Vol 9 - Number 7 October 1999 Total Maximum Daily Loads Demystified Portions of hundreds of lakes, rivers and streams in the Bay watershed fail to meet their water quality standards. Under the Clean Water Act, the states are required to write detailed cleanup plans, known as TMDLs, for each of those impaired waterways. In other words, it is the sum of the allowable loads of a single pollutant from all contributing sources, and includes a margin of safety and consideration of seasonal variations. In addition, a TMDL calculates the reductions needed to meet water quality standards and allocates those reductions among pollution sources in the watershed.
States are responsible.
If they fail to establish the TMDLs, the EPA must do it. The EPA is proposing that TDMLs should be established over a 15 year time frame, with TMDLs for high-priority waters to be completed first. Priorities are based on the severity of the pollution and uses of the waterbody. The proposed changes would also give high-priority status to impaired waters that are drinking water sources or have endangered species. Under current regulations, states identify their impaired or threatened waters and submit a list of these waters to the EPA every two years.