Thursday, August 20, 2009

The Diminishing of Groundwater Aquifers

On earth, groundwater is ubiquitous and like all water on earth it comes from precipitation that percolates through the soil until it reaches the zone of saturation. Though groundwater is everywhere the quantity and usability of groundwater varies from location to location based on geology and precipitation. The rate at which precipitation percolates through the soil to resupply the groundwater is called the recharge rate and also varies for site to site. Groundwater is water that fills the cracks and pores of rocks and sediments that lie beneath the surface of the earth saturating those materials. Gravel, sand, sandstone, or fractured rock have large connected spaces that allows water to flow through them allowing an aquifer to form. Impervious layers of clay and bedrock prevent ground water moving from one space to another. Rain and snow pass through the soils, rocks and sediments to constantly make more ground water. In order for the water supply to be sustainable, groundwater cannot be withdrawn faster than it is resupplied.

Due to its protected location underground, most groundwater is naturally clean and free from pollution. Not understanding the nature of groundwater and the important role it plays in sustaining life, we have over used it and abused it. In the past when we buried fuel tanks, industrial and household waste at landfills, poured solvents out into the dirt, used excessive amounts of fertilizer, had uncontrolled waste from animal feedlots we were contributing to the contamination of groundwater. Homeowner disposal of chemicals, treating a home for termites, excessive use of fertilizers (even organic), and malfunctioning septic systems can all impact onsite groundwater quality and potentially down gradient sites.

In addition to contamination we can damage groundwater supplies by pumping groundwater beyond its recharge rate literally using up this valuable resource. Fresh, potable, uncontaminated water is not unlimited. According to the Stockholm International Water Institute, about a fifth of water used globally is groundwater and that portion is growing. California has for several generations been a leader in water management, moving water from where the rain and snow falls to where the water is needed in what was hoped to be a reliable and sustainable way. Water banking is used within the state to reallocate water from lower use areas to recharge the aquifer in high demand areas. Through tight management techniques, California was until recently able to supply the state with water in a sustainable way. Periodic droughts have historically plagued the system, now though, less than average rainfall for more than one year seems to be all it takes to upset the cart.

Recent advances have made it possible to measure groundwater supplies using satellites. The orbiting satellites measure the gravitational pull of water below the earth’s surface and now are able to confirm that the groundwater level is falling in areas of India. Over the years the water table has fallen in California. While irrigation has allowed the world’s farmers to produce vastly increased amounts of wheat, rice and other staples. The demands of mankind for water to sustain life and to produce food have continued to grow with growing population. Internationally, both groundwater and surface water supplies are strained. In India the monsoon rains have been the weakest in five years and that is exacerbating demand for groundwater based irrigation. The India’s Central Ground Water Authority regulates the pumping from aquifers. Unsustainable pumping in some areas has resulted in a drop in the water table and sea water intrusion. Groundwater aquifers cross international borders and water rights and potable water supplies will become the crisis of the twenty first century.

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