The Kahe (oil powered) plant at electric beach is still operational. The coal fired power plant that shut down is a little further south of there, closer to Barbers point.
Seems like the presence of the accumulated gunk in the cylinder means the hot water must be cleaner by definition? The accumulation being the net difference between what was dissolved in the incoming water and what is dissolved in the outgoing water.
With the exception of gunk that is from the lining of the cylinder itself of course.