Traps, Mistakes, and Errors - Field Sampling: Principles and Practices in Environmental Analysis - page 290

sampling. In the analytical procedures, analysis for the wrong component, antagonisms
between analytes, sample analysis mismatches, and extraction using the wrong method
are important sources of errors. The characteristics of the environment and movement of
contaminants in that environment are important considerations. The use of proper
statistical tools is essential in obtaining good sampling results.
QUESTIONS
1. Describe the training personnel should have before beginning to field sample.
Include all aspects of sampling.
2. Think of an example in which knowledge of the history of a field would be
important in developing a sampling plan for that field.
3. A soil sample reported to be contaminated with lead is sampled and the analysis
shows a lead level of 10 ppm. What would you need to know before deciding that the
field from which the sample came needed to be remediated to remove lead?
4. A soil supposed to be contaminated with hydrocarbons is extracted with aqua regia
(a strong acid). The result is a solution that cannot be analyzed for hydrocarbons. Explain
why this is the case. What would aqua regia be expected to extract from a soil sample?
5. The results of analysis show that in week 1 the level of zinc in a field was 120 ppm.
The sample from a week later showed a level of 140 ppm. It is assumed that the analysis
is in error. What other explanation could there be for this increase, assuming it is not an
error?
6. Iron (Fe) in soil reacts with phosphate to form insoluble precipitates. After the
application of phosphate fertilizer to a field what would be expected to happen to the
level of soluble iron in the soil?
7. A field is contaminated with large amounts of nitrate. A 0-to-20-cm surface sample
from this field shows little nitrate. Does this mean that the nitrate has disappeared from
the soil? Where would you sample to make sure the nitrate is not in the soil? If the nitrate
is not in the soil, where might it be?
8. A sample extract used to remove VOCs from a sample is analyzed by atomic
absorption. An absence of metals is seen in the results of the analysis. Can you explain
why this might be the case?
9. A statistical analysis of the results of a series of extracts of the same soil shows a
large variation in the results. Is this to be expected?