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09002 '00 ITER 15 43 FAX 18259489968 ERMWEST WC [A 014 <br /> PAGE 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 /> estunat+e the rate constant for natural biodegradation, as described below <br /> The purpose of these calculations was to predict the tirne 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 statural degradation processes can <br /> be modeled using the First Order Kinetics equation(EPA Technical Protocol <br /> for Evaluating Natural Attenuation of Chlorinated Solvents in Grc nd Water, <br /> Appendix C-Data Interpretahon and Calculattons, EPA/600/R-98/123, <br /> September 1998)- The mathematical equation representing Fust Order <br /> Kuwtics is the fallowing <br /> C„ =COO-6 <br /> Where n :number of samples six the data set <br /> t =time m days <br /> C. -initial concentration of constituent,mg/L <br /> iC,, =constituent concentration taken after"t" days. <br /> The equation can be rewritten as- <br /> Ij 6 7� <br /> K 1ti <br /> Using this form of the First Order Kinetics equation, a plot was <br /> constructed with In(C4/C.)" on the y-axis and"t" on the x-axis A <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 k,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 plotted values and the regression line <br /> Well MW-5(Site#1)and MW-7.A (Site#2)have historically had lugh <br /> concentrations of CDCs and currently(as of 22 July 1999)have the hsghest <br /> site-specific reported values for bmuene and TPH-g (Tables 1 and 2) <br /> Therefore, the natural biodegradation constants estimated for MW-5 and <br /> MW-IA were used in the predictive calculations for TPH-g and benzene at <br /> Site#1 and Site#2, respectively <br />