California waste code 421 Chalky sludge built on lime, as from water softening.

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Based on California Title 22 and DTSC guidance
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Sludges
Lime sludge

Lime characterizes the hazardous sludge.

Hazardous sludge characterized by lime, as from water softening. Alum, gypsum and phosphate sludge take other codes.

Is California code 421 hazardous waste?

Not from the code alone. Waste must first be found hazardous. Code 421 isn't a restricted code, but a restricted category that fits takes priority over it. A code that isn't restricted doesn't make waste non-hazardous.

When a shipment needs the Uniform Hazardous Waste Manifest, enter 421 in Item 13 for the waste line. Use one California code, plus the federal RCRA codes when the waste is federally hazardous.

RCRA waste meets a federal listing or characteristic, with no federal exclusion that applies. Non-RCRA waste is hazardous under California rules only. California presumes hazardous waste is RCRA unless the generator shows it isn't, so keep that determination.

What does California code 421 cover?

This code is for hazardous sludge where lime is the marking material. The record must support lime through the producing process or analysis. A general treatment-sludge description isn't enough.

Official wording: 22 CCR division 4.5, chapter 11, Appendix XII(b)

Is lime sludge California code 421, 411 or 431?

Code	When it fits
421	Process inputs or analysis resolve lime as the material characterizing the sludge.
411	Process inputs or analysis resolve the sludge as alum or gypsum rather than another named material.
431	Process inputs or analysis resolve phosphate as the material characterizing the sludge.

Use process inputs or analysis, not appearance. If more than one named material fits, the regulations don't say which code wins.

Which wastes take California code 421?

Waste	When it’s 421
Lime sludge	Process inputs or analysis identify lime in the settled residue

Which codes sit beside California code 421?

Code	What it is
441	Sulfur sludge
451	Sludge from degreasing
461	Paint sludge
471	Paper-processing sludge or pulp
481	Tetraethyl-lead sludge
491	Other hazardous sludge