By Sara Wyant

© Copyright Agri-Pulse Communications, Inc.

Washington, Dec. 9 – The Environmental Protection Agency (EPA) should not finalize water quality rules for the Chesapeake Bay Watershed until federal regulators can figure out why there are such major differences between EPA and USDA data and modeling efforts, according to a report issued today by the Agricultural Nutrient Policy Council.


“We are not saying one is right and one is wrong,” says Tom Hebert, former USDA Deputy Under Secretary for Natural Resources and Environment during the Clinton Administration. “But with so much at stake, they should at least be on the same page.”


The Council hired Limno Tech, a water sciences and environmental engineering consulting firm, to compare the results of the EPA Watershed Model with a recently released, draft estimate of loads within the Bay watershed by USDA. LimnoTech found that there are substantial differences between the USDA and EPA pollutant load estimates. Their report calls for a “timeout” on the TMDL, which EPA plans to finalize by Dec. 31, until the two federal agencies reconcile differences in:

·         Land use and total acreage of the Bay watershed;

·         Hydrology;

·         Assumptions about conservation practices;

·         Model frameworks; and

·         Model results.


“The differences in land use alone are substantial,” says Hebert, who is now a principal with the Bayard Ridge Group.  In EPA’s Watershed Model, there are 41.1 million acres, excluding water surface areas in the Chesapeake Bay and tidal tributaries. This is 1.39 million acres (2,171 square miles) less than USDA’s estimate.


“This 3.4% difference is significant when EPA considers the Total Maximum Daily Load (TMDL) to be accurate to a single pound. For cropland, the differences are even more significant. EPA estimates 3.33 million acres (1.68 plus 1.65 million acres) are used for crops. USDA estimates that 4.38 million acres are in such use, a difference of 1.05 million acres, or approximately 32%,” according to the report.


“With respect to cropland and tillage practices, EPA estimates that 50% of cropped acres are farmed using conservation tillage (no-till) and 50% are farmed using conventional tillage. USDA estimates that 88% of cropland is farmed using conservation tillage (notill or mulch till); five (5) percent is between conservation tillage and conventional tillage; and seven (7) percent is in conventional tillage. These differences in assumptions about total acres, land use, and conservation tillage versus conventional are significant when predicting different loading estimates,” the report notes.


“The Watershed Model was originally developed when the Chesapeake Bay Program was a voluntary partnership between the states, the District of Columbia, and the EPA,” according to the report. “Now that the model is being applied in a regulatory environment, every pound of pollutant that exceeds the allocations in the total maximum daily load (TMDL) will result in mandated requirements on cities, businesses, industries, and private citizens to install and operate new technologies, without regard to economic feasibility of implementation. It is

therefore critical that the precision and accuracy of the models be defined.”


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