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san" les for laboratoryanalysis of petroleum hydrocarbons and bacterial populations. <br /> 6.L2.1.5 Selected Case Studies <br /> GeoAudit is presently operating three in-situ bioremediation projects in Southern California. <br /> ' At a site in Costa Mesa, a plume of gasoline-contaminated soil measuring 40 feet in <br /> diameter and 27 feet deep (roughly 1,200 cubic yards) is being treated. Each of the thirteen <br /> 1-inch diameter inoculation wells is screened over three 10-foot intervals. Each well was <br /> inoculated with 7.5 gallons of bacterial inoculum in August 1991. A second inoculation of <br /> 3 gallons per well was performed in February 1993, using a more highly concentrated <br /> inoculum. <br /> Organic vapor and carbon dioxide monitoring indicate that TPH concentrations have <br /> ' decreased by 99% since treatment began, and CO2 concentrations have fluctuated between <br /> 0.1 and 0.5%G of total vapor volume. Soil samples collected approximately 24 months after <br /> inoculation indicate that TPH concentrations have decreased significantly, up to 99% <br /> ' between a depth of 0 and 15 feet. Additional inoculation has recently been performed to <br /> accelerate remediation between 15 and 30 feet. <br /> ' Bacterial inoculation at a second site, in Santa Monica, took place in June 1993. Gasoline <br /> contamination at the site extends to approximately 60 feet, impacting 1,200 cubic yards of <br /> soil. Eleven wells, located on 15-foot centers, were inoculated with 550 gallons (50 gallons <br /> N per well) of inoculum. An additional 300 gallons were sprayed on the excavated soil (which <br /> was replaced in the tank cavity) and injected to a shallow infiltration gallery on the floor of <br /> the tank cavity. The limited organic vapor measurements made to date indicate that VOC <br /> ' concentrations have decreased. A blower has recently been installed to increase subsurface <br /> air flow, and borings will be drilled early in 1994 to assess the progress of the remediation. <br /> ' GeoAudit is currently awaiting final approval for inoculation of in-situ bioremediation wells <br /> at a third site, located in Lodi, California. At that site, a plume of gasoline-contaminated <br /> soil measuring 300 feet by 150 feet by 60 feet will be treated by several inoculation wells. <br /> Wells will be inoculated with 70 gallons of inoculum, and will be connected to a blower to <br /> increase air flow. <br /> 6.1.2.1.6 Duration <br />' Duration and cost are dependent on the volume of soil to be remediated, the number of <br /> inoculation and monitoring wells and events,the average concentrations of contaminants and <br /> nutrients, and the temperature and permeability of the soil. Theoretically, the radius of <br />' influence of the inoculation well should increase rapidly at first, then gradually decline as <br /> the . affected ..volume increases and the bacteria encounter decreasing hydrocarbon <br /> concentrations toward the margins of the contaminant plume. Based on the volume of <br /> contaminated soil, one inoculation well, TPH concentrations ranging from 200 to 12,000 <br /> ppm in RW-1, and the relatively high permeability of soil above 60 feet, we estimate that <br /> Geoloyu�Audx S. x-'1., 28 <br /> A&A PAWL-28$41147 <br /> 1 <br />