Methodology and Quality Assurance/Quality Control of Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 116

matrix. The QC samples rarely provide useful information on the project decision-
making process (e.g., to tell the extent of contamination if this is the project goal),
but it is used to identify the error, diagnose what caused the error, and, if an error
occurred, how to correct it. If the error is acceptable within the specified data quality
objective (Section 2.2.3), the results from QA/QC samples will help to direct the
reporting process so that the data user will know the level of confidence in the data.
Practical tips
By law, any EPA-funded monitoring project must have an EPA-approved
QAPP before it can begin collecting samples. However, even programs that
do not receive EPA money should consider developing a QAPP, especially if
data might be used by state, federal, or local resource managers.
QA/QC is required for all aspects of a monitoring program, including field
sampling, laboratory analysis, and data review and reporting.
The QA/QC samples required by EPA in some cases can account for 30% of
the total project cost. Efforts should be made in order to minimize the
number of QA/QC samples while maintaining data quality.
Personnel training is of utmost importance as the efficacy of QA/QC depends
on how it is executed by the field and lab personnel.
Always keep in mind that it is better to have a few reliable data points than
many unreliable ones!
5.3.1 Types of Field QA/QC Samples
Errors occurring in the field (sample collection, preservation, transportation, and
storage) may have originated from a single source or a combination of several
sources. These include: analyte carryover from sampling equipment, incomplete
decontamination of sample equipment between samples, cross-contamination
between samples, and absorption of volatile chemicals from air during transporta-
tion and storage. To test the absence or presence of these errors, the following field
QC samples should be collected:
Equipment (rinsate) blanks: Equipment blanks are used to detect any con-
tamination from sampling equipment. These blanks are prepared in the field
before sampling begins, by using the precleaned equipment and filling the
appropriate container with analyte-free water. If equipment is cleaned on site
(e.g., nondisposable bailers, nondedicated pumps and tubing, augers), then
additional equipment blanks should be collected after equipment decontami-
nation for each equipment group. Contaminants frequently found in equip-
ment blanks include common laboratory contaminants such as phthalates,
methylene chloride, and acetone. Occasionally, oily materials, PCBs, and
VOCs retained by groundwater pumps are found in equipment blanks after
samples with high contaminant concentration have been taken (Popek, 2003).