More than 96 percent of the Earth's water is salty. People who need drinking water must desalinate saltwater or obtain freshwater from other sources, many of which lie beneath the ground. Layers of soil and bedrock might seem like solid protective barriers to groundwater, but there are at least five ways that critical groundwater supplies can be polluted.
In the mid 1980s, a community in New Jersey felt the effects of groundwater contamination when chloroform, arsenic and other dangerous substances made their way into the local aquifer.
While the ground and underlying rock may seem solid, soil and rock contain pores into which water from above the ground can seep. The word aquifer comes from two Greek words that mean "water" and "to bear." An aquifer forms when pores in underground rock and soil become connected so that water below ground can flow to springs and wells. This groundwater can be critical when it's the main source of drinking water for hundreds of thousands of people in a community.
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Human Waste Sources
As the U.S. Geological Survey notes, "anthropogenic contamination of ground water is usually the result of carelessness, ignorance or negligence." Failing septic tanks can not only slow the growth of algae, but they contaminate groundwater with viruses, bacteria and nitrates. Nature contributes a small amount to nitrate production; humans cause more underground nitrate pollution. Nitrate is the most common groundwater contaminant in the United States. Cesspools and privies may also contaminate groundwater because so many homes in the country have them.
Farming may supply the world with food but it can also contaminate the underground water supplies if containers that store livestock waste leak. When farmers apply too much chemical fertilizer or manure to the ground, groundwater contamination can occur. Regular homeowners who apply pesticides and chemicals to laws, plants and gardens can also help pollute underground water sources.
Thousands of landfills across the nation help communities manage their garbage. Recent laws require newer landfills to use clay and other methods to prevent leakage. However, older landfills that don't have this protection can contribute to significant groundwater pollution.
Storage Container Leaks
As you might expect, contaminants that are already underground can contribute to underground water problems. If underground storage tanks containing chemicals, oil, gasoline or other hazardous liquids corrode, liquids inside them leak into the ground and can get into the groundwater.
Blame it on the Cold
Another beneficial human activity that pollutes underground water is highway deicing. While salt lowers water's freezing point and makes it melt faster, cities can clear roadways using calcium chloride, magnesium chloride and other chemicals. After ice melts, runoff from roadways can carry these substances into surface and groundwater sources.