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Allen Fossil Plant SCR Optimization

Shelby County, Tennessee

An environmental assessment (EA) and finding of no significant impact (FONSI) were completed in March 2001 for a proposal to install and operate selective catalytic reduction (SCR) systems at TVA’s Allen Fossil Plant Units 1, 2, and 3. The SCRs were needed to meet federal clean air requirements for ozone reduction.

As designed, the three SCR units at Allen were expected to remove 90 percent of the emissions of nitrogen oxides (NOx) at an ammonia slip rate of 2 parts per million by volume (ppmv) during year-round operations. (The ammonia slip rate is the amount of unreacted ammonia catalyst discharged into the plant waste stream.) Testing in fiscal years 2005 and 2006 revealed that the SCR units at Allen currently operate at approximately 3 to 4 ppmv and remove 92 percent of the NOx with no adverse opacity or toxicity problems.

In order to have a flexible approach to complying with the requirements of the recent Clean Air Interstate Rule, TVA now proposes to drop the 2 ppmv slip limit in favor of a requirement to optimize the performance of the Allen SCRs so that NOx removal goals can be reached while the plant remains in compliance with permit standards for effluent discharge and toxicity.

The analysis concluded that year-round operation of the SCR systems on Units 1, 2, and 3 at slip rates higher than 2 ppmv would have minimal additional adverse impacts as compared with those operations described in the 2001 Allen SCR environmental assessment or with current operations. Those effects are described in this supplemental EA.


PDF files require Adobe Acrobat Reader.

Supplemental Environmental Assessment (167 kb, PDF)

Finding of No Significant Impact (88 kb, PDF)

Original 2001 Environmental Assessment

Part 1 (729 kb, PDF)
Part 2 (505 kb, PDF)
Part 3 (2.8 mb, PDF)
Part 4 (1 mb, PDF)

Original 2001 Finding of No Significant Impact (301 kb, PDF)


Ruth M. Horton, NEPA Services
Tennessee Valley Authority
400 West Summit Hill Dr., WT 11D
Knoxville, TN 37902
Phone: 865-632-3719



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