Freeboards are a must for manure storage

Farmers need to be constantly aware of the remaining storage capacity of liquid manure storage structures in order to be in conformance with GAAMPs.

Freeboard is an unfamiliar term to many, but it should be well known to farmers with liquid manure storage. Free board is the top area of a storage structure that is reserved for emergencies, therefore, not to be occupied with manure. 

The Generally Accepted Agricultural Management Practices (GAAMPs) for manure management and utilization are guidelines set by Michigan Department of Agriculture. If farmers’ wish to have nuisance protection under Right To Farm act, then this and all pertinent GAAMPs must be followed. The Manure GAAMPs states “All manure storage structures shall maintain a minimum freeboard of 12 inches (six inches for fabricated structures) plus the additional storage volume necessary to contain the precipitation and runoff from a 25-year, 24-hour storm event. This amounts to about -4” in Michigan but varies by county. An earthen or otherwise slope sided storage having 12 inches of available space plus the amount of a 24 hour, 25 year precipitation event, being four inches, therefore a total of 16 inches of unused space. A straight sided storage, such as concrete or steel, is to have six inches of constant freeboard, and then room for the 24 hour, 25 year storm event, again approximately four inches in Michigan, therefore adding up to 10 inches of unused space.

Storage structures need to be checked periodically to see level of fullness. This gives a producer time to plan manure removal and application needed to empty the structure adequately and maintain the necessary freeboard. Producers can mark a storage structure to freeboard marker.

Storage marker built from PVC pipes.

Jeremy Brenner, a dairy producer from Hillsdale County, built this storage marker with PVC pipe. The pipe is color coded so he knows when the minimum freeboard level is reached. Green means adequate room to handle additional liquid, while red means manure removal and application needs to start when possible.

In addition, manure storage structure integrity should also be maintained by means of periodic inspections. During these inspections, identify any item that would minimize integrity, such as animal burrows, trees and shrubs growing on the berm, and low areas in the structure that may be conducive to leakage.

For a complete listing of the GAAMPs, please go to the Michigan Department of Agriculture & Rural Development website.

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