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USGS analysis examined concentrations of chloride, dissolved solids and nitrate in groundwater
There was no change in concentrations of chloride, dissolved solids or nitrate in groundwater for more than 50% of well networks sampled in a new analysis by the U.S. Geological Survey (USGS) that compared samples from 1988 to 2000 to samples from 2001 to 2010. For those networks that did have a change, seven times more networks saw increases as opposed to decreases.
The analysis was done by the USGS National Water Quality Assessment Program to determine if concentrations of these constituents have increased or decreased significantly from the 1990s to the early 2000s nationwide.
Though chloride, nitrate and dissolved solids occur naturally in the environment, human activities can cause concentrations to exceed levels that would be found naturally. At high concentrations, these chemicals can have adverse effects on human and environmental health.
High levels of chloride and dissolved solids in water do not present a risk to human health, but are considered nuisance chemicals that can cause the water to become unusable without treatment because of taste or hardness. Additionally, these chemicals can have adverse effects on ecosystems in streams and rivers when they discharge from groundwater to these water bodies.
Excessive nitrate concentrations in groundwater have the potential to affect its suitability for drinking water. Also, when nitrate-laden water is discharged from groundwater to streams, nitrate can end up in downstream water bodies, such as the Gulf of Mexico, and cause algal blooms. These algal blooms lead to low oxygen zones, which can be deadly to aquatic life.
Chloride, dissolved solids and nitrate have many sources, including agricultural fertilizers, wastewater disposal, runoff from salt used for deicing or other chemicals. Understanding changes in groundwater quality may help assess the effectiveness of management practices that have been implemented to control these sources.
Though a majority of the well networks tested saw no change, chloride concentrations increased in 43% of the well networks from the first decade to the second decade of study. Dissolved solids concentrations increased in 41%, and nitrate concentrations in 23% of well networks.