I'm new at this and don't know New Mexico well enough to know what "WIPP" stands for so I googled it. Just to make sure are you referring to the "Waste Isolation Pilot Plant?" I'll have to read more about it if that is the frequency you identified.
Correct the waste site that is stored deep in ground in similar caverns and sealed.
To answer the one question does caverns have a third or repeater channel, I believe so.
Seeing how they do white sands national park they have a main repeater, simplex channel, then law channel.
So cav rep would be most accurate listed though it would be toned, and probably mixed mode now with a NAC also. I hadn't heard a peep on it there.
Then cav fire would be the local ops, ems and fire ops simplex used down below and on top for on site chatter.
Then I'm thinking if they don't use any other NPS frequency for law they'd be using NPS bush for law and dispatch to a main head quarters which is microwaved or phone lined or satellite backed to Alamogordo. Maybe a mix of all 3 as backups.
White sands has NPS LAW but they never use it rarely they do but it's strapped these days. They stick to the main channel since local fire, law would be talking to them during medical and other issues.
Since it isn't a national park yet just monument they contract with Otero sheriff to run plates or traffic stops, anything pertaining to Law Enforcement.
I have heard them going out of service and in service with their localized dispatch in the museum, as well as checking out on stops or contacts then switching over to Otero fire or sheriff for whichever duty they are currently on.
I'm thinking caverns uses the simplex mostly since it's on site and to keep chatter local below and on top.
Then since they are a park they use the NPS bush or some other channel maybe the cav repeater channel.
I parked on it though and there wasn't any law enforcement issues or talk. When I got below I was in a tour and turned off my radio which had those programmed minus the cav rep for what ever reason state IT didn't have but left my 436 on. It didn't catch anything as far as I know but I'll go back and try to figure out if cav rep got a hit or if it changed. It definitely needs more study though to figure out if they just use bush mostly to check in at both parks or cav rep as well.
I do know in past when channels were limited and zones they would run the rx on csq or put the repeater in csq but have a tone for the inputs so my goal is to figure out what the input was for the cav rep as they tend to stick to that sites input as the rx tone.