U.S. EPA Superfund Innovative Technology Evaluation (SITE) Program
Solidification/Stabilization Treatment Process
STC Remediation
(Formerly Silicate Technology Corporation)

Abstract

STC Remediation, a division of Omega Environmental, Inc., Scottsdale, Arizona, developed a technology that stabilizes and solidifies inorganic and organic hazardous wastes into a concrete-like, high-strength, leach-resistant monolith. The key feature of this technology is a proprietary alumino-silicate reagent, SOILSORB, which binds with the contaminants and forms insoluble, less mobile compounds. STC Remediation's technology is applicable to hazardous soils, sludges, and wastewaters contaminated with inorganics, including most metals, cyanides, fluorides, arsenates, chromates, and selenium, and organics, including halogenated aromatics, polynuclear aromatic hydrocarbons, and aliphatic compounds. Treatability testing is required to determine the proper amount of reagent necessary for proper solidification/stabilization. The treatment process begins by screening and/or crushing excavated soil to no-greater-than 3/8-inch. The screened waste is conveyed to a batch plant where the SOILSORB reagent is added. The mixture is deposited in a pug mill or ready-mix cement truck for thorough blending and then poured into either on-site confining pits or curing forms for off-site disposal. STC Remediation's SITE demonstration was conducted in November 1990 at the Selma Pressure Treating (SPT) Superfund site in Selma, California. The SPT site was contaminated with organics, mainly pentachlorophenol (PCP), and inorganics, mainly arsenic, chromium, and copper. (The SPT site was ultimately remediated in 1993 using STC Remediation's treatment process.) The demonstration featured a number of physical and chemical tests, including critical measurements for arsenic, chromium, copper, and pentachlorophenol (PCP) by TCLP and TWA analysis. Results from pre- and post-treatment sampling show that the technology reduced total extractable PCP concentrations up to 97 percent and stabilized the residual PCP concentrations to very low leachable levels (from 5 to less than 0.3 milligrams per liter). The process immobilized arsenic and copper, while chromium remained well within regulatory limits. Long-term monitoring at 18 and 32 months following the demonstration provided comparable results for PCP, arsenic, and copper, while chromium remained well within regulatory limits. The treated wastes had moderately high unconfined compressive strength, averaging 300 pounds per square inch (psi) after 28 days, increasing to more than 700 psi after 18 months. Permeability of the treated waste was low (less than 1.7 x 10^-7 centimeters per second). The relative cumulative weight loss after 12 wet/dry and 12 freeze/thaw cycles was negligible (less than 1 percent). The economic analysis gave a range between $190 and $330 per cubic yard of waste depending upon the amount of waste, its initial total organic content, and other specific waste characteristics.

Posted July 12, 1999

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