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In Situ Solidification
and Stabilization Process
Geo-Con, Inc.
Technology Description
The in situ solidification and stabilization process technology immobilizes
organic and inorganic compounds in wet or dry soils, using reagents (additives)
to produce a cement-like mass. The basic components of this technology are:
1) Geo-Con, Inc.'s (GEO-CON), deep soil mixing system (DSM), to deliver
and mix the chemicals with the soil in situ; and
2) a batch mixing plant to supply International Waste Tech-nologies'
(IWT) proprietary additives (see figure below).
The proprietary additives generate a complex, crystalline, connective
network of inorganic polymers in a two-phase reaction. In the first phase,
contaminants are complexed in a fast-acting reaction. In the second phase,
macro-molecules build over a long period of time in a slow-acting reaction.
The DSM system involves mechanical mixing and injection. The system consists
of one set of cutting blades and two sets of mixing blades attached to a
vertical drive auger, which rotates at approximately 15 revolutions per
minute. Two conduits in the auger inject the additive slurry and supplemental
water. Additives are injected on the downstroke; the slurry is further mixed
upon auger withdrawal. The treated soil columns are 36 inches in diameter
and are positioned in an overlapping pattern of alternating primary and
secondary soil columns.
The in situ solidification and stabilization process treats soils, sediments,
and sludge-pond bottoms contaminated with organic compounds and metals.
The process has been laboratory-tested on soils containing polychlorinated
biphenyls (PCB), pentachlorophenol, refinery wastes, and chlorinated and
nitrated hydro-carbons. The process can treat any waste for which a physical
or chemical reagent is applicable.STATUS:
A SITE demonstration, using one-auger, was conducted at the General Electric
Service Shop site in Hialeah, Florida in April 1988. Two 10-by-20-foot areas
were treated - one to a depth of 18 feet, and the other to a depth of 14
feet. Ten months after the demonstration, long-term monitoring tests were
performed on the treated sectors. The Technology Evaluation Report (EPA/540/5-89/004a)
and the Applications Analysis Report (EPA/540/A5-89/004) have been published.
A four-auger process remedi-ated the PCB-contaminated Hialeah site during
the winter and spring of 1990. Geo-Con has used the process to complete
over 40 in situ stabilization projects throughout the United States. Several
significant projects completed to date include:
- Construction of a 110,000 square foot, 60-feet deep soil-bentonite
DSM wall to contain contaminated groundwater from a former waste pond.
All DSM permea-bilities were less than 10-7 centimeters per second, a first
for DSM construction
- Shallow soil mixing and stabilization of 82,000 cubic yards of contaminated
soils at a former manufactured gas plant site that was ultimately converted
to a city park
The equipment has been scaled up to diameters as large as 12 feet. Typical
process costs are $40 to $50 per cubic yard plus reagent costs. To date,
Geo-Con has utilized this process to treat over one million cubic yards
of contaminated soils and sludges.
The SITE demonstration yielded the following results:
- PCB immobilization appeared likely, but could not be confirmed because
of low PCB concentrations in the untreated soil. Leachate tests on treated
and untreated soil samples showed mostly undetectable PCB levels. Leachate
tests performed 1 year later on treated soil samples showed no increase
in PCB concentra-tions, indicating immobilization.
- Sufficient data were unavailable to evaluate the system's performance
on metals or other organic compounds.
- Each of the test samples showed high unconfined compressive strength
(UCS), low permeability, and low porosity. These physical properties improved
when retested one year later, indicating the potential for long-term durability.
- The soil's bulk density increased 21 per-cent after treatment. This
treatment increased the treated soil volume by 8.5 percent and caused a
small ground rise of 1 inch per foot of treated soil.
- The UCS of treated soil was satisfactory, with values up to 1,500 pounds
per square inch.
- The treated soil's permeability was satis-factory, decreasing to 10-6
and 10-7 centimeters per second (cps) compared to 10-2 cps for untreated
soil.
- The wet and dry weathering test on treated soil was satisfactory.
- Data provided by Geo-Con indicated some immobilization of volatile
and semivolatile organics, which may be due to organophilic clays present
in the reagent. Data are insufficient to confirm this immobilization.
- Performance data are limited outside of the SITE Program. Geo-Con modifies
the binding agent for different wastes. Treatability studies should be
performed for specific wastes.
- Process costs were $194 per ton for the 1-auger machine used in the
demonstration, and $111 per ton for a commercial 4-auger operation. More
recent experi-ence with larger scale equipment reduced process costs to
about $140 per cubic yard.FOR FURTHER INFORMATION:
EPA PROJECT MANAGER:
Mary Stinson
U.S. EPA
Risk Reduction Engineering Laboratory
2890 Woodbridge Avenue
Edison, NJ 08837-3679
908-321-6683
Fax: 908-321-6640
TECHNOLOGY DEVELOPER CONTACTS:
Chris Ryan or Linda Ward
Geo-Con, Inc.
4075 Monroeville Boulevard
Corporate One, Building II, Suite 400
Monroeville, PA 15146
412-856-7700
Fax: 412-373-3357 |
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