Ground water problems:
Subsidence: Surface Sinks - caused by heavy pumping of groundwater from sediment or drought that lowers water table
Salt water contamination: coastal areas-salt groundwater pumped toward coastal wells
Sewage: septic tanks, inadequate and broken sewer lines, barnyard waste (bacteria, nitrate, and chemicals)
Harmful bacteria: filtered by sand (filtered out, destroyed by oxidation or eaten by other organism) not filtered by limestone, gravel and highly fractured rock
Septic tanks: Bacterial action within a septic tank helps to break down the solids in the waste water that enters the tank. The tank must be large enough and the rate of flow small enough, to ensure sufficient "residence time" of waste water in the tank. Waste water flows from the tank into a drain field.
Arsenic: Naturally occurs in some groundwater at levels that are toxic. 53rd most abundant element in the earth's crust. Other sources are insecticides, herbicides, fungicides, glass and ceramics, folk remedies, metal alloys, and leathering tanning, paint pigments, fertilizers, semiconductors, light emitting diodes, and animal feed
About 140 million people worldwide drink groundwater containing unsafe levels of arsenic. Chronic exposure to this tasteless, odorless poison leads to health effects such as skin lesions and cacer. Issue in 1971 in Bangladesh. Origin from arsenic sulfides washed from ore bodies in the Himalayas and becoming part of the delta sediment submerged in the reducing groundwater. Intensive irrigation dropped the water tables bringing the sulfides into contact with oxygen. Oxidized water seeping through the sediment dissolved the arsenic that seeped into the tubes wells of Bangladesh.
Lead: natural abundance in groundwater and surface water is usually low. Thirty sixth most abundant element in the earth's crust. Lead has no known beneficial function in humans, but have many harmful health effects.
Drinking water in 1992 contained lead in 819 public water systems. Sources are batteries, radiation shielding, ammunition, glass and ceramics, and casting metals. Lead pollution in drinking water is caused by humans.