Leaching Processes and Evaluation Tests for Inorganic Constituent Release from Cement-Based Matrices - Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes - page 267

• The small amount of leachant that contacts the waste will be highly

alkaline (i.e., in the range of the cement pore water) due to percolation
through or contact with cementitious wastes above the subject material.

• The concentration in the infiltrating leachant will tend to come to a steady

state with the contaminants in the waste as a result of slow percolation
rates.

Under these assumed conditions, low L/S ratio leaching tests designed to eval-
uate equilibrium at the pH dictated by the ANC of the waste would provide an
estimate of percolating leachate in the short term. Higher L/S ratio tests would
indicate the effect of soluble species depletion on equilibrium chemistry. Suggested
tests would include batch tests like EN 12457, SR003.1, and ASTM D 3987 or
column tests like NEN 7343, ASTM D 4874, and prEN 14405.

10.6.2 U NCONTROLLED N EAR -S URFACE P LACEMENT

If a solidified material is used in a near-surface placement without leachate controls,
several conditions may exist that have significant consequences to constituent
release. Examples of such a situation may include beneficial reuse of stabilized
wastes in construction (e.g., as roadbase or backfill) or in-situ S/S treatment of
contaminated soils without leachate diversion. For the above release scenario, the
following statements may be considered:

• The cementitious material may be subjected to high volumes of infiltrating

water on an intermittent wetting basis (i.e., dependent on local precipita-
tion patterns and volumes).

• The contact mode for infiltrating liquid phases may be either percolation

(e.g., loose granulated fill) or flow-around (e.g., compacted granular or
monolithic materials).

• Release rates may be controlled by equilibrium or mass transport, depend-

ing on infiltration rates, leachant volume, and contact time.

• Degradation via chemical (e.g., carbonation, chloride penetration, sulfate

attack) or physical (e.g., cyclic loading, freeze/thaw) mechanisms will
change equilibrium- and mass-transport-based release parameters.

The most complete approach for testing in the above scenario would be to
combine the results of an equilibrium-based test over a range of pH values with a
mass-transport test for a monolithic test sample. Equilibrium testing will allow for
consideration of acid neutralization consumption from infiltrating acidic components
while the mass-transport tests would provide information on rates of constituent
release from the monolithic material. Suggested protocols would include pH-depen-
dent tests (e.g., prEN 14429, SR002.1, and Acid Neutralization Capacity Test) and
dynamic tests for monolithic materials (e.g., ANSI/ANS-16.1, NEN 7345, and
MT001.1).