Water Quality

TMDL stands for Total Maximum Daily Load. It is a calculation of the maximum amount of a pollutant that a water body can receive and still meet standards established by states and tribes to protect the beneficial uses of that water, such as municipal supply, body-contact recreation, agricultural irrigation and support of aquatic life. A TMDL sets the total amount of a single pollutant that can enter the water body, divides the total load among all of the sources of that pollutant in the watershed, and tells each discharger how much it can contribute.

Sewer plants, factories and other easily identifiable sources of pollution have long had to obtain permits regulating their waste discharges. TMDLs are primarily a way of addressing contamination from “non-point sources” that lack an easily identifiable discharge point, such as city streets, rangeland and farms.

They can be developed by state or federal agencies, or by stakeholder groups. Regardless of how they are developed, they are implemented in California by the state’s Regional Water Quality Control Boards following approval by the State Water Quality Control Board and the Environmental Protection Agency.

Although authorized under section 303 of the Clean Water Act of 1972, TMDLs and non-point-source pollution were largely ignored by state and federal regulatory agencies until relatively recently. The EPA did not even adopt regulations for them until 1985, refining those standards further in 1992; it has only been within the past decade that enforcement has begun, largely a consequence of lawsuits by environmental organizations seeking to force the EPA and the states to adopt TMDLs for impaired streams and lakes. There have been about 40 such legal actions in 38 states, and the EPA is under court order or consent decrees in many regions to ensure that TMDLs are established, either by the state or by EPA. One such consent decree is in place for the greater Los Angeles region, including Ventura County.

It starts with what regulators refer to as the “303 (d) list,” a comprehensive listing of all impaired waters within their jurisdiction that states, territories and tribes are required to submit periodically to the U.S. Environmental Protection Agency. Each listing identifies the specific pollutants for which the water fails to meet health and safety standards. Once the pollutants have been identified, researchers conduct studies to figure out where they are coming from, how much of each can be discharged into the watershed under varying hydrological conditions without posing a risk, and how much each discharger will be allowed to emit. After those studies have been completed, the TMDL limits are written, submitted to EPA for approval and adopted by the state.

It varies by watershed. For Calleguas Creek Watershed, seven TMDLS have been adopted: Nitrogen Compounds; Organochlorine Pesticides (DDT and chlordane) and PCBs; Siltation; Toxicity (anything that kills aquatic life or impairs its ability to reproduce), Chlorpyrifos, and Diazinon; Metals (copper) and Selenium; Salts (chloride, total dissolved solids, boron and sulfate); and Trash,  For the Santa Clara River Watershed, TMDLs for Nitrogen Compounds, Chloride, Toxaphene, and Bacteria have been developed for all or portions of the watershed.. For the Ventura River, a trash TMDL is in effect, as is one for nitrogen and algae.

There is some overlap in the requirements for compliance, but they are two different regulatory approaches to improving water quality. The Farm Bureau, VCAILG and their consultants (Larry Walker Associates) are working to ensure that the monitoring and mitigation requirements developed through the TMDL process take advantage of work already done — and money already spent — to develop the Conditional Waiver compliance program.