28 Feb 95
(3) Proprietary Processes. There are many proprietary
processes available which are generally a combination of the
above reagents. These proprietary processes may include
additives to fix specific constituents, or anti-inhibiting agents
to solidify wastes that are difficult to treat. A summary of
proprietary processes and their applicability is provided in the
text entitled "Chemical Fixation and Solidification of Hazardous
Wastes" by Jess Conner.
(4) Mix Ratios. The optimum reagent to waste mix ratio is
typically around .25 for contaminated soil. However, this ratio
can vary anywhere from .1 to 2.0 depending on the contaminants
present and the initial moisture content of the waste.
d. Treatment Technologies. S/S treatment can be performed
either in-situ or ex-situ. In-situ treatment of soil is
generally performed by injecting reagents into the ground and
then mixing the reagents and contaminated soil with an auger. An
ex-situ S/S system generally consists of a pug mill mixer,
and measuring equipment. Pumps or mechanical conveyors are used
to transport the waste into a surge tank or feed hopper which in
turn feeds the waste into the mixer where it is mixed with S/S
reagents and water. Depending on the process used, one or more
dry or liquid reagents may be added to the waste in the mixer.
Typical mixing times are reported to range from 1 to 30 minutes.
Stabilization reagents are often added prior to solidification
reagents to allow the stabilizing reagents time to react with the
contaminants. If the solidifying reagents are added too soon,
they could inhibit the stabilization reactions. After mixing,
the treated material is cured and then tested to verify it meets
all physical and chemical parameters specified.
(1) Post-treatment testing requirements vary from project to
project depending on the regulatory agencies involved. Post-
Required chemical testing often consists of performing the
Toxicity Characteristics Leaching Procedure (TCLP) and chemically
analyzing the extract. Physical parameters tested will vary from
project to project and may include unconfined compressive
strength, permeability, and durability.
(2) Frequency of post-treatment testing is also subject to
approval by regulatory agencies and varies from project to
project. The most common frequency for testing is one set of
tests per 400 to 800 cubic meters (500 to 1,000 cubic yards) of
treated material. However, testing frequencies of greater than
once every 75 cubic meters (100 cubic yards) have been used on