OWLS™ Water Education: What is Groundwater?
OWLS™ STEM Education Research Resources are for students of all ages and for assisting teachers and parents in the education of our children on the importance of clean healthy drinking water. The research material posted below is for educational purposes only. LTW™ endorses the following as OWLS™ STEM Educational Research Resources.
GroundWater Education courtesy of
Mother Nature Network.
Groundwater is simply water — mainly from rain and snow, but also from some human activities — that has soaked into the soil. That’s the end of its journey from our perspective, but the water keeps going long after it’s gone underground. It percolates downward, with dirt and rock particles filtering out dangerous bacteria as it sinks. When it finally reaches an impermeable layer of bedrock deep below the surface, it stops and begins to saturate the surrounding soil. Over many millennia, this pool of purified groundwater can grow into vast subterranean aquifers.
Some groundwater may eventually become encased in rock thanks to gradual geologic shifting, forming pressurized pockets known as “confined aquifers.” These require complex drilling and pumping operations to extract their contents, leaving such deep deposits mainly for industrial uses such as large-scale farm irrigation. Other groundwater deposits are limited only by water supply and the bedrock below, and these “unconfined aquifers” make up the majority of residential groundwater sources in the United States.
The Earth’s crust is so waterlogged that fresh groundwater alone — not counting salty groundwater, which is even more abundant — outweighs all aboveground liquid freshwater 100 to 1. Much of it’s too deep or blocked by rocks for us to economically reach, but we can still get to the roughly 1 million cubic miles closest to the surface.
In fact, some aquifers have been so heavily pumped that their water level has dropped too low for people to tap. Humans have overexploited many aquifers around the world, often trying to prop up an agriculture industry with a dwindling source of water.
Groundwater’s quantity is far from the only concern, however; its quality is also under constant assault from a variety of sources. Natural poisoning of groundwater has long been known to occur around the world, as underground deposits of arsenic, heavy metals or even radon can seep into an aquifer and contaminate its contents. It’s also possible that toxin-producing bacteria can naturally infiltrate an aquifer, despite the cleansing effects of soil and rocks above.
But humans indirectly pose an even greater threat to many aquifers — and to the fellow humans who drink from them. Although more Americans get their drinking water from surface sources like lakes and rivers, there are more water systems nationwide that use groundwater as their source than surface water (about 147,000 to 14,500), and hundreds of thousands more people who use private wells. And just as these wells are scattered throughout the country, often in remote rural areas, so are the diverse sources of pollutants that contaminate them.
Runoff in general is a daunting enemy. Whenever it rains — or when a large amount of snow or ice melts — an inconspicuous yet widespread flood of water picks up any loose liquids it passes along the way, including lawn chemicals, cleaning solvents and gasoline, and washes them through the watershed.
Some of this is dumped into streams and rivers, where it’s concentrated and carried far away. That’s how farm and lawn runoff has helped create hundreds of coastal “dead zones” around the world, or areas where a buildup of fertilizer feeds giant algae blooms that deplete the water’s oxygen, making it inhospitable to marine life. Major U.S. dead zones in the Gulf of Mexico and Chesapeake Bay are widely blamed on farm runoff, since their tributaries pass through many large agricultural areas.
Cities’ and suburbs’ stormwater is also a major source of trouble, often containing motor oil, gasoline, weed killers, insecticides, bleach, paint thinner, and any other substances dumped or left out in the open. Cleaning solvents such as dry cleaners’ perchloroethylene (a potential carcinogen) can be caught up in runoff, as can parabens and other suspected endocrine disruptors often found in laundry soap and shampoo — chemicals that seem to be turning male frogs and fish into females.
In urban places where impermeable surfaces like concrete or asphalt cover the ground, more of this runoff flows for longer distances, picking up more toxins on the way. And while much of it ends up in sewers and streams, plenty of runoff is also soaked up by soil, where it sinks downward and replenishes aquifers.
This can happen around big farms and animal-feeding operations, where fertilizers, pesticides, and manure often exist in large concentrations. When farm runoff drifts down into the ground, it can sometimes overload the soil’s filtration system and taint groundwater below. Some of the most dangerous agricultural pollutants include:Fertilizers: In estuaries and coastal waters, fertilizers often create algae blooms and dead zones. In groundwater, they can lead to the buildup of nitrates, which are carcinogenic. They can also impede infants’ ability to transport oxygen in their blood, leading to “blue baby syndrome.”