U.S. Groundwater Is Getting Saltier—What That Means for Infrastructure,
Ecosystems, and Human Health
Pittsburgh, Pa., USA: Scientists from the U.S. Geological Survey (USGS)
have been monitoring groundwater quality in wells across the country for
more than three decades, looking for harmful chemicals or residual
substances that may cause harm to ecosystems or humans. In all, they have
measured up to 500 chemical constituents, including major ions, metals,
pesticides, volatile organic compounds, fertilizers, and radionuclides.
Of these constituents, there have been significant increases of Na and Cl
ions and dissolved solids—all related to salinity. Details and trends found
in the multidecadal study
will be presented
at the Geological Society of America’s GSA Connects 2023 meeting on
Wednesday, 18 October.
The study is currently part of the National Water Quality Network,
continuing work that began in 1992 as part of the National Water Quality
Assessment Project. “The original goal was to evaluate the status of water
quality in the nation, including groundwater, surface water, and ecological
health,” says Bruce Lindsey, a hydrologist with USGS. Over time, they
focused on certain constituents that may have lingering detrimental
effects.
The researchers sampled wells within three different network types:
domestic areas, urban areas, and agricultural areas. Domestic wells, or
private wells that are not regulated by the Environmental Protection Agency
or a local municipality, represented medium depth aquifers and drinking
water. Urban and agricultural wells were shallower, usually around 30 to 50
ft deep. “The purpose of [sampling] those were to understand the status and
trends in the very shallowest water levels,” explains Lindsey. Those
shallow wells acted as “sort of a sentinel of what might be moving deeper
into the aquifer, so to speak.”
The team identified 82 networks, each with 20 to 30 wells, and identified
28 constituents to track that had levels of concern. Water was sampled
every 10 years to track changes in chemical concentrations. These
constituents and sampling results can be seen on the
USGS’s interactive groundwater map, which shows decadal changes.
“If we look at all 28 constituents across all 82 networks, dissolved
solids, chloride, and sodium had statistically significant increases more
frequently than any other constituents that we have on our list,” says
Lindsey. “If you look at the map, you’ll see patterns right away that jump
out.”
One of these spots is the Northeastern and Upper Midwest regions,
“particularly around urban areas where there’s cold weather and a lot of
road salt,” says Lindsey. “We obtained data on road salt application and
found correlations between these increases in chloride and sodium and
dissolved solids with the road salt application rates.”
But another region also had elevated levels of Cl, Na, and dissolved
solids: the arid regions of the country, especially in the southwest. These
regions naturally have high salinity in the soil to begin with, but
irrigation complicates the issue.
“When irrigating agriculture in arid regions, you get a lot of
evaporation,” Lindsey explains. “So if the salinity of the irrigation water
is relatively low, but a large percentage of it evaporates, [salinity
levels] can become high.”
These rising levels of Na, Cl, and dissolved solids can cause multiple
problems, starting with the environment. Many streams are fed by
groundwater, and higher concentrations of chloride in the water can knock
out the natural balance that aquatic life is used to. “[Rising levels] is
something that can take 20, 30, 40 years to develop … which means that it
can also take that long to recover if management of the sources of salinity
changes,” says Lindsey.
Dissolved salt ions can also pose problems for infrastructure. As the
salinity of groundwater increases, corrosivity can become an issue.
Corrosive groundwater, if untreated, can dissolve lead and other metals
from pipes and other components present in household plumbing.
Lastly, Lindsey and his colleagues have also
discovered a unique issue
related to rising salinity with implications for human health. In a sandy
aquifer in southern New Jersey, they found that a mixture of low pH water
and high salinity groundwater has mobilized the radium— a radioactive
element which is harmful to humans.
“It goes back to road salt,” he says. “Road salt is increasing, causing
sodium and chloride to increase, which is causing radium to increase.”
Lindsey notes that there seems to be increased awareness of the
environmental effects of road salt, with trucks spreading less salt or
municipalities switching to a lower-concentration brine. And while dead
grass near salted roadways is a clear hint at an oversalting problem,
Lindsey hopes that research like this will highlight other cascading
impacts of increasing salinity in groundwater. “The fact that there may be
streams that are not able to sustain aquatic life, or that your pipes might
start corroding, or this other more rare issue where there's radium, shows
there are other negative aspects [to rising groundwater salinity].”
Increasing salinization of groundwater in the United States
Contact: Bruce Lindsey, blindsey@usgs.gov
262: T96. Salinization of Freshwater
Wed., 18 Oct. 2023, 1:35–1:55 p.m.
The Geological Society of America (https://www.geosociety.org) unites
a diverse community of geoscientists in a common purpose to study the
mysteries of our planet (and beyond) and share scientific findings.
Members and friends around the world, from academia, government, and
industry, participate in GSA meetings, publications, and programs at
all career levels, to foster professional excellence. GSA values and
supports inclusion through cooperative research, public dialogue on
earth issues, science education, and the application of geoscience in
the service of humankind.
###