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Technical Briefing

  1. How METS works
  2. Why METS works
  3. Treatment agents
  4. Performance and efficiency
  5. Health, safety, environmental impacts
Top of Page How METS works. The METS remediation process equipment is about the size of a large SUV. It is fully mobile and self-propelled. Previously excavated soil is deposited in the hopper at the top of the apparatus by a conventional front-end loader. Very large debris, such as rock, concrete or asphalt, is usually screened off at the hopper opening. From the hopper, the soil is transferred in a regulated flow to a custom designed processing mill. The mill impacts and shreds the soil, while blending a treatment solution (chemical, biological, or both), along with air and moisture, into the soil using a method that is proprietary to EarthWorks Environmental. The contaminant molecules in the soil are already being degraded or neutralized by the time the soil emerges from the processing mill. The treated soil may be deposited directly to the ground from the mill. However, the apparatus includes a conveyor system at the back end, which may be used to deposit the soil in locations and configurations as desired or to meet site space constraints.
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Why METS works. There is, in nature a wide variability in soil conditions and soil content, even within small distances. This is the principal barrier to effective and efficient remediation of contaminated soil. The METS process is designed to eliminate this variability in the soil while introducing one or more chemical or biological reagent(s) known to degrade and/or neutralize the specific contaminants in that soil. In other words, METS is able to tailor the choice of chemical and/or biological reagent to the specific type and severity of contamination, and to the specific soil conditions at a site. Second, the METS process reduces the soil to a fine particle state in order to maximize access to the contaminant molecules. Third, the METS process ensures the even distribution of the reagent(s) throughout this soil matrix, and the degradation/neutralization is completed before the soil loses its homogenous and fine particulate composition. Finally, to improve speed and efficiency, the METS process creates a relatively high level of air entrainment in the soil, along with a carefully calibrated level of moisture content.

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Treatment agents. METS is designed to work with any chemical reagent or biological product that is or can be delivered in an aqueous solution. The choice of what to use in a given project is determined from analysis of the contaminant or combination of contaminants in the soil, and from analysis of the soil composition, moisture content, pH, etc. For example, commercially available products that are commonly used to degrade hydrocarbons as part of various cleaning and degreasing applications, can be adapted successfully by METS. Other products that can be adapted for METS are based on a chemical principle known as Fenton's Reagent Chemistry. FRC provides for direct oxidation -- release of nascent oxygen -- via an exothermic reaction between a peroxygen and a catalyst. The exothermic reaction as well as oxygen release, dependent upon catalyst, degrades the hydrocarbon molecule to its carbon and hydrogen elements. The nascent oxygen reacts with these elements to form benign compounds (for example, in the case of gasoline, the byproducts are water and carbon dioxide). Chemical reactions based on this chemistry are reliable and predictable, once the proper environment has been created.

Metals (for example, soluble lead) are neutralized by chemical bonding at the molecular level, resulting in byproducts that are stable and benign. METS is also able to apply a variety of products that release cultured microbes proven to degrade and/or neutralize various types of contaminants. In all known cases, these are naturally occurring biological organisms that have been found to thrive in environments where these contaminants have been introduced by man-made events or by natural causes.

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Performance and efficiency. The EarthWorks-manufactured line of remediation process equipment includes four configurations designed to process from 40 to 320 tons of soil per hour. Actual throughout will vary somewhat depending upon soil type, soil condition and moisture content. In many cases, the contaminant has been degraded and/or neutralized almost as soon as it exits the processing mill. In some cases, the degradation process must continue over a period of hours or a few days, to achieve the desired remediation level. When METS relies on a biological product to provide most of the degradation/ neutralization, the process may take longer -- up to a few weeks -- to achieve the desired results.

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Health, safety, environmental impacts. There are no significant, negative health, safety, or environmental impacts associated with operation of METS. There are no significant risks, direct or indirect, to the general public as long as the equipment and work site are reasonably secure from unauthorized entrance. Specifically:

  • Chemical hazard. The chemical and biological products used are biodegradable and environmentally benign. Equipment operators are trained to handle these materials with due care, with the most likely risk if any being direct exposure to themselves before the products are sufficiently diluted. There is no risk to the general public as long as the products are secure from access or tampering.
  • Noise. The soils processing machinery, when operating, produces a noise level comparable to a medium-sized residential gasoline generator. The noise level is typically less than that produced by the loader equipment being used to dump contaminated soil into the machinery. Equipment operators are not required to wear protective hearing devices.
  • Air pollution. The engine meets current emission control requirements for such equipment.
  • Water pollution. There is no contact with groundwater during the process (the contaminated soil is already excavated), nor is there any release of chemicals or biological products, diluted or undiluted, into public sewers or storm drains (note: some of these products, in a diluted form, are in fact prescribed for use in cleaning sewers and storm drains). Small amounts of the diluted treatment solution may puddle on the ground as an incidental byproduct of operating the equipment. This liquid quickly evaporates and/or is absorbed into the soil deposited from the remediation process.
  • Fugitive dust. The process may produce incidental dust as a natural result of the lifting and dumping of soil into the hopper, if the soil is particularly dry. During the process, moisture is added to the soil. As a result there is no dust that results from the action of discharging the remediated soil back to the ground. Remediated soil is in a fine particulate state. When it dries completely, which may take several days, there is the potential for windblown dust off of the soil stockpile. However, that dust is from remediated soil, and should not pose a health hazard.
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