Rapid Fluctuations in Groundwater Quality

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We think of groundwater as moving slowly, and groundwater quality as changing slowly—over decades or even centuries. But in some parts of some aquifers, groundwater quality can fluctuate rapidly, sometimes over just a few hours. Are such changes part of a long-term trend, or just part of a short-term cycle? And what does that mean for suitability for drinking?

As part of the National Water Quality Program, USGS scientists are investigating why, in some areas and at some depths, groundwater quality changes at short timescales—years to months to days to even hours, rather than decades. These fluctuations often occur in areas where groundwater and surface water interact. The Enhanced Trends Network study is evaluating these short-term fluctuations, identifying what causes them, and determining whether the water-quality changes are just part of a seasonal trend or are part of an overall long-term trend. For those chemical constituents with human-health benchmarks (thresholds for drinking-water quality), changes in constituent concentrations are being evaluated in the context of those benchmarks—in other words, are there certain conditions under which the groundwater might require treatment before drinking?


The sampling point on a large-volume public-supply well is designated

A large-volume public supply well in San Antonio, Texas. This well is being sampled for water-quality constituents as part of the NAWQA Enhanced Trend Network study. (Credit: Jennifer Wilson, USGS)


A major feature of this research is the development of instrumentation that collects and transmits high-frequency (hourly to daily)  groundwater-quality data at 24 sites. Follow the links below to view data for specific conductance, dissolved oxygen, pH, and nitrate in groundwater in real time.



New Mexico

New Hampshire






Interested in long-term trends in groundwater quality?  Try the groundwater change tool and see how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.

For information and science on additional aspects of groundwater quality, click here.