Research Publications

The implementation of the Clean Water Act has resulted in the provision of enhanced wastewater treatment facilities throughout this country. The initial effort focused upon providing a minimum of secondary treatment (or higher-order treatment if needed) to meet surface water quality standards under dry weather flow conditions. Since 1987, increased emphasis has been placed by both federal and state regulatory agencies upon meeting effluent limits from these treatment facilities under wet weather flow conditions. In communities served by combined sanitary and stormwater sewers, the treatment plant may experience very significant variations in flows to be treated at the facility. This paper will present both a Gumbel Type I extreme value distribution and a Gumbel Type II extreme value distribution to examine the probability of high flow exceedance at a treatment facility. This type of analysis provides a preliminary framework for consideration of the trade-off between fully capturing extreme value flows vs. occasionally by-passing extreme values flows with less than full treatment.