Study Details Ways to Reduce Risks to Water Resources from Waste Lagoons and Basins
January 29th, 2002
AMES, Iowa — A recent study on waste lagoons and basins, by researchers at Iowa State University and the National Soil Tilth Laboratory, has found that the structures pose potential risks to Iowa's water resources and that "common sense" guidelines could be enacted to ensure that future structures pose less risk.
The findings are from a study by William Simpkins, an ISU associate professor of geological and atmospheric sciences, and Mike Burkart, a hydrologist at the National Soil Tilth Laboratory, located at ISU.
Simpkins and Burkart's work summarizes the results of their 1998 hydrogeologic study of earthen waste storage structures in Iowa. The research was funded by the Iowa legislature, which is soliciting information on revised regulations for hog confinement facilities.
Simpkins and Burkart found that earthen waste storage structures (EWSS) associated with concentrated animal feeding operations and permitted between 1987 and 1994 pose potential risks to water resources in Iowa. Potential for water contamination from these structures is greater than previously thought, with more than 90 percent of the structure liners in Iowa built below the water table, Simpkins said.
"Topographic, hydrologic and geologic settings were not major factors in EWSS siting during this period, but they should be major factors in future sitings," Simpkins said.
Other findings of the study include:
Eighteen percent of the earthen waste storage structures are located on flood plains and in alluvial aquifers. Floods could affect EWSS structural integrity and increase the potential for direct stream contamination. Alluvial aquifers are the most widely used in Iowa for domestic and municipal water supplies. They also are the most vulnerable to contamination derived from surface activities.
Manure is being applied on permeable and frequently flooded soils. Application to permeable soils increases the potential for groundwater contamination. Manure applied to soils that are frequently flooded increases the potential for direct stream contamination.
Although most earthen waste storage structures are built in accordance with mandated setback distances from water bodies, such setbacks ignore the local topographic, geologic, and hydrologic settings.
Misinterpretation of the depth of the waste storage structures in relation to the water table and its seasonal variability during construction has resulted in a high percentage (as much as 94 percent) of the EWSS with liners below the water table at some time of the year. This is at odds with the current EWSS construction standards.
Based on these findings, the researchers recommend:
Discontinue construction of new waste storage structures on alluvial aquifers and flood plains.
The timing of manure application from waste storage structures should be controlled to minimize leaching to groundwater. Application on frequently flooded soils (such as flood plains overlying alluvial aquifers) should be discontinued.
More site-specific information should be utilized and regulations should incorporate topographic, geologic, hydrologic, soil, and ecologic data in assessing site suitability. Site-specific information could be used to deny permits or require additional groundwater or surface-water-quality monitoring at the sites.
More thorough groundwater monitoring techniques should be used to locate the position of the water table during construction. Continued water table monitoring should be used to confirm that the state-mandated separation between the liner and the water table is maintained during the life of the structure.
"We make fairly specific recommendations directed toward the Iowa state legislature and to the Department of Natural Resources," Simpkins said. "We addressed this briefly in our first report in 1999, but the results were not complete and we could support fewer recommendations at that time.
"The 'common sense' recommendations will provide guidance to the state and help it take a proactive role in safeguarding the quality of our water resources," he added.
William Simpkins, Geological and Atmospheric Sciences, (515) 294-7814
Bridget Bailey, News Service, (515) 294-6881
Skip Derra, News Service, (515) 294-4917