People from different Nations are going to have somewhat different answers to this question. The religions are different - hence, the ways of dealing with these things are going to vary.
ETA: Prairie Fairy, as long as people from a variety of Nations are weighing in, there will probably not be One True Best Way for you to dispose of it yourself. If you were part of one of these specific Nations, then it would be clear which religion's protocols apply. Again, it's not my place to advise here, but I would have seconded the suggestion to turn it over to an elder to deal with in the traditional ways of their people. But since it's been buried in the earth for a while, um, well, I'm not so sure anyone is going to want to get that package in the mail... I could be wrong...