What regulation covers supply operations in a CBRN Enviroment?

Try CATS? It's through the Army Training Network. If a task is within your unit's METL, it should be found in CATS, complete with task/condition/standard formatting. I sincerely doubt there's a regulation that specific to supply ops exclusively, but you can develop a more specific SOP based off the broader regs cited in 1SG (Join to see) comment.

I want to add to what I posted earlier. let's take a moment to examine what might happen in a CBRN attack with an engineering company. Let's make the assumption that your unit has a Vertical Element (Nail benders) and a Horizontal Element (Dirt Pushers).

Chemical: If it is a Non-persistent agent, the likely COA will be to decon as required, but probably MOPP up, work as needed for mission, but probably wait things out. If it is a persistent agent, I don't think it would b e unreasonable to potentially task a couple of pieces of heavy equipment under the guidance of a chemical unit, to mitigate. Maybe clear a path or bury the contaminated soil. They may also help with the decon operation, including taking care of the vehicles tasked. Other then logistical support for this, I think your supply ops will go on as normal, with MOPP status determined by conditions and the CO.

Radiological/Nuclear. There will likely be taskings for immediate structural damage assessment and support..after the nucelar dust settles. Again, most of the important things, (food and water) will be largely uneffected as long as those supplies are contained somewhere (I know when I was in the 4-shop, we kept that stuff in conexes until units came to draw rations.)

Biological: I put this last, because this may have the most potential for the supply to be involved. If the agent is dispersed in a way similar to chemical (aersol spray, for instance), then the unit's reaction will likely be similar to how it is done with a chemical attack. If there are more clandestine methods of dispersal (deliberate contamination of food and water supplies), then there will be a need to monitor these stuff..class I and VI become important, as well as Class VIII.
I assume that most of the folks with supply and S4 have received Field Sanitation Training. This will be come more important here as well as close relationships with the Medics and CBRN. BIDs unit especially.

I would recommend you refer to JP 3-11 or FM 3-11 (Operations in a Chemical Envronment

Other things to consider, The Army Environmental Policy and ISO 14001. (ISO is the International Organization for Standardization. )

I am confused by the question. Other then being made more difficult by potentially working at some MOPP level, i don't see much difference in how supply ops will change.

I would suggest some tasks if you suspect you may have to operate in an environment where there is CBRN threat, such as extra care with food and water supplies (covering or storing inside).

There is a role with resupply after decontamination activity. But that is a matter of anticipation of that event, and if CBRN threat is that strong, I'm sure your S4 will be on top of that.

What kind of issues are you thinking need to go in a SOP?