Environmental Sampling Techniques - Fundamentals of Environmental Sampling and Analysis - page 71

Water/wastewater samples
Minimal liquid sample volume varies considerably in the range of 5 mL for TPHs in
liquid wastes, 100 mL for total metals, and 1 L for trace organics such as pesticides.
This bulk estimate of sample size represents a volume sufficient to perform one
analysis only, and as a general guide, the minimum volume collected should be three
to four times the amount required for the analysis (EPA, 1995).
Soil/sediment/solid wastes
A full characterization of soil physicochemical properties including particle size and
soil texture, as required for most environmental projects, usually needs a minimum of
approximately 200 g of soil. For most of the contaminant analysis, however, a dry
mass of approximately 5-100 g is sufficient. More soil samples are needed if the goal
is to detect low solubility (hydrophobic) organic contaminants in the aquifer
materials since these chemicals tend to accumulate in the first six inches of surface
soils (EPA, 1995). The required sample size for the sediment is smaller than the water
samples because contaminants tend to accumulate in the sediment as a sink. Because
waste samples are generally of high concentrations, sample volumes are of less
concern, but the volume should be kept at a minimum to reduce disposal costs.
Air samples
Similar to other matrices, the volume of air required depends on the minimum
chemical concentration that can be detected and the sensitivity of the measurement.
Because the concentration range may be unknown, the sample size will have to be
determined by trial and error. Trial samples of more than 10 m 3 may be required to
determine ambient concentrations (Christian, 2004). This volume should be lower if
smoke stack emission samples are collected for the target contaminant.
Water/sediment samples for toxicity testing
Unlike chemical analysis, the water and sediment used as a substrate for toxicity
testing demand more samples. For instance, 20-40 L of water is needed to perform
an effluent acute toxicity test. For the sediment, 15 L is required to conduct
bioaccumulation tests (based on an average of 3 L sediment per test chamber and 5
replicates), and 8-16 L sediment is needed to conduct benthic macrointevertebrate
assessments (EPA, 2001).
4.1.3 Sample Preservation and Storage
The purpose of sample preservation is to minimize any physical, chemical, and/or
biological changes that may take place in a sample from the time of sample
collection to the time of sample analysis. Three approaches (i.e., refrigeration, use of
proper sample container, and addition of preserving chemicals) are generally used to
minimize such changes (Fig. 4.1).