Recharge from precipitation enters closed depressions in the unconsolidated deposits and is unable to percolate downward into the bedrock. The problem is intensified where the land is cultivated because plowing not only eliminates grasses and other natural vegetation that might transpire some of the precipitation, but loosens the soil and thus allows the precipitation to infiltrate rapidly into the unconsolidated deposits. Locally, concentrations of fluoride greater than those recommended for drinking water by the U.S. Environmental Protection Agency are in water from some aquifers in Segment 8. Large fluoride concentrations have been reported in ground water in eastern North Dakota and South Dakota. Excessive concentrations of fluoride can cause mottling of tooth enamel in children.
Human activities can degrade the quality of ground water.
This type of contamination is possible only where the hydraulic head in the shallower aquifers is less than that in the aquifer that contains saline water. The mineralized ground water can move into wells or surface streams and ponds. Large concentrations of sulfate, iron and other metals, or radionuclides can result from the leaching of mine tailings. Other human activities that affect the quality of ground water include application of fertilizer and pesticides to cultivated land, disposal of human wastes in septic tanks, cesspools, or waste-treatment plants, disposal of liquid and solid wastes in landfills, storage of petroleum or other liquids in leaky underground tanks, and disposal of oil and gas production water or liquid industrial wastes by injection wells. Declining water levels are a problem locally in unconfined and confined aquifers in all four States of Segment 8.