Environmental Sampling Design - Fundamentals of Environmental Sampling and Analysis - page 65

estimate with the same number of samples, or achieve the same precision with fewer
samples and lower cost.
(c) If you are estimating a population mean and you have an adequate budget. In the
meantime, you are also interesting in knowing the information of a spatial or
temporal pattern.
(d) If you are estimating a population mean and you have budget constrains. The
analytical costs are much higher compared with sampling costs. Your goal is to
produce an equally precise or a more precise estimate of the mean with fewer
analyses and lower cost.
(e) If you are developing an understanding of where contamination is present and you
have an adequate budget for the number of samples needed, your goal is to acquire
coverage of the area of concern with a given level of confidence that you would have
detected a hot spot of a given size.
(f) If you are developing an understanding of where contamination is present and you
have an adequate budget for the number of samples needed, your goal is to acquire
coverage of the time periods of interest.

16. A former small pesticide manufacturing facility was surveyed for pesticide
residues in surrounding soils. Historical data have shown that the pesticide is very
stable in soil, concentration is in the range of 40-200 ppb with a standard deviation of
5 ppb.

(a) If an error level of 2 ppb is acceptable, how many samples are needed to be 95%
confident that the requirement is met?
(b) If an area of 1 km 2 is to be surveyed (see the figure below), design the locations
using the method of simple random sampling. Use Excel to generate random
numbers and use the coordinate as shown below (i.e., x ¼ 0, y ¼ 0 for the
manufacturing facility, x ¼500 500; y ¼500 500). Attach the random
number from your Excel output and plot a x-y scatter plot showing the locations
of all samples calculated from (a).

y y

Former pesticide
manufacturing
facility (0, 0)

Former pesticide
manufacturing
facility (0, 0)

x x

1,000 m 1,000 m

1,000 m 1,000 m