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AIWRCERS OESGNERS CLY6Ll14it5 are the typical technologies used Given site conditions, a sheet pile barrier would be the most appropriate Sheet pile would be installed around the groundwater plume. Since the site appears to have a low permeability zone (Zone 4) at 29 to 59 feet below ground surface, a barrier of this ' type would need to be placed to a depth of at least 35 feet ' Evaluation A steel sheet pile wall would be effective in these soil conditions in isolating the plume The low permeable lower unit would serve well to act as a lower barrier to contaminant migration However, the barrier wall would need to be installed in a well developed area, intersecting streets, sidewalks, and many different utilities such as water, electrical and others Installation of the wall would be very disruptive, costly and has the potential to cause much public discontent because of the disruption of traffic flow and utility service. For these reasons, ' a barrier wall will not be considered for further evaluation Insitu Bioremediation Description Bioremediation is a process in which microorganisms degrade certain hazardous constituents in situ When microorganisms are stimulated to grow and use the contaminants as a food and energy source, contaminants are destroyed. Since this is a biological process, a certain range of pH and temperature along with oxygen, nutrients, and moisture are necessary for the microorganisms to act on the organic contaminants of concern Little to no residual treatment is required The implementation of this technology would include installing several new treatment wells and dosing them with an oxygen releasing compound This compound would '• slowly release oxygen over time, the oxygen would diffuse through the groundwater, enhancing biodegradation and destruction of BTEX compounds Evaluation Based on the site location, geology, hydrogeology, and the groundwater sampling conducted to date, it appears that all of the necessary conditions are present for the natural biodegradation of the contaminants Because oxygen can be rapidly consumed by microbes, the ' limiting factor in this process appears to be the presence of sufficient oxygen to carry out aerobic processes at a higher than natural rate In this alternative, the amount of oxygen in the groundwater would be enhanced by placement of a magnesium peroxide compound in wells ' completed in the zone with contaminated groundwater This compound reacts with the water to give off dissolved oxygen into the groundwater, higher dissolved oxygen levels are generated than those possible with air sparging Moderate pH levels are also maintained. Because this ' technology is relatively non-intrusive and simple in design, it has been retained for further/ consideration ' Intrinsic Remediation/Monitoring ' Description Intrinsic remediation is a remedial approach that relies on natural attenuation to remediate dissolved contaminants in groundwater Mechanisms of natural attenuation of dissolved fuel hydrocarbons in groundwater include advection, dispersion, dilution from ' recharge, sorption, volatilization, hydrolysis and biodegradation. Of these processes, hydrolysis and biodegradation are the only mechanisms that transform contaminants into innocuous LTROJ ECI'S\SANJOQWAIACCIONPL 32