The Total Threshold Limit Concentration (TTLC) test is a method
of chemical digestion, which was developed by the Department of
Toxic Substances Control (DTSC) to determine the total concentration
of a specific component in a sample (DTSC, 2004). The samples
were analyzed according to method EPA 7420 and EPA 6010 for Pb
and other metals respectively. Basically, it processes digestion in
order to take account of the soluble and insoluble fractions of the
sample. Concentration values that exceed the TTLC limits are characterized
as hazardous wastes and are given a code according to
the compounds that failed the test.