Netnapid Yossapol and Prof. Jay N. Meegoda, New Jersey Institute of Technology

The low-viscosity chemical grout, colloidal silica (CS), is extensively used as a grouting material in construction of grout curtains. CS with low viscosity and non-toxicity is injected into soil to stabilize fine-grained soils. It is also used as a viscous liquid barrier in some hazardous waste sites (Persoff, 1995). This paper presents a theoretical analysis of the applicability of injected CS grouts to stabilize/solidify chromium contaminated soils from Hudson County, NJ.

In this paper, physical mechanisms of CS grouting treatment of chromium contaminated soil will be investigated. During stabilization, after liquid CS is injected into contaminated soil, it moves though the voids inside soil matrix. The viscosity is increased while CS is moving, causing a reduction of flow velocity in soil. The above process results in thickening or coating of chromium contaminated soil with CS by transforming liquid CS into a gel. The gelling time and gelling mechanisms are controlled by the variation in viscosity, which depends on soil type, soil composition, concentration and chemical characteristics of CS. The movement of CS during the grouting process as a function of time, chemistry of grout and environmental factors is modeled at the microscopic level. The result will show the growth of film during grouting process.

William B. Empson and Jason M. Leibbert, U.S. Army Corps of Engineers Kansas City District, David Hixson, Jacobs Engineering Group, Raymond E. Bailey and Marjorie Wesley, MK-Ferguson Company.

The former Weldon Spring Ordnance Works produced Trinitrotoluene (TNT) and Dinitrotoluene (DNT) explosives in the early 1940s. As a result of the manufacturing, significant levels of explosives were present in site soils. Efforts between 1945 and the 1960s to clean up these explosives led to the co-mingling of explosives, lead, and asbestos wastes. A portion of the site was used by the Atomic Energy Commission (AEC) in the 1950s and 1960s for the processing of Uranium and Thorium. As a result, some site soils contained both explosives and radionuclides. The levels of 2,4 DNT in the soils were determined to be greater than the regulatory limit of 130 m g/l under the Resource Conservation and Recovery Act (RCRA). In order to facilitate disposal under the Land Disposal Restrictions (LDRs), an innovative treatment method was required since thermal treatment of soils containing explosives and radionuclides or asbestos would be exceptionally complicated. In a coordinated effort, the Department of Energy (DOE) (Formerly AEC) was responsible for any soils containing explosives and radionuclides while the U.S. Army was responsible for any soils containing explosives and lead or asbestos. Through bench testing and strictly controlled field implementation, the DOE determined that the addition of 20 percent by weight cement and fly ash could reduce the leachable 2,4-DNT from over 1000 m g/l to below the LDR limit of 130 m g/l. In cooperation with the DOE, the U.S. Army Corps of Engineers then expanded on the bench scale testing and implemented a similar and equally successful field treatment operation that demonstrated consistent compliance with the LDRs using less rigorous field controls. The results of these efforts indicate that the process is time dependent and that temperature and water content affect the rate at which the treatment process progressed. The process is cost competitive with thermal treatment.

Ralph S. Baker and John M. Bierschenk, TerraTherm, Inc.

In Situ Thermal Destruction (ISTD) is a soil and sediment remediation process in which heat and vacuum are applied simultaneously to subsurface soils or aboveground soil/sediment piles. Heat flows into the soil primarily by conduction from heaters typically operated at 700-800° C. The heaters are installed in wells at regular intervals within the soil. As soil is heated, organic contaminants in the soil are vaporized or destroyed by several mechanisms, including evaporation, steam distillation, boiling, oxidation, and pyrolysis. The vaporized constituents are drawn toward extraction wells for aboveground treatment. Compared to fluid injection processes, the conductive heating process during ISTD is very uniform in its vertical and horizontal sweep. The combined effectiveness of both heat and vapor flow leaves no area untreated. Laboratory treatability studies and field project experience at seven ISTD sites have confirmed that high temperatures applied over a period of days result in extremely high destruction and removal efficiency of even high boiling point contaminants such as PCBs, pesticides, PAHs and other heavy hydrocarbons. The effectiveness of the process is not limited by the presence of heterogeneous soil conditions or clay. Despite high pre-treatment soil contaminant concentrations, post-treatment soil concentrations have typically been non-detect. Moreover, most of the contaminants (95-99% or more) are destroyed in the soil before reaching the surface. Stack sampling has demonstrated that emissions of toxic air pollutants including dioxins are substantially below standards. ISTD thus offers a cost-effective means to reliably achieve stringent cleanup goals that have not been previously possible by in-place treatment. The implications for the setting of cleanup standards are discussed.