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Web-based Class Project on Geoenvironmental Remediation

Explore the construction, application, and advantages of permeable reactive barriers using ZVI and GAC through case studies and chemistry insights. Learn more about this geoenvironmental remediation project from the University of Michigan.

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Web-based Class Project on Geoenvironmental Remediation

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  1. Permeable Reactive Barriers Web-based Class Projecton Geoenvironmental Remediation Prepared by: Report prepared as part of course CEE 549: Geoenvironmental Engineering Winter 2013 Semester Instructor: Professor Dimitrios Zekkos Department of Civil and Environmental Engineering University of Michigan With the Support of:

  2. More Information More detailed technical information on this project can be found at: http://www.geoengineer.org/education/web-based-class-projects/geoenvironmental-remediation-technologies

  3. Overview • Physics • Chemistry • Application • Types of barriers • Construction methods • Advantages and disadvantages • ZVI case study • GAC case study

  4. Introduction • First implemented in 1991 • Reactive media dependent on contaminants • Common types: • Zero Valence Iron (ZVI) • Granular Activated Carbon (GAC) • Limestone • Oxygen Releasing Compounds (ORC) • Passive technique

  5. The Physics Funnel and Gate Continuous Wall

  6. The Chemistry • Common Materials: • Zero Valent Iron (ZVI) • Granular Activated Carbon (GAC) • Reactive Processes: • Abiotic Reduction • Biotic Reduction-Oxidation • Chemical Precipitation • Sorption or Ion Exchange (Bronstein, 2005)

  7. Application Types of Contaminants Applicable Soils Hydraulic Conductivity most important soil parameter Reactive material k > soil k Geochemical properties pH Minerals • Organic • Broken down and removed • Inorganic • Precipitates, adsorbed or transformed to non-toxic

  8. Types of Barriers • ZVI • Treats: organic-halogenated hydrocarbons, inorganics and metals • Degrades or precipitates out • GAC • High adsorption for organic compounds • Potential re-use after cleaning • Limestone • Effective in reducing certain metals • Inexpensive • ORC • Typically used with microorganisms • Aerobic environment  Microbiological growth

  9. Types of Barriers • Funnel and Gate • Impermeable sides • Reactive material forming middle • Velocity in PRB greater than natural velocity • Continuous wall • Trench perpendicular to groundwater flow • Simple • Covers entire width of plume (ITRC, 2005)

  10. Construction Methods • Slurry trenches, hydrofracturing, etc • Depends on: • type of configuration • depth of contaminant • Slurry trench: 27m depth • Hydrofracturing: 90m depth • Typically key-in bottom • Width of PRB • Residence time • Hydraulic properties • As important as the permeability (Day et al., 1999)

  11. ADVANTAGES DISADVANTAGES Long term conditions not evaluated ZVI: Contamination coating Silica or NOM reduces iron reactivity Creation of ZVI not environmentally friendly • Less expensive than pump and treat • ZVI: • Highly reactive with inorganic and organic • Adaptable • Used in combination • No health hazards • GAC • Limited data on field studies • Highly dependent on temperature • Changes in adsorption capacity • GAC: • Relatively inexpensive • Organic and heavy metals • Chemically stable

  12. Case Study: ZVI Pilot Scale Background Site Layout • East Helena, Montana • Lead smelter • Arsenic, selenium, lead, cadmium and zinc • Groundwater flow through alluvial deposits (EPA 2006)

  13. Case Study: ZVI Pilot Scale PRB Design • Continuous trench • 9.1 x 13.7 x 1.8-2.4 L x D x W in meters • ZVI filled partial depth • Entire construction took 6 days (EPA 2006)

  14. Case Study: ZVI Pilot Scale Results Profile view • Two years of monitoring • Initial arsenic concentration: >25 mg/L • Final: 99% removal of As from groundwater • No change in k from build up (Wilkin et al, 2009)

  15. Case Study: GAC Modeling Background Profile • Laboratory and Modeling • Removal of Cd • Case study located near a riverbank • Model parameters: • Aquifer bed depth • Hydraulic conductivity • Average Cd depth • Rainfall periods (Di Natale et al., 2008)

  16. Case Study: GAC Modeling • Continuous trench • Width determined by groundwater velocity and mass transfer coefficient • Movement of Cd plume using advection and dispersion code

  17. Case Study: GAC Modeling Results Contaminant Level over 7 months • Cd <0.005 mg/L for 7 months • Peak concentration at the center: desorption and resorption • self-cleaning • PRB dampen concentration peaks • not as a complete removal Conclusions

  18. Any Questions?

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