SUGGESTIONS FOR REDUCTION
OF ANALYTICAL COSTS BY
ELIMINATION OF UNNECESSARY
QUALITY CONTROL (QC) SAMPLES
by Douglas M. Chatham
A rationale is presented for collecting fewer QC samples for
hazardous-waste projects and to encourage project managers and
quality assurance project officers to question the need for every
QC sample or activity. Many field QC samples can be eliminated
from hazardous waste site investigations, resulting in significant
analytical cost savings, without any effect on the quality of
the overall investigation. The categories of QC samples or analyses
which could be reduced include second column confirmations, field
blanks, matrix spike and matrix spike duplicates, and duplicate
samples. Additional cost reductions could be realized through
careful selection of analytical methods and the use of on-site
methods, where feasible.
The purpose of this paper is to present a rationale for collecting
fewer QC samples for hazardous-waste projects and to encourage
project managers and quality assurance project officers to question
the need for every QC sample or activity. Many field QC samples
can be eliminated from hazardous waste site investigations without
any effect on the quality of the overall investigation. The QA/QC
requirements for environmental investigations were derived under
CERCLA and RCRA with the purpose of generating legally defensible
results. "The EPA Contract Laboratory Program (CLP) is intended
to provide analytical services for Superfund waste site samples.
As discussed in the User's Guide to the Contract Laboratory
Program (EPA 1988), the program was developed to fill the
need for legally defensible results supported by a high level
of quality assurance (i.e., data of known quality) and documentation."(1)
All analyses performed for CERCLA (Superfund) investigations were
initially required to be conducted at DQO Level IV (CLP). The
initial (discovery) stage of a site investigation should be conducted
at Level III or IV. Once the origin and responsibilities are established
for a site, the purpose of QA/QC should be adjusted to new DQOs.
Determining the extent of contamination, conducting RI/FS, and
monitoring remediations may be successfully accomplished with
field screening methods, on-site Level II analyses, and fixed
laboratory Level II, with some samples (generally 10%) confirmed
at Level III or Level IV.
Many projects have used GC/MS methods when lower cost GC methods
would have accomplished the project DQOs. GC/MS methods (SW8240/8260
and SW8270) are used when analyte confirmation is required. The
mass spectra provides information confirming the analyte identification
based on retention times. SW846 method 8240 has been used many
times when method 8010 and/or 8020 would cover all the analytes
of interest. SW846 methods 8260 and 8021 have essentially the
same analyte list. SW846 method 8270 has been used when other
methods could have been substituted at a lower cost.
Significant analytical cost reductions could be realized by eliminating
unnecessary second column confirmations, field blanks, matrix
spike and matrix spike duplicates, and duplicate samples. Second
column confirmations, field blanks, matrix spikes/spike duplicates,
and field duplicates can, in most cases, be reduced or eliminated.
If a particular type of QC sample is considered unnecessary, it
should not be included in the work plan or the QAPP. If comments
are made calling for these samples, the responses should state
the reasons for not collecting the QC sample in question. If these
responses are not accepted, the QC sample should then be included
in the work plan. This should result in a reduction in the number
of QC samples, a better understanding of the effect of QC on the
data, and reduced costs in time and money for the work.
A. QUALITY CONTROL SAMPLES AND PROCEDURES
1.0 SECOND-COLUMN CONFIRMATIONS
Second column confirmations apply to organic analyses using
GC methods , such as SW846 methods SW8010, SW8020, SW8021, SW8080,
SW8081 and SW8280. A second column confirmation often is billed
by the laboratory as a separate sample analysis. Method 8000A
of SW846 states in Paragraph 220.127.116.11 "Tentative identification
of an analyte occurs when a peak from a sample extract falls within
the daily retention time window. Normally, confirmation is required:
on a second GC column, by GC/MS if concentration permits, or by
other recognized confirmation techniques. Confirmation may not
be necessary if the composition of the sample matrix is well established
by prior analyses."(2) Methods SW8010B, SW8011, SW8015A,
SW8020B, SW8021A, and SW8030A, include the statement "If
analytical interferences are suspected, or for the purpose of
confirmation, analysis using the second GC column is recommended."
Many projects have specified that all positive results for GC
methods will be confirmed by second column confirmation only because
the SW846 method provides for it. Many more projects have suffered
from inflated analytical costs because second column confirmations
were not discussed in the work plan or the QAPP and the laboratory
performed these analyses because they were called for by the SW846
method. The large number of confirmations resulting from this
protocol is excessive and often results in an unnecessary inflation
of the analytical cost. If good historical data exist, the only
analytes requiring confirmation are compounds not previously detected
and confirmed. For example, if benzene was detected and confirmed
by method SW8240 (a GC/MS method) or by method SW8020 with second
column confirmation during Superfund investigations, a positive
result for benzene in the RI/FS investigation does not need to
be confirmed. Positive results less than Quantitation Limits,
MCLs, ARARs, or cleanup levels should not be confirmed. Sampling
efforts involving numerous samples at each site, e.g. grid sampling,
should include only enough confirmations to confirm the identity
of each analyte found at the site.
For example, a sampling grid of 100 sampling points with positive
results for benzene, toluene, ethylbenzene, and xylenes (BTEX)
in each sample would result in 200 analyses for BTEX if every
positive result is confirmed. At an analytical cost of $100/sample
for BTEX, the result analytical cost is $20,000. This example
should require no more than five confirming samples which would
be 105 analyses for BTEX and an analytical cost of $10,500.
One investigation submitted 107 samples for Herbicide analysis
costing $176 each. The site had been investigated several times
before, providing adequate historical data to eliminate the need
for 2nd column confirmations. There were 70 2nd column confirmations
resulting in 177 analyses for a total analytical cost of $31,152
(not including other QA/QC samples). These 70 additional analyses
were performed because SW846 method SW8150 provided for them and
they were not specifically addressed by the work plan or the QAPP.
Elimination of the unnecessary 2nd column confirmations would
have saved the project $12,320.
The only confirmations required for initial site investigations
conducted under CLP protocols are GC/MS confirmations of Pesticide/PCB
analyses since the volatiles and semi-volatiles are analyzed by
GC/MS methods. Cost reductions by limiting 2nd column confirmations
could be realized for any sampling investigation utilizing GC
The field blanks collected at a site could include trip blanks,
ambient blanks, bottle blanks, source water blanks, and equipment
rinseate blanks. The reason for analyzing different types of blanks
is to be able to trace the origin of contamination in order to
take corrective action. This requires that the results be available
as field work is being conducted. Generally, blank results are
not available before the sample results are reported, which can
be many weeks after the field effort is completed. A multiplicity
of blanks may be justified, but the project manager should develop
good reasons for them. Long-term programs involving numerous separate
projects could benefit from different types of blanks, since corrective
action can be taken between projects. If on-site analytical equipment
is available, analysis of blanks on-site would allow corrective
action to be taken rapidly and these are generally much less expensive
than fixed-base laboratory analyses. On-site analysis of blanks
must be conducted with methods which are analyte-specific, have
quantitation limits lower than the action levels, and documented
calibrations and detection limits. Many of the blanks submitted
to laboratories for analysis are probably not necessary.
In many cases, two or more blanks could be combined; e.g., an
equipment rinseate blank taken to the sampling site serves as
an ambient blank and a bottle blank, and if this blank is shipped
in a cooler with VOA analyses, it also serves as a trip blank.
Another approach might be to collect a full set of field blanks
and analyze only the most comprehensive (the equipment rinsate).
As stated by Dr. Keith (3), "Sample analysis is often expensive.
Sometimes it is prudent to collect a full suite of blanks but
only analyze the field blanks. If the field blanks indicate no
problems, the other blanks may be discarded or stored as necessary.
If a problem is discovered, the individual blanks can be analyzed
to determine its source. Resampling will still likely be necessary."
Data validation guidelines state that if a compound is found in
any blank, positive sample results greater than the quantitation
limit and less than five times the blank concentration are qualified
as not detected (U or ND) at a quantitation limit (QL) equal to
the sample result. If this adjusted QL is above the action level,
it cannot be used to demonstrate a concentration below the action
level. There is no difference between a positive sample result
greater than an action level and a blank qualified result with
a quantitation limit greater than the action level when the purpose
is to demonstrate a concentration below the action level. Thus,
if the purpose of sampling is to demonstrate that ARARs, MCLs,
or cleanup levels have been met, or for monitoring remediation
efforts, there may be no reason to take any field blanks. Since
the resulting corrective action (i.e., resampling) based on a
sample result above the action level is the same with or without
blanks, the blanks probably are not necessary.
Elimination of excessive blanks and duplicates from one proposal
has allowed a reduction in analytical costs from $53,500 to $45,700
3.0 MATRIX SPIKE/MATRIX SPIKE DUPLICATES
Matrix spike (MS) samples are analyzed to determine the effect
of the sample matrix on the accuracy of the analytical results.
The spike is the addition of a known amount of analyte to a normal
sample in the lab. Matrix spike duplicates (MSD) are the second
of a pair of lab matrix spike samples, and are analyzed to check
the precision of analytical procedures. In order to evaluate the
effect of the sample matrix on analytical data, triplicate volume
is collected for one sample out of every group of 20. Two portions
of the sample (the MS and MSD) are spiked with a standard solution.
These spiked samples are analyzed, and the percent recovery and
relative percent difference are calculated. Data validation guidelines
(5) include the following steps if MS/MSD results do not meet
1. No action is taken on MS/MSD data alone. (Decisions based on
MS/MSD data must be supported by other types of QC, such as surrogate
recoveries, which can stand alone.)
2. The data reviewer should first try to determine to what extent
the results of the MS/MSD effect the associated data.
3. In those instances where it can be determined that the results
of the MS/MSD effect only the sample spiked, then qualification
should be limited to this sample alone. However, it may be determined
through the MS/MSD results that a laboratory is having a systematic
problem in the analysis of one or more analytes, which affects
all associated samples.
It has been estimated that up to 90 percent of all environmental
measurement variability can be attributed to the sampling process.(6)
The matrix spiking protocol assumes that one sample out of a batch
of twenty is adequate to assess the effect of the matrix on accuracy
and precision. Much of the variability of the sampling process
is due to the variability of environmental media and the contaminants
within that media; likewise, the matrix effect is as variable
as each medium and its contaminants. To be effective in defining
method accuracy and precision, matrix spiking would have to be
done for all samples.
Since data validation based on MS/MSD results is applied only
to the sample spiked, the QA/QC value of MS/MSD samples is much
lower than the value of surrogate recoveries and of laboratory
control sample/laboratory control sample duplicate results (LCS/LCSD).
Surrogates are added to every sample analyzed for organics and
are the best measure of accuracy and matrix effects for an individual
sample. LCS/LCSD results for each batch and the laboratory control
charts are the best measure of laboratory accuracy and precision
for organic analyses. The LCS/LCSD program is also the best measure
of accuracy and precision for metals analyses. Laboratories do
not charge for surrogates or LCS samples. The digestion procedure
for metals virtually destroys the matrix so that the only interferences
normally encountered in ICP and atomic absorption methods are
from high concentrations of other metals. Elimination of MS/MSD
samples could reduce analytical costs by 10%. For a project with
analytical costs of $50,000, this represents a savings of $5,000.
4.0 FIELD DUPLICATES
The two types of Field Duplicates are split samples and co-located
samples. A split sample is a sample which has been thoroughly
blended and split between two containers. Often, the split samples
are sent to different laboratories. Split samples are intended
to measure the precision of the whole sampling and analysis procedure.
Most often, if they contain anything to measure, split samples
are a measure of how thoroughly the sample was blended before
being split. There is no way to determine an effect on the rest
of the samples at the site. Co-located samples are samples taken
in the same location but not blended. The intent of co-located
samples is to measure sampling precision or the variability of
"When designing experiments or procedures, it is important
to keep in mind that the overall objective is accuracy. It naturally
follows that those in charge of a project should ask whether additional
measurements really contribute to the accuracy of a method, or
simply to its precision.
In today's business world cost is very important, and each extra
measurement adds to the cost of a project. We all know that precision
is important, but we need to take a closer look at the costs and
benefits to the customer when expenses are increased for the sake
of improving precision without necessarily increasing accuracy."(7)
Often, the stated purpose of field duplicates is to measure the
precision of the complete process from sampling through analysis.
This is nice-sounding phraseology in a work plan, but what can
you do with the results? Due to the potentially large variability
inherent in the media being sampled particularly for soils and
sediments, one sample location out of twenty probably will not
represent the sampling or matrix variability. The result is that
these measurements are often reported as measures of "precision",
but they have no effect on the flagging or the use of the data.
As stated above, the source of the greatest variation in environmental
analytical results is the variability of the media. Comparable
results (<40% RPD) are seldom achieved from co-located duplicate
soil samples, even with the best efforts of the best sampling
technicians available. A statistical evaluation of all sample
results at a site should be used to measure the precision and
representativeness of the sampling program. These statistical
measures may provide confidence intervals for establishing extent
of contamination in a medium.
5.0 SELECTION OF METHODS
Many projects use GC/MS methods (SW846 methods 8240/8260 and
8270) when less costly methods (SW846 methods 8010 and 8020, or
8021) would satisfy the needs of the project. The primary advantage
of using GC/MS methods is analyte confirmation without an additional
analysis. Most projects in the RI/FS or remediation stages do
not require analyte confirmations, as discussed in the part 1.0
of this paper. Method 8260, based on laboratory fee schedules,
costs approximately $200 per sample while methods 601/602 or 8010/8020
costs approximately $150 per sample; a savings of 25% for the
same analyte list.
Since the purpose of this paper is to encourage the use of
performance-based criteria to the selection of QC samples, the
recommended guidelines listed in this section should not be used
as a prescriptive set of guidelines. Any and all QC which contributes
to the quality of the data or are required for other reasons should
be included regardless of arguments presented in this paper. For
each QC sample or analysis proposed, Project Managers (PMs) and
Quality Assurance Project Officers (QAPOs) should ask what that
determination contributes to the quality of the data and whether
it helps meet the project DQOs. If a QC sample contributes nothing
toward the DQOs, an argument should be made against incurring
the cost for that sample.
The following are recommended guidelines
and uses for QA/QC samples:
1.0 Second-Column Confirmations
1.1 If historical data exist, the laboratory should be directed
to conduct second-column confirmations only for compounds not
previously detected. When second-column confirmations are deemed
necessary, the laboratory should confer with the PM or the QAPO.
1.2 Positive results less than Quantitation Limits, MCLs, ARARs,
or cleanup levels should not be confirmed.
1.3 Sampling efforts involving numerous samples at each site,
e.g. grid sampling, should have a limited number of confirmations.
2.1 For sampling efforts undertaken to demonstrate that ARARs,
MCLs, or cleanup levels have been met, eliminate all field blanks.
2.2 For projects which require blanks, use the following criteria
for determining the frequency and type of blanks to take:
2.2.1 Ambient blanks - Collect only in the event that the field
team observes nearby activities that could contaminate VOC samples.
2.2.2 Equipment blanks - Collect rinseates on bailers used to
collect groundwater samples. Collect equipment rinseates for each
decontamination event. Do not collect rinseate blanks for soil
or sediment samples.
2.3 Combine blanks (Equipment Rinseate, Ambient, and Trip Blanks)
wherever possible. When equipment rinseate or ambient blanks are
taken, eliminate trip blanks and ship all sample VOCs in the same
cooler as the blank.
2.4 If sampling of multiple types of blanks cannot be avoided,
analyze only the equipment rinseate. If a problem is found, then
analyze the remainder of the blanks.
2.5 If corrective actions are possible, submit source blanks as
needed to implement those corrective actions. During long-term
programs, submit source water blanks from water purification systems
either to a fixed base laboratory or to an on-site chemist to
maintain quality control of that system.
3.0 Matrix Spike/Matrix Spike Duplicates
3.1 Use surrogate recoveries to measure matrix effects for
3.2 Use Laboratory Control Spikes/Duplicates (LCS/LCSD) rather
than MS/MSDs for determining precision and accuracy.
3.3 Use control charts for warning and control limits on precision
3.4 Avoid MS/MSD for metal analyses; metal analyses do not generally
require a measure of matrix effects since the digestion and analytical
methods destroy the matrix.
4.0 Field Duplicates
4.1 Collect and analyze field duplicates for Level IV (CLP)
projects only. Eliminate or greatly reduce the requirements for
field duplicates for Levels I, II, and III projects, unless it
is necessary to establish statistical measures of uncertainty
in the definition of extent of contamination.
5.0 Selection of Methods
- Use GC methods rather than GC/MS methods
unless analyte confirmations are required.
- Accuracy: Accuracy is the degree of agreement of a measurement
(or an average of measurements), X, with an accepted reference
or true value, T.
Batch: A group of twenty or fewer field samples, exclusive of
quality control samples, segregated by matrix and site.
Blank Spike: An analytical control sample consisting of all reagents
that are included with a group of samples and has been spiked
with a known quantity of the analyte(s) of interest.
Matrix Spike: An aliquot of sample spiked with a known concentration
of target analyte(s). The spiking occurs prior to sample preparation
and analysis. A matrix spike is used to document the bias of a
method in a given sample matrix.(2)
Matrix Spike Duplicates: Intralaboratory split samples spiked
with identical concentrations of target analyte(s). The spiking
occurs prior to sample preparation and analysis. They are used
to document the precision and bias of a method in a given sample
Equipment Rinseate Blank An equipment rinseate blank is a sample
of the water which has been used to rinse the sampling equipment.
They document adequate decontamination of the sampling equipment
after its use. These blanks are collected after equipment decontamination
and prior to resampling.(3)
Ambient Blank An ambient blank (field blank) is a sample of analyte-free
water, which is transferred from one vessel to another or exposed
to the sampling environment at the sampling site. They measure
incidental or accidental sample contamination during the whole
process (sampling, transport, sample preparation, and analysis).(3)
Bottle Blank A bottle blank is an empty bottle from the lot used
for the environmental samples. Analyte-free water is added and
the sample is analyzed.
Trip Blank A trip blank is a sample of laboratory distilled, deionized
water taken from the laboratory to the sampling site and returned
to the laboratory unopened. Trip blanks are used to measure cross-contamination
from the container and preservative during transport, field handling,
Source Blank A source blank is a sample of the water used for
well development, decontamination, and steam generation.
Method Blank A method blank is a sample of analyte-free water
to which all reagents are added in the same volumes or proportions
as used in sample processing.(2)
Precision: A measure of mutual agreement among individual measurements
of the same property, usually under prescribed similar conditions.
Surrogate: An organic compound used to spike samples which is
similar to the target analyte(s) in chemical composition and behavior
in the analytical process, but which is not normally found in
- LIST OF REFERENCES
- EPA, Risk Assessment Guidance for Superfund, Volume I,
Human Health Evaluation Manual (PartA), p. 5-5, EPA/540/1-89/002,
- EPA, Test Methods for Evaluating Solid Waste, Physical/Chemical
Methods, SW-846, 3rd Edition, Final Update 1, November 1990.
- Keith, Lawrence H., Ph.D., Environmental Sampling and Analysis,
A Practical Guide, Lewis Publishers, Inc., 1992.
- Taylor, John K., Ph.D., Quality Assurance of Chemical Measurements,
Lewis Publishers, Inc., 1990.
- USEPA Contract Laboratory Program, National Functional
Guidelines for Organic Data Review, June, 1991.
- Homsher, M.T., Haeberer, Fred, Marsden, Paul J., Mitchum,
R.K., Neptune, Dean, and Warren, John, Performance Based Criteria,
A Panel Discussion, Environmental Lab, October/November 1991.
- Phifer, Lyle H., Accuracy Versus Precision, Environmental
Testing & Analysis, March/April 1995.
- EPA, Data Quality Objectives Process for Superfund, Interim
Final Guidance, p. 42, EPA540-R-93-071, September 1993.
Submit your page to 34 popular sites for free, using one form!