General Discussion of AGY, page-62

They have underground storage tanks at the industrial pilot plant site at Campo Quijano on the outskirts of Salta. When concentrated brine in the ponds reaches desired ppm etc they fill a tanker and transport it to Campo Quijano.

In the unlikely event they have too much feedstock v storage capacity at Campo Quijano and needed to maintain a concentrated slurry in the final ponds (before it completely dried up), you could just add brine from the feeder pond above, diluting it somewhat but let it continue evaporating for a period of time before 'harvesting' at desired ppm levels.