The use of complex permittivity and electrical conductivity to detect soil contamination by landfill leachate is discussed in this paper. The electrical conductivity and complex permittivity of a natural clayey soil are measured before and after permeation with multiple aqueous ionic solutions (synthetic leachate) that simulate the composition of leachate from a domestic solid waste disposal facility, and with aqueous ${\mathrm{CaCl}}_2$ solutions at various concentrations. The dielectric and electrical characteristics of soil, the experimental apparatus and procedure, and the analysis methodology are discussed, followed by the results of complex permittivity measurement before and after permeation using the synthetic leachate and ${\mathrm{CaCl}}_2$ solutions at various concentrations. The results show that the experimental system provides reliable measurement of the soil complex permittivity at 250 MHz and of the soil static electrical conductivity. The relative permittivity of soil is shown to decrease linearly with the overall cationic concentrations in the pore fluid, whereas the relative loss factor and electrical conductivity of soil increases linearly with the overall cationic concentration in the soil pore fluid. The cationic species can be distinguished in terms of the different linear regression trend lines of the electrical conductivity, relative permittivity, and loss factor versus ionic concentrations.

Heavy metal contaminated soils can be a long-term environmental concern and a potential financial liability to landowners. Hence, the assessment of heavy metal contaminated soil has received much attention in the last few decades. For a reliable and cost-efficient investigation, a well-planned sampling strategy, appropriate selection and implementation of analytical methods, and careful interpretation of results are prerequisites. This paper presents a brief overview of the preparatory, sampling, and analytical stages of an investigation of heavy metal contamination of soils, particularly in the analysis of heavy metal contaminated soils.

This paper provides reviews and updates of surfactant-aided subsurface remediation. Experimental measurements were made of various systems comprising two non-ionic surfactants, five soils of different fractional organic carbon contents, and several typical hydrophobic organic compounds (HOCs). Soil-washing performance was quantified using reciprocal surfactant-soil solubilization coefficients $(1/K_d)\text{,}$ and two phases of soil-washing mechanisms were identified depending on the presence of surfactant micelles. Reciprocal surfactant-soil solubilization coefficients $(1/K_d)\text{,}$ octanol-water partition coefficients $\left(K_{\mathrm{ow}}\right)\text{,}$ fractional organic carbon content of the soil $\left(f_{\mathrm{oc}}\right)\text{,}$ and surfactant concentration were correlated for the soil-washing process using a proposed surfactant-aided soil-washing model.

The performance of a series-electrokinetic (EK) process in treating a clay soil artificially contaminated with 300 mg/kg trichloroethylene (TCE) was investigated. Constant voltage gradients of 1 or 2 V/cm to induce the movement of electrolyte solution in the soil were applied to the EK system for 3–5 days using synthetic groundwater as processing fluid. Results show that the values of electroosmotic permeability ranged from $3.7\times {10}^{-6}$ to $9.1\times {10}^{-6} {\mathrm{cm}}^2/V-s\text{.}$ Increasing applied voltage and prolonging processing time resulted in a better removal efficiency. With voltage gradient of 1 V/cm, TCE removal efficiency of 75.8 and 86.4% were achieved, respectively, for 3 and 5 days EK operation. It was found that nearly 100% TCE was removed in the vicinity of anode sides. When the applied voltage gradient was raised to 2 V/cm, the remaining TCE concentration in both cathode sides was effectively removed and a total removal efficiency of 91.3% was achieved. Energy requirements per unit ton of soil treated were around 12.6–46.2 kWh/ton.

This paper presents the study results for a novel stabilization/solidification (S/S) process for high mercury wastes (Hg >260 ppm). In this study, a low-cost powder reactivated carbon (PAC) was used to stabilize mercury in contaminated soils. Two types of contaminated soils were used: (1) a mercury-doped pure sand, used as a waste surrogate so as to minimize competitive adsorption by substances in real soils; and (2) a mercury-contaminated soil with about 2,300 ppm Hg from a mercury cell chlor-alkali plant. To improve the mercury adsorption capacity, PAC was impregnated with sulfides. It was found that sulfurized PAC significantly lowered mercury mobility. After stabilization, wastes were subjected to cement solidification. Results of toxicity characteristic leaching procedure and constant pH leaching tests showed that the S/S process successfully immobilized mercury in the treatment matrix. Even under attack from high chloride concentration, little mercury was leached from the matrix. Optimal S/S treatment parameters and treatment process flows are discussed for possible commercial implementation of the process. Based on the experimental data, it can be concluded that the S/S process by reactivated carbon and cement is a robust and effective technology for immobilization treatment of high mercury wastes.

Bentonite modified by cationic surfactants has been the focus of attention for engineering applications such as in horizontal cut-offs, grout mixes, cut-off slurries, soil motars, and landfill liners because of its high organic removal capacity. In this study, the feasibility of using modified clays in conjunction with conventional soil-bentonite admixtures as a waste containment barrier with the combined abilities of acting as a sealant and effectively retaining dissolved organic contaminants was investigated by a series of experimental tests. The sorption isotherms of total organic carbon, a gross organic term, by five types of soil admixtures are nonlinear. The soil specimen with more modified clays exhibits higher organic sorption capacity and a larger retardation factor. The specimens with 20% of pure bentonite by dry weight have a higher optimum water content and plasticity. With the addition of bentonite in the soil material consisting of natural soils and modified clays, the hydraulic conductivity to leachate decreases from about ${10}^{-7}$ to ${10}^{-8} \mathrm{cm}/s\text{.}$ No incompatibility between landfill leachate and soil specimens is found. The curve fitting technique was applied to determine the effective porosity and hydrodynamic dispersions of both Cl and total organic carbon. The 1D contaminant transport model was used to develop design charts for the determination of liner thickness. Results show that the presence of modified clays in the soil containing 20% bentonite largely reduces the required liner thickness.

Waste immobilization techniques prevent the free movement of contaminants in waste. Three major types of immobilization techniques, namely, the temporary containment techniques, cost effective solidification/stabilization techniques, and permanent vitrification techniques are described. The purpose of this paper is to provide a comprehensive list of waste immobilization techniques with sufficient descriptions including advantages, disadvantages, and limitations. The selection of an appropriate waste immobilization technique depends on site conditions and type and amount of waste. Several temporary containment techniques such as pumping, capping, draining, and slurry walls are discussed. Solidification/stabilization techniques can be either chemical or nonchemical. Chemical methods are very popular and cost effective. Contaminated soils can be effectively solidified and stabilized using chemical methods, but the resulting products may not always be reused as construction materials or consumable materials. Vitrification is an innovative technology that incorporates hazardous and contaminated waste into a chemically, durable glass-like product. Vitrification can be either in situ or ex situ. The containment techniques are usually used to “buy time” under emergency or temporary conditions. Contaminated soils can be effectively solidified and stabilized using chemical methods, but the resulting products may not always be reused as construction materials or consumable materials. The Environmental Protection Agency has declared vitrification to be the “best demonstrated available technology” for heavy metals and high-level radioactive waste.

High concentrations of Al, Fe, Ca, Mg, and Zn in the tanning agent are detrimental to the properties of tanned leather. To recycle the Cr(III) from the tannery sludge to the tanning agent, these five metals must be removed from the acid extract obtained by sulfuric-acid treatment of tannery sludge. A new approach has been developed to recycle the Cr(III) and to remove other metals. Summarily, this pilot test includes a simple six steps process for the extraction of metals from tannery sludge and the following separation of Cr(III) from interfering elements (Al, Fe, Ca, Mg, Zn) in the acid extract (or filtrate). In Step 1, metals were extracted from tannery sludge with sulfuric acid at about pH 1–2. A filtration was then performed to separate the residual solids and the liquid. The second step involves the dilution of filtrate and the precipitation of Al and Fe at pH 4.8. The third step involves the precipitation of Cr(III) at pH 7.0 for the separation of Ca and Mg from Cr(III). As a result, a precipitate containing less interfering metals was obtained in the third step. In order to recover more Cr(III), the precipitate obtained in Step 2 was dissolved once again with sulfuric acid in the fourth step. The fifth and sixth steps were similar to the second and third steps respectively, except that the pH in the sixth step was adjusted to 8.3 not 7.0. After the sixth step, a precipitate containing less interfering metals was also obtained. A 44% of Cr recovery yield was obtained in the final product. The Cr concentration in this product was 32.5% and the ratio of interfering metals to Cr concentration was inferior or equal to 0.02.