Isolating hazardous materials

I'll pose this as a thought experiment:

Let's say you are building an underground structure (a root cellar, fallout shelter, etc.)  This structure will require the use of some hazardous materials (plastics, etc).  What method would you recommend to isolate those materials from the environment and limit interactions as much as possible?

For example, a concrete sarcophagus was used to isolate the damaged reactors at Chernobyl (https://en.wikipedia.org/wiki/Chernobyl_disaster#Confinement).  So maybe a hydrolic cement could be used to isolate the materials and prevent interaction with the environment.

Or alternatively, some kind of tar sealant might be the answer (https://en.wikipedia.org/wiki/Sealcoat).  This would protect against water interacting with the materials.

What about silicone (https://en.wikipedia.org/wiki/Silicone#Coatings)?

Assume that this material must be used, and you are forced to mitigate risks.  How would you do it?

Do you need to have plastic if you are worried about it?

This is a general thought experiment.  There are many possible scenarios where something like this might occur.

Maybe, you've found an amazing piece of land at a ridiculously good price, but:

- It shares a small property boundary with some kind of dump, and you want to put a minimal barrier in to have some assurance that contaminants won't bleed across to your land.

- Or, part of the land contains an old fuel tank that might at some point crack open and contaminate the land

- Or, the previous owner has buried school buses to create an underground structure, but didn't do anything to ensure that they were stripped of hazardous material.

All environmental regulations aside, is there a way to compartmentalise, and isolate, so that you can have confidence that the rest of the land will be unaffected by it.

I guess to some degree, you could interpret this question as asking: "Is natural building only for pristine environments, or can it be done in less than optimal environments with certain mitigation strategies?"

Thanks for your input on this.

The broad answer has to be, yes and its expensive.
The issues you speak of are extreme, and I think there would be many other blocks far more suitable, without the hassles.

Wow man, I really don't wish to be unkind, but this scenario is the Kobayashi Maru + stranded on a desert island + Catch-22.

If the situation involves massive, long-term toxicity like an ancient dump, the solution is to be somewhere else far away.

If the situation involves a small-scale problem that a backhoe can dig out, moving the crud to an approved disposal facility is the best you can do.

My 2 cents. Hope I didn't offend.