TMDLs

TMDL stands for Total Maximum Daily Load. It is a scientific and regulatory process used in the United States to address water quality impairments. A TMDL is the maximum amount of a specific pollutant that a water body can receive daily and still meet water quality standards. It is essentially a cleanup plan for polluted waters.

The process of developing a TMDL begins with identifying water bodies that do not meet state water quality standards. These are often placed on what is known as the "303(d) list." Once a water body is identified as impaired, a TMDL study is conducted. This study involves calculating the existing load of the pollutant, determining the load reduction needed to meet water quality standards, and allocating that load among various sources.

Sources of pollution are categorized as either point sources, such as industrial discharges or sewage treatment plants, or nonpoint sources, which are diffuse and include agricultural runoff or urban stormwater. The TMDL allocates a portion of the total load to each of these sources, as well as a margin of safety to account for uncertainties.

Implementation of a TMDL involves developing strategies to reduce pollution from the identified sources. This can include regulatory actions, such as permits for point sources, and voluntary or incentive-based programs for nonpoint sources. Monitoring is also a crucial component to assess the effectiveness of the implemented measures and to ensure the water body is progressing towards meeting its water quality standards.