The southwest Wisconsin groundwater and geology study (SWIGG) was a cooperative effort between Grant, Iowa, and Lafayette county governments, with scientists from the U.S. Geological Survey, U.S. Department of Agriculture, Marshfield Clinic Research Institute, and WGNHS. Researchers tested water quality in hundreds of private water wells across the three counties. The report characterizes the types of contamination in those wells, describes sources of contamination, and identifies multiple factors that influence groundwater quality in this region. The age and depth of a well, the local geology, and the nearby land use all affect the probability that groundwater is contaminated.