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Web-based Class Project on Geoenvironmental Remediation

Permeable Reactive Barriers. Web-based Class Project on 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

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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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