Such a practice is similar to what would be done during the initial considerations of tradeoffs of loads between point and nonpoint sources. In the case of watershed or estuary management, this may be particularly useful to achieve pollution reduction in the most cost-effective manner possible. The incentive for trading load allocations is to achieve the required level of control by choosing to control one pollutant source over another. Technological feasibility, economic issues, and regulatory authority are all factors to consider when trading allocations. For example, to reduce nutrient loads to a receiving water, nonpoint source controls that can be adequately maintained and enforced, may be much more cost effective than increasing the level of control on a point source discharger.
Pollutant trades are most likely to occur between point and nonpoint sources.
Similarly, tradeoffs between nonpoint sources are also acceptable. Because of this cost differential, tradeoffs allowed publicly-owned treatment works to achieve reductions in phosphorus loads to the Dillon Reservoir by controlling NPSs rather than expanding the sewage treatment system. The primary concern is that toxic pollutants that enter a waterbody at levels that are non-toxic in the water column may accumulate in sediment or aquatic life. Chemicals that bioaccumulate at high rates include some metals, organic compounds, and organometallic compounds. Additional details for assessing and controlling risk have been addressed in technical support documentation.