Factors Affecting Nitrate Concentrations in Ground Water in Stafford County, Kansas

Nitrate contamination of the Great Bend Prairie aquifer in south-central Kansas is more pronounced at shallower than at deeper portions of the aquifer. Factors influencing the occurrence of nitrate in the shallow ground water include irrigation-well density, subsurface clay lenses, and land-use practices. Ground-water samples were taken from 42 wells, including deep (irrigation) wells and shallow (domestic and stock) wells. Except for one well with an anomalously high concentration due to a point source, nitrate-N concentrations of sampled wells ranged from 1.3 to 13.3 mg/L with a mean of 5.4 mg/L and a median of 4.7 mg/L. Statistical analyses indicate that shallow ground water is more susceptible to contamination than deeper ground water and that lower nitrate-N concentrations are probable in wells with a greater thickness of clay above the well screen. Irrigation-well density showed a statistically significant positive correlation with nitrate-N concentrations of shallow wells. No significant difference in nitrate-N concentrations was found to result from the two irrigation methods (flood versus center-pivot) used in the area. Nor were there significant differences in nitrate-N concentrations between sandy and loamy soils. Land-use practices and subsurface stratigraphy may be better indicators of potential nitrate contamination than the surface soils