The most recent meeting of the Potomac Watershed Roundtable was in Warrenton, VA at Lord Fairfax Community College and had a series of speakers on the Chesapeake Bay strict pollution diet, the Total Maximum Daily Load (TMDL) mandated by the EPA to the six Chesapeake Bay Watershed states and the District of the Columbia. The TMDL addresses only pollution from excess nitrogen, phosphorus and sediment. No action has been taken or at this time is intended on other pollutants that might be present in the Chesapeake Bay and its tributaries. Part of the meeting was devoted to educating the audience on the Chesapeake Bay Model.
The TMDLs were created by a series of models of the Chesapeake Bay Watershed that include various land use models, water quality models and watershed models. These computer models are mathematical representations of the real world that estimate environmental events and conditions. The models are at best imperfect, but they are nonetheless the best tool available to view the 64,000 square miles of the watershed. The Chesapeake Bay and its watershed are so large and complex, that scientists and regulators rely on computer models for critical information about the ecosystem’s characteristics and the impact of various environmental actions to reduce pollution.
Mike Rolband of Wetland Studies and Solutions, Inc. had some fun with what is apparently one of the large mistakes in the model that is expected to have a correction released in the near future. His professional interest is in managing impervious and pervious surface run off. His consulting firm looked at the underlying data used to create the Land Use estimates. Land Use model estimates the types and amounts of pollution that run off a particular land use are based on comprehensive reviews of the latest scientific literature there is limited measurement here for many of the land uses, but the responsible land use is assigned a numeric blame. Using EPA published data Wetland Studies and Solutions was participant in pointing out to the EPA that they had massively underestimated the impervious and pervious surface areas in the Urban Areas in Virginia (and I assume other areas).
It seems that the most recent version of the model had used approximately 675,917 acres for the impervious surface data and 1,885,915 acres for the pervious surface data. A review of the EPA’s own data found that there were 1,569,377 impervious acres and 3,442,346 pervious acres in the urban areas in the Virginia segments of the model. These include all the paved and landscaped areas of suburbia. Between the 1990 census and the 2010 census the population of Virginia grew from 6.2 million people to 8.0 million people. The bulk of that growth took place in the urban and suburban centers of the Chesapeake Bay watershed.
Now here is where it gets interesting. Pollutions loads for nitrogen, phosphorus and sediment in the urban areas are calculated using a constant pounds/acre/year for impervious acres as a fixed input, and the pervious load is based on total fertilizer sales data. The bottom line is that the EPA has confirmed that they will not change the loading rate because they have high confidence in the loading rate for the impervious surfaces and the total fertilizer sales are reported and tracked data and is a hard number. Thus the total current oad for the urban areas will increase by 2,238,449 pounds of nitrogen per year, 636,097 pounds of phosphorus/year and 137,680 pounds of sediment/per year. However, the total watershed loads for the overall model will remain the same. So, while the urban area loads will increase, other area(s) loads will have to decrease.
Mike Rolband has pointed out that the agricultural sector will probably have their load reduced. The waste water treatment plants numbers are based on constant sampling necessary for their permits so their overall total contaminant load will not change. The forest lands number is also believed to be a “good” number, so that leaves the agricultural sector and in the case of total nitrogen, also septic. Over 2.2 million pounds a year is a lot of nitrogen it represents of the total load attributed to agriculture. The farm segment has been protesting loudly that they are not being given proper credit for implementation of best management practices and that surface waters are already degraded when they reach their farms.
It seems that the American Farm Bureau Federation who have recently filed suit against the EPA claiming the models are flawed is right. The smug assumption that farmers are the bad guys by the new generation of environmentalists is to an extent wrong. Man is the animal contributing the most nitrogen to the Chesapeake Bay in the form of wastewater treatment plant permitted waste, septic and urban/ suburban runoff. The Chesapeake Bay Foundation owes the American Farm Bureau Federation an apology for their recent quote in the Washington Post.