7. Quantification of efficiency of recovery, recoverability, or other measures of “success,” particularly when considering water quality standards of the surface water bodies receiving recovered water.
8. Time scales of cycle testing and how these relate to anticipated operational cycles in recharge and recovery.
9. Use of data that may be available from studies of existing ASR systems to address questions related to feasibility.
10. Whether the pilot studies alone or in conjunction with other studies will provide sufficient information to demonstrate feasibility or infeasibility of a regional scale ASR system.
Based on the discussions at the workshop and also considering written material submitted prior to and after the workshop by the Project Development Team and others, the CROGEE formulated the following recommendations.
In order to maximize transferability of pilot project results to design and implementation of regional scale ASR systems, the pilot projects should be designed as tests to elucidate processes of “bubble” formation and migration under a variety of conditions. Some of these conditions include long and short open intervals of recharge wells, high and low injection pressures, homogeneous and heterogeneous aquifer properties within the storage zone, presence or absence of highly transmissive beds within the storage zone, greater and lesser contrasts in salinity between injected and native water, and long and short periods of storage prior to recovery.
Tests designed to compare effects of short and long open borehole sections in the ASR wells would be particularly useful to improving understanding of factors important to ASR well design at the selected pilot facilities and, more generally, throughout the UFA and in other aquifers with significant vertical variations in hydraulic properties. One possible way to conduct such tests within the constraints of a limited total number of pilot wells would be to construct an ASR well with multiple open sections for testing individually or in combination.
An important component of any test design is the monitoring strategy. Adequate monitoring is essential to obtaining data that can be used to develop conceptual models of bubble development and to test and calibrate numerical models of the relevant processes. Multiple monitoring wells at each pilot ASR site should be a high priority to delineate the geometry and heterogeneity of fresh water migration during recharge. The shape and heterogeneity of the fresh water bubble may ultimately dictate the extent of mixing between injected and ambient pore water during storage. This mixing is one of the important factors in limiting efficiency or recoverability. Multiple monitoring wells also are required to obtain better estimates of magnitudes, spatial variability and possible anisotropy of hydraulic properties of aquifers and confining units. Nested monitoring wells, or monitoring wells that can be packed off and sampled from discrete intervals, should be constructed for purposes of delineating potential preferential flow paths from the ASR wells and for quantifying mixing between relatively dilute recharged water and more saline ambient pore water in the storage zone.
The draft project management plans suggest that only a single UFA monitoring well and a single surficial aquifer well are anticipated in the conceptual designs for ASR pilot facilities. The CROGEE recognizes that significant costs would be associated with additional monitoring beyond those included in the initial plans. In case of budget constraints, the CROGEE concludes that it