GEO-CON, INC.

(In Situ Solidification and Stabilization Process)

TECHNOLOGY DESCRIPTION:

The in situ solidification and stabilization process 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 (DSM) system, to deliver and mix the chemicals with the soil in situ; and (2) a batch mixing plant to supply 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, macromolecules 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.

WASTE APPLICABILITY:

The 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 hydrocarbons.

STATUS:

A SITE demonstration was conducted as a joint effort between International Waste Technologies (IWT) and Geo-Con. The demonstration was conducted at the General Electric Service Shop site in Hialeah, Florida in April 1988. IWT provided the treatment reagent, specifically the proprietary additive (HWT-20), and Geo-Con provided both engineering and hardware for the in situ soil treatment. 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. A four-auger process was later used to remediate the PCB-contaminated Hialeah site during the winter and spring of 1990. Cooperative efforts between Geo-Con and IWT ended with the remediation of the Hialeah site.

Presently, Geo-Con offers the entire in situ stabilization package, including the treatment chemicals. Geo-Con has used the process to complete over 40 in situ stabilization projects throughout the United States. Significant projects completed to date include the following:

• Construction of a 110,000-square-foot, 60-foot-deep, soil-bentonite DSM wall to contain contaminated groundwater from a former waste pond. All DSM permeabilities were less than 10-7 centimeters per second (cm/s).
• Shallow soil mixing and stabilization of 82,000 cubic yards of contaminated soils at a former manufactured gas plant site. The site was declared clean and ultimately converted to a city park.

The DSM system augers have been scaled up to diameters as large as 12 feet. To date, Geo-Con has used this process to treat over 1 million cubic yards of contaminated soils and sludges.

DEMONSTRATION RESULTS:

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 concentrations, indicating immobilization.
• Data were insufficient to evaluate the system's performance on other organic compounds and metals.
• Each test sample showed high unconfined compressive strength (UCS), low permeability, and low porosity. These physical properties improved in samples retested 1 year later, indicating the potential for long-term durability.
• Bulk density of the soil increased 21 percent 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 permeability of the treated soil was satisfactory, decreasing to 10-6 and 10-7 cm/s compared to 10 -2 cm/s for untreated soil.
• Data were insufficient to confirm immobilization of volatile and semivolatile organics. This may be due to organophilic clays present in the reagent.
• Process costs were $194 per ton for the 1-auger machine used in the demonstration, and $111 per ton for a commercial four-auger operation. More recent experience with larger scale equipment reduced process costs to about $15 per ton plus the cost of reagents.

The Technology Evaluation Report (EPA/540/5-89/004a) and the Applications Analysis Report (EPA/540/A5-89/004) are available from EPA.

FOR FURTHER INFORMATION:

TECHNOLOGY DEVELOPER CONTACTS:
Linda Ward or Robert Hayden
Geo-Con, Inc.
4075 Monroeville Boulevard
Corporate One, Building II, Suite 400
Monroeville, PA 15146
412-856-7700
Fax: 412-373-3357