It looks like your well is in a crawl space so as long as you prevent water from getting in there you should have no problems. Of course, don't go burying and dead hookers down there either.
You said that some of the pipes were plastic. Since they didn't fill up with sediment or rust that proves that the steel pipes simply rusted. Its a well-known phenom in the plumbing field. That's one reason why they don't use galvanized pipe anymore.