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Section 4- Characterization

Develop a complete and comprehensive conceptual site model for successful in situ chemical oxidation (ISCO) remediation. The characterization of nature and mass of contaminants present, including sorbed, dissolved, and free product phases, is crucial. Identify major migration pathways and surface and subsurface structures, as well as groundwater flow direction, gradient, and velocity. Evaluate total contaminant mass and understand the importance of mass calculations. Consider site geochemistry and geology, as well as special site model considerations like limited access, deep aquifers, and confined formations.

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Section 4- Characterization

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  1. Section 4- Characterization • Characterization is 95% of the Success of ISCO • Develop a complete and comprehensive Conceptual Site Model • ISCO is a Mass Destruction Technology • Successful Treatment must Identify both target and non target analytes and contain all phases of Mass • Know Flow paths within soil Structure

  2. Conceptual Site Model Development First and most important step in remediation project includes • Characterization of nature and mass of contaminants present • Sorbed • Dissolved • Free product phases • Subsurface geology, site topography, aquifer geochemistry • Identification of major migration pathways for contaminants of concern (COC) • Surface and subsurface structures • Underground utilities • Direction / gradient / velocity of groundwater flow • Surface water features / uses, and potential receptors in the area

  3. Contaminant Mass PSH, Sorbed, Dissolved •

  4. Total Mass EvaluationNature of Contamination • Contamination mass exists in four phases in the contaminated zone • Soil gas • Sorbed • Dissolved • Non-aqueous phase liquid (NAPL) or phase-separated • Geochemistry, partitioning coefficient (Kow) determines the relationship between phases in the saturated zone • Majority of mass (normally >80%) is sorbed and phase-separated Graphic source: Suthersan, 1996

  5. Total Mass EvaluationImportance of Mass Calculations • Evaluate pre- and post- total contaminant mass • Sorbed and non-aqueous phase mass converts to dissolved during treatment and until site reaches post treatment final equilibrium • Possible “rebound” causes • Dissolution of sorbed or non-aqueous phase • Inadequate site characterization • Change in groundwater flow direction • Decrease in total mass may not be reflected in short-term dissolved concentrations Electroconductivity Diagram

  6. Treatment Volume Estimate

  7. Value of Data Quantity vs. Certified Analytical Data • ISCO requires contaminant delineation, precise concentration data quality not as critical as for closure confirmation • References – available at www.itrcweb.org under “Guidance Documents” • ITRC Technical and Regulatory Guidance for the Triad Approach: A New Paradigm for Environmental Project Management (SCM-1, December 2003) • ITRC Strategies for Monitoring the Performance of DNAPL Source Zone Remedies (DNAPLs-5, August 2004)

  8. Site Geochemistry/Geology

  9. Oxidant Demand Nomenclature • Natural oxidant demand (NOD) • Soil oxidant demand (SOD) • Total oxidant demand (TOD) • Natural organic matter (NOM) • Standard laboratory measurements of oxidizable matter in groundwater include • Chemical oxygen demand (COD) • Total organic carbon (TOC) • Total inorganic carbon (TIC)

  10. Site Geochemistry/Geology

  11. Conditions that Require Special Consideration • Low permeable soils • Deep aquifers • LNAPL/DNAPL • Confined formations • Swamps or high organic soils • Old landfills and dumps • River embankments • Under buildings

  12. Special Site Model Considerations No Utilities I-55 Limited Access Highway Private Property Access Only Pipeline Surface Water Body Flood Prone Area with Dirt Roads

  13. Lithology and Flow Path • Borings need to be properly installed by experienced personnel, which is contrary to reimbursement program pricing • Fine Sand lenses and variations in permeability are difficult to determine with Geoprobe programs • Wells need to be properly screened and developed (not three well volumes as in PST programs) • Confining layers are critical

  14. Target Interval Conceptual Site ModelTarget Interval Identification Soil Conductivity Contaminant Mass

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