How Is the Ground Water Table Depleted?

Groundwater provides drinking water for half the U.S. population and is vital for survival. It originates from aquifers, which are deep underground lakes or rivers that are “recharged” (replenished) by rainwater infiltration and water seeping down from surface storage, rivers, lakes and streams. “Depletion” means a long-term decline in the level of available groundwater. Pumping water from the aquifer at a faster rate than it can be restored is the main cause of depletion.

Needs of an Increasing Population

• Reduction of surface water has negative impacts on fish and wildlife.

  Sustained pumping is depleting groundwater in many areas of the country where there has been significant population and economic growth. Houston, Texas, has experienced a water level decline of approximately 400 feet, causing significant land surface “subsidence” (surface settling or sinking, related to groundwater removal). Like Houston, the desert Southwest has experienced increased growth and a fall in the water level of 300 to 500 feet, with as much as 12.5 feet of subsidence. Artesian wells and springs in Las Vegas, Nevada, have dried up; water levels have fallen as the population grew.

Increased Irrigation

• Lakes dry up when groundwater is seriously depleted.

  As population grows, agricultural needs increase. Water is necessary for raising food crops, and more is necessary in arid regions. Idaho’s Snake River Plain aquifer has been used for extensive agricultural irrigation, and water levels have dropped significantly. The Columbia River Basalt aquifer of Oregon and Washington has seen water level declines of 100 feet. Basins in Utah, New Mexico, Southern California and Nevada have seen substantial declines in groundwater levels.

Increased Industrial Use

• Groundwater is the source of more than half of U.S. drinking water.

  Every manufactured product uses water during some part of its production process. Producers of wood and paper products, chemicals, gasoline, metals and oil are major water users. Water is necessary in fabricating, washing, processing, cooling, diluting, transporting products, sanitation and incorporation into products.

Subsidence and Deterioration of Water Quality

• Increased populations lead to increased water demand.

  Removal of too much surface water causes subsidence where the earth’s surface sinks, collapses and compacts. Sinkholes form where underground channels or caverns cave in, creating a crater. This has happened in Florida and the Gulf Coastal Plain, where surface water depletion from area lakes is occurring. The natural boundary between freshwater and saltwater is disrupted by extensive pumping, which draws in saltwater and contaminates the water supply. Depleted inland aquifers experience similar problems, drawing underlying saline water upward. Contaminants can be pulled into the aquifer wherever groundwater is depleted.

Reduced Surface Water Flows

• Water quality deteriorates with a falling groundwater table.

  Surface water is linked to groundwater and aquifers. Pumping alters water movement between the surface and aquifers, disrupting natural flow. This interferes with groundwater levels as well as surface water, causing destruction of wetlands, riparian vegetation and wildlife habitat.

Declining Well Production, Failed Wells

• As the groundwater level declines, wells must be deeper and require more power to raise water to the surface, which increases pump costs and energy usage. As wells fail, new ones must be drilled; eventually, wells are no longer economically feasible. This has a significant impact on rural areas, where wells are the main water source.