There are many sources of contamination of groundwater, among the most common are:

• Naturally occurring minerals, nutrients, and metals (i.e., arsenic, lead, barium, fluoride)
  
• Local land use practices (fertilizers, pesticides, livestock, animal feeding operations, and biosolids application)
  
• Manufacturing processes
  
• Sewer overflows
  
• Malfunctioning wastewater treatment systems (for example, nearby septic systems)