Section
303(d) of the federal Clean Water Act requires that states make a list of
impaired waterbodies that are not attaining applicable water quality standards even
after technology-based discharge limits on point sources have been implemented.
Once listed, states must establish priority rankings for their impaired waters
and develop a total maximum daily load (TMDL) for each pollutant contributing
to the listing. A TMDL specifies the maximum amount of a pollutant that a
waterbody can receive while still meeting applicable water quality standards.
California ranks TMDLs as high, medium or low priorities based on a number of
factors including the severity of the impairments and the importance of the
waterbody's beneficial uses.
TMDLs
differ from other pollution management efforts in that all sources of
impairment must be accounted for, including contributions form point sources
(federally permitted discharge) and nonpoint sources. Moreover, all pollutant
loads must be allocated to specific sources. These allocations may be specific
to agencies or persons (businesses), or more general by source category or
sector.
In Orange County, the TMDL focus to date has been on the Newport Bay / San Diego Creek watershed, where TMDLs for nutrients, sediment and and fecal coliform have been developed by the State and are currently being implemented. An additional TMDL for toxicity is in the process of being developed for this watershed.