TMDLs

A TMDL (Total Maximum Daily Load) is defined in federal regulations as “the sum of the individual waste load allocations for point sources and load allocations for nonpoint sources and natural background such that the capacity of the waterbody to assimilate pollutants (the Loading Capacity) is not exceeded.”

In layman’s terms, a TMDL sets a limit for the total amount of a particular pollutant that can be discharged to a waterbody, such that the pollutant loads from all sources will not impair the designated beneficial uses of the waterbody. The timeframe for compliance with TMDL targets varies, but may take many years. TMDLs will often include a compliance schedule, identifying interim and final targets.

A TMDL is developed when a waterbody has been identified as impaired. Section 303(d) of the federal Clean Water Act requires states to establish a listing of all impaired waterbodies and to rank those waterbodies according to priority for TMDL development. This list, called the 303(d) List is updated every two years and is developed by the Regional and State Water Quality Control Boards and approved by EPA.

The following TMDLs have been established or are being developed for Orange County waterbodies. To find out more about each TMDL, please click on the links below: