Wet Weather Management Practices for Concentrated Animal Feeding Operations (CAFOs) - PUB2422

Concentrated Animal Feeding Operations (CAFOs) must meet Missouri’s protective design criteria that exceed design standards in federal regulations for manure storage facilities. Planning ahead and preparation for wet weather situations is paramount. The Missouri Department of Natural Resources prepared this wet weather management guide to aid producers in decision making and planning. With due diligence and guidance, agricultural producers can make decisions that protect water quality during adverse weather patterns. While this guidance has provisions for land application practices that are not typically allowed because of the potential for runoff, there still shall be no discharge as a result of these applications from land application fields during wet weather events.

At times, precipitation events may exceed the design criteria for the operation of manure storage facilities. Persistent heavy rain coupled with cool weather during a cropping season can create challenges for livestock and poultry operations. Even under normal weather conditions, land application opportunities are often limited after fall harvest or before spring planting; wet weather tends to aggravate this situation. During wet weather periods, CAFOs may experience high manure storage levels for extended periods of time. This can leave the environment and the CAFO at substantial risk for spills or overflows from uncovered liquid manure storage structures. To minimize the extent of this problem, CAFO owners or operators should lower the level of wastewater in liquid storage systems on a routine schedule based on the design storage and the nutrient management plan, especially when wet or freezing weather is anticipated.

Good communication is also extremely important. Producers, integrators, environmental consultants and private land-application companies are all encouraged to work together, communicate and be accommodating to each other. In addition, producers should communicate with their Department’s regional office to discuss concerns and solutions. The Department is ready to help CAFO operators find solutions that protect water quality. Resolution of concerns related to wet weather is not limited to options contained in this fact sheet; owners may contact the appropriate regional office and seek approval to implement alternative approaches to prevent wet weather failures and releases.

The Department issues site-specific CAFO National Pollutant Discharge Elimination System (NPDES) permits and has issued two CAFO general permits, an NPDES (MOG01) permit and a state no-discharge (MOGS1) permit. All CAFO permits have provisions for the implementation of the wet weather practices included in this publication, but MOGS1 permittees are not allowed to discharge for any reason. NPDES (site-specific and MOG01) CAFO permits allow for a discharge from an uncovered liquid storage structure when a chronic weather event or catastrophic storm event occurs and the operation has properly maintained liquid storage systems in accordance with permit conditions. As long as the discharge does not cause a violation of water quality standards. All permit holders must notify the Department at least 24 hours in advance of implementing wet weather practices. Producers should regularly review their permit to ensure that they understand the requirements. Both general CAFO permits contain wet weather management practices provisions and are available at the Department’s CAFO webpage.

The wet weather management practice permit provision states:
“A chronic weather event is a series of wet weather events and conditions that can delay planting, harvesting, and prevent land application and dewatering practices at wastewater storage structures. When wastewater storage structures are in danger of an overflow due to a chronic weather event, CAFO owners shall take reasonable steps to lower the liquid level in the structure through land application, or other suitable means, to prevent an overflow from the storage structure. Reasonable steps may include, but are not limited to following the Department’s current guidance entitled “Wet Weather Management Practices for CAFOs - PUB2422,” written to help minimize or eliminate water quality impacts from CAFOs during extreme wet weather periods. Typically, the Department determines Chronic Weather events based upon an evaluation of the 1 in 10 year return rainfall frequency over a 10-day, 90-day, 180-day, and 365-day operating period.”

The Department determines when a catastrophic storm or chronic weather event is occurring for any given county in Missouri by reviewing precipitation data including state-wide storm maps, updated daily published by the Missouri Climate Center. Producers, integrators, consultants, land-appliers and Department inspectors can sign up for weather alerts online.  

The following practices help minimize or eliminate water quality impacts from an overflow of a liquid storage structure during extreme wet weather periods. Once the liquid level in the storage structure is below the upper pump down level, land application is to resume under normal conditions. To continue using wet weather management practices to further lower the liquid level below the upper pump down level, please coordinate with the appropriate regional office.

Wet Weather Management Practices

1. 1. Avoid allowing a lagoon or storage structure to overflow. Liquid manure or wastewater likely contains pollutants, sometimes at high concentrations. As such, overflowing effluent can damage the ecosystem and harm fish and other aquatic life, when it enters a stream or pond. Additionally, overflows may compromise the structural integrity of a lagoon's berms, resulting in a more catastrophic discharge.
2. Do not lower manure storage structures by pumping or siphoning wastewater directly onto the ground surface or into a stream. Such activity is not authorized and is a violation and subject to enforcement action regardless of the circumstance. (NPDES authorized wet weather discharges are limited to overflows or emergency spillway/relief discharges, not active pumping or directing wastewater into state waters). In addition, do not attempt to increase lagoon storage levels by sandbagging or by raising lagoon berms.
3. Apply effluent to frozen or saturated soils, only if necessary to prevent a lagoon from overflowing. Note: The Concentrated Animal Feeding Operation Nutrient Management Technical Standard (NMTS) prohibits surface application of manure to frozen, snow-covered, or saturated soils during normal weather conditions. The state CAFO regulations incorporate the NMTS, available on the Department’s CAFO webpage at https://dnr-new.mo.gov/water/business-industry-other-entities/permits-certification-engineering-fees/concentrated-animal-feeding-operation-permits. 
4. Applying effluent on fields used for hay or pasture is preferable to reduce runoff potential. If hay or pasture land is not available, apply to fields with high levels of crop residue. For better access to wet fields, fill tankers to less than full capacity to reduce weight.
5. During wet weather conditions, the CAFO owner may use any fields suitable for land application with permission from the property owner, even if the land is not in the operation’s nutrient management plan. Applications to these fields under this guide must follow all relevant Best Management Practices in the nutrient management plan, NMTS, and permit requirements. Keep complete records of all applications on those fields and submit them on a separate sheet with the annual report. Application to fields not owned, leased, or rented by the CAFO owner is considered a manure transfer, requiring retention of transfer records in accordance with permit recordkeeping requirements.
6. Increase separation distances as much as possible between application areas and waterways, including streams, lakes, and other waters of the state. Required minimum separation distances for normal land application events are:
   • 300 feet from losing streams, sinkholes, caves, wells, abandoned wells, water supply structures, and impoundments or any other connection between surface and groundwater
   • 100 feet from permanent flowing streams, intermittent flowing streams, and privately owned impoundments not used as a water supply
   • 50 feet from property lines
   • 150 feet from dwellings or public use areas if applied with spray irrigation systems
   • 50 feet for application by tank wagon or solid spreader from dwellings or public use areas
7. Use land with the least slope to minimize runoff potential. Seek fields or even parts of fields with 2% slope or less. Avoid areas subject to flooding or that have shallow groundwater tables.
8. Reduce application rates to decrease runoff potential. Calibrate and operate irrigation equipment in a manner to ensure even distribution of applied wastewater. Surface applications less than 0.25 inches per pass and gun travel speeds of five feet per minute or more may be necessary.
9. Monitor the application operation continuously to minimize runoff potential or equipment malfunction. Observe points of potential runoff around the perimeter of the land application field. No discharge shall occur as a result of land application, even during wet weather events.
10. If overflow from a lagoon or runoff from land application does occur, cease application and start emergency secondary containment procedures by constructing berms or a dam to prevent wastewater from entering surface waters.
11. Report to the Department all discharges of manure or process wastewater to waters of the state no later than 24 hours after becoming aware of the discharge. Record and maintain reports of the date, time, location, duration, and estimated volume. To report a discharge, contact the Department’s nearest regional office or the 24-Hour Emergency Response Line at 573-634-2436.

Retain records. During times of unusual weather, it is particularly important to be thorough about keeping complete precipitation, manure storage level, and land application records.
If you have any questions or concerns, wish to discuss alternative release prevention methods, or need to report wet weather related conditions, please contact your regional office:

Missouri Department of Natural Resources’ Regional Offices

•    Kansas City Office 816-251-0700
•    Northeast Office 660-385-8000
•    Southeast Office 573-840-9750
•    Southwest Office 417-891-4300
•    St. Louis Office 314-416-2960
•    Central Field Operations 573-522-3322
•    MoDNR Emergency Response Line (24-Hours) 573-634-2436