Total Maximum Daily Loads


A Total Maximum Daily Load (TMDL) is often referred to as a “Pollution Diet” for streams, rivers and lakes.  It is the maximum pollution budget for a waterbody that is identified as being too polluted or otherwise degraded to meet water quality standards. 

Each of the County's 8 major watersheds have been identified as having some type of water quality impairment (e.g. too much bacteria, nutrients, etc) through EPA-approved quantitative assessment studies.

Meeting TMDL loading reductions is a requirement of the County's NPDES MS4 Stormwater Permit.



Setting the TMDL

A TMDL serves as a planning tool and potential starting point for restoration or protection activities with the ultimate goal of attaining or maintaining water quality standards.  Think of this as a diet and exercise program for a stream that when followed and implemented correctly, generates a stream that is fit and healthy.  

Pollutants can come from many different types of sources:

  • Point Sources, such as piped discharges; or 

  • Non-point sources, such as agricultural fields or our lawns.  

Pollutant loading from point and non-point sources is reduced by implementing a variety of measures known as best management practices or BMPs. 

The federal law requires that individual states establish priority rankings for waters on the impairment lists and develop a TMDL for these waters.  The Maryland Department of the Environment established specific TMDLs for the County to meet in order to address many of these identified impairments.