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the data. These data quality indicators are then compared to
those parameters established at the initiation of the project to
assess contract compliance.
k. Leaching Procedures. The primary objective of S/S is to
immobilize contaminants in waste. Leachability testing is used
single leaching test procedure can duplicate all possible field
conditions. Ideally, the treated waste would be leach-tested
with the actual surface water, ground water or rain water present
at the site. In practice, this is rarely possible, both because
of lack of definitive knowledge about site conditions and because
of regulatory philosophy. Therefore, standard leachability tests
have been developed by the EPA and several states. The major
test variables are normally specified for a given test procedure,
but latitude in the specification and controllability of the
variables can cause significant problems with reproducibility.
Most of the tests presently used for regulatory purposes are
batch procedures in which the waste is contacted with a leachate
for a specific period of time, agitating the mixture to achieve
continuous mixing. Chemical equilibrium is often obtained,
especially when the solidified waste is crushed before
extraction. After extraction and separation of the leachate
fluid from the solid waste, the leachate is analyzed for specific
constituents. Most of these tests use a leachate to waste ratio
of 20:1 so that the maximum concentration of constituent which
can be attained in the leachate is 5% of that in the original
solid waste. The leachate used in most cases is a dilute acid.
The total amount of acid added varies with the test and/or with
the alkalinity of the waste. The pH of the leachate at the end
of the test is usually controlled by the alkalinity of the waste
when the leachate is deionized water or dilute acid. Final pH is
one of the controlling factors in metal leaching.
l. TCLP. The TCLP is the regulatory leaching procedure
currently used in the United States. The TCLP involves passing
the solid portion of a sample through a 9.5 mm sieve. The sample
is then placed in a rotary agitation device along with an acetic
acid solution at a ratio of 1 part waste to 20 parts acetic acid.
The sample and acid solution are then mixed for 18 hours in the
rotary agitation device at a rate of 30 revolutions per minute.
Once the mixing has been completed, the acetic acid solution is
analyzed to determine how much of the contaminants have leached
out of the sample. If the amount of contaminants that have
leached out exceeds regulatory criteria, then the waste is
classified as hazardous. The complete procedure for the TCLP is
described in SW-846, Method 1311. Some precautions about