Environmental Engineering Reference
In-Depth Information
(either on or off site), where there is little or no chance of migration of the
contaminants of concern. This provides the basis for comparison between
contaminated and uncontaminated areas. Background sampling is appropriate when
sampling soil, surface water, groundwater, and air. For example, background water
samples must often be collected to verify groundwater plume direction, ambient
conditions, and attribution of sources. However, background sampling has less
application to waste sampling. In biological sampling, reference samples may be
taken from a reference area outside the influence of the site. The reference area
should be close to the site and have habitats, size, and terrain similar to the site under
investigations. These samples should be of the same species, sex, and developmental
stage as the field site samples.
5.3.2 Numbers of Field QA/QC Samples
Equipment blanks: Collect one equipment blank per type of sampling device
per day. At least one equipment blank should be collected for every 20
samples per parameter group and per matrix. The number of equipment
blanks can be reduced or eliminated if dedicated equipment (e.g., pump and
tubing) or disposable sampling tools are used.
Field blanks: Submit one field blank per day.
Trip blanks: A trip blank should be included with each shipment. At least one
trip blank should be prepared for each VOC method, and analyzed for each
cooler used for storing and transporting VOC samples.
Field duplicates: During each independent sampling event, at least one
sample per matrix type or 10% of the samples, whichever is greater, must be
collected for duplicate. In Superfund clean-up projects, when the goal is to
determine total error for critical samples with contamination concentrations
near the action level, a minimum of eight replicate samples is required to
have a valid statistical analysis.
Collocated samples: Determine the applicability on a site-by-site basis.
Background samples: Collect at least one per matrix (surface water, sediment).
5.4 ANALYTICAL QUALITY ASSURANCE/QUALITY
CONTROL
5.4.1 Quality Control Procedures for Sample
Preparation
Significant errors can occur during sample preparation, that is, digestion for metals
and extraction for semivolatile or nonvolatile organics. These errors are likely due to
cross-contamination from glassware or chemicals used, contaminant loss owing to
sorption or volatilization, matrix effects or interference, and incomplete digestion or
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