When considering a building site, there are three options commercial and residential sites may consider to meet their water demands. For those in urban and suburban locations, the choice is often made for them- they are automatically tied into the municipal water supply. Those who are “off grid” can opt to collect rain in cisterns or water storage tanks for later use, or water can be pumped up from a well or nearby water source. But not every location can provide a well. So how and where is water stored underground?
Aquifers: What and Where Are They?
Aquifers are underground soil and rock formations capable of storing water. In other words, an aquifer is an underground repository of water. They can be composed of sand, gravel, and fractured rock formations- all of which are porous, permeable, and allow water to be stored. Some dense and less porous rock formations are also capable of storing water in their cracks and fissures.
Notable aquifers in the United States:
- Ogallala Aquifer: covers portions of eight states; is a massive 450,000 square kilometer underground reservoir; supplies close to 30% of the water used for irrigation in the United States
- Edwards Aquifer: an artesian aquifer located on the eastern edge of the Edwards Plateau in Texas; provides drinking water for 2 million people
- Floridian Aquifer: one of the most productive artesian aquifers in the world; covers more than 100,000 square miles; lies beneath the entirety of Florida, as well as coastal parts of Georgia, Alabama, and South Carolina
Illustration 1: Spread of Ogallala aquifer
Recharge and Discharge
Rain that falls on open land will seep through layers of soil and eventually replenish the aquifer, but various factors may slow down the rate of recharge.
Among the factors that impede the recharge of aquifers:
- Evaporation of water from the top surface before it trickles down to the aquifer
- Clay like layers which are impermeable and obstruct the downward movement of water
- Land development leading to increased runoff and thereby reducing soil moisture retention
Discharge of water from the aquifer happens through pumping, often to meet the needs of the human population. When we drill a well, it may eventually cut through a fractured rock and yield water which can be pumped out.
Ilustration 2: Farmer and his Open well
Ground Water Imbalance and Consequences
Unfortunately, discharge more often than not outpaces recharge by a huge margin and this is taking a significant toll on the sustainability of these aquifers. This statement applies to aquifers globally.
Wells going dry is a classic indicator of the deteriorating health of the aquifers. In many places that have historically depended on wells for water, what they are pumping out now actually went into the aquifer thousands of years ago. This act is known as mining of fossil water.
The falling water levels have a variety of repercussions. As we extract water deeper from the ground, the energy required to do so is significantly higher. Hence energy bills are rising and older, shallower wells keep failing forcing the land owner to invest in a new well which is hundreds of feet deep. In places like Bangalore, India, well depths go as deep as 1,500 feet with no certainty of hitting water. One of the few similarities between Bangalore and California (apart from being a hotbed of startup ecosystem) is the falling water levels and the harsh fact that some home owners must depend on tanker trucks to deliver water to their homes.
Farming communities that depend on ground water to meet their irrigation needs are affected the worst by decreasing water levels. According to India’s National Crime Records Bureau, an average of 10 farmers have killed themselves every day over the last 3 years. The reason – failing wells, low rainfall, crop failures, and inability to pay mounting debts.
How Much Depletion Are We Talking About?
Since this depletion happens out of our sight, it adds to the delayed realization of the enormity of the problem at hand. Satellite imagery is now being used to map changes related to aquifers and the latest data reveal that ground water depletion is a global phenomenon accelerating at a rapid pace. An exercise in quantifying the magnitude of depletion of aquifers in the United States tells a grim story. Since the beginning of the 20th century, it is estimated that the aquifers in the US have lost more than 1,000 cubic kilometers of water – which is equivalent to 28 times the capacity of Lake Mead, which is the country’s largest reservoir.
Intrusion Alert
In addition to depleting water levels, another challenge for aquifers is the intrusion of salt water (mostly in coastal areas) and biological and chemical contaminants (due to faulty waste water discharge practices). Contamination from one overland point source can irreversibly damage the whole aquifer.
On That Note…
Well water has often been a go to method for supplying a building with water when the city couldn’t. Given the state of ground water supplies globally, the inclusion of rain harvesting and water conservation measures in both on and off grid sites is both practical and eco-friendly. In this way, we can all do our part to make what water is left go a long way.
References:
- https://en.wikipedia.org/wiki/Aquifers_in_the_United_States
- http://www.livescience.com/39625-aquifers.html
- http://www.scientificamerican.com/article/the-ogallala-aquifer/
- http://www.desertsun.com/story/news/environment/2015/12/10/pumped-beyond-limits-many-us-aquifers-decline/76570380/
- https://en.wikipedia.org/wiki/Edwards_Aquifer
- https://en.wikipedia.org/wiki/Floridan_aquifer