With our own rack we nearly went down the once-through river route, but the state made it clear the delta had to stay below about 3°F and we had to log DO/temperature/flow constantly before they would even look at the permit. In the end we sealed the cooling loop, run the plate heat exchangers into the office HVAC and a dry cooler, and we only add makeup water for the evaporative losses. That lets us reuse the waste heat and keeps the creek from seeing a hot plume.