The best way to dispose of it is in your pool...the only downside to it being "old" is that it may lose a lot of its strength as a sanitizer, but at least you still get some effect from it. The danger to opening a bucket of trichlor that has gotten wet is the pressure that builds inside the container from the heat let off by the pucks as they dissolve...and after several months of buildup over winter can turn a plastic bucket into somewhat of a missile, increasing the chances of injury by plastic shards, or by partially dissolved puck bits flying into the eyes.

I live in a very rural area of Northwestern Louisiana, where we have one major landfill open in the area but several satellite dump sites where things are sorted into bins and then picked up by the major disposal companies and dealt with accordingly. There is a bin at my satellite site for things marked with hazardous material labels that is separate from the other garbage or things that are recycled. However, I still think the best way to dispose of it is to put it into the pool.

Janet