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EPA Pushes States to Put the Bay on a Pollution Diet
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by Carol Nau | 2010

By Carol Nau—In August, the Environmental Protection Agency (EPA) announced further plans to put the ailing Chesapeake Bay on a “pollution diet,” and presented proposed sediment limits for the six states and the District of Columbia that comprise the Bay watershed. The limits are expressed in terms of total maximum daily load, or TMDL. The states and the District were charged with developing detailed watershed implementation plans (WIPs) to indicate how they would apportion these sediment limits, as well as the limits issued earlier for nitrogen and phosphorus, among their various pollution sources.

EPA Pushes States to Put the Bay on a Pollution Diet

 

By Carol Nau—In August, the Environmental Protection Agency (EPA) announced further plans to put the ailing Chesapeake Bay on a “pollution diet,” and presented proposed sediment limits for the six states and the District of Columbia that comprise the Bay watershed. The limits are expressed in terms of total maximum daily load, or TMDL. The states and the District were charged with developing detailed watershed implementation plans (WIPs) to indicate how they would apportion these sediment limits, as well as the limits issued earlier for nitrogen and phosphorus, among their various pollution sources. 

Sediment, particles of clay and silt, is not a nutrient pollutant like nitrogen and phosphorus, which stimulate the growth of algae that smother submerged grasses and deplete the bay of oxygen. But it impairs the health of the bay by blocking the sunlight needed by the underwater vegetation that harbors and feeds the bay’s aquatic and shore life.

The EPA reviewed each of the states preliminary plans to clean up the bay, and sent them all back, though Maryland and Washington, DC were cited for having made a “strong start.” Final plans were due by November 29, 2010. Once the EPA has received the plans they have until the end of this year to update the “pollution diet” numbers. 

Groups representing various interests such as agriculture, wastewater treatment, and construction are challenging  both the pollution diet numbers and the scientific model used to determine how much and where the nitrogen, phosphate, and sediment reductions need to be made.  In fact, interest in the bay’s TMDL model is high outside the bay watershed, as environmentalists and polluters consider that the EPA’s action regarding the bay may presage similar action on polluted watersheds elsewhere in the country. Personally I find those requesting the actual program code for the model (beyond assumptions and data) rather unusual. There are many things we use today that started with a computer model. I don’t think they would request to see the code that was used to design our airplanes or cars before they rode in them, or ask the bank to see the code before they deposit their money.

Below is some background on the model used, extracted from a report prepared with our coalition partners—Choose Clean Water Coalition. 

If you would like to read the EPA pollution diet, any of the WIPs from the states, or to learn more about the project visit the EPA’s website at www.epa.gov/chesapeakebaytmdl/.

 

Chesapeake Bay Program Computer Models

Prepared by the Choose Clean Water Coalition

Computer models play an important role in helping to simulate complex ecosystems. As one of the largest estuaries in the world with a watershed that extends 64,000 square miles, the Chesapeake Bay is a place where models can help show where and how water pollution begins and moves. Over the history of the Chesapeake Bay clean-up, managers and scientists have relied on a series of computer models to predict changes in water quality, better understand where pollution is coming from, and look at what management practices applied on the land do to impact water quality. These models have been continuously updated and improved.

In fact, the first Bay model was a two-dimensional hydraulic model constructed on several acres on Kent Island, Maryland, by the U.S. Army Corps of Engineers in 1976. This model was soon replaced by computer models in 1984.

 

“The Bay Model” is a Suite of Models Decades in the Making

What is commonly referred to as “the Bay model” is actually a series of linked three-dimensional models. The centerpiece of this set of models is the Chesapeake Bay watershed model, which measures all the sources of nutrient and sediment pollution in the watershed, and determines the loadings to the Bay.

The suite of Chesapeake Bay models has been developed through an extensive peer-reviewed scientific process over the past 20 to 30 years, with broad-based collaboration among federal, state, academic and private partners. Over the years these models have improved significantly in precision, scope, complexity and accuracy.

The watershed model, for example, has been refined considerably over the past six years. The segments in the model have expanded more than twentyfold from 94 in the phase 4 model to 2,000 in the current phase 5 model, providing data at the watershed, county and conservation district level. The model is calibrated with monitoring stations throughout the bay watershed, but those stations have expanded from 20 to 296. The types of land uses that can be fed into the phase 5 model is now 25, up from the previous 9, and the simulation is now run over a 20-year period, rather than 10 years, providing more accurate results.  

These models are used by scientists and managers in conjunction with other tools, such as monitoring and research.  The models provide simulations that are a valuable tool for decision-makers, who also consider achievable, equitable, and cost-effective approaches. The models play a significant, but not an exclusive role, in the decision by policymakers to establish nutrient and sediment allocations. The allocations in 2010 for the total maximum daily load (TMDL) were very close to those that the states were given six years earlier. The state tributary strategies were available to form the base for the watershed improvement plans (WIPs) that each bay state needs to have developed by November 29, 2010.

 

How Do the Models Work?

The Chesapeake Bay Program uses five primary models. In use since 1982, the Chesapeake Bay watershed model simulates nutrient and sediment loads delivered to the Chesapeake Bay. Water quality data are collected from federal and state agencies as well as universities.

The second model, also known as the estuary model, looks at the effects of pollution loads generated by the watershed model on bay water quality. The bay is represented by 57,000 cells in this model and simulates the mixing of waters in the bay and its tidal tributaries.

 The third, scenario builder model, simulates changes in the ecosystem due to changes in population, land use, or pollution management.

The fourth, airshed model, uses information about nitrogen emissions into the atmosphere and deposits them into the watershed model. Finally, the land change model analyzes and predicts land changes in the watershed.

 

The phase 5 watershed model has almost 100 collaborators and partners led by the Environmental Protection Agency (EPA), the Virginia Department of Conservation and Recreation, the Interstate Commission on the Potomac River Basin, the University System of Maryland, the Maryland Department of the Environment, the U.S. Geological Survey, the Chesapeake Research Consortium, and Virginia Polytechnic Institute. Special attention has been paid to the agricultural assumptions in the model with specific input from the agricultural nutrient and sediment reduction workgroup.  In addition, the Bay Program partnership recently funded the University of Maryland’s Mid-Atlantic Water Program to complete a two-year study to update the effectiveness estimates of every best management practice in the model.

 

Peer Review and Awards

The models developed by the Bay Program have been extensively peer reviewed and follow guidance developed by EPA’s Science Advisory Board. In addition the models have won numerous awards beginning in 1990. The Bay Program models are regularly cited as the best of their kind.  In its April 2007 report, Taking Environmental Protection to the Next Level7, the National Academy of Public Administration stated that:

EPA’s Chesapeake Bay Program (CBP) has led the way in developing a comprehensive water monitoring and assessment program that tracks and compiles the water quality conditions throughout the bay. Based on the monitoring data, the CBP has developed sophisticated Chesapeake Bay watershed and airshed models that have enhanced the understanding of the complex problem of nutrient pollution and its effects on the bay waters. This watershed-wide understanding provided the foundation for the 1987 Chesapeake Bay Agreement and helped to coordinate and assign responsibility among the bay states for achieving water quality goals.

 

Response to the Models’ Critics

Over the last several months we have seen wild accusations in the media about the soundness of the models and the science behind it; however, there is nothing to support these claims. The Bay Program partners have been extremely transparent and open about the modeling process and sought input from hundreds of stakeholders including agricultural specialists. The one criticism raised in the 2006 Government Accountability Office (GAO) report was that the credibility of Bay Program reports on the bay’s health “tended to downplay the deteriorated conditions of the bay” and “projected a rosier picture of the health of the bay than may have been warranted.”  While serious, the GAO’s criticism points to the fact that the Bay models, if anything, were over-reporting the nutrient and sediment-reducing value of practices on the land. This criticism also focused more on the use, or misuse, of modeled data, rather than the model itself. In 2008, a follow-up GAO report concluded that the Bay Program had made important progress in addressing their concerns and providing better management of the bay restoration effort.

Another public criticism of the model has been that many practices, particularly agricultural ones, implemented voluntarily, are not being accounted for in the model. While this statement is true, in reality, it is not a flaw of the model, but rather a failure to collect the proper input information to feed into the model.

The solution to this problem is to provide better accounting, not to change any of the model parameters.  In addition, this under-counting of implemented practices does not affect the TMDL load allocations to the states which were based.                                                n

 

This introduction to the Chesapeake Bay Model was extracted from comments submitted to Lisa Jackson, Administrator of the U. S. Environmental Protection Agency by Choose Clean Water Coalition, of which the Maryland Chapter is a member. The full text, including footnotes omitted here, is online at www.choosecleanwater.org/cms/documents/CCWCTMDLcomment.pdf. 

> 2010 Table of Contents

   
   

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