Environmental fate and transport

J L Schnoor; J P Connolly; D M Di Toro; N De Rooij; M Diamond; RS Jr Kinerson; D B Porcella; W L Richardson; J F Stine

Mathematical models of fate and transport of chemicals in the aquatic environment are the tools used to establish WLAs. Wasteload allocations for individual point source discharges or TMDLs for multiple sources are intended to ensure compliance with WQS, which in turn protect designated water uses and human and ecological health. Since the initiation of this process, the question has been "What modeling framework should be applied and to what level of physical, chemical, and biological resolution?" (Thomann and Mueller 1987). Generally, permit writers do not have the time to assemble the requisite data to apply the most realistic and holistic models; as a consequence, simple dilution formulations of pollutant load divided by receiving water flow (W/Q) are used. This approach to developing permit limits has achieved significant improvements in the quality of U.S. waters. However, there are concerns that it 1) may not provide protection in the most cost-effective manner (i.e., regulations are overprotective and result in costs without benefits) and/or 2) it may not adequately take into account the multiple uses and stresses placed on aquatic resources (Schnoor 1996). In order to protect aquatic organisms that spend their life cycles in the water column and/or in the bed sediments, it is important to consider the chemistry of the metals and their transformation between free ion and complexed forms; to consider the partitioning of metals between water column, sediments, and fish; and to consider all the sources of metals loadings to the aquatic ecosystem. This involves greater modeling sophistication than is evidenced by the simple dilution equation (W /Q) that has commonly been used for setting permit limits. In order to consider all sources of metal, not just those discharged from a single permitted facility, a more comprehensive framework is needed. Fortunately, an appropriate framework, the watershed approach, has been suggested and is being adopted increasingly by states for water management, planning, and permitting of effluent discharges. Properly applied, the watershed approach accounts for all sources of the metal, point source discharges as well as nonpoint source discharges (including metals from municipal stormwater runoff), metals occurring naturally in soils, and atmospheric inputs of metals. The goal is to improve present approaches for calculating effluent limits, taking into account the best science while maintaining the permit writer's ability to apply improved models accurately and efficiently.

Environmental fate and transport

View Online

Abstract

Details

Metrics