Water treatment plants (WTPs) can produce significant amounts of residual solids (i.e. sludge) as a result of coagulation, flocculation, clarification, and filtration processes to treat raw source water. In North America, alum is a common coagulant used in this process, resulting in the requirement for disposal of significant amounts of alum residual solids. Anticipated improved water quality treatment guidelines for trace metals such as arsenic in North America will result in more alum waste being generated in the future and hence increased pressure on water utilities to examine monofilling of alum-based residual solids to reduce waste management costs. GCLs are a potential cost-effective liner system for this type of application. However, there is currently a paucity of literature related to aluminium migration through GCLs.This paper presents results of GCL hydraulic conductivity, diffusion, and batch testing performed with a simulated WTP monofill leachate. Results of both short term and long term hydraulic conductivity tests show only modest increases in hydraulic conductivity, k, are observed for the tests conditions employed (k< 5x10 /s and a linear distribution coefficient, K d , of 30 mL/g. Batch testing is used to provide additional insight into the sorption behavior of aluminium with the bentonite from the GCL. Based on the limited results presented herein, it appears as if GCLs are suitable at maintaining low hydraulic conductivity values for at least 12 pore volumes of permeation with the high concentration alum residual monofill leachate simulated in this study. The information presented herein also provides WTP monofill designers with estimates of contaminant migration parameters necessary for establishing "alternative" GCL based liner designs.

In this paper a conservative tracer (tritiated water) is used to assess the diffusive properties of 14 different laboratory-prepared soil–cement mixtures. A single-reservoir diffusion test setup to determine the effective porosity (ne) and the effective diffusion coefficient (De) through saturated, monolithic, soil–cement materials is used to assess the importance of mixture design on ne and De. Values of De and ne were found to range from 2.5 × 10−10 to 7.0 × 10−10 m2/s and from 0.21 to 0.41, respectively. Results indicate that the water content of the initial mixture has a substantial effect on the diffusive properties of the soil–cement material. The results suggest, from a contaminant transport perspective, that designers should generally aim to minimize the water content of cement-based solidification–stabilization materials.

This paper presents the application of a single reservoir diffusion test to determine the effective porosity of the soil-cement matrix and the diffusivity of tritium through saturated, monolithic, cement solidified/stabilized wasteforms. Testing was performed on a laboratory mixture of cement paste, sand, and kaolinite. The influence of porosity on the proper interpretation of the diffusion tests was examined. Results of tests on three replicate specimens were consistent and indicate effective porosities of 0.26 to 0.28 and effective diffusive coefficients of 2.5×10-10 m 2 /s to 3.0×10-10 m 2 /s. The effect of curing time is discussed. Products of the effective diffusion coefficients and porosity (n e D e) decreased by 22% from specimens cured for 14 days to specimens cured for 28 days prior to testing while from 70 days to 126 days of curing n e D e only changed by 8%. This suggests that curing should be carried out for greater than 70 days prior to conducting these tests.

This paper presents a laboratory study that assesses the diffusive and sorptive parameters of three volatile organic compounds (benzene, ethylbenzene and trichloroethylene) though cured, monolithic soil-cement materials. A double-reservoir diffusion test setup is used to determine the effective diffusion coefficient (D e) and distribution coefficient (K d) for laboratory-prepared soil-cement specimens at three water-to-cement ratios. Batch testing was also performed to provide a measure of the distribution coefficient independent of the diffusion testing. Values of K d determined from batch testing, diffusion testing and theoretical estimates from the literature ranged from 0 to 1·3 cm3/g and were in general agreement. Values of D e determined from laboratory testing ranged from 1·50 × 10−10 m2/s to 3·0 × 10−10 m2/s. Practical applications of the laboratory testing methodology and results are discussed with respect to how they may be used in the pre-design and design phases of cement solidification/stabilisation (s/s) treatment. An illustrative example shows how the laboratory testing results could be used to estimate contaminant transport from a site and to provide an indication of the relative importance of the diffusive and sorptive parameters obtained from laboratory testing.

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