Factors that we considered most important include aquifer vulnerability, land use, and geology. Aquifer vulnerability Nitrate is denitrified in soil and ground water when oxygen is absent. Consequently, we selected only samples where nitrate will not be denitrified. Aquifers that meet these criteria are classified as nitrate-vulnerable samples. Figure 1 shows a close correlation between the location of nitrate-vulnerable aquifers and presence of permeable soils and geologic deposits.
Red areas correspond with permeable soils and surficial outwash.
Yellow areas encompass soils of moderate permeability and areas where stagnation moraines are prevalent. Purple areas illustrate locations where bedrock aquifers are close to the land surface. Land Use Nitrate concentrations in ground water correlate strongly with land use. This is because land use affects the amount of nitrate available for leaching. Figure 2 shows concentrations of nitrate from monitoring wells near St. Cloud Minnesota .