- Eliot Cooper

With EPA adopting Maximum Contaminant Levels (MCLs) and CERCLA regulations, it’s almost a given that Responsible Parties will be looking at colloidal carbon injected PRBs as an immediate risk reduction approach versus the long-term commitment to Pump and Treat. Which begs the question, how do you design to meet 4 ppt targets?

Unlike other contaminants where MCLs might not always be the target but rather Monitored Natural Attenuation (MNA), PFAS is different, especially for drinking water. At this point in time, “almost doesn’t count.”

This webinar will discuss the key components of a PRB design including:

  1. Comprehensive Site Characterization and Targeting:
    • The importance of thorough characterization of flux and target intervals both laterally and vertically.
    • The integration of these data into a 3D imaged targeted injection plan, addressing heterogeneous target intervals for effective PRB design.
  2. Bench and Column Testing for Accurate Dosage:
    • The necessity of bench or column testing to account for competing groundwater constituents and non-regulated PFAS compounds.
    • Accurate colloidal carbon dosing through the application of PFAS isotherms and Fluorinated Organic Compounds (FOCs) for estimating PFAS mass sorption.
  3. Strategic Injection and Design Optimization:
    • The calculation of injection volumes and the number of rows based on seepage velocities and the need for anchoring technologies in high-velocity scenarios.
    • Conducting a Design Optimization Test (DOT) to validate design assumptions and make necessary adjustments before full-scale implementation.
  4. Longevity and Performance Monitoring:
    • The estimation of PRB longevity considering seepage velocities and potential increases in PFAS concentrations from upgradient sources.
    • Performance monitoring to ensure sustained effectiveness and compliance with established MCLs.

The complexities of bedrock injection necessitate a different approach, requiring precise identification and isolation of fractures affecting compliance wells. This process involves considering advanced delivery options such as nested injection wells or straddle packer systems to effectively isolate and enhance the permeability of target fractures in open boreholes.

Unlike traditional design and implementation methods used for solvents and petroleum, where approximations might suffice, the stringent requirements for PFAS remediation demand meticulous planning and execution. Given the substantial cost and operational benefits of colloidal carbon in situ remediation over traditional Pump and Treat methods, these detailed steps are essential. They are pivotal in establishing in situ remediation of PFAS as a viable and cost-effective solution.

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