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Facts About Total Maximum Daily Loads (TMDLs)

What is a TMDL?

By definition, a Total Maximum Daily Load (TMDL) is an estimate of the maximum amount of an impairing substance or stressor (pollutant) that a wasterbody can assimilate without violating water quality standards.  The total load includes pollutants from pipes, called point sources, and stormwater runoff and groundwater flow called non-point sources.  A "margin of safety" is also included in the total load to account for the uncertainties.  Additional information can be found a

Why should Anne Arundel County be Concerned About TMDLs?

Based on the federal government’s Clean Water Act, all states are required to consider  the development of TMDLs for waterbodies that do not meet water quality standards for various pollutants. All of the twelve major waterbodies in Anne Arundel County are impaired by two or more substances (e.g., nutrients, sediments, fecal coliform bacteria, toxics, biological, or metals).  The Watershed Assessment and Planning program is continuously monitoring the state of TMDL development and water quality analyses to justify the delisting of waterbodies from the MDE 303(d) impairment list.

Anne Arundel County's Category 5 303(d) Waters and TMDLs

Watershed Assessment & Planning


MDE 2012-2013 Milestone Evaluations


MDE 2014-2015 Milestone Interim Report


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Anne Arundel County, Maryland. 44 Calvert Street, Annapolis, Maryland 21401 | Tele: (410) 222-7000