Hydrogeologic Settings of Earthen Waste Storage Structures Associated with Confined Animal Feeding Operations in Iowa

Thirty-four permitted earthen waste storage structures (EWSS) were investigated to characterize their hydrogeologic setting using digital soils data, digital elevation data, geologic maps, and oblique aerial photographs. Nearly 18 percent of the sites were constructed above alluvial aquifers and on flood plains. More than half of the area within 3.2 km of most sites had soils with a vertical permeability = 25.4 mm/hr and well or moderately to well-drained soils. The prevalence of EWSS depths exceeding 3 m and areas with water table less than 1.6 m deep suggests that most sites are below the water table. Ephemeral or perennial streams were found within 152 m at one-third of the sites. Risks to water resources may be reduced by using siting criteria that incorporate geologic, hydrogeologic, and soils data. Controlling the timing of manure application and avoiding application on frequently flooded and permeable soils may reduce the risk of water-resource contamination. Application of well-established, scientifically defensible groundwater monitoring techniques should be used to locate the position of the water table during construction and throughout the life of the EWSS. Uniform stream setbacks may not be appropriate for all hydrogeologic settings. These considerations, used with appropriate performance standards, would reduce the potential for contamination of water resources.