Technical Reviewer: Russ Perkinson (Virginia Department of Conservation and Recreation-Division of Soil and Water Conservation, Richmond, Virginia).
Publication Number 442-909, June 1996
*Overview of the Virginia Farm Assessment System
Livestock wastes if not properly managed can become a source of nitrate and disease-causing organisms to both surface water and groundwater. Nitrate-nitrogen levels above 10 milligrams per liter (mg/l; equivalent to parts per million for water measure) can pose health problems for infants under 6 months of age, including the condition known as blue baby syndrome (methemoglobinemia). Young livestock are alsosusceptible to health problems from high nitrate-nitrogen levels. Levels of 20-40 mg/l in the water supply may prove harmful, especially in combination with high levels (1,000 ppm) of nitrate-nitrogen from feed sources.
Dry manure can be stored in solid form in stockpiles, and liquid manure can be stored in tanks or earthen basins, or stored and treated in anaerobic lagoons. Manure storage facilities, if not designed or managed properly, can be potential sources of nitrate leaching to groundwater. For example, facilities for liquid manure storage sometimes leak or burst. Seasonal filling and emptying of earthen manure storage pits can cause damage to the organic and physical seal on the bottom and sides of the pit. Short-term solid manure storage and abandoned storage areas can also be sources of groundwater contamination by nitrates.
Regulations of the Virginia Department of Environmental Quality/Water Division (DEQ) apply to storage locations and to minimum standards for seepage control from storage/treatment facilities.
The environmental safety of storing large amounts of manure in one place for an extended period depends on the following:
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After a period of years, weathering, wave action, or wetting and drying cycles may cause the side walls of earthen pits to crack and erode, allowing wastes to seep into the underlying soil or subsurface geologic material. Groundwater contamination will result if the subsurface materials do not prevent leaching of contaminants.
While seepage from earthen waste storage facilities is not always easy to recognize, there are some tell-tale signs:
If construction of a holding pond or concrete/steel tank is not feasible, another option is to build a covered semi-solid manure storage structure to protect the manure stack from precipitation. Roofed storage systems require adequate bedding to absorb and retain the liquid portion of the waste.
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Short-term storage, which is restricted primarily to solid or semi-solid manure, has the disadvantage of requiring that the manure be handled often. Designs are available for short-term storage structures that facilitate handling and provide effective protection for surface water and groundwater.
Short-term storage systems may be applicable for those operations, such as small dairies, which often have to stack manure in fields, particularly during periods of bad weather or between cropping cycles. Field stacking is not a recommended practice. No matter how it is done, it may pose a contamination threat to surface water and groundwater. If manure is frequently stacked in fields, cover it with plastic sheets or consider constructing a short-term runoff detention pond at the storage site.
Likewise, many farmers and livestock feeders will scrape manure into piles in the open lots as temporary storage during bad weather or busy work periods. Mounds are constructed from dry manure materials that are shaped to accommodate cattle comfort. Regulations governing milk production require frequent manure collection and removal and do not allow milking cows to come in contact with stacked manure.
Many farmers have open housing for young livestock, such as pole sheds, where wastes are allowed to accumulate for extended periods of time. Roofs on these structures keep rain and snow off the manure. These structures are relatively effective for water quality protection if they are isolated from surface water runoff, and if adequate bedding is provided to absorb liquids in the wastes. To minimize water quality impacts, provide adequate bedding to reduce seepage, and clean these sheds as frequently as possible.
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Minimum separation distances regulate new well installation or the distance from existing wells to new waste storage facility construction. Existing wells are required by law only to meet separation requirements in effect at the time of well construction. However, for your own benefit make every effort to exceed "old regulations," and strive to meet current regulations whenever possible.
Observing these separation distances when siting a new facility is a good way to help protect your drinking water. Locating manure storage sites or facilities downslope from wells or springs is also important for protection of your water supply. (For more information about separation distances, and how the condition of your well or spring might affect the potential for contamination, see Fact/ Worksheet Sheet No. 2, Well and Spring Management.) Depth to seasonal high water table or fractured bedrock, along with soil type at the waste storage location, is another important factor. These characteristics are described in Fact/ Worksheet No. 1.
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Solid manure can be incorporated by tillage immediately following its application, and liquid manure slurry can be injected into the soil. Manure application should be applied near the time that planting will occur to maximize nitrogen uptake by crops and minimize the loss of nitrogen through runoff or leaching through the soil profile. Liquid manure and lagoon effluent can also be applied to land areas by irrigation over growing crops. Care must be taken, however, to prevent burning of some plants by the waste materials and to avoid excessive runoff.
Stored manure, prior to land application, should 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 usually involves taking a number of subsamples (e.g. 10 or more) and mixing the subsamples into one or more combined samples to be analyzed. This information, along with a knowledge of the amount of manure applied per acre, enables a farmer to determine whether or not additional commercial fertilizer is needed to meet crop production goals. A farm nutrient management plan will take all of these factors into consideration.
Land application should not be carried out during extended periods of bad weather which make application impractical or illegal. Virginia Department of Environmental Quality rules discourage application of wastes when the ground is frozen or saturated.
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Abandoned waste storage pits, especially earthen ones, can pose significant water quality as well as safety problems. Any abandoned structure should be completely emptied and the contents utilized. In the case of earthen waste storage facilities, liner materials (to a depth of about two feet) should be removed and spread over croplands. The remaining hole should be filled and leveled. Manure packs from pole barns or sheds no longer in use should also be removed and the wastes applied to cropland. If manure is stacked in fields, it should be appropriately spread as soon as conditions permit.
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Go to Work Sheet No. 9, "Livestock Manure Storage and Treatment Facilities."
Visit Virginia Cooperative Extension.
View a list of the Virginia Farmstead Assessment System publications.
