Geoenvironmental Engineering: Site and Contaminant Characterization, Containment Facilities, Solid Waste Materials, and Contaminated Ground Interventions

This chapter provides a brief overview of the concepts of contaminant transport and fate through porous media. Transport of aqueous miscible chemical species or solutes typically is governed by three primary processes: advection, diffusion, and dispersion. The transient advective-dispersive-reactive transport of a solute through a porous medium can be considered based on the conservation of mass for a representative elementary volume. The quality of the output generated from a numerical transport model is only as good as the accuracy and representativeness of the input parameters and conceptual model simulated. Chemical and biological mass transfer processes resulting in the loss or gain of solute mass govern the fate of solutes during migration through porous media. The impact of radioactive decay on contaminant transport may be minimal. Biological transformations are important processes for contaminant reduction but similar to radioactive decay, they can lead to undesirable byproducts as contaminants are broken down.

Recovery, processing, and testing of representative “undisturbed” or “intact” samples of municipal solid waste (MSW) are challenging. Therefore, in situ testing of MSW is the most reliable method for the evaluation of its material properties, including unit weight, shear strength, stiffness, and hydraulic and thermal conductivities. Field measurement techniques can be broadly grouped into non-intrusive, intrusive, and hybrid techniques. This chapter provides a critical review of the current state-of-the-practice of field methods as applied to the testing of MSW. Common non-intrusive techniques for field measurement of MSW characteristics include wave propagation velocity measurements, electrical resistivity surveys, surface measurements of settlement and lateral deformation, records of earthquake-strong ground motions, ambient vibration measurements, and load testing. Intrusive techniques for field measurement of MSW characteristics are in situ procedures that require physical penetration through the landfill cover into waste. Instrumentation can be added to the standard cone to provide additional measurements of waste characteristics.

This chapter describes laboratory methods to conduct chemical characterization of solids, liquids, and gases related to geoenvironmental practice. The analysis of solids extends to testing techniques that determine mineralogical composition, such as diffraction, thermogravimetric analyses, and spectroscopy, as these are highly relevant to engineering practice. Analysis of the chemical composition of solids in geoenvironmental practice is performed through a two-step process: digestion of the solid into the liquid phase followed by analysis of the resulting digestion solution. Liquid samples including aqueous and digestion solutions can be characterized by utilizing wet chemistry methods for testing general parameters, metals and metalloids, organics, and other compounds. Analysis of gases in geoenvironmental practice is mostly required for in situ or on-site applications such as volatile organic compound detection in contaminated sites and gas analysis in landfill collection systems including methane emissions. ATDSR provides a comprehensive guide on different requirements and testing methods for landfill gas.

According to the US Environmental Protection Agency (USEPA), a hazardous waste characteristic is a property that, when present in a waste, indicates that the waste poses enough threat to merit regulation as hazardous. USEPA has established four hazardous waste characteristics: ignitability, corrosivity, reactivity, and toxicity. Recycling hazardous waste has a variety of benefits including reducing the consumption of raw materials and the volume of waste materials that must be treated and/or disposed of. Recycling can reduce emissions of greenhouse gases. When hazardous wastes are recycled, less energy is needed to obtain raw materials to manufacture new products. Geoenvironmental engineers often lead projects involving the permitting, design, performance monitoring, and closure of Resource Conservation and Recovery Act hazardous waste landfills. The Toxic Substances Control Act of 1976 provides USEPA with authority to require reporting, record-keeping, and testing requirements, and restrictions relating to chemical substances and/or mixtures.

Municipal solid waste (MSW) consists of discarded everyday items from residential and commercial, as well as institutional settings such as government, education, and medical facilities. MSW includes materials such as product packaging, yard trimmings, furniture, clothing, bottles and cans, food, paper, appliances, electronics, and batteries. Design of MSW landfills requires an understanding of the engineering properties of MSW. The chapter presents an overview of the current understanding of MSW engineering properties. MSW is found to have a highly anisotropic structure, which has implications in engineering practice owing to variations in the shear capacity, compressibility, and especially the flow of liquids and gas through the waste mass. MSW has a significant biogas generation capacity, and the rate of degradation is affected by the presence of moisture. MSW is a highly compressible material, and landfill settlements resulting from this compressibility may affect not only the operation of a landfill.

Coal combustion residuals (CCRs) are one of the largest types of industrial waste generated in the United States. The US Environmental Protection Agency has published a final rule in the Federal Register to regulate the disposal of CCRs as solid waste under Subtitle D of the Resource Conservation and Recovery Act. The final rule is the culmination of extensive study on the effects of coal ash on the environment and public health. The coal fly ash particles are spherical, ranging from sand to fine silt in size. Fly ash consists primarily of oxides of silicon, aluminum, iron, and calcium. It is classified as either Class C or Class F ash based on its chemical composition. The range of specific gravities observed in fly ash is the result of a combination of many factors, such as gradation, particle shape, and chemical composition.

Biomass energy is generated from the combustion of wood and other biomass sources such as grassy or woody plants, wood waste such as sawdust, bark, or pallets, or some organic components of municipal solid waste, which can be combusted to produce energy. Woody and herbaceous biomasses are the most common forms of biomass fuels that are directly combusted or co-fired with coal for energy. This chapter focuses on the properties of woody biomass fly ash that results from the combustion of 100% biomass as the energy source. Biomass fly ashes with high-reactive lime, silicon, and aluminum content have self-hardening properties, which makes them successful binders for waste solidification compared to the self-hardening properties of four biomass fly ashes of varying compositions. Biomass ash is used as a soil amendment in agricultural applications, as adding alkaline ash balances the acidic effects of introducing nitrogen fertilizers while simultaneously providing necessary nutrients for plant growth.

The main goal of a liner system in solid or liquid waste containment facilities is to minimize the transport and/or transport rate of contaminants from the contained waste into the environment while remaining functional and stable during facility construction, operation, closure, and postclosure care. Many details of landfill liner systems are prescribed by US federal and state regulations, including the minimum required components and their configurations, hydraulic boundary conditions, and material hydraulic and mechanical properties. This chapter briefly summarizes the major regulatory requirements in the United States. It discusses relevant material properties and analysis regarding the hydraulic performance, mechanical performance, and construction of different components of liner systems. The soil-based liner is typically a compacted clay liner (CCL), geosynthetic clay liner (GCL), or GCL/CCL combination. The chapter also summarizes the leakage of liquids through solitary geomembranes, as they may be used in some situations as a single liner.

The functions of landfill cover include providing an aesthetically pleasing surface and serving as a final surface or foundation on which end use may occur. In municipal solid waste landfills, the primary landfill gas constituents are methane and carbon dioxide. Resistive composite covers typically consist of a geomembrane overlying a low-saturated hydraulic conductivity barrier layer containing soil. This chapter describes the additional technical design, construction, and operational issues for the final covers. The impact of waste settlement on the performance of the cover system barrier layer and other layers, as well as the infrastructure components, is a common concern for all types of final covers. The collection, control, and regulation of landfill gas is important to limit environmental, climate, human health impacts, and nuisance issues. Vegetation on landfill covers can be actively or passively managed. Many cover systems are required to be mowed to facilitate inspection and for aesthetic purposes.

This chapter presents guidelines and principles to guide geotechnical engineers in the planning, execution, and critique of slope stability calculations with an emphasis on slopes and modes of failure encountered in containment systems. It assumes that the geotechnical engineer conducting the analysis has completed coursework that includes some slope stability analyses and is conversant in engineering properties of soils. The chapter presents a set of principles for the engineer to consider when conducting slope stability analyses. Most slope stability analyses used in practice are limit equilibrium analyses that statically analyze driving forces and available resisting forces acting on a slope at the initiation of movement to compute a factor of safety. Containment systems offer even potential slip surface configurations owing to the construction of multiple layers of materials with differing properties. Soil reinforcement refers to constructing inclusions within the soil mass to improve the resistance of the slope to movement.

Seismic stability of waste containment systems may be assessed by a hierarchical set of analyses of increasing complexity. The hierarchical level that is required for the seismic stability assessment of a particular facility depends on the regional seismotectonic environment, seismic performance standard, and desired level of precision. The seismic performance standard is a key factor in determining the adequacy of a waste containment system subject to seismic loading. Prevention of a discharge of contaminants that are harmful to human health, or the environment provides a rational basis for economically and environmentally sound seismic design of waste containment systems. Many engineered waste containment systems have substantial built-in redundancy. Most final cover systems and liner systems provide multiple, redundant levels of protection against leachate migration to groundwater. In regions of low seismicity, and for ductile waste containment systems, seismic stability may be demonstrated by a simple pseudo-static limit equilibrium analysis.

Mine operations produce considerable quantities of waste materials as a result of ore extraction and refining processes. This chapter provides an overview of the characteristics, management techniques, and common challenges encountered by geotechnical engineers working on waste rock and tailings projects. The generation and management of waste rock is primarily a challenge encountered in open pit mining owing to the overall mass of uneconomical rock that must be removed to exhume ore. Mine tailings are the byproduct of ore processing, and the physical and chemical characteristics are a function of the ore mineralogy and physical-chemical extraction processes. Slurry-deposited tailings present challenges such as particle segregation, low shear strength, susceptibility to liquefaction, high settlement potential, and reduced tailings storage facility capacity. Common sources of mine waste generated at a given mine site that require management can include waste rock, tailings, spent ore on heap leach pads, process water, and contact water.

Excavation and replacement are frequently used to remediate contaminated land. The shape of contaminant plumes can be highly irregular, requiring excavations with complex shapes. Shoring for such irregular shapes can be intricate and costly to construct, especially if each excavation cell requires a unique shape. Sheetpiles are typically driven with a vibratory hammer, although an impact hammer may also be used in dense soils. Collection, treatment, and disposal of contaminated water can be costly, and it is usually beneficial to control and limit the quantity of water entering the excavation. Environmental investigations often include borings and test pits to evaluate and delineate the extent of contamination and type of contaminants. Contaminated sediments can also be remediated by removal using mechanical or hydraulic dredging techniques. Dredge excavations are often capped with a layer of clean sand fill; alternatively, they can be allowed to backfill by natural sedimentation.

Groundwater contamination has become a widespread problem in need of the urgent attention of various federal and state agencies. Electrokinetics (EK) is an in situ remediation technique applicable to low-hydraulic-conductivity soils. EK leverages electric fields for remediation. This chapter focuses on the fundamentals of the use of a direct electric field and the resulting direct current in soil remediation. The major flow mechanisms induced by EK are ionic migration, electrophoresis, electroosmotic advection, and, to a lesser extent, diffusion. Electrolysis is a side process occurring during the application of EK, which can interact or even interfere with the effectiveness of EK. The chapter provides a brief explanation of factors to be considered during the design of an EK remediation system. Contamination level is a factor controlling the efficiency of electrokinetic remediation.

It is sometimes necessary to perform ground improvement at sites with environmental challenges to modify the engineering characteristics of the subsurface material such that they are suitable for the project. At traditional waste disposal sites, ground improvement may be used to increase the strength properties and/or reduce the compressibility characteristics inherent in many waste materials. The depths of ground improvement at municipal solid waste sites have been successfully evaluated using a range of methods such as settlement measurement load tests using soil embankments and in situ testing such as SPT, Cone Penetration Tests (CPT), and seismic geophysics. CPTs were conducted pre- and post-construction to estimate the extent of ground improvement. An emerging area of grouting with potential applications in the field of geoenvironmental engineering is the use of biobased grouts, which utilize biogeochemical processes to form precipitates in granular soil.

Barrier walls have long been used to control vertical and horizontal migration of contaminants in the subsurface. Historically, the principal design parameters have been hydraulic conductivity and compatibility of the barrier material with the contaminated environment in which the barrier is placed. This chapter focuses on means and methods to construct in situ a vertical barrier of low hydraulic conductivity for geoenvironmental containment. There are several means and methods by which a vertical barrier can be installed in the subsurface. Understanding how each is constructed is key to choosing the correct vertical barrier for any contaminated site. The chapter addresses surface-built containments such as landfill liners and cover systems, respectively. Regardless of the method chosen to construct a vertical barrier for geoenvironmental conditions, consideration must be given to the longevity of the barrier. The chapter highlights the current practice in geoenvironmental engineering concerning vertical barriers.

Permeable reactive barriers (PRBs) are designed to be more permeable than the surrounding aquifer matrix, passively treating groundwater readily flowing through the material under the natural gradient, without significantly altering groundwater hydrogeology or plume morphology. A variety of materials can be utilized as a permeable barrier material, including zero-valent iron (ZVI), carbonaceous sources, alkaline materials, granular activated carbon, zeolites, and new materials. This chapter provides a concise and practical guide to the implementation of ZVI PRBs for the treatment of chlorinated aliphatic hydrocarbons and certain redox-reactive metals, such as chromium and arsenic. It details the application stages for this groundwater remediation method, including the initial feasibility assessment, site data collection, laboratory treatability studies, development of design parameters, PRB construction techniques, and long-term performance monitoring. The ZVI deactivation process is dependent on the type and mass flux of the passivating constituents. Sampling within and around a PRB requires special techniques to collect representative samples.