Spring 2004
Concrete solutions for confinement feeding operations
by Sara Smith, the Iowa Department of Natural Resources
Iowa livestock and poultry confinement producers have something to look forward to “better concrete standards” meaning better-built manure storage. Effective March 24, 2004, new concrete pits and tanks that store liquid or dry manure must be constructed to meet the revised concrete standards proposed by the Department of Natural Resources (DNR). Although more stringent, the updated standards will require new design guidelines to ensure that the concrete tanks and pits will provide liquid tightness and more uniform design and construction standards.
The DNR upgraded its minimum concrete design standards for confinement feeding operations in response to a legislative mandate. However, the discovery of sub-standard concrete pits and tanks in the field emphasized the need for using the most up-to-date technical information. The DNR developed the standards in cooperation with the MidWest Plan Service (MWPS) and the Portland Cement Association (PCA). Additional input came from the Natural Resources Conservation Service (NRCS), stakeholder groups and private contractors. The standards were studied for about eight months.
Confinements that are included: The new concrete standards would apply to any of the following confinement feeding operations:
1. New concrete
tanks or pits that store liquid or semi-liquid manure. The tank or
pit can be located belowground or aboveground, be circular or non-circular,
covered or uncovered. These new standards would be required for operations
larger than a small animal feeding operation (SAFO= operation has an animal
unit capacity (AUC) of 500 animal units or less). However, for all operations,
even for a SAFO, if a concrete tank or pit has walls deeper or higher
than 12 feet, the tank or pit must be specifically designed and signed
by a professional engineer (PE) or a NRCS engineer, regardless of the
size of operation.
2. New concrete tanks that store manure exclusively in dry form.
The tank can be belowground or aboveground, covered or uncovered. Dry
manure storage was specifically exempted from the older standards.
3. New concrete tanks or pits constructed in areas that exhibit karst
terrain or areas that drain into a known sinkhole. In these cases,
additional upgraded concrete standards must be followed, regardless of
the size of the operation.
Designs developed with a PE or NRCS Engineer. Only operations that meet or exceed the “threshold requirements” require a PE or a NRCS engineer to do the design of the concrete tanks and pits. The threshold requirements have been established for operations that need a construction permit and for operations that after construction or expansion of their facility have an animal unit capacity (AUC) equivalent to, or exceeding 1,250 AU (swine farrowing and gestating operation), 2,750 AU (swine farrow-to-finish operation), 4,000 AU (cattle operation), and 3,000 AU for all others.
The PE or NRCS engineer
must use the design considerations of the American Concrete Institute
(ACI), the Portland Cement Association (PCA) or the MidWest Plan Service
(MWPS).
There are advantages of engineered designs. Producers who voluntarily
choose to have a PE or an NRCS engineer design and sign the concrete tank
or pit will have a much shorter list of additional requirements to comply
with, because of the design considerations being required.
Designs developed without an engineer. The older standards were based
on minimums and often resulted in a typical but insufficient design and
construction. The new design standards are more site specific. The design
methods for walls are either the MWPS-36 for non-circular tanks, the MWPS
TR-9 for circular tanks, or the 567 Iowa Administrative Code (IAC) Chapter
65 new Appendix D. This new Appendix D was specifically developed for
a belowground tank with laterally braced walls such as a below-the-building
concrete pit. Appendix D contains tables with wall design specifications
based on tank depth, wall thickness, type of backfill material, and whether
vehicles will be allowed within five feet of the walls.
Additional requirements also apply to concrete tanks designed without a PE or NRCS engineer. These additional requirements are greater if the concrete tank is for liquid and semi-liquid manure, or for a belowground or a partially belowground tank that stores dry manure. Fewer additional requirements apply for an aboveground concrete tank used to store manure exclusively in a dry form.
The new concrete
standards address fundamental design considerations and construction aspects.
Among these, are the sub-grade preparation, the installation of a drainage
tile to artificially lower the groundwater table, and the concrete curing
and consolidation or vibration.
Furthermore, the new standards will no longer allow wire mesh as floor
reinforcement in concrete tanks or pits that are 4 feet deep or deeper.
DNR inspectors found out that during construction the floor wire was stepped
on or improperly placed, resulting in inadequate reinforcement and increased
cracking.
Table 1 summarizes
the major changes introduced with the new minimum concrete standards for
a concrete tank that will store liquid, semi-liquid and dry manure, above
or below ground.
New concrete standards for Karst and Sinkhole Areas. Finally, the new
concrete standards contain more stringent requirements if the proposed
concrete tank or pit will be located in an area that exhibits karst terrain
or that drains into a known sinkhole. These requirements apply to all
confinement feeding operations, regardless of their size. In these environmentally
sensitive locations, the DNR recommends that producers construct aboveground
tanks. However,
if construction of a belowground or partially belowground tank must take
place, the DNR will require a minimum vertical separation to the limestone,
dolomite or soluble rock of at least five feet. Otherwise, the design
must be prepared and sealed by a PE who will need to certify on the structural
stability of the tank. Groundwater monitoring requirements will be required
on these sites.
Although it is not always required, producers who are planning on constructing or expanding an operation should consult with a professional engineer or a NRCS engineer. If this is not possible, pertinent technical literature should be obtained. For additional information on these issues and the new concrete standards, please contact a DNR engineer at (515) 281-8941 or your nearest DNR field office. Complete copies of the concrete rules are available on the DNR Web site at www.IowaDNR.com under “Animal Feeding Operations.”
