The results also are evaluated with respect to overlying land use and land cover. Furthermore, samples from wells located in areas of high contamination susceptibility had pesticide detection frequencies and nitrate concentrations that correlated to overlying land use and land cover. Samples from wells located in high susceptibility areas that were surrounded by cropland had greater pesticide detection frequencies and greater nitrate concentrations than wells located in similar susceptibility areas but surrounded by different land use and land cover types such as forest, urban, and wetlands.
Ground water exists in pores between particles in subsurface sediment or rock units.
Surficial sand and gravel aquifers provide much of the drinking water for the Upper Mississippi River Basin study unit. These aquifers are relatively shallow and easily accessible. The evaluation presented by this Fact Sheet is based on data for wells completed in surficial unconfined sand and gravel aquifers. The models were designed to access the ease with which the infiltration of contaminants could occur between the land surface and the water tables. The susceptibility models may help agencies develop suitable plans and coordinate regulatory and monitoring efforts to aid in maintaining clean water supplies.