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Frequently Asked Questions


What is a Total Maximum Daily Load (TMDL)?

Total Maximum Daily Loads are quantitative analyses of water bodies where one or more water quality standards are not being met, and are aimed at identifying the management strategies necessary to attain those water quality standards. In essence, TMDLs describe the amount of each pollutant a water body can receive without violating standards, and are characterized as the sum of wasteload allocations, load allocations, and a margin of safety to account for uncertainties. Wasteload allocations are pollutant loads attributable to existing and future point sources, such as discharges from industry and sewage facilities.  Load allocations are pollutant loads attributable to existing and future nonpoint sources and natural background. Nonpoint sources include runoff from farms, forests, urban areas, and natural sources, such as decaying organic matter and nutrients in soil.

TMDLs take into account the water quality of an entire water body or watershed and assess all the pollutant loadings into that watershed, rather than simply considering whether each individual discharge meets its permit requirements. The management strategies that emerge from the TMDL process may encompass everything from traditional regulatory measures, agricultural best management practices and other pollution prevention measures, land acquisition, infrastructure funding, pollutant trading, and the like. They also will include an overall monitoring plan to test their effectiveness.

Why are TMDLs developed?

For the past twenty-five years, point source discharges have been regulated under the Clean Water Act (CWA). Over time, it has become clear in many instances that every individual discharge into a water body may meet effluent discharge requirements and yet that water body may still fail to meet the standards defining good water quality. This circumstance has proved true even as the limits on point source discharges have become more and more stringent, especially in Florida. There clearly are other sources of pollution for which existing control measures are simply not adequate. These sources are associated with diffuse runoff and habitat destruction, and originate in both urban and rural areas. 

The EPA requires states to set priorities for cleaning up impaired waters by establishing a TMDL for each one. Under the authority of section 303(d) of the CWA, EPA requires that TMDLs be developed where technology-based effluent limitations or other legally required pollution control mechanisms are not stringent enough to protect water quality. Florida has hundreds of impaired water bodies or water body segments that likely will have to be addressed through the development and implementation of TMDLs.

The development of Total Maximum Daily Loads (TMDLs) will take place in the context of chapter 99-223, Laws of Florida, which details the process for listing impaired waters, determining which waters will be subjected to TMDL calculations, adopting by rule those calculations and associated allocations of pollutant loadings, and implementing the management strategies designed to reduce the loadings and enable the water body to meet water quality standards.

How are TMDLs Established?

As noted, TMDLs are established for waters that fail to meet water quality standards, and characterize how much of each pollutant the water body can assimilate without violating those standards. The DEP considers future growth and development to the extent possible in establishing a TMDL, and accounts for the pollutant inputs from all sources, including discharges from industrial plants and sewage treatment facilities, runoff from farms, forests and urban areas, and natural sources.

In deriving a TMDL and subsequently setting forth the mechanisms that may be employed to enable the water body to meet standards, the DEP must balance the quantities of pollutants from all sources so that the total amount does not exceed the limits necessary to maintain water quality. Through these assessments, DEP can better determine permit effluent limits, best management practices, pollution prevention strategies, and other resource management activities necessary to ensure that waters are suitable for fishing, drinking, recreation, and aquatic life.

Using a TMDL approach for water bodies does not replace existing water quality control programs or standard treatment technologies. It provides a framework for evaluating all possible water quality control efforts and promotes closer coordination of local, state, and federal efforts to better guarantee that we collectively meet water quality goals.

What is the 303(d) list?

Under section 303(d) of the Clean Water Act, every two years each state must identify water bodies that do not meet water quality standards. These water bodies are "water quality-limited" estuaries, lakes, and streams that fall short of surface water quality standards, and that are not expected to improve within the subsequent two years. Florida's water quality standards are designed to ensure that our waters can be used for their designated purposes, such as swimming, drinking, industrial and agricultural uses, and wildlife habitat. Florida's 303(d) list identifies hundreds of "impaired" water segments, with the four most common water quality concerns being coliforms, nutrients, oxygen demanding substances, and turbidity. These water segments are candidates for more detailed assessments of water quality and, where necessary, the development and implementation of TMDLs.

How is the Florida 303(d) list developed?

The 303(d) list is developed based on the Florida Water Quality Assessment [305(b) report].  Section 305(b) of the CWA requires states to report biennially to the EPA on their water quality. The 305(b) report describes the existing programs to protect the quality of Florida's surface waters, ground water, and wetlands. In the 305(b) report, water quality is evaluated using biological data, chemistry data from the federal water quality database (STORET), violations of Florida's water quality standards, mercury fish consumption advisories, qualitative nonpoint source assessments, and other information solicited through public workshops. The information in the report is reviewed and water bodies are placed on the 303(d) list of impaired waters based on specific criteria designed to identify the highest priority water bodies in need of restoration based on the best available data.

For more information, send e-mail to Greg DeAngelo (Gregory.DeAngelo@dep.state.fl.us)

Water Quality Evaluation & TMDL Program
2600 Blair Stone Road - Mail Station 3555
 Tallahassee, FL, 32399-2400
Phone: (850) 245-7609

Last updated: September 21, 2011

  2600 Blair Stone Road M.S. 3500   Tallahassee, Florida 32399   850-245-8336 (phone) / 850-245-8356 (fax) 
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