Several items must be considered in sizing a manure storage facility. Many states have specific regulations regarding the size of manure storage structures, and these regulations should be investigated in the planning phase of the storage facility.
A manure storage structure is typically sized to contain some or all of the following contributions.
1. Sludge or unpumpable settled solids accumulated during the design storage period (defined below).
2. Treatment volume (if applicable as in the case of lagoons).
3. Volume of manure generated during the design storage period (typically includes bedding if used).
4. Contaminated runoff from production areas for the design storage period.
5. Additional planned input during the design storage period such as washwater, fresh water used for cleaning/flushing, etc.
6. Precipitation/evaporation occurring on the surface of exposed liquid storage facilities during the design storage period.
7. Runoff from berms or adjacent landscaped areas that cannot be diverted from the storage structure for the design storage period.
8. Any other volume fraction that may be required in addition to the above noted items. For example, some states may require that sufficient volume be included to contain the 25-year/24-hour storm in addition to the above items.
Evaluation of volume fractions affected by rainfall (i.e., lot runoff) is especially critical in humid areas. Some states require sizing manure storage structures using more stringent precipitation data such as the wettest-year-in-10 rather than average-year precipitation.
Another important consideration is the “design storage period.” This is the length of time between pumpdown or emptying of the manure storage structure. Factors affecting the design storage period selected include crop types and rotations, climatic conditions, labor and equipment availability as well as other considerations that may be unique to a given operation.
Obviously, there is not a “one size fits all” answer to the question of sizing a manure storage facility. Each must be evaluated on the basis of individual site conditions and the applicable regulatory requirements. Contact a qualified engineer, the Natural Resources Conservation Service, or the Cooperative Extension Service in your state for assistance in planning and sizing a manure storage facility.
Author: Charles Fulhage, University of Missouri
