would be preferable to do more detailed studies, with enhanced monitoring, at a reduced number of pilot ASR sites or with a reduced number of exploratory ASR wells, rather than to do more limited studies using the currently planned number of exploratory wells but with too few monitoring wells.
During the workshop discussion it was noted that data are available from a number of existing ASR systems that have operated for over a decade. These existing data can be quite useful in design of the pilot projects and in anticipating the hydraulic performance of ASR wells in general. However, because existing ASR systems that are used for water supply management generally operate on relatively short cycle periods, it may be difficult to use results from those systems to predict the degree of mixing and water-rock interactions during longer-term recharge and storage. Such mixing and water quality changes due to water-rock interactions may be the limiting factors in efficiency or recoverability of the regional scale ASRs proposed as part of the CERP. Design of cycle testing of the pilot wells must take into account the anticipated duration of recharge and recovery cycles that will be employed during the final operation. The hydrologic models used for design of the CERP indicate that continuous recharge is likely to be required in the Lake Okeechobee regional ASR for multi-year periods. This suggests that continued recharge for periods on the order of a year or more prior to recovery should be employed for the Lake Okeechobee pilot ASR cycle testing in order to obtain data that will be relevant to operational performance.
Interpretation of results
Observations obtained from a suitable network of monitoring wells can provide the basis for development of new or improved conceptual and numerical models to simulate “bubble” development and migration. Additional data may also be available from monitoring of other existing ASR systems, and this information would also be useful in developing and testing such models. Numerical codes used to test conceptual models and to simulate bubble migration may need to account for three-dimensional, density dependent flow and solute transport in multi-permeability media containing fractures and solution conduits. The CROGEE is not aware of any existing codes that have the full capability to accommodate these aquifer characteristics. Thus, construction of models for these local scale processes is likely to require substantial technical effort with a commensurate level of funding.
While the pilot projects are likely to be most useful in assessing local scale feasibility issues, they can also contribute data to the assessment of the regional hydrogeologic framework and aquifer characteristics. Use of data collected from the exploratory wells as part of a regional scale aquifer characterization is anticipated in the draft project management plans that were available prior to the workshop. The CROGEE encourages such use of data collected at the pilot sites, noting that careful coordination between the pilot studies and the regional study will maximize the value of these data to understanding the system at a variety of scales.
Fracture potential studies, which may be limited to desk-top analyses or expanded to more rigorous modeling approaches, are described briefly in the draft project management plans. The CROGEE recognizes the importance of such studies and commends the project management team for including them in the plans. The pilot studies should provide valuable additional information on the potential for fracture development due to a single ASR well or cluster. Results of fracture potential studies conducted as part of the pilot projects should be combined with results of the regional hydrogeologic models in order to assess the potential for fracturing during full-scale ASR operation.