Use of Probabilistic Information in the Water Quality Based Approach

摘要

During the past two decades, implementation procedures in wastewater management often resulted in a large margin of safety being incorporated into the use of water quality criteria for the protection of aquatic life and its uses. Wasteload allocation design conditions, such as the use of seven-day, ten-year low flow, gave assurances of instream concentrations well below the water quality criteria for a large percentage of time. Present-day economic conditions and the increasing cost of advanced wastewater treatment are necessitating a re-examination of how water quality criteria are being used in the water quality based approach for establishing effluent limitations. The relationships between water quality criteria and other components of the water quality based approach are identified. The need for a better defined and more consistent use of statistical information is suggested not only in the development of water quality criteria but also for the entire water quality based approach. Intensity, duration, and frequency of occurrence (return period) appear to be three common statistical parameters of the six-step water quality based approach.