First-of-its-kind study assesses fate of recharged water bacteria in FL aquifer

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ST. PETERSBURG, FL, March 13, 2014 -- A first-of-its-kind study from the U.S. Geological Survey (USGS) holds the potential to impact future regulatory decisions on water disinfection practices prior to recharge or following storage in the Floridan Aquifer. The report found that coliform bacteria die off faster in a regional aquifer system than was previously known, though a small percentage survives.

Aquifer storage and recovery facilities have been used in Florida for about 30 years to store large volumes of water over long periods of time, increasing water supply during seasonal and multi-year droughts. Potable water, treated and untreated groundwater, partially-treated surface water, and reclaimed water is recharged into zones of the Floridan Aquifer and later recovered when needed. Further, one of the state's regulatory criteria for ensuring the quality of recharged water is whether it contains coliform bacteria.

"Although it is commonly believed that bacteria are few in number and mostly inactive in the lower zones of the Floridan aquifer system, we found relatively high numbers of bacteria that are alive and active," said USGS microbiologist, John Lisle. "However, when we looked specifically at coliform bacteria, we found that they died off at higher rates in the aquifer than was previously known."

In addition to the coliform data, this study is the first to characterize both the geochemistry and natural microbial ecology of the Floridan Aquifer and how they influence groundwater quality. It provides a baseline that can be used to enhance geochemical models that predict changes in groundwater quality following any type of recharge event.

"Characterization of native bacterial communities in aquifers is important because of the direct connection between some groundwater quality variables and bacterial activities. Groundwater bacteria catalyze geochemical reactions under conditions that can be significantly different within the same aquifer," said June Mirecki, a hydrogeologist with the U.S. Army Corps of Engineers. "Fundamental studies, like this study, have significant implications for truly understanding the fate of contaminants in aquifers targeted for aquifer storage, carbon sequestration and deep well injection."

The Floridan Aquifer flows southward at between 800-3,000 feet below the ground. It is among the most productive groundwater sources in the U.S. The upper zones of the Floridan aquifer are used as a drinking water source, while the lower zones, like those in this study, have been targeted for the recharge of treated surface water and reclaimed water and carbon sequestration repositories.

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