Groundwater is often the main source of drinking water for rural communities, especially in the Midwestern United States, so it is important to keep that water at levels that are safe to drink while minimizing environmental impacts. Although animal manure has many benefits to farmers, it can contaminate groundwater supply if not managed properly. This article discusses important considerations when storing and applying manure and includes requirements for testing of well water.

Groundwater and Potential Manure Contaminants

Animal manure has a significant amount of nitrogen and phosphorus. These compounds are useful and valuable for agricultural systems when growing crops. However, they can be harmful when it enters the drinking water. Nitrogen, when converted to nitrate, is especially mobile and a common contaminant of groundwater. Excessive nitrate consumption can cause methemoglobinemia (“blue baby syndrome”), certain cancers, and adverse reproductive effects. Phosphorus and pathogens are less mobile and most likely to be concerns for surface water contamination. Excessive phosphorus consumption can cause problems with bones. Pathogens are also a serious potential contaminant to human health. Water-borne diseases caused by various bacteria, viruses, and protozoa have been the causes of many different outbreaks (Pandey et al., 2). Along with nitrogen, phosphorus, and pathogens, animal manure can also contain various antibiotics, and hormones which can also have negative effects on human health. Because these compounds can cause harm to humans, it is vital that they do not enter drinking water sources.

The most serious health risk from contaminated drinking water is pathogens. Microbial pathogens such as Salmonella, E. coli, S. faecalis, and enteroviruses are relatively stable in groundwater, and can survive at least 400 days in manure and soil, depending on temperature (Pandey et al., 7). Due to their long life and harm to humans, the prevention of pathogen spread is extremely important. Most soils will prevent pathogen movement to groundwater. However, pathogens can find pathways bypassing soils’ filtering capability. For example, water wells can provide a pathway to groundwater.  It is vital that proper well casings are used and maintained to prevent pathogens from entering drinking water.

Contaminants can enter and pollute groundwater through runoff after excessive land application of manure, leaching caused by improper spreading of manure, and through leaks or breaks in storage units (Hribar, 3). Generally, in order to undergo transportation, manure-borne contaminants move with water, either dissolved or bound to colloids.

Protecting Water from Stored Manure

One way to prevent the contaminants in manure from transporting is by using the proper storage facilities. Common storage facilities include outside tanks, earthen basins, and lagoons (Figure 1). For any storage facility, it is important to know how much manure is being produced to determine the correct storage size and site the location of the manure storage unit in respect to the drinking water supply. The State of Nebraska requires that any livestock manure control facility should be at least 100 feet away from a well used for domestic purposes and 1000 feet away from public water supply drinking well (NDEQ, 9-1). This 100 feet provides a buffer for the well to prevent any accidental contamination. Although 100 feet is the minimal distance, it should not be the standard. The isolation distance should be maximized in order to provide the well owner with the best possible chance of maintaining a clean drinking water supply (DEQ, 1).

The storage should also be checked frequently to make sure there are no signs of leaks or deterioration. Most of these problems occur when there is an overflow of manure in the storage facility, so one way to easily check the level of manure in storage facilities is to install a liquid level marker or gauge that can monitor depth. If there are leaks or deterioration in the storage facility, they should be fixed immediately in order to prevent excess manure from escaping.

One way to reduce the risk of exposure to pathogens is to compost manure for several weeks prior to land application.  High temperatures reached during composting can kill off unwanted pathogens and parasites (UNL Water, 1) Composting is a practical option for treating drier manures and generally not an option for slurry and liquid manures.

Protecting Water from Land Applied Manure

Another way that groundwater can be contaminated is through the improper, excessive spreading of manure. It is very important to consider the timing of manure spreading because incorrect timing can lead to risks such as losing nutrients and over-filling of storage for the manure. In the late winter and early spring, manure usually cannot be tilled in, held in place, utilized by crops, or completely soaked into the ground (Wisconsin Department of Health Services, 1). It is recommended that manure is spread in the late spring or early summer because the growing crops can use the nutrients, so there is a better chance that they will not be lost and pollute groundwater. Farmers should also avoid spreading manure on soils that are vulnerable to leaching (Madison et al., 11). Overall, manure application timing is very important and should be thought out to minimize risk of groundwater contamination. If one is unsure about timing of manure application, university extension programs, including Nebraska Extension, have land application training for individuals who would like to learn more.

On animal feeding operations and farms it is very important to understand and comply with all local regulations regarding groundwater contamination prevention protocols. Other laws concerning groundwater and livestock manure storage include groundwater monitoring. Monitoring wells are an important tool because they can keep track and control of groundwater pollution (Figure 2). Potential pollutants can enter the monitoring well which can raise concern for potential manure or chemical spills that can pollute groundwater (Wiegand, 1).  Some important groundwater monitoring laws are listed in Chapter 13 of the Nebraska Department of Environmental Quality Title 130. 

It is important that all individuals follow these protocols in order to make sure that their groundwater is not contaminated and they are following state law.

“What should I do if I think my well is contaminated?”

1. Do not drink the water if you believe it is contaminated. If present, the pollutants in the water may cause health problems, so only drink bottled water until your well is deemed clean.
2. Get your water tested for contaminants. Certified labs can be found at  epa.gov/dwlabcert/contact-information-certification-programs-and-certified-laboratories-drinking-water.
3. If water is contaminated, consult an expert to figure out ways to clean the water or find a new water source.

Further Reading from UNL’s Extension Program:

Groundwater Quality and Protection

Groundwater Protection: It's up to Everyone

Sources

Hribar, C. (2010). Understanding concentrated animal feeding operations and their impact on communities. Environmental Health, 3-4.

Madison, F., Kelling, K., Maisse, L., & Good, L.W. Guidelines for applying manure to croplands and pastures in Wisconsin, 1-20.

Michigan DEQ. (2014). Minimum Isolation Distances: Private and Public Water Wells. Office of Drinking Water and Municipal Assistance Policy and Procedure, 1-6.

Nebraska Department of Environmental Quality. (2011). Title 130 Livestock Waste Control Regulations, 1-94.

NRCS. (2012).Agricultural Wastes and Water, Air, and Animal Resources. Agricultural Waste Field Management Handbook, 1-27.

Pandey, P.K., Hass, P.H., Soupir, M.L., Biswas, S., Singh, V.P. (2014). Contamination of water resources by pathogenic bacteria. AMB Express, 1-16.

UNL Water. Pathogens and Organic Matter. Retrieved from Nebraska Land Application Training Course.

Wang, J. (2012). Polices for Controlling Groundwater Pollution from Concentrated Animal Feeding Operations. [PhD dissertation]. University of California Riverside.

Wiegand, A. (2020). Hydrostatic level measurement. 

Wisconsin Department of Health Services. (2015). Manure contamination of residential wells. Division of Public Health Reports. 1-4.