As with most situations, there are multiple reasons for nitrate contamination of groundwater.  In Portage County, a combination of natural features and human activities on the land surface increases the risks of higher nitrate levels in the County's groundwater. Some factors include:

• Sandy Soils
• Irrigated Agriculture and Excess Fertilizers
• High Water Table 

Water-soluble substances like nitrate easily enter the County's groundwater supply due to the sandy soils. Sandy soils have a high porosity and permeability.  This means the large pore spaces between the sand grains quickly transport water to the soil to the groundwater.

In the map on the right, all the brown, green, and yellow shaded areas represent a sandy type of soil.  The aquifer lying beneath the soil is also made of sand and gravel up to 250 feet deep.

In addition, large areas of irrigated cropland increase the risk of nitrate contamination. Fertilizers are applied to many of the crops and the irrigation water carries unused nitrate quickly through the sand into the groundwater.  From a watershed perspective, over 90% of nitrate in groundwater is from agricultural land uses ⁷.  But locally, subdivisions, septic systems and highly fertilized lawns may be an important contributor to nitrate contamination ⁵⁴.

High Water Table

Also, in many places throughout the County, the water table is high.  The depth from the land surface to the water table ranges from 0-30 feet.  The closer the water table is to the land surface, the shorter the amount of time and soil there is to hold or convert the nitrogen in the water.

However, if the water table is at the land surface, denitrification occurs.  Denitrification is the process carried out by bacteria that converts nitrate to nitrogen gas.  In order for nitrate leaching to occur, a zone of well-aerated soil must be present above the water table.