Basics

Essentially Strip Mining but of Landfills
Easier with modern landfills, but can be done with old (even informal) ones.
In older ones, it can even be of historic value (like a time capsule of sorts, anthropologists, and archeologits do this with old "mounds" with mainly shells and bones of food, but this is a similar modern form)
Leads to:
- Recovered Recyclable Materials (Metal, Glass, Plastic, Misc)
- Recovered Soil/Clay (cover material)
- Recovered Aggregate Materials
- Sometimes Methane Gas (if captured and not released)
- Typically large Sulfur Compound Gasses, and Mixed Chemical Leachate, which is toxic, but can be processed into useful products
- Refuse Derived Fuel (sort of like biomass, but much more unpredictable)
  - This can in turn be made into Syngas and Slag
Finally the land is returned to it's natural state and/or develped

Challenges

Nastiness of the work site
- Although Dedicated “Work Clothes” / “Junk Clothes” + Boots and a “Wash Out” + swap clothes and boots based Contamination Reduction Zone can help with this
- Also Automation/Mechanization or things like PAPR Helmets with Granulated Activated Carbon cartridges
Unknown/Varying Composition of the Landfill
- Modern landfills are a sort of cursed Lasagna of MSW , Landfill Daily Cover , and small amounts of Construction and Demolition Debris
- Compared to a more homogeneous Ore Vein / Petroleum Resevoir this can lead to challenges
- Also unknown hazmat that sneaked in such as in Disposable Vape Pens or Cell Phones etc
Hazards
- Combustible/Explosive Atmospheres (from accumulated Landfill Gas )
- Subsidence of the landfill as contents and/or daily cover are biodegraded
  - While Compactor Tires tend to be used, gradual compaction of the overall landfill may contribute to this as well

First you have the original stages of a landfill’s lifespan
The part where landfill mining would take place would largely be in if it is NEAR capacity (and they are trying to “squeeze some extra capacity out” so to speak), or in a completed/OLD landfill that is being mined due to liner failure, economically recoverable materials, or as a broader government policy of Landfill Phase Out
The main thing to consider is how stabilized is the landfill overall, is there still non-capped/covered sections one would be driving on, and how that impacts things.

There may be an advantage to let things ferment/stabilize for a bit, akin to a Wet Material Recovery Facility albeit Landfill Gas and Landfill Leachate are far “dirtier” products to do with
- Also recoverable non-biodegradable materials will potentially degrade in this period reducing value
  - Metals rusting, plastics being degraded (Think a BRAND NEW plastic bottle vs Litter on the side of the road that is heavily weathered)
  - Things such as electronics and batteries may become especially degraded/harder to separate out (although CITATION NEEDED)
One thing to note is if a Landfill got to the “stabilized” level where Landfill Gas is no longer being created, the Landfill as a whole could be Inerted
- This would HEAVILY reduce, if not eliminate Fire/Explosion Risk (at least in the context of Landfill Gas, Hazmat+Reactive Metals etc may still start smaller fires)

One Commercial Off The Shelf option is Steam Injection
- Parts Commonality with Enhanced Oil Recovery
- POTENTIALLY a Just Transition in terms of climate change adaptation, although again quality of life concerns are CRITICAL to that
Supposedly aids LFG production, also may help melt and consolidate plastics/do something akin to In-Situ Thermal Remediation where contaminants may be essentially Steam Distilled / “Sparged” Out

Landfill Fires already happen by accident
Although especially as they near completion (of a cell) they can be controlled by adjusting the air inlets/fans (akin to a Wood Stove Damper
In a similar manner to Coal Seam Fire->Underground Coal Gasification, i postulate one could do In-Situ Landfill Gasification
- If not high quality syngas generation, the Thermal Processing may be of use in of itself (more akin to Incineration , where waste reduction is the goal not the energy produced by it)

Due to Daily Cover, and how landfills are sometimes arranged as a stack of sealed “cells”, rather than one monolithic pile, Perforation of those Cells/Daily Fill upon Completion or Before Exploitation may aid in In-Situ Processes/Venting+Inerting the landfill