Have you ever wondered why one of your wells has consistent problems with nitrates, E. coli, or other contaminants, while another one has a different set of problems or is totally fine? The answer may be in the ground under your feet. The geology and aquifer characteristics of your area affect how vulnerable a well is to contamination and influence the kinds of contamination most likely to affect your well. A well in an aquifer that's mostly sand will behave very differently than a well drilled in an area with a lot of sinkholes. An aquifer that's nothing but sand from close to the surface all the way to the bottom will behave differently than an aquifer with a layer of clay between the sand and the surface. And the differences go on. To explore exactly how this works, the USGS studied four public supply wells, each from a distinct area of the country with a unique aquifer structure. Their findings on the kinds of contamination that affected these wells can be found in these four factsheets as well as in the 12-and-a-half minute video below: Now that you have some idea of the kinds of contamination that may be affecting your well, you might have new ideas for protecting your well as well. Check out the USEPA's sourcewater protection resources for more information on developing or improving a groundwater protection plan for your utility. If you'd like to provide local private well owners with similar information on their own wells, you might want to check out our education materials for well owners at The Private Well Class .