As part of the program, investigations will be conducted in more than 50 of the Nation's largest river basins and aquifers, known as Study Units , to provide a framework for national and regional water-quality assessment. Together, these areas account for 60 to 70 percent of the Nation's water use and population served by public water supplies, and cover about one-half of the land area of the Nation. Approximately 20 percent of the irrigated land in the United States is in the High Plains and about 30 percent of the ground water used for irrigation in the U.S. is pumped from the High Plains aquifer. Irrigation withdrawals in 1990 were greater than 14 billion gallons per day . In 1990, 2.2 million people were supplied by ground water from the High Plains aquifer with total public-supply withdrawals of 332 million gallons per day .
Nutrient data are available, to a varying degree, across the aquifer.
Beginning in 1999 and continuing for a period of 6 years, the High Plains Regional Ground Water Study will intensively investigate the quality of ground-water resources within the study area.