"The amount of brine they need to extract from trenches is...

"The amount of brine they need to extract from trenches is huge".
Are you being serious? Do you know what this type of mining involves and what determines the volume of brine required? Don't think that using bores (at Beyondie, as another poster has suggested incorrectly) leads to less brine.

As for the halite stockpiles, again, welcome to SOP brine mining. Check out the details in the RWD submission to the WA environmental department if you want some idea how big the piles will be at rehab. Around 1.8% of the lake surface after 20 years. The intention isn't to cart it off site or recirculate it but it will degrade with time.

KLL isn't that much different to RWD (upper aquifer Na:k, 8.9 versus 10-11) and note that the Na for RWD increases at depth and KLL only report shallow augers.
And as the Na goes up, the Mg goes down and I believe this has implications for processing.