Honestly, the Salton Sea would be a great place to dump the brine. It would keep the water levels up and reduce the respiratory issues caused by drying, and any ecosystem to be destroyed has been thoroughly destroyed for decades.

Nix the "turn the manmade salt lake to a manmade fresh lake" plan, and use the created freshwater for agriculture directly, or send it off to LA, or do anything with it that isn't "refill the accidental lake that already has evaporation and pollution issues". It's a salt lake, use it as one.