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Total Maximum Daily Loads

Total Maximum Daily Load (TMDL) is a tool to help protect and improve water quality. Since the Clean Water Act was passed in 1972, each state is required to set standards for water quality and periodically analyze the water to see if the particular stream, river, reservoir or inlet meets the standard. If it falls short of the standard, it is said to be impaired.

What is TMDL?

A TMDL is like a diet for a waterway. If a person has high cholesterol, for example, their doctor might recommend a restricted diet. The patient would be evaluated to determine how high their cholesterol is and their current consumption might be examined to see what foods should be eliminated. A plan is put in place for the patient to help reduce their cholesterol level to a healthy standard.

The TMDL works the same way. A water body is determined to have too high of a level of a particular pollutant. The TMDL describes the watershed, identifies likely sources for the pollutant, and identifies opportunities to reduce the amount of pollutant to meet the accepted standard. Each pollutant requires a separate TMDL.

Measuring Impairments

In order to better evaluate, monitor, and manage waterways, the state has segmented these waterways into drainage areas. Baltimore County has 2,145 miles of stream and 219 miles of tidal shoreline in 14 watersheds. Each of the 14 watersheds that are in or are connected to Baltimore County is impacted by pollutants and requires TMDLs.

An Example

Let's use the Back River as an example. In the Back River, the level of Total Phosphorus (TP) exceeds the standards. Phosphorus is a nutrient and may enter the waterway from sewage treatment plants, industry, fertilizers and other sources. In order for Back River to be considered healthy the TP load from all sources must be reduced to 99,991 pounds per year. The Back River Waste Water Treatment plant has already made recent investments to reduce phosphorus and is considered to have lowered its contribution as low as current technology allows. Therefore, the TMDL for Back River focuses on reducing TP entering the waterway from urban runoff by 15 percent.

TMDL Implementation Plans

There is an Implementation Plan for each TMDL to guide the restoration or cleanup to reach the target pollutant load. Calculations based on scientific studies are made to determine the amount and types of restoration practices to be completed.

We All Contribute

Since each of us contribute pollutants to our waterways through the cars we drive, the sewage we produce, and the choices we make for in home and lawn care, we can also help. The Watershed Management Program is leading a collaborative effort with citizens, businesses and watershed organizations to develop Small Watershed Action Plans (SWAPs) for each of the County's watersheds. Support Baltimore County’s efforts and check in with your local watershed association to find out ways you can protect your local stream. Baltimore County’s programs for stormwater retention and their requirements for stream setbacks are also providing additional protection for waterways and helping reduce pollutant loads in County waterways.

You can find TMDL reports for other areas in Baltimore County and across the state from the Maryland Department of the Environment.

Contact Us

Watershed Management and Monitoring
Phone: 410-887-5683
Fax: 410-887-4804

Revised May 18, 2018         


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