Agricultural Sources of Contaminants in Groundwater
Department of Agronomy
In agriculture, pesticides and plant nutrients can enter the groundwater and contaminate it. These chemicals may reach large enough levels to become harmful to animals and people. So we must understand how contamination may occur and how it can be avoided. With good management practices, we can keep the groundwater from becoming contaminated by agricultural chemicals.
Agricultural sources of contamination
The following substances used on the farm have the potential to contaminate groundwater:
- Livestock waste — a major source of plant nutrients such as nitrogen and phosphorous.
- Fuels and solvents.
Used to control weeds
Used to control insects, and
Used to control plant diseases.
- Chemical fertilizers:
How do these chemicals become groundwater contaminants?
- Animal wastes from confinement areas can potentially be a serious contaminant to well water. The contaminants are in the forms of microscopic pathogens (bacteria) and plant nutrients. Plant nutrient contaminants are predominantly nitrates and, to a lesser degree, phosphates. Animal waste contaminants can enter groundwater through poorly constructed wells, or by percolating through soil layers.
- Spills or leaks of fuels, solvents and pesticides are often the most reasonable explanations of well water contamination. The most common source of well contamination is inadequate well construction and maintenance. They combine to literally pour contaminants down the well into the groundwater.
- Plant nutrients from fertilizers and animal wastes are identical. Fertilizer spills near a well pose a contamination threat. To a much lesser degree, percolation of nitrates through soil layers to the groundwater can stem from land application of animal wastes or fertilizers.
Nitrogen does occur naturally. Commonly grown legume plants, such
as soybeans and alfalfa, produce nitrogen. This nitrogen also changes into nitrate.
One cannot distinguish between these naturally occurring sources of nitrates
and those added by fertilizers or animal wastes.
Nitrates can contaminate groundwater if more nitrate is applied to the soil than the plants and soil can use.
This publication was written by Karen DeFelice, former associate extension
agronomist; Nyle Wollenhaupt, former state extension agronomist; and Daryl Buchholz,
state extension agronomist. This material is based upon work supported by the
United States Department of Agriculture, Extension Service, under special project
WQ21, reviewed October 1993