Methodology and Quality Assurance/Quality Control of Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 117

Field blanks: A field blank sample undergoes the full handling and shipping
process of an actual sample. It is designed to detect sample contamination
that can occur during field operation or during shipment. Field blanks are
prepared in the field using certified clean water (HPLC-grade carbon-free
water for organic analysis or deionized water for inorganic analysis),
preserved in the same manner as other collected samples, and then submitted
to the laboratory for analysis. For soil samples, field blank samples can be
prepared with certified clean sand or soil rather than clean water. For high-
concentration samples such as wastes, the usefulness of field blanks is
limited. Parts per billion (ppb) or low parts per million (ppm) error has little
significance when identifying high concentration wastes in the hundreds of
ppm range. In air sampling, the preparation of field blanks varies depending
on the sampling device/adsorbent media used during sampling (see Fig. 4.9,
Section 4.1.5). For example, when using adsorbent media that is sealed by
the manufacturer, the field blank is opened with the other sample media,
resealed, and carried through the sample handling process.
Trip (travel) blanks: Unlike field blanks, the trip blanks are used for VOCs
analysis only. In addition, trip blanks are prepared prior to going into the field
by filling containers (VOC vials) with clean water (HPCL-grade) or sand. The
sample containers are kept closed, handled, transported to the field, and then
returned to the laboratory in the same manner as the other samples. Trip
blanks are used to evaluate error associated with shipping and handling,
and analytical procedures. They are used in conjunction with field blanks to
isolate sources of sample contamination already noted in previous field
blanks. Like field blanks, trip blanks are not typically used during waste
sampling because of the high concentrations in most waste samples. Special
precautions must be exercised for trip blanks used in air sampling such as
absorbent tubes, canister, and impinger-based sampling methods (EPA, 1995).
Several other field QC samples may be required depending on the specific data
quality objectives (DQOs) for a particular project. Field replicate samples, also
referred to as field duplicates and split samples, are field samples obtained from one
sampling point, homogenized, divided into separate containers, and treated as
separate samples throughout the remaining sample handling and analytical
processes. These field replicate samples are used to assess error associated with
sample heterogeneity, sample methodology, and analytical procedures. There are no
''true'' field replicates for biological samples. However, biological samples collected
from the same station are typically referred to as replicates. Samples can also be
collected next to each other (e.g., within a three-foot radius of the selected sampling
site); these are called collocated samples because they are ''co-located.'' Unlike field
replicates, collocated samples are not composited and used as discrete samples in
order to assess site variation in the immediate vicinity of the sampling area.
If the project purpose is to quantify true changes in contaminant concentrations
due to a contaminated source or site, background samples are often collected as the
QC sample. Background samples are collected upstream of area(s) of contamination