By Hydrosimulatics INC  

Human Influences on Groundwater Availability

Prior to a recent knowledge about groundwater resources, it was commonly thought that groundwater was so isolated from the land surface that it was unaffected by human activities.  As a more complete scientific understanding of groundwater developed, it became clear that large-scale agricultural practices and expanded urban centers created groundwater issues.  If more people had known some basic facts about groundwater in the 1930’s through the 1960’s, many of the legacy water contamination and water depletion issues could have been avoided.

 


Figure 1 – Estimated water use in the United States 2015.  (Source: US Geological Survey, Circular 1441, 2018; Figure 15; https://pubs.usgs.gov/circ/1441/circ1441.pdf, accessed 2/27/20)

 

Groundwater Withdrawal for Human Use

Total water use in the United States almost doubled between 1950 and 1980 when it peaked and has tapered off measurably between 2005 and 2015 (Figure 1).  Groundwater withdrawals were less than surface water but mirrored the increase in use until 1980 at which time the amount of groundwater withdrawn remained nearly constant.  Because groundwater now represents a larger percentage of total water used, we are now more dependent on it than ever before.  The reliance on groundwater for human use has placed new stresses on the groundwater system and has caused water levels to drop where pumping has increased.

 

Point and Nonpoint Sources of Contaminants

The more groundwater withdrawn also increases the likelihood of contaminants entering aquifers which can be contaminated by point sources and nonpoint sources.  Examples of point sources include leakage from gasoline storage tanks and seepage from landfills. Nonpoint sources of contaminants cover larger areas and, usually, at lower concentrations than point sources.  For example, agricultural fields, in aggregate, represent large areas through which fertilizers and pesticides can move into the groundwater system.

 

Agricultural Development

Irrigation

Between 1900 and World War II, groundwater was not a major source for irrigation and the pumps to lift groundwater from depth had not been invented (Figure 2).  After World War II, the more common use of submersible pumps allowed water to be efficiently extracted from deeper wells which paved the way to use groundwater for irrigation more economically especially with the center-pivot water systems that came into use in the 1950’s when the midwestern U.S. was undergoing a period of extensive drought.  This new technology was part of the trend toward larger, more mechanized farms.  It also allowed many more private wells to be drilled for domestic water use.  As a result, groundwater withdrawals rose from 34,000 million gallons per day (mgal/d) in 1950 to 83,000 mgal/d in 1975.  Withdrawals have remained at about this rate ever since.  Worldwide, the trend of groundwater use has generally tracked the usage trends in the U.S. although at generally lower volumes.