I got this achievement shortly after the DLC became live. What Atom said is doable and will take luck, but a SURE way is BOOST it. I got a team of eight players together and we stood in the pool outside the doors and had a grenade thrown at us.
With this method not only are you unlocking your achievement but also putting work towards your grind for grenades. Any weapon that explodes works great but I would highly suggest regular grenades because of the crazy physics in this game. Any questions please don't hesitate and if you down vote please say why.