A number of planned arrests occurred when people locked themselves to heavy machinery. On September 3, 2016, the DAPL brought in a private security firm. The company used bulldozers to dig up part of the pipeline route that was subject to a pending injunction motion; it contained possible Native graves and burial artifacts. The bulldozers arrived within a day from when the tribe filed legal action. When unarmed protesters moved near the bulldozers, the guards used pepper spray and guard dogs to attack the protesters. At least six protesters were treated for dog bites, and an estimated 30 protesters were pepper-sprayed before the security guards and their dogs exited the scene in trucks.