A study conducted by the National Water Quality Assessment program for the USGS sampled over 2100 wells across the nation. The samples were analyzed for up to 219 different properties (pH, pesticiedes, trace elements, radon, ions, nutrients, pesticides, bacteria etc). The data was plotted on a map of the US along with the different lithologies of the aquifers in which the wells were situated. Each plot was plotted as either red or white, red indicates that it has too high of certain concentration for human health, and white means that it is substantial. The study helped understand the water quality of some of the major aquifers that are tapped by domestic supply wells. If you click on the map, you can then keep clicking on the next figure tab above the map so that each level of certain contaminants can be viewed individually for each well.