The primary measure used to evaluate ASR site performance is the potable water per-cycle recovery efficiency. This measure, calculated for 18 sites, 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. Cumulative potable recovery efficiencies also were calculated and 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 banking—an operational approach in which a large volume of water is recharged during an initial cycle. This process flushes out the aquifer around the well and can build up 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.