Formed structures usually have concrete or steel walls and sides. By definition, a formed manure storage structure means a covered or uncovered impoundment used to store manure from an animal feeding operation, which has walls and a floor constructed of concrete, concrete block, wood, steel, or similar materials. Similar materials may include, but are not limited to, plastic, rubber, fiberglass, or other synthetic materials. Materials used in a formed manure storage structure shall have the structural integrity to withstand expected internal and external load pressures.
Left: A formed manure storage structure made of steel, Middle: A concrete formed manure storage structure overflowed after the producer accidentally left a hose running. State law requires producers to keep the liquid manure level at least one foot below the top of a formed structure, Right: A common type of manure storage used in Iowa for swine operations is the below-building pit. The manure is removed and land applied as a fertilizer for crops. Photo courtesy of ISU Extension.
Unformed manure storage structures include several types of impoundments, built of soil or earth. These earthen storage basins were very popular in Iowa until the mid-1990s, when concerns about their usage prompted legislative changes that encouraged formed storage. By definition, an unformed manure storage structure means a covered or uncovered impoundment used to store manure, other than a formed manure storage structure, which includes an anaerobic lagoon, aerobic structure, or earthen manure storage basin.
Left: Manure agitation and removal from an unformed manure storage structure, Right: Lagoon used for storage of liquid swine manure is an unformed manure storage structure.
