Environmental Sampling Design - Fundamentals of Environmental Sampling and Analysis - page 68

21. A lagoon waste pit has the following historical data for the barium concentration based
on a simple random sampling (n ¼ 4): 86, 90, 98, 104 mg/kg (the lower two thirds of
lagoon). The regulatory threshold for barium is 100 mg/kg. The waste on this site was
categorized to be hazardous, and therefore a more thorough sampling plan is needed.
Determine the number of samples required so that the reported mean has a 90%
confidence level.