Some Historical Statistics Related to Future Standards

Historical records have been examined to see how successful engineers designing small projects in Wisconsin have been in forecasting population, and to see how nearly the actual life of their projects equaled the intended design life. The data available indicate that, hazardous as population forecasting is, the greatest problem for the designer (measured in terms of having the plant decreed inadequate before reaching its intended design life) is changes in environmental standards. That this appears to have been true in the past, a rather stable era, creates a good deal of uneasiness for the designer contemplating the rapid changes in standards that will occur in the next 5 to 10 years. The question to be examined is how probabilistic language in standards, stated or implied, reflects on the designer's problem. Data from treatment plants have been analyzed to determine the typical frequency distributions of effluent quality. The shape of this statistical distribution bears heavily on how difficult a stated standard is to meet.