USACE Floridian Aquifer Study Scope of Work

1. Combine existing geologic, hydrogeologic, seismic, and engineering data from previous studies/projects, including available historic data from earlier USACE dredging projects, total Upper Floridan withdrawals, and USGS, GAEPD, and SCDHEC water-level data into the harbor-wide GIS being constructed for Savannah Harbor.  Add future supplemental data to the GIS to allow enhanced analysis and visualization.
   
   
2. Develop 3-D coupled flow and transport model of the hydrologic system focused on the navigation channel.  Use model to compare before and after dredging results as related to projected chloride changes in the Upper Floridan aquifer.  Model various combinations of hydraulic properties, confining unit thickness, and future pumping rates from existing and anticipated data.  Calibrated model will serve to estimate most likely impact scenario.  Model parameters will then be assigned at limits of reasonable range of properties to assess a worst case scenario.  Worst case defined as having relatively high vertical hydraulic conductivities and minimum likely thickness of upper confining unit with maximum upper Floridan aquifer pumping.
   
   
3. Conduct additional sub-bottom seismic surveying with particular emphasis in areas of paleochannels.  Initial phase of surveying will determine feasibility of acquiring high-resolution seismic data along the sides of the existing navigation channel.  If initial surveying proves useful data can be obtained, a second phase of surveying will be implemented to better define paleochannel geometry and Upper Floridan confining unit thickness.  All seismic data will be acquired in digital format to facilitate analysis and storage in the GIS.
   
   
4. Conduct Additional Marine Drilling Adjacent to Navigation Channel at Selected Locations within Deep Paleochannels that Cut Down into Lower MioceneConduct additional marine continuous core borings to further characterize in-filled sediments of paleochannels and Miocene confining unit below paleochannels.  Cores to be drilled to top of Upper Floridan aquifer and analyzed to determine grain size, porosity, vertical hydraulic conductivity, pore-water geochemistry, and radioisotope composition.  Geophysical logging will also be performed.  Four borings will be located in known deep paleochannels in principal area of concern between river stations 25+000 and – 30+000.  Two additional borings will be reserved for locations to be determined after completion of additional seismic surveying.
   
   
5. Conduct Additional Land Drilling to Complete Geologic Transect from Tybee Island to Savannah and Install Multi-Level Monitoring Wells at Selected LocationsConduct additional continuous core borings on land adjacent to navigation channel to top of Upper Floridan aquifer at three strategic locations where geologic or hydrogeologic data is sparse.  Core holes will be geophysically logged, and core samples will be analyzed to determine grain size, porosity, vertical hydraulic conductivity, pore-water geochemistry, and radioisotope composition.Install multi-level wells within surficial aquifer and Miocene confining unit at three locations along the transect.  Two locations will be near existing upper Floridan wells and one in the area of a known deep paleochannel.  An additional well may be installed outside the immediate Harbor area (and saltwater influence) but within the Savannah drawdown cone as a control well if deemed necessary.  The multi-level wells will be installed at various levels to allow data on hydraulic head and ground-water geochemistry of specific intervals to be obtained over time.  Rotosonic drilling methods will be used to install multi-level wells.
   
   
6. Conduct Trial Pumping Test on Existing Wells to Determine Feasibility of Performing Aquitard Test on Miocene Confining UnitConduct trial step-drawdown pumping test on two recently installed upper Floridan wells located adjacent to river channel to determine feasibility of hydraulic testing of confining unit.  Continuous cores, pore-water data, grain size data, and lab vertical hydraulic conductivity data for confining unit exist for these wells.  If results indicate hydraulic testing of confining unit is feasible, estimate design parameters and assumptions for full aquitard testing.If hydraulic testing of confining unit is deemed to be viable, appropriate methodology will be used to conduct testing at additional selected sites.