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Determination of vertical and horizontal pathways of injected fresh wastewater into a deep saline aquifer (Florida, USA) using natural chemical tracers |
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| Authors: | Virginia Walsh René M Price |
| Institution: | 1. Miami-Dade Water and Sewer Department, 3071 SW 38th Ave, Miami, FL, 33146, USA 2. Department of Earth and Environment, Florida International University, 11200 S.W. 8th Street, University Park, Miami, 33199, USA 3. Department of Earth and Environment and Southeast Environmental Research Center, Florida International University, 11200 S.W. 8th Street, University Park, Miami, 33199, USA |
| Abstract: | Two deep-well injection sites in south Florida, USA, inject an average of 430 million liters per day (MLD) of treated domestic fresh wastewater into a deep saline aquifer 900 m below land surface. Elevated levels of NH3 (highest concentration 939?µmol) in the overlying aquifer above ambient concentrations (concentration less than 30?µmol) were evidence of the upward migration of injected fluids. Three pathways were distinguished based on ammonium, chloride and bromide ratios, and temperature. At the South District Wastewater Treatment Plant, the tracer ratios showed that the injectate remained chemically distinct as it migrated upwards through rapid vertical pathways via density-driven buoyancy. The warmer injectate (mean 28°C) retained the temperature signal as it vertically migrated upwards; however, the temperature signal did not persist as the injectate moved horizontally into the overlying aquifers. Once introduced, the injectate moved slowly horizontally through the aquifer and mixed with ambient water. At the North District Wastewater Treatment Plant, data provide strong evidence of a one-time pulse of injectate into the overlying aquifers due to improper well construction. No evidence of rapid vertical pathways was observed at the North District Wastewater Treatment Plant. |
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