use CIDR masks.
static(inside,outside) 172.30.0.0 172.30.0.0 netmask 255.255.128.0
will cover 172.30.0.0/24 through 172.30.127.0/24
static(inside,outside) 172.30.128.0 172.30.128.0 netmask 255.255.192.0
will cover 172.30.128.0/24 through 172.30.192.0/24