Feasibility of In-situ Remedial Technologies,
    Hydrocarbon Plume, Phoenix, Arizona


    Gasoline and diesel releases from an active fuel station created a groundwater hydrocarbon plume that eventually migrated 1/4 mile from the facility. Previous remedial efforts were hampered by high arsenic concentrations and an off-site TCE plume commingled with the hydrocarbon plume. The client requested that Hydro Geo Chem manage remedial efforts, and specifically develop, test, and implement in-situ containment and source reduction technologies that would not result in additional waste streams or extracted groundwater.

    Hydro Geo Chem Approach

    Non-obtrusive and effective containment solutions were needed because of the plume's migration beyond the facility boundaries. We developed and field tested a sequence of air sparging tests using both horizontal and vertical wells. Tracer gases were injected and analyzed to evaluate the effective sparging radii. Oxygen injection and transport through closely spaced soil borings was also tested to evaluate its effectiveness in enhancing aerobic degradation. Both sparging and oxygen transport and consumption were numerically simulated to evaluate their effectiveness and optimize their use in full-scale remediation.


    The simulations agreed with test results from more than 50 oxygen release points, pointing to their limited effectiveness of only a few well radii. The field tests and modeling showed the usefulness of oxygen injection was restricted to small areas of the plume. The effectiveness of horizontal air sparging at containing downgradient plume migration was well demonstrated in the field tests, and full-scale systems were developed using numerical models. Hydro Geo Chem is currently managing the engineering design and construction of the remediation system.

    Figure: Idealized representation of sparging well zones of influence.



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