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simulation time 10 years Grid size 20 x 30 ' Cell size 50 ft x 50 ft Porosity 0 3 Longitudinal Dispersivity 10 ft Transverse Dispersivity 3 ft ' Txx 0025 ft'-/s Tyy 0025 ft2/s Aquifer thickness 25 ft Hydraulic Gradient 4 29E-3 ft/ft Injection well at cell X=10,Y=10 Injection rate 0 0002 cfs Conc of contaminant in injected water 150 mg/l Conc of oxygen in injected water 0 0 mg/l ' Initial Conc of oxygen 8 0 mg/l Conc of natural recharge of oxygen B 0 mg/l A detailed discussion of the sensitivity analyses is included in thefollowng sections ' 2 3.1 Variation of Concentrations with Hydraulic Conductivity The hydraulic conductivity(K)was vaned from 10-'ft/sec to 1 a'ft/sec Figure 2 3 is a plot of the contaminant and oxygen concentrations along the centerline of the plume(cross section A-A, Figure 2 2) for three values of hydraulic conductivity It can be seen that the hydraulic conductivity has a significant effect on biodegradation The maximum contanvnant concentration vaned from 29 6 mgh(K= 104 ft/sec) to 130 mg/1(K= 10-' ft(sec) The change in biodegraded mass with hydraulic conductivity is illustrated in Figure 2 4 2 3 2 Variation of Concentrations with Retardation The effect of retardation on biodegradation was studied by using a retardation factor, R,greater than 1 Figure 2 5 presents the variation in contaminant and oxygen concentrations along the centerline of the plume (section A-A, Figure 2 2)for three values of R It can be seen that the mass of hydrocarbon ' remaining at the end of the simulation period decreases with increasing values of R The percent of mass biodegraded relative to the total dissolved mass, however,decreases for increasing values of R(Figure 2 4b) ' Table 2 1 lists the percent of mass biodegraded relative to the total dissolved mass and the percent of mass biodegraded relative to the total stored mass Table 2 1 also lists the percent of mass adsorbed relative to the total stored mass for the three values of R Table 21 indicates that the percent of biodegraded mass decreases with increasing values of retardation (columns A and B) Table 2 1 -Percent Biodegraded Mass as a Function of the Retardation Factor(R) R A B C 1 3025 3025 000 2 2773 1386 5000 3 2574 858 6667 A= BMITDM BM = Biodegraded Mass B= BMITSM AM =Adsorbed Mass C=AM/TSM TDM = Dissolved Mass+ Biodegraded Mass TSM = Dissolved Mass+ Biodegraded Mass+Adsorbed Mass 2 3 3 Vanation of Concentrations with Dispersivity eThe vanabon of contaminant concentrations with dispersivity was examined by loolung at the longitudinal and transverse dispersivities independently r 2-4 I