1. U. Agena , 1998 . Overview and Status of State Programs Regulating Animal Feeding Operations . In: Proceedings for Watershed Partnerships: Protecting our Water Resources. 1998 , Ames, Iowa, pp.47 -51 .
2. J. L. Baker, T. D. Glanville, S. W. Melvin, and L. E. Shiers , 1999 . Soil Sampling and Analysis Around Earthen Waste Storage Structures in Iowa . In: Earthen Waste Storage Structures in Iowa: A Study for the Iowa Legislature, 1999 , pp.64 -114 .
3. R. L. Bates, and J. A. Jackson , 1980 . Glossary of Geology . American Geologic Institute, Falls Church, Virginia, 749 pp.
4. E. A. Bettis, D. J. Quade, and T. J. Kemmis , 1996 . Hogs, Bogs, and Logs: Quaternary Deposits and Environmental Geology of the Des Moines Lobe . Iowa Geological Survey Bureau Guidebook Series No. 18, 170 pp.