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i IEnhanced Bioremediation I The infection of air, oxygen, or hydrogen peroxide can be used to support aerobic biodegradation and enhance natural biological activity that degrades the CIO"' T hese may be introduced as gases or as a reactive chemical in a liquid or solid matrix form Additional nutrients (e g , phosphorus and nitrogen) may also be required to increase the natural bioactivity to levels sufficient to degrade the CDCs within a preferred zone or time frame This technology can be used for both impacted soil and groundwater Systems to deliver the required additives and I nutrients typically require moderate to high maintenance since the growth of biomass can clog the injection systems Soil samples collected from site bonngs were previously submitted for physicochemical and microbiological analyses The analyses revealed very low viable recoveries for heterotrophic and selective microorganisms at the dilutions tested The results suggested the possibility that some level of biotoxicity may exist at the site Further bench scale studies, to test for the effects of oxygen and nutrients on the stimulation of selective microbes,were recommended to assess the potential for enhanced bioremediation Enhanced bioremediation may be a viable option for the site 4.2 Technologies Screening Summary Three of the fourteen technologies screened were deemed feasible for remediation of both the impacted soil and groundwater at the site These technologies included In-Situ Air Spargmg, In- lie Situ Well Aeration, and Enhanced Bioremediation A comparison of each technology in terms of effectiveness, implementability, and long-term management requirements is presented below Enhanced bioremediation, as an in-situ treatment, appears feasible to meet the remedial objectives at this site Enhanced bioremediation can be implemented using temporary well points (e g , Geoprobe or Hydropunch) to infect the required nutrients into the soil and groundwater The nutrients would be infected along the approximate centerline of the groundwater plume This option would be the least intrusive, as surface based treatment equipment is not required and temporary well points are used for nutrient infection Operation Iand maintenance costs would be moderate to high and periodic monitoring of the site conditions would be required Characteristics that should be investigated prior to system design include aquifer permeability, site hydrology, dissolved oxygen content, pH, redox conditions, temperature, soil moisture content, organic content,biodegradability of contaminants, and the presence of a competent biodegrading population of microorganisms Enhanced bioremediation may be classified as a long-term technology that may take several years to reach cleanup goals Treatibility tests, especially for the soil matrix, should be performed to further determine the feasibility of this technology and to define the remediation time frame and parameters Typical costs for enhanced bioremediation of soils range from $20 to $80 per cubic yard For groundwater, oxygen enhanced treatment typically ranges from $40 to $80 per 1,000 gallons treated, hydrogen peroxide enhancement costs are an order of magnitude more expensive than ' oxygen enhancement, and nitrate enhancement ranges from $160 to $230 per gallon ' 4EGU�w 8 J I �LlCES�=