It's plastic. They sell it in the form of "hurdles" (http://en.wikipedia.org/wiki/Plastic_particle_water_pollutio...), small plastic particles, which are mostly standard sizes. These are then processed into their final form as required by simple machinery. Typically these are fed into an injection molding machine to make plastic parts, but could be used to produce plastic bags or sheet plastic for thermoforming.

Unless they're adding something to the plastic, or coating it in something, they could absolutely just ship it back as smaller than usual nurdles, or make use of it for something else in their manufacturing process, like making bottles or caps.

In any case, do you really think they have a two year supply of this stuff? That'd be crazy.