There are 48 caches in this series and every single one of them needs to be in good order and ready to be found if people are to be able to complete the quest. For every cache, there will occasionally be problems. These can vary greatly, from needing a new log book, cache wet to cache missing, to give just a few examples. In the normal run of events it is expected that the cache owner will sort these out within a few days but certainly within a few weeks. If/when it becomes apparent that there are serious issues with a cache and that the cache owner is not responding, then the cache will be listed here.
This can be done in a number of ways:-
Simplest is for a cache owner to archive their cache. However, if the cache owner is doing nothing to maintain a cache and if they will not respond to "Owner attention requested" logs and if they will not respond to emails, then put a "Reviewer attention requested" log on the cache. Include in your log the reasons it should be archived. A reviewer will normally pick this up within a few weeks. You might speed things up by drawing a reviewer's attention to it. The reviewer will normaly put a "Post Reviewer Note" on the cache. If there is no response after 30 days they then archive it.
See the Groundspeak help page 7. Ownership after publication - 7.14. Adopt or transfer a geocache for details of how to do this.