The current EPA Toxicity Characteristic Leaching Procedure (TCLP), SW 846 Method 1311, requires that all wastes be milled into smaller particles prior to being placed into the extractor. A multi-laboratory study has been conducted to determine if milling is necessary or if the tumbling action of the TCLP procedure will cause monolithic wastes, which are not strong enough to survive in the environment, to fall apart in the extractor. Multiple plugs of eight different solidified waste samples of variable strength were prepared. The unconfined compressive strength of a plug of each sample was measured and the environmental survivability was evaluated in two separate laboratories using the ASTM Freeze/Thaw (D4842-90) and Wet/Dry (D4843-88) testing procedures. Identical plugs of each sample were tumbled in glass bottles, equipped with a stainless cage as proposed by EPA. Additional identical plugs were tumbled in unbreakable plastic bottles following the same protocol used with the stainless steel cage. Five separate laboratories performed the stainless steel cage experiments in duplicate while three laboratories performed the plastic cage tumble, also in duplicate. No chemical analysis was performed; each laboratory simply weighed the amount of material which would not pass through a 9.5 mm sieve after the 18-hour tumble was complete. This weight compared to the initial plug weight was compared with the freeze/thaw, wet/dry and unconfined compressive strength results.
All samples that had low strength and failed the wet/dry tests fell apart when tumbled in either type of container. Comparison of the cage and plastic bottle results clearly showed the plastic bottle to be superior. The results better matched the strength data, the data were more reproducible on both an intra- and inter-laboratory basis, and a plastic bottle is easier to clean. ASTM D-34 is drafting a leaching procedure similar to the TCLP which will use a nonbreakable bottle and will not require particle size reduction of the waste prior to tumbling in the extractor.