HR: 1330h
AN: B32A-0377    [PDF]
TI: Tidal Pumping and the Fate of Wastewater Nutrients in the Florida Keys
AU: Bachmann, M
EM: mbachmann@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, Deike Building, University Park, PA 16802 United States
AU: * Kump, L
EM: kump@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, Deike Building, University Park, PA 16802 United States
AB: Nutrient-rich wastewater from injection wells in the Florida Keys has been implicated in the eutrophication of coastal waters and, through long-distance subsurface transport, the degradation of offshore coral reefs. The flowpath of such wastewater in the saline aquifer system of the Keys is determined not only by the local geology, but more significantly by the differential hydraulic head applied by the two distinct tidal signals on either side of the island chain. While the Atlantic Ocean to the south exhibits typical oceanic tides, the constrained Florida Bay tidal signal to the north is significantly damped as compared to the oceanic tide and has a higher mean value. This system of tides presumably results in a reversing groundwater flow regime in which wastewater plumes are tidally pumped across the Keys with net flow to the Atlantic Ocean \(the "tidal pumping mechanism" of Halley et al., 1997, Develop. Sedimentol. 54: 217-248\). We have performed a quantitative analysis of the tidal pumping mechanism using FEFLOW, a commercially available 3-dimensional finite-element model designed to simulate variable density flow and reactive contaminant transport. We find that the tidal-pumping mechanism does indeed influence the transport of wastewater plumes in the subsurface. However, the buoyancy of the low-salinity wastewater plume dominates transport when injection volumes are large, bringing wastewater to the surface in the near-vicinity of injection and discharging it to nearby canals or coastal zones. Discharging wastewaters have variably reduced nutrient loads depending on travel times (for nitrate) and pathlengths (for phosphate) because of biogeochemical transformation in the subsurface (denitrification and adsorption/precipitation, respectively). The interface between nitrate-rich wastewaters and sulfide-rich groundwaters may be supporting a chemoautotrophic bacterial community in the bedrock of the Florida Keys.
DE: 0330 Geochemical cycles
DE: 1615 Biogeochemical processes (4805)
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 3210 Modeling
SC: Biogeosciences [B]
MN: 2003 Fall Meeting