"Environmental History Timeline." Web. 09 Feb. 2011. <http://www.radford.edu/~wkovarik/envhist/>.

"Pollution Prevention Act of 1990, United States." Encyclopedia of Earth. Web. 09 Feb. 2011. <http://www.eoearth.org/article/Pollution_Prevention_Act_of_1990,_United_States>.

"History - Water, Effects, Environmental, Disasters, Pollutants, United States, Chemicals, Industrial, Wells, Toxic, World, Human, Power, Sources, Disposal, Use, Life, Health." Pollution Issues. Web. 09 Feb. 2011. <http://www.pollutionissues.com/Fo-Hi/History.html>

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"Duke Energy To Spend $93 Million To Resolve Clean Air Act." Pollution Online: Digital Marketplace for the Pollution Prevention Industry. Web. 11 Feb. 2011. http://www.pollutiononline.com/article.mvc/Duke-Energy-To-Spend-93-Million-To-Resolve-0001.