Balancing or failover connection

Hi,

I have a plan to maximize our WAN connection, is it possible on fortinet (fortigate 100E, firmware 6.02), we have some vlan and 2 WAN connection. Let say VLAN 10 & 20 internet connection through WAN 1, VLAN 30 & 40 through WAN 2, and if WAN 1 problem VLAN 10 & 20 will go to WAN 2, and vice versa. Is that a guide book or example for this case, i have some seacrh but commonly combine 2 WAN. 

Appreciate for answer and guidance.

Thank you