportation procedures,
and utilizing trained personnel. Common problems
with sampling include the use of inappropriate sample
containers and field composites, and the filtration of
turbid samples.
SAM RLE CONTAINERS
Field samples must be transferred from the sampling
equipment to the container that has been specifically
prepared for that given parameter. Samples must not
be composited in a common container in the field and
then split in the lab. The USEPA Regional policy on
sample containers should be consulted to determine
the appropriate containers for the specified analysis.
FIELD FILTRATION OF TURBID SAMPLES
The USEPA recognizes that in some hydrogeologic
environments, even with proper well design, installa-
tion, and development, in combination with the low-
flow purging and sampling techniques, sample turbid-
ity cannot be reduced to ambient levels. The well
construction, development, and sampling information
should be reviewed by the Regional geologists or
hydrologists to see if the source of the turbidity prob-
lems can be resolved or if alternative sampling meth-
odologies should be employed. If the water sample is
excessively turbid, the collection of both filtered and
unfiltered samples, in combination with turbidity, Total
Suspended Solids (TSS), Total Dissolved Solids
(TDS), pumping rate, and drawdown data is recom-
mended. The filter size used to determine TSS and
TDS should be the same as used in the field filtration.
An in-line filter should be used to minimize contact
with air to avoid precipitation of metals. The typical
filter media size used is 0.45 urn because this is
commonly accepted as the demarcation between
dissolved and non-dissolved species. Other filter
sizes may be appropriate but their use should be
determined based on site-specific criteria (examples
include grain-size distribution, ground-water-flow
velocities, mineralogy) and project DQOs. Filter sizes
up to 10.0 urn may be warranted because larger size
filters may allow particulates that are mobile in ground
water to pass through (Puls and Powell, 1992). The
changing of filter media size may limit the comparabil-
ity of the data obtained with other data sets and may
affect their use in some geochemical models. Filter
media size used on previous data sets from a site,
region or aquifer and the DQOs should be taken into
consideration. The filter media used during the
ground-water sampling program should be collected in
a suitable container and archived because potential
analysis of the media may be helpful for the determi-
nation of particulate size, mineralogy, etc.
The first 500 to 1000 milliliters of a ground-water
sample (depending on sample turbidity) taken through
the in-line filter will not be collected for a sample in
order to ensure that the filter media has equilibrated
to the sample (manufacturer's recommendations also
should be consulted). Because bailers have been
shown to increase turbidity while purging and sam-
pling, bailers should be avoided when sampling for
trace element, metal, PCB, and pesticide
constituents. If portable sampling pumps are used, the
10
-------
pumps should be gently lowered to the sampling depth
desired, carefully avoiding lowering it to the bottom of
the well, and allowed to sit in order to allow any par-
ticles mobilized by pump placement to settle. Dedi-
cated sampling equipment installed in the well prior to
the commencement of the sampling activities is one
of the recommended methods to reduce turbidity
artifacts (Puls and Powell, 1992; Kearl et al., 1992;
Puls et al., 1992; Puls and Barcelona, 1996).
SAMPLER DECONTAMINATION
The specific decontamination protocol for sampling
devices is dependent on site-specific conditions, types
of equipment used and the types of contaminants
encountered. Once removed from the well, non-
dedicated sampling equipment should be decontami-
nated to help ensure that there will be no cross-
contamination between wells. Disposable items such
as rope and low-grade tubing should be properly
disposed between wells. Cleaning thoroughly that
portion of the equipment that is going to come into
contact with well water is especially important. In
addition, a clean plastic sheet should be placed
adjacent to or around the well to prevent surface soils
from coming in contact with the purging and sampling
equipment. The effects of cross-contamination can be
minimized by sampling the least contaminated well
first and progressing to the more contaminated ones.
Equipment blanks should be collected on a regular
basis from non-dedicated equipment, the frequency
depending on the sampling plan and regional proto-
cols, to document the effectiveness of the decontami-
nation procedures.
The preferred method is to use dedicated sampling
equipment whenever possible. Dedicated equipment
should still be cleaned on a regular basis to reduce
biofouling, and to minimize adsorption effects. Dedi-
cated equipment should have equipment blanks taken
after every cleaning.
POST-SAMPLING ACTIVITIES
Specific activities should be completed at monitoring
wells at regular intervals to ensure the acquisition of
representative ground-water samples. Activities
include hydraulic conductivity testing to determine if a
monitoring well needs redeveloping and/or replacing.
Another activity that needs to be completed is regular
surveying of well measuring points impacted by frost
heaving and site activities. The schedules of these
activities are to be determined on a site-by-site basis
in consultation with regional geologists or hydrologists,
but at a minimum, should be every five years.
CONCLUSION
This document provides a brief summary of the state-
of-the-science to be used for Superfund and RCRA
ground-water studies. As additional research is
completed, additional sampling experience with other
sampling devices and methods and/or additional
contaminants are identified, this paper may be revised
to include the new information/concerns. Clearly there
is no one sampling method that is applicable for all
sampling objectives. As new methods and/or equip-
ment are developed, additional standard operating
procedures (SOPs) should be developed and at-
tached to this document. These SOPs for ground-
water sampling should include, at a minimum: intro-
duction, scope and application, equipment, purging
and sampling procedures, field quality control, decon-
tamination procedures and references. Example
SOP's for the low-stress/minimal-drawdown and well-
volume sampling procedures have been included as
Attachments 3 and 4. These example SOPs are to be
considered a pattern or starting point for site-specific
ground-water-sampling plans. A more detailed discus-
sion of sampling procedures, devices, techniques,
etc. is provided in various publications by the USEPA
(Barcelona etal., 1985; U.S. Environmental Protection
Agency, 1993) and the U.S. Geological Survey (Wilde
etal., 1998).
REFERENCES
Aller, L, T.W. Bennett, G. Hackett, R.J. Petty, J.H.
Lehr, H. Sedoris, D.M. Nielson and J.E. Denne, 1991,
Handbook of Suggested Practices for the Design and
Installation of Ground-Water Monitoring Wells; U.S.
Environmental Protection Agency, EPA/600/4-89/034,
221 pp.
Barcelona, M.J., J.P Gibb, J.A. Hellfrich, and E.E.
Garske, 1985, Practical Guide for Ground-Water
Sampling; U.S. Environmental Protection Agency,
EPA/600/2-85/104, 169 pp.
11
-------
Garske, E.E., and M.R. Schock, 1986, An Inexpensive
Flow-Through Cell and Measurement System for
Monitoring Selected Chemical Parameters in Ground
Water; Ground Water Monitoring Review, Vol. 6, No. 3,
pp. 79-84.
Gibs, J. and I.E. Imbrigiotta, 1990, Well-Purging
Criteria for Sampling Purgeable Organic Compounds;
Ground Water, Vol. 28, No. 1, pp.68-78.
Herzog, B.L, S.J. Chou, J.R. Valkenburg and R.A.
Griffin, 1988, Changes in Volatile Organic Chemical
Concentrations After Purging Slowly Recovering
Wells; Ground Water Monitoring Review, Vol. 8, No.
4, pp. 93-99.
Izraeli, R., D. Yeskis, M. Collins, K. Davies and B.
Zavala, 1992, GROUND WATER ISSUE PAPER:
Monitoring Well Development Guidelines for
Superfund Project Managers; U.S. Environmental
Protection Agency, 4 pp.
Kearl, P.M., N.E. Korte, and T.A. Cronk, 1992, Sug-
gested Modifications to Ground Water Sampling
Procedures Based on Observations from the Colloid
Borescope; Ground Water Monitoring Review, Vol. 12,
No. 2, pp. 155-161.
Keely, J.F. and K. Boateng, 1987, Monitoring well
Installation, Purging, and Sampling Techniques - Part
1: Conceptualizations; Ground Water, Vol. 25, No. 4,
pp. 427-439.
Lapham, WW, F.D. Wilde and M.T Koterba, 1997,
Guidelines and Standard Procedures for Studies of
Ground-Water Quality: Selection and Installation of
Wells, and Supporting Documentation; U.S. Geologi-
cal Survey Water-Resources Investigations Report
96-4233, 110pp.
McAlary, T.A. and J.F. Barker, 1987, Volatilization
Losses of Organics During Ground Water Sampling
from Low Permeability Materials; Ground Water
Monitoring Review, Vol. 7, No. 4, pp. 63-68.
Nielson, D.M., 1991, Practical Handbook of Ground-
Water Monitoring; Lewis Publishers, 717 pp.
Parker, L.V and T.A. Ranney, 1998, Sampling Trace-
Level Organic Solutes with Polymeric Tubing: Part 2,
Dynamic Studies; Ground Water Monitoring and
Remediation, Vol. 18, No. 1, pp. 148-155.
Pohlmann, K.F., R.P Blegen, and J.W Hess, 1990,
Field Comparison of Ground-Water Sampling Devices
for Hazardous Waste Sites: An Evaluation using
Volatile Organic Compounds; U.S. Environmental
Protection Agency, EPA/600/4-90/028, 102 pp.
Pohlmann, K.F. and A.J. Alduino, 1992, GROUND-
WATER ISSUE PAPER: Potential Sources of Error in
Ground-Water Sampling at Hazardous Waste Sites;
U.S. Environmental Protection Agency, EPA/540/S-92/
019.
Puls, R.W, J.H. Eychaner, and R.M. Powell, 1990,
ENVIRONMENTAL RESEARCH BRIEF: Colloidal-
Facilitated Transport of Inorganic Contaminants in
Ground Water: Part I. Sampling Considerations; U.S.
Environmental Protection Agency, EPA/600/M-90/023,
12pp.
Puls, R.W. and R.M. Powell, 1992, Acquisition of
Representative Ground Water Quality Samples for
Metals; Ground Water Monitoring Review, Vol. 12, No.
3, pp. 167-176.
Puls, R.W, D.A. Clark, B. Bledsoe, R.M. Powell and
C.J. Paul, 1992, Metals in Ground Water: Sampling
Artifacts and Reproducibility; Hazardous Waste and
Hazardous Materials, Vol. 9, No. 2, pp. 149-162.
Puls, R.W. and M.J. Barcelona, 1996, GROUND-
WATER ISSUE PAPER: Low-Flow (Minimal Draw-
down) Ground-Water Sampling Procedures; U.S.
Environmental Protection Agency, EPA/540/S-95/504,
12pp.
Tai, D.Y., K.S. Turner, and L.A. Garcia, 1991, The Use
of a Standpipe to Evaluate Ground Water Samples;
Ground Water Monitoring Review, Vol. 11, No. 1, pp.
125-132.
Thornhill, J.T., 1989, GROUND-WATER ISSUE
PAPER: Accuracy of Depth to Water Measurements;
U.S. Environmental Protection Agency, EPA/540/4-89/
002, 3 pp.
12
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U.S. Environmental Protection Agency, 1992, RCRA
Ground-Water Monitoring: Draft Technical Guidance;
EPA/530-R-93-001.
U.S. Environmental Protection Agency, 1993, Subsur-
face Characterization and Monitoring Techniques: A
Desk Reference Guide: Volume I: Solids and Ground
Water Appendices A and B; EPA/625/R-93/003a.
U.S. Environmental Protection Agency, 1995, Ground
Water Sampling - A Workshop Summary, Dallas,
Texas, November 30-December 2, 1993; EPA/600/R-
94/205, 146 pp.
Vroblesky, D.A., 2001a, User's Guide for Polyethylene-
Based Passive Diffusion Bag Samplers to Obtain
Volatile Organic Compound Concentrations in Wells,
Part 1: Deployment, Recovery, Data Interpretation,
and Quality Control and Assurance; U.S. Geological
Survey Water-Resources Investigations Report 01-
4060,
18pp.
Vroblesky, D.A. ed., 2001 b, User's Guide for Polyethyl-
ene-Based Passive Diffusion Bag Samplers to Obtain
Volatile Organic Compound Concentrations in Wells,
Part 2: Field Tests; U.S. Geological Survey Water-
Resources Investigations Report 01-4061, variously
paginated.
Vroblesky, D.A. and Hyde, W.T., 1997, Diffusion
Samplers as an Inexpensive Approach to Monitoring
VOCs in Ground Water; Ground Water Monitoring and
Remediation, Vol. 17, No. 3, pp. 177-184.
Wide, F.D., D.B. Radtke, J.Gibs and R.T Iwatsubo,
eds., 1998, National Field Manual for the Collection of
Water-Quality Data; U.S. Geological Survey Tech-
niques of Water-Resources Investigations, Book 9,
Handbooks for Water-Resources Investigations,
variously paginated.
Wlkin, R.T, M.S. McNeil, C.J. Adair and J.T Wilson,
2001, Field Measurement of Dissolved Oxygen: A
Comparison of Methods, Ground Water Monitoring
and Remediation, Vol. 21, No. 4, pp. 124-132.
Yeskis, D., K. Chiu, S. Meyers, J. Weiss, and T
Bloom, 1988, A Field Study of Various Sampling
Devices and Their Effects on Volatile Organic Con-
taminants; Proceedings of the Second National
Outdoor Action Conference on Aquifer Restoration,
Ground Water Monitoring and Geophysical Methods,
National Water Well Association, May 1988.
13
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This page is intentionally blank.
14
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TABLES:
Stablization Criteria with References for
Water-Quality-lndicator Parameters
and
Applicability of Different Approaches for Purging
and Sample Monitoring Wells
15
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This page is intentionally blank.
16
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TABLE 1: Stabilization Criteria with References forWater-Quality-lndicator Parameters
Parameter
PH
specific electrical
conductance (SEC)
oxidation-reduction
potential (ORP)
turbidity
dissolved oxygen (DO)
Stabilization Criteria
+/-0.1
+/- 3%
+/- 10 millivolts
+/- 10% (when turbidity is
greater than 10 NTUs)
+/- 0.3 milligrams per liter
Reference
Puls and Barcelona, 1996;
Wilde etal., 1998
Puls and Barcelona, 1996
Puls and Barcelona, 1996
Puls and Barcelona, 1996;
Wilde etal., 1998
Wilde etal., 1998
17
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ATTACHMENT 1
Example Sampling Checklist
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SAMPLING CHECKLIST
Well Identification:
Map of Site Included: Y or N
Wells Clearly Identified with Roads: Y or N
Well Construction Diagram Attached: Y or N
Well Construction:
Diameter of Borehole:_
Casing Material:
Screen Length:
Diameter of Casing:
Screen Material:
Total Depth:
Approximate Depth to Water:
Maximum Well Development Pumping Rate:
Date of Last Well Development:
Previous Sampling Information:
Was the Well Sampled Previously: Y or N
(If Sampled, Fill Out Table Below)
Table of Previous Sampling Information
Parameter
Previously
Sampled
Number of
Times Sampled
Maximum
Concentration
Notes (include previous purge rates)
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ATTACHMENT 2
Example Ground-Water Sampling Field Sheets
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GROUND-WATER SAMPLING RECORD
Well ID:
Facility Name:
Well Depth:
Casing Material.:_
Sampling Crew:
Type of Pump:
Weather Conditions:
Depth to Water:_
Well Diameter:
Volume Of Water per Well Volume:_
Station #:
Date: / /
.Tubing Material:,
.Pump set at
NOTES:
GROUND-WATER SAMPLING PARAMETERS
Time
Water Volume Pumping
Level Pumped Rate
DO
(mg/l)
Temp. SEC
PH
ORP Turbidity
(mV) (NTU)
Other Parameters:.
Sampled at:
Sample delivered to.
Sample CRL#:
Parameters taken with:
.by.
at
OTR#:
ITR#:
SAS#:
Parameters Collected
Number of Bottles
Bottle Lot Number
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Ground Water Sampling Log
Site Name:
Well Depth( Ft-BTOC1):
Well #:
Screen Interval (Ft):
Casing Material:
Date:
Well Dia.:
Pump placement(Ft from TOC2):
Measuring Point:
Water level (pumping)(Ft):
Sampling Personnel:
Other info: (such as sample numbers, weather conditions and field notes)
Water Quality Indicator Parameters
Sampling Device:
Water level (static)(Ft):
Pump rate(l_iter/min):
Time
Pumping
rates
(L/Min)
Water
level
(ft)
DO
(mg/L)
ORP
(mv)
SEC3
Turb.
(NTU)
PH
Temp.
(C°)
Volume
pumped
(L)
Type of Samples collected:
1 casing volume was:
Total volume purged prior to sample collection:
1BTOC-BelowTop of Casing
2TOC-Top of Casing
3Specific Electrical Conductance
Stabilization Criteria
D.O.
Turb.
S.C.
ORP
pH
+/- 0.3 mg/l
+/- 3%
+/-10mV
+/- 0.1 unit
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ATTACHMENT 3
Example Standard Operating Procedure:
Standard Operating Procedure for
Low-Stress (Low Flow)/Minimal Drawdow
Ground-Water Sample Collection
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Standard Operating Procedure for Low-Stress (Low-Flow)/
Minimal Drawdown Ground-Water Sample Collection
INTRODUCTION
The collection of "representative" water samples from
wells is neither straightforward nor easily accom-
plished. Ground-water sample collection can be a
source of variability through differences in sample
personnel and their individual sampling procedures,
the equipment used, and ambient temporal variability
in subsurface and environmental conditions. Many
site inspections and remedial investigations require
the sampling at ground-water monitoring wells within
a defined criterion of data confidence or data quality,
which necessitates that the personnel collecting the
samples are trained and aware of proper sample-
collection procedures.
The purpose of this standard operating procedure
(SOP) is to provide a method that minimizes the
impact the purging process has on the ground-water
chemistry and the volume of water that is being
purged and disposed of during sample collection. This
will take place by placing the pump intake within the
screen interval and by keeping the drawdown at a
minimal level (0.33 feet) (Puls and Barcelona, 1996)
until the water quality parameters have stabilized and
sample collection is complete. The flow rate at which
the pump will be operating will depend upon both
hydraulic conductivity of the aquifer and the drawdown
with the goal of minimizing the drawdown. The flow
rate from the pump during purging and sampling will
be at a rate that will not compromise the integrity of
the analyte that is being sampled. This sampling
procedure may or may not provide a discrete ground-
water sample at the location of the pump intake. The
flow of ground-water to the pump intake will be depen-
dent on the distribution of the hydraulic conductivity (K)
of the aquifer within the screen interval. In order to
minimize the drawdown in the monitoring well, a low-
flow rate must be used. "Low-Flow" refers to the
velocity with which water enters the pump intake from
the surrounding formation in the immediate vicinity of
the well screen. It does not necessarily refer to the
flow rate of water discharged at the surface, which
can be affected by flow regulators or restrictions (Puls
and Barcelona, 1996). This SOP was developed by
the Superfund/RCRA Ground Water Forum and draws
from an USEPA's Ground Water Issue Paper, Low-
Flow (Minimal Drawdown) Ground-Water Sampling
Procedure, by Robert W Puls and Michael J.
Barcelona. Also, available USEPA Regional SOPs
regarding Low-Stress (Low-Flow) Purging and Sam-
pling were used for this SOP.
SCOPE AND APPLICATION
This SOP should be used primarily at monitoring wells
that have a screen or an open interval with a length of
ten feet or less and can accept a sampling device that
minimizes the disturbance to the aquifer or the water
column in the well casing. The screen or open interval
should have been optimally located to intercept an
existing contaminant plume(s) or along flowpaths of
potential contaminant releases. Knowledge of the
contaminant distribution within the screen interval is
highly recommended and is essential for the success
of this sampling procedure. The ground-water
samples that are collected using this procedure are
acceptable for the analyses of ground-water contami-
nants that may be found at Superfund and RCRA
contamination sites. The analytes may be volatile,
semi-volatile organic compounds, pesticides, PCBs,
metals, and other inorganic compounds. The
screened interval should be located within the con-
taminant plume(s) and the pump intake should be
placed at or near the known source of the contamina-
tion within the screened interval. It is critical to place
the pump intake in the exact location or depth for
each sampling event. This argues for the use of
dedicated, permanently installed, sampling devices
whenever possible. If this is not possible, then the
placement of the pump intake should be positioned
with a calibrated sampling pump hose sounded with a
weighted-tape or using a pre-measured hose. The
pump intake should not be placed near the bottom of
the screened interval to avoid disturbing any sediment
that may have settled at the bottom of the well.
Water-quality-indicator parameters and water levels
must be measured during purging, prior to sample
collection. Stabilization of the water-quality-indicator
parameters as well as monitoring water levels are a
prerequisite to sample collection. The water-quality-
indicator parameters that are recommended include
the following: specific electrical conductance, dis-
solved oxygen, turbidity, oxidation-reduction potential,
pH, and temperature. The latter two parameters are
useful data, but are generally insensitive as purging
parameters. Oxidation-reduction potential may not
always be appropriate stabilization parameter, and will
depend on site-specific conditions. However, readings
29
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should be recorded because of its value as a double
check for oxidation conditions and for fate and trans-
port issues.
Also, when samples are collected for metals, semi-
volatile organic compounds, and pesticides, every
effort must be made to reduce turbidity to 10 NTUs or
less (not just the stabilization of turbidity) prior to the
collection of the water sample. In addition to the
measurement of the above parameters, depth to
water must be measured during purging (U.S. Envi-
ronmental Protection Agency, 1995).
Proper well construction, development, and mainte-
nance are essential for any ground-water sampling
procedure. Prior to conducting the field work, informa-
tion on the construction of the well and well develop-
ment should be obtained and that information factored
into the site specific sampling procedure. The Sam-
pling Checklist at the end of this attachment is an
example of the type of information that is useful.
Stabilization of the water-quality-indicator parameters
is the criterion for sample collection. But if stabilization
is not occurring and the procedure has been strictly
followed, then sample collection can take place once
three (minimum) to six (maximum) casing volumes
have been removed (Schuller et al., 1981 and U.S.
Environmental Protection Agency., 1986; Wilde et al.,
1998; Gibs and Imbrigiotta., 1990). The specific
information on what took place during purging must
be recorded in the field notebook or in the ground-
water sampling log.
This SOP is not to be used where non-aqueous
phase liquids (NAPL) (immiscible fluids) are present in
the monitoring well.
EQUIPMENT
• Depth-to-water measuring device - An electronic
water-level indicator or steel tape and chalk, with
marked intervals of 0.01 foot. Interface probe for
determination of liquid products (NAPL) presence,
if needed.
• D Steel tape and weight - Used for measuring total
depth of well. Lead weight should not be used.
• D Sampling pump - Submersible or bladder pumps
with adjustable rate controls are preferred. Pumps
are to be constructed of inert materials, such as
stainless steel and Teflon®. Pump types that are
acceptable include gear and helical driven, cen-
trifugal (low-flow type), and air-activated piston. An
adjustable rate, peristaltic pump can be used
when the depth to water is 20 feet or less.
• Tubing - Teflon® or Teflon®-lined polyethylene
tubing is preferred when sampling for organic
compounds. Polyethylene tubing can be used
when sampling inorganics.
• Power source - If a combustion type (gasoline or
diesel-driven) generator is used, it must be placed
downwind of the sampling area.
• Flow measurement supplies - flow meter, gradu-
ated cylinder, and a stop watch.
• Multi-parameter meter with flow-through cell - This
can be one instrument or more contained in a
flow-through cell. The water-quality-indicator
parameters that are monitored are pH, ORP/Eh,
(ORP) dissolved oxygen (DO), turbidity, specific
conductance, and temperature. Turbidity readings
must be collected before the flow cell because of
the potential for sediment buildup, which can bias
the turbidity measurements. Calibration fluids for
all instruments should be NIST-traceable and there
should be enough for daily calibration throughout
the sampling event. The inlet of the flow cell must
be located near the bottom of the flow cell and the
outlet near the top. The size of the flow cell should
be kept to a minimum and a closed cell is pre-
ferred. The flow cell must not contain any air or
gas bubbles when monitoring for the water-quality-
indicator parameters.
• Decontamination supplies - Including a reliable and
documented source of distilled water and any
solvents (if used). Pressure sprayers, buckets or
decontamination tubes for pumps, brushes and
non-phosphate soap will also be needed.
• Sample bottles, sample preservation supplies,
sample tags or labels, and chain-of-custody
forms.
• Approved Field Sampling and Quality Assurance
Project Plan.
• Well construction, field, and water quality data
from the previous sampling event.
• Well keys and map of well locations.
• Field notebook, ground-water sampling logs, and
calculator. A suggested field data sheet (ground-
water sampling record or ground-water sampling
log) are provided at the end of this attachment.
30
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• D Filtration equipment, if needed. An in-line dispos-
able filter is recommended.
• D Polyethylene sheeting placed on ground around
the well head.
• D Personal protective equipment as specified in the
site Health and Safety Plan.
• D Air monitoring equipment as specified in the Site
Health and Safety Plan.
• D Tool box - All needed tools for all site equipment
used.
• DA 55-gallon drum or container to contain the
purged water.
Construction materials of the sampling equipment
(bladders, pumps, tubing, and other equipment that
comes in contact with the sample) should be limited to
stainless steel, Teflon®, glass, and other inert mate-
rial. This will reduce the chance that sampling materi-
als alter the ground-water where concentrations of the
site contaminants are expected to be near the detec-
tion limits. The sample tubing diameter should be
maximized and the tubing length should be minimized
so that the loss of contaminants into and through the
tubing walls may be reduced and the rate of stabiliza-
tion of ground-water parameters is maximized. The
tendency of organics to sorb into and out of material
makes the appropriate selection of sample tubing
material critical for trace analyses (Pohlmann and
Alduino, 1992; Parker and Ranney, 1998).
PURGING AND SAMPLING PROCEDURES
The following describes the purging and sampling
procedures for the Low-Stress (Low-Flow)/ Minimal
Drawdown method for the collection of ground-water
samples. These procedures also describe steps for
dedicated and non-dedicated systems.
Pre-Sampling Activities (Non-dedicated and dedicated
system)
1. Sampling must begin at the monitoring well with the
least contamination, generally up-gradient or farthest
from the site or suspected source. Then proceed
systematically to the monitoring wells with the most
contaminated ground water.
2. Check and record the condition of the monitoring
well for damage or evidence of tampering. Lay out
polyethylene sheeting around the well to minimize the
likelihood of contamination of sampling/purging equip-
ment from the soil. Place monitoring, purging and
sampling equipment on the sheeting.
3. Unlock well head. Record location, time, date, and
appropriate information in a field logbook or on the
ground-water sampling log (See attached ground-
water sampling record and ground-water sampling log
as examples).
4. Remove inner casing cap.
5. Monitor the headspace of the monitoring well at the
rim of the casing for volatile organic compounds
(VOC) with a photo-ionization detector (PID) or flame
ionization detector (FID) and record in the logbook. If
the existing monitoring well has a history of positive
readings of the headspace, then the sampling must
be conducted in accordance with the Health and
Safety Plan.
6. Measure the depth to water (water level must be
measured to nearest 0.01 feet) relative to a reference
measuring point on the well casing with an electronic
water level indicator or steel tape and record in log-
book or ground-water sampling log. If no reference
point is found, measure relative to the top of the inner
casing, then mark that reference point and note that
location in the field logbook. Record information on
depth to ground water in the field logbook or ground-
water sampling log. Measure the depth to water a
second time to confirm initial measurement; measure-
ment should agree within 0.01 feet or re-measure.
7. Check the available well information or field infor-
mation for the total depth of the monitoring well. Use
the information from the depth of water in step six and
the total depth of the monitoring well to calculate the
volume of the water in the monitoring well or the
volume of one casing. Record information in field
logbook or ground-water sampling log.
Purging and Sampling Activities
8A. Non-dedicated system - Place the pump and
support equipment at the wellhead and slowly lower
the pump and tubing down into the monitoring well
until the location of the pump intake is set at a pre-
determined location within the screen interval. The
placement of the pump intake should be positioned
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with a calibrated sampling pump hose, sounded with a
weighted-tape, or using a pre-measured hose. Refer
to the available monitoring well information to deter-
mine the depth and length of the screen interval.
Measure the depth of the pump intake while lowering
the pump into location. Record pump location in field
logbook or ground-water sampling log.
8B. Dedicated system - Pump has already been
installed, refer to the available monitoring well informa-
tion and record the depth of the pump intake in the
field logbook or ground-water sampling log.
9. Non-dedicated system and dedicated systems -
Measure the water level (water level must be mea-
sured to nearest 0.01 feet) and record information on
the ground-water sampling log, leave water level
indicator probe in the monitoring well.
10. Non-dedicated and dedicated systems - Connect
the discharge line from the pump to a flow-through
cell. A "T" connection is needed prior to the flow-
through cell to allow for the collection of water for the
turbidity measurements. The discharge line from the
flow-through cell must be directed to a container to
contain the purge water during the purging and sam-
pling of the monitoring well.
11. Non-dedicated and dedicated systems - Start
pumping the well at a low flow rate (0.2 to 0.5 liter per
minute) and slowly increase the speed. Check water
level. Maintain a steady flow rate
while maintaining a drawdown of
less than 0.33 feet (Puls and
Barcelona, 1996). If drawdown is
greater than 0.33 feet, lower the
flow rate. 0.33 feet is a goal to help
guide with the flow rate adjust-
ment. It should be noted that this
goal may be difficult to achieve
under some circumstances due to
geologic heterogeneities within the
screened interval, and may require
adjustment based on site-specific
conditions and personal experi-
ence (Puls and Barcelona, 1996).
rate of the pump with a graduated cylinder and a stop
watch. Also, measure the water level and record both
flow rate and water level on the ground-water sam-
pling log. Continue purging, monitor and record water
level and pump rate every three to five minutes during
purging. Pumping rates should be kept at minimal flow
to ensure minimal drawdown in the monitoring well.
13. Non-dedicated and dedicated systems - During
the purging, a minimum of one tubing volume (includ-
ing the volume of water in the pump and flow cell)
must be purged prior to recording the water-quality
indicator parameters. Then monitor and record the
water-quality- indicator parameters every three to five
minutes. The water-quality indicator field parameters
are turbidity, dissolved oxygen, specific electrical
conductance, pH, redox potential, and temperature.
Oxidation-reduction potential may not always be an
appropriate stabilization parameter, and will depend on
site-specific conditions. However, readings should be
recorded because of its value as a double check for
oxidizing conditions. Also, for the final dissolved
oxygen measurement, if the readings are less than 1
milligram per liter, it should be collected and analyze
with the spectrophotometric method (Wilde et al.,
1998 Wilkin et al., 2001), colorimetric or Winkler
titration (Wilkin et al., 2001). The stabilization criterion
is based on three successive readings of the water
quality field parameters; the following are the criteria
which must be used:
12. Non-dedicated and dedicated
systems - Measure the discharge
Parameter
PH
specific electrical
conductance (SEC)
oxidation-reduction
potential (ORP)
turbidity
dissolved oxygen
Stabilization Criteria
+/-0.1 pH units
+/- 3% S/cm
+/- 10 millivolts
+/- 10% NTUs (when turbidity
is greater than 10 NTUs)
+/- 0.3 milligrams per liter
Reference
Puls and Barcelona, 1996;
Wilde etal., 1998
Puls and Barcelona, 1996
Puls and Barcelona, 1996
Puls and Barcelona, 1996;
Wilde etal., 1998
Wilde etal., 1998
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Once the criteria have been successfully met indicat-
ing that the water quality indicator parameters have
stabilized, then sample collection can take place.
14. If a stabilized drawdown in the well can't be main-
tained at 0.33 feet and the water level is approaching
the top of the screened interval, reduce the flow rate or
turn the pump off (for 15 minutes) and allow for recov-
ery. It should be noted whether or not the pump has a
check valve. A check valve is required if the pump is
shut off. Under no circumstances should the well be
pumped dry. Begin pumping at a lower flow rate, if the
water draws down to the top of the screened interval
again, turn pump off and allow for recovery. If two
tubing volumes (including the volume of water in the
pump and flow cell) have been removed during purg-
ing, then sampling can proceed next time the pump is
turned on. This information should be noted in the field
notebook or ground-water sampling log with a recom-
mendation for a different purging and sampling proce-
dure.
15. Non-dedicated and dedicated systems - Maintain
the same pumping rate or reduce slightly for sampling
(0.2 to 0.5 liter per minute) in order to minimize
disturbance of the water column. Samples should be
collected directly from the discharge port of the pump
tubing prior to passing through the flow-through cell.
Disconnect the pump's tubing from the flow-through
cell so that the samples are collected from the pump's
discharge tubing. For samples collected for dissolved
gases or VOC analyses, the pump tubing needs to be
completely full of ground water to prevent the ground
water from being aerated as it flows through the
tubing. The sequence of the samples is immaterial
unless filtered (dissolved) samples are collected and
they must be collected last (Puls and Barcelona,
1996). All sample containers should be filled with
minimal turbulence by allowing the ground water to
flow from the tubing gently down the inside of the
container. When filling the VOC samples, a meniscus
must be formed over the mouth of the vial to eliminate
the formation of air bubbles and head space prior to
capping. In the event that the ground water is turbid,
(greater then 10 NTUs), a filtered metal (dissolved)
sample also should be collected.
If filtered metal sample is to be collected, then an in-
line filter is fitted at the end of the discharge tubing
and the sample is collected after the filter. The in-line
filter must be pre-rinsed following manufacturer's
recommendations and if there are no recommenda-
tions for rinsing, a minimum of 0.5 to 1 liter of ground
water from the monitoring well must pass through the
filter prior to sampling.
16A. Non-dedicated system - Remove the pump from
the monitoring well. Decontaminate the pump and
dispose of the tubing if it is non-dedicated.
16B. Dedicated system - Disconnect the tubing that
extends from the plate at the wellhead (or cap) and
discard after use.
17. Non-dedicated system - Before locking the moni-
toring well, measure and record the well depth (to 0.1
feet).
Measure the total depth a second time to confirm
initial measurement; measurement should agree
within 0.01 feet or re-measure.
18. Non-dedicated and dedicated systems - Close
and lock the well.
DECONTAMINATION PROCEDURES
Decontamination procedures for the water level meter
and the water quality field parameter sensors.
The electronic water level indicator probe/steel tape
and the water-quality field parameter sensors will be
decontaminated by the following procedures:
1. The water level meter will be hand washed with
phosphate-free detergent and a scrubber, then thor-
oughly rinsed with distilled water.
2. Water quality field parameter sensors and flow-
through cell will be rinsed with distilled water between
sampling locations. No other decontamination proce-
dures are necessary or recommended for these
probes since they are sensitive. After the sampling
event, the flow cell and sensors must be cleaned and
maintained per the manufacturer's requirements.
Decontamination Procedure for the Sampling Pump
Upon completion of the ground water sample collec-
tion the sampling pump must be properly decontami-
nated between monitoring wells. The pump and
discharge line including support cable and electrical
33
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wires which were in contact with the ground water in
the well casing must be decontaminated by the
following procedure:
1. The outside of the pump, tubing, support cable and
electrical wires must be pressure-sprayed with
soapy water, tap water, and distilled water. Spray
outside of tubing and pump until water is flowing off
of tubing after each rinse. Use bristle brush to help
remove visible dirt and contaminants.
2. Place the sampling pump in a bucket or in a short
PVC casing (4-in. diameter) with one end capped.
The pump placed in this device must be completely
submerged in the water. A small amount of phos-
phate-free detergent must be added to the potable
water (tap water).
3. Remove the pump from the bucket or 4-in. casing
and scrub the outside of the pump housing and
cable.
4. Place pump and discharge line back in the 4-in.
casing or bucket, start pump and recirculate this
soapy water for 2 minutes (wash).
5. Re-direct discharge line to a 55-gallon drum. Con-
tinue to add 5 gallons of potable water (tap water) or
until soapy water is no longer visible.
6. Turn pump off and place pump into a second bucket
or 4-in. casing that contains tap water. Continue to
add 5 gallons of tap water (rinse).
7. Turn pump off and place pump into a third bucket or
4-in. casing which contains distilled/deionized
water, continue to add 3 to 5 gallons of distilled/
deionized water (final rinse).
8. If a hydrophobic contaminant is present (such as
separate phase, high levels of PCBs, etc.), an
additional decontamination step, or steps, may be
added. For example, an organic solvent, such as
reagent-grade isopropanol alcohol may be added as
a first spraying/bucket prior to the soapy water
rinse/bucket.
FIELD QUALITY CONTROL
Quality control (QC) samples must be collected to
verify that sample collection and handling procedures
were performed adequately and that they have not
compromised the quality of the ground-water
samples. The appropriate EPA program guidance
must be consulted in preparing the field QC sample
requirements for the site-specific Quality Assurance
Project Plan (QAPP).
There are five primary areas of concern for quality
assurance (QA) in the collection of representative
ground-water samples:
1. Obtaining a ground-water sample that is
representative of the aquifer or zone of interest in
the aquifer. Verification is based on the field log
documenting that the field water-quality
parameters stabilized during the purging of the
well, prior to sample collection.
2. Ensuring that the purging and sampling devices
are made of materials, and utilized in a manner
that will not interact with or alter the analyses.
3. Ensuring that results generated by these
procedures are reproducible; therefore, the
sampling scheme should incorporate co-located
samples (duplicates).
4. Preventing cross-contamination. Sampling should
proceed from least to most contaminated wells, if
known. Field equipment blanks should be
incorporated for all sampling and purging
equipment, and decontamination of the equipment
is therefore required.
5. Properly preserving, packaging, and shipping
samples.
All field QC samples must be prepared the same as
regular investigation samples with regard to sample
volume, containers, and preservation. The chain-of-
custody procedures for the QC samples will be
identical to the field ground-water samples. The
following are QC samples that must be collected
during the sampling event:
Sample Type
• D Field duplicates
• D Matrix spike
• D Matrix spike duplicate
• D Equipment blank
• D Trip blank (VOCs)
• D Temperature blank
Frequency
1 per 20 samples
1 per 20 samples
1 per 20 samples
per Regional
require-
ments or policy
1 per sample cooler
1 per sample cooler
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HEALTH AND SAFETY CONSIDERATIONS
Depending on the site-specific contaminants, various
protective programs must be implemented prior to
sampling the first well. The site Health and Safety Plan
should be reviewed with specific emphasis placed on
the protection program planned for the sampling
tasks. Standard safe operating practices should be
followed, such as minimizing contact with potential
contaminants in both the liquid and vapor phase
through the use of appropriate personal protective
equipment.
Depending on the type of contaminants expected or
determined in previous sampling efforts, the following
safe work practices will be employed:
Particulate or metals contaminants
1. Avoid skin contact with, and incidental ingestion of,
purge water.
2. Use protective gloves and splash protection.
Volatile organic contaminants
1. Avoid breathing constituents venting from well.
2. Pre-survey the well head space with an appropri-
ate device as specified in the site Health and
Safety Plan.
3. If monitoring results indicate elevated organic
constituents, sampling activities may be con-
ducted in level C protection. At a minimum, skin
protection will be afforded by disposable protective
clothing, such as Tyvek®.
General practices should include avoiding skin contact
with water from preserved sample bottles, as this
water will have pH less than 2 or greater than 10. Also,
when filling pre-acidified VOA bottles, hydrochloric
acid fumes may be released and should not be in-
haled.
POST-SAMPLING ACTIVITIES
Several activities need to be completed and docu-
mented once ground-water sampling has been com-
pleted. These activities include, but are not limited to
the following:
1. Ensuring that all field equipment has been decon-
taminated and returned to proper storage location.
Once the individual field equipment has been
decontaminated, tag it with date of cleaning, site
name, and name of individual responsible.
2. Processing all sample paperwork, including copies
provided to the Regional Laboratory, Sample
Management Office, or other appropriate sample
handling and tracking facility.
3. Compiling all field data for site records.
4. Verifying all analytical data processed by the
analytical laboratory against field sheets to ensure
all data has been returned to sampler.
REFERENCES
Gibs, J. and T.E. Imbrigiotta, 1990, Well-Purging
Criteria for Sampling Purgeable Organic Compounds;
Ground Water, Vol. 28, No. 1, pp 68-78.
Pohlmann, K.F. and A.J.AIduino, 1992, GROUND-
WATER ISSUE PAPER: Potential Sources of Error in
Ground-Water Sampling at Hazardous Waste Sites,
US Environmental Protection Agency. EPA/540/S-92/
019.
Puls, R.W and M.J. Barcelona, 1996, GROUND-
WATER ISSUE PAPER: Low-Flow (Minimal Draw-
down) Ground-Water Sampling Procedure, US Envi-
ronmental Protection Agency. EPA/540/S-95/504, 12
pp.
Schuller, R.M., J.P Gibb and R.A Griffin, 1981, Rec-
ommended Sampling Procedures for Monitoring
Wells; Ground Water Monitoring Review, Spring 1981,
pp. 42-46.
Parker, L.V and T.A. Ranney, 1998, Sampling Trace-
Level Organic Solutes with Polymeric Tubing: Part 2,
Dynamic Studies; Ground Water Monitoring and
Remediation, Vol. 18, No. 1, pp. 148-155.
U.S. Environmental Protection Agency, 1986, RCRA
Ground-Water Monitoring Technical Enforcement
Guidance Document; OSWER-9950.1, U.S. Govern-
ment Printing Office, Washington, D.C., 208 pp.,
appendices.
U.S. Environmental Protection Agency, 1995, Ground
Water Sampling - A Workshop Summary, Texas,
November 30-December 2, 1993, EPA/600/R-94/205,
146pp.
35
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U.S. Environmental Protection Agency Region 1,
1996, Low Stress (low flow) Purging and Sampling
Prodedure for the Collection of Ground water Samples
From Monitoring Wells, SOP#: GW 0001, July 30,
1996.
U.S. Environmental Protection Agency Region 2,
1998, Ground Water Sampling Procedure Low Stress
(Low Flow) Purging and Sampling, GW Sampling
SOP Final, March 16, 1998.
Wilde, F.D., D.B. Radtke, J.Gibs and R.T. Iwatsubo,
eds., 1998, National Field Manual for the Collection of
Water-Quality Data; U.S. Geological Survey Tech-
niques of Water-Resources Investigations, Book 9,
Handbooks for Water-Resources Investigations,
variously paginated.
Wilkin, R.T., M.S. McNeil, C.J. Adair and J.T. Wilson,
2001, Field Measurement of Dissolved Oxygen: A
Comparison of Methods, Ground Water Monitoring and
Remediation, Vol. 21, No. 4, pp. 124-132.
36
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SAMPLING CHECKLIST
Well Identification:
Map of Site Included: Y or N
Wells Clearly Identified with Roads: Y or N
Well Construction Diagram Attached: Y or N
Well Construction:
Diameter of Borehole:_
Casing Material:
Screen Length:
Diameter of Casing:
Screen Material:
Total Depth:
Approximate Depth to Water:
Maximum Well Development Pumping Rate:
Date of Last Well Development:
Previous Sampling Information:
Was the Well Sampled Previously: Y or N
(If Sampled, Fill Out Table Below)
Table of Previous Sampling Information
Parameter
Previously
Sampled
Number of
Times Sampled
Maximum
Concentration
Notes (include previous purge rates)
37
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Ground Water Sampling Log
Site Name:
Well Depth( Ft-BTOC1):
Well #:
Screen Interval(Ft):
Casing Material:
Date:
Well Dia.:
Pump placement(Ft from TOC2):
Measuring Point:
Water level (pumping)(Ft):
Sampling Personnel:
Other info: (such as sample numbers, weather conditions and field notes)
Water Quality Indicator Parameters
Sampling Device:
Water level (static)(Ft):
Pump rate(l_iter/min):
Time
Pumping
rates
(L/Min)
Water
level
(ft)
DO
(mg/L)
ORP
(mv)
Turb.
(NTU)
SEC3
(S/cm)
PH
Temp.
(C°)
Volume
pumped
(L)
Type of Samples collected:
1 casing volume was:
Total volume purged prior
to sample collection:
1BTOC-Below Top of Casing
2TOC-Top of Casing
3Specific Electrical Conductance
Stabilization Criteria
D.O.
Turb.
S.C.
ORP
PH
+/- 0.3 mg/l
+/- 3%
+/-10mV
+/-0.1 unit
38
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ATTACHMENT 4
Example Standard Operating Procedure:
Standard Operating Procedure for
the Standard/Well-Volume Method for
Collecting a Ground-Water Sample
39
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This page is intentionally blank.
40
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Standard Operating Procedure for the Well-Volume
Method for Collecting a Ground-Water Sample
INTRODUCTION
The collection of "representative" water samples from
wells is neither straightforward nor easily accom-
plished. Ground-water sample collection can be a
source of variability through differences in sampling
personnel and their individual sampling procedures,
the equipment used, and ambient temporal variability
in subsurface and environmental conditions. Many
site inspections and remedial investigations require
the sampling at ground-water monitoring wells within
a defined criterion of data confidence or data quality,
which necessitates that the personnel collecting the
samples are trained and aware of proper sample-
collection procedures.
The objectives of the sampling procedures described
in this document are to minimize changes in ground-
water chemistry during sample collection and trans-
port to the laboratory and to maximize the probability
of obtaining a representative, reproducible ground-
water sample. Sampling personnel may benefit from a
working knowledge of the chemical processes that
can influence the concentration of dissolved chemical
species.
The well-volume method described in this standard
operating procedure (SOP) provides a reproducible
sampling technique with the goal that the samples
obtained will represent water quality over an entire
open interval of a short-screened (ten feet or less)
well. This technique is appropriate for long-term and
detection monitoring of formation water quality. The
resulting sample generally represents a composite of
the screened interval, and thus integrates small-scale
vertical heterogeneities of ground-water chemistry.
This sampling technique also is useful for screening
purposes for detection monitoring of contaminants in
the subsurface. However, the detection of a low
concentration of contaminant in a thin contaminated
zone or with long well screens may be difficult and
should be determined using detailed vertical profiling
techniques.
This method may not be applicable for all ground-
water-sampling wells, such as wells with very low
yields, fractured rock, and some wells with turbidity
problems. As always, site-specific conditions and
objectives should be considered prior to the selection
of this method for sampling.
SCOPE AND APPLICATION
The objective of a good sampling program should be
the collection of a representative sample of the cur-
rent ground-water conditions over a known or speci-
fied volume of aquifer. To meet this objective, the
sampling equipment, the sampling method, the
monitoring well construction, monitoring well opera-
tion and maintenance, and sample-handling proce-
dures should not alter the chemistry of the sample.
An example of how a site's Data Quality Objectives
(DQOs) for a characterization sampling effort might
vary from those of a remediation monitoring sampling
effort could be a difference of how much of the
screened interval or aquifer should be sampled. A site
characterization objective may be to collect a sample
that represents a composite of the entire (or as close
as is possible) screened interval of the monitoring
well.
Additionally, the site characterization may require a
large suite of contaminants to be sampled and ana-
lyzed, whereas, the remediation monitoring program
may require fewer contaminants sampled and ana-
lyzed. These differences may dictate the type of
sampling equipment used, the type of information
collected, and the sampling protocol.
This sampling method described is for monitoring
wells. However, this method should not be used for
water-supply wells with a water-supply pump, with
long-screened wells in complex hydrogeologic envi-
ronments (such as fractured rock), or wells with
separate phases of liquids (such as a Dense or Light
Non-Aqueous Phase Liquids) present within the
screened interval.
EQUIPMENT
• D Depth-to-water measuring device - An electronic
water-level indicator or steel tape and chalk, with
marked intervals of 0.01 foot. Interface probe for
measuring separate phase liquids, if needed.
Pressure transducer and data logger optional for
frequent depth-to-water measuring in same well.
• D Steel tape and weight - Used for measuring
total depth of well. Lead weights should not be
used.
• D Sampling pump - Submersible or bladder pumps
with adjustable rate controls are preferred. Pumps
41
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are to be constructed of inert materials, such as
stainless steel and Teflon®. Pump types that are
acceptable include gear and helical driven,
centrifugal (low-flow type), and air-activated piston.
Adjustable rate, peristaltic pumps can be used
when the depth to water is 20 feet or less.
• Tubing - Inert tubing should be chosen based on
the types and concentrations of contaminants
present, or expected to be present in the
monitoring well. Generally, Teflon®-based tubing is
recommended when sampling for organic
compounds. Polyethylene or Teflon® tubing can be
used when sampling for inorganic constituents.
• Power source - If a combustion type (gasoline or
diesel-driven) device is used, it must be located
downwind of the point of sample collection. If
possible, it should also be transported to the site
and sampling location in a different vehicle from
the sampling equipment.
• Flow-measurement equipment - Graduated
cylinder or bucket and a stop watch, or a flow
meter that can be disconnected prior to sampling.
• Multi-parameter meter with flow-through cell - This
can be one instrument or multiple probes/instru-
ments contained in a flow-through cell. The water-
quality-indicator parameters that are measured in
the field are pH, oxidation/reduction potential (ORP,
redox, or Eh), dissolved oxygen (DO), turbidity,
specific electrical conductance (SEC), and
temperature. Calibration standards for all
instruments should be NIST-traceable, within
expiration dates of the solutions, and sufficient for
daily calibration throughout the sampling collection.
• Decontamination supplies - A reliable and
documented source of distilled water and any
solvents (if used). Pressure sprayers, buckets or
decontamination tubes for pumps, brushes and
non-phosphate soap also will be needed.
• Sample bottles, sample preservation supplies and
laboratory paperwork. Also, several coolers, and
sample packing supplies (absorbing packing
material, plastic baggies, etc.).
• Approved plans and background documents -
Approved Field Sampling Plan, Quality Assurance
Project Plan, well construction data, field and
water-quality data from the previous sampling
collection.
• Site Access/Permission documentation for site
entry.
• Well keys and map showing locations of wells.
• Field notebook, field data sheets and calculator. A
suggested field data sheet is provided at the end of
this attachment.
• Filtration equipment - If needed, this equipment
should be an in-line disposable filter used for the
collection of samples for analysis of dissolved
constituents.
• Polyethylene sheeting - Used for decontamination
stations and during sampling to keep equipment
clean.
• Site Health and Safety Plan and required
equipment - The health and safety plan along with
site sign-in sheet should be on site and be
presented by the site health and safety officer.
Personnel-protective and air-monitoring equipment
specified in the Site Health and Safety Plan should
be demonstrated, present and in good working
order on site at all times.
• D Tool box - All needed tools for all site equipment
used.
• DA 55-gallon drum or container to contain the
purged water.
Construction materials of the sampling equipment
(bladders, pump, bailers, tubing, etc.) should be
limited to stainless steel, Teflon®, glass, and other
inert materials when concentrations of the site con-
taminants are expected within the detection limit
range. The sample tubing thickness and diameter
should be maximized and the tubing length should be
minimized so that the loss of contaminants absorbed
to and through the tubing walls may be reduced and
the rate of stabilization of ground-water parameters is
maximized. The tendency of organics to sorb into and
out of many materials makes the appropriate
selection of sample tubing materials critical for these
trace analyses (Pohlmann and Alduino, 1992; Parker
andRanney, 1998).
Generally, wells should be purged and sampled using
the same positive-displacement pump and/or a low-
flow submersible pump with variable controlled flow
rates and constructed of chemically inert materials. If
a pump cannot be used because the recovery rate of
the well is so low (less than 100 to 200 ml/min) and
the volume of the water to be removed is minimal
(less than 5 feet of water in a small-diameter well),
then a Teflon® bailer, with a double check valve and
bottom-emptying device with a control-flow check
42
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valve may be used to obtain the samples. Otherwise,
a bailer should not be used when sampling for volatile
organics because of the potential bias introduced
during sampling (Yeskis et al., 1988; Pohlmann et al.,
1990; Tai et al., 1991). Bailers also should be avoided
when sampling for metals because repeated bailer
deployment has the potential to increase turbidity,
which biases concentrations of inorganic constituents.
Dedicated sampling pumps are recommended for
metals sampling (Puls et al., 1992).
In addition, for wells with long riser pipes above the
well screen, the purge volumes may be reduced by
using packers above the pumps. The packer materi-
als should be compatible with the parameters to be
analyzed. These packers should be used only on
wells screened in highly permeable materials, be-
cause of the lack of ability to monitor water levels in
the packed interval. Otherwise, if pumping rates
exceed the natural aquifer recovery rates into the
packed zone, a vacuum or negative pressure zone
may develop. This may result in a failure of the seal
by the packer and/or a gaseous phase may develop,
that may bias any sample taken.
PURGING AND SAMPLING PROCEDURE
WATER-LEVEL MEASUREMENTS
The field measurements should include total well
depth and depth to water from a permanently marked
reference point.
TOTAL WELL DEPTH
The depth of each well should be measured to the
nearest one-tenth of a foot when using a steel tape
with a weight attached and should be properly re-
corded. The steel tape should be decontaminated
before use in another well according to the site spe-
cific protocols. A concern is that when the steel tape
and weight hit the bottom of the well, sediment
present on the bottom of a well is stirred up, thus
increasing turbidity, which will affect the sampling
results. In these cases, as much time as possible
should be allowed prior to sampling, such as a mini-
mum of 24 hours. If possible, total well depth mea-
surements can be completed after sampling (Puls and
Barcelona, 1996). The weight of electric tapes is
generally too light to determine accurate total well
depth. If the total well depth is greater than 200 feet,
stretching of the tape must be taken into
consideration.
DEPTH TO WATER
All water levels should be measured from the
reference point by use of a weighted steel tape and
chalk or an electronic water-level indicator (a detailed
discussion of the pros and cons of the different water
level devices is provided in Thornhill, 1989). The steel
tape is a more accurate method to take water levels,
and is recommended where shallow flow gradients
(less than 0.05 feet/feet) or deep wells are
encountered. However, in those cases where large
flow gradients or large fluctuations in water levels are
expected, a calibrated electric tape is acceptable. The
water level is calculated using the well's surveyed
reference point minus the measured depth-to-water
and should be measured to the nearest one
hundredth of afoot.
The depth-to-water measurement must be made in
each well to be sampled prior to any other activities at
the well (such as bailing, pumping, and hydraulic
testing) to avoid bias to the measurement. All
readings are to be recorded to the nearest one
hundredth of a foot. When possible, depth-to-water
and total well depth measurements should be
completed at the beginning of a ground-water
sampling program, which will allow any turbidity to
settle and allow a more synoptic water-level
evaluation. However, if outside influences (such as
tidal cycles, nearby pumping effects, or major
barometric changes) may result in significant water-
level changes in the time between measurement and
sampling, a water-level measurement should be
completed immediately prior to sampling. In addition,
the depth-to-water measurement during purging
should be recorded, with the use of a pressure
transducer and data logger sometimes more efficient
(Barcelona etal., 1985, Wilde etal., 1998).
The time and date of the measurement, point of
reference, measurement method, depth-to-water
measurement, and any calculations should be
properly recorded in field notebook or sampling sheet.
STATIC WATER VOLUME
From the information obtained for casing diameter,
total well depth and depth-to-water measurements,
the volume of water in the well is calculated. This
value is one criteria that may be used to determine the
volume of water to be purged from the well before the
sample is collected.
43
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The static water volume may be calculated using the
following formula:
= r2h(0.163)
Where:
V = static volume of water in well
(in gallons)
r = inner radius of well casing
(in inches)
h = length of water column (in feet)
which is equal to the total well
depth minus depth to water.
0.163 = a constant conversion factor
that compensates for the
conversion of the casing radius
from inches to feet for 2-inch
diameter wells and the conver-
sion of cubic feet to gallons,
and pi (TI). This factor would
change for different diameter
wells.
Static water volumes also may be obtained from
various sources, such as Appendix 11.L in Driscoll
(1986).
WELL PURGING
PURGE VOLUMES
In most cases, the standing water in the well casing
can be of a different chemical composition than that
contained in the aquifer to be sampled. Solutes may
be adsorbed or desorbed from the casing material,
oxidation may occur, and biological activity is pos-
sible. Therefore, the stagnant water within the well
must be purged so that water that is representative of
the aquifer may enter the well.
The removal of at least three well volumes is sug-
gested (USEPA, 1986; Wilde et al., 1998). The
amount of water removed may be determined by
collecting it in a graduated pail of known volume to
determine pumping rate and time of pumping. A flow
meter may also be used, as well as capturing all
purged water in a container of known volume.
The actual number of well volumes to be removed is
based on the stabilization of water-quality-indicator
parameters of pH, ORP, SEC, DO, and turbidity. The
water initially pumped is commonly turbid. In order to
keep the turbidity and other probes from being clogged
with the sediment from the turbid water, the flow-
through cell should be bypassed initially for the first
well volume. These measurements should be taken
and recorded every 1/4 well volume after the removal of
1 to 1 1/4 well volume(s). Once three successive
readings of the water-quality-indicator parameters
provided in the table have stabilized, sampling may
begin. The water-quality-indicator parameters that are
recommended include pH and temperature, but these
are generally insensitive to indicate completion of
purging since they tend to stabilize rapidly (Puls and
Barcelona, 1996). ORP may not always be an appro-
priate stabilization parameter, and will depend on site-
specific conditions. However, readings should be
recorded because of its value as a double check for
oxidizing conditions, and for some fate and transport
issues. When possible, especially when sampling for
contaminants that may be biased by the presence of
turbidity, the turbidity reading is desired to stabilize at a
value below 10 Nephelometric Turbidity Units (NTUs).
For final DO measurements, if the readings are less
than 1 milligram per liter, they should be collected with
the spectrophotometric method (Wide et al., 1998,
Wlkin et al., 2001), colorimetric or Wnkler titration
(Wlkin etal., 2001). All of these water-quality-indicator
parameters should be evaluated against the specifica-
tions of the accuracy and resolution of the instruments
used. No more than six well volumes should be
purged, to minimize the over pumping effects de-
scribed by Gibs and Imbrigiotta (1990).
Purging Methods
In a well that is not being pumped, there will be little
or no vertical mixing in the water column between
sampling events, and stratification may occur. The
water in the screened section may mix with the
ground water due to normal flow patterns, but the
water above the screened section will remain isolated
and become stagnant. Persons sampling should
realize that stagnant water may contain foreign mate-
rial inadvertently or deliberately introduced from the
surface, resulting in unrepresentative water quality. To
safeguard against collecting nonrepresentative stag-
nant water in a sample, the following guidelines and
techniques should be adhered to during sample
collection:
44
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Table of Stabilization Criteria with References for Water-Quality-lndicator Parameters
Parameter
PH
specific electrical
conductance (SEC)
oxidation-reduction
potential (ORP)
turbidity
dissolved oxygen (DO)
Stabilization Criteria
+/-0.1
+/- 3%
+/- 10 millivolts
+/- 10% (when turbidity is
greater than 10 NTUs)
+/- 0.3 milligrams per liter
Reference
Puls and Barcelona, 1996;
Wilde etal., 1998
Puls and Barcelona, 1996
Puls and Barcelona, 1996
Puls and Barcelona, 1996;
Wilde etal., 1998
Wilde etal., 1998
1. As a general rule, monitoring wells should be
pumped or bailed (although bailing is to be strongly
avoided) prior to collecting a sample. Evacuation of a
minimum of three volumes of water in the well casing
is recommended for a representative sample. In a
high-yielding ground-water formation where there is
no stagnant water in the well above the screened
section (commonly referred to as a water-table well),
evacuation prior to sample withdrawal is not as critical
but serves to field rinse and condition sampling
equipment. The purge criteria has been described
previously and will be again in the SAMPLING PRO-
CEDURES section on the following page. The rate of
purging should be at a rate and by a method that does
not cause aeration of the water column and should
not exceed the rate at which well development was
completed.
2. For wells that can be pumped or bailed to dryness
with the sampling equipment being used, the well
should be evacuated to just above the well screen
interval and allowed to recover prior to sample with-
drawal. (Note: It is important not to completely de-
water the zone being sampled, as this may allow air
into that zone which could result in negative bias in
organic and metal constituents.) If the recovery rate is
fairly rapid and time allows, evacuation of more than
one volume of water is preferred.
3. A non-representative sample also can result from
excessive prepumping of the monitoring well. Stratifi-
cation of the contaminant concentrations in the
ground-water formation may occur or heavier-than-
water compounds may sink to the lower portions of
the aquifer. Excessive pumping can decrease or
increase the contaminant concentrations from what is
representative of the sampling point of interest, as
well as increase turbidity and create large quantities
of waste water.
The method used to purge a well depends on the
inner diameter, depth-to-water level, volume of water
in the well, recovery rate of the aquifer, and accessi-
bility of the well to be sampled. The types of equip-
ment available for well evacuation include hand-
operated or motor-driven suction pumps, peristaltic
pumps, submersible pumps, and bailers made of
various materials, such as stainless steel and
Teflon®. Whenever possible, the same device used
for purging the well should be left in the well and used
for sampling, generally in a continual manner from
purging directly to sampling without altering position
of the sampling device or turning off the device.
When purging/sampling equipment must be reused in
other wells, it should be decontaminated consistent
with the decontamination procedures outlined in this
document. Purged water should be collected and
screened with air-monitoring equipment as outlined in
the site health and safety plan, as well as water-
quality field instruments. If these parameters and/or
the facility background data suggest that the water is
hazardous, it should be contained and disposed of
properly as determined on a site-specific basis.
During purging, water-level measurements should be
recorded regularly for shallow wells, typically at 15- to
30-second intervals. These data may be useful in
45
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computing aquifer transmissivity and other hydraulic
characteristics, and for adjusting purging rates. In
addition, these data will assure that the water level
doesn't fall below the pump intake level
SAMPLING PROCEDURES
Ground-water sample collection should take place
immediately following well purging. Preferably, the
same device should be used for sample collection as
was used for well purging, minimize further distur-
bance of the water column, and reduce volatilization
and turbidity. In addition, this will save time and avoid
possible contamination from the introduction of addi-
tional equipment into the well, as well as using equip-
ment materials already equilibrated to the ground
water. Sampling should occur in a progression from
the least to most contaminated well, if known, when
the same sampling device is used.
The sampling procedure is as follows:
1) Remove locking well cap. Note location, time
of day, and date in field notebook or on an
appropriate log form.
2) Note wind direction. Stand upwind from the
well to avoid contact with gases/vapors ema-
nating from the well.
3) Remove well casing cap.
4) If required by site-specific conditions, monitor
headspace of well with appropriate air-moni-
toring equipment to determine presence of
volatile organic compounds or other com-
pounds of concern and record in field logbook.
5) If not already completed, measure the water
level from the reference measuring point on
the well casing or protective outer casing (if
inner casing not installed or inaccessible) and
record it in the field notebook. Alternatively, if no
reference point exists, note that the water level
measurement is from the top of the outer
protective casing, top of inside riser pipe,
ground surface, or some other position on the
well head. Have a permanent reference point
established as soon as possible after sam-
pling. Measure at least twice to confirm mea-
surement; the measurement should agree
within 0.01 feet or re-measure. Decontaminate
the water-level-measuring device.
6) If not already completed, measure the total
depth of the well (at least twice to confirm
measurement; the measurement should agree
within 0.01 feet or re-measure) and record it in
the field notebook or on log form. Decontami-
nate the device used to measure total depth. If
the total well depth has been measured re-
cently (in the past year), then measure it at the
conclusion of sampling.
7) Calculate the volume of water in the well and
the volume to be purged using the formula
previously provided.
8) Lay plastic sheeting around the well to mini-
mize the likelihood of contamination of equip-
ment from soil adjacent to the well.
9) Rinse the outside of sampling pump with
distilled water and then, while lowering the
pump, dry it with disposable paper towels.
10) Lower the pump (or bailer) and tubing down
the well. The sampling equipment should
never be dropped into the well because this
will cause degassing of the water upon impact.
This may also increase turbidity, which may
bias the metals analysis. The lowering of the
equipment should be slow and smooth!
11) The pump should be lowered to a point just
below the water level. If the water level is
above the screened interval, the pump should
be above the screened interval for the reasons
provided in the purging section.
12) Turn the pump on. The submersible pumps
should be operated in a continuous, low-flow
manner so that they do not produce pulsating
flows, which cause aeration in the discharge
tubing, aeration upon discharge, or
resuspension of sediments at the bottom of
the well. The sampling pump flow rates should
be lower than or the same as the purging
rates. The purging and sampling rates should
not be any greater than well development
rates.
13) Water levels should be monitored during
pumping to ensure that air does not enter the
pump and to help determine an appropriate
purging rate.
14) After approximately one to two well volumes
are removed, a flow-through cell will be hooked
up to the discharge tubing of the pump. If the
46
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well discharge water is not expected to be
highly turbid, contain separate liquid phases, or
minimal bacterial activitiy that may coat or clog
the electrodes within the flow-through cell, then
the cell can be immediately hooked up to the
discharge tubing. This cell will allow measure-
ments of water-quality-indicator parameters
without allowing contact with the atmosphere
prior to recording the readings for temperature,
pH, ORP, SEC, DO and turbidity.
15) Measurements for temperature, pH, ORP,
SEC, DO, and turbidity will be made at each
one-half well volume removed. Purging may
cease when measurements for all five param-
eters have stabilized (provided in the earlier
table) for three consecutive readings.
16) If the water level is lowered to the pump level
before three volumes have been removed, the
water level will be allowed to recover for 15
minutes, and then pumping can begin at a
lower flow rate. If the pump again lowers the
water level to below the pump intake, the
pump will be turned off and the water level
allowed to recover for a longer period of time.
This will continue until a minimum of two well
volumes are removed prior to taking the
ground-water sample.
17) If the water-quality-indicator parameters have
stabilized, sample the well. Samples will be
collected by lowering the flow rate to a rate
that minimizes aeration of the sample while
filling the bottles (approximately 300 ml/min).
Then a final set of water-quality-indicator
parameters is recorded. The pump discharge
line is rapidly disconnected from the flow-
through cell to allow filling of bottles from the
pump discharge line. The bottles should be
filled in the order of volatile organic com-
pounds bottles first, followed by semi-volatile
organic compound's/pesticides, inorganics,
and other unfiltered samples. Once the last set
of samples is taken, if filtering is necessary, an
in-line disposable filter (with appropriately
chosen filter size) will be added to the dis-
charge hose of the pump. Then the filtered
samples will be taken. If a bailer is used for
obtaining the samples, filtering occurs at the
sampling location immediately after the sample
is obtained from the bailer by using a suction
filter. The first one-half to one liter of sample
taken through the filter will not be collected, in
order to assure the filter media is acclimated to
the sample. If filtered samples are collected,
WITHOUT EXCEPTION, filtering should be
performed in the field as soon as possible after
collection, and not later in a laboratory.
18) All appropriate samples that are to be cooled,
are put into a cooler with ice immediately. All of
the samples should not be exposed to sunlight
after collection. Keep the samples from freez-
ing in the winter when outside temperatures
are below freezing. The samples, especially
organics, cyanide, nutrients, and other
analytes with short holding times, are recom-
mended to be shipped or delivered to the
laboratory daily. Ensure that the appropriate
samples that are to be cooled remain at 4°C,
but do not allow any of the samples to freeze.
19) If a pump cannot be used because the recov-
ery rate is slow and the volume of the water to
be removed is minimal (less than 5 feet of
water), then a Teflon® bailer, with a double
check valve and bottom-emptying device with
a control-flow check valve will be used to
obtain the samples. The polypropylene rope
used with the bailer will be disposed of follow-
ing the completion of sampling at each well.
20) The pump is removed from the well and
decontaminated for the next sampling location.
Additional precautions to ensure accurate and repre-
sentative sample collection are as follows:
• Check valves on bailers, if bailers are used, should
be designed and inspected to ensure that fouling
problems do not reduce delivery capabilities or
result in aeration of the sample.
• The water should be transferred to a sample
container in a way that will minimize agitation and
aeration.
• If the sample bottle contains no preservatives, the
bottle should be rinsed with sample water, which is
discarded before sampling. Bottles for sample
analyses that require preservation should be
prepared before they are taken to the well. Care
should be taken to avoid overfilling bottles so that
the preservative is not lost. The pH should be
checked and more preservatives added to inor-
47
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ganic sample bottles, if needed. VOA bottles that
do not meet the ph requirements need to be
discarded and new sample bottles with more
preservative added should be prepared immedi-
ately.
• Clean sampling equipment should not be placed
directly on the ground or other contaminated
surfaces either prior to sampling or during storage
and transport.
Special Consideration for Volatile Organic Compound
Sampling
The proper collection of a sample for dissolved volatile
organics requires minimal disturbance of the sample
to limit volatilization and therefore a loss of volatiles
from the samples. Preferred retrieval systems for the
collection of un-biased volatile organic samples
include positive displacement pumps, low-flow cen-
trifugal pumps, and some in-situ sampling devices.
Field conditions and other constraints will limit the
choice of appropriate systems. The principal objective
is to provide a valid sample for analysis, one that has
been subjected to the least amount of turbulence
possible.
1) Fill each vial to just overflowing. Do not rinse
the vial, nor excessively overflow it, as this will
effect the pH by diluting the acid preservative
previously placed in the bottle. Another option
is to add the acid at the well, after the sample
has been collected. There should be a convex
meniscus on the top of the vial.
2) Do not over tighten and break the cap.
3) Invert the vial and tap gently. Observe the vial
closely. If an air bubble appears, discard the
sample and collect another. It is imperative
that no entrapped air remains in the sample
vial. Bottles with bubbles should be discarded,
unless a new sample cannot be collected, and
then the presence of the bubble should be
noted in the field notes or field data sheet. If
an open sample bottle is dropped, the bottle
should be discarded.
4) Orient the VOC vial in the cooler so that it is
lying on its side, not straight up.
5) The holding time for VOCs is 14 days. It is
recommended that samples be shipped or
delivered to the laboratory daily. Ensure that
the samples remain at 4°C, but do not allow
the samples to freeze.
Field Filtration of Turbid Samples
The USEPA recognizes that in some hydrogeologic
environments, even with proper well design, installa-
tion, and development, in combination with the low-
flow rate purging and sampling techniques, sample
turbidity cannot be reduced to ambient levels. The well
construction, development, and sampling information
should be reviewed by the Regional geologists or
hydrologists to see if the source of the turbidity prob-
lems can be resolved or if alternative sampling meth-
ods should be employed. If the water sample is
excessively turbid, the collection of both filtered and
unfiltered samples, in combination with turbidity, Total
Suspended Solids (TSS), Total Dissolved Solids
(TDS), pumping rate, and drawdown data is recom-
mended. The filter size used to determine TSS and
TDS should be the same as used in the field filtration.
An in-line filter should be used to minimize contact
with air to avoid precipitation of metals. The typical
filter media size used is 0.45 urn because this is
commonly accepted as the demarcation between
dissolved and non-dissolved species. Other filter
sizes may be appropriate, but their use should be
determined based on site-specific criteria (examples
include grain-size distribution, ground-water flow
velocities, mineralogy) and project DQOs. Filter sizes
up to 10.0 urn may be warranted because larger size
filters may allow particulates that are mobile in ground
water to pass through (Puls and Powell, 1992). The
changing of filter media size may limit the comparabil-
ity of the data obtained with other data sets and may
affect their use in some geochemical models. Filter
media size used on previous data sets from a site,
region, or aquifer and the DQOs should be taken into
consideration. The filter media used during the
ground-water sampling program should be collected in
a suitable container and archived because potential
analysis of the media may be helpful for the determi-
nation of particulate size, mineralogy, etc.
The first 500 to 1000 milliliters of sample taken
through the filter, depending on sample turbidity, will
not be collected for a sample, in order to ensure that
the filter media has equilibrated to the sample. Manu-
facturers' recommendations also should be consulted.
Because bailers have been shown to increase
48
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turbidity while purging and sampling, they should be
avoided when sampling for trace element, metal,
PCB, and pesticide constituents. If portable sampling
pumps are used, the pumps should be gently lowered
to the sampling depth desired, carefully avoiding being
lowered to the bottom of the well. The pumps, once
placed in the well, should not be moved to allow any
particles mobilized by pump placement to settle.
Dedicated sampling equipment installed in the well
prior to the commencement of the sampling activities
is one of the recommended methods to reduce
turbidity artifacts (Puls and Powell, 1992; Kearl et al.,
1992; Puls etal., 1992; Puls and Barcelona, 1996).
DECONTAMINATION PROCEDURES
Once removed from the well, the purging and sam-
pling pumps should be decontaminated by scrubbing
with a brush and a non-phosphate soapy-water wash,
rinsed with water, and rinsed with distilled water to
help ensure that there is no cross-contamination
between wells. The step-by-step procedure is:
1) Pull pump out of previously sampled well (or
out of vehicle) and use three pressure spray-
ers filled with soapy water, tap water, and
distilled water. Spray outside of tubing and
pump until water is flowing off of tubing after
each rinse. Use bristle brush to help remove
visible dirt, contaminants, etc.
2) Have three long PVC tubes with caps or
buckets filled with soapy water, tap water and
distilled water. Run pump in each until approxi-
mately 2 to 3 gallons of each decon solution is
pumped through tubing. Pump at low rate to
increase contact time between the decon
solutions and the tubing.
3) Try to pump decon solutions out of tubing prior
to next well. If this cannot be done, com-
pressed air may be used to purge lines.
Another option is to install a check valve in the
pump line (usually just above the pump head)
so that the decon solutions do not run back
down the well as the pump is lowered down
the next well.
4) Prior to lowering the pump down the next well,
spray the outside of the pump and tubing with
distilled water. Use disposable paper towels to
dry the pump and tubing.
5) If a hydrophobic contaminant is present (such
as separate phase, high levels of PCBs, etc.),
an additional decon step, or steps, may be
added. For example, an organic solvent such
as reagent-grade isopropanol alcohol may be
added as a first rinse prior to the soapy water
rinse.
If the well has been sampled with a bailer that is not
disposable, the bailer should be cleaned by washing
with soapy water, rinsing with tap water, and finally
rinsing with distilled water. Bailers are most easily
cleaned using a long-handled bottle brush.
It is especially important to clean thoroughly the
portion of the equipment that will be in contact with
sample water. In addition, a clean plastic sheet should
be placed adjacent to or around the well to prevent
surface soils from coming in contact with the purging
equipment. The effects of cross-contamination also
can be minimized by sampling the least contaminated
well first and progressing to the more contaminated
ones. The bailer cable/rope (if a bailer is used) and
plastic sheet should be properly discarded, as pro-
vided in the site health and safety plan, and new
materials provided for the next well.
FIELD QUALITY CONTROL
The quality assurance (QA) targets for precision and
accuracy of sampling programs are based on accu-
racy and precision guidelines established by the
USEPA. When setting targets, keep in mind that all
measurements must be made so that the results are
representative of the sample water and site-specific
conditions. Various types of blanks are used to check
the cleanliness of the field-handling methods. These
are known as field blanks, and include field equipment
blanks and transport blanks. Other QA samples
include spike samples and duplicates.
There are five primary areas of concern for QA in the
collection of representative ground-water samples:
1. Obtaining a sample that is representative of
water in the aquifer or targeted zone of the
aquifer. Verify log documentation that the well
was purged of the required volume or that the
temperature, pH, ORP, SEC, DO and turbidity
stabilized before samples were extracted.
49
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2. Ensuring that the purging and sampling de-
vices are made of materials and utilized in a
manner that will not interact with or alter the
analyses.
3. Generating results that are reproducible.
Therefore, the sampling scheme should
incorporate co-located samples (duplicates).
4. Preventing cross-contamination. Sampling
should proceed from least to most contami-
nated wells, if known. Field equipment blanks
should be incorporated for all sampling and
purging equipment; decontamination of the
equipment is therefore required.
5. Ensuring that samples are properly preserved,
packaged, and shipped.
FIELD EQUIPMENT BLANKS
To ensure QA and quality control, a field equipment
blank must be included in each sampling run, or for
every twenty samples taken with the sampling device.
Equiptment blanks allow for a cross check and, in
some cases, quantitative correction for imprecision
that could arise due to handling, preservation, or
improper cleaning procedures.
Equipment blanks should be taken for each sample
bottle type that is filled. Distilled water is run through
the sampling equipment and placed in a sample bottle
(the blank), and the contents are analyzed in the lab
like any other sample. Following the collection of each
set of twenty samples, a field equipment blank will be
obtained. It is generally desirable to collect this field
equipment blank after sampling a relatively highly
contaminated well. These blanks may be obtained
through the following procedure:
a) Following the sampling event, decontaminate
all sampling equipment according to the site
decontamination procedures and before
collecting the blank.
b) VOA field blanks should be collected first, prior
to water collected for other TAL/TCL analyses.
A field blank must be taken for all analyses.
c) Be sure that there is enough distilled water in
the pump so that the field equipment blank can
be collected for each analysis.
d) The water used for the field equipment blank
should be from a reliable source, documented
in the field notebooks, and analyzed as a
separate water-quality sample.
TRIP BLANKS
A trip blank should be included in each sample ship-
ment and, at a minimum, one per 20 samples. Bottles,
identical to those used in the field, are filled with
reagent-grade water. The source of the reagent-grade
water should be documented in the field notebooks,
including lot number and manufacture. This sample is
labeled and stored as though it is a sample. The
sample is shipped back to the laboratory with the other
samples and analysis is carried out for all the same
constituents.
DUPLICATE SAMPLES
Duplicate samples are collected by taking separate
samples as close to each other in time and space as
practical, and should be taken for every 20 samples
collected. Duplicate samples are used to develop
criteria for acceptable variations in the physical and
chemical composition of samples that could result
from the sampling procedure. Duplicate results are
utilized by the QA officer and the project manager to
give an indication of the precision of the sampling and
analytical methods.
HEALTH AND SAFETY CONSIDERATIONS
Depending on the site-specific contaminants, various
protective programs must be implemented prior to
sampling the first well. The site health and safety plan
should be reviewed with specific emphasis placed on
the protection program planned for the sampling
tasks. Standard safe operating practices should be
followed, such as minimizing contact with potential
contaminants in both the liquid and vapor phases
through the use of appropriate personal protective
equipment.
Depending on the type of contaminant expected or
determined in previous sampling efforts, the following
safe work practices will be employed:
Particulate or metals contaminants
1. Avoid skin contact with, and accidental inges-
tion of, purge water.
2. Wear protective gloves and splash protection.
50
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Volatile organic contaminants
1. Avoid breathing constituents venting from well.
2. Pre-survey the well head space with an appro-
priate device as specified in the Site Health
and Safety Plan.
3. If air monitoring results indicate elevated
organic constituents, sampling activities may
be conducted in Level C protection. At a
minimum, skin protection will be afforded by
disposable protective clothing, such as
Tyvek®.
General practices should include avoiding skin con-
tact with water from preserved sample bottles, as this
water will have pH less than 2 or greater than 10.
Also, when filling, pre-preserved VOA bottles, hydro-
chloric acid fumes may be released and should not be
inhaled.
POST-SAMPLING ACTIVITIES
Several activities need to be completed and docu-
mented once ground-water sampling has been com-
pleted. These activities include, but are not limited to:
• Ensuring that all field equipment has been decon-
taminated and returned to proper storage location.
Once the individual field equipment has been
decontaminated, tag it with date of cleaning, site
name, and name of individual responsible.
• Processing all sample paperwork, including copies
provided to Central Regional Laboratory, Sample
Management Office, or other appropriate sample
handling and tracking facility.
• Compiling all field data for site records.
• Verifying all analytical data processed by the
analytical laboratory against field sheets to ensure
all data has been returned to sampler.
REFERENCES
Barcelona, M.J., J.P Gibb, J.A. Hellfrich and E.E.
Garske, 1985, Practical Guide for Ground-Water
Sampling; U.S. Environmental Protection Agency,
EPA/600/2-85/104, 169 pp.
Driscoll, F.G., 1986, Groundwater and Wells, 2nd Ed.;
Johnson Division, St. Paul, Minnesota, 1089 pp.
Gibs, J. and T.E. Imbrigiotta, 1990, Well-Purging
Criteria for Sampling Purgeable Organic Compounds;
Ground Water, Vol. 28, No. 1, pp 68-78.
Herzog, B.L., S.J. Chou, J.R. Valkenburg and R.A.
Griffin, 1988, Changes in Volatile Organic Chemical
Concentrations After Purging Slowly Recovering
Wells; Ground Water Monitoring Review, Vol. 8, No. 4,
pp. 93-99.
Kearl, P.M., N.E. Korte, and T.A. Cronk, 1992, Sug-
gested Modifications to Ground Water Sampling
Procedures Based on Observations from the Colloid
Borescope; Ground Water Monitoring Review, Vol. 12,
No. 2, pp. 155-161.
Keely, J.F. and K. Boateng, 1987, Monitoring Well
Installation, Purging, and Sampling Techniques - Part
1: Conceptualizations; Ground Water, Vol. 25, No. 4
pp. 427-439.
McAlary, T.A. and J.F. Barker, 1987, Volatilization
Losses of Organics During Ground Water Sampling
from Low Permeability Materials; Ground Water
Monitoring Review, Vol. 7, No. 4, pp. 63-68.
Nielson, D.M., 1991, Practical Handbook of Ground-
Water Monitoring; Lewis Publishers, 717 pp.
Parker, L.V and T.A. Ranney, 1998, Sampling Trace-
Level Organic Solutes with Polymeric Tubing: Part 2,
Dynamic Studies; Ground Water Monitoring and
Remediation, Vol. 18, No. 1, pp. 148-155.
Pohlmann, K.F., R.P Blegen, and J.W Hess, 1990,
Field Comparison of Ground-Water Sampling Devices
for Hazardous Waste Sites: An Evaluation using
Volatile Organic Compounds; EPA/600/4-90/028,
102 pp.
Pohlmann, K.F. and A.J. Alduino, 1992, GROUND-
WATER ISSUE PAPER: Potential Sources of Error in
Ground-Water Sampling at Hazardous Waste Sites;
US Environmental Protection Agency. EPA/540/S-92/
019.
Puls, R.W and R.M. Powell, 1992, Acquisition of
Representative Ground Water Quality Samples for
Metals; Ground Water Monitoring Review, Vol. 12, No.
3, pp. 167-176.
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Puls, R.W., D.A. Clark, B. Bledsoe, R.M. Powell and
C.J. Paul, 1992, Metals in Ground Water: Sampling
Artifacts and Reproducibility; Hazardous Waste and
Hazardous Materials, Vol. 9, No. 2, pp. 149-162.
Puls, R.W and M.J. Barcelona, 1996, GROUND-
WATER ISSUE PAPER: Low-Flow (Minimal Draw-
down) Ground-Water Sampling Procedures; U.S.
Environmental Protection Agency, EPA/540/S-95/504,
12pp.
Tai, D.Y., K.S. Turner, and L.A. Garcia, 1991, The Use
of a Standpipe to Evaluate Ground Water Samples;
Ground Water Monitoring Review, Vol. 11, No. 1, pp.
125-132.
Thornhill, J.T., 1989, SUPERFUND GROUND WATER
ISSUE: Accuracy of Depth to Water Measurements;
US Environmental Protection Agency. EPA/540/4-89/
002, 3 pp.
U.S. Environmental Protection Agency, 1986, RCRA
Ground-Water Monitoring Technical Enforcement
Guidance Document; OSWER-9950.1, U.S. Govern-
ment Printing Office, Washington, D.C., 208 pp.,
appendices.
U.S. Environmental Protection Agency, 1995, Ground
Water Sampling-A Workshop Summary, Dallas,
Texas, November 30-December 2, 1993, EPA/600/R-
94/025, 146 pp.
Wilde, F.D., D.B. Radtke, J.Gibs and R.T Iwatsubo,
eds., 1998, National Field Manual for the Collection of
Water-Quality Data; U.S. Geological Survey
Techniques of Water-Resources Investigations, Book
9, Handbooks for Water-Resources Investigations,
variously paginated.
Wilkin, R.T, M.S. McNeil, C.J. Adair and J.T Wlson,
2001, Field Measurement of Dissolved Oxygen: A
Comparison of Methods, Ground Water Monitoring
and Remediation, Vol. 21, No. 4, pp. 124-132.
Yeskis, D., K. Chiu, S. Meyers, J. Weiss and T Bloom,
1988, A Field Study of Various Sampling Devices and
Their Effects on Volatile Organic Contaminants;
Proceedings of the Second National Outdoor Action
Conference on Aquifer Restoration, Ground Water
Monitoring and Geophysical Methods, National Water
Well Association, May, 1988.
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GROUND-WATER SAMPLING RECORD
Well ID:
Facility Name:
Well Depth:
Casing Material.:_
Sampling Crew:
Type of Pump:
Weather Conditions:
Depth to Water:,
Well Diameter:
Volume Of Water per Well Volume:,
Station #:
Date: / /
.Tubing Material:,
.Pump set at
NOTES:
GROUND-WATER SAMPLING PARAMETERS
Time
Water Volume Pumping DO
Level Pumped Rate (mg/l)
Temp. SEC
(°C) (yS/cm)
PH
ORP Turbidity
(mV) (NTU)
Other Parameters:.
Sampled at:
Sample delivered to.
Sample CRL#:
Parameters taken with:
.by.
at
OTR#:
ITR#:
SAS#:
Parameters Collected
Number of Bottles
Bottle Lot Number
53
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