HGSYSTEM version 3.0 has added a significant number of new capabilities compared with version 1.0(1.1) and these are described in this WEB page. It is again intended that the use of the programs is not restricted to the sponsoring companies and that they are openly available for carrying out dispersion assessments. (It should be noted that there were no released versions of HGSYSTEM numbered 2.n).
HGSYSTEM version 3.1 has some updates to the officially released version of HGSYSTEM v3.0. However it is not deemed as an official release because version 1.0 and 3.0 have been independently reviewed and thus have a particular regulatory status. The last review we know of was conducted for the US DoE on version 3.0. Further details of version 3.1 can be found here