AQUIFER STORAGE AND RECOVERY PERFORMANCE AND HYDROGEOLOGY, UPPER FLORIDAN AQUIFER, SOUTHERN FLORIDA
Each ASR cycle is defined by three periods: recharge, storage, and recovery, and the primary measure used to evaluate the performance of ASR sites is the potable water per-cycle recovery efficiency, which is defined as the percentage of the volume of freshwater recharged that is recovered prior to exceeding a recovered water chloride concentration of 250 mg/L. Calculations of the cumulative potable recovery efficiency at ASR sites display substantially less variability than per-cycle efficiencies.
Per-cycle potable water recovery efficiencies vary from 0 to 94 percent. High potable efficiency on a per cycle basis can be related to water bankingan operational approach in which a large volume of water is recharged during an initial cycle. This process can flush the aquifer around the well creating a temporary buffer zone that increases recovery efficiency substantially during subsequent cycles conducted with much lower recharge volumes.
The relative performance for 15 of the 30 sites was determined by arbitrarily grouping performance into low (0-20 percent cumulative potable recovery efficiency), medium (20-40 percent) and high (>40 percent) categories; 3 sites were rated high, 6 were rated medium, and 6 were rated low. Although six sites have a high overall recharge rate that is associated with water banking, three of these are rated low.
Four hydrogeologic and design factors that may affect recovery are the thickness, transmissivity, and ambient salinity of the storage zone, and the thickness of the portion of the aquifer above the top of the storage zone; and threshold values for these factors above which recovery efficiency could be adversely affected were selected. Some general correlation of the site performance ratings with the number of these factors above the threshold value was found.