I have very little experience in geothermal systems but was surprised to hear that methanol is being used, primarily as an antifreeze and at about 25% concentration. I did a little digging and the following websites may offer some guidance to your reader:

http://www.oee.nrcan.gc.ca/publications/infosource/pub/ici/caddet/english/r413.cfm?attr=20

http://en.wikipedia.org/wiki/Geothermal_exchange_heat_pump

http://www.geoecs.com/14.html