Bacteria no match for deep Floridan Aquifer

New USGS study assesses the fate of coliform bacteria in recharged water

ST. PETERSBURG – A first of its kind study has the potential to impact future regulatory decisions on disinfection practices for water prior to its recharge or following its storage in the Floridan Aquifer.

The U.S Geological Survey report found that coliform bacteria die off faster in a regional aquifer system than was previously known, though a small percentage survives. One of the state's regulatory criteria for ensuring the quality of recharged water is whether it contains coliform bacteria.

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.

"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." Understanding that coliform bacteria die off faster than previously known has the potential to shape the standards or monitoring requirements that are set.