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r.lM"r..01 Flu 191014 <br /> P A G E 2 <br /> ERM used sample analytical data from the monitoring events completed <br /> prior to implementation of enhanced in situ bioremediation with Oxygen <br /> Releasing Compounds(ORC). ERM applied First Order Kinetics to' <br /> estimate the rate constant for natural biodegradation,as described below. <br /> The purpose of these calculations was to predict the time for COCl <br /> attenuating under natural biodegradation to attain their respective <br /> MCL/Target Concentration. To do this,a natural biodegradation constant <br /> was needed. It is well documented that natural degradation processes can <br />{ be modeled using the First Order Kinetics equation(EPA Ted nical Protocol <br /> E for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water, <br /> Appendix C-Data Interpretation and Calculations, EPA/600/R-98/128F, <br /> September 1998). The mathematical equation representing First Order <br /> Kinetics is the following: i <br /> i <br /> C. = <br /> Coe��, <br /> Where n =number of samples in the data set 1' <br /> t =time in days <br /> C. = initial concentration of constituent,mg/L <br /> C„ =constituent concentration taken after"t" days. <br /> �i <br /> The equation can be rewritten as: ; <br /> Co <br /> ,ft <br /> C. <br /> i� <br /> Using this form of the First Order Kineticseq uation,a plot was <br /> co - <br /> constructed with In C C on - <br /> o n the axis and ton the x <br /> / axis. A'' <br /> ( } y <br /> straight-line equation was fitted to the plotted points using linear <br /> regression to estimate the slope of the equation of the line,which is lc,the <br /> natural biodegradation constant. The k estimates are presented in Table 1 <br /> (Site#1)and Table 2(Site#2)and summarized in Table 3. Figures 1 <br /> through 3 show the platted values and the regression line. <br /> Well MW-5 (Site#1)and MW-1A (Site#2)have historically had high <br /> concentrations of COCl and currently (as of 22 July 1999)have:the highest <br /> site-specific reported values for benzene and TPH-g(Tables 1 and 2) <br /> Therefore,the natural biodegradation constants estimated for MW-5�and <br /> MW-1A were used in the predictive calculations for TPH-g and benzene at <br /> IF Site#1 and Site#2,respectively. <br />�1 <br /> I� <br />