42 NOVEMBER 2024 WorldWide Drilling Resource® Soil Mixing Solutions for Effective ISS Remediation Adapted from Information by Cascade Environmental If you’re new to environmental services, you might not know much about soil mixing. It is a versatile technique for In Situ Stabilization (ISS), a containment approach focused on the solidification of environmental contaminants. Soil mixing is common technology established in the geotechnical construction industry, applied for various ground improvement, hydraulic control, and structural applications. The technology has been successfully applied to numerous remedial actions and has been proven to be a cost-effective remedy to many subsurface environmental impacts where the nature of contamination and geologic conditions are well-suited to the technology. Soil mixing to achieve ISS is essentially the introduction and mixing of reactive admixtures into the soil matrix to create a desired change in the contaminant state or flux. This process solidifies and fixates the soil matrix reducing contaminant leachability and mobility, while improving strength and lowering permeability. Since most environmental releases, impacts, and residual sources are near surface or within the range of mixing capabilities, ISS can be considered for a large percentage of environmental remediation. There are two types of soil mixing used in ISS projects: shallow soil mixing, typically performed with conventional heavy equipment and also known as excavator or bucket mixing; and deep soil mixing, usually performed with larger and specialized drilling equipment. Both types are essentially the same process, deployed in different situations, each with advantages and constraints. The goal you’re trying to achieve with soil mixing, regardless of whether it is deep or shallow, is the creation of a uniform soil reagent mass, with improved physical properties, throughout the entire treatment footprint. The soil mixing technique works by chemically altering the contaminants, which remain in place. The chemical mix reduces contaminant leachability, mobility, permeability, and increases the soil’s compressive strength. Selecting the appropriate chemical reagents to mix into the soil, and formulating the right concentration, depends on site-specific factors. The contaminants of concerns suitable for soil mixing include metals, inorganics, volatile and nonvolatile organics, and semivolatile organics such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides, dioxins, and furans. Certain geotechnical properties are more appropriate for the soil mixing technique than others. You need accurate geotechnical information before choosing an approach for your project. If your site has cohesive or granular sediments of low to moderate density, it’s highly suitable because those soils are mixed easily and effectively. The presence of natural clay can make it easier to meet permeability goals. On the other hand, highly consolidated dense lithology can make mixing more difficult and put excessive wear on cutting surfaces. Lithified sediments, and bedrock can make mixing difficult or sometimes unfeasible. In addition to the mixing techniques used, changes in tooling that can be more effective and durable can be important. Typical reagents used in soil mixing to meet your project goals are: j Portland cement to improve unconfined compression strength. j Ground granulated blast furnace slag to reduce permeability. j Bentonite for a variety of purposes including permeability reduction, fluid loss mitigation, and mixing tool lubrication. j Carbon is to draw in certain organic contaminants, reducing leachability. This is a very important part of any ISS project, and in addition to planning the optimum reagents and ratios, acts as a benchmark to compare against the results of the full-scale ISS project. A treatability study can also help predict soil bulking or “swell” in the treatment zone; the soil mixing process expands the volume and the extent varies depending on the lithology and the reagent mix. In a typical soil mixing project, the contractor will use the appropriate formulation of reagents and mix it into the soil with an excavator or a drilling rig with an auger or mixing head, depending on the depth. Post-mixing, your expectation should be that the treatment zone will cure and harden, improving the strength of the area while reducing the permeability, mobility, and leachability. ENV 302-684-319 & Mfg., Inc. Atlantic Scree et om ducts 97 en E-mail: atlantic@ce.ne Atlantic-Screen.co Clear PVC Pipe j Inline Chemical Mixers j ell Rehabilitation Prod jW DE 142 Broadkill Rd Milton, ½” - 24 ranging fr Perforated of Slotted Manufactu Fax: 302-384-0643 more! MUCH And j Bailers Sampling j Locking Caps j Filter Sock j Bentonite j Manholes j Pipe Clear PVC 4” rom Pipe and urers E 19968
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