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a <br /> j <br /> IN Ell <br /> 1� <br /> were first spilled, the microbes have had an opportunity to <br /> adapt to the materials during their normal, very slow growth rate <br /> r� <br /> in the subsurface environment. <br /> j i } <br /> E Aerobic microbial growth is limited by the absence of various <br /> Iessential nutrients such as nitrogen, phosphorous, or oxygen. It <br /> E i,. <br /> is normal for microbes living in nutrient-limited <br /> 1 environments to double in population only once every week to { <br /> a,I <br /> month. Doubling times in more normal environments are on the <br /> order of every 20 to 60 minutes. ' <br /> 1BB provides the nutrients necessary for these microorganisms to <br /> grow at a rapid controlled rate while utilizing the contaminant <br /> as their source of carbon for growth and energy. Only nutrients t <br /> and oxygen are being added to the formation. There are no <br /> extraneous microbes, "super bugs", or "bug soups" needed, because <br /> -' the natural population contains the necessary diversity of types <br /> to degrade the contaminants. under laboratory conditions, it is <br /> possible for the microorganisms to reduce benzene, toluene, and <br /> xylene levels to 1-10 ug/L, and carbon dioxide and <br /> produce only <br /> r water. When nutrient addition ceases the microbial population <br /> 5 4 <br /> i <br /> Yr ' returns. to pre-treatment levels within days. No residual � <br /> ` nutrients are detectable after microbial growth has stopped. . <br /> This effectively returns a site to its pre-contamination <br /> -- --L4 -condition.=--The--3n-situ--approach-is-an-excel lent-remediation <br /> ------ -- --- --- <br /> } :. technique to apply to Kayo's Lodi site. <br /> 23 <br /> i <br /> 9 <br />