Ohia trees are dying rapidly, Why?

[kalakoa]

The current alternative to geothermal in Hawaii is fossil fuels

I'm always amazed that the anti-geothermal folks seem to forget this -- it's difficult to see how geothermal can have a worse environmental impact than burning oil (which is, itself, shipped here by burning more oil).

meeting baseload energy demand during non sunny/windy periods

Part of the problem (which nobody bothers to address) is that unlike all other commodities, power is generated to meet real-time demand. Install some battery buffer (eg, Tesla Powerwall), this makes local solar more useful and simplifies the grid management -- fewer peaks means better utilization of the baseload source, and baseload sources tend to be more efficient than peak sources.

some specific chemicals into the return brine that goes back into the geothermal reservoir

I believe those chemicals are a proprietary trade secret, just like with fracking...