Determine how the variable is set. Is the environment variable set via one of the shell script files (for your older, working Tomcat/Web Viewer?
If yes, review the old Tomcat shell scripts for modifications. The (Apache) recommended method is to create an stdenv.sh file to add environment variables. Alternatively, you might have modified the startup.sh or catalina.sh files. Assuming you did this for your old Tomcat, you'll need to do the same for your new Tomcat/Web Viewer system.