General Discussion of AGY, page-53

I think you'll find the reference to the smaller ponds being used to "store" concentrated brine from the larger ponds relates to the way AGY process their brine, ie they start by filling the large top ponds located on higher ground, and then progressively move the concentrated brine down into the smaller ponds. The below photo from the recent AGM presentation helps to see how the ponds are terraced down the slope.

I assume AGY have developed this pond design in order to maximise and efficiently manage the evaporation process/timeframe.