When animal manure is stored, it must be accumulated in some type of structure until the manure can be applied to land. Manure storage can be either positive or negative from an environmental standpoint.

Manure storage can benefit the environment if it is stored until it can be safely spread, incorporated into the soil, and used by a growing crop. The environmental safety of collecting large amounts of manure in one place for an extended period depends on three things:

1) Proper design, construction, and operation of the storage facility.

2) Proper land application of the manure once it leaves the storage facility.

3) Physical and chemical characteristics of the soil and subsurface geologic materials within the storage area, as well as the area to which any runoff might flow.

Stored manure can be applied to the soil when crops are actively growing and soil conditions are right. When manure is used this way, you receive the maximum fertilizer value from the materials and reduce risks of groundwater and surface water contamination from the over-application of nutrients. Land application of manure fertilizer can turn a "waste" into a resource with minimal risk of groundwater contamination, if done at agronomic rates.

Stored manure can easily be sampled and tested to determine how much nitrogen, phosphorus, and potassium it contains. When sampling manure, be sure to obtain as representative a sample as possible. This information, combined with a knowledge of the amount of manure applied per acre, determines whether additional commercial fertilizer is needed to meet realistic crop production goals.

Adequate manure storage reduces the need for land application during winter months when soil is saturated or frozen. This improves efficiency, saves wear and tear on equipment, conserves nutrients contained in the manure, and minimizes manure nutrient leaching and runoff.

Animal manure can be stored either in solid, semi-solid, or liquid states.

• Solid facilities stack heavily bedded manure against walls and on slabs.
• Semi-solid facilities use pumps to move manure into containment areas and may separate solids from liquids.
• Liquid facilities hold manure in tanks or manure storage ponds.

Figure 1: Earth basin for manure storage. Source: Livestock Waste Facilities Handbook, MWPS-18, Midwest Plan Service, Ames, Iowa.

Liquid and semi-solid storage systems are self-contained (Figure 1). Ground water contamination can occur if the facility is not structurally sound, allowing contaminants to seep into the soil. A threat to surface water exists if manure storage structures are not emptied frequently enough, thereby allowing manure to flow over the top of the structure.

Liquid storage systems should have sufficient storage capacity to handle animal manure during the rainy season and extreme storm events. Storage for 120 days and a once-every-25-years, 24-hour storm event is usually recommended for facilities in Washington.

Liquid storage systems require the use of pumps and pipes for moving wastes from the barn to the storage structure. These must be carefully installed and maintained to ensure that they do not leak.

Each time they are emptied, carefully check steel and concrete structures for cracks or the loss of watertight seals. If any breaks are apparent, repair them immediately. Likewise, check the walls of manure storage ponds when emptied to be certain that liner materials are not cracked or eroded.

While seepage from in-ground manure storage facilities is not always easy to recognize, there are some tell-tale signs:

• A properly designed structure has the capacity to handle manure from a specific number of animals for a known number of days. If a pit designed for 120 days of storage receives designated manure amounts but does not fill to the design level in four months, the pit may be leaking.
• Evaporation from liquid storage pits is minimal during the late fall, winter, and early spring. If additional liquids have to be added in the spring, before a pond can be agitated and pumped, it may be leaking. During warmer months addition of liquids may frequently be needed for pumping due to evaporation losses. Monitoring wells installed around the pond upslope and downslope would be required to confirm seepage.

Some facilities for storage of solid or semi-solid manure are designed to allow seepage from the stack. In these instances, structure design must include treatment for the wastes that seep out. Use of these facilities should only be for control and treatment of lot runoff wastes, not for continuous, concentrated wastes such as swine slurry or dairy wastes. If conditions allow, structures such as picket dams can be used to hold back solids, and grass filter strips can be used to help remove remaining pollutants in lot runoff water. These systems should not be considered on sites with coarse-textured soils, creviced bedrock, or shallow water tables. Care must be taken to ensure that the system is not overloaded.

Both systems require maintenance. With grass filter strips, it is important to ensure that the ammonia in highly concentrated manure does not "burn" vegetation in the filter strip. A thick, healthy stand of vegetation allows runoff to seep into the soil and uses the nutrients in the water.

The best way to handle seepage is to channel it into a watertight holding pond or storage tank. In those areas where not enough soil is available for the construction of filter strips, or where the construction of a holding pond is not feasible, another option is to build a roof over the structure to eliminate additional water being added to the manure stack. Roofed storage systems require adequate bedding to absorb and retain the liquid portion of the manure.

Short-term storage allows producers to hold animal manure during periods of bad weather when spreading may not be feasible, when crops are growing and land is not available for applying manure, or when there is a shortage of crop acres to handle frequent hauling and spreading of manure without the threat of runoff.

Short-term storage has the disadvantage of requiring that the manure be handled twice. Designs are available, though, for short-term storage structures that facilitate handling and provide effective protection for surface water and groundwater.

Short-term storage systems may be applicable if you often find that you must stack manure in fields, particularly during periods of bad weather. This is not a recommended practice. No matter how it is done, it poses a contamination threat to surface water and groundwater. If manure is frequently stacked in fields, it might be appropriate to consider constructing a short-term storage facility.

Do not scrape manure into piles in the animal lot rather than haul it during bad weather or busy work periods. This practice is not recommended because of possible herd health problems and water pollution. The severity of those problems depends on characteristics of the animal lot area where the manure is piled and the area to which runoff flows.

Open housing, such as pole sheds, is often used to allow manure to accumulate for extended periods of time. Roofs on these structures keep rain and snow off the manure. These structures are relatively safe for water quality if they are protected from surface water runoff, and if adequate bedding is provided to absorb liquids in the manure. To minimize water quality impacts, provide adequate bedding to reduce seepage and clean these sheds as frequently as possible.

The use of long-term storage methods is preferable to short-term techniques. Long-term storage practices and structures are generally better designed to deal with unplanned occurences, such as major storm events, and provide better overall protection of water quality.

Where animal manure is stored in relation to any well is an important factor in protecting the farm water supply. Washington regulations require a minimum separation distance of 100 feet for all animal manure facilities from the well, but larger distances are strongly recommended. For temporary manure stacks and earthen storage facilities, the minimum separation distance should be at least 250 feet.

Minimum separation distances should guide new well installation or the distance from existing wells to new manure storage facility construction. Make every effort, however, to exceed the regulations and strive to meet current recommendations whenever possible.

Observing these separation distances when siting a new facility is a good way to help protect your drinking water. Locate manure storage facilities downslope from the well to protect your water supply. For more information about separation distances and how the condition of your well might affect the potential for contamination, see worksheet and fact sheet 1, Drinking Water Well Condition.

While observing well separation minimum distances may help to protect your own well, poorly designed or poorly maintained animal manure storage facilities could still contaminate the groundwater that supplies other local drinking water wells. Protecting the groundwater resource as a whole can help protect your neighbors' wells, as well as the quality of drinking water supplies for future generations.

Depth to seasonal high water table or fractured bedrock and soil type at the manure storage location are other important factors. These are among the site vulnerability characteristics in worksheet 11, Site Evaulation.

It is important that earthen waste storage structures not leak or otherwise excessively discharge pollutants to groundwater potentially causing a violation of Washington State Ground Water Quality Standards. The Washington Department of Ecology administers these standards and encourages the use of U.S. Soil Conservation Service standards and specifications for the location, design, construction, and operation of these structures.

Depth to water table is sometimes available in the county soil survey, but this varies from county to county. Your county Cooperative Extension agent, Soil Conservation Service or Conservation District personnel, or a local well driller may also be able to help you gather this information.

Land application is the predominant method of using animal manure. When properly managed, land application offers safe and beneficial use of manure nutrients and water by vegetation. Both solid and liquid manure should be applied to land using rates and methods that prevent surface runoff of pollutants and leaching of pollutants to groundwater.

Soil analysis and a manure application plan that balances available manure nutrients with crop needs should be completed before manure application begins. Application rates should not exceed the nitrogen or moisture needs of the plants growing or to be grown on the field site and applied nutrients should be credited in the fertilizer program for the field site. Application of animal manure to cropland at low application rates poses little danger to groundwater or surface water due to filtering of contaminants by the soil or plant uptake of nutrients.

An effective method of land applying manure is using the traveling big gun sprinkler (Figure 2). The traveling big gun, may be used on large acreages irrigated several times a year.

Figure 2: Traveling big gun land application system. Source: Livestock Waste Facilities Handbook, MWPS-18, Midwest Plan Service, 1985.

Manure storage and structure design
Contact your county Cooperative Extension, Conservation District (CD), or Soil Conservation Service (SCS) office; or the Cooperative Extension Agricultural Engineers, (509) 335-2910.

Northwest: (206) 647-7000
Southwest: (206) 753-4089
Central: (509) 575-2809
Eastern: (509) 456-6198

Publications are available from sources listed at the end of the reference section. Refer to number in parentheses after each publication.

Groundwater contamination, protection and testing
Washington Agriculture-Sustaining Water, Land and People EB1634 (1)
Washington Groundwater: A Vital Resource EB1622 (1)
Protecting Groundwater: Managing Livestock on Small Acreage EB1713 (1)
Managing Livestock Manure to Protect Groundwater EB1717 (1)
Animal Manure Data Sheet EB1719 (1)
Livestock Manure Lagoons Protect Water Quality EB1642 (1)
Keys to Dairy Manure Management for Water Quality EB1658 (1)
How Fertilizers and Plant Nutrients Affect Groundwater Quality EB1722 (1)
Defining Water Quality EB1721 (1)

A list of laboratories certified to conduct water sample analysis is available from your Cooperative Extension agent or local health district/department.

Home·A·Syst team members: Christopher F. Feise and Edward B. Adams, WSU Cooperative Extension Water Quality Coordinators; James D. LaSpina, Homestead Assessment System Project Associate.

Animal Manure Storage Technical Reviewers: Ronald E. Hermanson, WSU Cooperative Extension; Andy Werkhoven, Dairy Farmer; Anne Schwartz, Washington Tilth; John A. Gillies, USDA-Soil Conservation Service; Philip A. KauzLoric, Washington Department of Ecology; John W. Bernard, WSU Cooperative Extension.

Adapted for Washington from material developed by the Wisconsin, Minnesota, and Kansas Extension Services and Farm·A·Syst Programs. Washington Home·A·Syst development was supported by the National Farmstead Assessment Program.