How do ADWs threaten groundwater quality?
Water from runoff or from drainage tile may contain nutrients, sediment, organic debris, pesticides, and bacteria. When this drainage water slowly seeps through a fine- or medium-textured, deep soil to the groundwater, it is somewhat purified by physical, chemical, and biological processes that absorb or break down many contaminants. Drainage water that flows into an ADW does not pass through much (if any) soil and it can carry contaminants deep into the ground. Drainage water can then make the groundwater unfit for human consumption. Nitrate, pesticides, and bacteria are the major contaminants that are of concern. Once the groundwater is contaminated, cleanup is usually difficult or practically impossible.
