According to other sources, Ganymede is within Jupiter's radiation belt and receives a level of radiation well above the acceptable amounts. Two of the three sources below mention a level of 8 rem per day.
Example sources:
http://colonyworlds.com/2008/03/radiation-safe-worlds.html
http://www.spacecolonization.xyz/colonization-of-ganymede/
http://phys.org/news/2015-10-jupiter-moon-ganymede.html
174.24.209.37 07:06, June 11, 2016 (UTC)