The National Pollutant Discharge Elimination Systems (NPDES) permit program seeks to reduce the amount of water pollution to surface waters. This is accomplished by regulating point sources such as pipes or man-made ditches that discharge pollutants into public waters.
In the summer of 2005, the Iowa Department of Natural Resources (IDNR) began to issue increasingly stringent discharge regulations to ethanol plants throughout the state in response to federal guidelines. These regulations included reduced maximum concentrations for iron discharged in the receiving water stream.
Minneapolis-based U.S. Water Services learned the limits placed on the levels of iron discharged to water sources in the NPDES permits were as low as 0.16 ppm. This would have a dramatic effect not only on ethanol plants but industrial plants throughout the state of Iowa. U.S. Water Services and the Iowa Renewable Fuels Association worked together to find the cause of the change and to the regulations.