Ann: March Quarterly Activities Report, page-20

Five years? A bit long there pj...

Anyway, a simple enough question. The following is lifted direct from the Seeking Alpha transcript of the half year conference call, complete with typo.
"If we move to the ponds, in overview, the ponds cover 4.5 square kilometers and there is a plan of those ponds shown in the top right in the presentation. These ponds, which pond
design has advantages of a lower capital cost intensity and lower operating cost. The
reason for the lower operating cost is we don’t harvest the full set of ponds and that
reduced our cost by about $250 a tonne of product."

To put it another way, they have designed the ponds with plenty of freeboard. Over time the unwanted salts precipitate out and settle to the bottom. Over time the salt/liquid interface at the bottom of the ponds rises and hence the bathymetric survey becomes important for knowing the volume of brine in each pond.

As the bottom of the pond starts filling with salt, they raise the surface level of the ponds - no salt harvest required from these ponds and, in any case, there is no economic value in recovering halite. In time, though, I am sure you will see them begin to harvest the potash from the final ponds in the sequence.