Many waterbodies have good water quality, but about 40 percent of the lakes, ponds, rivers, wetlands, and coastal waters in the nation are listed as impaired waters due to pollution. For nearly 30 years, states have concentrated on industrial and municipal discharges of pollution from point sources such as discharge pipes. Now Massachusetts and other states are expanding efforts and including nonpoint sources - such as stormwater runoff, septic systems, and erosion - to clean up our water, using the watershed approach and the total maximum daily load (TMDL) provision in the federal Clean Water Act.
What is a TMDL?
TMDL stands for "Total Maximum Daily Load". A TMDL is a calculation of the maximum amount of a pollutant that a waterbody can accept and still meet the state's Water Quality Standards for public health and healthy ecosystems. The federal Clean Water Act requires all states to identify waterbodies that do not meet state standards and develop TMDLs for them.
Massachusetts sets statewide Water Quality Standards for a variety of uses, such as drinking water supplies, fishing, recreational swimming and boating, and healthy ecosystems for plants and animals. Clean water is vital to human health and recreation, and TMDLs are a critical step in ensuring that degraded waters are restored and protected so that all citizens enjoy a clean and healthy environment.
A TMDL is the sum of loads that are allowable from all contributing point and nonpoint sources of pollution. Point sources are primarily wastewater treatment plants that discharge to surface waters or groundwater. Nonpoint sources include septic systems, stormwater discharges via runoff over the land surface, and fertilizer runoff from lawns and golf courses.