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Bioremediation - 6 - to September 1993 <br /> It is difficult to prove that in-situ bioremediation is occurring. It is necessary to show that the mass <br /> of gasoline has decreased and at the same time show that microorganisms are the causative agent. <br /> Difficulties arise because gasoline infiltrates the porous soil matrix, partially dissolves, disperses, is <br /> diluted, is sorbed onto soil and other particles, and volatilizes, thus mass balance estimates may be <br /> unattainable. in addition, there are no morphologically distinctive gasoline-degrading <br /> microorganisms, <br /> There is no accurate way to measure petroleum biodegradation directly. However, there are several <br /> methods to attempt to measure biodegradation indirectly. Mineralization or total degradation can be <br /> monitored by COz emissions. However, this does not measure the conversion of hydrocarbons to <br /> metabolites or cell mass. Lass of Total Organic Carbon measures mineralization but nothing more. <br /> Oxygen uptake does take in both mineralization as well as partial oxidation, but one does not know <br /> how far the oxidation has gone or what has been converted to biomass. It may also be possible to <br /> detect the presence of carbon dioxide produced from aerobic biodegradation of hydrocarbons using <br /> carbon isotope detection - VC versus CO-z. However, anaerobic degradation may also result in a <br /> range of VC values for the degradation of CQ=. Contaminant concentrations should also be <br /> monitored for decreases which may or may not indicate bioremediation. Increased numbers of <br /> microorganisms that utilize the contaminant may indicate that hioremediatton is occurring. <br /> Monitoring of other parameters may be useful as well in detecting changes in reactants, such as <br /> dissolved oxygen (DO), oxygen gas, and nutrients, and reaction products such as intermediate <br /> metabolites and COI. Methane, NOx, Oz, NO3, and NO,-/Br may be monitored to detect in-situ <br /> denitrification. In addition, DO, pH, temperature, and nitrate/nitrite concentrations may indicate <br /> that reactions are occurring, although they do not determine the type of reactions. <br /> In order to monitor in-situ bioremediation, it is necessary to collect periodic water level <br /> measurements and ground water and soil samples. This means maintaining monitoring wells and <br /> periodic soil borings. <br /> Before in-situ bioremediation is attempted, it is necessary to screen the site to determine if it will <br /> work. This procedure may he summarized as follows: <br /> SITESCREENING <br /> 1. Site Study <br /> a. Biodegradability of contaminants (gasoline is biodegradable) <br /> b. Time requirements (biodegradation takes up to two years) <br /> C. Space considerations (on-site versus in-situ) <br /> d. Volume of material to he treated (typical minimum volume of soil - 250 to 500 cu yds) <br /> C, Costs of alternative options ($25 - $75Jcu yd for bioremediation of hydrocarbons with <br /> boiling points C 650° F) <br /> 2. Regulatory Analysis <br /> a, Limiting Regulations (Basin Plans, Discharge Permits, Policies, etc.) <br /> b. Statutory Treatment Criteria (MCLS, SNARLS, Policies, etc.) <br /> II ' d 800- ON ££:6 £6` 9I dab ON Ill <br />