Conclusions and Recommendations
Based on the discussions at the workshop and also taking into account written material submitted prior to and after the workshop by the Project Development Team and others, the Committee on Restoration of the Greater Everglades Ecosystem (CROGEE) formulated the following recommendations.
Development of a preliminary list of information needs and compilation of available data should be undertaken as soon as possible. This exercise can be done for relatively low cost and within a short time can reveal where existing data are insufficient to meet identified needs. Categories of information needs include, but are not limited to, vertical distribution of potential recharge zones and their lateral extent, hydraulic properties, ambient water quality, and degree of confinement. Information on location, depth, and use of existing wells completed in the Floridan aquifer system is needed to assess potential impacts of proposed ASR wells on existing uses. Most of the existing well information is clustered in population centers along the coast. Little information is thought to be available inland where most of the ASR installations are proposed to be located.
A regional-scale three-dimensional numerical flow model will be required to assess impacts of proposed recharge and recovery volumes and rates on the UFA and adjacent hydrostratigraphic units. The model may need to account for variable density flow since the lower part of the UFA contains water that is somewhat saline, with several thousand or more mg/l of dissolved solids. Existing model codes based on an “equivalent porous medium” approach, such as HST3D (Kipp, 1997), are appropriate at a regional scale for estimation of head changes (Anderson and Woessner, 1992). Telescoped models of sub-regions, extracted from the regional model, also may be useful in assessing pressure buildup or drawdown at an intermediate scale. This regional and sub-regional modeling effort should be considered distinct from more detailed modeling that may be required to assess local scale feasibility questions related to recharge “bubble” growth and migration. Because of the solution conduit and fracture flow nature of the UFA, conventional models that employ an equivalent porous medium approach are likely to be poor simulators of solute transport in the vicinity of recharge wells (Long and Billeaux, 1987; Cacas et al., 1990). Development of suitable models for bubble growth and migration is considered in
Chapter 4 of this report.
Development of the regional scale numerical flow model should proceed in parallel with initial conceptualization of the hydrogeologic framework. Sensitivity studies employing preliminary versions of the model can be used to identify data needs and gaps and thus help guide the planning of the test-drilling program. The regional study should have a budget adequate for the necessary drilling, core sampling, downhole geophysical logging, hydraulic testing and water quality sampling of these test wells. The tests and data collection should include all items planned for the exploratory ASR wells as specified in the Project Management Plan for the Lake Okeechobee Aquifer Storage and Recovery Pilot Project. The CROGEE concurs with existing plans to instrument observation wells with pressure recorders early in the regional study to obtain data with which to calibrate the numerical model.
Surface geophysical techniques, such as seismic reflection surveys, should be a component of the regional study. Such surveys can help to constrain the three-dimensional geometry and continuity of hydrostratigraphic units (Kindinger et al., 1999), especially when used in conjunction with results from a relatively limited number of new exploratory wells. The surveys would provide a means for extrapolating detailed information collected at test well sites across broad areas where well control is sparse, thereby improving the quality of input to the regional-scale flow model. Surveys that use land-based techniques, as well as those that employ marine techniques (across Lake Okeechobee or along canals), should be considered. Without the geophysical surveys, a much more extensive and more costly drilling program may be required to adequately characterize the hydrogeology.
Once constructed, the regional flow model should be used to assess potential impacts related to full-scale implementation of ASR. Aggregate head buildup or drawdown estimated from the