Environmental Engineering Reference
In-Depth Information
original samples or added later may result in inaccurate results or hide the compounds of
interest altogether. The laboratory technician may incorrectly read or record data. With
sufficient numbers of controls—both positive and negative—these types of problems can
be caught and rectified.
In searching for errors often the first approach is to apply statistics rigorously to the
field samples and their analytical results. While statistical analysis is critical in any
sampling program, it is not sufficient in and of itself to ferret out all problems. An
example of statistics not being applicable to a specific set of data is given in Section 11.2.
A better first approach is to look for possible sources of errors recorded in the project
notebook and in the chain of custody, field calibration, and field information forms. A
summary of errors and mistakes made both in sampling and in analyzing samples is given
in Table 11.1.
11.1. HISTORY OF THE AREA
Because it is one of the first pieces of information obtained about a field, its history is a
beginning source of mistakes. Failing to obtain a complete history of an area can result in
costly and time-consuming errors in interpreting data and developing remediation plans.
A complete and thorough investigation of all aspects of an area will be invaluable in
TABLE 11.1 Sources of Mistakes and Errors Made in Sampling and Analyzing
Environmental Samples
Activity
Sources of error
Field
sampling
Incorrect field, incorrect position in field, inconsistent sample size, failure to
record in field notebook (also see Table 11.3), incorrect labeling, failure to fill out
proper forms, improper or failure to preserve (e.g. acidification, cooling)
Transportation Incorrect sample container, loss of sample, contamination from other samples or
surroundings, incorrect labeling, incorrect shipping container and container
conditions
Storage
Incorrect storage conditions (e.g. temperature, isolation, sunlight, time)
Analysis
Incorrect storage conditions, incorrect handling (e.g. wetting, drying, heating and
cooling, exposure to contamination, loss of contaminant), incorrect sample
preparation, wrong extraction method, incorrect solvent used
Reporting
Incorrect input of data, incorrect mathematical and statistical analysis
explaining both expected and unexpected analytical results. Examples of the importance
of obtaining the history of the field to be sampled have been given in previous chapters.
(See particularly Section 3.6 in Chapter 3.)
A field history can be of great help in determining what potential contaminants may be
present. For example, if the groundwater is being tested at the site of an old gasoline
 
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