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left over soil at each time interval was air dried for 1 week at room temperature, and then sent for <br />TOC analysis. <br />Carbon dioxide produced due to biodegradation of organics was measured in the headspace <br />of the mason jars at 3, 6, 13 and 23 weeks. Five hundred µl of gas was collected from the <br />headspace using a gas syringe and injected into a noncapillary GC (Varian/Becker) with porapak <br />p column and thermal conductivity detector (TCD). All measurements were done at room <br />temperature of 25° C. <br />Results and Discussion <br />Experiment Z <br />The weights of TPH at zero, 2 and 4 weeks can be observed from Table 2. It can be seen <br />that for the first two weeks there is a significant decrease in TPH which is due to biodegradation <br />and/or volatilization. Volatilization is expected to be an important factor when hydrocarbons are <br />exposed to the open surroundings. Then in the subsequent two weeks, there is only a small <br />reduction in TPH in Table 2. This shows that higher TPH concentration has a higher rate of <br />disappearance and that the rate slows down as the concentration of TPH decreases. <br />Significant disappearance of TPH occurced within the first two weeks in an open <br />environment; equilibrium was not reached when TPH was exposed to the surroundings in an open <br />container. The same set of components was studied by Dean-Ross (16) in her 15 day study of fate <br />of JP-4 in soil, which produced comparable results in terms of volatilization of undecane and <br />dodecane. <br />Biodegradation of TPH is studied best in a closed container where losses due to <br />volatilization are small. Experiment 2 studies the fate of TPH in a closed container where <br />biodegradation of TPH occurs in soil. The fifteen day study by Dean-Ross (16) also provides <br />evidence for the possibility of biodegradation of higher molecular weight organics like tridecane, <br />tetradecane and pentadecane in soil as volatilization of these compounds was found to be slow. <br />Modeling of TPH components is done to confirm that biodegradation and not volatilization is <br />responsible for the disappearance of TPH from the soil in the closed microcosm studies. <br />Experiment 2 <br />Discussion of TPH Disappearance With Time <br />The amount of TPH was obtained for the treatments A, B, C, D, E, and F by the <br />summation of area under the peaks. The concentration of TPH is plotted with time for all <br />treatments in Figure 1. The error bars in Figures 1 and 2 are for 1 standard deviation. <br />During the initial 3 weeks, the rate of disappearance of TPH is low with slight loss of TPH <br />from soil. Then for next 3 weeks, there was a more significant loss of TPH as shown in Figure 1. <br />The reason behind the increase in rate after 3 weeks can be due to microbial adaptation and a <br />possible increase in number of microorganisms in soil leading to this enhanced rate of <br />