What is Treated Wood Waste (TWW)?

On August 31, 2021, Governor Newsom signed Assembly Bill 332 and the bill takes effect immediately. AB332 adopts new Alternative Management Standards (AMS) for treated wood waste that are codified in Health and Safety Code section 25230. As a result of the chaptering of the bill, all treated wood waste variances issued by DTSC since March 2021 are now inoperative and have no further effect. The variances are no longer necessary because they have been replaced by the AMS. The new AMS are similar to the rules that applied under the variance program, except that no variance is required.

The California Department of Toxic Substances Control defines treated wood waste (TWW) as wood that has been treated with chemical preservatives. These chemicals help protect the wood from insect attack and fungal decay while it’s being used. Fence posts, sill plates, landscape timbers, pilings, guardrails, decking and grape stakes are all examples of chemically treated wood.

Is TWW Toxic?

TWW contains hazardous chemicals that pose a risk to human health and the environment. Arsenic, chromium, copper, creosote and pentachlorophenol are among the chemicals used to preserve wood and are known to be toxic or carcinogenic. Harmful exposure to these chemicals may result from touching, inhaling or ingesting TWW particulate (e.g., sawdust and smoke).

  • Disposal Locations
  • What do I need to know before taking my TWW to an authorized landfill for disposal?

How can I tell the difference between TWW and old wood?

Treated wood is wood that has gone through a treatment process with chemical preservatives to protect it against pests and environmental conditions. Typically, treated wood is used in exterior applications where ground or water contact is likely.

Treated wood can often be visually distinguished by its appearance. There are several signs to look out for when determining if a piece of wood has been treated or not. What are some things to look for when determining if wood is treated or not?

  • Treated wood end tag
  • Wood manufacturer stamp codes
  • Indentations on the surface of the wood
  • When cut, staining is visible around the perimeter only
  • Discoloration (e.g. green or dark brown appearance)
  • Odor

Example of treated wood end tag.

Example of wood manufacturer stamp codes.

Example of pressure treated wood showing indentations from treatment.


This information above is offered as a public service in an effort to eliminate illegal and improper waste disposal. As the information may not be comprehensive, the Department encourages the public to research additional companies that are available for the services sought. The companies are not affiliated, endorsed or regulated by the Department. Accordingly, as with any professional service, please confirm the accuracy of the company’s information and request copies or verification of the company's license and/or permits to provide the service, prior to utilizing its services. Under no circumstances, directly or indirectly, shall the Department be held responsible or liable for reliance on this information.  If you would like to include your company on the list, please contact Waste-Approval@rivco.org or call (951) 486-3200.