Total Maximum Daily Load (TMDL) and Why IT Matters

The Chesapeake Bay has poor water quality.  The EPA and Commonwealth of Virginia are working, along with other states in the Chesapeake Bay watershed, to develop TMDLs for nitrogen, phosporous, and sediment flowing into the Bay.

You should know this isn't anything new.

The 1987 Chesapeake Bay Agreement made the reduction of nutrients such as nitrogen, phosphorous, and sediment the focal point of plant to restore the water quality of the Bay.

I recently represented the James River Green Building Council in the Stakeholder Advisory Group to the Commonwealth of Virginia to develop TMDLs and create an implementation plan to reduce nutrient and sediment pollution into the Chesapeake Bay from the watersheds in Virginia.

The first meeting took place December 17th  in House Room 3 of the Virginia Capitol Building. The group will be meeting monthly for approximately six months to complete a draft implementation plan by June 1, 2010. 

How it works...

Think of the Bay as a closed box with an input and an output.  A river flows into the box with an amount of nitrogen (N) in it and some outfall removes the N from the box.  Additionally, some amount of N is used in the box by plants, animals, and settles to the bottom (i.e. removed from the water column).  The goal of the TMDL is to identify a total daily amount of N that can go into the Bay and then back calculating how much each input can contribute to reach, but not exceed, the TMDL.  It's that simple.

However, with everything in life things get more complicated simply because in the real life Chesapeake Bay there isn't only one input, use, or output.  Here is a quick drawing of how things can quickly become more complicated.

As you can see, it doesn't take long to understand the magnitude of the task at hand.  Theoretically every input and output needs to be studied and evaluated to determine what its current input is and the reduction necessary to meet the new TMDL goal.

The next problem...

Turns out it's not easy to determine the about of nutrients or sediment that flow from non-point sources (such as agriculture) because there is no single source that can be monitored or studied.  Regulated point sources like factories or treatment facilities have ample data available about their contribution to the TMDL.  So here is the rub, you can beg, incentivise, require, or threaten...but there is no exact way to determine that a single farmers fertilizer application has or hasn't made it to the Bay (at least no cost effective way).  There is, however, there is a way to do so for the point sources out there and you betcha these folks are sensitive to that fact.

How do you coordinate all of these factors?  


I will let you know by June 1, 2010...that's a promise.