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s " <br /> F <br /> TERRA VAC <br /> 2. Over Excavation with on-site soil aeration or off-site soil treatment or disposal (i.e., <br /> landfilling, soil venting, incineration) <br /> 3. Oxygen Releasing Compounds <br /> 4. Vapor Extraction/Air Sparging <br /> 9.1 Intrinsic Bioremediation / Natural Attenuation <br /> Intrinsic Bioremediation or Natural Attenuation, is the use of existing microorganisms <br /> (bacteria) to remove environmental pollutants from soil and water. Bioremediation <br /> accounts for a substantial 5 to 10 percent of all pollution treatment. <br /> Microorganisms decompose organic compounds using enzymes (protein-based <br /> molecules) that control metabolism to all living cells. Some of these enzymes act to <br /> metabolize (biodegrade) pollutants into non-toxic products. Bioremediation works best <br /> on natural carbon-containing substances called hydrocarbons or on chemicals <br /> resembling natural substances. Bacteria that metabolize naturally occurring <br /> hydrocarbons, such as certain petroleum products, are widespread in the environment. <br /> Bioremediation techniques vary widely in their degree of sophistication, but they have <br /> some features in common. Bioremediation is generally used to treat dispersed, dilute <br /> solutions containing one or more pollutants, such as gasoline. Bioremediation has been <br /> used successfully in the cleanup of thousands of leaking underground gasoline storage <br /> tanks commonly found at filling stations. <br /> Intrinsic Bioremediation or Natural Attenuation would require that groundwater <br /> monitoring continue for an indeterminate time period and that no active remediation will <br /> be conducted at the site. The annual costs associated with this approach are minimal. <br /> 9.2 Over Excavation and Various Soil Treatment or Disposal Options i <br /> The estimated quantify of impacted soil that would have to be removed by excavation is <br /> approximately 6,800 cubic yards. This would represent most of the site area between 7.5 <br /> and 25 feet bgs (Figures b and 7). This method would effectively remove the source <br /> contamination. However, this method would not address remediation of the smear zone or <br /> the groundwater contamination that currently exists. <br /> Excavating and stockpiling (or spreading) impacted soils for the purpose of on-site aeration <br /> would have to be staged due to the physical size of the site and San Joaquin Valley Air <br /> Management District restrictions. This would present the risk of dermal contact. <br /> Stockpiling may be required to effectively aerate the stockpiled soil to acceptable Class IIT <br /> disposal levels. Landfilling at a Class II facility and off-site soil treatment are feasible <br /> options, however they are costly. <br /> Three additional factors increase the cost of over excavation at this site. The first is <br /> excavating and stockpiling the unconsolidated overburden. The second is shoring the <br /> excavation prior to backfilling. The third is dewatering the excavation to facilitate soil i <br /> removal to the desired depth. <br /> i <br /> Project 30-0212 12 caalton130-02121cap\revncap-rev5.doc <br /> July 15, 1998 Zl�l <br />