Alaska Department of Environmental Conservation
Spill Prevention and Response Division

How to Interpret Laboratory Data
ENVIRONMENTAL CLEANUP EDUCATIONAL TOOLS SERIES

In this Fact Sheet
• Sections Found In A Lab Report
• What The Results Mean
• Common Terms Used In Lab
Reports
• Common Data Qualifiers

Glossary
kilogram: 1,000 grams
matrix: the type of sample (water, soil,
sediment, etc.)

Reading laboratory data reports and interpreting their results can be confusing. We
hope this fact sheet will make it more understandable. If you still have questions,
contact your ADEC project manager or the laboratory that analyzed the samples.
Most labs are very helpful in answering questions about their data.

Sections Found in a Lab Report

Lab reports typically have several sections. These sections may include: 1) the
transmittal or cover letter, 2) the case narrative, 3) the analytical results, and 4) the
quality assurance/quality control (QA/QC) sample results. QA/QC is performed to
give a much greater confidence in the
data. A lab report may also include a
printout of the analytical instrument
readings and evidence that the testing
equipment was properly calibrated.
The transmittal letter and case narrative
are sometimes combined into one
section. The narrative explains any
problems encountered in the analysis of
the samples. The problems may or may
not have affected the quality of the
results. The analytical results section will
show the analysis performed by the lab,
the test result, and notes that indicate any
problems encountered. These notes are called “data qualifiers.” Most labs use a
standard set of codes for data qualifiers (see page 2 for an explanation of data
qualifiers).

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maximum contaminant level (MCL): the
highest level of contamination allowed in public
drinking water. MCLs are designed to protect
human health.
method detection limit (MDL): the lowest
concentration (greater than zero) of the
substance tested that can be measured and
reported with 99 percent confidence

method reporting limit (MRL): the lowest
concentration of the substance tested that can
be reported reliably under normal laboratory
conditions
µg/L or kg: micrograms per liter or kilogram;
1/1,000,000th of a gram
mg /L or kg: milligrams per liter or kilogram;
1/1000th of a gram
non-detect (ND): the contaminant was not
detected above the MDL

quality assurance/quality control (QA/QC):
Quality assurance is the systematic process of
checking to see whether a product or service
being developed is meeting specified
requirements. Quality control are the tools used
to monitor or regulate the process. Quality
control is an aspect of quality assurance.
target compounds: the compounds being
tested for

June 2009

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Series 1, Fact Sheet #15

What Do the Results Mean?

When you look at the report’s analytical results section, you will see columns
indicating the sample matrix (soil, water, etc), the contaminants tested for, and the
test results. The results usually are reported in units of parts per million (ppm,
mg/L or mg/kg), parts per billion (ppb, µg/L or µg/kg), or percentages. If the
contaminant was not found, the column will show “ND” for not detected.
The abbreviation ND is often followed by a number, such as ND (0.5). This does
not necessarily mean that the chemical was actually there. It means simply that
anything below 0.5 ppm or ppb (whichever units were used for that analysis)
would not have been found because it was below the test equipment’s detection
limit.

When dealing with drinking water, another column that may be shown is the
“maximum contaminant level (MCL).” This number is the highest level of
contamination considered acceptable in drinking water. If the number on your
result is less than the MCL, your drinking water is considered acceptable. If the
MCL column is not present, ask your local DEC office about a regulatory standard

 Data qualifiers are used in lab reports
to indicate a problem or irregularity
with the analytical result. The most
common qualifiers are shown here;
most labs also will use footnotes to
explain the qualifiers they have used.
J:

The number is an estimated
concentration because something
in the sample interfered with the
analysis.

U: The contaminant was not detected
at a concentration greater than the
detection limit.
UJ: The contaminant was not detected,
but the detection limit is estimated
because of interference from
something in the sample.

A lab report may include the results of the lab’s QA/QC program. These results
may be confused with the sample results unless you can recognize the terms and
know what they mean. QA/QC tests you may see included in your lab report
include:
Trip Blank: This is a sample container, often filled with distilled water. The trip
blank travels unopened to the site with the empty sample containers and returns
unopened to the laboratory with the samples. This is done to confirm that no
contamination has been picked up during the “trip” to and from the sample
location. If contamination is found in the trip blank, it means that the samples also
may have been contaminated from a source outside the sample area. The trip blank
should be non-detect (ND). If it isn’t, your sample results may not be accurate, and
a new test should be run.
Duplicate: A duplicate is a second sample, as identical as possible to the first one.
The sampler will not usually tell the lab about a duplicate sample in order to check
on how well the lab reproduces an analytical result. The test results for both
samples should be the almost the same.
Surrogate: A lab will monitor its analytical system by “spiking” a sample with
another chemical similar to the contaminant to be tested for. If a good percentage
(usually 70-120%) of the surrogate chemical is recovered, it shows that the lab’s
test can accurately measure the contaminant sought. If you see “surrogate” results
on your analysis report, it does not mean that particular chemical that was really in
your sample.

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R: The data are unusable.
Resampling and reanalysis are
necessary for verification.

Common Terms Used in Quality Assurance Reports

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Common Data Qualifiers:

for the contaminant. The detection limit of the equipment should be lower than the
MCL. If not, you have nothing to compare your results to, and you should ask for a
new test or evaluate other labs and/or methods.

Reference List

Test Methods for Evaluation of Solid
Waste, Physical/Chemical Methods
(SW 846) Revision 4, January 1995
Fundamentals of Analytical
Chemistry, Douglas A. Skoog,
Donald M. West, Fourth Edition

This fact sheet is one of a series of free
publications prepared by DEC to help
people understand contaminated site
cleanup issues.

Matrix Spike: Occasionally something in the sample itself — its soil, water, or
sediment — interferes with the test for the contaminant. To check for that
interference, a lab may conduct a “matrix spike” (and a matrix spike duplicate). A
known amount of the same chemical being tested for is added to two extra samples
before the analysis. If your report shows “matrix spike” data, check to see that the
amount of chemical recovered is a good percentage (70-120%). If the percent
recovery is low, it means that something in the matrix is interfering with the test,
more work may need to be done to overcome the interference. The percent
recovery corresponds to the chemical added, not to what was in the original
sample. A non-spiked sample also is analyzed for that contaminant, so look for the
result which does not include the spike.

For More Information

DEC, Spill Prevention and Response Division

Main Offices: Anchorage: 269-7558
Kenai:
262-5210

Juneau:
465-5390
Fairbanks: 451-2153

Internet Homepage: www.dec.state.ak.us/spar/csp

This brochure is a free publication providing current information on DEC’s Contaminated Site Remediation Program. Contents may be reprinted without
permission; credit would be appreciated. The Alaska Department of Environmental Conservation complies with Title II of the Americans with Disabilities Act of
1990. This publication is available in alternative communication formats upon request. Please contact the Contaminated Sites Program receptionist in Juneau
through the Alaska Relay Service, TDD 1-800-770-8973/TTY or dial 711, or www.akrelay.com