Groundwater Depletion and Decline Caused by Sustained Pumping
A brief history of water pumping
2000 BC: The Egyptians invent the Shadoof (a seesaw-like device) to raise water from a river by using a long, suspended rod with a bucket on one end and a weight on the other. It was operated by one person (by lifting water from the river) and one could irrigate about an acre of agriculture. Depictions of the Shadoof can be seen in ancient hieroglyphics.
200 BC: The Archimedean Screw Pump (designed by Archimedes) is considered one of the greatest inventions of all time. In fact, Archimedes used his design to pump bilge water from a ship owned by one of his associates. Its most valuable application was for irrigating large areas of agriculture along the Nile River. The screw pump is still used today for pumping liquids and granulated solids. In third-world countries, it is the preferred method to irrigate crops without electric motors. Archimedes’ Screw Pump design is in use in our modern era and can be seen in some wastewater treatment plants, where screws as large eight feet (2.43 meters) in diameter and can lift as much as 20,000 gallons (75,708.23 liters ) per minute.
Today: The modern, multi-stage centrifugal pump used to lift groundwater from hundreds of feet beneath the surface are based on the Archimedes Screw. The difference between the two is the way each stage feeds the other, which compounds the pressure thereby creating the ability to pump from deep groundwater sources.
A recent statement from the United States Geological Survey raises concerns about this valuable resource both in the US and throughout the world. Groundwater depletion is defined as long-term water level declines caused by sustained groundwater pumping. Sustained pumping has created severe depletion of groundwater in many areas of the US, which may be likened to an ‘overdraft of the groundwater bank account.’ The USGS attributes negative effects of groundwater pumping to include (but are not limited to):
• Increased pumping costs. When groundwater levels drop, the water must be lifted farther to reach the surface for use. More energy is required to drive the pump, which increases the users’ costs, sometimes making the source prohibitively expensive to maintain and operate.
• Deterioration of water quality. Very deep groundwater and water beneath the oceans is saline. Where natural conditions are stable, the boundary between fresh water and saline water remain unchanged. Sustained pumping, however, can cause salt-water intrusion into the inland fresh-water sources and upward, resulting in salt-water contamination of the fresh-water supply.
• Drying up of wells. Estimated groundwater depletion in the US between 1900-2008 totaled approximately 239.91 mi3/1,000 cubic kilometers (km3).(A cubic mile of water equals approximately 1,101,117,147,352 gallons; a cubic kilometer of water is approximately 264,172,052,358 gallons. To give you an idea of how much water that is in US gallons, one cubic mile of water is equal to the amount of water that flows over Niagara Falls in one month.) Since 1950, groundwater depletion rates have increased markedly, with maximum rates occurring during the period between 2000-2008, when depletion averaged nearly six mi3/ 25 km3 per year, compared to 2.21 mi3/9.2 km3 per year averaged over the 1900-2008 time frame.
• Water reduction in lakes and streams. A significant percentage of water flowing in rivers is contributed by seepage of groundwater into a stream bed. Sustained pumping of groundwater can alter the way water moves between an aquifer and a stream, lake or wetland, either by intercepting groundwater flow that discharges into surface water under natural conditions or by the increased rate of water movement from the surface water into an aquifer. Sustained groundwater pumping will also yield a negative effect, whereby the lowering of groundwater levels below the depth of the stream bed or wetland results in a loss of vegetation and wildlife habitat.
• Land subsidence. When water is taken out of the soil, the soil collapses, compacts and drops because of the loss of saturated thickness. Land subsidence is most often the result of the removal of subsurface water by human activities. Case in point, the west-central Florida area of Tampa-St. Petersburg has experienced saltwater intrusion. Because of the extensive groundwater development in the area, sinkholes have appeared, which subsequently led to Tampa constructing a seawater desalination plant for municipal water supply.
A national problem
As stated earlier, many areas of the US are experiencing groundwater depletion. In the Pacific Northwest, Oregon and Washington states’ industrial use has caused groundwater level declines in the Columbia River Basalt Aquifer of more than 100 feet (30.48 meters) in several areas. In the High Plains, the Ogallala Aquifer underlies parts of eight states and has been intensively developed for irrigation of agriculture. Water levels have dropped more than 100 feet in some areas and the saturated thickness has been reduced in other areas by more than half.
The Desert Southwest has seen increased groundwater pumping to support population growth in the south-central Arizona Phoenix and Tucson areas. This has resulted in groundwater level declines of between 300 and 500 feet (91.44 and 152.4 meters) in much of the area. Land subsidence of as much as 12.5 feet (3.81 meters) has been recorded since 1940 and the lower water table has resulted in the loss of stream-side vegetation. Perennial streams, springs and wetlands in the southwestern United States are highly valued as a source of water for humans, plants and animals they support. Development of groundwater resources since the late 1800s has resulted in the elimination or alteration of many perennial streams, wetlands and associated ecosystems. The Santa Cruz River south of Tucson was a lush area with stands of mesquite and cottonwood trees along the river as late as the mid-1960s. By 1989, the trees had largely disappeared and the groundwater table declined more than 100 feet, which appears to be the principal reason for the decrease in vegetation and loss of wildlife habitat.
The Atlantic coastal plain has seen saline-water intrusion because of sustained groundwater pumping for domestic supply. Nassau and Suffolk counties’ (Long Island, NY) water tables have lowered to such an extent that the base flow of streams has been significantly reduced or eliminated. Many other Atlantic Coast locations are experiencing similar effects from groundwater depletion. Areas affected include the Ipswich River Basin, MA; in coastal counties in New Jersey; Hilton Head Island, SC; Brunswick and Savannah, GA and Jacksonville and Miami, FL.
In the Gulf Coast Plain, several areas are experiencing the effects of groundwater depletion. Baton Rouge, LA groundwater levels have dropped by approximately 200 feet (60.96 meters). In the Houston, TX area, groundwater levels have dropped by as much as 400 feet (121.92 meters), resulting in land subsidence of up to 10 feet (3.04 meters). Arkansas, Louisiana, Mississippi and Tennessee municipal water utilities obtain their water from the Sparta Aquifer, which has seen significant water level declines. The Memphis, TN area is one of the largest metropolitan areas in the world and relies completely on groundwater for municipal supply, which has caused groundwater level declines up to 70 feet (21.33 meters).
The Chicago-Milwaukee areas on Lake Michigan have been using the Great Lakes Watershed groundwater since around 1864 as their sole source of drinking water for 8.2 million people. This sustained groundwater pumping has lowered groundwater levels as much as 900 feet (274.32 meters) in some areas.
One can ascertain from the details presented herein that we as a nation have seriously overdrawn our groundwater bank account. While there are groundwater replenishment programs that have been instituted in the past decade, we still have a tremendous thirst for a resource we have taken for granted far too long. Water-saving plumbing fixtures, water rationing, rain catchment, water reuse and the like are cultural shifts we have made and are continuing to advance in this new century. We must all do our part in conserving this precious resource in view of other areas of the world that have run out of fresh-water sources and are faced with exorbitant costs for constructing purveyance systems to provide drinking and working water for their homes, businesses and agricultural needs. We here in the United States of America do not want to join a fraternity of countries that ignored the depletion of their water resources for too long and are now faced with paying the price. We owe it to our children to leave them with the same conveniences we enjoyed in years gone by.
As an industry, we can be very proud of the steps equipment and media manufacturers have taken to improve the efficiency of water-treatment products. Water use has been reduced by as much as 90 percent. Gone are the days when a residential softener used from 80 to 120 gallons (302.83 to 454.24 liters) of water to regenerate. Now there are certified products that can regenerate one cubic foot of softening resin with one pound (5.44 kilos) of salt and recover more than 5,000 grains capacity using only 12 gallons (45.4 liters) of water. Reverse osmosis products now recover up to 75 percent of the feed water compared to the 18-percent recovery that was typical in the early years of the residential technology. It is no exaggeration to say we are doing our part to reduce the excessive demand for water considering the problems we have created as a society.
About the author
Gary Battenberg is a Technical Support and Systems Design Specialist with the Fluid System Connectors Division of Parker Hannifin Corporation in Otsego, MI. He has 37 years of experience in the fields of domestic, commercial, industrial, high-purity and sterile water treatment processes. Battenberg has worked in the areas of sales, service, design and manufacturing of water treatment systems and processes utilizing filtration, ion exchange, UV sterilization, reverse osmosis and ozone technologies. He may be reached by phone at (269) 692-6632 or by email, firstname.lastname@example.org