OK. Not really a ‘Frequently Asked Question’, but I asked it. The answer is found in U.S. Environmental Protection Agency (USEPA) regulations at 40 CFR 264.314(d)(1) for permitted Treatment, Storage, and Disposal Facilities (TSDF) and §265.314(e)(1) for interim status TSDFs.  If you’re curious about the difference between a permitted TSDF and an interim status TSDF (and you needn’t be), you can read about it here:  What’s the difference between a permitted TSDF (40 CFR Part 264) and an interim status TSDF (40 CFR Part 265).

A sorbent used to treat – i.e., remove – free liquids from a waste prior to disposal in a hazardous waste landfill must be nonbiodegradable.  Nonbiodegradable sorbents are one of the following:

• Able to pass one of the tests specified by USEPA.
• Determined by USEPA to be nonbiodegradable through the part 260 petition process.

Or…

• One of the materials listed or described by USEPA at either §264.314(d)(1) or §265.314(e)(1) and any mixtures of these materials:
  • Inorganic minerals
  • Other inorganic materials
  • Elemental carbon (e.g.,):
    • Aluminosilicates
    • Clays
    • Smectites
    • Fuller’s earth
    • Bentonite
    • Calcium bentonite
    • Montmorillonite
    • Clacined montmorillonite
    • Kaolinite
    • Micas (illite)
    • Vermiculites
    • Zeolites
    • Calcium carbonate (organic free limestone)
    • Oxides/hydroxides
    • Alumina
    • Lime
    • Silica (sand)
    • Diatomaceous earth
    • Perlite (volcanic glass)
    • Expanded volcanic rock
    • Volcanic ash
    • Cement kiln dust
    • Fly ash
    • Rice hull ash
    • Activated charcoal/activated carbon

Or…

• • High molecular weight synthetic polymers.  This does not include polymers derived from biological material or polymers specifically designed to be degradable.  (e.g.,):
    • Polyethylene
    • High density polyethylene (HDPE)
    • Polypropylene
    • Polystyrene
    • Polyurethane
    • Polyacrylate
    • Polynorborene
    • Polyisobutylene
    • Ground synthetic rubber
    • Cross-linked allylstyrene
    • Tertiary butyl copolymers

Why does this matter?  Because preexisting regulations applicable solely to hazardous waste landfills prohibited the disposal of a hazardous waste containing free liquids.  However, the same regulations allow for the treatment of hazardous waste prior to landfill disposal to remove free-standing liquid with a nonbiodegradable sorbent.  After the Generator Improvements Rule, this same restriction now applies to both large quantity generators (LQG) and small quantity generators (SQG) of hazardous waste.

If you’re interested in this article you may also be interested in how the USEPA’s Generator Improvements Rule changed the regulations for placement of bulk or noncontainerized liquid hazardous waste in landfill.