Leaching Processes and Evaluation Tests for Inorganic Constituent Release from Cement-Based Matrices - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 247

“mismanagement” scenario described as disposal of hazardous waste in a biologi-
cally active municipal solid waste landfill. Leachate concentrations resulting from
TCLP are compared to the promulgated list of TC permissible limits, and the solid
waste is considered “hazardous” by toxicity characteristics if the concentration of
any constituents in the leachate exceeds the acceptable value. Technical and scientific
limitations of this protocol are well documented 3-5,40,178 and the TCLP has been
proven inadequately protective for highly alkaline waste forms. 181-182 Although not
promulgated for regulatory purposes other than classification, the TCLP often has
been the de fac t o basis for waste delisting applications, development of waste
acceptance criteria, prediction of long-term release, and evaluation of waste treat-
ment efficacy.

10.4.2.3 Intrinsic Property Tests

Many leaching tests are designed to provide insight into one or more of the intrinsic
leaching properties that characterize the leaching process. For example, the pH Static
Test, 183 a published leaching protocol currently in process of CEN/TC-292 standard-
ization as prEN 14429, 184 is an equilibrium-based protocol consisting of parallel
challenges of particle-size-reduced material to different-strength acid solutions. The
goal of the test is to determine the ANC of the material and the solubility of
constituents as a function of solution pH. The pH Static Test does not provide data
on the kinetics of release and provides only limited long-term performance infor-
mation. The results of the pH Static Test, or other equilibrium-based protocols, are
commonly combined with those of mass-transport characterization tests to fully
characterize waste leachability. 96,185-188
The results of a properly selected intrinsic property test may be used to create
a fundamental leaching profile of the solid material independent of release scenario
factors. A minimal fundamental leaching profile may be comprised of the following
intrinsic properties:

• Constituent availability or the leachable content under environmental con-

ditions

• ANC of the S/S material

• Solubility and release of constituents as a function of pH and L/S ratio

• Constituent diffusion coefficients for mass transfer through the S/S

material

The development of a fundamental leaching profile based on the above parameters
requires a combination of both equilibrium and dynamic testing under a range of
experimental conditions. Thus, this category of leaching evaluation tends to be relatively
complex. Although characterization tests may be time-consuming and expensive for
previously uncharacterized materials, the power and cost-savings benefit is evident when
developed intrinsic leaching profiles are used to provide comparative release estimates
for any number of release scenarios or sets of site-specific information. 5