Leaching Processes and Evaluation Tests for Inorganic Constituent Release from Cement-Based Matrices - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 246

material with chemical analysis of a limited set of constituents. Interpretation of
the leaching test results is a simple pass/fail comparison to acceptable leachant
concentrations for only those constituents critical for performance acceptance. One
significant disadvantage of screening tests is that little mechanistic information is
provided by most protocols without subsequent comparison to other more detailed
characterizations.
An example of a protocol that may serve to screen waste materials is the EN
12457-3 “shake test” for granular waste. 175 This procedure consists of a two-step
sequential extraction procedure of a particle-size reduced material in DI water
leachant at two levels of liquid-to-solid ratio. The solid phase from the first 3-hour
extraction at an L/S ratio of 2 ml/g is extracted for an additional 3 hours at an L/S
ratio of 8 ml/g. The concentrations in the leachate may be used to predict pore
solution in the fresh material, and infer pore chemistry after soluble species have
been leached. The leaching response using this test may be compared to leaching
behavior of previously characterized material to check for product consistency or
regulatory compliance.

10.4.2.2 Field Mimicking or Simulation Tests

Several hazardous and solid waste regulatory protocols promulgated for waste
screening are essentially field mimicking tests. 176,177 This category of leaching tests
is not explicitly distinguished by the CEN/TC-292 harmonization committee. Field
mimicking tests are designed to provide a representative leachate from a leaching
test by simulating specific release scenario conditions.
Simulation protocols may be useful when the exact release scenario, or a limiting
case, is known and duplicated in the laboratory. However, implementation of field
mimicking leaching tests may be quite complex, as leaching factors (e.g., leachant
composition, L/S ratios, particle size, and modes of water contact) may vary by
region or by release scenario (e.g., lined or unlined landfills, monofills, or co-
disposal). The application of these tests is severely limited or may be completely
irrelevant if the proposed field release conditions are uncertain or significantly differ
from test conditions. Interpretation of the leaching data applied to release scenarios
other than the particular scenario simulated by the test conditions may be misleading
at best and can result in significant errors in constituent release prediction (over-
and under-estimation).
As an example, the Synthetic Precipitation Leaching Procedure (SPLP) 177 uses
dilute nitric/sulfuric acid leachants to simulate contaminant release for scenarios
where acidic rainfall percolates through a high permeability fill. The exact compo-
sition of the SPLP leachant depends on the location of the disposal site, requiring
a priori knowledge of the disposal facility location. A higher level of acid in the
SPLP leachant is specified for disposal east of the Mississippi River in order to
account for the effects of dense industrialization on rainfall composition in the
eastern United States.
TCLP 176 is one example of a field mimicking test that is applied as a screening
protocol in practice. The field conditions adopted by TCLP are those of an assumed