Like the above solution, Arena 1 is the best place to get this. 5 waves, no deaths.
We fielded all Assaults with Impenetrable and a mix of Mauls with Killing Blow and chainswords with Swordsmans Zeal. All waves with have the Sanctioned Pyskers but only wave 5 has Marines, 4 in total with bolters and a slow power axe melee attack.
Ground pounds and single hits will kill any of the guardsman and gretchins while Impenetrable all but shields you from the melta gun blasts form the Stormtrooper guardsmen. The Pyskers can be killed with 1 direct hit because of Killing blow or a few indirect hits.
Berserker orks can be killed with 1 direct hit with the maul or 2 indirect but the first hit knocks them down to be finished unopposed. Last are the Space Marines, the bolter variant cannot stand up to most melee attacks and with Swordsmans Zeal, your chainsword friends can take them down without trouble. 2-3 hits for the maul, a couple more for the sword.
Only 2 real dangers are in the first arena.
1 is when the Berserkers spawn. They can and will overwhelm a Sword Assault Marines but Maul users can break through them without their armor being broken.
2 is the dead drops. My advice is do not jump over the chasm, use the bridges and Impenetrable will soak up the bulk of incoming fire until you reach swinging distance.