Groundwater Depletion

By Kenton Shepard

AQUIFERS

Aquifers are like huge underground lakes filled with permeable rock or loose material such as gravel and from which water can be pumped. Aquifers are charged (filled) by water seeping down through the earth from precipitation and from surface water such as streams, rivers and lakes. Aquifers can be gigantic. The High Plains Aquifer lies beneath eight states.

GROUNDWATER DEPLETION

Water in aquifers is called groundwater. Groundwater provides half of all drinking water in the US and almost all drinking water in rural areas. Over 50 billion gallons a day is pumped to the surface to support US agriculture.

When the rate at which water is pumped out of an aquifer exceeds the rate at which it re-charges, the aquifer will suffer from groundwater depletion. As the US population has grown, increased water demand has resulted in increased pumping rates of groundwater which in turn has increased groundwater depletion rates. Levels in aquifers across the US are dropping at an alarming rate and eventually, in some areas they may no longer be able to provide adequate water supply. The Ogallala Aquifer, which originally held 4 trillion tons of water, is now 50% depleted.

This US Dept. of Interior map shows areas which may suffer water supply crises by 2025

Water Quality

Aquifers may suffer water quality problems in several ways:

• Coastal aquifers experiencing excessive pumping rates may suffer salt water intrusion as salt water is drawn in to replace fresh water. Salt water intrusion is already a problem in New York, New Jersey, South Carolina, Georgia, Florida, Louisiana, S. California, Florida and others.
• Inland aquifers my suffer water quality problems when excessive pumping causes underlying saline water to rise and degrade water quality.
• Surface water drawn into an aquifer to replace water lost to excessive pumping may be of poorer quality, or of differing chemical composition. Because it’s chemically different, this water may cause a chemical reaction in the aquifer which activates naturally-occurring contaminants.

Water Well Problems

Lowered aquifer water levels has three effects on water wells.

• As water levels drop, the cost of pumping water increases, since water must travel further to reach the surface.
• Water levels may eventually drop below the intake of existing pumps, making additional drilling necessary, an added cost.
• Water levels may drop to the point at which a well may no longer yield enough water.

Reduced Surface Water Flow

 Streams, rivers and lakes are usually connected closely with an aquifer. Lowering water levels in aquifers may be reflected in reduced amounts of water flowing at the surface. This is now happening along the Atlantic Coastal Plain, especially in Massachusetts, Long Island and New York.

Subsidence

Subsidence (sub-SIGH-dens) is the lowering of land surface caused by changes which take place underground. In various places but especially in the Southwest and Florida, lowered water levels in aquifers due to excessive pumping are a major cause of subsidence. More than 80% of subsidence in the US is due to ground water depletion.

The following table lists approximate maximum subsidence amounts as of 1997 for selected locations in the Southwest:

Source: USGS

AGING WATER INFRASTRUCTURE

Practicing water conservation not only helps ease demand on shrinking aquifers, but it may help defray costs connected with maintaining and rebuilding our aging, deteriorating, national water infrastructure.

Our national water infrastructure consists of all those structures, systems and components required to supply the US with water every day. It includes vast numbers of groundwater wells, surface-water intakes, dams, reservoirs, storage tanks, drinking-water facilities, water treatment plants, pipes, and aqueducts. Some major structures are now over 100 years old.

About every two years, the American Society of Civil Engineers issues an accessment of U.S. infrastructure. Their grades for water infrastructure were...  Dams (D), Wastewater (D-) and Drinking Water (D-).

Nationwide, rehabilitation costs for water-related infrastructure for the next 20 years was estimated as follows...

Deficient and high-hazard dams...  $30 million.

Drinking water... $276 Billion (2000)

Wastewater... $390 Billion (2003)

Federal funding has not kept pace with deterioration or needs.

Photo Source

Pipes for public water supply

DRINKING WATER and ENERGY

Supplying consumers with drinking water requires using energy. Every phase through which water moves on its journey from its source to its final outflow as treated wastewater requires energy. Consider the following steps involved in supplying drinking water…

• Extraction from the source (groundwater, surface water, ocean, etc.)
• Pumping over long distances via aqueduct or pipeline, sometimes requiring pumping over mountain ranges.
• Treatment to remove contaminants, make adjustments for PH or corrosive properties and disinfection.
• Distribution to consumers
• Treatment and dispersal of wastewater.

Conserving water not only saves increasingly scarce and expensive water but also helps reduce the rate of increase of energy demand. The California Energy Commission (CEC) estimates that almost 20% of state water electricity demand and 30% of natural gas demand are associated with water.

SOURCES for MORE INFORMATION 

Conservation Technology Information Center- State by state environment contacts for water, soil and forests

• US Drought Monitor
• U.S. Geological Survey (USGS)- These pages are designed to provide useful information about ground-water resources of the U.S. and ground-water activities of the USGS.
• Rocky Mountain Institute (RMI) -  is an independent, entrepreneurial, nonprofit organization. We foster the efficient and restorative use of resources to make the world secure, just, prosperous, and life-sustaining. This link is to their water section.
• U.S. Govt. Atlas- A variety of water-based maps showing water bodies, dams, watersheds, aquifers, etc.
• Southwest Hydrology Magazine- Southwest Hydrology is written by and for consultants, regulators, researchers, water managers, lawyers, policymakers, and all the people in industry who work with water issues in semi-arid regions. Written for professionals but most articles will be understood by informed laymen. Free subscriptions.
• WaterSense - WaterSense is a voluntary partnership program sponsored by the U.S. Environmental Protection Agency. Its mission is to protect the future of our nation's water supply by promoting and enhancing the market for water-efficient products and services.
• WaterWiser- WaterWiser provides news, information, research results, discussion forums, references, calendar of events, searchable information databases, and other resources primarily targeted to water conservation professionals, but freely accessible to others in the water industry and the general public.
• Water is Life- Comprehensive website created by students from the University of Wisconsin. Covers a large number of water issues. Very informative site.
• Water Encyclopedia- Articles and information on water, listed alphabetically.