The Rock County Public Health Department created a Nitrate Risk Mapping Tool to display the potential risks of nitrate contamination in shallow groundwater. We developed this tool using research and data to estimate areas of Rock County that may be at greater risk of nitrate contamination. The risk estimates in this map are based off the following data:

1.  Land cover and crop type

Many crop and lawn fertilizers have nitrates in them because nitrates are an essential nutrient for healthy plant growth. Some of the nitrates in these fertilizers can end up in the groundwater.

2. Soil type

Soils naturally filter out many toxins from water, but certain soils allow nitrates to get into groundwater at a greater rate than other soils. Soil types were used to estimate the amount of nitrates that could leach into groundwater.

3.  Septic System Density

Septic systems can be a source of nitrates in groundwater, several septic systems in a small area could lead to greater nitrates in groundwater in that area.

4. Irrigation

The amount of water used on crops can cause more nitrates to end up in groundwater.

Through extensive research, we determined these four factors were the best to estimate the risk of nitrates in groundwater.

Well depth and other factors that are not accounted for in our model

The risk of nitrate contamination in your drinking water is also based on the depth of your well. A deep well is less likely to have nitrate contamination, so you may live in a high-risk area of Rock County based on our mapping tool, but you may not have nitrates in your drinking water

Also, we did not account for the flow of groundwater. Just like water in rivers and lakes, groundwater flows in certain directions depending on underground features. This can change your level of risk depending on the direction and speed at which the groundwater flows. We did not account for this in our model.

To get technical details on our model and the components we used to determine risk levels, please contact Nick Zupan at nicholas.zupan@co.rock.wi.us for more information.

The model we created provides an estimate of the risk of nitrates leaching into groundwater, but this does not necessarily mean there are high levels of nitrate in your drinking water. Even if your risk is determined to be “low” by the tool, it is important to have your water tested regularly. Because you cannot smell, taste, or see nitrate in your water, the Wisconsin DNR (Department of Natural Resources) recommends that you test for nitrates at least once a year.