Geoenvironmental Engineering

A field and laboratory investigation was performed on the site of a former settling basin for approximately 2.7 million cubic yards of Solvay process residue (mostly soda ash) to assess the feasibility of commercially developing the land for residential housing, light commercial structures, recreational facilities, parking lots, and associated utilities. The investigation included a test embankment surcharge program to assess the deformation behavior of the subsurface materials under additional loading. Of particular interest were the magnitude and rate of settlement associated with the surcharge loads. This field effort was undertaken to determine the feasibility of pre-loading as a ground improvement method, to obtain data for the design of future pre-loading schemes and to develop appropriate foundation recommendations for the desired improvements. A subsurface investigation program was performed both before and after the surcharge program. This field exploration included soil test borings with Standard Penetration Tests performed at regular vertical intervals. Undisturbed (Shelby tube) samples of the Solvay process residue were retrieved for laboratory testing. Field behavior was characterized through monitoring of settlement plates and piezometers. Additionally, strength and settlement properties of the Solvay were measured through laboratory testing before and after pre-loading. The results of this case study provide data which may be used to characterize the behavior of the fine-grained, Solvay process residue under loading and to enable the redevelopment of similar sites.

Utilization of recycled materials as a substitute for natural soils in engineering applications such as highway construction is an emerging application area. A research study was conducted to investigate the stabilization of petroleum-contaminated soils (PCSs) using another recycled material, high carbon content fly ash (HCCFA), and evaluate the feasibility of using the final product in highway embankment construction. A battery of laboratory tests was conducted to evaluate the environmental suitability of stabilized PCSs. The test program included batch adsorption and long-term column leaching tests. Naphthalene and o-xylene, and a tertiary model non-aqueous phase liquid were used as the pollutants in batch sorption and column tests, respectively. Batch sorption tests demonstrated a nonlinear sorption behavior for naphthalene and o-xylene onto HCCFA. Column leaching test results indicated that the naphthalene and o-xylene concentrations in the effluents collected from the stabilized PCSs columns were lower than those collected from the control columns. These laboratory test data suggest that HCCFA can be effective in remediation of PCSs; however, the level of petroleum contamination has a significant effect on the leaching properties.

Solid waste materials have been widely utilized as construction or geotechnical materials. Generally, regulatory leaching tests are performed to characterize the leaching potential of the constituent of concern (COC) contained in waste materials. However, the actual leaching concentration depends on the given field condition, and the environmental risk is difficult to be evaluated quantitatively. In this paper, leaching tests on steel slag and municipal solid waste incinerator ash slag are conducted, and a simplified method is proposed to assess the environmental suitability of these materials utilized as aggregate for the road base construction. It was assumed that the infiltration due to the precipitation led to the release of COC and the contamination of the subsurface. Environmental suitability was judged based on the potential human health risk by the intake of COC estimated from the results of laboratory column leaching tests and advection-dispersion chemical transport analyses. The risk estimated in the reuse of steel slag was 10^–4 order for groundwater consumption when the fluoride are leached under the given conditions.

The objective of this paper is to evaluate the hydraulic conductivity of a commercially-available geosynthetic clay liner (GCL) that has been amended with activated carbon as a means to enhance the sorptive capacity of the GCL for volatile organic compounds (VOCs). Flexible-wall hydraulic conductivity tests are performed on reconstructed GCL specimens amended with different carbon contents (i.e., 0, 10, and 18 % by dry mass) and carbon particle sizes. The results of these tests indicate that only a slight to moderate increase in hydraulic conductivity of the GCL may be expected due to the addition of activated carbon, depending on the mean particle size of the carbon. Measured hydraulic conductivities of unamended GCL specimens permeated with water under low stress conditions range from 2.3 x 10^–11 to 3.3 x 10^–11 m/s, whereas measured hydraulic conductivities of carbon-amended GCL specimens tested under similar conditions range between 2.8 x 10^–11 and 8.3 x 10^–11 m/s. The test results show that similar hydraulic conductivity values are obtained for GCL specimens in which the carbon replaces an equal mass of bentonite (10 % by dry weight) relative to specimens in which carbon is added to the bentonite. Analytical contaminant transport simulations for selected VOCs based on these results indicate that GCL amendment with 10 % activated carbon may provide equivalent or better waste containment performance relative to a 0.91-m-thick compacted clay liner (CCL) depending on the sorption characteristics of the contaminant.

The sorptivity S quantifies the effect of capillarity on liquid movement in a porous material. For liquid infiltration into an initially dry material, S is a parameter that is contingent on both liquid and material properties as well as the maximum liquid content behind the infiltrating front, θ_m. In prior work, Culligan et al. (2005) used scaling analyses to derive a dimensionless, intrinsic sorptivity S^* that is constant for different liquids, Miller-similar materials and differing values of S_e(av)·, the average degree of saturation behind the infiltrating front. The validity of the dimensionless S^*, and an accompanying dimensionless Boltzmann transformation Φ^*, was tested for different liquids by examining the horizontal infiltration profiles of water and Soltrol 220 in uniform dry sand at a constant S_e(av) = 0.79. This work extends the validity testing of S^* and Φ^* to conditions of varying S_e(av). Twenty-one distilled water horizontal infiltration experiments, with a range 0.64 · S_e(av) · 0.86, were preformed in uniform dry sand packed at an average porosity n = 0.36. The results of the tests indicate an intrinsic sorptivity value of 0.121, which compares well with the value of S_av^* = 0.128 reported by Culligan et al. The work also confirms that the dimensionless Boltzmann transformation Φ^* can be used to generate a similarity profile for moisture content, even when infiltration takes place under different degrees of saturation.

The knowledge of the rate and amount of settlement is important for effective design and operation of bioreactor landfills. Accurate knowledge of settlement would allow estimation of air space, planning of construction sequence, design of both intermediate and final covers as well as planning for expansions. It is also essential for the design of piping systems used for the delivery of re-circulated leachate and landfill gas recovery. Though the majority of settlement takes after landfill closure over a number of years, considerable amount occurs during the filling and construction stages, which usually goes unnoticed. In the Calgary biocell, which is a bioreactor landfill, real-time waste settlement data was collected during the filling of the cell. The field data collected during the cell construction stage is presented in this manuscript. The settlement trend follows the waste filling operation. The data was analyzed and the average unit weight of the waste matrix and the compression index were calculated. These two parameters are can be used in models to predict early stage waste settlement. The compression index was calculated as 0.21 while the unit weight of waste was 5.6 kPa.

A finite element model was developed to simulate construction of soil-bentonite cutoff walls, including excavation of the trench under a bentonite-water slurry, backfilling with soil-bentonite, and subsequent consolidation of the soil-bentonite. The finite element model, simulation of the construction steps, and calibration of the model using a well documented case history are described. Both the model and the case history indicate that most deformation in the adjacent ground occurs after backfilling. Good agreement was found between measured and calculated ground deformations. The finite element study demonstrated the importance of simulating consolidation of the soil-bentonite, and generating a realistic initial stress state in the soil-bentonite. The results of a parametric study are presented in which the trench depth, groundwater level, and soil properties were varied. Calculated deformations of adjacent ground as a function of distance from the trench are presented for several cases, with a discussion of the most influential factors. A correlation is presented relating deformation to factor of safety against trench instability and soil-bentonite backfill compressibility. The correlation can be used to predict settlement of ground adjacent to soil-bentonite cutoff walls constructed in sand deposits.

This paper describes findings from leach testing, total element analyses, and kinetic batch tests conducted to evaluate the feasibility of using iron foundry slag (an industrial byproduct of iron casting) as a reactive material in permeable reactive barriers used to remove arsenic (As) from groundwater. Tests were conducted on four slags from foundries in Wisconsin using solutions containing arsenite (As-III) and arsenate (As-V) having initial total As concentrations ranging from 100–2500 μg/L. Comparative tests were also conducted on zero valent iron (ZVI) and sand as a non-reactive control. Water leach testing and total elemental analyses suggested that leaching from slags is not appreciably different from ZVI, at least in the context of environmental regulations in Wisconsin. For the same liquid-to-solid ratio, As removal was slower with slag than ZVI. Arsenic removal rates also varied considerably from slag to slag, and did not depend on the quantity of iron in the slag. The removal rate typically decreased with increasing concentration, and was slower for As-III than As-V. Computations made using the rate coefficients measured in this study suggest that a common 1-m-thick PRB containing iron foundry slag could effectively treat groundwater contaminated with As-III or As-V at a concentration of 1000 μg/L, although other factors such as slag heterogeneity and competition with other species might influence effectiveness in a field setting.

Slurry cutoff walls have been used as vertical barriers to mitigate seepage of subsurface contaminant and to permit safe reuse of existing sites without extensive clean-up. The objective of the paper is to presents seepage analyses of soil bentonite (SB) cutoff walls that are part of the Dallas Floodway Extension project. The finite element program SEEP was utilized for the analyses. This flood control project in Dallas, Texas includes construction of wetlands for environmental mitigation purposes. The alignment of one of the wetland cells, Cell F, goes through the Linfield and UPRR landfills, requiring excavation of 1M yd³ of landfill materials. Due to the presence of water in these landfills, migration leachate from the landfills into the wetland cell could occur over time. To mitigate migration of leachate into the wetland cell, two SB slurry cutoff walls are being constructed parallel to the longitudinal axis of Cell F. This paper presents the numerical modeling of the cutoff walls for three different wall configurations. The lowest factor of safety for the under seepage analyses of all three wall configurations was more than 1.2, required by the regulatory agency.

Steady state contaminant transport through vertical barriers is reviewed, and the variability of hydraulic conductivity of barrier materials is discussed. Two important issues for containment systems operated with an inward directed hydraulic gradient across the vertical barrier are that: (1) there is not an advantage to achieving very low values of hydraulic conductivity for the barrier material and (2) the impact of variability in hydraulic conductivity on contaminant flux is to increase contaminant transport out of the contained area compared to an otherwise identical system with uniform hydraulic conductivity. A consequence is that vertical barriers with higher conductivity and greater uniformity are more effective than are vertical barriers with lower conductivity and lower uniformity. For containment systems operated with inward directed hydraulic gradients, it is recommended that more emphasis be placed on achieving and verifying uniform hydraulic conductivity than low hydraulic conductivity.

The changes in electrical resistivity of municipal solid waste (MSW) measured with electrical resistivity tomography (ERT) have been used to assess the influence of leachate recirculation events at bioreactor landfills. An attempt is made in this study to develop a direct correlation between the electrical resistivity and the moisture content of MSW. This correlation is based on a field testing program at Orchard Hills landfill (Illinois, USA) that included (1) ERT at three different locations that have been subjected to leachate recirculation events, and (2) moisture content of waste samples obtained at different depths from boreholes at the same three locations of ERT. It is shown that Archie's law can reasonably correlate the electrical resistivity and the moisture content of the waste; however, the two parameters, a and m, needed for the correlation appear to depend on the specific waste conditions. For the studied waste, the best fitted parameter a is 0.75 and the parameter m ranges from 1.6 to 2.15. Using this correlation, the influence of leachate recirculation on the distribution of moisture content at three locations of the landfill is evaluated. This study shows that the ERT can be a useful noninvasive technique to monitor the moisture content of MSW and to assess the effectiveness of recirculation systems at bioreactor landfills.

An estimated 29 million waste tires are stockpiled in noncompliant sites throughout New York State, presenting adverse environmental impacts, primarily fire and mosquito-transmitted health hazards. Because of these hazards, New York State has developed a program to abate all noncompliant waste tire stockpiles by 2010, with focus on beneficial reuse in Civil Engineering applications. To achieve this ambitious goal, the bulk of these stockpiled waste tires will be cleaned, shredded, and beneficially reused for roadway embankment fill in cooperation with the New York State Department of Transportation (NYSDOT) and the New York State Thruway Authority (NYSTA). High quality shred are required, with strict limitations on size gradation, cleanliness, and quantity of exposed steel. Although tire shredding is not a new technology, the magnitude of this project, with high production rates and exacting shred standards, is believed to be unprecedented. Abatement of three waste tire sites, totaling nearly 5 million tires, is summarized. These projects demonstrate that it is feasible to process waste tires with available equipment to high standards and at high production rates. Costs varied from about $3 to $8 per Passenger Tire Equivalent (PTE).

Only a few attempts of modeling settlement behavior of bioreactor landfills are reported in the literature. The use of soil compression based models to estimate the waste settlement in bioreactor landfills is questionable as waste decomposition influences waste settlement rates. Though these models may provide satisfactory prediction of settlement, several fundamental deficiencies were observed. A new model was proposed by considering the first-order reaction kinetics of waste biodegradation. Due to the absence of waste properties needed for detailed calculations, the new model was modified to a single equation that contains two model parameters. The simplified version of the model was validated using reported data from four pilot studies; two of them were laboratory lysimeter studies while the other two were field scale bioreactor landfills. The proposed model provided better settlement predictions especially the long-term performance of all four cases, when compared with the conventional that based on soil compression models.

The US Army Corps of Engineers (USACE) and various port authorities face many challenges with managing dredged material (DM) in their confined disposal facilities (CDFs). At the same time, quarries, mining companies, and other industrial concerns face serious challenges with managing fines. Chief among these challenges is identifying beneficial uses for soft compressible fine-grained soils (and/or residuals) such as ML, CL, MH, OH and CH soils as defined by the Unified Soil Classification System (USCS). Recent studies by Wartman et al. (2004a,b), Grubb et al. (2006 a,b) and Malasavage et al. (2006) provide the basic engineering and construction properties of 9.5 mm (3/8") minus curbside-collected crushed glass (CG) blended with these materials to demonstrate the potential use of the CG-soil blends in geotechnical construction. Select laboratory tests along with field verification illustrate the versatility of using CG to dramatically alter the properties of soft-marginal soils which, with basic pugmilling technology, can revolutionize materials selection, use and evaluation criteria. For example, switching from OH to CH soils at the same CG content, can mean a difference in K of 10^–4 cm/s, φ'_CIŪ of 13°, or γ_d,max of 15 lb/ft³, not to mention significantly different compressibility. This can enable the geotechnical design consultant with a soils improvement strategy to hand-craft fill materials for various site uses, often without changing the basic components of the blending operation. Comparisons to traditional blends of gravel/sand with fine grained soils illustrate that CG can achieve similar objectives and performance, and that the use of a "recycled material" is comparable to conventional aggregates for geo-mechanical stabilization of soft, fine-grained soils. These concepts have broad implications for those organizations confronted with long-term fines management issues and large fill projects.