The project objectives will be met by simulating the effects of injecting, and then withdrawing, water near Lake Okeechobee on the Floridan aquifer flow system using the USGS ‘Mega’ model (Sepulveda, 2002). The Mega model extends from the Suwannee River south to the middle of Lake Okeechobee, and from coast to coast. The model has a constant surficial aquifer fixed head array and is vertically discretized to simulate ground-water flow in both the Upper and Lower Floridan aquifers. The model input files, which are presently formatted for inclusion in the original version of the MODFLOW model, will need to be converted to the newer USGS MODFLOW-2000 format (Harbaugh and others, 2000). The locations of injection/withdrawal sites and accompanying rates will be provided by project development team members. Because of the close proximity of the model’s southern boundary to the proposed injection sites, the model cannot be used to evaluate the possible effects of injections and withdrawals to areas south of the lake.
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The locations of injection/withdrawal sites and accompanying rates will be provided by project development team members, including those from USACE, SFWMD, and USGS.
Simulate changes in the potentiometric surfaces of the Upper and Lower Floridan aquifers under both steady-state and transient conditions for bracketed (boundary) scenarios. Transient simulations will be conducted to simulate the temporal nature of head changes at and away from the well sites with monthly changes in municipal 1993-94 pumpage rates (period used to calibrate the model and for which water-use data are readily available for model input). Steady-state simulations will also be conducted to analyze the maximum possible effects of ASR injection and withdrawal. Because the Mega model’s southern boundary is comprised of specified heads and is relatively close to proposed injection sites, simulated head changes near this boundary may be subject to considerable error. It is possible that these errors may also affect simulated heads north of the well sites, which are of greater interest in this study. Accordingly, it will be necessary to conduct two simulations to bracket a possible range of affected heads. In the first scenario, where specified 1993-94 heads will be assigned along the model’s southern boundary, simulated heads will be unrealistically low during the injection period but unrealistically high during the withdrawal phase. In the second scenario, where constant 1993-94 lateral fluxes will be specified along the southern boundary, simulated heads will be too high during the injection period but too low during the withdrawal phase. Thus, the two simulations considered together should establish upper and lower bounds for simulated heads in the Upper and Lower Floridan aquifers.
Figures and tables depicting modeling results will be prepared. No formal USGS report will be produced.
Although the results of this project will not provide the basis for evaluating the feasibility of ASR, results should prove useful for later conceptualization and construction of the ASR regional model.
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U.S. Department of the Interior, U.S. Geological Survey, Center for
Coastal Geology
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