posted on 2002-12-06, 00:00authored byDouglas S. Kendall
The Toxicity Characteristic Leaching Procedure (TCLP) is
used by the United States Environmental Protection Agency
to determine if wastes contain extractable components
subject to hazardous waste regulations. This paper examines
the limitations of the TCLP and the way it is used by
studying a particular example. Waste casting sand from
brass foundries to which iron metal has been added passes
the TCLP test but when placed in a landfill for several
years may start to leach lead, copper, and zinc. Results
of TCLP tests of waste sand alone and with the additives
iron metal, zinc metal, hydrous ferric oxide, and hematite
are reported. Three processes were studied: reduction by
metallic iron, sorption by hydrous ferric oxide, and
precipitation of hydroxides. Lead, copper, and zinc behave
differently with respect to these three processes, and
their measurement allows some deductions as to what is
occurring in a TCLP test or a landfill. Iron addition does
not result in long-term stabilization of a waste placed in the
ground. The chemistry of a laboratory extraction can be
very different from the chemistry of a waste placed in the
environment. Wastes that are treated to pass the TCLP
test, but are not permanently stabilized, are a threat to the
environment.