National Water-Quality Assessment (NAWQA) Program
A total of 39 monitoring wells in two well networks were sampled in the glacial deposits aquifer in central Wisconsin in 1994 (Peters and others, 1998) and 2002-2004 (Saad, 2008). Concentrations of nitrate in groundwater have increased over time; concentrations of atrazine plus DEA increased and then decreased. Concentrations of nitrate and atrazine plus DEA were significantly correlated to historical fertilizer and atrazine use patterns over time. In addition to being correlated to agricultural chemical use, concentrations of nitrate were positively correlated to dissolved oxygen concentrations in the groundwater and screen depth below water level. Concentrations of atrazine plus DEA were positively correlated to annual precipitation.
Location of the Glacial Deposits in Wisconsin (WMIC) study area (from Saad, 2008).
Expected future changes of groundwater quality in the study areas, as well as similar settings, should reflect recent and future changes in agricultural chemical use. For shallow wells producing young water, concentrations of nitrate and atrazine plus DEA should remain relatively stable if fertilizer and atrazine use remains stable. Concentrations of atrazine plus DEA from shallow wells producing water that originated within areas where atrazine use was prohibited should be decreasing in the future. Concentrations of nitrate and atrazine plus DEA in deeper wells effected by agriculture (producing old water) should continue to increase for up to several decades (Saad, 2008).