Groundwater will normally look clear and clean because the ground naturally filters out particulate matter. But, natural and human-induced chemicals can be found in groundwater. As groundwater flows through the ground, metals such as iron and manganese are dissolved and may later be found in high concentrations in the water. Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality. Contaminants can be human-induced, as from leaking fuel tanks or toxic chemical spills. Pesticides and fertilizers applied to lawns and crops can accumulate and migrate to the water table. Leakage from septic tanks and/or waste-disposal sites also can introduce bacteria to the water, and pesticides and fertilizers that seep into farmed soil can eventually end up in water drawn from a well. Or, a well might have been placed in land that was once used for something like a garbage or chemical dump site. In any case, if you use your own well to supply drinking water to your home, it is wise to have your well water tested for contaminates. Some of the major sources of groundwater pollution include storage vessels and reservoirs of petroleum products, storage vessels or chemicals, septic systems, hazardous waste sites, landfills, agricultural fields with high amounts of unabsorbed fertilizers, pesticides, and other chemicals. Saline Ingress following over drafting of aquifers or natural leaching from naturally occurring deposits are natural sources of groundwater pollution. Leaching of minerals like arsenic and fluoride from their crystal lattice due to geological disturbance causes heavy groundwater contamination. While concern over groundwater contamination has focused on pollution associated with human activities, in many cases, groundwater contamination is related to private sewage disposal systems, land disposal of solid waste, municipal wastewater, wastewater impoundments, land spreading of sludge, brine disposal from the petroleum industry, mine wastes, deep-well disposal of liquid wastes, animal feedlot wastes, and radioactive wastes. Interactions between groundwater and surface water are complex. Consequently, groundwater pollution, sometimes referred to as groundwater contamination, is not as easily classified as surface water pollution. By its very nature, groundwater aquifer are susceptible to contamination from sources that may not directly affect surface water bodies. A spill or ongoing release of chemical or radionuclide contaminants into soil can contaminate the aquifer below, defined as a toxin plume.