United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV89114
Research and Development
EPA-600/S4-84-043 July 1984
Project Summary
Soil Sampling Quality
Assurance User's Guide
Delbert S. Barth and Benjamin J. Mason
The inherent inseparability of a cost-
effective Soil Sampling Quality
Assurance/Quality Control (QA/QC)
Plan from the objectives of a soil
monitoring program is emphasized.
Required precisions and confidence
levels for the data cannot be defined
until the decisions which will be made
on the basis of the data are clearly
stated and the consequences of making
Type I (false positive) or Type II (false
negative) errors are weighed. Statistical
considerations are presented with
special attention to analyses of variance
of soil monitoring data, methods of
calculating required numbers of soil
samples to achieve desired precisions
and confidence levels, possible
applications of Kriging, and assignment
of control limits to QA/QC data. The
value of an exploratory or preliminary
study to the cost-effective achievement
of both the soil monitoring objectives
and the objectives of the Soil Sampling
QA/QC Plan is strongly emphasized.
The value of developing a hypothetical
model to estimate the distribution in
space and time of soil pollutants and
thus to assist in the design of the moni-
toring network is discussed. Methods
for determination of the number and
location of soil sampling sites; sample
collection methods and procedures to
include frequency of sampling; sample
handling to include labeling,
preservation, preparation for analysis,
and transport; together with QA/QC
aspects are presented and discussed.
Finally, the importance of systems
audits and training to the achievement
of soil sampling QA/QC objectives is
presented and discussed.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory. Las Vegas, NV, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
An adequate quality assurance/quality
control (QA/QC) program requires the
identification and quantification of all
sources of error associated with each
step of a monitoring program so that the
resulting data will be of known quality.
The components of error, or variance,
include those associated with sampling,
sample preparation, extraction, analysis,
and residual error. In the past, major
emphasis has been placed on QA/QC
aspects of sample analysis and closely
associated operations such as sample
preparation and extraction. For monitor-
ing a relatively inhomogeneous medium
such as soil, the sampling component of
variance will usually significantly exceed
the analysis component. Thus, in this
case a minimum adequate QA/QC plan
must include a section dealing with soil
sampling. The purpose of this document
is to provide guidance in QA/QC aspects
related to soil sampling.
Generally, soil monitoring is
undertaken to carry out the provisions and
intent of applicable environmental laws
with high priority requirements associ-
ated with hazardous waste management.
The objectives of soil monitoring
programs are often to obtain data on the
basis of which to answer one or more of
the following questions:
e Are the concentrations of specified
soil pollutants in a defined study
region significantly different from
the concentrations in a control
region?
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• Do the concentrations of specified
soil pollutants in a defined study
region exceed established threshold
action levels?
• At the measured concentrations of
specified soil pollutants in a defined
study region what is the associated
risk of adverse effects to public
health, welfare, or the environment?
For each of these applications the QA/QC
required to determine precisions and
confidence levels for the data cannot be
specified without giving careful
consideration to the consequences of
making an error, for example, in a
decision to require, or not to require,
cleanup of a contaminated region. It
follows in general that to be maximally
cost-effective and defensible the QA/QC
objectives of a soil monitoring program .
cannot be separated from the objectives
of the soil monitoring program itself.
Approximately 20 percent of the total
monitoring program sample load should
be allocated to QA/QC with about 5
percent of this being dedicated to the
analytical effort and 15 percent to the
sampling effort. Soil sampling programs
must incorporate statistical designs and
QA/QC plans to provide quantitative
measures of both precision and repre-
sentativeness.
Control samples are normally as
important to a soil monitoring study as
are samples taken from the study region.
The data from control samples aid in the
interpretation of the results from the
study region and also help to identify
sources and important transport routes
for the soil pollutants. Accordingly, the
same level of effort and degree of QA/QC
checks should go into selecting and
sampling a control region as goes into
sampling the study region.
Experience has shown that requiring
approximately 5 percent of all analytical
samples to be duplicate samples will
provide adequate QA/QCfor determining
variance between samples collected at
approximately the same site. A precision
less than ±20 percent is probably unreal-
istic for a field soil sampling effort. Table 1
provides recommendations for
confidence levels and precisions for soil
sampling related to hazardous waste
investigations.
All statistical sampling plans are based
on frequency distributions with the most
common being normal or log normal.
Generally, the concentrations of
pollutants in soil and transport-related
properties of these pollutants are distrib-
uted log normally. In addition to obtaining
Table 1. Illustrative Confidence Levels
and Precisions
Confidence
Level Precision
(Percent) /Percent/
Emergency Cleanup
Activities
Remedial Response
Studies
Planned Removal
Studies
90
95
20
20
information on the areal distribution of
soil pollutants it is necessary to
determine the distribution with depth.
Both Type I (false positive) and Type II
(false negative) errors should be
considered in hypothesis testing. Tables
are provided for use in determining the
required number of samples to achieve
defined precision and confidence levels.
The location of sampling is important, and
a random process should normally be
used for selecting specific sampling sites.
Stratification of the sampling region may
reduce the variance in cases where the
variance is considered to be unacceptably
large. Compositing of samples is
generally not recommended since it
allows no estimate of the variance among
the samples being composited.
Suggested QA/QC procedures for soil
samples include preparation of the
following samples, generally on the basis
of one QA/QC sample for each 20
samples: field blank, sample bank blank,
reagent blank, calibration check
standard, spiked extract, spiked sample,
total recoverable, laboratory control
standard, re-extraction, split extract,
triplicate sample, and duplicate sample.
The major technique used to detect
bias in a soil sampling effort is the adding
of known amounts of standard solutions
to some of the samples and comparing
the resulting data. It is especially difficult
to demonstrate the complete absence of
bias.
The confidence interval for soil
samples is bounded by the confidence
limits (bounds of uncertainty about the
average caused by the variability of the
experiment). The confidence interval is
used in the development of control
charts, in identifying outliers, and in
determining if a set of samples exceeds
some established standard. Generally,
the analysis of variance of the data
provides the best method for obtaining
the information needed for calculating
the confidence interval. An approxima-
tion of the confidence interval can be
obtained by use of the ranges of
replicates in a series. The tolerance limits
are similar to the confidence limits but
are used to identify the interval and limits
into which data from the individual
samples should fall.
The simplest test of hypotheses is
either comparison of two mean values or
comparison between the mean and some
established standard, or action, value.
The Student's t test is generally used for
both cases.
Once objectives have been defined for
a soil monitoring study, a total study
protocol, including an appropriate
QA/QC program must be prepared.
Usually not enough is known about the
sources and transport properties of the
soil pollutants to accomplish this in a
cost-effective manner without additional
study. The suggested approach is to
conduct an exploratory study including
both a literature and information search
followed by selected field measurements
based on an assumed dispersion model.
The data resulting from this exploratory
study serve as the basis for the more
definitive total study protocol. If one is
dealing with a situation requiring
possible emergency action to protect
public health, it is necessary to compress
the planning and study design into a short
time period and proceed to the definitive
study without delay. In either case, the
objectives of the monitoring study consti-
tute the driving force for all elements of
the study design including the QA/QC
aspects.
To develop the exploratory study
protocol with its associated QA/QC plan
one needs to combine into an assumed
dispersion model the information
obtained priortoanyfield measurements.
On the basis of this model the standard
deviation of the mean for soil samples is
estimated. Value judgments are used to
define required precision and confidence
levels (relatedtoacceptable levelsofType
I or Type II errors). A control region is
selected. The numbers of required
samples may then be calculated.
Additional samples should be required to
provide for the validation of the assumed
model. The locationsof thesamplingsites
should be selected by an appropriate
combination of judgmental (use of the
assumed model), systematic (to allow for
the fact that the model may be wrong),
and random (to minimize bias) sampling.
Sampling and sample handling must be
accomplished according to standardized
procedures based on principles designed
to achieve both data of adequate quality
and maximal cost-effectiveness. Particu-
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lar attention should be given to factors
surrounding the disposition of non-soil
materials collected with the soil samples.
The requirements for QA/QC for the
exploratory study need not be as stringent
as for the more definitive study in the
sense that acceptable precisions and
confidence levels may be relaxed
somewhat. Allowance should be made,
however, for the collection of a modest
additional number of QA/QC samples
over that specified in the QA/QC plan to
verify that the QA/QC study design is
adequately achieving its assigned objec-
tives. Also, all normal analytical QA/QC
checks should be used.
If the exploratory study is conducted
well, it will provide some data for"
achieving the overall objectives of the
total monitoring study; it will provide a
check of the feasibility and efficacy of all
aspects of the monitoring design
including the QA/QC plan; it willserveas
a training vehicle for all participants; it
will pinpoint where additional
measurements need to be made; and it
will provide a body of information and
data which can be incorporated into the
final report for the total monitoring study.
For the more definitive study, the
selection of numbers of samples and
sampling sites, sample collection
procedures, and sample handling
methods and procedures follow and build
on the principles discussed and results
obtained in the exploratory study.
Frequency of sampling is an important
aspect of the more definitive study which
usually cannot be addressed in the ex-
ploratory study because of the relatively
short time span over which the
exploratory study is conducted. The
required frequency of sampling depends
on the objectives of the study, the sources
of pollution, the pollutants of interest,
transport rates, and disappearance rates
(physical, chemical, or biological trans-
formations as well as dilution or disper-
sion). Sampling frequency may be related
to changes over time, season, or
precipitation. An approach that has been
used successfully has been to provide
intensive sampling early in the life of the
study (e.g., monthly for the first year) and
then to decrease the frequency as the
levels begin to drop. The important
principle is that the sampling should be
conducted often enough that changes in
the concentrations of soil pollutants
important to the achievement of the
monitoring objectives are not missed.
The important questions to be
answered in the analyses and interpreta-
tion of QA/QC data are, "What is the
quality of the data?" and "Could the same
objectives have been achieved through
an improved QA/QC design which may
have required fewer resources?" It is
desirable to provide summarized tables of
validated QA/QC data in the final report.
This approach allows users to verify the
reported results as well as to begin to
build a body of QA/QC experimental data
in the literature whichallowcomparisons
to be made among studies. Special
emphasis should be placed on how
overall levels of precision and confidence
were derived from the data. If portions of
the study results are ambiguous and
supportable conclusions cannot be
drawn with regard to the reliability of the
data, that situation must be clearly stated.
The adequacy of all aspects of the
QA/QC plan should be examined in detail
with emphasis on defining for future
studies an appropriate minimum
adequate plan. Some aspects of the
QA/QC plan may have been too restric-
tive, some may not have been restrictive
enough. Soil monitoring studies should
have checks and balances built into the
QA/QC plan which will identify early in
the study whether the plan is adequate
and, if required; allowfor corrective action
to be taken before the study continues.
This is one of the major advantages of
conducting an exploratory study.
There is insufficient knowledge dealing
with soil monitoring studies to state with
confidence which portions of the QA/QC
plan will be generally applicable to all soil
monitoring studies and which portions
must be varied depending on site-specific
factors. As experience is gained it may be
possible to provide more adequate
guidance on this subject. Inthe meantime,
, it is recommended that many important
factors of QA/QC plans be considered as
site-specific until proven otherwise.
Another important aspect of QA/QC is
auditing. The purpose of an audit is to
ensure that all aspects of the QA/QC
system planned for the project are in
place and functioning well. This includes
all aspects of field, sample bank and lab-
oratory operations. Whenever a problem
is identified, corrective action should be
initiated and pursued until corrected.
Sample chain-of-custody procedures and
raw data are checked as appropriate and
results of blind QA/QC samples routinely
inserted into the sample load are
reviewed. Spot-checks of sampling
methods and techniques, sampling and
analysis calculations, and data
transcription are performed. Checks are
made to ascertain that required
documentation has been maintained and
in an orderly fashion, that each of the
recorded items is properly categorized,
and cross-checking can be easily
accomplished. Checksaremadetoensure
that data recording conforms to strict
document control protocols and the
program's QA/QC plan.
It is recommended that an audit of the
overall QA/QC plan for sample
documentation, collection, preparation,
storage, and transfer procedures be
performed just before sampling starts.
This is to review critically the entire
sampling operation to determine the
need for any corrective action early in the
program.
The project leader of a soil monitoring
project is responsible for ascertaining
that all members of his project team have
adequate training and experience to carry
out satisfactorily their assigned missions
and functions. This is normally
accomplished through a combination of
required classroom training, briefings on
the specific monitoring project about to
be implemented, and field training
exercises. Special training programs
should be completed by all personnel
prior to their involvement in conducting
audits.
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Delbert S. Barth and Benjamin J. Mason are with Environmental Research
Center, University of Nevada-Las Vegas, Las Vegas, NV 89154.
Kenneth W.
Brown is the EPA Project Officer (see below).
f Order No.
The complete report, entitled "Soil Sampling Quality Assurance User's Guide,"
PB 84-198 621; Cost: $13.00, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89114
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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